JPS6286688A - Manufacture of 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] <Industrial application field> The present invention relates to a method of manufacturing a sheathed heater.

Various sheathed heaters with circular cross sections are widely used in various industrial fields. In this type of sheathed heater, a coiled heating wire with a terminal bar connected to the tip is inserted into a metal pipe, the metal pipe is filled with insulating powder, and the opening at the end of the metal pipe is insulated and sealed. However, in its manufacture, it is particularly important that the insulating seal is an airtight seal that clearly separates the outside and inside of the metal pipe from moisture, and that there is sufficient space between the terminal bar protruding to the outside and the metal pipe. It is an airtight seal that maintains a creepage insulation distance and does not create a gap between the bottom surface of the sealing material and the insulating powder due to the electrical resistance test, and that such an airtight seal can be easily, stably and reliably realized. Strongly requested.

The present invention relates to a method of manufacturing a sheathed heater that meets the above requirements.

<Prior art and its problems> Conventionally, the following three methods have been proposed as a method for insulating sealing the end opening as described above in the manufacture of sheathed heaters, but each method has its own problems. be.

First, there is a typical method of glass sealing.

Generally, this method involves inserting a glass tablet into the protruding opening of the terminal bar and sealing the opening by heating and melting it. There is also an example of using cylindrical porcelain in combination (Japanese Patent Application Laid-Open No. 56-54780). However, such a method using a glass seal has a serious problem in that it requires a cumbersome and uneconomic sealing operation of heating and melting the glass. The weakness in strength has basically not been resolved, and after all, problems have arisen in the airtightness of the seal in actual use. Next, there is a method of sealing with resin or silicone rubber. This is a method in which epoxy resin, silicone RTV rubber, etc. is loaded into the protruding opening of the terminal bar and cured to seal the opening. An example of using a metal pipe with a recess in a part of the end in advance so that it does not float up due to thermal expansion of the air inside the heater, and preventing the epoxy resin or silicone RTV rubber from getting caught in the recess. (Utility Model Publication No. 54-11332) and an example of using fluororubber, which has excellent properties as a material (Japanese Patent Publication No. 55-7)
2391) etc. However, such methods using resin or silicone rubber seals are complicated in terms of manufacturing and processing, requiring liquid loading operations, and both methods still require the use of epoxy resins, silicone RTV rubber, etc. Problems related to ensuring creepage insulation distance and sealing airtightness caused by deformation have not been sufficiently resolved. Finally, there is a liquid seal method. This is a method in which a liquid sealant such as silicone grease or solvent-free face is loaded into the protruding opening of the terminal bar, and the opening is sealed by pressing it with a Teflon bushing. For example, an example of impregnating silicone oil to reduce the size of the metal pipe in the relevant part and making the impregnated part denser to improve the sealing effect (Japanese Patent Publication No. 55-444
No. 35) is also available.

However, such a method using a liquid seal tends to cause variations in the sealing effect, and there is a problem in that the liquid sealant is sucked into the internal insulating powder and the sealing effect deteriorates.

<Problems to be Solved by the Invention and Means for Solving the Problems> The present invention provides a method for manufacturing a sheathed heater that solves the conventional problems as described above and meets the above-mentioned demands.

However, as a result of intensive research from the above viewpoint, the present inventors found that
As a method for insulating and sealing the end opening in the manufacture of sheathed heaters, it has been found that a mechanical backing means that uses a relatively hard cap as the sealing material and uniformly applies the repulsive stress of the cap in the surface state is correct and suitable. This finding led to the completion of the present invention.

That is, in the present invention, a coiled heating wire with a terminal bar connected to the tip is inserted, and a relatively hard cap with a through hole is inserted into the opening at the end of a metal pipe filled with insulating powder. Fit the terminal bar so that a portion thereof protrudes outside the metal pipe so that it slides into contact with the outer peripheral surface of the terminal rod and the inner peripheral surface of the end of the metal pipe, and then move the end from the direction of the outer peripheral surface toward the center axis. The diameter of the cap is uniformly reduced around the center axis by surface pressing with a cross-sectional reduction rate of 8% or more, and the cap is deformed and expanded in the direction of the center axis for uniform diameter reduction, and the repulsive stress of the cap is applied to the terminals in a plane state. The present invention relates to a method of manufacturing a sheathed heater in which the outer peripheral surface of a rod and the inner peripheral surface of an end of a metal pipe are uniformly added to make the ends airtight.

Hereinafter, the configuration of the present invention will be explained in more detail based on the drawings.

1 to 4 are schematic cross-sectional views (FIG. 3 is a plan view) illustrating the implementation procedure of the present invention in the order of the figure numbers.

First, as shown in FIG. 1, a coiled heating wire 3 having a terminal bar 2 connected to its tip is inserted into a metal pipe 1 and filled with insulating powder 4. Separately, a cap 7 that fits into the opening 6 in the end 5 of the metal pipe 1 is prepared. The cap 7 is a relatively hard one with a through hole 8 bored in the center, and may be made of various synthetic resins or synthetic rubbers depending on the product application (particularly its operating temperature). In view of heat resistance, chemical resistance, backing effect, etc., those made of fluorine rubber are preferable. Since the cap 7 will be fitted into the opening 6 of the metal pipe 1 in a later step, the amount of insulating powder 4 to be filled into the metal pipe 1 should be enough to allow for the fitting of the cap 7. Since the coiled heating wire 3 is energized, a portion of the terminal bar 2 is made to protrude beyond the cap 7 after being fitted.

As the insulating powder 4 filled here, magnesium oxide powder can typically be used.

Next, in FIG. 2, the cap 7 is inserted into the opening 6 in the end 5 of the metal pipe 1. The inner peripheral surface of the through hole 8 bored in the cap 7 is in sliding contact with the outer peripheral surface of the terminal bar 2, and the outer peripheral surface of the cap 7 is in sliding contact with the inner peripheral surface of the end 5 of the metal pipe 1. , the cap 7 is fitted into the opening 6. In this case, the cap 7 is fitted into the opening 6 to such an extent that a portion of the cap 7 protrudes to the outside of the metal pipe 1. After fitting the cap 7,
This is to ensure a sufficient creeping insulation distance between the terminal bar 2 protruding to the outside and the extreme end of the metal pipe 1.

Finally, as shown by the arrow in FIG. 2, the end portion 5 of the metal pipe 1 is pressed against its outer circumferential surface toward the central axis so that the cross-sectional area of the cap 7 is reduced by 8% or more around the central axis. Uniform diameter reduction. Although a divided mold is used for surface pressing, it is preferable to use a mold divided into three or more parts so that the desired uniform diameter reduction can be completed in one step. FIG. 3 shows a state in which surface pressing is performed using four-part molds 9 to 12.

The surface pressure is applied so that the cross-sectional reduction rate of the cap 7 is 8 inches or more. If a fluorine rubber cap is used as the cap 7, the cross-sectional area reduction rate should be 10 to 15.
% is preferable. This is to cause excessive deformation, expansion and repulsive stress of the cap 7 as will be described later.

FIG. 4 shows a product after uniform diameter reduction by surface pressing. The end portion 5 of the metal pipe 1 is uniformly reduced in diameter by surface pressing as described above, and therefore the cap 7 of the corresponding portion is similarly reduced. When the surface is pressed and the diameter is uniformly reduced, the cap 7 is deformed and expanded in the direction of the central axis. In FIG. 2, if the cap 7 is simply inserted into the opening 6, a gap 13 is likely to occur between the bottom surface of the cap 7 and the top surface of the insulating powder 4. If this gap 13 is left as it is, a discharge phenomenon will occur due to the gap 13 that short-circuits the terminal bar 2 and the metal pipe 1. Difficult to satisfy. but,
When the cap 7 is deformed and expanded in the direction of the central axis due to the above-mentioned surface pressure, the deformation and expansion results in an inconvenient period 1.
! 113 is eliminated as shown in FIG. The outer peripheral surface of the terminal bar 2 and the metal pipe 1
It is applied uniformly to the inner circumferential surface at the end 5 of.

FIG. 5 is a schematic cross-sectional view illustrating the state in which such repulsive stress is applied, and FIG. 6 is a similar schematic perspective view from a thousand planes. In both cases, the arrow in the figure indicates the repulsive stress. As the repulsion stress of the cap 7 is uniformly applied to the surface as shown in the figure, a sufficient backing effect is obtained, and the end portion 5 of the metal pipe 1 is made completely airtight.

<Example> A sheathed heater was manufactured under the following conditions according to the procedure described above in FIGS. 1 to 4.

Cap = made of fluororubber, cross section reduction rate of cap: 1
2L metal pipe length: 5501 KIg, metal pipe outer diameter = 7 fl, metal pipe (# cap) surface press part length = 5 cod, sheathed heater made of insulating powder magnesium dioxide powder (number of samples: 10) The insulation state was measured immediately after manufacture and after 1.5 years had passed. The results are as shown in Table 10Table 1 <Effects of the Invention> As explained above, the present invention has the ability to maintain a sufficient creepage insulation distance and clearly satisfy the withstand voltage test. This has the effect that a sheathed heater having an airtight seal can be easily, stably and reliably manufactured.

[Brief explanation of drawings]

Figures 1 to 4 are schematic cross-sectional views (Figure 3 is a plan view) illustrating the implementation procedure of the present invention in the order of their figure numbers, and Figure 5 illustrates the state of application of repulsive stress to the cap in the present invention. FIG. 6 is a schematic plan view illustrating the added state. 1...Metal pipe, 2...Terminal bar, 3...
- Coiled heating wire, 4... Insulating powder, 5... End, 6... Opening, 7... Cap,
8...Through hole, 9-12...Mold, 13.
...Gap, Patent Applicant Kawai Electric Manufacturing Co., Ltd. Representative Patent Attorney Hiroshi Iriyama Figure 1 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A relatively hard cap with a through hole drilled into the opening at the end of a metal pipe into which a coiled heating wire with a terminal rod connected to the tip is inserted and filled with insulating powder. is fitted so that a part of it protrudes outside the metal pipe so that it slides into contact with the outer peripheral surface of the terminal bar and the inner peripheral surface of the end of the metal pipe, and then the end is inserted into the center axis from the direction of the outer peripheral surface. The diameter of the cap is uniformly reduced around the central axis with a cross-sectional reduction rate of 8% or more by pressing the cap in the direction of the surface, and the uniform diameter reduction causes the cap to deform and expand in the direction of the central axis, and the repulsive stress of the cap is released into the terminal in a flat state. A method of manufacturing a sheathed heater, in which the outer circumferential surface of a rod and the inner circumferential surface of an end of a metal pipe are uniformly added to make the ends airtight. 2. The method for manufacturing a sheathed heater according to claim 1, wherein the two-sided pressing is performed using a mold divided into three or more parts. 3. The method for manufacturing a sheathed heater according to claim 1 or 2, wherein the cap is made of fluorine rubber. 4. The method of manufacturing a sheathed heater according to claim 3, wherein the cross-sectional area of the cap is reduced by 10 to 15%.