Geschäftsbereich Kunststoffe
ATI 916
Anwendungstechnische
Process
Variables as Production Cost Factors
Information
in the
Injection Molding of Thermoplastics:
Melt, Mold and Demolding Temperature,
Prozeßgrößen
beim Spritzgießen von
Cycle
Time, p-v-ϑ diagrams
Allgemein
Thermoplasten als Produktionskostenfaktoren
– Schmelze-, Werkzeug-, Entformungstemperatur,
Zykluszeit, p-v-ϑ-Diagramme –
(in Anlehnung an den Vortrag �Die Temperierung im Werkzeug“ anläßlich des Fachseminars �Wirtschafliches Produzieren mit optimaler
Werkzeugtemperierung beim Spritzgießen“, SKZ Würzburg, Dezember 1993, Vortragender Dipl.-Ing. Olaf Zöllner, Bayer AG, Leverkusen)
Contents
Inhalt
1Introduction
1. Einführung
2 Melt temperature
2.1 Melt
during molded part filling
2. temperature
Schmelzetemperatur
2.2Melt
temperature
in the holding
pressure and
2.1 Schmelzetemperatur
während
coolingder
phases
Formteilfüllung
9
Heat
of a molten plastic
6. content
Entformungstemperatur
s2
tK = 2
· In
π · aeff
11References
8. Zykluszeit
Wärmeinhalt einer Kunststoffschmelze
10. Zusammenfassung
11. Literaturverzeichnis
Die vorstehenden Informationen und unsere anwendungstechnische Beratung in Wort, Schrift und durch Versuche erfolgen
COV00073621/Page
1 ofgelten
12 jedoch nur als unverbindliche Hinnach bestem Wissen,
weise, auch in bezug auf etwaige Schutzrechte Dritter. Die
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Edition 2016-03
Beratungshinweise und unserer Produkte im Hinblick auf ihre
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ϑW
(
4 ϑM – ϑW
·
π ϑE –�ϑW
Druck p
ϑE
10Summary
7. Kühlzeit
9.
(
spezifisches Volumen v
2.2 Schmelzetemperatur in der
3The cooling
of thermoplastic
melts,
Nachdruckund in der Kühlphase
thermodynamic state curve
3.1 Influence
of ambient
3. Abkühlung
derpressure
Schmelze von
3.2 Influence
of cooling rate
Thermoplasten,
thermodynamischer Zustands4 Meltingverlauf
temperature
3.1 Einfluß des Umgebungsdrucks
5 State
during
injection molding
3.2 curve
Einfluß
der Abkühlgeschwindigkeit
6 Demolding temperature and cooling time
4. Schmelztemperatur
7 Cooling time
5. Zustandsverlauf beim Spritz8 Cycle time
gießen
(α0>α1>α2)S,G
Glas
αG2
ϑR
αS0
freies
p
Volumen 1
3
αG0
αG1
Anwendung, Verwendung und Verarbeitung unserer Produkte
und der aufgrund unserer anwendungstechnischen Beratung
von Ihnen hergestellten Produkte erfolgen außerhalb unserer
Kontrollmöglichkeiten und liegen daher ausschließlich in Ihrem
Verantwortungsbereich. Der Verkauf unserer Produkte erfolgt
nach Maßgabe unserer Allgemeinen Verkaufs- und Lieferbedingungen.
1
Einfrierlinie
x
Wanddicke s
p0
Schmelze
αS1
αS2
p2
2
ϑGO ϑG1 ϑG2
Temperatur ϑ
ϑS
1 Introduction
The injection molding of thermoplastics is a form of
process­ing in which highly complex physical processes take
place.
The thermoplastic to be processed first has to be ­melted,
before being injected at high pressure into a “cold” mold.
Since the mold is cooler than the compound, the shaped
plastic part cools down and can be removed from the mold
1. Introduction
once it has solidified.
∆ϑM = ∆p
ρ · cp
∆ϑM = Mean temperature increase in the melt
∆p = Pressure differential (pressure loss) in a flow section
of the runner/gate system
ρ
= Melt density
cp = Specific heat capacity
The particular significance of this equation stems from the
fact that it can describe the process independently of the
The injection moulding of thermo- Once the injection signal has
been the
be melt
quitetemperature,
pronounced,the
forms
the
geometry,
wall over
temperature
and
The individual process stages of melting, injection and coolplastics is a form of processing in given, the screw moves forwards
and cross-section
of the As
flowhas
channel
asbeen
a menthe rheological
material values.
already
ing affect the quality of the subsequent molded part.
which highly complex physical pro- presses the molten plastictioned,
through
result
the elimination
via the
there
is noofallowance
made of
forheat
the exchange
of heat
cesses take place.
both the machine nozzle with
and the
thecold
mould
wall.
Figure
1
shows
a
typical
mold.
The temperature control system of the mold plays a central
runner/gate system into the cavity. The temperature profile of a flowing plastic
role in the quality-conscious and cost-efficient production of
The moulding compound to be pro- filling process frequently imposes a melt in a cooled injection mould.
Looking more closely at the temperature of the melt as the
injection-molded parts. This control system is known to
cessed first has to be melted, before high level of mechanical and thermal
molded part is being filled, it is seen that cooling can have a
­influence decisive quality features, such as surface appearbeing injected at high pressure into a stressing on the melt. The chief Right next to the mould wall, the melt
very considerable influence on the temperature of the melt.
ance and warpage.
“cold” mould. Since the mould is cooler parameters that affect this stress are has already solidified, giving rise to a
A temperature profile, which can be quite pronounced, forms
than the compound, the shaped plastic the:
frozen edge layer. The thickness of
over the cross-section of the flow channel as a result of the
Efficient mold temperature control also helps to cut costs,
part cools down and can be removed
this layer will be a function of the
dissipation of heat via the mold wall. Figure 1 shows a typical
cooling
time, and hence the cycle time as
from however,
the mouldsince
oncethe
it has
solidified.
Nozzle/gate geometry
processing conditions (injection time,
temperature profile of a flowing plastic melt in a cooled
well, can be optimized in this way.
Wall thickness of the moulded part melt temperature and mould wall
inject­ion mold.
The individual process stages of
temperature). In the centre of the flow
Filling rate
In
order
to
fully
appreciate
the
importance
of
cooling
in
an
melting, injection and cooling affect the
channel, there is a uniformly high
Moulding compound temperature
Right next to the mold wall, the melt has already solidified,
injection
it is wise moulded
to take a look at
the thermo­
dynamic
quality
of themold,
subsequent
temperature distribution. Peaks such
Mould
wall temperature
giving rise to a frozen edge layer. The thickness of this layer
part. processes that prevail during the injection molding process.
as those shown on the diagram can
will be a function of the processing conditions (injection
The stress acting on the melt as it develop between the centre of the
time, melt temperature and mold wall temperature). In the
This then supplies
answers
to the
following
questions:
The temperature
controlthe
system
of the
flows
can lead
to internal friction pro- channel and the mould wall. It is here
center
of the flow channel, there is a uniformly high temperamould plays a central role in the cesses, which then cause the
melt to that the shear stress acting on the melt
ture
­
d
istribution.
Peaksand
suchhence
as those
in the diagram
What
sort
of
temperature
changes
occur
in
the
molten
plasquality-conscious and cost-efficient heat up.
is greatest
hereshown
that most
between
the centerthrough
of the channel
and the mold
tic at the
individual stages of
the process, and what happens can developheat
production
of injection-moulded
parts.
is generated
internal
wall.
It
is
here
that
the
shear
stress
acting
on
the
melt is
inside
a
polymeric
melt
as
it
cools?
What
is
the
difference
This control system is known to Experimental investigations into differ- friction.
greatest
and
hence
here
that
most
heat
is
generated
between
an
amorphous
plastic
and
a
semi-crystalline
plasinfluence decisive quality features, ent gates and different materials [1]
through
friction.
suchtic.
as surface appearance and have shown that the mean
The temperature
profile can vary at diftem-internal
warpage.
Velocity Vx
Temperature ϑ
perature increase of Δ ϑM can be ferent points of the cavity (close to the
The temperature
profile can
at different
points
fromvary
the gate).
Hence,
an of the
described in approximate terms
as a gate, remote
cavity
(close
to
the
gate,
far
from
the
gate).
Therefore,
an in2
Melt
temperature
Efficient mould temperature control function of the pressure loss Δp, increasingly large frozen edge layer
frozenthe
edge
layer cantemperature
cause the maximum
also helps to save costs, however, whereby there is assumed creasingly
can cause
maximum
to be no large
temperature
(thetemperature
temperaturepeaks
peaks in
shift totemperature
molded
part filling
since2.1
theMelt
cooling
time, and during
hence the
in Fig.
Fig.1)1)toto
exchange
of . heat with the
mould (the
wards
the
center
of
the
channel.
This
situation
is
cycle time as well, can be optimised in (adiabatic => Qab= 0).
shift towards the centre of the channel.depicted in
Fig. 2.
When thermoplastics are injection molded, granules are
this way.
This situation is depicted in Fig. 2.
melted in a screw and conveyed into –the screw antechamber.
Δ ϑM = Δp
In order to fully appreciate the
ρ · cp
Once the
signal
has been given, the screw
moves
importance
of injection
cooling in
an injection
Polystyrene
250
ϑM = 190 °C
forward
and to
presses
molten
the
mould,
it is wise
take athe
look
at theplastic
Δ–ϑM through
= meanboth
temperature
increase
ϑW = 42 °C
°C
­machine nozzle
and the
runner/gate
cavity.
thermodynamic
processes
that
prevail systemininto
thethe
melt
ϑ
during
thefilling
injection
moulding
process.
The
process
frequently
imposes
high
level of differential
Δp a =
pressure
200
­mechanical and thermal stress on the melt. (pressure
The chief loss) in a flow
1.5
This ­p
then
supplies
theaffect
answers
to the are the: section of the runner/gate
arameters
that
this stress
m
following questions:
system
s
6 · 10 3
ρ
= melt density
• Nozzle/gate geometry
.
Vx
5
150
γ
What• Wall
sort thickness
of temperature
changes
of the molded
part cp = specific heat capacity
1.0 s–1 .
occur• Filling
in therate
molten plastic at the
4
individual
stages
of the process,
and The particular significance of this
• Molding
compound
temperature
3
100
what •happens
a polymeric melt equation stems from the fact that it can
Mold wallinside
temperature
0.5
as it cools? What is the difference describe the process independently of
2
between
an amorphous
and
the geometry,
melt temperature,
The stress
acting onplastic
the melt
asait flows
can lead tothe
internal
1
semi-crystalline
plastic. which then cause
the
wall
friction processes,
the
melttemperature
to heat up. and the rheo50
logical material values. As has already
0
0
–1.0 –0.5
0
0.5 mm 1.0
been mentioned,
there is no allowance
Experimental investigations into different
gates and different
Direction of shear y
2. Melt
temperature
made
for the exchange
of heat with the
materials
[1] have shown that the mean
temperature
increase
Fig. 1: Temperature profile in a flowing plastic melt [1]
cold terms
mould.as a function
of ∆ϑM can be described in approximate
Fig. 1: Temperature profile in a
2.1 Melt
temperature
during
of the
pressure loss
∆p, whereby there is assumed to be no
flowing plastic melt [1]
moulded
filling
Looking
more
closely at the temexchangepart
of heat
with the mold (adiabatic
=> Q
ab = 0).
perature of the melt as the moulded
When thermoplastics are injection part is being filled, it is seen that
moulded, granules are melted in a cooling can have a very considerable
screw
and conveyed2 into
COV00073621/Page
of 12 the screw influence on the temperature of the
antechamber.
melt. A temperature profile, which can
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Edition 2016-03
2.2 Melt temperature in the holding pressure and cooling
phases
Polystyrene
Polystyrene
ϑM =°C
220 °C
300 300 ϑM = 220
ϑW = 42
= 42 °C
ϑW°C
p(t)xz0p(t)
= 4750
4750 bar/s
xz0 = bar/s
tF =s0.14 s
°C °C tF = 0.14
Vx = 2.25
2.25 m/s
Vx =m/s
Once the mold has been volumetrically filled, the holding
pressure phase commences. In the course of this phase,
melt is conveyed into the mold cavity for as long as possi­ble,
in order to offset volumetric contraction. Since the flow of
melt is very small by comparison to the flow that prevails
during the filling phase, there is no further increase in
tempera­ture as a result of internal friction. The temperature
of the melt experiences a steady fall.
Immediately after the holding pressure phase comes the
­residual cooling phase. During this phase, the temperature of
the molten plastic, which has now almost completely soli­di­
fied, falls to the demolding temperature.
What happens in a plastic melt as it cools? At what temperature does it freeze? How high is its heat content, i.e. how
much heat energy is required to heat or cool plastics? The
answers to these questions will be provided in the section
that follows.
COV00073621/Page 3 of 12
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Edition 2016-03
150 150
Once Once
the mou
th
trically
filled,f
trically
phasephase
comme
co
this phase,
me
this phas
mouldmould
cavityca
fo
order order
to offset
to o
Since Since
the flow
the
comparison
to
comparis
duringduring
the filli
th
further
increai
further
a result
of inteo
a result
perature
of th
perature
steadysteady
fall. fa
Immediately
af
Immediat
phasephase
comes
c
phase.
During
phase.
D
perature
of the
perature
has now
hasalmos
now
falls tofalls
the to
dem
th
FigureFigure
3 shows
3
profiles
over t
profiles
0.5 0.5
0
mm mm 1.0 1.0
0
moulded
part d
moulded
(panel(panel
s = 3 sm
Direction
of shear
y
Direction
of shear
y
temperature
temperap
Fig. 2:Fig.Temperature
profileprofile
at different
flow locations
at the at
time
the the
2: Temperature
at different
flow locations
thewhen
time when
creasingly
wi
creasing
Fig. 2: Temperature
profile
different
moulded
part
ispart
fullatis
[1]
moulded
full [1] flow locations at the time when the
ximately
16 s,
ximately
molded part is full [1]
middle
has fal
middle
h
temperature.
temperat
240=°C
ϑMelt =ϑMelt
240 °C
It is evident
fro
0s 0s
It is evid
said said
that the
tha
4s 4s
subject
to cons
subject
to
injection
mould
injection
200 200
the processing
the proce
time, time,
tempera
te
8s 8s
compound
an
compoun
runner/gate
sy
runner/g
150 150
perature
cont
perature
12 s 12 s
major major
influence
inf
the melt.
the The
melt.c
16 s 16 s
particular,
lar
particula
100 100
uniformly
and
uniforml
18 s 18 s
eliminated
from
eliminate
24 s 24 s
permitpermit
demould
de
28 s 28 s
Temperature [°C]
It is evident from what has just been said that the melt temperature is subject to constant change during the injection
molding process. Apart from the processing parameters of
injection time, temperature of the injected compound and
temperature of the runner/gate system, the mold cooling
­system also has a major influence on the temperature of the
melt. The cooling of the mold, in particular, largely deter­
mines how uniformly and how rapidly heat is ­eliminated from
the plastic in order to permit demolding.
200 200
x = 66xmm
= 66 mm
x = 111
x =mm
111 mm
x = 200
x =mm
200 mm
Temperature [°C]
Fig. 3 shows computed temperature profiles over the crosssection of a molded part during the cooling phase
(panel s = 3 mm, material ABS). The temperature profile flattens out increasingly with time. After approximately 16 s, the
temperature in the middle has fallen to the demolding temperature.
Temperature ϑ
Temperature ϑ
250 250
2.2 Melt
2.2 temp
Melt
pressure
presa
What What
happens
hap
cools?
At wha
cools?
A
2.8
2.4
2.8
freeze? How h
ϑw = 40
ϑw°C
= 40 °C freeze? H
i.e. how
i.e. much
how
heat or
coolorplc
heat
Fig. 3:Fig.Temperature
profiles
in a cooling
thermoplastic
melt atmelt
different
3: Temperature
profiles
in a cooling
thermoplastic
at different these these
question
que
Fig 3: Temperature profiles in a cooling thermoplastic melt at different
pointspoints
in timein(computed)
time (computed)
section
that folth
section
points in time (computed)
50
50
0.4
ϑw = 40
= 40 °C
ϑw°C
0.40.8 0.81.2 1.21.6 1.62.0 2.02.4
Thickness
of molded
part [mm]
Thickness
of molded
part [mm]
thermoplastic melts
Thermodynamic state curve
fluid
Specific volume v
When
heat is eliminated
a
3 The cooling
of thermoplastic
melts,from
thermodynamic
polymeric melt, the chains lose their
state curve
mobility, and segment after segment is
by the
neighbouring
secondWhen heat captured
is eliminated
from
a polymeric
melt, the chains
3. The cooling of
ary valence
fields. The
melt
becomes
lose their mobility,
and segment
after
segment
ismelts
captured
thermoplastic
highly viscous.
Thermodynamic
by the neighbouring
secondary valence
fields. Thestate
meltcurve
be­
comes highly viscous.
VGa(0)
When offers
heat is eliminated
from
The “free volume theory”
a
polymeric melt, the chains lose their
particularly
appropriate
physical
in- after segment
The “free volume
theory”
offers a mobility,
particularly
appropriate
and segment
VTK (0)is
terpretation of
of polymeric
polymeric
melt
cooling.
captured
the neighbouring
secondphysical interpretation
melt by
cooling.
According
VK (0)
ary itvalence
fields. The melt becomes
According
to thistotheory,
is possible
to this theory,
it is possible
viewhighly
a polymeric
melt
as
a
to view a polymeric melt as aviscous.
vacancy­vacancy-saturated fluid (Fig. 4).
saturated fluid (Fig. 4).The “free volume theory” offers a
Glassy state
amorphous
free
volume
Supercooled
fluid
Fluid
Specific volume v
semi-crystalline
crystalline
p = konst.
partial
free
volume
volume
amorphous
VG (0)
semi-crystalline
particularly appropriate physical in-0
VTK (0)
TK partial
TG = TppE=const.
= konst.
Vg =Vm + Vf
terpretation of polymeric melt cooling.
Vg = Vm + V f
crystalline
VK (0)
volume
Vg = Overall volume
Temperature T
According to this theory, it is possible
Vg = overall volume to view a polymeric melt as a vacancyVm =Partial volume of molecules
molecules
Vm = partial volume of
saturated
fluid (Fig. 4).Fig. 5: Pressure-volume-temperature diagram (p-v-ϑ diagram)
(oscillation expansion volume)
(oscillation expansion volume)
Vf = Free volume (vacancy volume)
Vg = Vvolume)
m + Vf
Vf = free volume (vacancy
ϑ1
Vm
0
TG = T E
Temperature T
TK
K
K
Vg = overall volume The bottom curve in Fig. 5 is the profile tallising point. Apart from the semiFig. 5: Pressure-volume-temperature diagram (p-v-ϑ diagram)
Vm = partial volume of molecules
for a purely crystalline material. At the crystalline domains, there are amor(oscillation expansion volume) Fig. 5: Pressure-volume-temperature diagram (p-v-𝛝 diagram)
crystallisation
temperature, T K , the phous domains present too. Once the
Vf = free volume (vacancy
volume)
tallising point.
Apart
from T
the semiThe bottom
curve
in Fig. 5 is the profile
, these
temperature
falls
below
material becomes
fully
crystallised.
The
curve
shows
volume/temperature
behavior
crystalline domains, there
areGamormaterial.the
At the
for a middle
purely crystalline
assume
the
glassy
state.
The
free
The free volume
is
then
zero.
In
the
ϑ1
domains
too. some
Once thevocrystallisation
temperature,
T K , theIn phous
of
a semi-crystalline
material.
this class
ofpresent
material,
is smaller than
for purely
amorfurther coursematerial
of the process,
onlycrystallised.
the lume temperature
falls below
T G , these
becomes fully
of the polymer chains are lined up
closely
in parallel
during vothe glassy
state.
The freeof
The free volume
is then
zero. Inphous
the assume
materials
– on
account
the
oscillation expansion
volume
undercooling
and of
form
submicroscopically
small
smallercrystallites.
than for purely amorfurther course
the process,
onlycrystalline
the lume iscomponent.
goes any change.
phous materials
on account
of the
oscillation
volume
under-complete
­Inside
theexpansion
crystallites,
almost
order –prevails,
with
Vm
crystalline component.
goes any change.
the ­exception of a few defects.
In the case of amorphous thermo- The superposition of the state curves
The superposition
the state curves
thermoIn the case
of amorphous
for amorphous
andofsemi-crystalline
plastics (top curve),
the melt
is seen to
Vf
amorphous
and semi-crystalline
By
contrast
to purely
crystalline
materials,
these
materials
plastics
(top curve),
the melt
is seen to for
Vf
thermoplastics
that
is
shownonon
the
suffer undercooling
as
the
temperature
thermoplastics
that is shown
the
suffer a
undercooling
as the temperature
have
crystallization
interval
instead
of a crystallizing
point.
diagram
means
that
there
certain
falls. Once thefalls.
temperature
has fallen
certain
Once the temperature
has fallen diagram means that there isisa a
Apart
from
the
semicrystalline
domains,
there
are amoramount
of time
each
temperature in in
below
the
glass
transition
temperature
amount
of time
atateach
temperature
transition
temperature
ϑ1 > ϑ2 below the glass
ϑ1 > ϑ2
phous
domains
present
too.
Once
the
temperature
fallsvolume
bewhich
the
attendant
specific
TG,
the
specific
volume
falls
less
which the attendant specific
volume
TG, the specific volume falls less
develop.
The
cooling
or heating
sharply
(the
straight
lines have
a low can
low
T
,
these
assume
the
glassy
state.
The
free
volume
is
G
ϑ2
can develop.
The
cooling
or heating
sharply (the straight
lines
have
a low
rate,
and
also
the
ambient
pressure,
gradient).
At
below
the
glass
transition
ϑ2
smaller
than
for transition
purelyisamorphous
–ambient
on account
of
rate, have
andmaterials
the
pressure,
aalso
major
influence
on the
state
gradient). At below
the
glass
temperature
the material
in the
the
crystalline
component.
curve.
glassy
state
–
a
“supercooled
fluid”.
have a major influence on the state
temperature the material is in the
free volume that exists at the
curve.
glassy state –The
a
“supercooled
fluid”.
glass transition temperature is frozen
The
superposition
the state
curves for amorphous and
The free volume
exists
atof
the
in andthat
remains
virtually
constant
in the 3.1 Influence of ambient pressure
semi-crystalline
that is shown in the diagram
glassy
state.
glass transition
temperature
isthermoplastics
frozen
If
a plastics
meltambient
is subjected
to presmeans
that
there
is
a
certain
amount
of time
at
each pressure
of
in and remains virtually constant in the 3.1 Influence
Fig. 4: Free-volume model
sure and
then cooled,
lower
specific
The middle curve
emperature
in shows
whichthe
thevolume/
respective
specific
volume
can
according to [2]
glassy state. ­ttemperature
behaviour of a semi- volumes will result at each tem­dcrystalline
evelop. The
cooling
or class
heating
rate, and
also
ambient
If of
a plastics
melt
is the
subjected
to presperature.
The
glass
temperature
(in
material.
In this
Fig. 4:
Free-volume
Fig. 4: Free-volume
model
according to [2]model
ofcooled,
amorphous
thermoThe overall volume VThe
obtained curve
material,
some
of the
polymer
chains
pressure,
have
a volume/
major
influence
on case
the
state
curve.
sure the
and
then
lower
specific
shows
the
G is middle
according to [2]
from the sum of the partial volume of are lined up closely in parallel during plastics) and the crystallisation temtemperature behaviour of a semi- volumes will result at each temV m (oscillation expansion cooling and form submicroscopically perature (semi-crystalline thermoThe overall volume VG is obtained molecules
from
the
sum
of
the
partial
The
glass
temperature
crystalline
In thisInside
class
of perature.
plastics)
will be
shifted
towards higher (in
volume of molecules) and
the vacancymaterial.
small crystallites.
the crystallites
volume of molecules
Vm volume
(oscillation
expansion
volume
of change
3.1
Influence
of
ambient
pressure
temperatures.
almost
complete
order
prevails,
with
the
case
of
amorphous
thermo.
The
or
free
volume
V
The overall
Vvolume,
is
obtained
material,
some
of
the
polymer
chains
f
G
the exception
of a few during
defects. plastics) and the crystallisation temin the
of of
the melt
results
mole­cules)from
and the
volume,
orvolume
free volume
Vf.that
The
the vacancy
sum of the
partial
volume
are
lined
up closely
in parallel
from a change in temperature can be
Figure 6 shows the correlation bechange in the
volume of
melt that
results
from acooling
changeand form
If a plastic
melt is subjectedperature
to pressure
and then cooled,
(semi-crystalline
thermo(oscillation
expansion
molecules
V mthe
submicroscopically
illustrated by means of a pressure- By contrast to purely crystalline ma- tween specific volume and temperature
in ­tem­perature
canof
bemolecules)
illustrated and
by
means
of a pressureplastics)
will
betemperature.
shifted towards
higher
specific
volumes
resultatatdifferent
each
Thean
volume
the vacancy
small crystallites.
Inside
crystallites
pressures
for both
volume-temperature
diagram
(p-v-ϑ lower
terials,
thesethe
materials
havewill
a crysplastic
(left) and a semidiagram)
5).
tallisation
interval
instead
of acase
crysvolume-­temperature
(p-v-ϑ
(Fig. 5).
temperatures.
almost complete
order
prevails,
The(Fig.
change
volume, ordiagram
free volume
Vf.diagram)
glass
temperature
(inwith
the
ofamorphous
amorphous
thermoplasof aand
few the
defects.
in the volume of the melt that results the exceptiontics)
crystallization temperature (semi-crystalline
The bottomfrom
curve
in Fig. 5 in
is the
profile forcan
a purely
a change
temperature
be crystalFigure
6 shows the correlation bethermoplastics) shift to higher
temperatures.
illustrated
by means of
a pressure-TK, the
line material.
At the crystallization
temperature,
mate- to purely crystalline ma- tween specific volume and temperature
By contrast
for both
volume-temperature
diagram
(p-v-ϑ
terials,
materials
havethe
a correlation
crys- at different
rial becomes
fully crystallized. The
free volume
is then
zero.theseFigure
6 shows
betweenpressures
specific volume
andan
amorphous
plastic
and a semidiagram)
5).process, only the oscillation
tallisation interval
insteadatof
a crys-pressures
In the further
course(Fig.
of the
temperature
different
for both
an (left)
amorphous
­expansion volume undergoes any change.
plastic (left) and a semicrystalline plastic (right). The Figure
4
illustrates the differences that prevail between the two
In the case of amorphous thermoplastics (top curve), the
classes of material as of the transition from the molten state
melt is seen to undergo undercooling as the temperature
to the solid phase. The specific volume is generally lower for
falls. Once the temperature has fallen below the glass tran­
semi-crystalline materials than for amorphous thermo­
sition temperature TG, the specific volume falls less sharply
plastics on account of the crystallizing component of the
(the straight lines have a low gradient). Below the glass transtructure.
sition temperature, the material is in the glassy state –
4
a “super­cooled fluid”. The free volume that exists at the
glass tran­sition temperature is frozen in and remains virtually
constant in the glassy state.
COV00073621/Page 4 of 12
www.plastics.covestro.com
Edition 2016-03
Pressure p
11:56
Pressure p
2054.pdf
1
p < p1 < p2
29.01.13
11:48 0
melt
Specific volume v
freezing line
glass
2
freezing line
glass
αG0
ϑR
(α0>α1>α2)S,G
1
αS0
free
volume
Pressure p
1
p1
αG1
αG1
αG2
freezing line
αG2
glass
ϑG0
ϑRϑG1
Temperature ϑ
2
p0
αS0>αS1>αS2
free Pressure p
volume
p < p < pp1
p2
0
2
αS1
α
free S2
volume
p1
αS1
ϑG0 ϑG1 ϑS
αG0
Temperature ϑ
3
2
p0
3
ϑR ϑS
p2
p0 < p1 < p2
αS0
αS0>αS1>α
1 S2
p1
αS1
melt
2
Pressure
p1p
p0 < p1 < p2
3
p2
αS0>αS1>αS2
p0
αS0
1
semi-crystalline semi-crystalline
solidification line
phase
αS0p2
phase
3
1
1
Pressure p
p0
melt
solidification line solidification line
αS0
melt
αS1
3
2
(α0>α1>α2)S,G
αG0
melt
p0 < p1 < p2
p0
αS2
Specific volume v
Specific volume v
(α0>α1>α2)S,G
melt
p0 < p1 < p2
Specific volume v
29.01.13
Specific volume v
1
Specific volume v
2054.pdf
αS2
αS1
p0
αS0
p2
1
αS2
p1
2
3
αS1
p2
semi-crystalline
ϑK1
ϑK0 ϑK1ϑS
ϑRϑK0
phase
Temperature ϑ Temperature ϑ
αS2
ϑS
αS2
αG1
Fig. 6: p-v-𝛝
slowly
amorphous
(left)
and semi-crystalline
(right)
plastic
(source:
IKV)(Source:
ϑ aDiagram
Fig.diagram
6: p-v-of
slowly
coolingof
amorphous
(left) and
semi-crystalline
plastic
ϑ Diagram
Fig. cooling
6:of ap-va slowly
cooling
amorphous
(left)
and(right)
semi-crystalline
(right)IKV)
plastic (Source: IKV)
αG2
Specific volume v
Specific volume v
With semi-crystalline materials, the curve displays a sharp
Since the molecules are endeavouring to attain a state of
kink. This sudden change in specific volume is due to the start ­internal equilibrium, it is possible for a “reduction” to occur in
crystalline
plastic
(right).
The
crystalline plastic
(right).
rates.
The time
that
available
for an the
Figure
7inshows
the shift in glass
tranrates.
The
time
that
is available
for
anis Figure
7ϑshows
shift
glass
ϑG0Figure
ϑ
ϑexcessively
ϑS
ϑFigure
ϑK0subsequent
ϑtranof crystallization.
The point
ofThe
discontinuity
marks
the
the
large
free
volume
to production.
R
G1
S
K1
R
illustrates
theprevail
differences
thatstate
prevail
illustrates the differences
that
internal state
of equilibrium
develop sition
temperature
for an amorphous
internal
of equilibrium
to develop
sitiontotemperature
for an
amorphous
Temperature
ϑ
Temperature
ϑ
­crystallizing
point ϑK. classes
Below
this
temperature,
the
reduction
This
will
occur
all
the
more
rapidly,
the
higher
the
service
between
two classes
material
as
at
each
individual
temperature
bematerial
at
two
different
cooling
rates.
between the two
of the
material
as at of
each individual temperature be- material at two different cooling rates.
in specific
temperature
due
not only
the
reduced
thertemperature
of
the finished
component
– key word:
ofis
the
transition
fromto
the
molten
stateIt is
comes
shorter.
It is already
impossible
At thetemperature
higher
freezing
a “postof the
transition from
the
molten
state
comes
shorter.
already
impossible
At the
higher
freezing
a istemperature
to
the
solid
Thefor
specific
volume
forto
a state
ofshrinkage”.
equilibrium
to develop
at larger
free plastic
volume
is frozenIKV)
in, which
to the solid
The
specific
volume
a of
state
of equilibrium
to develop
at larger
free volume
is frozen
in, which
mal oscillation
ofphase.
the molecules,
but
also
(and
ϑ Diagram
Fig.
6: phase.
p-vaprimarily)
slowly
cooling
amorphous
(left)
and
semi-crystalline
(right)
(Source:
lower for high
high temperatures.
meansvolume
that theinoverall
is generally
lower is
forgenerally
semi-crystalline
means that the overall
the volume in the
the ­increasing
crystallization.
When
bothsemi-crystalline
of temperatures.
these are super­
than
for amorphous thermosolid phase is greater.
materials than for materials
amorphous
thermosolid phase is greater.
imposed,
this leads
to plastics
the
parabolic
curve
for the
As the cooling rate increases, no further increase comes
on account
of theprofile
crystallising
plastics
on account
of the
crystallising
component of the structure.
semi-crystalline
about in specific volume, however, and there is no further
component phase.
of the structure.
crystalline plastic (right). The Figure rates. The time that is available for an Figure 7 shows the shift in glass translow0.04
isobaric
0.04 °C/s
change
in the
glass
transition
temperature.
The specific
slow isobaric
cooling
°C/s cooling
illustrates
the differences
that prevail
internal state of equilibrium rapid
to develop
sition temperature
for an amorphous
With
semi-crystalline
materials,
the
isobaric
5.0 d °C/s The
With semi-crystalline
materials,
the
rapid
isobaric
coolingtransition
5.0
d °C/scooling
v
­
olume
and
glass
temperature.
specific
volbetween
the
two
classes
of
material
as
at
each
individual
temperature
bematerial
at
two
different
cooling
rates.
a sharp kink. This
curve displays acurve
sharpdisplays
kink. This
ofrate
thechange
transition
from the molten state comes shorter.
It1.00
is already
impossible temperature
At the higher freezing
temperature
a
3.2 Influence
cooling
ume and
glass transition
strive towards
a limit
1.00
sudden of
change
insudden
specific
volumeinisspecific volume is
totothe
solid
phase.
The specific The
volume for a state
of equilibrium to develop at larger free volume is frozen in, which
due
the
start
of
crystallisation.
value.
due to the start of crystallisation. The
is generally
lower for semi-crystalline
high temperatures.
means that the overall volume in the
point
ofmarks
discontinuity
marks the is simipoint volume
of discontinuity
the temperature
The specific
that
results
at room
3
cm 3
materials
than
for ϑ
amorphous
solid phase is greater.
. Below thermothis cm
crystallising
point
400 bar
K
.
Below
this
crystallising
point
ϑ
400 bar
K
g
larly a function of the cooling
rate.
Inreduction
the case
of
amorphous
plastics
onthe
account
of the
g
temperature
in crystallising
specific
temperature the reduction
in specific
component
of
the
structure.
thermoplastics,
theisglass
transition
temperature
temperature
is the
due
not only towill
themove
temperature
due
not
only to
slow isobaricPressure
cooling 0.04
thermal
oscillation
of the
­towardsreduced
high values
atreduced
high
cooling
rates.
The time
that is
thermal
oscillation
of the
pK °C/sPressure pK
0.95
With semi-crystalline
materials,to the 0.95
molecules
but also
rapid isobaric cooling 5.0 d °C/s
molecules
but also
(and primarily)
to (and primarily)
available
for an internal
state
of
equilibrium
to
develop
at
displays
a sharp kink.
This
thecurve
increasing
crystallisation.
When
the increasing crystallisation.
When
each individual
temperature
shorter.
isthis
already
1.00
sudden
change
in
specific Itvolume
is
of becomes
these
are
superimposed,
both of these are both
superimposed,
this
due
theparabolic
starttoofdevelop
crystallisation.
leads
totothe
curve profile
forThetem­
im­possible
a state
of
equilibrium
at high
leadsfor
to the
parabolic
curve
profile for
Δv
ΔϑG
Δv
point
of discontinuity
ΔϑG
semi-crystalline
phase. marks the
peratures.
the semi-crystallinethe
phase.
cm 3
Specific volume v
crystallising point ϑ K . Below this
400 bar
g
temperature the reduction in specific
0.90
Fig. 7 shows the shift in
transition
temperature
for0.90
an
temperature
due
not
3.2glass
Influence
of is
cooling
rateonly to the
3.2 Influence of cooling rate
reduced
thermal
oscillation
Pressure pK
amorphous material at two
different
cooling
rates.ofAtthe
the
0.95
molecules
but free
also that
(and
primarily)
to in,
The
specific
volume
results
at
­higher freezing
temperature
a
larger
volume
is
frozen
The specific volume that results at
the increasing
crystallisation.
room
temperature
is similarly When
a
0
50
100
150
200 °C 250
room temperature
is similarly
a the solid phase is
0
50
100
150
200 °C 250
which means
that the overall
volume
in
function
of
the
cooling
rate. In the casethis
both of
these
are
superimposed,
Temperature ϑ
function of the cooling rate. In the case
Temperature
ϑ
greater.
of leads
amorphous
thermoplastics,
the for
to the parabolic
curve profile
Δv
of amorphous thermoplastics, the
ΔϑG
of an amorphous
glass
temperature
will move Fig. 7: Comparison of slow and rapid isobaric cooling
thetransition
semi-crystalline
phase.
glass transition temperature will move Fig. 7: Comparison of slow and rapid isobaric cooling of an amorphous
thermoplastic (Source: IKV)
towards high values at high cooling
thermoplastic (Source: IKV)
towards high values at high cooling
0.90
5
3.2 Influence of cooling rate
5
The specific volume that results at
room temperature is similarly a
function of the cooling rate. In the case
of amorphous thermoplastics, the
glass transition temperature will move Fig. 7:
towards high values at high cooling
0
50
100
150
200 °C 250
Temperature ϑ
Comparison
of slowofand
isobaric
cooling
of an of
amorphous
Fig. 7: Comparison
slowrapid
and rapid
isobaric
cooling
an amorphous
thermoplastic
(source:
thermoplastic
(Source:
IKV) IKV)
5
COV00073621/Page 5 of 12
www.plastics.covestro.com
Edition 2016-03
Since the molecules are endeavouring
to attain
a state of are
internal
equilibrium,
Since
the volume
molecules
Fig. 8 shows the correlation between the specific
atendeavouring
it is possible
“reduction”
to occur
to attain
a statefor
of a
internal
equilibrium,
RT, in a normal atmosphere, and the coolingit rate
theand
excessively
large free
isinpossible
forpressure
a “reduction”
to volume
occur
to production.
This will
in subsequent
the excessively
large free volume
during the cooling phase.
occur all the
rapidly, This
the higher
subsequent
to more
production.
will
cm 3
3
cmg
g
the service
temperature
thehigher
finished
occur
all the more
rapidly,ofthe
component is – key word: “post-
the service temperature of the finished
Although the specific volume becomes larger
as theiscooling
shrinkage”.
component
– key word: “postshrinkage”.
rate increases, it relatively soon strives towards
a limit value.
As the cooling rate increases, no furThis means that, with the standard cooling rates
of > 20 °C/s
comes
about inno
specific
Asther
the increase
cooling
rate
increases,
furvolume,
however,
and
there
is no furincrease
comes
about
in specific
that are encountered in practice, a constantther
increase
in
ther
change
in
the
glass
transition
volume, however, and there is no furtemperature.
volume and
­volume can be expected.
ther
change in The
the specific
glass transition
0.95
0.95
200
200
Specific volume v
Specific volume v
1
1
Pressure pK
Pressure pK
600 bar
400
600 bar
400
glass transition
temperature
temperature.
The specific
volumestrive
and
towards
a limit value.
glass
transition
temperature strive
In the case of semi-crystalline plastics, a greater
specific
towards a limit
value.
Figure 8 shows the correlation be­volume is similarly seen with higher coolingFigure
rates.
tween theThe
specific volume at RT, in a
8 shows the correlation benormal atmosphere, and the cooling
tween the specific
volume at RT, in a
crystalli­zation conditions deteriorate. The degree
of crystalrate and pressure
during the cooling
normal atmosphere, and the cooling
phase. larger. At
lization is lower and the specific volume becomes
rate and pressure during the cooling
phase.
an elevated cooling rate, however, the crystallization
temperAlthough the specific
volume becomes
larger
as
the cooling rate increases, it
ature ­remains virtually constant. With these
high
cooling
Although
the
specific
volume
becomes
relatively soon strives towards a limit
larger
as the
cooling
rate
increases,
rates, it must be born in mind that post-crystallization
and
value.
This
means
that,
with theit
relatively
soon
strives
towards
standard
cooling
rates
of > a
20limit
°C/s
hence a sub­sequent reduction in the specific
volume
can
value.
Thisencountered
means
that,inwith
the a
that
are
practice,
standard
cooling
rates
of
>
20
°C/s
constant
in volume can be
occur. This is frequently the cause of warpage
andincrease
dimenthat
are encountered in practice, a
expected.
constant increase in volume can be
sional deviations in molded parts.
expected.
In the case of semi-crystalline plastics,
0.90
0.90
5
10
15
°C/s
dϑ
Mean cooling rate (
)
dt ϑG 10
5
15
°C/s
dϑ
Mean
cooling
rate
) ϑ rate and pressure of an
( dtcooling
as a
function
of the
a greater specific volume is similarly Fig. 8: Specific volume
G
In the
case
semi-crystalline
plastics,
thermoplastic
(Source:
Fig.
8: Specificamorphous
volume as
a function
of theIKV)
cooling rate and pressure of an
seen
with
higher
cooling rates.
The
Efficient, uniform mold cooling is thus essential
in ofthe
case
Fig.
8:
Specific
volume
as
a
function
of
the
cooling
rate and pressure of an
a greater
specificconditions
volume isdeteriorate.
similarly
crystallisation
amorphous
thermoplastic
(Source:
IKV)
of semicrystalline plastics. The properties seen
ofThe
the
molded
amorphous thermoplastic (Source: IKV)
with
higher
cooling rates.
degree
of crystallisation
is The
lower
crystallisation
deteriorate.
and the specific
becomes
slow isobaric cooling 0.03 °C/s
part are determined by the “processing operation
inconditions
thevolume
The
degree
is lower
larger.
At of
ancrystallisation
elevated cooling
rate,
rapid isobaric cooling 12.0 °C/s
mold”. If, for instance, identical cooling rates
are
achieved
in
and
the specific
volume becomes
however,
the crystallisation
temslow isobaric cooling 0.03 °C/s
larger.
At an
elevated
cooling
rate,
0.90
perature
remains
virtually
constant.
rapid isobaric cooling 12.0 °C/s
all the areas of the molded part, through identical
cooling
1 bar
however,
thehigh
crystallisation
With these
cooling rates,temit must
0.90
remains
constant.
born
in mindvirtually
that of
post-crysconditions, then this will mark a major stepperature
inbethe
direction
1 bar
cm 3
With
these high
it must
tallisation
andcooling
hencerates,
a subsequent
Pressure pK
identical molded part properties.
g
in thethat
specific
volume can
bereduction
born in mind
post-crys3
cm
occur. This
frequently
the cause of
tallisation
andishence
a subsequent
Pressure pK
g
warpageinand
deviations
reduction
the dimensional
specific volume
can
in
moulded
parts.
occur. This is frequently the cause of
warpage and dimensional deviations
4 Melting temperature
0.80
Efficient,parts.
uniform mould cooling is
in moulded
1600
thus essential in the case of semi0.80
crystalline
plastics.
The cooling
properties
Efficient,
uniform
mould
is of
It is clear from the p-v-ϑ diagram that thermoplastics
do
not
theessential
mouldedinpart
determined
1600
thus
theare
case
of semiby the “processing
operation
in of
the
crystalline
plastics.
The
properties
possess a melting point in the sense of a specific
temperaIf, part
for instance,
identical
themould”.
moulded
are determined
ture at which the material changes its aggregate
state
(melt
rates are
achieved
the
by cooling
the “processing
operationininall
the
areas of
the
moulded
part,
through
mould”.
If,
for
instance,
identical
-> solid). Thermoplastics have a melting range
or
a
freezing
identical
cooling
conditions,
this
0.70
cooling
rates
are achieved
in then
all the
will mark
major steppart,
in thethrough
direction
temperature range.
areas
of thea moulded
of
identical
moulded
part
properties.
identical cooling conditions, then this
0.70
will mark a major step in the direction
This transition, or the start of the change from
themoulded
molten
of identical
part properties.
0
50
100
150
200 °C 250
Temperature ϑ
0
Specific volume v
Specific volume v
0
Fig. 10 shows the difference between slow isobaric cooling
and heating at ambient pressure, and at 400 bar, for a polypropylene grade. It is only when the crystallization temperature established in the slow cooling test has been surpassed
by a considerable margin that the straightline curve for the
melt is attained. The point of contact characterises crystallite melting, and is denoted as the crystalline melting point
ϑKS.
Fig. 9: 0Comparison
of a semi-crystalline
50of slow and
100rapid isobaric
150 cooling
200
°C 250
thermoplastic at two different Temperature
pressures (Source:
IKV)
ϑ
Fig. 9: Comparison of slow and rapid isobaric cooling of a semi-crystalline
thermoplastic
at two
different
Fig. 9: Comparison
of slow
and
rapid pressures
isobaric (Source:
coolingIKV)
of a semi-crystalline
thermoplastic at two different ­pressures (source: IKV)
4. Melt temperature
isobaric heating
isobaric cooling
cm 3
g
(
1.30
melting line
dϑ
) = 0.04 °C/s
dt ϑG
1
1 bar
2
400
solidification
line
Specific volume v
phase to the solid phase, is known as the glass transition
temperature or the freezing temperature for amorphous
thermoplastics. The value of this temperature
6 is a function of
the cooling rate and the ambient pressure (see Figs. 6 and 7).
6
In the case of semi-crystalline thermoplastics,
reference is
made to the crystallization temperature. This crystallization
temperature is a function of the pressure and is hardly
­affected by the cooling rate (Fig. 9). There can, however, be
differences in the cooling and melting of semi-crystalline
thermoplastics.
4
5
Pressure pK
1
1.20
4
1
1.10
3
4
0
50
100
150
Temperature ϑ
200
°C
250
Fig. 10: Slow isobaric cooling and heating of a semi-crystalline thermoplastic
(Source: cooling
IKV)
Fig. 10: Slow isobaric
and heating of a
semi-crystalline thermoplastic (source: IKV)
200
1 bar
°C
180
erature ϑK
COV00073621/Page 6 of 12
www.plastics.covestro.com
Edition 2016-03
melting range (raw material producer)
It is clear from the p-v- ϑ
thermoplastics do not
melting point in the sense
temperature at which t
changes its aggregate
−> solid). Thermoplastics
ing range or a freezing
range.
This transition, or the s
change from the molten
solid phase, is known a
transition temperature or
temperature for amorph
plastics. The value of this
is a function of the coolin
ambient pressure (see F
In the case of semi-crysta
plastics, reference is m
crystallisation temperatu
tallisation temperature is
the pressure and is hardl
the cooling rate (Fig. 9)
however, be differences
and melting of semi-cryst
plastics.
Figure 10 shows the di
tween slow isobaric co
heating at ambient pres
one hand, and at 400 bar
hand. It is only when the
temperature established
cooling test has been su
considerable margin that
line curve for the melt is
point of contact charac
tallite melting and is de
crystalline melting point ϑ
The hysteresis between
cooling is due to suppr
tallisation during coolin
pressed crystallisation o
0
100
150
Temperature ϑ
°C
200
250
Fig. 10: Slow isobaric cooling and heating of a semi-crystalline thermoplastic
(Source: IKV)
The hysteresis between heating and cooling is due to
­suppressed crystallization during cooling. This suppressed
crystallization occurs already at very low cooling rates [3].
In other words, crystallization sets in at lower temperatures.
200
1 bar
°C
With the cooling rates encountered in practice (>> 0.02 ° C/s)
the fall in crystallization temperature is more or less constant (Fig. 11).
Crystallisation temperature ϑK
180
5 State curve during injection molding
Using the p-v-ϑ diagrams that have been presented, it is
possible to show the thermodynamic state curve prevailing
during injection molding for the three process stages of
molded part filling, holding pressure phase and residual
cooling phase.
This is done by transferring the pressures and temperatures
that prevail during the different process stages to a p-v-ϑ diagram, on an isochronous basis. Figure 12 shows a
­measured pressure profile close to the gate and a computed
mean temperature profile inside the molding in the course of
the injection molding cycle. The numbered points are transferred to the material’s p-v-ϑ diagram (Fig. 13).
50
The hysteresis between
cooling is due to suppr
tallisation during coolin
pressed crystallisation oc
low cooling rates already
words, crystallisation set
temperatures.
melting range (raw material producer)
160
With the cooling rates en
practice (>> 0.02 °C/s
crystallisation temperatu
less constant (Fig. 11).
140
120
0
5
Mean cooling rate
(
10
dϑ
)
dt ϑK
°C/s
Fig. 11: Influence of cooling rate on crystallisation temperature (Source: IKV)
Fig. 11: Influence of cooling rate on crystallization temperature
(source: IKV)
5. State curve during injection
500
300
(Fig. 13).
plotted
on Figs. 12 and 13 are as
follows:
meanings
of the state points
Based on state curves like this, it is possible toThe
make
meanplotted
onmould
Figs. filling
12 and 13 are as
Start of
ingful statements on the course of shrinkage1and
on
the
follows:
(melt touches pressure sensor)
movement of the melt at each stage of the process.
7
21 Mould
isPoint
volumetrically
Start of
mould
filling full
on the Figures (the attainment of atmospheric
ispressure
im-phase
3 pressure)
End
of touches
compression
(melt
sensor)
42 Switchover
to holding
Mould
is volumetrically
full
portant for the start of shrinkage. This point can
occur
at
dif- pressure
discharge
of cavity
3 (partial
End ofprofiles
compression
phasewith
ferent temperatures with different holding pressure
melt flowing
into melt
4 antechamber)
Switchover to holding pressure
and cooling ­conditions. It is possible to influence(partial
shrinkage
in
discharge of cavity with
5 Holding
pressure
melt flowing
into level
melt
this way.
Gate
has frozen
antechamber)
75 Pressure
has sunk level
to atmosHolding pressure
pressure
6 pheric
Gate has
frozen
(start of shrinkage)
7 Pressure has sunk to atmos8 Mean
temperature has
phericmelt
pressure
attained
temperature
(start offreezing
shrinkage)
98 Demoulding
Mean melt temperature has
v
SpecificSpecific
volume volume
v
Pressure
p
Pressure
p
Temperature
T
Temperature
T
moulding
4
The state points plotted on Figs. 12 and 13 indicate
the
bar
3
500
5.
curve diagrams
during injection
UsingState
the p-v-ϑ
that have
­following:
°C
400
300
beenmoulding
presented, it is possible to
4
mean molding compound
bar
3
1 Start of mold filling (melt touches pressure
sensor)
portray
the thermodynamic state curve
temperature in mold TM
Using
the
p-v-ϑ
diagrams
that
have
prevailing during injection moulding
200
°C
400
2 Mold is volumetrically full
300
been
presented,
is possible
to
for
the three
processit stages
of mouldmean molding compound
portray
the thermodynamic
state
curve
3 End of compression phase
ed
part filling,
holding pressure
phase
temperature in mold TM
prevailing
2
200
5
and
residualduring
coolinginjection
phase. moulding
4Switchover to holding pressure (partial discharge
300
for the three process stages of mould200
8
ed
part
filling,
holding
pressure
phase
This is done by transferring the
of cavity with melt flowing into melt antechamber)
100
2
5
and residualand
cooling
phase.
pressures
temperatures
that
5Holding pressure level
200
prevail during the different process
100
8
This istodone
byϑtransferring
the
mould pressure
stages
a p-vdiagram, on
an
100
6 Gate has frozen
pressures basis.
and temperatures
thata
isochronous
Figure 12 shows
start of shrinkage
6
7
prevail during
theprofile
different
process
1
7Pressure has sunk to atmospheric pressure
measured
pressure
close
to the
100
0
0
mould pressure
stages
p-v- ϑ diagram,
on an
gate
andtoa acomputed
mean tem0
5
(start of shrinkage)
10
15
20
25
30 s 35
isochronous
basis.
Figure
12 showsina
start of shrinkage
perature
profile
inside
the moulding
6
7
Time t
1
measured
profile close
to the
8Mean melt temperature has attained freezing
the
course pressure
of the injection
moulding
0
0
gate The
andnumbered
a computed
mean
cycle.
points
are temtrans- Fig. 12: Pressure
profile during
the25injection30moulding
0
5and temperature
10
15
20
s 35
temperature
perature
profile
inside
the
moulding
in
Fig. 12: Pressure
and
ferred to the material’s p-v-ϑ diagram
cycle
[4] temperature profile
Time­dt uring the injection molding
the course
of the injection moulding cycle [4]
(Fig.
13).
9Demolding
cycle. The numbered points are trans- Fig. 12: Pressure and temperature profile during the injection moulding
10 Molded part has reached room temperature
ferred
to the material’s
p-v-ϑpoints
diagram
cycle [4]
The
meanings
of the state
1
6
1.04
cm 3
g
1.04
1.02 3
cm
g
1.02
1.00
Material: polystyrene
2
10 Moulded
part has
Taking
state curves
likereached
this, it isroom
possible temperature
to make meaningful statements
on the course of shrinkage and on the
Taking state
curves
this, itstage
is posmovement
of the
meltlike
at each
of
sible
to makePoint
meaningful
statements
the
process.
7 on the
Figures
on
the
course
of
shrinkage
and
on
the
(the attainment of atmospheric presmovement
of the melt
each
stage
sure)
is important
for at
the
start
of of
the process.
onoccur
the Figures
shrinkage.
ThisPoint
point 7can
at dif(the
attainment
of
atmospheric
presferent temperatures with different
sure) is
important
for the
of
holding
pressure
profiles
andstart
cooling
shrinkage. ItThis
point cantooccur
at difconditions.
is possible
influence
ferent temperatures
shrinkage
in this way. with different
holding pressure profiles and cooling
conditions. It is possible to influence
shrinkage in this way.
COV00073621/Page 7 of 12
www.plastics.covestro.com
Edition 2016-03
8
1
Material: polystyrene
6
7
5
4
32
200
3
5
4
6400
600
1.00
8
200
0.98
800
400 1000
600 1200
8
0.98
800 1400
0.96
1000 1600
10
12001800
9
0.95
0
50
100
150
200 1400
°C 250
0.96
1600
10
Temperature T
1800
0.95
0 curve during
50 injection
100moulding150
200
°C 250
Fig. 13: State
Temperature T
~ volumetric
shrinkage
∆V
~ volumetric
shrinkage
∆V 9
7
10 Moulded
has reached
room
attained part
freezing
temperature
Fig. 13:curve
State curve
during
injectionmolding
moulding[4]
Fig. 13: State
during
injection
9 temperature
Demoulding
8
Figure 10 shows the dif
tween slow isobaric co
heating at ambient pres
one hand, and at 400 bar
hand. It is only when the
temperature established
cooling test has been sur
considerable margin that
line curve for the melt is a
point of contact charact
tallite melting and is de
crystalline melting point ϑ
dimensionally stable. The ejector pins
and their holes should not be allowed
to leave pronounced marks on the
moulding.
6 mm
tk
4 mm
100
If the target of a short cycle
time
is to
6 Demolding temperature
and
cooling
time
be fulfilled, then it is essential for the
6. Demoulding temperature
material-dependent demoulding temand cooling timeperature to be known. Mouldings are
An injection molded
cannot,
frequently part
left in the
mould for or
too should not be demolded
it has
cooled
the point
it is dimensionally staAn until
injection
moulded
part to
cannot,
or timewhere
although
the cooling
to the
demoulding
has
long should not be allowed to
should
be ejector
demoulded
untiland
ittemperature
has
ble.not
The
pins
their
holes
0
elapsed.
60
130 since
ϑE
(°C)
cooled
the point
where
it is
leavetopronounced
marks
on the molding.
Demolding temperature dimensionally
stable. The
ejector
pins
Knowledge
of the
demoulding temperature
is
important
6
mm
and time
their holes should not be allowed on economic
Fig. 14: Influence of demoulding
temperature
on cooling
6. Demoulding
temperature
grounds. Figure 14 shows the inand cooling time
to leave
oncycle
the time
If thepronounced
target offluence
amarks
short
is to be fulfilled, then it is
of the demoulding
temperature
moulding.
on the expected cooling time. The
An injection moulded part cannot, or
(s)
2 mm
100
long, in order to be on the safe side,
essential for the material-dependent demolding temperature to be known. Moldings are frequently left in the mold for
too long, in order to be on the safe side, although the cooling
time to the demolding temperature has long since lapsed.
(s)
lower the demoulding temperature is,
should not be demoulded until it has
longer the cooling time will be.
cooled to the point whereIf itthe
is target of a shortthe
cycle
time is to
ϑE
dimensionally stable. The ejector pins
beallowed
fulfilled, then it is essential
for the
6 mm
The demoulding
temperature, by
and their holes should not be
4 mm
definition, is the
temperature that
to leave pronounced marks
on the
material-dependent
demoulding
temmoulding.
prevails at a point of the moulded part
perature to be known.in Mouldings
are
the central layer of the wall
tk
left in thethickness
mould at
forthetoo
If the target of a short cyclefrequently
time is to
time of demoulding.
be fulfilled, then it is essential
for the
Figure
shows
a temperature profile
4 mm
long,
in order to be on
the 15
safe
side,
2 mm
material-dependent demoulding temin a thermoplastic moulding at the time
although
the
cooling
time
to
the
perature to be known. Mouldings are
of demoulding.
frequently left in the mould
for too
demoulding
temperature has long
0
long, in order to be on the safe side,
2 mm
Alongside this, a mean demoulding
elapsed.
60
130timesince
to the
ϑE
(°C)although the cooling
temperature, ϑ E , is frequently to be
demoulding temperature has long
found. This is the integral mean value
Demolding temperature
0
60
Knowledge of the demoulding
tem130 since elapsed.
ϑE
ϑW(°C)
of the temperature
profile at the time of
Demolding temperature
perature
is importantdemoulding.
on economic
x
Fig. 14: Influence of demoulding temperature on cooling
timeKnowledge of the demoulding
temperature is important on economic
grounds.
Figure profile
14 shows
the inFig.Fig.
14:
of demolding
temperature
14:Influence
Influence of demoulding
temperature
on cooling timeon cooling time
15: Temperature
in a thermoplastic
Wanddicke
ss Figure 14 shows Fig.
Wall
thickness
grounds.
the inmoulding
at the time of demoulding,
fluence
of the demoulding
temperature
fluence of the demoulding temperature
ϑ
in
theThe
centre
demoulding
temperature
E
on the
on the expected cooling time.
The expected cooling time.
lower the demoulding temperature
lower is,
the demoulding temperature is,
the longer the cooling time will be.
tk
Knowledge of the demolding temperature is important on
economic grounds. Fig. 14 shows the influence of the
­demolding temperature on the expected cooling time. The
lower the demolding temperature is, the longer the cooling
time will be.
The demolding temperature, by definition, is the temperature
that prevails at a point of the molded part in the central ­layer
thethe
wall
thickness
the of
longer
cooling
time will at
be.the time of demolding. Fig. 15 shows
The demoulding temperature,abytemperature profile in a thermoplastic molding at the time
definition, is the temperature that
Theof
demoulding
temperature, by
demolding.
prevails at a point of the moulded
part
ϑE
ϑE
is the temperature that
in the central layer of thedefinition,
wall
thickness at the time of demoulding.
prevails at a point of the moulded part
Figure 15 shows a temperature profile
in a thermoplastic moulding in
at thethe
timecentral layer of the wall
of demoulding.
thickness at the time of demoulding.
ϑE
Alongside this, a mean demolding temperature, ϑE, is
frequent­ly to be found. This is the ­integral mean value of the
Figure 15 shows a temperature profile
Alongside this, a mean demoulding
profileatatthethe
in atemperature
thermoplastic
moulding
timetime of demolding.
to
be
temperature, ϑ , is frequently
E
ϑW
ϑW
x
Wanddicke
Wall
thickness s
s
ϑFig.
W 15: Temperature profile in a therx
moplastic
mold­ing at the time
ϑE
of demolding, demolding
^
Wanddicke
Wall
thickness
scenter
temperature
𝛝E in the s
Abbreviations
ϑW
x
found. This is the integral mean
value
of demoulding.
of the temperature profile at the time of
demoulding.
How can the correct demolding temperatures for a
Alongside this, a mean demoulding
Fig.specific
16: Mean demoulding
ϑ
case temperature
be established?
temperature, ϑ E , is frequently Eto be
demoulding temperature ϑE in the centre
found. This is the integral mean value
9
temperature
profile
the time of manufacturers
Fig. 16: Mean
demold­ing tempera- of the
First
of all, the
rawat materials
issue recomdemoulding.
ture 𝛝E
Fig. 15: Temperature profile in a thermoplastic
Wanddicke
ss
moulding Wall
at thethickness
time of demoulding,
mendations as to the mean demolding temperatures for
Fig. 15: Temperature profile intheir
a thermoplastic
products (Fig. 17).
moulding at the time of demoulding,
demoulding temperature ϑE in the centre
Thermoplastics Mean demolding
temperatures (°C)
(Guide values)*
If there is no recommended guide temperature available
for demolding, it can be established from the shear modulus
curve of the material in question [6]:
–
To ensure successful demolding, the mean temperature ϑE
^
Apec® HT Fig. 16: Mean150
demoulding temperature ϑE
ϑPC-HT
or temperature in the center of the molded part ϑE, must not
Wanddicke
Wall
thickness ss
E
lie within the range where the plastic “yields” and is not able
9
(PC+ABS)
Bayblend®
110
to absorb
any force. It is possible to establish this temperature from shear modulus curves. Figure 18 shows the shear
­modulus curve for an ABS. Above a temperature of some
PC
Makrolon®
130
106 °C, the shear modulus falls sharply, which means that dimensional ­stability is no longer guaranteed. The maximum
* I
t
may
be
necessary
to
deviate
from
the
values
in
the
table
depending
on
ϑW
the product grade.
possible ­demolding temperature is thus approximately
x
106 °C.ϑ
Fig. 16: Mean demoulding temperature
E
Wanddicke
Wall
thickness
ss
Fig. 17: Recommended
mean demolding
temperatures for a number of
x
thermoplastics [5]
ϑE max = 106 °C
9
If no shear modulus curves are available, then the maximum
permitted demolding temperature for a given material can
be determined from the p-v-ϑ diagrams described above. In
the case of amorphous materials, this can be the softening
temperature or glass transition temperature and, in the case
of semi-crystalline materials, the crystallization temperature.
For the ABS shown in Fig. 18 (shear modulus curve), a temperature of approximately 110 °C is obtained as the softening temperature from the p-v-ϑ diagram. This tallies well with
the value from the shear modulus curve.
If no curves are available, then the demolding temperature
can be taken as being equivalent to the heat deflection temperature (Vicat temperature).
COV00073621/Page 8 of 12
www.plastics.covestro.com
Edition 2016-03
Measurement of the demolding temperature [7]
2.0
1000.0
500.0
100.0
50.0
1.5
10.0
1.0
1.0
0.5
5.0
As has already been mentioned, the demolding temperature
represents a key criterion for both the requisite cooling time
and the dimensional stability of the demolded part. This
should therefore be verified as precisely as possible on a
•
mean
cooling
rate, slow
part that has
just
been
demolded.
3
cm
g
isobaric cooling ABS
After ejection, the surface temperature of the molded part
rises fairly rapidly to reach a peak value and then falls gradually (Fig. 20). This increase is due to the equalization of the
temperature profile that developed during cooling (and is
Pressure p
1.05
particularly pronounced with larger wall thicknesses).
Specific volume v
N
)
mm2
log. damping decrement Λ
i curves are
ximum permitted
ure for a given
mined from the
ribed above. In
s materials this
temperature or
erature and, in
alline materials,
erature. For the
(shear modulus
of approximately
s the softening
p-v-ϑ diagram.
e value from the
(
Shear modulus G
ange where the
is not able to
is possible to
ture from shear
e 18 shows the
e for an ABS.
of some 106 °C,
s sharply, which
al stability is no
The maximum
temperature is
6 °C.
1 bar
The maximum value measured should be taken as the
0.5
200
­demolding temperature, since this ultimately constitutes a
400 Measuring
measure of the mean molded part temperature.
0.1
the demolding
temperature is important not only
1.0
600 for optimiz–100
+100 °C +150
–50
0
+50
ing the cooling time but also for monitoring the temperature
Temperature ϑ
ϑsolid = 106 °C
of the mold. With an effective form of mold temperature
1000
= ϑE max
lable, then the
­control (which presupposes no major differences in wall
re can be taken
Fig. 18: Determination of the maximum demoulding temperature from a shear
thickness over the molded part), the mean demolding temo the heat de1600
modulus curve
Vicat tempera-Fig. 18: Determination of the maximum demolding t­ emperature from a shear
perature measured should be as constant as possible over
modulus curve, ­material ABS
0.95
all the different regions of the molding. Any differences
would suggest that the mold temperature control has not
been ­efficiently
configured.
of the
• Measurement
demoulding temperature [7]
mean cooling rate, slow
isobaric cooling ABS
cm 3
g
Temperature-controllable contact sensors or noncontact
Pressure p
1.05
Specific volume v
ϑE max = 110 °C
As has already been mentioned, the
infra­rtemperature
ed 0.9
measuring
cells
demoulding
represents
a can suitably be used for measuring
150
250 °C 300
0
100
200
50
key criterion
for both thetemperature.
requisite
the demolding
Temperature ϑ
cooling time and the dimensional
stability of the demoulded part. This
Fig. 19: Demoulding temperature from the p-v-ϑ diagram, material ABS
should therefore be verified as
precisely as possible on a part that has
just been demoulded.
1 bar
400
Temperature
600
1000
1600
0.95
0.9
ϑE max = 110 °C
0
100
50
250 °C 300
150
200
Temperature ϑ
Fig. 19: Demolding temperature from the p-v-ϑ diagram, material ABS
Fig. 19: Demoulding temperature from the p-v-ϑ diagram, material ABS
250
°C
Temperature-controllable contact senspeaking,
the cooling phase in injection molding comsors orStrictly
noncontact
infrared measuring
cells can
suitablywith
be used
meas- signal and ends with the “open
mences
thefor
injection
uring the demoulding temperature.
Temperature
200
Demolding
150
Centre s = 3 mm
Molding material:
polystyrene
s = 6 mm
ϑM = 210 °C
ϑTM = 20 °C
mold” signal. This is because as soon as the hot molten plastic comes into contact with the cooler mold wall at any point
in the mold, cooling then commences in this region.
1.6 mm
100
0.9 mm
0.6 mm
50
Edge
20
0
25
50
75
Time
100
125
150
s
As has alread
demoulding te
key criterion
cooling time
stability of th
should there
precisely as p
just been dem
After ejection,
of the moulde
to reach a pe
gradually (Fig
due to the eq
perature profi
cooling (and is
with larger wa
The maximum
be taken as
perature, sin
stitutes a m
moulded part
the demould
portant not o
cooling time b
temperature
effective form
control (which
differences in
moulded part
temperature m
constant as p
ferent region
differences w
mould tempe
been efficientl
250
After ejection, the surface temperature
°Cpart rises fairly rapidly
of the moulded
to reach a peak value and then falls
Temperaturegradually (Fig.
sors or nonco
200 20). This increase is
due to the equalisation of the temcells can suit
Molding material:
perature profile that developed during
Demolding
uring the dem
polystyrene
cooling (and is particularly pronounced
s = 6 mm
with larger wall
150 thicknesses).
ϑM = 210 °C
Centre s = 3 mm
ϑTM = 20 °C
The maximum value measured should
1.6 mm
be taken as the demoulding
tem100 this ultimately conperature, since
stitutes a measure of0.9
themm
mean
moulded part temperature. Measuring
0.6 mm is imthe demoulding temperature
50 for optimising the
portant not only
Edge
cooling time but also for monitoring the
temperature20
of the mould. With an
effective form of
temperature
75
125
0 mould 25
50
100
150 s 175
control (which presupposes no major
Time
differences in wall thickness over the
Fig.
20:the
Temperature
profile in a plastics moulding before and after demoulding
moulded
part)
mean demoulding
Fig. 20:measured
Temperature
profile
in a plastics molding before and after
temperature
should
be as
demolding
constant as possible over all the different regions of the moulding. Any
differences would suggest that the
mould temperature control has not
7. Cooling
time
been efficiently
configured.
200
1.0
Measurem
demouldin
175
Fig. 20: Temperature profile in a plastics moulding before and after demoulding
COV00073621/Page 9 of 12
www.plastics.covestro.com
Edition 2016-03
Measures should be taken, however, to prevent the mold
from freezing during the filling phase. The loss of heat to the
mold wall should be offset by the flow heat. Most heat is
­released during the residence time (holding pressure phase
and residual cooling phase).
eßen von
au genomund endet
g öffnen“.
unststoffzeugwand
kzeug beeßen von
ereich
die
au genomund endet
g
phase
in
gFüllphase
öffnen“.
nces
with
unststoffze
verhinds
with zur
the
zeugwand
erlust
srkzeug
because
bedie Fließen
plastic
ereich
die
den.
Die
he Standcooler
der
he
mould,
RestkühlsFüllphase
in this
time, or the time by which the de- tK2 = 11.3986 · 2.0874
moulding temperature (see above) will
have been attained. In the case of a tK2 = 24 s
flat panel,
where
an exchange
Simple
cooling
equations
can be usedoftoheat
estimate the coolFigure 21 shows the computed mold surface temperature on
ing
time,takes
or the time
by which
thethe
demolding
the nozzle side for a box-shaped molded part. The
only
place
over
paneltemperature
(see
above)
will
have
been
attained.
In
the
case
of
a
flat
­temperature distribution shown is obtained as a result of the
thickness, the following equation can
­panel, where an exchange of heat only takes place
over
the
cooling
channelthis
positions
and the
temperature
control
estimate,
simple
Theother
temperature
distribution
shown
be used to estimate the cooling time Even if just an
panel thickness, the following equation can be used to
conditions (cooling medium temperature, flow rate). The
example
serves
to
show
that
if
too
low
obtained
as
a
result
of
the
cooli
(for
further
cooling
time
equations
see
­estimate the cooling time (for further cooling time equations
­temperature control for the top and lateral surfaces of the
a
demoulding
temperature
is
selected,
channel
positions
and
the
oth
ATI
892e,
Thermal
Mould
Design,
by
see Technical Information “Optimized Mold Temperature
molded part is not optimally configured.
this
will
have
a
pronounced
effect
on
temperature
control
conditions
(co
the
same
author):
Control”).
the cooling time.
the
example
ing medium
temperature,
TheIn
box
has
a uniformgiven,
wall thickness
yet, despite
this, differ- flow rat
ent
cooling
times
result
for
the
different
regions
on
account
the
20
°C
lower
demoulding
temThe
temperature
control for the t
s2
4 ϑM – ϑ W
of
the
dissimilar
mold
surface
temperatures.
tK = 2
· In
perature extends the cooling time by and lateral surfaces of the mould
·
π ϑE ϑW
π · aeff
part is not optimally configured.
some 30 %!
(
(
The example already set out above will be used once again
tK=
Cooling time
to show how the cooling time can be estimated for the differst = Wall
thickness
time is in- The box has a uniform wall thickne
The length ofent
the
= cooling
time
wallcooling
temperatures.
K
aeff = Effective temperature conductivity
fluenced not only by the demoulding yet, despite this, different cooli
s
= wall thickness
ϑM = Molding compound temperature at end of filling phase
Example:
temperature”
temperature but
also by“Mold
the mould
wall times result for the different regions
= effective
ϑa
= Mean
mold walltemperature
temperature
Weff
^
Wall
thickness:
= 3dissimilar
mm
mould s
temperature.
(For the influence of the account ofs the
conductivity
ϑE = Demolding
temperature at center of molded
part
2
Effective
thermal
diffusivity
of
ABS:
a
=
0.08
eff
wall thickness s and the melt tem- face temperatures. mm /s
ϑM = molding compound
temperature: ϑE = 100 °C
The fact that
the correct demolding
also has a and Demolding
perature,
also the influence
of the
temperature
at end of temperature
filling
Melt temperature after filling: ϑM = 240 °C
decisive influence
on
the
cost
efficiency
of
production
has
mould temperature
on the quality
ofof The
example already set out abo
phase
Wall
temperature
1
–
Center
top
and
Beispiel:
�Entformungstemperatur”
already been mentioned in the previous chapter.moulded
A simple parts see ATI 892e, Thermal will be used once again to show h
ϑW = mean mold wall temperature
lateral surfaces:
ϑWD≈ 50 °C
­example
will be given to illustrate this.
by the
same author.)
the cooling
time
can be estimated
Platte
= 3 mmDesignWall
temperature
2 – Edge of top:
ϑWR
≈ 30 °C
ϑE mit
= Wanddicke:
demolding temperature at s Mould
2/s
=
0,08
mm
Effektive Temperaturleitfähigkeit
für
ABS:
a
the
different
wall
temperatures.
eff a molded
centre of
molded temperature
part
The recommended
demolding
for
Massetemperatur nach der Füllung:
ϑM Figure
= 240 °C21 shows
Employing
the
cooling
time
formula
and
the
conditions
the computed mould
part
in ABS is approximately 100 °C. How is the
cooling time
Mittlere Werkzeugwandtemperatur:
ϑW = 50 °C
­specified, two
times are obtained for the two wall temsurface
temperature
on cooling
the nozzle
affected
if
the
part
is
demolded
at
approximately
80 °C
The
fact
that
the
correct
demoulding
Entformungstemperatur in der Formteilmitte: ϑE1 = 100 °C
peratures:
­instead
of�Entformungstemperatur”
at 100 °C?
for a box-shaped moulded part.
Beispiel:
temperature
also has a decisive inϑE2 side
= 80 °C
Center of top and lateral surfaces: tWR ≈ 18 s
fluence on the cost efficiency of proEdge of top: tWD ≈ 15 s
Example:
“Demoulding
temperature”
Example:
“Demolding
temperature”
Platte
mit 1:
Wanddicke:
s
= 3 mm
Kühlzeit
duction
has
already
been
mentioned
in
2
Panel
withTemperaturleitfähigkeit
a wall thickness of: für ABS: aseff ==3 0,08
mm mm /s
Effektive
Since the demolding temperature ϑE = 100 °C applies to both,
the previous
chapter.
simple exPanel
with
of:
s mm
2 a wall
Effective
diffusivity
ofAABS:
aM
Massetemperatur
nach der
Füllung:
240
°C 2=/s 3 mm
°C – 50 °C ϑ
3thermal
mm2 thickness
eff==0,08
4 240
2/s time is increased by approximately 20 % through
themm
cycle
tample
· In to· of
= 0.08
Effective
thermal
diffusivity
ABS:
aeff
K1 = 2 Werkzeugwandtemperatur:
will
be
given
illustrate
this.
2
Polymer
melt
temperature
after
filling:
ϑ
=
240 °C
Mittlere
ϑ
=
50
°C
M
π 100 °C – 50 °C
π · 0,08 mm /s
W
the
longer
cooling time that is required for the center of the
Moulding
compound
temperature
after
filling:
ϑ
=
240
°C
100M °C
Entformungstemperatur
in der Formteilmitte: ϑ
ϑW
Mean
mold wall temperature:
==50 °C
E1
top
and
the
lateral surfaces.
Mean
mould
wall
temperature:
ϑ
=
50
°C
ϑE2 Example:
= 80 W
°C
Demolding
temperature
center
tK1
= 11,3986
· 1,5766 atdemoulding
The
recommended
tem“Mold
temperature”
^part:
=
100
°C
Demoulding
temperature
at
centre
of
moulded
ϑ
E1
ofperature
molded part:
ϑE1= 100 °C
for a moulded part in ABS is
^
ϑE2 =
80
°C
Different
mold wall temperatures mean different cooling
tKühlzeit
= 18 s 1:
ϑE2= 80 °C
K1
approximately 100 °C. How is the
Wall thickness:
s sur=
3m
rates and hence different properties, such as shrinkage,
2 time
Cooling
time
1:2 affected
cooling
if
the
part
is
face
appearance,
structure
and
warpage.
=
0.08
mm
Effective
thermal
diffusivity
of
ABS:
a
240
°C
–
50
°C
3
mm
4
Kühlzeit
eff
tK1 = 2 2:
· In
·
demoulded
at2/sapproximately
π 100 °C – 5080
ϑE
=
100
°C °C Demolding temperature:
π · 0,08
mm
2
2
3 mm
4 240 °C – 50 °C
These
two filling:
examples have shown just how sensitively
the =
240
°C
–
50
°C
4
tK1
=2
·
In
instead
of
at
100
°C?
240
Melt
temperature
after
ϑ
·
M how
t K2 =π 11.3986
· In2/s · π 100 °C – 50 °C
· 0.08 mm
cooling time responds to the processing conditions and
tK1
= 11,3986
· 1,5766
π 80 °C – 50 °C
Wall temperature
1
–
Centre
of
top
and
lateral
surfaces:
ϑ
≈
50
WD
important temperature control in the mold and optimum
11.3986
· 1.5766
tK1 =
Wall temperature
2 – Edge
of topare for cost-efficient production.
ϑWR ≈
30
= 11,3986
18 s
processing
conditions
ttK2
· 2,0874
K1 =
(
(
(
(
ze verhinerlustbzw.
zur
lzeit
however,
Fließedie
Entformrden.
freezing
Die
oben)
erhe
loss
of
der
StandAbkühldrden.
be
offset
RestkühlFür
quantity
of tK1 = 18 s
er
nur der
= 24 s 2:
tKühlzeit
…/kstenk200.cer
BLOCK NUMBER: 2
BLOCK TEMP [deg. C]
residence K2
24.787
to
61.057
nrichtung
se
and
relzeit
bzw.
folgender
4 240 °C – 50 °C
t K2 = 11.3986
·
Cooling
time 2:· InBeispiel
12
e Entfor- Dieses
einfache
zeigt
– auch
Formteil dargestellt. Aufgrund der
bschätzen
π 80 °C
– 50
°C
oben)
er- wenn es sich nur4um
eine
AbschätLage der Kühlkanäle und der übrigen
gen
siehe
240 °C – 50 °C
can
be zung
tK2 = handelt
11.3986 · Indaß ·sich bei zu niedri- Temperierverhältnisse (KühlmediumAbkühlWerkzeugtK2 = 11,3986–,· 2,0874
π 80 °C – 50 °C
he cooling
erden.
Für ger Entformungstemperatur die Kühl- temperatur, Strömungsgeschwindigh
the
det
=
11.3986
·
2.0874
er nur der zeit
stark ändert. Im Beispiel wird keit) ergibt sich die dargestellte TemtK2
K2 = 24 s
above) will durch
enrichtung
die um 20 °C niedrigere Ent- peraturverteilung. Die Deckfläche und
case of a formungstemperatur
tK2 = 24 s
hfolgender
die Kühlzeit um die Seitenflächen des Kästchens werge of heat ca.
Dieses
einfache
Beispiel zeigt – auch den
Formteil
dargestellt.
Aufgrund der
bschätzen
30 %(!)
verlängert.
nicht optimal
temperiert.
he panel
wennif es
sich
nur
um
eine
AbschätLage
der
Kühlkanäle
und
der übrigen
gen
siehe Even
just an estimate, this simple example serves to show
uation can Neben
zungif handelt
–,
daß sich beitemperature
zu niedriTemperierverhältnisse
(KühlmediumWerkzeugderlow
Entformungstemperatur
hat Das
Kästchenthis
besitzt
gleichmäßi…/schl/kasten
that
too
a demolding
is selected,
will eine
Even
if just
an estimate, this
simple
The
temperature
distribution
is
oling time auch
y z
–40
ger Entformungstemperatur
die
Kühltemperatur,
Strömungsgeschwindigdie
Werkzeugwandtemperatur
ge
Wanddicke,
und
trotzdem shown
ergeben
eitfähigkeit
have
a
pronounced
effect
on
the
cooling
time.
In
the
exam20
example
serves
todie
show
thatder
if too
low sich
obtained
assich
ader
result
of the cooling
ations see einen
x
zeit
stark
ändert.
Im
Beispiel
wird
keit)
ergibt
die
dargestellte
TemEinfluß
auf
Länge
Kühlaufgrund
unterschiedlichen
h Ende
given, the 20 °C
lower demolding
temperature
extends andMOLDFLOW
0
a
demoulding
temperature
is
selected,
channel
positions
the
other
Design, by ple
durch
die um
°C
niedrigere
peraturverteilung. Die Deckfläche und
zeit.
(Einfluß
der20by
Wanddicke
s undEntder Werkzeugoberflächentemperaturen
the
cooling
time
some
30%!
Fig. 21: Computed
mould surface temperature on the nozzle side of a box-shaped moulded part
this
will
have
a
pronounced
effect
on
temperature
control
conditions
(coolformungstemperatur
die Kühlzeit
um unterschiedliche
die SeitenflächenKühlzeiten
des Kästchens
werMassetemperatur
sowie
Einfluß der
Fig.für
21: die
Calculated
je- mold surface temperature on the nozzle
dEmploying
cooling time formula 8. Cycle time
the
In theauf
example
given, weiligen
ing
temperature,
flowthe
rate).
side
of a box-shaped molded part
ca. cooling
30 %(!) time.
verlängert.
den medium
nichtBereiche.
optimal
temperiert.
Werkzeugtemperatur
die Qualität
and the conditions specified, two
The
length
oflower
the cooling
time is influenced
not
only by the
cooling
times
are obtained
for the two The cycle time is the time interval at The cycle time can be shown in
the
20
°C
demoulding
temThe
temperature
control
for
the
top
der Formteile siehe ATI 892, Therur in der
wall temperatures:
graphic form as below:
which the production sequence is
demolding
temperature
but also
byby
the and
moldlateral
wall temperamoulded
perature
extends
the
cooling
time
surfaces
of
the
periodically repeated. It is made up
Neben der
Entformungstemperatur
hat Zur
DasAbschätzung
Kästchen besitzt
eineCentre
gleichmäßimische
Werkzeugauslegung,
gleicher
der Kühlzeit
bei
of top
andden
lateral surfaces:
from the individual production steps The different times can be of different
ture
influence of the wall thickness
sisand
melt
part
notthe
optimally
configured.
some
30the
%!
tWD ≈ 18 s
and the ancillary time.
lengths as a function of the processing
auch(for
die
Werkzeugwandtemperatur
ge Wanddicke,
und
trotzdem
ergeben
verschiedenen
Wandtemperaturen
eitfähigkeit Autor)
conditions.
temperature,
and
also
the influence
of the
mold
temperature
Cycle time = filling time + holding
Edge of top: tWR ≈ 15 s
einen
Einfluß
auf
die
Länge
der
Kühlsich
aufgrund
der
unterschiedlichen
wird
das
obige
Beispiel
erneut
aufgeh Endeerwurde
pressure time + residence time (resi- Normally, however, the residence time
on
the
quality
of
molded
parts,
see
Technical
Information
The
box
has a uniform wall
The
length
ofder
the
cooling
time
is der
inor residual cooling time accounts for
Since thickness
the demoulding temperature dual cooling time) + ancillary time.
zeit.
(Einfluß
Wanddicke
s und
Werkzeugoberflächentemperaturen
Bild
21 ist
eine
berechnete
Werkgriffen.
formungs- Im
the largest time span.
ϑE = 100 °C applies to both, the cycle
yet,
despite
this,
different
cooling
fluenced
not
only
by
the
demoulding
“
­
Optimized
Mold
Temperature
Control”.
time
isfür
increased
approximately (Opening and closing of the mould,
Massetemperatur
sowie
Einfluß
der
unterschiedliche
Kühlzeiten
die byjenddend die zeugoberflächentemperatur auf der
20 % through the longer cooling time ejection, switchover time and, where
times
result
for
the
different
regions
on
temperature
but
also
by
the
mould
wall
re
that is required for the centre of the top appropriate, plasticisation time.)
Werkzeugtemperatur
auf die Qualität weiligen Bereiche.
Düsenseite
für ein kastenförmiges
uktion be- COV00073621/Page
10the
of 12
the lateral surfaces.
surtemperature.
influence
the account of the dissimilarandmould
der Formteile(For
siehe
ATI
892, of
Therur
in der
ches
Bei- www.plastics.covestro.com
Different
mould wall temperatures
face
temperatures.
wall
thickness
s
and
the
melt
temmische
Werkzeugauslegung,
gleicher
Zur
Abschätzung
der
Kühlzeit
bei
den rates and
Edition 2016-03
mean different cooling
hence different properties, such as
perature,
and also the influence of the verschiedenen Wandtemperaturen
of filling
Autor) �Werkzeugtemperatur”
Filling time
Holding pressure time Residence time/residual cooling time Ancillary time
Beispiel:
shrinkage, surface appearance, structure and
mould temperature on the quality of The
outwarpage.
above
wird example
das obigealready
Beispielset
erneut
aufgewurde
ereine Entmoulded parts see ATI 892e, Thermal will be used once again These
to show
how
two examples
have shown just
mperature
( (
(
(
( (
(
(
24.787
27.810
20.832
33.855
36.877
39.900
42.922
45.945
48.967
51.990
55.012
58.035
61.057
…/schl/kasten
y
z
x
8 Cycle time
pressure of
dependence
of the
number
amorphous
andspecific
semienthalpy plays
only a minor
crystalline
thermoplastics.
Since role
the
by comparison
to its oftemperaturepressure
dependence
the specific
dependence
(order
magnitude
enthalpy
plays
only of
a minor
role
approximately
bar) the
by
comparison 10
to %/1000
its temperaturediagrams measured
1 bar can
dependence
(order atofp =magnitude
suitably be applied
practice.
approximately
10 in
%/1000
bar) the
diagrams measured at p = 1 bar can
suitably be applied in practice.
–40
20
0
d surface temperature on the nozzle side of a box-shaped moulded part
ve shown just
oling time
ng conditions
temperaturethe optimum
e for the cost-
Normally, however, the residence time
or residual cooling time accounts for
thegraphic
largest time
span.
in
form
as below:
The cycle time can be shown
(Opening and closing of the mould,
The
different times can be of different lengths as a function
ejection, switchover time and, where
of
the processing
conditions.
appropriate,
plasticisation
time.)
Normally, however, the residence time or residual cooling
time accounts for the largest time span.
Specific
enthalpy
h
Specific
enthalpy
h
pressure time + residence time (residual cooling time) + ancillary time.
Temperature ϑ
Temperature ϑ
Filling time
Holding pressure time
Residence time/residual cooling time
Ancillary time
HDPE
HDPE
9. Cooling
Heattime
content
a in the cavity
for a specificof
point
molten
plasticof a
9. Heat
content
molten plastic
Cycle time
Before the requisite cooling capacity of The term specific enthalpy denotes the A comparison of the two classes of
the
mould
control
system
heat
content
of a mashowsofthat
Before
the temperature
requisite cooling
capacity
of mass-related
The term specific
enthalpy
denotes
the material
A comparison
thesemi-crystalline
two classes of
9 Heat
content
of a molten
plastic
can
be
established,
it iscontrol
necessary
to terial
as a function
temperature
and materials
have athat
considerably
higher
the mould
temperature
system
mass-related
heatofcontent
of a mamaterial shows
semi-crystalline
know
heat content
that
is released
The enthalpy
values and
for heat
content
amorphous
macan bethe
established,
it is
necessary
to pressure.
terial as a function
of temperature
materials
havethan
a considerably
higher
Before
requisite
cooling capacity of the mold temperaby
a the
molten
plastic.
plastics areThe
frequently
found
in diain the molten
range. Approknow
the heat
content that is released pressure.
enthalpy
values
for terials
heat content
than amorphous
mature control system can be established, it is necessary to
gram form,
the enthalpy
capacity
is required
by a molten plastic.
plastics
arewith
frequently
found plotted
in dia- ximately
terialsTemperature
intwice
the ϑthe
molten
range.
Approknow the heat content that is released by a molten plastic.
13
22: Specific enthalpy as a function of temperature for a number of thermoplastics; p = 1 bar
The mean quantity of heat to be over
temperature.
Figure
22plotted
shows to
meltTemperature
ortwice
cool ϑthe
semi-crystalline
mouldgramthe
form,
with theFig.
enthalpy
ximately
capacity is required
eliminated
time unitofis heat to be specific
enthalpy 14
diagrams
for
a
ing
compounds
in
the
same
period
The
meanper
quantity
over
the
temperature.
Figure
22
shows
to
melt
or
cool
semi-crystalline
mouldFig. 22: Specific enthalpy as a function of temperature for a number of thermoplastics;
p = 1 of
bar
The mean quantity of heat to be eliminated per time unit is
Fig.diagrams
22: Specific
enthalpy
asing
a function
of temperature
forsame
a number
of ther-of
number of
amorphous
and
semitime
as
amorphous
ones.
eliminated per time unit is
specific
enthalpy
for
a
compounds
in
the
period
14
moplastics; p = 1 bar
crystallineofthermoplastics.
Since
the time as amorphous ones.
number
amorphous and
semipressure dependence
of the
specific
crystalline
thermoplastics.
Since
the Whilst amorphous thermoplastics
enthalpy
plays only of
a the
minor
role display
a more or less
steady depressure dependence
specific
Whilst amorphous
thermoplastics
by
comparison
its atemperaturecrease inatheir
specific
enthalpy,
enthalpy
plays to
only
minor role display
more or less steadythere
deSummary
dependence
(order
oftemperaturemagnitude is
a sharp
bendspecific
in the curve
for semiby
comparison
to10its
crease
in their
enthalpy,
there
approximately(order
10 %/1000
bar) the crystalline
thermoplastics
the
dependence
of magnitude
is a sharp bend
in the curve forinsemiThe
being
processed passes
through differdiagrams measured
atthermoplastic
p = 1bar)
bar can
crystallisation
interval.
approximately
10 %/1000
the crystalline
thermoplastics
in the
thermodynamic states in the course of the injection
suitably bemeasured
appliedent
in at
practice.
diagrams
p = 1 bar can crystallisation interval.
molding process. Knowledge of the state curve during prosuitably be applied in practice.
cessing makes it easier to selectively control the processing
­sequence and exert a positive influence on it.
The term specific enthalpy denotes the mass-related heat
content of a material as a function of temperature and presThe cooling behavior of the melt can be influenced to a prosure. The enthalpy values for plastics are frequently found in
diagram form, with the enthalpy plotted as a function of tem- nounced extent by the cooling in the mold. Different mold
surface temperatures can lead to dissimilar cooling times
perature. Figure 22 shows specific enthalpy diagrams for a
­inside the molded part. The solidification behavior, i.e. the
number of amorphous and semicrystalline thermoplastics.
level of the glass transition or crystallization temperature, is
Since the pressure dependence of the specific enthalpy
a function of the ambient conditions (pressure, cooling and
plays only a minor role by comparison to its temperature deheating rate), where with amorphous and semi-crystalline
pendence (order of magnitude approximately 10 %/1000
thermoplastics, elevated cooling rates relatively soon lead
bar), the diagrams ­measured at p = 1 bar can suitably be apto specific volumes that remain constant. The position of
plied in practice.
the cooling channels also has an influence here. If the part
is not cooled uniformly then a dissimilar structure can
A comparison of the two classes of material shows that
develop ­inside it, leading to dissimilar shrinkage and warsemi-crystalline materials have a considerably higher heat
page behavior.
content than amorphous materials in the molten range.
Approxi­mately twice the capacity is required to melt or cool
A carefully selected demolding temperature makes temperasemi-crystalline molding compounds in the same period of
ture contributes to more cost-efficient production.
time as amorphous ones.
heat toheat
be to be
eliminated
eliminated
emperatures
g rates and
ties, such as
arance, struc-
graphic form as below:
Specific
enthalpy
h
Specific
enthalpy
h
temperature
oth, the cycle
pproximately
cooling time
ntre of the top
crystalline thermoplastics in
crystallisation interval.
Specific
Specific
enthalpy
enthalpy
h h
surfaces:
which the production sequence is
periodically
is made
up
Cycle
timerepeated.
= fillingIttime
+ holding
pressure time + residence
from the individual production steps The different times can be of different
time
(residual
cooling time) + ancillary
time
(opening
and
and the
ancillary time.
lengths as a
function
of the processing
conditions.
closing of the mold, ejection, switchover
time and, where
Cycle time = filling
time + holding
appropriate,
plasticization
time).
Knowledge of the material’s state curve during processing –
While amorphous thermoplastics display a more or less
and particularly during the cooling phase – is especially
steady decrease in their specific enthalpy, there is a sharp
Temperature
bend in the curve for semi-crystalline thermoplastics
in the ϑ ­important when engineering thermoplastics are to be procrystallization interval.
Temperature ϑ cessed into highly-stressed, high-grade molded parts.
COV00073621/Page 11 of 12
www.plastics.covestro.com
Edition 2016-03
lpy
h h
time formula
ecified, two
ed for the two
The cycle time is the time interval at which the production
8. Cycle time
sequence
is periodically repeated. It is made up from the individual
production steps and the ancillary time.
The cycle time is the time interval at The cycle time can be shown in
Whilst
amorphousones.
thermopla
time
as amorphous
display a more or less stead
crease
in
their
specific
enthalpy,
Whilst amorphous thermopla
is a sharp
curve
for
display
a bend
more inorthe
less
stead
crystalline
thermoplastics
in
crease in their specific enthalpy,
crystallisation
interval.
is a sharp bend in the curve for
HDPE
HDPE
11 References
[1]Thienel, P.: Der Formfüllvorgang beim Spritzgießen von
­Thermoplasten. Dissertation, RWTH Aachen, 1977
[2]Hirai, N./Eyring, H. B.: Viscosity of Polymeric Systems,
Journal Appl. Phys., Vol. 29, Nr. 5 (1958), S. 810–816
[3]Stuart, H. A.: Die Physik der Hochpolymeren. (Bd. 3, 1955,
Springerverlag, Berlin
[4]Thienel, P./Kemper, W./Schmidt, L.: Praktische Anwen­
dungsbeispiele für die Benutzung von p-v-ϑ-Diagrammen.
Mitteilung aus dem Institut für Kunststoffverarbeitung an
der RWTH Aachen
[5]N.N.: Verarbeitungsdaten für den Spritzgießer.
Informationsschrift. Covestro, Leverkusen
[6]Sarholz, R.: Rechnerische Abschätzung des Spritzgieß­prozesses als Hilfsmittel zur Maschineneinstellung.
Dissertation, RWTH Aachen, 1980
[7]N.N.: Spritzgießen – Verfahrensablauf, Verfahrensparameter, Prozessführung. Institut für Kunststoffverarbeitung
an der RWTH Aachen
Typical value
These values are typical values only. Unless explicitly agreed in written form, they do not constitute a binding material specification or warranted values. Values may
be affected by the design of the mold/die, the processing conditions and coloring/pigmentation of the product. Unless specified to the contrary, the property
values given have been established on standardized test specimens at room temperature.
The manner in which you use and the purpose to which you put and utilize our products, technical assistance and information (whether verbal, written or by way of
production evaluations), including any suggested formulations and recommendations, are beyond our control. Therefore, it is imperative that you test our products,
technical assistance, information and recommendations to determine to your own satisfaction whether our products, technical assistance and information are
suitable for your intended uses and applications. This application-specific analysis must at least include testing to determine suitability from a technical as well as
health, safety, and environmental standpoint. Such testing has not necessarily been done by Covestro.
Unless we otherwise agree in writing, all products are sold strictly pursuant to the terms of our standard conditions of sale which are available upon request. All
information and technical assistance is given without warranty or guarantee and is subject to change without notice. It is expressly understood and agreed that you
assume and hereby expressly release us from all liability, in tort, contract or otherwise, incurred in connection with the use of our products, technical assistance,
and information. Any statement or recommendation not contained herein is unauthorized and shall not bind us. Nothing herein shall be construed as a recommendation to use any product in conflict with any claim of any patent relative to any material or its use. No license is implied or in fact granted under the claims of any
patent.
With respect to health, safety and environment precautions, the relevant Material Safety Data Sheets (MSDS) and product labels must be observed prior to working
with our products.
Covestro Germany AG
Business Unit Polycarbonates
D-51365 Leverkusen, Germany
[email protected]
www.plastics.covestro.com
COV00073621/Page 12 of 12
Edition 2016-03