A The input torque, as well as the efficiency and side load ratings, is the same for both translating screw and rotating screw jacks.

A The input torque for a single screw jack depends on the load, the worm gear ratio, type of screw (machine screw, or ball screw) and the pitch of the lifting screw. Torque values are listed in the individual product specification charts based on capacity loads. For loads from 25% to 100% of screw jack model capacity, torque requirements are approximately proportional to the load.

A For reduced axial backlash of the lead screw in the screw jack select a model with the Anti-Backlash mechanism. This is typically used when the load direction changes from tension to compression and minimal axial backlash is required. This design is only available for translating screw jacks. It can be combined with Anti-Rotation mechanism as well.

A When the worm shaft is rotated the lead screw rotates in the body of the screw jack at the same rate as the worm gear. The nut on the lead screw moves in a linear direction along the screw when fixed to a structure that prevents it from rotating with the screw. This design is also available with a Safety Nut. When a screw jack unit is operated, the rotation of the worm shaft causes the worm gear to rotate. For rotating screw jacks the lead screw is fixed to the worm gear and they rotate at the same speed. As the worm gear turns, the friction forces on the screw thread act to turn the nut also. The greater the load on the screw jack unit, the greater the tendency of the nut to turn. It is obvious that if the nut turns with the screw, it will not raise the load. Therefore the nut needs to be fixed to a structure to prevent rotation.

A A screw jack is a gearbox assembly (either worm gear or bevel gear) and a transmission product (lead screw, ball screw or roller screw) which through use of a motor is used to convert rotary into linear motion. They can be used to push, pull, tension, lock, unlock, tilt, pivot, roll, slide and lift or lower loads, anything from a few kilos to thousands of tonnes. Screw jacks are essential components in automated machinery. Safety and legislative concerns drive the automation of handling and lifting of heavy loads, particularly in regions which have developed workplace and health and safety legislation. The trend to electromechanical actuation from hydraulic actuation. Screw jacks usually operate in high-load applications. The competing technology at high loads tends to be hydraulics; however, hydraulics are less energy-efficient than electro-mechanical actuation provided by screw jacks. Hydraulic systems waste energy as the fluid circulates at constant pressure, regardless of the amount of work required to be carried out by hydraulic positioning. A hydraulic jack or ram requires a constant pressure to maintain its position when holding a load in place. By contrast, an electric motor used to power a screw jack uses energy only when it drives the load to a required position. The advantages of electro-mechanical over hydraulic can be summarized by:
* Demand for increased safety, in the event of power loss, screw jacks can be self locking
* Demand for machinery that operates with better energy efficiency
* Demand for machinery that operates greater levels of precision
* Machinery that requires less maintenance
* Machinery that requires less manual intervention to set up processes
* Increased range of actuation in terms of variable positioning
* Accurate and smooth delivery of force
* Cleaner machinery

A The electric motors rotation drives the primary gear of the gearbox, which through a single or more gear stages turns the gearboxes output shaft (final gear). This rotates in unison with the lead screw, as the lead screw is fixed in place to the gear. When the lead screw rotates the lead nut that mates with the lead screw translates along the screw and so converts rotary motion to linear motion. The lead nut is fixed to the “ram” or “inner tube” so this item translates with the nut. Note that for linear motion to occur the ram (including lead nut) must be restrained from rotating with the lead screw. This is usually done by fixing the end of the ram via its end connection to the object that needs to be moved. If the object is in free space then the actuators ram needs an anti-rotation device fitted. The outer tube seals the lead screw into the ram which protects the screw from dirt, debris and damage and acts as a lubrication store. In addition the exposed portion of the ram can have a flexible covering attached to provide extra protection (e.g. bellows boot).

A The lead screw translates through the body of the screw jack when the lead screw is prevented from rotating with the worm gear. This is typically done by fixing the end of the lead screw to the structure that needs to be moved linearly. When a screw jack unit is operated, the rotation of the worm shaft causes the worm gear to rotate. For translating screw jacks the worm gear is threaded to accommodate the lead screw thread. As the worm gear turns, the friction forces on the screw thread act to turn the screw also. The greater the load on the screw jack unit, the greater the tendency of the screw to turn. It is obvious that if the screw turns with the nut (worm gear), it will not raise the load. In those cases where a single unit is used, and where the load cannot be restrained from turning, it is necessary to screw jack with an anti-rotation mechanism (keyed screw jack). Lead screw key torque must be checked as excessively heavy unguided loads could break the Anti-rotation mechanism (key).