Nozzles for Pre-treatment applications
Engineering Considerations - Chemical compatibility
Pre-treatment tunnels are a series of stations spraying a variety chemicals. Some chemicals like the phosphates used for anti-rust conversion coating are specifically used because they react with metals. The whole point of the phosphate spray is to cause a reaction on the surface of the metal being sprayed to form a corrosion resistant film. Spraying phosphates through metal nozzles is thus problematic. There are metals that are resistant to the actions of phosphate but they tend to be more expensive and as pre-treatment plants run and temperatures below 100 degrees plastics like glass filled poly-propolyene tend to be more cost effective choice of material.
Poly-propelyene, PVC, CPVC or PVDF quick change system
The Unispray quick change system is manufactured ins glass filled poly-propelyene, PVC, CPVC pr PVDF. These materials give excellent chemical resistance are hard wearing and relatively inexpensive. This makes them all ideal for use in pre-treatment tunnels. Indeed the Unispray system is regarded as the market leading system worldwide in this niche segment. A table of their relative properties is given below.
| PVC | 60oC | High | Good | Low | Low |
| CPVC | 100oC | High | Good | Medium | Medium |
| Glass filled poly-propeleyne | 70oC | High | Good | High | Medium |