Ball screws are prone to damage when they are exposed to harsh environments. Protective devices are of help in safeguarding other rolling element systems, but they don’t work as well with ball screws. Fortunately, a person can use other measures to protect ball screws and extend their lifespan. Failing to use these measures could lead to them needing to ask How to fix a ball screw.
Table of Contents
Materials play a role in how well ball screws will hold up in harsh conditions. Manufacturers typically use steel when making screw shafts and ball nuts. This material allows for high load capacity and rigidity. However, steel doesn’t hold up as well when the screw is exposed to liquid contamination from water, acids, or other cleaning solutions.
Manufacturers can apply a protective coating to the screw shaft and possibly the ball nut housing. These coatings are often made from electroless nickel, black oxide, and thin, dense chrome. Stainless steel is another option when the shaft is exposed to water or chemicals.
However, this method is not foolproof. The coatings may flake or separate under extreme pressures and loads. In addition, the coating increases the thickness of the surface, which may impact the ball nut load. Stainless steel screws cannot withstand the same load capacities their steel siblings can.
Sealing the Ball Nut Ends
Sealing each end of the ball nut stops liquid and other contaminants from coming between the balls and the raceway. At the same time, the seals lock lubrication in. Seals come in various forms, but all offer some level of protection from solid contamination. Certain materials, such as EPDM, are needed to protect against temperature extremes and certain chemicals. However, the seals add friction and drag torque. Account for this when sizing the ball screw.
Most ball screw assemblies have a normal operating temperature between 0 and 80 degrees Celsius. Temperatures outside of this range or drastic temperature fluctuations can bring about thermal expansion of the shaft. When this happens, the accuracy of the screw decreases.
Mounting the screw shaft in tension helps reduce this risk. It involves placing fixed bearings on each end of the shaft. With these bearings in place, the screw cannot expand or contract.
Another option involves the use of forced air cooling. However, a manufacturer might find it will benefit more from using hollow screw shafts with internal cooling. The shaft is one of several components they need to focus on when considering the effects of temperature. For instance, the temperature rating of the end bearings is also important.
The temperature also impacts the lubrication requirements of the ball screw. Viscosity is affected by temperature. Know the operating temperature range of the lubricant to ensure problems don’t develop.
Consider the above when designing or selecting ball screws for use under harsh conditions. When possible, keep the ball screw away from potential contaminants. If this cannot be done, put measures into place to offer protection. Doing so will extend the life of the assembly and save the company money.