Kinetic Friction Coefficientand Factors
Affecting Paddy Hulling
Veerapong Kanchanawongkul
Departmentof MechanicalEngineering,Faculty of Engineering.
South-EastAsia University,Bangkok, I 0160, Thailand.
Fax: (662) 8074528-30
Tel: (662) 8014500-21,
E-mail:[email protected]
Abstract
Paddy hulling is operatedby Thai farmersin a mannerthat the rotating machineis dependenton
the principle of transferringpotentialenergyto kinetic energy.The original machinewas constructed,
and particularly required to husk paddy and importantly developedto determinethe kinetic friction
coeff,rcientof a new machine.Three types of surfacematerials(phenolic discs, polyamide discs and
hardwood discs) were designed,tested and then compared to paddy hulling while the moisture
contents'were adjustedand maintainedto constant points. This investigationwas plenned for the
designedmachine to measure forces, determine kinetic friction coefficients and factors affecting
paddy hulling while the machine was operated.The experimentalresults of three moisture contents
were about ll, 16 and 23 ohw.b. of paddy types. The forces were measuredto increaseboth the
torquesand the kinetic friction coefficient,but decreasingthe percentagehulling as moisturecontents
were increased.The data comparisonsof paddy hulling found that the kinetic friction coefficient of
and 0.189-0.246for ll to 23
threetypes of surfacematerialsaveragedat0.155-0.221,0.214-0.288
%w.b. The resultswere used to find the important factors.Different resultswere due to the moisture
contentsof paddy grains and the contact between surfacediscs and paddy grains. The grains were
hulled betterwithin the rangesfrom ll to l6 %w.b. than the 23 ohw.b.of paddy types.The statistical
values of the phenolic discs and the hardwood discs were 0.7 to 1.0 of the significancerange with
good relative data,exceptsomeof the percentagehulling data.However,resultswere observedthat as
the moisture contentsincreased,there was no effect on the friction coefficient for somepaddy types.
This was oppositeto the percentageof hulling.
Keywords:
phenolic discs, polyamide discs, hardwood discs, kinetic friction coefficient, paddies
hullins.
1. Introduction
At present,Thai farmers are professingto
do paddy farming. Its agricultural productions
have been harvested (called paddy) and then
hulled (called rice). The standardof rice, brown
rice (cargo rice), meansrice obtainedfrom nonglutinous paddy or glutinous paddy of which
only the husk has been removed.This includes
its whole grain, head, big broken pieces, and
For inspection,
small broken pieces ll2]
gradingfactorsofpaddy and rice were separated
to determine qualities depending on moisture;
impurities and foreign matter; seedsand foreign
matter; red grains and streaks, chalky and
immature grains,damagedgrains,
foreign grains, total and head rice milling yield
in test milled rice [2]. The hulling was divided
according to family and commercial machines
were made up of rubber rolls to perform
shearing, which differed in space rolls,
diametersand speeds[4, 5, 8, 9, 13, l4l.
Figure I shows backgroundhulling with a
family machineusedby Thai farmerswhich was
a rotatingmachine,which relied on the principle
oftransferring potentialenergyto kinetic energy
for fixed rotation axis hulling [8]. The original
machinethat was usedto husk paddy was newly
designedand used by investigatorsto determine
the kinetic friction coefficient of agricultural
production.The usabletesting consistsof tilting
ThammasatInt. J.
ofvarious angle planesfor the static friction test
or moving for the kinetic friction test.
Figure l. Original machineof Thai farmers
The research of various investigators
employedfacility with a transmissionsystemto
drive a table which moved linearly and
horizontally at constant speed. The force
requirerrGntwas measuredby a transducerand
connectedto the cylinder stationaryon moving
surface.The results found that when moisture
contents were increased the static friction
coefficient decreasedfor soybeans on sheet
metals.On the other hand, for both soybeanson
sheetplywood and shelledcom on sheetmetal,
the resultsfound that when the moisturecontent
of grains increasedthe static friction coefficient
also increased.Increasingthe moisture content
ofgrains, such as shelledcorn, tendedto lead to
higher kinetic friction coefficient than soybeans
Investigationof the friction coefficientsfor
paddy hulling was conducted for what was
consideredworking forces for essentialpaddy
hulling. Past research was involved in an
improved machine for Thai farmers to decrease
forces in paddy hulling. The experimental
results showed that decreasingcomplete grain
hulling caused moisture content of grains to
decreaseby favorable rotation of surface discs
with moving air-velocitiesof 30 rym and 9 m/s
t5] The investigation of surface materials
involved effectivenessof paddy hulling. The
additionally selected surface materials were
phenolic (bakelite) and polyamide (nylon). The
experimentalresultsrevealedthat paddy hulling
of coarse phenolic was close to wood
Polyamidewas lower than wood and phenolic.It
was believed that the friction coefficient
affected paddy hulling as there were no different
moisturecontents[6]. Therefore,the purposeof
this investigationwas to plan on the designec
machine to measure forces. determine the
kinetic friction coefficientsand factors affecting
paddyhulling while the machinewas operated.
2. Materials and Methods
t3l.
For investigatedwheat on metal surfaces,it
was found that both normal pressure and
velocity have little affect on coefficients of
kinetic friction. An increase of both relative
humidity and moisturecontentof grainsaffected
an increaseofcoefficientofkinetic friction I l].
To determinethe friction coefficient, the static
force was first measured with forces on the
container transversely applied, and then the
kinetic forces were also measuredas read on a
scalewhen its force was connectedwith rotating
disc. It had been used to chop straw and hay
underdry conditions,while it had also beenused
to chop grass and silage with high moisture
contents.The resultsfound that normal pressure
had little affect on the static friction coefficient
in dry conditions and there was no significant
change in the kinetic friction coefficient for
moistureconditionsas well as dry conditionsfor
chopped straw on steel at speedsto 30.5 m/s
tl0l.
(a) Main componentsof machine
(b) Top cylinder container
Figure 2. The experimentalmachine
2008
ThammasatInt. J. Sc. Tech.,Vol. 13, No.3, July-September
Figure 2 shows the experimentalmachine
which was designed to investigate and
determine the kinetic friction coefficients and
factors affecting paddy hulling. Figure 2 (a)
shows the three main components of the
machineand a top containeras shown in Figure
2 (b). The working machine was driven with a
transmissionsystem of 0.5 hp and a rotation
blower of 0.25 hp. The speedsof the motors
were adjustedby an inverter for paddy hulling,
brown rice and then huskswere also separated.
(b) Drawing of low surfacedisc
Figure 4. Specificationofsurface disc
The frame of the experimentalmachine was
designedwith the transmissionsystemto rotate
the disc with two parts of a variablespeedmotor
separatedfrom the main frame of the machine.
This determiningspeedwas controlledat 30 rpm
for the rotating low surfacedisc and moving airvelocitiesof 9 m/s in a squarepipe of 120 x 120
mm and 1,200 mm in length. At the balance
center, the main shaft was connectedwith the
low surface disc. The side walls of the top
container were essentially supported by the
flanged bearing housingsand the main shaft of
38 mm. It was machinedto 25 mm in diameter
to the balancecenterfor paddy hulling.
The torque requirement can be calculated
by a fundamental equation of friction forces, an
observedon a scale of a force gage, multiplied
by the 0.225 m moment arm. This coefficient of
friction was calculated by a ratio of the friction
forces to normal forces. A general equation can
be written as [7]:
Figure 3. Settingand measuringfriction forces
Figure 3 shows the experimentalmachine,
in which each weight of paddy was replacedin
the top container, and then rotation of a low
container started. It was supported by a thrust
ball bearing. The low surface disc was
connected to a container. A top container was
pulled by a wire which was connectedwith SYG
78095 force gage 20 kg (spring gage) to
measureforces. The two rings of the container
were dimensional specified by outside diameter
and thickness of 450 ffrm and 40 nun,
respectively.Three types of surfacediscs were
used and made with phenolic (bakelite),
polyamide (nylon) and hardwood which were
dimensionalspecified as shown in Figure 4 (a
and b).
a c
-
T
F
wR
w
/ l r
where cp : friction coefficient
torque, kg-m
friction force, kg
F :
normal force, kg
moment arTn,m
The scale weight of paddy grains with top
cylinder container was determined as normal
forces.This requireda scaleweight equal to the
original machine, which was operatedby Thai
farmers. The testing method was repeated with
three replications per treatment of each paddy
type: Phitsanulok2, PathumThani I and Suphan
(a) Drawing of top surfacedisc
10
2008
13,No.3, July-September
Buri l. The moisturecontentswere testedby the
air-ovenmethod [2].
Powdered paddy samples(about 5 g with
container)were placed in an electricaloven for
'c
5 hours at 130 temperaturesand removedinto
a desiccator immediately. The container plus
dried sampleswere weighedand recorded[],2].
The percentage moisture contents were
calculated on a wet basis (zw'b.) and
algebraically,the equationcan be written as [2]:
%MC
3. Results and Discussions
The original results of the experimentamachine as shown in Tables I to 3 were
analyzedto find statistical correlations between
moisture contents affecting the torque, the
friction coefficient and percentagehulling. The
results also showed the trend lines while using
threetypes ofsurface discs,suchas the phenolic
(bakelite), the polyamide (nylon) and wood
(hardwood),which were designedand made for
essentialtesting.
Tatlle 1. Torque,friction coefficient and hulling
of the experimentalmachinewith phenolic discs
(density:1,210 kg/m') by moisturecontent'
m
=-x100
w
t
w
:xloo
(2)
Paddy grains
w - w
m
o
MC
(%w.b.)
T
(kg-m)
CF
(Kinetic)
Hulling
(%)
m
where %MC*6- percentagemolsturecontent
on a wetbasis
: weight of moisture(H2O)in
Wthe grain.g
: total weight of the grain, g
Wt
: weight of dry matter in the
Wagrain, g
Phitsanulok2
Three different moisture contents for each
paddy type were used to investigatethe kinetic
friction coefficient.The moisture contentswere
later changed, by injecting with water to
increase moisture contents and stored in a
container. The moisture contents were
maintained at constant points for about 2 to 3
moisturecontents
days.and then the percentage
were calculatedby Equation (2) on a wet basis
with the air-oven method to determine
percentagemoisture contents.These percentage
of moisture contentson a wet basis were I 1.58,
1 6 . 6 7a n d 2 2 . 9 3 : 1 1 . 4 51. 6 . 8 0a n d 2 2 . 8 4 ;l l . 6 l ,
16.60 and 23.00 for Phitsanulok 2, Pathum
Thani I and SuphanBuri l, respectively.
The data ofeach paddy type was testedand
evaluated from 2 to 4 kg with a setting clearance
of between 1.5 mm for the surface discs,
uniformly calibrated25.3,26.3and21.3kg. The
top weight and measured force deflection from
paddy hulling with previously specified speeds
and air-velocities[5] were usedto determinethe
torque and the kinetic friction coefficient by
Equation (1). These results were then analyzed
statistically.
Pathum Thani I
Suphan Buri I
0.765 0 . 13 4 38.00
I 1 . 5 8 0 . 8 1 0 0 . 1 3 6 37.66
0 . 8 6 8 0 . 1 4 1 33.00
0 . 8 8 4 0 . 15 5 33.00
16.67 0.990 0 . 1 6 7 39.00
1 . 0 9 3 0 .1 7 8 38.00
| . 2 2 1 0.2t4 25.50
22.93 1 . 3 0 5 0.220 28.66
1.440 0.234 2 2 . 5 0
0.823 0 . 1 4 4 32.00
n . 4 5 0.900 0.r52 ) Z . J J
r . 0 0 3 0 . 16 3 27.50
0.9'74 0 . 1 7 1 32.00
1 6 . 8 0 1 . 0 1 90 . 1 7 2 40.00
1 . 0 8 2 0 . t 7 6 40.00
l . t 8 3 0.207 20.00
22.84 t.260 0 . 2 1 2 t5.66
1 . 3 9 0 0.227 t ] . 7 5
0.992 0 . 1 1 4 42.50
I l . 6 r r . 0 3 50 . 17 5 28.33
1 . 1 2 5 0 . 18 3 39.00
0.990 0 . 1 7 3 37.00
1 6 . 6 0 1.048 0 . t ] 1 35.00
t . 1 0 9 0 . 18 0 37.50
r . 3 1 80.231 29.00
23.00 t.289 0 . 2 1 7 20.66
1 . 3 9 50.221 19.00
R e m a r k : P h i t s a n u l o2k: T : 0 . 7 3 8 1 - 0 . 0 1 2 7 M C +0 0 1 7 M C ' ,
: 0.9569);
R' : 0.8855,sE : 0.0927(Significance
c F : 0 . 1 2 2 5 - 0 . 0 0 1 9 M C + 0 . 0 0 0 3RM' :C 0' ,. 9 5 7 7 ,
c e0 9 7 8 6 ) iS E : 0 . 0 0 9 1( S i g n i f i c a n =
H : 3 . 5 1 7 5 + 4 . 1 2 4 9 M C - 0 . 1M
6 4C1" R ' : 0 . 8 11 3 ,
:
SE : 3.0346(Significance 0.5640.)
1l
2008
Thammasatlnt. J. Sc. Tech..Vol. 13. No.3. Julv-September
P a t h u m T h a n1i: T : 0 . 9 9 8 9 - 0 . 0 2 8 1 M C + 0 . 0 0 1 8 M C ' .
R ' : 0 . 8 2 8 9S, E : 0 . 0 8 5 7( S i g n i f i c a n-c:e0 . 8 2 5 5 ) ;
R' : , 0.9364,
cF : 0.1654-0.0044MC+0.0003MC'
SE: 0.0083(Significance:0.7098);
H - - 5 s . bI s 9 - l 2 . 3 q 3 4 M C - 0 . 1 9 4 2 MRC' ' -, 0 . 8 q 8 6 .
: 0.61I 7)
SE : 3.3329(Significance
S u p h aB
n u r i I : T : 1 . 8 1 3 7 - 0I.l15 M C + 0 . 0 0 3 g M C r ,
R' : 0.8787,sE : 0.06I 0 (Significance_:0.7942);
R' : 0.9629,
cF : 0.3089-0.0192MC+0.0007MC',
: 0.9938);
SE : 0.0054(Signiflcance
RC
' ' ,0 . 6 8 7 4 ,
H L2473.5.tqt6MC-0.I848M
Table
S E: 5 . 3 2 1 3( S i g n i f i c a n :c e0 . 9 9 8 5 )
SE : 0.0070 (Significance : 0.8710);
, ' 0.5llo,
H - t 8 . i 7 5 i - 0 . 8 0 1 8 M (- 0 . 0 5 4 3 M C ' R
SE : 5.7505 (Signifi cance : 0.9959)
Suphan Buri I : T : 0.8777+0.0216MC+0.0009MC',
R ' : 0 . 9 1 6 2 , s E : 0 . 0 9 0 4 ( S i g n i f i c a n r e: 0 . 7 4 2 2 ) ;
c F : 0 . 1 4 4 5 + 0 . 0 0 4 0 M C + 0 . 0 0 0 1 M CR" ' : 0 . 9 8 1 2 ,
SE : 0.0070 (Significance : 0.7700);
2.
H -S.6lll '4.4b4oMC-0.1577M(Rr =0.8361.
SE: 2.9005 (Significance :0.9930)
3. Torque, friction coefficient and
percentagehulling of the experimentalmachine
with hardwood discs (density : 800 kg/m') by
molsturecontent.
Table 2. Torque, friction coefficient and
percentagehulling of the experimentalmachine
with nylon discs (density : 1,140 kg/m') by
moisture content.
Paddy grains
Paddy grains
MC
(%w.b.)
T
(kg-m)
CF
(Kinetic)
Hulling
(%)
MC
(%w.b.)
T
(kg-m)
CF
(Kinetic)
Hulling
(%)
093 0 92 3 5 . 5 0
1 5 4 0 95 3 6 . 3 3
2t5 0 98 32.50
093 0 92 32.00
lo.o/
t54 0 95 3 8 . 3 3
260 0.205 34.09
395 0.245 I 1 . 6 6
22.93 469 0.248 1 5 . 0 0
.543 0.251 1 7 . 5 0
093 0.192 34.50
I 1 . 4 5 r 3 8 0.r92 32.66
244 0.202 30.00
199 0 . 2 1 0 1 7 . 5 0
1 6 . 8 0 260 0.2r3 29.66
3 1 8 0.214 24.75
.350 0.237 I 1 . 0 0
22.84 440 0.243 9 . 6 6
543 0.251 12.75
9 1 3 0 . 1 6 0 42.50
I l.6l
.064 0.179 42.00
221 0 . 19 8 42.00
363 0.239 21.00
16.60 424 0.240 z t . ) t
469 0.239 3 2 . 5 0
39s 0.245 1 3 . 5 0
23.00 469 0.248 19.00
543 0.2s1 1 4 . 5 0
11 . 5 8
.LJ
I1.58
Phitsanulok 2
PathumThani I
t6.67
I
260
.305
.282
363
440
543
22.93
588
11.45
768
215
282
395
228
1 6 . 8 0 289
350
543
22.84 649
780
t54
I l.6l
215
Jtz
SuphanBuri I
Remark:
408
16.60 .469
559
768
23.00 829
923
0.2t7 15.50
0.212 t7.66
0.2t2 20.00
Phitsanulok 2
0.22s 1 s . 0 0
0.230
0.234
0.271
0.268
0.287
0.213
0.216
0.227
0.216
0.2t7
0.2t9
0.27r
0.278
0.290
0.202
0.205
0.223
0.247
0.248
0.254
0.310
0.309
0 . 3l 3
I /.JJ
21.25
9.00
9.66
9.50
13.00
19.58
28.15
10.50
20.66
t8.44
6.50
I 1.66
7.00
23.00
20.66
t9.25
16.50
24.66
22.00
8.00
12.00
9.00
Pathum Thani I
Suphan Buri I
Phitsanulok2 : T : 1.4747-0.0432MC+0.0022MC',
R t : 0 . 8 3 3 4 ,S E= 0 . 0 8 4 9( S i g n i f i c a n c e : 0 . 9 6 1 8 ) ;
R' : , 0.9585,
cF : 0.2479-0.0072MC+0.0004MC'
= 0.9377);
SE:0.0067 (Significance
H - 6 . 0 8 7 5 - 3 . 4 6 5 0 M CI 2- 0l 7. M C ' ,R 7= 0 . 8 2 3 3 ,
: 0.7102)
SE : 2.2480(Significance
PathumThani| : T : 2.37l4-0.1567MC+0.0055MC'.
= 0.9448)t
R' :0.8357, SE: 0.0933(Significance
R' : 0.9623.
cF : 0.4000-0.0265MC+0.0009MC'.
I2
2 : T : 1.8848-0.
l090MC+0.0040MC' ,
Remark: Phitsanulok
: 0.9448);
Rt : 0.8529,SE : 0.0738(Significance
:
R' : , 0.9766,
cF 0.3196-0.0185MC+0.0007MC'
SE= 0.0046(Significance:0.9448);
H - - 1 s . 9 6 5 38 . 0 0 7| M C - 0 . 2 8 3 2 M CR' ,' 0 . s 4 5 s ,
: 0.9565)
SE: 2.7717(Significance
P a t h u m T h a1n:iT l . l 4 l l - 0 . 0 1 0 6 M C ' 0 . 0 0 1 O M C ' .
R' : 0.7698,sE:0.0793 (Significance
-=0.9587);
R' : 0.9540,
cF : 0.1929-0.0018MC+0.0002MC"
: 0.9839);
SE: 0.0054(Significance
R 'C- ' .0 . 8 8 4 1 .
H 4 t.0856-0.205iMC-0.0484M
ThammasatInt
:0.9737\
SE= 3.8705(Significance
SuphanBuri I : T : -0.8173+0.2262MC-0.0055MC',
R ' : 0 . 8 1 8 7S, E: 0 . 1 0 3 3( S i g n i f i c a n :c e0 . 9 6 5 2 ) ;
C F = - 0 . 1 4 3 0 + 0 . 0 3 8 7 M C - 0 . 0 0 0 9RM
' :C0' .. 9 1 9 6 ,
: 0.4787);
SE : 0.01I I (Significance
H : 99.3932-6.2128MC+0.
1I 32MCt,R' : 0.9269.
: 0.6665)
(Significance
SE: 3.73.+6
//8
9 "..
I
-z
._--
rcsdl*Nrhd$)
------
rc4lldh(l]de)
/
/
o.22
9,
P o:o
E
discs. The percentagehulling decreaseddue to
higher cohesionof the bark to the brown rice.
The percentagehulling exhibited with moisture
contents about 1l to 16 o/ow.b.had a better
percentage hulling than the 23 o/ow.b., which
was close to the phenolic discs and the
hardwood discs. The moisture contents were
varied up to 23 ohw.b. and the friction
coefficient increased with increasing of the
moisture contents,as shown in Figure 5. The
friction coefficient of the phenolic discs
exhibited good paddy hulling. The power of
machine decreasedfor higher driving energy
economization, when compared to the nylon
discsor the hardwooddiscs.
o13
a
bfic&
O
Xyb&
A
v | l f u &
-*1A
Mc4r1drhNyb&)
20
Ms]lro(ffiEM({v-b.)
(a) Friction coefficient
.
?-
t
4
1
6
l
i
a
MOFTlro6maiwt)
€ ' 2
9 : o
(a) Friction coefficient
(lMtu.)
-
*
-
rc.Htdh(Nrhdr,s)
@&)
@roEcffi(k-!.)
E f i l
8 3 2
(b) Hulling
t {
7 t "
Figure 5. Relationship of moisture content to
friction coefficientand hullins
The experimental results exhibited in
Tables I to 3 ofthe Phitsanulok2 type revealed
that varied moisture contents and surface discs
directly affected the friction coefficient, while
friction forces caused an appreciable increase
of the torques.It was possiblethat the moisture
contents were highly increased with the
adhesion of the paddy grains to the surface
1ffi-*'"'
Figure 6. Relationship of moisture content to
friction coefficientand hulling
I J
2008
ThammasatInt. J. Sc. Tech.,Vol. 13, No.3, July-September
%w.b. The friction coefficient increasedwhen
the moisture contentswere about 23 o/ow.b.The
friction coefficientsof the hardwood discs rose
and then were constant. The nylon discs as
shown in Figures 5, 6 and 7 exhibited high
friction coefficients,but low percentagehulling.
Nylon discsmay not be appropriatefor hulling.
The experimentalresultswere used to find
statistical correlations and plotted trend lines
from averagerepresentationvalues of the three
data points of dark circles, bright circles and
dark triangles. The friction coefficient and the
percentage hulling due to various moisture
contentsand materialsare shown in Figures5, 6
and 7. The phenolic discs and the hardwood
discs have good relative data (R') within
significanceranges of 0.7 to 1.0. The data
comparison of three values revealed that
differencesin experimentalresults were due to
physical properties of each paddy grains and
characteristiccontactbetweensurfacediscs and
paddygrains.
The experimental results exhibited in
Tables I to 3 of the Pathum Thani I type
showedthat Figure 6 was similar to figure 5 of
the Phitsanulok 2 type. However, percentage
hulfing increasedto about 16 o/ow.b.with the
phenolic discs while notmal decreaseoccurred
in the hardwooddiscsand the nylon discs.
0.&
'..-
Mcddh(Ildcd*t
...-**
Kc*dhNybne)
------....
./
,t'
/
Mcsdltu(9MAi*)
t
9 o.ro
t."d
g
E a u
---
- - - - -- - - - - -- -f
E
ol8
t4
16
18
20
4. Conclusions
wsre@l\llm(%*.b.)
The designedmachinewas usedto measure
forces. determine kinetic friction coefficients
and factors affecting paddy hulling while the
machine was operated.Three types of surface
materials (phenolic discs, polyamide discs and
hardwooddiscs) were designed,testedand then
comparedfor paddy hulling, while the moisture
contentswere adjusted.The experimentalresults
were shown for three moisture contents(about
11, 16 and 23 ohw.b.of paddytypes).The forces
were measuredto increaseboth the torquesand
the kinetic friction coefficient. The percentage
hulling decreasedas moisture contentincreased.
The friction coefficientvaluesofthe nylon discs
(polyamide discs), the hardwood discs and the
phenolic discs were directly opposite to the
percentagehulling. The data comparisons of
three values were determinedto find important
factors. Different results were due to the
moisture contents of paddy grains and the
contactbetweensurfacediscs and paddy grains.
The grains were hulled better within the ranges
hulling
from 11to 16 %w.b. of the percentage
than with 23 ohw.b.paddy. The statisticalvalues
of the phenolic discs and the hardwood discs
were 0.7 to 1.0 of the significancerange and
were good relative data, except some of the
percentagehulling data.
(a) Friction coefficient
o
___
|blLdb
rcFdhdyh&)
f , l
e t 2
2
n
t,,
22
1a
(b) Hulling
Figure 7. Relationshipof moisturecontentto
friction coefficientand hulling
Figure 7 shows the experimental results
exhibited in Tables I to 3 of the SuphanBuri I
type. The phenolic discs had constant friction
coefficients for moisture contents of 1l to 16
t4
2008
ThammasatInt. J. Sc. Tech.,Vol. 13, No.3, July-September
5. References
t1l ASAE Standard., Food and Process
EngineeringSection,36'n,St. Joseph.USA,
I 989.
l2l Araullo, E. V., D. B. De Paduaand Michael
Graham., Rice Postharvest Technology,
International Development Research
Center, Ottawa, Canada.1916.
t3l Brubaker, J.E. and J. Pos., Determining of
Static Coefficientsof Friction of Grains on
Structural Surfaces, Transactions of the
, o . l , P P . 5 3 - 5 51,9 6 5 .
A S A E , V o 1 . 8N
M. Goto, T. Saito,R'
H.,
J.
Shimizu,
Kano,
t4l
Ishihara,F. Miyazawa, T. Ashizawa and T.
husking ratio
on
Study
Miura.,
improvement for rice husker, Agricultural
Machinery Research 21, Shin-Norinsha,
Tokyo, 1959.
StudY and
t5l Kanchanawongkul, V.,
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