The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Bonding of sprabroze to steel

I am using a flame spray gun with sprabronze wire to coat steel. The trouble I am having is getting the material to bond. I am preparing the steel by machiningg rough grooves on the surface to be sprayed, then sandblasting, then preheating the steel to about 200 degrees then a thin coat of nickel followed by the coats of sprabronze. Everything that is sprayed is lifting off. As it cools down it lifts more. I am using a flame spray gun with acc, oxygen, and air. Should I let the material cool down to flame spray temperature (about 110 degreees) before I start spraying .

Gary Moore
machine shop - Charlotte, North Carolina
2004

---

Unless your part is heavy, it probably is well below 200 before you actually spray it.

The normal strike or bond coat would be nickel aluminide, not nickel. There is a huge difference. Parameters for this bond coat can be tough to meet and maintain. Are you doing any metallographic evaluations?

Are you spraying the bond coat very soon after the sand blast? This is important.

I do not like sand. Aluminum oxide, white preferred, is far better. Silicon carbide works very well and lasts longer. Both sand and silicon carbide have OSHA silicosis requirements that need to be met.

How long do you have between bond coat and top coat?

Are you positive that the bond coat is coming off? If so, the bond coat is where the problem is.

James Watts
- Navarre, Florida
2004

---

First of two simultaneous responses --

Either your powder or equipment suppliers should have a better answer and certainly enough experience, particularly on tried and true applications such as yours. Nothing new or secret about sprabronze.

Guillermo Marrufo
Monterrey, NL, Mexico
2004

---

Second of two simultaneous responses --

I'm the one doing the spray bronzing.Its done right after blasting. I have plenty of time between coats, so I may be spraying to much too soon. I'm probably putting on about .005 of the bond coat followed by .075 of spraybronze. Everything looks good , bonding wise when I finish, but when it cools off (about 1-2 hours later its lifting off the material.

Gary Moore
- Charlotte, North Carolina
2004

As Guillermo says, it is time to get the vendor involved.There are just too many unknowns for us to reasonably guess at the cause. Shape has a lot to do with it also. what equipment, Metco, Miller, Tafa or? Is it all wire or all powder or some of both? As I said before, if the bond coat is also coming off, start your trouble shooting with that step. Some parameter is wrong, or it would stick. Temp, settings, angles, distances, cleanliness are just a few of the possibilities. Also, if it is pure nickel, you need to start the topcoat immediately, and pure nickel is a rather poor choice.

James Watts
- Navarre, Florida
2004