DE1648293

1,220,832. Temperature indicators. CONTINENTAL ELEKTROINDUSTRIE A.G. [trading as CONTINENTAL ELEKTROINDUSTRIE A.G. ASKANIA-WERKE] May 13, 1968 [May 12, 1967; Sept. 20, 1967], No. 22669/68. Heading G1D. A device for indicating whether the temperature of an iron melt during refining is at or above a predetermined temperature comprises a body 3, e.g. of iron containing an explosive charge 8 to be ignited by a filament 7, and a tube 11 containing metal granules 18 which melt at the predetermined temperature thus shorting two electrodes 16, 17 disposed in the tube and normally spaced by a separator 14, the electric circuit to the filament 7 from a battery 5 being completed through the iron melt to ignite the charge 8 and provide an acoustic signal which may be detected by a microphone, if the temperature of the melt is above the predetermined temperature. If desired the tube 11 may contain two compartments containing granules having different melting points and having electrodes coupled to separate explosive charges to indicate whether one or both of the melting point temperatures have been exceeded, the action of the melt on the granules with the higher of the two melting points being delayed by the provision of a ceramic insulator round part of the tube 11. In alternative embodiments electrical ignition of the explosive charge is dispensed with and the heat of the melt is used to detonate the charge. In these cases the charge is disposed in a recess in a body of iron, the opening of which is closed by a disc of metal of predetermined melting point, so that when the disc melts the charge will ignite. Discs of silver plated copper foil may be disposed behind the metal disc to prevent radiated heat causing premature explosion of the charge. As before two recesses closed by discs of different melting temperatures may be provided to indicate the attainment of more than one temperature. Explosive mixtures which develop certain optical colour effects may be used to enable observation to be carried out optically rather than acoustically.