JPH0726877B2 - How to install the thermocouple - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A method of attaching a thermocouple that generates a thermoelectromotive force corresponding to a temperature to a chip base material for temperature measurement, in which dissimilar wires having a relatively small diameter are combined. With the aim of improving the adhesion strength between the thermocouple to be joined and the temperature measurement target, and at the same time improving the accuracy of temperature measurement, the extra length provided at the crossed wire ends corresponds to the molding volume of the thermocouple. After temporary welding the first wire rod and the second wire rod to achieve thermal equilibrium, main welding is performed by laser beam irradiation of a wide area that is the range of the extra length wire rod end and the tip base metal. The welding means of the thermocouple is constructed.

[Industrial application field]

TECHNICAL FIELD The present invention relates to a thermocouple mounting method for welding and joining a small-diameter wire rod to a chip base material (temperature measurement base material) such as a metal plate.

A thermocouple for industrial temperature measurement is a combination of metal wire rods, such as platinum-platinum rhodium, depending on the operating temperature.
Although chromel-alumel, copper-constantan, etc. are used, brazing, welding, etc. are generally used for joining these dissimilar wires. However, these joining methods tend to contain impurities during welding, which hinders accurate temperature measurement, and has insufficient adhesion strength with the chip base material. For this reason, laser beam welding has recently been performed. The present invention provides a method for welding a thermocouple body for temperature measurement including a chip base material.

[Conventional technology]

FIG. 5 is a front view showing a method of welding a thermocouple to a chip base material with a laser beam. FIG. 6 is a perspective view of the thermocouple chip to which FIG. 5 is applied.

In the front view in which the thermocouple is attached to the chip base material 1 which itself is a temperature measurement object, the chip base material 1 may be any metal as long as it has a high thermal conductivity, and its shape is also arbitrary. In the figure, the thermocouple 10 to be joined is exemplified by a chip base material 1 formed from a molybdenum thin plate.

The surface of the chip base material 1 is shown to be bonded by a laser beam including bonding of different kinds of wire rods 2 and 3 whose potential difference is known to be caused by temperature and welding to the chip base material 1.

In such laser beam welding, the wire diameter is 0.3 (m
Since it is a fusion splicing between the thin metal wire rods 2 and 3 of about m) and the chip base material 1 with a large heat capacity, only the wire rods 2 and 3 are easily melted and evaporated during beam irradiation with large thermal energy, In addition to joining, joining to the chip base material 1 becomes difficult.

For this reason, conventionally, a pulsed laser beam capable of suppressing the beam energy to be irradiated and controlling the beam irradiation time is used to bond the dissimilar wires (bonded surface 11) together with the thermocouple 10.
There was fusion bonding to the chip base material in the vicinity of.
A beam spot 12 which is continuous in the drawing is a base material joint portion of a thermocouple including a joint interface.

FIG. 6 is a perspective view of a measuring thermocouple chip to which the thermocouple bonded body described in FIG. 5 is applied.

The measuring thermocouple 10 is directly welded to the center position of the bottom side 13 of the U-shaped chip base material 1.

The U-shaped chip base material 1 is merely an example, and the position of mounting the thermocouple 10 on the chip base material, the shape of the base material, or the like is appropriately changed according to the temperature measurement target. In the figure, 14 is a plug terminal for connection to a potentiometer, and 15 is a lead wire for deriving a potential difference.

[Problems to be solved by the invention]

Both of the welding methods of welding between the small diameter wire rods 2 and 3, and the welding of the welded wire rods 2 and 3 and the thermocouple mounting welding in which the heat capacity difference between the tip base metal 1 is large, the beam energy is suppressed. Although a continuous multi-point irradiation type pulsed laser beam is used, there are the following problems.

(1) The welding work takes time because of the multi-point irradiation method, and (2) the bonding area between the wire rods 2 and 3 is very small, so that the thermocouple 10 has weak strength and is easily separated from each other. (3) It is difficult to keep the bonding interface 11 in close contact with the chip base material 1 and the yield of the thermocouple is poor.

[Means for solving problems]

According to the present invention, the above-mentioned problems are caused by different metals for forming thermocouples as shown in FIGS. 1 (a) and (b), and the first wire (2) and the second wire (3) having a small diameter are The extra lengths (4) and (5) of the pair of short tips that form a crossed arrangement form the thermocouple molding volume and are temporarily welded to each other so as to obtain thermal equilibrium between the wires, and then the thermoelectric The pair forming volume is placed on a metal chip base material (1) having a heat capacity higher than that of the wire and having a high thermal conductivity, and a single laser beam is applied in the range of the extra length wire end and the cross shape part of the wire. This is solved by a method of attaching a thermocouple, which comprises irradiating and melting the wire and the chip base material to form a spherical thermocouple junction.

[Action]

Pre-welding before the main welding improves the thermal conductivity between wires intersecting each other during laser beam irradiation (maintains thermal balance) and eliminates the temperature difference between the wires during main welding. In addition, the extra length of the crossed wire ends is a portion that secures the thermocouple molding volume necessary for fusion bonding.

Next, after performing relative positioning with the tip base metal, the main welding includes the intersection of the first and second wire rods and the end of the crossed wire rod, and only one wire rod is irradiated for high-energy laser beam irradiation. A spherical bonded compact is obtained without selective welding.

Thus, a thermocouple-bonded body is obtained in which the three-dimensional melt-bonded interface between the first and second wires is stably formed and which has a high strength with respect to the chip base material.

〔Example〕

Hereinafter, an example of a method for mounting the thermocouple of the present invention will be described. The embodiment is an example in which the first wire is chromel and the second wire is constantan (Cu / 45Ni alloy).

Diameter of 0.2 crossed at an appropriate angle in Fig. 1 (a)
Wires for forming thermocouples 2 to 0.3 mm each
And 3 are temporarily fixed by resistance heating welding or the like. It is not necessary to hold the mutual wires in parallel and in close contact with each other in the related art.

The extra length portions 4 and 5 from the crossing point to the end of the wire rod shown in FIG. 4A are portions that secure the thermocouple forming volume after the main welding. The temporary joined body 7 has improved heat conduction between the wire rods 2 and 3 and is effective in eliminating the temperature difference between the wire rods during the main welding described with reference to FIG.

In the same figure (b), the wire rods are fusion-bonded to each other by a high-energy irradiation laser beam including the temporarily joined wire rod intersections and the protruding portions of the wire rod terminal surplus lengths 4 and 5. In the figure, the circle 6 is a spot circle of the irradiation laser beam.

The diameter of the irradiation spot circle 6 is approximately 2 to 3 times the diameter of the wire rod, and its center is located near the root of the protrusion. If the fusion bonding to the chip base material is carried out simultaneously with the thermocouple bonding under the irradiation condition of such a wide area and with a single laser pulse, the spherical thermocouple bonded body 8 as shown in FIG. 2 is formed.

2A is a top view of the thermocouple assembly, and FIG. 2B is a side view of FIG.

FIG. 3 is a front view showing another example of the arrangement of the pair of wire rods 2 and 3 arranged on the surface of the tip base metal 1 during the main welding described in FIG. 1 (b).

That is, at the time of temporary welding, the wire rods 2 and 3 are crossed in a plane to form a temporary bonded body 7 ', and then the extra lengths 4 and 5 of the wire rod ends are formed.
A wide area laser beam irradiation by the irradiation spot circle 6 whose center is placed near the root of the above forms a thermocouple junction having the same function as in FIG.

FIG. 4 is a front view showing another embodiment of the main welding process. In the embodiment, a laser beam spot is formed by covering the wire rods 2 and 3 with a copper foil 9 having good thermal conductivity and closely adhering to the mutual wire rods. A method of performing welding by circle 6 is shown. When the wire diameter is particularly small, the heat radiation effect of the copper foil 9 during fusion bonding is used to prevent an excessive amount of heat input to the wire, and stable welding can be achieved without thinning the wire.

The thermocouple molded body 8 formed according to the above-described embodiment has a deep fusion bonding interface between the wire rods, and foreign matter does not enter the fusion bonding interface and the bonding surface with the chip base material 1 side. High temperature measurement is possible.

〔The invention's effect〕

As described in detail above, according to the thermocouple mounting method of the present invention, the adhesion between the thermocouple and the chip base metal, including the bonding wire between the thermocouple and the chip base metal at the time of thermocouple bonding is improved, and high strength welding becomes possible. , Yield of about 100% can be obtained. However, there is a remarkable advantage that the welding work time is significantly shortened because the processing is performed by irradiation with a single laser pulse of high energy as compared with the conventional method.

[Brief description of drawings]

FIGS. 1 (a) and 1 (b) are principle drawings of the thermocouple of the present invention, FIGS. 2 (a) and 2 (b) are a top view and a side view of the thermocouple molded body, and FIG. Another embodiment of temporary welding of the mutual wire of the present invention, FIG. 4 is another embodiment of the main welding according to the present invention, FIG. 5 is a front view showing a welding method of a conventional thermocouple, and FIG. 6 is temperature measurement. In the perspective view of the thermocouple chip for use in the figure, 1 is a chip base material, 2 and 3 are thermocouple wire rods, 4 and 5 are extra lengths provided at the ends of crossed wire rods, 6 is a laser beam (irradiation spot circle), and 7 and 7 ′ Is a joined body at the time of temporary welding, 8 is a fusion bonded portion of the present invention, and 10 is a conventional thermocouple bonded portion.

Claims (1)

[Claims] 1. A first wire rod (2) and a second wire rod (3) having different diameters, which are different metals for thermocouple molding, are formed in a crossed arrangement shape and have a pair of short tips. Extra length (4)
And (5) are thermocouple forming volume parts, and are temporarily welded to each other so as to obtain thermal equilibrium between the wire rods. Subsequently, the thermocouple forming volume part is a metal chip mother having a high heat conductivity and a high thermal conductivity. Placed on the wire (1), a single laser beam is irradiated to the area of the cross-shaped portion of the wire rod end and the extra length, the wire rod and the chip base metal are melted, and the spherical thermocouple bonded body is formed. A method for mounting a thermocouple, characterized in that the thermocouple is formed.