Small Rubber Damper Design - Information Please!! 3

[mprice]

I am designing a small (Dia 26mm x 200mm) roller mechanism that currently uses springs in parallel with relatively expensive oil dampers. I would like find a cheaper solution using rubber parts in series with the spring to replace the oil dampers.

Can anyone recommend any useful sources of data for small rubber damper design?

Many thanks
Matt

 

[Tgatica]

You can check out some pre-existing designs from E-A-R Specialty Composites (

http://www.earsc.com/).

They manufacture engineered damping materials that should perform better than plain rubber. Depending on your quantities, they may be able to mold the damping materials directly to your spring assembly.

Good luck!

Tony G

 

[GregLocock]

If you are designing for large quantities then you may find that a hydromount is an economic solution, we pay perhaps a 50% premium for suspension bushes that have a tunable hydraulic element moulded in, that use glycol as the working fluid.

The problem with using rubber as the damping element is that the damping factor is not especially high (say 10 degrees loss angle for 65 Shure), especially at low frequency. It is also fairly unrepeatable , that is the damping effect reduces after you've scragged the bush, or on repeated application. Cheers

Greg Locock

 

[butelja]

In addition to Greg's good points, don't forget the fairly extreme variation in properties with temperature change.

 

[mprice]

Thanks everyone for your helpful replies.

Greg: I am only looking at low volumes for this mechanism 500 units = 2000 damper units per year. I currently use an off the shelf miniature oil damper for around 40 Swiss Francs each. My target is to make something much simpler and cheaper perhaps a rubber bush for less than 5 Swiss Francs! I can see that this would not give as good damping qualities but I think I can live with that.

By scragging do you mean over-stressing beyond the elastic limit? If so, how would this apply to a rubber damper element working in compression?

All: I would like to know how to go about choosing the correct size and shape and material for a rubber damper, which will give the best fit over the temperature range 10 to 35°C. Any more advice?

Thanks again
Matt

 

[GregLocock]

Scragging is the proper term for taking a steel road spring beyond its elastic limit, in order to set its free length and possibly do something to residual stresses. By extension we use the term when testing bushes - before testing them we always exercise them for a defined number of cycles at a high load.

Typically after 10 cycles the hysteresis loop has only 1/3 the area of the first cycle.

2000 pa is not enough to justify a fancy rubber bush, I suspect, so I'd forget my hydrobush idea. Your estimated cost for a rubber bush is about right, for one perhpas 30-40 mm on its longest dimension. What duty cycle and life do you need?

That temperature range is fine. I strongly suggest that you talk to a rubber bush manufacturer when designing the part he will be able to guide the design. We often work from a known similar part, test it, and then juggle the geometry to get the desired rates.

Another form of cheap damping is to use foam pads to create friction.


Cheers

Greg Locock

 

[Lasker]

hi,
i also strongly reccomend "EAR" products.
be carefull with friction based dampers because of friction force (static and dynamic) changes with humidity and temprature changes.

sincerely,
lasker

 

http://www.sorbothane.com/

You might try Sorbothane. They also have free design software that you can download.

 

[tomaspin]

Standard hydrobushes and hydromounts are available from Freudenberg. Go to

http://www.simrit.com,

and look at products/vibration control.
These might solve the problem for you.

Tom Aspin

 

[plasgears]

I recently benchmarked a competitive product, which was an automotive headrest actuator. The motor package was silent when perceived running on table top. There were about 12 rubber dampers from motor to output:

- small DC motor mounted between two O rings, rubber pad on side;
- motor drove a blade coupling, which interfaced with a rubber coupling on the worm;
- the worm ran in bushings that were supported in rubber jaws;
- the worm drove a plastic output gear that was spaced within two O rings;
- the gear drove an acme shaft that traversed a shuttle running in rubber bushings;
- the whole actuator was encased in a wrap-around rubber enclosure.

The impression was that this design spared no feature that could act to dampen vibrations and other noise. But the dampers had to relatively inexpensive for the most part.

Yes, consider rubber dampers of all kinds to serve your purposes.