COOLING DEVICE AND THERMAL TREATMENT DEVICE

Abstract

A cooling device cools a workpiece using a mist-like coolant and includes a heat transfer coefficient switching device that switches a heat transfer coefficient of the mist-like coolant from a relatively low state to a relatively high state during cooling the workpiece.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application based on PCT Patent Application No. PCT/JP2017/006551, filed on Feb. 22, 2017, whose priority is claimed on Japanese Patent Application No. 2016-058930, filed on Mar. 23, 2016. The contents of both the PCT Patent Application and the Japanese Patent Application are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a cooling device and a thermal treatment device.

BACKGROUND ART

For example, Patent Document 1 discloses a quenching device. The quenching device, when a mist-like coolant is blown onto a part heated to a predetermined temperature so as to cool the part, lowers the atmospheric pressure before a temperature of the part exceeds a martensitic transformation temperature and lowers the boiling point of the coolant. According to the quenching device, a vapor film generated between a surface of the part and a droplet of the coolant is maintained by lowering the boiling point of the coolant, and thus, it is possible to suppress distortion or deformation of the part.

CITATION LIST

Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2013-181226

SUMMARY

Technical Problem

In the above-described quenching device, the distortion or the deformation of the part is suppressed by maintaining the vapor film. However, complicated factors such as a shape of the part which is a workpiece are involved in order to maintain the vapor film, and thus, it is difficult to stably maintain the vapor film by only lowering the boiling point of the coolant during a cooling period of the workpiece until the temperature of the workpiece exceeds the martensitic transformation temperature from a start of cooling. That is, it is not always practical to maintain the vapor film so as to suppress the distortion or the deformation of the part, and it is difficult to reliably suppress the distortion or the deformation of the workpiece.

The present disclosure is made in consideration of the above-described circumstances, and an object thereof is to reliably suppress the deformation of the workpiece when the workpiece is cooled by the mist-like coolant more than the related art.

Solution to Problem

In order to achieve the object, in the present disclosure, as a first solution, there is provided a cooling device which cools a workpiece using a mist-like coolant, including: heat transfer coefficient switching device that switches a heat transfer coefficient of the mist-like coolant from a relatively low state to a relatively high state during cooling the workpiece.

According to the present disclosure, a technique for switching the heat transfer coefficient of the mist-like coolant from the relatively low state to the relatively high state during cooling the workpiece is used, and thus, it is possible to suppress the deformation of the workpiece more reliably than the related art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a first longitudinal sectional view showing an overall configuration of a cooling device and a multi-chamber thermal treatment device according to an embodiment of the present disclosure.

FIG. 2 is a second longitudinal sectional view showing the overall configuration of the cooling device and the multi-chamber thermal treatment device according to the embodiment of the present disclosure.

FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2.

FIG. 4 is a cross-sectional view taken along line B-B in FIG. 2.

FIG. 5A is a graph showing a temperature change of a cooling treatment in the embodiment of the present disclosure.

FIG. 5B is a graph showing a change of mist particle diameters of a mist-like coolant in the cooling treatment in the embodiment of the present disclosure.

FIG. 6 is a graph showing a thermal conductivity of each cooling medium.

FIG. 7 is a graph showing a relationship between an injection amount of each nozzle and a heat transfer coefficient in an experimental result of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a cooling device R and a multi-chamber thermal treatment device M according to an embodiment of the present disclosure will be described with reference to the drawings.

As shown in FIG. 1, the multi-chamber thermal treatment device M is a thermal treatment device in which the cooling device R, an intermediate conveyance device H, and three heating devices are integrated with each other. In addition, FIG. 1 is a longitudinal sectional view at a center position in a horizontal direction of the intermediate conveyance device H, and in FIG. 1, two heating device among the three heating devices, that is, only a heating device K1 and a heating device K2 are shown.

The multi-chamber thermal treatment device M is a thermal treatment device for performing a quenching treatment on a workpiece X. The workpiece X is various metal parts, and is a part which is formed of a steel material such as die steel (SKD material) or high-speed steel (SKH material).

The cooling device R is a device for performing a cooling treatment on the workpiece X, and as shown in FIGS. 1 to 4, includes a cooling chamber 1, a plurality of first and second cooling nozzles 2a and 2b (first and second injection nozzles), a plurality of mist headers 3, a cooling pump 4, a heat exchanger 5, a cooling drain tube 6, a cooling water tank 7, first and second control valves 8a and 8b, a cooling control unit 9, or the like.

The plurality of mist headers 3, the cooling pump 4, the heat exchanger 5, the cooling water tank 7, the first and second control valves 8a and 8b, and the cooling control unit 9 configure a cooling supply device in the present disclosure. Moreover, the coolant supply device and the plurality of first and second cooling nozzles 2a and 2b configure the heat transfer coefficient switching device in the present disclosure.

The cooling chamber 1 is a vertically cylindrical container (a container whose central axis is in a vertical direction) which accommodates the workpiece X, and an internal space of the cooling chamber 1 is a cooling compartment RS. The intermediate conveyance device H is provided on the cooling chamber 1. An opening through which the cooling compartment RS communicates with the internal space (conveyance chamber HS) of the intermediate conveyance device H is formed in the cooling chamber 1. The workpiece X is loaded on or unloaded from the cooling compartment RS through the opening.

The plurality of first and second cooling nozzles 2a and 2b are the first and second injection nozzles which convert a predetermined coolant supplied from the cooling pump 4 via the mist headers 3 and the heat exchanger 5 into a mist-like coolant to inject the mist-like coolant to the workpiece X. Each of the first cooling nozzles 2a is a first injection nozzle of an injection hole having a relatively small hole diameter (first hole diameter) and each of the second cooling nozzles 2b is a second injection nozzle of an injection hole having a hole diameter (second hole diameter) larger than that of the first cooling nozzle 2a. That is, the particle diameter (first mist particle diameter) of the mist-like coolant injected from the first cooling nozzle 2a is smaller than the particle diameter (second mist particle diameter) of the mist-like coolant injected from the second cooling nozzle 2b. In addition, a supply destination of the coolant is switched from the first injection nozzle (first cooling nozzle 2a) to the second injection nozzle (second cooling nozzle 2b), and thus, the mist particle diameter of the mist-like coolant can be adjusted from the first mist particle diameter to the second mist particle diameter. In addition, the heat transfer coefficient switching device adjusts the mist particle diameter of the mist-like coolant from a relatively small particle diameter to a relatively large particle diameter to switch the heat transfer coefficient of the mist-like coolant.

As shown in FIGS. 1 to 4, the plurality of first and second nozzles 2a and 2b are disposed so as to be distributed around the workpiece X accommodated in the cooling compartment RS. More specifically, the plurality of first and second cooling nozzles 2a and 2b are disposed to be distributed around the workpiece X such that the cooling nozzles 2a and 2b surround the entire workpiece X and distances between the cooling nozzles 2a and 2b and the workpiece X are the same as each other as possible in a state where the cooling nozzles 2a and 2b are disposed in multiple stages (specifically, five stages) in the vertical direction and are separated from each other at a predetermined interval in a circumferential direction of the cooling chamber 1 (cooling compartment RS).

In addition, the plurality of first and second cooling nozzles 2a and 2b are grouped into a predetermined number. That is, the plurality of first and second cooling nozzles 2a and 2b are grouped for each stage in the vertical direction of the cooling compartment RS and are also grouped in plural in the circumferential direction of the cooling chamber 1 (cooling compartment RS). As shown in FIGS. 3 and 4, the mist header 3 is individually provided in each of a plurality of groups (nozzle groups).

More specifically, as shown in FIG. 1, the mist headers 3 are disposed in five stages in the vertical direction, and as shown in FIG. 3, two mist headers 3 are provided on the uppermost stage in an arc shape so as to surround the vicinity of the workpiece X. In addition, as shown in FIG. 4, three mist headers 3 are provided on each of four stages of the second stage from above to the lowermost stage, in an arc shape so as to surround the vicinity of the workpiece X. Among the mist header 3 having the five-stage configuration, the plurality of second cooling nozzles 2b are provided on the mist headers 3 of the uppermost stage, the mist headers 3 of the third stage from above, and the mist headers 3 of the uppermost stage, and in addition, the plurality of first cooling nozzles 2a are provided on the mist headers 3 of the second stage and the fourth stage from above. The plurality of first and second cooling nozzles 2a and 2b are adjusted such that a direction of each nozzle axis faces a direction of the workpiece X and inject the coolant supplied from the pump 4 via the mist headers 3 toward the workpiece X.

As shown in FIG. 1, the plurality of second cooling nozzles 2b belonging to the uppermost stage are disposed at a position higher than an upper end of the workpiece X in the vertical direction. Meanwhile, the plurality of second cooling nozzles 2b belonging to the lowermost stage are disposed at approximately the same height as that of a lower end of the workpiece X. In addition, the plurality of second cooling nozzles 2b belonging to the uppermost stage are disposed inside the first and second cooling nozzles 2a and 2b of other stages, that is, are disposed to be further separated from an inner surface of the cooling compartment RS than the first and second cooling stages 2a and 2b of other stages.

Here, the coolant is a liquid having viscosity lower than a cooling oil which is generally used for cooling in the heat treatment, and for example, is a water. The shape of each of the injection holes of the plurality of first and second cooling nozzles 2a and 2b is set such that the coolant such as a water is uniform at a predetermined injection angle and becomes a droplet having a predetermined particle diameter. In addition, as shown in FIGS. 1 to 4, the injection angle of each of the plurality of first and second nozzles 2a and 2b and an interval between the adjacent first and second cooling nozzles 2a and 2b are set such that droplets positioned on an outer peripheral side among the droplets injected from the first and second cooling nozzles 2a and 2b intersect or collide with the droplets on the outer peripheral side from the adjacent first and second cooling nozzles 2a and 2b.

In addition, the plurality of first and second cooling nozzles 2a and 2b inject the mist-like coolant to the workpiece X such that the entire workpiece X is surrounded by aggregation of the droplets, that is, the mist-like coolant. In the mist-like coolant, for example, the particle diameter of the droplet is 20 to 700 μm. Positions and angles of the plurality of first and second cooling nozzles 2a and 2b are appropriately set such that the mist-like coolant around the workpiece X has a uniform particle diameter and a uniform density.

The cooling device R of the present embodiment is a device for cooling the workpiece X using the mist-like coolant, that is, is a device which mist-cools the workpiece X. In addition, a cooling condition such as a cooling temperature or a cooling time in the cooling device R is appropriately set according to an object of the heat treatment in the workpiece X, a material of the workpiece X, or the like.

The plurality of mist headers 3 described above are an arc-shaped pipe communicating with the plurality of first and second cooling nozzles 2a and 2b, and distribute the coolant taken in from a supply port to the plurality of first and second cooling nozzles 2a and 2b. In the mist headers 3, the positions of the supply ports are set such that pressure losses in the plurality of first and second cooling nozzles 2a and 2b are approximately the same as each other, and thus, the coolant is uniformly distributed to the plurality of first and second nozzles 2a and 2b.

Here, the heat transfer coefficient of the mist-like coolant injected from the plurality of first and second nozzles 2a and 2b toward the workpiece X is dependent on the particle diameter (mist particle diameter) of the mist-like coolant. In addition, the mist particle diameter is determined by the hole diameters (first and second hole diameters) of the injection holes of the first and second cooling nozzles 2a and 2b. That is, the mist-like coolant having the first mist particle diameter injected from the first cooling nozzle 2a having the first hole diameter has a relatively small mist particle diameter, and thus, the heat transfer coefficient (first heat transfer coefficient) thereof is relatively low. Meanwhile, the mist-like coolant having the second mist particle diameter injected from the second cooling nozzle 2b having the second hole diameter has a mist particle diameter larger than the first mist particle diameter, and thus, the heat transfer coefficient (second heat transfer coefficient) thereof is relatively low.

The cooling pump 4 pumps the coolant of the cooling water tank 7 to the mist headers 3. The heat exchanger 5 is a temperature controller which adjusts (maintains) the temperature of the coolant supplied from the cooling pump 4 to the mist headers 3 to a predetermined temperature, based on a temperature instruction input from the cooling control unit 9. That is, the temperature of the coolant supplied from the cooling pump 4 to the mist headers 3 is controlled by the cooling control unit 9.

The cooling drain tube 6 is a pipe which communicates with a lower portion of the cooling chamber 1 and the cooling water tank 7, and a drain valve (not shown) is provided in an intermediate portion of the cooling drain tube 6. The cooling water tank 7 is a liquid container in which the coolant drained from the cooling chamber 1 via the cooling drain tube 6 or a cooling circulation pipe (not shown) is stored. In addition, the cooling circulation pipe is a pipe which communicates with an upper portion of the cooling chamber 1 and an upper portion of the cooling water tank 7 in order to return the coolant which has flowed from the cooling chamber 1 to the cooling water tank 7 during immersion cooling.

The first and second valves 8a and 8b are an on-off valve which is provided between the plurality of mist headers 3 and the heat exchanger 5. In the first and second control valves 8a and 8b, the second control valve 8b is provided between the mist header 3 of the uppermost stage, the third stage from above, and the lowermost stage in which the second cooling nozzles 2b are provided and the heat exchanger 5, and the first control valve 8a is provided between the mist headers 3 of the second stage and fourth stage from above in which the first cooling nozzles 2a are provided and the heat exchanger 5. That is, the first control valve 8a switches supply/non-supply of the coolant to the plurality of first cooling nozzles 2a, based on a first opening/closing signal input from the cooling control unit 8. Meanwhile, the second control valve 8b switches supply/non-supply of the coolant to the plurality of second cooling nozzles 2b, based on a second opening/closing signal input from the cooling control unit 8.

The cooling control unit 9 operates the heat exchanger 5, the first and second control valves 8a and 8b, the drain valve, or the like described above to control all operations of the cooling device R. As part of the control of the cooling device R, the cooling control unit 9 controls the first and second control valves 8a and 8b to switch the supply/non-supply of the coolant to the plurality of first and second cooling nozzles 2a and 2b. Accordingly, the heat transfer coefficient of the mist-like coolant during cooling the workpiece X is switched from a relatively low state to a relatively high state. In addition, switching processing of the heat transfer coefficient of the mist-like coolant performed by the cooling control unit 9 will be described in detail.

The intermediate conveyance device H includes a conveyance chamber 10, a conveyance chamber placement table 11, a cooling compartment lifting/lowering table 12, a cooling compartment lifting/lowering cylinder 13, a pair of conveyance rails 14, a pair of pusher cylinder (pusher cylinder 15 and pusher cylinder 16), a heating chamber lifting/lowering table 17, a heating chamber lifting/lowering cylinder 18, or the like. The conveyance chamber 10 is a container which is provided between the cooling device R and the three heating devices including the heating device K1 and the heating device K2, and the internal space of the conveyance chamber 10 is the conveyance chamber HS. The workpiece X is loaded into a conveyance chamber 10 from a load/unload opening (not shown) by an external conveyance device in a state of being accommodated in a container such as a basket.

The conveyance chamber placement table 11 is a support table which blocks a delivery port between the cooling chamber 1 and the conveyance chamber 10 when the workpiece X is cooled by the cooling device R, and other workpieces X can be placed on the conveyance chamber placement table 11. The cooling compartment lifting/lowering table 12 is a support table on which workpiece X is placed when the workpiece X is cooled by cooling device R, and supports the workpiece X so that a bottom portion of workpiece X is exposed as widely as possible. The cooling compartment lifting/lowering table 12 is fixed to a tip of a movable rod of the cooling compartment lifting/lowering cylinder 13.

The cooling compartment lifting/lowering cylinder 13 is an actuator which moves (lifts or lowers) the cooling compartment lifting/lowering table 12 vertically. That is, the cooling compartment lifting/lowering cylinder 13 and the cooling compartment lifting/lowering table 12 are a dedicated conveyance device of the cooling device R, and convey the workpiece X placed on the cooling compartment lifting/lowering table 12 from a conveyance chamber HS to the cooling compartment RS and conveys the workpiece X from the cooling compartment RS to the conveyance chamber HS.

The pair of conveyance rails 14 is installed to extend horizontally on a floor portion in the conveyance chamber 10. The conveyance rails 14 are a guide member for conveying the workpiece X between the cooling device R and the heating device K1. The pusher cylinder 15 is an actuator which presses the workpiece X when the workpiece X in the conveyance chamber 10 is conveyed toward the heating device K1. The pusher cylinder 16 is an actuator which presses the workpiece X when the workpiece X is conveyed from the heating device K1 to the cooling device R.

That is, the pair of conveyance rails 14, the pusher cylinder 15 and the pusher cylinder 16 are a dedicated conveyance device which conveys the workpiece X between the heating device K1 and the cooling device R. Moreover, in FIG. 1, the pair of conveyance rails 14, the pusher cylinder 15, and the pusher cylinder 16 are shown. However, an actual intermediate conveyance device H includes three pairs of conveyance rails 14, the pusher cylinder 15, and the pusher cylinder 16. That is, the conveyance rails 14, the pusher cylinder 15, and the pusher cylinder 16 are used not only for the heating device K1 but also for the other two heating devices.

The heating chamber lifting/lowering table 17 is a support table on which the workpiece X is placed when the workpiece X is conveyed from the intermediate conveyance device H to the heating device K1. That is, the workpiece X is pressed in a right direction in FIG. 1 by the pusher cylinder 15, and thus, the workpiece X is conveyed immediately on the heating chamber lifting/lowering table 17. The heating chamber lifting/lowering cylinder 18 is an actuator which moves (lifts or lowers) the workpiece X on the heating chamber lifting/lowering table 17 vertically. That is, the heating chamber lifting/lowering table 17 and the heating chamber lifting/lowering cylinder 18 are a dedicated conveyance device of the heating device K1, and conveys the workpiece X placed on the heating chamber lifting/lowering table 17 from the conveyance chamber HS to the inner portion (heating chamber KS) of the heating device K1 and conveys the workpiece X from the heating chamber KS to the conveyance chamber HS.

The three heating devices have substantially the same configuration as each other, and thus, in the following descriptions, the configuration of the heating device K1 will be described as a representative. The heating device K1 includes a heating chamber 20, a heat-insulating container 21, a plurality of heaters 22, a vacuum vent tube 23, a vacuum pump 24, a stirring blade 25, a stirring motor 26, or the like.

The heating chamber 20 is a container which is provided on the conveyance chamber 10, and the internal space of the heating chamber 20 is the heating chamber KS. Similarly to the above-described cooling chamber 1, the heating chamber 20 is a vertically cylindrical container (a container in which a central axis thereof is in the vertical direction). However, the heating chamber 20 is formed to be smaller than the cooling chamber 1. The heat-insulating container 21 is a vertically cylindrical container provided in the heating chamber 20, and is formed of a heat-insulating material having predetermined heat-insulating properties.

The plurality of heaters 22 are a rod-shaped heating element and are provided at a predetermined interval in the circumferential direction inside the heat-insulating container 21 in a vertical posture. The plurality of heaters 22 heats the workpiece X accommodated in the heating chamber KS to a desired temperature (heating temperature). In addition, a heating condition such as a heating temperature or a heating time is appropriately set according to an object of the heat treatment in the workpiece X, a material of the workpiece X, or the like.

Here, the heating condition includes a degree of vacuum (pressure) of the heating chamber KS. The vacuum vent tube 23 is a pipe which communicates with the heating chamber KS, and one end of the vacuum vent tube 23 is connected to an upper portion of the heat-insulating container 21 and the other end thereof is connected to the vacuum pump 24. The vacuum pump 24 is a vent pump which sucks air in the heating chamber KS via the vacuum vent tube 23. The degree of vacuum in the heating chamber KS is determined by a vent amount of air by the vacuum pump 24.

The stirring blade 25 is a rotating blade which is provided on the upper portion in the heat-insulating container 21 in a posture in which a direction of a rotary shaft thereof is the vertical direction (up-down direction). The stirring blade 25 is driven by the stirring motor 26 and stirs air in the heating chamber KS. The stirring motor 26 is a rotation drive source which is provided on the heating chamber 20 such that an output shaft thereof is in the vertical direction (up-down direction). The output shaft of the stirring motor 26 positioned on the heating chamber 20 is connected to the rotary shaft of the stirring blade 25 positioned in the heating chamber 20 so as not to damage airtightness (sealing properties) of the heating chamber 20.

In addition, the multi-chamber thermal treatment device M according to the present embodiment includes a control panel (not shown). This control panel includes an operation unit to which various conditions in the heat treatment are set and input by a user, and a control unit which operates the cooling device R, the intermediate conveyance device H, and the three heating devices in cooperation with each other, based on various conditions input from the operation unit and a control program stored in advance. That is, in the multi-chamber thermal treatment device M, the cooling device R, the intermediate conveyance device H, and the three heating devices are automatically controlled by the control panel, and thus, a quenching treatment is performed on the workpiece X.

Here, the above-described cooling control unit 8 is a functional component responsible for the cooling control of the workpiece X performed by the cooling device R, among the control functions of the control panel. That is, the control pane performs a conveyance control of the workpiece X by the intermediate conveyance device H and a heating control of the workpiece X by the three heating devices in addition to the cooling control of the workpiece X by the cooling device R.

Next, the operation (quenching treatment) of the multi-chamber thermal treatment device M according to the present embodiment will be described in detail with reference to FIGS. 5A and 5B.

In the quenching treatment by multi-chamber thermal treatment device M, after the workpiece X is heated to a predetermined temperature T1 (heating temperature), first cooling (rapid cooling) is performed on the workpiece X to a temperature T2 (cooling temperature), and thereafter, second cooling is performed on the workpiece X to a martensite transformation temperature. When the quenching treatment of the workpiece X is performed, the workpiece X is accommodated into the intermediate conveyance device H from the load/unload opening by a worker. In addition, if the load/unload opening is closed by the worker and the inside of the conveyance chamber HS is an enclosed space, the intermediate conveyance device H operates the pusher cylinder 15 to moves the workpiece X onto the heating chamber lifting/lowering table 17. In addition, the heating chamber lifting/lowering cylinder 18 is operated by the intermediate conveyance device H, and thus, the workpiece X is accommodated in the heating chamber KS of the heating device K1.

In addition, if the workpiece X is accommodated in the heating chamber KS, the heating device K1 operates the heater 22 to heat the workpiece X to the temperature T1. In addition, if the heating is completed, the intermediate conveyance device H operates the heating chamber lifting/lowering cylinder 18 and the pusher cylinder 16 to move the workpiece X onto the cooling compartment lifting/lowering table 12. In addition, the intermediate conveyance device H operates the cooling compartment lifting/lowering cylinder 13 to move the workpiece X to the cooling compartment RS, and a delivery port between the conveyance chamber 10 and the cooling chamber 1 is blocked by the conveyance chamber placement table 11. In addition, the cooling device R operate the cooling pump 4 to inject the mist-like coolant from the plurality of first and second cooling nozzles 2a and 2b toward the workpiece X. As a result, the workpiece X is subjected to primary cooling (mist cooling) from the temperature T1 to the temperature T2.

In the primary cooling (mist cooling), as shown in FIG. 5A, the workpiece X at the temperature T1, that is, the workpiece X having the austenitic structure is rapidly cooled so as to reach the temperature T2 avoiding a pearlite-structure-transformation point Ps (so-called pearlite nose). That is, the workpiece X is rapidly cooled from the temperature T1 to the temperature T2 by injection of the mist-like coolant from the plurality of first and second cooling nozzles 2a and 2b during a time t1 to a time t2 in FIG. 5A. In FIG. 5A, a surface temperature history of the workpiece X is indicated by a solid line and an internal temperature history of the workpiece X is indicated by a broken line.

Here, in the primary cooling (mist cooling) in the present embodiment, at a time ta which is an intermediate time between the time t1 and the time t2, switching of the heat transfer coefficient of the mist-like coolant from the relatively low state to the relatively high state is performed once. That is, in a period (early cooling period S1) from the time t1 to the time ta, the cooling control unit 9 sets the first control valve 8a to an open stage and sets the second control valve 8b to a closed state, and as shown in FIG. 5B, the mist-like coolant having a first particle diameter C1 is injected from the first cooling nozzles 2a toward the workpiece X. That is, in the early cooling period S1, the workpiece X is cooled by the mist-like coolant having the first heat transfer coefficient.

Moreover, in a period (late cooling period S2) from the time ta to the time t2, the cooling control unit 8 sets the first control valve 8a to the closed state and sets the second control valve 8b to the open state, that is, the supply destination of the coolant is switched from the first cooling nozzle 2a to the second cooling nozzle 2b, and thus, as shown in FIG. 5B, the mist-like coolant having a second mist particle diameter C2 is injected from the second cooling nozzle 2b toward the workpiece X. That is, in the late cooling period S2, the workpiece X is cooled by the mist-like coolant having the second heat transfer coefficient higher than the first heat transfer coefficient of the early cooling period S1.

Here, the first heat transfer coefficient of the mist-like coolant in the early cooling period S1, that is, the first mist particle diameter C1 is set so as to maximally suppress the deformation of the workpiece X caused by the primary cooling (mist cooling). That is, the first mist particle diameter C1 is determined for each material and shape of the workpiece X by an experiment or the like which is performed in advance. In addition, the early cooling period S1, that is, the time to is also determined for each material and shape of the workpiece X by an experiment or the like which is performed in advance.

As described in Background Art, in the mist cooling, the vapor film cannot be maintained, and thus, the part (workpiece) is deformed. However, in the present embodiment, the vapor film is not maintained. That is, the heat transfer coefficient of the mist-like coolant is lowered by the setting the first particle diameter C1 in a high-temperature period of the workpiece X in which the workpiece X is deformed, that is, in the early cooling period S1. In addition, as a result, the deformation of the workpiece X is suppressed by suppressing cooling efficiency with respect to the workpiece X.

In the mist cooling with respect to the workpiece X in the early cooling period S1, a decrease in the temperature of the workpiece X becomes relatively gentle. Accordingly, in a case where, similarly to the early cooling period S1, the mist cooling is performed by the mist-like coolant having the first mist particle diameter C1 in the late cooling period S2, it may be impossible to avoid the pearlite-structure-transformation point Ps in the primary cooling. Accordingly, in the present embodiment, the mist cooling is performed in the late cooling period S2 by the mist-like coolant having the second mist particle diameter C2 which is the particle diameter larger than the first mist particle diameter C1. Accordingly, the cooling efficiency in the late cooling period S2 is improved compared to the cooling efficiency in the early cooling period S1, the primary cooling in which the pearlite-structure-transformation point is avoided is realized.

Here, as shown in FIG. 6, from data of a cooling curve of a silver column specimen (10 mm in diameter, 30 mm in length) quenched in a representative cooling agent such as tap water, oil (JIS Nippon Industrial Standard C 2320-1999 Type 1 No. 2 oil), and nitrogen (10 bar 15 m/s), surface heat transfer characteristic curves of each cooling agent calculated by a concentrated heat capacity method are known.

According to FIG. 6, in a high-temperature region in which a surface temperature of the silver column specimen is 600° C. or more, it is understood that a surface heat transfer coefficient of the tap water of 30° C. is larger than that of the oil of 80° C.

Accordingly, for example, a mist cooling experiment using water as the mist-like coolant of a test piece (workpiece) was performed using the following cooling device simulating the above embodiment.

The cooling device included a water tank, a predetermined pipe, and a nozzle.

The water tank had a capacity of 60 L, and water used for cooling was stored in the water tank. In addition, the water tank was pressurized by nitrogen gas and was connected to the predetermined pipe.

Two types of nozzles including a one-fluid nozzle which ejects only water and a two-fluid nozzle that ejects fine particles of water using gas was adopted as a nozzle. More specifically, ¼M JJXP 060 HTPVC manufactured by Ikeuchi Co., Ltd. was used for one-fluid nozzle 1-1, ¼KSFHS 0865 manufactured by Everloy Co., Ltd. was used for one-fluid nozzle 1-3, M¼ EX 438 manufactured by Niikura Kogyo Co., Ltd was used for one-fluid nozzle 1-4, and ¼ KSAMF 1875-¼ A24 ¼ W20 manufactured by Everloy Co., Ltd. was used for two-fluid nozzle 2-2. In addition, the nozzle was provided on an end portion opposite to an end portion of the predetermined pipe to which the water tank was attached. Moreover, a tip of the nozzle was positioned at a position separated by 200 mm from the surface of the test piece.

For the test piece, a disc-shaped stainless steel (JIS Japanese Industrial Standard SUS 304) having a thickness of 50 mm and a diameter of 100 mm was used. The test piece was inserted into an electric furnace and heated to 1000° C.

The water stored in the water tank was pressurized by the nitrogen gas, and the pressurized water was injected to the test piece heated to 1000° C. In addition, the water was injected from each nozzle such that the injection liquid pressure was 0.03 to 0.5 MPa.

Next, a temperature measurement method will be described.

Thermocouples were installed at six locations in total including four locations of 2 mm, 6 mm, 10 mm, and 25 mm in the depth direction from the surface at a center position of the test piece and two locations shifted from each other by 180° in a circumferential direction at a position of 25 mm from the upper end and 2 mm from the surface on a side surface of the test piece.

In addition, the test piece heated to 1000° C. was subjected to mist cooling and a temperature change of the test piece was measured until the temperature of the test piece became a normal temperature.

FIG. 7 shows a result of performing the mist cooling test and calculating an average heat transfer coefficient from the time change of the temperature of the thermocouple inserted in the test piece. In addition, FIG. 7 shows the average heat transfer coefficient in a case where the surface temperature of the test piece corresponds to a range of 600 to 1000° C.

A dotted line in FIG. 7 shows a value in a case where oil cooling is performed, and if the nozzle of 1-3 which was the one-fluid nozzle or the nozzle of 2-2 which was the two-fluid nozzle was used, even in the mist cooling in which water was used, the heat transfer coefficient which was approximately the same as that of the cooling oil was realized. That is, according to the cooling device using the mist cooling, the heat transfer coefficient of the mist-like coolant can be lowered to be approximately the same as that of the cooling oil. In addition, it is possible to suppress the deformation of the workpiece X by suppressing the cooling efficiency of the workpiece X.

As described above, according to the cooling device R of the present embodiment, the mist particle diameter of the mist-like coolant is adjusted from the first mist particle diameter C1 to the second mist particle diameter C2 between the period in which the workpiece X has a relatively high temperature, that is, the early cooling period S1, and the period in which the workpiece X has a relatively low temperature, that is, the late cooling period S2. Therefore, the deformation of the workpiece X in the primary cooling is suppressed, and it is possible to avoid the perlite-structure-transformation point Ps.

In addition, the present disclosure is not limited to the above-described embodiment. For example, the following modification examples are considered.

(1) As shown in FIG. 5B, in the above-described embodiment, the mist particle diameter of the mist-like coolant is adjusted from the second mist particle diameter C1 to the first mist particle diameter C2, and thus, the heat transfer coefficient of the mist-like coolant is switched from the first heat transfer coefficient to the second heat transfer coefficient. However, the present disclosure is not limited to this. The density (mist density) of the mist-like coolant may be switched so as to switch the thermal conductivity from the first heat transfer coefficient to the second heat transfer coefficient. For example, the density of the mist-like coolant may be adjusted from a relatively low density to a relatively high density so as to switch the heat transfer coefficient of the mist-like coolant.

For example, a gas-liquid two-phase flow of including a coolant and a predetermined gas is injected to the workpiece X from the injection nozzle as the mist-like coolant, a mixing ratio of the gas to the coolant is adjusted such that a mist density is adjusted from a first mist density to the second mist density, and thus, the heat transfer coefficient is switched from the first heat transfer coefficient to the second heat transfer coefficient. In addition, instead of adjusting the mist density, the mist density may be switched by adjusting a flow rate of the coolant supplied to the injection nozzle.

(2) In the above-described embodiment, as shown in FIG. 5B, the first mist particle diameter C1 and the second mist particle diameter C2 are switched at the time ta. However, the present disclosure is not limited to this. For example, the mist-like coolant having the first mist particle diameter C1 and the mist-like coolant having the second mist particle diameter C2 may be injected from the first and second cooling nozzles 2a and 2b over a predetermined period (overlap period) from time ta, and after the overlap period, only the mist-like coolant having the second mist particle diameter C2 may be injected from the second cooling nozzle 2b.

That is, the mist particle diameter of the mist-like coolant may be adjusted from the first mist particle diameter to the second mist particle diameter via a state where the mist-like coolant having the first mist particle diameter and the mist-like coolant having the second mist particle diameter are mixed with each other.

The overlap period is a period in which the mist-like coolant having the first mist particle diameter C1 and the mist-like coolant having the second mist particle diameter C2 coexist. That is, the overlap period is a period in which a mist-like coolant having a heat transfer coefficient in the middle of the first heat transfer coefficient and the second heat transfer coefficient exists. The mist particle diameter of the mist-like coolant is adjusted from the first mist particle diameter C1 to the second mist particle diameter C2 through the overlap period, and thus, the switching from the first heat transfer coefficient to the second heat transfer coefficient can be gently performed. Therefore, according to the above-described configuration, it is possible to suppress accumulation of thermal stress in the workpiece X.

(3) In the above-described embodiment, the mist-like coolant having the first mist particle diameter C1 is injected in the early cooling period S1, and the mist-like coolant having the second mist particle diameter C2 is injected in the late cooling period S2. However, the disclosure is not limited to this. In the late cooling period S2, in addition to the mist-like coolant having the second mist particle diameter C2, the mist-like coolant having the first mist particle diameter C1 may be injected. In this case, not only the mist particle diameter increases and the heat transfer coefficient increases but also the mist density can be increased, and thus, the heat transfer coefficient can be further increased.

(4) As shown in FIG. 1, in the above-described embodiment, the multi-chamber thermal treatment device M (thermal treatment device) in which the cooling device R, the intermediate conveyance device H, and the three heating devices are integrated with each other is described. However, the present disclosure is not limited to this. The minimum configuration device of the thermal treatment apparatus is the heating device and the cooling device. That is, the heat treatment apparatus may be provided with the heating device for heating the workpiece and the cooling device for cooling the workpiece heated by the heating device. Therefore, a conveyance device such as an intermediate conveyance device may be separate from the thermal treating device.

INDUSTRIAL APPLICABILITY

According to the cooling device and the thermal treatment device of the present disclosure, the technique for switching the heat transfer coefficient of the mist-like coolant from the relatively low state to the relatively high state during cooling the workpiece is used, and thus, it is possible to suppress the deformation of the workpiece more reliably than the related art.

Claims

1. A cooling device which cools a workpiece using a mist-like coolant, comprising:

a heat transfer coefficient switching device that switches a heat transfer coefficient of the mist-like coolant from a relatively low state to a relatively high state during cooling the workpiece.

2. The cooling device according to claim 1,

wherein the heat transfer coefficient switching device adjusts a mist particle diameter of the mist-like coolant from a relatively small particle diameter to a relatively large particle diameter to switch the heat transfer coefficient of the mist-like coolant.

3. The cooling device according to claim 2,

wherein the heat transfer coefficient switching device includes,

a first injection nozzle that includes an injection hole having a first hole diameter and converts a coolant into the mist-like coolant having a first mist particle diameter of a relatively small mist particle diameter,

a second injection nozzle that includes an injection hole having a second hole diameter larger than the first hole diameter and converts the coolant into the mist-like coolant having a second mist particle diameter larger than the first mist particle diameter, and

a coolant supply device that supplies the coolant to the first injection nozzle and the second injection nozzle, and

wherein a supply destination of the coolant is switched from the first injection nozzle to the second injection nozzle to adjust the mist particle diameter of the mist-like coolant from the first mist particle diameter to the second mist particle diameter.

4. The cooling device according to claim 2,

wherein the heat transfer coefficient switching device adjusts the mist particle diameter of the mist-like coolant from a first mist particle diameter to a second mist particle diameter via a state where the mist-like coolant having the first mist particle diameter and the mist-like coolant having the second mist particle diameter are mixed.

5. The cooling device according to claim 3,

wherein the heat transfer coefficient switching device adjusts the mist particle diameter of the mist-like coolant from the first mist particle diameter to the second mist particle diameter via a state where the mist-like coolant having the first mist particle diameter and the mist-like coolant having the second mist particle diameter are mixed.

6. The cooling device according to claim 1,

wherein the heat transfer coefficient switching device adjusts a density of the mist-like coolant from a relatively low density to a relatively high density to switch the heat transfer coefficient of the mist-like coolant.

7. A thermal treatment device, comprising:

a heating device that heats a workpiece; and

the cooling device according to claim 1 that cools the workpiece heated by the heating device.

8. A thermal treatment device, comprising:

a heating device that heats a workpiece; and

the cooling device according to claim 2 that cools the workpiece heated by the heating device.

9. A thermal treatment device, comprising:

a heating device that heats a workpiece; and

the cooling device according to claim 3 that cools the workpiece heated by the heating device.

10. A thermal treatment device, comprising:

a heating device that heats a workpiece; and

the cooling device according to claim 4 that cools the workpiece heated by the heating device.

11. A thermal treatment device, comprising:

a heating device that heats a workpiece; and

the cooling device according to claim 5 that cools the workpiece heated by the heating device.

12. A thermal treatment device, comprising:

a heating device that heats a workpiece; and

the cooling device according to claim 6 that cools the workpiece heated by the heating device.