JPH06122926A - 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 13 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 and coolants are sprayed respectively on the addendum 13b and bottom 13c of the gear 13 from nozzles 20a and 20b, by which the tooth surface 13a of the gear 13 is subjected to quench cooling.

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. 10 to 12
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 above-mentioned 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. 13, the injection cooling is about 7 times larger than that in 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 influence of the flow rate of the injection 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 clear from FIG. 14, 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, the phenomenon that the cooling speeds of the tooth tips 5b and the tooth bottoms 5c differ due to the injection cooling while rotating the gear 5 (see FIG. 15),
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]

To achieve the above object, in the present invention, a gear to be quenched is heated to a required temperature while being rotated about its axis, and then the rotation of the gear is performed. Is stopped and the cooling liquid is sprayed to the tooth bottom and the tooth tips of the gear to quench and cool the tooth surface of the gear having the number of teeth.

[0017]

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

1 to 5 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 source 12 for supplying a high-frequency current to the coil 11, a jig 14 for holding and rotating a gear 13 which is a material to be hardened, and a four-phase supply for supplying a cooling liquid to the high-frequency induction heating coil 11. Cooling liquid supply pipes 15a, 15b, 15
c, 15d.

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 FIGS. 1 and 2, the inside thereof is partitioned by a partition wall 18 to form a concentric double hollow cross section, and the two hollow portions are each formed into a cooling liquid,
The two hollow portions are respectively the cooling liquid passages 17a, 17
It is said to be b. Then, the cooling liquid passage 17a on the outer peripheral side
Two cooling liquid supply pipes 15a and 15c are connected to
Two cooling liquid supply pipes 1 are provided in the cooling liquid passage 17b on the inner peripheral side.
5b and 15d are connected.

Further, as shown in FIGS. 3 to 5, the inner peripheral wall 19 of the high-frequency induction heating coil 11 is provided with a large number of injection holes 20 arranged in a staggered pattern. Of these injection holes 20, the injection holes 2 are arranged in a row and a column at regular intervals.
0a communicates with the cooling liquid passage 17a on the outer peripheral side, and injection holes 20b arranged alternately with the injection holes 20a communicate with the cooling liquid passage 17b on the inner peripheral side. The intervals L ₁ and L ₂ between the injection holes 20a and 20b in the inner circumferential direction of the high frequency induction heating coil 11 correspond to the pitches P ₁ and P ₂ of the tooth bottom 13c and the tooth tip 13b of the gear 13 to be quenched. Is configured. That is, the injection holes 20 a and 20 b are formed on the tooth top 13 of the gear 13.
b and the tooth bottom 13c, respectively, and the cooling fluid supplied from the cooling fluid supply pipes 15a to 15d to the cooling fluid passages 17a and 17b from the injection holes 20a and 20b to the tooth top 13b and the tooth bottom 13c of the gear. It is designed to be ejected almost at right angles.

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 the teeth of each gear 13 are caused by the action of a positioning mechanism (not shown) as shown in FIGS. 1, 4 and 5. Destination 1
The injection holes 20a and 20b of the high-frequency induction heating coil 11 are placed in the 3b and the tooth bottom 13c, respectively. That is, a plurality of (for example, three) injection holes 20a arranged in a row in the width direction of the high-frequency induction heating coil 11 are arranged corresponding to the respective tooth tips 13b of the gear 13 as shown in FIG. As shown in FIG. 5, the plurality of injection holes 20b arranged in a row in the width direction of the coil 11 are arranged corresponding to the tooth bottoms 13c of the gear 13 respectively.

Next, the cooling liquid is supplied to the supply pipes 15a-15
It is supplied to the passages 17a and 17b via d, and the cooling liquid having a required pressure, flow rate, and liquid temperature is injected from the respective injection holes 20a and 20b toward the tip 13c and the bottom 13c of the gear 13 in a substantially right-angled manner. Let It should be noted that the tooth tops 13b and the bottoms 13c are arranged so that the cooling rates of the tooth tops 13b and the bottoms 13c are equal.
The cooling conditions, that is, the quenching cooling is performed by making the pressure, flow rate, liquid temperature, etc. of the cooling liquid injected from the injection holes 20a, 20b different. 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, in the case of a gear having a large module (for example, the module has 2.5 or more), the cooling capacity is insufficient by only the jet cooling of the tooth bottom 13c, and therefore the tooth tip 13b is also quench-cooled under a predetermined cooling condition. Therefore, it is possible to easily cool the entire tooth surface 13a at a uniform cooling rate by adjusting the cooling rate. 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.

On the other hand, the tooth top 13b and the tooth bottom 13c of the gear 13 are
As a means for adjusting the cooling rate of the tooth tip 1 with a time lag after a predetermined time has elapsed from the start of cooling the tooth bottom 13c.
The cooling of 3b may be started. By selecting the time lag at this time and the cooling conditions for the tooth tip 13b and the tooth bottom 13c, it is possible to cool the entire tooth surface 13a at a uniform cooling rate, and to suppress the occurrence of quench cracks and deformation. You can

In order to confirm such action and effect, an experiment was conducted under the following conditions. Specific example 1. Gear type: Spur gear 2. Material: S-53C 3. Tip circle diameter: 75 mm 4. Pitch circle diameter: 70 mm 5. Number of teeth: 28 6. Tooth width: 10 mm 7. Module: 2.5 Quenching condition preheating 1. Frequency: 3 kHz 2. Output: 340kW 3. Heating time: 1.5 seconds 4. Gear rotation speed: 250 r. p. m. Main heating 1. Frequency: 200 kHz 2. Input: 210 kW 3. Heating time: 0.15 seconds 4. Gear rotation speed: 250 r. p. m. Cooling 1. Coolant: Yukon Quenchant (10
%) 2. Liquid temperature: 30 ° C 3. Flow rate: tooth bottom 50 l / min Pressure: 4 kg
/ Cm ² Tooth tip 20 l / min Pressure: 4 kg / cm ² 4. Cooling time: 8 seconds, tooth tip time lag 0.5 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. 6 to 9 were obtained. From the measurement results shown in FIG. 6, it was confirmed that the tooth bottom 13c and the tooth tip 13b were cooled at substantially the same cooling rate. From the measurement results shown in FIGS. 7 to 9, the hardness of the surface of the tooth surface 13a is 800 (Hv).
It was confirmed that a hardened layer having sufficient hardness as described above was obtained and the surface hardness of each part of the gear was substantially uniform.

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 20a and 20b 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. Furthermore, as heating means,
Not only the high frequency induction heating coil but also a heating furnace may be used.

[0035]

As described above, according to the present invention, after the tooth flanks of the gear are heated to the required temperature, the rotation of the gear is stopped, and the quenching is performed by injecting the cooling liquid to the tip and the bottom of the gear in the stationary state. Since it is designed to be cooled, the cooling rate is also adjusted so as to promote cooling of the tooth bottom, which has the largest mass and is most difficult to cool, and to suppress cooling of the tooth tip, which has the smallest mass and is most easily cooled. Therefore, it is possible to uniformly cool the tooth surface of the gear. In addition, since the cooling fluid is sprayed on the gears in a stationary state, the spray location of the cooling fluid can be reliably applied to the tooth bottom and the tip of the tooth instead of at random, so that the cooling fluid does not scatter. Since it flows along the surface, complicated residual stress does not occur on the tooth surface, and it is possible to prevent the occurrence of quench cracking and deformation. further,
By adjusting the conditions such as the injection pressure, flow rate, and liquid temperature of the cooling liquid, the cooling speed at each tooth surface of the module can be adjusted as desired even if it is a relatively large gear. It is possible to obtain an ideal quench hardening layer pattern that changes to.

[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 front view of an inner peripheral surface of a high frequency induction heating device.

FIG. 4 is an enlarged sectional view taken along line MM in FIG.

5 is an enlarged cross-sectional view taken along the line NN in FIG.

FIG. 6 is a graph showing cooling rates of tooth bottoms and tips of gears when the method of the present invention is carried out.

FIG. 7 is a graph showing the cross-sectional hardness distribution of the addendum of the gear obtained by the method of the present invention.

FIG. 8 is a graph showing the cross-sectional hardness distribution on the tooth flank of the gear obtained by the method of the present invention.

FIG. 9 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. 10 is a plan view of a quenching device for carrying out a conventional gear quenching method.

FIG. 11 is a cross-sectional view of the quenching device.

FIG. 12 is a cross-sectional view of a main part of a high frequency induction heating coil.

FIG. 13 is a graph showing cooling rates by jet cooling and zub cooling, respectively.

FIG. 14 is a graph showing a relationship between a flow rate in injection and a cooling curve.

FIG. 15 is a graph showing a cooling rate of a tooth bottom and a tooth tip of a gear 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 15a, 15b, 15c, 15d cooling liquid supply pipe 17a, 17b cooling liquid passage 20a, 20b cooling liquid injection Hole

Claims (3)

[Claims] 1. A gear to be quenched is heated to a required temperature while being rotated about its axis, and then rotation of the gear is stopped to supply a cooling liquid to the tooth bottoms and tips of the gear. A quenching method for a gear, characterized in that the tooth surface of the gear having the number of teeth of the gear is quenched and cooled by injection. 2. The cooling speed of the entire tooth surface of the gear is adjusted by making the cooling conditions of the tooth bottom and the tip of the tooth by the cooling liquid different from each other and adjusting the injection pressure, the flow rate, and the liquid temperature of the cooling liquid. The method for quenching a gear according to claim 1, wherein the quenching cooling is performed while adjusting the above. 3. A tooth bottom portion, a tooth tip portion, and other portions of the gear are started by starting the injection of the cooling liquid to the tooth tip after a predetermined time has elapsed from the start of the cooling fluid injection to the tooth root. The quenching method for a gear according to claim 1, wherein the quenching cooling is performed while adjusting the cooling rate of the tooth side surface portion.