Abstract
THE British Thomson-Houston Co., Ltd., has sent us specimens of a new bimetallic strip for use in thermostatically controlled devices. The strip is prepared by the permanent union over their entire length of two metals with widely differing coefficients of expansion. The union between the two component metals is complete and durable, and the strip may be bent, twisted, or hammered without causing the separation of the metals at any point, and even on heating the bond will not be broken so long as the temperature remains below the melting point of the softer of the two metals. Owing to this permanency of union the metal can be formed into any desired shape, annealed after formation, and safely employed at any temperature below 500° F. The component metals do not corrode under ordinary conditions, and may be used in any reasonable situation without fear of deterioration or change in operating characteristics. The amount of deflection obtained is always the same in a strip of given length and thickness for a given temperature change, and consequently the strip provides a trustworthy basis for the operation of any thermostatic device, and may be employed for work of high precision. The deflection due to temperature change varies inversely as the thickness, directly as the square of the length, and directly as the temperature change. With a strip in. long, 0.31 in. wide, and 0.03 in. thick the deflection obtained for a temperature change of 100° F. is about 0.57 in. The force exerted varies as the square of the number of decrees of temperature change and as the square of the thickness, and directly as the width, and is not affected bv changes of length. For a strip of the dimensions above-mentioned the force exerted for 100 ° F. change of temperature is about 3 oz. weight, whereas for a strip of the same dimensions but 0.1 in. thick the force exerted is about 24 oz. weight. To produce a permanent set in a strip 4 in. long, 0.31 in. wide, and 0.03 in. thick a force of about 7 oz. weight would be required. The metal is manufactured in standard sizes ranging from 0.01 in. to 0.25 in. in widths up to 6 in. and lengths up to 36 in. It can, however, generally be supplied cut to widths and lengths to suit the purchaser, and in special cases thermostatic metal parts mav be completely formed to the purchaser's specifications.
Article PDF
Rights and permissions
About this article
Cite this article
Thermostatic Metal. Nature 105, 793 (1920). https://doi.org/10.1038/105793b0
Issue Date:
DOI: https://doi.org/10.1038/105793b0