Cured Chromate Epoxy on Parts Before Assembly?

[Terry R662]

Cabin Torque Tube Caps and Control Arm Parts

Hello All:

Several years ago I got carried away, painting chromate epoxy on several Torque Tube Arm parts. Now that I am tackling "that darned flaperon torque tube" installation, I question whether pre-painting epoxy on the control arms was a good idea.

Will cured epoxy on a part affect the gripping power and structural integrity of the rivets and mating surfaces after assembly? Should I remove the cured epoxy from the arms where the rivet heads and mating surfaces (arm and cap) meet, then upon final rivet installation, paint fresh (wet) epoxy on the part, then rivet? Or is it okay to just scuff the cured epoxy mating areas including where the rivet heads sit and continue on? What is the preferred method here?

Note: In my past assembly of parts, I have always scuffed the bare aluminum parts, dipped the rivets assembling everything wet. The above was just one of my "outsmarting myself again" ideas.

Thank you in advance for thoughts.

Over-and-out . . .

Terry R662

[TongueTied]

I'm no expert and in fact, am really not knowledgable at all but here is my $0.02. Please correct me if I'm wrong.

I understand there are 2 reasons for using the Chromate/Primer between parts:
1. To provide a layer of protection between parts that protects between different chemistries of the metals (if any);
2. Protects the metal from corrosion from moisture that might get in-between the parts. Applying it wet, removes air and moisture to further seal the joint between the surfaces so no moisture can get in-between to cause corrosion.

I've also read that using the epoxy chromate provides a bond between the parts like a glue. I'm not convinced that it actually does do much.

So, with your chromated parts, I'd say that you have already covered off number 1. However, I'd suggest applying a little bit more between the surfaces when you rivet them together to cover off number 2. I'm not convinced about added strength that the wet chromate gives but if it does, by covering off number 2, you would also be covering the added strength issue (if it is even applicable).

Cheers,
Philip

[Ken]

Agree completely with Philip.
The epoxy increases strength sometimes and sometimes not so I wouldn't worry about that aspect.
Ken

[Terry R662]

Thank you Philip and Ken.

Years ago, I got carried away with these parts and spray painted them with several coats of epoxy (not one light coat), so the thickness was my concern. What I did was, light sanded the parts to remove most of the green, cleaned them, and upon assembly I painted fresh epoxy for a wet assembly. Sixteen rivets closer to finishing.

Over-and-out . . .
Terry R662