Spray carb cleaner vs. Nitrile O-rings

[robertbarr]

I think they're probably just being on the safe side, but here's the horse's mouth:

Dear Robert Barr:

Thank you for writing to Gumout. We would not recommend using the Carb & Choke product with the nitrile (Buna-N) O-Ring. We appreciate your interest in Gumout products. If you would like to speak to a technical representative, please feel free to contact us at 1-800-416-1600- option 2.

Regards,

M. Van Rossen
Technical Representative


As soon as I scare up a jar (what comes in a jar anymore??) I'll run a test of my own.

 

[Steve]

As soon as I scare up a jar (what comes in a jar anymore??) ...

How big a jar do you need? I am guessing a small one would suffice.

What comes in small jars? Food for small people. \\/

Yep, baby food. Not real expensive, so you won't feel real guilty about buying one and tossing the contents. 8-[

.

 

[Guest]

Use a shot glass.

In the rubber industry there are many ways to check solvent resistance. The best ways require specialized equipment such as tensile testing machines ($30K +) and the ability to mold the rubber into specific shapes. But there is an easier way that correlates well with solvent resistance, the swell test.

A solvent can't affect a rubber part unless the solvent is absorbed into the part. So the test is more or less to
1) weigh the part
2) drop it in solvent and let it sit
3) remove the part, wipe off excess solvent, and weigh it again.

The greater the increase in weight, the weaker the part. If solvent resistance is excellent, swell should be less than 5%. (Very crude estimate) Parts with poor solvent resistance could swell 20% or more, even more than 100%.

Test variables include time and temperature. Thick parts always require more time. High temperature will accelerate the process, but it is best to test at the temperatures that parts will actually see in service. For some, a part that can last forever at room temperature can fail rapidly at elevated temperature.

Practice with regular rubber O-rings in a variety of solvents, from water to mineral spirits to xylene or toluene to laquer thinner to carb dip with methylene chloride. Watch out for fumes!

The process needs a fairly sensitive scale. Fortunately, digital scales are getting cheaper and cheaper, and even Harbor Frieght sells them. You'll probably have to use several O-rings to get enough weight to detect changes.

 

[robertbarr]

I have a Lee powder scale, which is a mite more sensitive than my little digital (although that does a heck of a job too). It would be nice to have the money to own a digital that's as accurate as the Lee.

http://balance.balances.com/scales/854

 

[waterman]

I like themess idea of weighing before and after but how do you account for any material that is dissolved or the quantity that adheres to the rings? Even with an analytical balance, the small difference may not give you the most accurate results. I think I would subjectively try to determine if the ring is being softened and possibly dissolving. Maybe even a stress test of how far you can stretch one before and after exposure.

Give the company a call and ask the tech rep why, someone there certainly should be able to give you an answer.

 

[Guest]

Dissolved materials: Oils from the rubber compound dissolve pretty easily, but nitrile rubber usually has little of no oil added to it, so that shouldn't be much of a factor. If you want to take account for it, you could let the solvent evaporate in a tared dish, and weigh the residue. This takes one of the expensive balances to detect, because of the small amounts involved. Another approach is to look at the color of the solvent, which really needs a spectrometer. Again too much money for the instruments.

Hardness and physical properties can also be measured on swelled rubber, but it requires the instruments. A durometer costs several hundred dollars, and requires that special blocks be molded, which requires molds, a press, and uncured rubber. It might be possible to jury-rig something to press against an O-ring, but it really won't tell you much.

Let's try for something really simple:

Put the O-rings in solvent or oil in a shot glass and let it sit for a few days, covered with aluminum foil. Hold the glass up to the light, with a white background, and see if the color has changed, compared to the sampe solvent sitting the same way for the same time.

Then get out your trusty Vise-Grips, and an untreated O-ring. Set the pliers to just barely pinch the untreated O-ring. Then clamp down on the treated O-ring. Does it leave a mark, or extrude or break the rubber? If not, turn the adjustment screw on the Vise-Grips in a quarter turn and repeat. Keep on going until both O-ring obviously fail. If there's much of a difference, the solvent hurts the rubber. You should use several O-rings that are treated and several that aren't to be sure. Or else cut a couple of them into several pieces each.

 

[Guest]

Also, the tech rep doesn't know the answer to your question, neither the one the makes the carb cleaner nor the one that makes the O-rings. The carb cleaner company doesn't test their product against all kinds of rubber (there are hundreds of types of nitriles, and hundreds of thousand of ways that it is formulated with additives into a rubber compounds). And the O-ring company only tests their compounds against a very standard panel of solvents and oils, so they don't know either. A small difference in the mixture of solvents can make a huge difference in the corrosivity it has for rubber.

Example 1: 5% methanol in gasoline makes it 100 x more corrosive to most types of rubber than straight gasoline

Example 2: 2% sulfuric acid in concentrated nitric acid makes "aqua regia", a frightfully strong acid​

.

The carb cleaner company lab doesn't have the equipment to do the test. The O-ring company lab does, but doing the tested will cost them several hundred dollars at a minimum. A rubber chemist will need to design the tests, and a technician will spend at least ten hours or so to run them according to ASTM standards. That ten hours will be spread out over a week or more. Then the rubber chemist will evaluate the results and write a report. If your name is General Motors and you buy 10 million of those O-rings per years, the company will start on it immediately and eat the costs out of respect for the 800# gorilla. If you are a small company, the O-ring company sales department will start by quoting you a price for the service. For the rest of us, it just won't happen.

I used to do this stuff for a living.