Tech Update: Power Transmission Equipment - Increasing uptime in demanding environments
November 7, 2012
The key to long life and less energy usage is proper maintenance.
You probably don’t make too many demands on your car’s transmission system, other than it moves you from point A to B. And unless you do something really dumb, it runs for a long time without major breakdowns. Of course, engineers who designed the system carefully matched your car’s transmission to the engine and the rest of the drivetrain. Chances are, it needs little maintenance and works for the life of your car.
It’s hard to say the same thing about food plant power transmission equipment. But then, it has a tough life. It faces washdowns with pressures up to 1,500-1,700psi, and is scalded with hot, high-pH detergents and/or acid rinses. Add more stress to the equipment if it typically lives in your freezer—cold and hot and cold. Plus, it’s often run faster than it was designed to in order to meet production cycles, and you may load it down beyond its specified operating parameters. Your maintenance people may hit it with hammers to break the seals when they need to repair it, “have parts left over” when they rebuild it, fail to replace all the seals or force-fit the wrong ones, refill it with the wrong lubricant and fail to line up pulleys or over-tighten belts when they put it back in operation. Processors demand a lot from power transmission equipment. They want it to be easy to clean and not harbor bacteria. They want it to operate in cold, slimy environments and dry, gritty spaces—and be energy efficient, too.
Food processors face four key issues when selecting power transmission equipment, says Greg Cober, Altra Industrial Motion training manager. First and foremost is finding equipment that helps ensure a sanitary operating environment. Second, processors seek value and long life of this hardware. Third, it must also be easy to maintain and replace. “Many processors are struggling to find skilled maintenance staff, and the staff they have is hard-pressed for time to learn new [equipment components],” says Cober. Energy efficiency is the fourth priority, he adds.
Surviving cleaning operations through good design
Often, it’s not the maintenance crew or the lack of maintenance that’s the only problem. “The biggest problem I see is the wear and tear on the equipment during the cleaning process,” says Chris Wood, SEW-Eurodrive industry account manager for food and beverage. “A poorly trained cleaning crew can do more damage to equipment than the lack of attention from the maintenance department. The hardest things to do in food processing are keeping the environment out of electrical panels and motors, and with gear reducers, keeping the oil inside and the water outside.”
“Power transmission components are often exposed to harsh operating environments—high/low temperatures and moist, acidic, abrasive or other contamination from processing materials and cleaning regimes,” says Terry Fisher, SKF global strategic account manager. Each situation might require a specific way to address it—from the use of corrosion-resistant materials or self-lubricating properties for chains, to the use of synchronous timing belts and pulleys, which offer better efficiency and cleaner operation.
“When failures occur because of contamination or water ingress, we perform root-cause failure analysis and recommend [component] feature sets that specifically address the failure points,” says Jim Ludwig, Baldor Electric Company industry account manager. Sealing innovations have helped motors resist water. “Motor winding encapsulation is an example of entirely eliminating electrical/water issues that plagued the industry for years,” says Ludwig. In addition, the standard seal material in Dodge Tigear worm reducers is HNBR (hydrogenated nitrile butadiene rubber also known as highly saturated nitrile [HSN]), which Ludwig says offers superior heat and chemical resistance compared to standard offerings.
Food industry machine builders face hygienic regulations from government organizations, but one thing they have learned is that good hygienic design can ultimately increase the life of the machine and its power transmission components by using less washing in the first place. “Good hygienic design enables cleaning to be done in a shorter time, at lower temperatures and with less aggressive detergents, thus saving time and expense,” says Thomas Dwyer, Bosch Rexroth senior automation engineer, mechatronics.
Machine builders also need to be attentive to the specific application environment where the machine is to be used. For example, the composition of guide rails and housings must be adjusted for cleaning chemicals, and these changes need to be reflected in the machine’s PM (preventive maintenance) programs.
Bearings, a key component in machine design, have seen improvements. “Contamination ingress into the bearing cavity washes out grease or introduces contamination that shortens the grease life, which will reduce the overall life of the bearing,” says Ian A. Rubin, director of marketing, mounted bearings at Emerson Power Transmission Solutions. “We have developed a high-performance seal as standard on our Sealmaster PN Gold bearing, which uses a triple-lip design and rotating 300 SS flinger. In our testing, it has shown 10-times greater performance than our other contact seals.”
Eliminating water collection points in bearings reduces the potential for bacteria growth. “One of our bearing developments is a drain feature for use with keyway shafting,” says Aaron Loomer, Rexnord commercial marketing manager, ball bearings. Regardless of seal integrity, keyway shafting typically provides a channel for contaminants to enter the bearing housing. To help combat this problem, Rexnord designed a special housing, seal and cap configuration that allows water and other contaminants to drain from the mounted bearing, according to Loomer.
Stop putting out maintenance fires
Though many power transmission improvements are all about increasing uptime while reducing maintenance and repairs, processors are often faced with an unexpected breakdown. “We see many different levels of maintenance maturity—starting with the “firefighting strategy” and the resulting ‘overtime heroes,’” says SKF’s Fisher. “While some OEMs do provide PM programs, it is the processors’ maintenance culture that sets the direction.
“SKF recognizes the importance of starting from a maintenance level our customers feel comfortable with and, at the same time, looking to assess maintenance practices with them and develop a road map to improve maturity,” continues Fisher. For example, SKF offers a range of services, related products and training that are designed to improve the effectiveness of maintenance while developing maturity toward predictive and preventive strategies or optimizing use of resources through improving the reliability of operators.
“PM programs vary from processor to processor,” says SEW-Eurodrive’s Wood. “A lot depends on the size of the facility, the number of maintenance personnel and budgets. They understand that when a component failure occurs, damage to other parts of the process can have devastating effects on production.”
Many processors have PM programs or asset management programs in place, says Emerson’s Rubin. “Some do a great job monitoring performance and working with good cleaning and maintenance schedules, but sometimes we see a difference between what is documented and what is practiced.” Common problems, explains Rubin, are over-lubrication, improper re-lubrication, inadequate rinsing and overzealous washdown.
Although most processors focus on reliability and operational excellence and have a PM strategy in place, greasing bearings is where they can use some help from suppliers. According to Kay Cabaniss, Baldor Electric Company industry business manager for food, beverage and pharmaceutical, Baldor’s Dodge bearings are designed to allow proper grease purging while not blowing out the bearing seal.
Speaking of lubrication, Cober points to a gearbox with a design that reduces overall maintenance. When the Boston Gear SS700 gearbox was designed, it included a 25 percent increase in internal cavity over its non-stainless predecessor. The added lubricant capacity means the unit can be sealed for life, effectively designing out maintenance. “Where that goal is not possible, we have tried to locate lube access points to their most convenient position so properly lubing the unit is easier than with prior product generations,” adds Cober.
Improper setup kills equipment
The need to increase production sometimes forces food processors to run their equipment faster, at higher capacities or longer than the OEM specification, says Fisher. But these actions can lead to rapid wear, elongation, noise and, in the end, the premature failure of power transmission drives. However, pushing equipment is not the only problem.
Stephen Dunlap, Peerless-Winsmith marketing manager, states he more often sees power transmission systems are improperly set up, which leads to failures and downtime. “For example, the belt driving a gear assembly may be over-tightened, which can put excessive loads on the gearbox shafts. This causes overheating and, in some cases, shaft breakage.”
Dunlap points to two other issues that lead to inefficient production that are also related to improper maintenance. One is technicians failing to reinstall the critical sealing gaskets or O-rings of a motor used in a heavy washdown environment, allowing water to seep in between the motor and reducer interface. A second—no less important issue—is technicians using the incorrect lubricant in the reducer when they perform scheduled maintenance, leading to overheating and premature failure.
The weakest “link”
Ask any power transmission professional what the weakest links are in systems, and the vast majority will cite chain-link drive belts and sprockets. “Roller chains with a sliding, friction-based type of joint are commonly used for power transmission and material transfer,” says Dwyer. A suitable alternative method to reduce roller chain wear issues is the application of “silent chains” that use a two-pin rolling pivot joint to reduce wear. Cober calls roller chains and sprockets a weak link for another reason. Because they need to be lubricated—even when placed under a guard—they have the potential to contaminate food with lubrication. In addition, bacteria can hide under the guards and be difficult to reach with cleaning agents. One solution is to use a non-lubricate alternative such as synchronous belts.
The ultimate solution, according to Baldor’s Ludwig, is to design drive trains that don’t require belts and chains at all. This can be accomplished by mounting a gear reducer directly on a drive shaft with a C-face motor attached.
“In the typical food and beverage application, the electric motor often has the shortest life due to washdown or buildup of dust,” says Donna Akers, commercial marketing manager, gear, at Rexnord. “It is important to recognize this so it can be replaced quickly and easily and at low cost.”
However, the motor disassembly can be awkward, and replacement motors expensive or not readily available. Converting to industry standards such as 56C motor/gearbox interfaces allows for quicker disassembly and access to a readily available supply of off-the-shelf motors.
While gearmotors may not have many challenges at relatively normal temperatures, operating them in freezers can be another story. “One of the challenging environments for gearboxes is in freezer applications, where rapid temperature shifts resulting from cleaning procedures can cause breathing issues,” says SKF’s Fisher. The solutions are often complex, involving root-cause analysis through to implementing customized sealing solutions.
Looking for trouble
Today’s automobiles have a variety of sensors to keep an eye on engine operation and alert operators to potential problems. Likewise, the technology is available to monitor motors, bearings, gearboxes and other components, should processors want to use it. Coupled with condition monitoring software, these systems provide early warnings against imminent component failures that could bring down a line.
“SKF has developed a number of tools to identify early generation of problems on mechanical and power transmission systems,” says Fisher. Vibration analysis techniques are one of the most used and the most efficient. Thermography can be used for belts and couplings for misalignment identification. The company’s aptitude software provides the possibility to interface with CMMS systems, and inspection tools are an important element to capture the condition of power transmission components. According to Rubin, Emerson Process Management’s business unit offers a wide variety of power transmission monitoring systems. Some of these are used by bearing products users to help provide real-time analysis of information to better understand performance and predict problems early.
“Condition monitoring is an essential component for large gear systems,” says Rexnord’s Akers. “Rexnord’s V-Class parallel and right angle gear units are fitted for optional monitoring equipment.” The supplier offers three optional packages for central diagnostics, scheduled maintenance and troubleshooting to reduce unplanned downtime. In addition, the company offers an asset management program that can monitor in real time the operating conditions of all critical drives and identify and solve potential problems before they occur.
“SEW has monitoring units for oil life, vibration and brake function,” says Wood. “All of these can be tied into a CMMS. Our biggest user of this product so far has been automotive. It takes a fairly elaborate factory network system to tie all of these components together.”
While not technically condition monitoring programs, some software automatically keeps users up-to-date on maintenance issues. For machine builders, Bosch Rexroth provides pre-developed PM features within its IndraWorks automation software, according to Dwyer.
Since bearings are used in so many power transmission components, monitoring their performance, planning scheduled maintenance and using the proper lubricants can go a long way in extending the life of the component that uses them. Suppliers have come up with innovative methods to protect gearboxes and other power transmission components from harsh chemicals while minimizing bacteria collection points. Extending the life of power transmission equipment depends on careful washdowns and religiously following a good maintenance program where technicians are trained to repair equipment with the correct replacement parts and procedures. For lines that are “too big to fail,” condition monitoring systems and software may quickly pay for themselves.
Four lessons learned from the field
Speed reducers can take punishment from both process materials and washdowns. A large olive producer had tried various epoxy-coated speed reducers and found that they could not hold up to the acidic brine solutions and oils used on the processing lines at the plant. In addition, a caustic washdown environment also posed problems with the gearboxes. The plant installed Boston Gear stainless steel (SS) 700 Series speed reducers, which not only survived the acidic brine, but also survived the caustic washdown. The reducers are constructed from 316 SS and feature double-lipped shaft seals and a large, internal H1 food-grade oil reservoir.
In a North American brewery line application, Ian A. Rubin of Emerson Power Transmission found that excessive lubrication led to increased bearing operating temperatures, resulting in increased internal pressure that became strong enough to force the seal to pop out, and the chemicals used in the brewing process led to excessive corrosion in the bearing steel. Rubin recommended the brewery use Sealmaster reduced maintenance PN Gold mounted bearings because they don’t require additional lubrication, and the stainless steel housing with phosphorus nickel coated raceways help significantly reduce corrosion. While the old bearings lasted less than six months, the new bearings run for 18 months without failure, and the brewer is changing out 150 additional old bearings with the new ones.
Exposed power transmission system components—such as belts, chains, pulleys, friction brakes and sprockets—challenge machine builders to find ways of limiting surfaces for bacteria to grow. According to Stan Porter, vice president with Force Control Industries, an electric, open dry-fiction clutch brake, which had an attached high-maintenance cost and was part of a dairy processor’s cheese cutter, was replaced with a Posidyne Oil Shear Clutch brake, which allowed doubling the machine’s speed while eliminating adjustment, parts replacement and downtime. The brake is a totally enclosed, sealed unit.
A sugar producer was looking for a solution to low machine reliability that caused line stoppages during the main production season. During operation, the centrifuges suffered from acceleration/deceleration cycles, resulting in increased demands on the power transmission system, the motor and the centrifuge grouting system. SKF engineers performed a transmission assessment that identified a lack of rigidity in the motor support system. High vibration levels on the motor and misalignment of the pulleys caused excessive energy consumption. The engineering team recommended a new package of SKF belts using appropriate mounting practices to obtain correct alignment and belt tension. After the project was completed, there was an increase in machine reliability with no unexpected failures during the season. The belt, bearing and motor life increased, and the processor realized a 6.5 percent reduction in energy consumption, saving 24 MWh per year in the centrifuge motor.
For more information:
Ian A. Rubin, Emerson Power Solutions, 800-626-2120, email@example.com
Greg Cober, Altra Industrial Motion, 815-389-6423, firstname.lastname@example.org
Thomas Dwyer, Bosch Rexroth Corp., 800-739-7684, email@example.com
Kay Cabaniss, Baldor Electric Company, 864-297-4800, firstname.lastname@example.org
Jim Ludwig, Baldor Electric Company, 864-297-4800, email@example.com
Aaron Loomer, Rexnord, 317-273-5500, firstname.lastname@example.org
Donna Akers, Rexnord, 866-739-6673, email@example.com
Terry Fisher, SKF, 800-523-1745, firstname.lastname@example.org
Stan Porter, Force Control Industries, 513-868-0900, email@example.com
Stephen Dunlap, Peerless-Winsmith, 716-592-9310, firstname.lastname@example.org
Chris Wood, SEW-Eurodrive, 864-439-7537, email@example.com