JP2007315729A - Evacuating device for vacuum heat treating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evacuating device for a vacuum heat treating device capable of obtaining heat-treated articles of good quality with little dispersion by maintaining the interior of a furnace body to a predetermined pressure even when the fluctuation width of atmospheric gas flow exhausted from the furnace body is large like a multi-chamber type vacuum heat treating device. <P>SOLUTION: The evacuating device for the vacuum heat treating device performs control of pressure in the furnace body by controlling the rotating speed of a vacuum pump (a mechanical booster pump 7) connected to the furnace body 2 through an exhaust line 3. The exhaust line 3 is provided with a branch part 11 wherein a plurality of branch lines 12a, 12b, 12c with different passage resistance comprising on-off valves A, B, C are arranged in parallel, and a changeover control means (a control device 10) is provided for performing opening/closing control of the on-off valves A, B, C to select one branch line as an exhaust flow passage and changing the exhaust flow passage over to the branch line on the high resistance side when the rotating speed of the vacuum pump reaches a lower limit value, while changing the exhaust flow passage over to the branch line on the low resistance side when the rotating speed reaches an upper limit value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vacuum exhaust apparatus for exhausting atmospheric gas in a furnace of a vacuum heat treatment apparatus.

Conventionally, as a heat treatment apparatus for vacuum carburizing a processing material such as steel material, a batch furnace type or continuous furnace type furnace is generally used. However, the former is low in productivity, and the latter is under constant processing conditions. Although the productivity is high, there is a problem that it is not possible to respond quickly to changes in processing conditions and increase / decrease in quantity. In order to solve these problems, a multi-chamber vacuum heat treatment apparatus having a plurality of furnace bodies (processing chambers) and a conveying means for delivering the processing material to the furnace bodies has been proposed. (For example, see Patent Documents 1 and 2.)
JP 2006-63363 A Japanese Patent Laid-Open No. 2005-9702

In the above-described multi-chamber vacuum heat treatment apparatus, the respective vacuum exhaust ducts connected to the respective furnace bodies (processing chambers) as described in Patent Document 1 (paragraph [0028] thereof) In order to exhaust the atmosphere gas such as air and carburizing gas in the processing chamber in a lump, a single vacuum exhaust device having a vacuum pump is used. As in this conventional vacuum evacuation apparatus, a control method for maintaining the pressure in the furnace at a predetermined degree of vacuum by controlling the rotation speed of the vacuum pump by an inverter (hereinafter referred to as a rotation speed control method) The pressure inside the furnace is controlled to a predetermined vacuum by controlling the opening of a flow rate adjusting valve provided in the middle of an exhaust pipe connecting the vacuum pump and the furnace body (for example, refer to Patent Document 3). A vacuum evacuation device (see, for example, Patent Document 4) of a control method (hereinafter referred to as an opening degree control method) that is maintained frequently is used.
JP 2001-214868 A JP 2005-325371 A

  However, in the above-described multi-chamber vacuum heat treatment apparatus, the steps of vacuum carburizing such as soaking, carburizing, and diffusion in each furnace proceed at random, so the flow rate of the atmospheric gas discharged from each furnace varies greatly. On the other hand, in the case of the above-described rotation speed control method, since the exhaust capacity adjustable width by the rotation speed control is limited, the rotation speed of the vacuum pump becomes the lower limit reached state or the upper limit reached state, The pressure inside the furnace tends to deviate from the target pressure due to low internal pressure (high vacuum) due to excessive displacement or high internal pressure due to excessive displacement, resulting in variations in carburizing quality between lots or between furnace bodies. Have. Similarly, in the case of the above opening degree control method, the flow rate adjustment range in which the exhaust flow rate can be accurately adjusted by opening degree control is limited, so that the flow rate control valve reaches the opening lower limit value or the opening upper limit value. As a result, there was a problem that the pressure inside the furnace tends to deviate from the target pressure due to excessive or too small displacement similar to the above, resulting in variations in carburizing quality.

  The present invention is intended to solve the above-mentioned conventional problems, and maintains the furnace body at a predetermined pressure even when the fluctuation range of the flow rate of the atmospheric gas discharged from the furnace body is large as in a multi-chamber vacuum heat treatment apparatus. An object of the present invention is to provide a vacuum evacuation apparatus for a vacuum heat treatment apparatus capable of obtaining a heat treatment product of good quality with little variation.

  In order to achieve the above object, the vacuum exhaust apparatus of the vacuum heat treatment apparatus according to claim 1 is a vacuum heat treatment that controls the pressure in the furnace body by controlling the number of revolutions of a vacuum pump connected to the furnace body through an exhaust pipe line. In the vacuum evacuation device of the apparatus, the exhaust pipe is provided with a branch portion in which a plurality of branch pipes having different flow resistances provided with an open / close valve are arranged in parallel, and the open / close valve is controlled to open and close. When the number of revolutions of the vacuum pump reaches a lower limit value, the exhaust flow passage is switched to a branch line on the high resistance side, and the number of revolutions reaches the upper limit value. In this case, switching control means for switching the exhaust flow passage to the branch pipe on the low resistance side is provided.

  According to the first aspect of the present invention, by switching the branch pipe from which the exhaust flow rate controllable range different from the adjustable range of the rotation speed of the vacuum pump can be obtained due to the difference in flow path resistance, the exhaust flow path is switched. The range in which the exhaust gas flow rate can be controlled is expanded, and the exhaust pressure can be exhausted without excess or deficiency even with a large fluctuation range of the atmospheric gas flow rate from the furnace body, and the furnace body pressure can be maintained at the set value.

  According to a second aspect of the present invention, there is provided a vacuum evacuation apparatus for a vacuum heat treatment apparatus in which the pressure in the furnace is controlled by opening control of a flow control valve provided in an exhaust pipe connecting the furnace body and a vacuum pump. In the exhaust system, the exhaust pipe is provided with a branch portion in which a plurality of branch pipes each having a flow control valve having a different flow resistance are provided in parallel, and the open / close valve is controlled to open and close. One branch pipe is selected as the exhaust flow passage, and when the opening of the flow control valve during the opening control of the exhaust flow passage reaches a lower limit value, the exhaust flow passage and the opening control The target flow control valve is switched to a branch line having a flow control valve on the high resistance side and the flow control valve. When the opening reaches the upper limit value, the exhaust flow passage and the flow control valve are switched to the low resistance side. A branch line with a flow control valve of Characterized by comprising a switching control means for obtaining.

  According to the second aspect of the present invention, the exhaust flow rate controllable range can be obtained by switching the flow rate control valve capable of obtaining a different exhaust flow rate controllable range depending on the difference in flow path resistance and controlling the opening degree of the flow rate control valve. It is expanded, and even with respect to a large fluctuation range of the atmospheric gas flow rate from the furnace body, exhaust can be performed without excess and deficiency, and the furnace pressure can be maintained at a set value.

  The vacuum exhaust apparatus of the vacuum heat treatment apparatus according to claim 3 is a vacuum exhaust apparatus of a vacuum heat treatment furnace that controls the pressure in the furnace body by controlling the number of rotations of a vacuum pump connected to the furnace body through an exhaust pipe line. The exhaust pipe is provided with a branch portion in which a plurality of branch pipes each having an on-off valve and a flow rate control valve having different flow path resistances are arranged in parallel, and is selected from the flow rate control valves. Pressure control means for controlling the pressure inside the furnace by controlling the opening of one flow control valve, and opening and closing the on-off valve to select one branch pipe as an exhaust flow path, When the rotational speed reaches the lower limit value and the opening degree of the flow rate control valve during the opening degree control of the exhaust flow path reaches the lower limit value, the exhaust flow path and the flow rate control valve subject to opening degree control have high resistance. A branch pipe having a flow control valve on the side, and A branch pipe having a flow resistance control valve on the low resistance side when the number of rotations of the vacuum pump reaches an upper limit value and the opening degree reaches an upper limit value. And a switching control means for switching to the flow control valve.

  According to the third aspect of the present invention, the flow path is combined with the rotational speed control of the vacuum pump that can obtain different flow controllable ranges by switching the branch pipes having flow control valves having different flow path resistances. By switching the flow control valve that provides different exhaust flow controllable ranges depending on the resistance difference and controlling the opening of the flow control valve, the exhaust flow controllable range is greatly expanded, and the atmosphere gas flow rate from the furnace body is large. Exhaust can be performed without excess or deficiency with respect to the fluctuation range, and the pressure in the furnace can be maintained at a set value.

  As described above, according to the present invention, even when the fluctuation range of the atmospheric gas flow rate discharged from the furnace body is large as in a multi-chamber vacuum heat treatment apparatus, the furnace body is maintained at a predetermined pressure and there is little variation. A heat-treated product of good quality can be obtained.

  In addition to the above effect, according to the first aspect of the present invention, the pressure in the furnace is maintained at a predetermined pressure by a simple and low-cost device in which a plurality of branch pipes having different flow path resistances are switched by an on-off valve. can do.

  In addition to the above effects, according to the second aspect of the present invention, the flow rate control can be performed in comparison with the exhaust flow rate controllable range obtained by the rotational speed control of the vacuum pump that is generally limited in the rotational speed range that can be controlled by the motor. Since the exhaust flow rate controllable range obtained by controlling the opening of the valve is wider, the pressure in the furnace can be maintained at a predetermined pressure by a device having a small number of branch pipes, and hence a small number of flow control valves.

  In addition to the above effect, according to the invention described in claim 3, a large exhaust flow rate controllable range can be obtained by combining the rotation speed control of the vacuum pump and the opening degree control of the flow control valve.

  An embodiment of the invention according to claim 1 will be described below with reference to a first example shown in FIGS. In FIG. 1, 1 is a multi-chamber vacuum heat treatment apparatus for performing vacuum carburizing treatment of a treatment material, 2 is a plurality of furnace bodies containing a carburizing chamber, and 3 is an open / close valve 4 in each of these furnace bodies. The exhaust line 5 connected to the exhaust line 5 is an evacuation apparatus connected to the exhaust line 3 and includes an oil rotary pump 6 and a mechanical booster pump 7 provided on the front side as a vacuum evacuation means. 8 is an inverter for controlling the rotational speed of the mechanical booster pump 7, 9 is a vacuum gauge connected to the exhaust pipe 3 near the furnace body 2, and 10 is a control device.

Since the exhaust pipe line 3 communicates with each furnace body 2 via the on-off valve 4 that is individually opened according to the vacuum carburizing process that proceeds separately in each furnace body 2, The pressure inside the furnace is detected. Then, the control device 10 is based on the pressure detection value P of the vacuum gauge 9 and the pressure setting value P _{0 in} the furnace in the soaking period to the diffusion period (soaking period, carburizing period, and diffusion period) in the vacuum carburizing process. The pressure control unit controls the pressure in the furnace by controlling the rotational speed of the mechanical booster pump 7 via the inverter 8 (in this example, the power supply frequency of the mechanical booster pump 7 driven by a synchronous motor is controlled). Is provided. The control device 10 also performs opening / closing control of the on-off valves A, B, and C, which will be described later, which will be described later.

  Reference numeral 11 denotes a branch portion provided in the exhaust pipe 3, and is formed by arranging a plurality of (three in this example) branch pipes 12a to 12c in parallel. The branch pipe 12a includes an on-off valve A and a flow rate. The control valve 13a is provided with an on-off valve B and a flow rate control valve 13b on the branch pipe 12b, and an on-off valve C and a flow rate control valve 13c are provided on the branch pipe 12c. As described later, the on-off valves A, B, and C are arranged so that one of the branch pipes 12a to 12c becomes an open exhaust flow path according to the rotational speed of the mechanical booster pump 7. Open / close control is performed by a switching control unit of the control device 10.

Further, the flow rate control valves 13a to 13c are of the manual adjustment type, and by adjusting the flow rate, the flow channel resistance of each branch pipeline 12a to 12c in the open state is the lowest resistance (small resistance) in the branch pipeline 12a. The pipe 12b is set to have a higher resistance (large resistance), and the branch pipe 12c is set to have a higher resistance. Still describe these flow resistance, FIG. 2 is due to speed and the pump of the mechanical booster pump 7 in a state in which the furnace body pressure is maintained in the furnace body pressure setpoint P ₀ (and oil rotary pump 6) It is a diagram schematically showing the relationship with the exhaust flow rate (= atmospheric gas flow rate Q discharged from the furnace body 2), and the rotational speed of the mechanical booster pump 7 due to the difference in flow resistance between the branch pipes 12a to 12c. When the pumping speed of the pump changes between an upper limit value and a lower limit value that can be practically controlled, the exhaust flow rate when the small resistance branch pipe 12a is opened is a curve J (straight line). However, when the branch pipe 12b having a higher flow resistance is opened, the curve K on the low flow rate side is opened, and the branch pipe 12c having a higher flow resistance is further changed. When the circuit is opened, the exhaust flow rate changes according to the curve L on the lower flow rate side.

  As shown in FIG. 2, the flow resistance of each of the branch pipes 12a to 12c is set such that the maximum flow rate value on the curve K (flow rate when reaching the MB rotation speed upper limit value) is the minimum flow rate value on the curve J (MB rotation). The flow resistance values of the branch pipes 12a to 12c are selected so that the maximum flow value on the curve L is equal to or higher than the minimum flow value on the curve K. Accordingly, the fluctuation range of the pressure in the furnace body accompanying the fluctuation of the exhaust gas flow rate at the time of switching the open state of the branch pipe line by the opening / closing control of the opening / closing valves A, B, C can be suppressed to a small amount.

  Next, a pressure control method in the furnace during vacuum carburization by the apparatus having the above configuration will be described with reference to the flowchart shown in FIG. 3 and FIG. A plurality of furnace bodies 2 of the vacuum heat treatment apparatus 1 are loaded and sent with a processing material by a conveying means (not shown), and are subjected to a vacuum carburizing process separately in a carburizing chamber in each furnace body 2, and the soaking is performed. The atmospheric gas discharged from each furnace body during the period to the diffusion period is exhausted by a vacuum pump (mechanical booster pump 7 and oil rotary pump 6).

Therefore, at the start of operation of the vacuum heat treatment apparatus 1, in the vacuum exhaust apparatus 5, the on-off valve A is opened to open only the branch pipe 12 a (step 21), and the mechanical booster pump 7 is controlled by the controller 10 via the inverter 8. Is controlled to maintain the pressure inside the furnace at the set pressure P ₀ , and the MB speed n is fed back from the inverter 8 to the control device 10. The pressure in the furnace body is controlled by controlling the MB rotation speed so that an exhaust gas flow rate corresponding to the atmospheric gas flow rate Q discharged from the furnace body 2 is obtained according to the curve J shown in FIG.

  During the pressure control in the open state of the branch pipe 12a, when the atmospheric gas flow rate Q decreases and the MB rotational speed reaches the lower limit value (step 22), the on-off valve A is in the open state. After confirmation (step 23), the on-off valve A is closed and the on-off valve B is opened (step 24). As a result, the branch pipe 12b on the high flow resistance side is opened, so that the controllable range of the exhaust flow rate shifts to the curve K in FIG. By controlling the number, it is possible to control the pressure inside the furnace. When the branch gas passage 12b is in the open state (open / close valve B open state) and the atmospheric gas flow rate Q further decreases and the MB rotational speed reaches the lower limit (step 22), the open / close valve B is closed and the open / close valve C is closed. Is opened (steps 23, 25, 26). As a result, the branch pipe 12c on the high flow resistance side is further opened, and the controllable range of the exhaust flow rate shifts to the curve L in FIG. By controlling the number, it is possible to control the pressure inside the furnace.

  On the other hand, when the atmospheric gas flow rate Q from the furnace body 2 increases and the MB rotation speed reaches the upper limit in the open state of the branch pipe 12c (open / close valve C open state) (step 28), The on-off valve C is closed and the on-off valve B is opened (steps 29 and 30). As a result, the branch pipe 12b is opened and the exhaust flow rate controllable range shifts to the curve K in FIG. 2, and the pressure inside the furnace can be controlled by MB rotation speed control even when the atmospheric gas flow rate Q is increased. It becomes. Further, when the atmospheric gas flow rate Q further increases and the MB rotational speed reaches the upper limit value (step 28) in the open state of the branch pipe line 12b (open / close valve B open state), the open / close valve B is closed and the open / close valve A is closed. Is opened (steps 29, 31, 32). As a result, the branch pipe 12a is opened, the control range of the exhaust gas flow shifts to the curve J in FIG. 2, and the pressure inside the furnace is controlled by the MB rotation speed control even when the atmospheric gas flow is further increased. It becomes possible.

  In the flowchart of FIG. 3, step 27 is reached when the on-off valve C is open and the MB speed reaches the lower limit value, and when the actual displacement from the furnace body falls below the initial assumed minimum flow rate. In addition, step 33 is reached when the on-off valve A is open and the MB rotational speed reaches the upper limit value, and when the actual exhaust flow rate from the furnace body exceeds the initially assumed maximum flow rate. If these errors occur frequently, the flow resistance of the branch pipe 12c can be further increased or the flow resistance of the branch pipe 12a can be further reduced by adjusting the flow rate of the flow control valves 13c and 13a. Take measures such as

Switching of the branch pipes by the opening / closing control of the opening / closing valves A to C performed according to the above flowchart (FIG. 3) is performed by the switching control unit of the control device 10. As shown in FIG. 2, by switching the exhaust flow path to a branch pipe having a high flow resistance, the exhaust flow rate controllable range by only one branch pipe 12a that does not perform this switching is a range V ₀ . On the other hand, by switching the branch pipe, a large exhaust flow rate controllable range of range V is obtained. Exhaust is performed without excess or deficiency even with a large fluctuation range of the atmospheric gas flow rate Q, and the pressure inside the furnace is reduced. It can be maintained at a predetermined set pressure.

  Next, an embodiment of the invention according to claim 2 will be described with reference to a second example shown in FIGS. In this second example, instead of the rotational speed control of the mechanical booster pump 7 in the first example, the flow rate control is performed by a flow rate control valve. The specific configuration is the same as in the first example, and the same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description of those parts is omitted.

  In FIG. 4, reference numeral 41 denotes a multi-chamber vacuum heat treatment apparatus that performs vacuum carburizing treatment of a treatment material. A mechanical booster pump 7 and an oil rotary pump 6 are used as vacuum exhaust means in an exhaust pipe line 3 connected to each furnace body 2. The vacuum exhaust device 42 provided is connected.

  43 is a branch portion provided in the exhaust pipe 3 on the upstream side of the mechanical booster pump 7, and a plurality of (three in this example) branch pipes 44a to 44c are arranged in parallel to form a branch pipe 44a. Includes an on-off valve A and a flow control valve D, an on-off valve B and a flow control valve E on the branch pipe 44b, and an on-off valve C and a flow control valve F on the branch pipe 44c, respectively. The on-off valves A, B, and C are controlled by a switching control unit of the control device 45 so that one branch pipe becomes an open exhaust flow passage according to the opening degree of the flow control valve, as will be described later. Is done.

The flow rate control valves D to F have different flow path resistances. The flow rate control valve D is a low resistance (for large flow rate control) flow rate control valve and the flow rate control valve E has a lowest flow path resistance. The flow rate control valve and flow rate control valve F having a large path resistance are high resistance (for small flow rate control) flow rate control valves having a larger flow path resistance. The flow control valve of one branch pipe that is opened by the opening / closing control of the opening / closing valves A to C includes a pressure detection value P of the vacuum gauge 9 and a pressure setting value P ₀ in the furnace in the vacuum carburizing process. Therefore, the opening degree is controlled by the pressure control unit of the control device 45, and the pressure in the furnace is controlled.

It said flow control valve D, E, will be further explained. Passage resistance of F, 5 and opening of the flow control valve in a state in which the furnace body pressure is maintained in the furnace body pressure setpoint P _0, FIG. 5 is a diagram schematically showing a relationship with an exhaust flow rate (= atmospheric gas flow rate Q discharged from the furnace body 2) by a vacuum pump (mechanical booster pump 7 and oil rotary pump 6), and each flow control valve (hereinafter, control valve). The exhaust flow rate of the low resistance control valve D is a curve M (straight line) when the opening amount of the control valve D is changed between the upper limit value and the lower limit value. In the following, the other curves are also the same.), While the control valve E having a higher resistance than this changes the curve N on the low flow rate side, and further on the control valve F having a higher resistance, the flow rate on the lower flow rate side. Exhaust flow rate changes according to curve O To do.

  As shown in FIG. 5, the flow resistances of the control valves D, E, and F are such that the maximum flow value on the curve N (the flow when the control valve E opening upper limit value is reached) is the minimum flow value on the curve M ( Flow rate resistance value of each control valve D to F so that the maximum flow rate value on the curve O is equal to or higher than the minimum flow rate value on the curve N. By selecting this, it is possible to suppress the fluctuation range of the pressure in the furnace accompanying the fluctuation of the exhaust flow rate at the time of switching the control valve to be controlled for opening to a small amount.

  Next, a furnace pressure control method during vacuum carburization by the apparatus having the above configuration will be described with reference to the flowchart shown in FIG. 6 and FIG. A processing material is carried into and sent out to each of the plurality of furnace bodies 2 of the vacuum heat treatment apparatus 41 by a conveying means (not shown), and vacuum carburizing treatment is separately performed in the carburizing chamber in each furnace body 2, and the soaking is performed. The atmospheric gas discharged from each furnace body during the period to the diffusion period is exhausted by a vacuum pump (mechanical booster pump 7 and oil rotary pump 6).

  Therefore, at the start of the operation of the vacuum heat treatment apparatus 41, the evacuation apparatus 42 opens the on-off valve A to open the branch pipe 44a (step 51), and the control valve D of the pipe is controlled for opening control. As a valve, pressure control in the furnace is started by the control device 45 (pressure control unit thereof) (steps 52 and 53). The control of the furnace pressure is performed by controlling the opening of the control valve D so as to obtain an exhaust gas flow rate corresponding to the atmospheric gas flow rate Q discharged from the furnace body 2 according to the curve M shown in FIG.

  When the atmospheric gas flow rate Q decreases and the opening degree of the control valve D reaches the lower limit during the pressure control in the open state (control valve Don state) of the branch pipe 44a, the opening / closing is performed. The valve A is closed, the on-off valve B is opened, the branch pipe 44b is opened, and the control valve to be controlled for opening is switched from the control valve D to the control valve E (steps 55, 52, 57, 58). As a result, the opening degree control state by the control valve E on the high flow path resistance side is entered, so that the controllable range of the exhaust flow rate shifts to the curve N in FIG. The pressure inside the furnace can be controlled by controlling the opening of the valve. When the atmospheric gas flow rate Q further decreases in the open state of the branch pipe 44b (control valve Eon state) and the control valve opening reaches the lower limit (step 59), the on-off valve B is closed and the on-off valve C is closed. And the branch pipe 44c is opened, and the control valve to be controlled for opening is switched from the control valve E to the control valve F (steps 60, 52, 57, 63, 64). As a result, the opening degree control state by the control valve F on the higher flow path resistance side is further changed, so that the controllable range of the exhaust flow rate shifts to the curve O in FIG. The furnace pressure can be controlled by controlling the opening of the control valve.

  On the other hand, when the atmospheric gas flow rate Q from the furnace body 2 increases in the pressure control state (opening state of the on-off valve C) by the control valve F and the control valve opening reaches the upper limit (step 66). Then, the on-off valve C is closed, the on-off valve B is opened, the branch pipe 44b is opened, and the opening control target valve is switched from the control valve F to the control valve E (steps 67, 52, 57, 58). As a result, the opening control state by the control valve E on the low flow path resistance side is entered, and the exhaust flow rate controllable range shifts to the curve N in FIG. The pressure inside the furnace can be controlled by the control. When the atmospheric gas flow rate Q further increases and the control valve opening reaches the upper limit value (step 61) in the pressure control state by the control valve E (open / close valve B open state), the open / close valve B is closed and the open / close valve is closed. A is opened, the branch pipe 44a is opened, and the opening control target valve is switched from the control valve E to the control valve D (steps 62, 52, 53). As a result, the opening degree control state by the control valve D on the low flow resistance side is further changed, and the exhaust flow rate controllable range shifts to the curve M in FIG. It is possible to control the pressure inside the furnace by controlling the opening degree.

  In the flowchart of FIG. 6, the opening of the control valve D reaches the upper limit value in step 56 when the actual exhaust flow rate from the furnace body exceeds the initial assumed maximum flow rate, and the control is performed in step 65. The opening degree of the valve F reaches the lower limit value when the actual exhaust flow rate from the furnace body falls below the initial assumed minimum flow rate. If these errors occur frequently, take measures such as replacing the control valve D with a flow control valve with a smaller flow path resistance or replacing the control valve F with a flow control valve with a higher flow path resistance. That's fine.

The switching of the branch pipes and the switching of the control valve to be controlled by the opening / closing control of the opening / closing valves A to C performed according to the above flowchart (FIG. 6) are performed by the switching control unit of the control device 45. Then, as shown in FIG. 5, only the one branch pipe 12a and the control valve D that do not perform the switching are switched by switching the exhaust flow passage and the control valve to be controlled for opening to the control valve having a high flow resistance. Exhaust flow rate controllable range due to the above is the range V ₀ , whereas by switching the branch pipe and the control valve, a large exhaust flow rate controllable range of range V is obtained. However, the exhaust can be performed without excess and deficiency, and the furnace pressure can be maintained at a predetermined set pressure.

  Next, an embodiment of the invention according to claim 3 will be described with reference to a third example shown in FIGS. The third example is a combination of the rotational speed control of the mechanical booster pump 7 in the first example and the flow rate control by the flow rate control valve in the second example. The specific configurations of the flow control valve and the like provided in each branch pipe are the same as those in the first and second examples, and the same parts as those in FIGS. 1 and 4 are denoted by the same reference numerals. Detailed description of these parts is omitted.

  In FIG. 7, reference numeral 71 denotes a multi-chamber vacuum heat treatment apparatus for performing vacuum carburization treatment of a treated material. A mechanical booster pump 7 and an oil rotary pump 6 are used as vacuum exhaust means in an exhaust pipe line 3 connected to each furnace body 2. The evacuation apparatus 72 provided is connected.

  43 is a branch portion provided in the exhaust pipe 3 on the upstream side of the mechanical booster pump 7, and a plurality of (three in this example) branch pipes 44a to 44c are arranged in parallel to form a branch pipe 44a. Includes an on-off valve A and a flow control valve D, an on-off valve B and a flow control valve E on the branch pipe 44b, and an on-off valve C and a flow control valve F on the branch pipe 44c, respectively. As will be described later, the on-off valves A, B, and C are controlled so that one branch pipe becomes an open exhaust flow passage according to the rotational speed of the mechanical booster pump 7 and the opening degree of the flow control valve. Open / close control is performed by 73 switching control section.

The flow rate control valves D to F have different flow path resistances. The flow rate control valve D is a low resistance (for large flow rate control) flow rate control valve and the flow rate control valve E has a lowest flow path resistance. The flow rate control valve and flow rate control valve F having a large path resistance are high resistance (for small flow rate control) flow rate control valves having a larger flow path resistance. Then, the flow control valve of one branch pipe that is opened by the opening / closing control of the opening / closing valves A to C is in a state where the rotational speed of the mechanical booster pump 7 has reached the lower limit value as described later. and nine of the pressure detection value P, based on the furnace body pressure setpoint P ₀ in the vacuum carburization process, is opening control by the pressure control unit of the control device 45, control of the furnace body pressure is performed.

The flow resistance of the flow rate control valves (hereinafter abbreviated as control valves) D, E, and F and the flow rate characteristics of the vacuum pump will be further described. FIG. 8 shows that the pressure inside the furnace is the pressure set value P ₀ in the furnace. The rotational speed of the mechanical booster pump 7 and the opening degree of each control valve in the maintained state, and the exhaust gas flow rate (= atmospheric gas discharged from the furnace body 2) by the vacuum pump (mechanical booster pump 7 and oil rotary pump 6) In the diagram schematically showing the relationship with the flow rate Q), when the control valve D, E, F is fully open (opening upper limit), the MB rotation speed is between the upper limit value and the lower limit value that are allowed for the pump operation. When changed, the exhaust flow rate when the branch pipe 44a having the small resistance control valve D is opened changes according to the curve J, but is lower when the branch pipe 44b having the higher resistance control valve E is opened. Flow side song When the branch pipe 44c having the line K and the control valve F having a higher resistance than this is opened, the exhaust flow rate changes in accordance with the curve L on the lower flow rate side. Then, with the rotational speed of the mechanical booster pump 7 maintained at the lower limit value, the opening degree of each control valve is changed between the upper limit value and the lower limit value of the opening degree that can accurately adjust the exhaust gas flow rate by the opening degree control. The exhaust flow rate by the low resistance control valve D changes according to the straight line M, while the higher resistance control valve E has a lower flow rate side straight line N, and the higher resistance control valve F has a lower flow rate. The exhaust flow rate changes in accordance with the straight line O on the flow rate side.

  As shown in FIG. 8, the flow resistances of the control valves D, E, and F are such that the maximum flow rate value on the curve K (the flow rate when the MB rotation speed upper limit value is reached) is the minimum flow rate value on the straight line M (control valve). The flow resistance value of each control valve D to F is selected so that the maximum flow rate value on the curve L is equal to or higher than the minimum flow rate value on the curve N. By doing so, the fluctuation range of the pressure in the furnace due to the fluctuation of the exhaust flow rate at the time of switching the controlled object accompanying the switching of the open / close state of the on-off valves A, B, C can be suppressed to a small amount.

  Next, a pressure control method in the furnace during vacuum carburization by the apparatus having the above configuration will be described with reference to the flowcharts shown in FIGS. 9 to 11 and FIG. A plurality of furnace bodies 2 of the vacuum heat treatment apparatus 71 are loaded and sent with a processing material by a conveying means (not shown), and are subjected to a vacuum carburizing process separately in a carburizing chamber in each furnace body 2. The atmospheric gas discharged from each furnace body during the period to the diffusion period is exhausted by a vacuum pump (mechanical booster pump 7 and oil rotary pump 6).

Therefore, at the start of operation of the vacuum heat treatment device 71, the vacuum exhaust device 72 opens the on-off valve A to open the branch pipe 44a (step 81), and starts control of the mechanical booster pump 7 (step 82). The controller 73 controls the rotational speed of the mechanical booster pump 7 (hereinafter referred to as “MB rotational speed”) via the inverter 8 to maintain the pressure inside the furnace at the set pressure P ₀ , and the MB rotational speed n is controlled from the inverter 8 to the controller 73. Feedback. The pressure in the furnace body is controlled by controlling the MB rotation speed so as to obtain an exhaust gas flow rate corresponding to the atmospheric gas flow rate Q discharged from the furnace body 2 according to the curve J shown in FIG.

  When the atmospheric gas flow rate Q decreases and the MB rotational speed reaches the lower limit during the pressure control in the open state of the branch pipe 44a (step 83), the MB rotational speed is set as shown in FIG. The lower limit value is fixed (step 84), and it is confirmed that the on-off valve A is open (step 85). The control valve D of the pipe line is used as a control valve for opening control, and the control device 73 Pressure control in the furnace by the pressure control unit) is started (step 86). The pressure in the furnace body is controlled by controlling the opening of the control valve D so that an exhaust gas flow rate corresponding to the atmospheric gas flow rate Q discharged from the furnace body 2 is obtained according to the straight line M shown in FIG. The controllable range of the exhaust flow rate shifts to the straight line M in FIG. 8, and the furnace pressure can be controlled even when the atmospheric gas flow rate Q decreases.

  When the atmospheric gas flow rate Q decreases and the opening degree of the control valve D reaches the lower limit during the pressure control in the open state of the branch pipe 44a (control valve Don state) (step 87), it is opened and closed. The valve A is closed, the on-off valve B is opened, the branch pipe 44b is opened, the opening control of the control valve D is terminated (step 88), and the control of the mechanical booster pump 7 is resumed (step 82). As a result, the MB rotational speed control state in the open state of the branch pipe 44b on the high flow path resistance side is entered, so that the controllable range of the exhaust flow rate shifts to the curve K in FIG. However, the pressure inside the furnace can be controlled by the MB rotation speed control. When the atmospheric gas flow rate Q further decreases and the MB rotational speed reaches the lower limit during the pressure control in the open state of the branch pipe 44b (step 83), the MB rotational speed is fixed to the lower limit. (Step 84) After confirming that the on-off valve B is in an open state (Step 91), the control device 73 (its pressure control unit) uses the control valve E of the pipe as a control valve to be controlled for opening. The furnace pressure control is started (step 92). As a result, the controllable range of the exhaust flow rate shifts to the straight line N in FIG.

  When the atmospheric gas flow rate Q further decreases and the opening degree of the control valve E reaches the lower limit during pressure control in the open state (control valve Eon state) of the branch pipe 44b (step 93). Then, the on-off valve B is closed, the on-off valve C is opened, the branch pipe 44c is opened, the opening control of the control valve E is terminated (step 94), and the control of the mechanical booster pump 7 is resumed (step 82). As a result, the MB rotational speed control state in the open state of the branch pipe 44c on the high flow path resistance side is established, so that the controllable range of the exhaust flow rate shifts to the curve L in FIG. However, the pressure inside the furnace can be controlled by the MB rotation speed control. When the atmospheric gas flow rate Q further decreases and the MB rotational speed reaches the lower limit during the pressure control in the open state of the branch pipe 44c (step 83), the MB rotational speed is fixed to the lower limit. (Step 84) After confirming that the on-off valve C is in an open state (Step 97), the control device F (its pressure control unit) uses the control valve F of the pipe line as a control valve for opening degree control. The furnace pressure control is started (step 98). As a result, the controllable range of the exhaust flow rate shifts to the straight line O in FIG. 8, and the pressure in the furnace can be controlled even when the atmospheric gas flow rate Q decreases.

  On the other hand, when the atmospheric gas flow rate Q from the furnace body 2 increases in the pressure control state (opening state of the on-off valve C) by the control valve F and the control valve opening reaches the upper limit value (step 100). Then, the opening degree of the control valve F is fixed to the upper limit value (step 101), and the control of the mechanical booster pump 7 is resumed (step 82). As a result, the MB rotational speed control state in the open state of the branch pipe 44c is entered, so the controllable range of the exhaust flow rate shifts to the curve L in FIG. 8, and the MB rotational speed is increased even when the atmospheric gas flow rate Q is increased. The pressure inside the furnace can be controlled by the control.

  When the atmospheric gas flow rate Q further increases during the pressure control in the open state of the branch pipe 44c and the MB rotational speed reaches the upper limit (step 102), the MB rotational speed as shown in FIG. Is temporarily fixed to the upper limit (step 103), and it is confirmed that the on-off valve C is in the open state (step 106), the on-off valve C is closed, the on-off valve B is opened, and the branch pipe 44b is opened. The number is fixed to the lower limit value, the opening control of the control valve F is finished, and the opening control of the control valve E is started (step 107). As a result, the controllable range of the exhaust flow rate shifts to a straight line N in FIG. 8, and the pressure in the furnace can be controlled even when the atmospheric gas flow rate Q decreases. During the pressure control by the control valve E, when the atmospheric gas flow rate Q increases and the control valve opening reaches the upper limit (step 108), the opening of the control valve E is fixed to the upper limit (step 108). 109), the control of the mechanical booster pump 7 is resumed (step 82). As a result, the MB rotational speed control state in the open state of the branch pipe 44b is entered, so that the controllable range of the exhaust flow rate shifts to the curve K in FIG. The pressure inside the furnace can be controlled by the control.

  When the atmospheric gas flow rate Q further increases during the pressure control in the open state of the branch pipe 44b and the MB rotational speed reaches the upper limit (step 102), the MB rotational speed is temporarily fixed at the upper limit. (Step 103), confirm that the on-off valve B is in the open state (Step 105), close the on-off valve B, open the on-off valve A, open the branch pipe 44a, and set the MB speed to the lower limit. It fixes, the opening control of the control valve E is complete | finished, and the opening control of the control valve D is started (step 112). As a result, the controllable range of the exhaust flow rate shifts to a straight line M in FIG. 8, and the pressure in the furnace can be controlled even when the atmospheric gas flow rate Q decreases. During the pressure control by the control valve D, when the atmospheric gas flow rate Q further increases and the control valve opening reaches the upper limit (step 113), the opening of the control valve E is fixed to the upper limit ( Step 114), the control of the mechanical booster pump 7 is resumed (Step 82). As a result, the MB rotational speed control state in the open state of the branch pipe 44a is entered, so the controllable range of the exhaust flow rate shifts to the curve J in FIG. The pressure inside the furnace can be controlled by the control.

  As described above, the flowchart of FIG. 10 has been described when the atmospheric gas flow rate Q from the furnace body 2 is decreased, and the flowchart of FIG. 11 is described when the atmospheric gas flow rate Q is increased. When the gas flow rate Q increases and the opening degree of the control valve during opening degree control reaches the upper limit (steps 89 and 95), the opening degree of each control valve is set to the upper limit as described in the flowchart of FIG. (Steps 90 and 96) and switching to MB rotation speed control in the same branch pipe. Similarly, when the atmospheric gas flow rate Q is reversed and decreased in the flowchart of FIG. 11 and the opening of the control valve during the opening control reaches the lower limit (steps 110 and 115), as described in the flowchart of FIG. Then, the switching of the on-off valve and the opening control of the control valve are finished (steps 111 and 116), and the control may be switched to the MB rotational speed control in the branch line on the large flow resistance side.

  In the flowchart of FIG. 10, the opening degree of the control valve F reaches the lower limit value in step 99 when the actual exhaust flow rate from the furnace body falls below the initial assumed minimum flow rate, and in the flowchart of FIG. When the MB rotational speed reaches the upper limit value, the on-off valve A is in the open state at step 104 when the actual exhaust flow rate from the furnace body exceeds the initial assumed maximum flow rate. If these errors occur frequently, measures such as replacing the control valve F with a flow control valve having a larger flow resistance or replacing the mechanical booster pump 7 with a pump having a larger exhaust flow rate may be taken. .

Switching of branch pipes and switching of control valves to be controlled by opening / closing control of the on-off valves A to C performed according to the above flowcharts (FIGS. 9 to 11), and MB rotation speed control and control valve opening control Switching is performed by a switching control unit of the control device 45. Then, as shown in FIG. 8, by switching the exhaust flow passage and the control valve to be controlled for opening to the control valve having a high flow resistance, the MB rotation speed control in one branch pipe 44a that does not perform this switching is performed. The exhaust flow rate controllable range only by the range is the range V ₀ , whereas the range V is particularly compared with the first and second examples of the range V by the combination of the switching of the branch pipes and the control valve and the MB rotation speed control. A large exhaust flow rate controllable range can be obtained, and the exhaust in the atmosphere gas flow rate Q can be exhausted without excess or deficiency, and the furnace pressure can be maintained at a predetermined set pressure.

  The present invention is not limited to the above example. For example, in the third example, the control valve opening degree control in the open state of one branch pipe is performed in the state where the lower limit value of the MB speed is maintained. The opening degree control of the control valve may be performed in a state where the upper limit value of the MB rotational speed is maintained, or the MB rotational speed control and the opening degree control of the control valve may be performed simultaneously (in parallel). Good.

It is an equipment distribution diagram of a vacuum heat treatment apparatus showing an example of an embodiment of the invention according to claim 1. It is a diagram which shows the change of the exhaust flow volume with respect to the pump rotation speed in the vacuum exhaust apparatus of FIG. It is a flowchart of the branch line switching control operation | movement in the vacuum exhaust apparatus of FIG. It is an equipment distribution diagram of a vacuum heat treatment apparatus showing an example of an embodiment of the invention according to claim 2. It is a diagram which shows the change of the exhaust flow volume with respect to the opening degree of the flow control valve in the vacuum exhaust apparatus of FIG. 6 is a flowchart of a branch pipe line and flow rate control valve switching control operation in the vacuum exhaust device of FIG. 4. It is an equipment distribution diagram of a vacuum heat treatment apparatus showing an example of an embodiment of the invention according to claim 3. It is a diagram which shows the change of the exhaust flow volume with respect to the rotation speed of the pump in the vacuum exhaust apparatus of FIG. 7, and the opening degree of a flow control valve. It is a part of flowchart of the branch pipe line and flow control valve switching control operation | movement in the vacuum exhaust apparatus of FIG. It is a part of flowchart of the branch pipe line and flow control valve switching control operation | movement in the vacuum exhaust apparatus of FIG. It is a part of flowchart of the branch pipe line and flow control valve switching control operation | movement in the vacuum exhaust apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vacuum heat processing apparatus, 2 ... Furnace body, 3 ... Exhaust pipe line, 5 ... Vacuum exhaust apparatus, 6 ... Oil rotary pump, 7 ... Mechanical booster pump, 8 ... Inverter, 9 ... Vacuum gauge, 10 ... Control apparatus, 11 ... Branch part, 12a ... Branch line, 12b ... Branch line, 12c ... Branch line, 13a ... Flow control valve, 13b ... Flow control valve, 13c ... Flow control valve, 41 ... Vacuum heat treatment device, 42 ... Vacuum exhaust Device 43 ... Branching portion 44a ... Branching conduit 44b ... Branching conduit 44c ... Branching conduit 45 ... Control device 71 ... Vacuum heat treatment device 72 ... Vacuum exhaust device 73 ... Control device A ... Opening / closing Valve, B ... Open / close valve, C ... Open / close valve, D ... Flow control valve, E ... Flow control valve, F ... Flow control valve.

Claims (3)

In the vacuum exhaust apparatus of the vacuum heat treatment apparatus that controls the pressure in the furnace body by controlling the rotation speed of the vacuum pump connected to the furnace body through the exhaust pipe line,
The exhaust pipe is provided with a branch portion in which a plurality of branch pipes having different flow path resistances provided with on-off valves are arranged in parallel,
The on-off valve is controlled to open and close, and one branch pipe is selected as an exhaust flow path. When the number of revolutions of the vacuum pump reaches a lower limit value, the exhaust flow path is switched to a high resistance side branch pipe. A vacuum evacuation apparatus for a vacuum heat treatment apparatus, comprising switching control means for switching the exhaust flow passage to a branch pipe on the low resistance side when the rotational speed reaches an upper limit value. In the vacuum exhaust system of the vacuum heat treatment furnace that controls the pressure in the furnace body by controlling the opening degree of the flow rate control valve provided in the exhaust pipe connecting the furnace body and the vacuum pump,
The exhaust pipe is provided with a branch portion in which a plurality of branch pipes provided with on-off valves and flow rate control valves having different flow path resistances are arranged in parallel,
When the on-off valve is controlled to open and close, one branch pipe is selected as an exhaust flow passage, and when the opening of the flow control valve during the opening control of the exhaust flow passage reaches a lower limit value, The exhaust flow passage and the flow rate control valve subject to opening degree control are switched to the branch pipe having the high resistance side flow control valve and the flow rate control valve, and when the opening degree reaches the upper limit value, the exhaust flow passage and A vacuum evacuation apparatus for a vacuum heat treatment furnace, comprising a branch pipe having a flow resistance control valve on a low resistance side and switching control means for switching to the flow control valve. In the vacuum exhaust system of a vacuum heat treatment furnace that controls the pressure in the furnace body by controlling the number of rotations of a vacuum pump connected to the furnace body through an exhaust pipe line,
The exhaust pipe is provided with a branch portion in which a plurality of branch pipes provided with on-off valves and flow rate control valves having different flow path resistances are arranged in parallel,
Pressure control means for controlling the pressure in the furnace by opening control of one flow control valve selected from the flow control valves;
The flow control valve that controls opening and closing of the on-off valve to select one of the branch pipes as an exhaust flow passage, the rotation speed of the vacuum pump reaches a lower limit value, and the opening degree of the exhaust flow passage is being controlled. When the opening of the vacuum pump reaches the lower limit, the exhaust flow passage and the flow control valve subject to opening control are switched to the branch pipe having the high resistance flow control valve and the flow control valve, and the vacuum pump When the rotational speed reaches the upper limit value and the opening degree reaches the upper limit value, the exhaust flow passage and the flow control valve are switched to the branch pipe having the low resistance side flow control valve and the flow control valve. And a vacuum exhaust apparatus for a vacuum heat treatment furnace.

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