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Dry Off Temperature After Pre Treatment

In our Paintline, after pretreatment (degrease-rinse-zinc phosphate-rinse-DI water rinse) the next stage is "DRY-OFF" in an oven at a temperature of 120 °C for 25 minutes before powder painting. Is this is the right temperature ?. Can we reduce it ?. What is the practice in the painting industry ?

Nanda Srikakulam
- Bangalore, Karnataka, INDIA
2001

"Drying-Off" at 120 °C during 25 mins is common practice in the paint industry. However, at 120 °C the possibility of destroying the Zn-phosphate is likely.

Depending on your products following improvements could be possible:

1. Reduce the temperature. Given the time of 25 mins. this should be possible. If the result is bad, check the air flow in your dryer. In general: the higher the air speed, the better

2. A system commonly more and more used here in Europe is drying with dehumidfied air at ambient temperature. In fact the dryer is charged with extremely dry air (RH < 5%). Thus the water on the parts will evaporate very quickly. Normal: 5 -10 mins at 30 C.

Hope this is of help,

Remmelt Bosklopper
- Enschede, The Netherlands
2001