Correct lubrication is fundamental to ball screw life

Lubricants are often taken for granted, however, a correctly selected lubricant can:

• Minimise friction
• Reduce torque
• Diminish rolling resistance
• Increase efficiency
• Extend life

A ball screw must be thoroughly cleaned to remove contamination prior to lubrication and re-lubrication. Contamination is a leading cause of premature failure of ball screws. Proper lubrication keeps contaminants out, thus greatly reducing the damage they can cause.

Which lubricant should you use for your ball screw?

Oil can be applied at a controlled flow rate directly on to the point of need and will clean out any moisture or contaminants as it runs through the ball nut. It is also able to cool things down.

The only disadvantages of using oil as a lubricant for your ball screw is that it may be costly to buy the pump and metering system to apply the oil, and also excess oil may contaminate the process if it mixes with cutting fluids in a machine.

Grease is less expensive than oil, requires less frequent applications and does not contaminate process fluids.

The only disadvantages are that grease is hard to keep inside the ball nut and has the tendency to build up at the ends of the ball nut travel, where it accumulates chips and abrasive particles. The compatibility with old grease and the re-lubrication grease can also cause a problem so be sure to check this before application.

The following table shows the NLGI (National Lubricating Grease Institute) grades and the worked penetration ranges:

Below is a guide to grease quantity per circuit. To determine total volume required, you must multiply the volume determined from this figure by the number of circuits in the ball nut.

As a rule of thumb, replenish grease on your ball screw every 600 – 800 hours. Note however that because conditions can vary so widely, you should confirm this period by inspection and readjust if necessary. For extremely harsh conditions it is recommended you consult one of our technical engineers for advice on your ball screw.

Ball Screw tips

All ball screw assemblies should run smoothly throughout the entire stroke. If the torque is not uniform over the entire stroke you need to:

• Inspect the screw shaft for contamination
• Use cleaning fluid or a solvent and remove any dirt from the ball grooves.
• Cycle the ball nut along the screw shaft several times then wipe with a dry, lint-free cloth and lubricate immediately.

Ball screws should never be run without lubrication. The right oil or grease lubrication for ball screw assemblies reduces downtime by ensuring the assemblies deliver their expected service life.

Take a look at our range of ball screws on our website or for additional manufacturer information visit the Thomson Linear website.

Have any questions? Call us on +44 (0) 1403 792 300 or email sales@heason.com.