Method for manufacturing a sheathed heater and jig for manufacturing a sheathed heater

Abstract

To provide a sheathed heater manufacturing method, etc. with which it is possible to easily improve the accuracy of a sheath that is bent to a prescribed pattern.SOLUTION: A method for manufacturing a sheathed heater in which a heating wire and an insulating powder are accommodated in the inside of a sheath 110 is configured to include the steps of: performing bending work so that a sheath forms a prescribed pattern along a prescribed reference plane R and extends; and sandwiching sections P1-P6 that constitute the pattern in the sheath after bending work with a first and a second correction die 210, 220 that are made to be capable of approaching and separating along the normal of the reference plane, and correcting a variation in the distance from the reference plane of each section of the sheath, the contact plane with the sheath of the first and / or the second correction die being formed by an elastic substance 223, 224.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a sheath heater and a jig for manufacturing a sheath heater.

Background Art

[0002] A sheath heater is an electric heater that houses a heating wire embedded in an insulator powder inside a cylindrical metal sheath. Since such a sheath heater has a high degree of shape freedom by appropriately bending the sheath, for example, it is known to provide a portion where the sheath is wound along a predetermined plane. As a technique related to such a sheath heater, for example, Patent Document 1 describes that after reducing the diameter and annealing a metal pipe incorporating an insulating material and a heating wire, press working for planar processing is performed in two or more divisions. Patent Document 2 describes that in a method for forming a spiral sheath heater, a linear spacer made of a shape memory alloy is wound in a spiral shape together with the sheath heater. [[ID=二十]]In Patent Document 3, in a spiral sheath heater, while forming a metal pipe (sheath) into a spiral shape, a flat portion is formed at one end by press working, and both ends of the metal pipe located at the portion where the terminal is inserted are bent downward from the closed end to improve heat conduction to the object to be heated. Patent Document 4 describes that in a sheath heater for an electric heater, a metal pipe (sheath) is press worked, and flat portions are provided at appropriate intervals at once.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

[0004] In some sheathed heaters, the sheath is bent into a predetermined pattern along a flat surface (for example, a spiral shape). In the manufacturing of such sheathed heaters, the process of bending the sheath to form a pattern is often done manually by workers, requiring highly skilled workers and making it difficult to suppress variations in the finished product due to individual differences among workers. Alternatively, it could be considered to manually correct (correct) the areas where such patterns have formed to improve their flatness, but this would require a lot of manpower and time, leading to increased costs. In view of the above-mentioned problems, the object of the present invention is to provide a sheath heater manufacturing method and a sheath heater manufacturing jig that can easily improve the accuracy of a sheath that has been bent into a predetermined pattern. [Means for solving the problem]

[0005] To solve the above-mentioned problems, a sheath heater manufacturing method according to one aspect of the present invention is a sheath heater manufacturing method used for manufacturing a sheath heater in which a heating wire and insulating powder are housed inside a cylindrical sheath, comprising the steps of: bending the sheath so that it extends in a predetermined pattern along a predetermined reference plane; and clamping the portion of the sheath after bending that constitutes the pattern with a first straightening die and a second straightening die that can move closer to or further apart along the direction normal to the reference plane, thereby correcting the variation in the distance from the reference plane at each part of the sheath, wherein the contact surface between the sheath and at least one of the first straightening die and the second straightening die is made of an elastic material. According to this method, the bending shape of the sheath can be corrected so that the deviation of the predetermined pattern from the reference plane is reduced by pressing the sheath, which has been bent into a predetermined pattern, with first and second corrective dies, at least one of which has an elastic body. Furthermore, by making the contact surface with the sheath in at least one of the first and second straightening types an elastic body with a predetermined rigidity, unnecessary deformation of the cross-section of the tubular portion of the sheath can be prevented, and springback when straightening the bent portion of the sheath can be suppressed. This allows for improvements in the finish and yield of the final product.

[0006] In the present invention, the elastic body may have a configuration comprising a first layer and a second layer arranged in superimposition with the first layer and having a different elastic modulus from the first layer. According to this method, springback during the straightening of the bent portion of the sheath can be further suppressed, thereby enhancing the straightening effect.

[0007] In the present invention, the compressive force applied to the sheath when performing the straightening using the first straightening type and the second straightening type can be configured such that plastic deformation of the cross-sectional shape of the sheath does not occur. This ensures that the effects described above can be reliably achieved.

[0008] In the present invention, the elastic body may be provided in only one of the first or second corrective molds. According to this, the above-mentioned effects can be obtained while simplifying the configuration of each orthodontic device.

[0009] In the present invention, the pattern can be configured to include a plurality of arc-shaped portions arranged concentrically from a small diameter portion to a large diameter portion. According to this method, it is possible to appropriately correct shape irregularities such as when some parts of multiple arc-shaped sections are raised from the reference surface, and bring each arc-shaped section closer to the reference surface.

[0010] In the present invention, the reference surface can be a flat plane, and the contact surfaces of the first straightening mold and the second straightening mold with the sheath can be configured to be flat. According to this method, the flatness of the pattern formed by the bending process of the sheath can be easily improved.

[0011] To solve the above-mentioned problems, another embodiment of the present invention provides a jig for manufacturing a sheathed heater, which is used in the manufacture of a sheathed heater in which a heating wire and insulating powder are housed inside a cylindrical sheath, and comprises: a first straightening die that contacts a portion of the sheath that forms a predetermined pattern extending along a predetermined reference plane from a first direction along the normal direction of the reference plane; and a second straightening die that contacts the portion of the sheath that forms the pattern from a second direction along the normal direction of the reference plane and clamps the sheath together with the first straightening die, wherein the contact surface between the sheath and at least one of the first straightening die and the second straightening die is made of an elastic body having a rigidity lower than the rigidity when the cylindrical portion of the sheath is compressed in the radial direction in cross-section. This also provides the same effects as the sheath heater manufacturing method described above. [Effects of the Invention]

[0012] As described above, the present invention provides a method for manufacturing a sheath heater that can easily improve the accuracy of a sheath bent into a predetermined pattern, and a jig for manufacturing a sheath heater. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows the appearance of a sheathed heater before bending in an embodiment of the sheathed heater manufacturing method to which the present invention is applied. [Figure 2] This diagram shows the state of a sheathed heater after bending, and is a view of the bent portion from the direction normal to the reference plane. [Figure 3]It is a cross-sectional view taken along the line III-III of FIG. 2. [Figure 4] It is a diagram showing a state in which a semi-finished product of a sheath heater is set in a jig for manufacturing a sheath heater according to an embodiment. [Figure 5] It is a diagram showing a state in which a semi-finished product of a sheath heater is corrected by a jig for manufacturing a sheath heater according to an embodiment. [Figure 6] It is a diagram of the sheath heater after correcting the shape irregularity in the embodiment as viewed from a direction parallel to the reference plane.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of a method for manufacturing a sheath heater to which the present invention is applied and a jig for manufacturing a sheath heater will be described. In an embodiment, the sheath heater is configured by inserting a heating wire into a sheath, which is a cylinder made of a metal material such as a heat-resistant stainless alloy, and filling the gap with a powder made of an insulator.

[0015] FIG. 1 is a diagram showing the appearance of a sheath heater before bending in the method for manufacturing a sheath heater according to an embodiment. The sheath heater 100 has a sheath 110. The sheath 110 is a cylindrical body made of a metal material such as a stainless alloy or an aluminum alloy. In the state shown in FIG. 1, the sheath 110 is formed such that its central axis direction is straight.

[0016] Inside the sheath 110, a heating wire and insulator powder (not shown) are accommodated. The heating wire can be configured as, for example, a wire made of a nickel-chromium-based metal. Terminals 120 and 130 provided at both ends of the heating wire are connected to a power source (not shown) provided outside. The heating wire is resistively heated when energized and serves as a heat source for the sheath heater 100. The insulator powder is an insulating material such as magnesium oxide formed in a powder state. The insulating powder is filled between the outer surface of the heating wire and the inner surface of the sheath 110.

[0017] Next, the sheath heater 100 is subjected to a bending process on the sheath 110, thereby forming a predetermined pattern along the reference surface R (in this case, a flat surface as an example). Figure 2 shows the state of the sheathed heater after bending, and is a view from the direction normal to the reference plane of the bent portion. Figure 3 is a view along the line III-III in Figure 2. After bending, the sheath 110 has a series of sections formed on it, including a small diameter section P1, a folded section P2, a medium diameter section P3, a folded section P4, a large diameter section P5, a radially extending section P6, and a rising section P7.

[0018] The small-diameter portion P1 is a curved portion formed near the center in the longitudinal direction of the sheath 110 before bending, and extends in an arc shape along the reference plane R. The small-diameter portion P1 is formed with a central angle of, for example, 180 degrees or more.

[0019] The folded-over portion P2 is formed at both ends of the small-diameter portion P1 and is a portion that is curved, for example, by about 180° in the direction that it protrudes outward from the small-diameter portion P1. The folded-over section P2 is the part that connects the end of the small-diameter section P1 and the end of the medium-diameter section P3. Furthermore, the folded portion P2, the medium diameter portion P3, the folded portion P4, the large diameter portion P5, the radially extending portion P6, and the rising portion P7 are each provided in pairs symmetrically with respect to the axis along the radial direction (vertical direction in Figure 2) of the small diameter portion P1.

[0020] The medium diameter portion P3 is a curved portion that extends along a circular arc concentric with the small diameter portion P1 when viewed from the direction normal to the reference plane R. The radius of curvature of the medium diameter section P3 is larger than that of the small diameter section P1. The outer periphery of the small-diameter portion P1 and the inner periphery of the medium-diameter portion P3 are spaced apart in the radial direction. One end of the middle diameter section P3 is continuous with the folded-over section P2. The other end of the middle diameter section P3 is continuous with the folded-over section P4.

[0021] The folded portion P4 is formed at the end of the middle diameter portion P3 on the side opposite to the folded portion P2, and is a portion that is curved, for example, about 180° in the direction that protrudes from the middle diameter portion P3 toward the outer diameter. The folded-over section P4 is the part that connects the end of the medium-diameter section P3 and the end of the large-diameter section P5.

[0022] The large-diameter portion P5 is a curved section that extends along a circular arc concentric with the small-diameter portion P1 and the medium-diameter portion P3 when viewed from the direction normal to the reference plane R. The radius of curvature of the large-diameter section P5 is larger than that of the small-diameter section P1 and the medium-diameter section P3. The outer periphery of the medium-diameter section P3 and the inner periphery of the large-diameter section P5 are spaced apart in the radial direction. One end of the large-diameter section P5 is continuous with the folded-over section P4. The other end of the large-diameter section P5 is continuous with the radially extending section P6.

[0023] The radially extending portion P6 is a portion that extends almost straight along the radial direction of the small-diameter portion P1, from the end of the large-diameter portion P5 opposite to the folded portion P4, along the reference plane R, to the center of the small-diameter portion P1.

[0024] The rising portion P7 is the part that rises up from the end of the radially extending portion P6 opposite to the large-diameter portion P5 (the central part of the small-diameter portion P1), almost along the direction normal to the reference plane R. The pair of rising sections P7 are provided with terminals 120 and 130 for the sheathed heater 100, respectively.

[0025] The shapes of these parts P1 to P7 are formed, for example, by a worker manually wrapping them around a jig (not shown). In particular, the parts P1 to P6 that constitute the pattern formed along the reference plane R are ideally arranged planarly along the reference plane R (so that the center line of the sheath 110 does not deviate from the reference plane R). However, in reality, deviations from the reference plane R (irregular shape) may occur due to the skill level and habits of manual work. For example, in the example shown in Figure 3, it can be seen that the medium diameter portion P3 is floating above the large diameter portion P5. Furthermore, it can be seen that the large diameter portion P5 is also distorted with respect to the reference plane R, and its flatness is compromised.

[0026] When such irregularities in shape exceed a certain level, there are concerns that it may negatively affect the precision, finish, and yield of the final product. Previously, workers manually corrected irregular shapes, but this process was cumbersome, hindering the productivity of the sheath heater 100, and furthermore, the accuracy of the correction depended on the skill of the worker performing the correction.

[0027] Therefore, in this embodiment, the straightening after manual bending is performed using a jig for manufacturing sheath heaters, which will be described below. Figure 4 shows a semi-finished sheath heater set in the sheath heater manufacturing jig of the embodiment. The sheath heater manufacturing jig 200 has an upper mold (first straightening mold) 210 and a lower mold (second straightening mold) 220.

[0028] The upper mold 210 has a base plate 211, a protrusion 212, etc. The base plate 211 is, for example, a disc-shaped member that forms the upper end surface of the upper mold 210. The protruding portion 212 is a component that extends outward from the lower surface of the base plate 211. The protruding portion 212 can be formed, for example, in the shape of a disc or cylinder with a smaller outer diameter and thickness than the base plate 211. The protruding portion 212 acts as a plunger that presses against the parts (P1 to P5) of the sheath heater 100's sheath 110 that require straightening. An opening O is provided in the center of the base plate 211 and the protruding portion 212 to prevent interference with the rising portion P7 of the sheath heater 100. The rising portion P7, along with terminals 120 and 130, is designed to penetrate above the upper mold 210 through the opening O.

[0029] The lower mold 220 includes a base plate 221, a frame 222, a first elastic sheet 223, a second elastic sheet 224, and the like. The base plate 221 is, for example, a disc-shaped member that forms the lower end surface of the lower mold 220. The frame portion 222 is a wall-like member that protrudes from the upper surface of the base plate 221. The frame portion 222 is formed, for example, as a frame whose planar shape, when viewed from the direction normal to the reference plane (up and down direction in Figure 4), is annular. The frame portion 222 has an inner diameter that is substantially equal to and inevitably larger than the outer diameter of the protrusion portion 212, allowing the protrusion portion 212 to be inserted. The frame portion 222 has the function of positioning the upper mold 210 and the lower mold 220 within the reference plane R when correcting the irregular shape of the sheath 110 of the sheath heater 100 with the upper mold 210 and the lower mold 220, and similarly positioning the outer diameter portion P5 of the sheath 110 of the sheath heater 100 with the lower mold 220.

[0030] The first elastic sheet 223 and the second elastic sheet 224 are provided above the lower mold 220 and inside the frame portion 222, sequentially from the upper mold 210 side. The first elastic sheet 223 and the second elastic sheet 224 are each formed from an elastic material that has elasticity and has a lower modulus of elasticity than the other materials constituting the upper mold 210 and lower mold 220, such as rubber, elastomer, or foamed urethane. Here, the first elastic sheet 223 and the second elastic sheet 224 are composed of materials with different elastic moduli. For example, the first elastic sheet 223 can be configured to have lower rigidity against vertical compressive loads by using a material with a lower modulus of elasticity compared to the second elastic sheet 224. Furthermore, it is preferable to set the rigidity of the first elastic sheet 223 and the second elastic sheet 224 against vertical compression to be lower than the rigidity of the sheath 110 when the sheath 110 is compressed in the radial direction of its cross-section.

[0031] Each component constituting the upper mold 210 and the lower mold 220 (excluding the first elastic sheet 223 and the second elastic sheet 224) can be formed from, for example, metal materials such as steel or aluminum alloys, or resin materials such as engineering plastics. Furthermore, for example, the base plate 211 and protruding portion 212 of the upper mold 210, and the base plate 221 and frame portion 222 of the lower mold 220 can be formed integrally.

[0032] The sheathed heater 100 is placed on the lower mold 220 such that the bent portion of the sheath 110 fits inside the inner diameter of the frame 222 (so that the outer edge of the large diameter portion P5 follows the inner surface of the frame 222). At this time, the lower part of the sheath 110 is in contact with the upper surface of the first elastic sheet 223. Subsequently, the upper mold 210 is installed so as to cover the pattern portion (P1 to P6) of the sheath 110 from above. At this time, the lower end of the protruding portion 212 is inserted into the inner diameter side of the frame portion 222.

[0033] Subsequently, with the lower surface of the protrusion 212 in contact with the upper part of the pattern portion of the sheath 110, a downward load is applied to the upper die 210 to press the sheath 110 and correct any irregularities in shape. Figure 5 shows the process of straightening a semi-finished sheath heater using the sheath heater manufacturing jig of the embodiment. Such load application can be carried out, for example, using a press machine such as a hydraulic or electric press. Furthermore, if the sheath 110 is made of a relatively soft material, it may be possible to perform the process manually. In this case, it is preferable to set the compressive force applied to the sheath 110 so as not to cause plastic deformation of the cross-sectional shape of the sheath 110.

[0034] Next, the sheathed heater 100 is removed from the sheathed heater manufacturing jig 200. Figure 6 is a view of the sheath heater after its shape irregularities have been corrected, as seen from a direction parallel to the reference plane, according to the embodiment.

[0035] According to the embodiments described above, the following effects can be obtained. (1) The bent shape of the sheath 110 can be corrected so that the deviation of the predetermined pattern from the reference surface R is reduced by clamping the sheath 110, which has been bent into a predetermined pattern, between the upper die 210 and the lower die 220 which has an elastic body and pressing it. Furthermore, by making the contact surface between the lower mold 220 and the sheath 110 an elastic sheet 223 having a predetermined rigidity, unnecessary deformation is prevented from occurring in the cross-section of the cylindrical portion of the sheath 110, and springback when straightening the bent portion of the sheath 110 can be suppressed. (2) By laminating and arranging the first elastic sheet 223 and the second elastic sheet 224, which have different elasticities, the springback when straightening the bent portion of the sheath 110 can be further suppressed, thereby enhancing the straightening effect. (3) By setting the compressive force applied to the sheath 110 from the upper mold 210 and the lower mold 220 so as not to cause plastic deformation of the cross-sectional shape of the sheath 110, the above-mentioned effects can be reliably achieved. (4) By providing the elastic sheet only on the lower mold 220, the above-mentioned effects can be obtained while simplifying the configuration of the sheath heater manufacturing jig 200. (5) The pattern formed by bending the sheath 110 includes a small diameter section P1, a medium diameter section P3, and a large diameter section P5, which are multiple arc-shaped sections arranged concentrically from the small diameter section to the large diameter section. This configuration allows for the correction of shape irregularities such as parts of the small diameter section P1, medium diameter section P3, and large diameter section P5 lifting off the reference surface R, bringing each arc-shaped section closer to the reference surface R. (6) By having a flat reference surface R and a configuration in which the contact surfaces of the upper die 210 and lower die 220 with the sheath 110 are flat, the flatness of the pattern formed by the bending of the sheath 110 can be easily improved.

[0036] (modified version) The present invention is not limited to the embodiments described above, and various modifications and changes are possible, all of which fall within the technical scope of the present invention. (1) The configuration of the sheath heater manufacturing method and the jig for manufacturing the sheath heater, as well as the configuration of the manufactured sheath heater, are not limited to the configuration of the embodiments described above and can be modified as appropriate. (2) The semi-finished shape of the sheathed heater (shape immediately after bending), the finished product shape, and the shape, structure, material, and manufacturing method of each component constituting the jig for manufacturing the sheathed heater are not limited to the configuration of the embodiment and can be changed as appropriate. (3) In this embodiment, an elastic sheet (elastic body) is provided only in the lower mold, but the elastic body may be provided in the upper mold, or in both the upper and lower molds. Furthermore, while the embodiment shows two layers of elastic sheeting as an example, the present invention is not limited to this, and for example, three or more layers may be provided. (4) In the embodiments, the reference surface was a flat plane as an example, but the present invention is not limited to this, and the reference surface may be a curved surface or a bent surface. (5) The pattern formed by bending the sheath is not limited to the configuration of the embodiment and can be changed as appropriate. For example, the patterns could be spiral, double spiral, zigzag, or combinations of these with other elements. [Explanation of symbols]

[0037] 100 Sheath Heater 110 Sheath 120, 130 terminals 200 Sheath heater manufacturing jig 210 Upper mold 211 Base plate 212 Protrusion 220 Lower mold 221 Base plate 222 Frame section 223 First elastic sheet 224 Second Elastic Sheet R Reference Surface P1 Small diameter section P2 Folded section P3 Middle diameter section P4 Folded section P5 Large diameter section P6 Radial extension section P7 Standing part

Claims

1. A method for manufacturing a sheathed heater, which is used in the manufacture of a sheathed heater in which a heating wire and insulating powder are housed inside a cylindrical sheath, The process of bending the sheath so that it extends in a predetermined pattern along a predetermined reference plane, The process includes a step of clamping the portion constituting the pattern in the sheath after bending using a first straightening die and a second straightening die that can be moved closer to or further apart along the direction normal to the reference plane, thereby correcting the variation in the distance from the reference plane at each part of the sheath, The contact surface between the sheath and at least one of the first straightening mold and the second straightening mold is made of an elastic material. A sheathed heater manufacturing method characterized by the following.

2. The elastic body comprises a first layer and a second layer that is placed on top of the first layer and has a different modulus of elasticity from the first layer. A method for manufacturing a sheathed heater according to claim 1, characterized by the above.

3. The compressive force applied to the sheath when performing the correction using the first and second correction types is set so as not to cause plastic deformation of the cross-sectional shape of the sheath. A method for manufacturing a sheathed heater according to claim 1 or claim 2, characterized by the above.

4. The elastic body is provided in only one of the first or second corrective molds. A method for manufacturing a sheathed heater according to claim 1 or claim 2, characterized by the above.

5. The aforementioned pattern includes a plurality of arc-shaped portions arranged concentrically from a small diameter portion to a large diameter portion. A method for manufacturing a sheathed heater according to claim 1 or claim 2, characterized by the above.

6. The reference surface is a plane, and the contact surfaces of the first straightening mold and the second straightening mold with the sheath are also plane. A method for manufacturing a sheathed heater according to claim 1 or claim 2, characterized by the above.

7. A jig for manufacturing sheathed heaters, which is used in the manufacture of sheathed heaters in which a heating wire and insulating powder are housed inside a cylindrical sheath, A first straightening die is placed in contact with the portion of a sheath that has been bent to form and extend a predetermined pattern along a predetermined reference plane, from a first direction along the normal direction of the reference plane, The sheath comprises a second straightening die that contacts the portion of the sheath constituting the pattern from a second direction along the normal direction of the reference plane and clamps the sheath together with the first straightening die, The contact surface between the sheath and at least one of the first straightening mold and the second straightening mold is made of an elastic material. A jig for manufacturing sheathed heaters, characterized by the following features.

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