JP4557240B2

JP4557240B2 - Induction hardening method and gear

Info

Publication number: JP4557240B2
Application number: JP2001217613A
Authority: JP
Inventors: 純一合屋; 潤藤江
Original assignee: Neturen Co Ltd
Current assignee: Neturen Co Ltd
Priority date: 2001-07-18
Filing date: 2001-07-18
Publication date: 2010-10-06
Anticipated expiration: 2021-07-18
Also published as: JP2003027143A

Description

【０００１】
【発明の属する技術分野】
本発明は、歯先のうち歯すじ方向一端部を除いた他の部分を硬化させると共に歯底も硬化させるように歯車を高周波焼入れする高周波焼入方法及び歯車に関する。
【０００２】
【従来の技術】
従来から、様々な産業装置（機械）において、様々な歯車が使用されている。
歯車を製造する際には、一般に、その耐摩耗性や強度などを向上させるために、歯先、歯面、及び歯底を高周波焼入れしてこれらに硬化層を形成する。
【０００３】
ところで、様々な歯車のなかには、歯先のうち歯すじ方向一端部を除いた他の部分を硬化させるように高周波焼入れされるものがある。このような歯車では、歯先のうち歯すじ方向一端部は硬化されないので、通常、この一端部は高周波焼入れ後に機械加工される。
【０００４】
歯車の歯先のうち歯すじ方向一端部を硬化しないようにこの歯車を高周波焼入れする場合、上記の歯すじ方向一端部を除いた他の部分に誘導加熱コイルを接近させ、この他の部分を焼入温度に加熱して急冷する。この場合、歯面も歯底も焼入温度に加熱されて急冷される。しかし、歯先のうち歯すじ方向一端部には誘導加熱コイルが接近していないので、この歯すじ方向一端部に対応する歯底の部分も焼入温度に加熱されない。従って、この歯底の部分は硬化されにくい。即ち、この歯底の部分が硬化される面積は、歯先のうち歯すじ方向一端部を除いた他の部分が硬化される面積よりも狭くなる。
【０００５】
【発明が解決しようとする課題】
上記のように歯底のうち歯すじ方向一端部が硬化されにくい場合、その分、歯底の強度が低下して歯車の強度が低下することとなる。歯底の全て（全領域）を硬化して歯車の強度を向上させるためには、歯先の全面に誘導加熱コイルを接近させてこの全面を焼入温度に加熱する。しかし、このようにして歯先の全面を硬化させた場合、焼入れ後に、歯先の歯すじ方向一端部を非常に機械加工しにくい。
【０００６】
本発明は、上記事情に鑑み、歯先の歯すじ方向一端部を硬化させずに歯底を広い領域に渡って硬化させて歯車の強度を向上させる高周波焼入方法、及び強度を向上した歯車を提供することを目的とする。
【０００７】
【課題を解決するための手段】
上記目的を達成するための本発明の高周波焼入方法は、歯車の歯先のうち歯すじ方向一端部を除いた他の部分を硬化させると共に歯底及び歯面も硬化させるように前記歯車を高周波焼入れする高周波焼入方法において、
（１）前記歯先の前記他の部分に誘導加熱コイルを接近させて該他の部分、前記歯底、及び前記歯面を所定の予熱温度になるように誘導加熱し、この誘導加熱の直後に、
（２）前記歯車を所定の放冷時間だけ放冷し、この放冷の直後に、
（３）前記所定の予熱温度よりも高い所定の焼入温度になるように前記歯先の前記他の部分、前記歯底、及び前記歯面を誘導加熱し、
（４）前記歯先の前記他の部分、前記歯底、及び前記歯面を急冷して該他の部分、該歯底、及び該歯面を硬化することを特徴とするものである。
【０００８】
ここで、
（５）前記歯車を前記所定の放冷時間だけ放冷する際に、１秒間以上５秒間以下の範囲内の放冷時間だけ放冷してもよい。
【０００９】
また、
（６）前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の予熱温度に加熱する予熱時間は、前記所定の放冷時間よりも長い時間であり、
（７）前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の焼入温度に加熱する本加熱時間は、前記放冷時間と同じ時間若しくは該放冷時間よりも長い時間であり、前記予熱時間と同じ時間若しくは該予熱時間よりも短い時間であってもよい。
【００１０】
さらに、
（８）前記予熱時間を３乃至４としたときに、前記放冷時間は１乃至２となり、前記本加熱時間は２乃至３となるような比で、前記予熱時間、前記放冷時間、及び前記本加熱時間を設定してもよい。
【００１１】
さらにまた、
（９）前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の予熱温度になるように誘導加熱する際の周波数、及び、前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の焼入温度になるように誘導加熱する際の周波数を、２０ｋＨｚ以上４０ｋＨｚ以下の周波数に設定してもよい。
【００１２】
さらにまた、
（１０）前記周波数を２５ｋＨｚ以上３５ｋＨｚ以下の周波数に設定してもよい。
【００１３】
また、上記目的を達成するための本発明の歯車は、
（１１）歯すじ方向一端部に所定幅の未硬化部分が形成された歯先と、
（１２）前記所定幅と略同じ幅であって前記歯先の未硬化部分に連続する未硬化部分が形成された歯面と、
（１３）前記所定幅と略同じ幅であって前記歯面の未硬化部分に連続する未硬化部分が形成された歯底とを備えたことを特徴とするものである。
【００１４】
ここで、
（１４）前記歯先の未硬化部分は、機械加工代であってもよい。
【００１５】
【発明の実施の形態】
図面を参照して本発明の実施形態を説明する。
【００１６】
先ず、本発明の高周波焼入方法の一実施形態によって高周波焼入れされる歯車について、図１と図２を参照して説明する。
【００１７】
図１は、高周波焼入れの対象になる歯車を示す平面図である。図２は、歯車の一部を示す斜視図である。
【００１８】
歯車１０の歯部２０には、この歯部２０の外側に向いた歯先２２と歯底２４が交互に形成されている。歯先２２と歯底２４は、底部１２の厚さ方向（歯すじ方向。図２の矢印Ｂ方向であり、図１の紙面に垂直な方向である。）に延びている。なお、歯車１０は鋼製であり、Ｓ４５Ｃ（ＪＩＳ）から作製されている。
【００１９】
歯車１０を高周波焼入れするに当っては、歯先２２のうち歯すじ方向の一端部２２ａ（図２の斜線で示す領域）を硬化させず、他の部分２２ｂを硬化させる。
また、歯底２４は出来るだけ広い領域にわたって硬化させる。
【００２０】
図３と図４を参照して、歯車１０の歯部２０を高周波焼入れする方法を説明する。
【００２１】
図３は、歯車の歯部とこの歯部に接近させた誘導加熱コイルの一部を示す側面図である。図４は、歯部を誘導加熱して急冷するときのヒートパターンを示すグラフである。
【００２２】
歯車１０を高周波焼入れするに際しては、図３に示すように、歯車１０を治具４０に固定する。治具４０に固定された歯車１０の歯先２２の他の部分２２ｂに環状の誘導加熱コイル５０を接近させる。上記のように歯先２２の他の部分２２ｂに誘導加熱コイル５０を接近させた状態で誘導加熱コイル５０に高周波電流を通し、歯先２２の他の部分２２ｂ、歯面２３ｂ、及び歯底２４が所定の予熱温度になるように所定の予熱時間だけ加熱（予熱）する。ここでは、図５に示すように、歯先２２の他の部分２２ｂを９０８℃に加熱し、歯底２４を８９７℃に加熱した。また、誘導加熱の際の周波数を３０ｋＨｚとし、予熱時間を３．５秒間とした。
【００２３】
上記のようにして歯先２２の他の部分２２ｂ、歯面２３ｂ、及び歯底２４が所定の予熱温度に加熱された後、誘導加熱コイル５０に高周波電流を通さずに歯先２２の他の部分２２ｂ、歯面２３ｂ、及び歯底２４を所定の放冷時間（２秒間）だけ放冷した。この放冷によって、歯先２２の他の部分２２ｂ、歯面２３ｂ、及び歯底２４の温度は、約６５０〜６８０℃の範囲内の温度まで下がった。
【００２４】
上記の放冷の後、直ちに、誘導加熱コイル５０に高周波電流を通し、歯先２２の他の部分２２ｂ、歯面２３ｂ、及び歯底２４を所定の焼入温度に所定の時間（本加熱時間）だけ加熱した。ここでは、図５に示すように、歯先２２の他の部分２２ｂを１０１５℃に加熱し、歯底２４を１０２６℃に加熱した。また、誘導加熱の際の周波数を３０ｋＨｚとし、本加熱時間を２．５秒間とした。
【００２５】
歯先２２の他の部分２２ｂ、歯面２３ｂ、及び歯底２４が上記の焼入温度に加熱された後、これらの部分に冷却液を噴射してこれらを急冷した。冷却液の噴射量は６０リットル／分であり、１４秒間だけ噴射した。この結果、歯先２２の他の部分２２ｂ、歯面２３ｂ、及び歯底２４に所望の硬化深さをもつ硬化層が形成された。ここでは、限界硬さを４５０（Ｈｖ）としたときの有効硬化層深さは、歯先２２の他の部分２２ｂで２．８ｍｍであり、歯底２４で１．８ｍｍであった。次に、硬化された領域について説明する。
【００２６】
図５を参照して、歯車１０の歯先２２、歯面２３ｂ、及び歯底２４が硬化された領域（硬化領域）について説明する。
【００２７】
図５は、歯先、歯面、及び歯底の硬化領域を示す斜視図であり、斜線部分及びクロス線部分双方が硬化された領域である。
【００２８】
上述したように、高周波焼入れの際には、誘導加熱コイル５０を他の部分２２ｂに接近させる。しかし、歯すじ方向一端部２２ａ（斜線もクロス線も無い部分）に対向する位置には、誘導加熱コイル５０が存在しないので、この一端部２２ａは加熱されにくい。従って、一端部２２ａは硬化されていない。また、この一端部２２ａに連続する歯面２３の一部２３ａ（斜線もクロス線も無い部分）及び歯底２４の一部２４ａ（斜線もクロス線も無い部分）も硬化されていない。一端部２２ａと一部２４ａの歯すじ方向（矢印Ｂ方向）長さはほぼ同じであった。
【００２９】
ところで、上記した実施形態では、歯先２２、歯面２３ｂ、及び歯底２４を焼入温度に加熱するに先立って、これらを予熱して放冷した。この結果、歯底２４では、斜線部分とクロス線部分が硬化された領域となった。これに対し、上記した予熱と放冷を行わずに歯先２２、歯面２３ｂ、及び歯底２４を焼入温度に加熱した場合、歯底２４では斜線部分のみが硬化領域となり、クロス線部分は硬化されない非硬化領域となる。
【００３０】
このように予熱と放冷を行って焼入れをした場合、歯底２４の硬化領域が広くなるので、予熱と放冷を行わない焼入れに比べて歯車１０の強度が向上する。なお、上記の実施形態では予熱の後に放冷を行ったが、放冷時間が長すぎた場合、硬化深さが深くなり過ぎる。また、目的とする硬化深さによっては放冷を行わなくてもよい。
【００３１】
ここで、放冷時間について実験した結果を説明する。
【００３２】
上記した例では、放冷時間を２秒間としたが、放冷時間を種々に変えて実験を行った。この結果、放冷時間が１秒間未満のときは、歯底の硬化領域は狭くなり、歯底の強度は向上しなかった。この理由は、歯底の加熱領域を広げられずこの加熱領域が狭かったからであると考えられる。一方、放冷時間が５秒間を超えるときは、歯先の硬化領域が広くなりすぎた。このため、焼入れ後に歯先を機械加工しにくくなった。この理由は、歯先の加熱領域が広くなりすぎたからだと考えられる。以上の結果、放冷時間は、１秒間以上５秒間以下の範囲内が最適である
【００３３】
次に、予熱時間、放冷時間、及び本加熱時間の関係について実験した結果を説明する。
【００３４】
この実験では、予熱時間を所定の放冷時間よりも長くし、本加熱時間を放冷時間と同じ時間若しくは放冷時間よりも長くすると共に予熱時間と同じ時間若しくは予熱時間よりも短い時間とした。このように予熱時間、放冷時間、及び本加熱時間を設定することにより、歯先の硬化領域に比べて歯底の硬化領域が広くなり、歯底の強度が向上した。
【００３５】
上記した予熱時間、放冷時間、及び本加熱時間を比で表した場合、
予熱時間：放冷時間：本加熱時間＝（３乃至４）：（１乃至２）：（２乃至３）となった。
【００３６】
このような比で表される時間を設定することにより、歯先の硬化領域に比べて歯底の硬化領域がいっそう確実に広くなったので、歯底の強度がいっそう確実に向上した。
【００３７】
また、予熱と本加熱の際に周波数を種々に変えて実験した結果を説明する。
【００３８】
この実験によれば、予熱と本加熱の際の周波数が２０ｋＨｚ未満のときは、歯先の温度が上がり過ぎて歯先の硬化領域が広くなり過ぎたので、焼入れ後における歯先の機械加工が困難になった。一方、周波数が４０ｋＨｚを超えるときは、歯底の温度が十分に加熱されずに歯底の硬化領域が狭くなったので、歯底の強度が低下した。従って、歯先の他の部分、歯底、及び歯面を所定の予熱温度になるように誘導加熱する際の周波数、及び、歯先の他の部分、歯底、及び歯面を所定の焼入温度になるように誘導加熱する際の周波数を、２０ｋＨｚ以上４０ｋＨｚ以下の周波数に設定することにより、歯先と歯底の硬化領域を適宜に広げられる。
【００３９】
また、この実験によれば、上記の周波数を２５ｋＨｚ以上３５ｋＨｚ以下の周波数に設定することにより、歯先の硬化領域がいっそう確実に適切な広さになったので、焼入れ後における歯先の機械加工が容易になった。また、歯底の硬化領域もいっそう適切な広さになったので、歯底の強度が向上した。
【００４０】
なお、上記の周波数を８０ｋＨｚとした場合、予熱では、歯底温度が８６９℃になり、歯先温度は８６７℃になった。放冷後の本加熱では、歯底温度が９８４℃になり、歯先温度は１０２２℃になった。このように本加熱の際に歯先温度が歯底温度よりも高くなったときは歯先の硬化領域が広くなり過ぎるおそれがあり、歯底の硬化領域が狭まるおそれがあるので、都合が悪い。
【００４１】
【発明の効果】
以上説明したように本発明の高周波焼入方法によれば、歯底が所定の予熱温度になるように誘導加熱した後に、この歯車を所定の放冷時間だけ放冷するので、この放冷時間を適宜に選択することにより、歯底が加熱される（歯すじ方向の）領域（加熱領域）を広めたり狭めたりできることとなる。従って、焼入れ後において、歯底が硬化される（歯すじ方向の）領域（硬化領域）を広めたり狭めたりできる。また、放冷後に、歯底を所定の焼入温度に誘導加熱するので、歯底の加熱領域を広めていたときは、歯底は歯すじ方向の広い範囲にわたって焼入温度に加熱され、焼入温度になる加熱領域が広がる。このようにして焼入温度に加熱された歯底を急冷するので、歯底は歯すじ方向の広い範囲にわたって（広い加熱領域で）焼入れされて硬化される。この結果、歯車の強度が向上する。また、歯先のうち歯すじ方向一端部を誘導加熱しないようにしているので、この一端部は硬化されない。従って、焼入れ後に、この一端部を加工し易い。また、歯先の他の部分と歯底とを予熱温度及び焼入れ温度に誘導加熱する際には周知の誘導加熱コイルを使用できるので、歯車を低コストで焼入れできる。
【００４２】
ここで、前記歯車を前記所定の放冷時間だけ放冷する際に、１秒間以上５秒間以下の範囲内の放冷時間だけ放冷する場合は、歯底の硬化領域を最適に広げられる。放冷時間が１秒間未満のときは、歯底の加熱領域を広げられずこの加熱領域は狭くなるので、歯底の硬化領域も狭くなり、歯底の強度は向上しない。一方、放冷時間が５秒間を超えるときは、歯先の加熱領域が広くなりすぎてその硬化領域も広くなりすぎる。この結果、焼入れ後に歯先を機械加工しにくくなる。
【００４３】
また、前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の予熱温度に加熱する予熱時間は、前記所定の放冷時間よりも長い時間であり、前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の焼入温度に加熱する本加熱時間は、前記放冷時間と同じ時間若しくは該放冷時間よりも長い時間であり、前記予熱時間と同じ時間若しくは該予熱時間よりも短い時間である場合は、歯先の硬化領域に比べて歯底の硬化領域が広くなるので、歯底の強度が向上する。
【００４４】
さらに、前記予熱時間を３乃至４としたときに、前記放冷時間は１乃至２となり、前記本加熱時間は２乃至３となるような比で、前記予熱時間、前記放冷時間、及び前記本加熱時間を設定する場合は、歯先の硬化領域に比べて歯底の硬化領域がいっそう確実に広くなるので、歯底の強度がいっそう確実に向上する。
【００４５】
さらにまた、前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の予熱温度になるように誘導加熱する際の周波数、及び、前記歯先の前記他の部分、前記歯底、及び前記歯面を前記所定の焼入温度になるように誘導加熱する際の周波数を、２０ｋＨｚ以上４０ｋＨｚ以下の周波数に設定する場合は、歯先と歯底の硬化領域を適宜に広げられる。周波数が２０ｋＨｚ未満のときは、歯先の温度が上がり過ぎて歯先の硬化領域が広くなり過ぎるので、焼入れ後における歯先の機械加工が困難になる。一方、周波数が４０ｋＨｚを超えるときは、歯底の温度が十分に加熱されずに歯底の硬化領域が狭くなるので、歯底の強度が低下する。
【００４６】
さらにまた、前記周波数を２５ｋＨｚ以上３５ｋＨｚ以下の周波数に設定する場合は、歯先の硬化領域がいっそう確実に適切な広さになるので、焼入れ後における歯先の機械加工が容易になる。また、歯底の硬化領域もいっそう適切な広さになるので、歯底の強度が向上する。
【００４７】
また、本発明の歯車では、歯先、歯面、及び、歯底それぞれの未硬化部分の幅が略同じであるので、歯先のうち歯すじ方向一端部に機械加工などのための未硬化部分を形成しても、強度の高い歯車が得られる。
【図面の簡単な説明】
【図１】高周波焼入れの対象になる歯車を示す平面図である。
【図２】歯車の一部を示す斜視図である。
【図３】歯車の歯部とこの歯部に接近させた誘導加熱コイルの一部を示す側面図である。
【図４】歯部を誘導加熱して急冷するときのヒートパターンを示すグラフである。
【図５】歯先と歯底の硬化領域を示す斜視図である。
【符号の説明】
１０歯車
１２底部
２０歯部
２２歯先
２２ａ歯先の歯すじ方向一端部
２２ｂ歯先の他の部分
２３歯面
２４歯底
５０誘導加熱コイル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an induction hardening method and a gear for induction-hardening a gear so as to harden the other part of the tooth tip excluding one end portion in the streak direction and also harden the tooth bottom.
[0002]
[Prior art]
Conventionally, various gears are used in various industrial devices (machines).
When manufacturing a gear, generally, in order to improve the wear resistance, strength, and the like, the tooth tip, the tooth surface, and the tooth bottom are induction-hardened to form a hardened layer thereon.
[0003]
By the way, among various gears, there is a gear that is induction-hardened so as to harden other portions of the tooth tips excluding one end portion in the streak direction. In such a gear, one end portion in the tooth trace direction of the tooth tip is not hardened. Therefore, this one end portion is usually machined after induction hardening.
[0004]
When this gear is induction-hardened so as not to harden one end portion in the tooth trace direction of the tooth tip of the gear, the induction heating coil is brought close to the other portion except the one end portion in the tooth streak direction, and this other portion is Heat to quenching temperature and quench rapidly. In this case, both the tooth surface and the tooth bottom are heated to the quenching temperature and rapidly cooled. However, since the induction heating coil does not approach one end portion in the tooth trace direction of the tooth tip, the portion of the tooth bottom corresponding to the one end portion in the tooth trace direction is not heated to the quenching temperature. Therefore, the root portion is hard to be hardened. That is, the area where the root part is hardened is narrower than the area where the other part of the tooth tip other than the one end portion in the streak direction is hardened.
[0005]
[Problems to be solved by the invention]
As described above, in the case where one end portion in the tooth trace direction of the tooth bottom is hard to be hardened, the strength of the tooth bottom is lowered correspondingly, and the strength of the gear is lowered. In order to harden the entire tooth bottom (all areas) and improve the strength of the gear, an induction heating coil is brought close to the entire surface of the tooth tip and the entire surface is heated to the quenching temperature. However, when the entire surface of the tooth tip is hardened in this manner, it is very difficult to machine one end portion of the tooth tip in the streak direction after quenching.
[0006]
In view of the above circumstances, the present invention provides a high-frequency quenching method for improving the strength of a gear by hardening the bottom of a tooth over a wide region without hardening one end portion in the streak direction of the tooth tip, and a gear with improved strength. The purpose is to provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the induction hardening method of the present invention is to harden the other part of the tooth tip of the gear except for one end in the streak direction and to harden the tooth bottom and the tooth surface. In the induction hardening method of induction hardening,
(1) An induction heating coil is brought close to the other part of the tooth tip, and the other part, the tooth bottom, and the tooth surface are induction heated so as to reach a predetermined preheating temperature, immediately after the induction heating. In addition,
(2) The gear is allowed to cool for a predetermined cooling time, and immediately after the cooling,
(3) Inductively heating the other part of the tooth tip, the tooth bottom, and the tooth surface so as to have a predetermined quenching temperature higher than the predetermined preheating temperature,
(4) The other portion of the tooth tip, the tooth bottom, and the tooth surface are rapidly cooled to harden the other portion, the tooth bottom, and the tooth surface.
[0008]
here,
(5) When the gear is allowed to cool for the predetermined cooling time, the gear may be allowed to cool for a cooling time within a range of 1 second to 5 seconds.
[0009]
Also,
(6) The preheating time for heating the other portion of the tooth tip, the tooth bottom, and the tooth surface to the predetermined preheating temperature is a time longer than the predetermined cooling time,
(7) The main heating time for heating the other part of the tooth tip, the tooth bottom, and the tooth surface to the predetermined quenching temperature is equal to or longer than the cooling time. It may be the same time as the preheating time or a time shorter than the preheating time.
[0010]
further,
(8) When the preheating time is 3 to 4, the cooling time is 1 to 2, and the main heating time is 2 to 3, and the preheating time, the cooling time, and The main heating time may be set.
[0011]
Furthermore,
(9) Frequency when induction heating the other part of the tooth tip, the tooth bottom, and the tooth surface to the predetermined preheating temperature, and the other part of the tooth tip, the tooth You may set the frequency at the time of carrying out induction heating so that a bottom and the said tooth surface may become the said predetermined quenching temperature to the frequency of 20 kHz or more and 40 kHz or less.
[0012]
Furthermore,
(10) The frequency may be set to a frequency of 25 kHz to 35 kHz.
[0013]
The gear of the present invention for achieving the above object is
(11) A tooth tip in which an uncured portion having a predetermined width is formed at one end of the tooth trace direction;
(12) A tooth surface having an uncured portion that is substantially the same width as the predetermined width and is continuous with the uncured portion of the tooth tip;
(13) A tooth bottom having an uncured portion that is substantially the same as the predetermined width and that is continuous with the uncured portion of the tooth surface is provided.
[0014]
here,
(14) The uncured portion of the tooth tip may be a machining allowance.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0016]
First, a gear that is induction hardened by an embodiment of the induction hardening method of the present invention will be described with reference to FIGS. 1 and 2.
[0017]
FIG. 1 is a plan view showing a gear to be subjected to induction hardening. FIG. 2 is a perspective view showing a part of the gear.
[0018]
In the tooth portion 20 of the gear 10, tooth tips 22 and tooth bottoms 24 facing the outside of the tooth portion 20 are alternately formed. The tooth tip 22 and the tooth base 24 extend in the thickness direction of the bottom portion 12 (the direction of the tooth trace, which is the direction of arrow B in FIG. 2 and the direction perpendicular to the paper surface in FIG. 1). The gear 10 is made of steel and is made of S45C (JIS).
[0019]
When the gear 10 is induction-hardened, one end portion 22a (the region shown by hatching in FIG. 2) of the tooth tip direction of the tooth tip 22 is not cured, and the other portion 22b is cured.
Further, the root 24 is hardened over as wide an area as possible.
[0020]
With reference to FIG. 3 and FIG. 4, the method of induction-hardening the tooth | gear part 20 of the gearwheel 10 is demonstrated.
[0021]
FIG. 3 is a side view showing a tooth portion of the gear and a part of the induction heating coil brought close to the tooth portion. FIG. 4 is a graph showing a heat pattern when the tooth part is induction-heated and rapidly cooled.
[0022]
When the gear 10 is induction hardened, the gear 10 is fixed to a jig 40 as shown in FIG. The annular induction heating coil 50 is brought close to the other portion 22 b of the tooth tip 22 of the gear 10 fixed to the jig 40. As described above, a high-frequency current is passed through the induction heating coil 50 with the induction heating coil 50 approaching the other portion 22b of the tooth tip 22, and the other portion 22b of the tooth tip 22, the tooth surface 23b, and the tooth bottom 24 are passed. Is heated (preheated) for a predetermined preheating time so that becomes a predetermined preheating temperature. Here, as shown in FIG. 5, the other part 22b of the tooth tip 22 was heated to 908 ° C., and the tooth bottom 24 was heated to 897 ° C. The frequency during induction heating was 30 kHz, and the preheating time was 3.5 seconds.
[0023]
After the other portion 22b, the tooth surface 23b, and the tooth bottom 24 of the tooth tip 22 are heated to a predetermined preheating temperature as described above, the other tooth tips 22 are not passed through the induction heating coil 50 without passing a high-frequency current. The portion 22b, the tooth surface 23b, and the tooth bottom 24 were allowed to cool for a predetermined cooling time (2 seconds). By this cooling, the temperature of the other portion 22b of the tooth tip 22, the tooth surface 23b, and the tooth bottom 24 was lowered to a temperature in the range of about 650 to 680 ° C.
[0024]
Immediately after the above cooling, a high-frequency current is passed through the induction heating coil 50, and the other portion 22b of the tooth tip 22, the tooth surface 23b, and the tooth bottom 24 are kept at a predetermined quenching temperature for a predetermined time (main heating time). Only heated). Here, as shown in FIG. 5, the other part 22b of the tooth tip 22 was heated to 1015 ° C., and the tooth bottom 24 was heated to 1026 ° C. The frequency during induction heating was 30 kHz, and the main heating time was 2.5 seconds.
[0025]
After the other part 22b, the tooth surface 23b, and the tooth bottom 24 of the tooth tip 22 were heated to the above quenching temperature, the coolant was sprayed onto these parts to quench them. The amount of cooling liquid sprayed was 60 liters / minute, and sprayed for 14 seconds. As a result, a hardened layer having a desired hardened depth was formed on the other portion 22b of the tooth tip 22, the tooth surface 23b, and the tooth bottom 24. Here, when the limit hardness is 450 (Hv), the effective hardened layer depth is 2.8 mm at the other portion 22 b of the tooth tip 22 and 1.8 mm at the tooth bottom 24. Next, the cured region will be described.
[0026]
With reference to FIG. 5, the area | region (hardening area | region) in which the tooth tip 22, the tooth surface 23b, and the tooth bottom 24 of the gearwheel 10 were hardened is demonstrated.
[0027]
FIG. 5 is a perspective view showing the hardened regions of the tooth tip, the tooth surface, and the tooth bottom, where both the hatched portion and the cross line portion are hardened.
[0028]
As described above, the induction heating coil 50 is moved closer to the other portion 22b during induction hardening. However, since the induction heating coil 50 does not exist at a position facing the one end portion 22a in the tooth trace direction (the portion where neither the oblique line nor the cross line exists), the one end portion 22a is not easily heated. Therefore, the one end 22a is not cured. Further, a part 23a (a part without oblique lines and cross lines) of the tooth surface 23 continuous with the one end 22a and a part 24a (a part without oblique lines and cross lines) of the tooth bottom 24 are not hardened. The lengths of the one end portion 22a and the portion 24a in the tooth trace direction (arrow B direction) were substantially the same.
[0029]
By the way, in above-mentioned embodiment, before heating the tooth tip 22, the tooth surface 23b, and the tooth bottom 24 to quenching temperature, these were preheated and left to cool. As a result, in the tooth bottom 24, the hatched portion and the cross-line portion were hardened. On the other hand, when the tooth tip 22, the tooth surface 23b, and the tooth bottom 24 are heated to the quenching temperature without performing the above preheating and cooling, only the hatched portion becomes a hardened region in the tooth bottom 24, and the cross wire portion. Becomes a non-cured region which is not cured.
[0030]
When quenching is performed by preheating and cooling as described above, the hardened region of the tooth root 24 is widened, so that the strength of the gear 10 is improved as compared with quenching that does not perform preheating and cooling. In the above embodiment, cooling is performed after preheating. However, if the cooling time is too long, the curing depth becomes too deep. Further, the cooling may not be performed depending on the intended curing depth.
[0031]
Here, the results of experiments on the cooling time will be described.
[0032]
In the above example, the cooling time was set to 2 seconds, but the experiment was performed by changing the cooling time in various ways. As a result, when the cooling time was less than 1 second, the hardened area of the root became narrow and the strength of the root did not improve. The reason for this is considered to be that the heating area of the tooth bottom cannot be expanded and the heating area is narrow. On the other hand, when the cooling time exceeded 5 seconds, the hardened area of the tooth tip was too wide. For this reason, it became difficult to machine the tooth tip after quenching. The reason for this is considered that the heating area of the tooth tip has become too wide. As a result, the cooling time is optimally in the range of 1 second to 5 seconds. [0033]
Next, the results of experiments on the relationship between the preheating time, the cooling time, and the main heating time will be described.
[0034]
In this experiment, the preheating time is set longer than the predetermined cooling time, the main heating time is set to the same time as the cooling time or longer than the cooling time, and the same time as the preheating time or shorter than the preheating time. . By setting the preheating time, the cooling time, and the main heating time in this manner, the hardened area of the root becomes wider than the hardened area of the tooth tip, and the strength of the root is improved.
[0035]
When the preheating time, the cooling time, and the main heating time are expressed as a ratio,
Preheating time: Cooling time: Main heating time = (3 to 4): (1 to 2): (2 to 3).
[0036]
By setting the time represented by such a ratio, the hardened area of the root is more surely widened than the hardened area of the tooth tip, so that the strength of the root is further reliably improved.
[0037]
In addition, the results of experiments with different frequencies during preheating and main heating will be described.
[0038]
According to this experiment, when the frequency at the time of preheating and main heating is less than 20 kHz, the temperature of the tooth tip rises too much and the hardened region of the tooth tip becomes too wide. It became difficult. On the other hand, when the frequency exceeded 40 kHz, the temperature of the tooth bottom was not sufficiently heated and the hardened area of the tooth bottom was narrowed, and the strength of the tooth bottom was lowered. Therefore, the frequency at which the other part of the tooth tip, the tooth bottom, and the tooth surface are inductively heated to a predetermined preheating temperature, and the other part of the tooth tip, the tooth bottom, and the tooth surface are subjected to predetermined firing. By setting the frequency at the time of induction heating to a temperature of 20 kHz or more and 40 kHz or less, the hardened region of the tooth tip and the root can be appropriately expanded.
[0039]
Further, according to this experiment, since the above-mentioned frequency is set to a frequency of 25 kHz or more and 35 kHz or less, the hardened region of the tooth tip is more surely appropriate, so that the machining of the tooth tip after quenching is performed. Became easier. In addition, since the hardened region of the tooth root has become more appropriate, the strength of the tooth root has been improved.
[0040]
In addition, when said frequency was 80 kHz, in preheating, tooth root temperature became 869 degreeC and tooth tip temperature became 867 degreeC. In the main heating after cooling, the tooth bottom temperature was 984 ° C. and the tooth tip temperature was 1022 ° C. In this way, when the tooth tip temperature becomes higher than the tooth bottom temperature during the main heating, there is a possibility that the hardened region of the tooth tip becomes too wide and the hardened region of the tooth base may be narrowed, which is inconvenient. .
[0041]
【The invention's effect】
As described above, according to the induction hardening method of the present invention, this gear is allowed to cool for a predetermined cooling time after induction heating so that the tooth bottom has a predetermined preheating temperature. By selecting appropriately, it becomes possible to widen or narrow the region (heating region) where the tooth bottom is heated (in the direction of the tooth trace). Therefore, after quenching, the region (cured region) in which the tooth bottom is cured (in the direction of the streaks) can be widened or narrowed. In addition, since the bottom of the tooth is induction-heated to a predetermined quenching temperature after being allowed to cool, when the heating area of the root is widened, the bottom of the tooth is heated to the quenching temperature over a wide range in the direction of the tooth trace. The heating area that reaches the input temperature is expanded. In this way, the tooth bottom heated to the quenching temperature is rapidly cooled, so that the tooth bottom is quenched and hardened over a wide range (in a wide heating region) in the tooth trace direction. As a result, the strength of the gear is improved. Further, since one end portion in the tooth trace direction of the tooth tip is not induction-heated, this one end portion is not hardened. Therefore, it is easy to process this one end after quenching. In addition, when the other portion of the tooth tip and the tooth bottom are induction-heated to the preheating temperature and the quenching temperature, a known induction heating coil can be used, so that the gear can be quenched at a low cost.
[0042]
Here, when the gear is allowed to cool for the predetermined cooling time, if it is allowed to cool for a cooling time within a range of 1 second or more and 5 seconds or less, the hardened region of the tooth root can be expanded optimally. When the cooling time is less than 1 second, the heating area of the root cannot be expanded and the heating area becomes narrow, so that the hardening area of the root becomes narrow and the strength of the root does not improve. On the other hand, when the cooling time exceeds 5 seconds, the heating area of the tooth tip becomes too wide and the hardening area becomes too wide. As a result, it becomes difficult to machine the tooth tip after quenching.
[0043]
The preheating time for heating the other part of the tooth tip, the tooth bottom, and the tooth surface to the predetermined preheating temperature is longer than the predetermined cooling time, The main heating time for heating the other part, the tooth bottom, and the tooth surface to the predetermined quenching temperature is the same time as the cooling time or a time longer than the cooling time, and the preheating time When the time is the same time or shorter than the preheating time, the hardened region of the tooth base becomes wider than the hardened region of the tooth tip, so that the strength of the tooth base is improved.
[0044]
Further, when the preheating time is 3 to 4, the cooling time is 1 to 2, and the main heating time is 2 to 3, and the preheating time, the cooling time, and the When the main heating time is set, since the hardened area of the tooth base is more reliably widened than the hardened area of the tooth tip, the strength of the tooth base is more reliably improved.
[0045]
Furthermore, the frequency when induction heating the other part of the tooth tip, the tooth bottom, and the tooth surface to the predetermined preheating temperature, and the other part of the tooth tip, the tooth When the frequency at the time of induction heating the bottom and the tooth surface to the predetermined quenching temperature is set to a frequency of 20 kHz or more and 40 kHz or less, the hardened region of the tooth tip and the tooth base can be appropriately expanded. . When the frequency is less than 20 kHz, the temperature of the tooth tip rises too much and the hardened region of the tooth tip becomes too wide, making it difficult to machine the tooth tip after quenching. On the other hand, when the frequency exceeds 40 kHz, the temperature of the tooth bottom is not sufficiently heated, and the hardened area of the tooth bottom is narrowed, so that the strength of the tooth bottom is lowered.
[0046]
Furthermore, when the frequency is set to a frequency of 25 kHz or more and 35 kHz or less, the hardened region of the tooth tip is more surely appropriate and the tooth tip is easily machined after quenching. In addition, since the hardened region of the tooth base becomes a more appropriate area, the strength of the tooth base is improved.
[0047]
In the gear of the present invention, since the widths of the uncured portions of the tooth tip, the tooth surface, and the tooth bottom are substantially the same, the uncured portion for machining or the like at one end portion in the tooth stripe direction of the tooth tip. Even if the portion is formed, a strong gear can be obtained.
[Brief description of the drawings]
FIG. 1 is a plan view showing a gear to be subjected to induction hardening.
FIG. 2 is a perspective view showing a part of a gear.
FIG. 3 is a side view showing a tooth portion of a gear and a part of an induction heating coil brought close to the tooth portion.
FIG. 4 is a graph showing a heat pattern when a tooth part is rapidly heated by induction heating.
FIG. 5 is a perspective view showing a hardened region of a tooth tip and a tooth bottom.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Gear 12 Bottom part 20 Tooth part 22 Tooth tip 22a One end part 22b of tooth tip direction of tooth tip Other part 23 of tooth tip Tooth surface 24 Tooth bottom 50 Induction heating coil

Claims

In the induction hardening method in which the gear is induction-hardened so as to harden the other part of the tooth tip of the gear except the one end portion in the streak direction and also harden the tooth bottom and the tooth surface,
The frequency at the time of induction heating the gear is set to a value of 20 to 40 kHz,
An induction heating coil is brought close to the other part of the tooth tip, and the other part, the tooth bottom, and the tooth surface are induction heated for a predetermined preheating time so as to reach a predetermined preheating temperature. Immediately after
The gear is allowed to cool for a predetermined cooling time, and immediately after this cooling,
Inductively heating the other part of the tooth tip, the tooth bottom, and the tooth surface for a predetermined main heating time so as to have a predetermined quenching temperature higher than the predetermined preheating temperature,
In the induction heating, the cooling time is set to 1 to 5 seconds, and the ratio of the preheating time, the cooling time, and the main heating time is 3-4: 1 to 2: 2 to 3. Set to be
An induction hardening method, wherein the other part of the tooth tip, the tooth bottom, and the tooth surface are quenched to harden the other part, the tooth bottom, and the tooth surface.

The induction hardening method according to claim 1, wherein the frequency is set to a frequency of 25 kHz to 35 kHz.