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Join Date: Jan 2015
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Painting Corner Mitre Joints in Aluminium

04/23/2015 7:15 AM

Could anybody offer some assistance. I'm having difficulty painting over corner mitre joints using a powder coating process. The mitre corners are saw cut into aluminium. The angular cut is quite accurate but if held up to the light there is a small gap <0.1mm. The paint does not cover the gap unless filled with some kind of filler material. I have tried using spray on primer \ fillers to fill the gap but like the paint the gap remains. I assume the paint travels up the gap by capillary action.

Has anybody else got to grips with this and found a solution?

Thanks

Terry

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#1

Re: Painting corner mitre joints in aluminium

04/23/2015 7:31 AM

How are the parts joined (i.e. held together)?

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#2

Re: Painting corner mitre joints in aluminium

04/23/2015 7:37 AM

If your intent is to fill the gap with powder coat I don't think it will work.

Powder coat, by its nature, is drawn to the metal by an electrical charge (not capillary action), so paint will be drawn to either side of the gap and unless you really pile the paint on, it will never bridge that gap. However, too much paint has other issues.

You need to fill that gap with something conductive, but I don't know what that substance is. or simply weld it.

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#3

Re: Painting Corner Mitre Joints in Aluminium

04/23/2015 8:02 AM

Have to have a really good saw so you can not see the gap. There are imperfections in the cut. Do to saw stroke, blade flex and some do to vibration on the material as it's cut. Not knowing how many of these your trying to do it's hard to recomment a solution. If just a few. Gasket the miter with some paper. This should take care of those imperfections in the cut. The paper will draw paint in to itself. Making it some what ridgit when dry and bonding the edges of the miter. The downer is you have to dress the miter up where the paper sticks out before painting.

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#4

Re: Painting Corner Mitre Joints in Aluminium

04/23/2015 9:31 AM

We do a lot of powder coating here. It is true the powder clings to the parts thru static electricity until it melts in the furnace. But the powder can close holes and gaps, the powder goes on thick and I would surmise it would close a gap up to .03125".

Send a part out for powder coating and see what happens.

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#5

Re: Painting Corner Mitre Joints in Aluminium

04/23/2015 10:10 AM

Talk to your powder-coater, They will have a solution. They deal with things like that daily!

We send a lot of stuff out to the local powder-coat company.

However, even with the powder being laid on a bit thicker on the corner joint , you will still see the joint/corner telegraphing through the coating after it comes out of the oven!

One part I dealt with about 10 years ago had to have the joint TIG welded and sanded smooth, it added $5.00 to each $38.00 part. But seeing as we were selling the "base" part for $450.00, it didn't really impact the bottom line. It was a very low production part.

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#6

Re: Painting Corner Mitre Joints in Aluminium

04/23/2015 11:09 PM

You may be able do this by 'bridging' the gap with a backing plate. A simple piece of scrap aluminium wedged behind the joint. See #2. AH explains about the static elec process. The bridging part MAY alter the static field and allow the powder to collect at the join. As it is, the static fields are radiating at the edges and interfering with each other. If you want to get powder IN the joint you may be able to mix Gum Arabic with powder and paint it on the edges first. P.S. i have not tried this, experiment first.

Jim

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#7

Re: Painting Corner Mitre Joints in Aluminium

04/24/2015 7:02 AM

There are various aluminium loaded epoxy pastes on the market that you could use to butter one side of the joint as it is made, then wipe off the access and allow to dry before powder coating. Look for products with names like metal putty or similar.

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#8

Re: Painting Corner Mitre Joints in Aluminium

05/01/2015 3:44 PM

One Word: Alumaloy

Google it.

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