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What is a screw jack?

Nov 16, 2020 | Blog

A screw jack is a type of mechanical lifting device or jack that is used to apply great force with the help of small effort to lift heavy weights such as vehicles and as adjustable support system for heavy loads like foundation of houses. They are also used to pull, push, tilt, roll, slide, lock, unlock, lift or lower position, align and hold extremely heavy load, from a few kilos to thousands of tonnes.

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A screw jack system includes essential components such as heavy-duty vertical screw or power screw (leadscrew) with a load table mounted on its top, a worm or bevel gearbox assembly, and a motor to provide rotary motion. The screw jack is operated by turning the vertical screw or power screw with the help of gear system and motor, to convert rotary motion into linear motion.

What is the principle of screw jack?

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The principle on which a screw jack works is similar to the working principle of an inclined plane. In an industrial screw jack system, a worm screw is rotated by a motor which then rotates a worm gear. After that, a heavy-duty vertical lifting screw or power screw moves through the rotating worm gear, converting the rotary motion of the motor to liner motion. The speed of the lifting screw’s linear motion depends on thread size and rotation ratio of worm gears. A screw jack’s mechanical advantage (MA) is the ratio of the load applied to the effort applied.

How many types of screw jacks are there?

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According to movement type, screw jacks are of two types — Rotating screw jack and Translating screw jack.

  1. Rotating screw jack: This screw jack has a lifting shaft that is fixed to the worm gear and moves a nut as it rotates. As the nut moves, this causes the load attached to the travel nut to move along the lifting shaft.
  2. Translating screw jack: This type has lifting shaft which moves through the gearbox. A nut is fitted with worm gear in such a way that the worm gear and nut rotate simultaneously. Once the lifting shaft is prevented from rotating, it will move vertically through the gearbox to move the load.

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What are the uses and application of screw jack?

The screw jacks have high friction and low efficiency because of the extensive area of sliding contact between the screw threads. Due to this they are not used for continuous high power transmission, but they are widely used for occasional positioning of heavy appliances.

Screw jacks have high tonnage lifting capacity that blend loading with precise accuracy. They are highly reliable and synchronized, which make them suitable for a broad range of application where alternative methods of handling is not achievable. Some of the heavy duty applications are — lifting heavy vehicles, water processing, as actuators in industrial applications, steel works equipment, automated machinery, pharmaceutical industry, medical and laboratory equipment, packaging equipment, general machine handling, in electronic connectors, nuclear and aerospace handling and so on.


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