GB1337955A - Temperature control - Google Patents

Abstract

1337955 Automatic control of temperature BRITISH STEEL CORP 1 Dec 1970 [5 Dec 1969] 59430/69 Heading G3R An apparatus for controlling the temperature of a movable metal strip 1 (e.g. wherein a steel strip is undergoing a tinning process) comprises means for electrically heating the strip and means for electrically heating a reference heat source 20, infrared cell sensors to sense radiated heat from the strip and reference respectively, and electrical means responsive to any difference in temperatures sensed to adjust the electrical input to the strip and hence its temperature. Tinned strip 1 is looped through an insulated heating chamber 4 and is heated by current from transformers 10, 11 connected in parallel between conductive rollers 3, 6 and is quenched in water 9. Laminated steel reactors 13, 14 increase impedance to current paths toward earthed rollers 2, 8. Radiated heat from the strip is pulsated by a motor driven apertured disc 17 and sensed by an infrared cell 15. The amplified output of the cell is rectified at 19 and fed to winding 28 of an magnetic amplifier 29 in opposition to a like amplified rectified output of a cell 24 responsive to the pulsated radiated heat from a chrome plated plate 20 forming a reference heat-source. The plate 20 is heated by a constant voltage source 21 and the actual temperature of the plate is sensed by a thermocouple 22 and indicated on a meter 23. The output of amplifier 29 has a polarity indicative of the sense of any difference between the strip temperature and reference plate temperature and a magnitude proportional to any difference. The amplifier 29 output energizes the field winding of a D.C. generator 31 and controls the output thereof. In turn the D.C. generator varies the impedance of the primary circuits of transformers 10, 11 via saturable reactors 32, 33 respectively and hence also the heating current through the strip 1. Alternatively the strip may be heated inductively. The position of the transition of the tinned coating from solid to molten state, called the "flow line", is determinable by monitoring the strip temperature in the manner described. The sensor 15 is located opposite a slot in wall 4 coincident with the expected position of the 'flow line'.