Patent GB-883629-A (GB)
Title: An expendable immersion temperature-sensing unit
Inventor: MEAD HAROLD GRAY
IPC: G01K7/02
Filed: 1958-02-03
Abstract: 883,629. Thermocouples. LEEDS & NORTHRUP CO. Feb. 3, 1958, No. 3502/58. Class 37. [Also in Group XXXVIII] An expendable unit for measuring the temperature of molten metals comprises a supporting body made of an electrically insulating material of poor heat conductivity and having an immersible end face, a temperature-sensitive element extending outwards from the face and protected by a housing consisting of a heatconducting insulating member fixed to the body, and conductors connected within the body to the ends of the element and extending through the body to its other end face. In one embodiment a thermocouple consisting of platinum and platinum/rhodium elements 20, 21 (Fig. 2), welded together at 22 is housed within a refractory tube 23. The tube is cemented into the ends of holes formed by nailing together two supporting wooden strips 13, 14 so that pairs of grooves on their inner faces are in register. The thermocouple elements 21, 20 are welded at 24 to compensating wires 17, 18 of several times their cross-sectional area constructed of Cu and an alloy of 98% Cu, and 2% Ni by weight respectively. The assembly is completed by pushing an apertured thin metal cap 26 over the ends of the strips and nailing it in place. The lower end of the assembly is then coated with refractory cement to prevent the wood burning when immersed in the molten metal bath. The cap 26 which rapidly dissolves in the metal serves to protect the thermocouple on its passage through slag floating on the metal. In a second embodiment (Fig. 4), an expendable sub-assembly adapted to push-fit into a permanent supporting structure comprises two wooden blocks 31a, 31b, a refractory tube 23 containing the thermocouple element, and a thin metal cap 26. The refractory tube is sealed in block 31 by felt or paper tube 35 or by refractory cement and the compensating wires 36, 37 are adapted to engage spring contacts 47, 48 mounted in the supporting structure. The supporting structure comprises a pair of coaxial metal tubes 40, 41 insulated by ceramic spacers 42, and a terminal block 44. The immersible end of the structure is protected by an expendable paper sleeve 81 and cap 82. In a further embodiment comprising a supporting structure and an expendable subassembly the former (Fig. 5) comprises a series of drilled ceramic elements 72, 73 and a coaxial steel tube 68 separated by ceramic spacers. The drilled ceramic elements, the lowermost of which has a convex face, are threaded on a metal rod 71 on the lower end of which is pivotally mounted on insulating plate 74a. The plate is provided with horns 78, 79 (Fig. 6), which co-operate with pins 80, 81 to prevent the plate from burning, and with conductive segments 76, 77 to which the compensating leads 17, 18 are connected. The expendable subassembly differs from that in Fig. 4 in having the upper end of its cylindrical part of increased diameter and provided with grooves co-operating with pins 65, 66 on the tube 68. The sub-assembly is mounted by engaging the pins in the grooves, pushing it into tube 68 against the pressure of spring 84 until stops 85, 86 prevent further movement and then rotating the sub-assembly until stop 63 engages pin 65. Refractory cement is then applied about the ends of the tube and protective paper sleeve and cap 51, 52, fitted. The sub-assembly is removed by reversing the above process. In each of the above embodiments all parts between the compensating leads 17, 18, and the thermocouple elements are made of the same material as the respective leads. Specifications 883,630 and 883,631 are referred to.