JPH012302A - Manufacturing method of glass coated thermistor - 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 glass coated thermistor.

[Conventional technology]

Thermistors are made by starting with metal oxide powders, mixing them, molding them, and sintering them, and are available in various shapes such as bead shapes and disk shapes. Among these, thermistors that use glass for the exterior of one or less small elements have excellent stability, heat resistance,
Because it is superior to resin-coated products in terms of responsiveness and reliability, it has recently been used in environments with a lot of moisture or steam, measurements that require heat resistance, and equipment such as water heaters, microwave ovens, refrigerators, and air conditioners. It is widely used as a temperature control sensor.

Various methods of manufacturing glass-coated thermistors have been known in the past, and representative examples thereof will be described below.

In the first example, as shown in Fig. 3(a), a spherical element is made by depositing a paste-like mixture of metal oxide fine powder, a binder, and a solvent on platinum wires 2 and 2' stretched in parallel. After drying this, it is sintered at a temperature of about 300° C. to complete an element 1 using platinum wires 2 and 2' as electrodes. Lead wires 3 and 3' made of Dumet wire or nickel wire are welded to the platinum wires 2 and 2' depending on the purpose, and the element 1 is covered with glass 5.

As a second method, as shown in FIG. 3(b), two platinum wires 2 and 2' are stretched parallel to each other in a mold, and the above paste is press-fitted into the mold, whereby the platinum wires 2 and 2' are stretched in parallel. 1 on the line 2°2'
After drying the element 1 formed as a body, l, 000-1
, sintered at a temperature of 300°C. Lead wires 3, 3' such as dumet wires are welded to the platinum wires 2, 2', and the glass 5
The element 1 is coated with (Japanese Unexamined Patent Publication No. 12443/1989).

As a third method, as shown in Fig. 3(c),
A lead wire 3.3' formed into a flat plate according to the dimension of one side of the thermistor element 1 provided with k 4 + 4' is spot-welded at one end to the electrode surface of the thermistor element 1, and a glass coat 5 is applied to it. (Actual Publication No. 58-7696)
No. 6) There is an example.

The glass coating of such a glass-coated thermistor includes:
As shown in FIG. 4(a), a glass tube 5a whose inner diameter is slightly larger than the size of the bead element 1 and cut into an appropriate size is used.
is passed over element 1 and heated and melted in a heating furnace to form the fourth element.
The common method was to encapsulate it as shown in Figure (b).

[Problem that the invention seeks to solve]

By the way, when using the above method, the wall thickness is required to be as thick as a glass tube from the point of view of workability, etc., and the wall thickness is usually 0.5 mm.
3 to 0.5 mm is used, but with this thickness, air bubbles are likely to be trapped between the element 1, the platinum wires 2, 2', and the glass 5, and especially around the edges of the cord 1. It has the drawbacks that it is easy to contain and has a relatively large thermal time constant, and in terms of workability, positioning of the glass tube is troublesome, and the glass tube may be sealed out of position due to vibration or shock.

Furthermore, if the glass melting temperature becomes high, the glass will deform and the appearance will be poor.On the other hand, if the melting temperature is too low, airtightness will be lacking, resulting in a disadvantage that the yield will be poor due to slight fluctuations in conditions.

As another example, as shown in Fig. 5, a glass paste is made by mixing powdered glass with a binder and a solvent, and this is applied to cover the element 1 and the bases of the lead wires 3 and 3', and after drying. There is a method of melting it in a heating furnace and sealing it in the glass 5. This method is a simple method for glass coating, and can be applied to the shape of the element regardless of the shape or size of the element 1. The thickness of the glass film can also be changed by adjusting the viscosity of the glass paste. It has the advantage of having a degree of freedom.

However, even with this method, bead-shaped thermistors sealed in glass contain many fine bubbles in the coated glass, and the thickness of the coated glass tends to be uneven, resulting in uneven thermal time constants and poor appearance. . Furthermore, to remove air bubbles, there is a method in which the glass is softened to a viscosity that allows the air bubbles to come out again, and then annealed at that temperature for about 30 minutes, but this method has the drawback of requiring a lot of man-hours.

An object of the present invention is to provide a method for manufacturing a bead-type thermistor that eliminates the drawbacks of the glass-coated thermistor described above.

[Means for solving problems]

The present invention is a method for manufacturing a glass-coated thermistor, characterized in that a main body consisting of a cable body and a metal lead wire that can be sealed to glass is immersed in molten glass to coat the main body with glass.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an apparatus showing a specific example of carrying out the present invention. 10 is 2 stretched in parallel as in Figure 3 (a).
A paste-like mixture consisting of fine metal oxide powder, a binder, and a solvent is attached to a real platinum wire 2.2' to form a spherical element 1.
11 is a porcelain crucible. A heater 12 is provided on its outer periphery, and a preheating heater 13 is provided above it. Further, its outer periphery is sufficiently surrounded by a heat shield 14 made of glass wool, asbestos, etc. to prevent heat radiation.

Crushed glass or powdered glass is placed in this crucible 11, and the heater 12 is heated to melt the glass to produce molten glass 15.

In the embodiment, the thermistor 10 is lowered into the crucible 11, and first held at a position in front of the preheating heater 13 for 5 to 7 seconds to preheat the thermistor 10. This is thermistor 10
This is done to release the air contained therein and to prevent the occurrence of defects such as microcracks due to thermal shock, and the effect will be diminished if the preheating temperature is 200°C or more lower than the molten glass temperature.

Next, the preheated thermistor 10 is lowered and immersed in the molten glass 15 to the depth of the desired coating size, and then the thermistor 10 is gradually pulled up, and the pulling speed is further reduced at the position of the preheater 13 to allow it to pass through.

In the glass-coated thermistor 10 shown in FIG. 2 coated with glass in this way, the glass 5 is coated uniformly and thinly around the thermistor 10, and the glass does not contain any air bubbles. Even if it is mixed, only 2 to 3 extremely fine bubbles will be generated, and the properties will not be affected. 16 in Figure 1 is a thermal lightning pair.
17 indicates a thermometer.

Of course, this molten glass 15 must be made of a material that matches the coefficient of thermal expansion of the thermistor.

The temperature of the molten glass is 100~100° higher than the melting point of the glass.
Preferably, the temperature is higher by 150°C.

If the glass temperature is too low, the glass at the tip of the thermistor 10 will not cut easily and will take on the shape of a teardrop.

If the glass temperature is too high, the molten glass will become weathered,
The coated glass becomes devitrified.

When comparing 200 glass coated thermistors coated with glass using the manufacturing method of the present invention and 200 glass coated thermistors coated with glass using the conventional manufacturing method, as shown in Table 1, it was found that the glass coated thermistors coated with glass using the manufacturing method of the present invention It can be said that the thermal time constant is clearly small, there are no bubbles, and the yield of appearance and shape is superior to that of conventional products. Although it is easy to make the glass thickness less than the table value, it is desirable to keep the glass thickness within this range from the viewpoint of insulation and mechanical strength.

In the example, manufacturing was carried out using a very simple device, but it is possible to fully automate the process by automatically feeding the thermistor, and by providing a preheating section and an annealing section separately from the glass melting section to create an automatic line. is easy, and productivity can be improved compared to conventional methods.

Table 1 Glass thickness (a-a) is shown in FIGS. 2, 4(b), and 5.

【Effect of the invention〕

As described above, the present invention has the advantage of being able to manufacture a bead-shaped thermistor with excellent productivity, a small thermal time constant, and high reliability.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of an apparatus used in the method of the present invention;
FIG. 2 is a diagram showing the shape of a glass coated thermistor manufactured by the method of the present invention, FIGS. 3(a) to (c) are diagrams showing the shape of a glass coated thermistor manufactured by the conventional method, and FIG.
Figures a) and (b) are diagrams illustrating an example of glass covering IF by a conventional method in the order of steps, and Fig. 5 is a diagram showing the shape of a thermistor showing another example of coating. 1... Spherical element 2, 2'... Platinum wire 3
．． 3'... Lead wire IO... Thermistor 11... Crucible 12... Heater 13... Preheating heater -5... Molten glass patent applicant Daito Seisakusho Co., Ltd., Representative Patent attorney Academician Kanno Naka. , Figure 2 (Q,) (b) (C) Figure 3 (a) (b) Figure 4 Figure 5

Claims (1)

[Claims] (1) A method for manufacturing a glass-coated thermistor, which comprises immersing a main body consisting of an element and a metal lead wire that can be sealed on glass in molten glass to coat the main body with glass.