Ball Screws From Automotion
What is a Ball Screw
A ball screw is a screw which translates rotary motion into linear motion. Normally used as the driving mechanism in horizontal or vertically driven applications aided by linear guides for supports.
They are described by diameter and pitch or lead. The pitch or lead is the amount of travel you get, or distance the nuts travel along the screw for every complete revolution. They can be operated manually or motorised. They differ from lead screws in that they offer greater precision, speeds, efficiency and accuracy. They are a precision screw which cost considerably more than a lead screw of comparable size so it is important to determine if your application really requires a ball screw.
Please contact us if you need any help with this.
General Guidance
When selecting a ball screw some of the main factors to consider are:
- Maximum required travel speed
- Maximum axial compression (buckling load)
- Method of support of the ball screws
- Type of unit required, fl anged, cylindrical etc.
In general it is best to support the ball screws with our ball screw support units (L1388 to L1406) with a fixed end (generally where the motor is mounted) and a floating (support) end. The support units are selected to suit the loads likely to be required, the size of the ball screw (especially its core diameter) and the type of mounting required. Details of the machining required for each end of the ball screw are shown in the bearing mounts technical section.
The data table for the ball screws show the diameter, the lead of the ball screw (i.e. how far the nut travels for one complete revolution of the screw) as well as the mass moment of inertia (also known as the rotational moment of inertia) - this is the extent to which an object resists rotational acceleration about its axis.
Maximum speeds and buckling load data are shown in the technical pages. When using a ball screw the ambient temperature should not exceed +80°C.
During assembly, the parallel alignment of the guides should be ensure. The details on the concentricity of the ball nuts to the ball screws are shown on the technical pages. For linear guideways for use with ball screws please see our part numbers L1016 etc.
Lubrication - the ball screws must be adequately lubricated. This is dependent on load, speed, motion sequence and temperature. Do not use lubricants containing Mo/So or graphite.
In general, the ball nut is already on the ball screw and should not be removed. If you need to machine the ball screw, then the plastic mounting sleeve should be used to retain the ball bearings whilst the nut is removed.
Mounting the nut on the screw
Sometimes ball screws are delivered with a separate ball nut. When mounting the nut on to the screw take care as if done incorrectly the ball bearings may come off the ball nut.
Ball nuts should be mounted only with the help of a plastic mounting sleeve (delivered with the nut). The start of the thread should be aligned so that the seal and the internal parts of the nut are not damaged.
- Remove the rubber washer from one side of the sleeve. Push on the nut with the sleeve on the end of the screw. Press the sleeve against the start of the screw thread.
- Screw the nut onto the thread using a slight axial pressure, then screw the nut on for it’s entire length.
- Remove the mounting sleeve only when the nut is completely threaded on to the screw.
- Lock the nut on to the screw (to prevent any unscrewing) using an O ring or similar - whilst installing the system.
If the balls do unfortunately escape...
- Pick them up (the nut is only compatible with the original balls). The load capacity can still be achieved if one or two balls are missing.
- Carefully clean all parts, use the sleeve as a mounting jig and replace the balls.
- Start with the lowest circuit. Insert the balls into the nut circuit - the sleeve prevents the balls from falling out again.
- Do not place the balls in the empty circuit located between the two deflectors.
If you have any technical queries please call 01483 26 67 74