What are the Manufacturing Processes for Valves?

Valve manufacturing involves various processes, despite valves initially seeming to have few components, simple structures, and average precision, they demand exceptionally high standards at their core sealing areas. Complex manufacturing processes and significant technical challenges exist in valve production. Key considerations in valve manufacturing processes include:

Choice of Materials:
Valves come in diverse types and specifications, ranging from common valves like gate valves, globe valves, check valves, ball valves, butterfly valves, to specialized valves like solenoid valves, control valves, pressure reducing valves, high-temperature and high-pressure valves, and cryogenic valves. They serve numerous sectors in the national economy, operating under vastly different conditions such as high temperatures, high pressures, cryogenic temperatures, flammability, toxicity, and strong corrosive media. These conditions impose stringent requirements on valve materials, necessitating the use of materials like cast iron, carbon steel, alloy structural steel, as well as high-alloy materials such as CrNi stainless steel, CrMoAl nitriding steel, CrMoV heat-resistant steel, CrMnN acid-resistant steel, precipitation-hardened steel, duplex stainless steel, low-temperature steel, titanium alloys, Monel alloys, Inconel alloys, Hastelloy alloys, and G0CrW hard alloys. The use of these high-alloy materials poses challenges in casting, welding, and processing due to their poor casting, welding, and processing properties, as well as their high cost and limited availability.

Structure of Castings:
Most valve castings are complex thin-shell castings that demand excellent appearance and dense internal quality with no defects such as pores, shrinkage cavities, sand inclusions, or cracks. Consequently, the casting process is intricate, and heat treatment techniques face significant challenges. The casting difficulty for pressure-bearing thin-shell valve castings far exceeds that of other mechanical components.

Mechanical Processing:
Most high-strength, high-hardness, and highly corrosion-resistant materials used in valve production have poor machinability, posing challenges in achieving required dimensional accuracy and surface finish. Additionally, valve sealing surfaces require high precision in machining, angle matching, surface finish, and paired sealing surfaces, further complicating mechanical processing.

Process Arrangement for Valve Components:
Although valves have relatively few main components with simple structures, most dimensions do not require high machining accuracy, appearing rough externally, valves require precise machining of their core sealing areas. The "three degrees" of sealing surfaces (flatness, smoothness, hardness) and the alignment of the two sealing surfaces forming the sealing pair must both achieve zero clearance to meet the zero leakage requirement of the airtight test. This alignment requirement poses the greatest technical challenge in valve manufacturing, ensuring precise zero clearance in the core area while using rough reference points.

Testing and Inspection of Valves:
Valves are crucial opening and closing and regulating components in pressure pipelines, operating under diverse conditions such as high temperatures, high pressures, low temperatures, flammability, explosiveness, toxicity, and strong corrosion. However, valve manufacturing tests and inspection conditions cannot match the actual operating conditions. International and domestic valve testing standards typically conduct tests using gas or water as media under near-ambient conditions. This fundamental discrepancy poses a significant risk; valves passing normal factory tests may struggle to meet usage requirements in rigorous real-world conditions due to material selection, casting quality, and seal damage issues, leading to major quality incidents. Consequently, veteran valve experts, having spent their careers in the industry, become increasingly cautious and concerned with age.

In conclusion, while valve manufacturing processes present numerous challenges, ensuring the highest standards in material selection, casting, machining, and testing is essential for producing valves that meet the rigorous demands of various industrial applications, safeguarding both operational efficiency and safety.