Wash and No-Wear

Toroidal Bearing Enables Enhanced 
Performance in Commercial Washers

—edited by Richard Mandel

Hospitals, hotels, theme parks, cruise ships, prisons, blue jean manufacturers and many other institutions and enterprises share a common challenge: literally, tons of laundry. Sharing that challenge are industrial and commercial washer designers charged with assuring long-term reliability. Commercial laundries and in-house laundry facilities for businesses and institutions handle a staggering amount of laundry. An average home washing machine handles about 18 pounds of laundry and may run a few times a week. Commercial washers, which are often run around the clock, can handle from 40-800 pounds of dry laundry, depending on the machine model. Many commercial washing operations need not one, but many, machines to handle a volume that can easily reach more than 100 tons of laundry a week.

Most people have witnessed the vibration and movement that occurs when a home washing machine load becomes unbalanced. The problem is enormously magnified when hundreds of pounds of wet laundry clump to one side in a commercial machine. This consistent out-of-balance situation, coupled with extreme weight, high loading and high moisture levels, has traditionally challenged design engineers working to enhance commercial washer reliability and performance.

A cycle of wash and wear

Washing machines present a challenge for bearings that are at the heart of machine operation. That’s because the nature of the washing operation creates machine loads that impact the bearings at both the inner and outer ring.

Figures 1 and 2 illustrate this loading situation. During the wash cycle, as water is pumped into the tub that is rotating slowly back and forth, the predominant load is the downward pull of gravity. For this, a tight interference fit is required between the inner ring of the bearing and the shaft. During the extract cycle, as the load in spun at high speeds, centrifugal force causes the clothes to shift to one side, and the liklihood of an out-of-balance load develops. During this period the outer ring of the bearing needs to be held tight in the housing. 

Unfortunately, because most bearings are unable to handle both axial displacement and structural misalignment, it has not been feasible for bearings to be installed with an interference fit on both the inner and outer ring. Washer designers have been faced with the dilemma of where to compromise in the bearing arrangement, and are typically forced to choose between several evils. If one bearing ring is made loose on its shaft to accommodate thermal expansion, fretting corrosion and creep are likely to damage the shaft, making dismounting difficult and restricting axial freedom. If all the bearing rings are tight, fretting corrosion and creep can be eliminated but the designer must choose between two options: 1) using two spherical roller bearings that accommodate misalignment but do not have adequate axial displacement capability and thus potentially accept mutually opposed thrust loads; or 2) using a spherical roller bearing in combination with a cylindrical roller bearing that allows axial displacement but does not have adequate misalignment capability and thus accept uneven raceway load distribution.

Whatever path the designer chooses, the result has been bearing bore/shaft wear and reduced bearing life from misalignment—which leads to compromises in reliability, productivity and cost-effective operation. 

The CARB Solution

Major commercial washer manufacturers are finding a solution in Compact Aligning Roller Bearings (CARB) from SKF, a toroidal design that combines some of the best aspects of spherical, cylindrical and needle roller bearings. CARB has a single row of broad rollers with a slightly curved profile, which enables the bearing to find the best position to distribute the load evenly. According to SKF senior application engineer Gill Detweiler, “In a toroidal bearing, when a force is applied to one edge or the other, the roller slides to a new position in order to escape edge loading, finding a place where the stress is evenly distributed over the entire roller. This enables the bearing to accommodate both angular misalignment and axial displacement internally and without frictional resistance or reduction in service life.” 

CARB is intended for use at the non-locating end of a two-bearing arrangement. In a commercial washer application, the ideal arrangement is a CARB bearing used in combination with a spherical roller bearing. This enables all four bearing rings to be mounted with an interference fit that eliminates fretting corrosion and creep. With this configuration, the bearings can accommodate load-induced angular misalignment resulting from unbalanced loads, so shaft bending and support structure movement will not result in uneven raceway load distribution. And, because the CARB bearing can accommodate axial displacement internally, mounting inaccuracies and thermal expansions will not yield mutually opposed thrust loading.

CARB can enable a bearing downsize, a benefit that can result in savings related to material costs, and better compatibility with the size and configuration of customer facilities. This is because the bearing is designed to carry the load across the entire surface of one roller, as opposed to traditional bearings that use two rollers. The one-roller design results in a smaller bearing that can carry the same load as larger bearings. The smaller bearing size enables a corresponding downsizing of other machine components.

To further assure optimum operation of the bearings, SKF also offers a lubricant called System 24, in a system that attaches to the CARB housing and releases lubricant automatically as needed. SKF is working with washer manufacturers to develop a warning light to tell the operator when it’s time to replace the lubricant cartridge. 

Successful Test Applications

IPSO USA, a manufacturer of on-premise laundry equipment, was the first to test CARB. The company now uses CARB in all new machines and has more than 1000 in service. “We initially tried cylindrical bearings,” says IPSO engineering manager Tony Fitzsimmons, “but in testing conditions, they lasted less than 200 hours. They could not accommodate angular misalignment caused by the shaft deflection. The inner races of the bearing were actually broken.” IPSO then tried a bearing arrangement using a spherical bearing and a CARB. “In our first test of the CARB bearing, we ran 900 hours with no failure,” he said. CARB reliability is enabling higher productivity and lower costs in traditional machines, and opening doors to new machine capabilities. 

For commercial laundries, the greatest operational cost is the energy expense related to drying operations. The more moisture present in the clothes when they hit the dryer, the more energy it takes to evaporate the water. The best way to reduce moisture is to more effectively extract it from the clothes during the wash operation. This is accomplished by spinning the clothes faster during the extract cycle. IPSO has recently created the means to do this through a patented speed enhancer called SmartSpin, an electronic feature that measures the unbalance and then changes the speed of the extract cycle accordingly.

Enhanced Productivity

The enhanced extraction capability is also contributing to increased productivity in terms of operational efficiency. In commercial laundries, one important measure of productivity is timing. The ideal situation is for the washers and dryers to be working on the same cycle. But washers are often ahead of dryers because it takes longer for the clothes to be dried. According to IPSO sales and marketing coordinator Bobby Dewrell, “Our new machines extract at such a high force that there is far less moisture in the load when it gets to the dryer. This requires less drying time, so the dryers can get on the same rhythm as the washers. This cuts down on time, and for some customers, it has enabled them to run fewer shifts.”

Bleaches work best at a temperature of 180°F. While commercial washers are capable of running at these temperatures, the high heat contributes to shorter bearing life. The CARB bearing is less sensitive to high temperature, so laundries can run bleaches at high heat without compromising long-term bearing performance.

The bearings also provide the machines an extended lifespan and reduced maintenance. Replacing bearings is traditionally a huge job, requiring a complete teardown of the machine, and several days’ work. “When you consider these manufacturers have been in business for quite a few years, it eventually means that they could be servicing machines all the time,” explains Gill Detweiler. “CARB significantly extends bearing life, and by extension, the life of the machine. Customers therefore don’t experience as much downtime, and manufacturers can get out of the service business.”

Outstanding Customer Acceptance 

CARB’s unique capabilities are helping commercial washing machine manufacturers enhance both performance and customer satisfaction. “Our customers are very happy with our new CARB-enhanced machines,” says IPSO’s Bobby Dewrell. “We have yet to hear from a customer who has installed one and wanted something else. They can’t believe the output and throughput they’re getting.”

For more information:

Circle 400 - SKF, or connect directly to their website via the Online Reader Service Program at www.RSLeads.com/110df-400

Circle 401 - IPSO, or connect directly at www.RSLeads.com/110df-401