JPH0147873B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a sheathed heater, the purpose of which is to increase the moisture resistance of insulating powder filled between a heating wire and a pipe housed in the sheathed heater. .

As shown in FIG. 4, a conventional sheathed heater has an insulating powder 4 filled between a metal pipe 1 constituting the outside and a coil-shaped heating element 3 connected to a lead wire 2 and located inside the pipe. However, since the magnesia powder used as an insulating material has hygroscopic properties, it has the disadvantage that insulation resistance decreases when left in a humid atmosphere for a long time. Therefore, moisture-proofing can be achieved by mixing silicone resin 5 with magnesia powder to be filled in the pipe, or by applying an organic silicone material to the inner wall of the pipe and heating it to melt the silicone material and coating it on the surface of the magnesia powder. It was on.

However, even if a certain amount of silicone resin powder is mixed with magnesia powder, it is difficult to maintain a constant ratio due to the difference in specific gravity between the two, and there are also drawbacks such as the need for a drying process when silicone material is applied to the inner wall of the pipe. It was hot. Furthermore, when bending the heater, the pipe needs to be annealed, but if the magnesia powder inside the pipe contains silicone material, the annealing deteriorates the magnesia powder and causes the problem of loss of moisture resistance. .

The present invention has been made in view of such conventional drawbacks, and is made by filling insulating powder between a metal pipe and a heating element, allowing the lead wire connected to the heating wire to be drawn out from the opening of the pipe, and An assembly process in which the silicon material is accommodated in the opening separately from the insulating powder, a sealing process in which the opening is sealed with a mouth seal, and a bending process in which the bent part of the pipe that is away from the organic silicon material is annealed and then bent. and an evaporation step in which the organosilicon material is heated and evaporated at a temperature that does not lose its moisture resistance after the pipe is bent, and is spread throughout the pipe and deposited on the surface of the insulating powder. .

Since the organosilicon material is housed inside the opening of the pipe in addition to the hygroscopic insulating powder, the silicone material will not evaporate even if the bent part of the pipe away from the organosilicon material is annealed. By heating and evaporating the silicon material, it can be deposited on the surface of the insulating powder and inactivated.

Examples of the present invention will be described based on the drawings.
Reference numeral 11 denotes a bottomed or bottomless metal pipe made of stainless steel, iron, copper, etc., and has an opening 12 at one end or both ends, respectively. Next, a coiled heating wire 13 is housed in the pipe 11, and an insulating powder 14 made of ceramic powder such as magnesia is filled between the heating wire and the pipe 11, and leads are connected to both ends of the heating wire 13. The wires 15 are each led out from the openings 12. Furthermore, resin, rubber,
After containing an organic silicone material 16 made of oil, varnish, or other material alone or mixed with ceramic, a mouth seal part 17 is attached to the outside of the silicone material 16 to seal it, and a lead wire 15 is inserted from the mouth seal part. It's pulled out.

To bend the pipe 11, the bent part is annealed to prevent cracks from forming in the pipe, but if the pipe is a stainless steel pipe, annealing is performed at 1000°C.
That's all. However, since the heat-sensitive silicon material is located inside the opening at the end of the pipe,
Even if the bent portion is annealed, the silicone material will not be heated, and the moisture resistance of the insulating powder will not deteriorate.

During annealing, a tool such as pliers (not shown) can be used to hold the pipe between the opening and the bent portion to prevent heat conduction.

Next, the temperature at which the moisture resistance of the silicone material is not lost;
For example, it is heated at 300 to 700°C for 1 to 3 hours to evaporate it, and then it is deposited on the surface of the insulating powder inside the pipe to inactivate it and improve its moisture resistance.

In addition, the silicon material used in the present invention has a methyl group,
Any silicone material containing a dimethyl group can be used, and alumina, silica, or other ceramic materials other than magnesia can also be used as the inorganic insulating powder, if necessary.

Next, to explain the operation of this embodiment, an insulating powder 14 is filled between the coiled heating wire 13 and the pipe 11, and a mouth seal part 17 is attached to the opening 12 of the pipe. Then, the lead wires 21 are pulled out from the mouth seal part, and the organic silicon material 16 is placed inside the mouth seal part separately from the insulating powder.
Therefore, when annealing the bent part away from the silicone material 16 to 1000℃ or higher, if silicone material is mixed in the insulating powder inside the pipe, the moisture resistance of the silicone material will deteriorate due to the heating. However, before the organosilicon material is evaporated, it is only insulating powder, so the bent part that is annealed at 1000°C or higher is far from the organosilicon material 15 and does not reach high temperatures. Silicone material does not evaporate.

After bending the heater into a predetermined shape, the entire pipe is heated for 1 to 3 hours at a temperature of 300 to 700°C, which does not lose the moisture resistance of the silicone material placed inside the opening of the pipe, separately from the insulating powder. The silicon material 15 is evaporated and distributed throughout the pipe to perform a vapor deposition process on the surface of the insulating powder.

However, since the opening 12 of the pipe 11 is a non-heat generating part for the heater, the opening does not deteriorate due to overheating.

Conventional pipe heaters in which a silicone material is mixed into the insulator powder to inactivate the surface of the insulator powder are more susceptible to overheating and deterioration of the silicone material in contact with the heating wire. It's excellent.

In FIG. 2, A shows the change in insulation resistance of the heater of the present invention, and B shows the change in insulation resistance of a conventional heater that does not use a silicone material, and shows the characteristics at 40° C. and a relative humidity of 95% or more.

As described above, in the present invention, in addition to the insulating powder that is filled between the heating wire in the metal pipe and the pipe, the organic silicon material is stored in the mouth seal part that is attached to the opening of the pipe, making the storage work easy. and
Even if the bent part is annealed, the silicone material will not evaporate and deteriorate its hygroscopicity because it is separated from the organic silicone material.After the pipe is bent, the organic silicone material will be heated and evaporated to spread throughout the pipe. Therefore, the moisture resistance of the insulating powder at the bent portion can be maintained, and since the insulating powder has durability against humidity, deterioration of insulation resistance can be prevented even if the heater is used for a long period of time.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; Fig. 1 is an overall sectional view, Fig. 2 is an explanatory diagram showing the insulation resistance characteristics of insulators of the inventive and conventional heaters, and Fig. 3 is a folded view. FIG. 4 is a partially broken sectional view of a conventional heater. DESCRIPTION OF SYMBOLS 11...Metal pipe, 12...Opening part, 13...Heating wire, 14...Insulating powder, 15...Lead wire, 16...
Organic silicon material, 17... Mouth seal part, 20... Bent part.

Claims (1)

[Claims] 1 Fill insulating powder between the metal pipe and the heating element, pull out the lead wire connected to the heating wire from the opening of the pipe, and store the organic silicon material in the opening separately from the insulating powder. The assembly process, the sealing process in which the opening is sealed with the mouth seal, the bending process in which the bent part of the pipe away from the organic silicone material is annealed and then bent, and the pipe does not lose its moisture resistance after being bent. A method for manufacturing a sheathed heater that consists of an evaporation process in which an organic silicon material is heated at high temperature to evaporate it, spread it inside the pipe, and deposit it on the surface of the insulating powder.