How to produce a good non-standard screw? What factors do we need to pay attention to?
Firstly, it is about material selection. Different materials require different processing techniques. For example, when choosing 303 material, which can distinguish between easy to cut stainless steel containing sulfur and selenium, single-mode or multi station machines cannot be used for processing. We often encounter customers holding a drawing, such as a half round head mechanical screw with an inner hexagonal groove, with a specification of M4 * 12 according to the national standard, but the material requirement is 303. Usually, this type of screw cannot be produced because the material is turning material, but they also request to punch an inner hexagonal groove. Some of the inner hexagonal grooves require cold heading skills, and cold heading skills cannot punch 303 material. There is a conflict between material and craftsmanship. The cold heading techniques used in single-mode machines and multi station machines can only produce austenitic stainless steels such as 302, 304, and 316.
Secondly, once the material is selected, the production process of non-standard screws also needs to be considered. Non standard screws are divided into three main parts: size, mechanical properties, and surface defects. The specific inspection items for each section have different regulations based on different products. If the precision and appearance requirements for non-standard screws are particularly strict, it is recommended to choose machining methods. Cold heading is a natural forming method, and the control of edges and precision is not as high as machining.
Thirdly, nominal handling. The commonly used nominal treatment for stainless steel is scrubbing to remove oil and preserve its essence. However, there may also be requests for color, such as chemical coloring through anodizing, electrophoresis, electroplating, and mirror polishing. After completing the nominal processing, a screw suddenly became taller.
Fourth, handle the rest. Screw customization, such as size inspection items, specifies the thread gauge, thread stop gauge, thread small diameter, opposite edge width, diagonal dimension, nut height, and the perpendicularity of the nut support surface to the thread axis for hex nuts; The specifications for flat washers include inner diameter, outer diameter, thickness, coaxiality of the outer circle to the inner hole, and flatness. The mechanical performance inspection items for hexagonal nuts are specified as hardness and tensile strength; And only the hardness is specified for flat washers. Non standard screws are divided into three main parts: size, mechanical properties, and surface defects. The specific inspection items for each section have different regulations based on different products. Some people hope to increase hardness and usually advocate the use of 316 material, which has slightly higher hardness than 304 material. Some may have requests for appearance, which depend on the customer and the location where the screws are used. 316 material is less commonly used. Not only because of its rust prevention and corrosion resistance, but more importantly, its price is much higher compared to 304 stainless steel and other materials. Unless there are special environmental requirements, few users will use 316 stainless steel material.
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