JP2016058304A - Electric heater and method of manufacturing electric heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric heater in which disconnection of a wire is suppressed at a point where a heating wire is wound around a terminal and crimped.SOLUTION: An electric heater 1 having a terminal 40 for connection with a power supply, and a heating wire 30 at least one end 31 of which is crimped to the terminal while being wound around the terminal, is constituted to have a reinforcement tube 50 formed cylindrically and an area, where the heating wire is wound around the terminal, is inserted into the inner diameter side, where the reinforcement tube is formed of a material having a springback amount into the enlarged diameter direction, after a compressive load is applied from the outer diameter side, is smaller than that of the heating wire. An inner peripheral surface of the reinforcement tube abuts the heating wire.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electric heater and a method for manufacturing the electric heater, and more particularly, to one that suppresses disconnection of a portion where a heating wire is wound around a terminal and is crimped.

An electric heater generally referred to as a sheathed heater has a heating wire such as a nichrome wire formed in a spiral shape inside a cylindrical body (sheath) made of, for example, stainless steel, and an insulating material such as magnesium oxide is formed in a gap. It is configured to be filled with a powder.
In such an electric heater, after the end of the heating wire is wound around a cylindrical terminal formed of nickel or the like, for example, the sheath is compressed from the outer diameter side, and crimped to the terminal by reducing the diameter. Be made.
Patent Document 1 describes a method for manufacturing a sheathed heater in which a heating wire is wound around a terminal in this manner and placed in a cylinder filled with insulating powder to reduce the diameter.

JP 2007-109448 A

In the sheathed heater having the above-described configuration, there may be a failure that breaks at a place where the end of the heating wire is wound around the terminal.
The subject of this invention is providing the manufacturing method of the electric heater which suppressed the disconnection of the location which wound the heat generating wire around the terminal, and was crimped | bonded.

The present invention solves the above-described problems by the following means.
The invention according to claim 1 is an electric heater having a terminal connected to a power source and a heating wire that is crimped to the terminal in a state where at least one end is wound around the terminal. A region where the heating wire is wound around the terminal is inserted into the inner diameter side, and the reinforcement tube is a spring in the diameter expansion direction after a compressive load is applied from the outer diameter side. The electric heater is characterized in that a back amount is made of a material smaller than that of the heating wire, and an inner peripheral surface is in contact with the heating wire.

  In the invention according to claim 2, in the region where the heating wire is wound around the terminal connected to the power source, the springback amount in the diameter expanding direction after applying a compressive load from the outer diameter side is larger than that of the heating wire. The method of manufacturing an electric heater is characterized in that the heating wire is crimped to the terminal by inserting the reinforcing tube made of a small material into the inner diameter side and reducing the diameter of the reinforcing tube.

The inventors of the present invention found that the cause of the breakage of the heating wire at the portion wound around the terminal is an abnormality caused as a result of an increase in electrical resistance (contact resistance) due to insufficient contact area between the terminal and the heating wire. Found fever.
Such a shortage of contact area is thought to be due to diameter expansion (springback / elastic recovery) due to the elastic force after diameter reduction between the heating wire and the terminal.
In this regard, according to the present invention, a reinforcing tube formed of a material whose springback amount in the diameter expansion direction after applying a compressive load from the outer diameter side is smaller than the heating wire is disposed around the heating element, By suppressing the expansion of the heating wire due to the spring back by the reinforcing tube, it is possible to secure a contact area between the heating wire and the terminal, reduce contact resistance, suppress excessive heat generation, and prevent disconnection.

  As described above, according to the present invention, it is possible to provide an electric heater and an electric heater manufacturing method in which disconnection of a portion where a heating wire is wound around a terminal and crimped is suppressed.

It is a typical fragmentary sectional view which shows the structure of the electric heater which is a reference example of this invention. It is an enlarged view of the connection location of a heating wire and a terminal in the example of the electric heater to which the present invention is applied. It is a stress strain diagram of each member at the time of diameter reduction processing of the electric heater of an example.

Hereinafter, an embodiment of an electric heater and an electric heater manufacturing method to which the present invention is applied will be described.
First, as a reference example of the present invention, a conventional electric heater and a method for manufacturing the same will be described.

FIG. 1 is a schematic partial cross-sectional view showing a configuration of an end portion of an electric heater of a reference example.
The electric heater 1 of the reference example is a sheathed heater configured to include a heater cylinder 10, a sealing member 20, a heating wire 30, a terminal 40, and the like.
The heater cylinder 10 constitutes an outer surface portion of the electric heater 1A, and is formed in a cylindrical shape by, for example, stainless steel.
Further, the heater cylinder 10 may be curved or bent depending on the application of the electric heater 1.
The heater cylinder 10 is filled with an insulating powder made of an insulator (for example, MgO) having good thermal conductivity.

  The sealing member 20 is a lid-like member that closes the end of the heater cylinder 10.

The heating wire 30 is formed of a nickel-chromium alloy (nichrome) wire, and is wound spirally.
The heating wire 30 is arranged inside the heater cylinder 10 so that the center axis of the spiral winding is substantially concentric with the center axis of the heater cylinder 10.
The heating wire 30 is arranged at an interval from the inner surface of the heater cylinder 10, and this interval is filled with insulating powder.
The end 31 of the heating wire 30 is in a state of being crimped to the end 41 of the terminal 40 while being wound around the terminal 40.

The terminal 40 is a member (electrode) that electrically connects the electrical wiring connected to the power source and the heating wire 30.
The terminal 40 is formed in a cylindrical shape with, for example, nickel.
The terminals 40 are disposed substantially concentrically with the heater cylinder 10 and project through the central portion of the sealing member 20 to the inside and outside of the heater cylinder 10.
A wiring from the power source is connected to the end of the terminal 40 on the outside of the heater cylinder 10.
An end portion 31 of the heating wire 30 is wound around the end portion 41 on the inner side of the heater cylinder 10 of the terminal 40 and is crimped.

Next, a method for manufacturing the electric heater 1 described above will be described.
First, the heating wire 30 and the terminal 40 are disposed inside the heater cylinder 10, and the remainder is filled with insulating powder.
At this time, the diameter of the heater cylinder 10 is formed larger than the dimension at the time of completion (product dimension).
In addition, a gap necessary for inserting the terminal 40 on the inner diameter side of the end portion 31 is provided between the edge on the winding inner diameter side of the end portion 31 of the heating wire 30 and the surface of the terminal 40. Yes.
Thereafter, the heater cylinder 10 is reduced in diameter to a predetermined product size by pressing the outer peripheral surface of the heater cylinder 10 toward the inner diameter side.
At this time, the end 31 of the heating wire 30 is pressed toward the terminal 40 and is crimped to the outer peripheral surface of the end 41.

However, when the pressing force to the outer peripheral surface of the heater cylinder 10 is removed, the heating wire 30 is expanded in diameter by the spring back, and actually a minute gap is formed between the surface of the terminal 40 and the contact resistance is increased. There was a case.
After the diameter reduction processing, the sealing member 20 is attached to seal both ends of the heater cylinder 10, and the electric heater 1 is completed.

Next, an embodiment of an electric heater to which the present invention is applied and a manufacturing method thereof will be described.
In the description of the embodiments, portions that are substantially the same as those of the reference example described above are denoted by the same reference numerals, description thereof is omitted, and differences are mainly described.
FIG. 2 is an enlarged view of a connection portion between the heating wire and the terminal in the electric heater of the embodiment.
The electric heater according to the embodiment is characterized in that a reinforcing tube 50 is covered on the outer peripheral side of the portion where the end portion 31 of the heating wire 30 is wound around the end portion 41 of the terminal 40.
The reinforcing tube 50 is formed in a cylindrical shape substantially concentric with the terminal 40.
The inner peripheral surface of the reinforcing tube 50 is in contact with the region on the outer diameter side of the end portion 31 of the heating wire 30.
The outer peripheral surface of the reinforcing tube 50 is arranged at a distance from the inner peripheral surface of the heater cylinder 10, and this interval is filled with insulating powder.

The reinforcing tube 50 is formed of a material that has a small amount of springback (elastic recovery) that occurs after the diameter reduction of the heater cylinder 10 with respect to the material of the heating wire 30 and the terminal 40.
Such a material is, for example, a material having a lower yield point than the material of the heating wire 30 (preferably, the material of the heating element 30 and the terminal 40).
The reinforcing pipe 50 uses a so-called soft material that easily causes such plastic deformation, and the amount of spring back of the heating wire 30 suppressed by the reinforcing pipe 50 becomes smaller than the amount of free spring back of the terminal 40, thereby generating heat. It is preferable to form the wire 30 thick so that the wire 30 bites into the terminal 40.
For example, when the heating wire 30 is a nichrome wire and the terminal 40 is made of nickel, the reinforcing tube 50 can be formed of pure iron (Fe) as an example.

  In the electric heater 1 of the embodiment, the reinforcing pipe 50 is formed to have a diameter that can inevitably secure a gap that is inevitably necessary for inserting the end portion 31 of the heating wire 30. When performing, the diameter is reduced by receiving a compressive load from the outer diameter side through the insulating powder, and the end portion 31 of the heating wire 30 is pressed toward the inner diameter side (terminal 40 side).

Hereinafter, effects of the embodiment will be described with reference to FIG.
FIG. 3 is a stress strain diagram of each member during diameter reduction processing of the electric heater of the example.
In FIG. 3, the vertical axis indicates stress (upward is compression, lower is tensile), and the horizontal axis indicates strain.
The heating wire 30, the terminal 40, and the reinforcing pipe 50 all enter the plastic region past the yield point after passing through an elastic region in which strain is proportional to the stress during diameter reduction processing. Thereafter, when the compressive force from the outer diameter side is removed, a springback (elastic recovery) in which the strain is reduced by the residual stress occurs.
The points from point a to point c in the diagram of the heating wire 30, point f to point e in the diagram of the terminal 40, and portion from point f 'to point e' in the diagram of the reinforcing tube 50 correspond to springback.
The amount of free spring back when the heating wire 30, the terminal 40, and the reinforcing pipe 50 are individually compressed is the ε origin, the ε end, and the ε complement in FIG.

  If the reinforcing pipe 50 is not provided (in the case of the configuration of the reference example), the springback amount of the heating wire 30 and the terminal 40 is substantially equal to this free springback amount, and c in FIG. Strain corresponding to the distance from point to point e forms a gap.

In the embodiment, by providing the reinforcing tube 50 having a small spring back with respect to the heating wire 30, the reinforcing tube 50 acts to prevent the heating wire 30 from expanding in diameter.
That is, when the heating wire 30 attempts to expand the diameter while pressing the inner peripheral surface of the reinforcing tube 50, the compressive stress remaining inside the heating wire 30 and the result of being pressed by the heating wire 30 are inside the reinforcing tube 50. At the point where the generated tensile stress is balanced (point g in FIG. 3), the diameter expansion of the end 31 of the heating wire 30 is suppressed.
In this case, the gap generated between the end portion 31 of the heating wire 30 and the end portion 41 of the terminal 40 is formed by distortion corresponding to the distance from the point g to the point e in FIG.

Hereinafter, specific numerical examples will be described.
The heating wire 30 is assumed to be a nichrome wire having a wire diameter d = 0.65 mm.
The terminal 40 is made of nickel and has a terminal diameter D = 3 mm at the end 41.
As the reinforcing tube 50, a pure iron cylinder having a thickness h = 1 mm is used.
It is assumed that the longitudinal elastic modulus E of the heating wire 30, the terminal 40, and the reinforcing tube 50 is 21000 kg / mm ² .

It is assumed that the maximum stress when the heating wire 30, the terminal 40, and the reinforcing pipe 50 are reduced in diameter is σ1 = 45 kg / mm ² , σ2 = 25 kg / mm ² , and σ3 = 12 kg / mm ² , respectively.
In this case, the free springback amounts of the heating wire 30, the terminal 40, and the reinforcing pipe 50 are as follows.
ε departure = σ1 / E = 0.0021
ε end = σ2 / E = 0.0012
ε complement = σ3 / E = 0.00057

Under the above conditions, the gap between the heating wire 30 and the terminal 40 when the compressive stress of the heating wire 30 and the tensile stress of the reinforcing tube 50 are balanced is −0.38 μm in diameter.
Here, the fact that the gap is negative indicates that the heating wire 30 bites into the terminal 40 and is in close contact therewith.
If the reinforcing pipe 50 is not provided, the gap is 4.1 μm in diameter, and the contact resistance between the heating wire 30 and the terminal 40 increases, causing abnormal heat generation.

  Thus, in this embodiment, by providing the reinforcing pipe 50, the diameter of the heating wire 30 due to the spring back is suppressed, and the end portion 31 of the heating wire 30 is lifted from the end portion 41 of the terminal 40 and locally. It is possible to prevent electrical resistance (contact resistance) from increasing and abnormal heat generation to cause a failure such as disconnection.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
For example, the shape, structure, material, manufacturing method and the like of each member constituting the electric heater are not limited to the above-described embodiments, and can be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 Electric heater 10 Heater cylinder 20 Sealing member 30 Heating wire 31 End part 40 Terminal 50 Reinforcing pipe

Claims (2)

A terminal connected to a power source;
An electric heater having a heating wire crimped to the terminal in a state where at least one end is wound around the terminal,
A region where the heating wire is wound around the terminal and formed in a cylindrical shape has a reinforcing tube inserted into the inner diameter side,
The reinforcing pipe is formed of a material whose spring back amount in the diameter expansion direction after applying a compressive load from the outer diameter side is smaller than that of the heating wire, and an inner peripheral surface is in contact with the heating wire. Electric heater to do. Reinforcement formed of a material in which the amount of springback in the diameter-expanding direction after applying a compressive load from the outer diameter side is smaller than that of the heating wire in the region where the heating wire is wound around the terminal connected to the power source A method of manufacturing an electric heater, wherein the heating wire is crimped to the terminal by inserting into the inner diameter side of the tube and reducing the diameter of the reinforcing tube.

Images