Load type is a major consideration that can determine which style pulley (also referred to as a block) to use in your pulley system. Static loads are stationary, applying a constant load to the same area of the bearing. Dynamic loads occur when the line is in motion causing the pulley wheel (also known as the sheave) to turn. The type of bearing in a pulley can determine which type of load it is best suited for.
The sheave on a solid bearing pulley runs directly on the axle or utilizes a bushing style bearing. This bearing style is best suited for handling high static loads. Their primary benefit is their ability to withstand prolonged pressure from a largely unmoving load. While a ball bearing block will inherently have less friction at low loads, under a high static load the balls will deform inhibiting the performance of the block. A solid bearing pulley will retain its shape and is well-equipped to handle this type of static load.
As previously mentioned, ball bearing pulleys will have lower friction than their solid bearing counterparts, specifically at lower loads. The material of the balls is important to consider, with common materials including stainless steel or high quality plastics like acetal and Torlon®. As loads increase, the use of high quality materials and clever block design become critical factors in minimizing friction.
Specifying or designing the best block for a given application is often not as straightforward as simply using solid bearing blocks for static loads and ball bearing blocks for dynamic loads. In 2011, Ronstan was awarded the “Red Dot Design Award” for their new range of Core Blocks™, which featured a 2-stage bearing system aimed at providing excellent performance and low friction across the full working load range, equally adept at handling static or dynamic loads.
Stage 1 - Under moderate loads, acetal ball bearings ensure minimum friction.
Stage 2 - Under heavy loads, where deformation of ball bearings alone would result in increased friction, a sliding acetal bearing on a polished stainless steel race takes over, maintaining low friction. Additionally, the ball bearings are configured to act as a thrust bearing between the sheave and cheeks, preventing the sheave from rubbing on the cheeks and causing friction when the line lead in and out of the block isn’t perfect.
This versatile range of blocks is still available today in numerous sizes and configurations, and over the past ten years Ronstan Core Blocks™ have truly earning their catchline of “Use them Anywhere”.
If you need assistance finding the right hardware for your design, please don’t hesitate to contact us.