METHOD OF FORMING A WEAR-RESISTANT SELF-PROFILING COATING ON WORKING ELEMENTS OF A SPIRAL EXPANDER MADE OF ALUMINUM ALLOY Russian patent published in 2021 - IPC C25D11/06 

FIELD: technological processes.

SUBSTANCE: invention relates to electroplating and can be used in machine building, particularly in compressor building, pump building, engine building. Method involves application of coating on surfaces of movable and fixed spirals of expander by means of micro arc oxidation, which is carried out in an aqueous alkaline electrolyte based on potassium hydroxide with content of 4 g/l and liquid glass 18 g/l at a sinusoidal current density of frequency 50 Hz of 12-15 A/dm², at electrolyte temperature of 25±3°C and duration of formation of coating from 70 to 120 min initial thickness of 50-100 mcm, after which part is washed for 3 minutes and drying in air at 70-80°C for 60 minutes, then the outer rough porous process coating layer on the fixed spiral is removed by grinding to a depth at which residual volume porosity is maintained at 1.5-3.0% but not more than 50% of the initial thickness of the coating, and on movable spiral coating is removed to solid corundum layer at a depth of not less than 30% and not more than 50% of initial thickness of coating, with microhardness of ground coating should be not less than 8 GPa, and the roughness is not more than 0.32 mcm, after which the coating on the fixed spiral is impregnated at least once with polytetrafluoroethylene using vacuum to a value of not more than 0.2 bar, followed by drying at 70-90°C for 60 minutes and sintering at 300-310°C for 10-20 minutes to obtain composite antifriction coating with thickness of formed solid layer of polytetrafluoroethylene of not less than 5 mcm.

EFFECT: reduction of friction coefficient of conjugated spiral elements based on aluminum alloy, improvement of their resistance to wear and anticorrosion properties.

1 cl, 1 tbl, 2 ex, 6 dwg