JP6836162B2 - Cooling treatment method - Google Patents

Description

The present invention relates to a cooling treatment method applied to a cooling treatment when quenching an object to be processed such as a mold.

It is known that strain occurs when an object to be processed made of ordinary steel, special steel, etc. is hardened. In the case of a particularly large object to be processed such as a mold, distortion, that is, warpage and deformation becomes large, so it is necessary to increase the processing white to correct these, which increases the processing cost and processing time. Is inviting.
Here, since tool steel or the like having excellent hardenability can obtain the required quenching hardness without quenching during quenching cooling, it is necessary to use a material having excellent hardenability such as tool steel for a large object to be processed. It was effective in reducing distortion. However, in recent years, further reduction in strain has been required, and it has become impossible to achieve sufficient reduction in strain by the conventional heat treatment method in which the quenching cooling rate is slowed down by using tool steel or the like.

The following Patent Document 1 discloses that the heat transfer coefficient differs between the molding surface and the back surface of the mold in the cooling treatment at the time of quenching, but the one described in Patent Document 1 is molded. It cools the surface faster than the back surface, which is different from the present invention.

JP-A-2015-178634

Against the background of the above circumstances, the present invention has been made for the purpose of providing a cooling treatment method capable of satisfactorily suppressing distortion when an object to be treated such as a mold is quenched.

A first aspect of the present invention is a method of cooling an object to be treated, which has a molded surface having an uneven shape and a flat back surface paired with the molded surface and having a weight of 150 kg or more and less than 400 kg. hand,
When cooling the heated object to be treated, the cooling for the back surface is made stronger than the cooling for the molded surface.
Cooling is performed under cooling conditions where the heat transfer coefficient ratio, which is the ratio of the heat transfer coefficient of the back surface to the heat transfer coefficient of the molded surface, is 1.1 or more and 5 or less at 800 ° C. to suppress distortion due to the cooling process. It is characterized by the fact that it has become.

The cooling treatment method of the present invention is particularly suitable for application to hot tool steels (SKD61, SKD61 improved steel, etc.) containing 3 to 8% Cr, which can be quenched even at a cooling rate slower than 15 ° C./min. ..

Since the surface area of an object to be treated such as a mold having a molded surface having irregularities and a flat back surface is different between the molded surface and the back surface, the amount of heat removed from the molded surface during the cooling treatment after quenching and heating. Cooling unevenness occurred based on the difference between the amount of heat removed from the back surface and the amount of heat removed from the back surface, which was a factor in the occurrence of distortion. The difference in the amount of heat removed can be adjusted by making the cooling relatively strong on the back surface having a small surface area and increasing the amount of heat removed from the back surface. Specifically, since the heat removal amount is represented by the product of the surface area and the heat transfer coefficient, the adjustment of the difference in the heat removal amount is realized by increasing the heat transfer coefficient on the back surface.
As a result of evaluation of various mold shapes and cooling conditions by the present inventors, cooling in which the ratio of the heat transfer coefficient of the molded surface to the back surface (heat transfer coefficient of the back surface / heat transfer coefficient of the molded surface) is 1.1 or more. It was found that the effect of low distortion can be obtained under the conditions. The present invention has been made based on such findings.

If the heat transfer coefficient ratio is too large, it will be distorted in the opposite direction. Since the optimum heat transfer coefficient ratio depends on the weight and shape of the object to be processed, the optimum heat transfer coefficient ratio can be appropriately adopted in the range of 1.1 or more as needed. In claim 1, the weight of the object to be treated is 150 kg or more and less than 400 kg, the heat transfer coefficient ratio is 5 or less.

Here, the heat transfer coefficient (W / (m ² · k)) is the temperature difference between the surface of the object to be treated and the atmosphere around it per unit area, per unit time, and per 1 ° C. The amount of heat transfer that flows, and this heat transfer coefficient represents the degree of cooling to the object to be processed. Specifically, it indicates the degree of total cooling strength that integrates individual cooling conditions such as the amount of cooling gas sent to the object to be processed, gas pressure, atmospheric temperature, and material of the object to be processed. This heat transfer coefficient sets the target object to be processed such as a mold, measures the temperature change of the surface of the object to be processed and the atmosphere in the vicinity during cooling, and determines how much heat is transferred from the object to be processed. By knowing it, it can be obtained experimentally in advance. Since the heat transfer coefficient also changes depending on the temperature of the object to be treated, in the present invention, it is defined by the heat transfer coefficient at a surface temperature of 800 ° C. A thermocouple, a radiation thermometer, an infrared camera, or the like can be used for temperature measurement.

Here in the present invention, the weight of the workpiece is not less than 400 kg, the heat transfer coefficient ratio 1.12 or more, shall be the 1.3 (Claim 2).

In the present invention, the average cooling rate from 1000 ° C. to 500 ° C. can be made slower than 15 ° C./min at the slowest cooling site in the central portion of the object to be treated (claim 3). In order to reduce the strain of the object to be processed, it is also important to reduce the temperature difference between the surface and the center of the object to be processed. If the average cooling rate is faster than 15 ° C./min, the temperature difference between the surface and the center of the object to be treated becomes large, large thermal stress is generated, and low strain may not be achieved. Then, it is desirable to cool the slowest cooling portion in the central portion of the object to be treated at a cooling rate slower than 15 ° C./min.

Here, the slowest cooling portion in the central portion of the object to be processed is approximately the position of the center of gravity of the object to be processed or a position in the vicinity thereof. The temperature can be measured by making a hole at the center of gravity of the object to be processed or at a position near the center of gravity and using a thermocouple. When the object to be processed is a die or the like, a hole close to the center of gravity is selected from the holes for water cooling, the holes for the cast pin, the holes for the extrusion pin, etc. that are formed in the mold in advance. It is also possible to select and measure the temperature using a thermocouple inserted into the hole and use this as the temperature of the slowest cooling site in the center. This is because the cooling rate is almost the same near the center of the object to be processed even if the temperature measurement position is slightly deviated.

On the other hand, if the cooling rate is too slow, pearlite transformation occurs even in tool steel or the like having good hardenability, and the hardness required for the mold or the like cannot be obtained. Since the hardenability differs depending on the composition of the object to be treated, it is difficult to specify the cooling rate, but it is necessary to cool at least at a cooling rate at which the area ratio of pearlite transformation is 5% or less. In this case, the cooling rate at the slowest cooling site corresponds to about 2 ° C./min to 8 ° C./min or more.

In the present invention, if a difference of 1.1 times or more is given to the heat transfer coefficients of the molded surface and the back surface, it does not depend on the cooling means. For example, it is possible to directly inject a liquid such as water or alcohol or a mist thereof onto the back surface side of the object to be treated to strengthen the cooling of the back surface. Further, even when the cooling of the molded surface is weak (that is, the cooling of the back surface is relatively strong) by using a means such as applying a heat insulating material to the molded surface of the object to be processed, the heat transfer coefficient ratio is high. If they are the same, the same low distortion effect can be obtained, but in the present invention, the object to be processed can be cooled by allowing cooling, and the back surface of the object to be processed can be cooled by impulse cooling (claim). Item 4). In this case, nitrogen gas, argon gas, helium gas, the atmosphere, or the like can be used as the cooling gas.

In the present invention, the temperature detecting means for detecting the temperature distribution on the surface of the object to be processed, the cooling means for cooling the surface of the object to be processed by discharging the cooling gas from the discharge port, and the cooling means can be moved in position. Using a cooling treatment facility equipped with a moving means for holding, the cooling means can be moved to the vicinity of the slowest cooling portion on the back surface of the object to be treated to perform local cooling of the slowest cooling portion. Yes (claim 5). In this way, the cooling gas is discharged to the slowest cooling portion on the back surface side, that is, the portion having the slowest cooling rate, which is specified based on the temperature distribution on the back surface of the object to be processed obtained by the temperature detecting means. By doing so, it is possible to suppress the variation in the temperature distribution on the back surface, accelerate the cooling rate on the back surface, and obtain a predetermined heat transfer coefficient ratio.
When local cooling is performed, the heat transfer coefficient changes in the back surface of the object to be processed. When determining the heat transfer coefficient ratio in the present invention, the heat transfer coefficient at the slowest cooling point in the back surface of the object to be cooled during local cooling is defined as the heat transfer coefficient on the back surface.

According to the present invention as described above, it is possible to provide a cooling treatment method capable of satisfactorily suppressing distortion when an object to be treated such as a mold is quenched.

It is a figure which showed the whole structure of the cooling treatment equipment used for the cooling treatment method of one Embodiment of this invention. It is an enlarged view which showed the tip part of the movable arm of FIG. It is a figure which showed the state before and after the rotation when the tip part of the movable arm of FIG. 2 was rotated. It is a figure which showed the relationship between the color of a laser beam used for a strain measurement, and the measurement accuracy. It is a figure for demonstrating an example of a cooling operation in a cooling processing equipment. It is a figure which showed the mold which is cooled by the cooling treatment method of the same embodiment. It is a figure for demonstrating the measuring method of flatness. It is a figure which showed the relationship between the heat transfer coefficient ratio and flatness when the mold of FIG. 6 was cooled. It is a figure which showed the mold different from FIG. 6 which is cooled by the cooling treatment method of the same embodiment. It is a figure which showed the relationship between the heat transfer coefficient ratio and flatness when the mold of FIG. 9 was cooled.

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the cooling treatment equipment 10 used in the cooling treatment method of the present embodiment. In FIG. 1, reference numeral 12 denotes a mold as an object to be processed, which is placed on a set jig 14 by a crane or the like after being heated to a quenching temperature in a heating chamber (not shown). Reference numeral 20 denotes a robot to which a nozzle 22 for local cooling described later is attached, and reference numeral 24 denotes an infrared camera located in front of the mold 12 as a temperature detecting means for detecting the temperature distribution on the surface of the mold 12.
Further, the cooling processing equipment 10 has a compressor 26, a dryer 27, and an air tank 28, which are a series of devices for generating and storing compressed air, on the left side in FIG. 1A. Further, the cooling processing equipment 10 has a control unit 30 that controls the operation of the equipment.

The mold 12 is made of tool steel (SKD61) and has a molding surface (design surface) 12a having an uneven shape and a large surface area, and a flat back surface 12b located on the opposite side of the molding surface 12a. In this example, the mold 12 is placed on the set jig 14 with the back surface 12b facing forward (the side on which the robot 20 and the infrared camera 24 are arranged).
The steel type used for the mold 12 is not particularly limited, and a special steel having excellent hardenability can be appropriately used. Further, the size of the mold is not particularly limited, but the present invention is particularly effective in a mold having a weight of 150 kg or more in which uneven cooling is likely to occur in the cooling process of quenching.

The position of the infrared camera 24 is set so that the entire back surface 12b of the mold 12 is included in the detection range, the temperature distribution of the back surface 12b of the mold 12 is detected, and the rearmost surface 12b of the mold 12 is detected. The slow cooling part (highest temperature part) is specified, and the temperature of the slowest cooling part is detected. Then, the result of temperature detection by the infrared camera 24 is sent to the control unit 30. The control unit 30 controls the cooling conditions for the mold 12 based on the detection result. Further, it is also possible to provide an infrared camera 25 for detecting the temperature distribution of the molding surface 12a on the opposite side of the mold 12 from the infrared camera 24.

The robot 20 has a base 34 fixed on the gantry 32 and a movable arm 36 extending from the base 34. The movable arm 36 has a plurality of joints that rotate or bend, and the tip 38 of the movable arm 36 moves up and down, left and right, and anteroposteriorly, that is, in a three-dimensional direction within the movable range indicated by the two-dot chain line in FIG. It is said to be movable. A nozzle 22 for locally cooling the mold 12 is attached to the tip 38.
Immediately after being heated to the quenching temperature, the mold 12 becomes extremely hot. In this example, the robot 20 is installed at a position deviated from the front surface of the mold 12 in order to prevent the influence of the radiant heat from the mold 12 on the entire robot 20.

FIG. 2 is an enlarged view of the tip 38 of the movable arm 36. As shown in the figure, the tip portion 38 is rotatably connected to the root side of the movable arm 36 about the joint axis P. A box-shaped heat shield 42 is attached and fixed to the attachment member 40 of the tip 38 located on the side opposite to the joint axis P by the attachment bolt 44.

The heat shield 42 has a fixed portion 42a directly fixed to the mounting member 40 on the movable arm 36 side, a flat plate-shaped base 42b fixed in a state orthogonal to the fixed portion 42a, and a base 42b. It is provided with a lid 42c fixed to the base 42b so as to cover one surface, and has a box shape as a whole in which walls for heat shielding are formed in each of the vertical, horizontal, and front-rear directions. The heat shield 42 shields the heat radiated from the mold 12 toward the tip 38 of the movable arm 36, and protects the sensor and the like housed inside.

Reference numeral 46 denotes a laser-type displacement detection sensor used for measuring the strain on the surface of the mold 12, which is housed inside the heat shield 42 and is placed on the base 42b via a bracket 47 having a T-shaped cross section. It is fixed to the inner surface. As shown in FIGS. 2A and 2B, the sensor 46 is located at the position farthest from the joint axis P (on the left side in the drawing), that is, at the position closest to the surface of the mold 12. It is arranged in the vicinity of the first wall surface 48 of the shield body 42. An opening 51 is formed in the first wall surface 48, and the heat-resistant glass 52 is fitted therein. The detection laser beam emitted from the light emitting portion 46a of the sensor 46 is emitted to the outside through the opening 51. After being reflected on the surface of the mold 12 which is the object, the light is received by the light receiving portion 46b through the opening 51 as well. The received reflected light is imaged on the light position detecting element in the light receiving unit 46b, and the amount of displacement in the height direction to the surface of the mold 12 is measured based on the imaged position.
In this example, the non-contact strain measuring device 11 is configured by the sensor 46, the heat shield 42, and the movable arm 36 that holds them movable.

In this example, since the displacement amount (strain amount) of the surface of the mold 12 in a high temperature state heated to the quenching temperature is measured by using the sensor 46, if the laser beam emitted from the sensor 46 is red, the mold It is easily affected by the red heat of 12 itself. Therefore, the sensor 46 of this example uses a blue laser beam having a wavelength of 350 to 450 nm.

FIG. 4 shows the measurement accuracy when the laser beam emitted from the laser displacement sensor 46 is red (FIG. 4B) and blue (wavelength is 350 to 450 nm) (FIG. 4C). It is a figure. The measurement results shown in FIGS. 4 (B) and 4 (C) created a step of 10 mm × 10 mm × height 1 mm near the center of the block 13 of 300 mm × 300 mm × 300 mm shown in FIG. 4 (A). This is the result of measuring the step in the state where the block 13 is heated to 800 ° C. Specifically, this 1 mm step is measured 10 times, and the average value of the 10 times and the measured value having the largest difference from the average value are plotted as an error bar. The measurement is performed while sequentially changing the measurement distance between the block 13 and the sensor 46.

As shown in FIG. 4B, in the case of the red laser, it is not possible to measure a step of 1 mm properly due to the influence of the red heat of the block 13. On the other hand, in the case of the blue laser, as shown in FIG. 4C, the closer the measurement distance (distance between the block 13 and the sensor 46) is, the more accurately the step can be measured. Mold strain measurement requires a repeatability of 0.2 mm or less, but according to the results shown in FIG. 4, a blue laser has a repeatability of 0.2 mm or less by setting the measurement distance to 500 mm or less. That is, it can be seen that it is possible to measure within an error range of ± 0.1 mm with respect to a step of 1 mm.

However, since the mold 12 has an extremely high temperature, if the measurement distance (L _{1 in} FIG. 3A) is set to 500 mm or less, the temperature of the sensor 46 inside the heat shield 42 may exceed the operation guarantee range. Therefore, in this example, as shown in FIG. 2, the fixed portion 42a of the heat shield body 42 is provided with an introduction port 54 for introducing compressed air for cooling inside the heat shield body 42. Through this introduction port 54, the tip of the pipe 55 connected to the air tank 28 via a flow rate adjusting valve (not shown) is inserted inside the heat shield 42, and in this example, it is based on the control of the control unit 30. The compressed air in the air tank 28 is supplied from the introduction port 54 to the inside of the heat shield 42. The base 42b is formed with an exhaust port 58 communicating with the outside, and the compressed air introduced inside the heat shield 42 is discharged to the outside through the exhaust port 58.
As described above, in this example, the compressed air is configured to circulate inside the heat shield 42 to prevent the sensor 46 from becoming hot (specifically, 50 ° C. or higher). It is also possible to prevent the sensor 46 from becoming hot by providing a water cooling mechanism on the first wall surface 48, which is located between the sensor 46 and the mold 12 to shield heat during strain measurement. It is possible.

On the other hand, as shown in FIG. 2A, the nozzle 22 for locally cooling the mold 12 is attached and fixed to the inside of the fixed portion 42a of the heat shield 42 via the bracket 60, and the tip of the nozzle 22 is attached and fixed. The discharge port 22a protrudes outward from the second wall surface 49, which is different from the first wall surface 48 in which the sensor 46 in the heat shield 42 is arranged close to each other.
The nozzle 22 is connected to the air tank 28 via a flow rate adjusting valve (not shown), and the mold is cooled from the discharge port 22a of the nozzle 22 for local cooling based on the control of the control unit 30. Compressed air is discharged as a gas.

As described above, in the cooling treatment equipment 10, the discharge port 22a of the nozzle 22 is provided so that the cooling gas is discharged from the second wall surface 49 different from the first wall surface 48 of the heat shield 42. By rotating the tip 38 around the joint axis P, strain measurement and local cooling are switched. That is, when measuring the strain of the mold 12, as shown in FIG. 3A, the first wall surface 48 of the heat shield 42 faces the surface of the mold 12. When the mold 12 is locally cooled, the second wall surface 49 of the heat shield 42 faces the surface of the mold 12 as shown in FIG. 3 (B).

Next, an example of the operation when the cooling process is performed using the cooling process facility 10 of the present embodiment will be described. In this example, the cooling process is performed so that the cooling rate at the slowest cooling portion of the mold 12 made of SKD61 and having a width of 600 mm, a height of 600 mm, and a thickness of 150 mm is 10 ° C./min.
As shown in FIG. 1, first, the mold 12 is heated to the quenching temperature in a heating chamber (not shown) and then placed on the set jig 14 by a crane or the like.
Then, the mold 12 is allowed to cool in the atmosphere. At the same time, the infrared camera 24 detects the temperature distribution on the surface of the mold 12. Then, the slowest cooling portion on the surface of the mold 12 is specified based on the detection result of the temperature distribution. The control unit 30 outputs the position information (X, Y coordinates) of the slowest cooling portion to the robot 20.

As shown in FIG. 3B, the robot 20 moves the discharge port 22a of the nozzle 22 attached to the tip 38 of the movable arm 36 to the point G of the specified slowest cooling portion. _{Then, from the distance of L 2} above the point G of the slowest cooling part (300 mm in this case), compressed air for cooling is blown toward the slowest cooling part, and the slowest cooling part (or the slowest cooling part and its peripheral part). Is locally cooled.

In this example, this cooling operation is continued until the slowest cooling portion reaches 600 ° C. As shown by the alternate long and short dash line in FIG. 5, the control unit 30 has a preset transition of the planned surface temperature since the start of the cooling operation, that is, the cooling rate (10 ° C./min in this example), and is infrared. The cooling condition is controlled based on the difference between the detected temperature and the planned surface temperature while moving the position of the discharge port 22a of the nozzle 22 to the slowest cooling portion specified by the monitoring of the camera 24 at any time.
Specifically, when the detected temperature of the slowest cooling part is higher than the planned surface temperature shown in FIG. 5, the amount of compressed air for local cooling is increased, and when the detected temperature is lower than the planned surface temperature. Reduces the amount of compressed air for local cooling. By doing so, the slowest cooling portion on the back surface 12b, which is the target of the cooling treatment, can be cooled at a planned cooling rate or a cooling rate close to the planned cooling rate.
Even after the detection temperature of the slowest cooling portion falls below 600 ° C., it is possible to continue the cooling treatment so as to match the preset planned surface temperature transition. In some cases, when the detection temperature of the slowest cooling portion reaches a predetermined temperature of 600 ° C. or lower, it is possible to switch to oil cooling and continue the cooling process.

Next, the mold 70 (SKD6, 500 mm × 450 mm × 180 mm) having a weight of 190 kg shown in FIG. 6 is subjected to cooling treatment having different heat transfer coefficient ratios, and the pearlite area ratio and the back surface of the mold 70 after the cooling treatment are subjected to different cooling treatments. The results of evaluating the flatness of the above are shown in Table 1 below.

In the evaluation, before the heat treatment, after confirming that the flatness of the back surface of the mold 70 is 0.02 mm or less, the mold is heated and held at 1030 ° C. in a heating furnace, and then taken out from the heating furnace and gold. The mold 70 was allowed to cool, and impulse cooling was performed on the back surface 70b or the molding surface 70a of the mold 70 using the cooling treatment equipment 10.
Specifically, in Comparative Examples 1 and 2, the molding surface 70a was cooled by an impulse, and the cooling on the molding surface 70a was made stronger. In Examples 1 to 5 and Comparative Examples 4 to 13, blast cooling was performed on the back surface 70b, and the cooling on the back surface 70b was strengthened. In these Examples and Comparative Examples, the value of the heat transfer coefficient ratio is changed by changing the air volume of the okikaze cooling. In Comparative Example 3, cooling is performed only by allowing cooling.

The surface temperature of the mold 70 during okikaze cooling was measured by infrared cameras 24 and 25. Further, after making a hole of Φ3 inside the mold 70 (position near the center of gravity), a thermocouple was inserted and the temperature inside the mold 70 was measured. Then, after the cooling treatment was completed, the pearlite area ratio and the flatness of the back surface 70b of the mold 70 were measured.

<Heat transfer coefficient ratio>
The heat transfer coefficient corresponding to each cooling treatment condition can be obtained as follows. First, a 200 mm × 200 mm × 100 mm test piece made of the same steel type as the mold 70 was prepared, and thermocouples were embedded at a depth of 2 mm from the center of one surface of the test piece and at a depth of the center of gravity of the test piece. Then, the surface temperature of the test piece and the internal temperature of the mold (the temperature at the center of gravity) can be measured. In addition, the ambient temperature of the test piece, which is 20 mm away from the surface on which the temperature is measured, can also be measured with a thermocouple.

After heating this test piece to 1030 ° C and holding it for 1 hour, the test piece is cooled to 500 ° C by the same method as the cooling treatment method for which the heat transfer coefficient is to be obtained, and the temperature change of the test piece is converted into a thermocouple. To measure. Next, perform a simulation while changing the heat transfer coefficient so that the measured temperature change can be reproduced, and if the measured temperature change can be reproduced, use that heat transfer coefficient as the heat transfer coefficient in the cooling treatment method. Can be done. In this example, the heat transfer coefficient when the surface temperature of the test piece is 800 ° C. is taken as the heat transfer coefficient of the surface. In this way, the heat transfer coefficient of the molded surface and the heat transfer coefficient of the back surface in each cooling treatment method are obtained, and the value calculated by (heat transfer coefficient of the back surface) / (heat transfer coefficient of the molded surface) is the heat transfer coefficient. It was a ratio.

<Cooling rate of the slowest cooling part>
The cooling rate (° C./min) of the slowest cooling portion shown in Table 1 is the average cooling rate from 1000 ° C. to 500 ° C. inside the mold (position near the center of gravity) measured by a thermocouple.

<Flatness>
As shown in FIG. 7, the flatness (mm) is measured from the straight line m connecting the two reference points k located on the plane to be measured (here, the back surface 70b) to the back surface 70b located directly above the straight line m. It shows how much the point p is deviated in the vertical direction of the straight line m, and when two various reference points k are set in the back surface 70b, the one having the largest flatness is the plane on the back surface 70b. It was a degree. Here, the target flatness is 0.5 mm or less.

<Pearlite area ratio>
A test piece having a size of 10 × 10 × 10 mm is collected from the slowest cooling part of the mold 70 (here, a position near the center of gravity), one surface of the test piece is mirror-polished, and then etched with picric acid, nitric acid, or the like. To do. Since the pearlite-transformed portion turns black due to etching, the area ratio (%) of the black-colored region is obtained. Here, the target is a pearlite area ratio of 5% or less so that the hardness required for the mold can be obtained.

As shown in Table 1 and FIG. 8, in the mold 70, the flatness is changed by changing the heat transfer coefficient ratio during the cooling process. When the heat transfer coefficient ratio is less than 1, the back side of the mold 70 is deformed to be convex, and when the heat transfer coefficient ratio is close to 10, the back side is deformed to be concave. There is a tendency for the flatness to deteriorate in each case.
In this evaluation, the flatness of the back surface is excellent when the heat transfer coefficient ratio is in the range of 1.1 to 5. When the molding surface 70a and the back surface 70b are cooled with the same strength (that is, when the heat transfer coefficient ratio is 1), the flatness is 0.68 mm, whereas the cooling capacity on the back surface side is increased. By setting the heat transfer coefficient ratio within the range of 1.1 to 5, the flatness can be set to 0.5 mm or less, which is the target value.

Further, in the examples and comparative examples shown in Table 1, the cooling rate at the slowest cooling portion inside the mold was as fast as 23 ° C./min or more, the pearlite area ratio was 0%, and the generation of pearlite was observed. There wasn't.

Next, using a mold 80 (SKD61, width 660 mm × height 500 mm × thickness 220 mm) having a weight of 480 kg shown in FIG. 9, cooling treatments having different heat transfer coefficient ratios were performed to obtain the pearlite area ratio of the slowest cooling portion and the pearlite area ratio. The results of evaluating the flatness of the back surface are shown in Table 2 below. The evaluation method is the same as that for the mold 70.

As shown in Table 2 and FIG. 10, in the mold 80 as well, as in the case of the mold 70, when the heat transfer coefficient ratio is small, the back side is deformed so as to be convex, while the heat transfer coefficient ratio As the value increases, deformation occurs such that the back surface side becomes concave, and the flatness tends to deteriorate in each case. In this evaluation, the flatness of the back surface is excellent when the heat transfer coefficient ratio is in the range of 1.1 to 1.3. When the molded surface 80a and the back surface 80b are cooled with the same strength (that is, when the heat transfer coefficient ratio is 1), the flatness is 0.6 to 0.8 mm, whereas the cooling capacity on the back surface side is By increasing the heat transfer coefficient ratio within the range of 1.1 to 1.3, the flatness can be set to 0.5 mm or less, which is the target value. As described above, in both the molds 70 and 80 having different weights, by increasing the heat transfer coefficient ratio to 1.1 or more, it is possible to obtain a mold having a flatness of 0.5 mm or less and low distortion. ing.

Further, in the examples and comparative examples shown in Table 2, the cooling rate at the slowest cooling portion inside the mold was 9 to 13 ° C./min, and the pearlite area ratio both satisfied the target value of 5% or less. ing.

As described above, in the cooling treatment method of the present embodiment, when the heated mold is cooled, the cooling on the back surface is made stronger than the cooling on the molded surface, and the heat transfer coefficient of the back surface with respect to the heat transfer coefficient of the molded surface is set. By cooling under cooling conditions where the heat transfer coefficient ratio, which is the ratio, is 1.1 or more at 800 ° C., a mold having excellent flatness can be obtained.

According to the cooling processing method of the embodiment, when the mold 80 is mass 400kg or more, the heat transfer coefficient ratio with 1.1 2 to 1.3 is effective for reducing distortion reduction, further In Examples 6 to 12 in which the slowest cooling portion was cooled at a cooling rate slower than 15 ° C./min, a mold having a flatness of 0.5 mm or less was obtained.

In the present invention, the infrared camera 24 that detects the temperature distribution on the surface of the mold 12, the nozzle 22 that discharges cooling gas from the discharge port 22a to cool the surface of the mold, and the nozzle 22 can be moved in position. Using the cooling processing equipment 10 provided with the movable arm 36 for holding the nozzle 22, the nozzle 22 is moved to the vicinity of the slowest cooling portion (maximum temperature portion) on the surface of the back surface 12b of the mold 12 to perform the slowest cooling. Local cooling of the site is performed.
In this cooling processing facility 10, the cooling gas is discharged to the slowest cooling portion specified based on the temperature distribution on the back surface 12b of the mold 12 obtained by the infrared camera 24, so that the temperature distribution on the back surface 12b It is possible to obtain a predetermined heat transfer coefficient ratio by suppressing the variation in the temperature and increasing the cooling rate of the back surface 12b.

The embodiments of the present invention have been described in detail above, but this is merely an example. For example, it is possible to use something other than a mold as the object to be processed. Further, in the above embodiment, a predetermined heat transfer coefficient ratio is obtained by air-cooling the back surface side, but it is also possible to obtain a predetermined heat transfer coefficient ratio by using another method. It can be implemented with various changes within the range that does not deviate from the purpose.

10 Cooling treatment equipment 12, 70, 80 Mold (object to be treated)
12a, 70a, 80a Molded surface 12b, 70b, 80b Back surface 22 Nozzles (cooling means)
22a Discharge port 24 Infrared camera (temperature detection means)
36 Movable arm (means of transportation)

Claims (5)

A method of cooling an object to be processed having a molded surface having an uneven shape and a flat back surface paired with the molded surface and having a weight of 150 kg or more and less than 400 kg.
When cooling the heated object to be treated, the cooling for the back surface is made stronger than the cooling for the molded surface.
Cooling is performed under cooling conditions where the heat transfer coefficient ratio, which is the ratio of the heat transfer coefficient of the back surface to the heat transfer coefficient of the molded surface, is 1.1 or more and 5 or less at 800 ° C. to suppress distortion due to the cooling process. A cooling treatment method characterized by the above. A method of cooling an object to be processed, which has a molded surface having an uneven shape and a flat back surface paired with the molded surface and having a weight of 400 kg or more.
When cooling the heated object to be treated, the cooling for the back surface is made stronger than the cooling for the molded surface.
Cooling is performed under cooling conditions where the heat transfer coefficient ratio, which is the ratio of the heat transfer coefficient of the back surface to the heat transfer coefficient of the molded surface, is 1.12 or more and 1.3 or less at 800 ° C. A cooling treatment method characterized by being suppressed. The cooling according to any one of claims 1 and 2, wherein the average cooling rate from 1000 ° C. to 500 ° C. is slower than 15 ° C./min at the slowest cooling portion in the central portion of the object to be treated. Processing method. The cooling treatment method according to any one of claims 1 to 3, wherein the object to be processed is cooled by allowing to cool, and the back surface of the object to be processed is cooled by an impulse. A temperature detecting means for detecting the temperature distribution on the surface of the object to be treated, and
A cooling means that cools the surface of the object to be processed by discharging a cooling gas from the discharge port.
Using a cooling treatment facility provided with a moving means for holding the cooling means so as to be movable in position,
The cooling according to any one of claims 1 to 3, wherein the cooling means is moved to the vicinity of the slowest cooling portion on the back surface side of the object to be processed to perform local cooling of the slowest cooling portion. Processing method.

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