RU2514249C2 - Method of thermocyclic diffusion of metal powders for worn-out surface of bronze plain bearing bushes - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to reconditioning of plain bearings. Metal powders are diffused to plain bearing bush surface to be reconditioned. Cyclic heating of the bush and bronze-base powder is performed to the powder melt temperature and powder diffusion in bush metal. Bush is held at the temperature of initial diffusion process. Then, it is cooled to the phase sintering temperatures and held thereat. Secondary cooling is performed to powder melt temperature and held thereat for build-up of reconditioned diffusion ply and said ply is cooled down.

EFFECT: accelerated and simplified thermal diffusion at reconditioning of plain bearings.

1 dwg

Description

The proposed method relates to powder metallurgy, in particular to methods for coating powder materials on the surface of cylindrical parts such as slide bushings.

A known method of restoring worn bushings of sliding bearings (RU 2289499 C1, 12.20.2006), where the pressing and distribution of the sleeve is carried out simultaneously in the conductor by the action of the tool on the powder before sintering, the pressing and the distribution is carried out by a tool made of materials with a shape memory effect by heating it to the temperature of the reverse martensitic transformation, the inner diameter of the conductor is performed corresponding to the nominal outer diameter of the sleeve.

The disadvantages of these methods are the bulkiness of the equipment, the excessive length of the recovery time, the uneven deposition of powder on the restored surface, the small surface microhardness of the restored working surface.

As the closest analogue, the method of coating from metal powders was chosen (RU 2164966 C2, 04/10/2001), where the initial heating of the part is carried out until the melting point of the part at the junction of the surface of the part with the powder material is reached, and then the heating is stopped and reopened when the temperature decreases to the sintering temperature of the powder, at which isothermal exposure is carried out, simultaneously with the cessation of the initial heating, the free surface of the part is cooled and stopped when it is reached ns at the junction between the workpiece surface and the powder sintering temperature material last.

The disadvantage of this method is the insufficient diffusion of the metal powder into the metal of the restored part, a small increment of the deposited layer on the side, a slight surface microhardness of the restored working surface.

The technical problem to which the claimed technical solution is directed is reducing the time and simplifying the thermal diffusion process while restoring the performance of worn tin and aluminum-iron bronze sliding bushings, creating a thermocyclic mode of powder deposition, which is achieved by cyclic heating of the restored part. Increasing the adhesion of the powder to the metal of the restored part due to the deep diffusion of molten powder molecules into the metal of the worn surface of the part, increasing the surface strength and microhardness of the reduced metal layer.

The indicated technical result is achieved in that the thermocyclic method includes cyclic heating of the bronze-based sleeve and powder to the temperature of the powder melt and its diffusion into the sleeve metal, temporary exposure at the temperature of the initial diffusion process, then cooling the part to the phase sintering temperature of the powder, exposure to a given temperature range, secondary heating to the temperature of the initial powder melt with a holding time for the increment of the restored diffusion layer, then cooling to about rated temperature.

The invention is illustrated by the graph of the thermocyclic diffusion process, where the thermocyclic method includes cyclic heating of the sleeve and powder based on bronze to the temperature of the powder melt and diffusion into the sleeve metal T ° - 750 ... 780 ° C, τ ₂ - holding time at the initial diffusion temperature process for 7 ... 8 min, then cooling the part to a temperature of T ° - 480 ... 500 ° C to slow down the diffusion process τ ₄ - 4 ... 5 min, secondary heating to T ° - 750 ° C with a holding time of τ ₆ - 20 ... for 22 min increments layer to 0.3 mm, τ ₆ - 38-40 m chickpeas for the layer to 1.0 mm, τ ₆ - 65-70 min to increment layer to 2.0 mm. The entire process of the restoration of the sleeve lasts from 35 to 95 minutes, depending on the thickness of the layer to be built up.

Tribotechnical studies have shown that the distribution of hardness on the surface of the restored diffusion layer when applying the thermocyclic process occurs uniformly, the wear resistance of the restored bronze parts increases by 1.5 ... 2.5 times depending on the thickness of the incremental diffusion layer. The surface microhardness when using the thermocyclic diffusion method increases by 17 ... 20%, the durability of the “bronze bushing - steel shaft” interface as a whole increases by 1.6 ... 1.8 times due to the chromium and chromium-containing compounds present in the bronze-based powder.

Claims (1)

A method for restoring worn surfaces of bronze slide bushings, including thermocyclic diffusion of metal powders into a restored surface of slide bushings, characterized in that the sleeve and powder are bronze-based on a cyclic heating process to the temperature of the powder melt and diffusing it into the sleeve metal, holding at the temperature of the initial diffusion process, then cooling to the phase sintering temperature of the powder, holding in this temperature range, secondary heating to a temperature powder melt with exposure to increment the restored diffusion layer and then cooling.