JPS62254386A - 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 for manufacturing a sheathed heater, in which an opening at an end of the sheathed heater is efficiently made airtight by a mechanical backing means.

Various sheathed heaters with circular, elliptical, or triangular 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, and the metal pipe is filled with insulating powder, but when manufacturing such a sheathed heater, In order to seal the insulating powder inside 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 from the end of the metal pipe. Openings must be insulated and sealed. 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. To prevent moisture from entering the seal and causing insulation failure,
It must clearly be a moisture-tight seal with sufficient practical strength.

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 cumbersome and uneconomical sealing operation in which the glass is heated and melted, and the mechanical strength of the glass seal is insufficient. The above weaknesses have basically not been resolved, and in the end, there are problems with the moisture resistance 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. To prevent it from floating due to thermal expansion of the air inside the sheathed heater, use a metal pipe with a recess in a part of the end in advance, and prevent the epoxy resin or silicone RTV rubber from getting caught in the recess. There are examples (Japanese Utility Model Publication No. 54-11332) and examples using fluororubber, which has excellent properties as a material (Japanese Patent Application Laid-Open No. 55-72391). but,
Such methods using resin or silicone rubber seals suffer from complicated manufacturing processes that require liquid loading operations, and in both cases, thermal deformation of epoxy resins, silicone RTV rubber, etc. occurs during actual use of sheathed heaters. Problems related to securing creepage insulation distance and moisture proofing of seals have not been sufficiently resolved. Finally, there is a liquid seal method. This is done by filling the protruding opening of the terminal bar with a liquid sealant such as silicone grease or solvent-free face.
The method of sealing the opening by pressing it with a Teflon pushbutton is to impregnate the insulating powder near the opening with, for example, silicone oil, reduce the size of the metal pipe in that area, and densify the impregnated area. Example of increasing the sealing effect (
Special Publication No. 55-44435) 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.

Therefore, the present inventors have proposed a 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 with a glass seal mentioned above has excellent insulation recovery after use as long as the glass seal part is fully functional, but compared to the sheathed heater with a glass seal in this state, The sheathed heater using the mechanical backing means tends to have poor insulation recovery 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. An object of the present invention is to provide an improved method of manufacturing a sheathed heater 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 left in a relatively rough condition, which caused the leakage described above. In fact, if the outer circumferential surface of the terminal bar and the inner circumferential surface of the metal pipe at the end were sufficiently polished to form clearly smooth curved surfaces, the above-mentioned leakage was completely eliminated. However, it is extremely troublesome to thoroughly polish the inner circumferential surface of a metal pipe with an inner diameter of several layers, which is 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. Unfortunately, this also eliminates the great advantages mentioned above over conventional mechanical backing means. Therefore, as a result of intensive study, the inventors of the present invention have found that if a heat-resistant and insulating lubricant is applied very carefully, 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 found that even without polishing their peripheral surfaces, the leakage mentioned above is eliminated, and that the problems with mechanical backing means can be better and completely eliminated if the caps have shape characteristics after backing. I found it.

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 end 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 central axis to uniformly reduce the diameter, thereby reducing the repulsive stress of the cap in the corresponding area at the end. A method for producing a sheathed heater, in which the cap is uniformly attached to the outer circumferential surface of a terminal rod and the inner circumferential surface of a metal pipe, and a part of the fitting side of the cap is formed into a shape that widens toward the end, thereby making the end airtight. Pertains to.

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 at 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 fluororubber are preferred. Furthermore, as the insulating powder 4 to be filled here, magnesium oxide powder can typically 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. In the drawing, the cap 7 is fitted with a portion 7a on the head side remaining.

Finally, the end portion 5 of the metal pipe 1 is flat-pressed from the outer circumferential direction toward the central axis, as shown by the arrows in FIG. 2, to reduce the diameter uniformly 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 performed so that the cross-sectional area reduction rate of the cap 7 is 8 inches or more, and if the cap 7 is made of fluororubber, the cross-sectional area reduction rate is 10 to 15%. is preferable. Both of these are for the purpose of developing the repulsive stress of the cap 7 as described later.0 Figure 4 shows the product after uniform diameter reduction by surface pressing, When the diameter of the cap 7 is reduced uniformly by surface pressing as described above, the diameter of the corresponding cap 7 is also reduced uniformly, and the repulsive stress of the cap 7 is applied to the outer circumferential surface 2a of the terminal bar 2 at the end 5 and Inner peripheral surface 1 of metal pipe 1
Add evenly to a. Due to the uniform diameter reduction, a corresponding portion of the cap 7 is rolled along the central axis of the metal pipe 1, but at least a portion of the fitting side of the cap 7 is rolled as a result. 7b is formed into a square shape that widens towards the end. FIG. 5 is a schematic cross-sectional view illustrating the state in which repulsive stress is applied as described above, 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. Repulsive stress is applied uniformly to the cap 70 with a lubricant interposed therein as shown in the figure, and the part 7b on the fitting side of the cap 7 is formed in a shape that widens toward the end, so that it can last for a long period of time. Even during use, there is no displacement of the cap 7 at all, a durable and sufficient backing effect is obtained, and the end 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 Figures 1 to 4 (Example) Cap length = 7 tone (fluororubber, 5TF770, Japan Synthetic Rubber Co., Ltd.) ), cross-sectional reduction rate of cap: 12 inches, length of metal pipe: 550 m, outer diameter of metal pipe = 7 fins, insulation powder: magnesium oxide powder, lubricant: silicone oil (spray, KF96, Separately, a sheathed heater was manufactured without applying lubricant and other conditions were the same (comparative example).
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 described 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. and fit into the inner circumferential surface of a metal pipe so as to make sliding contact with it, and then press the end portion from the outer circumferential direction toward the center axis to uniformly reduce the diameter, thereby reducing the repulsive stress of the cap in the corresponding area. A method for manufacturing a sheathed heater, in which the cap is uniformly applied to the outer circumferential surface of the terminal rod and the inner circumferential surface of the metal pipe around the end, and a part of the fitting side of the cap is formed to widen toward the end, thereby making the end airtight. . 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.