DAMAGE IDENTIFICATION AND VIBRATION ANALYSIS TECHNIQUE FOR GEAR BOX

Transcription

1 DAMAGE IDENTIFICATION AND VIBRATION ANALYSIS TECHNIQUE FOR GEAR BOX Baquer Mohiuddin 1, Dr.S.B Kivade 2, ¹Asst.Professor.Department of Mechanical Engg,BKIT, Bhalki,Dist:Bidar. Mob: ²Principal of Basavakalyan Engineering College,Basavakalyan,Dist:Bidar. Abstract Gear pairs in gearboxes normally generate vibration and corresponding vibration signal could be used as reference characteristics when the gear is in good mechanical condition. If defects occur to one of the gears during operation, the faulty gearbox would result in serious damage. Changes in vibration signals are often an indication that the gear pair meshing condition is changing. Measuring vibration gearbox with the help of accelerometer mounting on the gearbox housing is one of the best methods for gear pair damage assessment. Therefore, condition monitoring of the gearbox system during its operation is crucial to prevent the system from malfunction that could cause damage or entire system shutdown. Up to now condition monitoring and damage identification of industrial gearboxes has received significant attention by researchers engaged in multidisciplinary activities. The rapid progress in materials technology, intelligent sensor technology, signal processing and information technologies brings new solutions to solve a variety of problems associated with failures of industrial gearboxes in a real operational environment accurately and efficiently. Many investigations have been carried out to monitor and assess of industrial gearboxes using different techniques. These methods are well-established for industrial practices and among them vibration signal processing technique is well known. However, since the vibration signals measured from gearboxes are non-stationary and transient in nature, when damage occurs it is even more interesting to carry out investigation. All those technique have some limitations and cannot be applied in all conditions, i.e. some types of failure cannot be detected by simple vibration methods. Hence it is more desirable to investigate possibilities of some of those methods. The simple spectral analysis is generally unable to detect gear damage at an early stage; for this reason, many researchers have proposed the application of other vibration assessment techniques for the early detection of damage symptoms. The aim of this research, on the basis of experimental results is to evaluate and compare detection and diagnostic capabilities of some of vibration signal processing techniques. KEYWORDS Condition Monitoring; Vibration Analysis; Fault Diagnosis; Gearbox. 1.INTRODUCTION Gear pairs in gearboxes normally generate vibration and corresponding vibration signal could be used as reference characteristics when the gear is in good mechanical condition. If defects NCADOMS-2016 Special Issue 1 Page 176

2 occur to one of the gears during operation, the faulty gearbox would result in serious damage. Changes in vibration signals are often an indication that the gear pair meshing condition is changing. Measuring vibration gearbox with the help of accelerometer mounting on the gearbox housing is one of the best methods for gear pair damage assessment. Therefore, condition monitoring of the gearbox system during its operation is crucial to prevent the system from malfunction that could cause damage or entire system shutdown. Up to now condition monitoring and damage identification of industrial gearboxes has received significant attention by researchers engaged in multidisciplinary activities[1]. The rapid progress in materials technology, intelligent sensor technology, signal processing and information technologies brings new solutions to solve a variety of problems associated with failures of industrial gearboxes in a real operational environment accurately and efficiently [2]. Many investigations have been carried out to monitor and assess of industrial gearboxes using different techniques. These methods are well-established for industrial practices and among them vibration signal processing technique is well known[3]. However, since the vibration signals measured from gearboxes are non-stationary and transient in nature, when damage occurs it is even more interesting to carry out investigation. All those technique have some limitations and cannot be applied in all conditions, i.e. some types of failure cannot be detected by simple vibration methods. Hence it is more desirable to investigate possibilities of some of those methods[4]. The simple spectral analysis is generally unable to detect gear damage at an early stage; for this reason, many researchers have proposed the application of other vibration assessment techniques for the early detection of damage symptoms. The aim of this research, on the basis of experimental results is to evaluate and compare detection and diagnostic capabilities of some of vibration signal processing techniques. Gears are very widely used in machines to transmit power from one shaft to another, usually with a change in speed and torque. The study of the dynamic behaviour of gearboxes has received moderate attention, but due the great dynamics complexity of gears, it remains critical area. In practice out of balance and bearing forces are active in gear dynamics, but also the geometry of the gear profile has a crucial effect NCADOMS-2016 Special Issue 1 Page 177

3 on the vibration behaviour[5]. In general flexural vibration will be more important then torsional vibration because flexural vibrations are transferred directly to the housing via the bearings [6]. In practice, the situation is not so ideal, as the teeth deform under load, introducing a meshing error or transmission error, even when the tooth profiles are perfect. In addition there are geometric deviations from the ideal profiles, both intentional and unintentional. Since perfect gears cannot be made, there is always transmission error [7]. Looking at the gearbox vibration mechanism of the most important vibration sources are: time variations in the mass stiffness, caused by variation of the number of teeth in contact and variation in the stiffness of the individual teeth; dynamic effects due the deviation from the ideal tooth profile, in practice all gears contain teeth manufacturing errors, such as errors due to the gear cutting process, deviation in the mesh angle, deviations from the involute profile, surface roughness of the gears; oscillations on the sliding velocity, where during the transmit ion of power there will be rolling and slipping in the point of contact and also oscillation may occur because of stick-slip effects. LITERATURE REVIEW Rusmir Bajric et al.[1] researched on Review of Vibration Signal Processing Techniques Towards Gear Pairs Damage Identification. Research in damage of gear and gear pairs using vibration signals is still very attractive, because vibration signals from a gear pairs are complex in nature and not easy to interpret. Predicting gear pairs defects by analyzing changes in vibration signal of gears pairs in operation is a very reliable method. Therefore, a suitable vibration signal processing technique is necessary to extract defect information usually covered under noise of other gear pairs dynamic factors. This paper presents the results of an evaluation of vibration analysis techniques as a method for the gear and gear pairs condition assessment. The origin of vibration in gear pairs and useful definition of damage identification techniques are presented. The detection and assessment capability of some of the most effective vibration techniques are discussed and experimentally compared, concerning a multistage industrial gearbox. In particular, the results of estimated vibration signal processing techniques are NCADOMS-2016 Special Issue 1 Page 178

4 compared. Advantages and disadvantages of estimated techniques having in mind specific limitation have been shown. Further research in damage identification of gear pairs have been pointed out[1]. Mr.vijaykumar et al.[2] studied on Vibration Analysis for Gearbox Casing Using Finite Element Analysis This paper contains the study about vibration analysis for gearbox casing using Finite Element Analysis (FEA). The aim of this paper is to apply ANSYS software to determine the natural vibration modes and forced harmonic frequency response for gearbox casing. The important elements in vibration analysis are the modelling of the bolted connections between the upper and lower casing and the modelling of the fixture to the support. This analysis is to find the natural frequency and harmonic frequency response of gearbox casing in order to prevent resonance for gearbox casing. From the result, this analysis can show the range of the frequency that is suitable for gearbox casing which can prevent maximum amplitude[2]. Ashwani Kumar[3] explained about Dynamic Vibration Analysis of Heavy Vehicle Truck Transmission Gearbox Housing Using FEA. The main objective of this original research article is to study the loose fixture mounting affect of heavy vehicle transmission gearbox housing. The studies were completed in three phases. In first phase the aim was to find the actualsuitable boundary condition. After finding the boundary condition in second phase the fixture bolts were loosened to monitor the affect of looseness and in third phase the positional looseness based study were completed. The looseness of transmission housing causes heavy vibration and noise. In order to prevent this noise and vibration the transmission housing is tightly mounted on the chassis frame using bolts. In our design transmission housing is constraint on chassis frame using 37 bolts. Truck transmission system determines the level of noise together with the chassis, engine and bodywork. Vehicle transmissions under torsional vibration condition caused rattling and clattering noises. Reciprocity Principle was used to determine the failure frequencies for transmission housing. In reciprocity principle gear and shafts are suppressed and all the forces transmitted through the bearings are applied on the empty housing. FEA based ANSYS 14.5 has been used as analysis tool. The free vibration frequency for zero displacement condition varies NCADOMS-2016 Special Issue 1 Page 179

5 from 1669 Hz to 2865 Hz and for loose transmission casing frequency varies from 1311 Hz to 3110 Hz. The analysis have theoretical and practical aspects and useful for transmission housing structure optimization[3]. Prashant Bagde1 et al[4] in his paper discusses Innovative Methods Of Modeling Gear Faults The gearbox is an important element of any machine so it is very important to make study on that and finding out faults accouring in the gearbox. It is possible every time to observe the gearbox for its faults so the vibration changes in the gearbox is used for the possible faults. In this thesis the faults accouring in the gears are studied and how the vibrations are changes for a particular faults are studied. The modeling of the elements will be done on the CATIA. Since perfect gears cannot be made, there is always transmission error. Looking at the gearbox vibration mechanism of the most important vibration sources are: time variations in the mass stiffness, caused by variation of the number of teeth in contact and variation in the stiffness of the individual teeth; dynamic effects due the deviation from the ideal to oth profile, in practice all gears contain teeth manufacturing errors, such as errors due to the gear cutting process, deviation in themesh angle, deviations from the involutes profile, surface roughness of the gears; oscillations on the sliding velocity, where during the transmit ion of power there will berolling and slipping in the point of contact and also oscillation may occur because of stick slip effects. Due to these mechanisms, amplitude or frequency vibration signal modulation may be caused[4]. Leila Nacib et al[5] explained about Detecting Gear Tooth Cracks Using Cepstral Analysis In Gearbox Of Helicopters.Gears are very important in the transmission of power between two shafts close together with a constant velocity ratio; search in gear damage by using vibration signals is still very attractive, because the vibration signals from gears are not easy to interpret. A failure diagnosis transmission based on Fourier analysis of the vibration signal produced from a speed reducer has shown its limits in terms of spectral resolution. For helicopter safety, early gear fault detection is important to prevent system break down and accident. Among the methods proposed in the literature, cepstral analysis has shown it efficiency. Cepstrum used to identify damage gear, it appears in the cepstrum clear peaks called rahmonic so it is easy to identify the NCADOMS-2016 Special Issue 1 Page 180

6 change in the system and able to detect and foresee the development of the lateral band. This paper proposes how to detect faults in gearbox of helicopter by registration signals during flight, with spectrum analysis and cepstrum analysis. Analyzed results show that the proposed method is effective to extract modulating signal and help to detect the early gear fault. 2.PROBLEM STATEMENT The presence of problems involving the gearbox is evident, the characterization and reasons for these problems are not as clear. Several observations have been made with respect to gearbox failures in an attempt to better characterize the problem. For example, over the years gearboxes have been streamlined by several independent manufacturers and progressively have converged to a similar configuration. This configuration thus represents a mature consensus design of manufacturers, and it is used almost universally in the industry. Failures occur in gearboxes of this configuration independent of the manufacturer and any slight differences in the actual design. This suggests that each independent manufacturer is performing the same design routine. Additionally, because the industry is highly competitive and because it can be assumed that manufacturers are capable of correcting quality-control problems, it follows logically that the failures experienced are not caused by poor workmanship. Therefore the problems inherent to gearboxes appear to be a product of flaws in the design process. METHODOLOGY: 1. To study existing design, assembly of Gear box. 2. Force calculation at the joints, stresses will be calculated analytically. 3. Geometry will be modelled to meet the specifications using CATIA software. 4. Geometrical model from CATIA will be meshed in Hypermesh and force from analytical method will be applied and simulated for results. NCADOMS-2016 Special Issue 1 Page 181

7 5. Comparison of simulation result with analytical calculation. 6. Perform similar analysis to support the modified design. 3.TIME DOMAIN ANALYSIS: The time domain methods try to analyse the amplitude and phase information of the vibration time signal to detect the fault of gear rotor bearing system. The time domain is perceptive that feels natural, and provides physical insight into the vibration. It is particularly useful in analysing impulsive signals from bearing and gear defects with non steady and short transient impulses. 4.TIME WAVEFORM ANALYSIS: Prior to commercial availability of spectral analysers, almost all vibration analysis was performed in the time domain. By studying the time domain waveform using equipment such as oscilloscopes, oscillographs or vibrograph, it was often possible to detect the changes in the vibration signature caused by faults. However, diagnosis of faults was a difficult task; relating a change to a particular component required the manual calculation of the repetition frequency based on the time difference observed between feature points. Waveform analysis can also be useful to identify vibrations that are non synchronous with shaft speed. In machine cost down analysis waveform can indicate the occurrence of resonance. The waveform of defected gear vibration signal is as shown in figure a. NCADOMS-2016 Special Issue 1 Page 182

8 Fig.a.:A typical waveform of defected gear vibration signal. Fig.b: A typical FFT Spectrum of defected gear vibration signal. NCADOMS-2016 Special Issue 1 Page 183

9 Item Gear Rotor and shaft Rolling element bearing Flexible coupling Electrical Machines Fault Tooth messing faults Misalignment, Cracked and worm teeth Eccentric gear Unbalance Bent shaft Misalignment Eccentric Journals Loose component Rubs Critical speed Cracked shaft Blade loss Blade resonance Pitting of race and ball/roller Spalling Other rolling elements defect Misalignment Unbalance Unbalance magnetic pulls NCADOMS-2016 Special Issue 1 Page 184

10 Broken /damaged rotor bars Air gap geometry vibrations Structural and foundation faults Structural resonance Piping resonance Table 1: Some typical faults and defects that can be detected with vibration analysis 5.REFERENCES: [1]Rusmir Bajrić et al. Review of Vibration Signal Processing Techniques Towards Gear Pairs Damage Identification in International journal of engineering and technology vol:11 no.04, Aug IJET-IJENS. [2]Mr.vijaykumar et al, Vibration Analysis for Gearbox Casing Using Finite Element Analysis The International Journal Of Engineering And Science (IJES) Volume 3,Issue 2,Pages 18-36,2014. ISSN (e): ISSN. [3]Ashwani Kumar et.al, Dynamic Vibration Analysis of Heavy Vehicle Truck Transmission Gearbox Housing Using FEA journal Of Engineering Science And Technology Review volume 4, P 59-65,2014. ISSN: [4] Prashant Bagdel et.al, Innovative Methods Of Modeling Gear Faults, International journal of Mechanical engineering and Robotics Research, Volume 2,no.4,Oct-2013, ISSN NCADOMS-2016 Special Issue 1 Page 185

11 [5] Leila Nacib et.al, Detecting Gear Tooth Cracks Using Cepstral Analysis In Gearbox Of Helicopters International Journal of Advances in Engineering & Technology, Vol. 5, Issue 2, pp Jan ISSN: [6] Milosav Ognjanović1.et.al, Gear Unit Housing Effect on the Noise Generation Caused by Gear Teeth Impacts Journal of Mechanical Engineering 58(2012)5, , paper accepted: [7] Kobra Heidarbeigi et.al, Adaptive Vibration Condition Monitoring Techniques for Local Tooth Damage in Gearbox Vol. 4, No. 7; July 2010, ISSN [8] A. de Kraker M.J.L. Stakenborg, 1986, Cepstrum analysis as a useful supplement to spectrum analysis for gear-box monitoring, Experimental stress analysis: proceedings of the 8th international conference, Amsterdam, Netherlands, May 12-16, p [9] Rao, B. K. N., Handbook of Condition Monitoring, Elsevier Advanced Technology, Oxford [10] Randall, R. B., 1982, A New Method of Modeling Gear Faults", ASME Journal of Mechanical Design, April 1982, Vol. 104, p NCADOMS-2016 Special Issue 1 Page 186