The multiple rolls that squeeze the moisture out of wastewater solids on belt filter presses need reliable bearings that can take the heavy loads imposed by the pressure applied to the rolls. One constant problem is the need to keep bearing mountings from loosening and allowing the shaft to turn relative to the bearing. Another is the need to exclude moisture and corrosive fluids from the bearings while retaining lubricant.
U.S. Filter/Envirex is now using spherical roller bearings that incorporate an eccentric cam locking design that locks the bearing to the shaft and prevents the loosening that can occur with set screw mountings.
In the company’s belt filter presses, multiple rollers mounted on shafts carry a serpentine double belt arrangement that progressively presses moisture out of the wastewater solids.
Conventional setscrew-mounted bearings sometimes tended to loosen, allowing the bearing to turn with respect to the shaft. Previously, the company had tried other bearing locking methods, including some with tapered adapters, to solve the problem. However, these were difficult to assemble and their cost was higher.
Recently, Envirex switched to Rex® 3000 Series Twist Lock™ spherical roller bearings. These use an eccentric cam locking design to mount the bearing securely to the shaft. The Twist Lock units feature a carburized inner race that is more ductile and resistant to fracture than other eccentric-mounted bearings, which have through-hardened inner races.
To support Envirex’s pre-engineered emphasis, Rexnord Corporation’s Rex Bearing Division, Downers Grove, Ill., was able to incorporate additional design features that included a special corrosion-resistant epoxy coating and stainless steel hardware, as well as end caps and Rex M seals. These tailored the bearing design to the specific needs of the application.
To simplify replacement and reduce spare parts stocks, U.S. Filter/Envirex uses one size for all 28 bearings on a press, according to Dennis Barnes, a project manager at the company.
Typically, all shafts are 2 15/16 inch in diameter to meet the requirements of the firm’s largest 2-meter-wide units. Radial forces per bearing can approach 4,200 pounds, Barnes said.
The improved sealing and epoxy coating are also important improvements. “It’s a very wet application, and we’re dealing with sewage sludge, which can be corrosive. The gasketed end caps give us the sealing we feel is necessary,” he said.
The outer caps and bearing housings are both epoxy-coated, while the inner caps are zinc-nickel plated. An outer barrier seal rides on the plated end cap and there is another seal inside the bearing, which helps keep the water out.
Another benefit is that the seals also retain the grease, reducing service requirements and extending bearing life.
“We’re able to go up to six months without lubrication, based on a 40-hour operating week,” he said. “This makes it easier for a treatment plant to keep its equipment in good running order.”
