机械专业毕业论文外文翻译--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、附录一英文科技文献翻译 英文原文 ： Experimental investigation of laser surface textured parallel thrustbearings 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

2、the relevant 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 b

3、earings, surface texturing 1. Introduction The classical theory of hydrodynamic lubricationyields linear (Couette) velocity distribution with zeropressure gradients between smooth parallel surfacesunder steady-state sliding. This results in an unstablehydrodynamic lm that would collapse under anyext

4、ernal force acting normal to the surfaces. However,experience shows that stable lubricating lms candevelop between parallel sliding surfaces, generally because of some mechanism that relaxes one or moreof the assumptions of the classical theory. A stable uid lm with sucient load-carryingcapacity in

5、parallel sliding surfacescan be obtained,for example, with macro or micro surface structure ofdierent types. These include waviness 1 and protruding microasperities 24. A good literature review onthe subject can be found in Ref. 5. More recently,laser surface texturing (LST) 68, as well as inletroug

6、hening by longitudinal or transverse grooves 9were suggested to provide load capacity in parallelsliding. The inlet roughness concept of Tonder 9 isbased on eective clearance reduction in the sliding direction and in this respect it is identical to the par-tial-LST concept described in ref. 10 for g

7、eneratinghydrostatic eect in high-pressure mechanical seals. Very recently Wang et al. 11 demonstrated experimentally a doubling of the load-carrying capacity forthe surface- texture design by reactive ion etching ofSiC parallel-thrust bearings sliding in water. Thesesimple parallel thrust bearings

8、are usually found inseal-less pumps where the pumped uid is used as thelubricant for the bearings. Due to the parallel slidingtheir performance is poorer than more sophisticatedtapered or stepped bearings. Brizmer et al. 12 demon-strated thepotential of laser surface texturing in theform of regular

9、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 maximum load-carrying ca

10、pacity. 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 Ref. 12 by testing

11、 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 analyzedin Ref. 12 is shown in figure 1. A slider having awidth B is

12、partially textured over a portion Bp = B ofits width. The textured surface consists of multipledimples with a diameter ， depth and area densitySp. As a result of the hydrodynamic pressure generatedby the dimples the sliding surfaces will be separated bya clearance depending on the sliding velocity U

13、, theuid viscosity l and the external load It was foundin Ref. 12 that an optimum ratio exists for the parameter that provides maximum dimensionlessload-carrying capacity where L is the bearing length, and this optimum value is hp=1.25. It was further found in Ref. 12 that an optimumvalue exists for

14、 the textured portion a depending onthe bearing aspect ratio L/B. This behavior is shown ingure 2 for a bearing with L/B = 0.75 at various values of the area density Sp. As can be seen in the rangeof Sp values from 0.18 to 0.72 the optimum a valuevaries from 0.7 to 0.55, respectively. It can also be

15、 seenfrom gure 2 that for a 0.85 no optimum valueexists for Sp and the maximum load W increases withincreasing Sp. Hence, the largest area density that canbe practically obtained with the laser texturing isdesired. It is also interesting to note from gure 2 theadvantage of partial-LST (a 1) over the

16、 full LST(a = 1) forbearing applications. At Sp= 0.5, forexample, the load W at a = 0.6 is about three timeshigher than its value at a = 1. A full account of thisbehavior is given in Ref. 12. 3. Experimental The tested bearings consist of sintered SiC disks10 mm thick, having 85 mm outer diameter an

17、d40 mm inner diameter. Each bearing (see gure 3)comprises a at rotor (a) and a six-pad stator (b). Thebearings were provided with an original surface nish by lapping to a roughness average Ra= 0.03 lm. Eachpad has an aspect ratio of 0.75 when its width is measured along the mean diameter of the stat

18、or. The photographs of two partial-LST stators are shown ingure 4 where the textured areas appear as brightermatt surfaces. The rst stator indicated (a) is a unidirectional bearing with the partial-LST adjacent to theleading edge of each pad, similar to the model shownin gure 1. The second stator (b

19、) is a bi-directionalversion of a partial-LST bearing having two equal textured portions, a/2, on each of the pad ends. The lasertexturing parameters were the following； dimple depth , dimple diameter and dimple area density Sp= 0.60.03. These dimpledimensions were obtained with 4 pulses of 30 ns du

20、ration and 4 mJ each using a 5 kHz pulsating Nd:YAGlaser. The textured portion of the unidirectional bearing was a= 0.73 and that of the bi-directional bearingwas a= 0.63. As can be seen from gure 2 both thesea values should produce load-carrying capacity varyclose to the maximum theoretical value.The test rig is shown schematically in gure 5. An electrical motor turns a spindle to which an upperholder of the rotor is attached. A second lower holderof the stator is xed to a housing, which rests on ajournal bearing and an axial loading mechanism that can freely move in the axial direction