Powder cure control is so important! The excitement builds as the start up procedure of a new powder finishing system begins. Months of planning and hundreds of thousands of dollars went into the project. Finally the washer is heated, the oven is started, and the conveyor begins to move. Minutes seem like hours in anticipation of the first coated test panels to emerge from the system. As the sample panels exit the oven they are allowed to cool before quality testing begins. So far everything looks great, the finish is glossy and smooth. On closer examination however, the panels have failed the simple impact test (ASTM D-2794). Additional testing was performed by cross-hatch adhesion (ASTM D3359) and confirms the coating did not complete the full cure cycle.
What could have been the problem?
Was the oven’s atmospheric temperature too low?
Was there uneven heat distribution within the oven?
Was there poor air-flow or venting of the air inside the oven?
Was the part in the oven for enough time to reach the proper temperature to allow cure?
The answer could be yes to one or all of the above. The cause of the problem is clearly under cure of the powder coated finish. The finish did not receive enough heat energy for the correct amount of time to properly cross-link and cure. But how do you know what to do to correct the problem? The answer is oven temperature profiling.
As soon as the construction of a powder coating convection oven is completed, adjustments are made to maximize the efficiency of the equipment as a unit. This is done by adjusting the operating parameters of the oven based upon a temperature profile obtained from a thermal profiling instrument.
Adjustments can now be made to the fuel and air ratios, air flow, air recirculation and air balance. All of these factors are critical to the oven’s performance. This is accomplished by increasing or decreasing air and fuel mixtures, opening and closing the air ducts, increasing the air volume and changing the direction of the air flow.
Sadly for many companies, this installation profiling will be the only time the oven is profiled and adjusted.
Many professional powder coaters profile their production runs for the following reasons.
To limit product liability risks
To reduce operating costs.
To improve processing capacity
To improve sales
Let’s candidly discuss each of these profiling issues in more detail.
Production profiling limits product liability risks
Risk management is a real concern for every business, and powder coating is no exception. The product liability of providing a poor quality powder coating finish could range from re-coating a few simple parts to the replacement of all products damaged by underexposure or overexposure to heat (a complete product recall).
The only way to totally manage risk is to be in total control. In turn, verification of control can only be certain when measurements are taken by proper testing equipment.