Infrared (IR) welding is a relative newcomer to the field of commercially developed welding techniques for thermoplastics. However, the possibility of using this heat source for processing polymers has been known for many years and there have been applications in the area of preheating of polymers prior to compression moulding or vacuum forming since the 1960s.
For welding of thermoplastics, two different approaches to infrared welding have emerged, both based around the principle of hot plate welding.
Non-contact hot plate
This system uses an electrically heated metal plate which, in some cases, is coated with a ceramic. The hot plate is heated to a temperature between 310°C and 510°C, depending on the thermoplastic to be welded, and the size of the welding machine. When the parts to be welded are brought in close proximity to the hot plate, (typically 0.2mm) but without touching, they heat up due to radiation and convection and subsequently soften and melt. The plate then withdraws and the parts are forced together to form a weld.
IR lamp welding
In this system, the standard heater plate is replaced with two banks of short wave infrared emitters clamped and spring-loaded on either side of a movable platen. Powers can be very much greater compared with conventional hot plate welding but weld times are significantly shorter. This technique is also capable of handling large surface area products, as it is a simple operation to add more emitters to the heating bank.
The newly developed, high power short wave infrared emitter is also proving more efficient and effective than infrared emitters previously considered for welding applications. Its high power density, developed at a lower operating temperature, means that it can transfer energy more efficiently than halogen emitters, while its lower mass filament makes it more responsive than ceramic emitters.
For further information see plastics welding and testing or please contact us.