Carefully, the engineers designed and tested a portable heating system, knowing they were on their way to perfecting a new product line as durable and reliable as their company's other welding systems. But one nagging problem held up development -- until they discovered Flexane®, a versatile, castable urethane compound from adhesive manufacturer Devcon.
These engineers worked in the laboratories of Wisconsin-based Miller Electric Mfg Co, the world's largest manufacturer of arc welding and cutting equipment. The new Miller heating system they developed, designed for pre-heat and post-weld heat treatment, uses a patent-pending flexible blanket or water-cooled coil that carries high-frequency alternating current. When laid against or wrapped around carbon steel material, the blanket or coil produces a magnetic field that heats the adjacent metal.
In post-weld heat-treat applications, the system has the capability to boost the metal's temperature to a predetermined level (as high as 1400° F), maintain that level, then slowly cool the metal back down again, all on a mathematical curve that can be programmed into and monitored with a built-in controller and digital recorder.
But in 1999, when this sophisticated system was in the final stages of development, Miller engineers were worried about the twist-lock connectors at the ends of the blankets, coils, and extension cables. The rest of the system was coming together nicely, but preliminary tests indicated that these connections were not holding up under rigorous use. Connector strain relief was the system's weak link.
Extension cables transfer current up to 50 ft from the power source to the heating coil. Miller engineers knew that users of the induction system might connect and disconnect the cables many times in the course of a single day. For example, to build or maintain a pipeline, the unit would have to be wheeled down the line, often outdoors, to treat welding zones at regular intervals. Unfortunately, the initial design using heat-shrink tubing with pre-applied adhesive was failing due to continual flexing, and the cable wire was detaching from the connector solder joint. The engineers tried other adhesives, with unsatisfactory results.
Finally, a Miller lab technician, working with Miller's assembly subcontractor, contacted Devcon. The local Devcon distributor and regional sales representative visited Miller's Appleton plant. After evaluating Miller's design and production requirements, Devcon technical specialist Steve Leslie recommended encapsulating the connectors with Flexane Cable Cast FR, one of a family of Devcon castable, nonshrinking liquid urethane compounds designed to form both flexible and rigid rubber parts for a variety of OEM applications. With a pot life of 8 minutes, flame-retardant Cable Cast FR cures at room temperature, dries to a hardness of Shore A 88, and is capable of 650% elongation.
Devcon technical service specialist Rodney Pendleton worked with the subcontractor to test adhesion and peel strength of the molded assembly, and coordinated with the local field representative to make sure the solution met all of Miller's performance requirements. Miller engineers were convinced, and development of the heating system went forward. Several models were introduced in late 1999 for shipbuilding; the manufacture of earthmoving equipment; the construction and maintenance of pipelines, power plants, and petrochemical facilities; and other applications.
All of these systems have connectors potted with Devcon Flexane. According to Jeff Thomas, manager of engineering for the Induction Technology Group at Miller, the results have been outstanding.
"Despite more than a year and a half of use in a variety of field applications, we haven't seen a single problem with any of these connections," observes Thomas. "And in some of those applications, the connectors really take a beating."
