What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
M15 grounding screw used to fix the grounding wire on household appliances and other equipment, the stud is cylindrical, and the thread is perpendicular to the end surface (section). However, the screw holes on the equipment all have tapping guide grooves for sinking and guiding due to the manufacturing process requirements. When fixing the ground wire, if the screw is not positioned accurately (the screw is inclined), the screw is pressed down hard, which is easy to cause the screw and the screw. The screw hole bites the teeth, and after biting the teeth, it is easy to cause the screw to loosen or fall off, posing a safety hazard.
The rivet provided by Yueluo Creation includes a mandrel and a coaxial matching nail sleeve outside the mandrel; the mandrel includes a head, a central rod and a tail, and a position close to the head is provided with an inner A concave section of the lock ring area, a position close to the tail is provided with a section of lock area that inclines and shrinks inward along the direction of the head to the tail; the lock ring area of the core rod is gap-fitted and fixed with a lock ring , a part of the lock ring is located inside the sleeve head of the nail sleeve, and the part of the lock ring located outside the sleeve head of the nail sleeve can be interference fit with the nail sleeve; the nail sleeve The sleeve is provided with a through hole for the core rod to penetrate into, the inner wall of the nail sleeve forming the through hole is provided with a protruding structure, and one end of the protruding structure is close to the sleeve head of the nail sleeve The end of the core rod is close to or adjacent to the end of the tail of the core rod.
Commonly used screw materials in my country are No. 45 steel, 40Cr, ammoniated steel, 38CrMOAl, superalloy, etc. 1) No. 45 steel is cheap and has good processing performance, but poor wear resistance and corrosion resistance. Heat treatment: quenched and tempered HB220-270, high-frequency quenched HRC45--48. 2) The performance of 40Cr is better than that of No. 45 steel, but it is often plated with a layer of chromium to improve its corrosion resistance and wear resistance. However, the requirements for the chrome plating layer are relatively high. If the plating layer is too thin, it is easy to wear, and if it is too thick, it is easy to peel off. After peeling off, it will accelerate the corrosion, and it has been rarely used. Heat treatment: quenched and tempered HB220—270, hard chrome plated HRC>553) nitrided steel, 38CrMoAl have excellent comprehensive properties and are widely used. Generally, the nitride layer reaches 0.4-0.6 mm. However, this material has low resistance to hydrogen chloride corrosion and is relatively expensive. 4) The superalloy material is superior to other materials. This material does not need coating, and is mainly used for the raw halogen-free screw of injection molding machine. The material has high oxidation resistance and corrosion resistance.
Spring washers are widely used in the load-bearing and non-load-bearing structures of general mechanical products. They are characterized by low cost and easy installation. They are suitable for parts with frequent assembly and disassembly. Quick and easy automatic selection of washers is included, but the anti-loosening ability of spring washers is very low! Especially in European and American countries that require high reliability, the adoption rate is extremely low, especially the important load-bearing structural connection parts have long been abandoned. Our country still has some applications in the military industry, but it has been improved to stainless steel. Steel spring washers have long been banned in CASC! It is also said to be very unsafe, because there are two reasons: 1 is circle rise and 2 is hydrogen embrittlement.
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