Infrared welds

The mechanical testing conducted on high-quality infrared welds has shown that the welding factors achieved for PVDF when tested at -40°C were greater than 0.9. 

Grimm, R. A., Infrared Welding of Polymers, Medical Device and Diagnostic Industry, May 2000 www.devicelink.com/mddi/archive... 

Infrared Welding of Thermoplastics. Colored Pigments and Carbon Black Levels on Transmission... 

Infrared welding has been characterized as unpredictable since different polymers or formulations have been observed to heat at widely different rates under similar conditions. A previous reference reported a significant difference in absorption between thermoplastics that contained no carbon black and a similar material with carbon black levels around 0.5 per-... 

This work shows that absorption is very sensitive to the level of carbon black in the polymer formulation and provides some data to quantify this effect. This sensitivity occurs at very low levels of carbon black. Thus, when a polymer is selected for infrared welding, it will be important to know the concentration of carbon black in the formulation. If it falls below 0.07 percent, there will be increasing depth of heating and less surface heating. 

Because infrared welding has the ability to penetrate polymers and heat them, it offers the potential for stronger joints because a deeper melt zone is created by absorption, at once, rather than by conduction through the polymer. 

Plastic parts with a thin black layer on one side can be continuously welded in place. For example, if the black layer is one part of a bUayer, coextruded sheet, it could be unroUed and welded in place. The heat needed for welding would be generated precisely where it is needed, minimizing damage to the part and allowing the joining of thin polymer films. Thin films, particularly when coated on a metal, that are hard to join by other methods should he readily and rapidly joined by infrared welding. 

Polymers of different colors can be expected to weld differently by infrared welding. Not only are the issues of pigment-polymer interactions present such as the differences in weldability caused by white (titanium dioxide), hlack (carbon black) or other pigments, but heating times and depth of heating are likely to he affected by part color. This kind of phenomenon can already occur in conventional hot plate welding when, in some cases, red and black parts weld differently. It can be expected to become even more of an issue with infrared welding. These effects can he easily handled, but workers must be aware of their presence and how to control them. 

R. A. Grimm, Through-Transmission Infrared Welding of Polymers, Conference Proceedings of the SPE ANTEC, 1996,... 

Other thermal welding processes that are less common than those described above but still used in industry are infrared welding and laser welding. These are generally used in specialty processes or with applications that require unique methods of heating because of the joint design or nature of the final product. 

Infrared welding has a number of advantages over hot-plate welding weld times are reduced, the joints are free from contamination (since it is a non-contact process) and low-modulus materials can be welded (since there is little or no shearing of the parts during heating). 

The current application for infrared welding is in the joining of plastic pipes, but it has the potential to be used in many areas where hoq>late welding is currently used, and has been demonstrated on composites. 

Infrared welding is at least 30 percent faster than heated-tool welding. High reproducibility and bond quality can be obtained. Infrared welding can be easily automated, and it can be used for continuous joining. Often, heated-tool welding equipment can be modified to accept infrared heating elements. 

Poor compatibility with processing solvents and acids low upper working temperature Opaque (though thin amorphous PEEK is translucent) interlayer bonding is difficult - can be done by through transmissive infrared welding... 

Figure 14.25 Pressure vs. time curve showing the three phases of infrared welding. Joint surfaces are heated to the melting temperature of the plastic in phase I Heating Time). In phase II (Change-over), parts are pressed together under pressure. Infrared heaters can be removed in this phase if they are in the way of the parts to be joined. In phase III (Joining and Cooiing), a weld is formed as the hot molten material cools under pressure.

Chen, Y.S., Benatar, A., Infrared Welding of Polypropylene, ANTEC Conf. Proc., Soc. Plastics Eng., 1995. 

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