Drives & Controls March 2022

34 n BELTS, BEARINGS AND CHAINS March 2022 www.drivesncontrols.com Three ways to cut friction in bearings I n recent years, bearings manufacturers have increasingly focused on creating energy-efficient bearings – using new materials, lubrication techniques and advanced geometries to cut losses without sacrificing load-carrying capacities. Energy losses in bearings are not usually the primary focus of efforts to optimise plants because they are already considered high-efficiency components. But you could argue that bearings are so ubiquitous that their energy consumption and potential energy savings cannot be ignored. Let’s take a closer look at three bearing design considerations that can cut friction and raise efficiency. Advanced materials Energy-efficient bearing designs focus primarily on reducing the contact between the rolling elements and the raceways or the cage. By reducing the roughness of the contacting elements, friction can be cut. Furthermore, the osculation of the bearing at both the inner and at outer rings affects the friction significantly by reducing the contact area and thus the microsliding of the contact. According to a recent study, friction- optimised bearing designs could have a significant impact on reducing energy losses on a global scale. Based on the designs of one bearing manufacturer, a preliminary estimate of this reduction is about 0.15–0.2% of global energy consumption. Traditionally, steel has been the material of choice for bearings, but polymer-based materials, such as PTFE and nylon, offer many benefits in less demanding environments, including corrosion resistance, weight savings, and a reduced need for lubrication. Geometry Geometry considerations such as special cage designs and the number of balls used in a bearing influences the amount of friction generated, because these factors determine the number of frictional contacts during operation. The geometry, as well as the process by which the retainer is manufactured, affect the friction generated. For example, 3D-printing retainers in nylon or other polymer materials can help to reduce bearing weights. In some cases, ceramics offer an attractive alternative to metal. They have similar properties to metal, but are much lighter. Carbon-fibre reinforced nylon is one of the most popular combinations for nylon- printed materials. It offers many of the benefits of standard nylon – including high strength and stiffness – but results in much lighter components. Surface coatings can have a significant effect on reducing bearing friction. Coatings such as molybdenum disulphide and tungsten disulphide increase wear resistance, fatigue durability, and reduce friction during bearing motion. Lubrication A suitable lubricant will reduce friction between the internal sliding surfaces of a bearing’s components, and reduce or prevent metal-to-metal contact of the rolling elements within their raceways. While this is a good way of cutting wear and preventing corrosion, there is a new material that, when used on bearings, can cut friction dramatically compared to the lubrication and surface treatment options currently on the market. This material is graphene. It is relatively simple to add a graphene coating to bearings, and is similar to adding a traditional lubricant. When graphene becomes more widely available, it will be time to study this form of lubrication more closely. As well as being environmentally friendly, graphene flakes added to the surface of a bearing can last a long time, due to the ability of the flakes to re-orient themselves during the initial wear cycles, providing a very low coefficient of friction. In a study of the potential of graphene as a lubricant, researchers estimated that the reduced loss of energy to friction achieved by the new materials would yield potential energy savings of 2.46TWh per year – equivalent to 1.5 million barrels of oil. By optimising each element of a bearing’s design to take account of friction, it is possible to cut bearing losses. By multiplying this saving for each bearing in a machine, plant or industry, significant energy savings are possible. n Reducing friction in bearings is an attractive way of raising energy efficiencies in industry. Chris Johnson, managing director of the miniature bearings supplier SMB Bearings, explores how bearings can help to boost efficiency in industrial applications. The potential for bearings to cut energy consumption is often ignored, but the savings can be substantial