Installation Guide - HRC Coupling

11 February, 2016

Author - Steve Hittmann Power Transmission Product Manager

Installation Guide - HRC Coupling
Author - Steve Hittmann Power Transmission Product Manager

CBC’s range of Martin and Fenner HRC Couplings provide a variety of hub selections to meet the demand for a low cost, general purpose, flexible shaft coupling. The Martin or Fenner style HRC Coupling is a flexible shaft connection that comes with the convenience of either Taper Lock Bushes for fixing to the shaft, or as a finished bore and key to suit a particular shaft size.

The HRC Coupling allows for incidental misalignment, it absorbs shock loads, and is able to dampen out small amplitude vibrations, making the HRC Coupling specially suited to hydraulic or combustion engine applications. The various different hub arrangements, in either F (Face), H (Hub), or B (finished Bore) allows the Taper Lock Bush to enter the hub from two different directions. Firstly, the bush may enter the hub from inside the coupling (F flange), which allows the coupling hub to be mounted against the bearing on a shaft, reducing overhung loads. Secondly, it is able to enter the hub from outside the coupling (H flange), which assists with ease of installation. Please see Figure 1.

Figure 1.

The HRC Coupling is a semi-elastomeric coupling and is designed for general purpose applications. It permits quick and easy assembly by means of a Taper Lock Bush. All outside diameters are fully machined, which allows for a high degree of accuracy via simple alignment methods, such as using a straight edge or the 6 inch rule method. The Martin or Fenner HRC Couplings are also a fail-safe design due to their interacting jaw design. The HRC Coupling is often referred to as a ‘capacity balanced coupling’ because, if the shaft fits, it will do the job.

Installation of an HRC Coupling

Installation of an HRC Coupling is as follows.

  1. Before installation, check all components for suitability, particularly where components previously in service, are being reused. Check taper bushes and the HRC coupling hubs are free of contaminants, lubricants, nicks, burns, and fatigue damage. Any type of contaminant or damage can affect the seating of the taper bush, both on the shaft and in the female bore of the coupling hub.
  2. When placing the taper bush into the HRC coupling hub, half holes should be matched to make complete holes. The taper bush should be oriented in order that each complete hole has thread on one side only.
  3. Before inserting the screws, ensure all threads are lubricated with oil. The screws should be started, but not tightened, in the threads in the HRC coupling hub. Shown as in diagram Figure 2.  

Figure 2.

4. Slide one of the HRC coupling hubs and taper bush assemblies into position. Locate the key into the keyway. Check there is a gap between the top of the key and the keyway slot in the taper bush.

5. Place the HRC coupling (rubber) element into the other hub and taper bush assembly. Slide into position, again inserting the key.

NOTE: Check for the presence of a gap above the key, as above.To ensure correct mating of the two tapers, check there is no lubricant present in either taper surface. 

Figure 3.

6. Locate the coupling halves and element assembly approximately in the desired position. HRC couplings are required to be mounted with an allowance for a small amount of float. This internal float allows for any linear expansion and maintains the coupling’s misalignment capability. This is achieved by giving accurate attention to setting the gap between the coupling hubs by measuring and setting the overall distance between the hubs designated by dimension L in figure 1 and the detailed relative to each coupling size in Figure 3 above.

7. Once dimension L is achieved, the screws need to be tightened alternately until the taper bushing is seated squarely in the HRC coupling hub. To ensure the tapers are seated correctly, it is recommended to tap the front face of the taper bush with a nylon hammer or suitable soft drift to ensure no damage occurs to the taper bush. A torque wrench must then be used to achieve the correct tension on the screws as defined in Figure 4 below. This procedure should be carried out a number of times to ensure the tapers are correctly seated. After setting the screws to the correct torque, they may require tightening again after tapping with the nylon hammer.

Figure 4.

8. HRC couplings have a maximum misalignment capability of 1 degree. Correct attention to accurate alignment of the coupling halves is, therefore, essential. Many methods of aligning shaft couplings are available, all with varying degrees of resultant accuracy and skills required. Laser alignment is the most effective and efficient in achieving accurate alignment. CBC provides Pruftechnik laser alignment and training, as well as on site services via our specialist technicians.

To view a coupling laser alignment video demonstration Click Below.

9. After a period of normal running, it is often prudent to recheck the torque settings on the taper lock bushing screws and re-tighten as necessary.

10. CBC also recommends that unfilled holes in the taper bush are filled with grease or silicon sealant to prevent the entrance of contaminants and facilitate future removal requirements.

To view a video demonstration on fitting an HRC coupling Click Below.

Martin and Fenner are leading manufacturers of the HRC coupling and have the advantage of offering the four hole balanced taper lock bush, which offers a preferred option for higher speed applications. CBC also has access to other makers of HRC couplings, including Rathi.

There are many alternative coupling designs available from the CBC range, including tyre couplings, grid couplings, gear couplings, disc couplings, and rigid couplings. Each offers a range of advantages and disadvantages. Selecting the correct coupling for the application is critical for achieving a maximum design life. CBC Power Transmission technical personnel require the following basic criteria to undertake a selection:

  • Application details
  • Input Power
  • Speed (RPM)
  • Shaft sizes 
  • Distance between shaft ends 
  • Duty cycle (stop/start etc) 
  • Operating environment

Selection via these criteria ensures the demand of the application can be met with the most suitable cost effective and maintenance friendly option.