Valve common spray welding defects in the production process, the main reason of defects and prevent methods/measures are as follows. Spray welding defects of the spray welding layer peeling spray welding layer peeling phenomenon are mostly found in the process of machining. Remelting operation too fast, the main reason is that coating substrate surface is not heated to a molten or semi-molten state, spray welding layer and the workpiece surface can't form the metallurgical bonding, but adhesive connection between molecules. The other workpiece preheating temperature is too high, the surface generated oxide film; Surface preparation is unqualified; Uneven coating thickness and the spray welding alloy brittleness, low melting point can cause false solder spray welding layer and matrix, led to the spray welding layer peeling off. To local spray welding layer peeling of the workpiece, can according to the technological requirements remelting spray welding layer again first, and then spray welding to the required thickness. Spray welding layer peeling off serious when need car off, spray welding again. Spray welding defects of the spray welding layer crack most common spray welding layer fracture and crack occurred in the process of cooling, have occurred in the process of using. Little crack expand to the parent metal. Causes of crack is sprayed welding alloy with the substrate metal expansion coefficient difference is too big; Preheating before welding temperature is too low and the cooling rate after welding is too fast. Prevent method, besides take the preheating gentle cooling measures when necessary in the matrix surfacing or better spray welding layer of plastic material as a transition layer. Artifacts after welding cracks will allow workpiece preheating after remelting again afresh, melt thoroughly. Temperature can be appropriately increase, the general is 400 ~ 500 ℃. Spray welding defects of the spray welding layer porosity surface oxidation film, rust, oil, or spraying the workpiece surface and the alloy powder by oxidation will produce the spray welding layer porosity, etc. So the workpiece welding surface should be clean, to strictly grasp the nature of the flame spraying. Surface melt overheat or excessive can also lead to the result of the spray welding layer of foam. At this moment need to put the fire away quickly, reduce molten pool and the workpiece surface temperature, to melt it again, then to escape of gas in the spray welding layer. Spray coating remelting urgent or flame suddenly close to the coating surface, the coating will be formed when too late to escape of gas in porosity. Spray welding defects of slag slag remelting operation related. Flame moving too fast when remelting, slag not completely, form slag and molten pool has been frozen. Oxide impurities on the surface of the workpiece will directly hinder the fusion of alloy spray welding layer and substrate, always appear discontinuous chains of slag on the fusion line. The slag with scum method is difficult to rule out, therefore, the surface of workpiece to be welded should be strictly in accordance with the foregoing conditions are ready to deal with.