Importance

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Abstract

A temperature warning device for indicating when a threshold temperature has been exceeded includes a threaded bolt having a bolt head and a bolt body. The bolt head and bolt body have a longitudinal bore defined by a surrounding surface with the bore having a closed end and an open end at the bolt head. A plunger in the bore has a plunger head and a plunger body terminating at the open end of the bore. A retaining cap is secured in the bore of the bolt head and has a cap hole through which the plunger body freely extends. A sleeve of a fusible material is contained in the bore which melts at the threshold temperature. This sleeve substantially fills a volume of the bore radially between the plunger body and the surrounding surface of the bore and longitudinally between the plunger head and the cap. A compressed spring is located in the bore between the closed end and the plunger head. With this construction, if the threshold temperature is exceeded, the fusible sleeve melts and the spring moves the plunger longitudinally so that the plunger body extends beyond the retaining cap and the bolt head and is easily visible to serve as a warning. A two stage signalling is achieved by forming the sleeve of two discrete longitudinal portions butted end to end with a fusible material of the portion adjacent the plunger head having a lower melting temperature than the other the portion.

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First Claim