The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Metal temp

What should be the metal temp while painting of the sheet metal component . What defects can be seen if parts are painted at low & high metal temp. What is the paint gloss unit.What is blushing off in painting.

alam ahmad
- Delhi, India
2007

---

Depending on the type of paint there will be a minimum temperature to start the chemical reaction, the next consideration is time at temperature in conjunction with peak metal temperature. On conveyor systems I have seen time at temperatures of anywhere from 20 to 45 minutes with a peak of around 350°F. On coil lines the time at temperature is measured in a few minutes so peak metal temperature is the main consideration, it can vary form 380 to 500°F. A polyester would be around 420, an epoxy around 480, and a phenolic around 500°F, Underbaking will cause problems with adhesion, cure, gloss and other properties. Overbaking can cause colour problems, brittleness.

Gloss is an indication of how much diffuse light is reflected from the surface. It is instrumentally measured at one of three specified angles. 20° for high gloss finishes, 60° for semi gloss finishes and 85° for low gloss finishes. 60° is most commonly used. The scale goes to 1000 not 100 as a lot of people mistakenly believe. It is also not linear. blushing is what you get if some paints are not completely cured. The colour and appearance look uneven.

Ronald Zeeman
Coil coating - Brampton, On., Canada
2007