ESTIMATION OF ENERGY LOADING OF METAL FRICTION ELEMENTS OF BRAKES
DOI:
https://doi.org/10.18372/0370-2197.3(92).15934Abstract
In the materials of this article the estimation of energy loading of metal friction elements of brakes is given and the following questions are considered: a design and work of frictional knots of brakes and their settlement schemes; internal and external parameters of metal-polymer friction pairs of tribosystems taking into account their energy load. It is established that the formation of the temperature regime of metal friction elements (rims of pulleys and drums, discs) of brake devices is significantly influenced by such factors as the ratio between their mass, heating (polished) and cooling (matte) and the rate of these processes. The quality and reliability of the created designs of friction units of brake devices depend on the processes, phenomena and effects that occur during the frictional interaction of the microprojections of their friction pairs. The contact of the microprojections is discrete in nature and is estimated by the dynamic coefficient of mutual overlap of friction pairs, and its value is up to 0.25 (for disc brake pads) and up to 0.75 (for drum and tape brake pads).
According to the molecular-mechanical model of electrothermomechanical friction, the interaction of microroughnesses of the surfaces of friction bodies can be represented in the form of a narrow sliding of the actual contact areas (adhesive component). This is accompanied by the deformation of irregularities (deformation component), which causes their stress state. Therefore, heat release during friction is caused, on the one hand, by the destruction of adhesive bonds in the actual contact zones, and on the other hand - by the stress-strain state of microroughnesses. The choice of metal friction elements of different types of brake devices is mainly due to the level of energy load and operating conditions of the brakes. During braking, currents are generated and heat is accumulated in the surface layers of the working parts of the friction unit. These processes cause the greatest changes in the subsurface layers of friction pads. In the process of plastic deformation in materials, their structure and properties change. At the same time, the mechanical, dynamic and temperature gradients in the surface layers of metal-polymer friction pairs, the level of which depends on the braking modes, are constantly changing. In real conditions, metal-polymer friction pairs are subjected to the following thermal loads: pulse heating and slow natural cooling; heating and cooling at a high rate; slow heating and forced cooling; heating and cooling at a low rate. The rates of heating, natural and forced cooling of the working surfaces of metal-lopolymer friction pairs of brake devices are determined by their electrothermally stimulated processes of polarization and depolarization.
