There are three main methods for processing trapezoidal threads of stainless steel valve stems: turning threads, whirlwind milling threads and rolling threads.
Stainless steel stem
Turning trapezoidal threads on a horizontal lathe is a commonly used method.The tool used for turning thread is simple and the processing range is wide.A higher thread accuracy and a smaller surface roughness with a smaller Ra value can be obtained.However, its efficiency is low, and the requirements for the technical level of workers are relatively high.The processing quality is also unstable.This processing method can be used when single-piece, small-batch production or high thread precision is required.In addition, the trapezoidal thread of the austenitic stainless steel valve stem is difficult to be processed by whirlwind milling and rolling, so turning is mostly used.
The trapezoidal thread of the cut-off valve stem is usually carried out on an ordinary milling machine or a thread milling machine.This processing method has the advantages of high productivity, relatively simple process equipment and no need for special equipment, and is widely used in batch production.Due to the poor rigidity of the valve stem, the low thread precision during whirlwind milling, and the large surface roughness threat, this method is generally only suitable for machining trapezoidal threads with Tr-8C precision.
Rolled thread is a chip-free machining method with high production efficiency.Its efficiency is ten times higher than that of turning thread, and the quality of threaded processing is stable, the precision is high, and the surface roughness value is small.This method requires a dedicated thread rolling machine tool.The manufacturing of the rolling wheel is also difficult.Therefore, it is only used in mass production.
The corrosion damage of the stainless steel ball valve stem is mainly caused by corrosive media.Depending on the corrosion situation, the main problem is the filler.In the use of the valve, the corrosion of the valve stem is unavoidable.Therefore, only preventive measures can be taken.So, what kind of protective measures should the stainless steel ball valve stem take?
    1. Do not add packing to the valve while maintaining the ball valve.Without the packing, the valve stem cannot be electrochemically translated and can be maintained for a long time without corrosion.
    2. Surface treatment of the ball valve stem to improve corrosion resistance.
    3. Reduce asbestos impurities, reduce the chlorine content in asbestos and reduce corrosiveness by washing with distilled water.
    4. Add corrosion inhibitor to asbestos packing to inhibit the corrosion of chloride ions.
    5. Use PTFE protection to reduce the corrosiveness of packing.
    6. Improve processing finish and reduce electrochemical corrosion.