There are a lot of factors to consider when designing a bearing pivot: lifetime, machine purpose, loading capabilities, and environment, just to name a few. However, the most crucial element is knowing how corrosion, the number one cause of pivot failure, affects the housing, shaft and bushing. Understanding this will help you achieve a successful, maintenance-free pivot design.
Protection against corrosion
When using a metallic bushing, you must use grease in order to keep the bearing pivot moving freely, and by doing this you are also protecting the shaft and housing from corrosion. However, there are downsides to this method. Dirt that is present in the environment sticks to the grease like a magnet, and since most end users don’t perform maintenance on their units as much as they should, the joint will most likely run on “dirty” grease (pictured left). A joint running in that condition is problematic since it causes excess wear on the shaft and bushing, eventually resulting in a premature failure of the joint.
Designing a maintenance-free bearing pivot
The first step is to think about how you will protect the housing (pictured below, right) and shaft (pictured below, left) from corrosion.
One way is to apply a coating to the housing prior to bushing installation. Tests have shown that synthetic wax-based coatings – which go on like paint and dry so there is no liquid for dirt to stick to – work best for outdoor environments. If you need help researching and choosing the best coating for your housing, contact an igus® expert here.
You can also use coatings on the shaft, the most common being zinc, chrome and nickel. However, these coatings are only effective until they are worn off by the bushing. Once the coatings wear off, the bare alloy is exposed to environmental elements, causing corrosion, degradation to the surface finish, and premature bushing wear.dry-running engineered composite plastic bushings instead of metallic ones. Plastic bushings don’t require any external lubrication, making them less likely to fail due to dirt, and can handle impact loads better than metallic bushings. Plastic bushings are easier to install too since they don’t require as precise housing tolerances.
For more information on designing a maintenance-free bearing pivot, check out this in-depth tech talk.