JPH0352233B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a thermocouple, and more particularly to a quick-response thermocouple suitable for detecting the presence or absence of a flame in a combustion device. [Prior Art] A thermocouple used to detect the temperature of an object to be measured is desired to have a large thermoelectromotive force and a fast response.
In particular, when a thermocouple is applied to detect the presence or absence of a flame in a combustion device, this improvement in responsiveness is most desired. If the responsiveness of the thermocouple is poor and there is a delay in detecting a flame misfire, an extremely dangerous situation may occur in which unburned gas is released. Further, thermocouples used in combustion devices are required to have durability because they are used for continuous intermittent heating, and corrosion resistance is particularly required for use in reducing flames. Conventionally, thermocouples applied to combustion equipment have used constantan-based materials (typical component values: Ni 40%, Cu 60%) for the internal element, and chromel-based materials (typical component values: Ni 80-90%,
Cr20~10%) or heat-resistant steel (typical component value: Cr23)
%, Fe77%) is the most commonly used. This conventional thermocouple has the advantage of generating a fairly large thermoelectromotive force of about 30 mV when inserted into a flame temperature of 800 to 1000°C, but under intermittent heating conditions, In the case of steel, cracks occur at the joint between the external and internal elements due to fatigue fracture, which is thought to be caused by the difference in coefficient of thermal expansion between the two, so to prevent this fracture, the wall thickness of the element material must be increased. It will stop happening. As the heat capacity increased, the thermal response deteriorated, and there was a delay of about 5 to 10 seconds to follow a change of about 10 mV, making it insufficient as a thermocouple for combustion equipment. .
Furthermore, since the chromel type mainly contains Ni, which is a corrosive component in a reducing flame, it has the disadvantage that it is not suitable for detecting the presence or absence of flame in a reducing flame. [Summary of the Invention] The present invention has been made in view of the above circumstances, and its main purpose is to provide a thermocouple using constantan-based materials for the internal element and aluminum-bronze-based materials for the external element. It is. With this configuration, the outer element is also made of a material whose main component is copper (Cu), just like the inner element, so the thermal expansion coefficients of the outer and inner elements can be made to have similar values, which improves durability against intermittent flame heating. Since the thermocouple can be used with a thin wall thickness, the response speed of the thermocouple can be extremely high, and the high thermal conductivity properties of copper combine to significantly enhance this effect. Moreover, unlike chromel-based aluminum bronze-based external elements, it contains almost no Ni component, which is a corrosive component, and aluminum (Al) has a corrosion-preventing effect.
Since the ingredients are added in small amounts, they work synergistically to significantly enhance this effect. [Embodiment of the Invention] An embodiment of a thermocouple according to the present invention will be described below with reference to FIG. In the figure, reference numeral 1 denotes an internal element constituting the thermocouple, and like the internal element of conventional thermocouples, a constantan-based material whose main components are 40% Ni and 60% Cu is used. 2
is the external element that constitutes the thermocouple, and is made of aluminum-bronze material. In addition, in the following table 1
The following is a table of component ratios for aluminum-bronze materials as defined by JIS standards.

[Table] Table 2 below shows the composition ratio of aluminum bronze materials commercially available from Mitsubishi Metals Corporation.

[Table] The thermocouple according to the present invention uses this aluminum bronze material as the external element of the thermocouple,
The component ratio is preferably within the range of Al: 5 to 12% Fe: 0.5 to 5% Ni: 6.0% MAX Mn: 3.5% MAX Cu: the remainder. Here, in conventional thermocouples, chromel or heat-resistant steel is used as the material for this external element. 3 is a protection tube, which is provided to prevent the inner element 1 and the outer element 2 from coming into contact with each other other than at the head, which is the heat detection part of the thermocouple. 4 is a first copper wire welded to the internal element 1, and 5 is a second copper wire welded to the external element 2, for transmitting the thermoelectromotive force detected by the heat detection section to a circuit section (not shown). belongs to. Next, the responsiveness of the thermocouple according to the present invention described above is
The improvement over conventional thermocouples will be explained using experimental data shown in FIG.
In the experimental data shown in FIG. 2, the horizontal axis shows the flow of time, and the vertical axis shows the thermoelectromotive force of the thermocouple. The thermocouples used in the experiment were a thermocouple according to the present invention (inner element is constantan-based, outer element is aluminum bronze-based) and a conventional thermocouple (internal element is constantan-based, outer element is chromel-based). ). The experiment determined the rise of the thermoelectromotive force of these two types of thermocouples placed in the flame when propane gas combustion was started, and the fall of the thermoelectromotive force when combustion was stopped. It is. In the data, P _N =200 mmAq and 280 mmAq indicate the nozzle back pressure of combustion gas, and the combustion flame temperature is approximately 800°C in a stable state. The time scale on the horizontal axis is 1 second per division, but the paper feed speed of the recorder is changed so that 1 division is 1 minute until a stable state is reached. As can be seen from the experimental data shown in Figure 2,
The final thermoelectromotive force at approximately 800℃ is approximately 30m for the conventional product.
Although the thermocouple according to the present invention has a high voltage of 15 mV, the rise time is quite long at approximately 11 seconds, whereas the final thermoelectromotive force of the thermocouple according to the present invention at approximately 800°C is low at approximately 20 mV. It can be seen that the time it takes to reach 10 mV, which is half of that, is extremely short, approximately 4 seconds. Furthermore, the data shows that the thermoelectromotive force fall when combustion is stopped is significantly shorter in the thermocouple according to the present invention than in the conventional product. The reason why the responsiveness of the thermocouple of the present invention is significantly improved compared to conventional products using chromel is that the thermal conductivity of the aluminum bronze used as the external element is higher than that of chromel, as shown in Table 3. This is considered to be extremely large compared to . In other words, the heat of the flame is quickly transferred to the joint between the outer element and the inner element, thereby speeding up the response. In addition, since the coefficients of linear expansion of aluminum bronze and constantan are extremely similar as shown in Table 3, cracks due to fatigue failure due to the difference in coefficient of linear expansion under intermittent heating conditions are prevented. The fact that the heat capacity can be reduced because there is no need to increase the wall thickness for this purpose is thought to be one of the reasons why this responsiveness is accelerated. In addition, although the conventional thermocouple in the experimental data shown in Figure 2 uses a chromel-based external element, similar experiments can also be performed with conventional thermocouples that use a heat-resistant steel external element. results are obtained,
The reason for this is also considered to be due to the difference in thermal conductivity and the difference in coefficient of linear expansion shown in Table 3. Although the thermovoltaic ability of the thermocouple according to the present invention is inferior to that of conventional products, this is a problem that can be covered by circuit technology. For thermocouples used for commercial purposes, this decrease in thermoelectric ability is not an essential problem. Another feature of the structure of the thermocouple according to the present invention is that while the structure of the outer element and inner element of the prior art thermocouple is welded through the outer element as shown in FIG. As shown in FIG. 1, the thermocouple is constructed by forming the head of an external element 2 with a sealed tip structure, and engaging the internal element 1 with the top and joining it by, for example, welding. With such a structure, when the internal element 1 and the external element 2 are joined, it is possible to prevent Ni, which is the main component of the constantan material that is the material of the internal element, from melting and precipitating to the outside. When Ni is used in a reducing flame, it corrodes and causes the thermocouple to break, so it is necessary to avoid depositing Ni on the surface of the thermocouple. In general, the internal elements are constantan-based,
Conventional thermocouples whose external elements are made of chromel are unsuitable for use in reducing flames because chromel has Ni as the main component.
As shown in Table 3 below, the coefficients of linear expansion of both elements are relatively close to each other, so they can be used even at high flame temperatures as long as they are not in a reducing flame.

〔Effect of the invention〕

As explained above, according to the present invention, since the external element is made of aluminum bronze material and the internal element is made of constantan material, the response can be fast, and it can be used in reducing flames and high-temperature flames. It is an object of the present invention to provide a quick-response thermocouple that can be used in a combustion safety device, has a long service life even when used in a reducing flame, and has excellent characteristics as a flame detector in a combustion safety device. can.

[Brief explanation of drawings]

Fig. 1 is a structural cross-sectional view showing one embodiment of the thermocouple according to the present invention, and Fig. 2 is experimental data showing a comparison between the conventional product and the product of the present invention, and shows the rise and fall of the thermoelectromotive force of the thermocouple. 3 is a cross-sectional view of the structure of a conventional thermocouple, and FIG. 4 is an experimental data diagram comparing the lifespan of the conventional thermocouple and the thermocouple of the present invention. 1... Internal element, 2... External element, 3... Protection tube, 4... First copper wire, 5... Second
Copper wire.

Claims (1)

[Scope of Claims] 1. A fastener comprising a first copper wire connected to an inner element of a thermocouple, a second copper wire connected to an outer element of the thermocouple, and a protection tube provided between the inner element and the outer element. A quick-response thermocouple characterized in that the inner element of the thermocouple is made of a constantan material, and the outer element of the thermocouple is made of an aluminum bronze material. 2 The material composition ratio of the aluminum bronze type used for the external element is Al: 5-12%, Fe: 0.5-5%, Ni: 6.0%
(MAX), Mn: 3.5% (MAX), and Cu: the remainder.