Letter 11024

Phosphating 

WHAT IS THE MAXIMUM TEMPERATURE THAT Mn.PHOSPHATED SURFACE WILL WIHTSTAND? CAN U EXPLAIN THE ADVATANGE AND DISADVANTAGE OF Zn AND Mn PHOSPHATING. WHICH IS BETTER AND WHY?

T R ANAND KUMAR
Shiva Polmers - India

Zinc phosphate is primarily a rust protection, has to be followed with oil or chrome seal to be effective. Zinc phos is applied at a temperature of 160-180 degrees F. 180 F is best.

Manganese phosphate is primarily utilized as a "break-in" or lubricant coating to protect the base steel from "galling". Manganese phosphate is applied on steel at 200-210 degrees F, 210 F best. Manganese is much more expensive than zinc.

As for the maximum temperature these coatings withstand, I have no idea. Phosphate coatings are a rust prevention, not an endurance coating. Tell us what the application or exposure these parts will endure.

Bill Hemp
- Grand Rapids, MI, USA

Hi,

Crystalline phosphates will totally dehydrate at temps above 260 deg C, causing degradation in about 15 -30 minutes. This does not apply during paint stoving schedules. MnPhos is recommended for wear resistance for engineering applications whereas as ZnPhos is more for corrosion resistance or wire drawing applications. It both types there is a vast range of processes formulated to give coating weight ranges or for performance requirements. Say what you are looking for and I can be more specific.

Roger Bridger
Walterisation UK Ltd - Croydon, UK

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