Machine Screw jacks are used for positioning loads in numerous applications, however when the load direction alternates between tension and compression within the operating cycle and a high position accuracy must be maintained then a specific type of screw jack is required. The Anti-Backlash Screw Jack is recommended for such applications, as it is able to reduce the axial backlash between the lead screw and the trapezoidal screw thread in the gear to a practical minimum.
Axial backlash exists in standard screw jacks as the “gap” or “play” between the flanks of the lead screw thread and the internal thread on the worm gear nut. This “gap” or “play” is due not only to normal manufacturing tolerances, but to the fact that there must be some clearances to prevent binding and galling when the screw jack is operating under load. In most applications either the load direction is constant so axial backlash does not occur or the position error caused by the axial backlash is considered negligible for the application. However some applications require minimal or regulated axial backlash for accurate and repeatable positioning. Such an application is for positioning the rollers in steel straightening machines for tube, bar or sheet steel production.
Power Jacks anti-backlash mechanism on screw jacks can be used to reduce axial-backlash to a practical minimum (typically 0.013mm) or a regulated value. Reduction in axial backlash below this minimum is not normally recommended as it can cause binding and excessive wear. As the screw jack is operated over time the axial backlash will increase as the lead screw thread on the gear wears due to normal operation. To compensate for this Power Jacks anti-backlash device can be adjusted to re-set for the required amount of regulated backlash. To help with the identification of wear Power Jacks screw jacks can also be fitted with a wear monitoring device for visual use or with electronic sensing for integration into a motion control system.
Power Jacks have been manufacturing and developing screw jacks with anti-backlash devices at their Fraserburgh factory since the 1960s. Screw Jacks whether in single-face gearbox, cubic gearbox or special designs can be supplied to suit customer requirements. They are available in metric (mm/kN) and imperial (inch/Ton) designs with capacity ratings range from 5kN to 1000kN and ¼Ton to 100Ton as standard. Further information on the anti-backlash device or for 3D CAD, catalogues and maintenance manuals are freely available from Power Jacks website www.powerjacks.com or alternatively contact Power Jacks for assistance.
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