GB889573A - Improvements in or relating to indicating devices for heat treatment - Google Patents

Abstract

889,573. Temperature indicators. MACARTHYS Ltd. Nov. 25, 1960 [Dec. 9, 1959], No. 41936/59. Class 97(3). An indicator for heat treatment comprises an envelope having first and second compartments, the two compartments Being connected by a wick or like porous member, but.otherwise sealed from each other, the wick or the like extending into the second compartment at least a part of the length thereof and the first compartment containing an indicating substance which liquifies, or undergoes a sharp reduction of viscosity at a temperature to be indicated or a little below. The envelope may be transparent and made of a thin thermoplastic sheet material. The indicating substance may be benzoic acid containing a dye and the wick may consist of a strip of filter paper running the whole length of the envelope, being retained by heat seals joining the top and bottom walls of the envelope and sealing off the envelope at the two ends. The indicator is unaffected until the temperature rises to about 120‹C. At this temperature the benzoic acid melts and begins to creep along the filter paper strip, the extent of the: creep being clearly visible due to the dye present. The device may be calibrated and an indicating mark provided along the length of the wick in the second compartment to indicate the maintainance of the temperature at 120‹C., or higher, for a certain period, say 30 minutes.