JPH06122925A - Quenching method of gear - Google Patents

Abstract

PURPOSE:To prevent the generation of complicated internal stress at the time of quench cooling and to prevent the generation of quenching cracks and quenching strains (deformation). CONSTITUTION:In a state in which a gear 14 to be quenched is rotated round its axial center, the tooth surface 13a is uniformly heated to a required temp. After that, the rotation of this gear 13 is stopped, a coolant is sprayed on the bottom 13c of the gear 13, the coolant is flowed along the addendum 13b from the bottom 13c and quench cooling is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quenching a gear, and more particularly to an improvement in a method for quenching and cooling a tooth surface by injecting a cooling liquid into a gear heated to a required quenching temperature. Is.

[0002]

2. Description of the Related Art As a hardening method for gears, a rotating one shot (stationary) hardening method is usually used. 8 to 10
Shows an induction hardening apparatus 1 that has been conventionally used to carry out this type of hardening method. The apparatus 1 has a cooling liquid passage 2 inside and an inner peripheral surface. It is composed of an annular high-frequency induction heating coil 4 having a large number of coolant injection holes 3 and a jig 6 for holding a gear 5.
The high frequency induction heating coil 4 has lead portions 7a, 7
A high frequency current is supplied from a high frequency power source 8 via b, and a cooling liquid is supplied to the cooling liquid passage 2 of the high frequency induction heating coil 4 through a plurality of cooling liquid supply pipes 9.

The cooling liquid injection holes 3 are arranged in a so-called zigzag pattern as shown in FIG. Also,
The diameter D of the injection hole 3, the arrangement intervals L and W of the injection hole 3 in the horizontal direction and the width direction, and the axial direction of the injection hole 3 and the tooth surface 5a.
Since the angle formed by and has a great influence on the quenching result,
These various conditions are determined according to the shape, size, module, etc. of the gear 5.

When quenching the tooth surface 5a of the gear 5, as shown in FIGS. 8 and 9, the gear 5 is placed on the jig 6 and the central hole 4a of the annular high-frequency induction heating coil 4 is placed. It is arranged inside and the gear 5 is rotated around its axis together with the jig 6. At the same time, from the power source 8 to the high frequency exciting coil 4
To the tooth surface 5a of the gear 5 by supplying a high-frequency current to
High frequency induction heating. Then, when the tooth surface 5a of the gear 5 reaches the required quenching temperature, the supply of the high frequency current is stopped and the cooling liquid is supplied to the cooling water passage 2 to rotate the tooth surface from the injection hole 3. The cooling liquid is injected toward 5a (diameter direction of gear 5). Thereby, the tooth surface 5a is rapidly cooled to form a quench-hardened layer on the tooth surface 5a.

By the way, when induction hardening is applied to steel parts for machine structures having complicated shapes such as the gear 5,
As a quenching cooling method, it is general to adopt the jet cooling method as described above. The mechanism of jet cooling is the same as that of zub cooling (cooling performed by immersing a material to be quenched in a cooling liquid), and cooling is performed through a vapor film stage, a boiling stage and a convection stage. The features of injection cooling are that the vapor film stage is extremely short and the temperature at which the vapor film breaks (the temperature at which quenching begins) is high. This is because the film of bubbles generated on the solid surface (the surface of the material to be hardened) is easily broken by the high-speed fluid (cooling liquid), so that the cooling by boiling increases as compared with the case of the subcooling. This is the main reason why injection cooling has been adopted conventionally.

When performing injection cooling, the hardness after quenching, quench cracking, deformation, distortion, etc. are important depending on various conditions such as the type of cooling liquid, liquid temperature, flow velocity, flow rate, and concentration. Is known to have a significant impact. In general, the cooling liquid used for quenching and cooling steel parts is 50 which corresponds to the nose of the S curve.
0 to 600 ° C. and greater cooling rate in the vicinity of the martensite transformation point of the steel (M _S point) as near as the cooling rate becomes small at less. However, about 30
Comparing the cooling rates in the vicinity of 0 ° C., as shown in FIG. 11, the injection cooling is about 7 times larger than the case of the zub cooling, so that the injection cooling causes quench cracks and strain (deformation). There is a problem that the risk becomes large.

Further, in the case of injection cooling, the most important factors are adjustment of the flow rate or pressure of the cooling liquid and selection of the type of cooling liquid. The effect of the flow rate of the jet cooling water on the cooling curve (cooling characteristics) is as shown in FIG. In this case, since the same cooling ring having the fixed array of injection holes is used, when the flow rate is increased, the injection pressure is also increased.
As is apparent from FIG. 12, the cooling capacity can be considerably adjusted by adjusting the flow rate. It is generally known that the vapor film collapse temperature increases as the injection flow rate or injection pressure increases.

[0008]

As described above, the injection cooling has a characteristic that the cooling rate at about 300 ° C. is about 7 times higher than that of the sub-cooling, so that the risk of occurrence of quench cracks and strains is high. In addition to the above, a phenomenon in which the cooling speed of the tooth tip 5b and the tooth bottom 5c is different due to the jet cooling while rotating the gear 5 occurs (see FIG. 13).
As compared with the case of a simple shaped part, the risk of occurrence of quench cracking is further increased.

That is, in the prior art, since the gear 5 which is the object to be hardened is rotated at a required rotational speed during the injection of the cooling liquid, the cooler injected in the diametrical direction of the gear 5 is a gear. Although it often hits the tooth tip 5b of 5,
The actual condition is that it does not hit the tooth bottom 5c very well. Therefore, in the tooth tip 5b portion, the tooth bottom 5c portion, and the tooth side surface 5d portion in the middle thereof, the cooling rates of the heating surfaces are different from each other. Specifically, the tooth tip 5b is cooled earliest, the cooling rate becomes slower as it approaches the tooth root 5c, the cooling rate becomes slower as it approaches the tooth root 5c, and the tooth root 5c portion is cooled the slowest. Become. This tendency becomes more remarkable as the rotation speed of the gear 5 during quenching and cooling increases. That is, as the rotational speed of the gear 5 increases, the amount of jetted cooling water that is repelled at the tip 5b and the tooth side surface 5d and the amount that is scattered by centrifugal force increases, so that the tip 5b and the tooth 5b The difference in the cooling rate of the bottom 5c portion becomes large.

Therefore, in order to eliminate the difference in cooling rate,
The tooth bottom 5 of the gear 5 that is rotating by biasing the injection direction of the cooling liquid
Although it may be considered to apply it at a right angle to c, the fact that the cooling rate of the tooth bottom 5c portion becomes slower than the tooth tip 5b portion due to the presence of centrifugal force or the like cannot be eliminated.

However, when the cooling rate of the tooth tip 5b is fast and the cooling rate of the tooth bottom 5c is slower than that, the volume change becomes non-uniform due to the uneven cooling of the heating surface, and the tooth tip 5b portion is Attempts to shrink faster than the tip 5c. Also,
The heated surface of each part tends to shrink faster than its inner part. However, this shrinkage is slow and is hindered by the cooled parts. Thus, non-uniform cooling for quenching causes thermal stress.

As for the stress due to quenching, a structural change (martensite formation) due to rapid cooling, that is, a transformation stress due to transformation occurs. This cause is induced by the different specific volumes of austenite and its decomposition products, and the transformation occurring at different times due to non-uniform cooling. When the internal stress (thermal stress and transformation stress) due to this quenching exceeds the yield point of steel, plastic deformation occurs. This is,
It is deformation or bending, and when the internal stress becomes larger than the tensile strength of steel, inevitably cracking occurs. However, the current situation is that the generation of internal stress due to quenching cannot be prevented.

On the other hand, in the injection cooling in the conventional gear quenching method, the cooling rate at each part of the tooth surface 5a is different, and the injection cooling liquid hits the tooth surface randomly (at random), so that it is uneven. It becomes cooling, and it is assumed that the internal stress distribution at each moment of cooling is complicated. Therefore, the internal stress distribution cannot be grasped at all, and it is very difficult to prevent quenching cracks and strains (deformations).

Thus, while the internal stresses generated in the surface quenching process cause cracking, the uneven cooling promotes cracking. Therefore, when adopting the jet cooling method as the quenching cooling, it is necessary to keep the cooling uniformity by spreading the individual jetting liquids over the entire surface of the object to be quenched. However, when quenching a complex surface such as the tooth flank of a gear, injection cooling in the conventional quenching method cannot uniformly cool the tooth flank, and there is a possibility that cracks may occur. Nevertheless, in the conventional practice, quenching cooling is performed based on the false recognition that it is desirable to jet-cool a gear under a rotating state in order to perform uniform cooling.

The present invention has been made in view of the above situation, and an object thereof is to prevent generation of complicated internal stress during quenching and cooling and to prevent quench cracking and strain. It is to provide a method of quenching a gear.

[0016]

In order to achieve the above object, the present invention heats a tooth surface to a required temperature in a state in which a gear to be hardened is rotated about its axis, and then the above-mentioned By stopping the rotation of the gears and injecting the cooling liquid into the bottoms of the gears, the cooling liquids are made to flow from the bottoms of the gears along the tips of the gears for quenching and cooling.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

1 to 3 show a quenching apparatus 10 used for carrying out the method for quenching a gear according to the present invention. The quenching apparatus 10 is an annular high frequency induction heating coil. 11, a power supply 12 for supplying a high-frequency current to the coil 11, a jig 14 for holding and rotating the gear 13 which is a material to be hardened, and a plurality of coils for supplying a cooling liquid to the high-frequency induction heating coil 11. A cooling liquid supply pipe 15 is provided.

The high frequency induction heating coil 11 described above is shown in FIG.
, A pair of lead portions 16a facing each other,
16b, and these lead portions 16a, 16b
An insulating plate 16c is interposed between them. Then, a high-frequency current is supplied from the power supply 12 to the high-frequency induction heating coil 11 through the lead portions 16a and 16b.

The annular high frequency induction heating coil 11
As shown in FIG. 1 and FIG. 2, the inside thereof is formed into a hollow box-shaped cross-sectional shape, and the hollow portion has a cooling liquid passage 1
It is said to be 7. And the high frequency induction heating coil 11
The inner peripheral wall 11b is thicker than the outer peripheral wall 11a, and a large number of cooling liquid injection holes 18 are provided in the thick inner peripheral wall 11b. In addition, these injection holes 18
As shown in FIG. 3, they are arranged in a row at predetermined intervals A and B along the coil width direction and the inner circumferential direction at predetermined intervals A and B, respectively. Further, the interval B of the injection holes 18 in the circumferential direction of the coil 11 is set according to the pitch P (see FIG. 1) of the tooth portion of the gear 13 that is the object to be hardened, and as described later, The injection holes 18 in the coil width direction are arranged correspondingly on the tooth bottom 13c.

Further, cooling liquid supply pipes 15 are connected to a plurality of locations on the outer peripheral wall 11a of the high frequency induction heating coil 11, and the cooling liquid is supplied to the passages 17 of the high frequency induction heating coil 11 through these pipes 15 to inject holes. It is configured to be sprayed from 18 at a substantially right angle to the tooth bottom 13 c of the gear 13.

A jig 14 is arranged concentrically with the high frequency induction heating coil 11, and a gear 13 is placed on the jig 14 so that the jig 14 is rotationally driven about its axis. Has been done.

Next, the gear 1 is manufactured by using the quenching apparatus 10 described above.
The operation when quenching the tooth flank 13a of No. 3 will be described.
First, the gear 13 which is the material to be hardened is placed on the jig 14,
By moving the jig 14, the gear 13 is coaxially arranged at the center of the high frequency induction heating coil 11. After that, the gear 13 is rotated about its axis by rotationally driving the jig 14, and a high-frequency current is supplied from the power supply 12 to the high-frequency induction heating coil 11 to cause the gear 13 to rotate.
The tooth surface 13a of is heated by high frequency induction. Then, when the tooth surface 13a reaches the required quenching temperature by the uniform heating in the rotating state, the energization to the high frequency induction heating is stopped. At the same time, the rotation of the jig 13 is suddenly stopped to bring the gear 13 into a stationary state, and an injection hole 18 of the high frequency induction heating coil 11 is formed in each tooth bottom 13c of the gear 13 by the action of a positioning mechanism (not shown). Make them correspond. That is, a plurality of (eg, three) injection holes 18 arranged in a row in the width direction of the high-frequency induction heating coil 11 are provided on the tooth bottoms 13 c of the gears 13.
The gears 13 are stopped and stopped while the gears 13 are arranged in correspondence with each other.

Next, the cooling liquid is sequentially supplied to the supply pipe 15 and the passage 17, and the required pressure and flow rate are supplied from the injection holes 18.
The cooling liquid having the liquid temperature is jetted toward the tooth bottom 13c of the gear 13. Then, after cooling for a required time under the required cooling condition, the quenching work is completed by cooling under a cooling condition different from the initial cooling condition, that is, a condition having a small cooling capacity.

The quenching method according to the present invention as described above has the following advantages. That is, when the uniformly heated gear 13 is stopped and the cooling liquid is sprayed toward the tooth bottom 13c portion where cooling is incomplete (the cooling rate is slow) in the related art, the cooling fluid is fed from the tooth bottom 13c portion. Side surface 13d
Flow to the tooth tip 13b portion, and this tooth tip 13b portion is finally cooled. However, from the tooth bottom 13c to the tooth tip 1
Since the mass gradually decreases toward 3b, the tooth bottom 13c
It is possible to easily cool the entire tooth surface 13a at a uniform cooling rate by adjusting the pressure, the flow rate, and the liquid temperature of the cooling liquid injected into the. The reason is that since the gear 13 is stationary and the injection position of the cooling liquid is determined, the flow of the cooling liquid is not at random and the flowing direction can be grasped. As a result, the entire tooth surface 13a can be cooled uniformly or with a predetermined change in cooling rate, deformation can be minimized, and quenching processing with high dimensional accuracy can be performed.

Further, after rapid cooling for a required time under the cooling conditions of required pressure and flow rate, deformation and quench cracking occur by switching to a more gradual cooling condition without cooling down to normal temperature under this cooling condition. Can be prevented.

In order to confirm such an effect, an experiment was conducted under the following conditions.

Concrete Example 1. Gear type: Spur gear 2. Material: S-53C 3. Outer diameter (diameter of tip circle): 87 mm 4. Pitch circle diameter: 84 mm 5. Tooth width: 10 mm 6. Number of teeth: 56 7. Module: 1.5 Quenching condition (1) Preheating (high frequency induction heating coil) (a) Frequency: 3 kHz (b) Output: 170 kW (c) Heating time: 2.8 seconds (d) Gear rotation speed: 250 r. p. m. (2) Main heating (high frequency induction heating coil) (a) Frequency: 400 kHz (b) Input: 200 kW (c) Heating time: 0.15 seconds (d) Gear rotation speed: 250 r. p. m. (3) Cooling (A) First cooling condition (a) Coolant: Yukon quenchant (10%) (b) Liquid temperature: 30 ° C (c) Flow rate: 60 l / min (d) Pressure: 4 kg / cm ² (E) Cooling time: 2 seconds (B) Second cooling condition (a) Coolant: Yukon quenchant (10%) (b) Liquid temperature: 30 ° C (c) Flow rate: 30 l / min (d) Pressure: 3 kg / cm ² (e) Cooling time: 6 seconds

When the cooling rate and the cross-section hardness of each part of the gear that had been subjected to the quenching treatment under the above conditions were measured, the results shown in FIGS. 4 to 7 were obtained. From the measurement results shown in FIG. 4, it was confirmed that the tooth bottom 13c was cooled earlier than the tooth tip 13b. Further, from the measurement results shown in FIGS. 5 to 7, a hardened layer having a hardness of 800 (Hv) or more is obtained on the surface of the tooth surface 13a, and the surface hardness of each portion of the gear is substantially uniform. Was confirmed.

Further, the residual stress on the tooth surface 13a of the gear 13 hardened by the method of this example and on the tooth surface of the gear hardened by the conventional method of jet cooling while rotating the gear is measured. Then, the results shown in Table 1 were obtained. The measurement points (a), (b) in Table 1
(C) and (d) are tooth surfaces (tooth roots or tooth tips) that are sequentially spaced at 90 ° angular intervals.

[0031]

[Table 1]

As is apparent from Table 1, the residual stress at the tooth bottom 13c of the gear 13 obtained by the method of this example is a compressive stress of a sufficiently large value as compared with that by the conventional method, and therefore the fatigue strength. It was confirmed that the gear 13 had a strong strength.

Further, according to this example, a gear having high dimensional accuracy with almost no quench cracking or deformation was obtained.

The above is a description of one embodiment of the present invention.
The present invention is not limited to the above-described embodiments, and various modifications and changes can be made based on the technical idea of the present invention. For example, the present invention is applicable not only to spur gears but also to quenching methods for various gears such as helical gears. In this case, the arrangement of the injection holes 18 may be set according to the tooth bottom of each gear. In addition to the high frequency induction heating coil 11, a cooling ring having a cooling liquid injection hole as described above may be arranged. Further, the heating means is not limited to the high frequency induction heating coil, but a heating furnace may be used.

[0035]

As described above, according to the present invention, after the tooth surface of the gear is heated to the required temperature, the rotation of the gear is stopped, and the cooling liquid is jetted to the tooth bottom of the gear in the stationary state to flow to the tooth tip side. Therefore, the cooling of the tooth bottom, which has the largest mass and is the most difficult to cool, is promoted, and the cooling of the tooth tip, which has the smallest mass and is most easily cooled, is suppressed. Uniform cooling of the tooth surface is possible. Also,
Coolant is sprayed on the gear under stationary condition, so the sprayed spot of coolant can be applied to the bottom of the tooth without being random, and the coolant flows along the tooth surface without scattering. Since it crosses over, complicated residual stress does not occur on the tooth surface, and it is possible to prevent the occurrence of quenching cracks and deformation. Furthermore, by adjusting the conditions such as the injection pressure, flow rate, and liquid temperature of the cooling liquid, the cooling rate at each part of the tooth surface can be adjusted arbitrarily, so ideal quench hardening that is uniform or changes uniformly. A layer pattern can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view of a quenching device for carrying out a gear quenching method according to the present invention.

FIG. 2 is a cross-sectional view of the quenching device.

FIG. 3 is a cross-sectional view of a main part of a high frequency induction heating device.

FIG. 4 is a graph showing cooling rates of tooth bottoms and tips of gears when the method of the present invention is carried out.

FIG. 5 is a graph showing the cross-sectional hardness distribution of the addendum of the gear obtained by the method of the present invention.

FIG. 6 is a graph showing the cross-sectional hardness distribution on the tooth flanks of the gear obtained by the method of the present invention.

FIG. 7 is a graph showing a cross-sectional hardness distribution at the boundary portion (R portion) between the tooth flank and the tooth bottom of the gear obtained by the method of the present invention.

FIG. 8 is a plan view of a quenching device for carrying out a conventional gear quenching method.

FIG. 9 is a cross-sectional view of the quenching device.

FIG. 10 is a cross-sectional view of a main part of a high frequency induction heating coil.

FIG. 11 is a graph showing cooling rates by jet cooling and zub cooling, respectively.

FIG. 12 is a graph showing a relationship between a flow rate in injection and a cooling curve.

FIG. 13 is a graph showing the cooling rates of the tooth bottoms and tips of gears when quenching and cooling by a conventional method.

[Explanation of symbols]

 10 induction hardening apparatus 11 induction heating coil 13 gear 13a tooth surface 13b tooth tip 13c tooth bottom 13d tooth side surface 14 jig 15 cooling fluid supply pipe 17 cooling fluid passage 18 cooling fluid injection hole

Claims (3)

[Claims] 1. A gear to be quenched is heated to a required temperature in a state in which the gear is rotated about its axis, and then rotation of the gear is stopped so that a cooling liquid is applied to the bottom of each tooth of the gear. A quenching method for gears, characterized in that the cooling liquid is caused to flow from the bottom of the gears along the tips of the gears for quenching and cooling. 2. The quenching cooling is performed while adjusting the cooling speed of the tooth bottom portion and the tooth tip portion by adjusting the injection pressure, the flow rate and the liquid temperature of the cooling fluid injected to the tooth bottom of the gear. The method for quenching a gear according to claim 1, wherein: 3. Quenching cooling while adjusting the cooling speed of the tooth flanks of the gear while changing the cooling conditions such as the injection pressure of the cooling liquid, the flow rate, the liquid temperature, and the cooling time in two or more steps. The method for quenching a gear according to claim 1, wherein: