JPS62216188A - 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 is widely used in the industrial field where various types of sheathed heaters are used, each having an opening at the end of the sheathed heater with a circular, elliptical or triangular cross section. 0 This type of sheathed heater is one in which a coiled heating wire with a terminal bar connected to the tip is inserted into a metal pipe, and the metal pipe is filled with insulating powder, but when manufacturing such a sheathed heater, , in order to seal the insulating powder in the metal pipe and bury the coiled heating wire in the insulating powder to insulate and fix it from the metal pipe, the terminal bar protrudes at the end of the metal pipe. It is necessary to insulate and seal the openings. Therefore, the insulating seal is used to prevent insulation powder such as magnesia, which has good thermal conductivity, from absorbing moisture in the surrounding environment and causing insulation deterioration during manufacturing and use of the sheathed heater. It must be clearly a moisture-proof seal with sufficient practical strength to prevent moisture from penetrating the seal and causing insulation failure.

The present invention relates to a method of manufacturing a sheathed heater that can efficiently achieve the moisture-proof seal as described above.

<Prior art and its problems> Conventionally, approximately three types of methods have been proposed as follows for sealing the opening at the end as described above, but each method has its own problems. 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.
Examples of using rubber and ceramic bushings together, and examples of using cylindrical porcelain with specific glass powder (Japanese Patent Application Laid-Open No. 56-54
780) etc. However, such a method using a glass seal has a serious problem in that it requires a troublesome and uneconomical sealing operation in which the glass is heated and melted, and in terms of equipment. However, the weaknesses in the seal's mechanical strength have not been fundamentally resolved, and in actual use, problems have also arisen in the moisture resistance of the seal. 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. (Jitko Sho 54-11332
There are also examples of using 7-stranded rubber, which has excellent properties as a material (Japanese Patent Application Laid-open No. 72391/1983). However, such methods using resin or silicone rubber seals are complicated in terms of manufacturing and processing, as they require liquid loading work.
In any of these examples, it is still not possible to sufficiently solve problems related to ensuring creepage insulation distance and moisture-proofing properties of seals, which occur due to thermal deformation of epoxy resin, silicone RTV rubber, etc. in actual use of sheathed heaters. Finally, there is a liquid seal method. This is a method in which a liquid sealant such as silicone grease or solvent-free phenol is loaded into the protruding opening of the terminal bar, and the opening is sealed by pressing it with a Teflon bushing. For example, there is an example (Japanese Patent Publication No. 55-44435) in which the metal pipe is impregnated with silicone oil, the metal pipe is reduced in size, and the impregnated part is densified to improve the sealing effect. However, such a method using a liquid seal tends to cause variations in the sealing effect, and there is a problem that the liquid sealant is attracted to the internal insulating powder over time, resulting in a decrease in the sealing effect.

Therefore, the present inventors have proposed a new method of sealing the above-mentioned opening at the end using a mechanical backing means (Japanese Patent Application Laid-Open No. 117589/1989). Although this method has the great advantage of being able to seal the openings at the ends very efficiently, there is a problem with restoring the insulation after use of the sealed sheathed heater.

The sheathed heater using the glass seal mentioned above has excellent insulation recovery after use as long as the glass seal part is fully functional, but in such a state,
Compared to the sheathed heater using glass cooling, the sheathed heater using the mechanical backing means tends to have poorer recovery of insulation after use.

<Problems to be Solved by the Invention and Means for Solving the Problems> The present invention solves the problems of the conventional mechanical backing means as described above, and has the great advantage of being able to seal very efficiently. To provide an improved sheathed heater cake method that solves the problems while making full use of its advantages.

However, as a result of studying the problems with conventional mechanical backing means, the present inventors found that the problem was caused by the occurrence of leakage, although very small, due to the airtightness of the opening at the end. It turns out. The outer circumferential surface of the terminal bar and the inner circumferential surface of the metal pipe at the ends were in a relatively rough state as they were, which caused the above-mentioned leakage. In fact, if the outer circumferential surface of the terminal rod and the inner circumferential surface of the metal pipe at the ends were sufficiently polished to make clearly smooth curved surfaces, the above-mentioned leakage was completely eliminated. However, it is extremely troublesome to sufficiently polish the inner circumferential surface of a metal pipe with an inner diameter commonly used in sheathed heaters, or the outer circumferential surface of a terminal rod with an even smaller outer diameter, to make it an obviously smooth curved surface. Dust, which eliminates the great advantages mentioned above over conventional mechanical backing means. Therefore, as a result of intensive study, the inventors of the present invention found that if a very small amount of heat-resistant and insulating lubricant is applied, for example, by spraying, to the outer peripheral surface of the terminal rod at the end or the inner peripheral surface of the metal pipe, It has been discovered that the problems with mechanical backing means can be completely solved without the need for polishing the circumferential surface of the backing means, without the aforementioned leakage.

That is, in the present invention, a coiled heating wire with a terminal rod connected to the tip is inserted into a metal pipe, and a terminal around the end is inserted into an opening at an end of a sheathed heater in which the metal pipe is filled with insulating powder. After applying a heat-resistant and insulating lubricant to the outer circumferential surface of the rod and the inner circumferential surface of the metal pipe, a relatively hard cap with a through hole is applied to the outer circumferential surface of the terminal rod and the metal pipe around the end. The cap is fitted so that it is in sliding contact with the inner circumferential surface of the manufactured pipe, and then the end is pressed from the outer circumferential direction toward the center axis to uniformly reduce the diameter of the cap. The present invention relates to a method of manufacturing a sheathed heater, in which the end portion is made airtight by uniformly adding it to the outer circumferential surface of a terminal bar and the inner circumferential surface of a metal pipe around the terminal rod.

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 terms of heat resistance, chemical resistance, and backing effect, those made of fluororubber are preferable. However, as the insulating powder 4 to be filled here, typically magnesium oxide powder can be used.

In this state, the outer circumferential surface 2 of the terminal bar 2 at the end 5
A and the inner peripheral surface 1a of the metal pipe 1 are coated with a heat-resistant and insulating lubricant, most conveniently by spraying from the opening 6. The lubricant is preferably silicone oil.
It is best to apply this in a very small amount and as evenly as possible.

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.

Finally, the end portion 5 of the metal pipe 1 is surface pressed from the outer circumferential direction toward the central axis, as shown by the arrows in FIG. 2, to uniformly reduce the diameter around the central axis. 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 pressing is preferably carried out so that the cross-sectional area reduction rate of the cap 7 is 8- or more, and if a fluororubber cap is used as the cap 7, the cross-sectional area reduction rate is 10 to 15%. is preferable. Both are for the purpose of producing the desired repulsive stress of the cap 7 as described later.

FIG. 4 shows a product after uniform diameter reduction by surface pressing. When the cap 7 is pressed to uniformly reduce its diameter, the repulsive stress of the cap 7 is uniformly applied to the outer circumferential surface 2a of the terminal bar 2 and the inner circumferential surface 1a of the metal pipe 1 at the end portion 5 in a plane state. 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 plan view. In both cases, the arrow in the figure indicates the repulsive stress. As shown in the figure, the repulsive stress of the cap 70 is uniformly applied to the surface, and the presence of lubricant provides a durable and sufficient backing effect, so that the end 5 of the metal pipe 1 is completely It will be made airtight.

<Example> A sheathed heater was manufactured under the following conditions according to the procedure described above in Figures 1 to 4 (Example) Cap length: 5 mm (fluororubber, 5TF770, Japan Synthetic Rubber Co., Ltd.) ), Cap cross-sectional reduction rate: 12%, Metal pipe length: 550 mm, Metal pipe outer diameter near Wjx,
Insulating powder: Magnesium oxide powder, Lubricant: Silicone oil (spray, KF96, manufactured by Shin-Etsu Chemical Co., Ltd.) Separately, a sheathed heater was manufactured without applying any lubricant under the same conditions (comparative example). Sheathed heater (
Measure the insulation state of 10 samples on each side,
The results are shown in Table 1.

Table 1 Note: The unit is MΩ. The upper row of the table is the average value, and the lower row in parentheses is the range.

<Effects of the Invention> As has been explained above, the present invention has the effect of making it possible to efficiently manufacture a sheathed heater having a clear airtight seal with excellent insulation recovery.

[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 cross-sectional view showing the addition 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, 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 coiled heating wire with a terminal rod connected to the tip is inserted into a metal pipe, and the metal pipe is filled with insulating powder and inserted into the opening at the end of the sheathed heater. After applying a heat-resistant and insulating lubricant to the outer peripheral surface of the terminal rod and the inner peripheral surface of the metal pipe, a relatively hard cap with a through hole is applied to the outer peripheral surface of the terminal rod around the end. The cap is fitted so as to be in sliding contact with the inner peripheral surface of the metal pipe, and then the end portion is pressed against the outer peripheral surface toward the center axis to uniformly reduce the diameter of the cap, thereby reducing the repulsive stress of the cap. A method of manufacturing a sheathed heater, in which the end portion is made airtight by uniformly adding it to the outer circumferential surface of a terminal bar and the inner circumferential surface of a metal pipe around the end portion. 2 Claim 1 in which the lubricant is silicone oil
A method for manufacturing a sheathed heater as described in Section 1. 3 Claim 1 in which the cap is made of fluororubber
A method for manufacturing a sheathed heater according to item 1 or 2. 4. Manufacture of a sheathed heater according to any one of claims 1 to 3, in which surface pressing is performed using a mold divided into three or more so that the cross-sectional area reduction rate of the cap is 8% or more. Method.