Hot spraying process of metal ceramic coating on surface of valve rod

Abstract

The invention discloses a hot spraying process of a metal ceramic coating on surface of a valve rod, and relates to the field of manufacture of a valve. The hot spraying process comprises the technical procedures of mechanical pre-processing, surface purifying, surface coarsening, pre-heating treatment, hot spraying, accurately grinding and polishing and the like; a vacuum electric furnace is adopted in the heat treatment; the valve rod is pre-heated to 80-150 DEG C; hypersonic flame hot-spraying is adopted; and a valve rod base body is cooled by a forcible air cooling device when being subjected to hot spraying, and a smooth and compact high-performance metal ceramic coating with wear resistance, corrosion resistance, high binding strength and low porosity is formed on the surface of the valve rod after being polished. The process is high in coating efficiency, free from pollution, high in binding strength of the coating and low in porosity; wear-resisting and corrosion-resisting performances and high-temperature and heat vibration resistance of the surface of the valve rod are greatly improved without changing the precision of the overall size of the valve rod; the usability of the valve rod is greatly improved; the service life of the valve rod can be improved by 2-5 times; and the hot spraying process can be applied to a steam valve of a steam turbine unit, a special valve for a power station and other valves.

Description

Technical field: [0001] The invention relates to the field of valve manufacturing, in particular to a thermal spraying process of a cermet coating on the surface of a valve stem. The valve stem can be used for steam valves of steam turbine units, special valves for power stations and other valves. Background technique: [0002] The valve stem is an important part of the valve. It is used for transmission. The upper part is connected to the actuator or the handle, and the lower part directly drives the valve core to move or rotate, so as to realize the valve opening and closing. The valve stem is not only a moving part, a stressed part, Moreover, it is a seal, which will be damaged by various corrosion and wear during work. Such as corrosion in high temperature steam, thermal shock wear in high temperature environment, impact and corrosion of medium, friction and wear of packing, and packing will also cause electrochemical corrosion to the valve stem. Not only the corrosive ...

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Problems solved by technology

For example, a steam turbine valve stem and its heat treatment method provided by Patent No. ZL200310104129.9, the material of the valve stem is improved, NiFeCrMoTiB alloy is used instead of 12% Cr martensitic heat-resistant steel, and the surface of the valve stem is also Nitriding treatment is used for surface strengthening, which to a certain extent solves the problem of valve stem sticking and fracture, but the nitriding treatment used on the surface still does not have high wear resistance and high temperature corrosion resistance.

Another example is spray welding, plasma spraying, laser cladding, electrochrome plating, electroplating nickel and other strengthening treatments on the surface of the valve stem. Among them, spray welding is easy to deform the whole, and the thermal stress is easy to cause cracks. The flame temperature of plasma spraying is high but The speed is low, it is easy to oxidize the powder and affect the coating performance, and the coating has low bonding force, the cost of laser cladding is high, and the high energy is difficult to avoid cracks due to thermal stress. Electroplating chromium and electroplating nickel can damage the surface of the valve stem. It has a certain degree of protection, but its strength is low, and its thermal shock resistance is poor. Moreover, the ordinary coated valve stem after scratches is easily peeled off due to electrochemistry, and the entire processing process is mostly complicated, and chemical plating still exists. a lot of pollution

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