Flame spray repair of main bearing seat hole of cylinder block

       1) Spray the object. Cylinder block is an important part of various engines. The wear and strain of the main bearing seat hole of the cylinder block are one of the common failure modes, so its repair has important economic value.



The cylinder block is usually made of alloy cast iron, which has a loose structure, many micropores, and more strip graphite. The main bearing seat hole is subjected to compressive stress, tangential stress and axial tensile stress during the working process of the engine, and is subjected to strong vibration for a long time, thus affecting the bonding strength of the coating and the substrate.



(2) Spraying process



1) Surface pretreatment. The main bearing seat hole is reshaped to eliminate the line profile (ovality) to ensure the coating design thickness (0.5~0.9mm) and its uniformity, and to expose the fresh metal on the surface to be sprayed. Oxygen-acetylene flame is used to heat the part to be sprayed to 300~350℃, so that the oil stains on the surface of the main bearing seat hole, micropores and graphite will emerge and burn off, and then clean with trichloroethylene. Use quartz sand to roughen the surface, and punch triangular holes on the surface of the main bearing seat hole every 2~3mm, plant four M3 screws on the upper and lower half rings, and the height is the same as the coating thickness, so as to improve the The bond strength of the coating to the substrate. Scrub with acetone again before spraying.



Cover the surfaces and cylinders that do not need to be sprayed with iron sheets, and then cover them with asbestos sheets or asbestos ropes for insulation.



2) Preheating. Use oxygen-acetylene neutral flame to uniformly heat the main bearing seat hole to 160~180℃. If oxidation discoloration occurs, the surface oxide film must be removed again.



3) Spray the adhesive bottom layer. The base layer is sprayed with nickel-clad aluminum composite powder with a thickness of 0.1mm.



4) Spray the working coat. Use a wire brush to remove a thin layer of deposits from the surface of the primer, then spray with a nickel-based powder. Spraying specification: oxygen pressure (0.5~0.6)MPa, acetylene pressure (0.05~0.06)MPa, spraying distance 150~200mm, coating surface temperature should not exceed 300℃ during spraying.



(3) Cooling. Since the coating shrinkage rate is usually greater than that of the base metal, the shrinkage stress of the inner surface coating on the inner surface of the cylinder such as the main bearing seat hole of the cylinder block is directed to the center of the inner hole, which is easy to make the coating peel off from the base material, so it must be taken immediately after spraying. appropriate cooling measures. The specific method is: due to the large volume of the lower half ring of the main bearing seat hole, the diameter of the inner hole caused by thermal expansion during spraying is not much enlarged. After spraying, it can be buried in asbestos powder at about 250 ° C or placed in a furnace to cool to room temperature slowly. : Due to the small size of the upper half ring, the inner diameter of the upper half ring expands more due to thermal expansion during spraying, and the substrate shrinks more slowly than the coating during cooling. Therefore, water accelerated cooling measures can be used on the outer surface of the bearing seat hole to make the shrinkage of the substrate as much as possible. The coating is kept consistent to avoid peeling of the coating.



(4) Effects. The main bearing seat hole of the cylinder block after spray repair has excellent wear resistance and oil storage and lubrication performance, and has significant economic and social benefits.