For years, a quiet revolution has been taking place in the industrial world. It's the move to reduce the use of hydraulics and replace it with more eco-friendly electromechanical actuation. Electric actuation delivers power on demand, eliminating waste associated with constantly running pumps. It also does away with fluid leaks that plague even the tightest hydraulic systems.
The next step in this ongoing effort is to clean up mechanical components, and when it comes to linear motion, that means ballscrews. In today's automation environment where many companies already practice the three “Rs” — Reduce, Reuse, and Recycle — ballscrews are ripe for a greening.
Waste reduction is the key here, and any waste that's created should consist of relatively inert materials. Bearing-related products, of course, can't be made of just anything. Corrosion and wear are ever-present threats. As a result, many coatings and platings have been developed over the years to provide protection, but these processes are costly and often use toxic chemicals. Cadmium, zinc, lead-based coatings, and chromium are among the worst offenders. A cleaner alternative is to use one of the newer grades of stainless steels that have excellent properties for bearing grade materials.
Although stainless steels are not a magic bullet, their use can reduce or eliminate the need for environmentally harmful coatings and platings. Be sure to ask for materials and processes that comply with RoHS (Restriction of Hazardous Substances directive). Acid-free zincs, nickel, and black oxide are a few of the friendlier coatings that reduce corrosion and wear. Another alternative, one that the machine tool industry has long preferred, is the use of high luster polishing in lieu of coatings and plating.
“Clean it up and use it again” is as simple as it gets. Although a few components may require replacement, refurbishment of worn-out ballscrews is a common occurrence. In fact, half of all ballscrews removed from service require only a thorough cleaning, restraightening, and ball replacement to return to proper working order. Removing the ballscrew from the application as part of a preventive maintenance cycle can dramatically extend its working life and significantly reduce lifecycle cost by avoiding damage that could render major components unusable.
Wear rates vary by application, but balls generally wear faster than the ball nut. Screws wear the least because contact is typically distributed along their length, barring “sweet spots,” limited regions of recurring motion, in the machine or application. Replacing balls and ball nuts (as needed) minimizes overall maintenance costs because it protects the screw, which is by far the most expensive component. Screws and ball nuts can also be reground to further extend their life.
Rebuilt and refurbished ballscrews function as well as new ones and usually offer the same lifespan. Be aware that bearing journals and other mounting surfaces may become damaged during removal (as well as normal use), but usually can be repaired. Consider using metalizing techniques that rebuild journals with a stainless steel additive, as opposed to having worn journals built up with chrome plate.
If a ballscrew is at the end of its life and cannot be refurbished, remember that all of the ballscrew elements are recyclable. Steel brings a good return at scrap value, so make sure to get that last bit of return on the initial investment. Polymers used in ball return systems, wipers, and seals are also reclaimable and may be sent to recyclers as well.
Ballscrews play a major role in products and technologies that contribute to a healthier environment. In electric vehicles, they replace conventional hydraulic systems, providing steering, traction control, and braking functions. Windmill farms use ballscrew actuation in blade pitch and directional positioning. Hydroelectric stations use ballscrews to control gates. Solar panels use them to track the sun and maximize efficiency. And finally, ballscrews are the actuator of choice among lawn care professionals for adjusting mower decks on equipment that manicures the “greens” at your favorite golf course.
This month's tips were provided by James Babinski, engineering manager, A&D Ballscrews, Thomson, a Danaher Motion company.