JPH02205623A - Cooling method for material to be treated in vacuum furnace and vacuum furnace - Google Patents

Abstract

PURPOSE:To cool a metallic member heated for the purpose of a heat treatment down to a target temp. in a short period of time at a specified linear cooling rate by continuously measuring the temp. of the metallic member and controlling the flow velocity and pressure of a cooling gas by the measured value thereof at the time of cooling the metallic member by the cooling gas. CONSTITUTION:After the metallic member 12 to be heated is put into a heating furnace 1, the inside of the furnace is evacuated to a vacuum by a vacuum pump 22 and a heater 7 is energized to heat the material 12 to be treated to a prescribed temp., by which the material is heat treated. When the material is cooled, a control valve 17 provided in a pipeline 21 of a cooling gas source 20 is opened to introduce the cooling gas, such as Ar, into the furnace and the cooling gas is circulated, as shown by arrows 31, by rotation of a fan 10 to cool the material 12 to be treated. The pressure of the cooling gas is set by a pressure setter 30 in this case and the temp. decreasing rate and the control range thereof are previously set by a controller 26. The temp. in the furnace is continuously detected by a temp. detector 15 and a flow means 8 for the cooling gas is controlled by a controller 27 in accordance with the detected temp.; in addition, the pressure of the cooling gas in the furnace is controlled by regulating the opening degree of a control valve 19 in a pipeline 24 communicating with the furnace body, by which the material 12 to be treated is linearly cooled down to the desired temp. in a short period of time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for cooling a heated workpiece in a vacuum furnace for heat-treating a workpiece, and a vacuum furnace equipped with a means for cooling the heated workpiece. Regarding.

[Conventional technology]

In this type of vacuum furnace, when a heated workpiece is cooled, the workpiece is left in the furnace and allowed to cool naturally.

[Problem to be solved by the invention]

This cooling method has the problem that it takes a very long time to cool the object to a desired low temperature. In order to solve this problem, cooling gas is fed into the furnace and is continuously circulated through a space in which the workpiece is kept by a distribution means. However, in this method, the temperature of the object to be processed decreases at a fast rate during the process from high to medium temperature, and slows down during the process from medium to low temperature. The temperature of the object to be processed decreased as shown in the curve below. That is, there is a problem in that the cooling conditions for the object to be processed are different between the former process and the latter process.

The present invention has been made in view of the above points, and its purpose is to cool the object to be processed in a short time based on thermal theory, and to cool the object to be processed at a predetermined linear cooling rate. An object of the present invention is to provide a method for cooling a workpiece in a vacuum furnace and a vacuum furnace.

[Means to solve problems]

In order to achieve the above object, the present invention takes the measures as described in the claims above, and its effects are as follows.

[Effect]

Cooling gas is passed through the workpiece storage space, and the workpiece is cooled by the gas. During the cooling process, the temperature of the object to be processed is continuously detected. The flow rate and pressure of the cooling gas are controlled based on the detected temperature, and the object to be processed is cooled at a predetermined linear temperature drop rate.

〔Example〕

The drawings showing the embodiments of the present application will be described below.

In FIG. 1, numerals 1 to 11 indicate well-known members in a vacuum furnace; 1 is a hollow furnace body; 2 is a heat insulating chamber having heat insulating lids 3 and 4 which can be opened and closed; The interior space of the heat insulating chamber 2 serves as a storage space 5 for the object 12 to be processed. 7 is a heater, 8 is a cooling gas distribution means, and a prototype consisting of a motor 9 and a fan 10 rotated by the motor is used. 11
is a gas cooling colander, and the cooling water is distributed as shown by the arrow.

Next, the control system of the vacuum furnace will be explained. A temperature detection means 15 is used to detect the temperature of the object 12 to be processed.

In this example, by detecting the temperature of the storage space 5, the temperature of the object to be processed 12 corresponding thereto is indirectly detected, and for example, a thermocouple is used.

The temperature detection means 15 may be connected to the object 12 to directly detect the temperature of the object 12. 16 indicates a pressure adjustment means, which adjusts the pressure of the cooling gas in the internal space of the furnace body l. In this example, there are three control valves 17.
It is configured using ~19. The control valve 17 is installed in the pipe line 21 that connects the furnace body 1 and the cooling gas supply source 20, and the control valve 18 is installed in the pipe line 21 that connects the furnace body l and the vacuum pump 22.
3, and the control valve 19 is interposed in a conduit 24 whose one end is connected to the furnace body l and the other end is open. 25
indicates a control means, which is composed of members indicated by numerals 26 to 30. 26 is a controller, which controls the object to be processed 1;
A program controller is used in which the temperature decreasing rate and the control range (deviation) of the temperature decreasing rate can be set in advance. Reference numeral 27 denotes a regulator for regulating the operating strength of the flow means, and an inverter for regulating the rotational speed of the motor 9 is used, for example. Reference numeral 28 denotes a heat generation amount regulator for the heater 7, for example, a circuit using a thyristor is used. A pressure transmitter 29 is designed to detect the pressure within the furnace body 1 and output a detection signal. 30 is a pressure setting device for setting the pressure inside the furnace body 1.

Describing the heat treatment of the workpiece 12 using the vacuum furnace 0 As is well known, the inside of the furnace body 1 is evacuated and the insulating lid 3.4 is closed. In this state, the heater 7 is energized and placed in the storage space 5. The treated object 12 is heated to a predetermined temperature.

After the heating step or the heating and soaking step performed as described above is completed, the cooling step is performed as follows. That is, the heat insulating lid 3.4 is opened, the control valve 17 is opened, and a cooling gas, such as an inert gas such as nitrogen or argon, is supplied to the furnace body 1.
be introduced within. The introduced cooling gas is circulated as shown by an arrow 31 by the operation of the blower 8 and flows through the storage space 5 .

The object to be processed 12 in the holding space 5 is cooled by the circulation of the cooling gas.

In the case of the above cooling, the operating strength of the flow means 8 or its operating strength and the pressure of the cooling gas in the furnace body 1 are adjusted as follows, and the workpiece 12 is cooled at a preset temperature decreasing rate. . That is, first, the pressure of the cooling gas is set using the pressure setting device 30, and the temperature lowering rate and the temperature lowering rate control range (deviation) are set using the controller 26. When the cooling process is performed in this setting state as described above, the detection means 15 continuously detects the temperature of the holding space 5, for example, as shown by the graph A in FIG. The controller 26 receives the signal from the above detection and moves the object 1 to be processed.
The actual temperature decreasing rate of 2 is calculated, and if it exceeds the set temperature decreasing rate, a command is given to the regulator 27 to reduce the operating strength of the distribution means 8. Then, the regulator 27
Decrease the rotation speed. As a result, the flow rate of the cooling gas flowing through the retention space 5 decreases, and the rate of temperature drop of the object to be processed 12 decreases. On the other hand, in the opposite case, controller 2
Since G issues a command to increase the operating strength of the circulation means 8, the rotational speed of the motor 9 increases, and as a result, the flow rate of the cooling gas increases and the rate of temperature drop of the object to be processed 12 increases.

In this way, the object to be processed 12 is cooled at a preset linear cooling rate, as shown, for example, in the graph B in FIG. Although the operating strength of the above-mentioned circulation means 8 is continuously variable in this example, it may be variable stepwise.Also, the continuous detection mode of the temperature by the detection means 15 is not limited to continuous detection. In the case of intermittent detection, if the temperature drop rate of the object 12 to be processed is fast, it is better to shorten the detection interval to obtain the necessary and sufficient detection accuracy. In some cases, the time just before detection may be extended.

In the above case, if the detected rate of temperature decrease of the object to be processed 12 exceeds the control range of the rate of temperature decrease by adjusting the operating strength of the flow means 8, the set pressure of the pressure setting device 30 is determined by a command from the controller 26. For example, if the detected temperature decreasing rate is too small, the set pressure is increased, and if it is too large, the set pressure is decreased.

As a result, the pressure of the cooling gas in the storage space 5 rises or falls, respectively, so the temperature drop rate of the object to be processed 12 increases in the former case and decreases in the latter case, both of which are controlled by the above-mentioned control. fall within range. Therefore, by adjusting the operating strength of the circulation means 8, the object to be treated 12 is cooled at a preset temperature decreasing rate.

The operation of the pressure regulating means when the enhanced setting pressure is changed is as follows. First, when the set pressure is increased, the control valve 17 is opened as appropriate in response to a command from the controller 26. As a result, the cooling gas supply source 20
Cooling gas flows into the furnace body 1, and the pressure increases. On the other hand, when the set pressure is lowered, the following two modes of operation are selectively performed. When the pressure inside the furnace body 1 is above atmospheric pressure, the control valve 19 is opened, and the cooling gas inside the furnace body 1 is discharged. Conversely, when the pressure inside the furnace body 1 is below atmospheric pressure, the control valve I8 is opened. The cooling gas inside the furnace body I is drawn out by the vacuum pump 22 . Due to these actions, the furnace body 1
The internal pressure decreases.

Next, Table 1 shows examples of various set temperature reduction rates and the set pressures of the furnace cooling gas in each case.

Table 1 In Table 1, for example, if the set cooling rate is 100'C/
If the set pressure is 2250 Torr, the actual temperature drop rate of the workpiece 12 is 100'C.
First, the operating strength of the flow means 8 is controlled so that the flow rate is 1/min. If the temperature drop rate detected during cooling is too small and exceeds the control range, the set pressure is set to 4/30.
The pressure is changed to 00 Torr, and the operating strength of the flow means 8 is controlled in that state. If it is still insufficient, the next step is changed to 3750 Torr in 5 and the same control is performed. 0 If it is too large, then 1500 Torr in 2
, 1 and 760 Torr, and the same control as above is performed.

Next, FIGS. 3(A) to 3(D) show various examples of temperature control patterns in the cooling process in the vacuum furnace,
In either case, by setting such a pattern in the controller 26 in advance, the temperature change of the object to be processed can be controlled in such a pattern.

First, (a) and (b) in (A) respectively show examples of different set temperature decreasing rates.

(B) shows an example in which the set temperature decreasing rate is changed at a point in the middle of the cooling process. In this case, the temperature decreasing rate in (c) and (e) is, for example, 100'C/min, and the temperature decreasing rate in (d) is, for example, 15 (1/min).

(C) is an example in which the workpiece is held at a constant temperature in the section (f) during cooling, and (D) is an example in which the workpiece is held at a constant temperature in the sections (g) and (su). , (H), the operation of the flow means 8 is stopped, and the heater 7 is Electricity is applied to heat the object 12 to be processed. In this case, based on the detected value by the temperature detection means 15, the electric power to the heater 7 is controlled by the heat generation amount regulator 28 in response to a command from the controller 26. For example, natural cooling is Sufficient electric power is supplied to compensate for this, and electric power sufficient to raise the temperature of the workpiece 12 at a predetermined temperature increase rate is supplied in the section (h). As a result, the temperature of the object 12 to be processed is controlled as set.

〔Effect of the invention〕

As described above, in the present invention, when the workpiece 12 is cooled in the furnace, the temperature of the workpiece 12 is lowered quickly by the flow of cooling gas, and the workpiece 12 is cooled to a desired low temperature in a short time. There is an effect that can be done.

Furthermore, since the temperature can be lowered at a linear rate during cooling, it is possible to lower the temperature at the same rate when bringing the object to be processed from a high temperature to a medium temperature or from a medium temperature to a low temperature. There are features that make it possible.

Moreover, it is linear like the one above! ! ! Since the flow rate of the cooling gas is controlled so as to achieve the temperature rate, it also has the advantage that the linear temperature drop rate (temperature gradient B in FIG. 2) can be varied in various ways.

For example, when cooling powder for magnets during sintering, it is necessary to repeatedly produce products of varying quality depending on the cooling process, and to obtain uniform products at any time. There are advantages that can be achieved.

[Brief explanation of the drawing]

The drawings show an embodiment of the present application, and FIG. 1 schematically shows the configuration of a vacuum furnace and shows its control system in blocks, FIG. 2 is a graph showing an example of a temperature control pattern, and FIG.
A) to (D) are diagrams showing different examples of temperature control patterns. l... Furnace body, 5... Storage space, 8... Distribution means,
12... Workpiece, 15... Temperature detection means, 16.
. . . Pressure adjustment means, 25 . . . Control means. Figure Time Figure (A) (D) Time

Claims (1)

[Claims] 1. A method for cooling the workpiece placed in the space by circulating cooling gas in a space for holding the workpiece in a vacuum furnace, wherein the temperature of the workpiece is maintained continuously. A method for cooling a workpiece in a vacuum furnace, characterized in that the flow rate of cooling gas in the space is controlled so that the temperature drop rate of the workpiece becomes a predetermined linear temperature fall rate. . 2. The workpiece in the vacuum furnace according to claim 1, wherein the pressure and flow rate of the cooling gas in the space are controlled so that the temperature drop rate of the workpiece becomes a predetermined linear temperature fall rate. How to cool things. 3. The method for cooling a workpiece in a vacuum furnace according to claim 1 or 2, wherein the predetermined temperature decreasing rate is changed midway through the cooling process. 4. In a vacuum furnace, the furnace body, which has a storage space for the workpiece inside, is equipped with a flow means for circulating cooling gas into the space, and the workpiece left in the storage space is A temperature detection means for detecting the temperature, a pressure adjustment means for adjusting the pressure of the cooling gas in the space, and a temperature reduction of the workpiece based on the temperature of the workpiece detected by the detection means. A vacuum furnace characterized by comprising: control means for controlling the operating strength of the flow means and the set pressure of the pressure adjustment means so that the speed becomes a predetermined linear temperature decreasing rate. .