coating aluminum fuel tanks necessary?

[poe21]

So we run an aluminum fuel tank every year, but the previous guys coated the tanks with KREEM. Although they followed the 40 step process to the letter, the stuff has not maintained well, and I have found it peeling off in some places. Both tanks were properly etched, and done over a couple of days. My question is, is there any need to coat these aluminum tanks? I mean, we're running 93 Octane, and as short of a lifespan as these cars have, is it worth it to try and continue this fruitless process? I searched, but got no real answers to my liking.

thanks

[Chapo]

Based on past experience there is no need to coat the tanks. We have had one of our cars running with the original tank for 5 years now with no problems.

[Sooner_Electrical]

I will second that, also in my experience people usually start trying to coat their aluminum gas tanks when they are unable to get them to seal by normal methods; Not because the corrosive properties of gas vs aluminum. We have never coated any of our gas tanks and have not had issues, well related to gas tanks :-).

[poe21]

so what are recommendations if the tank has trouble sealing? I have heard about fiberglass, or some other epoxy coated strips, and I'm assuming they are talking about externally?

Anyways thanks for clarifying, I hoped and figured that would be the answer.

[Adambomb]

Hmm...we've used Kreem for years, never had problems with it coming off. Were the previous guys following the 40 step process to an upper-case T, or just a lower case t? Generally with stuff like that you have to be super duper anal in prep work, especially in cleaning.

Although we run E85...if we weren't using E85 I wouldn't bother. Non-coated Al fuel rails seem to be good enough for OEM. If nothing else there are some Al alloys that are more corrosion resistant than others.

If you're having trouble with the tank sealing without any sort of lining, I personally recommend either changing your manufacturing process, getting the guys who are building it to be a little better at it, or finding someone else who can do it, that's pretty much all I've got.

I've also had good luck with a much simpler one-stage fuel tank liner called Johnson's that you get from Napa. One $35 can should do like 6+ FSAE fuel tanks. Works good on rusty motorcycle tanks at least, and is thick enough to fill in most small holes.

[poe21]

well, tig welding aluminum is not always exact, even when 20-24 year old college students do it. Tiny holes can be found at the wrong times if you don't do it perfect. Especially considering we are trying not to use material that is 1/4" thick to keep weight down. It is my understanding that the kreem is much more suited to a steel tank... which is the usual suspect in automotive and motorcycle tanks.

I also watched them do the cleaning process multiple times, and the etching process twice on the 2008 car. Still it peals off. I believe I will just forgo the sealant this year. Any other suggestions on sealing the seams other than tell your guys to do a better job?

[jd74914]

IMHO the best gas tank coating is made by Caswell Platings. It is called "Phenol Novolac Epoxy Gas Tank Sealer." It covers extremely well and leaves a hard, epoxy-finish which appears to be extremely durable. IMHO it is a much better product than Kreme.

Disclaimer: I have not tried it on aluminum, but we are planning on trying it this year on our aluminum gas tank.

[Chapo]

Do a better job with the welding http://fsae.com/groupee_common/emoticons/icon_wink.gif its one thing that i would look at getting done by a professional welder with years of experience after all we have all seen the pictures of various teams cars with fuel leaks. Its one thing that you cannot afford to risk.

Another solution (kinda crude) is to use a 2 part fuel proof epoxy on the inside of the seams. You can buy fuel tank repair materials from most auto stores (well you can in Australia, so im gonna guess you can in the US). Something like JB Weld, or QucikSteel should do it.

But as i said before its an area that could have catastrophic effects if things were not done properly, id seriously get it done by a professional who will then pressure test it and fix any bits they missed.

[poe21]

As much as having a professional welder do it would solve problems, I don't think myself or the rest of the team would learn a whole lot from it. I would like to say that we had mad skills that allowed us to make the tank ourselves. That being said, I don't think that we will have a problem with it leaking, I was just wondering if there were any precautions people were taking to keep aluminum tanks from doing so.

I keep hearing to use stuff that people are using with steel tanks, but I don't think that it is safe to assume that what works for steel tanks will work for aluminum. I may be off, and those products may be meant for both aluminum and steel, but I would be surprised considering how few motor vehicles come with aluminum tanks.

We will be pressure testing it with my boost leak tester when we get done.

How are you guys making making internal repairs through the tiny fuel filler neck hole? Do you have two piece tanks?

[jd74914]

Not to kick a dead horse or plug for Caswell, but they do advertise their coating as for aluminum tanks. Another company which also specifically states that it works on aluminum is God Standard.

Kreem does not state anything about working on aluminum and from what I have read has peeled on tons of people with steel tanks.

[poe21]

Originally posted by jd74914:
Not to kick a dead horse or plug for Caswell, but they do advertise their coating as for aluminum tanks. Another company which also specifically states that it works on aluminum is God Standard.

Kreem does not state anything about working on aluminum and from what I have read has peeled on tons of people with steel tanks.

No dead horses here... information is welcome. Sounds good, and I'll look them up.

[Chapo]

I am kicking a dead horse, sorry about that. But what do you hope to gain from having students weld the tank them selves? Its great to say that some people would get some welding experience but that effects a limited number of people (1 or 2) and is something that is unlikely to be practiced outside of FSAE (steel welding yes, but AL TIG welding?)
Further to that you can learn a lot from an engineering perspective from talking to a professional welder about how they would prefer to do things rather then having someone who is learning tell you what they require. This whole project is about gaining knowledge and that doesn't necessarily have to come from doing everything your self but can come from discussions about how to do things with the appropriate people.

Thats just my 2c please feel free to tell my im wrong, its all about learning.

[poe21]

YOU ARE WRONG http://fsae.com/groupee_common/emoticons/icon_wink.gif. No really, we had a professional welder come in last year, and talked to him... he welded our aluminum intake manifold. Some good and bad came out of that. First he took forever to do it all. Second he could only do it when he had time, and third, we still had other aluminum things that needed welding. That being said, i did learn about aluminum welding by just watching, and the few tips he so kindly gave us.

On the other hand, for anyone who likes to do anything automotive, TIG welding aluminum is a fantastic knowledge. I myself run a Turbo MR2 in autocross. Doing my own intake piping, intercooler piping, and even small brackets is huge to me. Someone who is less hands on might not care... but FSAE students tend to be pretty hands on.

[poe21]

double post

[Adambomb]

Originally posted by Chapo:
I am kicking a dead horse, sorry about that. But what do you hope to gain from having students weld the tank them selves? Its great to say that some people would get some welding experience but that effects a limited number of people (1 or 2) and is something that is unlikely to be practiced outside of FSAE (steel welding yes, but AL TIG welding?)
Further to that you can learn a lot from an engineering perspective from talking to a professional welder about how they would prefer to do things rather then having someone who is learning tell you what they require. This whole project is about gaining knowledge and that doesn't necessarily have to come from doing everything your self but can come from discussions about how to do things with the appropriate people.

Thats just my 2c please feel free to tell my im wrong, its all about learning.

+1

It's nice to learn to weld and all, but I surely wouldn't develop my skills welding a fuel tank for a race car http://fsae.com/groupee_common/emoticons/icon_eek.gif.

Not to say this is how you or anybody else should do it, but this is how we do it: We have probably 3 people on the team that are fully capable of welding a fuel tank without it leaking on the first try. They got their practice by welding up non-critical parts like heavy dyno intake manifolds, coat racks, and dry erase board eraser caddys (not to mention countless arbitrary bits of scrap). Hell, start with scrap, then cut the welds in half to see how good the welds REALLY are.

If those 3 people weren't here anymore, I would go to the chief ME Dept lab tech, who happens to be an AMAZING welder. If he couldn't help, I would go to the local welding shop owned by a crazy old dude who spent years doing underwater welding for the Navy.

Or I just wouldn't run a welded Al fuel tank...

Again, just my $0.02, what I would do.

[poe21]

Originally posted by Adambomb:
It's nice to learn to weld and all, but I surely wouldn't develop my skills welding a fuel tank for a race car http://fsae.com/groupee_common/emoticons/icon_eek.gif.


If you pressure tested it, I would say that you had little to worry about unless you hardmounted it to the chassis, and a weld cracked during cornering.(which would be stupid to do period, and also I believe against the rules)

We have basically 0 people that are tried and true aluminum welders, but need to weld a gas tank, seat, intake manifold, and oil pan. I'd rather not be paying for every weld someone else makes when we have a nice TIG, and all proper precautions taken. That being said, I did spend a large portion of my summer practicing on scrap just as you have mentioned.

It still seems baffling to me to have the correct equipment, time, and venue to learn to TIG aluminum (not to mention the need) and pay someone else to do it. On the other hand, if I did not feel that we could safely do it, with a pressure test at the end, I would not attempt something that could quickly destroy the car and hurt someone.

just my $0.02

I'm sure everyone would do it differently

[cjanota]

We use the Caswell stuff on our AL tanks and it works great. If you heat up about 20deg above room temp it flows very well into all the nooks.

[Teranfirbt]

An interesting one that works really well for us (and is mentioned in one of Carroll Smith's books, can't remember which) is green "wicking grade" locktite. We've used it to seal pinholes leaks in welded aluminum fuel tanks, radiators, fuel rails, etc that come from imperfect aluminum welding. Just drizzle some on the seams, let it soak into the pinholes and set up, and then wipe the rest away. A little heat goes a long way to curing the stuff.

[Adambomb]

one other thing, going on the Al welding tangent...

This is more of a long-term thing, but the local Miller dealer has been very helpful to us. They send an expert up once or twice a year to do both presentations and hands-on classes where they give individual critiques. That's where all of our good welders got their start.

[poe21]

ha, we aren't so lucky. We have a lincoln electric TIG, and we read books to become better welders. But the old saying, practice makes perfect is our biggest friend. Believe me, we aren't just picking up a TIG and welding aluminum for the first time or even the 20th time on any part of the car, but we aren't professionals by any means.

[exFSAE]

It's really not terribly difficult TIG'ing thin (<0.065") aluminum and making "good enough" welds for a FSAE car.

Couple tricks...

<LI>Don't use pure (green) tungsten. IMO it's a unnecessary carry over from ancient sine-wave machines. The balled ends are terrible for really tightly controlled arcs.
<LI>Ceriated (orange) will do, but 2% Lanthanated (blue) works great on both steel and aluminum. If you can't find it at your local shop, it's easy to get online. Try Arc Zone
<LI>Get 3/32" electrodes, grind them to a POINT, and then put a little blunt spot at the tip.
<LI>Use a squarewave TIG machine, even if it's not an inverter and a 'true' squarewave, it makes a big difference. If you do have an inverter TIG, try bumping the frequency up to 100Hz or so.
<LI>Clean the material well in advance with a wire brushed used on aluminum ONLY, and then usually I use ethanol to wipe away any excess oil
<LI>If the material is pretty clean you can run fairly (70%?) electrode negative bias on your AC setting. This, combined with the blunt pointed electrode, helps make for a pretty narrow and easy-to-control arc. Makes it more similar to steel welding.
<LI>I use 3/32 filler on corner welds, like you'd have on a gas tank. Lets you make quick dabs without having to jab lots of filler in with thin rod. On fillet welds you can even go up to 1/8" filler since you'll have to add that much more material
<LI>As usual, taking the extra 5 minutes in prep to get good fitup makes your welding go 10x faster
<LI>Don't be afraid to use plenty of heat (since the metal will conduct it away) and weld quickly.
<LI>For corners, make sure both edges are exposed, so you easily melt and fuse them both.

Tacking aluminum is super easy with the above tricks. Then you can take a small hammer and tap the rest of the material into place for your longer beads.

Once it's all done, let it cool, then do a quick leak check with water. Find any leaks and you can do quick spot fills.

Even with inexperienced welders you can get pretty decent beads with just a little bit of practice. You'd be surprised. Shouldn't have any need to coat them. The fuel tank on our '04 car is still holding up just fine.

[poe21]

I would agree with almost everything you said there exFSAE.

The Lanthanated tips work great, but we have several times realized that we were welding aluminum with pure tungsten after the fact. Although it may have been a bit more of a struggle, the bead was still acceptable.

We use denatured alcohol to clean aluminum... cleanliness is definitely next to godliness with aluminum welding. Totally agree with 5 there. As well as 8,9, and 10.

I'm not sure whether or not our machine is a true squarewave machine... although I think it is. Either way, it does a great job.

Number 3 is personal preference to me. I like to do just as you do, but some people prefer a little more rounded tip from what I've seen. Either way it's a good beginner's guideline.

Haven't fooled with different size filler rod that much. Probably something I should look at more, especially in tight corners.

Lastly, I would say that every TIG machine is different. We have a monster Miller at work that is different even on the same settings as the one in our shop. Practice, and some time with the machine will help you figure out the best settings you can run.

Practice will help you to work quickly, which will produce pretty and stronger welds. Once the material gets enough heat in it, it will flow very quickly.

[exFSAE]

True, the electrode (and filler) size are preferences. The nice things about 3/32" Lanthanted are that it holds a tip well on AC.. works on steel, where if you dip the electrode into the weld pool it just "tins" it for an easy regrind, and it works even down to 0.035" gauge stuff.

Going to bigger filler definitely helped the speed I could go at and just let me put down much better looking, consistent beads. You just need a quick light dab with 3/32 as opposed to more of a plunge with thinner.

As for the polarity thing.. so long as the welder isn't a million years old, it should be a "squarewave" machine. In reality it's not a perfect square wave, but it's more square than a sine wave. The quasi-squarewave machines you can adjust the AC polarity bias (more positive for cleaning, or more negative for electrode stability and penetration).

Inverter TIG's (the new, fancy, small ones) apparently can do true squarewave AC output and you can adjust the frequency instead of being stuck at 60Hz. I've been told both really help with arc stability, and "makes TIG'ing thin aluminum like welding steel."

Tempted to go in on a Miller Dynasty inverter with a buddy of mine. Pricey though.