attn o-ring and polymer gurus

Technical Technical Discussion
#1

*Hello o-ring and/or polymer gurus.

I have a small rock tumbler.

I use it to clean parts and extend the shelf life of pint-size (and smaller) cans of paint.

It works miracles.

But the drive belt failed.

The belt is circular in cross section, 97mm ID, and material diameter 4.5 mm.

So…

My question is, what would be the relative merits of the following materials for this application?

nitrile
flourocarbon
Buna-N
Viton
PTFE
silicone
EPDM
Neoprene
polyurethane

The belt is not under much tension. It connects the small pulley (10mm dia) on the motor shaft to a larger pulley (83mm dia).

#2

I am not certain on the exact merits of each of those materials, but for that application I think urethane round belting would work well. We have used it on rollers and intakes in our robots and have not had any issues. It is easy to make the size you need with a heat gun. There are several threads that people discuss round belt or polycord.

I don’t see a 4.5 mm listed on McMaster, but they do have 3/16 which if close, but I bet you could find the cross section you desire with a little looking.

https://www.mcmaster.com/#round-belts/=1724veu

Thread that describes making the belts:
https://www.chiefdelphi.com/forums/showthread.php?t=154670&highlight=intake+roller

The belts can be made without the tool they just don’t look as pretty and take a bit more trimming

#3

nitrile - Could be good, resistant to fuels and oils, used as alternative to latex.
flourocarbon - Might be too slick
Buna-N - This is basically nitrile rubber
Viton - Used in industry for o-rings.
PTFE - Also known as teflon, slippery, soft, not very rubbery from my experience. Probably not suitable.
silicone - Probably good.
EPDM - Usually a synthetic rubber, could work.
Neoprene - Used for fan belts sometimes
polyurethane - Typical FRC roller conveyor material.

Depending on how the belt broke you might be able to just clean the ends and super glue them back together.

#4

The Parker O-Ring Handbook has a lot of data about o-rings. I recommend it to almost anyone with a question about o-rings and their physical properties.

https://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

Page 21 has a great chart with most of the information you are looking for.

#5

I don’t know much about belts or O rings, but I do know that when we need special O rings such as for our underwater robots, we order a bag of a particular size, and depending on how large it is, we get 5 to 100 O rings in a bag, for $10-15, from McMaster-Carr. Go with EPDM, and you’ll probably get enough in the bag to outlive you…

(quick google search shows that EPDM is used in many modern automotive belts)

#6

You don’t want to pay for anything with fluorine in it because you don’t need the chemical resistance. The fluorine also makes these slippery. (Florocarbon, PTFE, viton)

You likely do not need the high-temperature properties of silicone, it has good tensile strength but not great abrasion resistance, so cross that off the list.

PU and EPDM would be decent, but aren’t as strong as nitrile and buna-n

Nitrile = Buna-N, these are the principle component of timing belts. Highly recommended.

Edit: a number of sources I found didn’t seem to jive together, which is a little disconcerting.

However, natural rubber seems like it would be a good candidate and should be considered.

#7

I would guess that degrading over time from exposure to the atmosphere, is the primary failure mode? :slight_smile:

#8

Or fatigue. Sometimes I run this for weeks at a time: I discovered, to my amazement, that I can restore an old can of paint, which has separated into seemingly irredeemable gum at the bottom and liquid at the top, to a creamy smooth homogenized state. It just takes a looong time.

#9

How long did the original belt last?

#10

I depends on whether you mean calendar time or operating time.

I bought the device, oh, maybe 15(?) years ago for the kids to experiment with rock polishing but they were not interested so it sat unused for 10 years or so until I “re-purposed” it. Then it got used intermittently, but when used, it was for long stretches of time (weeks). So it’s hard to say.

#11

I meant overall time…as I said earlier…time is hard on rubber parts.

#12

Viton is what I have most experience with, but primarily as a static seal for vacuum. It’s durable, relatively cheap, and (at least in my experience) degrades slower than Buna-N, but again this is from a static/chemical/vacuum standpoint.

Having said that I absolutely fell in love with polyurethane flat belting from McMaster Carr this season. We are abusing the heck out of it with our intake and it hasn’t skipped a beat.

#13

Viton is a trade name for fluorocarbon material. In aerospace we use mostly Viton GLT for seals (temperature range).

For belting the EDPM is probably the most long lasting. Gates timing belts are typically polyurethane. If you could find your belt in either material it should be quite suitable.

Some of these materials are likely more for food handling, Teflon (PFTE) and Silicon than performance. There are only a subset of materials that are FDA approved. The temperature range and PH are more relevent for selection of these.