Self-locking is a term used to describe jacks that require power to move in either direction. They hold their position when power to the system is off.
In general, the self-locking function depends on a variety of parameters:
- Large pitches
- Different gear ratios
- Friction parameters
- The mounting position
- Ambient influences, such as high or low temperatures, vibrations, etc.
Single start trapezoidal type screws are typically self locking.
Due to the large area of contact between the lead screw threads and the worm wheel, there is a large load carrying capacity. This results in high friction which is detrimental to efficiency but also means the system is more likely to be self-locking. In addition, the friction angle of the threads being greater than the lead angle, which also causes the single start worm jacks is self-locking.
Which makes them safer than the hydraulic jack itself, for example, if the force on the hydraulic actuator is released accidentally, it will move backwards under load. Thus, simple, safe, as well as cost effective are the machine screw jack’s greatest strengths.
A brake motor is usually NOT required to hold position on self-locking jacks. However, a brake is recommended for all applications involving vibration since there is dynamic loading on the threads which may overcome friction.
All screw jacks with double start lifting screws and ball screw jacks are considered not to be self-locking.
However, if you need higher duty cycle, faster travel speed, ball screw jacks is necessory. Worm gear screw jacks with multi-start screws also can be used for applications with high lifting speeds. In these application, you will need a brake or other holding device to guarantee holding position.
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