Cubic Screw Jack - System Builder

Increasing the number of screw jacks in the system reduces the load on each thus increasing the total load capacity of the system.

The static load is the load imposed on the screw jack system when not moving and may include some process imposed load when the jack is in a static state.

Screw jacks should be deployed in the system such that the total load is equally distributed.

The dynamic load is the load imposed on the jack during travel.

The assumption is made that the screw jack is required to lift and hold the load. In which case the dynamic load is the load imposed when moving and takes account of the accelerating forces. If the screw jack is not required to move the load and the drive motor is used only to position the screw jack height, then the power requirement of the system is considerably lower.

If the screw jack system is such that the screw jacks are horizontal, the ‘Compression’ option should be chosen.

This option is defined by system requirements and architecture.

The travelling element of a screw jack must be attached to the load to prevent rotation and allow linear movement. With a translating screw jack the end of the lifting screw is attached to the load whereas with a rotating screw jack it is the lifting nut which is attached to the load.

Both rotating and translating screw jacks can be mounted on either the top or bottom face.

Rotating Screw
The lead screw is fixed to the worm wheel such that rotation of the worm wheel causes rotation of the lead screw thus translating the nut along the lead screw.

Translating Screw
Text TBC

Translating Screw – Keyed
Rotation of the worm wheel acts directly on the lead screw and the lead screw translates linearly.

Kelston achieves the required lifting speed through manipulation of the following factors:

1. Screw lead, i.e. the linear distance travelled along the lead screw for each revolution of the screw.
2. Reduction ratio, i.e. the rotation speed ratio between the input worm shaft and the output lead screw.
3. Rotational speed of the screw jack input worm shaft. This can be varied by altering the drive motor basic speed by gearing or by an electrical frequency inverter or hydraulic control valves.

The screw jack should be specified to have a greater travel than is necessary in the actual installation. This will create clearance and allow for safe overrun should it happen.

The structure on which the jacks are to be mounted should have ample strength to carry the maximum load and should be rigid enough to prevent deflection or distortion of the jack support members.

Safety distances between moving and stationary components must be established to prevent the risk of the system fowling and causing damage to the screw jacks and system components.

On rotating screw jacks fine height positioning can be achieved with mounting plates. Refer to Accessories

Guide systems and compensation must be employed to limit the effects of expansion, contraction and deflection, and guide the moving parts parallel to the screw jack lead screw(s).