Worm gear mechanisms are widely used to transmit motion and power between two non-parallel shafts.
The worm gear and the worm are equivalent to the gear and the rack in the middle plane, and the worm is similar in shape to the screw.
Basic parameters
- Modulus
- Pressure angle
- Worm diameter coefficient
- Lead angle
- Number of worm heads
- Worm gear number
- Tip height factor
- Headspace coefficient
The modulus and pressure angle mentioned refer to those of the worm shaft surface, specifically, the turbine end face, which are standardized values.
The worm diameter coefficient is defined as the ratio of the diameter of the worm index circle to its modulus.
Characteristics
1）A higher gear ratio can be achieved with a more compact design compared to the staggered shaft helical gear mechanism.
2）The two-wheel meshing tooth surface has a higher bearing capacity due to its in-line contact, in contrast to the crossed-axis helical gear mechanism.
3）The worm drive is similar to the screw drive and utilizes multi-tooth meshing, resulting in a stable drive with low noise levels.
4）Has self-locking.
When the lead angle of the worm is less than the equivalent friction angle between the meshing teeth, the mechanism exhibits self-locking properties, which enables reverse self-locking.
This means that the worm wheel can only be driven by the worm, and the worm cannot be driven by the worm wheel.
In applications such as hoisting machinery that use self-locking worm mechanisms, the reverse self-locking property can serve as a safety protection.
5）The transmission efficiency is low and wear is severe when using worm gears.
This is because, when the worm gear is meshed and transmitted, there is a large relative sliding speed between the meshing teeth, resulting in significant friction loss and reduced efficiency. Additionally, the high relative sliding speed leads to severe wear on the tooth surface, generating substantial heat.
To mitigate these issues, materials with high friction reduction and abrasion resistance, as well as effective lubrication systems, are often used. However, this increases the cost of production.
6）The axial force of the worm is large.
