Method for monitoring electric heating element

Abstract

Provided is a method for monitoring an electric heating element whereby it is possible to prevent erroneous determination of the occurrence of a spark at a stage at which an applied current value is increased after the start of the flow of electric current to the electric heating element.　The present invention is a method for monitoring an electric heating element comprising: a current value increase step in which the flow of electric current to an electric heating element used in a heating furnace is started and the current value is increased to a predetermined current value; and a spark occurrence determination step in which it is determined whether a spark has occurred on the basis of an abnormal change in electrical information in the electric heating element in the current value increase step, wherein in the current value increase step, a detection disabled time Tn during which abnormal change in the electrical information in the electric heating element is not detected is set for a predetermined time after the start of the flow of electric current to the electric heating element.

Description

Method for monitoring electric heating elements

[0001] The present invention relates to a method for monitoring an electrically heated element used, for example, in the manufacture of glass fibers.

[0002] For example, when supplying molten glass to bushings for forming glass fibers or molded bodies for forming plate glass, it is necessary to keep the molten glass flowing inside the feeder warm and prevent excessive temperature drops. As a method for this, a method has been proposed in which an electric heating element is installed in the internal space of the feeder and the molten glass is heated by that heat (see, for example, Document 1).

[0003] Electric heating elements may generate sparks when energized due to an abnormal increase in resistance. Sparks can damage the heating element itself and surrounding components, potentially disrupting subsequent operations. Therefore, it is desirable to detect sparks in an electric heating element and cut off the power supply to it.

[0004] International Publication No. 2014 / 185132

[0005] One method for determining spark occurrence is to continuously monitor the resistance value of an electrical heating element and determine that a spark has occurred if it falls outside the normal range. However, even if no spark occurs, the resistance value may fluctuate and fall outside the normal range due to factors such as unstable output control of the equipment, resulting in a false determination.

[0006] When an electric heating element is energized, the applied current is gradually increased, and once it reaches a predetermined operating current value, it is usually kept constant at that value. While sparks are relatively unlikely to occur when the current value is maintained at the operating current value, the above-mentioned misjudgment is particularly likely to occur when the applied current value is increased after the electric heating element is energized.

[0007] In view of the above circumstances, the present invention aims to provide a method for monitoring an electric heating element that can prevent false detection of spark generation during the stage when the applied current value is increased after the start of energizing the electric heating element.

[0008] [1] The present invention provides a method for monitoring an electric heating element, comprising: a current value increase step of starting to energize an electric heating element used in a heating furnace and increasing the current value to a predetermined current value; and a spark occurrence determination step of determining whether or not a spark occurs based on an abnormal change in electrical information in the electric heating element during the current value increase step, wherein in the current value increase step, a detection invalidation period is set during which no abnormal change in electrical information in the electric heating element is detected for a predetermined time after the start of energizing the electric heating element.

[0009] Spark generation is accompanied by abnormal changes in electrical information, such as an abnormal increase in the resistance value of an electrical heating element. By detecting such abnormal changes in electrical information, it is possible to determine that a spark has occurred in the electrical heating element. However, in the initial stages of the process in which the current value of the electrical heating element increases, the output control of the equipment tends to be unstable, making it easy for false detections of abnormal changes in electrical information to occur. Therefore, by setting a detection invalidation period during which abnormal changes in electrical information of the electrical heating element are not detected for a predetermined time after the start of energization of the electrical heating element, the above-mentioned false detections can be prevented. This improves the accuracy of determining spark generation in an electrical heating element.

[0010] [2] In the method for monitoring an electric heating element of the present invention, the resistance value can be used as the electrical information, for example, in the above [1].

[0011] [3] The method for monitoring an electric heating element of the present invention preferably further comprises, in [1] or [2] above, a power supply deactivation step of stopping the supply of power to the electric heating element after determining in the spark generation determination step that a spark has occurred in the electric heating element. In this way, if the electric heating element or surrounding components are damaged in connection with the spark generation of the electric heating element, it is possible to prevent further disruption to operations.

[0012] [4] In the method for monitoring an electric heating element of the present invention, it is preferable to keep the current value increase gradient constant in the current value increase step in any of the above steps [1] to [3]. This makes it less likely for false detection of abnormal resistance value changes to occur after the detection invalidation time has elapsed.

[0013] [5] In the method for monitoring the electric heating element, it is preferable that the current value rise gradient is 250 A / min or less as described in [4] above. By making the current value rise gradient relatively small in this way, even if a spark occurs during the current value rise process, the current value at that time can be kept relatively small, and damage to the electric heating element and surrounding components can be suppressed as much as possible.

[0014] [6] The method for monitoring an electric heating element according to the present invention is preferable in any of the above [1] to [5] when the heating furnace is a heating furnace for manufacturing glass.

[0015] [7] The method for monitoring an electric heating element according to the present invention is preferable in the case described in [6] above when the heating furnace is a feeder through which molten glass flows.

[0016] [8] The present invention provides a method for manufacturing glass fibers, comprising the steps of: heating and melting raw materials in a melting furnace to obtain molten glass; flowing the molten glass through a feeder equipped with an electric heating element; and forming the molten glass into fibers using a bushing attached to the feeder, characterized in that the method for monitoring the electric heating element described in [7] above is performed when energizing the electric heating element.

[0017] According to the method for monitoring an electric heating element of the present invention, it is possible to prevent misjudgment of spark generation during the stage when the applied current value is increased after the start of energizing the electric heating element.

[0018] This is a longitudinal cross-sectional view showing a schematic of a glass fiber manufacturing apparatus. This is a cross-sectional view taken along line II-II in Figure 1. This is a flowchart illustrating the method for monitoring an electric heating element according to the present invention. This is a schematic graph illustrating an embodiment of the method for monitoring an electric heating element according to the present invention.

[0019] The following describes an embodiment of the method for monitoring an electrically heated element of the present invention applied to a glass fiber manufacturing apparatus, particularly a feeder serving as a heating furnace, with reference to the drawings. Note that, for the sake of clarity, some parts of the structure may be exaggerated or simplified in the drawings. Furthermore, the dimensional ratios of each part may differ from those of the actual apparatus.

[0020] Figure 1 is a longitudinal cross-sectional view showing a schematic of a glass fiber manufacturing apparatus.

[0021] The manufacturing apparatus 1 comprises a melting furnace 2 that melts glass raw material Gr to form molten glass Gm, and a feeder 3 connected downstream of the melting furnace 2 and circulating the molten glass Gm inside. The walls that partition the melting space of the melting furnace 2 and the circulation space of the feeder 3 are made of refractory material such as brick.

[0022] An inlet 2a is provided at the upstream end of the melting furnace 2 for introducing glass raw materials Gr, which are a mixture of silica sand, limestone, soda ash, cullet, etc., into the furnace. A raw material supply means (not shown) such as a screw feeder is arranged at the inlet 2a.

[0023] The melting furnace 2 is further equipped with a heating device (not shown). Examples of heating devices include a gas burner positioned above the molten glass Gm, an electric heater, or an electric heating device such as an electrode immersed in the molten glass Gm.

[0024] The glass raw material Gr introduced from the input port 2a is melted by heating with a heating device, thereby continuously forming molten glass Gm. The molten glass Gm flows into the feeder 3 from the downstream end of the melting furnace 2. The melting furnace 2 may melt the glass raw material Gr by gas combustion alone, by electric heating alone, or by a combination of gas combustion and electric heating.

[0025] At the bottom of the feeder 3, a plurality of bushings 4 made of platinum or a platinum alloy are provided at intervals in the longitudinal direction X of the feeder 3, i.e., in the flow direction of the molten glass Gm. Each bushing 4 is provided with a plurality of bushing nozzles (not shown). The molten glass Gm flowing down from each nozzle is stretched downward and formed into glass fibers Gf (glass filaments) of a predetermined diameter. After a sizing agent is applied, multiple glass fibers Gf are bundled together to form a glass strand.

[0026] Figure 2 is a cross-sectional view taken along line II-II in Figure 1. The feeder 3 is enclosed by a bottom wall 5, side walls 6a and 6b, and a ceiling 10, and is configured so that molten glass Gm flows on the bottom wall 5. Electric heating elements 11a and 11b are installed above the liquid surface of the molten glass Gm. The electric heating elements 11a and 11b have a U-shape and are fixed by inserting the terminals at both ends into the ceiling 10. As shown in Figure 1, the electric heating elements 11a, 11a... are installed so as to be aligned in the X direction of the feeder 3. Although not shown in Figure 1, electric heating elements 11b, 11b... are also installed in parallel with the electric heating elements 11a, 11a... so as to be aligned in the X direction of the feeder 3.

[0027] The electric heating elements 11a and 11b are electrically connected to the power supply 12. The power supply 12 may be an AC power supply or a DC power supply. In Figure 2, the two electric heating elements 11a and 11b are connected in series, but the figure is not limited to this, and multiple electric heating elements 11a, 11a... and electric heating elements 11b, 11b... arranged in the X direction in Figure 1 may be connected in series. Alternatively, each of the electric heating elements 11a and 11b may be connected to a separate power supply.

[0028] A state monitoring control unit 21 is connected to the electric heating element 11a. The state monitoring control unit 21 includes a potential difference acquisition unit 22, a resistance value calculation unit 23, an abnormality detection unit 24, and a spark generation determination unit 25. The state monitoring control unit 21 can be configured with a processor, memory, software, image display device, etc., which are not shown in the figures.

[0029] The potential difference acquisition unit 22 can measure the potential difference applied to the electric heating element 11a. Using the potential difference acquired from the potential difference acquisition unit 22 and the current value applied to the power supply 12, the resistance value calculation unit 23 can calculate the resistance value applied to the electric heating element 11a. In the present embodiment, the resistance value applied to the electric heating element 11a is used as electrical information. Note that the potential difference acquired from the potential difference acquisition unit 22 may be used as electrical information.

[0030] The resistance value calculation unit 23 constantly monitors the resistance value obtained by the resistance value calculation unit 23. When an abnormal change in the resistance value is detected, the spark generation determination unit 25 determines whether a spark has occurred. The abnormal change in the resistance value in the electric heating element 11a refers to, for example, comparing the measured resistance value with the average value of the resistance values in the immediately preceding predetermined time (for example, several seconds), and the difference between these exceeding a predetermined threshold value. When a spark occurs in the electric heating element 11a, the resistance value rapidly increases, so the above abnormal change in the resistance value becomes an index for determining spark generation.

[0031] FIG. 3 is a flowchart showing a method for monitoring an electric heating element of the present invention. FIG. 4 is a schematic graph for explaining an embodiment of the method for monitoring an electric heating element of the present invention, showing the first and second embodiments with different rising gradients of the current value. Hereinafter, these embodiments will be described in detail based on FIGS. 3 and 4.

[0032] First, the first embodiment will be described. As shown in FIGS. 3 and 4, the application of current to the electric heating element 11a is started (step S1), and the current value is increased until a predetermined operating current value is reached. After reaching the operating current value, the current value is held constant to heat the molten glass. In the present embodiment, at time t ,

[0033] and time t ２ an "abnormal change in resistance value" occurs in the electric heating element 11a.

[0033] In the current value increase process, the potential difference of the electric heating element 11a is constantly acquired by the potential difference acquisition unit 22 (step S2), and the resistance value calculation unit 23 calculates the resistance value based on the potential difference and the current value acquired from the power supply 12 (step S3). Here, the resistance value calculation unit 23 also calculates the average value R of the resistance values at a predetermined time immediately before the measurement. ａｖ is also calculated simultaneously. The abnormality detection unit 24 compares the measured resistance value with R ａｖ (step S4). If the resistance value is greater than R ａｖ (abnormal change in resistance value), the process proceeds to step S5. If the resistance value is less than or equal to R ａｖ , the process returns to step S2.

[0034] In this embodiment, a detection invalid time T ｎ is set during which no abnormal change in the resistance value of the electric heating element 11a is detected after the energization of the electric heating element 11a is started. Therefore, the spark generation determination unit 25 compares the time t from the start of the current value increase with the detection invalid time T ｎ (step S5). For example, when the measurement time t is t １ , since it is within the range of the detection invalid time T ｎ , even if an abnormal change in the resistance value occurs, no detection is performed and the process returns to step S2. On the other hand, the abnormal change in the resistance value that occurs when the measurement time t is t ２ is after the elapse of the detection invalid time T ｎ , so detection is performed and it is determined as spark generation (step S6). In the initial stage of the current value increase process of the electric heating element 11a, the output control of the device tends to be unstable, the resistance value is likely to change, and false detection is likely to occur. Therefore, as described above, by setting a detection invalid time T ｎ during which no abnormal change in the resistance value of the electric heating element 11a is detected after the energization of the electric heating element 11a is started, the above-mentioned false detection can be prevented. Thereby, the determination accuracy of spark generation of the electric heating element 11a can be improved.

[0035] The detection invalid time T ｎThis can be set appropriately according to the operating current value and the current rise gradient, for example, 10 to 300 seconds, and especially 15 to 100 seconds. The time from when the current rise starts until it reaches the operating current value is called the current rise time T. ０ In that case, T ｎ / T ０ This can be 0.05 to 0.5, and especially 0.1 to 0.3.

[0036] After determining that a spark has occurred based on an abnormal change in resistance, it is preferable to stop the power supply to the electric heating element 11a (step S7). This prevents damage to the electric heating element 11a itself or surrounding components that may occur as a result of the spark occurring in the electric heating element 11a, which could disrupt subsequent operations. In this case, by switching the circuit supplying power to the electric heating element 11a to a bypass circuit (not shown), it is possible to stop the power supply to the electric heating element 11a while maintaining the power supply to the electric heating element 11b.

[0037] Furthermore, if the current rise gradient is not constant during the current rise process, the change in resistance may become large even if no spark occurs, potentially leading to a false detection of an abnormal change in resistance. Therefore, it is preferable to keep the current rise gradient constant. In this way, the detection invalid time T is reduced. ｎ After this period, misjudgments of spark generation based on abnormal changes in resistance become less likely.

[0038] The above describes an example of spark generation determination for the electric heating element 11a, but as shown in Figure 2, the electric heating element 11b is also connected to the potential difference acquisition unit, and the presence or absence of spark generation based on abnormal changes in resistance can be determined in the same way.

[0039] The second embodiment differs from the first embodiment in that the current value rise gradient is smaller, and is otherwise the same as the first embodiment. In the second embodiment as well, there is a detection invalid time T during which an abnormal change in the resistance value of the electric heating element 11a is not detected for a predetermined time after energizing the electric heating element 11a. ｎ This is set. Therefore, the detection invalidation time T ｎ Time t within the range １Abnormal changes in resistance values ​​that occur are not detected, and the detection invalid period T ｎ Time t after the elapsed time ２ Any abnormal changes in resistance values ​​that occur are detected and determined to be spark generation. This improves the accuracy of determining spark generation in the electric heating element 11a.

[0040] In the first embodiment, since the current value rise gradient is relatively large, the detection invalid time T ｎ When a spark occurs after a certain period of time (for example, time t) ２ ) The current value tends to increase, and as a result, there is a risk that the damage to the electric heating element 11a and surrounding components when a spark occurs will be greater. On the other hand, in the second embodiment, the current value rise gradient is relatively small, so the detection invalid time T ｎ When a spark occurs after a certain period of time (for example, time t) ２ The current value in this case can be kept relatively small. As a result, damage to the electric heating element 11a and surrounding components when sparks occur can be suppressed as much as possible. From the viewpoint of suppressing damage to the electric heating element 11a and surrounding components when sparks occur as much as possible, it is preferable that the current value rise gradient is small, specifically 250 A / min or less, 200 A / min or less, 150 A / min or less, and especially 100 A / min or less. However, if the current value rise gradient is too small, it will take a long time to reach the operating current value and productivity will decrease, so it is preferable that it is 10 A / min or more, 30 A / min or more, and especially 50 A / min or more.

[0041] 3 Feeder 11a, 11b Electric heating element

Claims

1. A method for monitoring an electric heating element, comprising: a current value increase step of starting to energize an electric heating element used in a heating furnace and increasing the current value to a predetermined current value; and a spark occurrence determination step of determining whether or not a spark occurs based on an abnormal change in the electrical information of the electric heating element during the current value increase step, wherein in the current value increase step, a detection invalidation period is set during which no abnormal change in the electrical information of the electric heating element is detected for a predetermined time after the start of energizing the electric heating element.

2. The method for monitoring an electric heating element according to claim 1, wherein the electrical information is a resistance value.

3. The method for monitoring an electric heating element according to claim 1, further comprising a power supply deactivation step of stopping the supply of power to the electric heating element after determining in the spark generation determination step that a spark has occurred in the electric heating element.

4. The method for monitoring an electric heating element according to claim 1, wherein the current value increase gradient is kept constant during the current value increase step.

5. The method for monitoring an electric heating element according to claim 4, wherein the current value rise gradient is 250 A / min or less.

6. The method for monitoring an electric heating element according to any one of claims 1 to 5, wherein the heating furnace is a heating furnace for manufacturing glass.

7. The method for monitoring an electric heating element according to claim 6, wherein the heating furnace is a feeder through which molten glass flows.

8. A method for manufacturing glass fibers, comprising the steps of: heating and melting raw materials in a melting furnace to obtain molten glass; flowing the molten glass through a feeder equipped with an electric heating element; and forming the molten glass into fibers using a bushing attached to the feeder, wherein the method for monitoring the electric heating element described in claim 7 is performed when energizing the electric heating element.

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