Powder coating a frame

[Racer X]

Okay sorry bad wording. Lots of Santacruz's are coming out "anodised," are they prone to this same sort of failure.

[TokenFreak]

Dont fool yourself that paint on a frame is heavy Rob. Remember the paint gets sprayed on and not brushed on so it is only a couple of microns thick to say the least. Take a raw frame and weigh it before and after spraying it and you will see you cant even tell the differance on a scale ...

[Johan Bornman]

Okay sorry bad wording. Lots of Santacruz's are coming out "anodised' date='" are they prone to this same sort of failure.

[/quote']

 

In that case, the answer is simple. They don't get away with it. They simply pass the risk on to the rider. Maybe they offer a frame gaurantee, maybe they don't. However the risk is not financial but your arse.

 

Anodising is a bad idea and as I explained, the lighter the colour, the lower the risk. However, there isn't such a think as a no-risk anodise.

[Racer X]

Okay I think I'll stick to paint

[Dirtbreath]

Johan, many top end mountain bike frames are anodised, Santa Cruz, Yeti, Titus. Are you saying that there frames are potentially weaker than their sprayed counterparts?

[Johan Bornman]

Johan' date=' many top end mountain bike frames are anodised, Santa Cruz, Yeti, Titus. Are you saying that there frames are potentially weaker than their sprayed counterparts?[/quote']

 

 

Kexactly

[Dirtbreath]

So I might as well throw the wife's Yeti away then!

 

Tried to do some research on this thing and could only find bad reports on Titanium frames, not Aluminium. I would like to phone those guys in Pretoria and get their story.

[Johan Bornman]

So I might as well throw the wife's Yeti away then!

 

Tried to do some research on this thing and could only find bad reports on Titanium frames' date=' not Aluminium. I would like to phone those guys in Pretoria and get their story.

[/quote']

 

Yup, dispose of it immediately and responsibly. In fact I'll come and collect it and do the job for you.

 

I'll send you a study done on this to your e-mail address.

 

[DawieO]

Hi Johan,

 

I'd also like to see that study if possible?

 

Ellsworth also anodize and before I lay out that kind of money I would like to see the facts.

 

 

[greatwhite]

Johan is right about the anodising potentially being a cause of failure, but remember that an anodised bike rim that cracks around the nipple hole is a highly concentrated and rapidly cycling load. Loads on frames are:

1. usually distibuted over a greater area

2. subject to a great deal less fatigue cycles.

 

In a nut shell, paint is a bit better, but most poeple will be hard pressed to ever push a frame to an earlier failure as a result of the anodising - think of it this way: do you think all these manufacturers would put their reputation at risk and possibly expose themselves to legal action?

[Johan Bornman]

Johan is right about the anodising potentially being a cause of failure' date=' but remember that an anodised bike rim that cracks around the nipple hole is a highly concentrated and rapidly cycling load. Loads on frames are:

1. usually distibuted over a greater area

2. subject to a great deal less fatigue cycles.

 

In a nut shell, paint is a bit better, but most poeple will be hard pressed to ever push a frame to an earlier failure as a result of the anodising - think of it this way: do you think all these manufacturers would put their reputation at risk and possibly expose themselves to legal action?

[/quote']

 

You've put it elegantly and I agree with your general assessment of the risk.

 

I have come across one frame though that was definitely amputated by anodising. It was as one water bottle cage bolt on the downtube. It appeared to me at the time that the top surface of the welded-on lug that houses the thread wasn't flat. As you tighten the water bottle cage, the frame gave way and cracked the anodising, which very quickly propagated into the frame. It is easy to suggest that the frame cracked there because of bad heat treatment but I doubt it, I saw lots of crazing on the anodising to to suggest it was at fault.

 

One of the reasons I advised against it in this thread is because of the nature of the anodising company employees. The won't know about this and will easily give you black if you want black. I've taken bike stuff in to anodise and not once did they ask me if these components were structural.

 

Paint can't harm anyone and no-one can botch it enough to cause a hazard.

 

 

[GoLefty!!]

Anodising is usually not the cause of frame failure but rather it does bring out the imperfection in either the material or the manufacture technique.

 

It IS used on all structural aluminium components including the cyclinder walls of modern aluminium engine blocks where the cyclinder bore is hard anodised.

 

However if the frame material already had an imperfect grain structure then anodising it will result in a weak point where the crack formation can start.

 

In Aircraft parts and engine blocks the manufacturers take a lot more care in ensuring correct heat treatment and grain refinement than the manufacturers of bicycle frames.

 

People like Santa Cruz and titus and Ellsworth, hopefully select thebest tubes and take extra care when heatreating frames to be anodised.

 

If you do not know the condition of the material inyour frame then it's prpbably a bad idea to have it anodised.

 

Painting it as JB says is the least problematic route to a new look.

[Johan Bornman]

Anodising is thin, in the order of one micron and has no effect on imperfections already in the metal.

Anodising is used in engine parts such as pistons and cyclinder walls. However, these parts are hardly structural in a spaceframe sense of the word. On cyclinder walls it is used to decrease friction by two different modes. 1) It is very smooth and 2) It readily cracks at temperatures well below the boiling point of water. These cracks (crazing) don't peel and because there is no flex at those cracks (note, inside cylinders it cracks from temperature, not flex) don't propagate deeper. The cracks trap molecules of oil and help lubricate the cylinders.

 

Interesting to note, even on a big V8 engine, these cracks trap only a fraction of a drop of oil with each cycle. Unfortunately this treatment calls for a new engine block should you require an engine overhaul.

 

The other application for anodising on engines is on piston tops. Anodising is an excellent heat insulator and it helps prevent burn-through on high performance engines. However, it drastically reduce engine life, ironically since the pressurised oil squirting past the journal bearings now cannot cool the pistong right through.

 

The ban of anodising on space-frame structures by Aviation Authorities world-wide is well documented and well researched.

 

The other use of anodising is in the construction industy where so-called structural aluminium is anodised. However, structural aluminium (read windoframes and doors) is hardly structural. It's merely an architectural/construction term with no real engineering foundation.

 

Anodising does weaken structural components by the mode I've already explained. Whether this is relevant on a bicycle frame is probably moot. To keep it safe, the manufacturers stick to thin, cosmetic anodising. If only the rim manufacturers would now get to understand this phenomenum.

 

 

 

 

[GoLefty!!]

Johan, the main spar on jet fighters is aluminium and that is Anodised. It is also highly stressed and very structural.

 

The type of anodising used for aviation applications is less corrosive and also much thinner than that used for cosmetic applications.

 

It is important to understand that there are different types of anodising processes and that they have different applications.

 

Never the less, I still think anodising a bicycle frame is a poo idea.