JP3614508B2 - Linear motion bearing - Google Patents

Description

【００３７】
密度は、アルキメデス方法により測定している。硬度、破壊靭性値は、ビッカース硬度計を用いて測定しており、硬度は図４に示すビッカース圧痕の対角線の長さから算出し、破壊靭性値ＫＩＣは、ＩＦ（Ｉｎｄｅｎｔｉｏｎ Ｆｒａｃｔｕｒｅ）法により下記する新原の式を用いて算出する。曲げ強度は、直接材料の強度を測定するもので、ＪＩＳ Ｒ １６０１規格の３点曲げ強度試験方法を用いている。
【００３８】
新原の式＝０．０１１４Ｅ^０．４Ｐ^０．６ａ^−０．７（Ｃ／ａ−１）^−０．５
但し、Ｐは荷重（Ｋｇｆ）、ｄは圧痕の対角線長（ｍｍ）、Ｅはヤング率（Ｋｇｆ／ｍｍ^２ ）、Ｃは圧痕の中心点から亀裂の長さ（ｍｍ）、ａは圧痕の対角線長の１／２（ｍｍ）である。
【００３９】
ところで、上記製造方法の▲１▼の工程において、従来の高品質な原料を用いてもよい。この高品質な原料とは、例えば平均粒径０．２μｍのα型の窒化けい素の粉末（高グレード品例えば株式会社宇部興産の品種番号Ｅ−１０）に対してイットリア（Ｙ_２Ｏ_３），アルミナ（Ａｌ_２Ｏ_３），窒化アルミ（ＡｌＮ），チタニア（ＴｉＯ_２）などの焼結助剤を１０重量％以下添加したものである。この高品質な原料を用いて上記▲２▼〜▲８▼のような処理を施したものを、中品位セラミックスと称する。
【００４０】
この中品位セラミックス製のボールについて下記試験により評価する。試験は、ボールのスラスト試験、ラジアル試験を行った。
【００４１】
スラスト試験では、図５に示すようなスラスト軸受において、玉サイズを３／８インチ、１／４インチの２種類とし、油浴潤滑とし、軸の回転数を１２００ｒｐｍとし、面圧を３／８インチのものは２９１ｋｇｆ／ｍｍ^２（２．８５ＧＰａ）、１／４インチのものは３１９ｋｇｆ／ｍｍ^２（３．１３ＧＰａ）とした。いずれのサイズのボールも、１０００時間で打ち切ったが剥離などの異常はなかった。
【００４２】
ラジアル試験では、図６に示すようなラジアル試験機を用いる。試験軸受は、呼び番号＃６２０６のラジアル玉軸受とし、油浴潤滑とし、回転数を６０００ｒｐｍとし、面圧を３３５ｋｇｆ／ｍｍ^２（３．２８ＧＰａ）とした。４００時間で打ち切ったがボールに剥離などの異常がなかった。
【００４３】
このような試験より、直動型玉軸受のボールを安価な中品位セラミックスとしても、優れた特性を発揮することがわかった。但し、その場合、最大接触応力を所要以下（安全を考慮して２５０ｋｇｆ／ｍｍ^２以下）に規制するのが好ましい。低品位セラミックスについても、前述の評価試験を行っていないが、前述の物性評価によりほぼ同様になるものと考えられる。
【００４４】
そして、低品位、中品位セラミックスは、従来例で説明した製造方法で製造される高品位セラミックスに比べて密度が若干低下するため、その内部や表面にポアが点在するようになる。低品位セラミックスの場合、ポアの大きさが約２０〜３０μｍに、また、中品位セラミックスの場合、低品位セラミックスに比べてポアの大きさが約１〜１５μｍと小さくなり、その点在量が少なくなる。
【００４５】
しかし、このような低品位セラミックスや中品位セラミックスでも、上述した評価により実用上あまり問題ないことがわかる。その上、低品位セラミックスや中品位セラミックスの場合、高品位セラミックスに比べて次のような点で優位であると言える。つまり、表面に開口するポアが、潤滑膜の摩耗粉をトラップして貯溜するようになる。要するに、潤滑膜の摩耗粉のボール４に対する移着性が良好となる。これについて、上記製造方法の▲７▼のように超仕上げ加工を施していれば、焼結体の表面により多くのポアが開口するようになるので、より潤滑膜の摩耗粉のボール４に対する移着性が良好となる。
【００４６】
この移着性について、下記試験により調査しているので、説明する。この試験では、潤滑膜をコーティングした金属製（ＪＩＳ規格ＳＵＳ６３０）の平板試料を水平に置き、この平板試料の上面（潤滑膜形成面）に、超仕上げを施したセラミックス製の円柱試料の外周面を垂直方向に押し付けた状態で、水平方向に滑らせることにより、円柱試料に対する固体潤滑剤の移着状況を調べる。この垂直荷重は１０Ｋｇｆ、滑り距離を３０ｍｍ、摺動回数を１回としている。
【００４７】
円柱試料は、▲１▼低品位セラミックス（表面粗さＲ_Ｚ約０．５μｍ）、▲２▼中品位セラミックス（表面粗さＲ_Ｚ約０．２μｍ）、▲３▼高品位セラミックス（表面粗さＲ_Ｚ約０．２μｍ）、▲４▼高品位セラミックス（表面粗さＲ_Ｚ約０．５μｍ）の４つを用意している。これらの円柱試料は、いずれも直径φ４０ｍｍ、長さ１５ｍｍとし、平板試料に対する潤滑膜は、金、ＭｏＳ_２としている。金は、イオンプレーティングにて膜厚１μｍとし、ＭｏＳ_２は、樹脂バインダーを用いて、膜厚１０μｍとしている。
【００４８】
試験結果を、図７ないし図１０に添付する顕微鏡写真に示す。このうち、図７（ａ）〜（ｃ）は、前述の▲１▼に関するもの、図８（ａ）〜（ｃ）は前述の▲２▼に関するもの、図９（ａ）〜（ｃ）は前述の▲３▼に関するもの、図１０（ａ）〜（ｃ）は前述の▲４▼に関するものである。また、図７ないし図１０の各（ａ）は試験前の円柱試料表面の状態を表し、図７ないし図１０の各（ｂ）は潤滑膜を金とした場合での試験後の円柱試料表面の状態を表し、図７ないし図１０の各（ｃ）は潤滑膜をＭｏＳ_２とした場合での試験後の円柱試料表面の状態を表している。
【００４９】
これらの写真結果から、低品位、中品位セラミックスだと、表面に開口するポアに対して潤滑剤が入り込むことがわかり、高品位セラミックスだと、表面に開口するポアがほとんどないかもしくはかなり小さいので、潤滑剤が入り込まないことが分かる。結果的には、高品位セラミックスに比べて低品位、中品位セラミックスは、移着性が良好となっている。
【００５０】
なお、前述と同様の試験を球体試料により行ったが、図１１および図１２に添付する顕微鏡写真に示すように、前述と同様の結果が得られた。図１１（ａ）、（ｂ）は中品位セラミックスの球体試料に関するもの、図１２（ａ）、（ｂ）は高品位セラミックスの球体試料に関するものであり、図１１および図１２の各（ａ）は試験前の球体試料表面の状態を表し、図１１および図１２の各（ｂ）は試験後の球体試料表面の状態を表している。球体試料は、直径３／８インチで、表面粗さはいずれもＲａで０．０１μｍである。平板試料に形成する潤滑膜は樹脂バインダーを用いたＭｏＳ_２とし、膜厚１０μｍとしている。垂直荷重は５Ｋｇｆ、滑り距離を２０ｍｍ、摺動回数を５回往復とする。
【００５１】
さらに、直動型玉軸受の初期発塵試験を行ったので、説明する。この試験では、図１３に示すような発塵試験装置を用いる。試験に用いた直動型玉軸受は、光洋精工（株）製型番ＳＥＳＤＭ１０ＳＴ５である。レール１および移動体２をＪＩＳ規格ＳＵＳ４４０Ｃ、保持器３をＪＩＳ規格ＳＵＳ３０４とし、レール１の溝６、移動体２の溝９１および保持器３の環状溝３２に樹脂バインダーにＰＴＦＥを混合した固体潤滑剤をコーティングしている。ボールは、実施例として中品位セラミックスに、比較例として高品位セラミックスにしている。
【００５２】
試験条件は、下記のとおり。
【００５３】
・往復速度 ：２０〜３０ｍｍ／ｓ
・荷重 ：ラジアル荷重５０Ｎ
・ストローク：１００ｍｍ
・雰囲気 ：１０^−３Ｐａ以下、クリーンベンチ内（クラス１０）
・環境温度 ：室温
・計測条件 ：粒子径０．３８μｍ以上の発塵粒子数
計測タイミングを１０分間隔とし、試験時間を２０時間としている。
【００５４】
結果は、比率で言うと、比較例：実施例＝１：０．８になり、実施例のほうが優れている。そもそも、回転初期では、潤滑膜からの摩耗粉や剥離粉が発塵成分となる。これらの発塵成分は、中品位セラミックスの場合、表面に開口するポアにトラップされて貯溜されるので、前述の結果が得られたものと考えられる。なお、低品位セラミックスの場合だと、同等またはそれ以上の結果が得られるものと考えられる。
【００５５】
なお、本発明は上記実施例のみに限定されない。例えば、実施例で説明した直動型玉軸受の他の種類、例えば角状レールに跨がった鞍型移動体を備えた、いわゆる直動ガイドなどの直動型軸受にも本発明を適用できる。
【００５６】
【発明の効果】
本発明では、製造コストを削減するように工夫しているから、従来の高品位セラミックスよりも安価にでき、しかも、密度や強度については、従来の高品位セラミックスに比べると若干低くなるものの、実用上十分な強度を有している。しかも、原料についても低品質のものを用いれば、原料コストをも低減できるから、製品価格の一層の低減に貢献できる。このように、本発明では、直動型軸受を比較的安価に構成できるようになる。
【００５７】
また、焼結体には表面に開口するポアが存在するので、これが潤滑膜からの摩耗粉をトラップして貯溜するようになるなど、発塵の抑制と、潤滑作用の長期継続とに効果を奏する。
【００５８】
したがって、例えば半導体製造過程のように高精度な加工が要求されるところに本発明の直動型軸受を用いると、清浄雰囲気を阻害しにくくなるので、半導体製造品の歩留まり向上に貢献できる。
【図面の簡単な説明】
【図１】本発明の一実施例にかかる直動型玉軸受の縦断面図
【図２】図１の横断面図
【図３】レールの横断面図
【図４】本発明の実施例での硬度、破壊靭性値測定に関する圧痕を示す模式図
【図５】ボールの寿命試験の様子を示す図
【図６】ボールの寿命試験に用いるラジアル試験機を示す図
【図７】低品位セラミックスの円柱試料に関する潤滑剤移着試験の前後の顕微鏡写真
【図８】中品位セラミックスの円柱試料に関する潤滑剤移着試験の前後の顕微鏡写真
【図９】高品位セラミックスの円柱試料に関する潤滑剤移着試験の前後の顕微鏡写真
【図１０】他の高品位セラミックスの円柱試料に関する潤滑剤移着試験の前後の顕微鏡写真
【図１１】中品位セラミックスの球体試料に関する潤滑剤移着試験の前後の顕微鏡写真
【図１２】高品位セラミックスの球体試料に関する潤滑剤移着試験の前後の顕微鏡写真
【図１３】直動型玉軸受の発塵量測定に用いる試験装置の概略図。
【符号の説明】
Ａ 直動型玉軸受
１ レール
２ 移動体
３ 保持器
４ ボール
６ 軸の溝
９１ 移動体の溝
３１ 保持器の環状溝
１２ ボール転送路
１３ ボール循環路
１６ 潤滑油の薄膜[0001]
[Industrial application fields]
The present invention relates to a direct acting bearing, and more particularly to a direct acting bearing suitable for use in a clean environment.
[0002]
[Prior art]
As the above-mentioned environment, for example, a conveyance system disposed inside the semiconductor manufacturing apparatus can be cited. In such an environment, dust generation from the direct acting bearing becomes a problem.
[0003]
Therefore, a solid lubricant (soft metal such as gold, silver, lead, copper, carbon, molybdenum disulfide, etc.) that generates less dust than grease is used as the lubricant. This solid lubricant is coated in a film on the rails, the raceway surfaces of the moving body, the surface of the rolling element, and the like.
[0004]
In addition to this, in order to suppress the generation of wear powder accompanying rolling and sliding of the rolling elements, it is conceivable to form the rolling elements with ceramics. As this ceramic, the applicant of the present application is to produce a high-quality one with high density and high strength. In order to obtain such high quality ceramics, it is important to reduce the impurity concentration and the porosity.
[0005]
Here, the manufacturing method of the ceramic component currently implemented by the present applicant will be briefly described.
[0006]
First, y-tria (Y ₂ O ₃ ), alumina (Al ₂ O ₃ ) were used for α-type silicon nitride powder having an average particle size of 0.2 μm (high grade product, for example, product number E-10 of Ube Industries, Ltd.). ), A sintering aid such as aluminum nitride (AlN) or titania (TiO ₂ ) is added in an amount of 10% by weight or less. This is molded by uniaxial compression in a state where a binder is mixed and filled in a mold. The molded product is processed to a state close to the final shape and organic substances such as a binder are removed, and then sintered by a technique called so-called HP (hot press) or HIP (hot isostatic press). Superfinishing is performed on the rolling surface and sliding surface of the sintered body. In HP and HIP, a pressure as high as 1000 atm is applied during sintering.
[0007]
[Problems to be solved by the invention]
By the way, in the conventional ceramics as described above, the product price is very high due to high raw material costs and manufacturing costs.
[0008]
Thus, in the past, the price has become so high that high-quality ceramics are to be formed, and therefore the object of use has been limited.
[0009]
Accordingly, an object of the present invention is to reduce the price of the direct acting bearing while adopting a configuration capable of suppressing dust generation.
[0010]
[Means for Solving the Problems]
The linear motion bearing according to the present invention includes a shaft-shaped rail, a cylindrical movable body fitted on the shaft-shaped rail, and a rolling circulation circuit that is disposed between the rail and the movable body and moves relative to the rail. A linear motion type bearing in which the rail and the moving body are made of metal, and the rolling element is made of ceramics, and the ceramic rolling element has an average particle size of 0. A material in which at least 5 to 20% by weight of a sintering aid such as Y ₂ O ₃ or Al ₂ O ₃ is added to silicon nitride powder of ₂ to 1 μm is sintered at a pressure of 1 to 10 atm. The size of the pores that are formed on the sintered body and open to the surface of the ceramic rolling element is 20 to 30 μm.
Further, the linear motion bearing of the present invention is disposed between a shaft-shaped rail, a cylindrical moving body fitted on the rail, and the rail and the moving body, and is rotated in accordance with their relative sliding motion. And a plurality of rolling elements to be circulated, wherein the rail and the moving body are made of metal, and the rolling elements are made of ceramics. A material obtained by adding at least 5 to 20% by weight of a sintering aid such as Y ₂ O ₃ or Al ₂ O ₃ to a silicon nitride powder having a diameter of 0.2 to 1 μm under a pressure of 1 to 10 atm. The pores opened on the surface of the ceramic rolling element have a size of 1 to 15 μm.
[0011]
[Action]
When rolling silicon nitride powder, the rolling element can be simply applied by applying a relatively low pressure of 1 to 10 atm without applying a pressure as high as 1000 atm, such as HP and HIP cited in the prior art. Is formed. Although its density and strength are slightly lower than those of conventional high-quality ceramics, it has sufficient strength for practical use. When the amount of the sintering aid is less than 5% by weight, the sintering is poor, and when it exceeds 20% by weight, the amount of silicon nitride in the base material is relatively reduced, and sufficient strength is obtained. I can't. Furthermore, the thing of the range of 9-14 weight% is used suitably from a sinterability and intensity | strength. If the sintering pressure is about 1 to 10 atm, it can be achieved with a relatively inexpensive pressure vessel, so that a large-scale and expensive apparatus as in the prior art is not necessary.
[0012]
As described above, in the present invention, by reducing the manufacturing cost, the product price is kept lower than the conventional high-quality ceramics.
[0013]
In addition, since the sintered body has pores that open to the surface, it traps and accumulates the wear powder of the lubricating film. Thereby, not only the dust generation element is reduced, but also long-term continuity of lubricity can be expected.
[0014]
Further, in the present invention, a high-quality raw material (such as a silicon nitride powder having a small average particle diameter) such as a conventional high-grade ceramic is used, or a relatively low-quality raw material (silicon nitride powder Those having a mean particle diameter) can be used. Low-quality raw materials are cheaper (about half price) than high-quality raw materials, which can contribute to further reduction in product price.
[0015]
【Example】
Hereinafter, details of the present invention will be described based on embodiments shown in the drawings. 1 to 3 relate to one embodiment of the present invention, FIG. 1 is a longitudinal sectional view of a linear motion ball bearing, FIG. 2 is a transverse sectional view of FIG. 1, and FIG. 3 is a transverse sectional view of a rail. is there.
[0016]
In the figure, A is a direct acting ball bearing, 1 is a rail made of a cylindrical shaft, 2 is a moving body made of a cylindrical member, 3 is a cage made of press, 4 is a ball, and 5 is a holding cylinder.
[0017]
The rail 1 is made of JIS standard SUS440C, and linear grooves 6 along the axial direction are provided over the entire length at six locations on the outer peripheral surface of the rail 1.
[0018]
The moving body 2 is also made of JIS standard SUS440C, and has six circumferentially axial positions in the inner circumferential surface of the inner circumferential surface of the load circulating ball train and the circumferentially opposed groove 6 of the rail 1 so as to face each other. Track grooves 91 and 92 for unloaded circulation ball rows are provided.
[0019]
The cage 3 is made of JIS standard SUS304 and has a cylindrical shape that is curved so as to be along a part of the inner peripheral surface of the moving body 2. Both end portions thereof are supported by the holding cylinder 5. Six horizontally long annular grooves 31 and 32 are provided symmetrically in the central region. The straight portion of the annular groove 31 is used for the load circulation ball row 41 because the bottom is penetrated and the bottom is absent. The annular groove 32 has a bottom and is used for the no-load circulation ball row 42.
[0020]
The two linear grooves 6 and 91 facing each other on the rail 1 side and the moving body 2 side as a pair constitute a total of six load ball transfer paths 12. The group of balls 4 existing in the ball transfer path 12 is located at the bottomless straight portion of the annular groove 31 of the cage 3. In addition, the groove 92 of the moving body 2 and the bottom portion of the annular groove 32 of the cage 3 are paired to constitute a total of six no-load ball circulation paths 13. Each of the six ball transfer paths 12 and each of the six ball circulation paths 13 adjacent to the six ball transfer paths 12 are connected in communication one by one, thereby constituting a ball circulation circuit. Therefore, the balls 4 are rolled and circulated between the ball transfer path 12 and the ball circulation path 13 in accordance with the relative axial sliding operation of the rail 1 and the moving body 2. .
[0021]
By the way, the cross section of the groove 6 of the rail 1 and the groove 91 of the moving body 2 is formed in a circulator arc shape, but may be a gothic arch shape. In this case, the cross sections of the grooves are each formed in a V shape, and the ball 4 is supported in four-point contact by a pair of grooves 6 and 91 facing each other. The two slopes of each of the grooves 6 and 91 are each formed with a gently curved surface. In addition, the circumscribed circle diameter of the balls 4 group when the balls 4 are applied to the grooves 6 of the rail 1 and the inscribed circle diameter of the balls 4 groups when the balls 4 are applied to the grooves 91 of the moving body 2 respectively. The ball 4 is supported in a four-point contact manner by the pair of grooves 6 and 91 by adjusting the difference between them and applying a predetermined preload.
[0022]
The rail 1 and the moving body 2 described above are made of a corrosion resistant material. As this corrosion-resistant material, for example, in addition to martensitic stainless steel such as the above-mentioned JIS standard SUS440C, for example, a metal material obtained by subjecting a precipitation hardening type stainless steel such as JIS standard SUS630 to an appropriate hardening heat treatment. In light load applications, for example, austenitic stainless steel such as JIS standard SUS304 may be used. The retainer 3 is preferably made of brass, titanium, or the like in addition to JIS standard SUS304, but may be made of a synthetic resin material. Examples of the synthetic resin material include fluorine-based resins such as polytetrafluoroethylene (hereinafter abbreviated as PTFE) and ethylenetetrafluoroethylene (ETFE), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), and polyether. Engineering plastics such as Sulphone (PES) and nylon 46 can also be used. Reinforcing fibers such as glass fibers may be added to these resins.
[0023]
Although not shown, a lubricating film is formed on the groove 6 of the rail 1, the groove 91 of the moving body 2, and the annular groove 32 of the cage 3. A lubricating film may be formed on the entire outer peripheral surface of the rail 1. Examples of the lubricating film include solid lubricants such as gold, silver, lead, MoS ₂ , polytetrafluoroethylene (PTFE), and graphite. A thin film of lubricating oil such as perfluoropolyether (PFPF) can also be used.
[0024]
The ball 4 is formed of a ceramic material. This ceramic material will be described in detail below.
[0025]
If each component of the linear motion ball bearing A is formed of such a material, for example, it is possible to prevent corrosion with respect to a halogen-based corrosive gas used in a semiconductor manufacturing apparatus or the like, and a use environment. Dust generation can be reduced.
[0026]
Next, a manufacturing method related to the above-described ceramic ball 4 will be specifically described.
[0027]
(1) Use relatively low quality raw materials. Y-tria (Y ₂ O ₃ ), alumina (Al ₂ O) against α-type silicon nitride powder having an average particle size of 0.5 to 1 μm (for example, type number SN-9FW manufactured by Denki Kagaku Kogyo Co., Ltd.) ₃ ) Add 5-20% by weight of sintering aid such as aluminum nitride (AlN), titania (TiO ₂ ), etc., and mix it uniformly with an organic solvent or water using a suitable mixer (ball mill). (Formulation process).
[0028]
{Circle around (2)} A binder is mixed into the mixed slurry to produce spherical particles having a constant particle size (dry granulation step).
[0029]
(3) Uniaxial compression with the granulated powder filled in a simple mold (molding process). In addition, if the metal mold | die which makes a molded article into a desired shape here is used, the following primary processing process of (4) can be skipped.
[0030]
(4) The molded product is processed into a state close to the final shape according to the ball 4 (primary processing step).
[0031]
(5) The processed material is gradually heated in a degreasing furnace, and organic substances such as binders are removed from the object to be degreased by decomposing or volatilizing (degreasing process).
[0032]
(6) The degreased product is sintered under a pressure of 1 to 10 atm (sintering step). The sintering temperature and sintering time are 1800 ° C. and 2 to 4 hours. Although the molded product shrinks at a predetermined rate by sintering, the amount of shrinkage can be easily grasped by measuring the specific gravity, and can be appropriately adjusted depending on the mixing ratio of the base material and the auxiliary agent.
[0033]
(7) Superfinishing is performed on the rolling surface and sliding surface of the sintered body to obtain the dimensions and surface state of the final product (secondary processing step). In the superfinishing can the surface roughness to about 0.1~0.8μm with _{R Z.}
[0034]
(8) Inspect the presence of cracks and pinholes on the surface of the final product by fluorescent penetrant flaw detection.
[0035]
What is obtained by such a manufacturing method is referred to as low quality ceramics. Table 1 shows the physical properties of the low-quality ceramics and the high-quality ceramics obtained by the conventional manufacturing method.
[0036]
[Table 1]

[0037]
The density is measured by the Archimedes method. The hardness and fracture toughness values are measured using a Vickers hardness meter, the hardness is calculated from the diagonal length of the Vickers indentation shown in FIG. 4, and the fracture toughness value KIC is described below by an IF (Indentation Fracture) method. Calculated using Niihara's formula. The bending strength directly measures the strength of the material, and uses the JIS R 1601 standard three-point bending strength test method.
[0038]
Niihara's formula = 0.0114E ^0.4 P ^0.6 a ^-0.7 (C / a-1) ^-0.5
Where P is the load (Kgf), d is the diagonal length (mm) of the impression, E is the Young's modulus (Kgf / mm ² ), C is the crack length (mm) from the center point of the impression, and a is the diagonal line of the impression. It is 1/2 (mm) of the length.
[0039]
By the way, a conventional high-quality raw material may be used in the step (1) of the manufacturing method. This high-quality raw material is, for example, yttria (Y ₂ O ₃ ) for α-type silicon nitride powder having an average particle size of 0.2 μm (high grade product, for example, product number E-10 of Ube Industries, Ltd.). , Alumina (Al ₂ O ₃ ), aluminum nitride (AlN), titania (TiO ₂ ) and other sintering aids are added at 10 wt% or less. A material that has been subjected to the above-mentioned treatments (2) to (8) using this high-quality raw material is referred to as medium-grade ceramic.
[0040]
This medium-grade ceramic ball is evaluated by the following test. In the test, a ball thrust test and a radial test were performed.
[0041]
In the thrust test, in the thrust bearing as shown in FIG. 5, the ball size is 2/8 inch and 1/4 inch, oil bath lubrication is performed, the shaft rotation speed is 1200 rpm, and the surface pressure is 3/8. The inch was 291 kgf / mm ² (2.85 GPa), and the ¼ inch was 319 kgf / mm ² (3.13 GPa). All size balls were cut off in 1000 hours, but there was no abnormality such as peeling.
[0042]
In the radial test, a radial tester as shown in FIG. 6 is used. The test bearing was a radial ball bearing having a nominal number # 6206, oil bath lubrication, a rotational speed of 6000 rpm, and a surface pressure of 335 kgf / mm ² (3.28 GPa). The ball was cut off in 400 hours, but the ball had no abnormality such as peeling.
[0043]
From these tests, it was found that the ball of the direct acting ball bearing exhibited excellent characteristics even as an inexpensive medium grade ceramic. However, in that case, it is preferable to limit the maximum contact stress to a required value or less (250 kgf / mm ² or less in consideration of safety). Although the above-described evaluation test has not been performed on low-grade ceramics, it is considered that the quality is almost the same by the above-described physical property evaluation.
[0044]
Further, since the density of the low-quality and medium-quality ceramics is slightly lower than that of the high-quality ceramics manufactured by the manufacturing method described in the conventional example, pores are scattered on the inside and the surface. In the case of low-grade ceramics, the pore size is about 20-30 μm. In the case of medium-grade ceramics, the pore size is about 1-15 μm smaller than that of low-grade ceramics, and the amount of interspersed is small. Become.
[0045]
However, even with such low-grade ceramics and medium-grade ceramics, it can be seen that there is no practical problem with the above-described evaluation. In addition, it can be said that low-grade ceramics and medium-grade ceramics are superior to high-grade ceramics in the following points. That is, the pores that open to the surface trap and accumulate the abrasion powder of the lubricating film. In short, the transferability of the abrasion powder of the lubricating film to the balls 4 is improved. In this regard, if superfinishing is performed as in (7) of the above manufacturing method, more pores open on the surface of the sintered body. Wearability is good.
[0046]
The transferability is investigated by the following test, and will be described. In this test, a metal (JIS standard SUS630) flat plate sample coated with a lubricating film is placed horizontally, and the outer peripheral surface of a cylindrical sample made of ceramics that has been superfinished on the upper surface (lubricant film forming surface) of this flat plate sample. The state of the solid lubricant being transferred to the cylindrical sample is examined by sliding in the horizontal direction while pressing in the vertical direction. This vertical load is 10 kgf, the sliding distance is 30 mm, and the number of sliding times is one.
[0047]
Cylindrical samples, ▲ 1 ▼ low-grade ceramics (surface roughness _{R Z} of about 0.5μm), ▲ 2 ▼ medium grade ceramics (surface roughness _{R Z} of about 0.2μm), ▲ 3 ▼ high quality ceramics (surface roughness _{RZ is} about 0.2 μm) and {circle around (4)} high quality ceramics (surface roughness _{RZ is} about 0.5 μm). These cylindrical samples are both a diameter [phi] 40 mm, length 15 mm, the lubricating film to the flat sample is gold, and a MoS _2. Gold has a thickness of 1 μm by ion plating, and MoS ₂ has a thickness of 10 μm using a resin binder.
[0048]
The test results are shown in photomicrographs attached to FIGS. Of these, FIGS. 7 (a) to (c) are related to the above-mentioned (1), FIGS. 8 (a) to (c) are related to (2), and FIGS. 9 (a) to (c) are related to FIG. FIG. 10A to FIG. 10C relate to the above item (4). 7A to 10A show the state of the cylindrical sample surface before the test, and FIGS. 7B to 10B show the cylindrical sample surface after the test when the lubricating film is gold. represents the state, the (c) of FIG. 7 to FIG. 10 shows a state of the cylindrical surface of the sample after the test in the case where the lubricating film and MoS _2.
[0049]
From these photographic results, it can be seen that the low-grade and medium-grade ceramics have a lubricant entering the pores that open on the surface, and the high-grade ceramics have few or quite small pores opening on the surface. It can be seen that the lubricant does not enter. As a result, the low-grade and medium-grade ceramics have better transferability than the high-grade ceramics.
[0050]
Although the same test as described above was performed on a spherical sample, the same result as described above was obtained as shown in the micrographs attached to FIGS. FIGS. 11 (a) and 11 (b) relate to a medium quality ceramic sphere sample, and FIGS. 12 (a) and 12 (b) relate to a high quality ceramic sphere sample. Represents the state of the sphere sample surface before the test, and each (b) of FIGS. 11 and 12 represents the state of the sphere sample surface after the test. The spherical sample has a diameter of 3/8 inch and the surface roughness is 0.01 μm in Ra. The lubricating film formed on the flat plate sample is MoS ₂ using a resin binder and has a thickness of 10 μm. The vertical load is 5 kgf, the sliding distance is 20 mm, and the sliding frequency is 5 reciprocations.
[0051]
Further, an initial dust generation test of the direct acting ball bearing was performed, which will be described. In this test, a dust generation test apparatus as shown in FIG. 13 is used. The direct acting ball bearing used for the test is model number SESDM10ST5 manufactured by Koyo Seiko Co., Ltd. Solid lubrication in which rail 1 and moving body 2 are JIS standard SUS440C, cage 3 is JIS standard SUS304, groove 6 of rail 1, groove 91 of moving body 2 and annular groove 32 of cage 3 are mixed with resin binder and PTFE. The agent is coated. The balls are medium-grade ceramics as examples and high-grade ceramics as comparative examples.
[0052]
The test conditions are as follows.
[0053]
・ Reciprocating speed: 20-30mm / s
・ Load: Radial load 50N
・ Stroke: 100mm
・ Atmosphere: 10 ^-3 Pa or less, in a clean bench (class 10)
-Environmental temperature: Room temperature-Measurement conditions: The measurement timing of the number of dust particles with a particle size of 0.38 μm or more is set at 10-minute intervals, and the test time is 20 hours.
[0054]
In terms of ratio, the result is Comparative Example: Example = 1: 0.8, and the Example is superior. In the first place, at the initial stage of rotation, wear powder and peeling powder from the lubricant film become dust generating components. In the case of medium-grade ceramics, these dust-generating components are trapped and stored in pores that are open on the surface, and it is considered that the above-mentioned results were obtained. In the case of low-grade ceramics, it is considered that equivalent or better results can be obtained.
[0055]
In addition, this invention is not limited only to the said Example. For example, the present invention is also applied to other types of linear motion ball bearings described in the embodiments, for example, linear motion bearings such as so-called linear motion guides having a saddle type moving body straddling a square rail. it can.
[0056]
【The invention's effect】
In the present invention, since it is devised to reduce the manufacturing cost, it can be made cheaper than the conventional high-quality ceramics, and the density and strength are slightly lower than those of the conventional high-quality ceramics. It has sufficient strength. In addition, if the raw material is of low quality, the raw material cost can be reduced, which can contribute to further reduction of the product price. Thus, according to the present invention, the direct acting bearing can be configured at a relatively low cost.
[0057]
In addition, there are pores that open on the surface of the sintered body, and this helps trap dust particles from the lubricating film and store them. Play.
[0058]
Therefore, when the linear motion bearing of the present invention is used where high-precision processing is required, for example, in the semiconductor manufacturing process, it is difficult to inhibit the clean atmosphere, which can contribute to the improvement of the yield of semiconductor manufactured products.
[Brief description of the drawings]
1 is a longitudinal sectional view of a linear motion ball bearing according to an embodiment of the present invention. FIG. 2 is a transverse sectional view of FIG. 1. FIG. 3 is a transverse sectional view of a rail. Schematic diagram showing indentations related to the measurement of hardness and fracture toughness values of the ball. [Fig. 5] Diagram showing the state of the ball life test. [Fig. 6] Diagram showing the radial test machine used for the ball life test. Micrographs before and after lubricant transfer test on cylindrical sample [Fig. 8] Microscopic images before and after lubricant transfer test on cylindrical sample of medium-grade ceramic [Fig. 9] Lubricant transfer test on cylindrical sample of high-grade ceramic Micrograph before and after [Fig. 10] Micrograph before and after lubricant transfer test on other high quality ceramic cylindrical samples [Fig. 11] Micrograph before and after lubricant transfer test on spherical samples of medium quality ceramic [ Fig. 12 High quality Schematic diagram of a test apparatus used for the dust amount measurement before and after the micrograph 13 direct-acting ball bearing lubricant transfer adhesive test for spheres sample La mix.
[Explanation of symbols]
A Direct acting ball bearing 1 Rail 2 Moving body 3 Cage 4 Ball 6 Axle groove 91 Moving body groove 31 Cage annular groove 12 Ball transfer path 13 Ball circulation path 16 Lubricating oil thin film

Claims (3)

A shaft-shaped rail, a cylindrical moving body fitted on the rail, and a plurality of rolling elements that are arranged between the rail and the moving body and are circulated in association with their relative sliding motion. The rail and the moving body are made of metal and the rolling element is made of ceramics,
In the ceramic rolling element, at least 5 to 20% by weight of a sintering aid such as Y ₂ O ₃ or Al ₂ O ₃ is added to silicon nitride powder having an average particle size of 0.2 to 1 μm. A direct acting type comprising a sintered body obtained by sintering a material under a pressure of 1 to 10 atm, and a pore opening on a surface of the ceramic rolling element having a size of 20 to 30 μm. bearing. A shaft-shaped rail, a cylindrical moving body fitted on the rail, and a plurality of rolling elements that are arranged between the rail and the moving body and are circulated in association with their relative sliding motion. The rail and the moving body are made of metal and the rolling elements are made of ceramics,
The ceramic rolling element has at least Y for silicon nitride powder having an average particle size of 0.2 to 1 μm. ₂ O ₃ , Al ₂ O ₃ The size of the pores which are made of a sintered body obtained by sintering a material to which 5 to 20% by weight of a sintering aid is added at a pressure of 1 to 10 atm and which opens on the surface of the ceramic rolling element A linear motion bearing having a length of 1 to 15 μm. The direct acting bearing according to claim 1 or 2,
A linear motion bearing, wherein the sintering aid is 9 to 14% by weight.

Images