Elastomeric Couplings – Spider insert flexibility verses Torque

Elastomeric couplings

Elastomeric couplings, long used in different industries like food, beverage, mining, industrial. The common contaminants factor in their usage such as water, dust makes them the better choice over uni joints.

These kind of contaminants are problematic with other couplings such as universal joints due to the bearings used to make these coupling flexible failing due to bearing failure due to contamination, the main reason elastomeric couplings are used in environments that contain contaminants is that aren’t made of anything that is effected by moisture or other contaminants like dust.

They have their place but their usage is also constrained because the elastomeric portion of the coupling cannot be used at an angular misalignment of more than 4°. This makes applications where the need for more misalignment than offered by the elastomeric coupling difficult and be forced to use conventional couplings like universal joints.

The Universal joint is a industry standard because it offers flexibility, torque and speed in one coupling. The downside to these three benefits is maintenance and replacement of worn parts like bearings and broken hubs.

Elastomeric couplings by definition by couplingtips.com are “Elastomeric couplings are a form of flexible coupling that uses an insert made of an elastomeric polymer to help transmit torque.” The insert is the most important component, as it has 2 functions, 1. Absorb vibration and shock loads and 2. Allow for angular misalignment. This means in environments where the use of universal joints like 24/7 and clean environments is either too cost prohibitive, or too expensive to maintain due to contaminant infiltration of the bearings.

This is where the cross over of needs for more flexibility verses costs involved in operations. The universal joint is also broken into two versions, block and pin or friction bearing and needle bearing version. The block and pin while it requires less maintenance ( but still requires constant greasing) can only be used at 25° (which is more flexible than the < 4° of an elastomeric) but is only able to run at 1750 rpm, slow compared to the 7000+ rpm from various elastomeric couplings.

The needle bearing universal joint can run at up to 6000 rpm and is flexible to 45° but the cost of bearing replacement and the labor to do it every 80/250 hours make it an expensive replacement. This makes it the only real replacement for elastomeric coupling but at a much higher cost due to constant maintenance and replacement cost.

Elastomeric coupling make up a number of different couplings and brands, Rexnord and their Omega orange, Lovejoy and their Jaw coupling, Delta Flex and S Flex couplings, SKF with their jaw couplings and SKF Flex range. Ruland Jaw couplings , TB woods range of jaw couplings, Dura Flex and G Flex grid couplings. Altra Motion brands Boston Gear and Guardian Couplings range of jaw couplings are another range who do elastomeric couplings.

European brands and Japanese brands like SIT Trasco and KTR Rotex as well as Tsubaki also do ranges of jaw couplings.

So lets break these different coupling options down which make up elastomeric couplings.

Jaw couplings – The most common of all the elastomeric couplings, a simple 3 piece design, input hub, the spider insert (the elastomeric component) and output hub. This coupling represents the largest selling part of this marketplace, and is a commonly used coupling for OEMs looking for a high speed coupling that is cheap and easily replaced with either new hubs when they break or when the spider needs to be replaced when worn.

The only downsides to the coupling are 1. Angle of misalignment is only 1/2° to 1° so not very much flexibility especially if there is any movement between the motor and output. 2. Replacement of elastomeric coupling’s spider insert, the spider wears at the edges as the coupling has to flex and over time the spider compresses with use, reducing its ability to absorb vibration.

As vibration increases the likelihood of equipment damage increases as well. 3. No safety aspect built into it, so if equipment becomes overloaded the jaw coupling will continue to work making it likely the attached equipment will be damaged.

Twin Spring couplings are different, no spider or insert to maintain or replace, same high speed as a jaw coupling and built in shear pins ensure no overload of equipment. Twin Springs dual springs absorb vibration much like the spider insert in a jaw coupling but they dont wear due to angular misalignment or compression. Made in a number of different models means buying the specific model to suit your needs (misalignment, torque requirements).

Elastomeric insert Couplings – A more dedicated coupling and expensive coupling with 2 hubs and a elastomeric insert, like a jaw coupling but the coupling can flex of < 1°. Its use is predominately with Pumps, Conveyors. Its slower than a jaw coupling and with less torque but its make up means it has the ability to take some shock load.

The  3 piece design and with flexibility of less than 1° makes it better than a jaw coupling but Twin Spring Coupling still outperforms it at its higher speed, higher flexibility and one piece constructions, adding a rubber or stainless mesh cover means it can be used in the same hostile work environment like moisture and heat.

Rexnord Omega Orange, Lovejoy S Flex, SKF Flex, TB Woods Dura Flex WE series are all examples of coupling inserts.

Doughnut/Tire couplings – As the name suggest the insert is shaped like doughnut or tire, the coupling has 6 holes, so the input hub can be bolted to 3 and output to the other 3. This kind of coupling is made from rubber but has a low torque capacity and a low angular misalignment capability < 5°. The Twin Spring coupling again can run at a higher speed, transmit higher torque and capable of more flexibility. Centraflex A, Lovejoy Saga, SIT Juboflex, Lovejoy S Flex are all examples of Doughnut/Tire/Tyre couplings.

Going over all the different couplings that make up the elastomeric coupling market, we see the following and mostly the important ability for the couplings to flex past 4° isnt there. They are not designed to flex any more than that and its all due to the elastomeric component not being able to flex/compress any more than 1/2° to 4°.

This limits what it can be used with as both a power source (engine) and output (pump, conveyor, blower etc) if there is any variation over what coupling is used, it means quicker wear and earlier replacement. This means down time for both unscheduled and scheduled maintenance and the cost for both the replacement elastomeric insert and labor to replace the old worn components with new ones.

Add to that the hubs (both input and output) also fail as well, either through use/contact wear or failure due to the hubs breaking if the equipment is overwhelmed. Now some of the elastomeric inserts can seperate from the hubs to give it a degree of safety overload, but if they do they need to be replaced before the equipment can be used.

Twin Springs build in shear pins to stop any overload past their rated performance means equipment reset and a new shear pins inserted means a quicker return to production. Safe equipment and a easy reset saves time and money.

Look at Twin Spring Couplings to replace your OEM couplings, and OEMs look to build better equipment with a better coupling system, no more choices between universal joints or elastomeric couplings, Twin Spring coupling offers something new with the benefits of both, high speed, high torque and high flexibility in one coupling.

More coupling links https://en.wikipedia.org/wiki/Coupling#Twin_spring_coupling

For more information go to https://twinspringcoupling.com/coupling-products/

 

 

 

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