The mechanical strength of unreinforced abrasive wheels is determined by centrifugal and bending forces, but their distribution during reinforcement is unknown. It was assumed that the stresses are distributed evenly, but a comparison of calculations on the theory of elasticity and real characteristics on a special stand showed complete discrepancy. Tensile tests of the wheels made it possible to compare the stresses results in the circumferential and radial directions. Was found that the reinforced wheel is an anisotropic body. Anisotropy can be reduced by displacing one reinforcement mesh relatively to the other by angle of 45°. In this paper, a mathematical model of the stress-strain state of the abrasive reinforced wheel was developed, taking into account the anisotropy of its properties. To determine the centrifugal forces, the theory of elasticity for an orthotropic body is applied. The bending forces that arise in the working wheel were determined during solving the problem of the distribution of deformations in the anisotropic annular plate rigidly fixed along the inner contour. As a result of experimental studies, it was found that stresses reach 8...23 MPa, which can be compared with the ultimate strength of the wheel matrix. The elastic module of the wheel matrix is noticeably greater than the elastic module of the reinforcing mesh, which practically does not perceive the load at the initial stage. The developed mathematical model of the strength indicators for abrasive reinforced wheels makes it possible to predict their reliability and safe operation.
Abrasive reinforced wheels in combination with the use of manual and stationary grinding machines are widely used in construction and installation work and are among the most common types of hand tools. Domestic and foreign manufacturers of abrasive tools offer products for cutting, cleaning and grinding operations with different design and physical and mechanical properties for processing various materials. The optimal choice of technological and technical parameters of machines, combined with the correct selection of the required abrasive working tool, allows to reduce labor intensity and increase productivity and quality of work with the desired effect [1 ... 4]. It should be noted that the work of such machines is often carried out in an awkward position, at the cost of large additional and unreasonable efforts at high speeds of operations. The process of working with manual grinding machines (including those with abrasive reinforced wheels) has a number of features, they include: instability of the supply in size and direction; continuous change within the allowable power of the drive intensity of the work process; limiting the forces arising at the point of contact of the working tool (abrasive reinforced circle) with the working environment, both the power of the drive and the individual physiological data of the operator. The task of improving working conditions, improving the efficiency of the use of machines for construction and installation work and ensuring the safe operation of the operator requires a comprehensive assessment of the production environment of operators, taking into account the principles of ergonomics. With a clear shortage of manpower during construction and installation and repair work, such a factor in increasing labor productivity as maximum use of labor resources through the creation of comfortable working conditions and the involvement of ergonomically sound tools and its mode of operation can no longer be ignored. -ся. The analysis carried out by the authors [5, 6] of interaction in the system "operator - machine - working environment" when working with angle grinders equipped with cutting and cleaning abrasive reinforced working bodies shows a close relationship between the load on the working body and effort which are perceived by the machine operator, due to the significant influence of the operating parameters. Determining the load on the working body, based on technological conditions is an urgent task, as in the process of abrasive reinforced wheels torque on the spindle and rotation of the working body is created by the drive of the machine, and all other functions - longitudinal and transverse feed, maintenance of the car and general management - are carried out by the operator. When working with hand grinders, the operator can hold it in any position and ensure a sufficiently precise feed direction of the wheel.
The cost of abrasive cutting is mainly determined by the wear resistance of the abrasive wheel, which consists of abrasive grain, filler, phenolic binder and glass mesh. Due to the fact that during the cutting process, as a result of the summation of heat pulses from the cutting grains located on the cutting edge of the wheel, a significant amount of heat is released, high temperature values are reached in the cutting zone. Meanwhile, it is well known that the phenolic binder has low heat resistance, it breaks down at a temperature of 520-570 °K, therefore the nature of the thermal processes occurring during abrasive cutting determines the temperature in the circle and, accordingly, the speed of its wear. Ideally, of course, the speed of thermal destruction of the bond should correlate with the speed of mechanical destruction of abrasive grains, so that cutting is carried out only with sharp, unfired grains, while only blunt grains should be removed from the cutting edge. Since the rate of abrasion of abrasive grains is different for different processed materials, the characteristics of binders must also depend on the type of processed material, that is, it is necessary to create abrasive wheels for cutting different materials. In practice, abrasive wheels are produced without special consideration of the features of the cut material, which is largely explained by the lack of clarity of the nature of thermal processes in abrasive reinforced wheels and technological difficulties associated with changing the thermophysical properties of the wheels.
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