Plastic Bearings Case Study:
Fully Moulded Plastic Bearings Offer Longer Life
In this project, BNL’s unique technology and design expertise resulted in plastic ball bearings that delivered exceptional wear rates for a roof turbine manufacturer.
One of North America’s largest roofing and ventilation manufacturer, has signifi cantly improved the performance of its rotary roof turbines with a suite of custom-designed plastic ball bearing assemblies from BNL. Moulded from a specialist grade of acetal available only in Europe, the bearings are quiet, low friction and lubrication free.
BNL’s unique fully moulded bearing raceways - manufactured using a technique perfected during the company’s 35 year history - result in exceptional wear rates, giving the turbine a far greater life expectancy than that offered by competitor products that use bearings with machined raceways. Tests conducted by BNL show that their fully moulded bearings will outlast similar machined bearings by up to 700%.
The superior wear rates achieved by fully moulding a bearing raceway are due to the existence of a fine crystalline layer which is formed as a result of the rapid cooling of the hot plastic on contact with the tool. This fine crystalline boundary layer is very hard, but as the tool fills, it insulates the core and subsequently, the core plastic cools more slowly, giving more time for the crystal structure to grow with larger, less resistant crystals.The thicker the fine crystalline region, the greater wear resistance the surface (ie. the raceway) of the part has.
Competitors typically machine a raceway into this surface as a secondary operation, resulting in the removal of the hard crystalline layer and exposing the less wear resistant core - significantly increasing the wear rate.
BNL’s specialist in-house design expertise has resulted in greater added value to the bearings through the integration of additional features. Clips on the caps make them easy to snap into place, and an upper bearing that includes a bayonet fastening feature, means a simple ‘push in and twist’ movement is all that is needed to install and secure it to the roof turbine. Another integral snap feature on the bearing inner, secures the bearing to the central turbine shaft. These special cost reducing design features remove the need for additional heavy and expensive metal screws and bolts that are time consuming to assemble.
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