A screw jack is a simple machine that essentially consists of a gearbox and a screw. Though having a structure this simple, the screw jack can be used to accomplish a number of tasks such as pushing, pulling, locking, unlocking, tilting, pivoting, rolling, sliding, lifting or lowering loads. Generally speaking, a screw jack is a device designed for moving or positioning loads. The key advantage of using a screw jack is that the mechanism provides an easy approach to move heavy loads. Depending on the design, a screw jack can handle loads that weigh from only a couple kilos to thousands of tons.
A screw jack typically consisted of a screw, a worm gear and the housing. The screw and the worm gear are usually positioned in the configuration in which the screw lies horizontally and the worm gear stands vertically. These two components are positioned perpendicularly with their teeth engaged closely with each other. A shaft is connected to the worm gear. As the shaft turns, the worm gear rotates, and as the worm gear rotates, the screw rotates accordingly.
With such design, the screw can travel in two directions along its axial axis by means of turning the worm gear in the clockwise or counter clockwise orientation. By means of translating the motion from the gear to the screw, a screw jack can lift and lower loads. This mechanism is very versatile since it takes only a little adjustment to the configuration of the device to diversify the application of the screw jack.
A screw jack can be a manually operated mechanical device used to temporarily lift a heavy load such as a car or machinery; a screw jack can also incorporate other mechanical systems or power systems such as an electrical motor or a hydraulic pump for industrial applications. It is actually an essential component in automated machinery. Based on the mechanical structure, the screw jacks can be divided into three main types: the translating screw jacks, the keyed screw jacks, and the rotating nut screw jack.
The translating screw jack is one of the most common applications of the screw jack. A translating screw jack has the lead screw fixed on the object that needs to be moved. That way, when the worm gear rotates, the body of the jack moves instead of the screw. The screw of a translating jack is often attached to the load by bolting or pinning.
The keyed screw jack is another type of jack that functions by means of restricting the rotation of the lead screw. A key is positioned and fixed onto the jack housing. The key inserts into a keyway that is milled into the lead screw. Therefore, when the worm gear rotates, the lead screw does not rotate. This type of jack is used when the loads to be moved do not attach to the screw.
The rotating nut screw jack is also known as the traveling nut screw jack or keyed for traveling nut jack. This type of screw jack works on the opposite way of typical screw jacks. The screw rotates in place without traveling through the housing. A nut is attached to the body of the screw; therefore, when the screw rotates, the nut travels linearly along the axis of the screw. A load is attached to the nut so that it can travel upward and downward along the screw.
Jacks refer to the machines that are commonly implemented in industrial settings for high-load applications. To meet the requirements of industrial applications, power systems are applied to generate the force for lifting, lowering or in general positioning loads. The major types of powered jacks are the pneumatic jacks, the hydraulic jacks. Though the machines for positioning heavy loads are all referred to as jacks, the powered jacks are very different from the screw jacks mechanically.
The hydraulic jacks lift heavy loads by applying a force generated by a hydraulic cylinder. The hydraulic jack produces pressure by the movement of hydraulic fluids through two cylinders. A hydraulic jack is considered more powerful. However, they need constant pressure to perform the work and maintain the position. It costs more energy as a result. On the other hand, the pneumatic jacks are powered by compressed air instead of liquid oil. The compressed air transfers the force to lift heavy objects. Since it takes regular air as the power translating medium, though less powerful, the pneumatic jacks are more cost-effective than the hydraulic counterparts.
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