JPH0434276B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for manufacturing a sheathed heater that is used by being attached to a member to be attached by thermal bonding means, and particularly relates to a method for manufacturing a sheathed heater that is used by being attached to a member to be attached by thermal bonding means. This makes it possible to avoid thermal damage.

[Prior Art] Generally, a sheathed heater is known as a heating element for heating water or the like.

Fig. 2 shows the state after the sheathed heater 1 and the flange F as the attached member are attached according to the prior art, and 2 is a metal pipe made of stainless steel bent in a U-shape. A heating coil 3 is disposed.

At both ends of the heating coil 3, take-out terminals 4, 4 are provided.
are attached, and these extraction terminals 4, 4 protrude outward from both ends of the metal pipe 2.

The metal pipe 2 is filled with magnesia powder 5 as an insulating powder that insulates between the metal pipe 2 and the heating coil 3.

The magnesia powder 5 is filled in both end faces of the metal pipe 2 except for a predetermined dimension l, and both ends of the metal pipe 2 are closed with sealing materials 6, 6 having a dimension l.

Here, each of the sealing materials 6, 6 is formed with an insertion hole through which each of the above-mentioned lead-out terminals 4, 4 is inserted. The metal pipe 2, heating coil 3, extraction terminals 4, 4,
The sheathed heater 1 is roughly constituted by the sealing materials 6, 6.

Next, a conventional manufacturing procedure will be explained.

First, the extraction terminals 4, 4 are connected to both ends of the heating coil 3, and then these are inserted into the metal pipe 2. After that, magnesia powder 5 is placed inside the metal pipe 2.
Fill it with. Thereafter, the end opening of the metal pipe 2 is temporarily closed with a rubber stopper G (shown in FIG. 3), and then the outer diameter of the metal pipe 2 is reduced. This state is shown in FIG.

Next, the rubber stopper G is removed, and heat treatment is performed to soften the metal pipe 2 that has been work-hardened by the diameter reduction process. After this heat treatment, the sheathed heater 1 having the shape shown in FIG. 2 is obtained by bending it into a U-shape.

The end dimension l of the metal pipe 2 is the dimension in which the rubber stopper G used during the processing process was fitted, and it forms a space, so next, after inserting the sealing material 6 into this space and sealing it, This sheathed heater 1 is inserted into the hole 7b of the constricted portion 7a provided on the flange F, and set at a position a distance L from the end of the metal pipe 2. In this state, the constricted portion 7a of the flange F and the outer peripheral surface of the metal pipe 2 are welded together by arc welding or the like to form a welded portion Y, thereby fixing both. This welding part Y is heated to prevent gap A from forming in order to prevent gap corrosion in the case of water heating.
Welding is generally done from the side that enters the water.

On the other hand, the dimension l of the space of the metal pipe 2 is usually 5
The range is generally from 10 mm to 10 mm, and if it exceeds 10 mm, there is a risk that the rubber plug G will not come out after diameter reduction processing.

Furthermore, it is difficult to remove the magnesia powder 5 after the diameter reduction process because the magnesia powder 5 is hard and compressed, and there are problems such as severe wear of the cutting tool.

Furthermore, the dimension L between the end face of the metal pipe 2 and the flange F is generally set to 10 mm or more, and the reason for this is to prevent the sealing material 6 from being affected by temperature during welding as much as possible. It's for a reason.

Therefore, the welding portion Y was always performed on the outer circumferential surface of the metal pipe 2 in the portion filled with the magnesia powder 5.

[Problems to be Solved by the Invention] As described above, in the welded portion Y between this type of sheathed heater 1 and the flange F according to the conventional technology,
A metal pipe 2 is filled with magnesia powder 5. However, since the magnesia powder 5 is an extremely hygroscopic substance, it quickly adsorbs moisture in the air.

Therefore, when welding a product filled with magnesia powder 5 that adsorbs moisture, the adsorbed moisture rapidly vaporizes due to heat and expands in volume, and as a result, some of the metal The moisture is released to the outside from the opening of the pipe 2, but if the degree of adsorption is large, the moisture breaks through a part of the metal pipe 2 whose strength has decreased due to the welding heat and is released to the outside. , there is a hole in the metal pipe and it becomes defective.

Therefore, before welding, it is necessary to sufficiently dry the magnesia powder 5 in the metal pipe 2 and weld it before it absorbs moisture, resulting in extremely poor workability.

The present invention has been made in view of the above circumstances, and its purpose is to provide a method for manufacturing a sheathed heater with stable quality in which metal pipes are not damaged during installation.

[Means for Solving the Problems] The present invention provides an unfilled section with insulating powder at the end of a metal pipe, and applies thermal joining means such as welding or brazing to the outer peripheral surface of the metal pipe in the unfilled section. After joining the parts to be attached, fill the unfilled section of the metal pipe with insulating powder or sealing material,
It is characterized by sealing.

[Function] In the method for manufacturing a sheathed heater according to the present invention, when thermally bonding the metal pipe and the attached member, the insulating powder is not adsorbed because the corresponding part of the joint is not yet filled with the insulating powder. There is no evaporation of the water contained in the metal pipe, so there is no chance of holes forming in the metal pipe.

[Example] Hereinafter, the manufacturing method of the present invention will be explained based on FIG. 1.

A feature of the present invention is that when welding the metal pipe 2 and the flange F, welding is performed in such a manner that no magnesia powder 5 is present in the welded portion Y.

Next, a procedure for attaching the sheathed heater 1 to the flange F will be explained.

First, both ends of the sheathed heater 1 are inserted into the holes 7b of the flange F, and set so that both end surfaces of the metal pipe 2 and the flange F are substantially flush with each other.

Thereafter, the constricted portion 7a of the flange F and the metal pipe 2 are fixed together by electric arc welding.

During the above-mentioned welding, the end of the metal pipe 2 corresponding to the welded part Y of the constricted part 7a has a predetermined unfilled section in which the magnesia powder 5 is not filled. The moisture adsorbed by the welding part will not evaporate and expand due to the heat from the welding part Y, and therefore, unlike in the past,
There will be no damage to the metal pipe at the welded part Y due to the steam pressure during installation, which will prevent holes from forming.

After the attachment of the flange F is completed, the unfilled section of the metal pipe is supplementally filled with magnesia powder 8 as required, and finally the end opening is sealed with a sealing material 6.

In the above embodiments, the case where electric arc welding is used as the thermal joining means has been described, but the same applies to the case where joining is performed by means such as brazing.

[Effects of the Invention] As explained above, according to the present invention, when a member to be attached is attached to the end of a metal pipe by thermal joining means such as welding or brazing, the attachment point of the metal pipe corresponding to the joining part is An unfilled section without insulating powder was provided at the end, and the unfilled section was filled with insulating powder by supplementary filling as needed after thermal bonding. The moisture does not evaporate due to the thermal influence during the joining process, and therefore, the problem of damage to the metal pipe due to the evaporation pressure can be avoided.

[Brief explanation of drawings]

Fig. 1 is a side sectional view of a sheathed heater manufactured by the manufacturing method of the present invention, Fig. 2 is a side sectional view of a sheathed heater manufactured by the conventional technology, and Fig. 3 is a sectional side view of a sheathed heater manufactured by the manufacturing method of the present invention. FIG. In the figure, 1 is a sheathed heater, 2 is a metal pipe, and 3
5 is a heating coil, 5 is magnesia powder, 6 is a sealing material, and Y is a welding part (thermal joint).

Claims (1)

[Claims] 1. An unfilled section of a predetermined size in which the above-mentioned insulating powder is not filled is provided at the end of a metal pipe filled with insulating powder around the heating coil, and heat such as welding or brazing is applied to the outer circumferential surface of the pipe in the unfilled section. 1. A method for manufacturing a sheathed heater, which comprises joining the members to be attached using a mechanical joining means, and then embedding an insulating powder or a sealing material in the unfilled section of the metal pipe to perform a sealing process.