When the operator presses the handle of the screw jack to lift and lower heavy objects, they may have to temporarily stop the pressing operation due to other important matters. If the jack is restored to its original position, all previous efforts will be in vain. If the jack continues to lift heavy objects, it is necessary to consider whether it meets the self-locking conditions and can temporarily withstand heavy pressure without tilting or falling.

Spiral jacks are divided into two types: ordinary jacks and self-locking jacks. Ordinary jacks can only lift heavy objects, while self-locking jacks have smaller self-locking effects on their threads. The brake is a key component of the jack that can self lock, with stronger pressure resistance.

How can we determine if the screw jack we are using meets the self-locking condition?

Method 1: Lift the heavy object with a fully loaded jack, stop halfway, and observe whether the jack sleeve has a downward reaction;

Method 2: The equivalent friction coefficient of spiral patterns is related to the manufacturing material, and threads made of wear-resistant materials have better self-locking effects. In addition, if the helix angle α of the jack is smaller than the friction angle φ, the thread can self lock, but we have no way of knowing these data and need to consult with the manufacturer.

The self-locking behavior of a screw jack has directional characteristics, which are tested during vertical lifting, but there is no need to consider self-locking function during horizontal lifting.