Posted by Gordon England (220.127.116.11) on 13:01:10 04/04/05
In Reply to: Re: Adhesion Promoter posted by jim
: : : Looking for a good adhesive promoter. I've been trying PVA with little success. Maybe I'm not useing enough coats?
: : :
: : : Is there a better one I should look into?
: : Hi Jim
: : What materials are you trying to bond?
: : Regards gordon
: Silica Bronze arc sprayed onto break-away plaster molds. I've had to go with a fine texture on the smooth plaster surfaces, but I would like too just paint a adhesion promoter to speed up production.
: PVA doesn't seem to help, but it does make the plaster really hard to clean off. Zinc sticks on the smooth parts, but I want the bronze surface without having to re-spray after demolding.
A balancing act between holding the coating in place during spraying and releasing it when finished. PVA usually does a good job for zinc and some lower melting point materials, providing sufficient bond to substrate and coating, but allowing release with a good soak in water.
Problems occur though when trying to use higher melting point coatings like aluminium, bronze, steel etc. These materials do not tend to bond well to smooth surfaces, produce more coating stress and can damage PVA.
I once helped to do something similar using a nickel based alloy instead of bronze, but in the end the only successful method was to:
Increase surface texture of substrate to increase bond to PVA ( Stress in nickel coating released PVA before achieving desired thickness).
Apply a thin zinc or tin base alloy coating to PVA then apply nickel alloy (with extreme care in keeping everything cool).
The only problem then is that the initial zinc coating needs to be removed to reveal the nickel, so finishing is required.
I have come across the use of salt solutions being spray on and allowed to dry for use as bonding/release agent. May be worth a try.
At the end of the day I think you will need to do a fair bit of experimenting to get it right. Good luck.
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