Powder Coating Wheels Safely

FACTS YOU SHOULD KNOW

Does powder coating wheels effect the strength and integrity of cast or forged wheels?

 
  •        Most alloys do not anneal until 600F

  •        Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness.

  •       The common alloys used are 356-T6 or T7 for cast wheels and 6061-T6 for forged wheels.

 

The following ASM Handbook Volume 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials has the following information

  356-T6: aging at 305 to 315 °F for 2 to 5 hours                356-T7: aging at 435 to 445 °F for 7 to 9 hours
Yield stress = 185 MPa                                                   Yield stress = 165 MPa
Ultimate stress = 262 MPa                                              Ultimate stress = 220 MPa         
Fracture strain = 0.05                                                     Fracture strain = 0.06
 

6061-T6: The aging precipitation heat treatment is done at 350 F for 8 hours followed by air cooling. This produces the T6 temper.

Based on this data, a 375 °F treatment for less than 1 hour wouldn't reduce the fatigue strength significantly

 
  •       Another item that needs to be considered when powder coating aluminum is the coater's pre-treatment system. In some shops the cleaning stage is a caustic cleaner at 140F. I asked our tech rep about coating aluminum and he told me the caustic cleaner was not compatible with aluminum.

  •        As far as increasing weight by powder coating vs. painting that is marginal, powder is thicker than paint by about .004 but as far as weight is concerned we are talking adding maybe 1oz to a wheel. Sometimes you add more weight just by balancing a wheel. (16oz = 1lb)

  •       BBS uses both a powder coat primer and clear coat for their cast wheels.

  •       HRE uses powder coating on their forged wheels.

  •       J line uses powder coating on their forged wheels.

 

Powder coating is used by high end manufacturers on their wheels in a controlled environment which monitors the temperature and time the wheels are in the oven.  Unique Finish uses the same curing process as large manufacturers use on a smaller more custom scale. We do not cure our wheels over 375F or for more than 1 hour, most wheels are usually cured for 30-45 min depending on the size and type of powder. We do not shock the wheels with a temperature of 375F as soon as they are placed in the oven; rather we ramp up the temperature from 200F to 375F in a 10 min period then the curing cycle starts from there.

Painting is used only as an option when we cannot match a color to a customer’s specific needs otherwise powder coating is the more durable choice to use.