Journal of Food Engineeting 32 (1997) 339-345 0 1997 Elsevier Science Limited

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Development of a Cashew Nut Sheller

R. K. Jain & Sivala Kumar

Post Harvest Technology Centre, Department of Agricultural and Food Engineering, Indian Institute of Technology, Kharagpur 721 302, India

(Received 24 August 1995; accepted 25 March 1997)

ABSTRACT

Presently shelling of cashew nuts is done manually, which is not only labour intensive but also hazardous because of corrosiveness of cashew nut shell liquid. Therefore, a power-operated cashew nut sheller was developed based on the principles of compression and sheal: The rated capacity of the sheller was observed to be 18 kglh of roasted nuts at a shelling eficiency of 70%. The yields in terms of whole, half-splits and brokens were SOOro, 22% and 28% respectively. 0 1997 Elsevier Science Limited

INTRODUCTION

The cashew nut processing industry is typically located in the rural and backward areas (Sivala et al., 1994). The general steps in cashew nut processing are: condition- ing, drying (sun), roasting, shelling, kernel drying (oven), peeling and grading. The shelling, peeling and grading unit operations are carried out manually. The shelling of cashew nuts means breaking and complete removal of the shell and taking out the kernel without causing much damage. The shelling has always presented the greatest problem in the processing of cashew nuts. This is because of irregular shape and brittleness of the kernel. The manual shelling process is tedious, time consum- ing and labour intensive and thus it indulges drudgery in the system. Moreover, quantity and quality of out-turn depends upon the skill of the person (Jain & Sivala, 1996). The cashew nut shell liquid which comes out during the operation of roasting and shelling is highly corrosive and requires special care during manual shelling.

Oloso & Clarke (1993) cited different methods of shelling roasted nuts. In the Sturtevant system, roasted cashew nuts are thrown by centrifugal force on to a metal plate for shelling. It resulted in poor shelling efficiency. In the Oltmare system, well- graded nuts are held by a nut-shaped blade and cut along a natural line. The capacity of shelling is very low because each nut has to be placed for cutting. In spite of these developments, presently shelling is mainly carried out manually by hitting the nut with a wooden hammer along the longitudinal axis. Average shelling

339

340 R. K. Jain, S. Kumar

capacity was reported to be 8 kg/day per worker, which consists of 36% whole, 30% half-splits and 34% brokens (Jain, 1982; Kumar, 1989). Therefore, there is a need to develop a mechanical cashew nut sheller, which should be able to meet the wide range of cashew nut shelling requirements, reduce the drudgery and improve the quality of the product.

PROPERTIES OF CASHEW NUTS AND KERNEL

Some of the physical and mechanical properties of raw and roasted cashew nuts and kernels were determined. Cashew nuts were graded into two classes, namely large (largest dimension > 30 mm) and small. The three principal dimensions of 100 ran- domly selected nuts and kernels of each grade were measured with a dial gauge to the nearest 0.01 mm. Sphericity is an index of roundness for non-spherical particles which was calculated using eqn (1) (McCabe & Smith, 1984).

(1)

where a, b and c are the largest, second largest and the smallest dimensions of cashew nuts.

The weight of 1000 nuts or kernels of each grade was measured and termed the test weight. Bulk density of the nuts and kernels was measured with a hectometer. The actual volume of each grade of nuts and kernels was found by means of an air comparison pycnometer (Beckman model 930). True density is the ratio of mass of sample to its actual volume. It was also calculated for each grade. Porosity is the percentage of volume of voids in a bulk sample at a given moisture content. It is calculated as the ratio of the difference in true and bulk densities to the true density (eqn 2) and expressed as a percentage.

Porosity = True density-Bulk density

x 100 True density

(2)

The static coefficient of friction on a mild steel sheet and the dynamic angle of repose of nuts and kernels were found (Sheperd & Bhardwaj, 1986). The com- pressive load at fracture in quasi-static conditions was found on both longitudinal and dorsoventral axes for each grade of nuts and kernel. All the properties are given in Table 1.

DEVELOPMENT OF CASHEW NUT SHELLER

A mechanical sheller was designed and developed (Fig. 1) on the principles of compression and shear, based on the above-mentioned physical and mechanical properties. It consists of four sections: (i) feeding section, (ii) shelling section, (iii) discharging section and (iv) power supply and transmission.

Development of a cashew nut sheller 341

Feeding section

This consisted of a hopper and horizontal screw conveyor for positive feed of the roasted nuts to the shelling section. The hopper and screw conveyor were designed using size, bulk density, coefficient of friction and angle of repose of roasted cashew nuts. A flat plate sliding gate was used to control the feed rate.

Shelling section

Shelling of roasted nuts was done between two wooden discs. One was stationary (fixed to the casing) and the other one mounted on the shaft. The rotating disc was spring loaded so as to compress and shear the roasted cashew nut against the stationary disc. The spring exerted sufficient pressure to compress the nuts between the stationary and rotating discs. Shelling of nuts occurred due to compression and differential speed of the discs. In the first model both discs were made of 25 mm thick wood. It resulted in about 95% of the product consisting of more than 92% brokens. In the second model, a 15 mm thick rubber pad on the wooden disc was tried. The pads gave a cushioning effect. Thus the whole kernel recovery increased to more than 50% but shelling efficiency reduced to less than 40%. Therefore, in

TABLE 1 Some Physical and Mechanical Properties of Raw and Roasted Cashew Nuts and Kernels

Raw Roasted Kernels Small Large Small Large Small Large

Moisture content, % Size, mm Largest dimension

Second largest

dimension

Smallest dimension

Sphericity

Bulk density, kg/m’

Test weight, g

True density, kg/m’

Porosity, %

Coefficient of friction

Angle of repose, deg.

Compressive load under quasi-static condition, kg

Longitudinal axis

Dorsoventral axis

9.7io.4

26.46 31.62

( f 1.78) (f1.15)

21.81 25.63

( f 1.74) (k 1.28)

15.66 18.06

(k1.82) (k2.01)

0.75-0.80

57s ( + 11 S)

4994 6268

( f 15.3) ( * 33.7)

1053 (k23.7)

44.6-46.2

0.5

27.4

21.8 22.5

(k2.3) (k2.7) 43.6 44.8

( f 2.4) (k2.6)

8.0 + 0.3

27.67 33.36

(i2.05) ( * 1.94)

22.43 25.96

(& 1.75) (+ 1.68)

16.7 1 18.82

(* 1.7.5) ( f 1.78)

0.75-0.8

320 ( k 6.1)

2862 3730

(Ifr 19.7) (k21.3)

594 ( f 11.9)

45.4-47.0

0.65

33.6

19.4 20.72

(k2.7) (k2.3) 38.5 39.22

(k4.7) (k4.1)

5.5 f-o.2

21.55 25.40

(k1.31) (iO.44)

11.40 IS.37

( * 1.67) (* 1.50)

8.62 11.58

(k1.45) (i2.16)

0.55-0.62

726 ( + 19.2)

1680 2260

( k9.4) ( + 16.4)

968 (k43.1)

24.0-25.9

0.64

33.0

2.49 2.70

( + 0.46) (kO.20)

3.56 3.52

(k0.28) (kO.17)

Values in parenthesis are standard deviations.

342 R. K. Jain, S, Kumar

Development of a cashew nut sheller 343

the third model a rubber pad was used only on the stationary disc. It improved the shelling to about 70% and almost maintained the whole kernel recovery.

Discharging section

The entire disc assembly was enclosed in a mild steel casing (18 gauge). At the bottom of the casing a square opening of 150 x 150 mm was made to discharge the kernels and shells. A conduit, (120 mm diameter) 250 mm long was provided, so that cashew kernels were not damaged while falling on to the tray by gravity after shelling.

Power supply and transmission

A 1.5 kW DC motor (1500 rpm) was used to supply the power through a rectifier for variable speed of operation. A belt and pulley arrangement was used to transmit the power from motor to the shaft.

OPERATION OF THE SHELLER

Roasted cashew nuts were procured from a cashew nut factory. The nuts were graded into two grades, namely large and small, as described earlier. Each test run consisted of 4 kg roasted nuts. The clearance of the discs was adjusted according to the grade of the nuts (approximately 60% of the largest dimension) and the machine was operated at four different speeds, namely 160, 240, 320 and 400 rpm.

The time required for each test run was recorded so as to calculate capacity of the sheller. The output of the sheller was manually separated into unshelled, whole kernel, half-splits and brokens. The capacity, shelling efficiency and percentage yield of different fractions were calculated and are given in Table 2.

TABLE 2 Performance Testing of Developed Sheller

Speed Grade Capaci?, (kg/h)

Shelling ejj?ciency

(So)

Whole kernel yield f%;1)

Half-split (%)

Brokens (5%)

160 Small 8.1 60.7 + 4.8 160 Large 7.9 62.1 +S.6 240 Small 11.5 69.3 f 4.1 240 Large 11.4 70.9 * 4.3 z* * Small

Large 18.2 18.0 71.3k2.7 73.1 f5.1

400 Small 25.0 68.6 + 4.3 400 Large 24.7 69.7 + 3.2

“Average of 6 replications. All other data are average of 3 replications.

53.1 + 1.6 26.7k4.1 20. I + 2.1 52.Ok2.9 30.8 f 3.5 16.4&0.7 51.8f2.2 26.8 + 2.4 21.9+_0.6 53.7+ 1.4 27.5 f 0.3 19.0+1.1 52.8 50.9 * f 2.6 1.2 23.8f1.3 22.0 +_ 2.6 24.1 27.4k3.1 f 1.7

40.1 4 5.4 30.5 f. 2.7 28.0 + 3.3 42.3 5 3.4 31.3A2.5 26.8k4.1

344 R. K. Jain, S. Kumar

PERFORMANCE OF THE SHELLER

The data (Table 2) indicates that the grade of cashew nuts (large and small) did not affect the capacity of the sheller, shelling efficiency and quality of out-turn at the 5% probability level.

With an increase in the angular speed of the rotating disc, the capacity of the machine increases. In the experimental range (160-400 rpm), the capacity of the sheller varies between 8 and 25 kg/h.

Initially, with the increase in speed, the shelling efficiency also increased from 60% at 160 rpm to 70% at 240 rpm. However, with further increase in the speed from 240 to 400 rpm the change in shelling efficiency was not significant at the 5% probability level.

The whole kernel recovery varied between 50% and 53% when the speed ranged between 160 and 320 rpm. However, with further increase in speed (400 rpm), the whole kernel recovery reduced to 40-42%, which is significantly lower than the speed range of 160-320 rpm. The recovery of the half-splits had not followed any pattern. However, the percentage broken increased with the increase in speed. This may be due to increase in shear force on the cashew nuts at the higher speed.

CONCLUSIONS

(1) The principle of compression and shear works satisfactorily in shelling the cashew nuts.

(2) The cashew nut sheller operated at 320 rpm gave the following performance:

Capacity 18 kg/h Shelling efficiency 70% Whole kernel yield 50% Half-split yield 22% Broken yield 28%

ACKNOWLEDGEMENTS

The authors would like to gratefully acknowledge the Indian Council of Agricultural Research for financial assistance and the Indian Institute of Technology for provid- ing infrastructural facilities for this project.

REFERENCES

Jain, M. L. (1982). Some aspects of improved post harvest technology of cashewnuts. Unpublished M. Tech. thesis. Submitted to IIT, Kharagpur.

Jain, R. K. & Sivala, K. (1996). Development of continuous cashewnut sheller. Concluding report of project submitted to ICAR, New Delhi.

Kumar, A. (1989) Studies on cashewnut processing and development of related equipment. Unpublished Ph.D. thesis. Submitted to IIT, Kharagpur.

McCabe, W. L. & Smith, J. C. (1984) Unit Operations of Chemical Engineeting (3rd edn). McGraw-Hill, Japan.

Development of a cashew nut sheller 34s

Oloso, A. 0. & Clarke, B. (1993). Some aspects of strength properties of cashewnuts. J. Agric. Eng. Rex, 55, 27-43.

Sheperd, H. & Bhardwaj, R. K. (1986). Moisture dependent physical properties of pigeon pea. J. Agric. Eng. Rex, 35, 227-234.

Sivala, K., Srivastav, P. P. & Jain, R.K. (1994). Cashewnut processing in Midnapur district of West Bengal: a case study. Bombay, India. Beverage and Food World, 21, 5 25-27.