Method for determining burn-out implementation time

Abstract

Provided is a method for determining a burn-out implementation time, with which it is possible to determine the time at which burn-out is implemented with high accuracy. A method for determining a burn-out implementation time according to the present invention is a method for determining a time at which burn-out of a vacuum carburizing furnace is implemented, the method comprising: a first weight reference range setting step for setting a first weight reference range; setting a peak time difference reference range for the first weight on the basis of a peak time difference, which is the time difference between the time at which the pressure measured by the first pressure gauge peaks and the time at which the pressure measured by the second pressure gauge peaks when the pressure in the vacuum carburizing furnace is temporarily changed in a state in which an object of the first weight is placed; a peak value time difference acquisition step for acquiring a peak value time difference, which is the time difference between the time at which the pressure measured by the first pressure gauge peaks and the time at which the pressure measured by the second pressure gauge peaks, when the pressure in the vacuum carburizing furnace temporarily changes while the workpiece is carburized by the vacuum carburizing furnace; and a determination step.

Description

Technical Field

[0001] This invention relates to a method for determining the timing of burnout. Background Technology

[0002] It is known to burn off carbon deposits adhering to the furnace by combustion in a vacuum carburizing furnace. Patent Document 1 discloses a technique for monitoring the temperature or pressure inside the furnace and the composition of the exhaust gas during the burn-off process, and for determining the end time of burn-off.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2007-131936 Summary of the Invention

[0004] Since a vacuum carburizing furnace cannot be used during burn-out, it is necessary to control the burn-out process to a minimum. Therefore, it is essential to determine the burn-out timing with high precision. To address this issue, the present invention provides a method for determining the burn-out timing with high precision.

[0005] This invention relates to a method for determining the burn-out moment in a vacuum carburizing furnace, comprising the following steps: a step of configuring a first pressure gauge and a second pressure gauge at different positions within the vacuum carburizing furnace; a first weight reference range setting step, which sets a reference range for the peak time difference of the first weight based on the time difference between the peak time of the measured pressure of the first pressure gauge and the peak time of the measured pressure of the second pressure gauge when the pressure of the first pressure gauge reaches its peak during a temporary pressure change in the vacuum carburizing furnace with an object of a predetermined first weight placed therein; a peak time difference acquisition step, which obtains the peak time difference between the peak time of the measured pressure of the first pressure gauge and the peak time difference of the measured pressure of the second pressure gauge during a temporary pressure change in the vacuum carburizing furnace while the workpiece is being carburized in the vacuum carburizing furnace; and a determination step of determining the burn-out moment based on the peak time difference reference range of the first weight set in the first weight reference range setting step and the peak time difference obtained in the peak time difference acquisition step.

[0006] This structure allows for the precise determination of when burnout occurs.

[0007] The method for determining the burnout execution time includes the following steps: a second weight reference range setting step, which involves temporarily changing the pressure inside the vacuum carburizing furnace while an object of a predetermined second weight (different from the first weight) is placed inside the furnace, and setting a peak time difference (i.e., the time difference between the peak value of the first pressure gauge and the peak value of the second pressure gauge during this temporary pressure change) to define a peak time difference reference range for the second weight; and a workpiece reference range setting step, which sets a peak time difference reference range for the workpiece based on the weight of the workpiece undergoing carburizing 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. The determination step determines the burnout execution time based on the peak time difference reference range for the workpiece set in the workpiece reference range setting step and the peak time difference obtained in the peak time difference acquisition step. This structure allows for high-precision determination of the burnout execution time.

[0008] Invention Effects

[0009] This invention provides a method for determining the burnout time with high precision. Attached Figure Description

[0010] Figure 1 This is a schematic structural diagram of the vacuum carburizing apparatus according to Embodiment 1.

[0011] Figure 2 This is a flowchart illustrating an example of the process for determining the timing of burnout.

[0012] Figure 3 This is a graph representing an example of the peak time difference reference range. Detailed Implementation

[0013] The following uses Figures 1-3 The embodiments of the present invention will be described. Figure 1 This is a schematic structural diagram of the vacuum carburizing apparatus according to Embodiment 1. Figure 2 This is a flowchart illustrating an example of the process for determining the timing of burnout. Figure 3 This is a graph representing an example of the peak time difference reference range.

[0014] Implementation Method 1

[0015] refer to Figure 1The structure of the vacuum carburizing apparatus 10, which implements the burnout timing determination method according to the present invention, will be described. The vacuum carburizing apparatus 10 includes a vacuum carburizing furnace 11, a vacuum pump 12, a first pressure gauge 20, a second pressure gauge 30, and a control device 50.

[0016] The vacuum carburizing furnace 11 supplies carburizing gas under reduced pressure and heating conditions to perform carburizing treatment on workpieces. Workpieces undergoing carburizing treatment include, for example, automotive parts or mechanical parts made of steel. The vacuum carburizing furnace 11 is equipped with heaters 11a for heating the interior. 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 gases such as air during burn-out.

[0017] Vacuum pump 12 is connected to vacuum carburizing furnace 11 via exhaust port 12a. Vacuum pump 12 draws gas from vacuum carburizing furnace 11 and discharges it to the outside, thereby reducing the pressure inside vacuum carburizing furnace 11 to below atmospheric pressure.

[0018] In the vacuum carburizing apparatus 10, a first pressure gauge 20 and a second pressure gauge 30 are positioned at different locations. 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 positioned arbitrarily as long as they can measure the pressure inside the vacuum carburizing furnace 11.

[0019] The control device 50 includes a memory 51 and a CPU 52. The memory 51 stores programs for performing carburizing treatment of the workpiece or determining the timing of burn-off as described later. The CPU 52 executes the programs stored in the memory 51 to control the operation of the heater 11a, vacuum pump 12, etc.

[0020] As part of the carburizing process in the vacuum carburizing apparatus 10, firstly, a workpiece is placed inside the vacuum carburizing furnace 11, and the vacuum pump 12 is activated to reduce the pressure inside the vacuum carburizing furnace 11 while simultaneously heating it with the heater 11a. If the workpiece reaches the specified processing temperature (e.g., 950 degrees Celsius), carburizing gas is supplied into the vacuum carburizing furnace 11. The carburizing gas is a hydrocarbon gas, such as acetylene gas. The hydrocarbon gas decomposes under reduced pressure and high temperature to produce carbon. The produced carbon diffuses from the surface of the workpiece to its interior, thus performing the carburizing process on the workpiece.

[0021] Some of the carbon produced by the carburizing gas becomes coke and adheres to the inside of the vacuum carburizing furnace 11. If coke adheres to the inside of the vacuum carburizing furnace 11, it may cause malfunction of the vacuum carburizing furnace 11 or poor quality of the carburized product. Therefore, when coke adheres to the inside of the vacuum carburizing furnace 11, air is introduced into the vacuum carburizing furnace 11 to burn off the coke.

[0022] Next, the method for determining the time of burnout will be explained. Figure 2 This is a flowchart illustrating an example of the burnout execution time determination process performed by the control device 50.

[0023] In step S1, the vacuum carburizing furnace 11 is made empty. Specifically, only the tray on which the workpiece is placed during the carburizing process is placed inside the vacuum carburizing furnace 11.

[0024] In step S2, the vacuum pump 12 is activated to bring the vacuum carburizing furnace 11 to any pressure.

[0025] In step S3, the pressure inside the vacuum carburizing furnace 11 is temporarily changed. This temporary pressure change is achieved, for example, by preparing a pressure chamber with a pressure level higher than that inside the vacuum carburizing furnace 11 and connecting the vacuum carburizing furnace 11 to the pressure chamber. The location of the vacuum carburizing furnace 11 connected to the pressure chamber can be, for example, any location near the heater 11a. The temporary pressure change can be implemented in any way. The duration of the temporary pressure change is, for example, 1 second. The magnitude of the temporarily changed pressure is the amount of pressure change during discharge caused by carbon deposits adhering to the vacuum carburizing furnace 11. That is, in step S3, the phenomenon occurring when carbon deposits are adhering to the vacuum carburizing furnace 11 is simulated. Furthermore, the amount of pressure change during discharge caused by carbon deposits is not constant but has a range; therefore, the magnitude of the temporarily changed pressure is set within the range of pressure changes that may occur during discharge caused by carbon deposits.

[0026] In step S4, the pressure measured by the first pressure gauge 20 before the temporary pressure change in step S3 is obtained. Hereinafter, the pressure measured by the first pressure gauge 20 before the temporary pressure change will be defined as the reference pressure. That is, in step S4, the reference pressure is obtained.

[0027] In step S5, the time difference between the moment when the measured pressure of the first pressure gauge 20 reaches its peak value and the moment when the measured pressure of the second pressure gauge 30 reaches its peak value during the temporary pressure change in step S3 is obtained, i.e., the peak time difference. Through the processing of steps S4 and S5, data representing the relationship between the reference pressure and the peak time difference in the empty state of the vacuum carburizing furnace 11 can be obtained.

[0028] In step S6, while changing the reference pressure and the magnitude of the temporarily changed pressure each time, the processing of steps S2 to S5 is repeated multiple times to obtain multiple data representing the relationship between the reference pressure and the peak time difference.

[0029] Specifically, similar to step S2, the vacuum pump 12 is activated to change the pressure inside the vacuum carburizing furnace 11. Then, similar to step S3, the pressure inside the vacuum carburizing furnace 11 is temporarily changed. The magnitude of the temporarily changed pressure is different from the pressure at the time of the temporary pressure change in step S3. Then, a reference pressure is obtained similarly to step S4, and then, similarly to step S5, the peak time difference is obtained. Then, steps S2 to S5 are repeated multiple times while changing the reference pressure and the magnitude of the temporarily changed pressure each time. In this way, multiple data representing the relationship between the reference pressure and the peak time difference when the vacuum carburizing furnace 11 is empty are obtained.

[0030] In step S7, based on multiple data representing the relationship between the reference pressure and the peak time difference obtained in steps S4 to S6, a regression line G0 representing the relationship between the reference pressure and the peak time difference when the vacuum carburizing furnace 11 is empty is generated.

[0031] Specifically, multiple data points representing the relationship between the baseline pressure and the peak time difference obtained in steps S4 to S6 are plotted (not shown) on a graph. Figure 3 The diagram shows a two-dimensional coordinate system where the horizontal axis represents the baseline pressure and the vertical axis represents the peak time difference. Then, using least squares regression analysis, the line with the smallest least squares error is found. The obtained line is the regression line G0.

[0032] The regression line G0 rises to the right. Under low reference pressure, compared to high reference pressure, the propagation speed of pressure changes within the vacuum carburizing furnace 11 is faster, thus the peak time difference is shorter.

[0033] In step S8, a reference range R0 for the peak time difference when the vacuum carburizing furnace 11 is empty is set. Specifically, the regression line G01, which is shifted parallel to the regression line G0 obtained in step S7 only upwards by a first threshold Th1, is set as the upper limit of the reference range for the peak time difference. Furthermore, the regression line G02, which is shifted parallel to the regression line G1 obtained in step S7 only downwards by a second threshold Th2, is set as the lower limit of the reference range for the peak time difference. The first threshold Th1 and the second threshold Th2 are set considering the deviations of multiple data points representing the relationship between the reference pressure and the peak time difference obtained in steps S4 to S6. The first threshold Th1 and the second threshold Th2 can be the same value or different values. Thus, the reference range R0 for the peak time difference when the vacuum carburizing furnace 11 is empty is set.

[0034] In step S9, the processes of steps S2 to S8 are performed while an object is placed inside the vacuum carburizing furnace 11. Furthermore, the processes of steps S2 to S8 are performed while objects of different weights are placed inside the vacuum carburizing furnace 11 to obtain a reference range of the peak time difference for each weight.

[0035] Specifically, an object with a predetermined first weight (e.g., 100 kg) is placed inside the vacuum carburizing furnace 11, and the processes in steps S2 to S8 are performed. That is, a regression line G1 is generated representing the relationship between the reference pressure and the peak time difference when the object with the first weight is placed inside the vacuum carburizing furnace 11, and a reference range R1 for the peak time difference is set.

[0036] Next, an object with a predetermined second weight (e.g., 200 kg) different from the first weight is placed inside the vacuum carburizing furnace 11, and the processes of steps S2 to S8 are performed. That is, a regression line G2 is generated representing the relationship between the reference pressure and the peak time difference when the object with the second weight is placed inside the vacuum carburizing furnace 11, and a reference range R2 for the peak time difference is set.

[0037] 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, thus the peak time difference is longer. Therefore, the reference range of the peak time difference when an object is placed inside the vacuum carburizing furnace 11 shifts towards the side with a longer peak time difference compared to when no object is placed inside the furnace 11.

[0038] The heavier the object placed inside the vacuum carburizing furnace 11, the slower the propagation speed of pressure changes inside the vacuum carburizing furnace 11, and thus the longer the peak time difference. Therefore, the reference range of the peak time difference shifts towards the side with a longer peak time difference as the weight of the object placed inside the vacuum carburizing furnace 11 increases.

[0039] The processing in step S9 functions as a first weight reference range setting process for setting the peak time difference reference range of the first weight and a second weight reference range setting process for setting the peak time difference reference range of the second weight.

[0040] In step S10, a reference range for the peak time difference of the workpiece undergoing carburizing is set. Specifically, the weight of the workpiece undergoing carburizing is measured, and a reference range for the peak time difference of the workpiece undergoing carburizing is set based on the measured weight of the workpiece and multiple reference ranges for peak time differences set in steps S8 to 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 workpiece weight is 120 kg, the reference range for the peak time difference of the first weight is selected. Alternatively, the reference range can be set by interpolation. The process in step S10 functions as a workpiece reference range setting process, which sets the reference range for the peak time difference of the workpiece based on the weight of the workpiece undergoing carburizing, the reference range for the peak time difference of the first weight set in the first weight reference range setting process, and the reference range for the peak time difference of the second weight set in the second weight reference range setting process.

[0041] In step S11, data representing the relationship between the reference pressure and the peak time difference during carburizing of the workpiece is obtained.

[0042] Specifically, a workpiece is placed inside a vacuum carburizing furnace 11 for carburizing treatment. In the event of a temporary pressure change during the carburizing process, the pressure measured by a first pressure gauge 20 before the pressure change, i.e., the reference pressure, is acquired. Furthermore, the time difference between the moment when the measured pressure of the first pressure gauge 20 reaches its peak and the moment when the measured pressure of the second pressure gauge 30 reaches its peak during the temporary pressure change, i.e., the peak time difference, is acquired. Thus, data representing the relationship between the reference pressure and the peak time difference during the carburizing treatment of the workpiece is obtained.

[0043] The process in step S11 serves as a peak time difference acquisition process, which obtains the time difference between the moment when the measured pressure of the first pressure gauge reaches its peak and the moment when the measured pressure of the second pressure gauge reaches its peak during the carburizing process of the workpiece in the vacuum carburizing furnace.

[0044] In step S12, it is determined whether the peak time difference obtained in step S11 is within the reference range of the peak time difference set in step S10. If the peak time difference is within the reference range, proceed to step S13; otherwise, proceed to step S14. For example, if... Figure 3 As shown, the reference range for the peak time difference set in step S10 is the reference range R1 for the peak time difference under the first weight. If the data representing the relationship between the reference pressure and the peak time difference obtained in step S11 is D1, it is determined to be 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 to be outside the reference range.

[0045] In step S13, the moment of burn-out is determined. That is, it is determined that a pressure change caused by discharge has occurred due to carbon deposits adhering to the vacuum carburizing furnace 11. On the other hand, in step S14, it is determined that the moment of burn-out is not. It is determined that the pressure change that occurs during the carburizing process of the workpiece is caused by a false detection of the first pressure gauge 20, etc., and is not a pressure change caused by the discharge of carbon deposits.

[0046] The processing of steps S12 to S14 serves as a determination process for determining the time of burnout based on 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 and the peak time difference obtained in the peak time difference acquisition process.

[0047] In this invention, the peak time difference of the pressure temporary change within the vacuum carburizing furnace caused by discharge due to carbon deposits adhering to the furnace is used to determine the burn-out timing. Therefore, compared to using only the pressure value, the burn-out timing can be determined with high precision. Furthermore, in this invention, a reference range of the peak time difference, set with an object placed inside the vacuum carburizing furnace, is used to determine the burn-out timing. The propagation speed of the pressure change within the vacuum carburizing furnace varies depending on whether an object is present. Therefore, in this invention, a reference range of the peak time difference is set with an object placed inside the vacuum carburizing furnace. This allows for high-precision determination of the burn-out timing.

[0048] Furthermore, in this invention, the weight of the workpiece undergoing carburizing is measured, and the timing of burn-off is determined using a reference range of peak time difference set based on the measured weight of the workpiece. The propagation speed of pressure changes within the vacuum carburizing furnace varies depending on the weight of the object placed within the furnace. Therefore, in this invention, a reference range of peak time difference is set based on the weight of the workpiece undergoing carburizing. This allows for highly accurate determination of the timing of burn-off.

[0049] In this embodiment, a reference range for the peak time difference between the first weight and the second weight is determined. However, if the weight of the workpiece undergoing carburizing is constant, the weight of the workpiece undergoing carburizing can be used as the first weight, and only the reference range for the peak time difference of the first weight can be determined for judgment. Furthermore, not only can a reference range for the peak time difference between the first weight and the second weight be set, but a third weight and a fourth weight can also be added to set the reference range for the peak time difference.

[0050] In this embodiment, the reference range of the peak time difference is set based on the reference pressure, but the reference pressure can also be fixed to set the reference range of the peak time difference.

[0051] Furthermore, the present invention is not limited to the above-described embodiments, and appropriate modifications can be made without departing from the spirit of the invention.

[0052] Symbol Explanation

[0053] 10 - Vacuum carburizing device, 11 - Vacuum carburizing furnace, 20 - First pressure gauge, 30 - Second pressure gauge.

Claims

1. A method for determining the burnout time in a vacuum carburizing furnace, characterized in that, The process includes the following steps: The process of configuring the first pressure gauge and the second pressure gauge at different positions inside the vacuum carburizing furnace; The first weight reference range setting process involves temporarily changing the pressure inside the vacuum carburizing furnace while an object of a predetermined first weight is placed inside the vacuum carburizing furnace, and setting the peak time difference reference range for the first weight based on the time difference between the moment when the measured pressure of the first pressure gauge reaches its peak and the moment when the measured pressure of the second pressure gauge reaches its peak during the temporary pressure change. The process of obtaining the peak time difference, i.e., the time difference between the peak value of the measured pressure of the first pressure gauge and the peak value of the measured pressure of the second pressure gauge during a temporary pressure change in the vacuum carburizing furnace when the workpiece is carburized in the vacuum carburizing furnace; and The determination process for determining the moment of burnout is based on the peak time difference reference range of the first weight set in the first weight reference range setting process and the peak time difference obtained in the peak time difference acquisition process.

2. The method for determining the burnout time according to claim 1, characterized in that, The process includes the following steps: The second weight reference range setting process involves temporarily changing the pressure inside the vacuum carburizing furnace while an object of a predetermined second weight (different from the first weight) is placed inside the furnace. The peak time difference (i.e., the time difference between the peak value of the first pressure gauge and the peak value of the second pressure gauge during this temporary pressure change is used to set the peak time difference reference range for the second weight. The workpiece reference range setting process sets the peak time difference reference range of the workpiece based on the weight of the workpiece undergoing carburizing treatment in the vacuum carburizing furnace, 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. The determination process determines the moment of burnout based on the peak time difference reference range of the workpiece set in the workpiece reference range setting process and the peak time difference obtained in the peak time difference acquisition process.

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