Design of a Walnut Cracking Machine Based on Acquired Mechanical ...

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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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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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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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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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. 830


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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