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Critical Compression Buckling Load, Critical Resonance Speed, Overheating and Lateral Load of a Screw Jack

CRITICAL COMPRESSION BUCKLING LOAD OF A SCREW JACK: When there are compression loads on the screw, it may fail due to buckling, before reaching its static load capacity. If the critical compression buckling load calculated is lower than the actual compression buckling load applied, a screw jack with a larger diameter screw must be selected and its suitability checked. In general, the load applied on the screw jack, including possible impacts, must not surpass the calculated value. The safety factor considered is 3; reconsider this if so considered opportune for the specific application. As a recommendation, when a hypothetical screw jack failure may involve injuries to people, multiply the critical load calculated by an additional factor of 0.6.
 
CRITICAL RESONANCE SPEED OF A SCREW JACK: Applicable to the TRAVELLING NUT SCREW JACKS version (the screw rotates and the nut moves). With reduced diameter and long length screws, there is a risk of having considerable vibration on turning if this occurs at speeds close to the first vibration frequency (the second and highest correspond to very high speeds, at which the screws never work). In the worst cases, the screw may break and, additionally, the risk of collapse due to side buckling considerably increases. For these reasons, be sure that the screw jack screw works at considerably lower rotation speeds than resonance speeds. If not, select a screw of a larger diameter and/or reduce its turning speed and/or modify the screw jack end supports.
 
OVERHEATING OF A SCREW JACK: With the aim of avoiding overheating due to internal friction of the screw jacks, the axial strength and the advance speed must be controlled. To do this, check the unit selected. If it does not comply, choose a larger screw jack and/or reduce the load and/or reduce the speed. For very small strokes, please contact the NIASA technical department.
 
LATERAL LOAD OF A SCREW JACK: JACTON recommends that, if they exist, the lateral loads on the screw must be supported by guide systems designed for this purpose, in addition to the guide for the gearbox, so that the screw or the nut exclusively support axial traction/ compression loads. If there are side loads, the life of the screw jack will be notably reduced, as there will be premature wear of the screw and the nut, which is often the origin of faults.