Bearing selection [18/08/2009] By working together early in the design process, gearbox manufacturers and bearing suppliers can reduce development times and improve the overall safety, quality and reliability of the end product, explains Dr Steve Lacey, engineering manager at Schaeffler (UK) Ltd Image: By bringing in a bearing manufacturer early in the design process, problems associated with adequate space or accessibility can be tackled. If the design is already advanced, compromises might need to be made Developing precision rolling bearings for industrial gearboxes has never been more challenging. Like most engineered components and systems today, gearboxes are becoming smaller – especially in automotive applications – but also more powerful. The supporting bearings must therefore offer optimum performance. The bearings must be compact, reliable, durable and offer high load ratings. In addition, gearbox designers will also look for other factors, including low noise levels, reduced friction, as well as how safe and straightforward the mounting of the bearings will be. In the UK, Schaeffler supplies bearings to a number of gearbox manufacturers. Typical applications for these gearboxes include wind turbines, tidal energy systems, planetary gearboxes for power generation, construction vehicles, racing car transmissions, as well as gearboxes for gas, water and vacuum pump applications. Typically, the gearbox manufacturer provides a design specification and/or drawings to the bearing supplier. Most (around 85%) of Schaeffler gearbox bearings are standard catalogue products. The remainder are custom-designed bearings to suit specific applications. Here, the customer often requires careful guidance and technical support from the bearing supplier. Image: Click here At this point, important decisions are made and design factors that determine the suitability of a bearing for a specific application are discussed. These include the space available for the bearing; the loading the bearing has to withstand; the speed at which the bearing needs to perform; the environment in which the bearing will operate; lubrication requirements; and the required life expectancy of the bearing. For some applications, it may simply be a question of mounting the appropriate bearing in the correct manner in order to ensure optimum performance. However, if the bearings are only considered much later in the design process, the customer may have already signed off important parts of the machine design, without giving much thought to the bearing requirements. As a result, there may not be sufficient space to mount the ideal bearing or lubrication method. This means the bearing engineer has to select a compromised bearing solution that may not meet all of the customers' requirements. The ideal scenario is therefore to invite the bearing supplier into your design process early, in order to avoid potential costly design errors, over- or under-engineering the product, and to eliminate safety or reliability issues that will need rectifying later on. Product development times will be reduced considerably, if bearing design issues are resolved early. Furthermore, a standard bearing (which is always more preferable to the customer) is more likely to be recommended for the gearbox, if the customer starts the design with a clean sheet of paper. If the design of the gearbox is already set in stone when the bearing supplier is invited to specify bearings, the chance of a special, custom-designed bearing solution being offered is higher. The collaborative design process starts with a detailed brief from the customer, which is passed to Schaeffler's in-house engineering team. These engineers use the latest design software – including kinematics, dynamic, finite element analysis (FEA) software and Schaeffler's own, unique BEARINX© calculation software – to simulate the function of the proposed bearing or system. This results in a bearing design that achieves the required performance and operating life. BEARINX®, is a software tool that enables engineers to simulate bearing designs for complex gearbox systems quickly and accurately. The software supports the rapid modelling of complete geared systems, taking into account important design factors, such as material elasticity and deformation. Calculations and design simulation help to improve the understanding of the overall system, so that critical points can be identified and eliminated at an early stage in the design process. Image: Wind turbines are an increasing challenge for bearing makers. Larger power outputs demand bigger bearings, while for offshore turbines conditions of operation can be harsh The software models the complete power transmission system in a gearbox, taking into account the type of gears used, loads, speeds and existing collective loads. Gear shafts that deform elastically under the given loads based on materials used, are also taken into account. For example, the elastic deformation of the gear unit housing can have a significant influence on bearing life. Combining BEARINX® with FEA calculations for gearbox housings makes it possible to include the rigidity of the housing in any design analysis. As well as examining static conditions of the gear unit, dynamic effects on the bearings and shaft can also be simulated. Reports from BEARINX® can be emailed to the customer. 3D models of the geared drive can be included here. Different operating scenarios, such as changing the load or speed conditions can be input to BEARINX® and the results analysed graphically if required. In a recent customer application, Schaeffler UK used BEARINX® to analyse 53 separate bearings in an agricultural gearbox. A total of 73 different gear selections and configurations were made on the four-wheel drive system. This simulation model took four weeks to set up and then seven hours to run the software calculations. Selecting the "best bearing for the job" and "fit-for-purpose" are the objectives at Schaeffler: understanding exactly what the customer (and end user) requires is, therefore, critical. First published in Engineering Apprentice, Summer 2009 Related Companies: Schaeffler (UK) Ltd