Powder Coating Troubleshooting Guide
Chapter Eleven: Powder Curing Process
Baking Needs for Powder Coatings
- Enough heat to liquefy and smooth out coating film
- Sufficient heat to liquefy film
- adequate time at the specified bake temperature to develop full design properties.
Although the bake/cure process generally follows after the coating is applied, there are instances when it’s preferable to heat the substrate first.
- With cast iron / aluminum, preheating allows trapped gases to escape from the porous metal surfaces and reduces the tendency for blisters to form in the film.
- When the mass of the part is sufficient to allow residual heat to adequately cure it.
- If higher than normal film thickness (greater than 6 mils) or fast film deposition is required.
Factors Affecting Cure
- Powder chemistry
- Type of oven
- Metal thickness
- Temperature / voltage / wavelength
- Bake time
- Oven efficiency
- Air velocity
Recommended cure times are based on time at METAL TEMPERATURE.
Stages of Cure Development
- Powder particles begin changing from a solid to semi-liquid state.
- Powder is fully liquefied, reaching lowest viscosity, allowing film to smooth out
Cross linking stage:
- Sufficient, sustained heat triggers large scale reaction within film, initial steps to total chemical/physical change of product
- When sufficient crosslinking has occurred, for solidification of the film from a liquid to a solid
- The final, and most critical stage when baking results in reaction of majority of crosslinking sites and development of full design properties
Typical Cure Development
|% Cure Properties
||Cure Time (minutes)
Importance of Metal Thickness
|Metal Temperature (°F)
||Oven Time (minutes)
Bake Oven Designs and Energy Consumption
- Electron Beam
IR Curing Sources
- Reflected energy: energy that bounces back.
- Absorbed energy: energy absorbed by the coating (usually by the pigment).
- Transmitted energy: energy that passes through the film where the substrate either absorbs or reflects the energy.
Different wave lengths have different curing properties to be considered.
Organic coatings with C-H and O-H bonds have a peak absorption in the 2.2 to 3.3 micron wave length range.
- Short wave: 0.76 to 2.3 micron wave length with a source temperature of 2000° to 5000° F.
- Medium wave: 2.3 to 3.3 microns with a source temperature of 860° to 2000° F.
- Long wave: 3.3 to 1,000 microns with a source temperature of 100° to 860° F.
The Frequency Spectrum
The Frequency Spectrum
Optimum Infrared Wave Lengths