IR Emitters improve plastic weld precision

Pipes, tubes and vats are typical of the plastic containers which are joined together by heating and softening the exposed rims of the two injection moulded half shells and then bringing these two halves together under pressure to effect a fusion welding. Polypropylene filter housings for swimming pools are manufactured using this method but they present an additional challenge as, when they are installed, they are readily visible to users of the pool, so the weld joint needs to be optically perfect. These large, thick-walled and pressure-resistant filters had formerly been assembled using a welding system with resistance heating elements in an aluminium block with a Teflon coating. The heating elements were pneumatically swivelled in and out of position. However, the polypropylene, which flows easily when melted, tended to stick on the heating element, so that quality and speed of production could no longer meet the increased production requirements. Consequently, a more efficient solution was sought. This solution was provided in a custom-built welding system designed by Dr Uwe Egen of IPCW. It features two 61 cm diameter Omega infra-red emitters (so-called because they are in the shape of the Greek letter omega), each emitter being fitted with a 180° gold reflector, so that emitted heat is precisely targeted. The emitters are fitted within a custom-built system, which was purpose-designed for a South East Asian client of IPCW. In operation, two Omega emitters are swivelled into position to project their radiated heat onto the rims of the half shells. After they have sufficiently melted the plastic rims, they are swivelled away so that two halves can then be fused together. An intelligent control system, which was fitted in the existing control cabinet, helps to maintain an intensity/time profile. Combined with the correct welding pressure, this ensures an optimum welded joint. "The infra-red system has replaced the contact heating elements, so that now we have much shorter cycle times," commented Dr Egen. "However the main advantage of the infra-red technology for me is that the two halves can be precisely centred. Infra-red heats without contact, so there is no longer any possibility of contact surfaces sticking together and then shifting out of position." Heraeus Noblelight specialises in the production and application of high quality energy sources covering the electro-magnetic spectrum from ultraviolet to infra-red. It has over 40 years' experience in infra-red technology and offers the expertise, products and systems to provide efficient and effective solutions to drying, heating and curing problems throughout industry.