Evaluation of kinematic and geometric parameters of disc knives of mobile sutter cutting machines

Along with this, a significant drawback of disc knives, which often leads to low cutting quality, is their significant thickness. This factor increases the compression and friction of the product, which affects the amount of waste and rejects, and an increase in the roughness of the cut surface. An attempt to decrease the thickness of the circular knives and increase the cutting speed, as a rule, leads to a decrease in their stability and rigidity.

MATERIALS AND METHODS

Evaluation of the indicated phenomena A scientifically substantiated resolution of the stated contradiction is possible through a comprehensive analysis and evaluation of the mechanics of cutting with circular knives. A flat disc knife can be schematically considered a thin ring of variable thickness with the following support device. The sedan disc is rigid along the inner contour, and free along the outer contour. The corresponding moment of loss of stability by the knife disk and flat form of equilibrium can be called critical:

p =

-Л^Е^ З fGA^J

12 1-^ 2      D-d ф

Where: E is the modulus of elasticity of the knives material, µ Poisson's ratio, S is the thickness of the knives, P_ԏ P_n are the tangential and normal components of the cutting force, respectively, df is the diameter of the flanges of the knives, C is the ratio of the diameter of the flanges to the diameter of the knives.

The condition for stable operation of the circular knife can be written in the following form:

____ rr л COS(

< P n ^ v (2)

where: P_ (l) ^ "is the component of the cutting force on the blade in the direction of the product movement, φ is the angle that depends on the mutual arrangement of cutting and feed mechanisms.

Then the minimum required knife thickness is:

S >

12 1-^²В-Йф Рл л n*E*fC₁X₁P₁P_n

Taking into account the specific values of the parameters of circular knives used for cutting materials, we take in accordance with the tabular data fCi*iPiPn=0,1 (4)

The calculations show that the normal component of the total arising during cutting is comparable to P at small S. Therefore, the loss of stability of the flat shape of the balance of the circular knife from forces is possible when cutting food materials with thin knives (S <1.0 mm). At the same time, it is necessary to take into account that, due to the initial imperfections, the disk bends already at low values of the force P.

Cutting forces and unbalanced forces in the "knife shaft - support" system can cause resonance vibrations when the knife speed increases. Despite the relatively small value, under certain conditions they can cause significant lateral vibrations of the knives, i.e. their dynamic instability, leading to the shear leaving and the emergence of the risk of destruction.

RESULTS AND DISCUSSION

Experimental studies of circular knives showed that their critical rotation frequency can be determined by the formula:

П= 60 f (Л² - В)^- 0,5 мм^-1 (5)

f- natural vibration frequency of the circular knife f=2,5*100,5SR-2A(6)

S,R- respectively the thickness and radius of the knife;

Я- number of nodal diameters,

А,В - constant coefficients selected depending on Я.

Experiments have shown that when С< 0,2;Я=2. Тогда А=567; В=2,3.

Thus, the choice of kinematic and geometric parameters of circular knives used in machines for cutting materials and semifinished products should be made not from the point of view of the transition of the disk to the plastic state (1), but according to the values of the critical force, which causes the loss of the flat form of stability and the critical rotation frequency leading to resonant fluctuations.

CONCLUSION

The choice of the optimal characteristics of the circular knives can be carried out according to the existing volume. In this case, the value of the normal component Pp of the total cutting force P is preliminarily calculated. Since the force on the blade Pl is equal to 70-90% P, for the control of the calculations, we will assume that the resulting difference compensates for the initial imperfections of the disk shape. we restore the perpendicular to the intersection with the straight line corresponding to the selected value of R. Then, on the ordinate axis, we find the knife thickness S, which satisfies condition (1). After that, we determine the maximum allowable cutting speed;

^=non (7)

This technique ensures the selection of the minimum possible knife thickness and maximum cutting speed, which is a necessary condition for high- quality cutting of materials and semi-finished products.