Teflon Theory v. Practice

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OneTimeRunner
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Teflon Theory v. Practice

Post by OneTimeRunner »

Okay, lots of people saying that teflon is a big no-no. Stan has even published test results that show that the "white powder of death" makes a car run slower. It's the perfect example of theory not meshing with practice.

But, darn my luck, while explaining CoF to my son, I showed him a table that had teflon on it. He asked why we didn't try it, and I showed him Stans results. I thought that would be the end of it, but then he asked, "if it has a lower CoF, why does it slow the car down?" :scratching:

How 'bout it gang, any theories?
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FatSebastian
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Re: Teflon Theory v. Practice

Post by FatSebastian »

OneTimeRunner wrote:How 'bout it gang, any theories?
Well, here's one suggesting that it is the amount and method of application that determines PTFE's effectiveness (or not):
....eventually it became visually obvious that it was "caking up" and causing added friction. The more teflon we added, the slower we ran. Likewise, when we washed the teflon off (we thought!) with soap, we expected to attain similar slowness to the out-of-the-box axles and the graphite-washed-off axles. Exactly the opposite happened, the car became very fast -- we concluded that a thin, slick film of teflon had been left behind.
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Darin McGrew
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Re: Teflon Theory v. Practice

Post by Darin McGrew »

FatSebastian wrote:
OneTimeRunner wrote:How 'bout it gang, any theories?
Well, here's one suggesting that it is the amount and method of application that determines PTFE's effectiveness (or not):
....eventually it became visually obvious that it was "caking up" and causing added friction. The more teflon we added, the slower we ran. Likewise, when we washed the teflon off (we thought!) with soap, we expected to attain similar slowness to the out-of-the-box axles and the graphite-washed-off axles. Exactly the opposite happened, the car became very fast -- we concluded that a thin, slick film of teflon had been left behind.
Interesting. It sounds like teflon lubes work best as a thin-film lube, similar to Krytox 100, et al.
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Stan Pope
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Re: Teflon Theory v. Practice

Post by Stan Pope »

The "washed off, thin film" result is consistent with Cory Young's testing. (Or, maybe it was Cory Young's tests that you looked at.) I wasn't able to duplicate the results, so would not recommend it to anyone.
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Re: Teflon Theory v. Practice

Post by FatSebastian »

Stan Pope wrote:(Or, maybe it was Cory Young's tests that you looked at.)
:nod: I was quoting Cory.
Stan Pope wrote:I wasn't able to duplicate the results, so would not recommend it to anyone.
Good to know!
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Re: Teflon Theory v. Practice

Post by rpcarpe »

I saw rules in another pack that mentioned Teflon. So I asked the author.
David Meade answered my question with 'Avoid At All Costs'.
I've never looked at Teflon again.
My wife started a new support group... Widows of the Pinewood Derby.
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Re: Teflon Theory v. Practice

Post by FatSebastian »

rpcarpe wrote:David Meade answered my question with 'Avoid At All Costs'.
OTR acknowledges that the consensus opinion is to avoid Teflon. So the question is: why doesn't Telfon live up to expectations?
rpcarpe wrote:I've never looked at Teflon again.
:nod: Yes, many of us just accepted the consensus opinion and moved on...
OneTimeRunner
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Re: Teflon Theory v. Practice

Post by OneTimeRunner »

Okay, I've been chatting with a German tribologist, who seems to be very knowledgable on the subject. He confirmed that, if improperly applied, teflon will slow a pinewood derby car down. Teflon doesn't stick to anything well, except itself. The accumulation of the loose powdered teflon builds up and the axle has to push it out of the way to keep rolling. That's why powdered teflon slows a PWD car down.

In order for it to be properly applied, teflon had to be bonded to the surface of an item. The bonding process usually involves etching the surface with teflon primers and curing the teflon with high heat. Steps that are usually beyond the average PWD racer.

He did give me some suggestions to try, and I plan on doing some experiments to see if they have any merit. I'll publish my results as soon as I'm done.

One thing I'll share with you now: He said that Dr. Jobe's axle polishing method was very good advice, but he had a suggestion for improvement. He said that 91% Isopropyl alcohol still contains enough water that oxidation occurs. He recommended using 100%.

He also said that oxidation happens in milliseconds. He recommended doing the final polish while the axle is submerged in the 100% Iso., then immediately putting it into a paste of graphite and Iso. while the axle is still soaked.

I haven't tried any of this myself, so use this advice with caution!

One more thing, I found a site that tells a simple way to convert 70% Iso. to 99.9%. http://www.instructables.com/id/How-to-Salt-Out/, of course, I would recommend buying 100% over salting out, but it may be fun to try!
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FatSebastian
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Re: Teflon Theory v. Practice

Post by FatSebastian »

OneTimeRunner wrote:He said that 91% Isopropyl alcohol still contains enough water that oxidation occurs. He recommended using 100%.
FWIW, the oxidizing effects of 91% alcohol have also been recognized here.
OneTimeRunner wrote:I haven't tried any of this myself, so use this advice with caution!
:thinking: Yes, I wonder if the supposed speed improvement from minimizing oxidation (if any) would be worth the hassle...

Great info, OTR!
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Re: Teflon Theory v. Practice

Post by FinePine »

A good test for Teflon would be to ream out a wheel bore and sleeve it with a Teflon liner, and run that on a dry axle. Then you could test the low CoF of Teflon seperately from the issue of the powder form.
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Re: Teflon Theory v. Practice

Post by MaxV »

It is also important to read the fine print on the test results. When a table says that teflon has the lowest COF of any lube, make sure to check the PSI at which the COF was determined.

Oftentimes, the PSI used in the testing is extremely high, much higher than is encountered in a pinewood derby car. The results in the table are only valid for that PSI. A lower PSI will result in a different COF.

Here is an example chart showing that Tungsten Disulfide has the lowest COF - but note the extremely high PSI at which this occurs:

Image
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Re: Teflon Theory v. Practice

Post by GravityRacer »

By my engineering estimate, the pressure at the wheel-axle interface is about 13 psi, give or take. A bit below 300 kips.

Soap and water aren't going to be a good method for removing teflon, and in fact may make it worse. I'd mechanically scrub it off, if I were ever to use it (as if).

Teflon sleeves (and graphite, for that matter) are something I've considered, but they're illegal in most venues- they'd be considered "bearings", unless you were pretty careful! :scratching: Also, if the tube was even slightly bent, it would defeat the purpose.

I wouldn't use IPA at all. It's seriously hygroscopic, so in almost any environment is going to pull water from the surrounding atmosphere. You can't even make pure alcohol, due to this hygroscopic property. Even reagent grade alcohol has water in it. If you want to store your axles in a water- exclusive environment, use acetone- you can find it in your wife's pharmacy- nail polish remover (non-oily). BTW, acetone will also exclude moisture from your Gorilla Glue, and help it last a lot longer. Just put a thin layer on top and snap on the cap. Machine oil would actually be a better choice for storing axles, as long as you clean it all of with a good petroleum solvent before you graphite them again. Machine oil also won't be as much of a fire hazard in the shop...and the wife won't be poking around in your second obsession stuff; nor will it melt your custom paint job if it spills.

Graphite relies on slipping plates of material, and in fact pretty much needs moisture to help this lubricating property. Keep your powder dry?

Extrapolating (always a dangerous business) on the graph above, it looks like Tungsten Disulphide would be the way to go, based on the curvature at the low pressure end. I dunno. I just use any graphite I have available, and haven't experienced markedly different results. My favorite lube is an old tube I bought at an auto parts store in Florida to lube locks and speedometer cables- a winning formula from the automotive industry. Guess I'll have to go there again to pick up a properly seasoned and humidified tube, sometime soon.

If you WERE to use teflon, and etched the surface of the axle with the appropriate chemicals, that would pretty much obviate that fine polishing job some people rightly swear by.
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Re: Teflon Theory v. Practice

Post by FatSebastian »

GravityRacer wrote:Extrapolating (always a dangerous business) on the graph above, it looks like Tungsten Disulphide would be the way to go, based on the curvature at the low pressure end. I dunno. I just use any graphite...
MaxV once offered a product review that suggested WS2 is inferior to graphite in PWD applications.
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sporty
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Re: Teflon Theory v. Practice

Post by sporty »

I have gave these posts more than a once over and some of things I would like to say. I may just not be ready to discuss yet.

However,

There our different kinds of teflon and grades of teflon. It's not just teflon, because it says so.

Some products only contain 5% or 10% some are pure teflon, some gun oils are 100% pure teflon, but the quality can sometimes not be as pure as one might think.

Off topic, but this is my true story.

I once had a motorcycle magizine subscription. Wrote it to them, when my bike that I owned, I took to a drag race, I had done alot to my bike and still did not see there times on a stock bike.

So they did reply and published my questions. It turns out, they were slipping the cluth plates so bad, that they might only get one run, before burning them out, that they go through as many as 10 -12 sets to get those times.

So after reading the article, I went back to the drag strip playing with slipping my clutch, even though I had installed racing clutch plates and better clutch springs.

I litterally was damaging the rod journals and bearings and cam brearings. to get those times also.

So my point is, that we really never know what test or tests were done and conditions to get those claimed numbers.

Like Randy, mentioned, the psi factor is a factor and can give a misleading perception.

BTW, the slickest material now is not teflon, but it is called (BAM) .
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Re: Teflon Theory v. Practice

Post by GravityRacer »

Like I said, extrapolation is a dangerous business. However, I don't see anything quantitative at either of these links, just "This works better". No offense to MaxV.
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