Patent GB-1383904-A (GB)
Title: Electrically heated vessels
IPC: A47J27/21
Filed: 1971-02-05
Abstract: 1383904 Heated vessels BRITISH DOMESTIC APPLIANCES Ltd 3 May 1972 [5 Feb 1971] 4025/71 Heading A4A [Also in Divisions H1 H2 and H5] An electrically heated domestic vessel e.g. a jug, kettle, pan or percolator, comprises a first housing 8 carrying an immersion heater 6 and accommodating a "boil dry" thermally responsive device mounted on a wall 1 of the vessel and a second housing 5, preferably in the form of a handle, mounted on the wall 1 and accommodating steam operated thermal switch, the first housing 8 carrying a conductor 12 which automatically engages a conductor 14 carried by the second housing 5 when the housings are mounted on the wall 1, the "boil dry" thermally responsive device being arranged to break the electrical contact between the conductors 12, 14 when it operates. The housing 8 is secured to wall 1 by means of screws 21 which pass through a sealing member 22. The housing 5 is secured to wall 1 by an upper screw 27 and by a U-shaped bracket 29 which is welded to the wall 1 with its two limbs embracing the housing 5. Screws secure the two limbs of the bracket to the handle housing 5. A shroud 24 is secured to the housing 5 by screws 25 and surrounds a terminal pin assembly, pins 13 and 18 being shown. Thus the two housings 5 and 8 may be independently removed. The housing 8 carries an earth terminal 18 connected to the metal sheath of the heating element 6 and a further terminal (not shown) connected to one end of the heating element, and the housing 5 carries the other terminal 13 of the three pin terminal assembly. A plunger 15, 16 actuated by the "boil dry" thermal device separates conductors 12, 14 in the event of overheating. The steam operated thermal switch comprises a bi-metallic strip 33 provided with an adjustment screw 36 and mounted in a compartment 34 defined between the housing 5 and wall 1. An aperture 37 in the wall 1 admits steam to a duct 38 provided with a plurality of outlets 39 for direction on to the bi-metallic element 33. The element 33 acts on a plunger 56 covered by a diaphragm 57 impervious to steam. The plunger 56 acts on a trifurcated blade spring 48 stressed by a bow spring 50. The centre limb of spring 48 carries a contact 43 which co-operates with a fixed contact 44. The trifurcated blade spring 48 is secured at its lower end by a screw and rivet 52 to the housing 5, the rivet 52 also securing the blade 48 to a conductive strip 53 formed integrally with the U-shaped spring contact 14. The fixed contact 44 is mounted on a conductive strip 45 rivetted to terminal pin 13. A spring device 55 operable between two stable positions to modify the action of the snap-action blades 48 is mounted on a cover 54 of housing 5. The spring device 55 is actuated by a push rod 58 slidable in an aperture 59 of housing 5. Rotation of a control knob 61 provided with a cam surface 60 controls the position of the spring device 55. In one position of spring device 55 its upper end allows only limited movement of the centre limb 49 of the trifurcated blade spring 48 and prevents it moving over-centre so that it will reset when the liquid in the vessel cools down. In the second position of the control device 55, the trifurcated blade spring 48 is permitted to move over-centre and must be manually reset by control knob 61. A lamp 63 is illuminated when contacts 43, 44 separate. In a modification, the steam duct 38 is omitted, a tube or aperture conveying steam to the bi-metallic element which is U-shaped.