JP4709955B2 - Gas cooling method for steel parts - Google Patents

Description

  The present invention relates to a gas cooling method for steel parts.

  In the vacuum furnace, steel parts loaded on the tray are carburized or austenite heated, and then the cooling gas is injected into the vessel that has been treated as described above, and forced convection cooling is performed by circulating the gas using a circulation fan, and this cooling gas is circulated. Cooling by a heat exchanger provided in the flow path is known as disclosed in, for example, Japanese Patent Laid-Open No. 4-280916.

  However, since the conventional gas cooling method and apparatus have a low cooling gas flow rate and an insufficient cooling rate, the application is limited to some tool steels and the like that do not require a very high cooling rate, such as SCM420 and SCr420. It was not applicable to baked steel.

  In order to increase the cooling rate, the cooling gas pressure may be set to a very high pressure, such as about 4 MPa. However, increasing the cooling gas pressure increases the size, increases the equipment cost, and decreases the handling and safety. Invite.

  In addition, when steel parts are loaded on a tray for processing, the flow rates for the individual steel parts are not uniform, so that the cooling rate is different and the quality of the steel parts varies. Moreover, if a heat exchanger is provided, flow path resistance will increase and the flow velocity will fall.

  The present invention eliminates the above-mentioned drawbacks.

In the gas cooling method for steel parts of the present invention, the cooling gas is enclosed in a vacuum sealed container containing the steel parts to be processed , and the cooling gas is sealed under reduced pressure by an axial fan provided in the upper center of the vacuum sealed container. A gas cooling method for a steel part that circulates in a vessel and forcibly convectively cools the steel part, and is disposed in an upper part of an annular wall 22 having an inverted conical space 20 in the center and the inverted conical space. and an upper annular space formed between the inverted truncated cone-shaped core portion 26 is formed between the lower portion of the annular wall 22 having a conical space 21 in the center, the passage cross section is narrowed, cooled The steel parts are arranged in a flow path where the gas flow rate increases, and the steel parts are forcibly cooled.

The gas cooling method for steel parts is characterized in that the cooling gas circulation passage has a plurality of guide pieces that extend in the vertical direction and radially outward, and whose upper ends are curved in an arc shape in the same circumferential direction. .

  The gas cooling method for steel parts according to the present invention is characterized in that an arbitrary cooling history is given to the steel parts by changing the rotational speed of the fan.

  The cooling gas may be nitrogen having a pressure of 1 MPa or less, an inert gas such as helium, hydrogen gas, or a mixed gas of two or more of these, or nitrogen having a pressure of 0.6 MPa. To do.

  As described above, according to the gas cooling method of the present invention, an inexpensive and easy-to-handle nitrogen gas is used as the cooling gas, which is difficult with the conventional apparatus at a lower pressure than the conventional apparatus of 0.6 MPa. The case-hardened steel can be quenched. In addition, since the operating pressure is low, a complicated heat exchanger is not required, and the motor can use a low-power general-purpose motor, the equipment can be simplified, equipment costs can be reduced, and safety is high. is there.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a vacuum sealed container 1, a vacuum pump 2, an exhaust path 3 connecting the vacuum pump 2 and the container 1, an exhaust valve 4 interposed in the exhaust path 3, and a reservoir storing cooling gas. The steel part cooling device includes a tank 5, a cooling gas introduction path 6 connecting the reservoir tank 5 and the container 1, and an introduction valve 7 inserted in the cooling gas introduction path 6.

  The decompression sealed container 1 in the steel parts cooling apparatus has a double cylinder structure composed of an outer cylinder 8 and an inner cylinder 9 as shown in FIG. 2, and a cooling water passage 10 is formed between the double cylinders. A steel part 11 to be treated is held at the center portion 13 of the inner cylinder 9 by a support base 12, and an intermediate cylindrical body 14 is disposed between the inner cylinder 9 and the support base 12, and this intermediate cylindrical body 14 and the inner cylinder 9, between the top lid 15 of the container 1 and between the bottom plate 16, fluid passages 17 to 19 are formed, respectively, and the inner peripheral surface of the intermediate cylindrical body 14 is narrowest at the central portion 13. In addition, an annular wall 22 having a trapezoidal longitudinal side surface is formed so that spaces 20 and 21 having an inverted frustoconical shape and a frustoconical cross-sectional shape gradually spreading in the vertical direction are formed.

  A circulation fan 23 is disposed at the upper center in the intermediate cylindrical body 14 and is rotated by a motor 24 placed on the upper lid 15.

Further, an internal duct 25 for rectifying the fluid flowing in the space 20 is disposed in the space 20 between the lower surface of the circulation fan 23 and the support base 12, and this internal duct 25 is shown in FIGS. As shown in the figure, a core portion 26 having an inverted circular frustoconical cross section extending from the upper portion of the space 20 toward the central portion 13, and an outer circumferential surface of the core portion 26 spaced apart from each other in the circumferential direction, A plurality of guide pieces 27 extending outward in the radial direction and having upper ends curved in an arc shape in the same circumferential direction, and any one of the guide pieces 27 is formed on the wall 22 of the intermediate cylindrical body 14. Fix it. This guide piece 27 changes the cooling gas from a swirling flow to a downward flow.

  Further, on the inner peripheral surface of the inner cylinder 9, a plurality of steel heat transfer fins 28, which are V-shaped radially inward and extend in the vertical direction as shown in FIG. A lower rectifying plate 31 whose central portion 29 swells upward in a conical shape and whose peripheral portion 30 curves upward in an arc shape is disposed on the upper surface 16, and the central portion 32 has an inverted conical shape on the lower surface of the upper lid 15. An upper baffle plate 33 that protrudes downward in a trapezoidal shape is disposed, and the rotation shaft 34 of the motor 24 extends toward the circulation fan 23 through the central portion.

  Reference numeral 35 denotes a magnetic seal formed between the upper lid 15 and the rotating shaft 34 of the motor 24, and 36 denotes a vacuum seal formed between the bottom plate 16 and the support rod 37 of the support base 12.

  In the gas cooling method for steel parts of the present invention, the internal pressure of the vacuum sealed container 1 is reduced to about 1 Pa (pressure at which the steel parts to be treated are not oxidized at the quenching temperature) through the exhaust valve 3 by the vacuum pump 2. After evacuating and holding the steel part 11 to be processed at a predetermined position in the vacuum sealed container 1, the exhaust valve 4 is closed, and then the cooling stored in the reservoir tank 5 installed outside in the vacuum sealed container 1 is stored. The gas is introduced until the introduction valve 7 is opened and a predetermined pressure, for example, 1 MPa to 0.6 MPa is reached. After the introduction valve 7 is closed and the cooling gas is sealed in the container 1, the circulation fan 23 provided on the upper part of the steel part 11 to be processed is driven by the motor 24, and the cooling gas is supplied to the space 20 as shown by an arrow in FIG. , 21 and the fluid passages 19, 17, 18.

  The circulating fan 23 is driven for a predetermined time to cool the steel part 11 to be processed, and during that time, the cooling gas is cooled via the inner cylinder 9 having the heat transfer fins 28 that are water-cooled.

  As the cooling gas, one kind of inert gas, one kind or a mixture of two or more kinds of inert gas, or hydrogen gas alone or a mixed gas of hydrogen gas and inert gas is used.

  As the circulation fan 23, an axial fan is used, and the output of the drive motor 24 is adjusted by an inverter or the like, and the rotation speed is changed to give an optimum heat history to the steel parts to be processed.

(Experimental example 1)

  In the gas cooling apparatus shown in FIG. 1, a ring-shaped steel part having a square cross section having an outer diameter of 190 mm, an inner diameter of 140 mm, a thickness of 25 mm, and a weight of 2.4 kg as the steel part 11 to be processed is heated to about 870 ° C. in the previous step. And quenching was performed. The material of the steel parts was SCM420 and SCr420, which are general case-hardened steel, the cooling gas was nitrogen alone, and the introduction pressure was 0.6 MPa.

  As the circulation fan drive motor 24, a 2-pole general-purpose motor with an output of 18.5 kw was used, the operation frequency was 60 Hz, and the rotation speed of the circulation fan 23 was 3600 rpm.

  FIG. 6 shows the change in cooling time-temperature of each part of the steel part to be treated during cooling. Curves (1) to (3) in FIG. 6 show temperature changes at the front, back, and side portions of the ring-shaped steel parts arranged as shown in FIG. As is apparent from FIG. 6, the respective parts of the steel parts to be treated were cooled substantially uniformly, and the temperature of the steel parts to be treated at the time of starting the fan was lowered to about 850 ° C. during the conveyance. Was 530 ° C. after 30 seconds, 300 ° C. after 60 seconds, 150 ° C. after 90 seconds, and 100 ° C. after 120 seconds.

  Moreover, the flow velocity of the cooling gas of the steel parts to be treated was 34 m / s (measured with an impeller-type current meter under atmospheric pressure). As a result of quenching, the core hardness of the steel parts to be processed was Rockwell hardness, SCM420 material was HRC32.5, and SCr420 material was HRC31.4. This value is substantially equivalent to the quenching hardness by quenching oil.

  FIG. 7 shows the relationship between the hardness of the hardened core part of the steel part to be treated when the material pressure of the steel part to be treated is SCM420 and the gas pressure is changed with the fan rotation speed of 3600 rpm, and FIG. Fig. 4 shows the relationship between the fan rotation speed and the hardness of the hardened core part of the steel part to be processed. Thus, it becomes possible to obtain arbitrary core hardness by changing a gas pressure and fan rotation speed.

(Experimental example 2)

  A ring gear having an outer diameter of 220 mm was placed in the gas cooling apparatus shown in FIG. 1 and quenched. The material of the steel part was SCM420, which is a general case-hardened steel, the cooling gas was nitrogen alone, and the introduction pressure was 0.6 MPa.

  As the circulation fan drive motor 24, a 2-pole general-purpose motor with an output of 18.5 kw was used, the operation frequency was 60 Hz, and the rotation speed of the circulation fan 23 was 3600 rpm.

  The temperature of the steel part to be treated at the time of starting the fan was lowered to about 830 ° C. during the conveyance, but the temperature (maximum wall thickness) of the steel part to be treated after the start of the fan was 430 ° C., 60 seconds after 30 seconds. It was 200 ° C. after 90 seconds, 80 ° C. after 90 seconds, and 50 ° C. after 120 seconds.

  FIG. 9 shows the results of measurement of the hardness distribution of the cross section of each part of the steel part to be treated after quenching after carburizing. Curves (1) to (3) in FIG. 9 show changes in the hardness of the front, back, and side portions of the ring-shaped steel parts arranged as shown in FIG. The hardness of the 0.05 mm portion from the surface of the steel part to be treated was about Hmv (0.5) 730 in terms of micro Vickers hardness, and the core hardness after quenching was HRC 30 in terms of Rockwell hardness. As is clear from FIG. 9, a uniform hardness distribution is obtained at each part of the steel part to be processed.

FIG. 10 shows the change in cooling time-temperature when the rotational speed of the circulation fan is changed using SCM420 as a steel part. Curves (1) to (4) use N ₂ gas of 6 bar, respectively. This is the case where the number is 3600 rpm, 3000 rpm, 1800 rpm, 600 rpm.

It is explanatory drawing of a gas cooling device. It is a vertical front view of the pressure-reduced airtight container in a gas cooling device. It is a top view of the internal duct in the pressure-reduced airtight container shown in FIG. It is a front view of the internal duct shown in FIG. FIG. 3 is a cross-sectional plan view of a part of the vacuum sealed container shown in FIG. 2. It is a diagram which shows the relationship of the cooling time-temperature of the steel components processed with the gas cooling method of the steel components of this invention. It is a diagram which shows the relationship between the core part hardness of the steel components processed by the gas cooling method of the steel components of this invention, and a cooling gas pressure. It is a diagram which shows the relationship between the core part hardness of a steel component processed with the gas cooling method of the steel component of this invention, and a fan rotation speed. It is a diagram which shows the relationship from the distance from the surface of the carburized steel part processed with the gas cooling method of the steel part of this invention, and hardness. It is a diagram which shows the relationship between the temperature-cooling time of the steel component processed with the gas cooling method of the steel component of this invention, and a circulation fan rotation speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressure-reduced airtight container 2 Vacuum pump 3 Exhaust path 4 Exhaust valve 5 Reservoir tank 6 Cooling gas introduction path 7 Introducing valve 8 Outer cylinder 9 Inner cylinder 10 Cooling water path 11 Steel part 12 to be processed 12 Support base 13 Central part 14 Intermediate cylindrical body 15 Upper lid 16 Bottom plate 17 Fluid passage 18 Fluid passage 19 Fluid passage 20 Space 21 Space 22 Annular wall 23 Circulating fan 24 Motor 25 Internal duct 26 Core portion 27 Guide piece 28 Heat transfer fin 29 Central portion 30 Peripheral portion 31 Lower rectifying plate 32 Center Part 33 Upper rectifying plate 34 Rotating shaft 35 Magnetic seal 36 Vacuum seal 37 Support rod

Claims (5)

Cooling gas is enclosed in a vacuum sealed container containing steel parts to be treated , and the cooling gas is circulated in the vacuum sealed container by an axial fan provided in the upper center of the vacuum sealed container, forcing the steel parts. A gas cooling method for steel parts for convection cooling,
An upper annular space formed between an upper portion of an annular wall 22 having an inverted conical space 20 in the center and an inverted frustoconical core portion 26 disposed in the inverted conical space;
The steel part is disposed in a flow path formed between the lower portion of the annular wall 22 having the conical space 21 at the center, the passage cross section becomes narrower, and the flow rate of the cooling gas is increased.
A method for gas cooling a steel part, comprising forcibly cooling the steel part. The steel part according to claim 1, wherein the outer peripheral surface of the core portion (26) has a plurality of guide pieces (27) extending in the vertical direction and radially outward, and having an upper end curved in an arc shape in the same circumferential direction. Gas cooling method.   The gas cooling method for a steel part according to claim 1 or 2, wherein an arbitrary cooling history is given to the steel part by changing the rotational speed of the fan.   The steel according to claim 1, 2 or 3, wherein the cooling gas is an inert gas such as nitrogen or helium at a pressure of 1 MPa or less, hydrogen gas, or a mixed gas of two or more of these. Gas cooling method for parts.   5. The method for cooling a steel part gas according to claim 1, wherein the cooling gas is nitrogen at a pressure of 0.6 MPa.

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