AGMA 92FTM1-1992 Experimental Characterization of Surface Durability of Materials for Worm Gears《蜗轮材料表面耐用度的实验鉴定》.pdf
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1、92 FTM1Experimental Characterizationof Surface Durability ofMaterials for Worm Gearsby: Michel Octrue and Mich_le GuingandCETIM, FranceAmerican Gear Manufacturers AssociationTECHNICAL PAPERExperimental Characterization of Surface Durability ofMaterials for Worm GearsMichel Octrue and Mich_ie Guingan
2、d, CET1M, FranceThe statementsand opinionscontainedherein arethoseof the authorand shouldnotbe construedas an official action oropinion of the American Gear Manufacturers Association.ABSTRACT:Thispaperpresentsthemethodology usedfor testing materialswithaworm gearset-up andwith a disc-roller machine.
3、Several experimental results are discussed and analysed.A correlation between metallurgical analyses of the structure of bronzes and experimental observations of subsurfacecracks is given.On the subject of wear, a specific method of measurement is explained and results are described.Copyright 1992Am
4、erican Gear Manufacturers Association1500 King Street, Suite 201Alexandria, Virginia, 22314October, 1992ISBN: 1-55589-581-61 INTRODUCTION The geometry and test conditions have been determinedso as to obtain pitting before 200 hours of testing on rollersThe admissible values for the same combination
5、of two submitted to average loads. No wear has been observedmaterials, such as Bronze/Steel, varies according to the on rollers: the rolling track is formed very quickly whenauthor ofthe document (see references 2, 4, 6). Also the disc contacts it and there is no width modificationthe method and pre
6、cise conditions of the tests differs during test. Controls were undertaken before the tests tobetween them and in some cases is unknown. CETIM has measure thecrown and the external diameter of each roller.thus manufactured three disc/roller simulators for testing After the tests the width of the rol
7、ling track was alsocombinations of materials used in worm gears, determined accurately.The fatigue curves obtained will be introduced later in theanalytical calculation methods for load capacities 3, 8, The appearance, to the naked eye, of the first visible pitting9. For each combination of material
8、s tested it was decided was recorded whenever possible. In fact during tests withto metallurgically analyse the structure of the different heavy loads, pitting evolves very quickly towards a largebronze types. Also the cracks within simulated test rollers and unique scaling. However with rollers sub
9、mitted towere observed to try and explain the fatigue phenomenon lower loads, very small size pittings appear on theof contact pressure on the bronze surface, periphery of the roller and evolve slowly. With the lattercase a criteria to stop the test had to be set and was definedas the time when sign
10、ificant pitting of a least 2 mm in2 FATIGUE TESTS diameter appeared.2.1 Test descriptionThe fatigue tests have been performed on a disc/roller 2.3 Examination of testssimulator which reproduces the kinematic conditionsparticular to worm gears: a bronze roller represents the Contact pressures are cal
11、culated in accordance with theworm wheel and rolls and slides on a steel disc which Hertz model applied to a cylindrical type contact. In factrepresents the worm. if the contact is at a point at the beginning of the test (dueto the crowning), it evolves very quickly towards aThe two mobile axles are
12、 orthogonal and independently cylindrical contact, the roller track being formed m a shortdriven. The roller can be positionned anywhere on the time to the detriment of the crowning disappearance. Thesurface of the disc. It is thus possible to simulate any length of the cylinder in contact is taken
13、account in thecontact segment with a choice of the applied load and of width of the track.the slipping speed (in magnitude and direction ).D,_c 2.4 Material analysisDisc: case hardened tempered: 35NCD 16L_ Hardness: H_,jz5 = 750Rollers: Three types are available, all of the same grade:Fig. 1: Disc/r
14、oller contact UEI2P, but obtained by different methods of manufacture.The hardness is given in the following chart:Over 20000 hours of tests have been completed. The finalcurves concerning the first bronze type (chilled castUE12P) have been drawn up. A few results have also been SAND CAST 103,33 Hbo
15、btained for a second type : centrifugal UEI2P. CHILLED CAST 108,07 HbCENTRIFUGAL 110,44 Hb2.2 Test methodThe geometry of the bronze rollers and the test conditionsused are as follows: 2.5 Results obtainedGEOMETRY OF ROLLERSExternal radius: 49 mm 2.5.1 UEI2P chill east bronzeRadius of crown: 250 mmWi
16、dth: 18 or 25 mm 14.000 hours of testing on 35 rollers have been requiredto set out the fatigue curve for this grade (figure 2). TheTEST CONDITIONS longest test lasted 41 million cycles while the roller wasRoller speed: 420 rpm submitted to a pressure of 344MPa. The roller with theDisc speed: 850 rp
17、m heaviest load (671 MPa) produced scaling after 0, 8 millionRoller position: x=50 y= 34mm cycles. The envelope curves give an off-set of 150 MPa._)tllm2.5.3 Verification on actual gear-boxes“950“.,. In order to validate the analytical method for the loadcapacity calculation, it is should be noted t
18、hat tests on twot “:. worm gears reducers were undertaken in parallel. For both1.50 ,t_ttma - the center distance was fixed to 125ram with a gear ratioof 1/40 for one and 1/31 for the other._o “. The materials chosen were identical to those tested in thedisc/roller simulator. The endurance of these
19、gears allowedconfimation of the results obtained for rollers.t“/_1.em,t _t 3 METALLURGICAL ANALYSISLt t Lt6 I7 LtaFig. 2 : UEI2P chili cast bronze 3.1 IntroductionThe lower curve in figure 3 represents the appearance of The analysis made of the two rollers tested on the simulatorthe first visible pi
20、tting, the upper curve corresponds to (chill casting and centrifugal) had two aims. The first wasthe appearence of the scaling. It was only possible to to observe the structure of the three different types ofrecord the first pitting after 10 million cycles. Below this bronze to try and predict their
21、 behavior to fatigue and thevalue, the evolution of the pit is too quick (see the end of second was to interpret the structural effects of fatigue dueto the surface pressure. These different analysis were madeparagraph 2.2) at the ECAM Metallurgy Laboratory under the supervisiona“m, of Mr P. COUVRAT
22、.3.2 Structural observations of the different types ofbronzestm g SAND CASTf it st pit t _ng_ In this case the cooling of the bronze during its solidifi-cation is slow. The process of solidificationstarts by thea_m _. formation of SSct “germs“ followed by their growth. Aheterogeneous structure forme
23、d of dentntes is thenobtained. Between these dentrites, the remaining liquid, r , _r:1- provides the eutectoid component._ l.L7 IXa The first tests made on this grade did not produceFig. 3: UEI2P chili cast fatigue curve conclusive results. In fact the rolling track did not stabilizeand had a tenden
24、cy to occupy the whole width of the rollerin a very short time, even when the roller was submittedto light loads.2.5.2 UEI2P centrifugal bronzeAt CETIM the new test benches, that permit the applicationof heavierloads, have allowedresults concerningthis germsgrade to be supplyed. An off-set of 150 MP
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