Abstract
A new sensitive lead sulphide cell pyrometer has been developed which enables the temperatures of aluminium extrusions to be continuously monitored or controlled during processing to about ± 10 degC. The narrow field of view (¾ in width at 7 ft viewing distance) enables the pyrometer to be mounted on the guillotine of the press to view the extrusion down the tunnel at a point close to the die. The pyrometer does not detect any stray radiation emitted from the die holder and reflected by the top surface of the extrusion provided a suitable geometrical arrangement is adopted. The sensitivity of the pyrometer to variations in the surface emissivities of extrusions has been minimized by shortening the maximum wavelength of the incident radiation to 1·4 μm by the insertion of a 1 cm thick water cell. This reduces the emissivity errors to half those encountered with a Thermodot lead sulphide cell pyrometer.
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