Can not find anything about cracking after respray. or powder coating. How exactly does painting change aluminium or steel to make it crack?

The pic definitely is cracked though.

Can be welded by sheet metal fabricator, shouldn’t cost to much and if done properly is no more likely to crack than when it was new.

Bit of helicopter tape round it and you’ll be fine 😉

How exactly does painting change aluminium or steel to make it crack?

raw aluminium is very soft and weak. stuff like copper is added in small amounts to make it harder/stronger – the alloy strengthening effect is ‘activated’ by heat. typically at around 200degrees (or more) for a few hours.

the hotter the process, the harder the alloy becomes.

the longer the process goes on for, the harder/stronger the alloy becomes.

unfortunately, the harder/stronger the aluminium becomes, the more brittle it becomes – it’s more likely to crack.

(hard = brittle = bad)

i don’t know enough about powder coating to say if it’s hot enough or lasts long enough to have a significant effect on the properties of the alloy – but i guess it’s a concern…

(i’d want to do my homework before i’d tell anyone it was definitely ok)

alloy strengthening effect is ‘activated’ by heat

No its not. Alloy is alloy (subject to its specific composition, and basic characteristics of course)

Heat treating allows the re-alignment of a metals crystalline structure, and can alter the size and shape of those crystals. The duration of the bake can also make a difference.

You can heat treat a pure element (iron for example) and change its characteristics in the same manner.

Low temperature powder coating that should be used for tempered aluminium is between 100 and 120 usually – this won’t affect the alloy in any way. You need a bit more to re-temper aluminium last time I made enquiries of a frame manufacturer about this, I was told 175 celcius max.

So, my frame was put in the wrong oven by the powder coaters and taken to 400 degrees. It didn’t come out superhard by the way, it lost all its temper, and was malleable as roofing lead.

No its not. Alloy is alloy (subject to its specific composition, and basic characteristics of course)

TBH as materials engineer with 15 years experience of heat treatment of steels and Al alloys I though Awhiles description was pretty good explanation to the layman.

I think Awhiles was trying to simplify how he explained typical heat treatment of a bike Al alloy, which would be something like a 6061, a precipitation hardening alloy, and the heat does “activate”the strengthening mechanism. It’s known as age hardening, or ageing. A major problem in Al alloys is over ageing where they are heat treated for too long. This is what may happen if you powder coat your frame.

I would always advise against powder coating of Al alloys unless you are very famailiar with how it was heat treated and how accurate the temp control of the powder oven is.

Science officers tale is not surprsing at all as powder coating is often not subject to as tight controls as heat treatement.

Ok, Avoid powder coating. Your Ali frame can be made from a large number of different alloys and a similarly large number of different heat treatments. Plus some frame builders use post weld heat treatment and some do not. Powder coaters often have cheap simple ovens which have much less temp control and their processes are aimed at quality powder coat finish and durability, not frame grain structure care.

It is true that there are low temp powder coat systems, even 150 degree heat can affect the strength of your frame if it is a particular alloy variant. Do you know, does the powder coater know. BIG RISK.

Respraying in no way affects your frame. Good frame sprayers know to keep paint oven temps low and you can just dry your frame in warm air not much above room temp. Heat is mostly used to cure paint faster for productivity reasons and to make it harder quicker for movement on production lines etc.

Get it painted by a pro with 2 part polyeurathane paint as used on aeroplanes. it is hard as hell(can with stand dust erosion at 600mph) and even affords some dent resistance. I am sure someone will doubt this but I fix planes for a living so know what I am talking about.

Hard luck on buying a cracked frame.

Rockitman where are you based? I’m in Chester and for the princely sum of a 4 pack I’ll have one of my industrial radiographers (the beer will be for him) X-Ray the frame for you and then you’ll know for definite what the STW collective already suspects!

Ohh now there is an offer.

Get it painted by a pro with 2 part polyeurathane paint as used on aeroplanes. it is hard as hell(can with stand dust erosion at 600mph) and even affords some dent resistance. I am sure someone will doubt this but I fix planes for a living so know what I am talking about.

I develop paint for aircraft

I also investigate impact damage prevention on composites using coatings 😉

PU isn’t ‘hard’ it is ‘tough’. It is was hard it wouldn’t be so resistant to sand erosion.

Dent protection – need quite a thick coat to protect from dents so I wouldn’t rely on paint alone to protect a down tube from stones and branches. The paint often just masks the visual appearance of the dent as bare metal shows up defects better.

But yes, PU is the best paint, or at least lacquer to use for a frame. You can even buy PU lacquer in halfords now if anyone is DIY spraying a frame or wheels etc. Normal paint is pretty crap compared to it for harsh environments.

My alloy frame was powder coated by kinesis when made. I would not get it powder coated again as the heating will alter the aluminium. Kinesis will have heat treated it after welding due to the local effect of the welding.

There has been a lot of problems with slender spoke alloy wheels, especially light weight ones, being powdercoated and then failing. I use an etch primer on aluminium and then apply the paint. I may also use an adhesion promoter on top of the primer before the paint depending on how strong a bond I want.

If into de void is too far you can try this. gently remove paint with fine wet and dry not metal blade or scraper. If crack still visible it is 99% certain to be a real one. for 100% turn frame upside down so crack is below you. cover in blue ink as purchased from art supplies shop. leave for 20 mins. wipe off excess carefully with dry cloth damped with nail polish remover. once dry, coat area with talcum powder or better still french chalk. if cracked the chalk will draw ink from the crack.

This is a home version of a commonly used method in aircraft damage assessment called dye-penetrant testing.

There has been a lot of problems with slender spoke alloy wheels, especially light weight ones, being powdercoated and then failing

Do you mean car wheels? If so this is v interesting as there are lots of companies offering to recon your alloys and they all seem to use powder coating. Had me worried. Got any links about the wheels failing post powdercoat so I can look into this further AndyL?

I told you someone would doubt. AndyL definition of hardness. Ability of a material to withstand scratching indentation or abrasion. Toughness is resistance to deformation or bending. PU has elements of both, obviously relative to the fact that it is a paint not a cladding or mineral coating, hence the word some in my statement. I agree not to rely on it alone but it is way better than acrylic. The work you do sounds interesting, there is huge pace in the use of composites in my field at present but not all the repair solutions are well thought thru in terms of practicality.
Cheers

Scienceofficer – Member

“alloy strengthening effect is ‘activated’ by heat”

No its not. Alloy is alloy (subject to its specific composition, and basic characteristics of course)

er, yes it is.

your homework: read about ‘solution / precipitation heat treatment of aluminium alloys’

i want a 500 word summary submitted by the morning.

x

You’re slow to call me on that one. I’ve been corrected twice aleady. 😉

alright, alright, i’ve been busy!

This is STW you know. You’ve got to be on the ball! 😛

Hi,

Sorry for the radio silence, been trying to sort this out with Orange. Have to say they’ve been really helpful, great customer service, particularly considering they have no liability.

I scratched the paint off last night and it looks like it might just be a crack in the paint… No evidence of a crack underneath that. Would upload a photo but no access to picassa at work and I didn’t do it successfully last time! Can email to someone though if they would like to upload.

I’d like to still get it checked to be 100% sure.

into de void… I’d love to take you up on your offer if it’s still available but no contact details in your profile. I live in Manchester & work in Preston so Chester ain’t too far away. When would suit you?

Thanks for the feedback guys. If it turns out it isn’t cracked, I will be mighty relieved. I am due some good bike karma having done someone a decent favour recently so hopefully I can call on it now!

If you can get orange to check it themselves thats your best option – even if they have to take the paint back to check it, im sure they will do you a good deal on a respray. If you really lucky and it is cracked they might well repair it for you.

How did you remove the paint? Really need to chip / flake it off so it comes away from the metal clean. Seen a couple of cracks missed as the paint was sanded / scratched off in such a way that it effectively filled the crack making it practically invisible.

I took all the paint back with a blade… so should be OK.

Not sure I’d risk having it resprayed again. I’ll just touch it up with nail polish if it isn’t cracked!

<pedant mode>

Toughness is resistance to deformation or bending

Stiffness is the resistance to deformation – toughness, in a material sense, is defined as the ability of the material to resist cracking/arrest crack propagation.

</pedant mode>

Rockitman, I’m still happy to do a test on the frame if you’re still happy to provide booze! If you put your e-mail in your profile I’ll fire you my contact details.

More than happy to provide the booze mate… what do you and your associate drink?

Have included email in contacts but also here:

georgedthompson at hotmail dot co dot uk

Cheers!

There are some “crack detection” products which work well. (3 cans of cleaner, penetrating dye and activator) tiny cracks magically turn red before your eyes..

probably more expensive than the booze though

edit: the one i have used at work is “flawfinder” 57 quid 😯 http://www.my-tool-shed.co.uk/p16123/Rocol_Flawfinder_System_Kit_63181/product_info.html?utm_source=google&utm_medium=shopping&utm_campaign=allprods

Rockitman – My associate is a man of exquisite taste so it’ll be Kestrel Supa Strength out of a brown bag for him! I’ll settle for a coffee the next time you venture down to Llandegla.

aeromarcuk – Member
I told you someone would doubt. AndyL definition of hardness. Ability of a material to withstand scratching indentation or abrasion. Toughness is resistance to deformation or bending.[b] PU has elements of both, obviously relative to the fact that it is a paint not a cladding or mineral coating, hence the word some in my statement. I agree not to rely on it alone but it is way better than acrylic. The work you do sounds interesting, there is huge pace in the use of composites in my field at present but not all the repair solutions are well thought thru in terms of practicality.
Cheers

sorry but those definitions are a bit misguided.

Hardness: resistance to scratching and indentation yes.

Abrasion – depends completely on the type of abrasion. Pin on disc? Taber? Solid particle? slurry? etc etc. In the latter two PU and rubber will often outlast steel.

toughness is most definitely not resistance to deformation or bending. That is modulus.

toughness is the ability to take deformations and impacts and not fail. PU is tough because it can withstand impacts without fracturing. The reason it does so is it is able to deform but it also has high strength so it doesnt break. A plastic bottle has low stiffness but you can drop it and it won’t break. A glass bottle is very stiff but will shatter. Epoxy resin is quite fragile and low modulus. Stick some fibres in it and it is tougher and stiffer.

Sorry for the radio silence, been trying to sort this out with Orange. Have to say they’ve been really helpful, great customer service, particularly considering they have no liability.

Doesn’t matter – either way the PR damage is already done. The pic posted at the beginning of the thread is going to prove to every know all armchair expert on planet internet that all Orange bikes ever made snap into a thousand pieces at the first sign of a new born gnat sneezing in a neighbouring town.

True that, the armchair engineers are very quiet!

(To be fair, i’m sure we all learned something from the second picture)

IDV has the only answer, x-ray it.
For anyone not fortunate enough to live near him ask any mates in the RAF very nicely, they have the machines for it too, had one of my frames x-rayed at RAF Leuchars. (good PR for Marin, three weeks later I had a brand new Mt Vision Pro 🙂 )

Rockitman I’ve e-mailed you some info, hopefully my payment into the ‘MTB-good-karma-bank’ will be credited soon as I’m in need of some since breaking my thumb (The Beast at C-Y-B bit me) and being off my bike for 3 weeks now