1. What are the reasons and measures for preventing threaded connections from loosening?
Reason: Under the action of impact, vibration and load change, the pretightening force of threaded connections may disappear at a certain moment, and the connection may loosen. High-temperature threaded connections may also loosen due to differences in temperature deformation and other reasons. Therefore, anti-loosening must be considered during design.
Measures: Use additional friction to prevent loosening, such as channel nuts, cotter pins, stop washers, etc., and use other methods to prevent loosening, such as punching points to prevent loosening, and adhesive methods to prevent loosening.
2. Measures to improve the strength of bolted connections
1) Reduce the variation range of the total tensile load Fa of the bolt:
In order to reduce the stiffness of the bolt, the diameter of the polished rod of the bolt can be reduced or a hollow screw can be used, or the length of the screw can be increased.
The stiffness of the connected parts themselves is relatively large, but the joint surface between the connected parts needs to be sealed and the stiffness will be reduced when a soft gasket is used. If a thin metal gasket or an O-ring is used as the sealing element, the joint surface can still be maintained. The original stiffness value of the connection.
2) Improve the load distribution between thread teeth.
3) Reduce stress concentration.
4) Avoid or reduce additional stress.
3． Failure modes of gear teeth
1) Gear tooth fracture usually occurs in the tooth root part, because the bending stress of the tooth root is the largest when the gear tooth is stressed, and there is stress concentration, which can be divided into overload fracture and fatigue fracture. 2) Pitting corrosion on the tooth surface. 3) Tooth surface gluing. 4) Tooth surface wear. 5) Plastic deformation of tooth surface.
4. Gear transmission lubrication
Open gear transmission is usually manually lubricated regularly, and lubricating oil or grease can be used. Generally, the lubrication method of closed gear transmission is determined according to the circumferential speed V of the gear. When V <= 12, oil pool lubrication is often used. When V>12, oil pool lubrication is not suitable.
This is because: 1) The peripheral speed is too high, and most of the oil on the gear is thrown out and cannot reach the meshing area. 2) Stirring the oil too vigorously will increase the temperature rise of the oil and reduce the lubrication performance. 3) It will stir up the impurities deposited at the bottom of the box and accelerate the wear of the gears. Oil injection lubrication is often used.
5. Why does the worm drive require heat balance calculation and cooling measures?
Since the worm drive has low efficiency and generates a lot of heat, if the heat is not dissipated in time, it will cause the oil temperature in the box to rise, lubrication to fail, leading to increased gear wear and even gluing. Therefore, thermal balance calculations must be performed for closed worm drives that work continuously.
Measures: 1) Increase the heat dissipation area, rationally design the box structure, and cast or weld heat sinks. 2) Improve the surface heat transfer coefficient, install a fan on the worm shaft, or install a serpentine cooling water pipe in the oil pool of the box.