Complex blank structure: Valve blanks, especially casting blanks, are usually thin-walled shell parts with complex structures. This structure requires the blank surface to be smooth, the casting characters to be clear, and the internal structure to be dense, without defects such as pores, shrinkage holes, sand inclusions, and cracks.

 

High casting process requirements: In order to meet the quality requirements of the blank, a series of process measures must be taken during casting, such as selecting high-refractory molding materials, controlling the moisture content of the molding sand, layering to ensure the hardness of the sand mold, adopting a reasonable pouring and riser system, and strictly controlling the pouring speed and temperature. These measures make the casting process of valve blanks far more complicated than that of general castings.

 

Complex inspection process: In addition to size, position accuracy and appearance inspection, valve blanks also need to undergo multiple inspections such as metallographic structure, chemical composition, mechanical properties, corrosion resistance and non-destructive testing to ensure that the quality of the blank meets the design requirements.

 

2. Difficulty in machining

 

Poor material cutting performance: Valves use a wide variety of materials, including various cast irons, carbon steels, alloy structural steels and non-ferrous metals. Among them, most high-strength, corrosion-resistant and high-hardness materials have poor cutting performance, such as stainless steel, titanium alloys, etc. The cutting and machining of these materials is difficult, which brings many challenges to machining.

 

High sealing surface machining accuracy: The geometric shape accuracy and surface roughness of the valve sealing surface are very high to ensure the sealing performance of the valve. This requires that the machining accuracy and surface quality must be strictly controlled during the machining process, which increases the difficulty of machining.

 

3. Difficulty in clamping and positioning of parts

 

Complex structure leads to difficulty in clamping: The structure and shape of the main parts of the valve are complex, and some parts are thin-walled, slender parts with poor rigidity. During machine tool processing, the positioning and clamping of parts are difficult, and complex special tooling fixtures need to be designed.

 

High positioning base surface accuracy requirements: The positioning base surface accuracy of some valve parts is low, the surface roughness is high, and even non-machined surface positioning is used. In order to meet the process requirements, it is necessary to improve the accuracy of the positioning base surface and reduce the surface roughness, or to process the positioning base surface on the non-machined surface, which increases the complexity of the manufacturing process.

 

4. The particularity of testing and inspection

 

Limited test conditions: Valves are important opening and closing and regulating components of pressure pipelines, and their operating conditions vary greatly. However, the test and inspection conditions for valve manufacturing can usually only be carried out under conditions close to normal temperature, using gas or water as the medium for testing. This leads to the valve products that have passed the normal factory test, which may be difficult to meet the use requirements under harsh actual working conditions due to problems such as material selection, casting quality and seal damage.

 

Strict inspection standards: In order to ensure the quality and safety and reliability of the valve, strict inspection and testing are required during the valve manufacturing process. This includes strength testing, sealing testing, non-destructive testing and other inspection methods to ensure that the various performance indicators of the valve meet the design requirements.