Sintered Powder Materials for Friction Units of Antonov Aircrafts

The materials of braking assemblies must provide for transformation of large quantities of energy into heat in a friction unit while preserving its serviceability for subsequent multiple braking cycles without significant damage to the friction couple. The main types of sintered materials for braking devices and transmission gears were produced on iron and copper base. At the Antonov Aircraft Scientific and Technical Complex (AASTC), articles for operation under conditions of dry friction are manufactured of FMK-79 and FMKM-1 friction materials, developed at the State Scientific Center 'VIAM' (Russia). Such articles represent a steelwork, which guarantees the necessary strength, with cermet material baked to it on one or both sides. In order to improve adhesion in the course of baking of compacted blanks to the steelwork, one usually nickel-plates the latter. Iron powder serves as the base of FMK-79 friction material, owing to which this material withstands a temperature up to 1000DGC on the friction surface when the volume heating is 500-600DGC. To remove adhesion and to enhance the thermal conductivity of the material, one introduces 9-11 mass% of copper into it. As a solid lubricant in the material, graphite (7-8 mass%), boron nitride (2-4 mass%), and barite (4.0-6.5 mass%) are usually applied. They decrease the wear of a rubbing couple, enhance the resistance to adhesion, but, at the same time, reduce the friction coefficient. To increase it, one introduces 5-7 mass% of silicon carbide into the mixture. Friction linings of FMK-79 material are compacted under a specific pressure of 500-700 MPa and baked to the base under pressure at a temperature of 1000DGC in hydrogen. After sintering, the density of this material is 5.5 g/cm3, its hardness is 80-105 HRF, and the friction coefficient in a couple with ChNMKh cast iron is 0.34-0.40. Brake disks for the combined drive of high-lift devices of An-72, An-74, An-70, and An-140 airplanes are manufactured of this material. In addition to iron, copper is also widely used as the base of friction materials. Copper possesses high thermal conductivity, which guarantees good heat removal in friction. Copper powder, owing to its plasticity, is easily compacted, and its sintering presents no difficulty. For example, FMKM-1 is a copper-based cermet material. In this material, graphite (2.5-3.5 mass%), lead (5-7 mass%), and tin (7-9 mass%) serve as the solid lubricant, and silicon oxide (2-3 mass%) and molybdenum oxide (