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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Powder adhesion problems on MIG welds
I am powder coating heavy steel cabinets, 5/16 inch steel plate, in a custom job shop. These cabinets are mig welded and there seems to be a silicone like residue left from the welding that our powder will not adhere to. We can pre -heat the part and make it cover but we would prefer to have a real solution. We have tried sand blasting the welds but it doesn't seem to matter.
DAVID WILLIBEY- BLOOMINGTON, Indiana
David,
In the cases we were confronted with this problem always one of the two following where the solution:
1. The welder use a spray to clean their welding heads. Sometimes this liquid contains silicones ore similar
2. The type of gas(mixture) that is used at welding. We learned that in some cases changing the type (or once even the supplier) did the trick.
Good luck,
Remmelt Bosklopper
- Enschede, The Netherlands
The deposit you are seeing is probably silica. Silicon is a non metallic element while silica is silicon combined with oxygen. Silica is both very hard and chemically inert having a hardness of 7 on the mohs scale while steel has a hardness of 6. This makes the silica very difficult to remove either mechanically or chemically. Mohs scale is logarithmic so 7 is 10 times harder than 6.
The reason you are getting this is that silica is often added to weld wire to improve the flow characteristics of the weld puddle. You could try using a low silica weld wire and/or changing your weld gas. I have seen good results with a mixture that contains nitrous. Unfortunately I do not have the information available just now and the rules of this site discourage public endorsements anyway. If you are interested in more information you can email me and I will send you the details.
Good luck.
- Elkhorn, Wisconsin
Thank you for the responses. Being a painter I felt it must be a silicone type substance by the way the powder was repelled, very similar to liquid paint. I am not sure my customer will change their material. They feel it is a finishing problem and I should solve it. Thank you again for the help.
David Willibey- Bloomington, Indiana
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