Anti-Rotation for Screw Jacks - it's indispensable

1. Physical background

All spindle drives are based on sliding friction or rolling friction. When properly executed, axial movement is achieved through sliding on the spindle thread flanks. However, this effect only occurs when a component of the spindle-nut combination is secured against rotation. The cause of this is static friction within these systems. The spindle starts to slide only when a counterforce overcomes the static friction and the nut is actively turned. This applies to both ball screws and trapezoidal screws, with balls initiating movement faster than sliding thread flanks.

2. Types of anti-rotation

An anti-rotation mechanism is always necessary. However, there are different ways to implement rotation prevention either on-site or within the lifting drive.

2.1 On-site rotation prevention

A table lifted by a single spindle drive, where the spindle is the only connection between the floor and the tabletop, will not move upward but will only cause the tabletop to rotate. Once the tabletop itself is secured, an axial movement will occur from the drive's perspective. This can be prevented by using guide rods, multiple screw jacks, scissors mechanisms, sliding rails, etc.

2.2 Rotation prevention grooved with key in the spindle drive

If on-site rotation prevention cannot be provided, the spindle drive itself should be secured against rotation. This is achieved by having a continuous groove along the length of the trapezoidal thread and inserting a fitting key in the housing cover. The form-fit prevents the spindle from rotating. This design is economically viable for spindle diameters up to approximately 60 mm and stroke lengths up to approximately 2000 mm.

2.3 Rotation prevention using square protective tube and sliding block

An alternative technical solution to achieve form closure is using a square tube and a sliding block within the tube. In this method, a bronze or cast sliding block (square) is screwed onto the end of the spindle within the protective tube. This square block forms a form-fitting connection with the square protective tube, which is available for all screw jacks. This configuration is useful when large and long spindles are used or when ball screws are employed.

3. Briefly summarized

1. On-site rotation prevention: Load is moved by at least two screw jacks; load is secured against rotation using other guide components.
2. Grooved rotation prevention: Used when on-site prevention is not possible, economically sensible for strokes up to 2 meters and spindle diameters up to 60 mm, not suitable for ball screw jacks.
3. Rotation prevention using a square protection tube: Used when on-site prevention is not possible, suitable for large and long spindles, compatible with all spindle types.

NOTE: For screw jacks with a traveling nut version, rotation prevention must always be implemented on-site.