Patent GB-744885-A (GB)
Title: Electrical immersion heater
IPC: H05B1/02
Filed: 1953-12-22
Abstract: 744,885. Thermal switch. STIEBEL, T. H. Dec. 22, 1953, No. 35636/53. Class 38(5) [Also in Group XI] An immersion heater has a hollow shank 2 extending between an electric heater and a handle 3 which contains a thermal switch controlling current supply to the heater by the differential expansion or contraction of the shank'2 and an element 6 extending within the shank and attached to the interior of an envelope surrounding the heater. Thus the shank 2 may be of brass and contains a rod 6 of a metal with a low coefficient of expansion, or the inner element may be a tube containing liquid. The temperature of switch actuation is adjustable by a knob 36 in the handle and when such temperature has been reached, the supply is either permanently disconnected until a push button 68 in the handle is operated, or the switch may operate to maintain the temperature by intermittent operation. Thus in Fig. 2 the temperature of operation is adjusted by rotation of a shaft 33 screwed over the threaded end of the rod 6, so that on expansion of the shank 2 on rise in temperature, the shaft 33 is lowered until it engages an angular member 53 mounted on a lever 39, which is thereby tilted. The lever 39 has pointed ends engaging at one end in a groove in a U-shaped member 23 in the handle and at other end in a groove in a lever 40, which tilts in a groove in a lower lever 41 itself tilting in a groove in the lower end of the U-shaped member 23. Tilting of the lever 39 tilts the levers 40, 41, the latter carrying a spring arm 50 carrying at its upper insulated end a conductive bridge 51 normally bridging two spaced contacts 20 to which supply cables 5 are connected; and tilting of the lever 41 removes the bridge 51 from the contacts 20 to break the circuit. A coiled spring 60 is adjustably mounted on a pin 59 extending into a slot in the lever 39 and as the shank 2 contracts on cooling, the shaft 33 is raised away from the member 53 and the levers 39, 40, 41 are moved into aligned position by pressure of the spring 60 on the lever 39, whereby the heating circuit is reestablished. The spring 60 bears on a collar 57 on a pin 56 which is threaded into the handle 3 and may be moved out by turning a key 62 to release pressure on the spring 60 so that contacts 20, 52 once broken are not automatically re-established. In this case, the contacts may be brought together by pressing on the end of a pin 65 which then bears on lever 39 to align the levers 39-41, the pin 65 being retracted by the rubber 68 in which it is mounted. When a tube containing liquid replaces the rod 6, a capsule at the top end of the tube operates an elbow lever system (Fig. 3 not shown) to tilt the lever 39. and contacts may be remade as described above. In Fig. 5, the rod 6 carries near the top end an arm 104 with a notched outer end engaging the rim of an aperture in a spring arm 105 carrying at its free end a contact 106 engaging a fixed contact 107. Downward movement of the rod 6 on expansion of the shank 2 releases the spring arm 105 from the notch and opens the contacts. The arm 105 may be re-set when cold by pressure thereon of a push rod 121. The handle 3 is made watertight and with the heaters may be built into a utensil or the lid thereof.