Edited by Mike Santora
In the traditional product design model, bearing selection isn’t usually a large factor. Not much differentiates one bearing from another, the thinking goes, so why spend time considering the type of bearing to be used when they’re all basically the same?
Jonathan Checketts and Kim Evans are on a mission to change that way of thinking. In fact, if they had their way, bearings would not only enter the product development conversation, they would sit at the head of the table.
According to Checketts, a global product manager at GGB Bearing Technology, considering bearings early in the design process yields improvements in the final product, including lower weight, a smaller profile, fewer parts, increased strength and improved energy efficiency. And when GGB is brought in during the early stages of the design process, Checketts says, they can help achieve those results while helping ensure budgets and deadlines are met.
Plain bearings are used to reduce friction between rotating shafts and stationary support members, but they have no rolling elements. They are used where failure may have severe consequences—such as in aircraft landing gear. Plain bearings also excel because of their low cost and simplicity.
The reason bearings can make such a difference is that, while they all perform the same basic function, recent developments in bearing technology have created such diversity in performance characteristics that saying they’re all the same would be like saying there’s no difference between a Model T and a Ferrari because they’re both cars.
And, speaking of cars, the potential of this approach to bearing selection can be seen in automakers’ responses to the European Union’s End of Life Vehicles Directive, passed in the early 2000s.
The directive aims to reduce the impact of harmful pollutants, such as lead, left behind during the process of recycling end-of-life vehicles. Auto manufacturers had to adapt their products to the new regulations. When asked for help, Checketts and saw the perfect opportunity to demonstrate the efficiencies that can be gained when they’re consulted from the start.
“It’s important for us to be involved early. It allows us to offer so much more than if we are brought in later—new designs, innovative products, a better level of understanding,” says Checketts. “If you’re brought in late when everything’s been finalized, launched and validated, it’s very hard to backtrack and make improvements.”
Lead was being used by many in the automotive industry in the form of GGB’s DU metal-polymer, anti-friction plain bearings. Checketts and his team worked with companies to offer alternatives. After several trials, the DP11 metal-polymer, anti-friction plain bearing came through as the best alternative to the DU for isolator pulley dampers. But why?
Mounted on the engine crankshaft, isolator pulley dampers transmit torque to the rubber belt that drives the various engine accessories. Out-of-balance forces generated by the pistons transmit vibrations to the distribution belt that can be felt by passengers and that reduce the belt’s service life. In order to support the radial load from the belt, increase the belt life and reduce noise and vibration, isolator pulley dampers are fitted with DP11 metal polymer, self-lubricating plain bushings. Their composite bearing structure consists of a steel backing to which is bonded a porous, bronze sinter interlayer impregnated and overlaid with a PTFE-enriched, wear-resistant bearing layer.
In isolator pulley damper applications, the antifriction properties of DP11 self-lubricating bushings provide low-friction performance that doesn’t impair the damping quality of the pulley as it reduces vibrations and extends service life. Using the DP11 also offers a compact and weight-saving design, simplified assembly and—of course—a lead-free bearing.
In addition to satisfying the lead-free requirement, the DP11 alternative was an opportunity to propose a patented bearing design that moved from using two separate components (the cylindrical bearing and a thrust washer) to one single component called a reversed flange cylindrical bearing. Similar to the original function of supporting radial loads from the belt with a two-piece cylindrical bearing, the reversed flange cylindrical bearing enables the induced axial loads to be supported. The reduction to one component with the same function resulted in a simplified, more compact design, an easier assembly process and reduced logistical costs.
During product development, choosing and working closely with pilot customers ensures a product meets its technical and economical specifications.
Checketts was also involved in to creating more compact designs for automotive air conditioning compressors. To improve performance, manufacturers were looking to reduce weight, installation difficulty and environmental impact.
The structure of DP31 metal-polymer, self-lubricating bearings consists of a strong steel backing and a sintered bronze interlayer impregnated and overlaid with an anti-friction layer consisting of PTFE (a fluoropolymer) and other performance-enhancing fillers. Their design, structure, and composition are ideally suited to HVAC compressors. As a result of the collaboration between designers and manufacturers, DP31 plain bearings have successfully replaced traditional needle roller bearings with a lighter, more compact solution, reducing fuel consumption and environmental impact.
“My greatest satisfaction as an application engineer is physically standing by the forming machines and thinking back to the initial contacts with the customer, to the design and successful prototype testing, and then seeing everything being shipped to the customer,” Checketts said. “When you know a product you’ve helped create is going out and directly helping customers, that’s a great feeling.”
It’s a feeling GGB application engineer Kim Evans also knows well. Being brought in early allows aerospace design engineers like Evans to make what might be considered minor tweaks to a design that can make a big impact. For example, replacing large, heavy roller bearings with smaller, lighter plain bearings early in product development might allow a reduced housing size and the removal of no-longer-necessary features prior to development and testing. But when bearing engineers are brought in late in product development, a bearing may have to fit a predetermined size that is thicker and heavier than necessary. When that happens, manufacturing costs are not optimized, which ultimately reduces profits for the manufacturer or increases the cost of the product to the customer.
An example of being brought in too late in the process happened when the landing gear upgrades GGB worked on included strut bearings and other greased metallic bearings. The manufacturer’s wish list included reducing weight, reducing or eliminating maintenance, and increasing shelf life. The manufacturer originally wanted to replace a greased competitive bearing that wasn’t working well with a DU-B bearing. Although the DU-B bearing didn’t need to be greased, machined features had to be added so the bearing would drop into the greased metallic bearing’s spot without modifications to the shaft or housing. This change required specialty machining, additional inspections and the production of additional parts for machine shop setups—which translated to an unneeded increase in cost per bearing.
“Using a bearing that requires machined features can cost 50% more than a bearing without those features that works just as well, which adds up to a few thousand dollars each month,” Evans said. “If a project runs several years, which they typically do, that cost certainly adds up.” Earlier integration into the design process could have helped avoidcosts.
Later, GGB was selected for a project to help upgrade landing gear for military and commercial planes. In this case, GGB was involved much earlier, allowing for a more effective solution based on stronger relationships, clear expectations and the ability to make a larger impact on bearing selection.
Because they were brought in early enough in the design stage, GGB was able to recommend fiber reinforced composite (FRC) bearings for testing. The benefits of choosing FRC bearings include a wide operating temperature range, chemical compatibility with key aviation fluids, high load capability, shock loading performance, and the ability for the self-lubricating liner to be on either the inner or outer diameter, or both, if necessary. Additionally, the bearings can be wound with a thicker wall than standard, making a separate housing unnecessary.
“Being brought in as early as possible and being told what is needed right from the start is ideal,” Evans said. “It allows us to choose the best materials for that application and work with the customer to create the best manufacturing process for everyone. Thankfully this is what happens in a majority of cases, but sometimes we’re brought in late, and it means attempting to drop things into a space that is not ideal.”
Over the past several years, the aerospace industry has been focused on reducing airplane weight to reduce fuel costs. As with bearings, landing gear isn’t usually the main focus of weight-saving efforts in airplane design. However, there’s significant money saved for every pound of weight reduced using GGB’s FRC products—depending on the aircraft, some experts have estimated that savings as approximately $500 per pound.
While GGB’s DU-B metal-polymer, bronze-backed, PTFE plain bearing is the standard in the industry, Evans and her team are now looking at FRC bearings for use in newer designs and developments. They work better with product specs that call for lighter materials and the potential to last longer without greasing.
“Being brought in early allows us to make everything more cost-effective for all involved,” Evans said. “When we are brought in late, without the benefit of that early design review, the manufacturing cost goes up and the customer pays more. It’s simply more efficient to get involved early, while there is still the opportunity to make design improvements.”