Patent GB-1310093-A (GB)
Title: Vacuum furnaces
IPC: C21D1/773
Filed: 1971-03-26
Abstract: 1310093 Vacuum furnaces C I HAYES Inc 26 March 1971 8721/71 Heading F4B A water cooled, double walled vacuum furnace for heat treating metal articles includes a heating zone 30 containing a graphite walled heating chamber 32, a transfer zone 28 and a water jacketed oil filled quench zone 31. The heating chamber 32 contains flexible woven tubular graphite resistors 44 fed from water cooled bus-bars 48, and may be closed by a pivotable door 60 automatically operated from outside the furnace through a metal tape 62 connected to it. Cooling water introduced through tangentially disposed jets, is forcedly circulated between the plastics coated circular sectioned mild steel inner shell 16 of the furnace and an open topped rectangular cross-sectioned mild steel outer housing around it (Fig. 10, not shown). A circulating gas fan 260 and annular inspection ports in the outer housing (Fig. 3a, not shown) are also provided. In operation, a basket (not shown) containing the articles to be treated is placed on a work cart 72 formed from molybdenum bars 84, Fig. 7, interconnecting the channel shaped legs 78 of a three sided frame. The cart 72 is introduced from transfer zone 28 into heating zone 30 along fixed rollers 56 mounted outside of the heating chamber 32. Longitudinal slots 90, Fig. 7, in side walls 37 of heating chamber 32 allow passage of the bars 84 as the basket carrying work cart 72 is introduced into heating chamber 32, outer and inner heat shields 94, 98, 100 carried on the cart blocking heat loss through the slots. After the heating the furnace is filled with nitrogen, preferably at subatmospheric pressure, and work cart 72 is automatically retracted by the winding up of a metal tape 172, Fig. 8, secured thereto, on to rollers 142, Fig. 1, carried by a framework elevator structure 74. This moves along fixed vertical channel shaped tracks 144 to convey the cart from transfer zone 28 to quench zone 31 and then back for discharge through sliding door 20 after release of metal tape 172. An hydraulically operated piston-cylinder lift mechanism 152, 156, 158, Figs. 1 and 8, controls movement of elevator structure 74, the front frame member 122 of which is suspended by chains 166, 167, which are fixed at their other ends and passed around the crosshead 160 of upper piston 158 of the lift mechanism, so that on vertical movement of the lift mechanism, a movement twice as far of the elevator structure 74 is obtained. A movable idler 189, Fig. 8, over which the metal tape 172 passes is connected to the crosshead 160 to move with it during movement of the lift mechanism and the elevator structure 74, so that tape 172 is kept taut to positively hold work cart 72 in place on vertical movement of the elevator structure 74. The lifting mechanism is operated using the quench oil which slowly bleeds from cylinder 152 to lower the elevator structure 74 until an associated arm 202 engages a valve (238, Fig. 11, not shown) to cause a rapid bleed of oil from the cylinder and so a rapid lowering of the elevator structure from just above to completely below the quench oil surface. On complete immersion of the basket the lowering speed of the elevator structure is once more reduced. After a predetermined quench period an air driven pump (not shown) forces quench oil into the cylinder 152 to lift elevator structure 74 and the quenched articles back to the transfer zone 28. In a modified treatment process, after an initial evacuation, the whole furnace is filled with nitrogen, preferably at a reduced pressure before heating of the articles is commenced.