Letter 36082

Cooling spots or heat spots on anodized extrusions [Arkansas] 

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I am having problems with grey, black and somtimes white spots on our clear anodize. We believe the problem is coming from the press, we have tried water spray on the extrusions as they enter the runout table, nothing seems to help. A webster hardness checker indicates 9-10 at the spot.Somtimes it helps to rerun through anodizing, more often not.We sent some extrusions to another anodizer and they came back with nom visable spots.Anyone have any ideas?

Thank you,

Mel Hankins
Extrusion plant - Harrison, AR, USA

What makes you think that it is coming from the press rather than the anodizing? It would seem to me that if you took some of the same parts to another anodizer and came back with no spots (that WAS "no visible spots" right? if it was "non-visible spots", then nevermind) it would seem like the problem is more likely to be in your anodizing. Possible areas you may want to look into would be the amount of agitation your supplying in the anodizing bath, and the quality of the air (assuming air agitation) your using - any grease or oil would be a bad thing.

That's just a guess though - I haven't run into that problem before.

Good luck,

Jim Gorsich Accurate Anodizing Inc. Compton, CA, USA

Thanks Jim we will check out the air agitation, we thought it was coming from the press because somtimes the area where the spot is is dead soft or 0 on a webster. They also match the carbon slats on the runout table. Thanks again for your help.

Mel Hankins
- Harrison, AR, USA

Other information that has been discovered is that the shower heads on the press runout table is dropping water droplets on the extrusions after they are shut off and the press has stopped, dripping water on the hot extrusion, possibly causing uneven cooling on the metal, explaining the 10 webster reading.We are still exploring the anodizing process, my guess is both processes are somewhat at fault, because some of the spots do not have contact with the runout table but do have the water dripping onthem sporadically.

Mel Hankins
Extrusion plant - Harrison, AR, USA

I ran an anodizing line for 20 years doing aluminum extrusions. Your problem is coming from the extrusion run out table not having enough cooling fans.Most cooling spots are on thick extruded parts laying on cross members on the extrusion run out table. We had these problems on heavy thick parts until we added more cooling fans.After adding more fans our problem went away.

Raymond Hendrix H&H Equipment Troy, Tennessee

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