When HydroWorx International, Inc. began to design its unique water therapy and conditioning equipment, one of the biggest challenges was to find a bearing material for the rollers capable of operating submerged in water. After trying a number of alternatives, the company’s engineers selected GRAPHALLOY bearing materials from Graphite Metallizing Corp., Yonkers, New York. The new bearings have been used in every treadmill produced by the company over the last eight years and only a single bearing has required replacement over that period. “The ability of GRAPHALLOY bearings to provide completely trouble-free underwater operation without any lubrication has been a key factor in the success of our treadmills,” said Jason Kratzer, Materials Manager for HydroWorx.
The main reason for putting a treadmill underwater is that the ability to run or walk naturally in a reduced-weight environment saves significant wear and tear on joints. This helps explain why growing numbers of professional sports teams, such as the Indiana Pacers, San Antonio Spurs, Philadelphia Eagles, Detroit Lions, Charlotte Bobcats, universities such as Notre Dame, Stanford, University of Kansas, University of Idaho, and even the U.S. Navy Seals use HydroWorx underwater treadmills. The treadmills speed recovery from injuries by making it possible to duplicate dry-land running or walking form at a fraction of their real weight. By adjusting the water level in the pool, trainers can increase or decrease the weight the patient puts on the injury. The result is typically a speedier and more complete recovery from an injury or surgery. Athletes and fitness enthusiasts also use underwater treadmills in order to experience cardiovascular workouts with much less stress on the joints than would be received from the same amount of land-based training.
For example, when the Philadelphia Eagles’ best defensive player, Cornerback Troy Vincent hyper-extended his right knee during practice, Head Athletic Trainer Rick Burkholder said, “It seemed like the world stopped.” Just four days before the season opening game against the St. Louis Rams Vincent was listed as questionable on the official injury report with only a 50% chance of playing in the game. When it was determined that Vincent suffered from a deep bone bruise and had only 10% range of motion in the knee, Burkholder immediately placed Vincent in the HydroWorx® 2000TM pool for pain reduction and therapy. Burkholder told team owner Jeffrey Lurie, “This pool paid for itself today, if he plays in the game Sunday.” Lurie agreed. Vincent ended up playing in the game, making three tackles and an interception to assist the Eagles in victory over the Rams. Vincent earns $216,000 per game in a 16-game season, which is more than the cost of a HydroWorx 2000 pool!
Bearing performance was a critical design challenge
When employees of Hetrick Chiropractic Associates, who would later form HydroWorx, originally began conceiving their underwater treadmill designs in the early 1990s, one of the first areas they focused on was underwater bearing technology. “The founders of the company knew from the beginning that finding a bearing that would run underwater for a long period of time was one of the keys to developing a successful product,” Kratzer said. The material had to resist attack not only from water but also from bromine, which the pool contains. Lubricants could not be used since they would contaminate the water, which had to remain hygienic for human use. In addition to the lubrication concerns, any housing holding the bearings had to be rustproof to keep from contaminating the water. The engineers searched through trade journals and requested information on a number of promising materials. In many cases, the bearing manufacturers admitted up front that their product could not handle the application. In others, the samples provided by the bearing manufacturers failed quickly when the engineers tested them.
“In the early stages of this project, it looked like the bearing material might be a major obstacle to the development of the submerged treadmill,” Kratzer said. “Up to that point, everything that we had tried didn’t work. Then Graphite Metallizing sent a sales engineer to meet with us. I thought it was interesting that he took the time to visit with us and understand our application before he even attempted to sell his product. After a series of conversations, he provided samples of GRAPHALLOY bushings and pillow blocks suitable for use in the initial pool assemblies. The initial tests showed that the products performed very well. They passed our accelerated wear tests and still looked just like new at the end of the tests. It was obvious at this point that we had a winner. The sizing, quantities and physical mounting arrangements have changed slightly over the years as design improvements were made on the pool and additional sizes and configurations were developed. But we have never had any reason to reconsider our original decision to select this excellent material.”
Graphite alloy material meets requirements
GRAPHALLOY provides unique advantages because it combines the properties of graphite and metal. The graphite structure can be compared to a deck of cards with individual layers that are able to easily slide off the deck. This phenomenon gives the material a self-lubricating ability that is matched by no other material. External lubricants are simply not necessary. GRAPHALLOY is graphite impregnated with metal to enhance the chemical, mechanical and tribological properties of the material. The material, most commonly used in bushings, is available in over 100 grades and can be designed to fit a variety of machinery. While a high percentage of GRAPHALLOY products are produced to meet custom requirements, standard designs are available including cylindrical bushings with or without grooves, single, double-flanged, split and metal backed bushings as well as pillow block and flange units. Grades and designs are engineered to best serve the application.
GRAPHALLOY is a bearing material that works when most other materials will not. In addition to being self-lubricating and having temperature capabilities of up to 1000oF in an oxidizing environment, GRAPHALLOY functions well in cryogenic conditions, can survive dry run conditions and maintains it’s integrity even when submerged in hostile liquids such as acids, alkalies, hydrocarbons, black liquor, and liquid gases. The material provides a constant, low coefficient of friction and its uniform consistency protects against catastrophic failure. Lubrication is maintained even in linear motion applications; lubricant is not drawn out and dust is not pulled in. GRAPHALLOY wear components also improve reliability under conditions such as low speed operation, frequent starts and stops and switchovers from standby to continuous running. FDA accepted grades are available for food contact applications.
Bearings have lasted eight years and still going strong
The current design uses 1.5 inch stainless steel pillow blocks with GRAPHALLOY bushings. With over 100 bearings in the field in machines that have been produced over the past eight y ears, only one single bearing has had to be replaced. The bearings are still going strong even on machines that have racked up thousands of miles of use. At various times machines have been assembled and the bearings were inspected but no wear was ever seen. Over the years, the engineering staffs from the two companies have worked together to select the right bearings for new products and accommodate design changes. For example, in one case Graphite Metallizing discontinued a bearing size that was being used in a particular treadmill but immediately provided a substitute that worked as well as the original and did not require any design modifications. As a result, a strong partnership has developed between the two companies.
“The selection of GRAPHALLOY bearings early in the life of this company has played a role in its success,” Kratzer said. “Quickly finding an effective solution to a major design challenge provided the opportunity to direct our scarce engineering resources in other important directions. In addition, the fact that the bearings have performed so well in the field has reduced our warranty expenses and allowed us to direct our field service efforts in other directions. The performance of the bearings has also played a role in the high level of satisfaction that customers have experienced with our product. As we continue to develop innovative products designed for both therapy and athletic training, we will continue to specify GRAPHALLOY bearing materials because of the excellent performance that they have provided up to this point.”