JP2019163490A - Cooling device - Google Patents

Abstract

To suppress uneven cooling when cooling a cooling target member by spraying a spray fluid, and to reduce occurrence of deformation, defective reforming or the like.SOLUTION: The cooling device according to the present invention includes: an injection portion for injecting a spray fluid to a cooling target member; and a control portion for selecting an injection condition based on characteristics of the cooling target member and the spray fluid, and for controlling a holding time of the injection by the injection portion.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a cooling device, and more particularly to a cooling device suitable for application to quenching.

  In the cooling process of members, spray cooling (or mist cooling) has been used in recent years, in which a spray fluid in the form of shower or mist is sprayed from a nozzle and sprayed onto a cooling target member for heat treatment to cool.

  In spray cooling, in addition to a method in which only a refrigerant is injected from a nozzle at a high pressure, a two-fluid spray method is also used in which refrigerant and gas are mixed and injected while changing the quantity ratio. In particular, in the two-fluid spray method, the droplet diameter of the spray (mist) to be sprayed and the spray speed can be changed in more detail, so that the cooling control property is excellent.

  For example, in Patent Document 1, a mixed fluid of air and water is injected onto a steel material to be cooled, and a droplet diameter of the mixed fluid to be injected is adjusted according to the surface temperature of the steel material. There has been proposed a cooling method for preventing the residue from remaining.

  On the other hand, when there is a distribution in the spray density of the spray that reaches the surface of the cooling target member due to the shape of the cooling target member and the nozzle arrangement, the cooling rate varies depending on the location, which may cause deformation and poor reforming.

  In order to suppress this cooling unevenness, Patent Document 2 proposes an apparatus that has an adjustment unit that adjusts the flow direction of the sprayed refrigerant so that the refrigerant uniformly contacts the entire cooling target member. Patent Document 3 proposes a method of reducing temperature unevenness by changing the spray density during cooling and changing the cooling rate.

JP 2001-262220 A JP 2014-095548 A JP 2014-141747 A

  An object of this invention is to provide the cooling method and apparatus which reduce the temperature nonuniformity produced by the difference in the evaporation behavior of a spray fluid.

  In order to achieve the above object, a cooling device according to the present invention selects an injection condition based on characteristics of an injection unit that injects a spray fluid to a member to be cooled, and the member to be cooled and the spray fluid. And a control unit for controlling a stop time of the injection by the injection unit.

  The present invention makes it possible to stabilize the transition from the film boiling state to the transition boiling state of the spray fluid injected to the member to be cooled, thereby suppressing uneven cooling and generating deformation and defective reforming. Can be reduced.

It is a schematic diagram of the evaporation behavior of droplets on the contact surface with the member to be cooled. It is a block diagram of the apparatus of this embodiment. It is a schematic diagram which shows the temperature change of the cooling target member in the center point of a contact surface in the contact surface of a droplet and a cooling target member. It is a graph which shows the cooling curve measured during the spray cooling test for SUS304. It is a figure which shows the temperature dependence of the heat transfer coefficient derived from the cooling curve which implemented the spray cooling test using the prior art for SUS304, and was acquired. It is a figure which shows the temperature dependence of the heat transfer coefficient derived | led-out from the cooling curve measured during the spray cooling test using SUS304 as object.

  Hereinafter, the cooling method and apparatus of the present invention will be described with reference to the drawings.

  The present embodiment relates to a cooling method in which a spray fluid is sprayed from a nozzle as a mist or shower-like spray fluid onto a heated cooling target member. It has a control part which controls injection execution and injection stop of spray fluid, and repeats injection and injection stop in a short time.

  At this time, temperature non-uniformity is reduced by heat conduction generated in the cooling target member while the injection is stopped, and local vapor film collapse is less likely to occur, so that it is possible to stably shift from film boiling to transition boiling during cooling. . Thereby, the stability of cooling increases, and the temperature nonuniformity at the time of cooling can be reduced. Therefore, deformation and cracking of the member to be cooled and occurrence of uneven heat treatment can be reduced.

  At this time, the optimal injection execution time and injection stop time at which the desired effect is obtained are determined by the characteristics of the spray fluid, the cooling target member, and the cooling target member. Specifically, it is derived based on the amount of heat taken from the member to be cooled in the course of evaporation of the droplets in the spray fluid and the time during which sufficient heat conduction occurs in the member to be cooled. More specifically, the droplet size distribution in the spray fluid, the heat transfer coefficient between the spray fluid and the member to be cooled, the latent heat of vaporization of the spray fluid, the specific heat of the spray fluid, the density of the spray fluid, the heat conduction of the member to be cooled. It is derived from the coefficient, the specific heat of the member to be cooled, and the density of the member to be cooled.

  The injection execution time and the injection stop time may be obtained from the correlation obtained by experimentally acquiring beforehand a condition in which cooling is stabilized for the spray fluid and the cooling target member of the cooling target member.

  In the cooling process, the supply amount of the spray fluid, the spray speed, and the droplet diameter of the spray fluid may be changed while maintaining the correlation between the injection execution time and the injection stop time.

  The prior art has the following problems.

  In general, when spray fluid (refrigerant) is sprayed onto a cooling target member in a high temperature state, the evaporation behavior of the droplets varies depending on the temperature of the cooling target member at the contact portion between the droplet formed by the spray fluid and the cooling target member.

  FIG. 1 shows a schematic diagram thereof. If the member to be cooled at the contact portion between the droplet and the member to be cooled is equal to or higher than the Leidenfrost temperature of the spray fluid shown in the figure, the droplet in contact with the surface of the member to be cooled is vaporized to form a thin vapor film (Leiden Frost phenomenon) Film boiling occurs. In the film boiling state, direct contact between the droplet and the surface of the member to be cooled is hindered, so that the heat transfer coefficient between the spray fluid and the member to be cooled is decreased and the cooling rate is decreased.

  On the other hand, when the temperature of the surface of the cooling target member in contact with the droplet is lower than the Leidenfrost temperature, a transition boiling state occurs in which the droplet directly contacts the surface of the cooling target member. In the transition boiling state, the amount of heat taken from the surface of the member to be cooled by the latent heat of vaporization of the spray fluid increases, and the cooling proceeds rapidly.

  The Leidenfrost temperature at this time varies depending on the type and temperature of the spray fluid and the spraying speed of the spray.

  In the cooling process, as the surface temperature of the member to be cooled decreases, the evaporation behavior of the spray fluid shifts from the film boiling state to the transition boiling state. In the prior art, when the average surface temperature of the member to be cooled decreases and passes through the Leidenfrost point, the vapor film that has been formed so far collapses, so that the cooling rate increases rapidly. At that time, if there is a location that is locally below the Leidenfrost point due to uneven spraying amount or the like, transition boiling occurs in advance at the location and the cooling is rapidly performed. When a droplet continuously collides with a corresponding portion that has been locally cooled, cooling due to transition boiling is performed, and thus the temperature difference from the average surface temperature further increases. When this rapid change in the cooling rate or temperature unevenness occurs in the workpiece, it may cause deformation or cracking, and heat treatment unevenness may occur in the member to be cooled.

  The present embodiment has been made in consideration of the above points, and an object thereof is to provide a cooling method and apparatus that can reduce temperature unevenness caused by a difference in evaporation behavior of spray fluid.

  FIG. 2 is a configuration diagram of the apparatus according to the present embodiment. A heating furnace 1 that overheats the cooling target member M, a drive unit 2 that transports the cooling target member M heated in the heating furnace 1, and a cooling tank 3 in which the heated cooling target member M is transported. The tank 3 has a nozzle 4 for spraying a spray, a spray unit 5 connected to the nozzle 4, a cylinder 6 for opening and closing the nozzle 4, and a control unit 7 for controlling the air pressure sent to the cylinder 6. .

  The drive unit 2 can convey and feed the cooling target member M in the vertical direction. The driving unit 2 fixes the cooling target member M to the support frame 8 and heats the cooling target member M to a predetermined temperature in the heating furnace 1. Is opened and conveyed to the cooling bath 3. The cooling target member M conveyed to the cooling tank 3 is cooled by the spray sprayed from the nozzle 4.

  The temperature change of the cooling target member during cooling is measured by a thermocouple installed on the cooling target member M. The spray unit 5 is controlled to be sprayed and stopped by a cylinder 6 that opens and closes by air pressure sent from the control unit 7. The control unit 7 can change the spray speed and the droplet diameter by controlling the flow rate and pressure of the fluid sent to the nozzle.

This embodiment is based on the following ideas. First, the water sprayed from the nozzle becomes fine droplets and collides with the surface of the member to be cooled. When the collided droplet becomes hemispherical and further forms a vapor film and is cooled in a film boiling state, the time t _w [s] until the droplet in contact with the surface of the object to be cooled evaporates is expressed by the following equation: Desired.

At this time, r is the diameter of the droplet constituting the spray fluid [m], ρ _w is the density of the spray fluid [kg / m ³ ], He is the latent heat of vaporization of the spray fluid [J / kg], and c _pw is the spray fluid Specific heat [J / (kg · K)], T _m is the surface temperature of the member to be cooled [K], T _w is the temperature of the spray fluid [K], h is the heat transfer coefficient between the spray fluid and the member to be cooled [ W / (m ² · K)].
Furthermore, the temperature difference θ (t) between the local temperature at a position L [m] away from the point where the droplet and the member to be cooled are in contact with the bulk temperature of the member to be cooled is the temperature change with respect to time [s]. It is given by the following formula.

θ (0) is the temperature difference between the local temperature and the bulk temperature of the contact surface of the member to be cooled when the droplets are evaporated, and λm is the thermal conductivity coefficient [W / (m · K)] of the member to be cooled. c _pm is the specific heat [J / (kg · K)] of the member to be cooled, and ρ _m is the density [kg / m ³ ] of the member to be cooled.

  At this time, when the average temperature of the cooling target member surface is in the vicinity of the Leidenfrost point and the contact surface is not sufficiently conducting heat and the next droplet collides in a state where θ is large, transition boiling starts at that location and abruptly occurs. Cooling occurs. As a result, the temperature unevenness is further enlarged.

  FIG. 3 is a schematic diagram of a temperature change on the surface in contact with the droplet. The liquid droplet that comes into contact with the member to be cooled becomes hemispherical and comes into contact with the member to be cooled. This schematic diagram shows the temperature change at the center point.

Droplets in contact with the cooling target member surface removes heat from the cooling target member until time t _W until the evaporation reduces the cooling target member surface temperature to θ relative to the bulk temperature (0). The surface temperature of the member to be cooled approaches the bulk temperature due to heat conduction from there to the bulk. At this time, although the bulk temperature also decreases with time due to cooling, the injection stop time is not considered because it is sufficiently small with respect to the bulk temperature decrease. The temperature of the portion in contact with the droplet is more desirable as it approaches the bulk temperature, but if the jet stop time is too long, the cooling ability will decrease. Experimentally, if the temperature difference θ is about 1/10 at the position separated from the contact point between the droplet and the member to be cooled, the temperature distribution is sufficiently relaxed, and stable cooling is possible. .

That is, the optimum injection stop time t _p is determined from the following equation.

  The spray stop time may be obtained experimentally by performing a cooling experiment under different conditions of the spray stop time in advance.

  The spray stop time is preferably set to 1 second or less so that the cooling capacity does not deteriorate too much.

  As described above, the present embodiment obtains the optimum spray stop time and sets the spray execution time of the spray using this spray stop time. The injection execution time is preferably 1 second or less in order to suppress the expansion of the temperature distribution on the surface of the cooling target member, and more preferably in the range of 0.5 to 2 times the injection stop time.

Moreover, the injection execution time and the injection stop time of a spray, transition is possible to to follow the surface temperature T _m of a cooling target member temporally change is desired from the viewpoint of controllability, the film boiling conditions to transition boiling condition _Tm may be set in the vicinity of the Leidenfrost point of the atomizing fluid so that the effect appears most in the vicinity of the temperature at which it is applied.

  As the spray fluid of the spray fluid, for example, oil, salt water, polymer solution or the like can be used, but it is desirable to use city water or ion exchange water from the viewpoint of economy. Further, argon, helium, nitrogen, or the like can be used as the atomizing fluid gas, but it is desirable to use air.

  Cooling can also be performed in a reduced pressure or pressurized atmosphere, but it is preferably 1 atm from the viewpoint of economy.

  In the above cooling method, when city water is used as the spray fluid, air is used as the gas, the atmosphere is set to 1 atm, and the cooling target member is an iron-based member, the spray fluid droplets are set to 10 to 100 μm, and injection is performed. It is preferable that the time is 10 to 1000 milliseconds and the injection stop time is 10 to 1000 milliseconds.

  More preferably, the droplets of the spray fluid are 50 to 100 μm, the injection execution time is 10 to 100 milliseconds, and the injection stop time is 10 to 100 milliseconds.

  When the cooling target member constituting the cooling target member is an aluminum-based member, the spray fluid droplets are set to 10 to 100 μm, the injection execution time is set to 10 to 500 milliseconds, and the injection stop time is set to 10 to 500. It is preferable to use milliseconds.

  More preferably, the spray fluid droplets are 50 to 100 μm, the jetting execution time is 10 to 50 milliseconds, and the jetting stop time is 10 to 50 milliseconds.

  Examples will be described below.

  In order to confirm the effect of this embodiment, a test using a disk-shaped test piece was performed. SUS304, which is stainless steel, was used as a target cooling target member for spray cooling. Table 1 shows the thermophysical properties of SUS304.

  The test piece was cut from a round bar extruded material, and a test piece having a diameter of 30 mm and a thickness of 10 mm was used. The atomizing fluid was water at 25 ° C., and the atmosphere was 1 atm. A spray nozzle used for cooling was a two-fluid conical nozzle with a spray angle of 70 °, and one spray nozzle was installed at a position sprayed vertically from the lower part of the cooling tank. As the spray unit, one that can individually set the spray amount of the spray fluid, the spray pressure, and the droplet diameter of the spray fluid was used. The spray amount of the spray fluid was 20 liters per minute, and the spray pressure was 0.2 MPa. The droplet diameter of the atomizing fluid was adjusted to fall within the range of about 50 to 100 μm. A heat resistant ceramic paper with a thickness of about 3 mm was bonded to the upper and side surfaces of the test piece with a heat resistant inorganic adhesive, and the test piece was considered to be cooled in a one-dimensional direction (thickness direction) from the lower surface. . The temperature change was measured by making a hole 1 mm inside from the lower part of the test piece and inserting a K-type thermocouple. The heat treatment temperature before cooling was 850 ° C.

  The test piece was fixed to the support frame at the tip of the drive unit, heated in a heating furnace, and then transported to the cooling bath to start spraying.

  The conditions for the injection execution time and the injection stop time during spray cooling were implemented under four conditions. Each condition is shown in Table 2.

  FIG. 4 shows a cooling curve measured during the cooling test. Compared with the prior art shown in Condition 1, when cooling is performed using the present embodiment, the transition of the cooling curve is gentle, and the boiling condition of the spray fluid stably and gradually shifts from film boiling to transition boiling. You can see that The time until the temperature of the test piece decreases to about 100 ° C. is shorter when cooled using this embodiment, and this is because the latent heat of vaporization of water is effectively used, so that the cooling can be made more efficient. Indicates that The cooling rate is faster under conditions 3 and 4 than under condition 2, indicating that the cooling capacity is higher.

  FIG. 5 shows the heat transfer coefficient derived by the concentrated heat capacity method from the cooling curve of the test conducted in the prior art. In the prior art, a rapid increase in the heat transfer coefficient is observed at a temperature higher than the original Leidenfrost point, and transition boiling and film boiling are repeated. This indicates that there is a portion that is locally cooled on the member to be cooled, and cooling unevenness occurs.

  FIG. 6 shows the heat transfer coefficient derived by the concentrated heat capacity method from the cooling curve of the test carried out by the inventive technique. In the present embodiment, the heat transfer coefficient changes gently. Thereby, this embodiment can stabilize the transition from the film boiling state of the spray fluid injected to the cooling target member to the transition boiling state, suppress uneven cooling, and prevent deformation, poor reforming, etc. It has been shown that it is possible to reduce the occurrence.

DESCRIPTION OF SYMBOLS 1 ... Heating furnace, 2 ... Drive part, 3 ... Cooling tank, 4 ... Nozzle, 5 ... Spray unit,
6 ... Cylinder, 7 ... Control unit, 8 ... Support frame,

Claims (7)

An injection unit for injecting a spray fluid to a member to be cooled;
A cooling device comprising: a control unit that selects an injection condition based on characteristics of the cooling target member and the spray fluid and controls a stop time of the injection by the injection unit. The cooling device according to claim 1,
The cooling device characterized in that the characteristic of the member to be cooled is a surface temperature, a specific heat, a density or a heat conduction coefficient. The cooling device according to claim 1 or 2,
The cooling device characterized in that the characteristic of the spray fluid is the diameter, density, latent heat of vaporization, specific heat or temperature of the droplet. The cooling device according to claim 1,
The expression of the control unit the following, the cooling apparatus characterized by controlling the stopping time t _p of injection by the injection unit.

t _W : Time until the atomized fluid in contact with the surface of the member to be cooled evaporates [s]
r: Diameter of droplets constituting the spray fluid [m]
ρ _w is the density of the spray fluid [kg / m ³ ]
He: latent heat of vaporization of spray fluid [J / kg]
c _pw : Specific heat of spray fluid [J / (kg · K)],
T _m : surface temperature of the member to be cooled [K],
T _w : temperature of spray fluid [K]
h: Heat transfer coefficient between spray fluid and member to be cooled [W / (m ² · K)]
c _pm : Specific heat of the member to be cooled [J / kg · K]
ρ _m : Density of cooling target member [kg / m ³ ]
λm: Thermal conductivity coefficient of cooling target member [W / (m · K)] The cooling device according to claim 4,
Wherein the control unit, the cooling apparatus characterized by controlling the execution time of injection by the injection unit to 0.5-2 times the range of the stop time t _p. The cooling device according to claim 5,
The cooling object member is an iron-based member,
The droplet diameter of the spray fluid is in the range of 10 to 100 μm,
The execution time of the jet is in the range of 10 to 1000 milliseconds,
The cooling apparatus according to claim 1, wherein a stop time of the injection is in a range of 10 to 1000 milliseconds. The cooling device according to claim 5,
The cooling object member is an aluminum-based member,
The droplet diameter of the spray fluid is in the range of 10 to 100 μm,
The execution time of the jet is in the range of 10 to 500 milliseconds,
The cooling apparatus according to claim 1, wherein the injection stop time is in the range of 10 to 500 milliseconds.

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