GB1301711A - - Google Patents

Abstract

1301711 Vacuum furnaces K HINTENBERGER 21 April 1970 [27 May 1969] 19045/70 Heading F4B An electrically heated vacuum furnace 1 for firing dental ceramics is provided with pneumatically actuated telescopic charging and discharging means 9. These means comprise a cylinder 11 located in a control unit 6 below the furnace 1, a hollow piston 10 within the cylinder 12, and a further piston 13 within hollow piston 10. In operation a compressed air supply from a pump used to evacuate the furnace, first actuates the hollow piston 10 to raise the object 14 to be fired and its ceramic support 15 into the evacuating zone 8<SP>1</SP> of the furnace, and gaskets 16 on a cover-plate 10<SP>1</SP> into contact with casing 4 to seal off the charging opening of the furnace. At this time a further object located between pillars 26 may be preheated in the zone 8. Subsequently aperture 19 in cylinder 12 is closed by a valve so the compressed air passes through bore 18 to actuate piston 13 and raise object 14 on its support 15 from the evacuating zone 81 to firing zone 1<SP>1</SP>. At the end of firing the means 9 may be lowered in a damped fashion on release of pressure through aperture 19. A handle 20 secured to a collar 21 below plate 10<SP>1</SP> allows limited manual operation of the charging means 9. Microswitch and pilot light means may be provided to indicate maximum extension of the charging means. The whole charging, firing and discharging sequence may be automatically controlled. In a modification (not shown) the bore at the lower end of the hollow piston is located in its side wall, so as to be aligned when the hollow piston is fully extended with an air inlet in the side wall of the cylinder, through which inlet air to lift the innermost piston may be supplied.