There are not many components of the valve, ranging from several to dozens. These parts are generally divided into metal parts, rubber plastic parts and standard parts according to the material.
Standard parts can be purchased directly through market according to national standards or industry standards. Rubber plastic parts generally need mold forming. After material selection and mold forming sample confirmation, the quality is relatively stable. Unless there is a defect in the design, the failure of valve products is rarely caused by rubber plastic parts.
According to the forming process, the metal parts of the valve can be divided into casting parts, forging parts, profiles (such as bar stock) direct processing parts, etc. But in the metal parts of these valves, the valve body and bonnet parts are generally thin-walled parts, which tend to be realized by casting process. Generally, forging and other forming processes can only obtain its shape, but it is difficult to realize its thin wall. Therefore, after forming process, it is necessary to arrange machining process to make thin wall parts. However, compared with forging parts, the material density and mechanical strength of casting parts are relatively poor. When the shape of valve inner cavity is not complex, forging forming is generally selected.
Within the allowable range of process capability, the difficulty of three kinds of forming process is: casting process gt; forging process directly. However, from the perspective of valve manufacturing process, when considering mechanical strength, the valve will preferentially adopt forging process to obtain the minimum wall thickness allowed by process capacity, and then adopt casting process to shorten machining workload, and finally adopt direct machining.
In the manufacturing process of parts, the valve enterprise will select some parts suitable for its own conditions for self processing, and outsourcing processing or direct procurement will be carried out for parts without production capacity or competitive advantage. After obtaining all parts and components and confirming that they meet the requirements of drawings and technical specifications, the valve manufacturer shall carry out assembly and 100% performance test, and carry out relevant tests according to the factory inspection requirements.
It can be seen that the quality instability factors that may occur in the manufacturing process of the valve include the following aspects:
(1) Purchased standard parts are unqualified
(2) Purchased or self-made rubber and plastic parts are unqualified
(3) Purchased casting parts are unqualified
(4) The purchased or self-made forging parts are unqualified
(5) The purchased or self-made direct machining parts are unqualified
(6) Assembly not as required
(7) The test was not carried out as required