JP6459697B2 - Carburizing and quenching control device and carburizing and quenching method - Google Patents

Description

  The present invention relates to a carburizing and quenching control device and a carburizing and quenching method, and is particularly suitable for use in carburizing and quenching a gear.

  Gears used in automobiles and industrial machines are repeatedly subjected to high stress. Therefore, such gears are required to have high fatigue resistance and wear resistance. Therefore, carburizing and quenching is performed on gears formed using SCr420, SCM420, SCM435, and the like defined for JIS G 4053 alloy steel for machine structural use. Thereby, the surface of a gear can be hardened and the fatigue resistance and wear resistance of a gear can be improved.

  Carburizing and quenching is performed as follows. First, a heat treatment is performed on the steel member (heating process). In the heat treatment, the steel member is heated to an austenite transformation temperature or higher. Then, carburizing process is performed with respect to the steel member by which the heat processing was performed (carburizing process). In the carburizing process, carbon is diffused and penetrated from the surface of the steel member to increase the carbon concentration on the surface of the steel member. Thereafter, a quenching process is performed on the steel member that has been carburized (cooling step). In the quenching process, the steel member is rapidly cooled to generate a martensite structure on the surface of the steel member. By performing carburizing and quenching including the above heat treatment, carburizing treatment, and quenching treatment, a steel member having high surface hardness and toughness can be obtained.

  However, when carburizing and quenching is performed, thermal stress due to a temperature difference between the surface portion and the inside of the steel member and transformation stress due to volume change accompanying the phase transformation of the steel member are generated in the cooling step (quenching treatment). For this reason, heat treatment distortion occurs in the steel member. One such heat treatment strain is an internal warping strain. The warpage distortion affects the quality of a gear that has teeth formed on one of the top surface and the bottom surface and has no teeth formed on the other surface, such as a hypoid gear or a bevel gear. Inward warping means that, on a surface where no teeth are formed, the outer peripheral side warps in a direction opposite to the surface where the teeth are formed, rather than the inner peripheral side. The flat surface on which the teeth are not formed and the surface on which the teeth are formed have different surface areas and thus have different cooling rates. The warpage occurs due to the difference in cooling rate.

Therefore, there is a technique called press quench as a technique for quenching gears that have been carburized in a carburizing furnace. In press quench, the gear is constrained by a bore holder so that the inner diameter of the gear does not change, and the gear is hardened by holding the gear with a presser mold so that displacement in the thickness direction of the gear does not occur. Do.
However, in the press quench, it is necessary to set the gears one by one in the equipment and perform the quenching process. Therefore, it is not easy to improve production efficiency. In addition, since special equipment for press quenching is required, it is not easy to reduce production costs.

Therefore, there is a demand for a technique for suppressing gear distortion that occurs in the quenching process without using a press quench. As this type of technology, there are technologies described in Patent Documents 1 and 2.
Patent Document 1 discloses a technique for forming an annular step at a corner between a gear mounting surface and an outer peripheral surface.
Patent Document 2 discloses that, during the quenching process, an extremely thin coating layer is coated on the surface of a portion where gear cooling is difficult to proceed to increase the apparent heat transfer coefficient of the portion. Further, Patent Document 2 discloses that a heat treatment jig is provided at a portion where the gear cooling is likely to proceed to lower the apparent heat transfer coefficient of the portion.

JP 2009-52125 A JP 2010-174289 A

M.VITOR LI et al., "A Computational Model for the Prediction of Steel Hardenability", METALLURGICAL AND MATERIALS TANSACTIONS B, VOLUME 29B, JUNE 1998, pp.661-672 JYRKI MIETTINEN, "Caluculation of Solidification-Related Thermophysical Properties for Steels", METALLURGICAL AND MATERIALS TANSACTIONS B, VOLUME 28B, JUNE 1997, pp.281-297 D.P.KOISTINEN et al., "A general equation prescribing the extent of the austenite-martensite transformation in pure iron-carbon allows and plain carbon steels", ACTA METALLURGICA, VOL.7, 1959, pp.59-60 S. Denis, E. Gautier, A. Simon, G. Beck "Stress-phase-transformation interactions-basic principles, modeling, and calculation of internal stresses", Materials Science and Technology Vol.1, October 1985, pp.805- 814 Dassault Systemes. Abaqus 6.11: Analysis user's manual. Providence, RI: Dassault Systemes Simulia Corp., 2011. P. Maynier, J. Dollet and P. Bastien, in: Hardenability Concepts with Applications to Steels, edited by D.V.Doane and J.S. Kirkaldy, AIME, New York, NY, (1978), pp.518-544

  However, in the technique described in Patent Document 1, the shape of the gear must be different from the original shape. Furthermore, since it is necessary to form a step in the gear, the cost of the gear increases. In addition, the technique described in Patent Document 2 requires a coating layer and a heat treatment jig, which increases the cost of gears.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to suppress warping distortion generated in a gear after quenching without increasing the cost of the gear as much as possible.

The carburizing and quenching control device of the present invention is a gear in which teeth are formed on one surface of the upper surface and the bottom surface, and teeth are not formed on the other surface, and the gear that has been subjected to carburizing treatment, A carburizing and quenching control device for performing quenching by immersing in the cooling medium in a state in which the other surface is on the cooling medium side and movement in a direction along the rotation axis is not restricted,
Have a control means for controlling a constant immersion speed is the moving speed of the gear at the time of immersing the gear to the cooling medium, said control means of the gear at the time of immersing the gear to the cooling medium The moving speed is controlled to be constant at the immersion speed V _i [mm / s] determined by the following formulas (A) to (D) .
δ = a ₁ {1-exp (−a ₂ V _i )} + a ₃ (A)
a ₁ = A ₁ + A ₂ G _x + A ₃ G _y + A ₄ w (B)
a ₂ = B ₁ + B ₂ G _x + B ₃ G _y + B ₄ w (C)
a ₃ = C ₁ + C ₂ G _x + C ₃ G _y + C ₄ w (D)
Here, δ is a warp strain [mm] which is a displacement amount of the other surface of the gear caused by warping of the gear due to the quenching and is a displacement amount in a direction along the rotation axis, A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are predetermined coefficients, and G _x is the warpage When the gear is assumed to have no distortion, the centroid of the region excluding the portion where the teeth are formed out of the cross-sectional region cut along the rotation axis, and the rotation shaft G _y is a shape parameter represented by the shortest distance [mm], and G _y is a tooth in a cross-sectional area obtained by cutting the gear along the rotation axis when it is assumed that the warp distortion is not generated. Is expressed by the shortest distance [mm] between the centroid of the region excluding the portion where the is formed and the other surface of the gear. W is the difference between the inner diameter and the outer diameter of the region of the gear excluding the portion where the teeth are formed when it is assumed that the warp distortion has not occurred. Is a shape parameter represented by a length [mm] of [1/2].

The carburizing and quenching control method of the present invention is a gear in which teeth are formed on one surface of the upper surface and the bottom surface, and teeth are not formed on the other surface, and a gear that has been subjected to carburizing treatment, A carburizing and quenching method in which the other surface is on the cooling medium side and is quenched by being immersed in the cooling medium in a state in which movement in a direction along the rotation axis is not restricted. The moving speed of the gear when immersed in the cooling medium is made constant at an immersion speed V _i [mm / s] determined by the following expressions (A) to (D).
δ = a ₁ {1-exp (−a ₂ V _i )} + a ₃ (A)
a ₁ = A ₁ + A ₂ G _x + A ₃ G _y + A ₄ w (B)
a ₂ = B ₁ + B ₂ G _x + B ₃ G _y + B ₄ w (C)
a ₃ = C ₁ + C ₂ G _x + C ₃ G _y + C ₄ w (D)
Here, δ is a warp strain [mm] which is a displacement amount of the other surface of the gear caused by warping of the gear due to the quenching and is a displacement amount in a direction along the rotation axis, A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are predetermined coefficients, and G _x is the warpage When the gear is assumed to have no distortion, the centroid of the region excluding the portion where the teeth are formed out of the cross-sectional region cut along the rotation axis, and the rotation shaft G _y is a shape parameter represented by the shortest distance [mm], and G _y is a tooth in a cross-sectional area obtained by cutting the gear along the rotation axis when it is assumed that the warp distortion is not generated. Is expressed by the shortest distance [mm] between the centroid of the region excluding the portion where the is formed and the other surface of the gear. W is the difference between the inner diameter and the outer diameter of the region of the gear excluding the portion where the teeth are formed when it is assumed that the warp distortion has not occurred. Is a shape parameter represented by a length [mm] of [1/2].

  According to the present invention, since the immersion speed when the gear is immersed in the cooling medium is controlled, it is possible to suppress warping distortion generated in the gear after quenching without performing any special treatment on the gear. Therefore, the warp distortion generated in the gear after quenching can be suppressed without increasing the cost of the gear as much as possible.

It is a figure which shows an example of quenching equipment. It is a figure explaining an example of an internal curvature distortion. It is a figure which shows an example of a shape parameter. It is a figure which shows an example of the isothermal transformation curve of the steel materials in arbitrary alloy elements. It is a figure which shows the 1st example of the relationship between the temperature of steel materials, and distortion. It is a figure which shows the 2nd example of the relationship between the temperature of steel materials, and distortion. It is a figure explaining a pitch circle diameter. It is a figure which shows an example of the three-dimensional model of a gearwheel. It is a figure which shows an example of heat processing conditions (heat pattern). It is a figure which shows the 1st example of a heat transfer coefficient. It is a figure which shows the shape of the gear after hardening. It is a figure which shows the residual stress of the circumferential direction generate | occur | produced inside the gear after hardening. It is a figure which shows the plastic strain of the circumferential direction generate | occur | produced inside the gear after hardening. It is a figure which shows the transformation plastic strain of the circumferential direction generate | occur | produced in the inside of the gear after hardening. It is a figure which shows an example of the relationship between the generation | occurrence | production position of the internal curvature distortion and external curvature distortion which generate | occur | produce in a gearwheel, and tensile stress. It is a figure which shows the shape data of a gear in a table | surface form. It is a figure which shows the 1st example of the relationship between the immersion speed of each gear, and the curvature distortion by hardening. It is a figure explaining that the curvature distortion which generate | occur | produces in each gearwheel reduces. It is a figure which shows the carbon concentration in each position of the depth direction from the surface of the gear after hardening. It is a figure which shows distribution of the Vickers hardness of the gear after hardening. It is a figure which shows the Vickers hardness in each position of the depth direction from the points A and B of the surface of a gearwheel. It is a figure which shows the outermost surface hardness and effective hardened layer depth in the points A and B of the surface of a gear, and the Vickers hardness in the point C inside a gear. It is a figure which shows the 1st example of the relationship between the immersion speed of each gear, and the curvature distortion by hardening. It is a figure which shows the relationship between the immersion speed of each gear shown in FIG. 23, and the curvature distortion by quenching with a semi-logarithmic graph. It is a figure which shows the 2nd example of a heat transfer coefficient. It is a figure which shows the 3rd example of the relationship between the immersion speed of each gear, and the curvature distortion by hardening. It is a figure which shows the relationship between the immersion speed of each gear shown in FIG. 27, and the curvature distortion by quenching with a semi-logarithmic graph.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
(Hardening equipment)
FIG. 1 is a diagram illustrating an example of a quenching facility for performing a quenching process in carburizing and quenching.
In FIG. 1, a plurality of gears 100a to 100d are gears that have been carburized in a carburizing furnace. Since the plurality of gears 100a to 100d are the same, in the following description, when the plurality of gears 100a to 100d are collectively referred to, they are referred to as the gear 100 as necessary.

The gear 100 has teeth formed on one surface of the upper surface and the bottom surface, and no teeth are formed on the other surface. If it is such a gear, the kind of gear 100 will not be specifically limited. For example, a hypoid gear or a bevel gear can be employed as the gear 100. In the example shown in FIG. 1, the other surface of the gear 100 is a substantially flat surface.
In the following description, such a gear is simply abbreviated as a gear as necessary. In the following description, a surface on which teeth are formed is referred to as an upper surface, and a surface on which teeth are not formed is referred to as a bottom surface.

  As a material constituting the gear 100, case hardening steel is used. A more specific material of the gear 100 is, for example, any one of a chrome steel material (for example, SCr420) and a chrome molybdenum steel material (for example, SCM420, SCM435) defined in JIS G 4053 alloy steel material for machine structure.

  The plurality of gears 100 a to 100 d are accommodated in the container 200. In the present embodiment, a plurality of gears 100a to 100d (before carburizing treatment) are accommodated in the container 200. The plurality of gears 100a to 100d are placed in the carburizing furnace while being housed in the container 200 in this manner, and a known carburizing process is performed. Thereafter, the plurality of gears 100a to 100d subjected to the carburizing process are conveyed to equipment for performing a quenching process as shown in FIG.

  As shown in FIG. 1, in the present embodiment, the plurality of gears 100 a to 100 d have bottom surfaces 102 a to 102 d on the cooling medium 300 side (the bottom surfaces 102 a to 102 d of the plurality of gears 100 a to 100 d and the cooling medium 300. It is accommodated in the container 200 (with the surface facing it). The region on the upper surface 101 side of the gear 100 has a larger surface area than the region on the bottom surface 102 side. For this reason, when the upper surface 101 of the gear 100 is on the cooling medium 300 side, the region on the upper surface 101 side of the gear 100 is cooled too much faster than the region on the bottom surface 102 side, and the cooling rate in these regions is increased. It will be very different. In addition, when the rotation shaft of the gear 100 is largely inclined with respect to the cooling medium, the cooling rate in the circumferential direction of the gear 100 is greatly different. Therefore, in the present embodiment, the bottom surfaces 102a to 102d of the plurality of gears 100a to 100d are arranged on the cooling medium 300 side.

As shown in FIG. 1, in the present embodiment, the plurality of gears 100 a to 100 d are accommodated in the container 200 in a state in which movement in the direction along the rotation axis (thickness direction) is not restrained by a jig or the like. The In addition, in the example shown in FIG. 1, in addition to the movement in the direction (thickness direction) along the rotation axis of the plurality of gears 100a to 100d, the movement in the radial direction of the plurality of gears 100a to 100d is not restricted.
The shape of the container 200 is preferably a shape in which a region as wide as possible is open, but the configuration of the container 200 is not particularly limited as long as at least a part of the region is open. . For example, a mesh-shaped cage container or a tray-shaped container can be used as the container 200. Moreover, you may use the container which accommodates a gear divided into several steps in a height direction. Moreover, it is not necessary to divert the container used by the carburizing process. However, as described above, the gear 100 is accommodated in the container 200 in a state where the movement of the gear 100 in the direction along the rotation axis is not restricted.

  In the present embodiment, the cooling medium 300 is oil. Oil generally used in quenching in carburizing and quenching can be used as the cooling medium 300. For example, oil that is No. 1 or No. 2 specified in JIS K 2242 (2012) heat-treated oil can be used as the cooling medium 300.

In the example illustrated in FIG. 1, the container 200 in which the plurality of gears 100 a to 100 d are accommodated as described above is lifted by the crane device 400, and the container 200 is positioned above the cooling medium 300. Then, the container 200 is suspended by the crane device 400, and the plurality of gears 100 a to 100 d are completely immersed in the cooling medium 300 while being accommodated in the container 200. After the state in which the plurality of gears 100a to 100d are completely immersed in the cooling medium 300 is continued for a preset time, the container 200 is lifted by the crane device 400, and the plurality of gears 100a to 100d are lifted from the cooling medium 300. Take out.
In the present embodiment, the quenching process in carburizing and quenching is performed as described above.

  In the present embodiment, the immersion speed that is the moving speed of the gear 100 when the gear 100 is immersed in the cooling medium 300 is controlled to be constant as described above. The immersion speed of the gear 100 is at least the moving speed (lowering speed) of the gear 100 from the timing when the gear 100 first contacts the cooling medium 300 to the timing when the gear 100 completely enters the cooling medium 300.

In this embodiment, since the several gears 100a-100d are accommodated in the container 200, the immersion speed of the gear 100 is made constant by making the moving speed (falling speed) of the container 200 constant.
Although details will be described later, in the present embodiment, the immersion speed of the gear 100 is made constant at an immersion speed V _i [mm / s] based on the following equation (1).
V _i = − (1 / a ₂ ) × log _e {(a ₁ + a ₃ ) / a ₁ } (1)
Here, a ₁ , a ₂ , and a ₃ are coefficients represented by the following equations (2), (3), and (4), respectively, and are variables that depend on the shape of the gear 100.
a ₁ = A ₁ + A ₂ G _x + A ₃ G _y + A ₄ w (2)
a ₂ = B ₁ + B ₂ G _x + B ₃ G _y + B ₄ w (3)
a ₃ = C ₁ + C ₂ G _x + C ₃ G _y + C ₄ w (4)

Although details will be described later, the equation (1) indicates the immersion speed V _i when the warp strain δ [mm] of the gear 100 becomes 0 (zero) (see the description of (derivation example 1)).
That is, in this embodiment, the relationship between the warp strain δ of the gear 100 and the immersion speed V _i is expressed by the following equation (5) (this point is also described in detail in the section of (derivation example 1)). Describe).
δ = a ₁ {1-exp (−a ₂ V _i )} + a ₃ (5)

FIG. 2 is a diagram conceptually illustrating an example of the internal warping distortion. FIG. 2 shows a cross section of the gear 100 taken along its rotational axis. In FIG. 2, the solid line indicates a cross section of the gear 100 in which no warp distortion has occurred, and the broken line indicates a cross section of the gear 100 in which an internal warp distortion has occurred.
As described above, the inward warping means that the outer peripheral side of the bottom surface 102 of the gear 100 is warped in the direction opposite to the side where the upper surface 101 is located, rather than the inner peripheral side. On the contrary, when the inner peripheral side of the bottom surface 102 of the gear 100 is warped in the direction opposite to the side where the upper surface 101 is present than the outer peripheral side is referred to as outward warping.

  In the present embodiment, the amount of displacement of the bottom surface 102 of the gear 100 caused by warping of the gear 100 by quenching, and the amount of displacement in the direction along the rotation axis is defined as warp strain. In the example illustrated in FIG. 2, the rotation of the gear 100 at the position 22 of the bottom surface 102 of the gear 100 in which the warp distortion is generated with respect to the position 21 of the bottom surface 102 of the gear 100 when it is assumed that no warp distortion has occurred. The maximum value of the amount of displacement in the direction along the axis 23 (thickness direction) (that is, the length of the positions 21 and 22 in the thickness direction) becomes warp distortion.

As shown in FIG. 2, when the outer peripheral end of the bottom surface 102 of the gear 100 is in the lower side of FIG. 2 than the inner peripheral end (the side opposite to the side where the upper surface 101 of the gear 100 is present), warping distortion occurs. The value of is assumed to be a positive value. In this case, the warp strain is an internal warp strain.
On the other hand, when the inner peripheral end of the bottom surface 102 of the gear 100 is in the lower side of FIG. 2 than the outer peripheral end (the side opposite to the side where the upper surface 101 of the gear 100 is present), the warp strain value is negative. Take the value. In this case, the warp strain is an outward warp strain.

In the expressions (2) to (4) described above, G _x , G _y , and w are shape parameters.
FIG. 3 is a diagram illustrating an example of the shape parameters G _x , G _y , and w. FIG. 3 shows one of two cross sections that appear on both sides of the rotation shaft 31 when the gear 100 is cut along the rotation shaft 31.
The shape parameter G _x is a region (annular region) excluding a portion where teeth are formed in a region of a cross section obtained by cutting the gear 100 along the rotation axis 31 when it is assumed that no warp distortion has occurred. Part) is the x coordinate ([mm]) of the centroid 32. That is, the shape parameter G _x is a region excluding a portion where teeth are formed in a cross-sectional region obtained by cutting the gear 100 along the rotation axis 31 when it is assumed that no warp distortion has occurred. This is the shortest distance [mm] between the centroid 32 of the (annular portion) and the rotation shaft 31.

The shape parameter G _y is a region excluding a portion where teeth are formed in a cross-sectional region obtained by cutting the gear 100 along the rotation axis 31 when it is assumed that no warp distortion is generated. It is y coordinate ([mm]) of the centroid 32 of (annular part). That is, the shape parameter G _y is a region excluding a portion where teeth are formed in a cross-sectional region obtained by cutting the gear 100 along the rotation axis 31 when it is assumed that no warp distortion has occurred. This is the shortest distance [mm] between the centroid 32 of the (annular portion) and the bottom surface 102 of the gear 100.
The coordinates (G _x , G _y ) of a centroid having a certain two-dimensional shape having an area S are defined as the following expressions (6) and (7). The origin 0 of the coordinates (G _x , G _y ) is the position shown in FIG.
G _x = ∫ _S xdS / S (6)
G _y = ∫ _S ydS / S (7)

  The shape parameter w is a length that is ½ of the difference between the inner diameter and the outer diameter of the region (annular portion) excluding the portion where the teeth of the gear 100 are formed when it is assumed that no warp distortion has occurred. [Mm]. In other words, the shape parameter w is a region excluding a portion where teeth are formed in a cross-sectional region obtained by cutting the gear 100 along the rotation axis 31 when it is assumed that no warp distortion has occurred. This is the maximum value of the length (width) of the (annular portion) in the direction perpendicular to the rotation shaft 31 (lateral direction in FIG. 3).

In the equations (2) to (4), the coefficients A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are as follows: It is derived as follows. First, the relationship between the immersion speed of the gear 100 and the warp distortion when the gear 100 is carburized and quenched is derived from the results of numerical analysis. Next, the coefficients A ₁ , A ₂ , A ₃ when the equations (2) to (4) given the shape parameters G _x , G _y , w used in the numerical analysis are closest to the derived relationship. , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are derived by the least square method. Details of the method of deriving the coefficients A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ will be described later ((Derivation Example 1 ).

Returning to the description of FIG. 1, the carburizing and quenching control device 500 controls the operation of the crane device 400 when quenching the gear 100.
The hardware of the carburizing and quenching control device 500 is realized by using, for example, an information processing device including a CPU, ROM, RAM, HDD, and various interfaces, a PLC (pluggable logic controller), or dedicated hardware. .

The carburizing and quenching control apparatus 500 includes a speed acquisition unit 501, a deviation derivation unit 502, and a control unit 503.
The speed acquisition unit 501 acquires the moving speed of the gear 100. In the present embodiment, the gear 100 is accommodated in the container 200. Therefore, the speed acquisition unit 501 acquires the moving speed of the container 200 as the moving speed of the gear 100. The moving speed of the container 200 is measured by, for example, an encoder that detects the feeding speed and the rewinding speed of the wire 402 of the crane apparatus 400. In this case, the speed acquisition unit 501 acquires the measurement value of the encoder.

The deviation deriving unit 502 derives a speed deviation that is a value obtained by subtracting the speed acquired by the speed acquiring unit 501 from the immersion speed V _i previously calculated by performing the calculations of Expressions (1) to (4). To do.
The control unit 503 derives a value at which the speed deviation derived by the deviation deriving unit 502 approaches 0 (zero) as the value of the rotation speed of the motor provided in the driving device 401 of the crane device 400, and uses the derived value as the driving device. 401 is output. For example, by using a PID controller, the control unit 503 sets a value at which the speed deviation derived by the deviation deriving unit 502 approaches 0 (zero) as the value of the rotation speed of the motor provided in the driving device 401 of the crane device 400. To derive.

The driving device 401 rotates the motor according to the value derived by the control unit 503, and feeds the wire 402 of the crane device 400. Thus, the container 200 descends at a constant speed close to the immersion speed V _i derived in advance by performing the calculations of Expressions (1) to (4).
When the container 200 descends to a predetermined position where the gear 100 can be regarded as completely entering the inside of the cooling medium 300, the control unit 503 instructs the rotation of the motor provided in the driving device 401 of the crane device 400 to stop. The drive device 401 of the crane device 400 stops the rotation of the motor according to this instruction. Thereby, the movement of the container 200 stops.

The control unit 503 determines whether or not the gear 100 is at a predetermined position that can be regarded as completely entering the inside of the cooling medium 300, for example, whether or not the feed length of the wire 402 of the crane device 400 has reached a predetermined length. Can be determined.
Thereafter, when a preset time has elapsed, the control unit 503 instructs the start of rotation of the motor provided in the drive device 401 of the crane device 400. The drive device 401 of the crane apparatus 400 rotates the motor according to this instruction, and rewinds the wire 402 of the crane apparatus 400. Thereby, the container 200 rises and the gear 100 is pulled up from the cooling medium 300. At this time, the rising speed of the container 200 may not be constant.
In the present embodiment, the quenching equipment is configured as described above.

Here, although described as a case where the PID control as an example, if to perform the feedback control for the constant immersion speed V _i, it is not always necessary to perform PID control. For example, PI control may be performed.
Here, the case where the plurality of gears 100 a to 100 d housed in the container 200 is immersed in the cooling medium 300 by the crane device 400 has been described as an example. However, it is not always necessary to use the crane device 400 as long as it can be an operation target when controlling the immersion speed of the plurality of gears 100a to 100d accommodated in the container 200.

(Numerical analysis)
The inventors of the present invention have found that the inside of a gear when carburizing and quenching is performed on a gear having a shape in which teeth are formed on one surface of the upper surface and the bottom surface and teeth are not formed on the other surface. We tried to derive the distribution of stress and strain generated by finite element method by numerical analysis (simulation).

Hereinafter, main calculation formulas used for numerical analysis will be described.
<< About Phase Transformation >>
Temperature T time after phase transformation initiation in tissue I when the isothermal holding in tau _I, the relationship of the transformation rate xi] _I, the following equation (8), (9), represented by the formula (10). F, P, B, M, and γ in the structure I represent ferrite, pearlite, bainite, martensite, and austenite, respectively.

Here, G is a number that identifies the austenite grain size. C, Si, Mn, Cr, Ni, and Mo represent the mass of each alloy element in mass%. Here, the carbon concentration C is determined in consideration of the distribution in the depth direction of the steel material caused by carburization. Q is the activation energy of the diffusion transformation. R is a gas constant.
The transformation ratio ξ _M of the martensitic transformation, which is a non-diffusion transformation, is expressed by the following equation (11).

If the equations (8) to (11) are used, the time τ _I required to reach an arbitrary transformation rate ξ _I at an arbitrary temperature T can be obtained. Therefore, by changing the temperature T, ξ _I = 0.01 is the transformation start line, and ξ _I = 0.99 is the transformation end line, as shown in FIG. 4, the isothermal transformation of the steel material in an arbitrary alloy element. A diagram can be predicted.

  Further, when the equations (8) to (9) are differentiated by the transformation rate and the addition rule is applied under the assumption that the temperature is constant for a certain minute time, the continuous cooling transformation can be predicted. it can. The transformation temperature is calculated by the following formulas (12) to (15).

<< About thermal strain >>
The density ρ _{I of the} tissue I is calculated by the following equations (16) to (18).

Accordingly, the thermal strain increment dε ^T _I of the tissue I at the temperature T is calculated by the following equation (19).

<< About transformation distortion >>
When considering phase transformation, it is necessary to calculate transformation strain and transformation plastic strain in addition to elastic strain, plastic strain, and thermal strain in ordinary thermoelastic-plastic analysis. FIG. 5 is a diagram conceptually showing an example of the relationship between the temperature and strain of a steel material when the steel material is heated to Ac3 point or higher and then rapidly cooled (that is, quenched) and martensitic transformation mainly occurs. is there. By transforming from austenite to martensite during rapid cooling, the density of the steel material decreases and the volume increases. The strain resulting from the volume change accompanying this phase transformation is the transformation strain. The transformation strain increment dε ^{TR at} a temperature T from austenite to structure I is calculated by the following equation (20).

<< About transformation plastic strain >>
FIG. 6 is a diagram conceptually illustrating an example of the relationship between the temperature and strain of the steel material when a constant stress is applied during rapid cooling (that is, during quenching) after the steel material is heated to the Ac3 point or higher.
When stress is applied to the steel material during the progression of transformation, inelastic strain occurs in the steel material. This strain is the transformation plastic strain. The transformation plastic strain is generated in proportion to the deviation stress. The transformation plastic strain increment dε ^TP is calculated by the following (21).

(21) In the equation, K _I is the transformation plasticity coefficient of the tissue I. S is the deviation stress. The transformation plasticity coefficients of each structure are K _F = K _P = 1.3 × 10 ⁻⁴ , K _B = 6.3 × 10 ⁻⁵ , and K _M = 7.4 × 10 ⁻⁵ , respectively. The deviation stress S is obtained by subtracting an isotropic component from the stress, and is calculated by the following equation (22).

In the equation (22), σ is stress. σ _ij is an ij component of the stress σ. I is a unit tensor. σ _m is the hydrostatic pressure stress and is calculated by the following equation (23).

  The calculation part of thermal strain, transformation strain, and transformation plastic strain defined by the above equations is added to a user subroutine of Abaqus (trade name) which is a general-purpose finite element method package (application software). Thereby, thermoelastic analysis in consideration of phase transformation becomes possible. Expressions (8) to (18) include a term of carbon concentration C. For this reason, the analysis which considered the change of the carbon concentration by carburization can be performed.

  It should be noted that the above-described contents incorporated into the Abaqus user subroutine can be realized by known techniques as described in Non-Patent Documents 1 to 4, for example. Further, the part (standard function) other than the user subroutine of Abaqus is a known technique as described in Non-Patent Document 5, for example.

  When setting the calculation conditions by Abaqus, gear material data (Young's modulus, deformation resistance curve, density, specific heat, thermal conductivity, diffusion coefficient, etc.), gear shape data, carburizing and quenching in each process Input the relationship between temperature and time (so-called heat pattern), surface carbon concentration, heat transfer coefficient of oil used for quenching treatment, etc. Here, the boundary condition in the finite element method is set so that the region to be cooled on the surface of the gear gradually rises from the bottom side according to the immersion speed.

The Vickers hardness of the gear was calculated using the gear structure fraction and the temperature history (cooling rate) at the time of completion of quenching obtained by thermoelastic-plastic analysis considering the above phase transformation. Vickers hardness HV _I of each tissue I during quenching completion is calculated by the following (24) to (26) from the chemical composition and cooling rate V _r of the gear. As the prediction expression of Vickers hardness HV _I of each tissue I during quenching completed, a plurality of expression is proposed, in which, using the equation described in Non-Patent Document 6.

Here, the cooling rate V _r is the cooling rate [° C./hour] at 700 [° C.] of the gear being cooled. The overall Vickers hardness HV of the gear is calculated by the sum of the products of the hardness HV _I of each structure _I and the structure fraction ξ _I as shown in the following equation (27).

(About new knowledge)
The inventors of the present invention have a gear formed with teeth on one surface of the upper surface and the bottom surface and not formed with teeth on the other surface, internal stress after carburizing and quenching, plastic strain, and The transformation plastic strain was investigated by performing the numerical analysis (simulation) described above. In such a gear, it is assumed that the generation mechanism of the generated warp strain does not change. Here, a straight bevel gear having a number of teeth of “39” and a pitch circle diameter of 230 [mm] is used as an object of numerical analysis. It was.

FIG. 7 is a diagram for explaining the pitch circle diameter PD. In FIG. 7, the cross section which cut the gearwheel in the direction in alignment with the rotating shaft is shown.
A pitch circle is a circle drawn by the contact point of two gears meshing with each other. In the bevel gear, the circle drawn by the contact points of the outer peripheral ends of the teeth of the two gears meshing with each other is the pitch circle. The pitch circle diameter is the diameter of such a pitch circle.

FIG. 8 is a diagram illustrating an example of a three-dimensional model of a gear.
Specifically, FIG. 8A is a diagram showing an overall model of the three-dimensional gear model used in the numerical analysis. FIG. 8B shows a three-dimensional model of the gear used in the numerical analysis. Using the symmetry of the whole model shown in FIG. 8A, as shown in FIG. 8B, 1/78 model of the whole model shown in FIG. 8A (half the area of one tooth) Model). Data indicating the shape of such a model was used as gear shape data.

  In addition, as the material data of gears, the data of SCr420 specified in JIS G 4053 (2008) alloy steel for machine structural use was used. Table 1 shows chemical components of SCr420.

  Further, the heat treatment conditions (heat pattern) shown in FIG. 9 were used. That is, the heat treatment temperature in the carburizing treatment was 930 [° C.], the holding time at the heat treatment temperature was 100 [min], and the carbon potential CP was 0.7. Here, the soaking process is performed after the carburizing process, the heat treatment temperature in the soaking process is 870 [° C.], and the holding time at the heat treatment temperature is 65 [min]. Further, here, oil quenching is performed after soaking, and the temperature of the oil is 50 [° C.]. This oil has Class 1 No. 1 cooling performance as defined in JIS K 2242 (2012) Heat Treatment Fluid, and the heat transfer coefficient shown in FIG. 10 was used as the heat transfer coefficient.

At different dipping speeds V _i under the above conditions show the results of numerical analysis below.
FIG. 11 is a diagram showing the shape of the gear after quenching. 11 (a) shows, when uniformly (instantly) cooling the gear entire indicates (when subjected to immersion in a high speed), FIG. 11 (b), the gear dipping speed V _i as 5 [mm / s] Is shown (when immersion is performed at low speed). FIG. 11 shows one of the cross sections of the gear model (see FIG. 8B) cut along the rotation axis of the gear. Further, the deformation magnification in FIG. 11 is 50 times.

  In Fig.11 (a) and FIG.11 (b), the shape after a quenching process is shown by white, and the shape after a quenching process is piled up on it and is shown by gray. As shown to Fig.11 (a), when the immersion was performed at high speed, the knowledge that internal curvature distortion generate | occur | produces by quenching was acquired. On the other hand, as shown in FIG. 11B, it has been found that when immersion is performed at a low speed, warping strain (outward warping strain) is generated in a direction opposite to that performed when immersion is performed at a high speed.

FIG. 12 is a diagram showing the circumferential residual stress generated in the gear after quenching. FIG. 13 is a view showing the plastic strain in the circumferential direction generated inside the gear after quenching. FIG. 14 is a diagram showing a circumferential transformation plastic strain generated inside the gear after quenching. FIGS. 12 (a), 13 (a), and 14 (a) show the case where the entire gear surface is cooled uniformly (instantaneously) (when immersion is performed at high speed), and FIGS. (b), FIG. 14 (b) shows a case where the cooling wheel (when performing immersion at a low speed) the immersion velocity V _i as 5 [mm / s]. 12 to 14 show cross sections of a gear model (see FIG. 8B) cut along the rotation axis of the gear. Further, the deformation magnification in FIGS. 12 to 14 is 0 times.

  As shown in FIGS. 12 to 14, it has been found that tensile residual stress, compressive plastic strain, and tensile transformation plastic strain are generated inside the gear. Also, by comparing FIG. 12 (a), FIG. 13 (a), and FIG. 14 (a) with FIG. 12 (b), FIG. 13 (b), and FIG. The direction where the residual tensile stress, the compressive plastic strain, and the tensile transformation plastic strain are generated is on the side where the teeth are formed (upper side in FIGS. 12 to 14) than when the immersion is performed at a high speed. Obtained knowledge.

FIG. 15 is a diagram conceptually illustrating an example of the relationship between the inner warp strain and the outer warp strain generated in the gear and the generation position of the tensile stress. FIG. 15A shows a case where immersion is performed at a high speed, and FIG. 15B shows a case where immersion is performed at a low speed.
As shown in FIGS. 15 (a) and 15 (b), the tensile residual stress generated in the gear works in a direction to reduce the gear diameter. For this reason, as shown in FIG. 15A, it is considered that the warp strain increases as the position 1501 where the tensile residual stress is generated is on the side where the teeth are not formed (the lower side in FIG. 15A). It is done. On the other hand, as shown in FIG. 15B, it is considered that when the tensile residual stress generation position 1502 is on the side where the teeth are formed (the upper side of FIG. 15B), outward warping distortion occurs. Therefore, when the immersion is performed at a high speed, the position where the tensile residual stress is generated is on the side where the teeth are not formed (the lower side in FIG. 15A), and as shown in FIG. When an internal warping strain is generated and the immersion is performed at a low speed, the tensile residual stress is generated on the side where the teeth are formed (the upper side of FIG. 15B). ), It is considered that outward warping distortion occurred in the gear.

Moreover, it is thought that the stress and distortion which generate | occur | produce in the inside of a gearwheel generate | occur | produce with the mechanism shown to the following (A)-(C).
(A) When the quenching process is started, first, the surface of the gear is cooled and thermal contraction is started. As the surface shrinks, a compressive stress is applied to the inside of the gear. Since the inside of the gear is high temperature and low in strength, it is in a yielding state, and compressive plastic strain occurs.
(B) Thereafter, the inside of the gear is also cooled by the quenching process, and thermal shrinkage also starts inside the gear. Since the inside of the gear is contracted from the surface due to the plastic strain of compression generated in (A), it is restrained from the surface. For this reason, a tensile stress is generated inside the gear.
(C) When the temperature further decreases, phase transformation starts inside the gear. Since tensile stress is applied to the inside of the gear, tensile transformation plastic strain is generated.

  When the immersion is performed at high speed, cooling of the entire surface of the gear is started at the same time, and the entire surface of the gear starts to shrink. In particular, the area where the gear teeth are formed has a larger surface area than the area where the teeth are not formed. Therefore, the amount of heat shrinkage is greater in the region where the gear teeth are formed than in the region where the teeth are not formed. Therefore, the compressive plastic strain generated inside the gear is relatively generated from the bottom surface of the gear. And the tensile residual stress of the circumferential direction remains corresponding to the generation | occurrence | production position of this compressive plastic strain (refer Fig.15 (a)).

  On the other hand, when the immersion is performed at a low speed, since cooling is gradually started from the bottom surface of the gear, the thermal contraction starts from the bottom surface side of the gear, contrary to the case where the immersion is performed at a high speed. For this reason, in the cooling process in which immersion is performed at a low speed, the amount of heat shrinkage on the bottom surface of the gear is larger than in the case where immersion is performed at a high speed. Therefore, when the immersion is performed at a low speed, the position where the compressive plastic strain is generated is pushed up to the upper surface side of the gear than when the immersion is performed at a high speed. Accordingly, the corresponding tensile residual stress in the circumferential direction is generated on the upper surface side of the gear when the immersion is performed at a low speed than when the immersion is performed at a high speed (see FIG. 15B). ).

As described above, as the immersion speed V _i is decreased, the amount of thermal shrinkage in the region on the bottom surface side of the gear increases, so that the generation position of the compressive plastic strain inside the gear moves to the top surface side of the gear. The occurrence position of the residual tensile stress is also considered to move in the negative direction (that is, the outward warping strain is generated) because it moves to the upper surface side of the gear.
From the above, if internal warping distortion occurs in the gear when dipping at a high speed, the immersion speed V _i is searched by reducing the immersion speed V _i so that the warping distortion becomes 0 (zero). by immersion in a cooling medium the gear dipping speed V _i as to obtain a finding that can reduce the warpage distortion inner occurring gear after quenching. Under such knowledge, the above-described numerical analysis is performed to derive the relationship between the immersion speed V _i and the warp strain. From the derived result, the immersion speed V _{i at} which the warp strain is 0 (zero) is derived. Tried to do. The results will be described below.

(Derivation example 1)
In this example, the numerical analysis described above was performed for each of a plurality of gears that differ only in shape, and the relationship between the immersion speed V _i and the warp strain δ was derived. Even in this example, if the gear has a tooth formed on one surface of the top surface and the bottom surface and no tooth on the other surface, it is assumed that the generation mechanism of the warp distortion does not change, and the bevel gear is immediately Used as the target of numerical analysis. Also in this example, as shown in FIG. 8 (b), the symmetry of the whole model is used, and a model (1 / n half the number of teeth) of 1 / n (n is twice the number of teeth) of the whole model. Region model) was used in the numerical analysis.

FIG. 16 is a diagram showing, in a tabular form, gear shape data to be subjected to numerical analysis.
The gears 2 and 3 change only the number of teeth on the basis of the shape of the gear 1 shown in FIG. 16 and the gears 4 and 5 change only the pitch circle diameter. Gears 6 and 7 are obtained by multiplying the node coordinates of the three-dimensional model of the gear 1 by 0.8 and 1.2 (the three-dimensional model of the gear 1 is similar to the three-dimensional model of the gears 6 and 7). become). The gears 8 and 9 are obtained by multiplying only the radial coordinate of the three-dimensional model of the gear 1 by 0.8 and 1.2 (the inner diameter and the outer diameter of the three-dimensional model of the gears 8 and 9 are the gears). The inner diameter and outer diameter of the three-dimensional model 1 are 0.8 times and 1.2 times as large). Further, gears 10 and 11 are obtained by multiplying only the nodal coordinates of the three-dimensional model of the gear 1 in the rotation axis direction by 0.8 and 1.2 (directions along the rotation axis of the three-dimensional model of the gears 10 and 11). Is 0.8 times and 1.2 times the length (thickness) in the direction along the rotation axis of the three-dimensional model of the gear 1).

Also, for each of the gears 1 to 11, 100 a dipping speed _{V i [mm / s],} 50 [mm / s], 25 [mm / s], 12.5 [mm / s], 6.25 [mm / S], 3.125 [mm / s], and numerical analysis was performed. Other analysis conditions are the same as the analysis conditions described in the above section (about new knowledge).

FIG. 17 shows the result of the numerical analysis of this example, and is a diagram showing the relationship between the immersion speed V _i of each gear 1 to 11 and the warp strain δ due to quenching.
As shown in FIG. 17, in the gear 1 to 11 of any shape, in the range of dipping speed V _i is 25 [mm / s] ~100 [ mm / s], the size of the inner warp distortion almost unchanged First, when the immersion speed V _i is 25 [mm / s] or less, the internal warpage distortion starts to decrease. Further, when the immersion speed V _i is decreased, the warping strain becomes a negative value, and external warping strain is generated. If warp distortion δ varies continuously by immersion velocity V _i, so that the immersion speed V _i warp distortion δ becomes 0 (zero) is present. Therefore, regardless of the shape of the gear, it is considered possible to suppress the warp distortion by adjusting the immersion velocity V _i. From the results shown in FIG. 17, assuming that the warp strain δ in the range where the immersion speed is 25 [mm / s] or less can be expressed by an exponential function, the relationship between the immersion speed V _i and the warp strain δ is expressed by the following equation (28). Approximated by
δ = a ₁ {1-exp (−a ₂ V _i )} + a ₃ (28)

Expression (28) is the same as Expression (5) described above.
The coefficients a ₁ , a ₂ , and a ₃ in the equation (28) that are closest to the relationship between the immersion speed V _i and the warp strain δ of each gear 1 to 11 shown in FIG. 17 were derived by curve fitting. Here, the coefficients a ₁ , a ₂ , and a ₃ of Equation (28) that are closest to the relationship between the immersion speed V _i and the warp strain δ of each gear 1 to 11 are derived by the least square method.
Here, as shown in the equations (2) to (4), in the present embodiment, the coefficients a ₁ , a ₂ , and a ₃ are objective variables, and the shape parameters G _x , G _y , and w are design variables. The coefficients a ₁ , a ₂ , and a ₃ are expressed by a linear expression. The shape parameters G _x , G _y , and w are as described with reference to FIG.

As a result, the following equations (29), (30), and (31) were obtained as regression equations of the coefficients a ₁ , a ₂ , and a ₃ .
a ₁ = −2.314 × 10 ⁻¹ + 1.954 × 10 ⁻³ G _x −1.665 × 10 ⁻² G _y + 1.570 × 10 ⁻² w (29)
a ₂ = 2.085 × 10 ⁻¹ + 4.616 × 10 ⁻⁵ G _x −4.735 × 10 ⁻³ G _y + 7.155 × 10 ⁻⁴ w (30)
a ₃ = 2.901 × 10 ⁻¹ −1.144 × 10 ⁻³ G _x −8.633 × 10 ⁻³ G _y −1.384 × 10 ⁻² w (31)

If conditions other than the shape of the gear are the same, the shape parameter G _x , G _y , w is substituted into the equations (29), (30), and (31) for a gear of any shape, and the coefficient a ₁ , A ₂ , a ₃ and substituting the derived coefficients a ₁ , a ₂ , a ₃ into the equation (28), it is possible to derive the immersion speed V _{i at} which the warp strain δ becomes 0 (zero). it can.

As described above, the expressions (29), (30), and (31) are expressions approximated by the method of least squares. Therefore, an error is included in the relational expression between the immersion speed V _i and the warping strain δ in the expression (28) derived using the expressions (29), (30), and (31). Therefore, the validity of the approximate expression of the expressions (29), (30), and (31) was verified.

That is, by using the equations (28) to (31), the immersion speed V _iopt that the warp strain δ is predicted to be 0 (zero) is derived from the shape parameters G _x , G _y , and w of the gears 1 to 11. The above-described numerical analysis was performed on the gears 1 to 11 using the derived immersion speed V _iopt to derive the warp strain δ _opt of the gears 1 to 11. Further, the immersion speed corresponding to the immersion speed in the normal quenching process is 100 [mm / s], and the numerical analysis described above for each of the gears 1 to 11 is performed using this immersion speed. The warp strain δ ₁₀₀ was derived.

FIG. 18 is a diagram for explaining that the warp distortion generated in each of the gears 1 to 11 is reduced. Specifically, FIG. 18 shows the shape parameters G _x , G _y , w of the gears 1 to 11, the immersion speed V _{iopt at} which the warp strain δ is predicted to be 0 (zero), and the warp strain at the immersion speed V _iopt. and [delta] _opt, the warp distortion [delta] ₁₀₀ when the immersion speed is 100 [mm / s], and the reduction rate of the size of the warp distortion is a diagram showing in a tabular form. The reduction rate of the magnitude of the warp strain is derived by calculating the following equation (32).
{(| Δ ₁₀₀ | − | δ _opt |) ÷ | δ ₁₀₀ |} × 100 (32)
As shown in FIG. 18, it was confirmed that the warp distortion generated in the gear by quenching can be reduced even by using approximate expressions such as Expressions (29), (30), and (31).

FIG. 19 is a diagram showing the carbon concentration at each position in the depth direction from the surface of the gear 1 after quenching. The values shown in FIG. 19 are derived for the gear 1 by using the equations (28) to (31) to derive the immersion speed V _i at which the warp strain δ is 0 (zero), and using the derived immersion speed V _i. Obtained by performing the numerical analysis. In FIG. 19, the matrix carbon concentration is 0.23 [%]. As shown in FIG. 19, even if the gear is immersed in the cooling medium at the immersion speed V _i at which the warp strain δ becomes 0 (zero) using the equations (28) to (31), the surface is 1 [ mm], it was confirmed that the carburization to a depth of more than.

FIG. 20 is a diagram showing a distribution of Vickers hardness of the gear 1 after quenching. FIG. 20 shows a cross section of the gear 1 model (see FIG. 8B) cut along the rotation axis of the gear. The distribution shown in FIG. 20A is obtained by performing the numerical analysis described above for the gear 1 with the immersion speed V _i being 100 [mm / s]. The distribution shown in FIG. 20B is obtained by performing the above-described numerical analysis on the gear 1 with the immersion speed V _i being 6.25 [mm / s].

  FIG. 21 is a diagram showing Vickers hardness at each position in the depth direction from points A and B on the surface of the gear 1 shown in FIG. 21A shows the Vickers hardness at each position in the depth direction from the point A on the surface of the gear 1 shown in FIG. 20, and FIG. 21B shows the point on the surface of the gear 1 shown in FIG. Vickers hardness at each position in the depth direction from B is shown.

22, point A of the surface of the gear 1 shown in FIG. 20, the outermost surface hardness and effective hardened layer depth in B, and Vickers hardness at point C of the internal gear 1 shown in FIG. 20, immersed velocity V _i It is a figure shown in a tabular form about the case where is 100 [mm / s] and the case where it is 6.25 [mm / s]. Here, the effective hardened layer depth is a depth at which the Vickers hardness is 500 [Hv].
As shown in FIGS. 20 to 22, it was confirmed that the hardness of the gears was equal even if the immersion speed V _i was changed.

(Derivation example 2)
In this example, only the material of the gear is different from that in the derivation example 1, and the numerical analysis described above is performed to derive the relationship between the immersion speed V _i and the warp strain δ. Also in this example, as in the first derivation example, the gears 1 to 11 shown in FIG. However, in this example, as the material data of the gears 1 to 11, the data of SCM420 defined in JIS G 4053 alloy steel for machine structure was used. Table 2 shows the chemical components of SCM420. Other analysis conditions are the same as those in derivation example 1.

FIG. 23 shows the result of the numerical analysis of this example, and is a diagram showing the relationship between the immersion speed V _i of each gear 1 to 11 and the warpage distortion δ due to quenching. Similar to the derivation Example 1 of the results shown in FIG. 17 (results for the material of the gears is SCr420), in the range dipping speed V _i is large, the size of the inner warp distortion hardly changes, immersion speed V It was confirmed that when _i becomes smaller, the inner warping strain starts to decrease, and when the immersion speed V _i becomes smaller, the warping strain becomes a negative value and the outer warping strain occurs.

Figure 24 is a diagram showing a relationship between the warp distortion δ by immersion velocity V _i and hardening of the gear 1 shown in FIG. 23, the scale of the axis of the dipping speed V _i in semi-log plot of the logarithmic scale (natural log scale) It is.
As shown in FIG. 24, in the region of the curve indicating the relationship between the immersion speed V _i and the warp strain δ, the warp strain δ and the natural logarithm are obtained in a region where the immersion speed V _i decreases and the warp strain δ decreases rapidly. relationship between the immersion velocity log _e V _i expressed in can linearly approximated. Accordingly, in the vicinity of the immersion speed V _i where the warp strain δ becomes 0 (zero), the warp strain δ can be approximated by an exponential function as shown in Equation (28), and even if the gear material is different, It was confirmed that the same result as in the derivation example 1 was obtained.

(Derivation Example 3)
In the numerical analysis described above, the characteristics of the cooling medium are determined by the heat transfer coefficient. Therefore, in this example, only the heat transfer coefficient of the cooling medium is different from that in the derivation example 1, and the above-described numerical analysis is performed to derive the relationship between the immersion speed V _i and the warp strain δ. Also in this example, as in the first derivation example, the gears 1 to 11 shown in FIG. However, in this example, the temperature of the oil is 120 [° C.], and this oil has Type 2 No. 1 cooling performance defined in JIS K 2242 (2012) heat treatment oil, and the heat transfer coefficient is shown in FIG. The heat transfer coefficient shown was used. Other analysis conditions are the same as those in derivation example 1.

FIG. 26 shows the result of the numerical analysis of this example, and is a diagram showing the relationship between the immersion speed V _i of each gear 1 to 11 and the warp strain δ due to quenching. Similar to the derivation Example 1 of the results shown in FIG. 17 (results for the material of the gears is SCr420), in the range dipping speed V _i is large, the size of the inner warp distortion hardly changes, immersion speed V It was confirmed that when _i becomes smaller, the inner warping strain starts to decrease, and when the immersion speed V _i becomes smaller, the warping strain becomes a negative value and the outer warping strain occurs. However, in this example, since the temperature of the cooling medium is high and the heat transfer coefficient is small, heat treatment distortion hardly occurs in the gear. For this reason, with respect to the gears 4, 8, and 11, the warp strain δ is reduced even in the range where the immersion speed V _i is large. Even in such a case, it was confirmed that the warping strain δ changes rapidly by decreasing the immersion speed V _i .

Figure 27 is a diagram showing a relationship between the warp distortion δ by immersion velocity V _i and hardening of the gear 1 shown in FIG. 26, the scale of the axis of the dipping speed V _i in semi-log plot of the logarithmic scale (natural log scale) It is.
As shown in FIG. 27, in the region of the curve showing the relationship between the immersion speed V _i and the warp strain δ, the warp strain δ and the natural logarithm are obtained in a region where the soak rate V _i decreases and the warp strain δ decreases rapidly. relationship between the immersion velocity log _e V _i expressed in can linearly approximated. Therefore, in the vicinity of the immersion speed V _i where the warp strain δ becomes 0 (zero), the warp strain δ can be approximated by an exponential function as shown in Equation (28), and is derived even if the cooling medium is different. It was confirmed that the same result as in Example 1 was obtained.

In addition to the numerical analysis described above, the derivation of the coefficients a ₁ , a ₂ , a _{3 and} the derivation of the immersion speed V _i at which the warp strain δ becomes 0 (zero) are performed by the carburizing and quenching control device 500 or the carburizing and quenching. It can be performed by an apparatus different from the control apparatus 500 (for example, an information processing apparatus including a CPU, a ROM, a RAM, an HDD, and various interfaces). In this case, variables such as shape parameters G _x , G _y , and w necessary for derivation are input to the apparatus based on a user interface operation by the user, for example.

(Summary)
As described above, in this embodiment, the carburizing process is performed in a state where the bottom surface 102 of the gear 100 is on the cooling medium 300 side and the movement in the direction along the rotation axis of the gear 100 (thickness direction) is not restricted. The gear 100 is immersed in the cooling medium 300 for quenching. At that time, from the relational expression between the warp strain δ obtained from the numerical analysis result and the immersion speed V _i and the shape parameters G _x , G _y , w, the immersion speed V _i at which the warp strain δ becomes 0 (zero). And the immersion speed V _i of the gear 100 is controlled to be constant at the predicted immersion speed V _i . Thereby, the generation | occurrence | production position of the tensile residual stress in the inside of the gearwheel 100 can be controlled. Therefore, even if the movement in the direction (thickness direction) along the rotation axis of the gear 100 is not constrained, the amount of warpage generated in the gear 100 after quenching can be controlled, and warpage distortion can be reduced. Therefore, it is not necessary to process the shape of the gear or attach a coating layer or a heat treatment jig to the gear, so that warpage distortion generated in the gear after quenching can be suppressed without increasing the cost of the gear as much as possible. be able to.

  In the embodiment of the present invention described above, the processing performed by the carburizing and quenching control device 500 can be realized by a computer executing a program. Further, a computer-readable recording medium in which the program is recorded and a computer program product such as the program can also be applied as an embodiment of the present invention. As the recording medium, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

In addition, the embodiments of the present invention described above are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. Is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.
For example, in the present embodiment, the immersion speed V _i when the warp strain δ [mm] of the gear 100 becomes 0 (zero) is derived. However, for example, when some warp strain δ is allowed due to the specifications of the gear 100, the immersion speed V _i with a value that the warp strain δ [mm] of the gear 100 is not 0 (zero) is derived. Good. In this case, the immersion speed V _i is derived from an equation in which a value other than 0 (zero) is substituted for the value of the warping strain δ in the equation (5) instead of the equation (1).

  100a to 100d: gear, 200: container, 300: cooling medium, 400: crane device, 401: drive device, 500: carburizing and quenching control device, 501: speed acquisition unit, 502: deviation derivation unit, 503: control unit

Claims (8)

Of the upper surface and the bottom surface, a gear having teeth formed on one surface and no teeth formed on the other surface, the gear having been subjected to carburizing treatment, the other surface facing the cooling medium side A carburizing and quenching control device for performing quenching by immersing in the cooling medium in a state where movement in the direction along the rotation axis is not constrained,
It has a control means for controlling a constant immersion speed is the moving speed of the gear at the time of immersing the gear to the cooling medium,
The control means controls the moving speed of the gear when the gear is immersed in the cooling medium to be constant at the immersion speed V _i [mm / s] determined by the following equations (A) to (D). Carburizing and quenching control device characterized by
δ = a ₁ {1-exp (−a ₂ V _i )} + a ₃ (A)
a ₁ = A ₁ + A ₂ G _x + A ₃ G _y + A ₄ w (B)
a ₂ = B ₁ + B ₂ G _x + B ₃ G _y + B ₄ w (C)
a ₃ = C ₁ + C ₂ G _x + C ₃ G _y + C ₄ w (D)
Here, δ is a warp strain [mm] which is a displacement amount of the other surface of the gear caused by warping of the gear due to the quenching and is a displacement amount in a direction along the rotation axis,
A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are predetermined coefficients,
G _x is a centroid of a region excluding a portion where teeth are formed out of a cross-sectional region cut along the rotation axis of the gear when it is assumed that no warp distortion has occurred. , A shape parameter represented by the shortest distance [mm] from the rotation axis,
G _y is a centroid of a region excluding a portion where teeth are formed in a region of a cross section of the gear when it is assumed that the warp distortion is not generated, along the rotation axis. , A shape parameter represented by the shortest distance [mm] from the other surface of the gear,
w is a region of the gear when it is assumed that the warp distortion has not occurred, and is a length of ½ of the difference between the inner diameter and the outer diameter of the region excluding the portion where the teeth are formed. This is a shape parameter expressed in [mm]. The control means is configured so that the moving speed of the gear when the gear is immersed in the cooling medium is the immersion speed V _i [mm / s at which the warp strain δ is 0 (zero) in the equation (A). carburizing control device according to claim 1, characterized in that set to be constant at. The coefficients A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are related to the warping strain and the immersion speed. On the other hand, it is a coefficient derived by curve fitting the equation (A) in which the shape parameters G _x , G _y , w of the gear are substituted,
The relationship between the warp strain and the immersion speed is obtained when a gear having the same material as that of the gear is immersed in a cooling medium having the same heat transfer coefficient as that of the cooling medium at a different immersion speed. The carburizing and quenching control apparatus according to claim 1 or 2 , wherein the warp distortion generated in the gear is determined based on a result derived by numerical analysis. Of the upper surface and the bottom surface, a gear having teeth formed on one surface and no teeth formed on the other surface, the gear having been subjected to carburizing treatment, the other surface facing the cooling medium side A carburizing and quenching method in which quenching is performed by immersing in the cooling medium in a state where movement in a direction along the rotation axis is not constrained,
Carburization characterized in that a moving speed of the gear when the gear is immersed in the cooling medium is constant at an immersion speed V _i [mm / s] determined by the following equations (A) to (D). Quenching method.
δ = a ₁ {1-exp (−a ₂ V _i )} + a ₃ (A)
a ₁ = A ₁ + A ₂ G _x + A ₃ G _y + A ₄ w (B)
a ₂ = B ₁ + B ₂ G _x + B ₃ G _y + B ₄ w (C)
a ₃ = C ₁ + C ₂ G _x + C ₃ G _y + C ₄ w (D)
Here, δ is a warp strain [mm] which is a displacement amount of the other surface of the gear caused by warping of the gear due to the quenching and is a displacement amount in a direction along the rotation axis,
A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are predetermined coefficients,
G _x is a centroid of a region excluding a portion where teeth are formed out of a cross-sectional region cut along the rotation axis of the gear when it is assumed that no warp distortion has occurred. , A shape parameter represented by the shortest distance [mm] from the rotation axis,
G _y is a centroid of a region excluding a portion where teeth are formed in a region of a cross section of the gear when it is assumed that the warp distortion is not generated, along the rotation axis. , A shape parameter represented by the shortest distance [mm] from the other surface of the gear,
w is a region of the gear when it is assumed that the warp distortion has not occurred, and is a length of ½ of the difference between the inner diameter and the outer diameter of the region excluding the portion where the teeth are formed. This is a shape parameter expressed in [mm]. The moving speed of the gear when the gear is immersed in the cooling medium is constant at the immersion speed V _i [mm / s] at which the warp strain δ is 0 (zero) in the equation (A). The carburizing and quenching method according to claim 4 . The coefficients A ₁ , A ₂ , A ₃ , A ₄ , B ₁ , B ₂ , B ₃ , B ₄ , C ₁ , C ₂ , C ₃ , C ₄ are related to the warping strain and the immersion speed. On the other hand, it is a coefficient derived by curve fitting the equation (A) in which the shape parameters G _x , G _y , w of the gear are substituted,
The relationship between the warp strain and the immersion speed is obtained when a gear having the same material as that of the gear is immersed in a cooling medium having the same heat transfer coefficient as that of the cooling medium at a different immersion speed. The carburizing and quenching method according to claim 4 or 5 , wherein the warp distortion generated in the gear is determined based on a result derived by numerical analysis. The carburizing and quenching method according to any one of claims 4 to 6 , wherein the gear is formed of a chrome steel material or a chrome molybdenum steel material defined in JIS G 4053 (2008). The carburizing and quenching according to any one of claims 4 to 7 , wherein the cooling medium is oil of type 1 type 1 or type 2 type 1 specified in JIS K 2242 (2012). Method.