How to determine the timing of burnout

Abstract

This invention provides a method for determining the timing of burnout, which can accurately determine when burnout should occur. [Solution] A method for determining the timing of burnout in a vacuum carburizing furnace, comprising: temporarily changing the pressure inside the vacuum carburizing furnace with an object of a first weight placed inside, setting a peak time difference reference range for the first weight based on the time difference between the timing when the measured pressure of a first pressure gauge reaches its peak and the timing when the measured pressure of a second pressure gauge reaches its peak; obtaining the peak time difference, which is the time difference between the timing when the measured pressure of a first pressure gauge reaches its peak and the timing when the measured pressure of a second pressure gauge reaches its peak when the pressure inside the vacuum carburizing furnace is temporarily changed while the workpiece is being carburized in the vacuum carburizing furnace; and determining the timing of burnout based on the peak time difference reference range for the first weight and the peak time difference.

Description

Technical Field

[0005] , ,

[0001] The present disclosure relates to a method for determining the burnout execution timing.

Background Art

[0002] In a vacuum carburizing furnace, burnout for burning and removing soot adhering to the furnace interior is known. Patent Document 1 discloses a technique for monitoring the temperature, pressure, and exhaust gas components inside the furnace during burnout and determining the end timing of burnout.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] During the execution of burnout, the vacuum carburizing furnace cannot be used, so burnout is required to be carried out with the minimum necessary. For this reason, it is necessary to accurately determine the timing for carrying out burnout. The present disclosure solves such problems and provides a method for determining the burnout execution timing that can accurately determine the burnout execution timing.

Means for Solving the Problems

[0005] This disclosure relates to a method for determining the timing of burnout in a vacuum carburizing furnace, comprising: a step of arranging a first pressure gauge and a second pressure gauge in different locations within the vacuum carburizing furnace; a first weight reference range setting step of temporarily changing the pressure inside the vacuum carburizing furnace with an object having a predetermined first weight placed inside the vacuum carburizing furnace, and setting a first weight peak time difference reference range based on the peak time difference between the timing when the measured pressure of the first pressure gauge reaches its peak and the timing when the measured pressure of the second pressure gauge reaches its peak when the pressure is temporarily changed; a peak time difference acquisition step of acquiring the peak time difference between the timing when the measured pressure of the first pressure gauge reaches its peak and the timing when the measured pressure of the second pressure gauge reaches its peak when the pressure inside the vacuum carburizing furnace is carburizing a workpiece; and a determination step of determining the timing of burnout based on the first weight peak time difference reference range set in the first weight reference range setting step and the peak time difference acquired in the peak time difference acquisition step. This configuration allows for highly accurate determination of the timing of burnout.

[0006] The determination step includes a second weight reference range setting step in which an object of a predetermined second weight, whose weight is different from the first weight, is placed in the vacuum carburizing furnace, the pressure inside the vacuum carburizing furnace is temporarily changed, and a peak time difference reference range for the second weight is set based on the time difference between the timing when the measured pressure of the first pressure gauge reaches its peak and the timing when the measured pressure of the second pressure gauge reaches its peak when the pressure is temporarily changed; and a workpiece reference range setting step in which a peak time difference reference range for the workpiece is set based on the weight of the workpiece to be carburized in the vacuum carburizing furnace, the peak time difference reference range for the first weight set in the first weight reference range setting step, and the peak time difference reference range for the second weight set in the second weight reference range setting step, wherein the determination step determines the timing for burnout based on the peak time difference reference range for the workpiece set in the workpiece reference range setting step and the peak time difference acquired in the peak time difference acquisition step. With this configuration, the timing for burnout can be determined with high accuracy. [Effects of the Invention]

[0007] This disclosure provides a method for determining the timing of burnout, which allows for highly accurate determination of the timing of burnout. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing the vacuum carburizing apparatus of Embodiment 1. [Figure 2] This flowchart shows an example of a burnout timing determination process. [Figure 3] This figure shows an example of a peak time difference reference range. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to Figures 1 to 3. Figure 1 is a schematic diagram showing a vacuum carburizing apparatus of Embodiment 1. Figure 2 is a flowchart showing an example of the burnout timing determination process. Figure 3 is a diagram showing an example of the peak time difference reference range.

[0010] Embodiment 1 Referring to Figure 1, the configuration of the vacuum carburizing apparatus 10 for implementing the burnout timing determination method according to this disclosure will be described. The vacuum carburizing apparatus 10 comprises a vacuum carburizing furnace 11, a vacuum pump 12, a first pressure gauge 20, a second pressure gauge 30, and a control device 50.

[0011] The vacuum carburizing furnace 11 supplies carburizing gas under reduced pressure and heating conditions to perform carburizing treatment on workpieces. Workpieces subjected to carburizing treatment include, for example, automobile parts and machine parts made of steel. The vacuum carburizing furnace 11 is equipped with heaters 11a to heat the inside of the vacuum carburizing furnace 11. Multiple heaters 11a are arranged on the upper and lower surfaces of the vacuum carburizing furnace 11. The vacuum carburizing furnace 11 is also equipped with a gas inlet (not shown) for introducing combustion gas such as air when burnout is performed.

[0012] The vacuum pump 12 is connected to the vacuum carburizing furnace 11 via the exhaust port 12a. The vacuum pump 12 sucks gas from inside the vacuum carburizing furnace 11 and discharges it to the outside, thereby reducing the pressure inside the vacuum carburizing furnace 11 to below atmospheric pressure.

[0013] The vacuum carburizing apparatus 10 has a first pressure gauge 20 and a second pressure gauge 30 located in different positions. The first pressure gauge 20 is located inside the vacuum carburizing furnace 11. The second pressure gauge 30 is located at the exhaust port 12a. The first pressure gauge 20 and the second pressure gauge 30 measure the pressure inside the vacuum carburizing furnace 11. The first pressure gauge 20 and the second pressure gauge 30 output the measured pressure to the control device 50. The first pressure gauge 20 and the second pressure gauge 30 can be located in any position as long as they can measure the pressure inside the vacuum carburizing furnace 11.

[0014] The control device 50 includes a memory 51 and a CPU 52. The memory 51 stores a program for executing operations such as the carburizing treatment of the workpiece and the determination process of the burnout execution timing described later. The CPU 52 executes the program stored in the memory 51 to control the operations of the heater 11a, the vacuum pump 12, and the like.

[0015] As a procedure for performing the carburizing treatment in the vacuum carburizing device 10, first, a workpiece is placed in the vacuum carburizing furnace 11, and the vacuum pump 12 is operated to heat with the heater 11a while reducing the pressure inside the vacuum carburizing furnace 11. When the workpiece reaches a predetermined processing temperature (for example, 950 degrees Celsius), carburizing gas is supplied into the vacuum carburizing furnace 11. The carburizing gas is a hydrocarbon gas, for example, acetylene gas. The hydrocarbon gas decomposes under reduced pressure and high temperature to generate carbon. The generated carbon diffuses from the surface of the workpiece into the interior, and the carburizing treatment of the workpiece is performed.

[0016] A part of the carbon generated from the carburizing gas adheres to the inside of the vacuum carburizing furnace 11 as soot. If soot adheres to the inside of the vacuum carburizing furnace 11, there is a risk of causing troubles in the vacuum carburizing furnace 11 and poor quality of the products subjected to the carburizing treatment. Therefore, when soot adheres to the inside of the vacuum carburizing furnace 11, burnout is performed by introducing air into the vacuum carburizing furnace 11 to burn and remove the soot.

[0017] Subsequently, a method for determining the burnout execution timing will be described. FIG. 2 is a flowchart showing an example of the burnout execution timing determination process executed by the control device 50.

[0018] In step S1, the inside of the vacuum carburizing furnace 11 is made empty. Specifically, only the tray on which the workpiece is placed during the carburizing treatment is placed inside the vacuum carburizing furnace 11.

[0019] In step S2, the vacuum pump 12 is operated to set an arbitrary pressure inside the vacuum carburizing furnace 11.

[0020] In step S3, the pressure inside the vacuum carburizing furnace 11 is temporarily changed. The temporary change in pressure is carried out, for example, by preparing a pressure chamber in a pressure state higher than the pressure inside the vacuum carburizing furnace 11 and connecting the vacuum carburizing furnace 11 and the pressure chamber. The location of the vacuum carburizing furnace 11 communicating with the pressure chamber may be anywhere, such as near the heater 11a. The temporary change in pressure may be implemented by any method. The time for temporarily changing the pressure is, for example, 1 sec. The magnitude of the pressure to be temporarily changed is set to the amount of pressure change during the pressure change caused by the discharge due to the soot adhering inside the vacuum carburizing furnace 11. That is, in step S3, the phenomenon that occurs when soot adheres inside the vacuum carburizing furnace 11 is simulated and reproduced. Note that since the amount of pressure change due to the discharge by the soot is not constant but has a range, the magnitude of the pressure to be temporarily changed is set from within the range of the possible amount of pressure change caused by the discharge by the soot.

[0021] In step S4, the pressure measured by the first pressure gauge 20 before temporarily changing the pressure in step S3 is acquired. Hereinafter, the pressure measured by the first pressure gauge 20 before temporarily changing the pressure is defined as the reference pressure. That is, in step S4, the reference pressure is acquired.

[0022] In step S5, when the pressure is temporarily changed in step S3, a peak time difference, which is the time difference between the timing when the measured pressure of the first pressure gauge 20 reaches a peak and the timing when the measured pressure of the second pressure gauge 30 reaches a peak, is acquired. Through the processes of step S4 and step S5, data representing the relationship between the reference pressure and the peak time difference in the state where the inside of the vacuum carburizing furnace 11 is empty is obtained.

[0023] In step S6, while repeatedly changing the reference pressure and the magnitude of the pressure to be temporarily changed each time, the processes from step S2 to step S5 are repeatedly performed a plurality of times to acquire a plurality of data representing the relationship between the reference pressure and the peak time difference. Specifically, similar to the process in step S2, the vacuum pump 12 is activated to change the pressure inside the vacuum carburizing furnace 11. Then, similar to the process in step S3, the pressure inside the vacuum carburizing furnace 11 is temporarily changed. The magnitude of the temporarily changed pressure is different from the magnitude of the pressure that was temporarily changed in step S3. Then, similar to the process in step S4, a reference pressure is obtained, and further, similar to the process in step S5, the peak time difference is obtained. Then, the process from step S2 to step S5 is repeated multiple times, while changing the reference pressure and the magnitude of the temporarily changed pressure each time. In this way, multiple data points representing the relationship between the reference pressure and the peak time difference are obtained when the vacuum carburizing furnace 11 is empty.

[0024] In step S7, a regression line G0 is created that represents the relationship between the reference pressure and the peak time difference when the vacuum carburizing furnace 11 is empty, based on multiple data representing the relationship between the reference pressure and the peak time difference obtained in the processes from steps S4 to S6. Specifically, multiple data points representing the relationship between reference pressure and peak time difference obtained in steps S4 to S6 are plotted (not shown) on a two-dimensional coordinate system with reference pressure on the horizontal axis and peak time difference on the vertical axis, as shown in Figure 3. Then, regression analysis using the least squares method is performed to find the straight line that minimizes the squared error. This obtained straight line is the regression line G0. The regression line G0 slopes upward. When the reference pressure is low, the propagation speed of pressure changes within the vacuum carburizing furnace 11 is faster compared to when the reference pressure is high, resulting in a shorter peak time difference.

[0025] In step S8, the reference range R0 of the peak time difference is set when the vacuum carburizing furnace 11 is empty. Specifically, the regression line G01 obtained by shifting the regression line G0 obtained in step S7 upward by the first threshold Th1 is set as the upper limit of the reference range of the peak time difference. Also, the regression line G02 obtained by shifting the regression line G1 obtained in step S7 downward by the second threshold Th2 is set as the lower limit of the reference range of the peak time difference. The first threshold Th1 and the second threshold Th2 are set considering the variability of multiple data representing the relationship between the reference pressure and the peak time difference obtained in the processing from step S4 to step S6. The first threshold Th1 and the second threshold Th2 may be the same value or different values. In this way, the reference range R0 of the peak time difference is set when the vacuum carburizing furnace 11 is empty.

[0026] In step S9, the processes from steps S2 to S8 are performed with an object placed inside the vacuum carburizing furnace 11, and then the processes from steps S2 to S8 are performed again with objects of different weights placed inside the vacuum carburizing furnace 11 to obtain a reference range for the peak time difference for each weight. Specifically, an object with a predetermined first weight (e.g., 100 kg) is placed inside the vacuum carburizing furnace 11, and the processes from step S2 to step S8 are carried out. That is, a regression line G1 is created that represents the relationship between the reference pressure and the peak time difference when the object of the first weight is placed inside the vacuum carburizing furnace 11, and a reference range R1 of the peak time difference is set. Next, an object with a predetermined second weight (e.g., 200 kg) that is different in weight from the first weight is placed in the vacuum carburizing furnace 11, and the processes from step S2 to step S8 are carried out. That is, a regression line G2 is created that represents the relationship between the reference pressure and the peak time difference when the object of the second weight is placed in the vacuum carburizing furnace 11, and the reference range R2 of the peak time difference is set.

[0027] When an object is placed inside the vacuum carburizing furnace 11, the propagation speed of pressure changes inside the furnace 11 is slower compared to when no object is placed inside, resulting in a longer peak time difference. Therefore, the reference range for the peak time difference when an object is placed inside the vacuum carburizing furnace 11 shifts towards the side where the peak time difference is longer compared to when no object is placed inside the vacuum carburizing furnace 11.

[0028] As the weight of the object placed inside the vacuum carburizing furnace 11 increases, the propagation speed of pressure changes inside the vacuum carburizing furnace 11 slows down, resulting in a longer peak time difference. Therefore, the reference range for the peak time difference shifts towards the side where the peak time difference becomes longer as the weight of the object placed inside the vacuum carburizing furnace 11 increases. The process in step S9 functions as a first weight reference range setting step, which sets the peak time difference reference range for the first weight, and a second weight reference range setting step, which sets the peak time difference reference range for the second weight.

[0029] In step S10, a reference range for the peak time difference of the workpiece to be carburized is set. Specifically, the weight of the workpiece to be carburized is measured, and the reference range for the peak time difference of the workpiece to be carburized is set based on the measured weight of the workpiece and the multiple reference ranges for the peak time difference set in the processes from step S8 to step S9. Here, the reference range for the peak time difference of the weight closest to the measured weight of the workpiece is selected. For example, if the first weight is 100 kg, the second weight is 200 kg, and the weight of the workpiece is 120 kg, the reference range for the peak time difference of the first weight is selected. Note that the reference range may also be set by interpolation. The process in step S10 functions as a workpiece reference range setting process that sets the peak time difference reference range of the workpiece based on the weight of the workpiece to be carburized, the peak time difference reference range of the first weight set in the first weight reference range setting process, and the peak time difference reference range of the second weight set in the second weight reference range setting process.

[0030] In step S11, data representing the relationship between the reference pressure and the peak time difference when the workpiece is carburized is obtained. Specifically, the workpiece is placed in the vacuum carburizing furnace 11 and subjected to carburizing treatment. If there is a temporary pressure change during the carburizing treatment, the reference pressure, which is the pressure measured by the first pressure gauge 20 before the pressure change, is acquired. In addition, the peak time difference, which is the time difference between when the measured pressure of the first pressure gauge 20 peaks and when the measured pressure of the second pressure gauge 30 peaks when the pressure changes temporarily, is acquired. In this way, data representing the relationship between the reference pressure and the peak time difference when the workpiece is carburized is acquired. The process in step S11 functions as a peak time difference acquisition process, which acquires the peak time difference between the timing when the measured pressure of the first pressure gauge peaks and the timing when the measured pressure of the second pressure gauge peaks when the pressure of the vacuum carburizing furnace temporarily changes while the workpiece is being carburized in the vacuum carburizing furnace.

[0031] In step S12, it is determined whether the peak time difference obtained in step S11 falls within the reference range of the peak time difference set in step S10. If the peak time difference is within the reference range of the peak time difference, the process proceeds to step S13; otherwise, the process proceeds to step S14. For example, as shown in Figure 3, if the reference range of the peak time difference set in step S10 is the reference range R1 for the peak time difference at the first weight, and the data representing the relationship between the reference pressure and the peak time difference obtained in step S11 is D1, it is determined that the value is within the reference range. On the other hand, if the data representing the relationship between the reference pressure and the peak time difference obtained in step S11 is D2, it is determined that the value is not within the reference range.

[0032] In step S13, it is determined that it is time to perform burnout. That is, it is determined that soot has accumulated inside the vacuum carburizing furnace 11 and that there has been a pressure change due to discharge. On the other hand, in step S14, it is determined that it is not time to perform burnout. It is determined that the pressure change that occurred when the workpiece was carburized was due to a false detection by the first pressure gauge 20, etc., and not a pressure change due to soot discharge. The processes from step S12 to step S14 function as a determination process that determines the timing for performing burnout based on the peak time difference obtained in the peak time difference acquisition process, and the peak time difference reference range of the first weight set in the first weight reference range setting process, or the peak time difference reference range of the workpiece set in the workpiece reference range setting process.

[0033] This disclosure uses the peak time difference when the pressure inside a vacuum carburizing furnace temporarily changes due to discharge caused by soot adhering to the furnace to determine the timing of burnout. Therefore, it is possible to determine the timing of burnout with higher accuracy than when simply using the pressure value. Furthermore, this disclosure determines the timing of burnout using a reference range of peak time differences set with an object placed inside the vacuum carburizing furnace. The propagation speed of pressure changes inside the vacuum carburizing furnace differs depending on whether or not an object is present inside the furnace. Therefore, in this disclosure, a reference range of peak time differences is set with an object placed inside the vacuum carburizing furnace. In this way, the timing of burnout can be determined with high accuracy.

[0034] Furthermore, this disclosure measures the weight of the workpiece to be carburized and uses a reference range of peak time differences set based on the measured weight of the workpiece to determine the timing of burnout. The propagation speed of pressure changes in a vacuum carburizing furnace differs depending on the weight of the object placed in the furnace. Therefore, in this disclosure, a reference range of peak time differences is set based on the weight of the workpiece to be carburized. In this way, the timing of burnout can be determined with high accuracy.

[0035] In this embodiment, a reference range for the peak time difference between the first and second weights was determined. However, if the weight of the workpiece to be carburized is constant, the weight of the workpiece to be carburized can be used as the first weight, and only the reference range for the peak time difference of the first weight can be determined and judged. Furthermore, the reference range for the peak time difference can be set not only for the first and second weights, but also for a third weight, a fourth weight, and so on.

[0036] In this embodiment, the reference range for the peak time difference is set according to the reference pressure, but the reference range for the peak time difference may also be set with the reference pressure fixed.

[0037] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its spirit. [Explanation of symbols]

[0038] 10...Vacuum carburizing equipment 11...Vacuum carburizing furnace 20. First pressure gauge 30... Second pressure gauge

Claims

1. A method for determining the timing of burnout in a vacuum carburizing furnace, The steps include: arranging a first pressure gauge and a second pressure gauge in different locations within the vacuum carburizing furnace; A first weight reference range setting step involves placing an object having a predetermined first weight inside the vacuum carburizing furnace, temporarily changing the pressure inside the furnace, and setting a first weight reference range based on the peak time difference, which is the time difference between the timing at which the measured pressure of the first pressure gauge peaks and the timing at which the measured pressure of the second pressure gauge peaks when the pressure is temporarily changed. A peak time difference acquisition step is performed to acquire the peak time difference, which is the time difference between the timing when the measured pressure of the first pressure gauge reaches its peak and the timing when the measured pressure of the second pressure gauge reaches its peak, while the workpiece is being carburized in the vacuum carburizing furnace. The process includes a first weight peak time difference reference range set in the first weight reference range setting step, and a determination step that determines the timing for performing burnout based on the peak time difference acquired in the peak time difference acquisition step, How to determine the timing for burnout.

2. A second weight reference range setting step involves placing an object of a predetermined second weight, which has a weight different from the first weight, into the vacuum carburizing furnace, temporarily changing the pressure inside the vacuum carburizing furnace, and setting a peak time difference reference range for the second weight based on the peak time difference, which is the time difference between the timing when the measured pressure of the first pressure gauge reaches its peak and the timing when the measured pressure of the second pressure gauge reaches its peak when the pressure is temporarily changed. The process includes a workpiece reference range setting step, which sets a peak time difference reference range for the workpiece based on the weight of the workpiece to be carburized in the vacuum carburizing furnace, the peak time difference reference range of the first weight set in the first weight reference range setting step, and the peak time difference reference range of the second weight set in the second weight reference range setting step, The determination step determines the timing for performing burnout based on the peak time difference reference range of the work set in the work reference range setting step and the peak time difference acquired in the peak time difference acquisition step. A method for determining the timing of burnout implementation according to claim 1.

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