How To Work a Screw Jack

Jack—a mechanical device that is used to lift and support heavy loads or weight. Its mechanism uses a hydraulic cylinder or screw thread for high linear forces. Forms of jack include mechanical jack, hydraulic jack, house jack, automotive jack or garage jack, strand jack, smoke jack, aluminum jack, and so on. The most common form of jack, however, is the lifting jack used for cars or vehicles. The car jack is placed underneath the vehicle when a mechanic or driver is performing repair, maintenance, and change of tire or other car parts. The simplest kind of car or automotive jack that is still very much used is the jackscrew or screw jack, which is operated by turning a leadscrew. It employs an Acme thread that can withstand large loads and does not easily wear over frequency of use. It is ideal for pushing, pulling, lifting, lowering and positioning objects from a few kilograms to tons. It has a self-locking ability that makes it safe to use compared to hydraulic jacks, which require incessant pressure to retain a locked position.

The mechanism of an ordinary screw jack is composed of a screw in combination with a lever. It has a threaded rod with a head, which is called the screw head. The screw rod passes through a threaded block and a handle. The screw has the industrial utility in raising weights, and has an inclined plane that moves spirally around a cylinder. The force with which the screw turns and mounts depends on the rate of the ascent. Screw jacks operated with a worm gear, which lifts by the rotation of the worm shaft. The worm gear is threaded to allow the ascent of the screw head. When the worm gear turns, the friction forces the screw thread to turn the screw as well. Other screw-type jacks used in cars are scissor jack and bumper jacks. Contrary to the screw type jack, a hydraulic jack uses incompressible or enclosed fluid that exerts pressure throughout its volume and against the surface containing it, thereby allowing hydraulic lift.

While screw jacks are designed purposely for raising and lowering loads, they are not ideal for side loads, although some can withstand side loads depending on the diameter and size of the lifting screw. Shock loads should also be avoided or minimized. Some screw jacks are built with anti-backlash. The anti-backlash device moderates the axial backlash in the lifting screw and nut assembly to a regulated minimum.

A large amount of heat is generated in the screw jack and long lifts can cause serious overheating. To retain the efficiency of the screw jack, it must be used under ambient temperatures, otherwise lubricants must be applied. There are oil lubricants intended to enhance the equipment’s capabilities. Apart from proper maintenance, to optimize the capability and usefulness of a screw jack it is imperative to employ it according to its design and manufacturer’s instruction. Ensure that you follow the speed, load capacity, temperature recommendation and other relevant factors for application. 


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