CC BY
13COMBINED INFLUENCE OF THE FRUIT CUTTING PARAMETERS ON THE NORMAL COMPONENT OF THE CUTTING FORCE WHEN USING A DISC KNIFE
Ass. eng. Ganchovska D. G.
Ass.eng.Hodzheva Z. I.
Bulgaria, Plovdiv, University of Food Technologies
Abstract. This paper presents the results of an experimental combined influence study of some of the most characteristic fruit cutting parameters: velocity coefficient X, knife sharpness and kinematic transformation of the sharpening angle, on the horizontal component of the cutting force. Experiments were performed by using a disc knife with 210 mm diameter and a sharpening angle of 15°, and the apples variety Granny Smith. The frequency rotation of the disc knife was changed in the range of 110 and 420 min1 at the feed rate of the test sample 0,125 m/s.The lowest cutting force values - 108,9 N was recorded for the highest value of velocity coefficient X (36,4).The obtained results confirm the advantages of cutting food with disc cutting devices.
Keywords: horizontal component of the cutting force, velocity coefficient X, knife sharpness, kinematic transformation of the sharpening angle
Introduction. The cutting device type, process parameters and structural and mechanical properties of the processed product have the greatest influence on the food cutting.
The shape of the knife cutting edge and its geometric parameters: diameter, sharpening angle, thickness, and sharpness of the cutting edge are essential for the cutting device operation.
Disc knives with a single bevel or double bevel circular cutting edge are widespread in the food industry [3]. Cutting with a disk cutting tool is possible only when two movements are available: feed movement performed by the tool or processed product and movement of cutting which is rotation about the axis of the disc, carried out by the disc knife. Moreover the feed movement may be in a direction normal to the cutting edge or at an angle relative to the tangent to the cutting edge. Disc knife works under the sliding type of cutting. As a basic kinematic characteristic is accepted the velocity coefficient X, which is the ratio between the cutting speed Vp and the feed rate Vn. A number of studies have foundout that increasing the coefficient X results in an improvement of the quality of the cut, reduction of cutting forces and cost of energy, decrease in deformation of the cut particles and keeping the juice content when cutting fruit [5].
Another important characteristics of the cutting process with a disk cutting tool is the knife sharpness and the kinematic transformation of the sharpening angle. During the cutting process the sharpening angle decreases in the direction of cutting (Fig.1) and the shape of the cutting edge in cross-section changes from an arc with radius r of the circle inscribed inside it into an arc with effective radius rk of an ellipse vertex (Fig. 2).
Fig.1. Kinematic sharpening angle Fig.2. Cutting edge shape
of the disc knife changing during cutting
The factor that is of practical interest for the cutting process with a disc knife is the combined influence of the velocity coefficient, kinematic transformation of the cutting edge angle and the knife sharpness on the horizontal component of the cutting force which causes deformation and parting of the cut sample to a greater extent than the vertical component.
Materials and methods. A disc knife with the following parameters: diameter 210mm, thickness 0,8mm, doubleedge angle of 15° made of tool steel was used for the experiments determining the combined influence of the velocity coefficient, kinematic transformation of the edge angle and the sharpness of the cutting edge on the horizontal component of the cutting force. The frequency rotation of the disc knife was changed in the range of 110 and 420 min-1 at the feed rate of the test sample 0,125 m/s. Determining the horizontal component of the cutting force was carried out by a strain measurement device [1].
The apples variety „Granny Smith" were chosen from the local market in Plovdiv, Bulgaria. The apples were firm, larger than average with a diameter of about 100 mm, free of breaks in the skin and stored at 20-25°C for three days after their picking. Samples with a length of 100 mm, width of 60 mm and thickness of 10 mm were prepared [2].
The kinematic angle Cif. was calculated at different values of the velocity coefficient '/. by the following equation: [4]
tgak =
tga
Vl + A2
(1)
The change of the cutting edge sharpness during operation can be estimated by the sharpening coefficient kS: [4]
s-sk 8
= 1 - cosy
(2)
where Sk = Scosy; y - rake angle of the elemental cutting edge (Fig.3)
Fig. 3. Cutting process by a disc knife
8
It is obvious that the coefficient ks does not depend from the geometric parameters of the disc knife such as the angle of its sharpening and initial sharpness S, but varies depending on the size of the angle y.
Results and discussion. The graphs showing the combined influence of the velocity coefficient X, kinematic angle ak and sharpening coefficient kS on the value of the horizontal
component of the cutting force Fx are represented in Fig. 4.
The results indicated that for the given above cutting conditions (cutting speed and feed rate) the increase of the velocity coefficient X caused decreasing in the horizontal component of the cutting
WORLD SCIENCE
№ 8(12), Vol.1, August 2016 43
force. The lowest cutting force values - 108,9 N was recorded for the highest value of velocity coefficient X (36,4).
The kinematic angle Ctf. was reduced by 1°11 in the range of the range of the accepted velocity coefficient.
Moreover the kinematic transformation was more intensive at the beginning of the coefficient X increase (up to 23) and smoother with further increasing of the velocity coefficient.
The cutting edge sharpening coefficient «¿increased by 8, 4% which indicated the extent to which the initial thickness of the disk knife edge was reduced.
k5 FJLN
0,98 ISO k5 1,6
0,96 160 1.4
0,94 140
1.2
i;o
0,92 100 ——— - 1
0.9 so / ^ o.s
60 0,6
O.SS ok
40 0.4
0,86 20
0,S4 0.2
0 1 1 1 1 1 1
9,3
14.:
IS,6
Z3.1
17.1
51.9
56.4
Fig. 4: Combined influence of the velocity coefficient X, kinematic angle ak and sharpening coefficient kg on the value of the horizontal component of the cutting force Fx
Conclusions. Based on the result obtained in this work, the following conclusions can be drawn for the cutting process with disk knife:
The considerable decrease of the horizontal cutting force component Fx (c 52,5 N)when increasing the velocity coefficient X in the range of 9,8 - 36,4 confirms the advantage of the cutting with sliding as a means of reducing the force Fx, which in turn would reduce the energy costs of the process of fruit cutting.
The functions ak = /(A) and ks= f (A) alteration when cutting apples is characteristic of cutting food with a disc knife and is one of the reasons for the widespread use of this tool in practice.
The decrease of the horizontal cutting force component Fx at the given above cutting conditions is 32,5%, i.e. the kinematic transformation of the sharpening angle and the increase of the sharpness depending on the velocity coefficient X are just some of the factors that have a positive effect on cutting with sliding.
REFERENCES
1. Boteva M., S. Vasilev, I. Mihaylov, Stand for determining the forces when cutting food, Union of scientists Stara Zagora, 23rd International Conference, 6-7June, 2013, Volume III, Number 4, 2013: Technical studies, ISSN 1314-4111, pp150-156.
2. BotevaM ., Studying the process of cutting food with disc knife based on dynamic modeling, Thesis, Plovdiv,2015.
3. Vasilev S., Modeling and dynamic analysis of mechanical processes and systems in the food industry, Qualifying research paperPlovdiv, 2010.
4. Reznik N. Theory of cutting with a knife and fundamentals of cutting mechanisms calculations, Moscow, Mashinostroene1975, pp148-161.
5. George D. Saravacos, Athanasios E. Kostaropoulos, Handbook of Food Processing equipment, Springer science + business media New York, 2002, pp 133-142
