International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-8 Issue-6, August, 2019 1947 Published By: Blue Eyes Intelligence Engineering & Sciences Publication Retrieval Number F7928088619/2019©BEIESP DOI: 10.35940/ijeat.F7928.088619 Abstract: Industrial gearboxes are designed for minimum 3 to 5 years of life considering normal working conditions. Theoretical life of gearbox system can be predicted by calculating the life of individual components of the gearbox like bearings, coupling and gear-pair. There is significant amount of research work done on estimating individual component life perdition however combined life prediction of a gearbox is a quite complex phenomenon. The challenge in developing a single life prediction model for variety of gearboxes available in today’s market. There is a huge variety in their types, sizes, costs, application conditions (indoor, outdoor, marine, aerospace), safety requirements (domestic to hazardous). Providing a common solution that address all these is near to impossible. Major cause of early gearbox failure is wrong selection for application, improper installation, contaminants and excessive shock and impact loads. Vibration measurement gives an early indication of failure of rotating parts in gearbox which are primarily bearings and gear-pair. This research focuses on step by step approach to calculate the life of bearings in a gear box and gearbox life prediction models. The methodology followed can be used for other types of industrial gearboxes. Key words: American Bearing Manufacturers Association (ABMA), American Gearing Manufacturers Association (AGMA), Fast Fourier Transform (FFT), Rolling Contact Fatigue (RCF) I. INTRODUCTION Gearbox life depends upon minimum life of its components. Gear pair is designed for higher life as per the application for which it is selected [1], [2]. Bearings are the most critical components in deciding overall life of gearbox. Hence it is important to understand causes of bearing failures and the life prediction models of bearings[2], [3]. Both ABMA standard and ISO 281 give detailed life prediction procedure. Theoretically it can be proven that bearings can last almost infinitely for a given application if they are properly mounted, lubricated and kept free from contaminants. However in real-life conditions this is not possible and bearings early due to various reasons[4], [5] and [6]. Bearing failures can be broken down in to two basic categories, one premature failure where bearings don’t even run for minimum life for which they are selected and second is the fatigue failures where bearing run for sufficient time and then fail. Many a times premature failures can be catastrophic hence it is important to understand their root causes and make a plan to avoid them in applications[3]. A. Causes of bearing failure – i. Inadequate lubrication – about 43% of the bearings fail due to inadequate lubrication which results due to insufficient Revised Manuscript Received on August 22, 2019. Ajeet Arvind Majali, Engineering, College of Engineering Pune, Dr. Maheshwar Dinkar Jaybhaye, Production & Industrial Management, College of Engineering Pune, Pune, India or interrupted supply of lubrication or many a times wrong selection of lubricants. Proper heat transfer from bearing hot races to lubricant needs to be ensured, else bearings can fail due to overheating[3]. ii. Improper installation – about 29% of the bearings fail due to improper installation. The reasons for this could be shaft or mounting defects, misalignment, incorrect fit of inner race with shaft or outer race within housing, excessive clearance, surface finish of mounting surface or housing, excessive axial play, false brinelling due to vibrations, end shield or bearing seal damage while mounting[3]. iii. Improper sealing – about 18% bearings fail due to ineffective seals. This can be due to contaminants from inside the lubricant or outside the bearings, moisture in the lubricant, corrosion[3]. iv. Subsurface fatigue - about 8% bearings fail due to subsurface fatigue. This can be due subsurface crack development coming out of Rolling Contact Fatigue (RCF) [8], [9]. The details of RCF are explained in section B. v. Miscellaneous reasons – about 2% bearings fail due to other miscellaneous reasons which can be due to an electric current passing through bearings which are not properly insulated, quality of bearing steel and impurities in bearing steel processing. Vacuum degassed 52100 steel are most popular bearing material. Also incorrect selection of bearing can also result in premature failure. Bearing failure statistic shown in table 1 gives the common causes of failure and their % occurrence based on general industrial bearing failure analysis[3]. B. Rolling Contact Fatigue – Fatigue failures are due to rolling contact fatigue (RCF). RCF theory for bearing material is not new, however it’s interpretation and implementation in real-life bearings is important [7]. Rolling contact fatigue failure is made up of two dominant mechanisms, one is subsurface originated spalling [9] and the other is surface originated pitting. First step to avoid fatigue failures is to test the bearing steels using rolling contact fatigue type testing. These type of testing equipment are available and can be customized as per customer needs. Most popular types of machines are rotary tribometers which press the pins or balls on a rotating disk. Different combinations like Ball-on-disk [24], Cylinder-on-disk, Pin-on-disk, Cross cylinder, Block-on-ring, Block-on-cylinder, Ball-on-ring, Linear Reciprocating (Ball/Pin on Plate), ball on rod types are available [3]. A constant load is applied on the material to be evaluated. The material is either stationary or rotating based on machine configuration. Load is applied using a standard 52100 vacuum degassed steel material either in the form of balls or a flat plate. Worm Gearbox Bearing Life Prediction Ajeet Majali, M. D. Jaybhaye