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Turning Up the Heat on Coatings

Fri, 08/10/2007 - 8:03am

The Project: Implement a technology to ensure a reliable consistent temperature is achieved for a coating process.
The Solution: Utilize an iron-chrome-aluminum heating element wire with ceramic fiber insulation to ensure a satisfactory result.

By Peggy Cobb
Uniform and repeatable temperature is a critical process variable for many manufactured products. The slightest variation can result in lost product, wasted time, and headaches for both the manufacturer and supplier. Such is the case for Indianapolis-based Specialty Coating Systems (SCS), a global leader in Parylene conformal coatings for a variety of industries, including medical devices and device components.

SCS' PDS 2060PC is a Parylene deposition system that utilizes a ceramic fiber heater from Watlow.
Parylene coatings offer protection for a variety of surface materials used in medical applications, including stents, electrostimulation devices, electrosurgical tools, catheters, elastomeric products, forming devices, and medical electronics. Parylene thin-film coatings conform to all surfaces, edges, and crevices of a substrate and provide excellent moisture, chemical, and dielectric barrier protection. Since Parylene is not a liquid, the coating does not suffer the meniscus and edge effects of conventional liquid coatings. SCS has been developing and applying Parylene coatings to critical medical devices for over 35 years.“Parylene is chemically and biologically inert, so the human body will not reject or react negatively to products that are coated in Parylene,” explains Bill Boyd, equipment program manager at SCS. “This protects the body from the device and the device from the body.”

SCS’s Parylene deposition systems are designed for accurate and repeatable operation. Utilizing a Windows XP-based computer control system, SCS production coating systems feature user-configurable parameters and a flat panel display. Operating temperatures and pressures are continuously monitored and recorded and can be uploaded for system and coating run analysis.

The deposition system must be kept precisely at the high temperature of 680°C (1256°F), with no variation. With a requirement for precision operating temperature, SCS turned to industry leader Watlow to develop a high performance ceramic heater that would reduce temperature deviation.

Watlow’s ceramic fiber heaters integrate a high temperature iron-chrome-aluminum (ICA) heating element wire with ceramic fiber insulation. The ceramic fiber insulation isolates the high temperatures inside the heated chamber from the outside, so energy is used to heat the load instead of the surrounding equipment. Ceramic fiber heaters are low mass, 10 to 15 lb/ft (160 to 240 kg/m), which allows the heater to reach process temperature quickly. The heater’s high insulation value and self-supported heating elements enable operating temperatures up to 1204°C (2200°F).

SCS Parylene coatings are applied to a variety of surfaces with deposition equipment that enables control of both coating rate and thickness. Polymer deposition takes place at the molecular level as Parylene dimer, a white powder, is vaporized under vacuum and heated to form a dimeric gas, then pyrolized to cleave the dimer to its monomeric form, and finally deposited as a transparent polymer film. This manufacturing process takes gas to a solid and essentially skips the liquid step, and that requires a highly accurate, stable heat-up temperature. Coating occurs in an ambient temperature chamber and components are required to have only a reasonable vacuum tolerance.

SCS not only has nine coatings centers around the world, they also sell the equipment to customers. With many systems running worldwide, uptime of the machines for SCS is important. With Watlow’s reputation of quality heaters, SCS does not have to worry about heater failure in their equipment.

“Our baseline requirement was for safe, reliable heaters,” Boyd says. “We have had no recorded technical problems or maintenance issues with Watlow heaters and that reliability and peace of mind is important for our tight process parameters.”
ONLINE
For additional information on the technologies and products discussed in this article, visit the following websites:
  • www.scscoatings.com
  • www.watlow.com

    Peggy Cobb is Watlow’s Value Stream Leader for Ceramic Fiber Products. Her current duties include management of all plant aspects including safety, quality, delivery, and cost, as well as product application. Cobb holds a Masters in Project Management from Devry University and a Bachelor of Science in Engineering Management from the University of Missouri-Rolla. She can be reached at pcobb@watlow.com.
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