How to Install a Disc Coupling
A disc coupling is a relatively simple coupling design, consisting only of two hubs, a center member, two disc packs and fastening hardware. Below are a few tips that will help ensure a proper disc coupling installation that will provide years of reliable service.
1) Safety and inspection
Before starting, please make sure to wear the proper personal protective equipment (PPE) and be certain lock-out tag-out procedures are followed on stationary equipment to assure the system is safely isolated from all sources of potential energy. Inspect both the driving and the driven shaft, as well as the hub bores, to make sure they are free of dirt and burrs. Clean and de-burr as necessary. Measure the bore and shaft diameters to assure proper fit. If the bore is tapered, check for good contact pattern, also ensure the keys fit on the shaft properly; Keys should have a snug side-to-side fit with a small clearance over the top and have chamfered corners.
2) Mount the hubs
Install the key(s) in the shaft. If the hub is an interference fit bore, heat the hub in an oven to expand the bore sufficiently larger than the shaft, 350°F is usually adequate. An open flame is not recommended; however, if the only option, use very large rosebud tip to provide even heating. A thermal heat stick provides the most accurate measure of hub temperature. With the hub expanded slide it on shaft to desired position. Axial stops can be helpful in getting position set accurately. For clearance fit bores, be sure that the set screws in the hub do not protrude into the keyway of the bore before installing. Slide the hub up the shaft until it is in the desired axial position. Tighten the set screws to the torque value shown in the manufacturer’s installation guide.
- Angular misalignment
Rigidly mount a dial indicator on one hub and place indicator on the face of the other hub. Rotate both shafts together one revolution noting minimum and maximum dial indicator readings. The difference of these values should not exceed the TIR value specified in the manufacturer’s installation guide.
- Parallel misalignment
Rigidly mount a dial indicator on one hub and place indicator on the other hub flange outside diameter. Rotate both shafts together one revolution noting minimum and maximum dial indicator readings. The difference of these values should not exceed the TIR value specified in the manufacturer’s installation guide.
- Axial misalignment
The axial spacing of the hubs should be positioned so the disc packs are flat with no visual waviness. The distance between the hub faces that sandwich the disc packs should both be within the limits given for the “N” dimension in the manufacturer’s installation guide.
4) Attach the center member to the hubs
The center member comes in several configurations. Depending on the coupling design you can have a split center member, adapter mount center member and non-adapter mount center member. The below procedure covers center member mounting for the most current adapter mount coupling configuration: For adapter mounted center members, the center member sub-assembly must be compressed to allow it to be dropped between the two piloted hubs. The center member mounting capscrews, are reverse installed from the center member side to compress the disc packs, thereby shortening the overall length of the center member. The disc packs should be compressed equally on both sides of the center member and only enough so the center member assembly will fit between the hubs. After placing the compressed center member between the hubs, the compression capscrews can be loosened to allow the center member assembly to expand into the hub pilots.
5) Insert and tighten the cap screws
Compression capscrews are now fully removed and inserted thru the hubs and threaded into the center member adapter holes. Tighten the cap screw to the torque listed in the manufacturer’s installation manual.
6) Check final shaft alignment
Re-check final alignment by again measuring the “N”. Measure at the 3, 6, 9 and 12 o’clock position for each of the two disc packs. The “N” dimension should be within the range shown in the manufacturer’s installation manual.
All Thomas Disc couplings are replace-in-place designs. To replace disc packs of the coupling, simply reverse the above installation procedure given for the adapter style coupling. When replacing the center hub assembly, you can either replace the disc packs only, or the entire center member assembly.
For more information and documentation on Rexnord disc couplings, visit www.rexnord.com, or call 1-866-Rexnord for technical support.