The Case of the Dying Drive Belts
Solved with a Urethane O-ring Belt
Like
everyone, we get requests for quotes over the internet. It's not what
we do as a general rule. We are more interesting in solving sealing
problems than offering the lowest price, but we will quote if it appears
that the customer needs more than just a price. A few years ago a company
asked us to quote on four sizes of Viton® o-rings and mentioned
in the inquiry that they were using a nitrile o-ring as a drive belt
and it was failing on a weekly basis. Someone had recommended Viton®
as a possible solution to the o-ring
belt problem.
We sent
the quote but also mentioned that we didn't really think Viton®
was the best approach. Viton's® claim to fame is excellent temperature
and fluid resistance and that probably was not what was causing the
o-ring belt failure. When many synthetic rubbers stretch they age and
crack much more rapidly. We knew that another o-ring, such as a urethane
o-ring, had properties that might solve the problem.
The company
responded that our price was not the lowest, but that we were the only
company which had questioned using Viton®. They wanted to talk further.
So we asked about the application.
They made
a small office type machine which they leased out. The lease on the
machine included maintenance. There were hundred of machines in operation
throughout their country. The cost of the o-ring belt, no matter what
material, was a small fraction of what the failures were costing them.
Once we had determined that there was no actual temperature problem
involved, we recommended a urethane o-ring. Urethane is a plastic, not
an elastomer, and doesn't have the same stretch/aging problem. We expected
the urethane to last much longer under the conditions the o-ring belt
was subjected to.
Our progress
in getting the urethane o-ring belt to work was not smooth. Initially
we sent them an urethane o-ring that was the same size as the nitrile
o-ring they were using. We forgot that nitrile has a lot more stretch
than urethane and so they were using a smaller diameter o-ring to compensate.
Sorry about that. The company then shipped us a machine so we could
figure out the right size. It took some trial and error, but we did.
An urethane
o-ring has a service life in excess of one year, but the company replaces
them annually just to be safe. This means that they now use one urethane
o-ring where they used to use fifty-two. And oddly enough that is the
smallest part of the savings. They still send maintenance people out
but at much longer intervals so labor costs have dropped a lot. For
what it's worth, a urethane o-ring
(metric cross section and non-standard ID) costs more than the Viton®
o-ring we quoted but the price of the o-ring is no longer an important
consideration.
Conclusion:
The cost to use a product is often much more than the cost to buy it.
Note: Some
characteristics of an urethane o-ring: The temperature range of an urethane
o-ring is -40 C to +105 C. Urethane is an excellent elastomer with high
abrasion resistance characteristics and high tensile strength. Urethane
o-rings are often used in high pressure hydraulic systems where highly
stressed parts are subject to wear.]