Anyone have any evidence or thoughts on how many times a steel frame can be powder coated before if starts to affect the integrity of the material? Thanks!
As long as they arenāt aggressively media blasting it every time I would say quite a few times.
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Use a powder coater who is familiar with thin walled bicycle tubing and they will use media that minimizes impact to the tubes. I have had a couple coated 3x and measured the tubing after the blasting with nearly immeasurable difference. I also used a powder coater who showed me an alum frame that his āapprenticeā blasted and the frame was warped and destroyed. He had to buy the guy a new frame!
yikes! i have also read that the baking process will affect the heat treatment of aluminum frames.
With most powder coating happening between 350 and 410 F there wonāt be any significant change to the steel. For aluminium you are at the āagingā temperature where both 6000 series and 7000 series alloys are aged (precipitation hardening) to make them stop being loose and floppy (annealed) and start being stiff and springy. Now Iām not the aluminium guy so donāt quote me on this but I think the aluminium has already gone for a full transformation at the factory when it was heat treated so you arenāt changing any mechanical properties with a powder coat. Or, if you are changing anything, itās not significant. A heat-tratment for aluminium lasts hours, or all day, or something like that whereas the powder coat time will only be 7-15 minutes at bake temperature.
I have always been wary of blasting off powdercoat, since it is so much less āchippyā than enamels.
Consequently, I have all frames chemically stripped, rather than abrasive blasted, then surface finished with soda or glass bead to clean off any remnants in the nooks.
On aluminium frames, blasting is definitely not advised, as the base metal is so much softer. This tends to cause ripples in the surface as the PC resists the blast media. Also, there tends to be a lot of heat buildup and stress relieving, which causes warping of thin walled tube or sheet material.
There are some alloys that could be adversely affected at PC temps, but not the 6061 or 7005/7020 used in most bike frames. The heat cycles typically involved in powder coating (15mins @ 180C) do not over-age or affect the temper of aluminium frames. Anything above that length of time, or 200C will age 6061, but 7005/7020 has an exponential flattening of its response, so additional cycles have almost no effect on mechanical properties.
All the best,
Dan Chambers
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Agreed. My powder coater stripped powder coat chemically. The disaster with media blasting was stripping paint off.
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