High-precision internal gears work by the meshing of teeth and teeth

High-precision internal gears work by the meshing of teeth and teeth

Gear transmission works by the meshing of teeth and teeth, and the gear teeth are the part of the gear that directly participates in the work, so the failure of the gear mainly occurs on the gear teeth. The main failure modes are gear tooth fracture, tooth surface pitting, tooth surface wear, tooth surface gluing and plastic deformation, etc.

1. Broken gear teeth

There are usually two cases of gear tooth fracture: one is fatigue fracture caused by repeated bending stress and stress concentration; the other is overload fracture caused by sudden severe overload or impact load. Especially gears made of brittle materials (cast iron, hardened steel, etc.) are more prone to tooth breakage. Both fractures start on the side of the tooth that is under tensile stress. Increasing the radius of the transition fillet of the tooth root, improving the mechanical properties of the material, reducing the surface roughness to reduce stress concentration, and strengthening the tooth root (such as shot peening, rolling extrusion), etc. Breaking resistance.

2. Tooth surface pitting

When the gear teeth work, under the repeated action of the alternating contact stress at the front meshing, several small cracks will be generated on the tooth surface near the pitch line. As the crack grows, it will cause small pieces of metal to flake off, a phenomenon known as flank pitting. The continued expansion of pitting on the tooth surface will affect the smoothness of the transmission, and generate vibration and noise, which will cause the gear to not work properly. Pitting is a common failure form in well-lubricated closed gear drives. Increasing the hardness of the tooth surface and reducing the surface roughness value can improve the pitting corrosion resistance of the tooth surface. Open gear transmission, because the tooth surface wears quickly, there is no pitting corrosion.

3. Tooth surface wear

When the gear teeth mesh, the surface of the gear teeth will be worn due to relative sliding, especially when the external hard particles enter between the meshing working surfaces. After the tooth surface is gradually worn, the tooth surface will lose the correct tooth shape, and in severe cases, the gear teeth will be too thin and broken. The tooth surface wear is the main failure form of open gear transmission. In order to reduce wear and tear, the important gear transmission should adopt closed transmission and pay attention to lubrication.

4. Tooth surface gluing

In high-speed and heavy-load gear transmission, the pressure between the tooth surfaces is large, the temperature rises, and the lubrication effect is poor. When the instantaneous temperature is too high, the two tooth surfaces will be partially melted and the metals will stick to each other. When the two tooth surfaces move relative to each other When the sticking area is torn, a band-shaped or large-area scar is formed on the tooth surface along the sliding direction. The low-speed and heavy-load transmission is not easy to form an oil film, and although the frictional heat is not large, it may also be Cold gluing occurs. Use lubricating oil with high viscosity or good anti-glue performance, reduce the surface roughness to form a good lubricating condition; increase the hardness of the tooth surface, etc., can enhance the anti-glue ability of the tooth surface.

5. Plastic deformation of tooth surface

For soft tooth surface gears with low hardness, when the tooth surface pressure is too large at low speed and heavy load, under the action of friction, the tooth surface metal produces plastic flow and loses the original tooth shape. Increasing the hardness of the tooth surface and using lubricating oil with higher viscosity can help prevent or reduce the plastic deformation of the tooth surface.