GB871111A - Improvements relating to a recirculating atmosphere furnace - Google Patents

Abstract

871,111. Annealing bell furnaces. STEIN & ATKINSON Ltd. June 18, 1957 [June 18, 1956], No. 19205/57. Classes 51 (1) and 51 (2). In a recirculating atmosphere furnace of the kind having a base supporting the charge, a removable inner cover, a fan in the base for circulating the atmosphere within the inner cover and an outer cover arranged to supply heat to the inner cover, radiant heat is concentrated on a limited zone of the inner cover. A portable heating hood 10 and inner belltype muffle 11 seat on a base 15 comprising a stand 18 for supporting a column of coils of metal to be annealed. The furnace atmosphere is circulated by fan 23 coaxial with a central aperture in the top plate of the stand 18, which has radial gas passages defined by spacers. The furnace is heated by tangentially directed burners 34 within a groove 35 in the peripheral wall 16 of the base 15, on which the hood 10 seats. An annular air supply passage 37 supplies air tangentially to the track 35. The track 35 may be of rectangular, curved or triangular cross-section or it may be formed below a projecting lip or ledge on the inside wall, but its radial depth should be at least half of its vertical height in order to concentrate the radiant heat on the lower part of the inner bell 11. Pilot burners may be arranged in a small annular recess within the track 35. Secondary air from passage 42 is supplied at low velocity through radial ports 43 below the hot track, and the proportion of secondary air supplied is controlled in accordance with the temperature at thermocouples 45 and 46 in the lower and upper parts of the bell 11 respectively. A higher proportion of secondary air raises the level of the hottest part of the bell. The total fuel and air input is controlled in accordance with the temperature at a third thermocouple 55 in the stand 18. A wall 60 close to but spaced from the side wall of the inner bell 11 forms a nozzle directing the gases against the side wall. A horizontal flange 62 at the bottom of wall 60, seats on the top plate of the stand 18, and vertical slots in the wall 60 enables the flange 62 to seat properly on different bases when the inner bell 11 seats on the base, Fig. 6. The wall 60 extends to the same height as the intense radiation from the hot track 35. The wall of the bell 11 may be corrugated. In a modification, Fig. 3 (not shown), the hot track 35 is formed in the'outer cover rather than in the base.