New deep groove ball bearings high frequencies vibration testing/Nauju radialiuju rutuliniu vienaeiliu guoliu aukstojo daznio virpesiu tyrimas.

Barzdaitis, V. ; Barzdaitis, V.V. ; Maskvytis, R. 等

1. Introduction

The rolling bearings generate mechanical vibration in wide frequencies range: from low mechanical kinematic vibration frequencies (up to 1000 Hz) caused by bearing elements macro-defects up to high mechanical vibration frequencies (up to 10 000 Hz and greater) generated by micro-defects existing in each element. The study of high frequency vibration response due to micro-defects is the task for quality assessment of new bearings.

In general, bearing defects may be categorized as kinematic (macro) and micro-defects. Kinematic defects in the bearings dominate during long term of rotor operation. The rolling element bearings are spallings of the races or the rolling elements. This is caused when a fatigue cracks appear below the surface of the metal and propagates towards the surface until a piece of metal breaks away leaving a small pit or spall. This is fatigue failure and may be expedited by overloading or shock loading of the bearings during long time operation or improper installation. Microdefects in new bearings are caused by manufacturing technology. Micro-defects exist in each element of new bearing and include surface roughness, waviness, misaligned races, and off-size rolling elements [1]. The analytical model is proposed to study the nonlinear dynamic behavior of rolling element bearing 6205 2RSL JEM SKF, including surface micro-defects. The stability of rotor bearing system with ball bearings is studied and emphasized that there are a lot of parameters which can act as a source of nonlinearity in such systems as: radial internal clearance, local surface micro-defects, slipping and skidding effects between the rolling elements. The basic routs to chaos in rolling bearing systems are discussed detail [2]. The vibration response has been studied mostly in the time domain and vibration frequency domain formats. The simulation of kinematic, dynamic and structural behavior in low frequency range of the rolling bearings vibration response without faults presented and analytical model is designed using Lagrange formulation and simulation results characterize the error signal in the inner raceway [3]. The novel approach to diagnose bearing faults using Artificial Neural Networks with pattern classification theory is presented in [4]. Experimentally tested and theoretically simulated diagnostic method of low speed rotors with antifriction bearings raceways micro-defects and changes in dynamic stiffness are presented in [5]. The quantification diagnosis for rolling element bearings with fully restrained background noise and extraction of the entire impulsive attenuation signal for assessing the operating condition and faulty se verity of rolling bearings during all of the life cycle are presented in [6]. Bearings were tested at rotational speed of 3000 r/min and loading with permanent magnets [7]. The permanent magnet usage involves damping effect on high frequencies vibration acceleration values and changes the dynamic properties of bearing.

The primary aim of this research was to design a quantitative diagnostic experimental method for quality assessment of new with micro-defects in the races and balls deep groove ball bearings. The vibration generated by direct metallic contact of rolling elements--raceways cages is caused by micro-defects and results in high frequency vibration acceleration of tested grease lubricated and dry bearings.

2. Research method and theory

To evaluate the quality of the new deep groove ball bearings elements and manufactured technology by high frequency mechanical vibration acceleration measurements, have the following acceptances:

1. New bearings do not excite low frequency kinematic vibrations as fatigue failures (e.g. spots) in the new bearing element materials do not exist.

2. The new bearings were tested with experimental kit horizontal rotor rotating in journal bearings at 1800 r/min.

3. The micro-defects of new bearings (surface roughness [R.sub.z], [R.sub.zmax], waviness [W.sub.s] and of size rolling elements) excite high frequency vibration accelerations up to 10 000 Hz and higher.

4. The mechanical vibration of bearings were experimentally tested without and with grease lubricant, with and without stationary radial preloads attached to the outer rings.

5. Bearings' absolute vibration accelerations were measured with two seismic transducers attached with 180[degrees] phase difference. The accelerometers were rigidly attached to the non-rotating outer bearing ring with screws.

6. Tested bearings contacting elements with the surfaces roughness [R.sub.z], [R.sub.zmax], waviness [W.sub.s], misaligned races and off-size rolling elements, roundness' were measured with high quality devices disassembling tested bearings, (Fig. 1). Measurements of inner raceway, outer raceway and balls roundness, waviness and roughness were provided with high accuracy measurement devices. Bearing 6205 C3P6 elements measurement results indicated the existence of micro-defects (surface roughness [R.sub.z], [R.sub.zmax], [R.sub.a] waviness [W.sub.s]) in the new bearing elements (Fig. 1, Table).

[FIGURE 1 OMITTED]

Two external preload radial forces [F.sub.1] = 100 N values were each loaded at the stationary outer ring. [F.sub.1] added symmetrically reference to the first accelerometer PK1 location in order to measure bearing's outer-inner raceways contacts with balls excited vibration (Fig. 2). These forces guarantee permanent dynamic contact between rolling elements at PK1 transducer location. Radial external forces F1 values were limited by minimum frictional moment (M = ~0.5 [mu] [F.sub.1] d = 3.75 N mm) in the bearing elements ([mu] = 0.0015 is the coefficient of friction for the deep groove ball bearing, d is bearing ball diameter). The second accelerometer PK2 measures bearing outer ring raceway contact with balls excited vibration. The balls are in permanent contact with outer raceway at the PK2 attached location. The existing nominal radial internal clearance [DELTA]r between inner raceway and balls are guaranteed by this loading scheme. Such vibration measurement method with two accelerometers and external loading allow separating inner raceway micro-defects excited vibration from outer raceway micro-defects excited vibration. The vibration measurement excited by the inner raceway and balls contacts in practice is complicated. Each bearing was tested when two accelerometers were attached at outer ring with screws in two conditions: lubricated and dry bearing.

When bearing's inner ring rotates at [n.sub.1] = 1800 r/min rotational speed around rotor axis, and outer ring is fixed; each ball rotates together with cage about rotor axis at [n.sub.cage] = 714 r/min rotational speed. Each ball mass [m.sub.r] generates eccentric inertia force [F.sub.2] = 0.383 N which guaranties permanent contact of balls with outer ring raceway.

[F.sub.2] = [1/2] [m.sub.r] [d.sub.m] = [[omega].sup.2.sub.cage] [1/2] = -0.00355 x 0.0385 x [74.84.sub.2] = 0.383N,

where [m.sub.r] = 0.00355 kg is the mass of the ball 4 (Fig. 2); [[omega].sub.cage] = 74.84 1/s, cage with balls angular velocity about shaft axis, cage radius of rotation V dm = 1/2 0.0385 = = 0.01925 m, dm = (d + D)/2 = 0.0385 m is the mean diameter of bearing, d = 0.025 m is nominal bore diameter, D = 0.052 m is nominal outside diameter, [d.sub.r] = 7.933 mm is ball diameter, z = 9 is the number of balls.

[FIGURE 2 OMITTED]

The balls are in permanent contacts with inner and outer raceways at the same time at the accelerometer PK1 attached location. These dynamic contacts between bearing elements generate high frequency vibration acceleration proportional to micro-defects values existing in both raceways and balls. Preloading forces [F.sub.1] pushed outer ring through balls to inner ring eliminating radial internal clearance [DELTA]r at the transducer PK1 location. At the same time, the radial internal clearance [DELTA]r between balls and inner raceway exists during rotation at the PK2 transducer location, because ball mass eccentric F2 force pushes each ball towards the outer raceway (Fig. 2). The balls at the accelerometer PK2 attached location are in permanent contacts only with the outer raceway, but not with the inner raceway. The high frequency vibration generated by these contacting elements with micro-defects describes manufacturing technological quality of the outer ring raceway and balls. The radial internal clearance of the tested 6205 C3P6 bearings according ISO 5753:1991 are of 13-28 [micro]m value.

It was possible to evaluate micro-defects separately of both inner and outer raceways and balls through vibration measurements using both output vibration signals from PK1 and PK2 transducers. Algebraically subtracting vibration responses signals acquiring from the PK1 and PK2 accelerometers and synchronizing signals pickups by tachometer probe TP from rotation speed measurement device it is possible to evaluate technological quality of outer and inner raceways separately.

3. Experimental testing of 6205 C3/P6 bearings vibration

Vibration measurements of deep groove ball bearings 6205 C3P6 were pursued with accelerometer of 787A type (WR USA, dynamic sensitivity of 100 mV/g, resonance frequency of 22 000 Hz, frequency response of [+ or -] 3 dB at frequency interval of 0.7-10 000 Hz), vibration signal analyzer OROS Mobi-Pack OR-36 (FR), software OROS NVGate V7.00 and OROS ORBIGate V3.00 (FR), oscilloscope ScopiXII OX7104 (Metrix, FR). The new bearing was tested during each experimental run it was lubricated with standard grease and without grease (dry run). The high frequency vibration acceleration data formats as time plots and spectra were used together to analyze vibration response. Handing weighting window method was chosen for vibration evaluation and FFT transformation of original acceleration signal.

Bearing vibration was measured when acting with preloading forces F1 and vibration acceleration-time base plots shown in (Fig. 3). TP signals indicated each full rotation time (0.0333 s) of bearing inner ring. The maximum acceleration magnitude value of the bearing with grease lubricant reached [a.sub.p-pmax] = ~1.2 m/[s.sup.2] and was ~2.5 times less in comparison with dry bearing vibration acceleration [a.sub.p-pmax] = ~3 m/[s.sup.2] (Fig. 3, a, b).

With grease and preloads F1 = 100 N bearing vibration acceleration magnitudes are 2-2.5 times greater at accelerometer PK1 measurement location in comparison with PK2 data, as ball shocks at outer and inner raceways were more intensive in comparison with outer raceway at PK2 accelerometer location.

The vibration acceleration spectra acquired from acceleration-time signals (Fig. 3, a, b) are shown in Fig. 4, a, b. Outer and inner ring raceways and balls stochastic vibration were damped by the grease. Vibration acceleration spectra (Fig. 4, a) indicated low frequency 700 Hz vibration acceleration amplitudes in the spectra of both PK1 and PK2 transducers output signals. This frequency was generated by z = 9 balls rotating about their own axes, but not of the micro-defect. The vibration acceleration spectra of dry bearing indicated dominating high frequency of 2 750 Hz and 1825 Hz (Fig. 4, b). The high frequency of 2750 Hz vibration acceleration at 1.4 m/[s.sup.2] amplitude was measured with PK1 accelerometer indicated the first resonance frequency of the outer ring. The vibration acceleration frequency of 1825 Hz indicated outer raceway and balls dynamic shocks excited vibration when bearing was tested without grease (Fig. 4, b).

[FIGURE 3 OMITTED]

With grease but without preloads F1 = 0 N vibration acceleration magnitudes are ~3 times less in comparison with loaded bearings and shown in Fig. 5, a and dominated low frequencies 325 Hz. Vibration intensity is of the same values measured with accelerometers PK1 and PK2. The vibration acceleration spectra of dry bearing indicated the dominant harmonics of high frequencies in the range from 1700 up to 2800 Hz including outer ring resonance frequency (Fig. 5, b). These high frequency vibration accelerations are generated by shocks of outer and inner raceways and balls micro-defects, were characterized by maximum roughness depth RzMax. The low frequency magnitudes were negligible. The vibration acceleration frequency 1700-2750 Hz indicated outer raceway and balls dynamic shock frequencies, resonance when bearings were tested without grease (Fig. 5, b).

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

4. Conclusions

1. Lubricated and dry new bearings high frequency vibration is stochastic and correlated with [R.sub.zMax]--maximum roughness depth of bearings elements surfaces. Lubricated bearings high frequencies vibration intensity is ~2-2.5 times smaller in comparison with dry bearings. This issue is valid for transducers PK1 and PK2 measurement data.

2. The high frequency (1500-2800 Hz) vibration acceleration damped by grease lubricant when lubricated bearings loaded with external forces [F.sub.1] = 100 N and without external forces [F.sub.1] = 0 N. When dry (unlubricated) bearings loaded with external forces [F.sub.1] = 100 N and without external forces [F.sub.1] = 0 N the high frequency vibration acceleration amplitudes dominated in the spectra.

3. The resonance frequency 2750 Hz of outer ring dominated in the vibration acceleration spectra when measured with PK1 and tested bearing is loaded with external forces [F.sub.1] = 100 N but without grease lubricant.

4. It is recommended to test dry bearings (without lubricant) loaded with external forces for evaluation of quality of new bearings elements using high frequencies vibration. Such method separates the high frequency vibration generated by the outer raceway from inner raceway micro-defects generated vibration.

http://dx.doi.Org/10.5755/j01.mech.20.3.6740

References

[1.] Tandon, N.; Choudhury, A. 1999. Review of vibration and acustic measurement methods for the detection of defects in rolling element bearings, Tribology International 32: 469-480. http://dx.doi.org/10.1016/S0301-679X(99)00077-8.

[2.] Rafsanjani, A.; Abbasion, S.; Farshidianfar, A.; Moeenfard, H. 2009. Nonlinear dynamic modeling of surface defects in rolling element bearings systems, Journal of Sound and Vibration 319: 1150-1174. http://dx.doi.org/10.1016/jjsv.2008.06.043.

[3.] Rubio, H.; Garcia-Prada, J.C.; Castejon, C.; Laniado, E. 2007. Dynamic analysis of rolling bearing system using Lagrangian model; Vs. FEM code.--Proc. of 12th World Congress in Mechanism and Machine Science, IFToMM, June 17-21, 2007, Besancon-France, vol. 4: 205-210.

[4.] Garcia-Prada, J.C.; Castejon, C.; Lara, O.J. 2007. Incipient bearings fault diagnosis using DWT for feature extraction. Proc. of 12th World Congress in Mechanism and Machine Science, IFToMM, June 17-21, 2007, Besancon-France, vol. 6: 394-399.

[5.] Mazeika, P. 2008. Diagnostics and Failures Prevention Researches of Rotors with Rolling Element Bearings. Summary of Doctoral Disertation. In Technological Sciences, Mechanical Engineering. Kaunas, Technologija, UDK 62-251 (043) 36p.

[6.] Kuosheng Jiang, Guanghua Xu, Lin Liang, Guoqiang Zhao, Tangfei Tao, 2012. A quantitative diagnosis method for rolling element bearings using signal complexity and morphology filtering. Journal of Vibroengineering, 14(4): 1862-1875.

[7.] Barzdaitis, V.; Mazeika, P; Barzdaitis, V.V. 2013. Quality assessment of new deep groove ball bearings.Proceedings of 18thInternational Conference Mechanika 2013, 4-5 April Kaunas University of Technology, Technologija, Kaunas: 27-31.

Received January 15, 2014 Accepted April 18, 2014

V. Barzdaitis *, V. V. Barzdaitis **, R. Maskvytis ***, A. Tadzijevas****, M. Vasylius****

* Kaunas University of Technology, A. Mickeviciaus str. 37-304, 44239 Kaunas, Lithuania, E-mail: vytautas. barzdaitis@ktu. lt

** Vytautas Magnus University, Vileikos str. 8, 44404, Kaunas, Lithuania, E-mail: v.barzdaitis@if.vdu.lt

*** JSC Craft Bearings, Draugystes str. 19, 51230, Kaunas, Lithuania, E-mail: r.maskvytis@craft-bearings.com

**** Klaipeda University Mechatronics Science Institute, Bijunu str. 17, 91225, Klaipeda, Lithuania, E-mail: mariusvasylius@ku.lt, arturastadzijevas@ku.lt

Table

The measured geometric dimensions of new tested 6205 C3P6
bearing

6205        Parameters       Ball     Inner     Outer
C3P6                                  ring      ring
bearing                              raceway   raceway

           Diameter, mm     7.933    30.567    46.433

1.            Raceway       2.188     3.367    29.447
           roundness and    +1.186   +1.548    +14.450
            deviations,     -1.002   -1.819    -14.996
             [micro]m

2.            Sphere        7.941     8.164     8.459
           diameter, mm

3.                       Raceway roughness, [micro]m

4.        [R.sub.z]--mean   0.878     0.814     0.754
          roughness depth

           [R.sub.zMax]     1.054     1.109     0.938
             --maximum
          roughness depth

             [R.sub.a]      0.1404    0.131     0.124
             --average
             roughness