机械外文翻译---实验研究激光加工表面微观造型平行的推力轴承

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1、 英文原文： Experimental investigation of laser surface textured parallel thrust bearings Performance enhancements by laser surface texturing (LST) of parallel-thrust bearings is experimentally investigated. Test results are compared with a theoretical model and good correlation is found over the relevan

2、t operating conditions. A compari- son of the performance of unidirectional and bi-directional partial-LST bearings with that of a baseline, untextured bearing is presented showing the benets of LST in terms of increased clearance and reduced friction. KEY WORDS: uid lm bearings, slider bearings, su

3、rface texturing 1. Introduction The classical theory of hydrodynamic lubrication yields linear (Couette) velocity distribution with zero pressure gradients between smooth parallel surfaces under steady-state sliding. This results in an unstable hydrodynamic lm that would collapse under any external

4、force acting normal to the surfaces. However, experience shows that stable lubricating lms can develop between parallel sliding surfaces, generally because of some mechanism that relaxes one or more of the assumptions of the classical theory. A stable uid lm with sucient load-carrying capacity in pa

5、rallel sliding surfaces can be obtained, for example, with macro or micro surface structure of dierent types. These include waviness 1 and protruding microasperities 24. A good literature review on the subject can be found in Ref. 5. More recently, laser surface texturing (LST) 68, as well as inlet

6、roughening by longitudinal or transverse grooves 9 were suggested to provide load capacity in parallel sliding. The inlet roughness concept of Tonder 9 is based on eective clearance reduction in the sliding direction and in this respect it is identical to the par- tial-LST concept described in ref.

7、10 for generating hydrostatic eect in high-pressure mechanical seals. Very recently Wang et al. 11 demonstrated experimentally a doubling of the load-carrying capacity for the surface- texture design by reactive ion etching of SiC parallel-thrust bearings sliding in water. These simple parallel thru

8、st bearings are usually found in seal-less pumps where the pumped uid is used as the lubricant for the bearings. Due to the parallel sliding their performance is poorer than more sophisticated tapered or stepped bearings. Brizmer et al. 12 demon-strated the potential of laser surface texturing in th

9、e form of regular micro-dimples for providing load-carrying capacity with parallel-thrust bearings. A model of a textured parallel slider was developed and the eect of surface texturing on load-carrying capacity was analyzed. The optimum parameters of the dimples were found in order to obtain maximu

10、m load-carrying capacity. A micro-dimple collective eect was identi- ed that is capable of generating substantial load-carrying capacity, approaching that of optimumconventional thrust bearings. The purpose of the present paper is to investigate experimentally the validity of the model described in

11、Ref. 12 by testing practical thrust bearings and comparing the performance of LST bearings with that of the theoretical predictions and with the performance of standard non-textured bearings 2. Background A cross section of the basic model that was analyzed in Ref. 12 is shown in figure 1. A slider

12、having a width B is partially textured over a portion Bp = B of its width. The textured surface consists of multiple dimples with a diameter ， depth and area density Sp. As a result of the hydrodynamic pressure generated by the dimples the sliding surfaces will be separated by a clearance depending

13、on the sliding velocity U, the uid viscosity l and the external load It was found in Ref. 12 that an optimum ratio exists for the parameter that provides maximum dimensionless load-carrying capacity where L is the bearing length, and this optimum value is hp=1.25. It was further found in Ref. 12 tha

14、t an optimum value exists for the textured portion a depending onthe bearing aspect ratio L/B. This behavior is shown in gure 2 for a bearing with L/B = 0.75 at various values of the area density Sp. As can be seen in the range of Sp values from 0.18 to 0.72 the optimum a value varies from 0.7 to 0.

15、55, respectively. It can also be seen from gure 2 that for a 0.85 no optimum value exists for Sp and the maximum load W increases with increasing Sp. Hence, the largest area density that can be practically obtained with the laser texturing is desired. It is also interesting to note from gure 2 the a

16、dvantage of partial-LST (a 1) over the full LST (a = 1) for bearing applications. At Sp= 0.5, for example, the load W at a = 0.6 is about three times higher than its value at a = 1. A full account of this behavior is given in Ref. 12. 3. Experimental The tested bearings consist of sintered SiC disks

17、 10 mm thick, having 85 mm outer diameter and 40 mm inner diameter. Each bearing (see gure 3) comprises a at rotor (a) and a six-pad stator (b). The bearings were provided with an original surface nish by lapping to a roughness average Ra= 0.03 lm. Each pad has an aspect ratio of 0.75 when its width

18、 is measured along the mean diameter of the stator. The photographs of two partial-LST stators are shown in gure 4 where the textured areas appear as brighter matt surfaces. The rst stator indicated (a) is a unidirectional bearing with the partial-LST adjacent to the leading edge of each pad, simila

19、r to the model shown in gure 1. The second stator (b) is a bi-directional version of a partial-LST bearing having two equal textured portions, a/2, on each of the pad ends. The laser texturing parameters were the following； dimple depth , dimple diameter and dimple area density Sp= 0.60.03. These di

20、mple dimensions were obtained with 4 pulses of 30 ns duration and 4 mJ each using a 5 kHz pulsating Nd:YAG laser. The textured portion of the unidirectional bearing was a= 0.73 and that of the bi-directional bearing was a= 0.63. As can be seen from gure 2 both these a values should produce load-carr

21、ying capacity vary close to the maximum theoretical value.The test rig is shown schematically in gure 5. An electrical motor turns a spindle to which an upper holder of the rotor is attached. A second lower holder of the stator is xed to a housing, which rests on a journal bearing and an axial loading mechanism that can freely move in the axial direction