Pipes, tubes, barrels and pressure-resistant filter housings are some of the plastic products that need to be assembled from individual components after injection molding. Infrared heating helps to weld the plastic components together without the need for adhesives or other fastening devices, says Heraeus Noblelight, Hanau, Germany. Many production steps can be sped up by using infrared emitters, says the company, and both time and energy can be saved when quartz glass emitters are matched to the product and process.

Welding together large, thick-walled plastic components presents processing challenges because the filter housing, when in its operating position, is clearly visible. When welded with infrared heating, the welding seam is optically perfect.
Photo courtesy of Heraeus Noblelight

Housings for swimming bath filters are relatively large and thick walled and must be pressure resistant. They are injection molded in two halves in polypropylene, and the two halves are then welded together. For one company in Southeast Asia, the welding together of these large and thick-walled plastic components presented a real challenge, as the filter housing, when in its operating position, was clearly visible, which required the welding seam to be optically perfect.

Previously, the company had used a welding system with resistance heating elements in an aluminum block with a Teflon coating. The heating elements were pneumatically swiveled in and out of position. The polypropylene, which flows easily when melted, tended to stick on the heating element, so quality and speed of production could no longer meet increased production requirements. A more efficient solution was sought that would save energy, and Omega infrared emitters from Heraeus provided this solution.

For this customer, Dr. Uwe Egen of International Plastic Welding Consultancy (IPCW) designed and built a system that contains one of the largest Omega infrared emitters ever manufactured, according to Heraeus Noblelight. The special emitter has the shape of a Greek letter omega, a diameter of ~24" (61 cm) and is fitted with a 180° gold reflector, so that the heat can be targeted to where it is needed. Two of the ring-shaped emitters project their heat radiation onto the edges of the half shells. They sit in a swivel device and are turned away after they have melted the plastic edge. The two halves can then be joined together.

An intelligent control system, which was fitted in the existing control cabinet, helps to maintain the intensity/time profile. Combined with the correct welding pressure, this ensures an optimum welded joint, according to Heraeus.

“The infrared system has replaced the contact heating elements, so that now we have much shorter cycle times,” Egen says. The infrared technology also allows the two halves to be centered precisely because there is no contact with infrared heat, eliminating the possibility that the contact surfaces will shift out of position after sticking together.

 Infrared radiation is transmitted without contact and generates heat directly in the product to be heated. Unlike welding with contact heating, there is no chance of hot plastic sticking to the heat source. Visit www.heraeus-noblelight.com to learn more.