Elastomeric couplings – The 2 spider insert trade offs

Elastomeric Couplings - Twin Spring Coupling components

Elastomeric couplings come in many shapes, sizes and capabilities.

Lets break these down into what’s currently available and how they work or don’t work for the average user.

So why use Elastomeric couplings then? What’s the options, there are a number of elastomeric type couplings. It depends a lot on what the industry is. Is there moisture involved? FDA requirements? 24/7 operation? A coupling that cant break (this is why the jaw type coupling are also called safety couplings)

These requirements mean that most other elastomeric couplings are the same, so lets break down what’s on the market.

Jaw couplings

Jaw Couplings are small, cheap and work across in most cases, a large number of industries. Jaw couplings being made up of 3 pieces, input and output hubs plus the elastomeric insert, so its a simple coupling. They have a number of different elastomeric insert or spider insert is another term for that.

These couplings have their own disadvantages, mainly they can only flex to 1° with the softer inserts, Buna-N which is also called SOX, NBR or Nitrile Butadiene Rubber, another soft insert is made from Urethane, which is a slightly harder insert than the Buna-N.

This softness allows the coupling to absorb vibration being transferred from power source to equipment. The last two are Hytrel and Bronze.

Hytrel and Bronze due to their hardness can only flex to 1/2° and due to their hardness isn’t able to absorb vibration transferred through the power train.

Lets look at the three components, which is the same across all elastomeric couplings. The main “wear part” is the elastomeric spider insert, it wears in two different ways.

  1. Angle of use – The more the coupling and this also includes couplings like universal joints and other elastomeric couplings, is used off center the more the outer edges wear, so in the case of a jaw type coupling the “legs” wear faster and this wear allows the hubs to touch, increasing the vibration and leading to premature failure and replacement.
  2. General compression due to wear – The spider insert, the soft elastomer’s being made of Buna-N or Urethane compresses over time, this compression leads to increased vibration and decreased angle of use so again the inserts will need to be replaced.
  3. Sunlight and high heat – The UV from sunlight also accelerates the breakdown of the insert, as does high heat, this applied predominately to the softer inserts like Buna-N.

Tire Coupling 

Tire couplings are also elastomeric couplings, it is a bigger coupling than a jaw coupling and while it uses a polyurethane insert and is flexible to 2° (twice that of a jaw coupling)

Tire couplings vary slightly from jaw couplings in the elastomeric insert is bonded re-enforced polyurethane construction to a metal inner that allows the outer hubs that are bolted to them holds the coupling together.

 

  1. Angle of use – While more than the standard soft insert jaw coupling, the typical tire coupling can only work up to an angle of 2°, this means its usefulness is also limited especially if the user needs more than 2°.
  2. Replacement due to over flexing – Due to the tire coupling like the TB Woods WE40 being used at angles at that 2° limit, the tire starts to delaminate from the inner metal hub. Once that starts to happen, the tire will need to be replaced as this is a sign of premature failure.

What are your no maintenance coupling options?

No maintenance option are pretty limited especially if you need your couplings to be able to flex, either consistently or occasionally. Add to that a hostile working environment i.e. moisture, heat, UV exposure.

These are all factors that wear couplings out quicker than the user would like. So this means increased maintenance schedules and increased elastomeric replacement.

These add significantly to the cost of a “cheap coupling” as the maintenance and component replacement far eclipse the initial cost of the coupling.

What can Twin Spring Coupling do for you?

Twin Spring Coupling offers the best of all coupling solutions, the flexibility of the universal joint without the bearings to replace, and the high speed and flexibility most jaw coupling owners want.

A simple product like the elastomeric coupling, 2 hubs a set of torsion springs all rotating around one central ball bearing. This one piece design (its assembled as a single unit so no components like bearings or spider inserts to replace.

The dual springs absorb vibration much like the elastomeric insert does in a jaw type coupling.

The twin springs also means it can flex much like a universal joints but it has no bearing cross that needs constant greasing and replacing when worn.

Shear pins that hold the 2 spring sets together makes it a safety coupling, this means no excess torque which will damage delicate equipment. Even if it exceeds its limitations the springs will deform but keep the coupling together, adding another level to safety coupling.

The Twin Spring couplings come in 3 sizes, 150, 300 and 500ft lbs. of nominal torque, this take into account most types of equipment, regardless of whether its industrial, automotive, farming or mining. The coupling can run and replace other couplings please check our range for the size and spline type to suit you.

 

 

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Wikipedia.org/wiki/Coupling#Twin_spring_coupling.

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