# Will powder coating my cranks anneal them?



## dickt3030 (Dec 5, 2010)

I have a set of M960 XTR cranks that I want to get powder coated. Then I started thinking into it, and am worried that I will receive a set of noodles after they have left the curing oven.

Does anybody here have experience with powder coating aluminum, or expert advice in heat treating alloys?

I imagine, from the great stiffness and strength of these cranks, that they were cold-worked to a high degree. Also, I imagine they are probably a very specific alloy, that may or may not be able to be annealed at lower temperatures. I remember seeing the annealing can begin as low as 200*F? What temperature do powder coating ovens get to?

Anybody with experience or knowledge on this subject, your voice is greatly appreciated.


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## SuspectDevice (Apr 12, 2004)

No effect whatsoever. Have at it.


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## chizler62 (Oct 31, 2009)

Never done cranks, but I do frames at 350 for 10 minutes. Some colors need to be baked a couple of times. If you have it done please post results. Interested to know how they hold up .etc.......


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## Rody (Sep 10, 2005)

Chizler,

Most ovens tend to process the powder around 275-300 F for around 20-28 minutes, with thinner material or smaller items with less mass taking less time.

I've done a number of 960 cranks for customers in both powder and ceramic and have not had any issues.

Express your concerns to your contractor and have him review the spec sheet for the powders he uses with you, so you can both proceed with confidence.

rody


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## red dog bikes (Aug 10, 2011)

All the powders I use cure at 350-400 for ten minutes. Including ten minutes of pre-heat time, you're still not exposing them to all that much heat. 

Do those crank arms have some sort of anodize finish on them?


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## skipnay (May 8, 2012)

Not near as think but the alumunim intakes from motors we haven't had any problems. They also powder coat alot of alumunim wheels, alumunim brake calipers, and alot of other alumunim parts.


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## dickt3030 (Dec 5, 2010)

skipnay said:


> Not near as think but the alumunim intakes from motors we haven't had any problems. They also powder coat alot of alumunim wheels, alumunim brake calipers, and alot of other alumunim parts.


Yes, but most of those parts, if not all, that you just mentioned would be cast aluminum, with no cold work. Their grain structure at that cast state is at it's most stable, thus not being affected much by heat. These cranks, and other highly cold-worked or cold-forged aluminum products, are easily affected by heat because it's grain structure wants to return to it's most "stable" state, which is done by annealing. That's the way I understand it, atleast.



> Do those crank arms have some sort of anodize finish on them?


Yes, they have what looks like a dark grey anodize.


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## skipnay (May 8, 2012)

dickt3030 said:


> Yes, but most of those parts, if not all, that you just mentioned would be cast aluminum, with no cold work. Their grain structure at that cast state is at it's most stable, thus not being affected much by heat. These cranks, and other highly cold-worked or cold-forged aluminum products, are easily affected by heat because it's grain structure wants to return to it's most "stable" state, which is done by annealing. That's the way I understand it, atleast.
> 
> Yes, they have what looks like a dark grey anodize.


Thankyou for clearing that up....


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## red dog bikes (Aug 10, 2011)

In many cases you will want to lightly rough up the surface of an anodized part with a scotch-brite pad or something, since the anodize finish acts as an electrical and thermal insulator.


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## SuspectDevice (Apr 12, 2004)

red dog bikes said:


> In many cases you will want to lightly rough up the surface of an anodized part with a scotch-brite pad or something, since the anodize finish acts as an electrical and thermal insulator.


A competent powdercoater will media blast and phosphate dip the part- there will be no problems.

We've powdercoated dozens of anodized frames that are already a matte bead-blast finish.
With those all that's necessary is a phosphate dip.
Any powdercoater would laugh at the idea that it's sketchy to powder forgings.

(disclaimer- I have somewhere around 100 aluminum frames a year powdercoated and regularly re-powder 20 year old Yetis)


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## o1marc (May 31, 2012)

The annealing process for aluminum requires that it be taken to the neighborhood of 700f+ for 4-6 hours then bathed in a solution at close to 900f for an hour or so and then another cure process in excess of 700f for more hours. Taking the substrate to the needed temp of 400 for 10 minutes does not negatively effect the part at all.


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## mtnbke (Jun 4, 2008)

Rody said:


> Chizler,
> 
> Most ovens tend to process the powder around 275-300 F for around 20-28 minutes, with thinner material or smaller items with less mass taking less time.
> 
> ...


Those are low temp powders...MOST powders are closer to 400 degrees, not three hundred!

Yes heating heat treated and cold forged aluminum frames and components will affect the heat treatment. Yes it can anneal the aluminum. To what degree is a crapshoot.

Most have no problems doing it mind you, but to categorically say that the grain and temper of the aluminum isn't changing is absurd.


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## mtnbke (Jun 4, 2008)

o1marc said:


> The annealing process for aluminum requires that it be taken to the neighborhood of 700f+ for 4-6 hours then bathed in a solution at close to 900f for an hour or so and then another cure process in excess of 700f for more hours. Taking the substrate to the needed temp of 400 for 10 minutes does not negatively effect the part at all.


Not true.

Easton does NOT recommend that frames be powder coated, as the heat treatment can be compromised between mid-200s and high 300s. Most powders back around 400 degrees to 420 although more and more there are low temp powders coming out (each alloy has its own characteristics, it is absurd to post the generalizations that you did).

Even Leonnard Zinn couldn't give a definitive answer on this. He best advice was to try it.

That thousands of people have powdercoated vintage aluminum frames is not representative that those frames maintained their stiffness and heat treatment. The bikes weren't going to become simply noodly like steel. To represent that there is no fundamental change in the strength or stiffness is just disingenuous. Anecdotal accounts are worth what you pay for them.


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## whydomylegshurt? (Jul 28, 2004)

mtnbke said:


> Not true.
> 
> Easton does NOT recommend that frames be powder coated, as the heat treatment can be compromised between mid-200s and high 300s. Most powders back around 400 degrees to 420 although more and more there are low temp powders coming out (each alloy has its own characteristics, it is absurd to post the generalizations that you did).
> 
> ...


Kind of digging into an old thread here, but I don't believe everything you have said is true. To start with, Easton doesn't recommend powder coating Scandium frames. They are ok with powder coating their standard 6061 and 7005 series aluminum frames.

Second, the assumption that the heat treatment of the aluminum would have an effect on the stiffness of the frame is flawed. The modulus of elasticity is not changed by the temper of an aluminum alloy. For example, the modulus of elasticity for 6061 aluminum is 10,000 Ksi in the T0, T4 and T6 condition. The strength of the material is changed dramatically by the heat treatment, but not the stiffness.


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## mtnbke (Jun 4, 2008)

You are suggesting that oversized thinwall aluminum frames do not get some of their stiffness from the heat-treating of the frames? To make that argument you are suggesting that the frames didn't need to be heat treated in the first place to improve the strength of the thin wall oversized designs. Stiffness of an aluminum bicycle frame is a function of its strength. 

Take some data. Compare raw aluminum stock that has minimal strength. Do some deflection tests as a baseline for stiffness. Heat treat that same aluminum stock. Tell me what your deflection numbers show.


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## whydomylegshurt? (Jul 28, 2004)

mtnbke said:


> You are suggesting that oversized thinwall aluminum frames do not get some of their stiffness from the heat-treating of the frames? To make that argument you are suggesting that the frames didn't need to be heat treated in the first place to improve the strength of the thin wall oversized designs. Stiffness of an aluminum bicycle frame is a function of its strength.
> 
> Take some data. Compare raw aluminum stock that has minimal strength. Do some deflection tests as a baseline for stiffness. Heat treat that same aluminum stock. Tell me what your deflection numbers show.


Funny you should mention taking some data, I'm currently running and Instron 3384 tensile test frame with 2219 T86 aluminum samples. It is what I do for a living.

I am not suggesting the heat treating aluminum frames is unnecessary at all, it is required to gain the strength needed for a thin walled tube to handle the stress. What I am saying is that the stiffness of the material is not affected by the temper. The stiffness, or stress/strain relationship, or modulus is the same in each temper. Heck, it is pretty much the same for all aluminum alloys. Raw aluminum is 9800 ksi, 2219 is 10700 ksi, 6061 is 10000 ksi.

So the stiffness of an aluminum bicycle frame is not a function of its strength, it is a function of the material and the diameter of the tube used as well as the design of the frame. Heat treating of the frame is required to create a light weight frame that is strong enough to ride, but it does not change the stiffness.


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## mtnbke (Jun 4, 2008)

whydomylegshurt? said:


> Funny you should mention taking some data, I'm currently running and Instron 3384 tensile test frame with 2219 T86 aluminum samples. It is what I do for a living.
> 
> I am not suggesting the heat treating aluminum frames is unnecessary at all, it is required to gain the strength needed for a thin walled tube to handle the stress. What I am saying is that the stiffness of the material is not affected by the temper. The stiffness, or stress/strain relationship, or modulus is the same in each temper. Heck, it is pretty much the same for all aluminum alloys. Raw aluminum is 9800 ksi, 2219 is 10700 ksi, 6061 is 10000 ksi.
> 
> So the stiffness of an aluminum bicycle frame is not a function of its strength, it is a function of the material and the diameter of the tube used as well as the design of the frame. Heat treating of the frame is required to create a light weight frame that is strong enough to ride, but it does not change the stiffness.


Get a old 3.0 Series Cannondale frame, then get another in the same size from the same year. Cheap at a swap or off craigslist. Have one powdercoated but don't use low temp powder.

Then use your test frame to measure stiffness and deflection at the bottom bracket. Post your results in this thread.


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## whydomylegshurt? (Jul 28, 2004)

mtnbke said:


> Get a old 3.0 Series Cannondale frame, then get another in the same size from the same year. Cheap at a swap or off craigslist. Have one powdercoated but don't use low temp powder.
> 
> Then use your test frame to measure stiffness and deflection at the bottom bracket. Post your results in this thread.


I think you and I both know I'm not about to waste my time and money hunting down old bike frames to be powder coated and tested. From your comment I gather that you feel your old 3.0 series Cannondale was damaged by powder coating and this is more of an emotional topic than a logical discussion of material properties.

For anyone else who is interested in learning a bit about materials:

-Stiffness of the material is not a function of temper or strength.
-The modulus of elasticity is the "stiffness" of a material
-If you heat treat a frame to a T0 or T4 or some other temper besides T6 it will be MUCH weaker but no less stiff.
-If you were to ride a frame in the T0 condition it would most likely feel less stiff due to the fact that your are putting more stress through the material than it can handle and are yielding the material causing plastic deformation. If you have plastic deformation in your frame you have far bigger issues than the feel of the bike.


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## mtnbke (Jun 4, 2008)

No. Your entire argument is based on presumptions and assumptions. I've never had a bad experience, nor have I been ignorant enough to powder coat an aluminum bicycle frame that had been heat treated.

You are thinking about non-engineered structures.

Less talk more tests. For someone claiming to work with a testing frame you sure are posting a lot. For your information, and everyone else's, this data has already been done. 

Bicycling magazine did it way back in the day using their "tarantula" testing frame. The Cannondale series 3.0 was the stiffest frame ever tested which is why I chose that one.

Even someone all talk and no data like yourself probably wouldn't fudge the numbers upon seeing them. You'd probably have the intellectual honesty to admit you were wrong.

I've seen the raw data, non-heat treated frames are less stiff. AS TESTED


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## whydomylegshurt? (Jul 28, 2004)

mtnbke said:


> No. Your entire argument is based on presumptions and assumptions. I've never had a bad experience, nor have I been ignorant enough to powder coat an aluminum bicycle frame that had been heat treated.
> 
> You are thinking about non-engineered structures.
> 
> ...


I am presenting data, the modulus of 6061 aluminum is 10000ksi in T0, T4 and T6. This is the stiffness of the material. If you want to see this in writing please go to the following three links to see the material properties of 6061 in T0, T4 and T6.

MatWeb - The Online Materials Information Resource

MatWeb - The Online Materials Information Resource

MatWeb - The Online Materials Information Resource

I am actually working on a tensile test frame now, and according to ASTM E8 test standards failure should occur in 3 to 6 minutes, providing lots of time to surf the internet durring the test cycle.

If bicycling magazine published raw data (a link would be great if you have one) that showed a change in stiffness due purely to heat treatment they must have been applying enough load to yield the frame. Once you have reached the yield point of the material you are causing plastic deformation which means your frame is no longer in alignment. This is a function of the strength of the material not the stiffness. In the elastic load range the temper of aluminum will not change the stiffness.

If you have data to share that can disprove my understanding of materials I would love to see it. I don't mind admitting I'm wrong but in this case I don't believe that I am.


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## whydomylegshurt? (Jul 28, 2004)

By the way, it was an assumption that you ruined a Cannondale frame. So in that respect I do admit to being wrong. Sorry if that post was a bit snide.


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## Busdriver1959 (Jul 1, 2011)

Using data generated by Bicycling Magazine may not be the best plan. These are the same people that, years ago, concluded through their own aero testing that a rider will lose 8 seconds on a 40K time trial each time they drink from their waterbottle. Now, I was a business major so I'm far from being an aero expert but I think their data and conclusions were a load of crap. I don't think I would lose 8 seconds doing something that takes less than 8 seconds to accomplish. It does'nt pass the "does it make sense" test. Just my 2 cents worth.


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## SuspectDevice (Apr 12, 2004)

Once again- powdercoat the hell out of your cranks. 
Do you guys have any idea HOW MANY powdercoated aluminum cranks are sold every year?
Hundreds of thousands. Maybe millions?


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## aBicycle (Jun 13, 2012)

Why don't you just call shimano and ask them?


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## TacoMan (Apr 18, 2007)

A little late here, but I once ruined a 2024 race car hub while heating it to remove the bearing races. I had trouble with one of them and took it up to 425F and it softened the material. The other I heated to 350F. Put both of them back on the car and the one that was over heated had the race pound itself loose due to loss of strength in the material.

Found this:

http://www.google.com/url?q=http://...UQFjAG&usg=AFQjCNG8aXAkoEmymbP6ArrI1Gwu90c01g

The effects of curing temperature, based on new, low-temperature powder coating methods and traditional
high-temperature powder coating methods, were studied. Heat-sensitive aluminum alloys (2024-T3, 6061-
T6, and 7075-T6) were subjected to two different heat-treatment cycles, which were based on temperatures
of 121 and 204C. Findings indicate that although both cure temperatures achieved powder coatings
adhesion and thickness appropriate for industrial uses, the high-temperature cure treatment negatively
affected the mechanical properties.

3. The effect of 1, 3, and 5 cycles of low-temperature
(121C for 30 min) heat treatment was almost negligible
on the mechanical and electrical properties of 6061-T6,
2024-T3, and 7075-T6 alloys.

4. The effect of 1, 3, and 5 cycles of high temperature 204C
for 12 min was significant: 6061-T6 and 7075-T6 showed
overaging trends (7075-T6 showed more pronounced overaging)
while 2024-T3 showed age hardening trends.


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## mtnbke (Jun 4, 2008)

Thanks for finding that. I'm no scientist but it seemed pretty obvious that heating heat treated aluminum compromised the heat treatment and weakened the metal itself. 

Read: Turns a stiff and strong fantastic frame into something brittle and noodly (or rather noodlier as much as aluminum can actually be), and something, perhaps, dangerous.


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## TrailMaker (Sep 16, 2007)

Rep-worthy stuff, Taco! :thumbsup:

Makes me wonder about PC-ing other stuff like rims, which is quite popular these days. I'm considering it myself, but I do not know what alloy they use for such parts, and it occurs to me to wonder first or risk wasting money. Do they use non heat treated alloys like 3003 or 5052, and count on the forming process for work hardnening them? Seems regardless of the alloy used, the PC process stands to anneal the metal if done improperly.


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## whydomylegshurt? (Jul 28, 2004)

3. The effect of 1 said:


> I don't fully understand point 4 of their conclusion. Looking at the provided data the only material with significant degradation of properties was 7075. The results for 6061 and 2024 changed very little. You are looking at less than 3% change in ultimate and a 9% increase in yield after cycling the part five times. From the data provided I see no reason to not powder coat the aluminum part.


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## TacoMan (Apr 18, 2007)

You can find more data on it. I learned the hard way, so the risk is up to you. Took a while for me to gather information about it back then since the internet had not begun yet. Much easier now. I just know I will never heat a critical part over 325F.

If the PC shop uses the low temp cure, then you should be ok.

This paper shows how 6061-T6 goes from tensile/yield of 45/40 at 350F to 29/21 at 450F, strength drops the longer it is heated.

http://www.google.com/url?q=http://...QQFjAA&usg=AFQjCNFBx2GGqtc4ah7fn_bhtN9mCDBxDQ


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## SuspectDevice (Apr 12, 2004)

Repeat:
Millions of aluminum frames get powdercoated every year, as do millions of crank arms.


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