JP2014041789A - Induction heating apparatus, and induction heating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency heat treatment device and a high frequency heat treatment method, which can manufacture a bearing: having life characteristics excellent in durability against any of breakage modes due to internal fatigue and surface fatigue; and excellent in fracture strength.SOLUTION: An induction heating apparatus 10 has a surface induction-heating coil 20 that heats an entire surface and a raceway surface induction-heating coil 30 that heats a raceway surface, both provided on a circle. The surface induction-heating coil 20 is disposed so that a plurality of pairs of an inner diameter side pillar conductor 21 and an outer diameter side pillar conductor 22, extending together in an axial direction so as to interpose a raceway ring therebetween on a virtual straight line extending in a radial direction from the center of the raceway ring, are arranged at a predetermined interval in a circumferential direction. Through the inner diameter side pillar conductor 21 and the outer diameter side pillar conductor 22 of each pair, current flows in an opposite direction to each other.

Description

  The present invention relates to an induction heating apparatus that includes a plurality of induction heating coils on a circumference and induction heats a bearing ring of a bearing, and an induction heating method using the same.

  Rolling bearings are required to have longevity and toughness. Especially for industrial bearings, which are often subjected to high loads or shock loads, the balance between them is regarded as important.

  The rolling life of rolling bearings is roughly classified into internal origin type peeling and surface origin type peeling. Since the former is based on non-metallic inclusions contained in the steel, the life has been extended by a technique for reducing the oxygen content of the steel material. Until now, the amount of oxygen has been reduced by improving various steelmaking processes. However, it is desirable that the chemical component has a large amount of carbon with respect to a decrease in the amount of oxygen. In fact, it is known that bearing steel represented by SUJ2 exhibits higher cleanliness than S53C, which is medium carbon steel.

  With regard to the latter surface-origin type peeling, since the peeling occurs due to stress concentration at the edge of the indentation caused by the inclusion of foreign matter such as metal powder contained in the oil, the amount of retained austenite is controlled for the purpose of mitigating this, We have measured the lifetime. In general, surface-origin-type delamination has a significantly shorter life than internal-origin-type delamination, so the development of long-life bearings is mostly related to surface-origin-type delamination. However, in order to precipitate a large amount of retained austenite, it is necessary to form a carbon or nitrogen-enriched region on the surface, which requires a quenching treatment in a special gas atmosphere such as carburizing or carbonitriding. Become. Furthermore, the precipitation of a large amount of retained austenite brings about the decrease in the surface hardness that is most necessary for rolling bearings. Therefore, it is necessary to supplement this with hard carbonitrides. For this reason, when expensive alloy elements such as Mo are added. There is also.

  On the other hand, the toughness has a trade-off relationship with the hardness of the material. Therefore, in order to improve toughness, it is a basic policy to secure as many regions with low hardness as possible. From this point of view, carburized bearings have been developed in which only the surface is hardened by carburizing or carbonitriding the low and medium carbon steel. However, carburized steel is often used for relatively large bearings such as steel bearings, and in order to ensure hardenability, it is mainstream to add relatively expensive alloy elements such as Ni, Mo and Cr. The present situation is that the production cost is increased together with the complicated heat treatment such as carburizing treatment.

  In response to the above-described problems, in recent years, high-frequency heat treatment has been attracting attention in which only a necessary portion is quenched and hardened. This is a technique for achieving both life and toughness by creating a hardened layer that can withstand high surface pressure and a non-hardened layer having excellent toughness in one part. Furthermore, it is considered that by having a non-cured layer, a compressive residual stress is imparted to the cured layer on the surface, and it is effective in suppressing the life and propagation of cracks. In addition, since the hardness can be controlled by the presence or absence of quenching treatment, high carbon steel represented by general-purpose bearing steel having excellent cleanliness can be used instead of high alloy low carbon steel. By the way, with respect to surface damage, it has been shown earlier that retained austenite is effective. However, due to the characteristics of induction hardening, if the surface has a high current density and the carbon concentration of the base material is about 0.7%, only the extreme surface layer is present. In addition, retained austenite comparable to carburized steel can be secured. It is also known that a large amount of retained austenite is one of the negative factors of dimensional change, but when viewed in the depth direction, the amount of retained austenite decreases rapidly, so the extreme surface area below the maximum shear stress depth There is also an advantage that the entire volume ratio can be kept low while being present in a large amount. That is, by using high-carbon steel typified by bearing steel and induction hardening, it is possible to manufacture a bearing having excellent life characteristics in both internal fatigue and surface fatigue failure modes and excellent crack resistance. it is conceivable that.

  However, there are problems when applying induction hardening to bearings. This relates to the manufacturing method, and is caused by the fact that the high-frequency heat treatment is a very short time treatment and that the region to be heated depends on the shape of the coil. Therefore, many literatures relating to the high frequency heat treatment method have been reported, such as those relating to steel materials suitable for high frequency, items relating to pre-heat treatment, and items relating to equipment.

  For example, Patent Document 1 reports that in heating an annular member, uniform heating is realized by arranging a plurality of coils in the circumferential direction and adjusting the distance between the coils and the workpiece.

Japanese Patent No. 4365311

  In the present invention, the product of the rolling bearing has a long life against surface fatigue produced by carburizing or the like, and it is necessary to secure 15% or more of retained austenite on the raceway surface. On the other hand, in steel with a large total amount of retained austenite, deterioration of dimensional stability due to long-term use is inevitable, so it is necessary to keep the retained austenite in portions other than the raceway surface as low as possible. However, when the induction heating coil described in Patent Document 1 is used, it is heated uniformly to a portion other than the raceway surface (for example, a fitting surface or an end surface on which the coil is applied). It is difficult to increase only the amount of retained austenite. Moreover, since coils having the same shape are arranged in the circumferential direction, it is difficult to make adjustments that raise the temperature of only the raceway surface.

  Thus, the present condition is that the high frequency heat processing method with respect to the bearing for which the life extension by surface fatigue is calculated | required is not established.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to produce a bearing having excellent life characteristics in both internal fatigue and surface fatigue failure modes and excellent crack resistance. An object is to provide a high-frequency heat treatment apparatus and a high-frequency heat treatment method.

  In high-frequency heat treatment, eddy current flows in the part where the coil is directly facing the work, which causes heat generation of the work. If this control is not appropriate, a phenomenon called overheating occurs in which a large amount of current flows through a specific portion and the temperature rises extremely in that portion. When overheating occurs, the crystal grains in that portion are remarkably coarsened, and the mechanical properties centering on toughness are deteriorated. On the other hand, when the heating temperature is insufficient, the penetration of carbon into the base becomes insufficient. Hardness is a very important characteristic for rolling fatigue and wear, and its hardness depends on the amount of carbon in the base in the component range called structural steel, including bearing steel. Need to be dissolved in That is, it can be said that a coil having a difference between a high temperature part and a low temperature part of the workpiece is a good coil that easily adjusts the heat treatment quality of the workpiece according to the output condition.

  On the other hand, it is known that the bearing has a concave and convex portion such as a collar except for a specific workpiece, heat tends to concentrate on the convex portion, and the concave portion is difficult to receive heat. As a result of repeating trial production using various coils for an inner ring workpiece having various collar portions, the present inventors have found that overheating of the collar portion is more likely to occur as the current flowing in the circumferential direction increases. It was. For example, a turn coil (coil is arranged concentrically with a workpiece) and the above occur extremely extremely, and heating concentrates only on the collar portion, and no excessive current is generated in the vicinity without current flowing.

  In order to solve this, it is necessary to flow a current uniformly in the workpiece cross-sectional direction. Specifically, when the work is viewed from above, the same circumferential angle direction is arranged in the order of coil → work → coil in a straight line from the center line, and the inner diameter side coil and the outer diameter side coil It turns out that the direction of the current needs to be reversed. By controlling the coil in this way, the current flows in a pseudo closed circuit on the workpiece cross section, so that the workpiece surface is not limited to irregularities, and a uniform current can easily flow.

  On the other hand, although the above is a coil for uniformly heating the entire workpiece surface, in the case of a rolling bearing, more strict quality control is required for the raceway surface on which the rolling element rolls. Specifically, it is necessary to control the prior austenite grain size to 30 μm or less while controlling the residual austenite amount to 15 to 40% by volume. In order to achieve this, in addition to the surface uniform heating coil described above, a coil capable of raising the temperature of only the raceway surface is required. This coil must face the raceway accurately and minimize the flow of current to the adjacent collar.

The present invention provides the following configuration that achieves the above object, based on these findings obtained as a result of intensive studies by the present inventors.
(1) An induction heating device having a plurality of induction heating coils on the circumference and induction heating the bearing raceway,
The plurality of induction heating coils include a surface induction heating coil that heats the entire surface, and a raceway surface induction heating coil that heats the raceway surface,
The surface induction heating coil includes a coil having an inner diameter side columnar conductor and an outer diameter side columnar conductor both extending in the axial direction so as to sandwich the raceway on a virtual straight line extending in the radial direction from the center of the bearing ring. As a set, a plurality of sets are arranged at predetermined intervals in the circumferential direction,
An induction heating apparatus, wherein a reverse current flows through the inner diameter side columnar conductor and the outer diameter side columnar conductor of each set.
(2) The induction heating device according to (1), wherein a current in a reverse direction flows between the inner diameter side columnar conductors and the outer diameter side columnar conductors of adjacent groups.
(3) The adjacent inner diameter side columnar conductors and the outer diameter side columnar conductors of the adjacent sets are connected with a connecting conductor on the same side in the axial direction,
The connecting conductors are alternately arranged in the circumferential direction on one axial side and the other axial side,
The inner diameter side columnar conductor and the outer diameter side columnar conductor of the set located on one end side in the circumferential direction are connected on the side where the connection conductor is not connected,
The inner diameter side columnar conductor and the outer diameter side columnar conductor of the set located on the other end side in the circumferential direction are connected to a power source on the side where the connection conductor is not connected. Induction heating device.
(4) A radial distance between the inner diameter side columnar conductor and the raceway and a radial distance between the outer diameter side columnar conductor and the raceway are equal,
The induction heating apparatus according to (3), wherein an axial distance between the connection conductor and the raceway is at least twice the radial distance.
(5) An induction heating method using the induction heating device according to any one of (1) to (4),
The induction is characterized in that, while rotating the raceway, the surface induction heating coil is heated so that the core remains and the entire surface is hardened, and then the raceway surface is heated by the raceway induction heating coil. Heating method.
(6) An induction heating device having a plurality of induction heating coils on the circumference and induction heating the bearing raceway,
The plurality of induction heating coils include a surface induction heating coil that heats the entire surface, and a raceway surface induction heating coil that heats the raceway surface,
The surface induction heating coil is arranged so that an inner diameter side columnar conductor and an outer diameter side columnar conductor sandwich the raceway on a virtual straight line extending from the center of the raceway to the outer diameter side,
An induction heating apparatus, wherein a reverse current flows through the inner diameter side columnar conductor and the outer diameter side columnar conductor.
(7) An induction heating method using the induction heating device according to (6),
The induction is characterized in that, while rotating the raceway, the surface induction heating coil is heated so that the core remains and the entire surface is hardened, and then the raceway surface is heated by the raceway induction heating coil. Heating method.

  According to the induction heating apparatus and the induction heating method of the present invention, a hardened layer that can withstand high surface pressure and a non-hardened layer having excellent toughness can be formed by a surface induction heating coil that heats the entire surface. The amount of retained austenite resistant to surface damage can be ensured by the raceway surface induction heating coil for heating the surface. Thereby, it is possible to produce a bearing having excellent life characteristics in both internal fatigue and surface fatigue failure modes and excellent crack resistance.

It is a perspective view showing typically the induction heating device of one embodiment concerning the present invention. It is surface induction heating coil explanatory drawing which looked at the surface induction heating coil from the axial direction one side.

  Hereinafter, an induction heating method of an induction heating apparatus for induction heating the bearing ring of the bearing of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view schematically showing an induction heating apparatus according to an embodiment of the present invention, and FIG. 2 is an explanatory view of a surface induction heating coil when the surface induction heating coil is viewed from one side in the axial direction.

  As shown in FIG. 1, the induction heating device 10 according to an embodiment of the present invention includes two induction heating coils 20 and 30 having different roles in the circumferential direction of the bearing ring W of a bearing to be processed. Yes. In FIG. 1, an inner ring having a raceway surface Wa on the outer peripheral surface is shown as the bearing ring W of the bearing.

  The induction heating coil 20 is a surface induction heating coil that heats the entire surface of the raceway ring W, and the induction heating coil 30 is a raceway surface induction heating coil that heats the raceway surface Wa of the raceway ring W. Hereinafter, the induction heating coil 20 is referred to as a surface induction heating coil, and the induction heating coil 30 is referred to as a raceway surface induction heating coil.

First, the surface induction heating coil 20 will be described with reference to FIG.
In order to heat the surface uniformly, it is important to pass a current in the cross section of the raceway ring W, in other words, not to flow a current in the circumferential direction to the collar portion. Therefore, the surface induction heating coil 20 includes an inner diameter side columnar conductor 21 and an outer diameter side column portion that extend in the axial direction so as to sandwich the raceway ring W on a virtual straight line P extending in the radial direction from the center O of the raceway ring W. Four sets of coils 23 </ b> A to 23 </ b> D are formed at a predetermined interval in the circumferential direction, with a set of coils having a conductor 22. The coils of each set are arranged such that the distance L1 from the inner diameter side columnar conductor 21 to the inner circumferential surface of the race ring W and the distance L2 from the outer diameter side columnar conductor 22 to the outer circumferential surface of the race ring W are equal. (L1 = L2).

  Further, in order to pass a current in the cross section of the raceway ring W, it is necessary to feed a current in the opposite direction to each set of the inner diameter side columnar conductor 21 and the outer diameter side columnar conductor 22 across the raceway ring W. Further, in order to form a plurality of independent closed circuits, the adjacent inner diameter side column conductors 21 and 21 and the outer diameter side column conductors 22 and 22 are connected so that reverse currents flow between them. There is a need to. Therefore, the adjacent inner diameter side columnar conductors 21 and 21 and the outer diameter side columnar conductors 22 and 22 are connected by the connection conductor 24 on the same side in the axial direction.

  More specifically, the second assembled coil 23B is arranged at a position with an angle α from the first assembled coil 23A located on one end side in the circumferential direction, and the third assembled coil 23C is disposed at a position with an angle α from the second assembled coil 23B. And a fourth coil assembly 23D is disposed at an angle α from the third coil assembly 23C. Therefore, the distance L3 between the inner diameter side columnar conductors 21 of the adjacent sets is shorter than the distance L4 between the outer diameter side columnar conductors 22 of the adjacent sets (L3 <L4).

  The inner diameter side columnar conductor 21 of the first assembled coil 23A and the inner diameter side columnar conductor 21 of the second assembled coil 23B, and the outer diameter side columnar conductor 22 of the first assembled coil 23A and the outside of the second assembled coil 23B. The radial columnar conductors 22 are connected to each other by a connection conductor 24 on one side in the axial direction (downward in FIG. 1). The inner diameter side columnar conductor 21 of the second assembled coil 23B and the inner diameter side columnar conductor 21 of the third assembled coil 23C, and the outer diameter side columnar conductor 22 of the second assembled coil 23B and the outside of the third assembled coil 23C. The radial columnar conductors 22 are connected to each other by a connecting conductor 24 on the other axial side (upper side in FIG. 1). The inner diameter side columnar conductor 21 of the third assembled coil 23C and the inner diameter side columnar conductor 21 of the fourth assembled coil 23D, and the outer diameter side columnar conductor 22 of the third assembled coil 23C and the outside of the fourth assembled coil 23D. The radial columnar conductors 22 are connected to each other by a connection conductor 24 on one side in the axial direction (downward in FIG. 1). That is, the connection conductors 24 are alternately arranged on the one axial side (lower side in FIG. 1) and the other axial side (upper side in FIG. 1) in the circumferential direction.

  The first coil assembly 23A located on one end side in the circumferential direction is connected to the inner diameter side columnar conductor 21 and the outer diameter side by the connecting conductor 24 on the other axial side (upper side in FIG. 1) that is not connected to the connecting conductor 24. The fourth coil assembly 23D connected to the columnar conductor 22 and located on the other circumferential end is a power source (not shown) on the other axial side (upper side in FIG. 1) that is not connected to the connecting conductor 24. Connected to.

  The axial distance L5 between the connection conductor 24 and the raceway ring W is secured at least twice the radial distance (L1, L2) between the inner diameter side columnar conductor 21 or the outer diameter side columnar conductor 22 and the raceway ring W. (L5 ≧ 2 × L1 (L2)). The connection conductor 24 also generates a magnetic field and generates heat when it acts on the raceway ring W. However, the heat generated by the connection conductor 24 causes excessive heat generation at the collar portion of the raceway ring W and is likely to cause overheating. Should be limited to typical connections.

  When a current is passed through the surface induction heating coil 20 configured in this way, the inner diameter side columnar conductor 21 of the first assembled coil 23A, the outer diameter side columnar conductor 22 of the second assembled coil 23B, and the third assembled coil 23C A current in the same direction flows through the inner diameter side columnar conductor 21 and the outer diameter side columnar conductor 22 of the fourth set coil 23D, and a current in the opposite direction flows to the outer diameter side columnar conductor 22 of the first set coil 23A. It flows to the inner diameter side columnar conductor 21 of the second set coil 23B, the outer diameter side columnar conductor 22 of the third set coil 23C, and the inner diameter side columnar conductor 21 of the fourth set coil 23D.

  That is, a current in the opposite direction flows through the inner diameter side columnar conductor 21 and the outer diameter side columnar conductor 22 of each set, and the inner diameter side columnar conductors 21, 21 of the adjacent groups, the outer diameter side columnar conductor 22. , 22 flow in opposite directions, and form four pseudo independent closed circuits.

  On the other hand, in order to ensure the quality of the raceway ring W, the temperature of the raceway surface Wa through which the rolling elements pass needs to be higher than that of the other portions. Therefore, in the raceway surface induction heating coil 30, the arc-shaped coil 31 along the raceway surface Wa is arranged at an equal distance from the raceway surface Wa so as to heat only the raceway surface. The arc-shaped coil 31 is connected to a power source (not shown) at both ends in the circumferential direction.

Then, the induction heating method using this induction heating apparatus 10 is demonstrated.
First, after placing the race ring W on a turntable (not shown) and securing the center of rotation, the surface induction heating coil 20 and the raceway surface induction heating coil 30 are moved to a predetermined position. Next, after rotating the race ring W and confirming that it has reached a steady state, an electric current is passed through the surface induction heating coil 20 to start heating. After heating for a predetermined time, electric power is supplied to the raceway surface induction heating coil 30, and after a predetermined time has elapsed, the power is cut and water cooling is performed.

  The bearing ring W as a workpiece is preferably a baked steel having a hypereutectoid composition represented by general-purpose high carbon chrome steel (SUJ2, SUJ3, SUJ4, SUJ5). The surface induction heating coil 20 suppresses overheating of the collar portion, and the surface temperature of the race ring W is heated to the A1 transformation point or higher so that the core remains and the entire surface is cured. Induction heat treatment is performed. Further, by adding heating to the raceway surface Wa by the raceway surface induction heating coil 30, it is possible to control the structure of the retained austenite on the raceway surface and the region subjected to a large shear stress. The retained austenite on the raceway surface Wa is controlled to 15 to 40%, and the prior austenite grain size is controlled to 30 μm or less. By the above method, it becomes possible to manufacture a high-quality bearing in a short time while ensuring the rolling durability of the raceway surface Wa, and it shows a long life in applications where there is a concern about a decrease in the life such as in a lubricating environment containing foreign matter. Rolling bearings can be manufactured.

In addition, this invention is not limited to each embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably.
For example, the surface induction heating coil 20 is composed of four sets of coils 23A to 23D in the above embodiment, but may be composed of one or more sets of coils. The number may be increased by a necessary amount depending on the heating capacity.
Further, when the raceway ring W as the workpiece is an outer race, the arc-shaped coil 31 of the raceway surface induction heating coil 30 is disposed inside the raceway ring W.

DESCRIPTION OF SYMBOLS 10 Induction heating apparatus 20 Surface induction heating coil 21 Inner diameter side column part conductor 22 Outer diameter side column part conductor 24 Connection conductor 30 Track surface induction heating coil W Track ring Wa Track surface

Claims (7)

An induction heating device having a plurality of induction heating coils on the circumference and induction heating the bearing raceway,
The plurality of induction heating coils include a surface induction heating coil that heats the entire surface, and a raceway surface induction heating coil that heats the raceway surface,
The surface induction heating coil includes a coil having an inner diameter side columnar conductor and an outer diameter side columnar conductor both extending in the axial direction so as to sandwich the raceway on a virtual straight line extending in the radial direction from the center of the bearing ring. As a set, a plurality of sets are arranged at predetermined intervals in the circumferential direction,
An induction heating apparatus, wherein a reverse current flows through the inner diameter side columnar conductor and the outer diameter side columnar conductor of each set.   2. The induction heating device according to claim 1, wherein currents in opposite directions flow between the inner diameter side columnar conductors and the outer diameter side columnar conductors of adjacent sets. The adjacent inner diameter side column part conductors and the outer diameter side column part conductors of the adjacent sets are connected with a connection conductor on the same side in the axial direction,
The connecting conductors are alternately arranged in the circumferential direction on one axial side and the other axial side,
The inner diameter side columnar conductor and the outer diameter side columnar conductor of the set located on one end side in the circumferential direction are connected on the side where the connection conductor is not connected,
The said inner diameter side column part conductor and the said outer diameter side column part conductor of the group located in the other end side of the circumferential direction are connected to a power source on the side where the connection conductor is not connected. Induction heating device. The radial distance between the inner diameter side columnar conductor and the raceway and the radial distance between the outer diameter side columnar conductor and the raceway are equal,
The induction heating device according to claim 3, wherein an axial distance between the connection conductor and the raceway is twice or more of the radial distance. An induction heating method using the induction heating device according to any one of claims 1 to 4,
The induction is characterized in that, while rotating the raceway, the surface induction heating coil is heated so that the core remains and the entire surface is hardened, and then the raceway surface is heated by the raceway induction heating coil. Heating method. An induction heating device having a plurality of induction heating coils on the circumference and induction heating the bearing raceway,
The plurality of induction heating coils include a surface induction heating coil that heats the entire surface, and a raceway surface induction heating coil that heats the raceway surface,
The surface induction heating coil is arranged so that an inner diameter side columnar conductor and an outer diameter side columnar conductor sandwich the raceway on a virtual straight line extending from the center of the raceway to the outer diameter side,
An induction heating apparatus, wherein a reverse current flows through the inner diameter side columnar conductor and the outer diameter side columnar conductor. An induction heating method using the induction heating device according to claim 6,
The induction is characterized in that, while rotating the raceway, the surface induction heating coil is heated so that the core remains and the entire surface is hardened, and then the raceway surface is heated by the raceway induction heating coil. Heating method.

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