OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 The dependencies (1) and (4) are shown on the diagram in Fig. 8. As it can be seen from the diagrams, in both grinding modes the increase in the grinding wheel speed occurs in proportion to the increase in the grinding train speed. In this case, the rate of change in the speed of the grinding wheel is signifi cantly affected by the angle α for the HSG method and the eccentricity e for the STU method. a b Fig. 8. Dependence of a grinding wheel rotation speed on grinding train speed: a – HSG method; b – STU method The area shaded in gray highlights the possible values of the grinding wheel speed depending on the initial conditions. The graph (Fig. 8, a) shows that in the HSG grinding method, the grinding wheel speed can reach a maximum value of 27.7 m/s at a train speed of 100 km/h and α = 0°. This indicates the rotationrolling of the grinding wheel without slipping. In other words, the chip cutting process will not occur when α = 0° regardless of the speed of the train. Looking at the graph of the STU grinding method (Fig. 8, b) it can be seen that unlike the HSG scheme, a wheel speed of 27.7 m/s is the minimum possible value for the speed of the train moving at 100 km/h and this speed is realized at the maximum eccentricity e, which is equal to the radius of the grinding wheel (e = 125 mm). With a decrease in eccentricity e, the speed of the grinding wheel increases signifi cantly, and at values e close to zero, it can theoretically reach value of 3,500 m/s (beyond the scope of the diagram). Thus, all other things being equal, the STU grinding method initially has a higher grinding wheel speed, which indicates greater possible potential effi ciency of the grinding process. However, a separate kinematic analysis does not give a full picture of the machining process effectiveness. Let’s analyse the force effect on the grinding wheel which occurs during the implementation of the grinding methods under consideration. The diagrams are shown in Fig. 9. The movement of the grinding train transmits the force effect Ft through the rail on the grinding wheel, which in turn consists of the force that drives the grinding wheel into rotation Fr and the force Fg preventing rotation which can be conditionally taken as the force of direct grinding (cutting force). It should be noted that in both cases, the force effect from the grinding train Ft is the same and is determined by the equation: , t F Q (5) where Q is the pressing force of the grinding wheel to the machined surface of the rail head, N; λ is the coeffi cient of interaction of the grinding wheel with the surface of the rail. This coeffi cient is an analogue of the coeffi cient of friction, depending on the properties of the abrasive tool (abrasive grit, material of the abrasive grain, etc.) and the machined surface of the rail. This coeffi cient is determined empirically based on the ratio of the friction force to the reaction of the force when perpendicular to the surface that occurs when the grinding wheel is pressed against the rail. Since we are comparing two grinding methods, the
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