18 May, 2020

A coupling is a mechanical device that connects two shafts to properly transmit power. It accurately transmits the power from the input shaft to the output shaft. There are various gear arrangements to transmit power. But coupling can work only when the shafts are in a straight line and able to get connected end to end. 

Role of coupling

Power transfer:

Coupling helps in transmitting power from the turning side to the turned side.

Mounting error absorption:

It also absorbs mounting errors between the axes of the input side and output side. 

Vibration control:

It effectively controls vibration and protects other nearby elements. 

Heat Control:

With the power, it does not transfer the heat from the motor on the turning side to the turned side. 

Based on the applications of couplings they are mainly categorized in the following varieties:

  • Rigid couplings
  • Compensating or non-flexible couplings

Rigid couplings are for the places where two shafts are coaxial to each other. The rigid coupling has two categories:

  • Muff couplings
  • Flanged Coupling

Flexible couplings are for the areas where coaxially between the shafts is not always fixed. Areas with possibilities of occurrence of shock in power transmission mainly need Flexible couplings. There are various types of couplings, such as:

  • Bibbly Coupling
  • Flanged Pin Bush Couplings
  • Gear Tooth Coupling
  • Elastomeric Couplings
  • Tire couplings
  • Oldhams Coupling
  • Bellows Coupling
  • Hooke’s Coupling

Using the right type of coupling is important otherwise it can harm the power transmission or even can bring power-related danger. Choosing the right type of coupling requires some guidance from the expert.

Tips to use coupling:

  • Do not depend on price or habit alone:

    Following the habit should not be the best practice for engineers. Trying the previous project’s coupling type everywhere is not a good option. All couplings are not designed equally. Choosing a coupling based on familiarity can result in mismatches. Apart from this, if you only concentrate on affordability, there is a risk of the system being wrecked in the near future. To choose the best type, checking load, force, and nature of shafts is mandatory. 

  • Find the best way to mount coupling:

     Even after choosing the right model, power transmission can be failed. That’s why how you mount a coupling on a shaft is important. In the case of using unidirectional models, taking the help of traditional keys, keyways, and taper bushings would be appropriate. Application with reversing loads should pick keyless locking devices due to their backlash-free nature. 

  • Determine what you want the coupling to do:

     What will the couplings do and how- these questions should be asked before purchasing. There are various kinds of couplings available in the market, to check their effectiveness, try to get answers for the below questions-

  • Will the process be high or low speed?
  • Is it backlash-free?
  • What is the highest load capacity of the application?
  • Will the coupling transmit high or low torque? 

Evaluating all the answers will direct you to the right type of coupling to support your project. 

  • Keep an eye for under or overrating: Picking the right coupling type may seem a complicated task. To make it easy and to get the best type, you need to focus on shaft misalignment, stiffness, torque, rpm, inertia, space needs, and shaft mountings. 
  • Avoid general coupling pitfalls: You need to choose couplings that match application parameters and intended goals. Serviceability, speed of replacement, and application environment should be checked by the designers. After choosing the right type, you need to install it properly; otherwise, it can cause a malfunctioning system and lower the efficiency. 
  • Stick to the correct terminology: Inch-ounces and inch-pounds are confusing terms when it comes to expressing a coupling’s torque. Wrong specs can damage your system. ‘Keyways’ is another important fact. It has been noticed that if the application requires reversing torques and precise positioning, only keyways will not the appropriate there. 
  • Check for over or undertaking: 

            Underrated coupling- It denotes a coupling with a torque rate that is insufficient for the application

            Overrated couplings- This means your selected flexible coupling has the required torque rating

And you need to choose one that matches your system requirements. 

  • Do not pick the wrong type and size: Picking the wrong size and type is another common mistake by engineers. There are various types of couplings available in the market that can work well in the system but there will be some types that will not work. To get the best one, checking temperature capability, stiffness, inherent balance, brake loads, and speed capability are important. 
  • Avoid inadequate torsional stiffness: If your chosen coupling lacks required torsional stiffness, it can cause resonance and failure. Now it has become a common problem because now machines are required to stimulate cam profiles. These profiles produce torsional vibrations. It results in more vibration, excess noise, and ultimate failure. And that’s why you need to be sure about the right torsional stiffness before committing the purchase and installation. 
  • Check supplier sizing methods and shaft joints: You should be tempted to match the coupling torque rating to RMS info. It cut down the torque spikes. It happens because of load inertia changes. To avoid this kind of problem, you need to check the right torque rating.

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