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Abstract

Emissivity is an important property of the materials used in technologies such as MultiJet Fusion and

Metaljet, as it affects the radiative thermal exchange and, because of this, also the temperature

measurements that rely on a device such as a pyrometer or a thermal camera. Due to that, it has a

direct impact on the actual temperatures to which the system is controlled.

The device object of this article enables the emissivity measurement for diffuse materials, such as

metallic or plastic powder; in particular, in the thermal infrared wavelength range (8 to 14

micrometers), but the methodology could be extended to other parts of the spectrum or focused on

a smaller region. This device can either be used as a separate tool in the process or integrated in

other machine, and the results can be used for process adjustment or tracking.

The device and the procedure followed rely on the comparison of the increase in reflected energy

coming from a constant source between a known emissivity sample and the sample which emissivity

is of interest. The procedure has inherent robustness thanks to the measurement by comparison, as:

‐ There is no high accuracy needed in the temperature of the source, if it has stabilized and in

a reasonable range.

‐ There is no high accuracy needed in the readings from the pyrometer, if the uncertainties

that affect it (internal temperature, third surfaces reflections) don’t change quickly through

the test or between the measurement of the sample and the reference.

‐ It can admit some uncertainty on the emissivity of the reference sample if this emissivity is

low (0‐0.1)

The concept has been prototyped and has shown good performance compared with the

measurements provided by a commercial emissometer.

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