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<veeduber@isp.com> wrote in message
news:1154039112.140299.62110@h48g2000cwc.googlegroups.com...
> Dear Peter,
>
> Coatings were originally developed as a means of prolonging the life of
> the blades in the hot-section of turbines was metal spray using
> plasma-arc, which meant the base metal had to withstand some
> significant temperatures during the coating process.
>
> Tech-Line's approach (and others) successfully bonds a
> zirconium-ceramic alloy to a properly prepared aluminum surface at a
> temperature of only 350F. Since this is clearly impossible I am sure
> most folks have discounted such coatings out of hand :-)
>
> The thermal barrier coating material comes as a thick water-based
> 'paint' having unusual wetting qualities. After being sprayed or
> brushed onto a properly prepared surface the stuff is allowed to dry.
> The coated pistons & heads are then put into an oven, brought up to the
> cited temperature and held there for a given amount of time. The
> result is an apparently alloyed ceramic-metallic surface.
>
> I do not know how it works but here are some guesses based on my
> experiments.
>
> The most critical factor appears to be the proper preparation of the
> surface, which must be abraded with a sharp, relatively fine-grained
> media, such as #120 aluminum-carbide. Examined under a 30x binocular
> inspection scope your nicely machined surface has been converted to an
> infinity of edges so fine that they refract light. (If you put an
> abraded but un-coated sample into the oven for the required amount of
> time, on examination you will see that the refraction vanishes; the
> surface still appears abraided but is now smoother.)
>
> Getting the coating material to 'wet' the abraided surface can be
> difficult. The metal must be perfectly clean -- touching an abraided
> surface with your bare hand is enough to cause the coating to fail (but
> leaves a nifty metallized fingerprint :-)
>
> The coating material appears to consist of a combination of finely
> divided (ie, powdered) frits. During the heat-soak period -- after the
> coated part is brought up to the required temperature -- the frits
> appear to melt in a eutectic-like process, with those which melt at a
> low temperature forming a solution which cascades the melting of those
> having a higher melting temperature.
>
> I cannot say if the result is a true alloy or simply an exotic form of
> hard-facing but the result is a durable, heat-resistant surface. You
> can bend it or beat it with a hammer and it stays put. You can also
> heat it with an O/A torch immediately adjacent to an untreated coupon
> and see the latter melt (!) will the treated surface remains unchanged.
>
> Obviously, impossible, right? :-)
>
> --------------------------------------------------------------------------
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>
> So what does all that mean?
>
> According to Sir Harry Ricardo (and others) during the intake cycle the
> residual heat causes the incoming charge to expand, effectively
> reducing the engines volumetric efficiency. In a similar vein, the
> instant combustion is initiated the surrounding structure begins
> absorbing heat produced by the combustion process, so that by the time
> the process ends the temperature within the combustion chamber -- and
> the pressure resulting from it -- are reduced.
>
> In the Otto cycle engine TBC's yield slightly higher torque for the
> same fuel consumption. I have no idea how much of this may be attributed
> to improved VE or increased BMEP -- and on a small engine, with
> home-made sensors it's impossible to quantify those results -- but with
> a test club turning the same rpm I have seen a reduction of fuel
> consumption of 3% to 7%.
>
> --------------------------------------------------------------------------
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>
> As you've pointed out, there's no such thing as a free lunch. Thermal
> barrier coatings cause more heat to appear in the exhaust port and
> exhaust stack.
>
> The need to coat the head & neck of the exhaust valve is clearly
> indicated but even so, the stock VW valve is a rather dinky bit of
> goods having a stem only 8mm in dia. On the advice of Tech-Line I have
> treated the valve stems and guides with tungsten disulfide, a dry-film
> lubricant that is merely burnished into the clean, unabraided metal
> surface. I have also modified the VW's lubrication system so as to
> increase the amount of oil reaching the rocker galleries by about 8x.
> The valve gallery was abraided with coarse media (sand, in this case --
> I was worried about media residue contaminating the oil) cleaned
> ultrasonically and treated with a thermal dispursant. On the stock test
> engine the oil temp was 8% to 10% higher, compared to an untreated
> engine.
>
> As for the exhaust stacks, while monel or stainless steel might serve,
> my budget dictated plain carbon steel. This was treated with another
> type of thermal barrier coating and held up quite well, assuming the
> coating was properly applied. The tricky bit here was getting a
> uniform coating on the interior of the tubes, which proved impossible
> when the stack was made up of welded sections. Although unsuitable for
> flight, I fell back on cheap, after-market headers and 'J-tubes.'
> These are seamless, mandrel-bent tubes which were easy to prep and
> coat.
>
> (As a point of interest, the test engine had a unique 'bark' unlike
> anything I would heard before. To keep peace in the family I fitted
> mufflers to the stacks.)
>
> --------------------------------------------------------------------------
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>
> Finally, as with most experiments I had more failures than successes.
> But there were enough of the latter to convince me that, when properly
> applied, coatings would do no harm and had the potential to provide
> some improvement in the durability of an engine assembled from
> after-market VW components.
>
> -R.S.Hoover
>
Thanks,
Those are truly fascinating results, and I wish that your experiments could
continue. If a local EAA chapter in your area has 501c3 status, and if
enough of the lurkers are interested, anything is possible, although not
necessarily probable. That would at least allow the original goal of
determining durability to be met. Obviously the addition of the mufflers
during the experiment add a "fudge factor", but the circumstance you
described is interesting in that it suggests that the residual pressure from
combustion is higher in the treated engine at the time that the exhaust
valve opens.
All of this suggests, at least to me, that the claims made by both Tech-Line
and the maker of the MPG-CAPS applied through the fuel system are true.
BTW, I'm currently trying MPG-CAPS in my car, which does appear to run
better and more smoothly at the lowpower levels at which cars normally
operate; however I doubt that I'll ever be able to accurately quantify the
effect on fuel consumption. I'm sorry that I do not have more training
and/or real world engine experience to contribute.
Peter
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Re: Veedubber's Tech-Line Coatings
