Powder Coating / Media Blasting Questions

[catalytic]

I'm going to have this Burr King media blasted and powder coated (everything except the motor and wheels). It is made entirely of aluminum castings except for the sheet metal belt guard. I have never had anything powder coated before, and I have some questions:



1. How should I do masking for the many tapped and untapped holes? I can put throwaway bolts in them, but I don't want the bolt heads to cause missed spots. (for tapped holes, should I leave the bolts a bit unscrewed?). I have seen masking tape for powder coating, but does this hold up to blasting as well?

2. The picture below shows the place where the main casting mates with the lower wheel bearing housing. Should I powder coat over this mating surface, or is powder coating thick/uneven enough to mess up alignment / chip off when I tighten another piece onto it?



3. The only cast iron parts are the little work rest and the platen. Can these be powder coated, or is the heat a no-go with machined cast iron?

I'd also appreciate any other tips you have.

 

[Fcvapor05]

I'm going to have this Burr King media blasted and powder coated (everything except the motor and wheels). It is made entirely of aluminum castings except for the sheet metal belt guard. I have never had anything powder coated before, and I have some questions:

1. How should I do masking for the many tapped and untapped holes? I can put throwaway bolts in them, but I don't want the bolt heads to cause missed spots. (for tapped holes, should I leave the bolts a bit unscrewed?). I have seen masking tape for powder coating, but does this hold up to blasting as well?

Whenever I've had parts coated in the past, I've just reamed untapped holes out after coating, and tapped threaded holes. If you plug them, the coating will be stuck to both parts- when you turn the threaded bolt you used to plug the hole, you run the risk of the 'tear' in the coating spreading to the part and flaking the coating. Any taping method likely won't hold up to the type of blasting that will remove the old paint, but that's 0K- for this application they should be using a blast media that removes the paint ONLY, and not any base metal.

2. The picture below shows the place where the main casting mates with the lower wheel bearing housing. Should I powder coat over this mating surface, or is powder coating thick/uneven enough to mess up alignment / chip off when I tighten another piece onto it?

Something like a bearing needs to go on a flat, machined surface, so you should not coat that surface. You could maybe get away with having coating there as the coating will be very uniform if your coater knows what he's doing, but it's not the 'right' way to do it. You can mask the area, or easily remove the coating later with a scotch brite roloc disk on a die grinder- this will remove the coating but not any of the base material, which is what you want.


3. The only cast iron parts are the little work rest and the platen. Can these be powder coated, or is the heat a no-go with machined cast iron?

Any cast material can be coated, but should be THOROUGHLY pre-heated before being sprayed with powder, to outgass any contaminants. If you're doing this yourself, that means heating the parts to the bake temp and letting them soak at that temp until they are hot through-and-through, at least a couple hours. If you're paying someone to coat this for you, make SURE they know how to coat castings.

I'd also appreciate any other tips you have.

Asked and answered

 

[BTG]

1. Have your Powdercoater plug any holes that you don't want coated. Any good powdercoater will have silicone plugs for these. If they don't, find a different powdercoater.

2. Ares like these can be masked off before coating. Go over any area like this in detail. It is a good idea take a few photos, print them, and add notes on the prints on area to mask and plug. Better off taking a few minutes to communicate your wishes. Powdercoaters have a lot of parts in process at the same time- misunderstandings and miscommunication happens.

3. Yes- cast iron can be coated.
These responses come from a powdercoater. We have a custom coating (powder, ceramic, thermal, sacrificial, protective, etc) shop in Indy. We get stuff like this all the time.

 

[Tucko]

1. Have your Powdercoater plug any holes that you don't want coated. Any good powdercoater will have silicone plugs for these. If they don't, find a different powdercoater.

2. Ares like these can be masked off before coating. Go over any area like this in detail. It is a good idea take a few photos, print them, and add notes on the prints on area to mask and plug. Better off taking a few minutes to communicate your wishes. Powdercoaters have a lot of parts in process at the same time- misunderstandings and miscommunication happens.

3. Yes- cast iron can be coated.
These responses come from a powdercoater. We have a custom coating (powder, ceramic, thermal, sacrificial, protective, etc) shop in Indy. We get stuff like this all the time.

^^^^^^^
All good advice above. I know this doesn't apply to this item, but in the future keep in mind that Bondo can't go through a powdercoating application because it will melt. If you need to, use a product called Allmetal, which is metal based and can withstand the heat. It mixes and applies just like bondo...

 

[CudaChick1968]

^^^^^^^
All good advice above. I know this doesn't apply to this item, but in the future keep in mind that Bondo can't go through a powdercoating application because it will melt. If you need to, use a product called Allmetal, which is metal based and can withstand the heat. It mixes and applies just like bondo...

Powder coating is an electrostatic process. It is not suitable for use on Bondo / plastic body filler at all not only because it will melt, but because it isn't metal -- the powder won't stick to it to start with. There are a few fillers out there specifically made for powder coating but they all **** in my opinion (PM me if you need to use metal filler and I'll point you in a better direction).

Unless you're going to prep and coat it yourself, do yourself a favor and check out the coaters you're considering; ask to see real work samples and actually talk with their references first to make sure you're hiring the right one for the job. Lots of people will tell you they're qualified but unless you hear it over and over from outside sources, rest assured they probably aren't. The industry has been saturated over the last decade with thousands of uhhhhhhhh people who could use a lot more practice, lemme put it that way.

Disassembly and prep cleaning can be done yourself to save money (unless you expect your coater to put it back together when it's finished, and then it's a lot easier to do if she knows how it came apart ).

As the customer, you shouldn't have to worry about plugging threaded holes and masking stuff off yourself. (The high temp tape used by coaters works in an oven but it's not going to be any help for the blasting.) As BTG mentioned, good communication is absolutely key to getting what you want within your coater's abilities.

Good luck with the resto! Keep us posted on your progress and post up some pictures when you get it back.

 

[-Brent-]

3M makes a silicone adhesive tape that is specifically for powdercoating. The guys I use use it (as well as silicone plugs). Your guys should be using the same stuff.

However, some outfits are high volume, commercial coaters that don't do much prep or protection. They just blast and coat. I would stay away from a place like that since this is a restoration piece.