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Infrared heating absorption and wavelength characteristics


Frequently Asked Questions

The infrared heat absorption characteristics of thermoplastics are generally affected by polymer type, colour, pigmentation or other additives that can affect the absorption, reflection or scattering properties of the material, and these are important factors for consideration when selecting optimum welding conditions.

For example, a thermoplastic containing a black pigment would be expected to infrared weld in a totally different manner to the same thermoplastic containing a white pigment.

These absorption characteristics are also wavelength dependent and it is important to select a lamp or other source of infrared radiation with an output wavelength characteristic which is suitable for the thermoplastic being welded. Available infrared wavelengths are generally divided into three:

a) short wave from 0.9 to 1.8µm
b) medium wave from 1.8 to 3.3µm
c) long wave from 3.3 to 7.2µm

Long wave infrared is the easiest to generate but the least efficient (~50% from source). Short wave infrared is more difficult to generate but is far more efficient (~90% from source). The infrared adsorption/reflection spectrum of a thermoplastic should be measured as a first indication of the most suitable heat source to use, and then experimental trials should be carried out in order to confirm the welding procedure for a given system.

See further information about plastics welding and testing or please contact us.

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