[0002] 滾珠裝置的一種亦即滾珠螺桿裝置，一般來說，係由以下所構成：在外周面具有螺槽的螺桿軸、在內周面具有與螺桿軸的螺槽相對向之螺槽的螺帽、中介插入於兩螺槽間並一起藉由設在螺帽的滾珠循環路而成為可循環的複數個滾珠。滾珠螺桿裝置，係將旋轉運動變換成軸方向移動的裝置，作為其用途，大致分為電動射出成形機等之高負載驅動用途與工作機械等之精密定位用途。特別是在近年，要求著汽車零件的輕量化，作為其中的一種手段，檢討著零件的樹脂化。如上述般的需求，對電動射出成形機所要求的輸出會增大，使得裝置的大型化逐漸成為必要，但為了盡可能抑制大型化，滾珠螺桿裝置的長壽命化漸漸變得重要。 [0003] 作為製造業界的動向，不只是從降低CO2
排出的觀點來看，還期待著滾珠螺桿裝置之構成零件亦即螺桿軸或螺帽、滾珠等之生產的效率化。滾珠螺桿裝置中，多為使用將螺桿軸與螺帽予以滲碳處理成表面硬化鋼者。且，為了謀求生產性提升，在螺桿軸的熱處理工程中，廣泛使用高頻熱處理化，且伴隨於此，在軸材料使用中碳鋼的產品亦增加。因此，現在的素材與熱處理的構成，多成為以下組合：螺桿軸為「中碳鋼+高頻熱處理」、螺帽為「表面硬化鋼+滲碳處理」、滾珠為「軸承鋼+浸淬處理」。高頻熱處理，由於僅加熱工件故熱能量的消費較少，且就產線化等之生產效率提升的觀點來看，以後持續、擴大的可能性亦較高，故功能的提升有必要考慮以高頻熱處理為基礎。 [0004] 且，電動射出成形機所使用之高負載用途的滾珠螺桿裝置，與以往的油壓驅動方式相比之下較能抑制空閒時間的能量消費，而且可貢獻出高精度的射出成形，從該等特徵來看，就實現油壓驅動所致之高負載線性致動器的電動伺服化來說，成為重要的高負載驅動機械要件。近年來，滾珠螺桿驅動所致的電動射出成形機中，以塑料產品之世界性的需求增加或生產成本的削減為背景，例如努力使加工週期時間減半藉此使生產能力大幅提升。但是，若成形機的加工週期減半的話，滾珠螺桿裝置到達週期壽命的時間亦會減半，故滾珠螺桿裝置的交換成本會倍增。此情況時，只要使滾珠螺桿裝置的負載容量增大來使壽命倍增即可抑制交換成本的增加，但伴隨著負載容量增大之滾珠螺桿裝置的大型化，亦有著招致成形機自身的成本上升，或是成形機設置空間的增大之虞。 [0005] 滾珠螺桿裝置的壽命，係與轉動軸承相同，依照螺桿軸或螺帽甚至滾珠之轉動面的剝離破損來決定。亦即，比以往還能長時間地對剝離的耐性優異的滾珠螺桿裝置，可稱之為符合現今趨勢的產品。滾珠螺桿裝置的剝離形態多為在軌道面產生的壓痕，或是以切線力為原因的表面起始型剝離。針對表面起始型剝離的長壽命化技術，在轉動軸承的領域中存在有多種的見解，例如已知有增加軌道面表面之殘留奧氏體(Austenite)量γR
的方法。 [0006] 作為關於此方法的先前技術，專利文獻1中，係以對軸承使用高頻熱處理為前提，來限定軌道面的殘留奧氏體量γR
。只要將該專利文獻1中的熱處理方法以滲碳處理進行的話，由於滲碳媒體為氣體而形狀依存性較少，故容易將軸承的技術轉用於滾珠螺桿。但是，若以高頻熱處理為前提的話，技術的轉用就並不容易。這是因為，特別是組織控制所必要之包含轉動面之區域的形狀、以及高頻熱處理的特性所導致。於滾珠螺桿裝置的螺桿軸適用高頻熱處理的情況雖然如前述般，但作為轉動面亦即螺槽的淬燒方法，有著沿著鄰接的螺槽進行熱處理的方法、將螺桿軸視作圓棒來以馬鞍型線圈進行熱處理的方法。由於後者較不受螺槽形狀的影響，故生產效率較高，就高頻熱處理的導入目的亦即生產性提升的觀點來看亦採用該方法。但是，螺桿軸的軸方向剖面中，螺槽成為峰形狀，此外由於峰頂部較接近線圈所以峰的部分容易累積熱。因此，峰部容易發生過熱。滾珠螺桿或軸承等之高硬度的產品中，過熱會明顯招致韌性的劣化，故這在容易進行技術轉用上成為障礙。如滾珠螺桿裝置的螺桿軸那般，以高頻熱處理為前提的情況，作為素材係以中碳鋼為標準，而這就是原因。 [0007] 關於此點，本申請人，先行於專利文獻2中報告出高碳鋼的高頻熱處理技術，係在線圈的形狀或熱處理前的材質進行處理藉此避免過熱並提供對表面疲勞較強的螺桿軸。但是，實際產品的壽命，係以螺桿軸或螺帽、滾珠之任一者剝離的時間點來決定。雖亦考量有將螺帽或滾珠藉由碳氮共滲等的處理來長壽命化的手段，但該等與現行的處理相比之下，會使工程的增加或管理基準的高度化成為必要，進而導致成本上升。因此，為了得到最大限度的成本效益比，必須探討該採用何種構造。 [0008] 且，專利文獻3中，係將滾珠表面的殘留奧氏體量γR
作為基準，來限定螺桿軸及螺帽的各殘留奧氏體量γR
。但是，專利文獻3中，其技術性的觀點，係維持滾珠表面的表面狀態藉此不增加賦予給螺桿軸或螺帽的切線力。換言之，滾珠表面之殘留奧氏體量γR
的控制，係以螺桿軸或螺帽本身的長壽命化為目的，其手段並非以對滾珠適用碳氮共滲等之兼具生產性與裝置壽命為主旨。 [先前技術文獻] [專利文獻] [0009] [專利文獻1] 日本特開2016-006340號公報 [專利文獻2] 日本特開2015-042897號公報 [專利文獻3] 日本特開2009-204069號公報[0002] One type of ball device, that is, a ball screw device, is generally composed of a screw shaft having a screw groove on an outer peripheral surface, and a screw shaft having a screw groove opposite to the screw groove of the screw shaft on an inner peripheral surface. The nut and the intermediary are inserted between the two screw grooves and become a plurality of balls that can be circulated together through a ball circulation path provided in the nut. The ball screw device is a device that converts rotary motion into axial movement. As its application, it is roughly divided into high load driving applications such as electric injection molding machines and precision positioning applications such as work machines. Especially in recent years, lightweighting of automobile parts is required. As one of the means, the resinization of parts is being reviewed. As described above, the output required for an electric injection molding machine will increase, making the device larger in size gradually necessary. However, in order to suppress the increase in size as much as possible, the long life of the ball screw device becomes increasingly important. [0003] As a trend in the manufacturing industry, not only from the standpoint of reducing CO 2 emissions, efficiency in production of screw shafts, nuts, balls, and the like, which are components of a ball screw device, is also expected. In the ball screw device, the screw shaft and the nut are usually carburized to harden steel. In addition, in order to improve productivity, high-frequency heat treatment is widely used in the heat treatment process of screw shafts, and with this, carbon steel products have also increased in the use of shaft materials. Therefore, the current composition of materials and heat treatment is mostly the following combination: screw shaft is "medium carbon steel + high frequency heat treatment", nut is "surface hardened steel + carburizing treatment", and ball is "bearing steel + hardening treatment"". In the high-frequency heat treatment, because only the workpiece is heated, the consumption of thermal energy is small, and from the viewpoint of improving production efficiency such as production line, the possibility of continued and expansion in the future is also high. Therefore, it is necessary to consider the improvement of the function. Based on high frequency heat treatment. [0004] In addition, the ball screw device for high-load applications used in electric injection molding machines can reduce idle time energy consumption compared to conventional hydraulic driving methods, and can contribute to high-precision injection molding. From these characteristics, it becomes an important high-load driving mechanical element in order to realize the electric servo of the high-load linear actuator caused by hydraulic driving. In recent years, electric injection molding machines driven by ball screws have been set against the background of increasing global demand for plastic products or reduction in production costs. For example, efforts have been made to halve the processing cycle time to significantly increase production capacity. However, if the processing cycle of the forming machine is halved, the time to reach the cycle life of the ball screw device will also be halved, so the exchange cost of the ball screw device will double. In this case, as long as the load capacity of the ball screw device is increased to double the life, the increase in exchange costs can be suppressed. However, with the increase in the load capacity of the ball screw device, the cost of the forming machine itself has also increased. Or, the installation space of the forming machine may increase. [0005] The life of a ball screw device is the same as that of a rotary bearing, and is determined according to the peeling and damage of the screw shaft or nut or even the rotating surface of the ball. In other words, a ball screw device that is superior in resistance to peeling over a long period of time can be called a product that meets the current trend. The peeling form of the ball screw device is mostly an indentation generated on the track surface, or a surface-initiated peeling due to a tangential force. For long-life type release technology is the starting surface, the presence in the area of the rotary bearing in a variety of views, such known methods of surface residual austenite increases raceway surface (Austenite) the amount of γ R. [0006] As a prior art regarding this method, Patent Document 1 presupposes that a high frequency heat treatment is applied to a bearing to limit the amount of retained austenite γ R of the track surface. As long as the heat treatment method in this patent document 1 is performed by carburizing, since the carburizing medium is a gas and has less shape dependency, it is easy to transfer the technology of the bearing to a ball screw. However, if high-frequency heat treatment is premised, the transfer of technology will not be easy. This is due to the shape of the area including the turning surface and the characteristics of the high-frequency heat treatment, which are necessary for microstructure control. When high-frequency heat treatment is applied to the screw shaft of a ball screw device, as described above, as the quenching method of the rotating surface, that is, the screw groove, there is a method of heat treatment along the adjacent screw groove, and the screw shaft is regarded as a round bar Let's heat-treat a saddle coil. Since the latter is less affected by the shape of the spiral groove, the production efficiency is higher, and this method is also adopted from the viewpoint of the introduction purpose of the high-frequency heat treatment, that is, to improve the productivity. However, in the axial direction cross section of the screw shaft, the spiral groove has a peak shape, and since the top of the peak is closer to the coil, heat is easily accumulated in the peak portion. Therefore, the peak portion is liable to overheat. In high-hardness products such as ball screws and bearings, overheating will obviously cause deterioration of toughness, so this is an obstacle to ease of technology transfer. In the case of the screw shaft of a ball screw device, in the case of high-frequency heat treatment, medium carbon steel is used as the material, and this is the reason. [0007] In this regard, the applicant first reported the high-frequency heat treatment technology of high carbon steel in Patent Document 2. The shape of the coil or the material before the heat treatment was processed to avoid overheating and provide surface fatigue. Strong screw shaft. However, the life of an actual product is determined by the time at which any one of a screw shaft, a nut, and a ball is peeled off. Although measures have been taken to increase the life of the nut or ball by treatment such as carbonitriding, these methods will require an increase in engineering or a higher management standard than the current treatment. , Which in turn leads to rising costs. Therefore, in order to obtain the maximum cost-benefit ratio, it is necessary to explore which structure to use. [0008] Moreover, Patent Document 3, the amount of retained austenite-based ball surface γ R as a reference, the screw shaft and the nut to define the respective amount of retained austenite γ R. However, in Patent Document 3, the technical point is to maintain the surface state of the ball surface so as not to increase the tangential force applied to the screw shaft or the nut. In other words, the control of the amount of retained austenite γ R on the surface of the ball is for the purpose of increasing the life of the screw shaft or the nut itself, and the means is not to have both productivity and device life by applying carbonitriding to the ball. Main purpose. [Prior Art Document] [Patent Document] [0009] [Patent Document 1] Japanese Patent Laid-Open No. 2016-006340 [Patent Document 2] Japanese Patent Laid-Open No. 2015-042897 [Patent Document 3] Japanese Patent Laid-Open No. 2009-204069 Bulletin
[發明所欲解決的課題] [0010] 本發明係有鑑於上述狀況而完成者，在電動射出成形機等之以高負載驅動，且行程係數較小之用途所使用的滾珠螺桿裝置或滾柱螺桿裝置等之螺桿裝置中，以謀求進一步的長壽命化與生產性的效率提升為目的。 [用以解決課題的手段] [0011] 本發明者們，對於螺桿裝置的長壽命化進行深入研究的結果，發現在行程較短的螺桿裝置中，在構成構件之中，因螺桿軸的剝離所致的破損較多，從而發現到使螺桿軸之螺槽表面的殘留奧氏體量比螺帽之螺槽或轉動體之各表面的殘留奧氏體量還大的時候為有效，終至完成本發明。亦即，本發明係將螺桿軸、螺帽及轉動體的組合，由該等表面之殘留奧氏體量的大小關係來限定而成者，進而提供以下的螺桿裝置。 (1)一種螺桿裝置，其特徵為，具備：螺桿軸，其在外周面具有螺槽；螺帽，其在內周面具有與前述螺桿軸之螺槽相對應的螺槽；複數個轉動體，其中介安裝於前述兩螺槽間，且藉由設在前述螺帽的轉動體循環路而成為可循環，該螺桿裝置，在行程係數fS
未達4.8之下來使用，且前述螺桿軸之螺槽表面的殘留奧氏體量γRS
符合以下式子。 [0012]（式中，αS
為螺桿軸的要求壽命倍率。） [0013] (2)如上述(1)所述之螺桿裝置，其特徵為，前述螺帽之螺槽表面的殘留奧氏體量γRN
符合以下式子。 [0014]（式中，αN
為螺帽的要求壽命倍率。） [0015] (3)如上述(1)或(2)所述之螺桿裝置，其特徵為，前述螺桿軸之螺槽表面的殘留奧氏體量γRS
與前述螺帽之螺槽表面的殘留奧氏體量γRN
，為「γRS
＞γRN
」的關係。 (4)如上述(1)~(3)中任1項所述之螺桿裝置，其特徵為，將前述轉動體之表面的殘留奧氏體量設為γRB
時，為「γRS
＞γRN
＞γRB
」的關係。 (5)如上述(1)~(4)中任1項所述之螺桿裝置，其特徵為，前述轉動體為滾珠或滾柱。 (6)如上述(1)~(5)中任1項所述之螺桿裝置，其特徵為，電動射出成形機用、電動伺服沖壓機用、電動致動器用、伺服缸用、或電動千斤頂用。 [發明的效果] [0016] 根據本發明，限定螺桿裝置之構成構件亦即螺桿軸及螺帽之各螺槽表面的殘留奧氏體量，並限定兩者的大小關係，甚至是包含轉動體之3者之殘留奧氏體量的大小關係，藉此成為更長壽命的螺桿裝置。此外，只要使螺桿軸之螺槽表面的殘留奧氏體量變得比其他構成構件還要大即可，作為螺帽或轉動體亦可使用以往產品，故可提高螺桿裝置的生產效率，且抑制螺桿裝置的成本上昇。[Problems to be Solved by the Invention] [0010] The present invention was completed in view of the above situation, and is a ball screw device or roller used in applications such as electric injection molding machines that are driven at high loads and have a small stroke coefficient. In screw devices such as screw devices, the purpose is to further increase the life and increase productivity. [Means for Solving the Problems] As a result of intensive research on the long life of the screw device, the present inventors found that in a screw device with a short stroke, among the constituent members, the screw shaft is peeled off. There are many damages, so it is found that it is effective when the amount of retained austenite on the surface of the screw groove of the screw shaft is larger than the amount of retained austenite on the surface of the screw groove of the screw nut or the rotor. The present invention has been completed. That is, the present invention is a combination of a screw shaft, a nut, and a rotating body, which is defined by the relationship between the amount of retained austenite on these surfaces, and further provides the following screw device. (1) A screw device, comprising: a screw shaft having a screw groove on an outer peripheral surface; a nut having a screw groove corresponding to the screw groove of the screw shaft on an inner peripheral surface; and a plurality of rotating bodies The intermediary is installed between the two screw grooves and can be circulated by the rotating body circulation path provided in the nut. The screw device is used with a stroke coefficient f S of less than 4.8, and the screw of the screw shaft The amount of retained austenite γ RS on the groove surface conforms to the following formula. [0012] (In the formula, α S is the required life ratio of the screw shaft.) [0013] (2) The screw device according to the above (1), wherein the amount of retained austenite on the surface of the screw groove of the nut is γ RN complies with the following formula. [0014] (In the formula, α N is the required life ratio of the nut.) [0015] (3) The screw device according to (1) or (2) above, characterized in that the residual screw surface of the screw groove of the screw shaft is The relationship between the amount of austenite γ RS and the amount of retained austenite γ RN on the surface of the screw groove of the nut is “γ RS > γ RN ”. (4) The screw device according to any one of (1) to (3) above, wherein when the amount of retained austenite on the surface of the rotating body is set to γ RB , it is "γ RS > γ RN > γ RB ”. (5) The screw device according to any one of (1) to (4), wherein the rotating body is a ball or a roller. (6) The screw device according to any one of (1) to (5) above, characterized in that it is used for an electric injection molding machine, an electric servo press, an electric actuator, a servo cylinder, or an electric jack use. [Effect of the Invention] [0016] According to the present invention, the amount of retained austenite on the surface of each screw groove of the screw shaft and the nut, which is the constituent member of the screw device, is limited, and the size relationship between the two is included, even including the rotating body. The relationship between the amount of retained austenite of the three is a screw device with a longer life. In addition, as long as the amount of retained austenite on the surface of the screw groove of the screw shaft is larger than that of other constituent members, conventional products can be used as the nut or the rotating body. Therefore, the production efficiency of the screw device can be improved and suppressed The cost of the screw device increases.
[0018] 以下，針對本發明的螺桿裝置進行詳細說明。 [0019] 本發明的螺桿裝置，係在行程係數fS
未達4.8之下使用。作為此種螺桿裝置，有電動射出成形機或電動伺服沖壓機、伺服缸、電動千斤頂等，本發明的螺桿裝置適用於該等。且，以下雖示例滾珠螺桿裝置來進行說明，但作為轉動體亦可為滾柱(滾柱螺桿裝置)。而且，本發明的滾珠螺桿裝置中，螺桿軸之螺槽表面的殘留奧氏體量γRS
符合以下式子。 [0020]（式中，αS
為螺桿軸的要求壽命倍率。） [0021] 且，螺帽之螺槽表面的殘留奧氏體量γRN
以符合以下式子為佳。 [0022]（式中，αN
為螺帽的要求壽命倍率。） [0023] 在正常運轉條件下的滾珠螺桿裝置，與轉動軸承不同，因軌道的扭曲導致滾珠與螺桿軸或螺帽軌道間的滑動變大，故轉動疲勞所致之軌道破損的形態會成為表面起始型剝離。到達該表面起始型剝離之損傷的發生或進展與轉動面表面的殘留奧氏體量γR
之間有相互關係，使軌道面表面的殘留奧氏體量γR
比以往還增加而可期待得到長壽命化效果。而且，本發明者們，就定量評估殘留奧氏體量γR
之增加所致之長壽命化效果的目的，係使用以高頻熱處理過之軌道面表面之殘留奧氏體量γR
不同的各種要素試驗片來實驗調查表面起始型剝離壽命。其結果，對於高頻熱處理過之材料表面的殘留奧氏體量γR
[%]與以往的螺桿軸材料(SAE4150)的壽命變化率α之間，得到以下的關係式。 [0024][0025] 由式(1)發現，為了比以往的滾珠螺桿裝置還要長壽命化(α＞1)，必須使螺桿軸之螺槽表面的殘留奧氏體量γR
大於9%，且對於螺桿裝置所要求的壽命，迴避過高品質、或是品質不足，而可推測最適合的殘留奧氏體量γR
。 [0026] 但是，若將對軸方向施加有靜負重的滾珠螺桿裝置予以驅動的話，螺帽會在螺桿軸上相對地往直線方向移動。此時，在螺帽軌道面的任意位置上，伴隨著負載滾珠的通過，會承受到反覆的應力。另一方面，在螺桿軸軌道中，只有在伴隨著螺帽之直線移動之負載滾珠的通過時受到應力。因此，在螺帽的行程充分長的情況，負載滾珠通過所致之對軌道的反覆施加應力數為螺帽側比螺桿軸側還要多，故得知最初的轉動疲勞破損會在螺帽軌道上發生。因此，以往係將螺帽之螺槽表面的殘留奧氏體量γR
，設成比螺桿軸之螺槽表面的殘留奧氏體量γR
還大。 [0027] 但是，在電動射出成形機等所使用的滾珠螺桿裝置中，螺帽的行程較短，故伴隨著負載滾珠通過之對軌道的反覆施加應力數的大小關係會逆轉，成為螺桿軸側比螺帽側還多。因此，行程較短之運轉條件下的滾珠螺桿耐久試驗中，確認到最初的轉動疲勞破損有在螺桿軸側發生的傾向。且，從滾珠與軌道間之接觸面壓的觀點來考慮，也是螺桿軸側那邊的面壓較高，故成為支持最初的破損發生位置偏向螺桿軸側的根據。 [0028] 根據上述般的接觸面壓與反覆施加應力數所起因的螺桿軸與螺帽軌道的破損特性，轉動面的疲勞壽命係與接觸面壓的9次方成比例，且，與反覆施加應力數成比例，故螺桿軸與螺帽軌道的壽命比β可由下式(2)來表示。 [0029][0030] 式中，pS
與pN
係表示在螺桿軸及螺帽軌道的接觸面壓，NS
與NN
係表示在1行程運轉之際螺桿軸及螺帽軌道的反覆施加應力數。 [0031] 然後，以在實際的使用條件下調查滾珠螺桿裝置的螺桿軸與螺帽軌道的壽命比β為目的來看，從投入實用之電動射出成形機用共20種型號之滾珠螺桿裝置的軸方向負重或行程，求出pS
與pN
以及NS
與NN
，並藉由式(2)來算出各型號的β。藉此，在β、以及將行程St
除以滾珠螺桿裝置的有效圈數(ζ)、回路數(ξ)、及導程(l)的積所得的行程係數fS
之間，得到以下的關係式(3)。 [0032][0033] 藉由式(3)，在電動射出成形機等之短行程(fS
＜4.8)條件下來驅動的情況，與螺桿軸相比，螺帽的軌道壽命較長(β＞1)。 [0034] 因此，考量到如前述般行程係數為fS
＜4.8之螺桿軸與螺帽之軌道壽命的關係之後，為了滿足滾珠螺桿裝置的要求壽命，分別決定螺桿軸與螺帽之各螺槽表面的殘留奧氏體量γR
，這樣就生產性的進一步提升而言較佳。於是，使用式(1)~(3)來分別推測螺桿軸與螺帽之各螺槽表面所必要的各殘留奧氏體量γRS
與γRN
。 [0035] 若將螺桿軸軌道對滾珠螺桿裝置的壽命比設為αS
的話，螺桿軸之螺槽表面的殘留奧氏體量γRS
係由式(1)而成為如下。 [0036][0037] 接著，若將螺帽軌道對滾珠螺桿裝置的壽命比設為αN
的話，螺帽對螺桿軸的軌道壽命比β會成為「β=αN
/αS
」，故藉由式(2)及式(3)，螺帽之螺槽表面的殘留奧氏體量γRN
會成為如下。 [0038][0039] 於是，使滾珠螺桿裝置的要求壽命、以及螺桿軸與螺帽的軌道壽命成為一致之螺桿軸與螺帽之各螺槽表面的殘留奧氏體量γRS
與γRN
，係在式(4)與式(5)中作為「αS
=αN
=α＞1」代入即可推測。亦即，在行程係數為fS
＜4.8所使用的滾珠螺桿裝置中，為了不損及生產性且成為長壽命化(α＞1)，係藉由式(4)與式(5)，使各螺槽表面之殘留奧氏體量γR
的大小關係中，以成為螺桿軸比螺帽還大的組合較為合理。 [0040] 如上述般，只要符合螺桿軸及螺帽之各螺槽的殘留奧氏體量γRS
及γRN
、較佳為「γRS
＞γRN
」的話，螺桿軸及螺帽的素材並無限制。但是，就滾珠螺桿裝置之生產性的觀點來看，於螺桿軸係適用高頻熱處理為主流，為了在適合高頻熱處理的材料之中使螺桿軸之螺槽表面的殘留奧氏體量γRS
成為上述那般，作為螺桿軸材料以高碳軸承鋼為佳。 [0041] 且，關於螺帽，係使用與以往相同的表面硬化鋼，以碳氮共滲處理為佳，由於可直接使用以往產品故作為滾珠螺桿裝置整體會變得便宜。 [0042] 又，高頻熱處理可用公知的方法，只要以能夠確立迴避過熱的手法為前提，來控制感應加熱線圈的輸出即可。 [0043] 且，關於滾珠螺桿裝置的另一個轉動零件亦即滾珠，因為滾珠的隨機旋轉而難以用相同基準來計算壽命。但是，由於轉動面為隨機，產生剝離的面之負重的負載次數亦較少，故壽命最長。因此，其表面的殘留奧氏體量γRB
，係比螺桿軸或螺帽還小為佳。亦即，各自的殘留奧氏體量γR
以成為「γRS
＞γRN
＞γRB
」的大小關係為佳。若符合該3者的大小關係，不論任何構成零件破損的情況，均可使功能與生產性的平衡最大化。 [0044] 又，滾珠可使用以往產品，可使用將軸承鋼予以浸淬者等，可抑制滾珠螺桿裝置的成本上升。 [實施例] [0045] 以下舉出實施例來進一步說明本發明，但本發明並不因此受到任何限制。 [0046] 在此，係使用電動射出成形機之射出軸等的用途上多被使用的滾珠螺桿裝置：型號BS6316-10.5來進行驗證。滾珠螺桿裝置BS6316-10.5之主要的內部參數如下。 ･螺桿軸外徑(d)：63mm ･導程(l)：16mm ･螺桿圈數(ζ)：3.5 ･循環回路數(ξ)：3 ･螺桿有效圈數(ζ×ξ)：10.5(=3.5×3) [0047] 作為比較例，使用標準品。又，各零件的材料與熱處理的組合係如以下所述，將各零件之殘留奧氏體量的大小關係設為「螺帽＞滾珠＞螺桿軸」。 ･螺桿軸：中碳鋼、高頻熱處理 ･螺帽：表面硬化鋼、滲碳處理 ･滾珠：軸承鋼、浸淬 [0048] 對此，作為實施例，使用下述的螺桿軸、螺帽及滾珠。且，將行程長度St
設為80mm，算出行程係數fS
時，會算出fS
=St
/ζ･ξ･l=80/(3.5×3×16)=0.48。此時所要求之螺桿軸與螺帽的壽命比，係由式(2)而成為5倍左右。因此，由式(1)算出成為目標之螺桿軸之螺槽表面的殘留奧氏體量γRS
約為25%。 [0049] 根據上述，與比較例相同形狀時，係製作以下構造的滾珠螺桿裝置。 ･螺桿軸：高碳鋼、高頻熱處理 ･螺帽：表面硬化鋼、滲碳處理 ･滾珠：軸承鋼、浸淬 [0050] 如上述般，一邊抑制過熱並確保軌道面的殘留奧氏體量γR
並不容易，故在本試驗中也是，在螺桿軸的加工時，調整線圈形狀及高頻熱處理條件。其結果，得到將軌道面的殘留奧氏體量γR
設為26%的螺桿軸。藉此，實施例之殘留奧氏體γR
的大小關係成為「螺桿軸＞螺帽＞滾珠」。 [0051] 關於上述比較例及實施例的滾珠螺桿裝置(型號BS6316-10.5)的耐久性，係在下述條件求出L10
壽命比及L50
壽命比來進行評價。又，試驗次數在實施例為7次、在比較例為13次，各壽命係藉由威布爾分布(Weibull distribution)來求得。 ･最大軸方向負重(Famax
)：300kN ･最高螺桿軸旋轉數(nmax
)：500min-1
･行程(St
)：80mm ･潤滑劑：潤滑脂 [0052] 將結果示於圖1，可確認到相較於比較例，實施例為長壽命化。壽命的增加量，在L10
壽命為3.0倍，在L50
壽命為5.3倍。 [0053] 且，確認破損部位時，比較例係在螺桿軸發生剝離，相對於此，實施例係發生滾珠的剝離。本實施例之螺桿軸與螺帽的壽命倍率為大約5倍，故可將螺桿軸的壽命延長5倍的話，能預測出得到作為本構造之滾珠螺桿裝置之功能的最大化。關於此，從實施例的耐久試驗結果得到幾乎是最大值。又，滾珠的剝離壽命，從其殘留奧氏體量γRB
來看，作為單體推測為比較例之螺桿軸之壽命的1.5倍左右。如上述般，滾珠螺桿裝置中，具備有滾珠的循環機構，在循環回路內，滾珠幾乎為無負載狀態，而且公轉或自轉動作被認為是隨機。因此，滾珠受到負載的位置亦為隨機故難以預測壽命延長效果，但即使殘留奧氏體量γRB
較少，亦可發揮作為裝置之理論上的壽命。不論如何，由於難以控制循環回路內之滾珠的運動，故在初期破損部位從螺桿軸或螺帽變成滾珠的時間點時，就應認為該組合得到滾珠螺桿裝置的最大壽命。 [0054] 亦即，實施例所示般的行程係數未達4.8的滾珠螺桿裝置中，藉由將各構成零件的單體壽命設為「螺桿軸＞螺帽＞滾珠」，而可使施加於各部位的長壽命化處理發揮至最大極限。且，如實施例所示般，剝離的形態為表面起始型剝離，故有必要使各零件之殘留奧氏體量γR
的關係成為「螺桿軸＞螺帽＞滾珠」。[0018] Hereinafter, the screw device of the present invention will be described in detail. [0019] The screw device of the present invention is used when the stroke coefficient f S does not reach 4.8. As such a screw device, there are an electric injection molding machine or an electric servo press, a servo cylinder, an electric jack, and the like, and the screw device of the present invention is applicable to these. In addition, although a ball screw device is described below as an example, a roller (roller screw device) may be used as a rotating body. Further, in the ball screw device of the present invention, the amount of retained austenite γ RS on the surface of the groove of the screw shaft conforms to the following formula. [0020] (In the formula, α S is the required life ratio of the screw shaft.) [0021] It is preferable that the amount of retained austenite γ RN on the surface of the groove of the nut is in accordance with the following formula. [0022] (In the formula, α N is the required life multiplier of the nut.) [0023] Under normal operating conditions, the ball screw device is different from a rotary bearing in that the sliding between the ball and the screw shaft or the nut track changes due to the distortion of the track. Large, so the morphology of track damage caused by rotation fatigue will become surface-initiated peeling. There is a correlation between the occurrence or progression of damage to the surface-type peeling and the amount of retained austenite γ R on the surface of the rotating surface, and it is expected that the amount of retained austenite γ R on the surface of the orbital surface will increase more than before. Get long life effect. In addition, for the purpose of quantitatively evaluating the effect of increasing the lifetime by increasing the amount of retained austenite γ R , the present inventors used a different amount of retained austenite γ R on the surface of the orbital surface subjected to high-frequency heat treatment. Various element test pieces were used to experimentally investigate the surface-initiated peel life. As a result, the following relational expression was obtained between the amount of retained austenite γ R [%] on the surface of the material subjected to the high-frequency heat treatment and the life change rate α of the conventional screw shaft material (SAE4150). [0024] [0025] It is found from the formula (1) that in order to have a longer life (α> 1) than the conventional ball screw device, the amount of retained austenite γ R on the surface of the groove of the screw shaft must be greater than 9%, and The life required for the screw device avoids high quality or insufficient quality, and the most suitable amount of retained austenite γ R can be estimated. [0026] However, if a ball screw device that applies a static load to the axial direction is driven, the nut moves relatively linearly on the screw shaft. At this time, at any position on the track surface of the nut, as the load ball passes, it will receive repeated stress. On the other hand, in the screw shaft orbit, stress is only applied when a load ball is passed along with the linear movement of the nut. Therefore, when the stroke of the nut is sufficiently long, the number of repeated stresses on the track caused by the passing of the load ball is more on the nut side than on the screw shaft side, so it is known that the initial rotational fatigue damage will be on the nut track Happen on. Therefore, conventionally, the amount of retained austenite γ R on the surface of the screw groove of the nut is set larger than the amount of retained austenite γ R on the surface of the screw groove of the screw shaft. [0027] However, in a ball screw device used in an electric injection molding machine or the like, the stroke of the nut is short, so the magnitude relationship of the number of repeated stresses applied to the track along with the load ball passing through is reversed and becomes the screw shaft side. More than the nut side. Therefore, in the ball screw endurance test under operating conditions with a short stroke, it was confirmed that the first rotational fatigue damage tended to occur on the screw shaft side. In addition, from the viewpoint of the contact surface pressure between the ball and the rail, the surface pressure on the screw shaft side is also high, so it is the basis for supporting the initial damage occurrence position to be shifted to the screw shaft side. [0028] According to the damage characteristics of the screw shaft and the nut track caused by the above-mentioned contact surface pressure and the number of repeated applied stresses, the fatigue life of the rotating surface is proportional to the ninth power of the contact surface pressure, and is repeatedly applied The stress number is proportional, so the life ratio β of the screw shaft and the nut track can be expressed by the following formula (2). [0029] [0030] In the formula, p S and p N are the contact surface pressures at the screw shaft and the nut track, and N S and N N are the repeated stress numbers applied to the screw shaft and the nut track during 1-stroke operation. [0031] Then, in order to investigate the life ratio β between the screw shaft and the nut track of the ball screw device under actual use conditions, from the introduction of a total of 20 types of ball screw devices for practical electric injection molding machines, The load or stroke in the axial direction is used to obtain p S and p N and N S and N N , and β of each model is calculated by the formula (2). With this, between β and the stroke coefficient f S obtained by dividing the stroke S t by the product of the effective number of turns (ζ) of the ball screw device, the number of loops (ξ), and the lead (l), the following Relationship (3). [0032] [0033] When driven by a short stroke (f S <4.8) of an electric injection molding machine or the like by Expression (3), the nut has a longer track life than a screw shaft (β> 1). [0034] Therefore, after considering the relationship between the screw shaft and the track life of the nut with a stroke coefficient f S <4.8 as described above, in order to meet the required life of the ball screw device, each screw groove of the screw shaft and the nut is determined. The amount of retained austenite γ R on the surface is preferable in terms of further improvement in productivity. Then, using equations (1) to (3), the amounts of retained austenite γ RS and γ RN necessary for the surfaces of the screw grooves of the screw shaft and the nut are estimated, respectively. [0035] When the life ratio of the screw shaft track to the ball screw device is α S , the amount of retained austenite γ RS on the surface of the screw groove of the screw shaft is expressed by the following formula (1). [0036] [0037] Next, if the life ratio of the nut orbit to the ball screw device is α N , the orbit life ratio β of the nut to the screw shaft becomes “β = α N / α S ”. 2) and formula (3), the amount of retained austenite γ RN on the surface of the screw groove of the nut is as follows. [0038] [0039] Thus, the amount of retained austenite γ RS and γ RN on the surfaces of the screw grooves of the screw shaft and the nut to match the required life of the ball screw device and the orbital life of the screw shaft and the nut are expressed by the formula (4) It can be estimated by substituting it as "α S = α N = α ＞ 1" in Equation (5). In other words, in the ball screw device used in the stroke coefficient f S <4.8, in order to achieve a long life without compromising productivity (α> 1), Equations (4) and (5) are used to make In the magnitude relationship of the amount of retained austenite γ R on the surface of each screw groove, a combination in which the screw shaft is larger than the nut is more reasonable. [0040] As described above, as long as the amount of retained austenite γ RS and γ RN of each screw groove of the screw shaft and the nut is satisfied, preferably “γ RS > γ RN ”, the material of the screw shaft and the nut is combined. Unlimited. However, from the viewpoint of the productivity of the ball screw device, it is mainstream to apply high-frequency heat treatment to the screw shaft system. In order to reduce the amount of retained austenite on the surface of the groove of the screw shaft among materials suitable for high-frequency heat treatment, γ RS As such, high-carbon bearing steel is preferred as the material of the screw shaft. [0041] In addition, as for the nut, the same surface-hardened steel as in the past is preferably used, and carbonitriding treatment is preferred. Since the conventional product can be directly used, it becomes cheaper as a whole ball screw device. [0042] In addition, a known method may be used for the high-frequency heat treatment, and the output of the induction heating coil may be controlled on the premise that a method for avoiding overheating can be established. [0043] Moreover, regarding the other rotating part of the ball screw device, that is, the ball, it is difficult to calculate the life using the same reference because of the random rotation of the ball. However, since the rotating surface is random, the number of times of load on the surface where peeling occurs is also small, so the life is the longest. Therefore, the amount of retained austenite γ RB on the surface is preferably smaller than that of the screw shaft or the nut. That is, the respective retained austenite amounts γ R preferably have a magnitude relationship of “γ RS > γ RN > γ RB ”. If the size relationship between these three is met, the balance between function and productivity can be maximized regardless of the damage of any constituent parts. [0044] In addition, conventional products can be used as the balls, and the bearing steel can be hardened, and the cost of the ball screw device can be suppressed from increasing. [Examples] [0045] Examples are given below to further illustrate the present invention, but the present invention is not limited thereto. [0046] Here, the ball screw device, which is often used for applications such as the injection shaft of an electric injection molding machine, is model BS6316-10.5 for verification. The main internal parameters of the ball screw device BS6316-10.5 are as follows.外径 Screw shaft outer diameter (d): 63mm ･ Lead (l): 16mm ･ Screw turns (ζ): 3.5 ･ Circulation loop number (ξ): 3 ･ Screw effective turns (ζ × ξ): 10.5 (= 3.5 × 3) [0047] As a comparative example, a standard product was used. In addition, the combination of the material and heat treatment of each part is as follows, and the magnitude relationship of the amount of retained austenite of each part is set as "nut>balls> screw shaft". ･ Screw shaft: Medium carbon steel, high-frequency heat treatment ･ Nuts: Case hardened steel, carburizing treatment ･ Balls: Bearing steel, impregnated Ball. In addition, when the stroke length S t is set to 80 mm and the stroke coefficient f S is calculated, f S = S t / ζ ･ ξ ･ l = 80 / (3.5 × 3 × 16) = 0.48. The required life ratio of the screw shaft to the nut at this time is about 5 times from the formula (2). Therefore, the amount of retained austenite γ RS on the surface of the groove of the screw shaft to be targeted is calculated by Equation (1) to be about 25%. [0049] According to the above, when the shape is the same as that of the comparative example, a ball screw device having the following structure is produced. ･ Screw shaft: High-carbon steel, high-frequency heat treatment ･ Nut: Surface hardened steel, carburizing treatment ･ Ball: Bearing steel, impregnated [0050] As described above, while suppressing overheating and ensuring the amount of retained austenite on the track surface γ R is not easy, so in this test, the coil shape and high-frequency heat treatment conditions were adjusted during the processing of the screw shaft. As a result, a screw shaft was obtained in which the amount of retained austenite γ R on the raceway surface was 26%. Thereby, the magnitude relationship of the retained austenite γ R in the example becomes "screw shaft>nut>ball". [0051] The durability of the ball screw device (model BS6316-10.5) of the above-mentioned Comparative Examples and Examples was evaluated by determining the L 10 life ratio and L 50 life ratio under the following conditions. The number of tests was 7 in the example and 13 in the comparative example. Each life was obtained by a Weibull distribution. ･ Maximum axial load (Fa max ): 300kN ･ Maximum screw shaft rotation number (n max ): 500min -1 ･ Stroke (S t ): 80mm ･ Lubricant: Grease [0052] The results are shown in Figure 1, but It was confirmed that the example has a longer life than the comparative example. The increase in life span is 3.0 times the L 10 life and 5.3 times the L 50 life. [0053] In the case of confirming the damaged portion, the comparative example was peeling of the screw shaft, whereas the example was peeling of the ball. The life ratio of the screw shaft and the nut of this embodiment is about 5 times. Therefore, if the life of the screw shaft can be extended by 5 times, it can be predicted that the function of the ball screw device of this structure can be maximized. Regarding this, almost the maximum value was obtained from the endurance test results of the examples. The peeling life of the ball is estimated to be about 1.5 times the life of the screw shaft of the comparative example from the standpoint of the retained austenite amount γ RB . As described above, the ball screw device is provided with a ball circulation mechanism. In the circulation circuit, the ball is almost in a no-load state, and the revolution or rotation operation is considered to be random. Therefore, the position where the ball is subjected to the load is also random, so it is difficult to predict the life extension effect, but even if the amount of retained austenite γ RB is small, the theoretical life as a device can be exhibited. In any case, because it is difficult to control the movement of the balls in the circulation circuit, when the initial damage site changes from a screw shaft or a nut to a ball, the combination should be considered to obtain the maximum life of the ball screw device. [0054] That is, in a ball screw device having a stroke coefficient of less than 4.8 as shown in the embodiment, the individual component life of each component is set to "screw shaft>nut>ball", which can be applied to The long-life treatment of each part is performed to the maximum. In addition, as shown in the examples, the form of peeling is surface-initiated peeling. Therefore, it is necessary to make the relationship between the amount of retained austenite γ R of each part "screw shaft>nut>ball".