Influence of Surface Roughness on Sliding Characteristics of Rubber Seals

Transcription

1 TECHNICAL REPORT Influence of Surface Roughness on Sliing Characteristics of Seals K. YAMAMOTO D. OZAKI T. NAKAGAWA The influence of surface roughness on frictional vibration of a bearing seal has been stuie to establish the etho for ientifying generation echanis of frictional vibration. As a result, the egree of influence on frictional vibration coul be clarifie by the power spectru arising fro the roughness of sliing surface. Stability of frictional vibration was exaine by using viscous coefficient obtaine fro FEM analysis, contact loa an l- curve of rubber aterial. The result was approxiately consistent with actual easureent results. Key Wors: seal, frictional vibration, surface roughness, power spectru. Introuction seals, incluing bearing seals, are liable to generate abnoral noise ue to frictional vibration cause by stick-slip (hereinafter referre to as "S-S") when seals slie uner starve lubrication conitions. Generally, rubber aterials ten to generate S-S because its coefficient of friction eclines with the increase of sliing spee. An noise is generate when frictional vibration ue to S-S is unstable (self-excite vibration), an is influence by the change of frictional coefficient relative to the spee incluing the effect of surface roughness, viscosity of the aterial an contact loa. There have been any papers reporte concerning the analysis of this echanis of frictional vibration generation ). However, preiction of noise generation ue to frictional vibration of rubber proucts base on echanical an frictional properties of rubber aterials was yet ipossible. In this stuy, therefore, influence of the sliing surface roughness on the frictional vibration of bearing seals in ry conition was clarifie an generation of frictional vibration was stuie in relation to frictional an vibration characteristics of rubber aterials.. Test Metho. Test Specien seals of 6 eep groove ball bearing as shown in Fig. were chosen for testing. Four ifferent nitrile rubber aterials (hereinafter referre to as NBR), as suarize in Table, were use.. Effect of Sliing Surface Roughness Sliing surface roughness (unevenness) was prepare by oling seals with each cavity treate with at finish or san blasting, respectively. Surface roughness was easure with a laser icroscope, an sliing test was perfore with seals uner ry conition. Koyo Engineering Journal English Eition No.66E (5) 9 A u u3 u7.9 u5.. 3 Distinction of Frictional ibration Scheatic sliing part of the seal was shown in Fig. an sliing-otion oel use was shown in Fig. 3. u7.9 u5. Magnifie view of A RM type Fig. Bearing seal Table Property of rubber aterial NBR Harness, HA Tensile strength, MPa Elongation, % % oulus, MPa tan (RT, Hz) F 3P Fig. Scheatic of sliing part 3F : friction force 3P : contact loa : spee 5

2 Influence of Surface Roughness on Sliing Characteristics of Seals k (x) c (x) P x ( t), x ( t) l( x ) F = l P x k c P l( ) Fig. 3 Sliing otion oel The otion equation is expresse as follows: x = k ( x x ) c ( x x ) t t l ( x x ) P a t Then, by Taylor expansion, l( x ) = l( ) x l( ) x l( ) l( ) x l ( ) Supposing l( ) P k X = x, x =, k : ass : location : sliing spee : spring constant : aping coefficient : loa : coefficient of friction P c X l( ) X x X = s P Thus, stable or unstable frictional vibration can be istinguishe as follows ) : c -----Stable (no abnoral noise) P l ( ) > c Unstable (abnoral noise generate) P l ( ) In orer to istinguish stable fro unstable frictional vibration generate on the seals, the l- curve for each rubber aterial as well as the aping coefficient, c, an ipose loa, P, were eterine by FEM analysis an were copare with the test result. The l- curve was obtaine by the ring-on-isc friction tester as shown in Fig. 4. This test was conucte uner the average contact pressure conition base on the loa, P that was obtaine fro the seal sliing velocity an static FEM analysis. Rotation Fig. 4 Ring-on-isk type test etho Loa Mating aterial (fixe) Specien (rotating) Table OD : u65 ID : u55 As the aping coefficient, c, is expresse as c = 4pf f(f : natural frequency, : ass, f: aping ratio), f an were calculate by the natural frequency analysis, an f by the transissibility analysis. The environent for the analysis was as follows: Harware: Octane/SI R/95MHz by SGI Solver: ABAQUS ver.6.3- by ABAQUS, Inc. Pre-post: I-DEAS Master Series ver. 9 by SDRC 3. Test Result 3. Influence of Sliing Surface Roughness on Frictional ibration The test results on the conventional seals without any roughing on the sliing surface are shown in Fig. 5 for frictional torque an Fig. 6 for noise generating spee range. In both figures, the test plot an the spee range at which noise was generate are shae ark. The result of FFT analysis when noise generates is shown in Fig. 7. Frequency of the noise ue to frictional vibration was aroun khz. The noise was generate in the spee range where the frictional torque arkely ecrease. Furtherore, the noise generating spee range epene on the rubber aterial an interference. rubber showe wier noise generating range an further wier with larger interference. A easureent exaple of frictional torques with the seals with rough sliing surface that showe wie noise generating range in the previous tests was shown in Fig. 8, wherein ark shae plotting showe noise generation. As seen in Fig. 8, seals with the san blaste surface inicate lower friction torque an no noise generation. Although observations of two types of sliing surfaces were ifferent as shown in Fig. 9, roughness values of the i not show any significant ifference as seen in Table. However, when these surfaces were copare by the power spectru as shown in Fig., significant ifference was istinguishe. Specifically, the san blaste surface ha larger short wave coponent an saller long wave coponent copare with at finish surface. As a result, it was foun that proviing the sliing surface with fine an eep roughness was effective to prevent generation of noise ue to frictional vibration.. Noise generate Interference Interference Interference 5 5 Rotational spee, in Fig. 5 Measureent exaple of friction torque (, type RD) 5 Koyo Engineering Journal English Eition No.66E (5)

3 Influence of Surface Roughness on Sliing Characteristics of Seals aterial NBR Interference Rotational spee, in Mat-finishe San blaste Fig. 6 Noise generating region cause by frictional vibration (type RD) [s](noinal alues) Noise generate 4k 8k k 6k k 4k [Hz]. Fig. 7 FFT analysis result on noise Mat-finishe Noise generate [B(A)/uPa] Interference Interference Interference Fig. 9 Exaple of sliing surface observation () Table Roughness of sliing surface (non-treate) Mat-finishe San blaste Ra.~.5 3~8 ~4 Ry ~ 3~5 5~6 Rz ~4 5~4 3~55 S 4~65 3~55 5~4 Power spectru, l. Mat-finishe San blaste 5 5. San blaste Rotational spee, in 5 5 Rotational spee, in Interference Interference Interference Wavelength, l Fig. ariation of power spectra on surface roughness 3. Distinction of Frictional ibration To obtain aping ratio, f, vibration at the en of the seal lip when force vibration was given on the etal ring was siulate by use of the oel shown in Fig.. For each frequency, aping ratio f was eterine by the relation aong the vibration frequency, the ratio of aplitue at the etal ring an that at the lip en. Fig. 8 Measureent exaple of friction torque (, type RD) Koyo Engineering Journal English Eition No.66E (5) 53

4 Influence of Surface Roughness on Sliing Characteristics of Seals f f f f Force vibration f where, f : frequency f : natural frequency Transissibility: ratio of aplitues Lip en /etal ring Fig. FEM analysis oel In this analysis, Rayleigh's aping coefficient, a, (provie b= ), obtaine by coparison between vibration analysis an experiental results on a strip specien (5 5 ) of each rubber aterial were use. Also, f was calculate by way of regression of transissibility epenence on the frequency using the following expression: Transissibility f f f Measureent results Analysis results Analysis exaples of transissibility for each frequency were shown in Fig.. In any seal type, as the transissibility obtaine by the analysis was alost consistent with that obtaine fro the experient, the effectiveness of the analysis etho was confire. Base on the analysis of transissibility, etc. the values, c an P, for seal with each aterial was calculate an suarize in Table 3. Frequency, Hz Fig. Exaple of analysis on transissibility (, type RD) f The aping ratio, c, is foun to epen significantly on the rubber aterial, but not uch on the seal esign fro coparison of c values for RM an seals. There was no correlation between aping ratio an physical properties of rubber aterials shown in Table. Friction characteristics of seal with roughene surface are shown in Fig. 3. Also, Fig. 4 shows result of analysis to istinguish the frictional vibration. In this stuy, the interference was. The result for the seal with the at finish surface was that the frictional vibration appeare in the sae spee ranges as that for conventional non-treate seals. On the other han, the san blaste surface seal i not show any frictional vibration even at the lowest spee, coinciing with the experiental fining. In aition, Fig. 5 shows coparison between the analysis of frictional vibration an the noise generation in the test on seals. Though the test result i not agree with the analysis at low spee range because of ifficulty in recognizing noise, these results were consistent on the highspee sie. Therefore, the values obtaine by the forula of iscriination base on the aping ratio, contact pressure an l- curve of each seal aterial was prove effective for estiation of frictional vibration range for seals. Coefficient of friction Discriination forula, s/ Range of frictional vibration generate.5.5 Sliing spee, /s Mat-finishe San blaste Fig. 3 Friction characteristics of nitrile rubber Sliing spee, /s Mat-finishe San blaste Range of frictional vibration generate Fig. 4 Analysis on frictional vibration for each treatent 54 Koyo Engineering Journal English Eition No.66E (5)

5 Influence of Surface Roughness on Sliing Characteristics of Seals Table 3 Results of FEM calculation for c an P aterial NBR RM type Natural frequency analysis Transissibility analysis Daping coefficient Interference Loa f f c P c/p Hz ( = sec ) kg kg/s = N s/ N s/. 5E E E. 7.78E E E E. E E E. 3.57E E E. 3.6E E E. 3.6E 3.74 aterial NBR Interference Rotational spee, in Measureent results Analysis results References ) C. Liu an Y. Uchiyaa: Tribologist (Journal of Japanese Society of Tribologists), 43, (998) 4. ) Y. Hattori an T. Kato: Transactions of the JSME, 6, 589, C (995) Fig. 5 Coparison of frictional vibration between analyze an actual easureent 4. Conclusions The effect of roughness of seal sliing surface on the frictional vibration of bearing seals was exaine an the etho to iscriinate the conition that causes frictional vibration was establishe. The results are suarize as follows: ) As a etho to prevent noise ue to frictional vibration, it is effective to roughen the seal sliing surface by applying san blasting on the oling cavity. ) It was also foun that the agnitue of the effect of seal roughness on frictional vibration coul be ientifie by power spectru. Also, increasing the short wave coponent an reucing the long wave coponent can iniize frictional vibration. 3) The results of iscriination analysis for frictional vibration base on viscosity ratio, contact loa pressure obtaine by FEM analysis, an l- curve of rubber aterial were well consistent with the test results. This etho was foun effective to estiate frictional vibration range for seals. K. YAMAMOTO * D. OZAKI ** T. NAKAGAWA * * Core Technology Research & Developent Departent, Research & Developent Center ** Tennessee Koyo Steering Systes Copany Koyo Engineering Journal English Eition No.66E (5) 55