Screw Jacks
What is a screw jack?
A screw jack is basically a gearbox with a lead screw ( or ball screw ) which when attached to a motor can be used to push and pull , lift and lower usually very high loads.
There are two types of Mecvel Screw Jacks ;Rotating ( HR ) and Translating ( HT )
What are the main factors to be considered in the sizing of a Screw Jack?
| Capacity/Load | The total weight or force required to move and hold the load |
| Type of Load | Tension, compression, guided or unguided, orientation |
| Speed | The rate at which the screw jack moves the load |
| Duty Cycle | Percentage of time the screw jack is in motion relative to total time |
| Environmental/Temperature | The surrounding conditions that the screw jack will safely operate |
How to choose between Rotating (HR) and Translating (HT ) screw jacks ?
Main consideration is the method of mounting as HR and HT screw jacks have the same performance.
HT screw jacks have the screw passing through the housing of the jack and the screw remains below the load , whereas HR screw jacks are in a fixed position with the nut passing up and down the screw.
Ballscrew or Acme screw jacks
For most applications Acme screws are sufficient , however for high duty cycles and high loads ball screw screw jacks are preferred , however there cost is much higher than for Acme.
Also ball screw versions are over 75% efficient compared to around 30% for Acme
Duty Cycle
Standard screw jacks have a max. duty cycle of 30%-40%, when higher duty cycles are required there are two options;
oversize the screw jack or select a ball screw version which can increase the duty cycle to up to 70%.
Speed
Screw jack speeds can be varied by selecting the required gear ratio and changing the pitch and start lead of the screw , from very slow with hand wind option to very high speeds screw jacks that use ball screws and bevel gears.
Options
Mecvel screw jacks are available with many options for help with controlling ,installation , safe operation and environment:
Protective bellows
Stainless Steel versions
Limit switches
Encoder or potentiometer
safety nut
wear indicator
handwheel
anti-rotation device
mounting ends; clevis,rose bearing, threaded
Screw Jack Systems
Where multiple screw jacks are required CRD Devices can size and select the most suitable configuration of screw jacks and supply the full system needed such as the drive motor , transmission shafts , couplings and bevel gear boxes.
Please take a look at our product range , if you need further information or would like to discuss a particular application please give us a call on 01388 778400 or alternatively drop us an email at sales@mecvel.co.uk