JPH1081913A - Isothermal quenching apparatus by gas cooling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an isothermal quenching apparatus easily controlling temp. with gas cooling. SOLUTION: This apparatus is provided with a pressure vessel 1, a gas pressure adjusting device 12 for adjusting the gas pressure in the pressure vessel 1, a furnace 2 surrounding a heat insulating wall arranged in the pressure vessel 1 and being openable/closable to a part of the heat insulating wall, a cooling line 8 arranged in the pressure vessel 1 and cooling the gas in the furnace with a heat exchanger 5 and circulating with a cooling fan 6, a heater 11 arranged in the furnace and heating the gas in the furnace, a circulating fan for circulating the gas in the furnace and a control part for controlling so that the surface temp. and the center temp. of a treating body 9 becomes a setting temps. by inputting the surface and the center temps. of the treating body 9, the temp. in the furnace and the pressure in the pressure vessel and controlling the gas pressure adjusting device 12, cooling line 8, heater 11 and circulating fan.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an isothermal quenching apparatus for performing isothermal quenching by gas cooling.

[0002]

2. Description of the Related Art Isothermal quenching (referred to as marquenching or martempering) is performed by quenching in a coolant maintained at a temperature above or slightly above the martensite formation temperature range of a workpiece (this is called a set temperature). Then, after each part is uniformly maintained at the temperature, a heat treatment method of cooling is performed to prevent generation of distortion and quenching cracks due to quenching, and to obtain an appropriate quenched structure.

[0003]

Conventionally, the isothermal quenching is performed by a salt bath treatment. In the salt bath treatment, the object to be processed is placed in a salt bath kept at a set temperature, and after the surface and the inside temperature are made uniform, it is removed from the salt bath and cooled. This method is widely used because of easy temperature control, but has a problem that the working environment is poor. For this reason, isothermal quenching by gas cooling is also performed, but there is a problem that temperature control is difficult.

[0004] The present invention has been made in view of the above-mentioned problems, and has as its object to provide an isothermal quenching apparatus by gas cooling which can easily control the temperature.

[0005]

According to the first aspect of the present invention, there is provided a pressure vessel, a gas pressure adjusting device for adjusting a gas pressure in the pressure vessel, and a heat insulating apparatus provided in the pressure vessel. A furnace surrounded by walls, a part of which can be opened and closed,
A cooling line provided in the pressure vessel and cooling the furnace gas with a heat exchanger and circulating with a cooling fan; a heater provided in the furnace for heating the furnace gas; and a furnace provided in the furnace and provided in the furnace. A circulation fan for circulating gas, a gas temperature sensor provided in the furnace for measuring the temperature of the gas in the furnace, a gas pressure sensor provided in the pressure vessel for detecting a gas pressure, and mounted in the furnace. The temperature sensor for measuring the surface and center temperatures of the object to be processed, the detected values of the gas temperature sensor and the gas pressure sensor are input, and the gas pressure adjusting device, the cooling line, the heater, and the circulation fan are controlled to A control unit that cools the body and controls the surface temperature and the center temperature of the object to be processed to be set temperatures.

[0006] By opening a part of the heat insulating wall of the furnace and cooling the gas in the furnace by a cooling line, the object to be processed is cooled to near a set temperature. At this time, by increasing the gas pressure in the pressure vessel by the gas adjusting device, the density of the gas in the furnace increases, the heat transfer capacity increases, and the cooling capacity of the cooling line increases. In addition, by closing the furnace wall and operating the circulation fan, uniformization of the surface temperature and the center temperature of the object to be processed is promoted. When the surface temperature is lower than the set temperature, the gas in the furnace is heated by the heater so that the surface temperature becomes close to the set temperature and the center temperature approaches the set temperature.
In this way, by cooling, pressurizing, heating and circulating the gas in the furnace, it is possible to control the surface temperature and the center temperature of the object to be processed to the set temperature.

According to the second aspect of the present invention, the control unit is configured to determine a difference D between a surface temperature T2 of the object to be processed and the set temperature T1.
According to (= T2−T1), in the cooling area of D> K1, the furnace is opened and the cooling line is operated, and the gas pressure in the furnace is adjusted by the gas pressure adjusting device according to the value of D. In the buffer region of ≧ D> K2, the cooling fan of the cooling line is stopped, the gas pressure in the furnace is kept at a constant value, the furnace gas is naturally circulated with the furnace opened, and the adjustment region of K2 ≧ D> −K3 is satisfied. In the heating zone of -K3 ≧ D, the furnace is closed and the circulating fan and the heater are operated, and the furnace gas pressure is set to a constant value. Control is performed with K2 and K3 being positive numbers.

The temperature control of the furnace gas in accordance with the difference D between the surface temperature T2 of the object to be processed and the set temperature T1 is performed in the following four cases. In the cooling zone where the difference D is larger than K1, the furnace is opened, and by operating the cooling line and the gas pressure adjusting device, the gas having a high density is cooled in the cooling line and circulated through the furnace to lower the temperature of the workpiece. . In the buffer region where D is between K1 and K2 temperatures, the cooling fan of the cooling line is stopped, the furnace gas pressure is kept at a constant value, and the furnace gas is naturally circulated through the cooling line. During the natural circulation, the object to be processed is cooled and the temperature approaches the set temperature. In the adjustment region where D is between K2 and -K3, the furnace is closed and the gas pressure in the furnace is kept at a constant value. In this case, the surface temperature of the object to be processed is almost the set value, but since the center temperature is higher than the set value, the gas naturally circulates in the furnace and exchanges heat with the object. At this time, when the circulation fan is operated, the temperature distribution in the furnace becomes uniform and the cooling time can be reduced. In the heating region where D is smaller than -K3, the gas pressure in the furnace is kept constant while the furnace is closed, and the circulation fan and the heater are operated. In this case, since the surface temperature of the object to be processed is too low than the set temperature, the object is heated to approach the set temperature. The center temperature continues cooling and approaches the set temperature. By performing such four-stage control, the surface temperature and the center temperature of the object to be processed can be set to the set temperature. Note that K
The values of 1, K2 and K3 are determined according to the material of the object to be processed.

According to the third aspect of the present invention, when the difference between the set temperature T1 of the object and the gas temperature in the furnace reaches a predetermined value in the heating area, the control unit sets the temperature T1 of the object.
It is determined that the difference between the temperature and the center temperature is within a predetermined range.

The center temperature of the object to be processed is different from the gas temperature in the furnace in the cooling region, the buffer region, and the adjustment region, but when the temperature approaches the set temperature T1 in the heating region, the gas temperature in the furnace also approaches the set temperature T1. This has been clarified experimentally. This makes it possible to measure the gas temperature in the furnace and determine that the difference between the set temperature T1 and the center temperature has fallen into a predetermined range when the difference between the set temperature T1 has reached a predetermined value. It is a useful method when it is difficult to provide a temperature sensor at the center of the object.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of the isothermal quenching apparatus of the present embodiment, and FIG. 2 is a sectional view taken along line XX of FIG. Reference numeral 1 denotes a pressure vessel which holds a negative pressure with respect to the atmospheric pressure. Reference numeral 2 denotes a furnace surrounded by heat insulating walls, and an upper lid 3a and a lower lid 3
b, a front lid 3c is provided, and the upper lid 3a and the lower lid 3b are opened for ventilation of gas in the furnace during cooling. The front lid 3c is opened and closed when the object 9 is carried in and out. 5 is a heat exchanger for cooling the gas in the furnace. Water is used as a coolant, and is supplied from the outside of the pressure vessel 1 through a pipe (not shown) and discharged. 6
The gas in the furnace is sucked into the heat exchanger 5 by a cooling fan, cooled, and circulated into the furnace 2 again. Numeral 7 denotes a gas distributor which distributes and supplies the cooling gas sent from the cooling fan 6 into the furnace so that the gas flows uniformly in the furnace. The heat exchanger 5, the cooling fan 6, and the gas distributor 7 constitute a cooling line 8. In the present embodiment, a case where the gas distributor 7 is provided will be described. However, the same processing can be performed without the device 7 and is not an indispensable device.

In the furnace 2, a support table 1 for supporting a workpiece 9 is provided.
0 is provided. The support base 10 is formed of a frame such as a lattice, and has a shape that allows sufficient ventilation. An electric heater 11 is provided for heating the object 9 along the peripheral wall, ceiling, and floor of the furnace 2. Reference numeral 12 denotes a gas pressure adjusting device for adjusting the gas pressure in the pressure vessel 1. Reference numeral 13 denotes a gas distributor driving device that adjusts the opening of the gas distributor 7 and adjusts the flow rate of the cooling gas circulating in the furnace. 14 is a lid driving device,
The upper lid 3a and the lower lid 3b of the furnace are opened and closed. Reference numeral 15 denotes a circulation fan provided in the furnace for forcibly circulating gas in the furnace with the upper and lower lids 3a and 3b and the front lid 3c of the furnace 2 closed. A heater electrode 16 supplies electric power to an electric heater in the furnace.

FIG. 3 shows a control block diagram for controlling the furnace. The control unit 20 is connected to a surface temperature sensor 21 for detecting the surface temperature of the object 9 and a center temperature sensor 22 for detecting the center temperature. Further, a gas pressure sensor 23 for detecting the internal pressure of the pressure vessel 1 and a gas pressure sensor inside the furnace. A gas temperature sensor 24 for detecting gas temperature is connected. The control unit 20 inputs the detection values of these sensors, and according to a preset procedure, the gas pressure adjusting device 12, the cooling line 8, and the circulation fan 1
5. Control the electric heater 11 and the lid driving device 14.

An isothermal quenching process performed by the isothermal quenching apparatus configured as described above will be described. In the isothermal quenching, the surface of the object 9 is cooled by cooling from an appropriate temperature determined by the material of the object 9 to the upper part of the martensite generation temperature range or a temperature slightly higher than the temperature (this is referred to as a set temperature T1). After the temperature at the center is set to the set temperature T1 within a predetermined allowable value, cooling is performed. The cooling gas used in the furnace is an inert gas such as a nitrogen gas or an argon gas.

The first embodiment will be described with reference to Table 1 and FIG. Table 1 shows a four-stage controlled cooling procedure of the present invention, and FIG. 4 shows a cooling temperature curve. In FIG. 4, the solid line indicates the center temperature of the object, the broken line indicates the surface temperature, and the diamond-shaped line indicates the furnace gas temperature. The object to be processed in the present embodiment is a medium material of carbon steel,
The case where the temperature is set to T1 = 370 ° C. and cooled from 1000 ° C. is shown. The surface temperature of the object to be processed is T2, the center temperature is T4, and the gas temperature in the furnace is T3. The four-stage control is performed based on the difference D = T2-T1 between the surface temperature T2 and the set temperature T1.

[0016]

[Table 1]

When the temperature difference D is equal to or higher than 10 ° C., it is called a cooling zone, the upper lid 3a and the lower lid 3b of the furnace 2 are opened, and the cooling line 8 is opened.
Is operated, and the gas pressure in the pressure vessel 1 is increased from 600 kPa to 130 kPa according to D by the gas pressure adjusting device 12.
Adjust until The cooling is promoted by increasing the gas pressure to increase the density of the cooling gas. In this cooling region, the surface temperature T2 rapidly decreases, but the decrease in the central temperature T4 is delayed. The gas temperature T3 in the furnace is rapidly lowered by passing through the heat exchanger 5.

The temperature difference D between 10 ° C. and 3 ° C. is called a buffer zone. Since the surface temperature T2 is almost approaching the set temperature T1, the cooling line 8 is stopped, and the pressure in the furnace is 130 k.
The pressure is maintained at Pa, the upper lid 3a and the lower lid 3b are opened, the natural gas circulation in the furnace is performed, and the central temperature T4 is awaited.
In this case, the heat exchanger 5 is operating. In this area,
The surface temperature T2 rises due to heat radiation from the center and then falls again. The center temperature T4 suddenly increases due to heat radiation.
Approach 2.

The range in which the temperature difference D is between 3 ° C. and −10 ° C. (that is, the surface temperature T2 is lower than the set temperature T1) is called an adjustment range. The surface temperature T2 has almost reached the set temperature T1, but the center temperature T4 has not yet reached T1. In this case, the upper lid 3a and the lower lid 3b of the furnace 2 are closed to bring the furnace 2 into a closed state, the circulation fan 15 is operated to circulate the furnace gas in the furnace, and the center temperature T4 is lowered. In this case, although the furnace 2 is constituted by a heat insulating wall, it has a heat radiation effect and the surface temperature T2 decreases, but the center temperature T4 has not yet reached the set temperature T1. The gas pressure is 130k
It is constant at Pa.

When the temperature difference D is between -10.degree. C. and -30.degree. C. or less, it is called a heating zone. Since the surface temperature T2 has dropped below the set temperature T1 while waiting for the center temperature T4 to drop to the set temperature T1, the electric heater 11 is operated with the circulation fan 15 operated. As a result, the furnace gas temperature T3 increases, and the surface temperature T3 increases.
2 rises and approaches the set temperature T1, and the central temperature T
4 is also approaching the set temperature T1 and has an allowable range (for example, 1
0 ° C). At this point, it is considered that the surface temperature T2 and the center temperature T4 have reached the set temperature T1, and the cooling control ends. In this case, the in-furnace gas temperature T3 sharply rises and comes to be fairly close to the set temperature T1. Thereafter, the electric heater 11 is stopped, the circulation fan 15 is stopped, the upper lid 3a and the lower lid 3b of the furnace 2 are opened, and cooling by the cooling line 8 is performed.

Next, a second embodiment will be described with reference to Table 2 and FIG. Table 2 shows a four-stage controlled cooling procedure of the present invention, and FIG. 5 shows a cooling temperature curve. The meaning of each curve in FIG. 5 is the same as that in FIG. The object to be processed in this embodiment is a case of a large carbon steel, and the set temperature T1 = 370 ° C.
Cool from 0 ° C. The difference from the first embodiment is that the object to be processed is a large object, and the cooling in the cooling area is performed under the same conditions without performing stepwise cooling.

[0022]

[Table 2]

In Table 2 and FIG. 5, the gas pressure in the pressure vessel 1 was kept constant at the initial cooling set pressure of 600 kPa until the temperature difference D between the surface temperature T2 and the set temperature T1 once became 3 ° C. or less. Cooling is performed with only 8. Thereafter, the gas pressure in the pressure vessel 1 is set to 130 kPa, and when the temperature becomes equal to or higher than + 10 ° C. according to the value of the temperature difference D, the cooling zone is operated, and thereafter, the buffer zone from 10 ° C. to 3 ° C. The treatment in the adjustment range from -10 ° C to -10 ° C and the heating range below -10 ° C is the same as in Table 1 and FIG.

In the above embodiment, the center temperature T4 of the object is measured by a thermocouple provided at the center of the object. However, there is a case where the thermocouple cannot be set at the center as described above depending on the object to be processed. At the end of the heating zone in FIGS. 4 and 5, that is, when the surface temperature T2 and the center temperature T4 coincide with the set temperature T1 within an allowable deviation (for example, 10 ° C.),
As shown by a circle A in the figure, the furnace gas temperature T3 is also approaching the set temperature T1. Furnace gas temperature T3 and set temperature T
When the difference from 1 becomes a predetermined value, it can be determined that the center temperature T4 has reached the set temperature T1. The predetermined value is determined based on data obtained by measuring the center temperature and isothermally quenching the workpieces having the same material and substantially the same size. If there is data on the isothermal quenching of the object to be processed having the same material and size, the same processing is performed, and the surface temperature T2 and the center temperature T2 are set by the timer.
4 can reach the set temperature T1.

[0025]

As is apparent from the above description, the present invention relates to a gas pressure regulating device in a furnace: a cooling line, a circulating fan in the furnace, and a heater. Isothermal quenching can be performed by detecting the internal gas temperature and performing gas cooling. Also, by setting and processing the cooling area, the buffer area, the adjustment area, and the heating area based on the temperature difference between the surface temperature and the set temperature, it is possible to perform the isothermal quenching with high accuracy. At this time, the center temperature can be estimated from the gas temperature in the furnace instead of measuring the center temperature.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an isothermal quenching apparatus according to the present embodiment.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a diagram showing a control system.

FIG. 4 is a diagram showing a processing temperature curve of the first embodiment.

FIG. 5 is a diagram illustrating a processing temperature curve according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pressure vessel 2 Furnace 3a Upper lid 3b Lower lid 3c Front lid 5 Heat exchanger 6 Cooling fan 7 Gas distributor 8 Cooling line 9 Workpiece 10 Support stand 11 Electric heater 12 Gas pressure adjusting device 13 Gas distributor driving device 14 Cover Drive device 15 Circulation fan 16 Heater electrode

Claims (3)

[Claims] 1. A pressure vessel, a gas pressure adjusting device for adjusting a gas pressure in the pressure vessel, and a furnace provided in the pressure vessel and surrounded by a heat insulating wall, and a part of the heat insulating wall can be opened and closed. A cooling line provided in the pressure vessel and cooling the furnace gas with a heat exchanger and circulating with a cooling fan; a heater provided in the furnace to heat the furnace gas; and a furnace provided in the furnace. A circulation fan for circulating the internal gas, a gas temperature sensor provided in the furnace for measuring the temperature of the gas in the furnace, a gas pressure sensor provided in the pressure vessel for detecting the gas pressure, and mounted in the furnace. The temperature sensor for measuring the surface and center temperature of the object to be processed, the gas temperature sensor, and the detection values of the gas pressure sensor are input, and the gas pressure regulator, the cooling line, the heater, and the circulation fan are controlled to control the temperature. Cool the processing object, and adjust the surface temperature and An isothermal quenching device by gas cooling, comprising: a control unit for controlling a core temperature to a set temperature. 2. The control section opens a furnace in a cooling area where D> K1 according to a difference D (= T2−T1) between a surface temperature T2 of the object to be processed and the set temperature T1. Activating the cooling line and adjusting the gas pressure in the furnace by the gas pressure adjusting device according to the value of D. In a buffer region of K1 ≧ D> K2, the cooling fan of the cooling line is stopped and the gas pressure in the furnace is reduced. Is constant, the furnace gas is naturally circulated while the furnace is open, the furnace is closed in the adjustment range of K2 ≧ D> −K3 and the furnace gas pressure is maintained at a constant value, and in the heating range of −K3 ≧ D, The gas cooling according to claim 1, wherein the furnace is closed, the circulation fan and the heater are operated, the gas pressure in the furnace is set to a constant value, and K1, K2, and K3 are set to positive numbers, and control is performed. By isothermal quenching equipment. 3. The method according to claim 1, wherein when the difference between the set temperature of the object to be processed and the gas temperature in the furnace reaches a predetermined value in the heating area, the control unit determines a difference between the set temperature of the object to be processed and the center temperature. 3. The isothermal quenching apparatus by gas cooling according to claim 2, wherein it is determined that the temperature falls within a predetermined range.