(11-08-2014, 11:42 AM)cristi.genes Wrote: Hello everybody,
I read your answer on babbit topic and I saw you have a lot of practical experience in babbit applications. I'm trying now to apply on a big bush from a cement factory (crusher) but I have big problems with adherence. I understand from your advices that before spraying babbit to increase the adhesion is better to preheat the bush (200C). OK total agree but I must spray on both sides of the bush and this means that the depot on both surfaces must be made in the same time after preheating. Correct?
Circumstances:If I have to repair only the inside surface how will I proceed? Because if I will preheat at 230C this will affect the outside layer. Or not? Can advice someone?
If I make a thread this will increase the adhesion? Take in consideration that the bush have the outside axis eccentrically and inclined beside internal axis. The outside diameter is 900mm and inside diameter 700mm.
Regarding the water based flux and tin powder mixture can you be more specifically, how are these two components used? If you need more details please contact anytime. Thank you.
Hi Cristi,
Sounds like a fun job!
Tinning the surface is a good idea, but not absolutely necessary. To increase the adhesion, you could do the following;
1. Use a very coarse sprayed bond coat of either Molybdenum or nickel-aluminum powder cored wire. These are "self bonding", meaning they will sort of micro-weld to the surface, and their rough surface gives a good anchor for the Babbitt.
2. Make sure the surface is abrasive blasted with clean grit; garnet or AlO2 is preferred.
3. Arc or flame spray wire? Or are you using flame spray powder? Flame spray wire will be best, but make sure he flame is fuel rich (reducing) so that the oxides are minimized.
4. When applying the first coating pass, try to angle the gun in such a way that the spray dust goes over the area just coated and not the uncoated surface. This way, spray dust will not interfere with the bond of the first pass.
If you decide to tin, your surface needs to be smooth but sanded clean (mechanically clean), then solvent cleaned (chemically), and then you can preheat only the surface to be tinned.
Remember, the tinning is done at a pretty low temperature, so you can just heat the surface with a large rosebud torch and just tin the area around the torch and not the entire shell. It takes a while for heat to get complexly through the shell.
If you are worried about the other side melting, just wrap a wet towel around it to keep it cool.
You can use a flux similar to this one;
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Or better yet, this E-127 tinning paste specifically used for tinning bearing shells;
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The flux is washed away with water after you are done tinning. Make sure you wash the entire shell.
Just prior to spraying, start heating the surface again (you will see the tin go from dull to shiny) and apply your first coating pass. It will slightly melt into the wet, tin surface. You can use the rosebud torch just ahead of the spray gun to maintain a wet surface. Again, if you are worried, keep a wet towel wrapped around the other side of the shell to keep it cool.
After the first pass, there is no need to keep the shell hot.
Hopefully this helps you. Send some photos when you have a chance.
Regards,
Jim Weber
James K. Weber Consulting LLC
114 North Clinton Ave.
Bay Shore, NY 11706
(631)767-8099