[Closed] Stripping paint from an aluminium frame?

best bet is get it blasted and powder coated!!

Heard some misgivings re the temps used in powder coating having an effect upon the integrity of aluminium frames - anyone heard of this?
Also any recommendations for blasting & coating?

Powdercoating isn't that high a temperature - not high enough to mess up heat treating. Or if you just want to shift the paint then a blowtorch and a wire brush...

DO NOT shot blast aluminium-it'll blow holes in it, get it soda or crushed walnut shell blasted.

sorry mate should have said glass bead blasting

Sand blasted a couple of my alu frames - perfectly safe.
Powder coating an alu frame is a no-no though ... too high temperatures. It will non-age the alu .. Prob snap not long after!

If your anywhere near Cardiff? I can sand blast it FOC
email in profile.

I would try some car paint stripper as you may find blasting it to aggressive and make a mess of you frame. Car paint strippers will remove 2pack paints etc so have a bit more strength than nitromorse.
Many frames are powder coated so you should have no problems

The guy who powder coated one of my alu frames wouldn't sand blast it cos he was concerned it could damage thin wall alu tubing. It was chemical dipped instead.

He had no such concerns that powder coat would damage the alloy.

I use a local alloy wheel refurbishing company that use a soft media blast I then hand finish for either a brushed or polished finish, cost me £15.00

bead blasting must be best bet. Sand blasting is NOT to be recommended, roughing up the surface of aluminium like that is a recipe for micro stress raisers for future fatigue fracture

Pretty much every alu bike I sell has a powdercoat finish from the manufacturers - there is absolutely no problem whatsoever in powdercoating alloy frames.

In fact I'd bet you'd struggle to find a painted alu frame that wasn't powdercoat - no-one stove-enamels any more, and two-part is rubbish....

For christs sake don't take a blowtorch to it...!!! :-I
Powder coating is perfectly fine for an alloy frame. Likewise a very light blast to give the paint a key. Chemical strip is the normal approach, it won't hurt it. Nitrimors is a hit & miss affair & it depends on the original paint. I've had plenty of alloy frames powder coated.

Nowt wrong with a blowtorch - as long as you're sensible and only bubbling the paint, not cooking the thing.

Cheers for the help everyone.
Have ordered some POR 15 stripper and I'll see how far I get. (up in the Peak District so a bit of a drive to get to you Mooman but thanks for the offer.)
Once this is done I will investigate the powder coating - seems as many mixed views here as there are elsewhere on the web. May be worth an email to Corratec to see what they say.
Thanks again, more dumb questions will follow, rest assured!!!

Well, there's opinions from people who have been building bikes from the raw metal for 20 years, and there opinions from people who read something on the internet once 🙂

raw metal hey, as opposed to what other metal?

I mean as compared to buying a frame from the far east and bolting the bits to it...

Update: I invoked my rights as a Yorkshireman to do this for as little as possible. The Corratec was cleaned of all paint in quick time by POR15 stripper - £15 for a can and a plastic sprayer (like ones used for indoor plants) not a trace of old paint/decals anywhere. The frame looks in great nick other than one small dent on a chainstay. Pic below of it in the stand. I have some nice etch primer (£8) ready and some paint (leftover from the singlespeed). So let's see how it turns out.

[img] [/img]

Anyone got any tech info on these bikes? before I start cross threading and using the knocking stick to make things fit?

Ive used Nitromors on a few frames and a couple of pairs of fork lowers, worked fine in all instances, it's not pleasant stuff you need to wear a monkey mask and gloves and make sure you have good ventilation, takes a good long while but it does the job and it is quite satisfying stripping a whole frame for yourself.

They've changed nitromors as dichloromethane is now banned in consumer products and most commercial ones too. The new one is less effective. It should get rid of any paint used on a mountainbike, it can shift most of the paints I work with and they are much much much much tougher.

A decent powder coater will know how to prep the frame. There are a miriad of different ways. Often chemical dipping is easiest as reduces the risk of damage.

As alluded too above there are a number of different materials you can blast with. We use chilled iron grit at work and for certain tests have to use 4mm or more thick panels because blasting bends anything thinner. You can use walnut shell, glass, PE, sponge etc. I think they banned sand due to issues with respiritable silica but there are probably similar materials still allowed (or certain sand types).

Heats involved are around 220°C IIRC. Finish is normally ok if the powder coater is good, won't be as good as a conventionally sprayed frame done with automotive paint and an experienced sprayer.

Ok quick update on the Corratec rebuild.
Been in touch with Corratec who have been great with info and are supplying me some new decals but in black and the new style - so it's going to be powder coated brilliant white later in the week.

Rainer at Corratec has been a fountain of information, which leads me to ask a few questions.

The original bottom bracket was a Shimano XTR 1996. BSA 112,5mm - is there a decent modern equivalent - internal or external would be fine, the lighter the better - going for an updated resto using the lightest bits I can afford to get the best out of a very nice frame.

Also for info have been quoted £20 to powdercoat the frame by these guys, they seem to have done plenty before [url] http://www.meadowhallpowdercoatings61.co.uk/ [/url].

So, the Kona was project based upon green, the Corratec is going monochrome - the only pain at the moment is finding a 30.6mm seatpost in white at 400mm long - anyone got any ideas?

Not all alloys of aluminium are heat-treatable.
But high strength aluminium alloys for example 6061 is heat-treatable.

http://www.keytometals.com/article39.htm

"Precipitation heat treatments generally are low-temperature, long-term processes. Temperatures range from 115 to 190°C; times vary from 5 to 48 h.

Choice of time-temperature cycles for precipitation heat treatment should receive careful consideration. Larger particles of precipitate result from longer times and higher temperatures; however, the larger particles must, of necessity, be fewer in number with greater distances between them.

The objective is to select the cycle that produces optimum precipitate size and distribution pattern. Unfortunately, the cycle required to maximize one property, such as tensile strength, is usually different from that required to maximize others, such as yield strength and corrosion resistance. Consequently, the cycles used represent compromises that provide the best combinations of properties. "

The temperature that some plastic powder coat is cured at is approx 180 degrees C.

New frames in 6000 series alloy, if to be powder-coated can be heat treated and plastic / powder-coated in one go.

Although,
"It is not easy to make materials that are both strong and tough. All the [aluminium] alloys have a higher strength and lower toughness than pure aluminium"
Materials engineering, science, processing and design. Michael Ashby, Hugh Shercliff, David Cebon

Correct heat-treating of aluminium alloys can increase the tensile strength but it will loose some fracture toughness in the process. Higher tensile strength is not always as useful as fracture toughness.