RU2097943C1 - Tubular electric heater with thermal switch - Google Patents

Abstract

FIELD: electric instrumentation engineering. SUBSTANCE: in proposed tubular electric heater loose compacted heat- resistant material used in the capacity of electric insulator is placed into internal unfilled space of shell which makes it possible to get rid of own insulation shell of thermal switch. EFFECT: simplified design of heater. 1 cl, 1 dwg

Description

 The invention relates to electrical engineering and can be used in the manufacture of a tubular electric heater (TENA) with a thermal switch installed inside it.

 A large number of technical solutions for the creation of heating elements with thermal switches are known, for example, [1-3] As an analysis of the technical solutions of recent years has shown, specialists tend to place a thermal switch inside the heating elements.

 However, whatever designs of the thermal switch itself were not applied in this case, they all have a protective sheath made of electrical insulation material. In all cases, in the space between the shell of the heating element and the thermal switch there is no compacted, loose, insulating material. If this material, as a rule, is located in the entire inner space of the heater shell without a thermal switch, this was not possible for structures with a thermal switch. This is due to the fact that during the manufacturing process during compression of the TENA shell, the thermal switch is destroyed. All of these designs are difficult to manufacture.

The technical solution closest to the invention is the design of a heating element with a thermal switch [4]
The disadvantage of this solution is also the complexity of the design.

 The purpose of the invention is to simplify the design.

 The drawing shows a longitudinal section of a heating element with a thermal switch.

 This design consists of an external metal shell 1 in the form of a tube, closed at both ends by heat-insulating heat-insulating elements, such as bushings 2. Inside the shell there is a heater 3, which is made in the form of a spiral-wound wire, one end of which is electrically connected to the terminal 4, partially incoming into the shell through an opening in the sleeve 2, and the other end with a contact rod 5, electrically connected, in turn, with a thermal switch made in the form of a hermetically sealed tube 6 of fusible conductive material, the internal volume of which is filled with a substance activator 7, non-conductive electric current. On the other hand, the thermal switch is electrically connected to terminal 8. Electrical terminals 4 and 8, heater 3, contact rod 5 and tube 6 of the thermal switch are insulated from shell 1 by gas-permeable sealed granular material 9, for example, periclase grade PPE-1M (GOST 13-236-83) or quartz sand PK95 (GOST 7031-75).

 A heater with a thermal switch works as follows.

In cases of using a heating element with a thermal switch as a water heater with a sufficient water level, when the area of the thermal switch is washed with water, the temperature of the thermal switch does not exceed 120 ^o C, the thermal switch does not work and the product operates normally. When boiling water or turning on a heating element with a thermal switch without water, the temperature of the thermal switch rises, reaching the melting point of the alloy of the thermal switch tube. The tube melts. The activator substance, by reducing the surface tension, helps to collect the melt into droplets and break the electrical circuit. This creates an electric arc. The gaseous decomposition products of the activator substance formed in the electric arc pass through the compacted bulk material surrounding the thermoswitch, preventing a sharp increase in pressure in the small volume occupied by the thermoswitch and the deformation of the heater shell.

 On the other hand, the compacted bulk material, enveloping the thermal switch, does not allow the melt to reach the inner surface of the shell of the heating element, thus there is no danger of short circuit to the shell.

 The design of the thermal switch does not contain moving parts and its deformation during compression during the manufacture of the heating element does not lead to a loss of operability. This allows the use of compacted bulk material as an electrical insulator, placing it in the entire internal empty space of the heater shell, and refusing to install its own insulating shell of the thermal switch, which simplifies the design of the heating element with a thermal switch and its assembly technology.

 Tests have shown that if the thermal switch is located closer than 5 mm from the heater, false alarms are possible. Therefore, it is recommended to install the thermal switch at a distance of at least 5 mm from the heater.

 Industrial applicability of the proposed design is obvious. This design has passed pilot tests at AOOT Nizhny Novgorod Plant "Start" and has shown good results. The simplicity of the proposed design of the heating element with a thermal switch allows it to be manufactured without complicated additional equipment at any of the enterprises involved in the manufacture of heating elements.

 These signs distinguish the proposed technical solution from the prototype and determine the compliance of this solution with the requirements of the invention.

Claims (2)

 1. A tubular electric heater with a thermal switch containing a metal sheath, closed at both ends by electrical insulating elements, for example, in the form of a sleeve, with holes through which two electrical leads partially entering the sheath pass, a heater in the form of a spiral-wound wire, located in the sheath, one the end of which is electrically connected to one of the terminals, and the other end to a contact rod electrically connected, in turn, to a thermal switch, which is hermetically sealed a closed tube made of a fusible conductive material, the internal volume of which is filled with an activator substance that does not conduct electric current, on the other hand, the thermal switch is electrically connected to another terminal, while the internal space between the shell and the heater with the connected terminal is filled with a sealed, loose, heat-resistant material, electrically insulating them, characterized in that the sealed, heat-resistant material is placed throughout the empty space of the shell directly adjacent to the contact rod, thermal switch and other output, electrically isolating them from the shell.  2. The electric heater according to claim 1, characterized in that the distance from the thermal switch to the heater is at least 5 mm.