JPH059584A - Heat treatment of outer ring of uniform-speed universal joint - Google Patents

Abstract

PURPOSE:To increase the torsional destruction torque by forming the hardened layer near the mouth part side end on the outer peripheral surface of a stem part to the surface hardness lower than the surface hardness of a running groove. CONSTITUTION:The outer ring 3 of the uniform-speed universal joint is integrally formed of the mouth part 2 having the running groove in which a rolling body runs on the inside surface and the stem part 1 having a toothed part 15, such as serration. The quench hardened layers are formed within the mouth part 2 and on the outer peripheral surface of the stem 1, etc., by using high-frequency coils 41, 42. The outer ring 3 is tempered by heating and holding the ring in a heating furnace 6. Only the outer peripheral surface of the stem part 1 is thereafter subjected to secondary tempering by using a low-frequency coil 43, by which the hardness of the hardened layer near the mouth part 2 side end of at least the toothed part 15 on the outer peripheral surface of the stem part 1 is made lower than the hardness of the hardened layer of the running groove. The workability and productivity are enhanced in this way and the production cost is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a heat treatment method for strengthening a stem portion of an outer ring of a universal joint.

[0002]

2. Description of the Related Art Among constant-velocity universal joint outer rings, steel outer rings such as fixed ball joints are provided with several rolling grooves on the inner surface of which the rolling elements such as balls roll. The hardened layer formed by quenching and tempering is formed on the surface of the rolling element to prevent the rolling groove from being worn or separated by the rolling element.
Guaranteed rolling life. Also, there is a method in which the stem portion is integrally projected on the outer ring, and there is one in which a tooth shape portion such as serration is carved on the outer peripheral surface of the stem portion, but it is inserted and fitted into the hollow portion of the external transmission shaft member. Prevents deformation and destruction of the tooth model,
In order to ensure the fatigue strength of the stem portion, a hardened layer formed by quenching and tempering is formed on the outer peripheral surface of the stem portion including the toothed portion.

As a conventional heat treatment method for forming a hardened layer on the outer ring, the inner surface of the mouth portion of the outer ring and the outer peripheral surface of the stem portion are individually induction hardened to form a hardened layer, and then the hardened layer is formed. A method has been adopted in which the outer ring is placed in an electric furnace, heated and held to temper the hardened layer. By this heat treatment, the surface hardness of the tempered hardened layer on the inner surface of the mouth portion is the hardness required from the viewpoint of rolling life in a constant velocity universal joint with high speed and high load, Rockwell C hardness H _RC 60 to.
It could be easily adjusted to the range of 64. Further, tempering is performed by continuous operation in a continuous furnace, and the outer ring is integrally heated by the atmosphere in the furnace, so the tempering temperature control is easy and the productivity and economy are excellent.

[0004]

In recent years, particularly in the case of constant velocity universal joints for automobiles, miniaturization and weight reduction have been pursued in order to improve the fuel efficiency of automobiles, and the outer ring of the joint has been improved in accordance with the high performance of the engine. The applied load torque becomes higher,
We need an outer ring that can withstand this.

In the conventional outer ring described above, when a rotational torque is applied between the rolling groove of the mouth portion and the serration shaft of the stem portion, torsional fracture occurs at the stress concentration portion of the stem portion. Considering the above, it is still low, and it is necessary to strengthen the stem portion. In order to deal with this, there is a limit in the conventional method of tempering the rolling groove of the mouth part and the outer peripheral surface of the stem part by the same heating in the furnace under the same conditions.

In view of the above problems, the present invention aims to provide a heat treatment method for a universal joint outer ring for strengthening the stem portion to improve the torsional strength.

[0007]

A heat treatment method for an outer ring of a constant velocity universal joint according to the present invention is a stem having a mouth portion having a rolling groove for rolling a rolling element on an inner surface and a toothed portion such as serration on an outer peripheral surface. In the constant velocity universal joint outer ring integrally formed from the part, the quenching hardened layer by induction heating quenching is formed on the inner surface of the mouth part and the outer peripheral surface of the stem part, respectively.
Then, after the outer ring is heated and held in a heating furnace to be tempered, only the outer peripheral surface of the stem is subjected to secondary tempering by induction heating, and at least the end of the outer peripheral surface of the stem on the mouth side of the tooth part. The hardness of the hardened layer near the portion is lower than the hardness of the hardened layer of the rolling groove.

Further, in the heat treatment method of the present invention, a quench-hardened layer is formed individually on the inner surface of the mouse portion of the outer ring and the outer peripheral surface of the stem portion by induction heating and quenching, and then the inner surface of the mouse portion and the outer surface of the mouse portion are formed. The stem outer peripheral surface and the tempering are individually performed by induction heating, and the hardness of the hardened layer at least in the vicinity of the mouse side end portion of the tooth profile of the stem outer peripheral surface is higher than the hardness of the hardened layer of the rolling groove. It is characterized by a heat treatment method for lowering it.

The steel type of the outer ring to which the heat treatment method of the present invention is applied may be any structural steel such as general induction hardened steel or carburized and hardened steel. It is particularly preferable that the hardness of the hardened layer in the vicinity of the mouse side end of the mold part is adjusted so as to be in the range of Rockwell C hardness H _RC 55 to 60.

[0010]

[Function] In the outer ring integrally formed of the mouse portion and the stem portion, the inner surface of the mouse portion and the outer peripheral surface of the stem portion are separately quenched by induction heating, so that a quench-hardened layer of martensite phase is formed, Next, since the outer ring itself is charged into a heating furnace and subjected to a low temperature tempering treatment, the hardened layer becomes a tempered martensite phase, part of the transformation residual stress is released, and the toughness is restored. Conditions of the induction hardening and furnace tempering may be the same as the conventional method, exclusively, the required surface hardness of the rolling groove hardened layer of the rolling life H _RC
The hardness is determined to be 60 to 64, and therefore the hardness of the outer peripheral surface of the stem portion is also about H _RC 60 to 64.

After the in-furnace tempering, only the outer peripheral surface of the stem portion is subjected to secondary tempering by induction heating, and the outer peripheral surface temperature at the time of this induction heating is made higher than the heating temperature of the in-furnace inner peripheral surface. The hardened layer is slightly softened and stretched, the impact value is increased, and the toughness is improved.

When the stem portion is broken by applying a rotating torque, the stem portion is broken at the mouse side end portion of the toothed portion such as serration formed on the outer peripheral surface of the stem portion. This is because cracks occur in the hardened layer at the serration end where the torsional stress concentrates,
The main stress type fracture propagates to the inner portion of the stem portion and the stem portion is broken.

In the heat treatment method of the present invention, since at least the hardened layer at least in the vicinity of the mouth side of the tooth pattern portion is softened to enhance the toughness, the susceptibility to cracking is lowered and the torsion at the fracture initiation site is twisted. It will increase the strength and therefore the breaking torque.

[0014] The surface hardness of the hardened layer of the stem portion outer peripheral surface is a mouth-side end portion of the tooth-shaped portion, when it is adjusted to H _RC 55 to 60, to the surface hardness lower than H _RC 55, the curing It is not appropriate because the residual compressive stress of the layer is also reduced and the fatigue strength against repeated stress is reduced.

The surface hardness of the hardened layer of the stem portion is calculated as H above.
_To adjust to the range of _RC 55 to 60, when the heating temperature of the heating and tempering in the furnace is 180 ° C. (60 minutes), the secondary tempering temperature is 180 to 220 ° C. and the heating time is about 10 to 20 seconds. To do.

In the heat treatment method for the outer ring of the present invention, the quenching and hardening in the furnace are omitted, and the quenching and hardening layer on the inner surface of the mouth and the hardening and hardening layer on the outer circumference of the stem are induction-heated by separate induction coils. In the case of a tempering method, the hardness of the tempered hardened layer on the outer peripheral surface of the stem portion can be easily made lower than the hardness of the tempered hardened layer on the inner surface of the mouse portion.

The induction heating method for direct tempering without the secondary tempering or heating in the furnace may be high frequency heating or low frequency heating. If the frequency is lowered, the induction skin current layer on the steel surface becomes thicker, which is convenient for uniform heating of the surface layer portion. Further, as the frequency becomes lower, even if the gap between the coil and the surface of the steel material is increased, a sufficient current can be induced in the surface layer portion, so that the present invention has a circumferential surface having different outer diameters in the longitudinal direction. It is convenient to heat the outer ring stem part, and the centering adjustment for inserting and fixing the stem part in the coil is extremely easy because a small flat core is allowed.
The low-frequency heating is also used for tempering the stem part described above, but for tempering the quench-hardened layer on the inner surface of the mouse part, a low-frequency coil is inserted and fixed on the inner surface of the mouse part to induction-heat the quench-hardened layer. A method can be used, and a low frequency coil in which the outer peripheral portion of the mouse portion is inserted and fixed in the hollow portion of the coil is used to heat the quench-hardened layer by heating in the thickness direction from the outer peripheral surface of the mouse portion to the inner surface. Can be adopted. In tempering, the high-frequency heating, frequency 1～10KH _Z, in the case of low-frequency heating, but is the frequency 50~500H _Z ,,
Intermediate medium frequency heating is also available.

[0018]

EXAMPLES The test materials were outer rings of the fixed type ball joint shown in FIG. 1 and the plunging type joint shown in FIG. 2. Induction hardened steel was integrally formed by die forging. The outer ring of both methods is integrally formed of a stem portion 1 and a mouse portion 2, a plurality of rolling grooves 23 are formed on an inner surface 22 of the mouse portion, and a stem protruding from the back portion of the mouse portion 2 is formed. Part 1
The bearing support portion 14, the serration portion 15, the screw portion 16 or the retaining ring groove 17 are provided on the front side of the. The serration portion 15 has a trapezoidal serration formed by rolling, and in FIG. 1, the large diameter is 24 mm and the tooth height is 2 mm. In FIG. 1 (A) and FIG. 2, the surface hardened layer 11 on the outer peripheral surface of the stem portion 1 and the surface hardened layer 21 on the inner surface of the mouse portion 2 are schematically shown.

(Example 1) As a heat treatment method, the steps of induction hardening and secondary tempering of a stem portion after tempering in a furnace will be described below.

As shown in FIG. 3 (A), the outer peripheral surface of the stem portion 1 of the outer ring is inserted and fixed in the high frequency coil 41,
950 ° C on the outer peripheral surface due to induction power with a frequency of 10 KHz
After heating for 4 to 5 seconds and then immediately pouring water, the surface was quenched. Further, another high-frequency coil 42 is inserted on the inner surface of the mouse portion 2, and induction heating and water injection are similarly performed,
The surface was quenched.

Next, as shown in FIG. 3 (B), the induction-hardened outer ring 3 is placed in a continuous electric furnace 6 and heated by an electric heater 61 while being conveyed by a conveyor 62. Then, after heating and holding at 180 ° C for 60 minutes,
It stood to cool and tempered.

The above induction hardening and tempering in the furnace are almost the same as the conditions in actual operation. The outer ring after tempering in the furnace is used as a comparative example, and the rolling groove 23 on the inner surface of the mouth portion of the outer ring and the outer peripheral surface of the stem portion 1 are taken as a comparative example. The surface hardness of the hardened layers 11 and 21 was measured by the micro Vickers hardness tester at the position of the tooth bottom 151 (FIG. 1B) of the serration 15 lowering part.

The average Vickers hardness H _V 71 on the bottom surface 23 of the rolling groove of the mouth of the fixed ball joint
5.2 (converted to H _RC 60.8), while H _V 732.8 at the tooth bottom 151 at the serration end of the stem.
(Converted H _RC 61.5), and in the plunging type, H _V 721.2 (converted H _RC 61.5) at the bottom surface 23 of the rolling groove.
_RC 61.0), while the root 151 at the serration end has an average H _V 742.0 (converted H _RC 61.8).
(In each case, the number of samples was 25), and the hardness of the tooth bottom 151 at the serration end was higher.

Next, as shown in FIG. 3 (C), the stem portion 1 of the outer ring after tempering in the furnace is inserted into the low frequency coil 43, and the space between the serration portion 15 and the bearing support portion 14 is inserted. As a center, induction heating was performed at a frequency of 180 Hz to perform secondary tempering. At this time, set the temperature of the outer peripheral surface of the stem to 1
The heating conditions were adjusted to two levels of 60 ° C. for 12 seconds and 220 ° C. for 15 seconds.

The hardness of the test material after the secondary tempering was measured in the same manner as in the comparative example. Further, with respect to the comparative material and the test material, a breaking torque until the stem portion was broken was measured by a static torsion tester. The breakage occurs from the bottom tooth bottom 151 of the serrated portion 15 of FIG.
No. 4 was obliquely cut, but no particular difference was observed in the rupture form between the example and the comparative example. The test results are shown together in FIG.

The surface hardness of the serration lowered portion tooth bottom of the stem portion is softened extent H _RC 55.8 by condition 220 ° C. × 15 sec heating of the secondary tempering, as shown at this time is 4, and most damaging torque is It becomes higher, and it can be seen that the heat treatment method of the present invention is effective for strengthening the toughness of the stem portion.

(Embodiment 2) Next, an embodiment will be described in which the tempering in the furnace is omitted and the induction-hardened outer ring is tempered by low-frequency heating.

FIG. 5 is a schematic diagram of the low frequency tempering of the outer ring having the quench hardened layer formed by the induction hardening described in Example 1. The stem portion 1 is inserted into the hollow portion of the low frequency coil 45. The mouse portion 2 is inserted into the hollow portion of another low frequency coil 46. Since the induction current is a low frequency of 180 Hz, the quench hardening layer on the inner surface of the mouse is
Sufficiently uniform heating could be achieved by low frequency induction heating from the outer peripheral surface of the mouse.

When the tempering temperature of the outer peripheral surface of the stem portion is 220 ° C., 1
After heating for 5 seconds, the average hardness of the serration part H _RC 55-56
Got Further, the tempering temperature of the inner surface of the mouse portion was heated to 155 ° C. for 12 seconds to obtain the hardness of H _RC 60 on the bottom surface of the rolling groove.

A static torsion test was carried out on the fixed type ball joint which had been subjected to low frequency tempering, and the breaking torque was increased by lowering the surface hardness of the hardened layer of the stem portion as in Example 1. confirmed.

[0031]

By carrying out the heat treatment method for the outer ring of the present invention,
The following effects can be achieved. After induction hardening of the outer ring and tempering in the furnace, only the hardened layer on the outer peripheral surface of the stem is subjected to secondary tempering by induction heating.Therefore, the hardness of the hardened layer on the inner surface of the mouse is adjusted exclusively from the viewpoint of rolling life, and The hardness of the hardened layer on the outer peripheral surface of the part can be easily adjusted from the viewpoint of toughness in response to torsional fracture, and by slightly softening the hardened stem part by secondary tempering, cracking of the hardened layer surface Sensitivity can be slowed down and breaking torque can be increased. Also, if induction heating is performed on the outer peripheral surface of the stem portion and the inner surface of the mouse portion by separate induction coils,
Further, tempering in the furnace can be omitted, and the hardness of the inner surface of the mouth portion and the hardness of the outer peripheral surface of the stem portion can be adjusted independently.

In particular, when a low frequency current is used for induction heating and tempering, the penetration depth of the low frequency current into the outer ring surface portion is large, so that even if the distance between the coil and the outer ring surface is increased, the hardened layer is uniformly heated. Since it is easy, even for tempering of the hardened layer on the inner surface of the mouse part, it is sufficient to cover the outer peripheral surface of the mouse part with a low-frequency coil, and strict accuracy of centering is not required, so workability and productivity are improved. It is expensive and effective in reducing production costs.

[Brief description of drawings]

FIG. 1 Appearance and cross-sectional view of a fixed ball joint (A)
And a partial cross section near the serration end of the stem (B).

FIG. 2 is a sectional view of a plunging type joint.

FIG. 3 is a heating procedure diagram of a heat treatment process in an embodiment of a fixed ball joint.

FIG. 4 is a diagram showing a relationship between a stem surface hardness and a breaking torque in Examples and Comparative Examples.

FIG. 5 is a diagram showing an arrangement relationship of low-frequency coils in tempering the outer ring by induction heating.

[Explanation of symbols]

1 Stem part 11 Hardened layer 14 Bearing support 15 Serration part 2 mouse part 23 Rolling groove 3 outer ring 41 high frequency coil 43 low frequency coil

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[Procedure amendment]

[Submission date] August 15, 1991

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

Next, as shown in FIG. 3C, the stem portion 1 of the outer ring after tempering in the furnace is inserted into the low frequency coil 43, and the space between the serration portion 15 and the bearing support portion 14 is inserted. As a center, induction heating was performed at a frequency of 180 Hz to perform secondary tempering. At this time, the temperature of the outer peripheral surface of the stem portion
And adjusted to the heating conditions of 15 Byoho lifting at 22 0 ° C..

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Fig. 2]

[Figure 1]

[Figure 3]

[Figure 4]

[Figure 5]

Claims (3)

[Claims] 1. A mouse of a constant velocity universal joint outer ring formed integrally from a mouth part having a rolling groove on which an rolling element rolls and an stem part having a tooth profile part such as serration on an outer peripheral surface. After forming a quench-hardened layer by induction heating and quenching on the inner surface of the part and the outer peripheral surface of the stem, respectively, the outer ring is heated and held in a heating furnace for tempering, and then only the outer peripheral surface of the stem is induction heated. By performing secondary tempering with a constant velocity universal joint so that the hardness of the hardened layer at least in the vicinity of the mouth side end of the tooth profile on the outer peripheral surface of the stem is lower than the hardness of the hardened layer of the rolling groove. Heat treatment method for outer ring. 2. A mouse having a constant velocity universal joint outer ring integrally formed from a mouth portion having a rolling groove on which an rolling element rolls on an inner surface and a stem portion having a toothed portion such as serration on an outer peripheral surface. On the inner surface of the portion and the outer peripheral surface of the stem portion, a quenching hardened layer is formed by induction heating and quenching individually, and then the inner surface of the mouse portion and the outer peripheral surface of the stem portion are individually tempered by induction heating, A heat treatment method for a constant velocity universal joint outer ring, wherein the hardness of the hardened layer on the outer peripheral surface of the stem portion at least in the vicinity of the mouse side end portion of the tooth profile is lower than the hardness of the hardened layer of the rolling groove. 3. The uniform velocity control according to claim 1, wherein the hardness of the hardened layer on the outer peripheral surface of the stem portion at least in the vicinity of the mouse side end portion of the toothed portion is in the range of Rockwell C hardness H _RC 55 to 60. Heat treatment method for outer ring of joint.