Keyways aren’t the only way to couple heavy-duty motor and gearbox shafts. In fact, keyways aren’t even the best way when you consider the alignment and installation difficulties you’ll encounter when installing keyed shaft couplings that may weigh thousands of pounds. A better alternative is to use couplings that employ a mechanical shrink fit around the shafts.
Ringfeder 5571 Flange Coupling
How high? To take one recent example, we delivered a set of shrink disc flange couplings that have a maximum rating of 240,000 ft-lb. These heavy-duty couplings, nine in all, join the motors and gearboxes that drive a big mining conveyor system. In this particular application, the couplings have to transmit reversing torques in excess of 180,000 ft-lb. No bending loads apply in this case, but these rigid couplings could have tolerated another 75,000 ft-lb of bending forces in addition to the torque loads.
Better Than Keyways. The shrink disc coupling beat out keyway-based couplings in this application for four reasons:
- Eases installation. Each one of the couplings weighs more than 1,720 pounds. Trying to align and engage keyways with couplings this big is a job that the mine’s engineers wanted to avoid.
- And eases disassembly too. The mine’s engineering team likewise wanted a coupling solution that could be disassembled easily for maintenance. With the shrink discs, loosening the locking screws releases the pressure on the flange hub. The connection returns to its original clearance fit dimensions, freeing the shaft for removal. Traditional machined shrink fits have no such release mechanism. To undo a traditional shrink fit, you have to heat the connection for hours to expand the coupling ID. Sometimes this procedure doesn’t go as planned, damaging the parts.
- Resists contamination. Once the locking screws are engaged and all the contact surfaces are under pressure, the shrink discs shut out dust and debris. This capability was important in a contamination-prone mining application.
- Prevents misalignment. Thanks to the even distribution of compression forces around the circumference of the shaft, shrink disc couplings inherently prevent misalignment.
In addition to use on mining and other large conveyers, flanged shaft couplings with shrink disc technology are also used in other heavy-duty applications—including gearboxes, process equipment, material handling systems and aggregate production.