Locking analysis of stainless steel fasteners

Fastener users often reflect: why stainless steel fasteners sometimes have locking problems, and similar phenomena do not occur frequently when using carbon steel fasteners. Is stainless steel fasteners softer, carbon steel? What are the reasons why fasteners are relatively hard? That's right! Stainless steel is essentially different from carbon steel. Stainless steel has good ductility, but its hardness has a certain gap with carbon steel. The hardness of the austenitic stainless steel grade 316 head and A4--80 can only reach 8.8 grades equivalent to the hardness grade of carbon steel. However, this statement can only be said to be half right. Locking often occurs on fasteners made of stainless steel, aluminum alloys and titanium alloys. These metal alloys have rust resistance and produce a thin oxide layer on the metal surface when the surface is damaged. Prevent further deeper rust. When the stainless steel fasteners are locked, the pressure and heat generated between the ridges will destroy and erase the oxidized grid during the process, causing the metal dents to directly block/shear, and then sticking. When the sticking phenomenon continues, the stainless steel fasteners will be completely locked and can no longer be removed or locked. Usually a series of blocking--shear-adhesive-locked actions occur in just a few seconds. Therefore, understanding the characteristics of stainless steel fabrication and following proper procedures is the first step in preventing the locking of stainless steel fasteners. External causes of lock-up: 1. If the product is not properly selected, make sure that the mechanical properties of the product meet the requirements before use. In addition, the length of the screw is selected properly, and the nut is tightened to expose the nut one to two pitches. 2. Rough tooth or foreign matter If there is solder joint, other metal chips are caught between the teeth, which often leads to locking. 3. If the force is too strong or the locking speed is too fast, use a torque wrench or a socket wrench as much as possible to avoid using an adjustable wrench or an electric wrench. Because the electric wrench often causes the locking speed to be too fast, the temperature rises rapidly and locks up. 4. The direction of the force direction error nut must be screwed perpendicular to the axis of the screw, do not tilt. 5. The use of flat and elastic washers can effectively prevent the problem of too tight locking. Precautions to prevent locking of stainless steel fasteners 1. When using stainless steel fasteners, do you always lock the nut at a fixed speed? If you are a first-time user or a user who is not familiar with the stainless steel product process, generally slowing down the speed of locking can greatly reduce the chance of locking. Because heat often occurs when it is locked, so when heat energy increases, the probability of locking increases. When in use, the speed of locking the stainless steel fasteners should be lower than the speed of locking the carbon steel. 2. Is the screw or nut lubricated before locking? If the answer is “No”, it may be recommended to use butter, molybdenum disulfide, graphite, mica or talc to lubricate the inner and outer teeth to reduce the lock. The layer is also an effective way to lubricate the layered snail. The cap will shrink like a lubricant film between the nut and the screw. 3. Do you choose the same grade of screws and nuts? If the answer is yes, it is recommended to use different grades of screws and nuts, such as 304 with 316, etc., but pay attention to the selected grade of stainless steel to meet its own rust and corrosion resistance requirements. In addition, the most common case of locking when locking the flange. If you have noticed and followed the above points, including the use of washers, nuts, nuts in diagonal order, slow rotation to the appropriate tightness, etc., if still can not be resolved, often after pre-locking I can't unload it. Finally, I have to temporarily use the carbon steel nut when pre-locking the flange device. When the lock is finally officially used, use the stainless steel nut to find a good between rust and lock. balance point.