JP2004077206A - Ultrasonic flaw detection and inspection method for rolling bearing and rolling element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prevent short life separation and roller cracks caused by internal defects in strict usage conditions of a high load and high surface pressure. <P>SOLUTION: In a roller bearing where a plurality of rollers are arranged between inner and outer wheels so that they can be rolled in a peripheral direction, it is assured that there are no defects where square root length exceeds 0.2 mm within a range where an average diameter Da is 2% deep from the surface of the rolling surface in the rollers, and there are no defects where the maximum length exceeds 0.5 mm within the total sectional range of the rollers. <P>COPYRIGHT: (C)2004,JPO

Description

【００１９】
表１から判るように、ころ２の転動面表面から２　％Ｄａ深さまでの欠陥平方根長さが０．２ｍｍ以下の軸受（試料Ｎｏ．１〜Ｎｏ．３）と、欠陥平方根長さが０．２ｍｍを超えていたが、ころ２の転動面表面から２％Ｄａより深い位置にあった軸受（試料Ｎｏ．６）は、　試験時間の５００時間を達成し試験を中断した。　これに対し、ころ２の転動面表面から２％Ｄａ範囲までの欠陥平方根長さが０．２ｍｍを超えた軸受（試料Ｎｏ．４、Ｎｏ．５）は試験時間が５００時間未満でころのはくりを起こし短寿命であった。
【００２０】
一方、　ころ２の全断面範囲内に欠陥最大長さ０．５ｍｍ以下の軸受（試料Ｎｏ．７、Ｎｏ．８）は試験時間の５００時間を達成し試験を中断した。
これに対し、ころ２の全断面範囲内に欠陥最大長さ０．５ｍｍを超える軸受（試料Ｎｏ．９、Ｎｏ．１０）は３７０、４３０時間でころの割れを起した。
したがって、超音波探傷を行うことにより、　ころの表面から内部までの全断面の欠陥を精度良く、　しかも短時間で検出することができるので、　ころの寿命低下に大きく影響を及ぼす介在物等の欠陥を効果的に検出することが可能になり、　この結果、内部欠陥に起因した短寿命はくりや割れを効率的に防止することができる。
【００２１】
次に、本発明の第２実施の形態である転動体の超音波探傷検査方法を説明する。図１の超音波探傷検査装置を用い、円筒ころ軸受のころ（外径３０ｍｍ）２を超音波探傷用探触子３としての焦点型探触子（周波数１０ＭＨｚ、　振動子径１０ｍｍ）　と共に水槽１内の水に浸漬し、　この状態でころ２の転動面（外周面）　の表面からころ２のＤ（ころ直径）／４　となる８ｍｍ程度までの探傷及びそれより更に深い範囲の探傷を上述したころ２の回転と超音波探傷用探触子３をころ２の軸方向移動により行い、　ころ２の全断面を探傷する。
【００２２】
なお、　ころ２の転動面表面から８ｍｍ（Ｄ／４）程度までの斜角探傷については、水中焦点距離２５ｍｍの探触子を用いて水距離（ころ２の外周面と超音波探傷用探触子３との距離）　を１５ｍｍにセットし、　それより更に深い範囲の垂直探傷については、水中焦点距離５０ｍｍの探触子を用いて水距離を１０ｍｍにセットした。
【００２３】
まず、　ころ２の転動面表面から８ｍｍ（Ｄ／４）までの深さの探傷について説明すると、　図３に示すように、ころ２の転動面表面に探傷方向（円周方向）に対して垂直になるように長さ１０ｍｍ、　幅０．５ｍｍ、　深さ０．５ｍｍの人工欠陥３０を形成すると共に、　ころ２の転動面に探傷方向（円周方向）に対して垂直にφ０．５ｍｍ×２０ｍｍの穴（人工欠陥）５０をころ２の転動面表面からの深さＡ＝２，　５，　８，　１５ｍｍの位置に個別に形成した試験片を作製し、　図１の超音波探傷検査装置を用いて超音波探傷用探触子３から発疹される超音波の入射角（転動面に立てた法線に対して円周方向に傾く角度）を０〜２８°の間で変更して探傷を行った。
【００２４】
探傷結果を図４及び図５に示す。図４から明らかなように、入射角が１０〜２８°の斜角探傷で人工欠陥３０の検出が可能であったが、０°と５°では表面欠陥（Ａ＝０ｍｍ）との分離ができず、探傷不可能であった。
図４より、ころ２の転動面表面からの深さＡ＝２〜８ｍｍの欠陥の探傷では、入射角が０〜５°の場合において高い探傷感度が得られたが、入射角が０°と５°では表面エコーと欠陥エコー（欠陥がある時のみ出る信号）の位置（最大高さの距離）が接近しており、目視での分類は可能であるものの自動探傷とした場合に分類の判断が困難な場合があるため、２〜８ｍｍまでの深さの欠陥については、各深さ毎のエコー強度の差が小さい、入射角が１９〜２８°の条件が好適である。
【００２５】
図６に入射角５°、図７に入射角１９°にて探傷を行った際に、パソコンＣＲＴ上に表示された探傷結果を示す。ＣＲＴ上では入射角１９°より入射角５°の方が表面エコーと欠陥エコーの距離が接近しているのが判る。
次に、ころ２の転動面表面から８ｍｍ（Ｄ／４）より深い位置の探傷について説明する。
【００２６】
図５より、ころ２の転動面表面からの深さＡ＝８〜１５ｍｍの探傷では、入射角が０〜５°の垂直探傷での検出結果がエコー強度が高く好適であった。また、ころ２の転動面表面から８ｍｍを越える深い位置の欠陥であるため、垂直探傷を利用した場合でも表面エコーと欠陥エコーとの分類性もよい。
これらのことから、　ころ２の転動面表面から８ｍｍ（Ｄ／４）より深い位置の探傷については、　入射角は０〜５°がより好ましいことが判る。　また、　入射角が０°の場合は垂直波の伝播が欠陥に対して最短距離となるため、表面エコーと欠陥エコーの判別の点から少し傾きを持たせた入射角５°が最も好ましい。　但し、分類性に問題がない場合は、（Ｄ／４）にこだわらず、深さを変更して探傷を行うことができる。
【００２７】
上記の記載から明らかなように、　この実施の形態では、従来、　生産性の観点から、　数百μｍレベルの大型介在物の検出が困難であったころ転動面の超音波探傷が可能となり、　ころの表面から内部までの全断面の欠陥を精度良く、　しかも短時間で検出することができるので、内部欠陥に起因した短寿命はくりやころの割れを効率良く防止することができる。
【００２８】
円筒ころ軸受のころ２（外径３０ｍｍ）を図１の超音波探傷検査装置にセットし、　ころ２を回転速度２５０ｍｍ／ｓで回転させ、　軸方向の探傷ピッチを０．５ｍｍとして３００個のころ２について探傷を行った。
ここで、ころ２の転動面表面から８ｍｍ（Ｄ／４）までの深さの探傷は入射角が１９°の斜角探傷法で行い、　それより更に深い範囲の探傷は入射角が５°の垂直探傷法で行った。
【００２９】
３００個のころ２を探傷した結果、３個について欠陥エコーが観察され、１個は表面近傍で、２個は内部に観察された。　この欠陥部を切断、　研削にて詳細に調査したところ、　それぞれに幅０．０５〜０．　２ｍｍ程度、　長さ０．２〜最大で３ｍｍの欠陥が発見され、分析調査の結果、　大型の非金属介在物であることが判った。
【００３０】
次に、　本発明における第３の実施の形態である転動体の超音波探傷検査方法を図１、図２、図８、図９を参照して説明する。
この実施の形態では、超音波の減衰及び林状エコーの影響を少なくすべく、焼入れ、焼戻しの熱硬化処理（又は浸炭若しくは浸炭窒化、焼入れ、焼戻しの熱硬化処理）　を行って熱処理後の結晶粒度が８番以上となるマルテンサイト組織とした後に、外径面に研削加工を施して円錐ころ軸受ＨＲ３２０１７ＸＪのころ２を作製し、図１の超音波探傷検査装置で各種の周波数の超音波探傷用探触子３を用いて３００個のころ２について、５，１０，１５，２０，３０，５０ＭＨｚと低い周波数から順に全断面の探傷を行った。
【００３１】
この際、それぞれの周波数で欠陥が検出されたころ２は取り除き、欠陥が検出されなかったころ２のみを次の大きな周波数での探傷検査へと使用した。なお、超音波探傷法としては斜角探傷法及び垂直探傷法の両方を用いることができるが、この実施の形態では斜角探傷法を用いた。
図８に探傷結果を示す。図８の縦軸の欠陥指数は周波数５ＭＨｚで探傷を行った際に、欠陥が発見されたころ２の内での欠陥の平均数を１として、　それぞれの５，１０，１５，２０，３０，５０ＭＨｚ周波数で発見されたころ２の欠陥数の平均値を欠陥指数として示したものである。
【００３２】
図８から明らかなように、　探傷にて欠陥が検出されたころ２の中でのころ１個あたりに存在する欠陥数は、　周波数３０ＭＨｚを超えると急激に増えることが分かる。
周波数特性より低い周波数にて検出される欠陥は、比較的大きな欠陥しか検出できない。　周波数を高くした場合は、　大きい欠陥はもとより小さな欠陥までも検出することができるから、　ころ２には３０ＭＨｚを超えた周波数で検出できるレベルの小さな介在物等の欠陥が数多く存在することが良く分かる。
【００３３】
次に、　各周波数にて欠陥が検出されたころ２を使用して円錐ころ軸受を製作し、　図２に示す寿命試験機を用いて以下の条件で寿命試験を行った。
軸受：円錐ころ軸受ＨＲ３２０１７ＸＪ
ラジアル荷重：３５７５０Ｎ
アキシアル荷重：１５６８０Ｎ
内輪回転数：１５００ｍｉｎ^−１
潤滑：グリース
寿命評価は、　各々の周波数にて欠陥が検出されたころ２を寿命試験して各々のＬ_１０寿命を求め、　周波数５０ＭＨｚの条件にて欠陥が検出されたころ２のＬ_１０寿命を１００とした場合のＬ_１０寿命に対する３０ＭＨｚ以下の周波数で欠陥が検出されたころ２のＬ_１０寿命の寿命減少率を求めた。
【００３４】
試験結果を図９に示す。
図９から明らかなように、３０ＭＨｚ以下の周波数で欠陥が検出されたころ２は５０ＭＨｚの周波数で欠陥が検出されたころ２に比べて大幅に寿命が低下しているのが分かる。
なお、　周波数が５ＭＨｚ以下でも探傷は可能であるが、　ころ２内部の小さな欠陥を検出することが極めて困難なため、　周波数は５〜３０ＭＨｚが好ましい。
【００３５】
上記の記載から明らかなように、　この実施の形態では、マルテンサイト組織のころに対して３０ＭＨｚ以下の周波数で超音波探傷を行うことにより、　ころの表面から内部までの全断面の欠陥を精度良く、　しかも短時間で検出することができるので、　軸受の寿命低下に大きく影響を及ぼす介在物等の欠陥を効果的に検出することが可能になり、　この結果、内部欠陥に起因した短寿命はくりを効率的に防止することができる。
【００３６】
【発明の効果】
上記の説明から明らかなように、請求項１の転がり軸受によれば、転動体の２％Ｄａ範囲内に平方根長さが０．２ｍｍを超える欠陥が存在せず、且つ前記転動体の全断面範囲内に最大長さが０．５ｍｍを超える欠陥がないことが保証されているため、高荷重、高面圧という苛酷な使用条件においても内部欠陥に起因した短寿命はくりやころ割れを効果的に防止することができるという効果が得られる。
【００３７】
請求項２又は３の転動体の超音波探傷検査方法では、転動体の表面から内部までの全断面の欠陥、　特に転動体内部の大きな非金属介在物の存在を精度良く検出することができる。
請求項４の転がり軸受の製造方法では、転動体の表面から内部までの全断面の欠陥、　特に転動体内部の大きな非金属介在物の存在を精度良く検出することができるので、高荷重、高面圧という苛酷な使用条件においても内部欠陥に起因した短寿命はくりやころ割れを効果的に防止することができる信頼性の高い転がり軸受を提供することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態である転がり軸受の転動体の超音波探傷検査に使用する装置の概略図である。
【図２】寿命試験機の概略を示す断面図である。
【図３】本発明の第２の実施の形態である転動体の超音波探傷検査方法を説明するための説明図であり、人工欠陥が形成されたころの斜視図である。
【図４】入射角とエコー強度との関係をころの転動面表面からの深さを変えて比較した結果を示すグラフ図である。
【図５】入射角とエコー強度との関係をころの転動面表面からの深さを変えて比較した結果を示すグラフ図である。
【図６】入射角５°で探傷を行った際の表面エコーと欠陥エコーの分離距離と反射エコーの強さとの関係を示すグラフ図である。
【図７】入射角１９°で探傷を行った際の表面エコーと欠陥エコーの分離距離と反射エコーの強さとの関係を示すグラフ図である。
【図８】本発明の第３の実施の形態である転動体の超音波探傷検査方法を説明するための探傷周波数と欠陥指数との関係を示すグラフ図である。
【図９】探傷周波数と軸受の寿命減少率との関係を示すグラフ図である。
【符号の説明】
１…水槽
２…ころ（転動体）
３…超音波探傷用探触子
５…回転駆動用モータ
７…ベルト
８…モータ駆動用制御アンプ
９…制御装置
１０…リニアガイド装置
１４…超音波探傷装置
１５…ロータリエンコーダ
１６…リニアガイド用コントローラ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic flaw inspection which is particularly suitable for detecting rolling bearings such as tapered roller bearings, cylindrical roller bearings, and spherical roller bearings to which a large load is applied, such as roll neck bearings for steel, and for detecting defects in the rolling elements of the rolling bearings. TECHNICAL FIELD The present invention relates to a method and a method for manufacturing a rolling bearing using the inspection method.
[0002]
[Prior art]
Conventionally, the detection of defects existing in the steel material used in the rolling element of the rolling bearing is, for example, after being rolled into a steel bar in the middle of manufacturing in a steelmaking maker, the entire number is due to unbonded ground flaws and holes over the entire cross section Defects are detected by inspection using ultrasonic flaw detection. The removal of the defects found has eliminated major defects in the bearing rolling elements.
[0003]
However, the size of a defect that can be detected by ultrasonic flaw detection for a rolled steel material is one having a length of several tens of mm. Defects of this size are inspected in the steelmaking process in the point where high-speed flaw detection is performed in order to improve productivity and the inspection surface is performed in a rolled surface state and the crystal grains and surface layer inside the steel material are rough, Under the influence of this, the detection noise of the flaw detection increases, so that high-precision flaw detection is impossible, and the detectable size is several tens mm or more.
[0004]
In addition, only the defects opened on the surface by flaw detection or ECT could be detected.
[0005]
[Problems to be solved by the invention]
Recent technological advances have made it possible to detect fine non-metallic inclusions up to about 0.01 mm (10 μm) by using higher frequencies (for example, 50 to 150 MHz). Then, the attenuation of the ultrasonic wave inside the steel material increases (the lower the roughness of the steel material surface, the greater the attenuation of the ultrasonic wave). It is possible to detect a flaw only from the surface of the steel material to, for example, about 3 mm. For this reason, it has not been possible to efficiently detect a product that requires flaw detection of a defect to the inside of a work so as to have a diameter of several tens of mm, such as a roller bearing roller.
[0006]
In addition, the total amount of nonmetallic inclusions in steel materials used for rolling elements has decreased due to recent improvements in steelmaking technology, and defects such as ground flaws typified by large nonmetallic inclusions have a low frequency of occurrence. However, they could remain inside the steel material (especially at the center), and the rolling elements could crack due to these ground flaws. For this reason, in order to improve the reliability of the bearing, a method of effectively detecting a defect such as a ground flaw remaining inside the steel material in advance has been desired. While there is a limit to the size at which defects can be detected, the rollers used in bearings that receive extremely large loads, such as steel rolling bearings, are within a depth of 2% of the average diameter Da of the rollers from the surface. Defects exceeding 0.2 mm square root length (non-metallic inclusions, etc.) cause peeling due to rolling fatigue, and defects (non-metallic inclusions) exceeding a maximum length of 0.5 mm within the entire cross-sectional area of the roller. ) Is repeatedly subjected to stresses such as bending, pulling, and compression, which may cause a serious problem that causes the rollers to crack.
[0007]
The present invention has been made in order to solve such a problem, and it is necessary to accurately detect defects in the entire cross section from the surface of the rolling element to the core, particularly, the presence of large non-metallic inclusions inside the rolling element. It is an object of the present invention to provide a rolling bearing provided with a rolling element having no internal defect, an ultrasonic inspection method for the rolling element, and a method for manufacturing a rolling bearing using the inspection method.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is a rolling bearing in which a plurality of rolling elements are arranged between an inner ring and an outer ring so as to be able to roll in a circumferential direction.
There is no defect whose square root length exceeds 0.2 mm within a range of 2% of the average diameter Da of the rolling element from the surface of the rolling element, and the maximum length is within the entire cross-sectional area of the rolling element. It is guaranteed that there is no defect exceeding 0.5 mm. The invention according to claim 2 is that the rolling element of the rolling bearing and the probe for ultrasonic flaw detection are arranged in an ultrasonic transmission medium such as water, for example, and the probe for ultrasonic flaw detection is directed toward the rolling element from the probe for ultrasonic flaw detection. In an ultrasonic flaw detection inspection method for a rolling element for detecting a defect of the rolling element by an ultrasonic echo reflected from the rolling element by transmitting an acoustic wave,
Assuming that the diameter of the rolling element is D, the range from the surface of the rolling element to at least D / 4 deeper than the maximum shear stress position of the rolling element is an incident angle of 10 to 28 °, preferably 19 to 28 °. Flaw detection using a vertical flaw detection method at an incident angle of 0 to 10 °, preferably 0 to 5 °, which is deeper than the flaw detection range obtained by the bevel flaw detection method. Is characterized in that the entire cross section is flaw-detected.
[0009]
The invention according to claim 3 is that the rolling element of the rolling bearing and the ultrasonic test probe are arranged in an ultrasonic transmission medium such as water, and the ultrasonic test probe is directed toward the rolling element from the ultrasonic test probe. An ultrasonic flaw inspection method for a rolling element for detecting a defect of the rolling element by transmitting an acoustic wave and reflecting an ultrasonic echo reflected from the rolling element,
The ultrasonic wave transmitted from the ultrasonic flaw detector to the rolling element has a frequency of 30 MHz or less, preferably 5 to 30 MHz, and the rolling element from which the ultrasonic wave is transmitted is a quenching and tempering thermosetting treatment. Alternatively, after carburizing or carbonitriding, quenching, and tempering, a thermosetting treatment is performed, and an outer diameter surface is subjected to a grinding process.
[0010]
The invention according to claim 4 is a method for manufacturing a rolling bearing in which a plurality of rolling elements are arranged between an inner ring and an outer ring so as to be rollable in a circumferential direction,
A defect whose square root length exceeds 0.2 mm within a range of 2% of the average diameter Da of the rolling element from the surface of the rolling element using the ultrasonic inspection method for rolling elements according to claim 2 or 3. The present invention is characterized in that a rolling bearing is manufactured in which there is no defect and that there is no defect having a maximum length exceeding 0.5 mm in the entire cross-sectional area of the rolling element.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view of an apparatus used for ultrasonic inspection of a rolling element of a rolling bearing according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view schematically showing a life tester, and FIG. FIG. 4 is an explanatory view for explaining an ultrasonic inspection method for rolling elements according to a second embodiment of the present invention. FIG. 4 is a perspective view of a roller in which an artificial defect is formed. FIGS. FIG. 6 is a graph showing the results of comparing the depth of the roller from the rolling surface and changing the depth. FIG. 6 shows the separation distance between the surface echo and the defect echo and the intensity of the reflection echo when a flaw was detected at an incident angle of 5 °. FIG. 7 is a graph showing the relationship between the separation distance between a surface echo and a defect echo and the intensity of a reflected echo when flaw detection is performed at an incident angle of 19 °, and FIG. Flaw detection frequency and defect for explaining the ultrasonic flaw detection method for rolling elements according to the third embodiment. FIG. 9 is a graph showing the relationship between the index and the flaw detection frequency and the life reduction rate of the bearing.
[0012]
First, the rolling bearing according to the first embodiment will be described. The present inventors have found that a large defect echo portion that is rarely detected in ultrasonic flaw detection of a roller bearing incorporated in a backup roll or the like. When they were examined in detail, large non-metallic inclusions having a length of several hundred μm were found.
Therefore, in order to further determine the correlation between the intensity of this defect echo and the length, size, and bearing life of the found inclusions, a roller life test was performed. Non-metallic inclusions exist within a range of 2% depth (hereinafter, referred to as 2% Da) of the average diameter Da of the rollers from the roller surface or in the entire cross-sectional area of the rollers. When present, it was found that the life of the rollers was extremely reduced. Since large inclusions tend to be long and small inclusions tend to be close to circular, small inclusions within the 2% Da range have a square root length, and large inclusions having a total cross section have a maximum length. Stipulated.
[0013]
Next, a comparative test will be described. The test bearing was a tapered roller bearing HR32017XJ, and the rollers of the bearing were inspected by an ultrasonic flaw detector shown in FIG.
The ultrasonic flaw detector will be described. In FIG. 1, reference numeral 1 denotes a water tank in which water as an ultrasonic transmission medium is stored. In the water tank 1, a roller 2 as a rolling element of a tapered roller bearing and an ultrasonic flaw detector The probes 3 are arranged in a state of being immersed in water, respectively. As the ultrasonic flaw detector 3, a focus type probe having strong directivity and less affected by the curvature of the roller 2 is used. The roller 2 is mounted on two pulleys 4 horizontally spaced from each other in the water tank 1, and a belt 7 is fixed to each pulley 4 and a pulley 6 fixed to the motor shaft of the rotation driving motor 5. It is wound. The rotation driving motor 5 is controlled by a control device 9 via a motor driving control amplifier 8. The rollers 2 mounted on each pulley 4 by the rotation driving motor 5 drive at a predetermined speed. It is designed to rotate. The control device 9 is constituted by a personal computer or the like having a display means such as a CRT.
[0014]
The ultrasonic inspection probe 3 is attached via a probe attachment 13 to an XY stage 12 of a linear guide device 10 movably arranged along the axial direction of the roller 2. The roller 2 is arranged to face the outer peripheral surface. The ultrasonic test probe 3 transmits an ultrasonic pulse toward the outer peripheral surface of the roller 2 according to a voltage signal from the ultrasonic test device 14, receives a reflected echo thereof, and converts it into an electric signal. And transmits it to the ultrasonic flaw detector 14.
[0015]
The ultrasonic flaw detector 14 transmits a command signal consisting of an electric signal to the ultrasonic flaw detector 3 based on a command from the control device 9 and is obtained based on the transmitted signal and the received signal. The flaw detection information is transmitted to the control device 9, which displays the information on the CRT.
The linear guide device 10 moves the ultrasonic inspection probe 3 in the axial direction of the roller 2 via a servo motor (not shown) controlled by the linear guide controller 16. When the rotary encoder 15 installed on the outer peripheral surface of the roller 2 detects that the roller 2 has made one rotation (360 °), the servo motor is controlled based on a command from the control device 9 to perform ultrasonic flaw detection. The contact 3 is moved by a predetermined dimension in the axial direction of the roller 2. As a result, flaw detection of the entire cross section of the roller 2 is performed.
[0016]
According to this embodiment, ultrasonic inspection of the rolling surface of the roller, which has been difficult because of the large number of rollers used in the past, can be performed. , The short life caused by the internal defect can be effectively prevented from being broken and the roller from cracking.
Next, a tapered roller bearing was manufactured using the roller 2 in which a defect was detected by ultrasonic inspection using the ultrasonic inspection apparatus shown in FIG. 1, and a life tester shown in FIG. 2 was used under the following conditions. A life test was performed.
[0017]
Bearing: tapered roller bearing HR32017XJ
Radial load: 71500N
Axial load: 31360N
Inner ring rotation speed: 1500 min ^-1
Lubrication: Table 1 shows the grease test results.
[0018]
[Table 1]

[0019]
As can be seen from Table 1, a bearing having a defect square root length of 0.2 mm or less from the rolling surface surface of the roller 2 to a depth of 2% Da (Sample Nos. 1 to 3) and a defect square root length of 0 mm The bearing (sample No. 6), which was larger than 0.2 mm but was deeper than 2% Da from the surface of the rolling surface of the roller 2, achieved the test time of 500 hours and stopped the test. On the other hand, the bearings (samples No. 4 and No. 5) in which the square root length of the defect from the rolling surface surface of the roller 2 to the range of 2% Da exceeded 0.2 mm (sample Nos. 4 and 5) had a test time of less than 500 hours. It was short-lived due to peeling.
[0020]
On the other hand, the bearings with a maximum defect length of 0.5 mm or less (samples No. 7 and No. 8) in the entire cross-sectional area of the roller 2 achieved the test time of 500 hours and the test was stopped.
On the other hand, the bearings (samples No. 9 and No. 10) exceeding the maximum defect length of 0.5 mm in the entire cross-sectional area of the roller 2 caused the roller to crack in 370 and 430 hours.
Therefore, by performing ultrasonic testing, defects in all cross sections from the roller surface to the inside can be detected accurately and in a short time, and defects such as inclusions that greatly affect the life of the rollers can be detected. Can be effectively detected, and as a result, the short life caused by the internal defect can be effectively prevented from cracking or cracking.
[0021]
Next, an ultrasonic inspection method for rolling elements according to a second embodiment of the present invention will be described. Using the ultrasonic inspection device shown in FIG. 1, a water tank 1 is mounted on a cylindrical roller bearing roller (outer diameter 30 mm) 2 together with a focus type probe (frequency 10 MHz, transducer diameter 10 mm) as an ultrasonic inspection probe 3. In this state, the flaw detection from the surface of the rolling surface (outer peripheral surface) of the roller 2 to about 8 mm which is D (roller diameter) / 4 of the roller 2 and the flaw detection in a deeper range are performed as described above. The roller 2 is rotated and the ultrasonic inspection probe 3 is moved in the axial direction of the roller 2 to detect the entire cross section of the roller 2.
[0022]
In addition, for the oblique flaw detection up to about 8 mm (D / 4) from the surface of the rolling surface of the roller 2, a probe having an underwater focal length of 25 mm was used to measure the water distance (the outer circumferential surface of the roller 2 and the ultrasonic flaw detection). The distance to the probe 3 was set to 15 mm, and for vertical flaw detection in a deeper range, the water distance was set to 10 mm using a probe with an underwater focal length of 50 mm.
[0023]
First, the flaw detection at a depth of 8 mm (D / 4) from the surface of the rolling surface of the roller 2 will be described. As shown in FIG. The artificial defect 30 having a length of 10 mm, a width of 0.5 mm, and a depth of 0.5 mm is formed so as to be perpendicular to the surface of the roller 2. A test piece in which a hole (artificial defect) 50 of 5 mm × 20 mm was individually formed at a depth A = 2, 5, 8, 15 mm from the surface of the rolling surface of the roller 2 was prepared, and the ultrasonic test shown in FIG. Using an inspection device, change the incident angle (angle inclined in the circumferential direction with respect to the normal set on the rolling surface) of the ultrasonic rash from the ultrasonic flaw detector 3 between 0 and 28 °. And conducted flaw detection.
[0024]
The results of the flaw detection are shown in FIGS. As is clear from FIG. 4, the artificial defect 30 could be detected by oblique flaw detection at an incident angle of 10 to 28 °, but at 0 ° and 5 °, a surface defect (A = 0 mm) could be separated. No flaw detection was possible.
From FIG. 4, in the flaw detection of a defect having a depth A = 2 to 8 mm from the rolling surface of the roller 2, high flaw detection sensitivity was obtained when the incident angle was 0 to 5 °, but the incident angle was 0 °. At 5 ° and 5 °, the positions (maximum height distance) of the surface echo and the defect echo (a signal that is emitted only when there is a defect) are close to each other. Since it may be difficult to make a determination, it is preferable for a defect having a depth of 2 to 8 mm that the difference in echo intensity at each depth is small and the incident angle is 19 to 28 °.
[0025]
FIG. 6 shows a flaw detection result displayed on a personal computer CRT when flaw detection was performed at an incident angle of 5 ° and FIG. 7 shows a flaw detection at an incident angle of 19 °. On the CRT, it can be seen that the distance between the surface echo and the defect echo is closer at an incident angle of 5 ° than at an incident angle of 19 °.
Next, flaw detection at a position deeper than 8 mm (D / 4) from the surface of the rolling surface of the roller 2 will be described.
[0026]
From FIG. 5, in the flaw detection at a depth A = 8 to 15 mm from the surface of the rolling surface of the roller 2, the detection result obtained by the vertical flaw detection at an incident angle of 0 to 5 ° has a high echo intensity and is suitable. In addition, since the defect is located at a position deeper than 8 mm from the rolling surface of the roller 2, the classification of the surface echo and the defect echo is good even when the vertical flaw detection is used.
From these facts, it can be seen that for flaw detection at a position deeper than 8 mm (D / 4) from the rolling surface of the roller 2, the incident angle is more preferably 0 to 5 °. When the incident angle is 0 °, the propagation of the vertical wave is the shortest distance to the defect. Therefore, the incident angle of 5 ° with a slight inclination from the point of discriminating between the surface echo and the defect echo is most preferable. However, when there is no problem in the classification property, the flaw detection can be performed by changing the depth without being limited to (D / 4).
[0027]
As is apparent from the above description, in this embodiment, from the viewpoint of productivity, it has been possible to perform ultrasonic flaw detection of the rolling contact surface at the time when it was difficult to detect a large inclusion of several hundred μm level, Since defects in the entire cross section from the roller surface to the inside can be detected with high accuracy and in a short time, the short life caused by the internal defect can be efficiently prevented from cutting and roller cracking.
[0028]
The roller 2 (outer diameter 30 mm) of the cylindrical roller bearing is set in the ultrasonic inspection equipment shown in FIG. 1, and the roller 2 is rotated at a rotation speed of 250 mm / s. No. 2 was inspected for flaws.
Here, flaw detection at a depth of 8 mm (D / 4) from the surface of the rolling surface of the roller 2 is performed by the oblique flaw detection method with an incident angle of 19 °, and flaw detection in a deeper range with an incident angle of 5 °. Vertical inspection method.
[0029]
As a result of inspecting 300 rollers 2, defect echoes were observed in three of them, one in the vicinity of the surface, and two in the inside. When this defective portion was examined in detail by cutting and grinding, each had a width of 0.05-0. A defect with a length of about 2 mm and a length of 0.2 to 3 mm at the maximum was found, and as a result of analysis and investigation, it was found to be a large nonmetallic inclusion.
[0030]
Next, an ultrasonic inspection method for rolling elements according to a third embodiment of the present invention will be described with reference to FIGS. 1, 2, 8, and 9. FIG.
In this embodiment, in order to reduce the effects of ultrasonic attenuation and forest echo, a quenching and tempering thermosetting treatment (or a carburizing or carbonitriding, quenching and tempering thermosetting treatment) is performed to obtain a crystal after the heat treatment. After forming a martensite structure having a grain size of 8 or more, the outer diameter surface is subjected to grinding to produce rollers 2 of a tapered roller bearing HR32017XJ, and ultrasonic inspection of various frequencies by the ultrasonic inspection apparatus of FIG. For the 300 rollers 2, flaw detection was performed on all cross sections of the 300 rollers 2 in ascending order of frequency from 5, 10, 15, 20, 30, 50 MHz.
[0031]
At this time, the roller 2 where a defect was detected at each frequency was removed, and only the roller 2 where no defect was detected was used for the flaw detection inspection at the next larger frequency. As the ultrasonic flaw detection method, both the oblique flaw detection method and the vertical flaw detection method can be used. In this embodiment, the oblique flaw detection method is used.
FIG. 8 shows the results of flaw detection. The defect index on the vertical axis of FIG. 8 indicates that the average number of defects in the roller 2 when the defect was found when the flaw detection was performed at a frequency of 5 MHz was 1, and that the respective defects were 5, 10, 15, 20, 30, and 30, respectively. The average value of the number of defects of roller 2 discovered at a frequency of 50 MHz is shown as a defect index.
[0032]
As is clear from FIG. 8, it can be seen that the number of defects existing per roller among the rollers 2 in which defects were detected by the flaw detection sharply increases when the frequency exceeds 30 MHz.
Defects detected at a frequency lower than the frequency characteristic can only detect relatively large defects. When the frequency is increased, not only a large defect but also a small defect can be detected. Therefore, it is clear that there are many defects such as small inclusions at the roller 2 which can be detected at a frequency exceeding 30 MHz. .
[0033]
Next, tapered roller bearings were manufactured using the rollers 2 in which a defect was detected at each frequency, and a life test was performed using the life tester shown in FIG. 2 under the following conditions.
Bearing: tapered roller bearing HR32017XJ
Radial load: 35750N
Axial load: 15680N
Inner ring rotation speed: 1500 min ^-1
Lubrication: grease life rating is calculated each L ₁₀ life of 2 days a defect is detected in each frequency to life test, the second L ₁₀ life time the defect is detected at a frequency of 50MHz 100 defects at frequencies below 30MHz for _{L 10} life in the case of the calculated service life reduction rate of 2 _{L 10} life time was detected.
[0034]
The test results are shown in FIG.
As is clear from FIG. 9, it can be seen that the life of the roller 2 where a defect is detected at a frequency of 30 MHz or less is significantly shorter than that of the roller 2 where a defect is detected at a frequency of 50 MHz.
Although flaw detection is possible even at a frequency of 5 MHz or less, it is extremely difficult to detect a small defect inside the roller 2. Therefore, the frequency is preferably 5 to 30 MHz.
[0035]
As is clear from the above description, in this embodiment, by performing ultrasonic flaw detection at a frequency of 30 MHz or less on the rollers of the martensite structure, defects in the entire cross section from the surface to the inside of the rollers can be accurately detected. In addition, since it can be detected in a short period of time, it is possible to effectively detect defects such as inclusions that greatly affect the life of the bearing. As a result, the short life caused by internal defects is reduced. Can be efficiently prevented.
[0036]
【The invention's effect】
As is clear from the above description, according to the rolling bearing of claim 1, there is no defect whose square root length exceeds 0.2 mm within the 2% Da range of the rolling element, and the entire cross section of the rolling element. It is guaranteed that there is no defect whose maximum length exceeds 0.5 mm within the range, so even under severe conditions such as high load and high surface pressure, short life due to internal defect is effective for cutting and roller cracking Is obtained.
[0037]
According to the ultrasonic inspection method for a rolling element according to the second or third aspect, it is possible to accurately detect defects in the entire cross section from the surface to the inside of the rolling element, particularly, the presence of large nonmetallic inclusions inside the rolling element.
According to the method for manufacturing a rolling bearing according to the fourth aspect, it is possible to accurately detect defects in the entire cross section from the surface to the inside of the rolling element, in particular, the presence of a large nonmetallic inclusion inside the rolling element. It is possible to provide a highly reliable rolling bearing capable of effectively preventing cutting and roller cracking due to short life caused by internal defects even under severe use conditions such as surface pressure.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus used for ultrasonic inspection of a rolling element of a rolling bearing according to a first embodiment of the present invention.
FIG. 2 is a sectional view schematically showing a life tester.
FIG. 3 is an explanatory diagram for explaining an ultrasonic inspection method for rolling elements according to a second embodiment of the present invention, and is a perspective view of a roller where an artificial defect is formed.
FIG. 4 is a graph showing the result of comparing the relationship between the incident angle and the echo intensity by changing the depth of the roller from the surface of the rolling surface.
FIG. 5 is a graph showing the result of comparing the relationship between the incident angle and the echo intensity by changing the depth of the roller from the surface of the rolling surface.
FIG. 6 is a graph showing the relationship between the separation distance between a surface echo and a defect echo and the intensity of a reflected echo when flaw detection is performed at an incident angle of 5 °.
FIG. 7 is a graph showing the relationship between the separation distance between a surface echo and a defect echo and the intensity of a reflected echo when flaw detection is performed at an incident angle of 19 °.
FIG. 8 is a graph showing a relationship between a flaw detection frequency and a defect index for describing an ultrasonic flaw detection method for rolling elements according to a third embodiment of the present invention.
FIG. 9 is a graph showing a relationship between a flaw detection frequency and a life reduction rate of a bearing.
[Explanation of symbols]
1 ... water tank 2 ... roller (rolling element)
3 Ultrasonic flaw detector 5 Rotary drive motor 7 Belt 8 Motor drive control amplifier 9 Controller 10 Linear guide device 14 Ultrasonic flaw detector 15 Rotary encoder 16 Linear guide controller

Claims (4)

In a rolling bearing in which a plurality of rolling elements are arranged so as to be able to roll in a circumferential direction between an inner ring and an outer ring,
There is no defect whose square root length exceeds 0.2 mm within a range of 2% of the average diameter Da of the rolling element from the surface of the rolling element, and the maximum length is within the entire cross-sectional area of the rolling element. A rolling bearing characterized in that no defect exceeding 0.5 mm is guaranteed. The rolling element of the rolling bearing and the probe for ultrasonic flaw detection are arranged in an ultrasonic transmission medium, and ultrasonic waves are transmitted from the probe for ultrasonic flaw detection toward the rolling element and reflected from the rolling element. In the ultrasonic inspection method for rolling elements for detecting defects of the rolling elements by ultrasonic echo coming,
When the diameter of the rolling element is D, at least a range from the surface of the rolling element to D / 4 deeper than the maximum shear stress position of the rolling element is inspected by oblique flaw detection. A flaw detection area deeper than the flaw detection range by the flaw detection using the vertical flaw detection method, thereby flaw-detecting the entire cross section of the rolling element. The rolling element of the rolling bearing and the probe for ultrasonic flaw detection are arranged in an ultrasonic transmission medium, and ultrasonic waves are transmitted from the probe for ultrasonic flaw detection toward the rolling element and reflected from the rolling element. In the ultrasonic flaw detection inspection method for the rolling element for detecting the defect of the rolling element by the ultrasonic echo coming,
The ultrasonic wave transmitted from the ultrasonic flaw detector to the rolling element has a frequency of 30 MHz or less. An ultrasonic flaw inspection method for rolling elements, characterized in that a quenching and tempering heat-hardening treatment is performed, and then an outer diameter surface is subjected to grinding processing. A method for manufacturing a rolling bearing in which a plurality of rolling elements are disposed so as to be able to roll in a circumferential direction between an inner ring and an outer ring,
A defect whose square root length exceeds 0.2 mm within a range of 2% of the average diameter Da of the rolling element from the surface of the rolling element by using the ultrasonic inspection method for rolling elements according to claim 2 or 3. A method for producing a rolling bearing, characterized by producing a rolling bearing that is free from defects and is guaranteed not to have a defect whose maximum length exceeds 0.5 mm in the entire cross-sectional area of the rolling element.

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