JP4010276B2

JP4010276B2 - Life test method for bearing ring with artificial defect and rolling bearing with artificial defect and rolling bearing

Info

Publication number: JP4010276B2
Application number: JP2003138997A
Authority: JP
Inventors: 浩道武村
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 2003-05-16
Filing date: 2003-05-16
Publication date: 2007-11-21
Anticipated expiration: 2023-05-16
Also published as: JP2004340808A

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Ｚ₀ ＝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]
BACKGROUND OF THE INVENTION
The life test method of the bearing ring with an artificial defect and the rolling bearing with the artificial defect and the rolling bearing according to the present invention is such that the position and size of the defect existing under the surface of the raceway It is used to examine the occurrence or the effect on the life of the rolling bearing.
[0002]
[Prior art]
In general, the rolling fatigue life of a rolling bearing is defined by the total number of revolutions of the rolling bearing until the initial damage due to material fatigue occurs on the raceway formed on the raceway or the rolling surface of the rolling element. Among such damages on the raceway and rolling surface, the internal origin type separation of the raceway, which is the subject of the present invention, originates from minute defects (non-metallic inclusions) existing under the surface of this raceway. . That is, during the operation of the rolling bearing, every time the rolling element passes on the raceway in the load zone, shear stress repeatedly acts below the surface of the raceway. As a result of this shear stress value becoming particularly large at the defect portion, after a long period of operation, a crack is generated starting from the defect, and this further develops to cause internal origin type separation on the track.
[0003]
As described above, since the internal origin type separation of the raceway starts 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. Therefore, it is important to examine beforehand what kind of influence 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 provided at a desired position (for example, a position where the maximum shearing stress is generated or the vicinity thereof) below the surface of the raceway 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 eliminate such inconveniences, Non-Patent Document 1 describes a technique that employs holes instead of the non-metallic 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 above, as shown in FIGS. 5 to 7, a part of the outer ring 1 constituting the experimental rolling bearing (radial ball bearing in the illustrated example). A hole 3 having a very small inner diameter is formed by electric discharge machining from the outer peripheral surface of the outer ring 1 toward the inner peripheral surface. Thereby, the tip (the upper end in FIGS. 5 to 7) of the hole 3 is disposed below the surface of the outer ring raceway 2 formed on the inner peripheral surface of the outer ring 1. The tip portion of the hole 3 disposed below the surface of the outer ring raceway 2 is used as an artificial defect corresponding to the non-metallic inclusion. In this case, in order to place the artificial defect at a desired position below the surface of the outer ring raceway 2 (for example, a position of about 200 to 300 μm (0.2 to 0.3 mm) below the surface), Regulate the depth of 3. Further, in order to make the artificial defect a desired size, the inner diameter of the hole 3 is restricted {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 ring raceway 2. At the same time, starting from this artificial defect, it is possible to cause internal origin type separation (similar to the case where the defect is a non-metallic inclusion) in a part of the outer ring raceway 2.
[0006]
[Non-Patent Document 1]
Yasuo Murakami, Hiromichi Takemura, Nobuo Takagi, “Proposal of Reproduction Method for Internally Originated 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 conventional technique described in Non-Patent Document 1 described above to an inner ring constituting a radial rolling bearing and to provide an artificial defect below the surface of the inner ring raceway formed on the outer peripheral surface of the inner ring. That is, when the above-described prior art 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 wide space needs to exist on the front side of the surface where holes are formed by electric discharge machining. On the other hand, a sufficiently wide space does not exist on the front side (in the radial direction) of the inner peripheral surface of the inner ring. For this reason, a hole cannot be formed 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-described conventional technology to the inner ring (it cannot be applied unless the structure of the electric discharge machine is improved).
[0008]
In the case of the above-described prior art, it is necessary to regulate the depth of the hole 3 in order to place the tip portion of the hole 3 at a desired position below the surface of the outer ring raceway 2. However, the electrode (wire) for electric discharge machining used to form the hole 3 has a situation that the tip portion is gradually consumed (shortened) as the hole 3 is formed by the electric discharge machining. . For this reason, when the hole 3 is formed, the electrode is inserted inside the hole 3 while being displaced in the direction of insertion / removal with respect to the hole 3, thereby reducing the amount of insertion from the insertion amount at the time of insertion. It is necessary to confirm the depth of the hole 3 by calculating back the depth of 3. However, when the hole 3 is formed in this manner, the inner diameter of the hole 3 becomes larger than necessary as the electrode is displaced in the direction of inserting / removing the electrode inside the hole 3. For this reason, it becomes difficult to form the hole 3 having a small inner diameter as desired. Further, as shown in detail in FIG. 7, the shape of the tip of the hole 3 becomes a slightly different tapered shape each time the hole 3 is formed (not an ideal hemispherical or cylindrical shape). Thus, if the shape of the tip of the hole 3 which is an artificial defect is different every time the hole 3 is formed (although slightly), an experimental rolling bearing having such a hole 3 is used. It is difficult to ensure the reliability of the degree of influence (and the life of the rolling bearing) of the artificial defect measured on the occurrence of internal origin-type peeling. 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 prior art, when a rolling bearing for an experiment that is loaded only with a radial load is formed, the formation position of the hole 3 with respect to the outer ring 1 is set to the center in the width direction of the outer ring raceway 2. However, it is difficult to determine an appropriate formation position of the hole 3 with respect to the outer ring 1 in the case of making a product that is loaded with not only a radial load but also an axial load or the like. That is, even if the formation position of the hole 3 is slightly deviated from the direction in which the load is applied, it is difficult for internal origin type peeling to occur, and it is impossible to ensure reliability of the life test. 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 an artificial defect and the rolling bearing with an artificial defect and the life test method of the rolling bearing according to the present invention have been invented to eliminate the above-mentioned disadvantages.
[0010]
[Means for Solving the Problems]
Of the bearing ring with artificial defects and the life test method for rolling bearings with artificial defects and rolling bearings according to the present invention, the bearing ring with artificial defects according to claim 1 constitutes a rolling bearing. It is a formed race. Then, a hole is formed from one side of the raceway ring to the other side across the raceway, and a part of the hole is formed under the surface of the raceway to cause internal origin type separation on the raceway. It is arranged as an artificial defect.
[0011]
In particular, in the case of the raceway 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 side of the raceway ring existing across the raceway are , Respectively, are both side surfaces in the axial direction of the race. Such a bearing ring with artificial defects according to claim 2 is for a radial rolling bearing.
When such a bearing ring with artificial defects described in claim 2 is applied to an inner ring constituting a single row deep groove type radial ball bearing, for example, as shown in FIGS. Of the inner ring raceway 5 formed on the surface, a part of the inner ring 4 is formed in a state of penetrating in the axial direction (left and right direction in FIGS. 1 and 2) by electric discharge machining under at least one surface in the circumferential direction. The intermediate part of the hole 3a is arranged. And the intermediate part of this hole 3a is utilized as said artificial defect. Further, when such artificial defects are provided below the surface of a plurality of circumferential directions of the inner ring raceway 5, for example, as shown in FIG. 3, a plurality of circumferential positions of the inner ring 4 (in the illustrated example, The

holes

3a and 3a as described above are formed at four positions at equal intervals in the circumferential direction. Regardless of the number of 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 the axial direction. The direction of inclination is the direction in which the load is applied, and is controlled so that a part of the hole 3a is closest to the inner ring raceway 5.
[0012]
On the other hand, in the case of the bearing ring with an artificial defect described in claim 3, the track is formed on the side surface in the axial direction of the track ring, and one surface of the track ring and the other that are present across the track. Of the surfaces, one surface is the outer peripheral surface of the race and the other surface is the inner periphery of the race. Such a bearing ring with artificial defects described in claim 3 is for thrust rolling bearings.
When such a bearing ring with an artificial defect described in claim 3 is applied to, for example, any one of the bearing rings constituting the thrust ball bearing, for example, as shown in FIG. Of the raceway 7 formed on one side surface (upper side surface in FIG. 4), a portion of the raceway ring 6 is radiated in the radial direction (left-right direction in FIG. 4) by electric discharge machining under at least one surface in the circumferential direction. An intermediate portion of the hole 3b formed so as to penetrate through is disposed. And the intermediate part of this hole 3b is utilized as said artificial defect. Although not shown in the drawings, when such artificial defects are provided below the surface of the track 7 at a plurality of locations in the circumferential direction, the track 6 is provided at a plurality of locations in the circumferential direction (for example, with respect to the circumferential direction). The holes 3b as described above are formed at equal intervals. Also in this example, the formation direction of the hole 3b may coincide with the radial direction of the raceway ring or may be inclined with respect to the radial direction. The direction of inclination is regulated according to the direction of action of the load.
[0013]
In addition, when the rolling bearing with an artificial defect described in claim 4 is used to implement the rolling bearing with an artificial defect according to any one of claims 1 to 3, a part of the hole is formed on the surface of the track. On the condition that it 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 arranged below the surface of this track is 50 to 500 μm (0.05 to 0.5 mm). ) (In the range corresponding to the position where the maximum shear stress occurs or in the vicinity thereof), and the inner diameter D of the hole (see FIG. 2) 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 non-metallic inclusion).
[0014]
Further, the rolling bearing with an artificial defect described in claim 5 is similar to a conventionally known radial rolling bearing, 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 these outer rings. A plurality of rolling elements provided between the raceway and the inner ring raceway so as to be freely rollable;
In particular, in the rolling bearing with an artificial defect according to claim 5, at least one of the outer ring and the inner ring has the artificial ring according to any one of

claims

1, 2, and 4. It is a bearing ring with defects.
[0015]
Further, the rolling bearing with an artificial defect described in claim 6 is similar to a conventionally known thrust rolling bearing, and a pair of race rings each having a raceway formed on a side surface facing each other, and between these raceways. And a plurality of rolling elements provided so as to be freely rollable.
In particular, in the rolling bearing with an artificial defect described in claim 6, at least one of the pair of track rings is the artificial ring according to any one of

claims

1, 3, and 4 described above. It is a bearing ring with defects.
[0016]
Further, the rolling bearing life test method described in claim 7 is provided with artificial defects by rotating the rolling bearing with artificial defects described in claim 5 or 6 while applying a load. Calculate the rolling fatigue life value of the above-mentioned rolling bearing with artificial defects based on the internal origin type separation starting from this artificial defect on the raceway formed in a part of the raceway (measure the rolling fatigue life) To do).
[0017]
[Action]
As described above, in the case of the bearing ring with an artificial defect and the rolling bearing with an artificial defect of the present invention, one side surface of the bearing ring (in the case of a radial rolling bearing, 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 in the axial direction, or the inner peripheral surface in the case of a thrust rolling bearing). A part of the hole formed in this way is used as an artificial defect. A sufficiently wide space is secured on the front side of one side of the race. Therefore, regardless of the type of bearing ring (in the case of radial rolling bearings, regardless of whether the bearing ring is an outer ring or an inner ring), the hole is easily formed in this bearing ring by electric discharge machining. I can do it.
[0018]
Further, in the case of the present invention, if a part of the hole passes below the surface of the track, it is not necessary to regulate the depth of the hole. For this reason, the hole forming operation for the raceway is different from the above-described prior art (that is, without displacing the electrode for electric discharge machining inside the hole), and can be performed at once. Accordingly, the hole can be formed quickly, and the inner diameter of the hole can be prevented from being unnecessarily widened to form a hole having a desired small inner diameter. In addition, since the intermediate part of the hole can be formed in the same shape (for example, a cylindrical shape) every time the hole is formed, if the intermediate part of the hole is used as an artificial defect, the shape of the artificial defect is changed. It can be stabilized.
[0019]
Therefore, in the case of the bearing ring with artificial defect and the rolling bearing with artificial defect according to the present invention, the desired position under the surface of the raceway formed on the peripheral surface of the raceway is set to a desired position regardless of the type of the raceway. Artificial defects having a shape and size can be provided. Further, as shown in the examples described later, starting from this artificial defect, it is possible to cause internal origin type separation (similar to the case where the defect is a non-metallic inclusion) in a part of the track. In addition, since the hole is formed so as to cross the track, even if the acting direction of the load on the track is slightly deviated, an artificial defect exists in the acting direction of the load. Therefore, even if this action direction is slightly deviated, it is possible to reliably generate the internal origin-type separation from the artificial defect portion.
[0020]
That is, in the case of the present invention, since a part of the hole formed from one axial end surface to the other axial end surface of the bearing ring or from the outer peripheral surface to the inner peripheral surface is used as a defect, Not only rolling bearings that are loaded only, but also rolling bearings that are loaded with both radial and axial loads, and rolling bearings that are loaded only with axial loads, a part of the hole (any of the axial directions) ) Function as an artificial defect. In this case, which portion of the hole functions as an artificial defect can be confirmed by examining the position of the internal origin type peeling that occurs in the track. If the point of action of the load is off the bottom of the track, and if it is necessary to provide an artificial defect as close to this point of action as possible, a part of the hole can be The part corresponding to the action point is made to be closest to the trajectory.
[0021]
In the case of the rolling bearing life test method of the present invention, since the rolling bearing with artificial defects as described above is used as the rolling bearing for testing, the position and size of the artificial defects corresponding to the inclusions are determined. Can be controlled and simulated. Therefore, the reliability of the measured rolling fatigue life can be sufficiently secured.
[0022]
【Example】
An experiment conducted for confirming the effect of the present invention will be described. In this experiment, as shown in Table 1 below, a rolling bearing with artificial defects of the present invention (Examples 1 to 7) and a conventional rolling bearing (without artificial defects) (Comparative Example 1) were prepared. In each of these, it was investigated whether or not proper internal origin-type separation (including damage associated with this internal origin-type separation) could be caused on the track.
[Table 1]

[0023]
In this experiment, each of the rolling bearings (Examples 1 to 7 and Comparative Example 1) is a single-row deep groove type radial ball bearing (JIS nominal number 6206: inner diameter = 30 mm, outer diameter = a kind of radial rolling bearing). 62 mm, width = 16 mm) was adopted. Moreover, although bearing steel was used as the bearing material, in Examples 1 to 7 as such bearing steel, the oxygen content in the steel is 7 ppm or less, and the cleanliness is high (starting from non-metallic inclusions). In Comparative Example 1, the amount of oxygen in the steel is 15 ppm, and the degree of cleanliness is lower than that of SUJ2, which is a general bearing steel (separation starts from non-metallic inclusions). Easy to use). Further, for the outer ring and the inner ring constituting each of the rolling bearings (Examples 1 to 7 and Comparative Example 1), after heating and oil cooling at 820 to 870 ° C., further tempering treatment was performed. The outer ring raceway and the inner ring raceway were finished and polished. Thereby, the surface hardness of these outer ring raceway and inner ring raceway was set to Hv650-750, and the surface roughness was also set to 0.01-0.04 μmRa. Further, the radius of curvature of the generatrix of the outer ring raceway and the inner ring raceway (cross-sectional shape at the cut surface including the central axis) is set to the diameter of each ball constituting each rolling bearing (Examples 1 to 7 and Comparative Example 1). The size was 52%.
[0024]
In Examples 1 to 7, an artificial defect which is a characteristic part of the present invention was provided below the surface of the inner ring raceway. For this purpose, as shown in FIGS. 1 and 2, the inner ring 4 is formed on the inner ring raceway 5 formed on the outer circumferential surface of the inner ring 4 at a desired position below at least one surface in the circumferential direction. An intermediate portion of a hole 3a having a desired inner diameter formed so as to penetrate the portion in the axial direction was disposed. And the intermediate part of this hole 3a was made into the said artificial defect. The hole 3a was formed by electric discharge machining, and a tungsten wire was used as an electrode for performing electric discharge machining. Further, in each of the first to seventh embodiments, the inner diameter D of the hole 3a, the distance L from the central portion (bottom) in the width direction of the inner ring raceway 5 to the central axis of the hole 3a, and the inner ring 4 The number of the holes 3a formed in each is as shown in Table 1 above. Of these, in the case of Example 6 and Example 7 in which the number of holes 3a formed in the inner ring 4 is plural, the arrangement positions of the holes 3a with respect to the inner ring 4 are determined with respect to the circumferential direction, etc. The interval. Further, the generation position of the maximum shear stress in calculation is the depth Z from the surface of the inner ring raceway 5. ₀ = 120 μm (0.12 mm).
[0025]
Next, a specific experimental method performed using each of the above 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 one. And each of these rolling bearings (Examples 1 to 7 and Comparative Example 1) is loaded with a radial load F. _r = 7500N (P / C _r = 0.38), rotation speed = 10000 min ^-1 Whether or not the inner ring raceway 5 can cause the desired internal origin type separation. For this reason, during the operation of each of the above-described rolling bearings (Examples 1 to 7 and Comparative Example 1), the vibration amplitude 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 when the ratio became five times, and it was examined whether or not the inner ring type separation occurred on the inner ring raceway 5. In addition, the calculated life L of each of the above rolling bearings (Examples 1 to 7 and Comparative Example 1) _CAL Is 30 hours (hr), and about five times 150 hours (hr) was taken as the experiment abort time. The results of the experiment conducted in this way are shown in Table 1 above.
[0026]
First, in Example 1, no internal origin-type peeling was observed on the inner ring raceway 5 even when 150 hours (hr), which is the test abort time, was reached. However, as a result of observing the cross section of the surface layer portion of the inner ring raceway 5 after the truncation, a fatigue crack propagates 30 μm from the artificial defect toward the surface under the surface of the central portion in the width direction of the inner ring 5. Further, a structural change called butterfly, which was associated with the above internal origin type peeling, was also confirmed. Therefore, in Example 1, it was found that the internal origin type separation can be reproduced on the inner ring raceway 5.
[0027]
Next, in Example 2, separation occurred on the inner ring raceway 5 in 120 hours (hr). Further, as a result of observing the cross section of the surface layer portion of the inner ring raceway 5 at the part where the separation occurred, fatigue cracks propagated from the artificial defects existing under the surface of the inner ring raceway 5, and this reached the part where the separation occurred. Therefore, it was confirmed that this peeling was an internal origin type peeling starting from the artificial defect. Thus, in Example 2, it was found that the internal origin type separation can be reproduced on the inner ring raceway 5.
[0028]
Next, for Examples 3, 4, and 5 (each of which the distance from the surface of the center portion in the width direction of the inner ring raceway 5 to the edge on the near side of the artificial defect is set to 100 μm (0.1 mm)), In each case, the inner ring raceway 5 was separated before 150 hours (hr), which was the operation stop time. Then, as a result of cross-sectional observation of the surface layer portion of the inner ring raceway 5 at the portion where the separation occurred, the separation is an internal origin type separation starting from the artificial defect, as in the case of Example 2 described above. Things were confirmed. As is clear from the experimental results of Examples 3, 4, and 5, when the distance from the surface of the central portion in the width direction of the inner ring raceway 5 to the edge on the near side of the artificial defect is equal (100 μm) The operation until the internal origin type peeling occurs as the diameter of the artificial defect (inner diameter of the hole 3a) increases to 200 μm (Example 3), 500 μm (Example 4), and 2000 μm (Example 5). It can be seen that the time is shortened to 67 hours (hr) (Example 3), 29 hours (hr) (Example 4), and 11 hours (hr) (Example 5). In any case, from these experimental results, it was found that in Examples 3, 4, and 5, the internal origin type separation can be reproduced on the inner ring raceway 5, respectively.
[0029]
Next, in Examples 6 and 7, separation occurred in the inner ring raceway 5 before 150 hours (hr), which is the operation stop time. Then, as a result of cross-sectional observation of the surface layer portion of the inner ring raceway 5 at the portion where the separation occurred, the separation is an internal origin type separation starting from the artificial defect, as in the case of Example 2 described above. Things were confirmed. Further, as is apparent from comparing the experimental results of Example 6 and Example 2 and comparing the experimental results of Example 7 and Example 4, the diameter of the artificial defect (the inner diameter of the hole 3a) is clear. In the case where they are equal, it can be seen that as the depth (distance L) of the artificial defect from the surface of the inner ring raceway 5 increases, the operation time until the internal origin type separation occurs increases. In any case, from these experimental results, in Examples 6 and 7, it was found that the internal origin type separation can be reproduced on the inner ring raceway 5, respectively.
[0030]
Next, with respect to Comparative Example 1, no internal origin-type separation was observed on the inner ring raceway 5 in appearance even when 150 hours (hr), which is the test abort time, was reached. Further, a cross-sectional observation of the surface layer portion of the inner ring raceway 5 was performed, but fatigue cracks and the butterfly described above were not confirmed under the surface of the inner ring raceway 5. As described above, in Comparative Example 1, it was impossible to reproduce the internal origin type separation on the inner ring raceway 5. Despite the reason why such an experimental result was obtained, that is, the comparative example 1 used a bearing steel having a low cleanliness (a non-metallic inclusion as a starting point and easily peeled), the inner ring raceway described above. The reason why internal origin type separation could not be reproduced in Fig. 5 is that even when a bearing steel having a low cleanliness is used, there is a low possibility that nonmetallic inclusions can be arranged at the position where the maximum shear stress is generated (actually This is because it could not be arranged in Comparative Example 1. Such a fact has been conventionally known, but could be confirmed again by the experimental result of Comparative Example 1.
[0031]
In the above-described embodiment, the artificial defect is provided only under the surface of the inner ring raceway, but the same action and effect can be obtained even when the artificial defect is provided under the surface of the outer ring raceway. In addition, the bearing material is not limited to two types of bearing steel (SUJ2), and the same action and effect can be obtained even when various materials such as a case-hardening material are used. In the above-described embodiments, the present invention is applied to a single row deep groove type radial ball bearing. However, the present invention is not limited to a single row deep groove type radial ball bearing, and includes, for example, an angular type ball bearing, a cylindrical roller bearing, and a tapered roller. The present invention can be applied to various types of rolling bearings such as a bearing and a double row rolling bearing. In the above-described embodiment, the radial rolling bearing is adopted as the rolling bearing. However, the same operation and effect can be obtained even when the thrust rolling bearing is adopted. In this case, when applied to any rolling bearing, a part of the hole is placed at a desired position below the surface of a part of the raceway (for example, inclined in parallel with a part of the raceway or according to the direction of the load application). If it is arranged, it is possible to cause internal origin type peeling in a part of the track starting from a part of the hole (artificial defect).
[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 a part of the surface of the track. Then, using this artificial defect as a starting point, it is possible to cause (reproduce) an internal starting type peeling in a part of the trajectory. Therefore, for example, the maximum diameter of nonmetallic inclusions contained in the stress volume (volume of the portion where the maximum shear stress is generated) in one rolling bearing in 100 ton-melted steel is calculated as an extreme value statistic. Further, if an artificial defect having the same size as the maximum diameter is arranged at a position where the maximum shear stress is generated below the surface of the raceway formed on the peripheral surface of the raceway ring, the non-metallic inclusions are caused by the rolling bearing. The degree of influence on the rolling fatigue life can be quantitatively determined.
[0033]
【The invention's effect】
Since the life test method of the bearing ring with artificial defects and the rolling bearing with artificial defects and the rolling bearing according to the present invention is configured and operates as described above, the artificial defects corresponding to non-metallic inclusions contribute to 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 secured.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a first example of an embodiment of an orbital ring with an artificial defect (inner ring) according to the present invention, exaggerating the inner diameter of a hole.
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 raceway (inner ring) with artificial defect according to the present invention, exaggerating the inner diameter of the hole.
FIG. 4 is a partial cross-sectional view showing the third example exaggerating the inner diameter of a hole.
FIG. 5 is a side view showing a conventional bearing ring with an artificial defect (outer ring) with an exaggerated inner diameter of a hole.
6 is a cross-sectional view taken along the line BB in FIG.
7 is an enlarged view of a portion C in FIG.
[Explanation of symbols]
1 outer ring
2 Outer ring raceway
3, 3a, 3b hole
4 inner ring
5 Inner ring raceway
6 race rings
7 orbit

Claims

In order to constitute a rolling bearing, a raceway in which a raceway is formed in a part thereof, a hole is formed from one side of this raceway ring that is located across the raceway to the other side, and a part of this hole is formed. A track ring with an artificial defect placed under the surface of the track as an artificial defect for causing internal origin type separation on the track.

The track with the artificial defect according to claim 1, wherein the raceway is formed on a peripheral surface of the raceway ring, and one side and the other side of the raceway ring sandwiching the raceway are both side surfaces in the axial direction of the raceway ring. Race ring.

The raceway is formed on the side surface in the axial direction of the raceway, and one side of this raceway ring that exists across this raceway and the other side is the outer peripheral surface of this raceway ring, and the other side is this raceway ring. The track ring with an artificial defect according to claim 1, which is an inner peripheral surface of the ring.

On the condition 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 the part of the hole arranged below the surface of the track is a value within the range of 50 to 500 μm. The track ring with artificial defects according to any one of claims 1 to 3, wherein an inner diameter of the hole is set to a value within a range of 20 to 2000 µm.

A rolling bearing comprising 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 provided between the outer ring raceway and the inner ring raceway so as to roll freely. A rolling bearing with an artificial defect, wherein at least one of the outer ring and the inner ring is the bearing ring with an artificial defect according to any one of claims 1, 2, and 4.

In a rolling bearing comprising a pair of race rings each having a raceway formed on each of opposite axial side surfaces, and a plurality of rolling elements provided between the raceways so as to be freely rollable, the above 1 A rolling 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.

By turning the rolling bearing with an artificial defect according to claim 5 or 6 while applying a load, the artificial defect is set as a starting point on a track formed in a part of the raceway ring provided with the artificial defect. A rolling bearing life test method for determining a rolling fatigue life value of the artificial bearing-equipped rolling bearing based on causing internal origin type separation.