GB776913A - Method of and apparatus for controlling circulation of furnace atmosphere - Google Patents

Abstract

776,913. Furnaces for heat-treating metals. WILSON, L. Oct. 10, 1955 [Nov. 5, 1954], No. 28826/55. Class 51 (2). In a furnace for the heat treatment of metals, e.g. the annealing of steel &c. strip, of the kind in which spaced, superposed coils of strip are enclosed in a cover 25, Fig. 1, within a bell F heated by combustion tubes lining the wall of the bell and supplied with oil and air through manifolds 3, 4, respectively, and in which the atmosphere within the cover is circulated over the coils by a centrifugal fan 9 driven by an electric motor, the coils are supported upon a base S constituting a diffuser unit for the fan and formed of vanes 15, Fig. 2, disposed between plates 14, 16 enclosed by a rim 17, said vanes having attached to their inner ends bimetal plates 28 which restrict the output of the fan while the furnace is warming up, and which flex and lie against the vanes when the annealing temperature is reached and permit increased circulation of the atmosphere within the cover. The atmosphere flows through an annular space 18 between the plate 16 and the rim 17 over the outsides of the coils and through the spaces between the coils and down the centres of the coils back to the fan. The cover has an outlet for circulating atmosphere so that the pressure within the cover remains substantially constant as the temperature rises. In a modification, the circulation is controlled by a movable plate 31, Fig. 5, which coacts with an apertured plate 30 placed over the central passage formed by the superposed coils and attached to a bellows 36, the lower end of which is secured to a plate 35 carried by bolts 34 mounted on webs 33 integral with the plate 30. As the temperature rises, the plate 31 is moved by the free end of the bellows towards the dotted line position. In another arrangement, the circulation is controlled by counterweighted flaps 42, Fig. 6, coacting with apertures 41 in a plate covering the top of the central passage through the coils. Fig. 8 shows a further modification in which the flow is controlled by fixed and rotatable apertured plates 47, 48 respectively and in which the inner plate 48 is rotated by a biinetal strip 55 secured at one end to the plates and at the other to a fixed bar 54. The plates are closed by a cover, not shown.