Wedge method simplifies strip temperature measurement

Citation

(2001), "Wedge method simplifies strip temperature measurement", Sensor Review, Vol. 21 No. 1. https://doi.org/10.1108/sr.2001.08721aaf.006

Wedge method simplifies strip temperature measurement

Wedge method simplifies strip temperature measurement

Keywords: Temperature, Measurement, Infrared, Radiation, Thermometers

Land Infrared has developed a simple, low-cost means of measuring the temperature of steel and other bright metal strip during continuous annealing, which is proving successful in strip mills in the UK, Japan and Scandinavia.

Known as the "wedge" method it is based on the principle of sighting a Land System 4 infrared radiation thermometer onto the wedge or roll-nip – the point where the strip and the roller around which it is passing converge (see Plate 5).

This target spot was selected because the background energy reflected from the hot surroundings is absorbed by multiple reflections between the strip and the roller, reducing the effect of emissivity, which can cause inaccuracies when measuring the temperature of highly reflective materials.

Plate 5 Land Infrared's "wedge" temperature measurement system for bright metal strip has all the component parts housed in a single assembly

A single assembly containing the thermometer and all its ancillary equipment – including the sighting tube, purge device and sealing window – is installed in the side wall of the furnace so that the thermometer can be aimed at a low angle into the narrowing roll-nip.

This arrangement is much simpler than methods using a water-cooled flange and sighting tube, which require substantial engineering and are also prone to errors caused by emissivity.

Land Infrared's trials showed a close correlation between strip temperatures measured in this way and the metallurgy of the annealed product, making it possible to use the wedge thermometer to control furnace temperatures in each zone to achieve the correct temperature/time profile.

Although in most instances Land recommends its System 4 thermometer for this application, the operating wavelength, field of view and precise aiming of the thermometer are not critical, giving the user the latitude to choose an instrument on the basis of cost and reliability.

For further information contact Tom McDougall, Land Infrared, Dronfield, S18 1DJ, UK. Tel: +44 (0)1246 417691; Fax: +44 (0)1246 410585; E-mail: infrared@landinst.com; Web site: http://www.landinst.com