Applying Chrome to Aluminum after Coating

Q. I am a production manager for an aluminum storm door manufacturer. While pretreating our parts we use a temporary corner gusset to keep the door rails separated at the corners (the rails are the aluminum extrusion that make up the main body of the door frame). The solutions from the washer can easily drain out of the door after washing. After drying off in the oven, we then powder coat the doors. In assembly, we use a finishing corner gusset to join the rails, but because the corners were separated when they were powder coated, powder has baked non-uniformly onto the inside edge of the rails. If we do nothing about it and join the corners with the finishing gusset, the powder coat along the inside edge of the rails will leave a minor gap between the joining rails because of the non-uniform powder buildup. To remedy this, we file down to the metal the powder coat along the inside edge of the miters, so when we join the rails with the finishing gusset, there is no gap between the joining rails.

The problem is that if the door is installed in a highly corrosive environment, like near a shoreline, the elements will cause the powder coat to separate from the aluminum rail where we do the filing. It is out of the question to join the miters before washing, so I think it goes without saying that filing must be involved during assembly. I am wondering if, while in assembly, I can apply a chromate conversion coating with some kind of applicator to the filed inside edge of the miter to promote adhesion at this vulnerable edge of the door.–K.V.

A. There are materials that can be applied by hand to passivate and protect exposed surfaces. Most chemical suppliers will have something. If you contact companies that supply conversion coatings, you will find that many have chrome-based materials that can be brushed on. You may also want to investigate some type of seal or touchup material that can protect those corners.