JPS58155691A - Method of producing sheathed heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a sheathed heater, and a method for manufacturing a sheathed heater that easily forms an S L 02 layer on the surface of a heating wire in order to obtain a sheathed heater with a long life and insulation resistance at high temperatures. It provides:

Generally, a sheathed heater has a structure in which a heating wire is arranged inside a metal pipe with an insulating filler interposed therebetween. In a sheathed heater with such a structure, 900
Because the temperature reaches the level of a layer, low melting point substances such as oxidizing power and sodium oxide contained in the VC in the insulating filler may react with the heating wire, and metal components such as pipes and heating wires may react with each other. Phenomena such as water and evaporation occur, reducing the insulation resistance and dielectric strength voltage of the sheathed heater.
There is a problem with shortening the lifespan.

By the way, conventional sheathed heaters are manufactured as follows. After the heating wire is housed in the metal pipe, an insulating filler is filled into the C-ib from one end of the pipe, and then the diameter of the C-ib is reduced by rolling, and the work hardening caused by rolling is removed through an annealing furnace. After further bending, the pipe is heated and dehumidified, and both ends of the pipe are sealed.

Since the sheathed heater manufactured by such a method undergoes two heating steps, an oxide film having a thickness of about several μm is formed on the surface of the heating wire.

This oxide film acts as a protective layer on the surface of the heating wire, and has the role of preventing to some extent the phenomenon of reaction with low melting point substances and metal components of the pipe, etc., and evaporation of the metal components of the heating wire itself. However, since the film thickness is only about several μm, the effect as a protective layer is not necessarily sufficient. The thicker this oxide film is, the longer the life of the sheathed heater can be expected. However, the thickness of the oxide film on the heating wire is determined by the heating temperature and heating time. It is difficult to form a sufficiently thick film because the temperature and heating time cannot be increased. Furthermore, if a film is formed due to oxidation of the heating wire itself, there are problems such as the heating wire becomes thinner and the wire resistance increases.

The present invention solves the above-mentioned conventional drawbacks by proposing a manufacturing method that can easily form a Sio2 layer, which is a heating wire protective layer, on the surface of a heating wire, thereby making it possible to provide a sheathed heater with a long life. be.

Examples of the present invention will be described below.

FIG. 1 is a diagram showing a cross section of a heating wire coated with polysiloxane, where 1 is an electrical resistance wire and 2 is a film made of polysiloxane coated on the surface of the electrical resistance wire. As the polysiloxane film 2, silicone resin, silicone varnish, silicone grease, silicone oil, etc. can be used. FIG. 2 is a cross-sectional view of the sheathed heater when the heating wire and the insulating filler material are housed inside the tube and rolled.

In FIG. 2, 3 is a heating wire having a polysiloxane coating, and 4 is an insulating filler stuffed inside the vibro. By heating the sheathed heater in this state, the polysiloxane film coated on the electrical resistance wire is decomposed, and a 5102 layer 6 is formed on the surface of the electrical resistance wire as shown in FIG.
is formed.

In FIG. 3, the same components as in FIG. 2 are given the same reference numbers. Thereafter, the sheathed heater according to the present invention is obtained by bending the pipe, heating and dehumidifying it, and sealing both ends of the pipe.

According to the manufacturing method of the present invention, the polysiloxane film coated on the surface of the electrical resistance wire can be easily decomposed in the annealing process to form the 5102 layer, and special reinforcement and
No process required. During the heating process, both ends of the pipe remain open, so the carbon in the polysiloxane becomes CO2 gas and scatters to the outside from both ends of the pipe, so it does not remain as carbon inside the pipe. Decrease in insulation resistance due to carbon can be prevented.

Further, if dimethylpolysiloxane, methylphenolpolysiloxane, or the like having a small carbon content is used as the polysiloxane, a decrease in insulation resistance can be further prevented.

The generated S z 02 layer is relatively porous and cracks occur due to bending etc. later, but it is sufficiently effective in preventing deterioration of the heating wire, has little deterioration of insulation resistance during heating, and is superior to conventional A sheathed heater with a lifespan several times longer than a sheathed heater can be created.

FIG. 4 shows changes over time in insulation resistance of the sheathed heater obtained by the manufacturing method of the present invention and the sheathed heater obtained by the conventional manufacturing method. In FIG. 4, A shows a change in the characteristics of the sheathed heater obtained by the manufacturing method of the present invention, and B shows a change in the characteristics of the sheathed heater obtained by the conventional manufacturing method. Note that these data were obtained when the surface temperatures of the heating wire were 950° C. and 750° C. during energization and measurement, respectively. It can be seen from FIG. 4 that the sheathed heater obtained by the method of the present invention has much less deterioration in insulation resistance than the conventional one.

As is clear from the above explanation, according to the sheathed heater manufacturing method of the present invention, it is possible to easily form a thick protective layer made of 5i02 on the surface of the heating wire to prevent deterioration of the heating wire, and the insulation resistance It is possible to provide a sheathed heater with little deterioration and long life, and its industrial value is significant.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a heating wire coated with polysiloxane, FIGS. 2 and 3 are cross-sectional views of essential parts of a sheathed heater for explaining the manufacturing method of a sheathed heater according to the present invention, and FIG. FIG. 2 is a characteristic diagram showing changes in insulation resistance over time in a sheathed heater. 1 , , , , Electric resistance wire 2 , , Polysiloxane ruptured membrane 13 ... Heating wire 14 ...
・Dicolor edge filling material S6...'' Eve 0

Claims (1)

[Claims] A method for manufacturing a sheathed heater, which comprises filling a metal pipe with a heating wire whose surface is coated with polysiloxane and an insulating filler, and then forming an S102 layer on the surface of the heating wire through a heating process.