Screw jack is used in applications where linear motion is required. Lifting of any load, pushing or pulling of mechanical equipment, adjusting of tight clearances of mechanical parts can be done by screw jacks. Mechanical capacity of screw jacks is between 5kN and 2000kN. Jack screws can be used as linear motors, linear actuators, or mechanical lifts depending on type of motion. Please download the Polimak Screw Jack Catalog for more information.
How Screw Jacks Work ?
Main components of screw jacks are; trapezoidal lifting screw, worm screw, worm gear and gear housing. Worm screw is rotated manually or by motor. With the rotation of the worm gear, the screw in it moves upwards or downwards linearly. The feed rate of the screw depends on the turning speed, the number of teeth of the gears and the size of the screw pitch. There are three main types of screw jacks; Travelling Ball Screw Type, Travelling Ball Wedge Screw Type and Travelling Ball Nut Type.
In some models of jack screws, The lifting screw does not move up and down. It only rotates around its axis. A lifting nut (also known as travelling nut) moves along the screw. The lifting nut of jack screw is made of bronze to decrease friction.
Working Principle of Screw Jacks
V-Travelling Ball Screw Type
If the screw end connection is connected to the free load, the screw rotates circularly and moves up and down. If it is connected to a fixed load, the gearbox in the jack receives the movement from the gear unit and the trapezoidal screw moves only linearly up and down. In other words, it acts the same as the Wedged type, so there is no need to open wedge channel to trapezoidal screw.
K-Travelling Ball Wedge Screw Type
The wedge channel is opened to the screw to prevent the rotation of the screw and only the upward and downward movement of the screw is provided. In this way, the importance of the screw connection is eliminated.
T-Travelling Ball Nut Type
With the rotation of the gear, the screw that is inside the screw jack only makes rotation around it’s axis. The flange, which is produced from the bronze material on the screw shaft moves linearly upwards or downwards. One of the purposes of using such systems is the lack of ducting or storage for the movement of the screw used in the ball screw type and ball wedge screw type. In addition, the screw does not come down from the jack base.
Screw Jack End Types
Plain end type screw jacks are used in multipurpose applications. Linear motion is provided thanks to the wedge option in free loads. Screw jack systems with self-locking system prevent the load from slipping back. This type used in projects that require efficiency and precision.
Clevis end type screw jacks provide positive mechanical movement, precise positioning and smooth lifting speeds. Its standard configurations include pulling and pushing features. Its self-locking system keeps the load steady and prevent the load from going back . Due to its movable head, it is used in angular moving mechanisms.
Flanged screw jacks provide positive mechanical movement, precise positioning and smooth lifting speeds. Its standard configurations include pulling and pushing features. Its self-locking feature keeps the load steady and prevents it from going back.
Travelling Ball Nut
Travelling ball nut type screw jacks provide positive mechanical movement, precise positioning and smooth lifting speeds. Its selflocking feature keeps the load steady and prevents it from escaping. It can be used as a product lifting system on movable bronze nuts with fixed rotation of the screw in places where the trapezoidal screw should not come down, like platform lifting units.
Screw Jack Applications
- Paper, press, printing industry
- Gypsum factories
- Sheet metal forming machinery
- Mechanical lifting applications
- Platform lifting applications
- Food processing machinery
- Construction sector
- Bridge jacks for road and bridge lifting
- Opening and closing of penstocks
- Industrial process
- Roll form machinery
- Mining industry
- Defense industry
- Lift tables
- Stage setup applications