In-furnace heat measurement element and in-furnace heat measurement method

Abstract

To measure a temperature distribution in a heating furnace.SOLUTION: An in-furnace heat amount measurement element 10 is made of quartz and has a rectangular parallelepiped shape being 4 mm wide, 3 mm long, and 2 mm high. In the vicinity of the center in a width direction and a thickness direction of the in-furnace heat amount measurement element 10, five through holes 11 to 15 having a circular cross section are formed in parallel with a side surface, a top surface and a bottom surface. A diameter D of the cross section of each of the through holes is 0.2 mm. When the in-furnace heat amount measurement element 10 is placed in a heating furnace and heated, the in-furnace heat amount measurement element 10 is softened, and the through holes are deformed by the action of surface tension, and the diameter D is reduced. An amount of deformation of the diameter D has strong correlation with a heat amount received by the in-furnace heat amount measurement element 10. Therefore, the heat amount received by the in-furnace heat amount measurement element 10 due to heating can be measured at an arbitrary place in the heating furnace by using the in-furnace heat amount measurement element 10. When a temperature profile is known, further the received heat amount can be converted to a temperature and a temperature distribution in the heating furnace can be measured.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an element and a method for measuring the amount of heat generated by heating in a heating furnace.

Background Art

[0002] In the process of forming a preform or the like using glass, resin, or the like for forming an optical fiber, heating is performed in a heating furnace. In the heating process, it is important to sequentially grasp the change in the heating temperature, but it is also very important to grasp the amount of heat received by the object to be heated throughout the heating process. Generally, since a temperature distribution occurs in the heating furnace, the amount of heat received by the object to be heated throughout the heating process also varies depending on the temperature distribution, which greatly affects the characteristics of the product. From such a perspective, for example, Patent Document 1 discloses a technique for minimizing the variation in the characteristics of a glass base material after firing by measuring the temperature distribution in a furnace and adjusting the peak temperature in the furnace when manufacturing the glass base material. Conventionally, in order to measure the temperature distribution in a heating furnace, thermocouples, infrared radiation thermometers, etc. have been used. In addition, a method has also been used in which a ceramic device called a major ring is placed in a heating furnace, and the heating temperature is calculated by measuring the diameter of the major ring after contraction due to heating.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, thermocouples and infrared radiation thermometers have a problem in that it is not easy to measure a plurality of arbitrary locations in a heating furnace in order to obtain a temperature distribution. In the case of using chlorine gas or other reactive gases during heating, the major ring had a problem that it would react with the reactive gas and temperature measurement could not be performed. In addition, the major ring had instability in that the composition ratio varied slightly for each production batch. As a result, the shrinkage rate during heating also varied, so it was necessary to correct for this.

[0005] The above-described problems were common problems not only in the case of forming a molded body such as a preform but also in various processes involving heating in a heating furnace. An object of the present invention is to solve such problems and provide a technique for relatively easily and stably measuring the amount of heat in the heating process by a heating furnace.

Means for Solving the Problems

[0006] The present invention is an in-furnace heat amount measurement element for measuring the amount of heat in a heating furnace, comprising a main body formed of a material that softens upon heating, and a hole formed in the main body, and can be configured as an in-furnace heat amount measurement element.

[0007] Since the in-furnace heat amount measurement element of the present invention softens upon heating, the shape of the hole changes. Therefore, if the correlation between the amount of heat and the change in the shape of the hole is grasped in advance by experiments or the like, the amount of heat received by the in-furnace heat amount measurement element can be measured according to the change in the shape of the hole accompanying heating in the heating furnace. In addition, since the in-furnace heat amount measurement element can be arranged at an arbitrary location in the heating furnace, there is also an advantage that the amount of heat at an arbitrary location can be easily measured. Note that the amount of heat means a value obtained by integrating the temperature over the heating time, that is, the total amount of thermal energy given to the in-furnace heat amount measurement element. The change in the shape of the hole can be measured by various parameters such as the radius of the circumscribed circle, inscribed circle, or minimum enclosing circle, or the cross-sectional area, maximum width, minimum width, etc. In the prior art, major rings shrink as a whole with the removal of moisture, binders, etc. during heating, and unfavorable reactions may occur during this process. However, in the present invention, since softening during heating is utilized, there is also an advantage that such reactions are less likely to occur.

[0008] In the present invention, the main body can take various shapes, but from the perspective of being stably placed in a heating furnace, a shape having at least a flat bottom surface is preferable. Also, from the perspective of causing uniform shape changes due to softening, it is preferable to have the same shape in the height direction, that is, a columnar shape. In particular, a rectangular parallelepiped is preferable. The holes can be formed in various modes such as vertical holes in the vertical direction and horizontal holes in the horizontal direction with the in-furnace heat measurement element placed. It may be a through hole or a non-through hole that stops in the middle of the main body. The shape can also be arbitrarily selected. Also, the cross-sectional shape of the hole may be changed along the axis of the hole, but in order to improve the measurement accuracy, it is preferable to have a uniform shape.

[0009] In the present invention, It is preferable that the hole has a circular cross-section.

[0010] The deformation in the present invention is due to the softening of the surface of the main body due to overheating and the action of surface tension. If the cross-sectional shape of the hole is circular, since the surface tension acts uniformly, the deformation occurs almost uniformly, so there is an advantage that the measurement accuracy can be improved. The hole with a circular cross-section also has an advantage that it can be formed with relatively high accuracy easily. In the case of a circular cross-section, the change in shape can be measured using the diameter or radius as a parameter.

[0011] When the hole has a circular cross-section, It is preferable that the diameter of the hole is 2 mm or less.

[0012] For example, when the periphery of the hole is shortened by a predetermined length due to heating, the larger the diameter, the smaller the change amount that appears in the diameter. That is, it becomes difficult to accurately detect the change amount. Although the diameter of the hole can be arbitrarily determined, from the viewpoint of ensuring accuracy, it is preferable to suppress the diameter of the hole to 2 mm or less.

[0013] When the hole has a circular cross-section, it is preferable that the diameter of the hole after the heating is 100 μm or more.

[0014] This is because when the diameter after heating becomes smaller, it becomes more difficult to accurately measure the diameter of the hole accordingly.

[0015] Regardless of the cross-sectional shape, in the present invention, it is preferable that the hole is a through-hole penetrating the main body.

[0016] In the case of a non-through hole, it is difficult to accurately machine the depth and shape of the hole. On the other hand, in the case of a through hole, there is an advantage that it is easy to machine accurately. Further, in the case of a through hole, since the softening of the in-furnace heat measurement element occurs over the entire hole, the influence of the surface tension mainly acts in the circumferential direction of the hole, and there is an advantage that a good correlation between the heat quantity and the deformation can be maintained.

[0017] In the present invention, a plurality of the holes may be formed.

[0018] By doing so, since the heat quantity can be measured based on the changes of the plurality of holes, the accuracy can be improved. The plurality of holes may have the same shape or different shapes. Further, through holes and non-through holes may be mixed. Further, it is preferable that the plurality of holes are arranged such that their axial directions are parallel. By doing so, there is an advantage that the holes can be easily machined.

[0019] Although the present invention is applicable to the measurement of various temperature ranges, A heat quantity measuring element in the furnace for measuring the heat quantity in the temperature range above 1300°C, The material may be quartz.

[0020] As the temperature range in which quartz softens, 1300°C or higher is the measurement target. Quartz softens in such a temperature range and its deformation occurs stably, so it is optimal as the material of the present invention.

[0021] It is preferable that the quartz has an impurity concentration of 1% by weight or less.

[0022] This is because when the impurity concentration is high, there is a risk that it will soften too much and the shape of the hole will collapse.

[0023] The present invention can also be configured as a method for measuring the heat quantity in the furnace using the above-described heat quantity measuring element in the furnace. That is, a method for measuring the heat quantity in the heating furnace, comprising: A step of preparing a heat quantity measuring element in the furnace formed of a material that softens by heating; A step of disposing the heat quantity measuring element in the heating furnace; A step of measuring a predetermined deformation amount of the heat quantity measuring element in the furnace due to overheating of the heating furnace; A step of calculating the heat quantity in the furnace based on the deformation amount.

[0024] Since the heat quantity measuring element in the furnace deforms according to the heat quantity during heating, the heat quantity in the furnace can be measured based on the deformation amount. The method of calculating the heat quantity in the furnace from the deformation amount can be a method using a calculation formula or a database preset based on the correlation between the two. Since the heat quantity in the furnace is the time integral of the temperature, when the temperature profile of heating is specified, the temperature may be obtained from the deformation amount.

[0025] In the method for measuring the heat quantity in the furnace of the present invention, The heat quantity measuring element in the furnace is, A main body formed of a material that softens upon heating, and a furnace internal heat quantity measurement element including a hole formed in the main body, wherein the amount of deformation may be an index representing the deformation of the cross section of the hole.

[0026] When using a hole, since the influence of softening appears in the form of shrinkage of the hole, the heat quantity can be measured by the deformation of the cross section. As described above, the deformation of the cross section can be measured by various parameters such as the cross-sectional area and the diameter.

[0027] In the method for measuring the heat quantity in the furnace according to the present invention, as described for the furnace internal heat quantity measurement element, the material of the furnace internal heat quantity measurement element is quartz, and it may be configured to measure the heat quantity in the temperature range of 1300 °C or higher.

[0028] Also, when using quartz, the step of preparing the furnace internal heat quantity measurement element (a) A step of preparing a slurry containing quartz powder, (b) A step of preparing a mold according to the shape of the furnace internal heat quantity measurement element, (c) A step of mixing and injecting the slurry and a curing agent into the mold, and curing the mixture to form a molded body having the shape of the furnace internal heat quantity measurement element may be provided.

[0029] This corresponds to a mode of manufacturing a furnace internal heat quantity measurement element by a method called the so-called slurry casting method. According to such a method, a fine shape can also be formed with high accuracy. In particular, when forming a hole in the furnace internal heat quantity measurement element, by installing a wire having a shape corresponding to the hole in the mold, there is an advantage that a uniform hole can be formed with high accuracy. Since the accuracy of furnace internal heat quantity measurement greatly depends on the formation accuracy of the hole, the ability to form the hole with high accuracy also greatly contributes to the improvement of the measurement accuracy.

[0030] The present invention does not necessarily have to have all the various features described above, and some of them may be omitted or combined as appropriate. Further, the present invention is not limited to the aspect as an in-furnace heat quantity measurement element or an in-furnace heat quantity measurement method, and can be configured in various aspects such as, for example, configured as a heating control method for controlling heating by reflecting the measurement result of the in-furnace heat quantity.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0032] Hereinafter, embodiments of the present invention will be described. FIG. 1 is an explanatory diagram showing the configuration of the in-furnace heat quantity measurement element. The in-furnace heat quantity measurement element is placed at an arbitrary position in the heating furnace and is deformed into holes when heated, and is used to calculate the amount of heat received by the in-furnace heat quantity measurement element based on this deformation.

[0033] The in-furnace heat quantity measurement element 10 of the embodiment is made of quartz and has a rectangular parallelepiped shape. The width W × length L × height H can be arbitrarily determined, but in this embodiment, it is about 4 mm × 3 mm × 2 mm. It is placed in the furnace in the state shown in the figure. Hereinafter, the plane of width W × length L is referred to as the upper surface and the bottom surface, respectively, the plane of width W × height H is referred to as the front surface and the back surface, and the surface of length L × height H is referred to as the side surface. Near the center in the width direction and the thickness direction, five through holes 11 to 15 having a circular cross section are formed parallel to the side surface, the upper surface, and the bottom surface. In this embodiment, the diameter D of the cross-section of the through-hole was set to 0.2 mm. The diameter D can be arbitrarily determined, but it is preferably in a range smaller than 2 mm. As will be described later, the in-furnace heat measurement element softens upon heating, and the through-hole deforms due to the action of surface tension, causing the diameter D to decrease. Surface tension is basically a force that attempts to reduce the surface area. In the case of a hole, it is inversely proportional to the radius. That is, the smaller the hole diameter, the stronger the surface tension acts, and changes can be observed even at a low temperature with high viscosity. Conversely, at a high temperature, it is necessary to increase the hole diameter so that the hole diameter does not change too much. Thus, it is preferable to determine the diameter D according to the temperature to be measured, and from the viewpoint of ensuring measurement accuracy, the diameter D is preferably 2 mm or less.

[0034] In this embodiment, five through-holes 11 to 15 are formed. By doing so, the measurement accuracy can be improved by analyzing based on the average and variation of the changes in the diameters D of the five through-holes. The number of through-holes may be less than five or more than five. Also, in this embodiment, the five through-holes 11 to 15 have the same diameter D, but they may be different. Furthermore, shapes other than circular may be mixed.

[0035] FIG. 2 is an explanatory diagram showing the internal structure of the in-furnace heat measurement element. On the left side, a side cross-sectional view including the through-hole 12 is shown, and on the right side, a front view of the through-hole 12 is shown. As shown on the left side, in the in-furnace heat measurement element 10, before heating, the through-hole 12 is linearly formed in the main body like the boundary line h. The hole diameter is D. When the in-furnace heat measurement element 10 is heated, due to the action of surface tension accompanying softening, the through-hole 12 contracts and becomes the hole diameter D1 as shown on the right side. At this time, inside the main body, the through-hole 12 contracts while maintaining a cylindrical shape in the region c near the center like the boundary line h1, and deforms into a slightly bent shape in the regions a and b near the entrance. In this embodiment, in order to measure the amount of heat received by the in-furnace heat measurement element 10, the hole diameter D1 after heating is measured in the region c near the center where the cylindrical shape is maintained.

[0036] Figure 3 is a process diagram showing the manufacturing process of the in-furnace heat quantity measurement element. The process of manufacturing the in-furnace heat quantity measurement element by the slurry casting method is shown. In the slurry casting method, first, the slurry is prepared (step S1). In this step, a glass raw material solution containing quartz powder, a solvent, a dispersant, and a curable resin is mixed in a ball mill for a predetermined time. As the solvent, distilled water or the like can be used. This glass raw material solution may contain various additives and impurities.

[0037] Next, a curing agent is added to the prepared slurry, poured into a mold, and cured (step S2). After setting a wire or the like for forming the through holes 11 to 15 of the in-furnace heat quantity measurement element 10 in the mold, the slurry may be poured and cured. For curing, it may be left at room temperature, but heating is also acceptable.

[0038] When the formed body is cured, it is detached from the mold (step S3), and the solvent in the formed body is removed by drying (step S4). Further, thereafter, the curable resin in the formed body is removed by degreasing. The degreasing can be performed under various conditions. For example, it may be performed under a temperature condition of about 850°C.

[0039] The formed body that has been completed up to degreasing is subjected to a densification treatment (step S6). The densification treatment is a heat treatment at 1000°C or higher to eliminate the fine gaps generated inside the formed body by degreasing. By this treatment, a part of the formed body may be vitrified. Note that the densification treatment may be omitted if not necessary. By the above steps, the in-furnace heat quantity measurement element 10 can be manufactured. By using the slurry casting method, there is an advantage that even a fine in-furnace heat quantity measurement element 10 can be accurately formed.

[0040] In this example, the above manufacturing was performed under the condition that the impurity concentration of the in-furnace heat quantity measurement element 10 is 1 wt% or less.

[0041] Figure 4 is a graph showing the change in sintering temperature and pore diameter. The in-furnace heat quantity measurement element 10 was placed in the heating furnace and heated according to a predetermined temperature profile, and then the pore diameters D1 of the through holes 11 to 15 were measured. In the temperature profile of the example, after heating, it was heated at 1550 °C for 30 minutes and then cooled at a constant rate. In this experiment, the temperature at the position where the in-furnace heat quantity measurement element 10 was placed in the heating furnace was measured with a thermocouple. The sintering temperature on the horizontal axis of Figure 4 is the measurement result by the thermocouple. As shown in the figure, a strong negative correlation is confirmed between the sintering temperature and the pore diameter D1. If a mathematical formula approximating this measurement result is obtained, hereafter, by measuring the pore diameter after heating, it will be possible to convert it into the sintering temperature. The in-furnace heat quantity measurement element 10 of the example measures the heat quantity received by heating, but when the temperature profile is known and constant, it is also possible to measure the temperature.

[0042] Figure 5 is an explanatory diagram showing the measurement results of the temperature distribution in the furnace by the in-furnace heat quantity measurement element. Figure 5(a) is a plan view of the furnace, showing the arrangement of the in-furnace heat quantity measurement element 10. As shown in the figure, five points, namely the position P1 at the deepest part of the furnace, the position P2 approximately in the center left in the front-rear direction, the position P3 in the center, the position P4 on the right side, and the position P5 near the furnace door, were measured. Figure 5(b) shows the pore diameter D1 of the in-furnace heat quantity measurement element 10 after heating at the above-mentioned five points. Each measured value represents the average value of a plurality of through holes. A plurality of stages are provided in the furnace, and the pore diameter DM1 represents the result of the upper stage, and the pore diameter DM2 represents the result of the lower stage. Figure 5(c) is the result of converting the result shown in Figure 5(b) into temperature based on the correlation obtained in Figure 4. The temperature T1 represents the result of the upper stage, and the temperature T2 represents the result of the lower stage. According to this result, it can be confirmed that the positions near the center in the left-right direction in the furnace (P1, P3, P5) have a temperature distribution where the temperature is relatively lower than that of the left and right positions (P2, P4). Since the heating furnace of the example is equipped with heaters on the left and right, this is considered to be a natural result. It was also confirmed that the temperature T1 above the furnace is relatively lower than the temperature T2 below. It is considered that the arrangement of the heater and the convection in the furnace have an impact. Thus, by using the in-furnace heat quantity measurement element 10 of this embodiment, the temperature distribution in the heating furnace can be measured relatively easily and accurately.

[0043] As described above, the embodiments of the present invention have been explained. By using this embodiment, there is an advantage that the temperature distribution in the heating furnace can be measured accurately and simply. The present invention does not necessarily have to include all of the above-described features, and a part of them may be omitted or combined as appropriate. Further, the present invention is not limited to the above embodiments, and various modifications can be configured.

Industrial Applicability

[0044] The present invention relates to an element and a method for measuring the heat quantity generated by heating in a heating furnace.

Explanation of Signs

[0045] 10 In-furnace heat quantity measurement element 11, 12, 13, 14, 15 Through holes

Claims

1. A furnace internal heat quantity measurement element for measuring the heat quantity in a heating furnace, comprising a main body formed of a single material that softens upon heating, and a hole formed in the main body for measuring the heat quantity by deformation of a cross-section accompanying heating.

2. The furnace internal heat quantity measurement element according to claim 1, wherein the hole has a circular cross-section.

3. The furnace internal heat quantity measurement element according to claim 2, wherein the diameter of the hole is 2 mm or less.

4. The furnace internal heat quantity measurement element according to claim 2, wherein the diameter of the hole after heating is 100 μm or more.

5. The furnace internal heat quantity measurement element according to claim 1, wherein the hole is a through-hole penetrating the main body.

6. The furnace internal heat quantity measurement element according to claim 1, wherein a plurality of the holes are formed.

7. A furnace internal heat quantity measurement element for measuring the heat quantity in a temperature range of 1300°C or higher, wherein the material is quartz, as claimed in claim 1.

8. The furnace internal heat quantity measurement element according to claim 7, wherein the quartz has an impurity concentration of 1 wt% or less.

9. A furnace internal heat quantity measurement method for measuring the heat quantity in a heating furnace, comprising the steps of preparing a furnace internal heat quantity measurement element formed of a material that softens upon heating, disposing the furnace internal heat quantity measurement element in the heating furnace, measuring a predetermined deformation amount of the furnace internal heat quantity measurement element due to heating of the heating furnace, and calculating the furnace internal heat quantity based on the deformation amount, wherein the furnace internal heat quantity measurement element comprises a main body formed of a material that softens upon heating, It is an in-furnace heat quantity measurement element including a hole formed in the main body. The deformation amount is an in-furnace heat quantity measurement method that is an index representing the deformation of the cross-section of the hole.

10. The in-furnace heat quantity measurement method according to Claim 9, The material of the in-furnace heat quantity measurement element is quartz, An in-furnace heat quantity measurement method for measuring the heat quantity in a temperature range of 1300 °C or higher.

11. The in-furnace heat quantity measurement method according to Claim 10, The step of preparing the in-furnace heat quantity measurement element is (a) A step of preparing a slurry containing quartz powder, (b) A step of preparing a mold according to the shape of the in-furnace heat quantity measurement element, (c) An in-furnace heat quantity measurement method comprising a step of mixing and injecting the slurry and a curing agent into the mold, and curing the mixture to form a molded body having the shape of the in-furnace heat quantity measurement element.

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