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1、低温高速摩擦试验机的发展：设计理念和实验结果Subramoniana and Bikramjit Basub, a 印度特拉凡得伦JSPS Ronpaku空间部门 b印度坎普尔高级陶瓷材料及冶金工程实验室摘要：为了评估安装在液体火箭发动机中的高速低温涡轮泵里的滚珠轴承的摩擦特性，需要一台能在高速低温环境中操作的摩擦试验机。为了满足以上要求，已经设计出了一台这样的机器。利用这台试验机，可以对在低温流体中受到高接触应力（高达2.5Gpa）的情况下快速运转（0.5-45m/s）的各种不同材料与润滑剂配合形式的机构进行摩擦磨损情况评估。这台试验机还有另外两个特点：（a）含有一个滚球和圆盘状测试仪，目的
2、是测量在以上条件下的摩擦；(b)无润滑或有润滑的滚珠轴承（孔径为10mm）的测试要在液氮或液氦环境中进行，而且此时轴承的转速非常高（36000rpm）。此外，也考虑到了轴承在承受50N的最大轴向载荷时摩擦力矩的连续测量问题。这篇文章讨论的重点是这台新型摩擦试验机的设计细节。这篇文章也记录了新型试验机最初的试验结果，试验是在液氮环境中和满足以上实验条件的前提下，测试440C和AISI304无润滑状态下摩擦磨损情况的。在液氮环境中以Pb-IP为润滑剂的滚珠轴承，转速达36000rpm时的摩擦磨损情况也已经有试验结果了。关键词：低温摩擦试验机；摩擦系数；真空摩擦学文章大纲1.绪论2.新型低温摩擦试验
3、机介绍 2.1主轴部件 2.2带有球形面的试样装卡部件和轴承安装部件 2.3试验样本安装单元和施加载荷装置 2.4驱动马达和齿轮箱 2.5数据采集系统和电子控制器3高速低温摩擦试验机的初期试验4结论参考文献1.绪论有关在低温环境下新型材料摩擦磨损的研究成果关系到真空摩擦学的应用。关于金属材料的报告有很多，但是有关陶瓷应用的资料，与疏松物质和润滑剂的研究成果一样是有限的。Boes等人1研究了使用不同固体润滑剂的球轴承在-142C到537C温度下转速达20000rpm时的特性。研究的润滑剂包括70Ag20PTFE10MoSe2, 80Ag15PTFE5MoSe2 and 70AgHg20PTFE1
4、0MoSe2（都是体积百分比）。在24C时，所研究的材料的摩擦系数从0.11到0.21不等，而其中70AgHg20PTFE10MoSe2的摩擦系数最低。在315C时，这种材料的摩擦系数甚至达到0.06,。Chaudhuri 等人研究了440C在纯氧气中，在无润滑剂的前提下从-185C到675C时的滑动磨损情况2。很明显滑动摩擦系数的平均值取决于平衡状态下施加载荷的大小，而载荷随着滑动速度和整体温度的增加而减小。在众多金属材料中，AISI 440C马氏体不锈钢是航天飞机主发动机中高压氧气涡轮泵的首选材料。Chaudhuri等人测试了440C在无润滑条件下滑动时，载荷、速度、温度（-185C到67
5、5C）对其摩擦磨损（平均滑动摩擦系数和磨耗率）情况的影响3。在剧烈的磨损过程中有一瞬间温度超过了1000C。当达到稳定状态时温度降到了200C。随着温度的下降，滑动摩擦系数从0.6降到了0.25左右4。除了金属材料的摩擦特性，也在室温和不同湿度的条件下研究了陶瓷、高分子材料和润滑剂5，这样的研究在零度以下是受限制的6，首先是因为可以在这么苛刻的条件下使用的摩擦试验机很少见。然而，应用于航天飞机的主机或液体火箭发动机中的具有代表性的球轴承，需要克服高的摩擦和磨损以高速（35000rpm）运转几分钟（高达十分钟）。因此，需要一个能够模仿高应力与快速滑行实验条件的摩擦试验机。首先，这台摩擦试验机设计
6、和制造完成后，要能够估测各种不同疏松物质或润滑剂的潜能，为的是以后能应用于火箭发动机中。其次，可以实现有关机械性能的改变（在零摄氏度以下）对不同材料磨损情况的影响的基础研究。另外，这台机器还可以研究低温环境对不同润滑剂的润滑作用是否有影响。基于以上动机，目前的工作就是设计和制造一台高速、球盘式摩擦试验机，而且它可以在低温环境下操作。这篇文章也记录了新型试验机最初的试验结果，试验是在液氮环境中和满足以上实验条件的前提下，测试440C和AISI304无润滑状态下摩擦磨损情况的。在液氮环境中以Pb-IP为润滑剂的滚珠轴承，转速达36000rpm时的摩擦磨损情况也已经有试验结果了。另外，这篇文章还讨论
7、了在低温液体中无润滑的钢铁的磨损机构。2. 新型低温摩擦试验机介绍为了研究在低温流体中高速滑行时的摩擦磨损情况设计了一种新型高速、带有滚球测试仪的低温摩擦试验机。而且也包含测试球轴承在低温流体中以高达36000rpm的速度运转时的力矩的装置。低温流体为液态氮或液态氦。滑动发生在固定的球与高速旋转的盘状物之间。载荷和旋转速度都是可调的。在实验过程中，与施加载荷和旋转速度相对应的切线方向的滑动摩擦力可以被测量出来。摩擦系数可以通过持续测量出来的载荷、速度和环境因素组成的函数关系求得。表1给出了这台新型试验机的全部技术规格。图1a中给出了球盘式低温摩擦试验机的大体轮廓，设计细节可以在图1b中看出。这
8、台试验机包括以下几个主要模块，下面是它们的概括介绍：a主轴部件b带有球形面的试样装卡部件和轴承安装部件c. 试验样本安装单元和施加载荷装置d. 驱动马达和齿轮箱e. 数据采集系统和电子控制器表1 低温摩擦试验机的技术规格参数最小值最大值变量球直径 (mm)4104, 6, 8 and 10mm圆盘直径 (mm)20402040mm轴向载荷 (N)0501, 2, 5, 10 and 20N磨损轨迹直径 (mm)103010, 15, 20, 25 and 30mm试验速度 (rpm)850360007 级摩擦力 (N)05任何值的准确性在0.1N试验环境标准状况, 液氮, 液氦图1 低温摩擦试
9、验机的大体轮廓（a）；球盘式高速低温摩擦试验机设计细节2.1 主轴部件主轴部件包括可绕驱动轴，为了确保其安全性安装在材料为不锈钢440C的轴内，而这根这根轴被直线运动轴承支撑着共同安装在铝合金架内。可绕驱动轴的一端与盘状测试仪相连，另一端与驱动马达相连。图2展示了与盘状测试仪连接的可绕驱动轴。摩擦试验机的盘状测试仪底部设计了球形固定装置，可以与可绕驱动轴紧密连接。这一特色保证了磨屑脱落时及时逼真的得出测试数据。通过使用辐射加热器抵御低温流体传过来的低温的方法来保证主轴的轴承始终处在室温下。图2 可绕驱动轴2.2 球形外壳样本装卡装置和轴承安装单元球形外壳装卡装置有一个独有的特点，可以在旋转盘的
10、四个不同半径位置处安装测试球，这样就能获得不同范围内的直线滑行速度。直线滑行速度（v）可以通过以下方法计算获得：因此，一个旋转盘可以完成四个不同直线滑行速度的试验。在我们的试验机中，半径为7.5、10、12.5和15mm的磨损轨迹有利于从0.6到45m/s的不同滑行速度的提高。轴承安装单元有利于试验用轴承刚性固定的内圈与可绕驱动轴的连接。也可以通过轴承安装单元来测试球轴承（速度高达36000rpm）的力矩。2.3 试验样本安装单元和施加载荷装置有一个吊桶装载斗竖直悬挂在自重平衡的滑轮上，它可以在整个试验过程中维持一个恒定的额定载荷。这种施加载荷的装置，可以保证在多次滑动摩擦磨损试验中有一个恒定
11、负载的环境，无论有任何薄膜的移动或者润滑剂/基材的磨损等动态改变。最大可以施加50N的载荷。一旦施加载荷滚球就会进入并与旋转盘接触。图3标示出了两个测压元件，一个是测试恒定额定载荷的，一个是测试在动态测试中的摩擦载荷的。图4是测试用轴承的安装细节图，而图5是摩擦试验机中的测试圆盘安装图。图3 额定载荷和摩擦载荷测压元件图4 测试用轴承的安装图5 测试盘和测试盘装卡装置 2.4 驱动马达和齿轮箱用在低温摩擦试验机中的驱动马达，运转速度可高达36000rpm，且没有任何振动和噪音。因为安装有嵌入式的齿轮箱，测试轴的速度可以从850到36000rpm之间实现14级变动。由于驱动轴的可绕性，附带齿轮的
12、主电动机可以从摩擦试验机中独立出来。这使得摩擦试验机在保持对摩擦力测量与相关数据采集的高灵敏性的同时可以平稳运转。2.5数据采集系统和电子控制器数据采集系统由电脑控制，而且摩擦力的测量要基于由压力传感器测得的高速力矩，压力传感器有足够的频带宽度，而且所需数据通过LABVIEW（图形化编程软件）持续获得。3.高速低温摩擦试验机的初始试验结果为了评估这台新机器的性能，初步做了几个低温磨损试验，分别用表面平滑光亮的SS 304和不锈钢440C做样本与以各自的材料做成的直径为10mm的滚珠摩擦做了实验。 以SS 304做实验时，主轴转速达17100rpm，而以不锈钢440C做实验时，主轴速度为850r
13、pm。利用固定载荷时滚珠与测试盘紧密接触。所有的试验用样本都进行了抛光处理，使他们具有同样的粗糙度，而且用丙酮溶剂做了清洁处理，以去除表面的铁屑。由于低温摩擦试验机的特色，尽管球轴承力矩的测量是在液氮环境中测量的，但这次试验也成功了。测量SS 304和不锈钢440C的摩擦系数的试验是在液氮环境下进行的，而且以不同参数进行了多次测量，通过试验也了解了它们的摩擦学特性。从图6、7、8中可以看出，当滑动速度很大（13.4,17.9,和22.4m/s）而其他参数不变时，SS 304的摩擦系数在滑动速度为22.4m/s时接近0.1，而在滑动速度为17.9和13.4m/s时接近0.2.参照图9，可以看出，
14、不锈钢440C的摩擦系数在开始的旋转周期内（前10s）从很低涨到了0.15左右，而且之后在前5分钟内都保持这一摩擦系数。摩擦系数的轻微涨幅，从0.15到0.27，发生在测试周期的最后5分钟。我们注意到，0.5-0.6是经常在参考文献里查到的材料在室温和正常湿度（35-40%RH）下的自相摩擦系数。从以上的观察中可以得出这样的结论，低温对SS 304摩擦系数的减小有很重要的影响。图6 SS 304在滑动速度为22.4m/s时的摩擦系数（COF）-时间曲线图7 SS 304在滑动速度为17.94m/s时的摩擦系数（COF）-时间曲线图8 SS 304在滑动速度为13.4m/s时的摩擦系数（COF）
15、-时间曲线图9 不锈钢440C滑动速度为0.89m/s时的摩擦系数（COF）-时间曲线浸在液氮环境中转速为36000rpm的、应用于火箭发动机涡轮泵里的向心推力球轴承的测试试验也已经完成，目的是了解固体润滑剂对轴承转速的影响。这种轴承的内径为10mm，外径为26mm，轴承套由复合材料PTFE加工而成，这种轴承广泛应用于低温环境中。图10和图11分别为轴承无润滑和渡铅离子润滑（轴承内圈和外圈均渡上0.7m厚的铅离子润滑剂）时的摩擦系数（COF）-时间曲线。在这两种情况下，由于开始时运动状态的瞬变和笼罩在特殊材料内两方面的原因，摩擦系数的初始值都偏高。在无润滑的条件下，初始值为rolling=0.
16、037，而之后从第120s到第800s摩擦系数都保持在rolling=0.009左右。而使用了润滑剂的轴承，最初的摩擦系数值为rolling=0.017，之后从第150s到第800摩擦系数都保持在rolling=0.008左右。图10 无润滑剂的情况下，轴承转速为36000rpm时的摩擦系数（COF）-时间曲线图11 渡铅离子润滑剂情况下，轴承转速为36000rpm时的摩擦系数（COF）-时间曲线4.结论目前所做工作的主要结论如下：（a）随着新型高速球盘测试仪低温摩擦试验机的发展，在更加贴近实际的条件下已经可以对不同材料和不同润滑剂在低温流体（液氮/液氦）环境中有较高滑动速度时的摩擦磨损特性进
17、行分析。从对机器的描述中可以看出这台摩擦试验机的特色就是可以在高转速（36000rpm）下工作，而且拥有达到这种高速的特殊驱动装置。（b）考虑到球盘测试仪得出的SS 304 steel自相摩擦的摩擦学特性，可以反映出高的滑动速度和低温条件对摩擦系数的稳定值有很大影响。SS 304 steel在液氮环境中滑动速度达22.4m/s时，=0.1，而速度为13.4m/s时，=0.190.21。可以得出这样的结论，摩擦系数（）随滑动速度的增大逐渐减小。（c）从在液氮环境中进行的高速向心推力球轴承的试验中，可以得出这样的结论，在有固体润滑剂的情况下，比如铅离子，轴承的使用寿命更长，而且与无润滑剂的轴承相比
18、可靠性高。参考文献1 D.J. Boes, J.S. Cunningham and M.R. Chasman, The solid lubrication of ball bearing under high speed-high load conditions from 225 to +1000F, J. Am. Soc. Lubr. Eng. (1971) (May) 2 D.K. Chaudhuri, A.J. Slifka and J.D. Siegwarth, Friction and oxidative wear of 440C ball bearing steels under
19、high load and extreme bulk temperatures, Wear 160 (1993), pp. 3750. 3 D.K. Chaudhuri, A.J. Slifka and J.D. Siegwarth, Friction and oxidative wear of 440C ball bearing steels under high load and extreme bulk temperature, Wear 160 (1993), pp. 3750. 4 D.K. Chaudhuri and R. Verma, Wear of liquid nitroge
20、n-cooled 440C bearing steels in an oxygen environment, Engineered Materials for Advanced Friction and Wear Applications. Proceedings of an International Conference Gaitherburg, 13rd March, ASM International-8801-006, Maryland, USA (1988).5 M. Nosaka, M. Kikuchi, M. Oke and N. Kawai, Tribo-characteri
21、stics of cryogenic hybrid ceramic ball bearings for rocket turbopumps: bearing wear and transfer film, Tribo. Trans. 42 (1999) (1), pp. 106115. 6 B. Bhushan, Principles and Applications of Tribology, Wiley-Interscience Publication, John Wiley & Sons, Inc. (1999) p. 447Development of a high-speed cry
22、ogenic tribometer: Design concept and experimental results Subramoniana and Bikramjit Basub, aJSPS Ronpaku fellow, Department of Space, Thiruvananthapuram, IndiabLaboratory for Advanced Ceramics, Department of Materials and Metallurgical Engineering, Indian AbstractIn order to evaluate the tribologi
23、cal properties of ball bearings used in high-speed cryo-turbopumps of liquid rocket engines, a tribometer to operate at high sliding speed in cryogenic environment is required. In order to meet the above requirements, a new high-speed cryo-tribometer has been designed. With this new tribometer, the
24、evaluation of friction and wear mechanisms of various self-mated materials and solid lubricant coatings under high sliding speeds (0.545m/s) with high Hertzian contact stresses (up to 2.5GPa) in cryogenic fluid is now possible. Two additional features available with this new cryo-tribometer are: (a)
25、 a mono-ball rolling-on-disk tester under the above conditions for the analysis of rolling friction and (b) the testing of unlubricated and lubricated ball bearing (10mm diameter bore) submerged in liquid nitrogen or liquid helium under very high-speed (36,000rpm). An additional provision has been m
26、ade for the continuous measurement of bearing frictional torque at a maximum axial load of 50N. The design details of the new tribometer are the major focus of discussion in this paper. This paper also reports the results of a very first set of experiments conducted on self-mated 440C steel and AISI
27、 304 steel under liquid nitrogen (LN2) immersed condition with selected testing parameters. Testing of ball bearings with Pb-IP coating at 36,000rpm under liquid nitrogen also has been carried out. Keywords: Cryo-tribometer; COF; Space tribologyArticle Outline1. Introduction2. Description of the new
28、 cryo-tribometer2.1. Spindle assembly unit 2.2. Specimen housing with ball-pot assembly and bearing-mounting unit 2.3. Mounting arrangement of test specimen and loading arrangement 2.4. Drive motor and gear box 2.5. Data acquisition system and electronic controller3. Preliminary experimental results
29、 of the high-speed cryo-tribometer4. ConclusionsReferences1. IntroductionThe research results related to the friction and wear of potential materials in cryogenic environment are of relevance to space tribological applications. The literature reports on metallic materials are available and the repor
30、ts on the use of ceramics, as bulk material or coating are limited. Boes et al. 1 investigated the performance of different solid lubricated ball bearings in the temperature range of 142 to +537C with rotational speed up to 20,000rpm. The investigated coatings include 70Ag20PTFE10MoSe2, 80Ag15PTFE5M
31、oSe2 and 70AgHg20PTFE10MoSe2 (all compositions in vol%). At temperature of 24C, the coefficient of friction (COF) of investigated materials varies from 0.11 to 0.21 with the lowest measured for 70AgHg20PTFE10MoSe2. At 315C, even lower COF of 0.06 is measured with the same coating composition. Chaudh
32、uri et al. investigated the sliding wear of self-mated 440C steel in the temperature range of 185 to 675C in an oxygen atmosphere 2. It was observed that the mean kinetic COF is independent of load under steady state conditions, while it decreases with increase in sliding speed and bulk temperature.
33、Among the metallic materials, AISI 440C martensitic stainless steel is the material of choice for the high-pressure oxygen turbo pump (HPOTP) of the space shuttle main engine (SSME). Chaudhuri et al. 3 examined the effects of load, speed and temperature (185 to 675C) on unlubricated sliding friction
34、 and wear (average dynamic coefficient of friction and wear rate) of 440C steels. Very high flash temperature in excess of 1000C is generated during the severe wear. The temperature drops to about 200C when a steady state is reached. The decrease in temperature follows similar decrease in the COF fr
35、om a sliding value of 0.60 to a steady state value of about 0.25 4. Although the tribological properties of metallic, ceramic and polymer-based bulk materials and coatings are relatively well investigated at room temperature in varying humidity conditions 5, such a study in cryogenic/sub-zero temper
36、ature is limited 1, 2, 3, 4 and 6, primarily because of the availability of a few tribometer to be operated under such severe conditions.However, the ball bearings, typically used in space shuttle main engine or liquid rocket engines, need to survive the high friction and wear loss during its operat
37、ion at high-speed (up to a 35,000rpm) for a few minutes (up to 10min). Therefore, a tribometer, to simulate high stress high-speed sliding conditions is required. Firstly, such a tribometer, once designed and fabricated can be used to assess the potential of various bulk materials/coatings for appli
38、cation in rocket engines. Secondly, the fundamental studies to probe into the influence of change in mechanical properties (at sub-zero temperature) on wear of materials can be conducted for a variety of materials. Thirdly, one can also study whether cryogenic environment can potentially provide any
39、 lubrication effect for different tribomaterials. It is with the above motivation, the present work is taken up to design and fabricate a high-speed ball-on-disk tribometer, which can operate in cryogenic conditions. This paper also reports the results of a very first set of experiments conducted on
40、 SS 304 and 440C grade stainless steels, widely used currently as space shuttle bearing materials. Additionally, the torque testing of angular contact ball bearings with Pb-IP coating and without any coating also has been carried out at 36,000rpm in liquid nitrogen immersed condition. The overall te
41、chnical details of the apparatus, the salient features and typical test results are discussed in this paper.2. Description of the new cryo-tribometerA new high-speed ball-on-disk type cryo-tribometer is basically designed to study friction and wear characteristics in sliding contacts under cryogenic
42、 fluid conditions at high sliding speeds. Also, a provision has been made for the torque testing of a ball bearing under cryo-fluid immersed condition at a maximum speed of 36,000rpm. Cryogenic media is either liquid nitrogen or liquid helium. Sliding occurs between a stationary ball and a high-spee
43、d rotating disk. The normal load and rotational speed can be varied. The tangential frictional force along with normal load and speed can be simultaneously monitored during the test. The coefficient of friction data can be acquired as functions of load, speed and environmental condition for continuo
44、us monitoring. Table 1 gives the overall technical specifications of the newly developed high-speed cryo-tribometer. Fig. 1a shows the external view of the ball-on-disk cryo-tribometer and the details of the design drawing are shown in Fig. 1b. The tribometer consists of the following major modules;
45、 a brief description of which follows subsequently: a. Spindle assembly unit. b. Specimen housing with ball-pot assembly and bearing-mounting unit.c. Mounting arrangement of test specimen and loading arrangement.d. Drive motor and gear box.e. Data acquisition system and electronic controller.Table 1
46、. Specifications of the high-speed ball-on-disk cryo-tribometer Parameter Minimum Maximum Variables Ball diameter (mm)4104, 6, 8 and 10mmDisk diameter (mm)20402040mmAxial load (N)0501, 2, 5, 10 and 20NWear track diameter (mm)103010, 15, 20, 25 and 30mmTest speed (rpm)850360007 stepsFrictional force
47、(N)05Any value in 0.1N accuracyTest environmentNormal ambient, liquid nitrogen, liquid heliumView Within ArticleFig. 1.Overall external look at the cryo-tribometer (a) and the detailed design description of the ball-on-disk high-speed cryo-tribometer (b).View Within Article2.1. Spindle assembly unitThe spindle assembly consists of flexible drive shaft, which is secured into a Stainless steel 440C shaft, which is held by
