A UV-curable powder coating allowed Baldor Electric to coat and cure fully assembled motors without damaging internal components. Infrared and convection zones melt and flow the powder before UV light crosslinks the coating.

Fully assembled electric motors are exposed to short wave infrared energy for 1 min. The short infrared zone is able to quickly bring the part up to temperature in a minimum amount of space.

What do you do when you want to apply finish coatings to fully assembled parts, but sensitive components can't take the heat? To satisfy production requirements and limitations, Baldor Electric Co., a manufacturer of industrial electric motors, was willing to try new coatings and technologies. Working with a systems house and a host of suppliers, Baldor arrived at a truly unique solution: The first commercial application of a UV-curable powder coating, cured using a finishing system that incorporates infrared, convection and ultraviolet (UV) curing zones.

Installed at its Westville, OK, facility, the finishing system is the result of a successful partnership drawing on the expertise of a range of suppliers. Systems house Nutro Corp., Strongsville, OH, spearheaded the project's construction and installation for Baldor. Other members of the team -- Herberts Powder Coatings Inc., Hilliard, OH; Fusion UV Systems Inc., Gaithersburg, MD; Nordson Corp., Amherst, OH; and Henkel Surface Technologies, Madison Heights, MI -- helped ensure that this first commercial application of a UV-curable powder coating was a success from the start.

The Motivating Factors

Using UV technology allows Baldor to powder coat assembled motors for the first time. In the past, it was necessary to paint or powder coat individual motor components prior to assembly, or to use a liquid paint to finish an assembled unit.

"Liquid coatings present problems -- dripping and messy application -- as well as difficulties with environmental compliance," explained Paul Mills, sales manager at Nutro Corp. Many liquid coatings are solvent-borne materials that produce unwanted volatile organic compound (VOC) emissions.

Traditional powder coatings were an attractive alternative but could not be used on the assembled motors. To use a thermoset powder coating, the part must be heated to 400oF (204oC) during curing -- too high for an electric motor. The heat could seriously damage the motor's internal parts such as electric wiring and varnish on the windings.

In an effort to find a coating without the restrictions of traditional powder coatings, Baldor decided to examine UV-curable powder coatings. These new formulations offer the same advantages as standard powder coatings:

  • High heat transfer efficiency.

  • No VOC emissions.

  • Ease of application.

  • Quick clean up.

  • The ability to easily change colors.

  • High rate of reclaimability.

But, while traditional thermoset powder coatings require high heat to achieve crosslinking by thermal reaction to form a hard, durable finish, UV-curable powders only require temperatures of 250oF (121oC) to melt and flow the powder. Then, UV energy is used to trigger the chemical reactions that cure the coating.

No Need to Heat?

While UV-curable powder coatings do not need to be heated to the temperatures used for traditional thermoset powder coatings, heat still plays an important role in the curing process. "The advent of UV-curable powder coatings is likely to broaden the market for traditional process heating equipment because the powder coating still must be melted prior to UV exposure," said Mills. "As new applications for powder coatings are developed, additional convection and infrared units will be required as a part of the finishing line."

The Baldor project uses both infrared and convection zones for melting and flowing the powder coating.

"The trick is to build temperature as quickly and uniformly as possible, without damaging the internal components of the motor such as the solder connections, wiring or plastic components," Mills added.

Carefully evaluating the parts to be finished helped Nutro specify infrared and convection zones that achieve Baldor's production objectives in a minimum amount of floor space. For example, the construction of the motor makes some portions of the part act like a heat sink, drawing heat away from the finish substrate. Short-wave infrared T3 lamps are used to build temperature rapidly in these difficult areas. The motor is exposed to the infrared energy for approximately 1 min.

After initial heating in the infrared zone, a direct-fired, recirculating gas convection oven heated to 250oF is used to flow out the powder. The goal is to smoothly flow the coating across the entire complex surface of the part. Convection heating also helps cure the powder in the more difficult contours where radiation curing by infrared often is difficult to achieve. Finally, the motors convey past UV lights that crosslink the flowed powder into a formed, hardened finish.

Each zone of the curing line is optimized to accommodate a range of part sizes and shapes while consuming a minimum amount of floor space. The top, bottom and side infrared lamps are zoned and controlled by SCRs that respond to commands from the system's programmable logic controller (PLC). Baldor can alter the power settings to individual infrared zones to accommodate different parts shapes and sizes simply by entering a preprogrammed part recipe code.

In addition, a specially designed power-and-free conveyor system allows the motors to be more densely packed in the convection oven, reducing the oven's size requirements.

New System, Old Refrain Leads to Successful Implementation

The complex mix of coating technology and curing methods used at Baldor's facility satisfies all of the company's objectives. (Once in full production, Baldor switched to a UV-curable coating from Morton Powder Coatings, Redding, PA.) But, Mills cautioned, this unique combination may not be right for every application.

"Although a combination of short wave infrared, convection and UV was used at Baldor, laboratory testing on powder and liquid coatings has shown that the best process depends on both the part being coated and issues related to capital and operating costs, which vary with each installation," Mills noted.

No one technology is right for every application. "Nontraditional substrates for powder coating -- wood, for example -- react much differently when the infrared wavelength is varied, or when convection is used, either alone or in combination with an infrared zone," Mills said.

As powder becomes more attractive to manufacturers of products made of these substrates, much development and process testing will be required to select the appropriate heating equipment.