Analysis of seizing phenomenon in aluminum alloy thread fitting
1、 Influencing factors of aluminum alloy thread biting
1. Characteristics of aluminum alloy materials
Aluminum alloy thread has active chemical properties and strong oxidation. The thread surface is easy to form oxide film in the air. When the thread is assembled, it bears the effect of friction and pressure, which is easy to lead to the destruction of oxide film on the thread surface and the accumulation of waste chips between threads. When the thread pair materials are similar or the strength difference is small, thread adhesion is easy to occur during assembly. If the locking torque is too large or the tightening speed is too fast during assembly, the thread will be seriously rubbed and even deformed.
Fig. 2 thread tear after forcibly screwing out the aluminum alloy thread after being bitten
2. Influence of thread error
Thread error is mainly manifested in pitch error and profile angle error. Pitch error includes local error and cumulative error. During thread machining, some accidental factors are easy to lead to local wear on the thread surface and local pitch error. The cumulative error of pitch depends on the screwing length. The longer the screwing length, the greater the cumulative error. The tooth profile angle error mainly affects the contact surface of internal and external thread matching. If the tooth profile angle error is large, the force on the contact surface will be uneven, the local stress will be large, and the wear will be serious.
3. Influence of thread surface quality
Thread seizure is directly related to thread surface quality. When the aluminum alloy thread is tightened, if the thread surface roughness is low or the lubrication is poor, the friction between threads is serious, the aluminum alloy temperature rises, and then expands, the volume increases, and the thread fit clearance becomes smaller. It will become tighter and tighter until the thread bites.
4. Effect of locking torque
Proper locking torque can ensure that the thread pair will not loosen and damage the thread during use. If the locking torque is too large, it will increase the friction between threads, resulting in thread deformation. Therefore, the thread tightening torque should be controlled during thread assembly.
2、 Measures to prevent aluminum alloy thread from seizing
1. Eliminate the influence of thread error
On the premise of ensuring the strength of threaded connection, making the thread fit length as short as possible can effectively reduce the influence of thread cumulative error.
2. Take proper surface treatment
Aluminum alloy threads can be hard oxidized on the surface. Hard oxidation can significantly reduce the friction coefficient of thread surface and enhance the surface hardness and wear resistance. Reduce the generation of waste in the matching process and reduce the risk of thread blockage and seizure.
3. Control the thread locking torque and locking speed
Too much locking torque and too fast tightening speed will lead to serious thread friction and thread stress deformation. Control the locking torque and locking speed during assembly.