Thread galling is a common problem with stainless steel bolt fasteners. Seizing is similar to a cold welding process, the main reason is that the speed and friction of fasteners during assembly/locking produce instantaneous high temperature and cause metal fusion to cause sticking. Seizure often occurs on screws and nuts of stainless steel and alloy materials (stainless steel is particularly sensitive to seizure), because when the surface of these metal alloys is damaged, an oxide film layer will be formed on the surface to prevent further corrosion. When the fastener is tightened, the pressure on the contacting thread surface will destroy the oxide film, and the metal contact points that lose the oxide film will peel off and cause mutual seizure.
The main reason is that stainless steel 304 contains more nickel, so the toughness and stickiness of the material, especially the bolts and nuts made of the same material, are easy to bite to death.
Solution
There are many kinds of solutions: apply some lubricating grease or other anti-stick coatings on the surface; use bolts and nuts made of different grades of materials; use variable thread threads and other methods.
1. Apply some lubricating oil on the surface of fasteners Disadvantages: serious pollution, may not be applicable in special environments; when using coatings, molybdenum disulfide coatings are currently the best solid lubricants, and the coating thickness can be controlled, and the torque coefficient can also be Controllable, durable and effective, but molybdenum disulfide anti-sintering agents can only withstand 400°C.
2. 304 bolts and 316 nuts can be used together, and bolts and nuts made of the same furnace number should not be used together.
3. Using variable tooth thread, there is a wedge-shaped slope at the bottom of the female thread. When the bolt and nut are tightened together, the cusp of the bolt is tightly pressed against the wedge-shaped slope of the variable-tooth thread thread, resulting in a lot of Great locking force. Moreover, the thread contact area is small, and the degree of metal fusion will be much smaller, so it is not easy to seize the phenomenon.
4. There are some other methods, using stainless steel screws to soak and dry in self-prepared ethyl cellulose and alcohol solution, and drop a few drops of carbon tetrachloride on the stainless steel threads.
