JP2004340808A

JP2004340808A - Bearing ring with artificial defect, roller bearing with an artificial defect, and lifetime testing method for roller bearing

Info

Publication number: JP2004340808A
Application number: JP2003138997A
Authority: JP
Inventors: Hiromichi Takemura; 浩道武村
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 2003-05-16
Filing date: 2003-05-16
Publication date: 2004-12-02
Anticipated expiration: 2023-05-16
Also published as: JP4010276B2

Abstract

<P>PROBLEM TO BE SOLVED: To improve reliability of a lifetime test related to an internal start point type separation. <P>SOLUTION: A bearing ring is constructed so that a hole 3a penetrating a part of an inner ring 4 in a shaft direction is formed with electric discharge machining. Then, the intermediate part of this hole 3a arranged under the surface of an inner ring orbit 5 is made work as an artificial defect. At this time, the internal start point type separation is generated by controlling the formation position of the hole 3a to the inner ring 4 and the internal diameter thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
この発明に係る人工欠陥付軌道輪及び人工欠陥付転がり軸受と転がり軸受の寿命試験方法は、軌道の表面下に存在する欠陥の位置及び大きさ等が、この軌道に於ける内部起点型剥離の発生又は当該転がり軸受の寿命に如何なる影響を及ぼすかを調べる為に利用する。
【０００２】
【従来の技術】
一般に、転がり軸受の転がり疲れ寿命は、軌道輪に形成した軌道又は転動体の転動面に、材料の疲れによる最初の損傷が生じるまでの、当該転がり軸受の総回転数で定義される。この様な軌道や転動面に生じる損傷のうち、本発明が対象とする、軌道の内部起点型剥離は、この軌道の表面下に存在する微小な欠陥（非金属介在物）を起点として生じる。即ち、転がり軸受の運転中、負荷圏では、軌道上を転動体が通過する度に、この軌道の表面下に剪断応力が繰り返し作用する。この剪断応力の値が、上記欠陥部分で特に大きくなる結果、長時間の運転後、上記欠陥を起点として亀裂が生じ、更にはこれが進展して、上記軌道に内部起点型剥離が生じる。
【０００３】
この様に、軌道の内部起点型剥離は、この軌道の表面下に存在する欠陥を起点として生じる為、上記転がり軸受の転がり疲れ寿命を評価する場合には、上記欠陥の位置及び大きさ等が、上記内部起点型剥離の発生に如何なる影響を及ぼすかを、予め実験により調べておく事が重要となる。ところが、この様な実験を行なう場合、実験用の転がり軸受を構成する軌道の表面下の所望の位置（例えば、最大剪断応力が発生する位置又はその近傍）に、所望の大きさの非金属介在物（欠陥）を設ける事は、例えば最新の製鋼技術等を駆使したとしても、非常に難しい。
【０００４】
そこで、この様な不都合を解消すべく、非特許文献１には、軌道の表面下に設ける欠陥として、上記非金属介在物の代わりに、空孔を採用する技術が記載されている。即ち、上記非特許文献１に記載された従来技術の場合には、図５〜７に示す様に、実験用の転がり軸受（図示の例では、ラジアル玉軸受）を構成する外輪１の一部に微小な内径を有する孔３を、この外輪１の外周面から内周面に向けて、放電加工により形成する。これにより、この孔３の先端（図５〜７の上端）部分を、上記外輪１の内周面に形成した外輪軌道２の表面下に配置する。そして、この様に外輪軌道２の表面下に配置した孔３の先端部分を、上記非金属介在物に相当する人工欠陥として利用する。又、この場合に、この人工欠陥を上記外輪軌道２の表面下の所望の位置｛例えば、表面下２００〜３００μｍ（０．２〜０．３ｍｍ）程度の位置｝に配置する為に、上記孔３の深さを規制する。又、上記人工欠陥を所望の大きさにする為に、上記孔３の内径を規制する｛例えば、２００〜４００μｍ（０．２〜０．４ｍｍ）程度にする｝。
【０００５】
この様な非特許文献１に記載された従来技術によれば、上記外輪軌道２の表面下の所望の位置に、所望の大きさの人工欠陥を設ける事ができる。これと共に、この人工欠陥を起点として、上記外輪軌道２の一部に内部起点型剥離（欠陥が非金属介在物である場合と同様のもの）を生じさせる事ができる。
【０００６】
【非特許文献１】
村上保夫、武村浩道、高木節雄、「内部起点型疲労破損の再現法の提案」、熱処理、社団法人日本熱処理技術協会、平成１３年２月、第４１巻、第１号
【０００７】
【発明が解決しようとする課題】
上述した非特許文献１に記載された従来技術をラジアル転がり軸受を構成する内輪に適用して、この内輪の外周面に形成した内輪軌道の表面下に人工欠陥を設ける事は、非常に難しい。即ち、上述した従来技術を上記内輪に適用する場合には、この内輪の一部に孔を、この内輪の内周面から外周面（上記内輪軌道）に向けて、放電加工により形成する必要がある。ところが、放電加工機の構造上、放電加工により孔を形成し始める面の手前側には、十分に広い空間が存在する必要がある。これに対し、上記内輪の内周面の手前側（径方向内側）には、十分に広い空間は存在しない。この為、上記内輪の内周面から放電加工によって孔を形成する事は（放電加工機の構造を改良しない限り）できない。従って、上述した従来技術を上記内輪に適用する事は、非常に難しい（放電加工機の構造を改良しない限り適用できない）。
【０００８】
又、上述した従来技術の場合には、上記孔３の先端部分を上記外輪軌道２の表面下の所望の位置に配置する為に、この孔３の深さを規制する必要がある。ところが、この孔３を形成する為に使用する放電加工用の電極（ワイヤ）は、この放電加工による孔３の形成に伴い、先端部が徐々に消耗する（短くなる）と言った事情がある。この為、上記孔３を形成する際には、この孔３の内側に上記電極を、この孔３に対して抜き差しする方向に変位させつつ挿入する事により、各挿入時の挿入量から上記孔３の深さを逆算して、この孔３の深さを確認する必要がある。ところが、この様にして孔３を形成すると、この孔３の内側で上記電極を抜き差しする方向に変位させる事に伴い、この孔３の内径が必要以上に大きくなる。この為、所望通りの小さい内径を有する孔３を形成するのが難しくなる。又、図７に詳示する様に、上記孔３の先端部分の形状が、この孔３を形成する度に若干異なる、先細りした形状となる（理想的な半球状若しくは円柱状にならない）。この様に人工欠陥である上記孔３の先端部の形状が、この孔３を形成する度に（若干とは言え）異なると、この様な孔３を備えた実験用の転がり軸受を使用して測定した、上記人工欠陥が内部起点型剥離の発生に及ぼす影響度（更には、当該転がり軸受の寿命）の信頼性を確保するのが難しくなる。この様な不都合は、転がり軸受がラジアル転がり軸受である場合だけでなく、スラスト転がり軸受である場合にも生じる。
【０００９】
又、上述した従来技術の場合、実験用の転がり軸受としてラジアル荷重のみが負荷されるものを造る場合には、上記外輪１に対する上記孔３の形成位置を上記外輪軌道２の幅方向中央部とすれば良いが、ラジアル荷重のみならずアキシアル荷重等が負荷されるものを造る場合には、上記外輪１に対する上記孔３の適切な形成位置を決定するのが難しい。即ち、孔３の形成位置が荷重の作用方向と少しずれただけでも、内部起点型剥離が発生しにくくなり、寿命試験の信頼性確保を図れなくなる。この様な不都合も、転がり軸受がラジアル転がり軸受である場合だけでなく、接触角を持ったスラスト転がり軸受である場合にも生じる。
本発明の人工欠陥付軌道輪及び人工欠陥付転がり軸受と転がり軸受の寿命試験方法は、上述の様な不都合を解消すべく発明したものである。
【００１０】
【課題を解決するための手段】
本発明の人工欠陥付軌道輪及び人工欠陥付転がり軸受と転がり軸受の寿命試験方法のうち、請求項１に記載した人工欠陥付軌道輪は、転がり軸受を構成する為、その一部に軌道を形成した軌道輪である。そして、この軌道を挟んで存在するこの軌道輪の片面から他面に向けて、孔を形成し、この孔の一部を上記軌道の表面下に、この軌道に内部起点型剥離を生じさせる為の人工欠陥として配置している。
【００１１】
特に、請求項２に記載した人工欠陥付軌道輪の場合には、上記軌道が上記軌道輪の周面に形成されており、この軌道を挟んで存在する、この軌道輪の片面及び他面が、それぞれこの軌道輪の軸方向両側面である。この様な請求項２に記載した人工欠陥付軌道輪は、ラジアル転がり軸受用のものである。
この様な請求項２に記載した人工欠陥付軌道輪を、例えば単列深溝型ラジアル玉軸受を構成する内輪に適用する場合には、例えば図１〜２に示す様に、この内輪４の外周面に形成した内輪軌道５のうち、円周方向に関する少なくとも１個所の表面下に、放電加工により上記内輪４の一部を軸方向（図１〜２の左右方向）に貫通する状態で形成した、孔３ａの中間部を配置する。そして、この孔３ａの中間部を、上記人工欠陥として利用する。又、この様な人工欠陥を上記内輪軌道５の円周方向複数個所の表面下に設ける場合には、例えば図３に示す様に、上記内輪４の円周方向複数個所（図示の例では、円周方向等間隔の４個所）位置に、それぞれ上述の様な孔３ａ、３ａを形成する。尚、孔３ａの数に拘らず、この孔３ａの方向は、上記内輪４の軸方向に一致させても、或はこの軸方向に対し傾斜させても良い。傾斜させる方向は、荷重の作用方向で、上記孔３ａの一部が上記内輪軌道５に最も近づく様に規制する。
【００１２】
これに対し、請求項３に記載した人工欠陥付軌道輪の場合には、上記軌道が軌道輪の軸方向側面に形成されており、この軌道を挟んで存在する、この軌道輪の片面と他面とのうち、片面がこの軌道輪の外周面であり、他面がこの軌道輪の内周面である。この様な請求項３に記載した人工欠陥付軌道輪は、スラスト転がり軸受用のものである。
この様な請求項３に記載した人工欠陥付軌道輪を、例えばスラスト玉軸受を構成する何れか一方の軌道輪に適用する場合には、例えば図４に示す様に、この軌道輪６の軸方向片側面（図４の上側面）に形成した軌道７のうち、円周方向に関する少なくとも１個所の表面下に、放電加工により上記軌道輪６の一部を径方向（図４の左右方向）に貫通する状態で形成した、孔３ｂの中間部を配置する。そして、この孔３ｂの中間部を、上記人工欠陥として利用する。又、図示は省略するが、この様な人工欠陥を上記軌道７の円周方向複数個所の表面下に設ける場合には、上記軌道輪６の円周方向複数個所に（例えば、円周方向に関して等間隔に）、それぞれ上述の様な孔３ｂを形成する。本例の場合も、この孔３ｂの形成方向は、上記軌道輪の径方向に一致させても、或はこの径方向に対し傾斜させても良い。傾斜方向は、荷重の作用方向に応じて規制する。
【００１３】
又、請求項４に記載した人工欠陥付転がり軸受は、上述した請求項１〜３の何れかに記載した人工欠陥付転がり軸受を実施する場合に、上記孔の一部が上記軌道の表面に露出しない事を条件として、この軌道の表面からこの軌道の表面下に配置した上記孔の一部の中心軸までの距離Ｌ（図２参照）を、５０〜５００μｍ（０．０５〜０．５ｍｍ）の範囲内（最大剪断応力が発生する位置又はその近傍に相当する範囲内）の値とし、且つ、上記孔の内径Ｄ（図２参照）を、２０〜２０００μｍ（０．０２〜２ｍｍ）の範囲内（凡そ、実際の非金属介在物の大きさに相当する範囲内）の値としている。
【００１４】
又、請求項５に記載した人工欠陥付転がり軸受は、従来から知られているラジアル転がり軸受と同様、内周面に外輪軌道を有する外輪と、外周面に内輪軌道を有する内輪と、これら外輪軌道と内輪軌道との間に転動自在に設けられた複数個の転動体とを備える。
特に、請求項５に記載した人工欠陥付転がり軸受に於いては、上記外輪と上記内輪とのうちの少なくとも一方の軌道輪が、上述した請求項１、２、４の何れかに記載した人工欠陥付軌道輪である。
【００１５】
又、請求項６に記載した人工欠陥付転がり軸受は、従来から知られているスラスト転がり軸受と同様、互いに対向する側面にそれぞれ軌道を形成した１対の軌道輪と、これら両軌道同士の間に転動自在に設けられた複数個の転動体とを備える。
特に、請求項６に記載した人工欠陥付転がり軸受に於いては、上記１対の軌道輪のうちの少なくとも一方の軌道輪が、上述した請求項１、３、４の何れかに記載した人工欠陥付軌道輪である。
【００１６】
又、請求項７に記載した転がり軸受の寿命試験方法は、上述した請求項５又は請求項６に記載した人工欠陥付転がり軸受を、荷重を負荷しつつ回転させる事により、人工欠陥を設けた軌道輪の一部に形成した軌道に、この人工欠陥を起点とする内部起点型剥離を生じさせる事に基づいて、上記人工欠陥付転がり軸受の転がり疲れ寿命の値を求める（転がり疲れ寿命を測定する）。
【００１７】
【作用】
上述の様に、本発明の人工欠陥付軌道輪及び人工欠陥付転がり軸受の場合には、軌道輪の片面（ラジアル転がり軸受の場合には、軸方向両側面のうちの何れか一方の側面。スラスト転がり軸受の場合には、外周面。）から他面（ラジアル転がり軸受の場合には、軸方向両側面のうちの他方の側面。スラスト転がり軸受の場合には、内周面。）に向けて形成した孔の一部を、人工欠陥として利用する。この軌道輪の片面の手前側には、十分に広い空間が確保されている。この為、軌道輪の種類に拘わらず（ラジアル転がり軸受の場合には、軌道輪が外輪であると内輪であるとに拘わらず）、この軌道輪に対し、上記孔を放電加工により容易に形成する事ができる。
【００１８】
又、本発明の場合、上記孔の一部が軌道の表面下を通過していれば、この孔の深さを特に規制する必要はない。この為、軌道輪に対する孔の形成作業は、前述した従来技術とは異なり（即ち、この孔の内側で放電加工用の電極を抜き差しする方向に変位させる事なく）、一気に行なえる。従って、この孔の形成作業を迅速に行なえると共に、この孔の内径が必要以上に広がる事を防止して、所望通りの小さい内径を有する孔を形成する事ができる。又、上記孔の中間部は、この孔を形成する度に等しい形状（例えば、円柱状）にする事ができる為、この孔の中間部を人工欠陥として使用すれば、この人工欠陥の形状を安定させる事ができる。
【００１９】
従って、本発明の人工欠陥付軌道輪及び人工欠陥付転がり軸受の場合には、軌道輪の種類に拘わらず、この軌道輪の周面に形成した軌道の表面下の所望の位置に、所望の形状及び大きさを有する人工欠陥を設ける事ができる。又、後述する実施例で示す様に、この人工欠陥を起点として、軌道の一部に内部起点型剥離（欠陥が非金属介在物である場合と同様のもの）を生じさせる事ができる。又、上記孔を、軌道を横切る状態で形成する為、この軌道に対する荷重の作用方向が多少ずれても、この荷重の作用方向に人工欠陥が存在する状態となる。従って、この作用方向が多少ずれても、人工欠陥部分から内部起点型剥離を確実に発生させる事ができる。
【００２０】
即ち、本発明の場合には、軌道輪の軸方向一端面から軸方向他端面に向けて、或は外周面から内周面に向けて形成した孔の一部を欠陥として利用する為、ラジアル荷重のみが負荷される転がり軸受に限らず、ラジアル荷重とアキシアル荷重との双方が負荷される転がり軸受や、アキシアル荷重のみが負荷される転がり軸受でも、上記孔の一部（軸方向に関する何れかの部分）が人工欠陥として機能する。尚、この場合、上記孔のうち、何れの部分が人工欠陥として機能したかは、軌道に生じた内部起点型剥離の位置を調べる事により確認できる。尚、荷重の作用点が軌道の底から外れている場合で、できる限りこの作用点の近くに人工欠陥を設ける必要があれば、孔の形成方向を適宜傾斜させて、この孔の一部が、上記作用点に対応する部分で、最も軌道に近づく様にする。
【００２１】
又、本発明の転がり軸受の寿命試験方法の場合には、試験用の転がり軸受として上述した様な人工欠陥付転がり軸受を使用する為、介在物に相当する人工欠陥の位置及び大きさ等を制御してシミュレートできる。従って、測定した転がり疲れ寿命の信頼性を十分に確保できる。
【００２２】
【実施例】
本発明の効果を確かめる為に行なった実験に就いて説明する。本実験では、以下の表１に示す様な、本発明の人工欠陥付転がり軸受（実施例１〜７）と、従来の（人工欠陥を有しない）転がり軸受（比較例１）とを用意し、これらに就いてそれぞれ、軌道に適正な内部起点型剥離（この内部起点型剥離に結びつく損傷を含む）を生じさせる事ができるか否かを調べた。
【表１】

【００２３】
本実験では、上記各転がり軸受（実施例１〜７及び比較例１）としてそれぞれ、ラジアル転がり軸受の一種である、単列深溝型ラジアル玉軸受（ＪＩＳ呼び番号６２０６：内径＝３０ｍｍ、外径＝６２ｍｍ、幅＝１６ｍｍ）を採用した。又、軸受材料としては、軸受鋼を使用したが、この様な軸受鋼として、実施例１〜７では、鋼中酸素量が７ｐｐｍ以下である、清浄度が高いもの（非金属介在物を起点として剥離が発生しにくいもの）を、比較例１では、鋼中酸素量が１５ｐｐｍである、軸受鋼として一般的なＳＵＪ２よりも清浄度が低いもの（非金属介在物を起点として剥離が発生し易いもの）を、それぞれ使用した。又、上記各転がり軸受（実施例１〜７及び比較例１）を構成する外輪及び内輪に就いては、８２０〜８７０℃で加温・油冷却した後、更に焼き戻し処理を行なってから、外輪軌道及び内輪軌道に仕上げ研磨加工を施した。これにより、これら外輪軌道及び内輪軌道の表面硬さをＨｖ６５０〜７５０とし、同じく表面粗さを０．０１〜０．０４μｍＲａとした。又、上記外輪軌道及び内輪軌道の母線（中心軸を含む切断面での断面形状）の曲率半径を、上記各転がり軸受（実施例１〜７及び比較例１）を構成する各玉の直径の５２％の大きさとした。
【００２４】
又、実施例１〜７に就いては、内輪軌道の表面下に、本発明の特徴部分である人工欠陥を設けた。この為に、前述の図１〜２に示す様に、内輪４の外周面に形成した内輪軌道５のうち、円周方向に関する少なくとも１個所の表面下の所望の位置に、上記内輪４の一部を軸方向に貫通する状態で形成した、所望の内径を有する孔３ａの中間部を配置した。そして、この孔３ａの中間部を、上記人工欠陥とした。この孔３ａは、放電加工により形成し、この放電加工を行なう為の電極として、タングステンのワイヤを使用した。又、上記各実施例１〜７に就いての、上記孔３ａの内径Ｄと、上記内輪軌道５の幅方向中央部（底部）から上記孔３ａの中心軸までの距離Ｌと、上記内輪４に形成する上記孔３ａの個数とは、それぞれ前記表１に示す通りとした。尚、このうち、上記内輪４に形成する孔３ａの個数を複数とした、実施例６及び実施例７に就いては、上記内輪４に対する上記各孔３ａの配置個所を、円周方向に関して等間隔とした。又、計算上の最大剪断応力の発生位置は、上記内輪軌道５の表面から深さＺ_０＝１２０μｍ（０．１２ｍｍ）の位置である。
【００２５】
次に、上述の様な各転がり軸受（実施例１〜７及び比較例１）を使用して行なった、具体的な実験の方法に就いて説明する。本実験では、上記各転がり軸受（実施例１〜７及び比較例１）の試料数を、それぞれ１個とした。そして、これら各転がり軸受（実施例１〜７及び比較例１）を、それぞれ負荷ラジアル荷重Ｆ_ｒ＝７５００Ｎ（Ｐ／Ｃ_ｒ＝０．３８）、回転速度＝１００００ｍｉｎ^−１で運転し、上記内輪軌道５に所望の内部起点型剥離を生じさせる事ができるか否かを調べた。この為に、上述の様な各転がり軸受（実施例１〜７及び比較例１）の運転中、これら各転がり軸受（実施例１〜７及び比較例１）の振動の振幅が初期の振幅の５倍となった時点で運転を中断し、上記内輪軌道５に内部起点型剥離が生じているか否かを調べた。又、上記各転がり軸受（実施例１〜７及び比較例１）の計算寿命Ｌ_ＣＡＬが３０時間（ｈｒ）である為、その約５倍の１５０時間（ｈｒ）を、実験の打ち切り時間とした。この様にして行なった実験の結果を、前記表１に示す。
【００２６】
先ず、実施例１に就いては、実験の打ち切り時間である１５０時間（ｈｒ）に至っても、外観上、内輪軌道５に内部起点型剥離は観察されなかった。しかしながら、打ち切り後にこの内輪軌道５の表層部の断面観察を行なった結果、この内輪５の幅方向中央部の表面下で、上記人工欠陥からこの表面に向かって疲労亀裂が３０μｍ進展しているのが確認され、更には、バタフライと呼ばれる、上記内部起点型剥離に結び付く組織変化も確認された。従って、この実施例１では、上記内輪軌道５に内部起点型剥離を再現できる事が分かった。
【００２７】
次に、実施例２に就いては、１２０時間（ｈｒ）で内輪軌道５に剥離が発生した。又、この剥離が生じた部分でこの内輪軌道５の表層部の断面観察を行なった結果、この内輪軌道５の表面下に存在する人工欠陥から疲労亀裂が進展し、これが上記剥離の部分に到達している事から、この剥離が上記人工欠陥を起点とする、内部起点型剥離である事が確認された。この様に、この実施例２では、上記内輪軌道５に内部起点型剥離を再現できる事が分かった。
【００２８】
次に、実施例３、４、５｛それぞれ内輪軌道５の幅方向中央部の表面から人工欠陥の手前側の縁までの距離を１００μｍ（０．１ｍｍ）に設定したもの｝に就いては、やはりそれぞれ、運転の打ち切り時間である１５０時間（ｈｒ）以前に、上記内輪軌道５に剥離が発生した。そして、この剥離が生じた部分で上記内輪軌道５の表層部の断面観察を行なった結果、上述した実施例２の場合と同様、当該剥離が上記人工欠陥を起点とする内部起点型剥離である事が確認された。又、これら実施例３、４、５の実験結果から明らかな様に、上記内輪軌道５の幅方向中央部の表面から上記人工欠陥の手前側の縁までの距離が等しい（１００μｍである）場合には、上記人工欠陥の直径（孔３ａの内径）が２００μｍ（実施例３）、５００μｍ（実施例４）、２０００μｍ（実施例５）と大きくなるに従い、上記内部起点型剥離が生じるまでの運転時間が６７時間（ｈｒ）（実施例３）、２９時間（ｈｒ）（実施例４）、１１時間（ｈｒ）（実施例５）と短くなるのが分かる。何れにしても、この様な実験結果から、実施例３、４、５では、それぞれ上記内輪軌道５に内部起点型剥離を再現できる事が分かった。
【００２９】
次に、実施例６、７に就いては、やはりそれぞれ、運転の打ち切り時間である１５０時間（ｈｒ）以前に、上記内輪軌道５に剥離が発生した。そして、この剥離が生じた部分で上記内輪軌道５の表層部の断面観察を行なった結果、上述した実施例２の場合と同様、当該剥離が上記人工欠陥を起点とする内部起点型剥離である事が確認された。又、実施例６と実施例２との実験結果同士を比較し、実施例７と実施例４との実験結果同士を比較すれば明らかな様に、人工欠陥の直径（孔３ａの内径）が等しい場合には、この人工欠陥の上記内輪軌道５の表面からの深さ（距離Ｌ）が大きくなる程、上記内部起点型剥離が生じるまでの運転時間が長くなる事が分かる。何れにしても、この様な実験結果から、実施例６、７では、それぞれ上記内輪軌道５に内部起点型剥離を再現できる事が分かった。
【００３０】
次に、比較例１に就いては、実験の打ち切り時間である１５０時間（ｈｒ）に至っても、外観上、内輪軌道５に内部起点型剥離は観察されなかった。又、この内輪軌道５の表層部の断面観察を行なったが、この内輪軌道５の表面下で疲労亀裂や前述したバタフライは確認されなかった。この様に比較例１では、上記内輪軌道５に内部起点型剥離を再現する事ができなかった。この様な実験結果が出た理由、即ち、比較例１が軸受鋼として清浄度が低いもの（非金属介在物を起点として剥離が発生し易いもの）を使用したにも拘わらず、上記内輪軌道５に内部起点型剥離を再現できなかった理由は、軸受鋼として清浄度が低いものを使用した場合でも、最大剪断応力が発生する位置に非金属介在物を配置できる可能性が低い（実際に、比較例１では配置できなかった）為である。この様な事実は、従来から知られていた事であるが、この比較例１の実験結果によって再度確認できた。
【００３１】
尚、上述した実施例では、内輪軌道の表面下にのみ人工欠陥を設けたが、外輪軌道の表面下に人工欠陥を設けた場合でも、同様の作用・効果が得られる。又、軸受材料に関しては、軸受鋼２種（ＳＵＪ２）に限らず、肌焼材料等の各種の材料を使用する場合でも、同様の作用・効果が得られる。又、上述した実施例では、本発明を単列深溝型ラジアル玉軸受に適用したが、本発明は、単列深溝型ラジアル玉軸受に限らず、例えばアンギュラ型玉軸受、円筒ころ軸受、円すいころ軸受、複列転がり軸受等、各種の転がり軸受に適用可能である。又、上述した実施例では、転がり軸受としてラジアル転がり軸受を採用したが、スラスト転がり軸受を採用する場合でも、同様の作用・効果が得られる。この場合、何れの転がり軸受に適用する場合でも、軌道の一部の表面下の所望の位置に孔の一部を（例えば、この軌道の一部と平行に或は荷重の作用方向に応じ傾斜させて）配置すれば、この孔の一部（人工欠陥）を起点として、上記軌道の一部に内部起点型剥離を生じさせる事ができる。
【００３２】
上述した様に、本発明によれば、軌道の一部の表面下の所望の位置に、所望の形状及び大きさの人工欠陥を設ける事ができる。そして、この人工欠陥を起点として、上記軌道の一部に内部起点型剥離を生じさせる（再現する）事ができる。従って、例えば、１００トン溶解の鋼中で、１個の転がり軸受に就いての応力体積（最大剪断応力が発生する部分の体積）中に含まれる非金属介在物の最大直径を、極値統計により求め、更に、この最大直径と同じ大きさの人工欠陥を、軌道輪の周面に形成した軌道の表面下の最大剪断応力が発生する位置に配置すれば、非金属介在物が当該転がり軸受の転がり疲れ寿命に与える影響度を、定量的に求める事ができる。
【００３３】
【発明の効果】
本発明の人工欠陥付軌道輪及び人工欠陥付転がり軸受と転がり軸受の寿命試験方法は、以上に述べた様に構成され作用する為、非金属介在物に相当する人工欠陥が転がり軸受の寿命に与える影響度を、定量的に求める事ができる。言い換えれば、この様にして求めた影響度の信頼性を十分に確保できる。
【図面の簡単な説明】
【図１】本発明の人工欠陥付軌道輪（内輪）の実施の形態の第１例を、孔の内径を誇張して示す部分断面図。
【図２】図１のＡ部拡大図。
【図３】本発明の人工欠陥付軌道輪（内輪）の実施の形態の第２例を、孔の内径を誇張して示す側面図。
【図４】同第３例を、孔の内径を誇張して示す部分断面図。
【図５】従来の人工欠陥付軌道輪（外輪）を、孔の内径を誇張して示す側面図。
【図６】図５のＢ−Ｂ断面図。
【図７】図６のＣ部拡大図。
【符号の説明】
１外輪
２外輪軌道
３、３ａ、３ｂ孔
４内輪
５内輪軌道
６軌道輪
７軌道[0001]
TECHNICAL FIELD OF THE INVENTION
The bearing ring with artificial defect and the rolling bearing with artificial defect according to the present invention and the method for testing the life of the rolling bearing are characterized in that the position and size of the defect existing under the surface of the track are determined by the internal origin type peeling in this track. It is used to check the occurrence or the effect on the life of the rolling bearing.
[0002]
[Prior art]
Generally, the rolling fatigue life of a rolling bearing is defined by the total number of revolutions of the rolling bearing until the first damage due to material fatigue occurs on the raceway formed on the raceway or the rolling surface of the rolling element. Among the damages occurring on such raceways and rolling surfaces, the internal origin type peeling of the raceway targeted by the present invention is caused by a minute defect (non-metallic inclusion) existing below the surface of the raceway. . That is, during the operation of the rolling bearing, in the load zone, each time the rolling element passes on the track, the shear stress repeatedly acts below the surface of the track. As a result of the value of the shear stress being particularly large at the defect portion, a crack is generated starting from the defect after a long-time operation, and further, the crack develops and the internal orbital delamination occurs in the track.
[0003]
As described above, since the internal origin type peeling of the raceway occurs starting from a defect existing below the surface of the raceway, when evaluating the rolling fatigue life of the rolling bearing, the position and size of the defect are determined. It is important to check in advance by experiment what effect it has on the occurrence of the internal origin type peeling. However, when such an experiment is performed, a non-metallic interposition of a desired size is placed at a desired position (for example, at or near the position where the maximum shear stress is generated) below the surface of the track constituting the experimental rolling bearing. It is very difficult to provide an object (defect) even if, for example, the latest steelmaking technology is used.
[0004]
Therefore, in order to solve such inconvenience, Non-Patent Document 1 describes a technology that employs holes instead of the nonmetallic inclusions as defects provided below the surface of the track. That is, in the case of the prior art described in Non-Patent Document 1, as shown in FIGS. 5 to 7, a part of the outer ring 1 constituting an experimental rolling bearing (in the illustrated example, a radial ball bearing). A hole 3 having a very small inner diameter is formed from the outer peripheral surface of the outer ring 1 toward the inner peripheral surface by electric discharge machining. Thereby, the tip (the upper end in FIGS. 5 to 7) of the hole 3 is arranged below the surface of the outer raceway 2 formed on the inner peripheral surface of the outer race 1. The tip of the hole 3 disposed below the surface of the outer raceway 2 is used as an artificial defect corresponding to the nonmetallic inclusion. In this case, in order to arrange the artificial defect at a desired position below the surface of the outer raceway 2 (for example, at a position of about 200 to 300 μm (0.2 to 0.3 mm) below the surface), the hole is formed. Limit the depth of 3. Further, in order to make the artificial defect a desired size, the inner diameter of the hole 3 is regulated (for example, about 200 to 400 μm (0.2 to 0.4 mm)).
[0005]
According to such a conventional technique described in Non-Patent Document 1, an artificial defect having a desired size can be provided at a desired position below the surface of the outer raceway 2. At the same time, with this artificial defect as a starting point, an internal starting type peeling (similar to the case where the defect is a non-metallic inclusion) can be generated in a part of the outer raceway 2.
[0006]
[Non-patent document 1]
Yasuo Murakami, Hiromichi Takemura, Setsuo Takagi, "Proposal of Reproduction Method for Internal Origin Fatigue Failure", Heat Treatment, Japan Heat Treatment Technology Association, February 2001, Vol. 41, No. 1,
[0007]
[Problems to be solved by the invention]
It is very difficult to apply the prior art described in Non-Patent Document 1 to an inner ring that constitutes a radial rolling bearing and provide an artificial defect below the surface of an inner ring raceway formed on the outer peripheral surface of the inner ring. That is, when the above-described conventional technology is applied to the inner ring, it is necessary to form a hole in a part of the inner ring by electric discharge machining from the inner peripheral surface of the inner ring toward the outer peripheral surface (the inner ring raceway). is there. However, due to the structure of the electric discharge machine, a sufficiently large space needs to exist on the front side of the surface where the holes start to be formed by electric discharge machining. On the other hand, there is no sufficiently large space on the near side (radially inward) of the inner peripheral surface of the inner ring. For this reason, it is impossible to form a hole from the inner peripheral surface of the inner ring by electric discharge machining (unless the structure of the electric discharge machine is improved). Therefore, it is very difficult to apply the above-mentioned prior art to the inner ring (it cannot be applied unless the structure of the electric discharge machine is improved).
[0008]
Further, in the case of the above-described conventional technique, it is necessary to regulate the depth of the hole 3 in order to arrange the tip portion of the hole 3 at a desired position below the surface of the outer raceway 2. However, the electrode (wire) for electric discharge machining used to form the hole 3 has a situation in which the tip is gradually consumed (shortened) as the hole 3 is formed by the electric discharge machining. . For this reason, when forming the hole 3, the electrode is inserted inside the hole 3 while displacing the electrode 3 in the direction of insertion and removal with respect to the hole 3 so that the amount of insertion at the time of each insertion is reduced. It is necessary to check the depth of the hole 3 by calculating the depth of the hole 3 back. However, when the hole 3 is formed in this manner, the inside diameter of the hole 3 becomes larger than necessary due to the displacement inside the hole 3 in the direction in which the electrode is inserted and withdrawn. For this reason, it is difficult to form the hole 3 having a desired small inner diameter. Further, as shown in detail in FIG. 7, the shape of the tip portion of the hole 3 becomes a slightly tapered shape each time the hole 3 is formed (it does not become an ideal hemispherical or cylindrical shape). If the shape of the tip of the hole 3, which is an artificial defect, is different (although slightly) each time the hole 3 is formed, an experimental rolling bearing having such a hole 3 is used. It is difficult to ensure the reliability of the degree of influence of the artificial defect on the occurrence of the internal origin type separation (further, the life of the rolling bearing) measured as described above. Such inconvenience occurs not only when the rolling bearing is a radial rolling bearing but also when it is a thrust rolling bearing.
[0009]
Further, in the case of the above-described conventional technique, when a rolling bearing for an experiment that receives only a radial load is manufactured, the position where the hole 3 is formed with respect to the outer ring 1 is set at the center of the outer ring raceway 2 in the width direction. However, it is difficult to determine an appropriate position for forming the hole 3 with respect to the outer ring 1 when manufacturing a structure that receives not only a radial load but also an axial load. That is, even if the formation position of the hole 3 is slightly deviated from the acting direction of the load, it is difficult for the internal origin type peeling to occur, and the reliability of the life test cannot be ensured. Such inconvenience occurs not only when the rolling bearing is a radial rolling bearing, but also when it is a thrust rolling bearing having a contact angle.
The bearing ring with artificial defect, the rolling bearing with artificial defect, and the life testing method of the rolling bearing according to the present invention have been invented in order to solve the above-mentioned disadvantages.
[0010]
[Means for Solving the Problems]
Among the bearing rings with artificial defects, the rolling bearings with artificial defects, and the life testing method of the rolling bearings of the present invention, the bearing rings with artificial defects according to claim 1 constitute a rolling bearing, so that a part of the race has a track. It is a formed bearing ring. Then, a hole is formed from one side of the raceway present across the raceway to the other surface, and a part of the hole is formed below the surface of the raceway so as to cause internal origin type separation in the raceway. Are placed as artificial defects.
[0011]
In particular, in the case of the bearing ring with artificial defects described in claim 2, the raceway is formed on the peripheral surface of the raceway ring, and one side and the other surface of the raceway that are present across the raceway are formed. , Respectively, are both axial side surfaces of this bearing ring. The bearing ring with an artificial defect described in claim 2 is for a radial rolling bearing.
In the case where such an artificial defect bearing ring described in claim 2 is applied to, for example, an inner ring constituting a single-row deep groove type radial ball bearing, as shown in FIGS. Of the inner raceway 5 formed on the surface, a portion of the inner race 4 was formed in a state penetrating in the axial direction (the left-right direction in FIGS. 1 and 2) by electric discharge machining below at least one surface in the circumferential direction. , An intermediate portion of the hole 3a. Then, the intermediate portion of the hole 3a is used as the artificial defect. In the case where such artificial defects are provided below the surface of a plurality of locations in the circumferential direction of the inner raceway 5, for example, as shown in FIG. 3, a plurality of locations in the circumferential direction of the inner race 4 (in the illustrated example, The

holes

3a, 3a as described above are formed at four positions at equal intervals in the circumferential direction). Regardless of the number of the holes 3a, the direction of the holes 3a may coincide with the axial direction of the inner ring 4, or may be inclined with respect to this axial direction. The inclining direction is the direction in which the load acts, and is regulated so that a part of the hole 3a approaches the inner raceway 5 most.
[0012]
On the other hand, in the case of the bearing ring with artificial defects according to the third aspect, the track is formed on the axial side surface of the track ring, and one side of the track ring and the other surface sandwiching the track exist. One of the surfaces is the outer peripheral surface of the bearing ring, and the other surface is the inner peripheral surface of the bearing ring. The bearing ring with artificial defects described in claim 3 is for a thrust rolling bearing.
When such a bearing ring with an artificial defect described in claim 3 is applied to, for example, one of the bearing rings constituting a thrust ball bearing, for example, as shown in FIG. In the track 7 formed on one side surface (upper surface in FIG. 4), a part of the race 6 is radially moved (left-right direction in FIG. 4) by electric discharge machining below at least one surface in the circumferential direction. An intermediate portion of the hole 3b formed so as to penetrate through the hole 3b is arranged. Then, the intermediate portion of the hole 3b is used as the artificial defect. Although not shown, when such an artificial defect is provided below the surface of the track 7 at a plurality of positions in the circumferential direction, the artificial defect is provided at a plurality of positions in the circumferential direction of the track ring 6 (for example, with respect to the circumferential direction). The holes 3b as described above are formed at regular intervals). Also in the case of this example, the direction in which the holes 3b are formed may coincide with the radial direction of the bearing ring, or may be inclined with respect to this radial direction. The direction of inclination is regulated according to the direction in which the load acts.
[0013]
In the rolling bearing with artificial defects according to claim 4, when the rolling bearing with artificial defects according to any one of claims 1 to 3 described above, a part of the hole is formed on the surface of the track. On condition that the track is not exposed, the distance L (see FIG. 2) from the surface of this track to the central axis of a part of the hole disposed below the surface of the track is 50 to 500 μm (0.05 to 0.5 mm). ) (In the range corresponding to the position where the maximum shear stress is generated or in the vicinity thereof), and the inner diameter D (see FIG. 2) of the hole is 20 to 2000 μm (0.02 to 2 mm). The value is within the range (approximately within the range corresponding to the actual size of the nonmetallic inclusion).
[0014]
Further, the rolling bearing with artificial defects according to claim 5 is, like the conventionally known radial rolling bearing, an outer race having an outer raceway on an inner peripheral surface, an inner race having an inner raceway on an outer peripheral surface, and these outer races. A plurality of rolling elements rotatably provided between the raceway and the inner raceway.
In particular, in the rolling bearing with artificial defects described in claim 5, at least one of the races of the outer ring and the inner ring is provided with the artificial ring according to any one of

claims

1, 2, and 4 described above. It is a bearing ring with defects.
[0015]
A rolling bearing with an artificial defect according to a sixth aspect of the present invention has a pair of races having raceways formed on opposing side surfaces and a pair of raceways between these raceways, similarly to a conventionally known thrust rolling bearing. And a plurality of rolling elements provided so as to be freely rotatable.
In particular, in the rolling bearing with artificial defects according to claim 6, at least one of the pair of bearing rings is the artificial bearing according to any one of claims 1, 3, and 4. It is a bearing ring with defects.
[0016]
According to a seventh aspect of the present invention, there is provided a rolling bearing life testing method in which an artificial defect is provided by rotating the above-described rolling bearing with an artificial defect according to the fifth or sixth aspect while applying a load. The value of the rolling fatigue life of the above-mentioned rolling bearing with artificial defects is determined based on the occurrence of internal origin type delamination starting from this artificial defect in the track formed on a part of the raceway (measure the rolling fatigue life). Do).
[0017]
[Action]
As described above, in the case of the bearing ring with the artificial defect and the rolling bearing with the artificial defect of the present invention, one side of the race (in the case of the radial rolling bearing, any one of the side surfaces in the axial direction). From the outer peripheral surface in the case of a thrust rolling bearing) to the other surface (in the case of a radial rolling bearing, the other side surface of both axial side surfaces; in the case of a thrust rolling bearing, the inner peripheral surface). Some of the holes formed are used as artificial defects. A sufficiently large space is secured on one side of the raceway. For this reason, regardless of the type of race, (in the case of a radial rolling bearing, regardless of whether the race is an outer race or an inner race), the above-mentioned hole is easily formed in this race by electric discharge machining. You can do it.
[0018]
In the case of the present invention, if a part of the hole passes below the surface of the track, the depth of the hole does not need to be particularly limited. For this reason, the hole forming operation for the race is different from that of the above-described conventional technique (that is, without displacing the electrode for electric discharge machining inside and outside the hole), and can be performed at once. Therefore, the hole can be formed quickly, and the inner diameter of the hole is prevented from expanding more than necessary, so that the hole having the desired small inner diameter can be formed. In addition, since the intermediate portion of the hole can be formed into a shape (for example, a column) each time the hole is formed, if the intermediate portion of the hole is used as an artificial defect, the shape of the artificial defect can be reduced. Can be stabilized.
[0019]
Therefore, in the case of the bearing ring with artificial defect and the rolling bearing with artificial defect of the present invention, regardless of the type of the bearing ring, a desired position is provided at a desired position below the surface of the track formed on the peripheral surface of the bearing ring. An artificial defect having a shape and a size can be provided. Further, as shown in an embodiment described later, an internal origin type peeling (similar to the case where the defect is a non-metallic inclusion) can be generated in a part of the track starting from the artificial defect. Further, since the hole is formed so as to cross the track, even if the acting direction of the load on the track slightly shifts, an artificial defect exists in the acting direction of the load. Therefore, even if the action direction is slightly shifted, the internal origin type peeling can be reliably generated from the artificial defect portion.
[0020]
That is, in the case of the present invention, since a part of a hole formed from one axial end surface of the bearing ring to the other axial end surface or from the outer peripheral surface to the inner peripheral surface is used as a defect, Not only rolling bearings in which only a load is applied, but also rolling bearings in which both a radial load and an axial load are applied, and rolling bearings in which only an axial load is applied, a part of the hole (any one in the axial direction). Part) functions as an artificial defect. In this case, which part of the hole functions as an artificial defect can be confirmed by examining the position of the internal origin type peeling generated in the track. If the point of application of the load is off the bottom of the track, and it is necessary to provide an artificial defect as close to the point of application as possible, the formation direction of the hole is appropriately inclined so that a part of this hole is In the portion corresponding to the above-mentioned action point, it is made to approach the orbit most.
[0021]
Further, in the case of the rolling bearing life test method of the present invention, since the above-described rolling bearing with artificial defects is used as the rolling bearing for testing, the position and size of the artificial defect corresponding to the inclusion are determined. Can be controlled and simulated. Therefore, the reliability of the measured rolling fatigue life can be sufficiently ensured.
[0022]
【Example】
An experiment performed to confirm the effect of the present invention will be described. In this experiment, a rolling bearing with an artificial defect of the present invention (Examples 1 to 7) and a conventional (no artificial defect) rolling bearing (Comparative Example 1) as shown in Table 1 below were prepared. Each of these was examined to determine whether or not it was possible to cause a proper internal origin type peeling (including damage associated with the internal origin type peeling) on the track.
[Table 1]

[0023]
In this experiment, each of the above-mentioned rolling bearings (Examples 1 to 7 and Comparative Example 1) is a single row deep groove type radial ball bearing (JIS call number 6206: inner diameter = 30 mm, outer diameter = (62 mm, width = 16 mm). As the bearing material, a bearing steel was used. In Examples 1 to 7, such a bearing steel having an oxygen content in steel of 7 ppm or less and having high cleanliness (starting from nonmetallic inclusions) was used. In Comparative Example 1, a bearing steel having an oxygen content of 15 ppm and having a lower degree of cleanliness than SUJ2, which is common as a bearing steel (non-metallic inclusions, was used as a starting point). Which are easy to use). For the outer ring and the inner ring constituting each of the above rolling bearings (Examples 1 to 7 and Comparative Example 1), after heating and oil cooling at 820 to 870 ° C., and further performing a tempering process, The outer raceway and inner raceway were finished and polished. Thus, the surface hardness of the outer raceway and the inner raceway was set to Hv650 to 750, and the surface roughness was set to 0.01 to 0.04 μmRa. Further, the radius of curvature of the generatrix of the outer raceway and the inner raceway (the cross-sectional shape at the cross section including the central axis) is determined by the diameter of each ball constituting each of the rolling bearings (Examples 1 to 7 and Comparative Example 1). The size was 52%.
[0024]
In Examples 1 to 7, an artificial defect, which is a feature of the present invention, was provided below the surface of the inner raceway. For this purpose, as shown in FIGS. 1 and 2 described above, the inner race 4 is formed at a desired position below at least one circumferential surface of the inner raceway 5 formed on the outer peripheral surface of the inner race 4. An intermediate portion of a hole 3a having a desired inner diameter formed so as to penetrate the portion in the axial direction was arranged. The intermediate portion of the hole 3a was used as the artificial defect. The hole 3a was formed by electric discharge machining, and a tungsten wire was used as an electrode for performing the electric discharge machining. The inner diameter D of the hole 3a, the distance L from the center (bottom) in the width direction of the inner raceway 5 to the center axis of the hole 3a, and the inner race 4 The number of the holes 3a to be formed is as shown in Table 1 above. In the sixth and seventh embodiments in which the number of holes 3a formed in the inner ring 4 is plural, the location of each hole 3a with respect to the inner ring 4 is determined in the circumferential direction. It was an interval. The calculated maximum shear stress is generated at a depth Z from the surface of the inner raceway 5. ₀ = 120 μm (0.12 mm).
[0025]
Next, a specific experimental method performed using each of the above-described rolling bearings (Examples 1 to 7 and Comparative Example 1) will be described. In this experiment, the number of samples of each of the rolling bearings (Examples 1 to 7 and Comparative Example 1) was set to one. Each of these rolling bearings (Examples 1 to 7 and Comparative Example 1) was loaded with a radial load F, respectively. _r = 7500N (P / C _r = 0.38), rotation speed = 10000 min ^-1 And it was examined whether or not the inner ring raceway 5 could have a desired internal origin type separation. For this reason, during the operation of each of the rolling bearings (Examples 1 to 7 and Comparative Example 1) as described above, the amplitude of the vibration of each of the rolling bearings (Examples 1 to 7 and Comparative Example 1) is the initial amplitude. The operation was interrupted at the time of the increase of 5 times, and it was examined whether or not the internal origin type peeling occurred in the inner raceway 5. Also, the calculated life L of each of the above-mentioned rolling bearings (Examples 1 to 7 and Comparative Example 1). _CAL Is 30 hours (hr), so 150 hours (hr), which is about 5 times that of the time, was set as the censoring time of the experiment. The results of the experiments performed in this way are shown in Table 1 above.
[0026]
First, in the case of Example 1, even at 150 hours (hr), which is the cutoff time of the experiment, the internal origin type peeling was not observed on the inner raceway 5 in appearance. However, a cross-sectional observation of the surface layer portion of the inner raceway 5 after the discontinuation revealed that a fatigue crack had grown by 30 μm from the artificial defect toward the surface below the surface at the center in the width direction of the inner raceway 5. Was confirmed, and further, a structural change called “butterfly”, which was linked to the above-mentioned internal origin type exfoliation, was also confirmed. Therefore, it was found that in the first embodiment, the inner origin type separation can be reproduced on the inner raceway 5.
[0027]
Next, in Example 2, peeling occurred on the inner raceway 5 in 120 hours (hr). In addition, as a result of observing a cross section of the surface layer of the inner raceway 5 at a portion where the separation occurred, a fatigue crack propagated from an artificial defect existing below the surface of the inner raceway 5 and reached the separated portion. From this, it was confirmed that this peeling was an internal origin type peeling starting from the artificial defect. As described above, it was found that in the second embodiment, the inner origin type separation can be reproduced on the inner raceway 5.
[0028]
Next, in Examples 3, 4, and 5 {where the distance from the surface at the center in the width direction of the inner raceway 5 to the front edge of the artificial defect was set to 100 μm (0.1 mm)}, Also, peeling occurred in the inner raceway 5 before 150 hours (hr), which is the operation cutoff time. Then, as a result of observing a cross section of the surface layer portion of the inner raceway 5 at a portion where the peeling occurred, the peeling was an internal origin type peeling starting from the artificial defect as in the case of Example 2 described above. The thing was confirmed. In addition, as is apparent from the experimental results of Examples 3, 4, and 5, when the distances from the surface at the center in the width direction of the inner raceway 5 to the front edge of the artificial defect are equal (100 μm). As the diameter of the artificial defect (the inner diameter of the hole 3a) increases to 200 μm (Example 3), 500 μm (Example 4), and 2000 μm (Example 5), the operation until the internal origin type separation occurs. It can be seen that the time was shortened to 67 hours (hr) (Example 3), 29 hours (hr) (Example 4), and 11 hours (hr) (Example 5). In any case, from such experimental results, in Examples 3, 4, and 5, it was found that the internal origin type peeling could be reproduced on the inner raceway 5 respectively.
[0029]
Next, in Examples 6 and 7, peeling occurred on the inner raceway 5 before 150 hours (hr), which is the operation cutoff time, respectively. Then, as a result of observing a cross section of the surface layer portion of the inner raceway 5 at a portion where the peeling occurred, the peeling was an internal origin type peeling starting from the artificial defect as in the case of Example 2 described above. The thing was confirmed. In addition, comparing the experimental results of Example 6 and Example 2 with each other and comparing the experimental results of Example 7 and Example 4 with each other, it is clear that the diameter of the artificial defect (the inner diameter of the hole 3a) is small. In the case of being equal, it can be seen that as the depth (distance L) of the artificial defect from the surface of the inner raceway 5 increases, the operation time until the internal origin type separation occurs increases. In any case, from such experimental results, in Examples 6 and 7, it was found that the internal origin type peeling could be reproduced on the inner raceway 5 respectively.
[0030]
Next, in Comparative Example 1, no internal-origin type peeling was observed on the inner raceway 5 even in 150 hours (hr), which is the time when the experiment was terminated. A cross section of the surface layer of the inner raceway 5 was observed, but no fatigue cracks or the aforementioned butterfly were found under the surface of the inner raceway 5. As described above, in Comparative Example 1, it was not possible to reproduce the internal origin type separation on the inner raceway 5. Despite the reason why such an experimental result was obtained, that is, despite the fact that Comparative Example 1 used a bearing steel having a low cleanliness (one in which peeling was likely to occur starting from nonmetallic inclusions), the inner ring raceway was used. The reason why the internal origin type peeling could not be reproduced in Fig. 5 is that even if a bearing steel having low cleanliness is used, there is a low possibility that a nonmetallic inclusion can be arranged at a position where the maximum shear stress occurs (actually, , In Comparative Example 1). Such a fact has been conventionally known, but was confirmed again by the experimental result of Comparative Example 1.
[0031]
In the above-described embodiment, the artificial defect is provided only below the surface of the inner raceway. However, the same operation and effect can be obtained even when the artificial defect is provided below the surface of the outer raceway. Further, the bearing material is not limited to two types of bearing steel (SUJ2), and the same operation and effect can be obtained even when various materials such as case hardening materials are used. Further, in the above-described embodiment, the present invention is applied to a single-row deep-groove type radial ball bearing, but the present invention is not limited to a single-row deep-groove type radial ball bearing, for example, an angular-type ball bearing, a cylindrical roller bearing, and a tapered roller. The present invention is applicable to various types of rolling bearings such as bearings and double row rolling bearings. Further, in the above-described embodiment, the radial rolling bearing is used as the rolling bearing. However, the same operation and effect can be obtained when a thrust rolling bearing is used. In this case, when applied to any of the rolling bearings, a part of the hole is placed at a desired position below the surface of a part of the track (for example, inclined in parallel with the part of the track or according to the direction of load application). If it arrange | positions, it can generate | occur | produce the internal origin type peeling in a part of said track | truck starting from a part (artificial defect) of this hole.
[0032]
As described above, according to the present invention, an artificial defect having a desired shape and size can be provided at a desired position below the surface of a part of the track. Then, with this artificial defect as a starting point, internal starting type separation can be caused (reproduced) in a part of the track. Therefore, for example, in a steel of 100 tons melting, the maximum diameter of the non-metallic inclusion included in the stress volume (volume of the portion where the maximum shear stress occurs) for one rolling bearing is determined by the extreme value statistics. Further, if an artificial defect having the same size as the maximum diameter is arranged at a position where the maximum shear stress occurs below the surface of the raceway formed on the peripheral surface of the raceway, the non-metallic inclusions can be used as the rolling bearing. Of the rolling fatigue life can be quantitatively determined.
[0033]
【The invention's effect】
The life test method of the bearing ring with artificial defect, the rolling bearing with artificial defect, and the rolling bearing with artificial defect of the present invention is configured and operates as described above, so that the artificial defect corresponding to the nonmetallic inclusions affects the life of the rolling bearing. The degree of influence can be obtained quantitatively. In other words, the reliability of the degree of influence obtained in this way can be sufficiently ensured.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a first example of an embodiment of an orbiting ring (inner ring) with an artificial defect of the present invention, in which an inner diameter of a hole is exaggerated.
FIG. 2 is an enlarged view of a portion A in FIG.
FIG. 3 is a side view showing a second example of the embodiment of the orbital ring (inner ring) with artificial defects of the present invention, in which the inner diameter of the hole is exaggerated.
FIG. 4 is a partial cross-sectional view showing the third example in which the inner diameter of a hole is exaggerated.
FIG. 5 is a side view showing a conventional orbital ring (outer ring) with artificial defects in which the inner diameter of a hole is exaggerated.
FIG. 6 is a sectional view taken along line BB of FIG. 5;
FIG. 7 is an enlarged view of a portion C in FIG. 6;
[Explanation of symbols]
1 outer ring
2 Outer ring track
3, 3a, 3b holes
4 Inner ring
5 Inner ring track
6 race rings
7 orbit

Claims

A bearing ring having a raceway formed in a part thereof to constitute a rolling bearing, and a hole is formed from one side of the raceway ring existing across the raceway to the other surface, and a part of the hole is formed. A track ring with an artificial defect, which is disposed below the surface of the track as an artificial defect for causing internal origin type separation in the track.

2. An artificial defect according to claim 1, wherein the raceway is formed on a peripheral surface of the raceway, and one side and the other surface of the raceway present on both sides of the raceway are axially opposite side surfaces of the raceway. Track ring.

A raceway is formed on an axial side surface of the raceway, and one surface and the other surface of the raceway which sandwich the raceway, one surface is an outer peripheral surface of the raceway, and the other surface is the raceway ring. The orbit ring with an artificial defect according to claim 1, which is an inner peripheral surface of the bearing ring.

Provided that a part of the hole is not exposed on the surface of the track, the distance from the surface of the track to the central axis of a part of the hole arranged below the surface of the track is a value within a range of 50 to 500 μm. The orbit ring with artificial defects according to any one of claims 1 to 3, wherein the inner diameter of the hole is a value within a range of 20 to 2000 µm.

A rolling bearing including an outer ring having an outer ring raceway on an inner peripheral surface, an inner ring having an inner ring raceway on an outer peripheral surface, and a plurality of rolling elements rotatably provided between the outer raceway and the inner raceway. A rolling bearing with an artificial defect, wherein at least one of the outer ring and the inner ring is the race with an artificial defect according to any one of claims 1, 2 and 4.

In a rolling bearing comprising a pair of races each having a raceway formed on an axial side surface facing each other and a plurality of rolling elements rotatably provided between the raceways. A bearing bearing with an artificial defect, wherein at least one of the pair of bearing rings is the bearing ring with an artificial defect according to any one of claims 1, 3, and 4.

The rolling bearing with an artificial defect according to claim 5 or 6 is rotated while applying a load, so that the artificial defect is used as a starting point on a track formed on a part of a bearing ring provided with the artificial defect. A method for testing the life of a rolling bearing, wherein the value of the rolling fatigue life of the above-mentioned rolling bearing with artificial defects is determined based on the occurrence of internal origin type peeling.