机床外文翻译-高性能机床主轴的发展【中文3140字】【PDF+中文WORD】

机床外文翻译-高性能机床主轴的发展【中文3140字】【PDF+中文WORD】,中文3140字,PDF+中文WORD,机床,外文,翻译,性能,主轴,发展,中文,3140,PDF,WORD 【中文3140字】 高性能机床主轴的发展 摘要：主轴系统在现代机床中的一个重要要求是实现更高的转速从而提高加工效率。此外，要使主轴系统在一个给定的转速范围内免受不正当的操作条件且具有较好的稳定性。本文提出了有助于主轴轴承在不同的领域的改进研究系统。首先，提出了替代主轴轴承运动学四触点的新结果。其次，对于浮动轴承的配置进行了新的解决方案的讨论。提出一种改进的圆柱滚子轴承，可以在更高的速度下操作。最后，讨论了在改进后的涂层轴承组件的故障安全性能下的潜能。在本文中介绍了这两个的分析研究和实验测试。 关键词：机械，主轴，轴承 1.介绍 现代机床的生产率主要取决于转速限制和主轴单元的负荷能力。 一方面，现代切削刀具采用铝或镁，并配有立方氮化硼（ CBN）或多晶金刚石（PCD）的刀片，这样的切削加工工具，使得切削速率从5000m/min高达10000m/min。铣削刀具应用20至30毫米的直径来实现非常高的切削速度，从而达到主轴速度超过100000 rpm的要求。根据滚动轴承的技术在本领域的实际状态，这种需求目前只能用平均直径为30毫米的主轴轴承来实现。然而，由于这些极端工作条件下，主轴单元的所有功能部件主轴轴承、电动机旋转转子会加载到其物理极限。 另一方面，主轴还被应用于通用机床。这些特点是由不同的需求所决定的。例如，具有高的切割力和力矩适中的转速的钢的粗加工，在这种情况下，大直径的主轴和轴承来承受这些载荷。 主轴设计方法的不同是源于需求的不同。为了满足这些需求，速度特性系数nxdm必须增加高达3.5 ～4.0×106mm/min，来充分确保主轴本身和主轴轴承的刚度和稳定性。 图1 铣刀电机主轴滚动轴承 2.多位（3P，4P）主轴轴承 2.1轴承几何优化的推动 轴承被主要应用在现代主轴机床中，必须履行最高要求运行精度和刚度。在过去，为了提高轴承的性能开发了各种修改方法。其中，通过给较小的陶瓷球以及优化的外圈使用特殊润滑剂。尽管如此，高速运转还是极大地降低乐轴承的使用寿命。在操作过程中底层的主要作用是由不同的用途来决定的。尤其是，高速运转的内圈和外圈上的接触角的依赖性偏差导致轴向和径向刚度的减少。另外，在外圈上的接触区域的离心力作用下，陶瓷球受到强烈的负荷。 轴承之所以具有不同的内部几何形状是为了减少作用在滚珠上离心力所带来的负面影响。此外，对轴承的稳定性也有所提高，并对传统轴承的内圈和外圈滚道提供额外的接触点。因此，滚珠的轴向和径向移动被阻止，恒定的接触角和轴向位移使内圈可以保证在很宽的速度范围内运动。上述这种思想被引入到轴承的设计概念中，如图2所示（a）和（b）。图2中的第三个（c）这种新概念的设计方法在文中也介绍了。 图2 轴承的不同多点(3 p,4 p)选择 2.2多点分析研究（4P）轴承 表一主要研究多点（3P）轴承的操作过程及理论和实践调查。实验室测试的轴承制造机床和生产工程(WZL)是在传统主轴轴承的基础上的。也有一些通过数值计算分析特性的多点（4P)轴承。 随后,关于新轴承的发展有了进一步的结果,运动学和四个接触分球正在考虑被使用。所有的计算都是在轴承型号为7014、直径为12.7mm的陶瓷球上完成的。下面的图中使用缩略语，在表1的中列出。 表1 3.、4、5使用的是缩用词 在[1]的计算中表明，内圈的轴向位移可以减少不到两个微米，接触角的变化依赖速度是可以预防的。但是，多点轴承(4 p)的安装与径向间是有间隙的。因此，他们对热有非常敏感的影响，特别是过度的高温使得轴承的内圈可能会引起相互干扰。这些影响也发生在高速旋转的圆柱滚子轴承。图3说明了多点（4P）轴承的内圈和外圈在1赫兹和4赫兹下的接触压力。这些直接接触直接传递到轴向荷载（见图表）和最大程度所受压力上。轴承的径向间隙显示为22微米的。为了防止内圈弹出，应选择合适的内圈并与轴之间有35微米的间隙量。因此，轴承是提前被安装上的。曲线1和2不考虑轴承计算的热效应。高应力值在内圈滚道曲率的结果上是很广的。赫兹压力的增加造成的内圈离心的扩张以及作用在球上的离心力增大。 图3 在多点（4P）轴承在赫兹压力下速度和温度 相反，曲线3和4显示内圈结合离心力超温（线性增加）的影响。通过假设并计算一个梯度为1K/2000 rpm的曲线，其内部应力显著增加，这是可以注意到的。在最大转速30000 rpm的赫兹压力下，内环上升超过限制值为2000 N/mm²。除了这些理论结果，还要必须考虑到内部应力的热增加和过载的耦合效应。因此，人们可以看到一点对多点（4P）轴承的干扰在高速运转的情况下内圈温度明显过剩。这个假设将在第2.3节中进行研究。 图2（c）显示出第三个概念的新轴承几何形状的。它是为了防止在多点（4P）轴承的内部超载而开发的。概念的特征是分割内环，它是一半固定在主轴体面向主轴的刀具侧面的环。于是，它可以承受从加工过程中产生的力。环下半部分可沿轴轴向移动，并通过碟形弹簧压向球，形成轴承的内部预压功能。 图4中说明了假设多余的温度高达15 K线性（见图3），多点（4P）轴承的内圈在计算速度依赖性和运动学预装中的发展，内部弹簧预紧量为370N。 图4 内部弹簧预紧为370N的多点（4P）轴承 2.3多点（4P）轴承的试验及研究 该试验台用于实验研究如图6，其直接驱动可实现高达40,000 rpm的最大转速，额定扭矩达4.2Nm，额定转速为23,000 rpm。测试主轴和驱动由一个爪式离合器相连接，试验轴承可沿轴向由一个液压活塞被加载，外圈的回火是通过水的循环在凸缘上实现的。由此，引起的附加滚动接触的外圈的加热可被减小。内轴承的温度是由一个接近内圈旋转的非接触式传感器来测量的。 图6 试验台 图7中显示的是实验结果为对多点（4P）轴承的一个刚性和一个弹性点。起初，刚性轴承（概念(b)，图2所示）是测试的，在测试中进行不回火的外圈。接着，将柔性轴承（概念(c)，图2 所示）与所述外圈的回火进行了测试，测得的温度显示相关的环境温度。在测试过程中的扭矩值来自电动机的电流。在图7中使用的缩写在表2中说明。 表2 在图7中使用的缩写 曲线[IT1]和[ OT1]说明第一个试验轴承的内圈和外圈的温度，如概念(b)所示。轴向载荷达1,000 N，5克的轴承转速高达19000转，每2小时增加2000转。 图7 多点（4P)轴承的行为操作 3.可移动的弹性圆柱滚子轴承 最高转速主轴单元通常是基于角接触球轴承的弹性装置设计的。这种主轴由一个固定和移动轴承单元，以补偿热运动的主轴伸长率来设计的。主轴在温度梯度的情况下，轴承套圈的外壳的轴向运动可减少甚至避免造成主轴故障。 在这种情况下，圆柱滚子轴承可称为一个“理想”的移动轴承。轴向相对的内、外环是由一个螺旋滚筒的旋转来运动的。然而，由于径向干扰温度及离心力作用于轴承组件而造成可达到的旋转速度。因此，对高速圆柱滚子轴承的方法是减少基于功率损失而造成内部产生的热量和增加在线接触赫兹压力。 4.对轴承的故障安全特性功率的优化 除了轴承设计的开发，更多的研究工作集中在传统主轴轴承的故障安全性能的最优化上。主轴故障往往是由润滑不足造成的，特别是润滑脂的润滑，润滑剂的供给不足，这些都可能会导致轴承的保持架破损或过热。 5.总结 根据所设计的主轴角接触球轴承以及圆柱滚子轴承的现有技术的状态，被广泛用于高速主轴的应用程序中。然而，这两种类型的轴承的旋转速度是有限的，特别是通过物理作用如热和离心载荷。在本文中，一些方法都瞄准在轴承上的提高稳定性和速度性能。 然而，由于不充分的滑动轴承衬套，可动轴承可能也会失败。因此，适应于高速运转的圆柱滚子轴承的开发工作尤为重要。轴承比传统的圆柱滚子轴承表现出更高的合规性。这个属性是通过提供狭窄水道或外圈和内圈与地面形成凹槽来实现的。在实际测试中，这些轴承比传统类型达到更高的转速。最后，介绍了涂层下故障安全特性的主轴轴承润滑不足的情况的优化。 6.参考文献 [1] Weck, M., Spachtholz, G., 2003, 3- and 4-Contact Point Spindle Bearings-a new Approach for High Speed Spindle Systems, Annals of the CIRP, 52/1: 311-316. [2] Moller, B., 2006, Hochgeschwindigkeits-Spindellager, Proceedings Gestaltung von Spindel-Lager-Systemen“, WZL Forum (Publisher), Aachen. [3] Harris, T.A., 2001, Rolling Bearing Analysis, 4th Edition, John Wiley & Sons, Inc, New York. [4] Cao, Y., Altintas, Y., 2004, A General Method for the Modeling of Spindle-Bearing Systems, Journal of Mechanical Design, Vol. 126: 1089 -1104. [5] Yangang, W. et al., 2004, FE-Analysis of a novel Roller Form – a deep End Cavity Roller for Roller Type Bearings, Journal of Materials Processing Technology 145: 233-241. Developments for High Performance Machine Tool Spindles C. Brecher1 (2), G. Spachtholz1, F. Paepenmüller1 1Laboratory for Machine Tools and Production Engineering, Aachen, Germany Abstract One important demand on spindle systems in modern machine tools is to realise higher rotational speeds in order to increase the machining efficiency. Additionally, for a given speed range a better robustness is demanded so that the spindle system is desensitised against improper operating conditions. The paper presents research results in various fields which contribute to the improvement of spindle-bearing systems. At first, new results for alternative spindle bearing kinematics with four contact points are presented. Secondly, a new solution for floating bearing arrangements is discussed. A modified cylindrical roller bearing is presented which can be operated at higher speeds. Finally, the potential of coated bearing components is discussed in the context of improved fail-safe properties. In this paper both analytic studies and experimental tests are presented. Keywords: Machine, Spindle, Bearing 1 INTRODUCTION The productivity of modern machine tools is mainly determined by the rotational speed limits and the load carrying capacities of their main spindle units. On the one hand, the machining of aluminium or magnesium with modern cutting tools, equipped with cubic boron nitride (CBN) or polycrystalline diamond (PCD) inserts, allows cutting rates from 5,000 m/min up to 10,000 m/min. In the case of the application of end mills with diameters between 20 and 30 mm the realisation of these very high cutting speeds requires spindle speeds of more than 100,000 rpm. According to the actual state of the art of rolling bearing technology, this demand can currently only be realised by spindle bearings with a mean diameter of 30 mm. However, due to these extreme operating conditions, all functional components of a main spindle unit – the spindle bearings, the rotor of the motor as well as the rotating unions – are loaded up to their physical limits. On the other hand, the main spindles also need to be suitable for versatile machine tool applications. These are characterised by varying demands. The rough machining of steel, for example, is characterised by high cutting forces and moments and moderate rotational speeds. In those cases, bigger spindle and bearing diameters are essential to bear these loads. The following basic approaches for the design of main spindles can be derived from the diverging demands presented above. To fulfil those demands, the characteristic speed coefficient n x dm has to be increased up to 3.5 – 4.0x106 mm/min, ensuring a sufficient stiffness and robustness of the spindle body and the spindle bearings. Figure 1 presents a typical motor spindle with a power output of 80 kW and a maximum rotational speed of 30,000 rpm. The stator of the drive is water-cooled. The spindle body has a hollow shaft taper and is rotationally supported by an elastically preloaded back-to-back spindle bearing arrangement. In order to develop an improved spindle and bearing design the optimisation of the fixed bearing unit (varied  elastically preloaded back-to-back arrangement HSK A 63/80 bearing diameter: 70 mm max. rotational speed: 30,000 rpm Figure 1: Milling motor spindle with rolling bearings. inner bearing geometry), of the movable bearing unit(elastic cylindrical roller bearings) as well as of the tribological properties (surface coatings, lubrication) shall be analysed. These topics are discussed in the following. 2 MULTIPOINT(3P,4P)-SPINDLE BEARINGS 2.1 Motivation for the Optimisation of the Bearing Geometry Spindle bearings for the application in main spindles of modern machine tools have to fulfil highest demands on running accuracy and stiffness. In the past, various modifications have been developed in order to improve the bearing performance. Among others, one can enumerate special lubricant supplies through the outer ring, smaller or ceramic balls as well as optimised cages. Nevertheless, highest speeds extremely reduce the life time of spindle bearings. The underlying main effects during the operation process were investigated by various authors and were, e.g., summarised in [1], [2], [3], [4]. Especially, the speed dependent deviation of the contact angles on the inner and outer ring causes a decrease of axial and radial stiffness. In addition, the contact areas on Annals of the CIRP Vol. 56/1/2007 -395- doi:10.1016/j.cirp.2007.05.092 the outer ring are strongly loaded by the centrifugal forces acting on the balls. Weck et al. presented in [1] spindle bearings with varied inner geometries in order to reduce the negative effects of the centrifugal forces acting on the balls. In addition, the robustness of the bearings should be improved. Weck et al. provided additional contact points on the raceways of the inner and outer ring of conventional spindle bearings. Due to this, the axial and radial movement of the balls is prevented and constant contact angles and a reduced axial displacement of the inner ring can be ensured over a wide speed range. The bearing concepts introduced in [1] are shown in Figure 2 (a), (b). Figure 2 (c) presents a third, novel concept introduced in this paper. increase of the Hertzian pressures is caused by the centrifugal expansion of the inner ring as well as by the centrifugal forces acting on the balls. However, the stresses do not exceed critical values of the conventional bearing material 100Cr6 (2,000 N/mm²). ax. load 500 N ET 3 4 1 1: in. ring1 2: out. ring4 3: in. ring1, ET 4: out. ring4, ET 2 2 3 4 axial preload 1 Hertzian pressure [kN/mm²] excess temperature [K] 2,5 15 2 12 1,5 9 1 6 0,5 3 -399- 0 0 0 5 10 15 20 25 30 rotational speed [1,000 rpm] (a) Multipoint(3P)- bearing  (b) Multipoint(4P)- bearing  (c) Multipoint(4P)- bearing, internal spring preload Figure 3: Hertzian pressures in a multipoint(4P)-bearing dependent on speed and excess temperature. In contrast, the curves 3 and 4 show the influence of the inner ring excess temperature (linear increase) in combination with the centrifugal effects. These curves were calculated by assuming a gradient of 1 K per Figure 2: Different alternatives of multipoint(3P,4P)- spindle bearings. 2.2 Analytic Investigation of Multipoint(4P)-Bearings The contents of [1] focus on the operating behaviour of multipoint(3P)-bearings, both theoretic and experimental investigation. The test bearings were manufactured at the Laboratory for Machine Tools and Production Engineering (WZL) based on conventional spindle bearings. Also some characteristics of multipoint(4P)-Bearings were analysed by means of numerical calculations. Subsequently, further results regarding the development of new bearing kinematics with four contact points per ball under consideration of thermal effects will be presented. All calculations are done for the bearing size 7014 with ceramic balls of the diameter 12.7 mm. The contact angles amount to 15°. The abbreviations used in the following diagrams are listed in Table 1. in.ring1/2 Inner ring, contact point 1 or 2 out.ring3/4 Outer ring, contact point 3 or 4 ET Excess temperature Table 1: Abbreviations used in Figures 3, 4, 5. In [1] it was shown by calculations that the axial displacement of the inner ring can be reduced to less than two microns and that a speed dependent change of the contact angles can be prevented. However, the 2,000 rpm. A significant rise of the internal stresses can be noticed. At a maximum rotational speed of 30,000 rpm the Hertzian pressures on the inner ring rise above the limiting value of 2,000 N/mm². In addition to these theoretical results, one has to take into consideration that the increase of internal stresses on the one hand and the thermal overloading on the other are coupled self- energising effects. Therefore, one can expect jamming of a multipoint(4P)-bearing with a pronounced excess temperature of the inner ring in case of higher rotational speeds. This assumption will be investigated in experimental tests in section 2.3. Figure 2 (c) shows a third concept of a new bearing geometry. It was developed in order to prevent the internal overloading of the multipoint(4P)-bearing. The concept is characterised by a divided inner ring. One half of the ring which is oriented towards the tool side of the spindle is fixed to the spindle body. By that, it can bear the forces resulting from the machining process. The second half of the ring is axially movable and pressed against the balls by a disc spring, creating an internal preloading of the bearing. The diagram in Figure 4 illustrates the calculated speed dependent development of kinematics in the preloaded multipoint(4P)-bearing assuming a linear increase of the inner ring’s excess temperature up to 15 K (see Figure 3). The internal spring preload amounts to 370 N. multipoint(4P)-bearings are mounted with zero radial clearance. Therefore, they are extremely sensitive to thermal effects. Especially excess temperatures of the inner ring may cause jamming of the bearing. This effect also occurs in cylindrical roller bearings under high rotational speeds. Figure 3 illustrates the Hertzian pressures in the contact 1, inner ring, and contact 4, outer ring of a multipoint(4P)- bearing. These contacts directly transfer the axial load (see pictogram) and are stressed to the highest extent. The bearing shows a radial clearance of 22 microns. The 25 Ax. Load 370 N 3, 4 spring preload 2a 2b 1: in.ring1, ET 2: in.ring2, ET 2a: in.ring2 2b: in.ring2, ET, 20° 3: out.ring3, ET 4: out.ring4, ET contact angles [°] 20 15 10 5 0 425 spring preload [N] 1 405 385 2 365 345 325 fit between inner ring and spindle amounts to 35 microns in order to prevent lifting-off of the inner ring. Therefore, the bearing is slightly preloaded. The curves 1 and 2 represent a bearing calculation without consideration of thermal effects. The higher stress values on the raceway of the inner ring result from a wider curvature. The 0 5 10 15 20 25 30 rotational speed [1,000 rpm] Figure 4: Contact angles in a multipoint(4P)-bearing with internal spring preload of 370 N. The outer axial load is decreased to 370 N in order to assure the same initial loading of the contact points as in Figure 3. As explained in [1] the outer contact angles (curves 3, 4) stay constant over the whole speed range. Caused by the thermal and centrifugal effects the first half of the inner ring expands (contact 1). Therefore, a slight decrease of the corresponding contact angle (curve 1) and, consequently, a spindle displacement occur. The second movable half of the inner ring is not mounted by press fit to the spindle resulting in a strong centrifugal expansion and a strongly decreasing contact angle (curve 2). Curve 2a shows the reduction of the contact angle without consideration of thermal effects. In addition to the contact angles the spring preload curve is shown. The load increases to 406 N caused by the displacement of the spindle body and the movable ring half. The diagram in Figure 5 shows the Hertzian pressures in the preloaded multipoint(4P)-bearing. Again, curves 1 to 4 represent the loading of contacts 1 (inner ring) and 4 (outer ring) with and without an excess temperature on the inner ring. It becomes obvious, that the stress level is clearly lower than in the rigid multipoint(4P)-bearing variant (see Figure 3). The maximum stress value is 1,600 N/mm². To understand the effect of the decreasing contact angle on the movable half of the inner ring, the Hertzian pressure in contact 2 (movable inner ring) is also analysed. Curve 5 illustrates a maximum value of about 2,000 N/mm². This Hertzian pressure can be reduced by providing a larger contact angle. This effect is shown by the curve 6 in the diagrams in Figures 4 and 5. By increasing the contact angle to 20° a pressure reduction to 1,200 N/mm² is possible. The theoretical analysis of the multipoint(4P)-bearing with internal spring preload shows that the elastic arrangement of the two halves of the inner ring can prevent the bearing from jamming. The negative effects which result from inner ring excess temperatures can be reduced. In the following, experimental results regarding the operating behaviour of multipoint(4P)-bearings under the influence of an excess temperature are presented. measured by a non-contacting sensor positioned closely to the rotating inner ring. Direct drive Hydraulic unit Temperature sensor Flange with test bearing Test spindle Figure 6: Test stand. The diagram in Figure 7 presents experimental results for both a rigid and an elastic multipoint(4P)-bearing. At first, the rigid bearing (concept (b), Figure 2) was tested. The tests were performed with and without tempering of the outer ring. Subsequently, the flexible bearing (concept (c), Figure 2) was tested with tempering of the outer ring. The measured temperatures are shown related to ambient temperature. The torque values are derived from the motor current during the tests. The abbreviations used in Figure 7 are explained in Table 2. it1, ot1, t1 Inner / outer ring excess temperature / torque, concept (b), no tempering it2, ot2, t2 Inner / outer ring excess temperature / torque, concept (b), tempering 40°C it3, ot3, t3 Inner / outer ring excess temperature / torque, concept (c), tempering 40°C Table 2: Abbreviations used in Figure 7. The curves [it1] and [ot1] illustrate the inner and outer temperatures of first test bearing, concept (b). The axial Hertzian pressure [kN/mm²] 2 1,6 1,2 0,8 ET 15 ax. load 370 N 1 1: in.ring1 2: out.ring4 3: in.ring1, ET 4: out.ring4, ET 5: in.ring2, ET 6: in.ring2, ET, 20° 5 3 4 12 9 excess temperature [K] excess temperature (rel. to Tambient) [K] 2 6 6 load amounts to 1,000 N. The bearing is grease- lubricated with 5 g of KlüberSpeed BF72-22. Up to 19,000 rpm the rotational speed is increased by 2,000 rpm every 2 hours, then by 1,000 rpm every 2 hours. The test is stopped if a shut-off temperature of 55°K is exceeded. 0,4 0 60 3 50 0 0 5 10 15 20 25 30 40 rotational speed [1,000 rpm] 1,2 it1, ot1 ot2 t2 t3 t1 15t 19t 21t 25t 27t 29t 7t 11t ax. load: 1000 N it2 it3 ot3 23t friction torque [Nm] 1 0,8 Figure 5: Hertzian pressure in a multipoint(4P)-bearing with internal spring preload of 370 N. 2.3 Experimental Investigation of Multipoint(4P)- Bearings The test stand used for the experimental investigations is shown in Figure 6. The direct drive can realise maximum rotational speeds of up to 40,000 rpm. The nominal torque amounts to 4.2 Nm for a nominal speed of 23,000 rpm. The test spindle and the drive are connected by a jaw clutch. The test bearings can be loaded axially  30 20 10 0 0 4 8 12 16 20 24 28 32 36 time [h]  0,6 0,4 0,2 0 by a hydraulic piston. A tempering of the outer ring is realised by a water circulation in the flange. Thereby, the heating of the outer ring caused by the additional rolling contact can be reduced. The inner bearing temperature is Figure 7: Operational behaviour of multipoint(4P)- bearings. With this first bearing alternative, a maximum rotational speed of 21,000 rpm can be realised. Inner and outer bearing temperatures reach the same values and rise up to the shut-off temperature of 55 K (curves [it1], [ot1]). The torque amounts to 0.25 Nm. In the next step, the same bearing was tested tempering the outer ring. At the tempering unit, a supply temperature of 40°C was adjusted. Compared to the first test, up to 17,000 rpm the bearing temperatures are clearly reduced (curves [it2], [ot2]). The temperature of the outer ring is up to 4 K lower than the one of the inner ring. This is caused by the optimised heat dissipation through the water internal friction (narrow raceway, ceramic rollers) and at a reduction of the speed and heat-dependent Hertzian pressures in the line contacts (elastic bearing rings). circulation in the flange. The operating state of the bearing corresponds to the calculation in Figure 3. After increasing the speed to the next level (19,000 rpm) a (a) Narrow raceway (b) Ceramic rollers (c) Elastic rings sudden rise of the temperatures and the friction torque occurs. The test is stopped immediately. This effect corroborates the assumption that the bearing concept (b) will fail in case of high exceed temperatures of the inner ring. Finally, the third bearing concept (c) with the elastically preloaded, movable half of the inner ring was examined. The axial load was decreased to 800 N in order to adapt the loading of the rolling contacts to the first tests. Again, the outer ring was tempered by water circulation. The measured temperatures of the concept (c) are in between the results of the two foregoing tests. They are lower than those of test 1 due to tempering and higher than test 2 because of the additional internal spring preload of about 380 N. Again, an excess temperature of the inner ring can be observed. Nevertheless, the bearing reaches the final rotational speed of the test cycle of 30,000 rpm with maximum excess temperatures relative to ambient temperature of 50 K (inner ring) and 43 K (outer ring),respectively. The tests with the bearing concepts (b) and (c) were performed in order to verify the results of the calculations. Although a direct measurement of the internal bearing kinematics is not possible during operation the basic findings regarding the operational behaviour of the multipoint(4P)-bearings could be proven. 3 ELASTIC CYLINDRICAL ROLLER BEARING AS MOVABLE BEARING Main spindle units for highest rotational speeds are usually designed based on an elastic arrangement of angular contact ball bearings. This spindle design is characterised by a fixed and a movable bearing unit in order to compensate thermal and kinematic elongations Figure 8: Different alternatives of modified cylindrical roller bearings. In the following section test results for the first (a) and the third bearing concept (c) are presented. The cylindrical roller bearings are equipped with crowned steel rollers. The modifications are ground grooves in the outer or inner ring or a narrow inner ring raceway, respectively. By these measures the stiffness of the bearings and the heat generation are reduced. The design of the grooves is developed by means of FE-calculations [5] so that the rings comply equally in case of rising internal loads. All test bearings are mounted with an initial radial clearance of -2 μm and are air-oil lubricated (oil viscosity 32 mm²/s, air pressure 1.7 bar). During the tests the rotational speed is increased stepwise. Curve 1 in Figure 9 illustrates the operating behaviour of a reference bearing. The temperatures measured at the outer ring clearly rise after passing rotational speeds of 12,000 rpm. The final rotational speed is 15,000 rpm with an absolute outer ring temperature of 70°C. Curves 2 to 4 show the test results for the modified bearings. The best temperature behaviour and, in consequence, the highest rotational speeds are realised with the bearing with a narrow inner ring raceway. The maximum speed amounts to 23,000 rpm. The bearings with elastic rings show a significant increase in temperature after passing 16,000 rpm (curve 4) and 18,000 rpm (curve 3). Both reach final speeds of 18,000 rpm. According to the test results all modified bearing types allow for the realisation of higher rotational speeds. The