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11EXPERIMENTAL DETERMINATION OF THE SPECIFIC CUTTING FORCE OF FROZEN MEAT BY DISC KNIFE
Ilieva I.
Bulgaria, Plovdiv University of Food Technologies
Abstract. Results of experimental determination of the specific cutting force of pork meet which is frozen up to -180C by disc knife has been suggested in the following paper. The experiments are accomplished with three feed rate of the food sample: 0.05 m/s, 0.083 m/s and 0.125 m/s and frequency of rotation of the disc knife in a range from 111 min-1 to 450 min-1. It is established that the value of the specific cutting force decreases when the cutting velocity increases and the feed rate decreases. The lowest values of the specific cutting force (11042 N/m) is obtained during feed velocity 0.05 m/s and frequency of rotation of the disc knife 414 min-1.
Keywords: specific cutting force, disc knife, pork meat
Introduction. Disc knife works under the sliding type of cutting. In this case the normal cutting force is considerably decreased compared to the orthogonal cutting. The main reason for this is the transmitting of the part of the friction force from normal to tangential direction, kinematic transformation of the sharpening angle of the cutting edge of the tool [1], sharpening of the cutting edge during cutting [2], cutting the material by the micro teeth of the cutting edge. The influence of these factors grows with the increase of the kinematic factor X, representing the ratio of the tangential and normal component of the cutting force [3]:
V,
(1)
Vn
where Vt - tangential component of the cutting force, m/s
vn - normal component of the cutting force, m/s
In the food industry the meat is cut in fresh or in frozen state. To make frozen meat suitable for next treatment in grinders or cutters frozen meat blocks can be cut without previous thawing. The directly chopping of the frozen meat particles avoids drip losses, discoloration, bacterial growth which would happen during thawing [4]. The machines cut frozen meat with temperature from -300C to -50C. In the production of sausages the temperature of the grinding meat is -200C.
A matter of practical interest for a disc cutting tools design is the value of the specific cutting force, which represents the cutting force of a linear meter of the cutting edge of the tool. The established results of the specific cutting force investigation when frozen meat is cutting by disc knife could be used for designing of energy-saving technological processes which could provide the necessary quality of the production.
Materials and methods. The experiments for determine the cutting force were made with pork meat from upper extremity, which was chosen from the local market in Plovdiv, Bulgaria. The meat was kept 48 hours under temperature from +10C to +40C. The samples were prepared with sizes 100 mm/60 mm/10 mm. Before the experiments they were transferred in the fridge at temperature -18°C for 72 hours. Before every experiment the temperature of the samples was controlled by an electronic thermometer.
The experiments were accomplished with three feed rate of the food sample: 0.05 m/s, 0.083 m/s and 0.125 m/s and frequency of rotation of the disc knife: 111.45; 162.25; 212.65; 263; 311.75; 363.8; 413.9 min-1.
The horizontal component Fx and vertical component Fy of the cutting force F were determined by tensometers and the cutting force was calculated:
f = JFf+FF ,N
\ x y (2)
Fig. 1. Scheme of cutting by disc knife The length of the cutting edge of the disc knife l = KN is determined by (Figure 1):
l =
n.R.Ap 1800
(3)
where R - radius of the disc knife, m;
P - angle between the vertical diameter of the disc knife and the radius vector of the middle point M of the intersection of the cutting edge of the disc knife and the sample;
Ap - central angle with endpoints K and N of the arc l . For the current experiments
Ap = 450 - 350 = 100.
The specific cutting force for all cutting conditions is calculated by the formula:
f = —, N / m
Jl l
(4)
Results and discussion. The results of the frequency of rotation of the disc knife on the specific cutting force f are shown on Figure 2, Figure 3 and Figure 4 when cutting with velocity feed of the frozen samples 0.05; 0.083; 0.125 m/s respectively. The obtained graphs are straight lines. The relation presented in Figure 2 is described by:
f = -40.405n + 27726
R2 = 0.9935
where
f - specific cutting force, N/m; n - frequency of rotation of the disc knife, min-1; R - correlation coefficient.
(5)
Fig. 2. Relation of specific cutting force f to frequency of rotation of the disc knife n when cutting with velocity feed of 0.05 m/s
The relation presented in Figure 3 and Figure 4 are described by the equations (6) and (7) respectively:
f = -32.509n + 28463
(6)
r2 = 0.9991
f = -26.67n + 30309
(7)
R2 = 0.9819
where f - specific cutting force, N/m; n - frequency of rotation of the disc knife, min-1; R - correlation coefficient.
Fig. 3. Relation of specific cutting force f to frequency of rotation of the disc knife n when cutting with velocity feed of0.083 m/s
The analysis of the three graphs which shows the relation between the specific cutting force and the frequency of rotation of the disc knife when cutting frozen meat samples shows the significant decreasing of the specific cutting force when the frequency of rotation increases.
The difference between the boundary values within the adopted range of the frequency of rotation of the disc knife is 12575.76 N/m when cutting with velocity feed of 0.05 m/s; 9952 N/m when cutting with velocity feed of 0.083 m/s and 8436.36 N/m when cutting with velocity feed of 0.125 m/s.
f, N/m V = 0,125 m/s
30000 25000 20000 15000 10000 5000 0
0 100 200 300 400 500
n, 1/min
Fig. 4. Relation of specific cutting force f to frequency of rotation of the disc knife n when cutting with velocity feed of 0.125 m/s
It follows that when the velocity feed is 0.05 m/s then the specific cutting force decreases 1.5 times compared with the cutting with velocity feed of 0.125 m/s. Therefore cutting frozen meat with lower velocity feed is recommended if the energy efficiency criteria is intended. When the aim is high productivity, then higher velocity feeds would have advantage.
Conclusions. The regression equations and regression coefficients were obtained for describing the relation of specific cutting force and frequency of rotation of the disc knife when cutting frozen meat.
In the range of frequency speed of the disc knife from 110 min-1 to 414 min-1 and feed rates of the food sample 0.05; 0.083 and 0.125 m/s were obtained straight line relations of specific cutting force and frequency of rotation of the disc knife.
The lowest value of the specific cutting force 11042 N/m is recorded at the highest value of the frequency of rotation of the disc knife 414 min-1 when cutting with velocity feed of 0.05 m/s.
The highest value of specific cutting force 27612 N/m is recorded when cutting with velocity feed of 0,125 m/s with the lowest value of frequency of rotation of the disc knife 111 min-1.
REFERENCES
1. Boteva M., I. Mihaylov, Determination of the actual edge angle of a disc knife for cutting foods, International conference on technics, technologies and education ICCTE 2014, Oktober 30-31 2014, Yambol, Bulgaria, pp 68-72.
2. Boteva M., I. Mihaylov, A sharpness factor of the disc knife edge, International conference on technics, technologies and education ICCTE 2014, Oktober 30-31 2014, Yambol, Bulgaria, pp 63-67.
3. Vasilev S., Modeling and dynamic analysis of mechanical processings and systems in food industry, research work qualifying, Plovdiv, 2010.
4. Pionov I., Technological fitting-up of meat- and fishprocessing industry, Plovdiv, VIHVP, 1982, p.372
