Development and Performance Evaluation of a Slicing Machine for Selected vegetables

Greener Journal of Physical Sciences

Vol. 6(1), pp. 1-9, 2020

ISSN: 2276-7851

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Development and Performance Evaluation of a Slicing Machine for Selected vegetables

Ezeanya, Nnaemeka Charles

Department of Agricultural and Bioresources Engineering, Federal University of Technology, PMB 1526, Owerri, Nigeria.

ARTICLE INFO	ABSTRACT
*Article No.:*01162010 *Type: Research*	The purpose of this study was to develop an efficient and ergonomically safe slicing machine that is affordable to a small scale farmer. Slicing machine is useful for farmers in chopping of fodder; and for crop processing industries in slicing of vegetables in readiness for other processing activities. A slicing machine, equipped with two slicing blades was designed, fabricated and evaluated for performance. The machine was powered by a 0.25hp, single phase electric motor. The performance of the machine was evaluated using three selected crops (onion bulbs, carrots, and Irish potatoes); grouped into small-sized samples (22.62-33.14 mm) and medium-sized samples (33.35-49.9) ; at four machine speeds of 53, 58, 62, and 69 rpm. The parameters investigated were slicing efficiency and throughput capacity. Results showed that the highest mean slicing efficiency of 87.6% was attained from the machine when slicing small-sized Irish potatoes at rotational speed of 58 rpm; while the lowest mean slicing efficiency of 60.7% was attained from the machine when slicing medium-sized onion bulbs at rotational speed of 69 rpm. The throughput capacities developed by the slicer were affected by slicing speeds; and ranged from 20.52 – 44.28 kg/hr. It was also observed that the machine could slice onion bulbs, carrots and Irish potatoes satisfactorily with slice thicknesses ranging from 5mm to 6mm.
*Accepted:* 21/01/2020 *Published:* 27/06/2020
Corresponding Author Ezeanya, NC* *E-mail:* n_ezeanya@yahoo.com *Phone:* 08037529679
*Keywords: Vegetable slicer; Single phase; electric motor; machine speeds; Slicing efficiency; throughput capacity*

1. INTRODUCTION

Most of the horticultural commodities are larger in size and therefore size reduction is a preliminary stage for various food processing activities. Depending on whether the material is solid or liquid, the operation of size reduction can be subdivided into two major categories. In the case of solids the operations are called grinding and slicing (cutting) while in the case of liquids the process is defined as emulsification or atomization. The general term ‘size reduction’ includes cutting, crushing, grinding and milling. Such processes as cutting of fruits and vegetables for canning, shredding of sweet potatoes for drying, chopping of corn fodder, grinding limestone for fertilizer, grinding grain for livestock feed, and milling of flour are all size reduction processes (Federick, 2008). Slicing involves cutting materials into smaller sizes by the use of a sharp blade or cutter.

The three selected vegetables used in this research are onion bulbs, carrots, and Irish potatoes. These vegetables are of great importance both as source of food for mankind as well as valuable raw materials for the industry. In 2018, the global production data for onion bulbs, Irish potatoes and carrots are 5.47 million tonnes, 36.82 million tonnes, and 39.99 million tonnes respectively (FAO, 2019). Processed onion products include dried onion flakes and powders usually made from white cultivars with high dry matter content, and onion oil which is produced by distillation. Medically onion reduces the clothing of platelet in the body, lowers raised blood sugar, and cures all bronchial complaints like cough (Elesha, 2002). Carrot is generally consumed due to high content of beta-carotene. In the food sector, potatoes are processed into deep frozen chips, crisps, and mashed potato. By-products such as potato starch, glucose, and dextrose are used in biscuit production and brewing industries in the production of confectioneries and distillation of alcohol. In the non-food sector, by-products such as potato starch and dextrins are used as ingredients for the manufacture of cardboard, glues, textiles, and paints (Raemaekers, 2001).

Traditionally fruits are sliced using sharp kitchen knife. Above a certain scale of production, this method is labourious, time consuming and prone to finger injury and eye irritation. Also slices produced in this method are not normally of uniform size. Some slicing machines had been developed by several researchers for slicing crops. Rajesh et al. (2016) developed and evaluated a plantain peeler cum slicer. Research findings from their work revealed that the developed slicer had an average slicing efficiency of 88.94% and throughput capacities of 89.27, 89.16, and 79.59 kg/hr. Ehiem and Obetta (2011) developed a motorized yam slicer which was operated by a 1.5 hp motor. Research findings from their work revealed that a maximum slicing efficiency of 52.3%, average throughput capacity of 315 kg/hr, and percentage of non-uniform slices of 42.65% were developed by the slicer. Agbetonye and Balogun (2009) developed a multi-crop slicing machine which uses a set of nine blades for slicing carrot, potato, onion and yam. Their research established that the slicing efficiency and throughput capacity increased with slicing speed. A maximum efficiency of 97.9% and maximum throughput capacity of 135.7 kg/hr was reported by their work. However, these developed crop slicers are relatively bulky in size and thus have high cost of production and therefore needs to be improved upon. This work aimed at developing and evaluating an improved vegetable slicer which will slice with greater efficiency and reduced cost.

2. MATERIALS AND METHOD

2.1 Design considerations

The following factors were considered in the design of the slicing machine:

1. The machine should be portable

2. The slicing components should be corrosion resistant to avoid contamination of the crops being sliced

3. The machine would be cost effective

4. Ergonomics was given due consideration in the design to reduce operator fatigue.

2.2 Description of the machine

The machine consists of hopper, slicing disc, slicing blade, power drive mechanism, processing chamber, electric motor, speed regulator, and frame. The orthographic view of the slicing machine is shown in Figure 1, while the exploded view is shown in Figure 2.

The Hopper

The hopper has dimensions of 135 x 75 mm in cross section with length of 170 mm and is attached to the front of the machine. The crops to be sliced were fed into the hopper. It has a feed control plate which exposes only the desired vegetable to be fed to the slicing blade. The base of the hopper opens into the slicing chamber from the top such that feeding of the crops is aided by gravity. This was achieved by tilting the hopper at an angle of 35º. Angle of 35º was chosen because it is slightly greater than the angle of repose of the selected crops. Stainless steel (grade 304: ISO 3506 ‘A2’) was used in constructing the hopper, so as to reduce corrosion and rust.

Slicing disc

This is a detachable disc, having radius of 145mm and thickness of 2mm which houses the two slicing blades.It was constructed with stainless steel (grade 304: ISO 3506 ‘A2’) so as to minimize corrosion and food contamination. It was connected to the shaft via the flange and held by series of screws.

Slicing blades

The slicing blades are sharp slits on the surface of the disc which are hollow beneath. They were fixed adjacent to each other and equally spaced on the slicing disc. They each have thickness of 2.5mm and length of 150mm. They were constructed with stainless steel (grade 304: ISO 3506 ‘A2’).The blades were designed to slice the product and in the same motion push the sliced piece downward where it drops by gravity into the discharge chute. A slice clearance of 5 mm was designed for the output thicknesses. The slicing blades are held firmly to the disc with series of bolts.

Power drive mechanism

The slicing machine is powered by a single phase, 0.25 horsepower 200 rpm electric motor, which converts the electric energy into mechanical (rotational) motion. This rotational force is transmitted via the shaft and is utilized by the slicing discs for operation.

Processing chamber

This is a hollow cylinder made of stainless steel; having radius of 160 mm and length of 70 mm. It houses the internal components of the machine like the slicing disc and blades. The design of the processing chamber enables the temporary opening of the chamber for easy maintenance and changing of the slicing blades. It also contains an internal partition that separates the slicing chamber from the motor.

Frame

This was constructed with mild steel and serves as the support for the machine. It has length of 540mm, width of 450mm and height of 400mm.

2.3 Design calculations

i Radius of slicing disc

Saravacos and Kostaropoulos (2002) recommended that radius of slicing disc for cutting equipment should be above thrice the diameter of product to be sliced. The average diameter for the crops to be sliced was obtained from sampling as 4.5 cm. Therefore 3×4.5 cm=13.5 cm. Therefore a disc radius of 14.5cm (0.145m) was chosen.

ii Volume of slicing disc

Volume (V) of slicing disc was determined using

Where r = radius of slicing disc

h = thickness of slicing disc (2mm = 0.002m)

Therefore,

V = π× (0.145m)²×0.002m = 1.32 × 10^-4m³

iii Mass of Slicing Disc

Mass of slicing disc was determined using

Where ρ = density of stainless steel = 7800 kgm^-3

Therefore M = 7800 kgm^-3×1.32 × 10^-4m³= 1.0296 kg

iv Power required to drive the machine

Force due to centrifugal action of the disc (F) is given by

Where V= velocity = ωr

ω = angular velocity =

Therefore, angular velocity, ω = = 20.94 rad s^-1

Velocity of slicing disc, V=20.94 rad s^-1 ×0.145m =3.036 m s^-1

Therefore, = 65.45 N

Total torque required (T) is given as

Therefore,

Power required to drive the machine is given as

P = 198.7 watts = 0.25 horsepower

2.4 Experimental procedure

The test samples used for the experiment were onion bulbs, carrots and Irish potatoes. These were purchased from a local market in Owerri, Imo state, Nigeria. The samples were prepared by washing, peeling and cutting into shape. The test samples were classified into small-sized samples (22.62 – 33.14 mm) and medium – sized samples (33.35 – 49.9mm). A vernier caliper was used to measure the major and minor diameters of the selected crops; while the masses and volumes of the selected crops were determined using electronic weighing machine and volume displacement method respectively. The machine was switched on and operated under no load for 10 minutes to ensure that all the components were functioning properly. A tachometer of model (Luitron: DT – 2236C) was used to detect and mark off accurate calibrations on the speed regulator to ensure correctness of operating speeds as determined in the design calculation. A measured mass of the samples was introduced into the slicer, and operated at four different speeds of 53, 58, 62, and 69 rpm. The choice of these speed values was based on the speed values used in previous research works. The machine was operated for 5 minutes for each experimental test. Each experimental test was replicated three times, and the average of the results was taken. The output materials obtained from the machine outlet were collected and separated into two groups of sliced and unsliced/damaged materials.

3.5 Determination of slicing efficiency

The slicing efficiency (η_p) of the machine was determined using Equation (6)

Where M_s = mass of sliced materials (Kg)

M_t = total mass of sliced and damaged materials (Kg)

3.6 Determination of Throughput Capacity

The throughput capacity of the slicing machine was determined using Equation (7)

Where: T= throughput capacity (kg/hr)

t =time of slicing (hr)

4 RESULTS AND DISCUSSION

The size classifications of the crops used in the experiment are summarized in Table 1.

Table 1. Size Classifications of the crops used for the experiment

Crop	Category	Mean Size (mm)
Onion	Small Medium	28.74 49.9
Carrot	Small Medium	22.62 33.35
Potato	Small Medium	33.14 48

The results of slicing efficiencies obtained for different speeds are summarized in Tables 2, 3, and 4. The results in Tables 2 to 4 showed that the developed slicing machine successfully sliced the selected crops to the required size range of 5mm to 6mm thick at high efficiency. The maximum efficiency of 87.6% was attained by the machine for slicing small-sized Irish potatoes at rotational speed of 58 rpm; while the least efficiency of 60.7% was attained by the machine for slicing medium-sized onion bulbs at rotational speed of 69 rpm. The throughput capacities obtained for the slicer ranged from 20.52 kg/hr to 44.28 kg/hr.

Table 2. Results of slicing efficiency and Throughput capacity obtained for onion bulbs

Category	Speed (rpm)	M_s (Kg)	M_d(Kg)	Efficiency (%)	Time (mins)	T(Kg/hr)
Small	53	1.92	0.89	68.3	5	23.04
	58	2.67	0.88	75.2	5	32.04
	62	2.65	0.74	78.2	5	31.8
	69	2.24	0.90	71.3	5	26.88
Medium	53	2.22	1.31	62.9	5	26.64
	58	2.96	0.95	75.7	5	35.52
	62	3.10	1.13	73.3	5	37.2
	69	2.87	1.86	60.7	5	34.44

M_s=mass of properly sliced materials; M_d=mass of damaged and unsliced materials; T=Throughput capacity

Table 3. Results of slicing efficiency and Throughput capacity obtained for carrots

Category	Speed (rpm)	M_s(Kg)	M_d(Kg)	Efficiency (%)	Time (mins)	T (Kg/hr)
Small	53	1.71	0.57	75	5	20.52
	58	2.07	0.46	81.8	5	24.87
	62	2.25	0.61	78.7	5	27.00
	69	1.97	0.83	70.4	5	23.64
Medium	53	1.89	1.01	65.2	5	22.68
	58	2.40	0.81	74.8	5	28.8
	62	2.65	0.70	79.1	5	31.8
	69	2.38	0.92	72.1	5	28.56

M_s=mass of properly sliced materials; M_d=mass of damaged and unsliced materials; T=Throughput capacity

Table 4. Results of slicing efficiency and Throughput capacity obtained for Irish potatoes

Category	Speed (rpm)	M_s(Kg)	M_d(Kg)	Efficiency (%)	Time (mins)	T(Kg/hr)
Small	53	2.06	0.56	78.6	5	24.74
	58	2.76	0.39	87.6	5	33.12
	62	2.68	0.55	83	5	32.16
	69	2.85	0.69	80.5	5	34.2
Medium	53	2.53	1.04	70.9	5	30.36
	58	3.15	1.16	73.1	5	37.8
	62	3.69	0.89	80.6	5	44.28
	69	3.08	1.01	75.3	5	36.96

M_s=mass of properly sliced materials; M_d=mass of damaged and unsliced materials; T=Throughput capacity

5 CONCLUSION

A machine suitable for the slicing of onion bulbs, carrots and potatoes, for the purpose of drying, grinding, and processing has been designed and fabricated. During the slicing of the crops using the slicer, it was observed that the machine sliced the selected samples with high efficiency. It was also observed that the speed of the slicing disc and size of the samples affected both the slicing efficiency and throughput capacity. The slicing efficiency increased with increase in rotational speeds of the slicing disc from speed of 52 to 62 rpm. Beyond this speed, the slicing efficiency decreased for all the samples. The slicing efficiency also increased with decrease in size of the samples as well as with the samples themselves. The throughput capacity also increased with increase in rotational speeds of the slicing disc from speed of 52 to 62 rpm. Beyond this speed, the throughput capacity decreased for most of the samples except for the small-sized Irish potato.

6 REFERENCES

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