10th International Congress on Mechanization and Energy in Agriculture
“14-17 October 2008, Antalya-TURKIYE”
Design of a Walnut Cracking Machine Based on Acquired Mechanical
Properties
Faroogh SHARIFIAN, Allaeddin RAHMANI DIDAR, Mohammadali HADDAD DERAFSHI
Dept. of Agricultural Machinery, Agricultural Faculty, Urmia University, Urmia, Iran.,
E-mail address: m.derafshi@ mail.urmia.ac.ir,
Abstract: The most important post-harvest process of walnut fruit is the separation of the nut from its shell.
For this purpose, a cracking machine was designed on the basis of local walnut mechanical properties which were
obtained through an Instron test machine. The designed machine has the potential to apply variable deformation
according to the degree of flexibility of the walnut fruit. The range of shell deformation required to rupture,
according to the testing machine, appeared to be between 1.75 and 3.15 mm. The maximum cracking force and
power required, accordingly, was calculated to be 797 Newton and 1.99 Watt, respectively. The speed of applied
force for proper cracking action was 500 mm min-1. The walnut had the maximum strain (flexibility) at this
speed. The higher the flexibility, the lower is the damaged fruits in the cracking process. In this machine, sizing
and breaking process occur simultaneously within 6 cone-shaped breaking units. The time required for the
breaking process consisting of walnut entering into the units, breaking action, and the emission process was
estimated at 6 seconds. Thus, the theoretical capacity of the machine is one nut per second. The present
technology of this machine, with slight modifications, can also be applied to some other types of nuts.
Key words: Walnut, mecihanical properties, design, cracking machine
INTRODUCTION
orientation of sized nuts can be controlled. But this
Iran is ranked third in the world (Statistical Year
design is not satisfactory, because the magnitude of
Book, 2005) with 170000 tones of walnut (Juglans
required deformation to each nut was dependent on
regia L.) production. This is equivalent to 11% of the
its size (Tang et al. 1982).
world walnut production (University of Georgia). The
most
important
processing
step
after
Borghei et al. (2000) designed and constructed a
walnut
walnut cracker which consisted of two indented plates
harvesting is separation of kernel from the shell. This
that were positioned in a v-shaped form. One plate
process is still carried out manually in Iran, which
moves against the other plate and each point of the
results in increased cost and processing time for
moving plate follows an elliptical path. Due to the
kernel extraction (Borghei et al. 2000). Therefore, a
movement of the plates walnuts are gradually pulled
walnut cracker should be developed and designed on
downward and pressed between the plates, so the
the basis of physical characteristics and mechanical
shells were broken and fruits were separated from the
properties of walnuts.
shells. However, in this experiment, the rate of the
Compressing nuts in a shell to a constant
intact kernel was 20 percent and required time for
deformation is one of the most widely used means to
crushing a walnut was about 6 seconds which
crack macadamia nuts for kernel extraction (Liang T.,
suggests more researches in this area.
1980).
The main objective of existing study was to design
Liang T. (1980) designed a constant deformation
macadamia
nut
cracker.
The
magnitude
a walnut cracker, suitable for local walnut varieties
of
and conforming to local conditions in terms of
deformation is controlled by the difference between
capacity and costs.
the size of the nut and the clearance between two
compression or cracking edges. A tapered clearance
was found to be capable of compressing nuts of all
sizes
to
the
same
deformation
provided
the
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10th International Congress on Mechanization and Energy in Agriculture
“14-17 October 2008, Antalya-TURKIYE”
Where, P is the required power in W, E is the
MATERIALS AND METHODS
absorbed energy in mJ, V is the loading velocity in
mm min-1, and Δl is the deformation up to initial
Due to the machine design requirements, some
mechanical
properties
of
walnut
shell
rupture of the walnut shell occurred, in mm. In this
were
research, the highest power (1.99W) was calculated
determined. Then, considering these data and also
at 500 mm min-1 of loading velocity.
some important design parameters such as; lower
cost, machine efficiency, and smaller dimensions, the
500
machine was designed.
Force, N
Fresh harvested walnut fruits in September 2006,
in the West Azerbaijan province, Iran were dried in
the sunshine and were used for all the compression
tests. Walnuts were compression loaded by an Instron
mechanical behaviors of walnuts were expressed in
compression
0.5
1
1.5
2
2.5
3
Deformation, mm
power required to rupture the nut shell. These values
each
Area=Energy
0
shell, nut specific deformation, absorbed energy, and
from
200
0
terms of maximum force required to fracture the
developed
300
100
test machine until the shell rupture was initiated. The
were
First crack
400
The measured mechanical properties
curve,
Figure 1. Typical force-deformation curve for
compressed walnut.
obtained from the Instron test machine. In this
experiments, the highest recorded cracking force was
Machine design
A pattern of a prototype machine has been
797N,.
The absorbed energy, as shown in Figure 1, was
performed by using Catia software. This pattern
determined directly by measuring the area under the
shows different parts of the machine and also their
force-deformation curve (Koyuncu et al. 2004). This
dimensions (Fig. 2 and 5). The designed machine
measurement was performed by applying a digital
planimeter with an accuracy of ±0.2 % (Güner et al. •
2003). The highest required energy to rupture the
walnut shell, 952 mJ, was recorded.
•
The specific deformation, ε , was obtained from •
the following expression (Braga et al. 1999):
consisted of 3 main mechanisms:
the mechanism for transmitting walnuts from
the bin to the funnels (1, 2, 3, 4),
the breaking funnel (5),
funnels emitting mechanism (6, 7, 8, 9, 10).
Transmitting of walnuts from the bin to the
funnels occurs when the bottom plate of the bin
L − Lf
ε= u
Lu
rotates with its shaft (Fig. 2). This action opens 6
(1)
openings in the bottom of the bin and a walnut from
Where, Lu and Lf are the un-deformed and deformed
each opening drops into the related funnel. The
nut dimensions on the direction of the compression
openings are left open only for 1 second (a spring,
axis, in mm, respectively. Deformation required to
mounted on the plate shaft, will close the openings).
rupture of walnut for the size spectral (25 - 45 mm)
Therefore, there is no chance for another walnut to
varied 1.75- 3.15 mm.
drop down.
The required power was also calculated as below
In this machine, 6 semi-cone shaped funnels were
(Khazaei et al. 2002):
used to break walnuts (Fig. 2, no. 5). Maximum and
minimum diameters of the funnel were determined
E×V
P=
60000 × Δl
according to the largest and the smallest walnuts in
(2)
the sample which appeared to be 45 and 25 mm,
respectively. Each funnel has a lengthwise groove in
its sidewall (Fig. 3). There is spout-shaped bar in each
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10th International Congress on Mechanization and Energy in Agriculture
“14-17 October 2008, Antalya-TURKIYE”
groove which bottom end of this bar is fixed to the
funnel, whereas the top end of it is free. The bar will
be forced inside the funnel by special cam mounted
on the cam rod driven by its own gear (Fig. 5). This
action will break the walnut inside the funnel. As soon
as the cam passed the bar, a spring which is located
near the bottom of the bar, will return the bar to its
original position. According to Tang et al., 1982,
complete walnut break occurs when the force is
applied from 4 points around the walnut shell. For this
reason, 2 lengthwise splines were constructed inside
each funnel across the pushing bar (Fig. 4). This
special pattern would cause applying force from 4
points across each other.
Following the breaking action, the funnel shaft
rotates about 154 degrees around its axial. This
results in emitting all funnels to the collecting plate
(Fig. 5). The funnel shaft again rotates back to its
original position. The rotation of the funnel shaft and
its return action is provided through a crank-androcker mechanism. Funnel shaft speed was calculated
according to the time required for emitting and
returning the funnels, 3 seconds, which appeared to
be 20 rpm. After this, a lag of 3 seconds was provided
during the rotation of funnel shaft. This period of time
was cosidered for funnel filling and walnut breaking.
The power required for the operation of 3
different mechanisms; walnut transmitting, walnut
breaking, and funnel emitting, was provided by
employing an electromotor with a capacity of about
50 Watt. Electromotor shaft has 3 different gears.
Gear no. 1 (Fig. 2) which toothed only 60 degrees of
it circumference, incorporate for walnut transmitting.
This special pattern of the gear opens the bottom
plate (Fig. 2, no. 4) of the bin and let a spring action
to close it again. The time calculated for this action
was 1.5 seconds. The breaking action receives the
required power through 2 gears; First one is maunted
on the electromotor shaft and the other one wich
engaged with the first one is located on the cam shaft
(Fig. 5). The emitting action of funnels provided by
gears no. 6 and 7 (Fig. 2). Gear no. 6 has been
toothed only 180 degrees which causes the funnels to
turn over for emptying and then to return to its
original position.
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10th International Congress on Mechanization and Energy in Agriculture
“14-17 October 2008, Antalya-TURKIYE”
3
1
11
2
4
5
7
6
10
9
8
Figure 2. Complete machine pattern performed by Catia software. 1, 2, 3, 4- Walnut transmitting mechanism.
5- Funnel, 6- Gear, driving crank-and-rocker mechanism. 7, 8, 9- crank-and-rocker mechanism. 10- Funnels
shaft.11- Walnut bin.
Figure 3. Funnel with the groove.
Cam follower
Rod width at
the top end
Rod width at the
bottom end
‫ﻦ‬
‫ﺎ‬
Spline
Figure 4. The funnel inside view.
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10th International Congress on Mechanization and Energy in Agriculture
“14-17 October 2008, Antalya-TURKIYE”
3
2
1
4
Figure 5. The funnels in emitting position. 1- Cam, 2- cam shaft, 3- cam shaft gear, 4- collecting plate.
Figure 6. Electromotor shaft with 3 gears.
The walnut dimensions had no significant effect on
RESULTS and DISCUSSION
Rupture force, rupture strain, and required power
the rupture force, energy, and power required for
for walnut rupture appeared to be the most important
walnut rupture which this also simplified the machine
mechanical parameters to be considered in design of
design very much. However, rupture strain was
walnut
tests
affected by the walnut size significantly. Therefore,
revealed that the direction of force applied to the
breading
machine.
Biomechanical
the machine has been designed somehow to apply
walnut did not affect the rupture strain. Therefore,
variable deformation according to the degree of
there was no need to control the direction of the
flexibility of the walnut fruit.
applied force and this, remarkably, simplified the
The average rupture strain, measured at 500 mm
min-1 speed, was 0.07. Considering the maximum and
machine design.
The maximum force, energy, and power to
the minimum walnut dimensions (25-45 mm) the
rupture the walnut shell were measured 797 N, 953
range of deformation required for walnut rupture
mJ, and 1.99 W, respectively. These values were used
calculated 1.75-3.15 mm. These values were used to
for machine design. The speed of applied force for
determine the amount of the displacement of the
proper cracking action was 500 mm min-1. The
breaking bar.
walnut had the maximum strain (flexibility) at this
Considering the time required for transmitting and
speed. The higher the flexibility, the lower is the
breaking walnuts and also for emitting funnels, 6
damaged fruits in the cracking process.
seconds, the machine capacity was calculated to be
3600 walnuts per hour.
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10th International Congress on Mechanization and Energy in Agriculture
“14-17 October 2008, Antalya-TURKIYE”
Tang, G. P., T. Liang and F. Munchmeyer. 1982. A
CONCLUSION
Although the designed machine has not been
Variable Deformation Macadamia Nut Cracker.
manufactured and hence cannot be evaluated, but
Transactions of the ASAE. 25(6): 1506-1511.
since all important walnut mechanical parameters are
considered in designing the machine, it is expected
that the prototype machine operate satisfactorily. It is
also suggested that to supplement walnut breaking
machine with a separating system to separate kernels
out of shells.
The existing technology, with slight modification,
can be used for some other nuts.
REFERENCES
Borghei, A. M., T. Tavakoli and J. Khazaei. 2000.
Design, Construction and Testing of Walnut
Cracker.
In:
Proceedings
of
European
Agricultural Engineering Conference. Warwick
University, England.
Güner, M., E. Dursun and I.G. Dursun. 2003.
Mechanical
Behaviour
of
Hazelnut
Under
Compression Loading. Biosystems Engineering.
85(4): 485-491
Khazaei, J., M. Rasekh and A. M. Borghei. 2002.
Physical and Mechanical Properties of Almond
and its Kernel Related to Cracking and Peeling.
. In: Proceedings of ASAE Annual International
Meeting. Chicago, Illinois, USA.
Koyuncu, M. A., K. Ekinci and E. Savran. 2004.
Cracking Characteristics of Walnut. Biosystems
Engineering. 87(3): 305-311.
Liang, T., 1980. Designing a Constant Deformation
Macadamia Nut Cracker. Transactions of the
ASAE. 23(5): 1093-1096.
Statistical Year Book, 2005. Farm and Orchard
Products. Vol. 1. Ministry of Jahad Agriculture,
Islamic Republic of Iran.
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