THERMO-CHEMICAL CLEANING THE SURFACE OF CAST-IRON PARTS OF MACHINES FOR FORMING ADHESIVE LINKS IN A CASE OF COLD GAS-DYNAMIC COVER
To maintain Machine and Tractor Fleet in working order, it is necessary to comply with conditions of its maintenance, repair, and also to protect it against corrosion. An effective and common way to protect metals and alloys from corrosion is coating. The aim of the work is developing conditions to reduce free carbon on the surface of cast-iron base in order to form adhesion links when cold gas-dynamic coating. One of the factors influencing adhesion strength is the temperature range of flux activity. The presence of up to 40 % free carbon on the cast-iron surface due to its presence in the structure of cast-iron prevents formation of chemical links and slows diffusion processes between the base and covering, and thereby reduces adhesion strength. In order to form adhesion links between gas-dynamic coating and cast-iron base some technological activities providing adhesion strength of the coating on cast-iron details are proposed and technological factors of coating are determined. To increase adhesion strength it is proposed to remove free carbon from the surface of the base by thermo-chemical cleaning with low temperature flux consisting of 30 % ammonium chloride NH4Cl, up to 70 % zinc chloride ZnCl2 and up to 2 % potassium hypermanganate KMnO4, put on the surface for 3-7 minutes and heated up to 473- 673 К. As a result the number of active particles, reaction rate, number of chemical links and adhesion strength increase.