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The type of lubricant and the method of applying it to the tooth flanks of large open gears is very important from the point of view of lubrication technology and maintenance. When selecting the type of lubricant and the application method, it is important to check whether it is possible to feed the required lubricant quantity to the load-carrying tooth flanks, This is necessary to avoid deficient lubrication, damage to the gear and operational malfunctions. It is important to determine the type of lubricant, which may be fluid or grease-like. The consistency of the lubricant will have a direct impact on the ability of the lubrication system to feed adequately the lubricant to the gear. The interactions between the common types of lubricant and the lubrication application methods for open gear drives are shown in Fig. 1.
In the lubrication and cooling of gear teeth a variety of oil jet lubrication schemes is sometimes used. A method commonly used is a low pressure, low velocity oil jet directed at the ingoing mesh of the gears, as was analyzed in Reference 1. Sometimes an oil jet is directed at the outgoing mesh at low pressures. It was shown in Reference 2 that the out-of-mesh lubrication method provides a minimal impingement depth and low cooling of the gears because of the short fling-off time and fling-off angle.(3) In References 4 and 5 it was shown that a radially directed oil jet near the out-of-mesh position with the right oil pressure was the method that provided the best impingement depth.
Several methods of oil jet lubrication of gears are practiced by the gear industry. These include the oil jet directed into the mesh, out of the mesh and radially directed into the gear teeth. In most cases an exact analysis is not used to determine the optimum condition such as, jet nozzle location, direction and oil jet velocity, for best cooling. As a result many gear sets are operating without optimum oil jet lubrication and cooling.
This is a three-part article explaining the principles of gear lubrication. It reviews current knowledge of the field of gear tribology and is intended for both gear designers and gear operators. Part 1 classifies gear tooth failures into five modes and explains the factors that a gear designer and operator must consider to avoid gear failures. It defines the nomenclature and gives a list of references for those interested in further research. It also contains an in-depth discussion of the gear tooth failure modes that are influenced by lubrication and gives methods for preventing gear tooth failures.
What follows is Part 2 of a three-part article covering the principles of gear lubrication. Part 2 gives an equation for calculating the lubricant film thickness, which determines whether the gears operate in the boundary, elastohydrodynamic, or full-film lubrication regime. An equation for Blok's flash temperature, which is used for predicting the risk of scuffing, is also given.
In the gearing industry, gears are lubricated and cooled by various methods. At low to moderate speeds and loads, gears may be partly submerged in the lubricant which provides lubrication and cooling by splash lubrication. With splash lubrication, power loss increases considerably with speed. This is partially because of churning losses. It is shown that gear scoring and surface pitting can occur when the gear teeth are not adequately lubricated and cooled.
A reader asks about how to specify a method of lubrication for a speed reducer with a three-stage helical gear with a low peripheral speed.
Pitting and micropitting resistance of case-carburized gears depends on lubricants and lubrication conditions. Pitting is a form of fatigue damage. On this account a short time test was developed. The test procedure is described. The "pitting test" was developed as a short time test to examine the influence of lubricants on micropitting. Test results showing the influence of case-carburized gears on pitting and micropitting are presented.
This is the final part of a three-part series on the basics of gear lubrication. It covers selection of lubricant types and viscosities, the application of lubricants, and a case history
In the wide, wide world of moving parts, the gears required for the big jobs—the really big jobs—often experience big problems. Proper lubrication of these gears is paramount in industrial applications such as wind turbines, kilns, sugar mills, crushers, heavy construction, offshore drilling rigs, mining and quarrying.
Excess lubricant supply in gearing contributes to power loss due to churning as well as the requirements of the lubrication system itself. Normally, a much larger amount of oil than required is used for cooling because so much of it is thrown away by centrifugal force. To lower the amount of lubricant required and reduce those losses, it is necessary to discover the ideal location of the supplying nozzle.
This review of elastohydrodynamic lubrication (EHL) was derived from many excellent sources (Refs. 1–5). The review of Blok’s flash temperature theory was derived from his publications (Refs. 6–9). An excellent general reference on all aspects of tribology is the Encyclopedia of Tribology (Ref. 10).
I must confess I sometimes find myself a bit dazed when discussing lubrication issues with either staff or vendors. The terminology seems to be all over the lot, with some terms having double meanings. Can you help cut through the confusion?
A main limiting factor in extending the use of hard coatings to machine component application is the lack of knowledge about how these inert coatings perform under lubricated conditions using today's lubricants.
Surface measurement of any metal gear tooth contact surface will indicate some degree of peaks and valleys. When gears are placed in mesh, irregular contact surfaces are brought together in the typical combination of rolling and sliding motion. The surface peaks, or asperities, of one tooth randomly contact the asperities of the mating tooth. Under the right conditions, the asperities form momentary welds that are broken off as the gear tooth action continues. Increased friction and higher temperatures, plus wear debris introduced into the system are the result of this action.
Myth No. 1: Oil Is Oil. Using the wrong oil is a common cause of gear failure. Gears require lubricants blended specifically for the application. For example, slow-speed spur gears, high-speed helical gears, hypoid gears and worm gears all require different lubricants. Application parameters, such as operating speeds, transmitted loads, temperature extremes and contamination risks, must be considered when choosing an oil. Using the right oil can improve efficiency and extend gear life.
This work establishes a baseline for aerospace spur gear behavior under oil-off conditions. The collected test results document a different oil-off time, dictated by material used.
The effect of the lubrication regime on gear performance has been recognized, qualitatively, for decades. Often the lubrication regime is characterized by the specific film thickness defined as the ratio of lubricant film thickness to the composite surface roughness. It can be difficult to combine results of studies to create a cohesive and comprehensive data set. In this work gear surface fatigue lives for a wide range of specific film values were studied using tests done with common rigs, speeds, lubricant temperatures, and test procedures.
Prior to receiving airworthiness certification, extensive testing is required during the development of rotary wing aircraft drive systems. Many of these tests are conducted to demonstrate the drive system’s ability to operate at extreme conditions, i.e. — beyond that called for in the normal to maximum power operating range.
Three years ago, coated gears seemed to be the perfect solution for the Micro Marine Corporation. The early designs for the gear drive of their MicroCAT human-powered boat used a combination of thin-film dry gear coatings with lubrication and wear-resistance properties. These coatings simplified their design, provided corrosion resistance, made the gear drive environmentally safe and eliminated the need for gear drive lubrication and maintenance. It was a success story in the making.
The objective of this study was to investigate the limits concerning possible reduction of lubricant quantity in gears that could be tolerated without detrimental effects on their load carrying capacity.
Worm gear speed reducers give the design engineer considerable options, but these gear systems present a challenge to the lubrication engineer. Heat energy generated by the high rate of sliding and friction in the contact zone causes worm gears to be relatively inefficient compared to other gear types. Because worm gears operate under a boundary or near-boundary lubrication regime, a satisfactory lubricant should contain a friction modifier to alleviate these conditions.
In order to properly select a grease for a particular application, a sound knowledge of the influence of different grease components and operating conditions on the lubrication supply mechanism and on different failure modes is of great benefit.
Today gear drive operations have several options when selecting the proper lubricant for their gearboxes. As in the past, the primary lubricant used for gearbox lubrication is mineral oil. But with the advances in technology, synthetic hydrocarbons (PAOs) and polyglycols show very specific advantages in certain applications. With gear drives becoming more and more precise, it is now also to the benefit of the gear operator to verify that he or she has the proper additive package and viscosity in the lubricant selected. Fig. 1 shoes that a gear oil is a combination of a base oil and specific additives. The base oils can be either mineral oil, a synthetic or even in some cases a combination of the two.
The diagnosis and prevention of gear tooth and bearing wear requires the discovery and understanding of the particular mechanism of wear, which in turn indicates the best method of prevention. Because a gearbox is a tribologically dependent mechanism, some understanding of gear and bearing tribology is essential for this process. Tribology is the general term for the study and practice of lubrication, friction and wear. If tribology is neglected or considered insignificant, poor reliability and short life will result.
A sampling of newsletter articles and videos related to gear manufacturing from March/April 2013.
Understanding the morphology of micropitting is critical in determining the root cause of failure. Examples of micropitting in gears and rolling-element bearings are presented to illustrate morphological variations that can occur in practice.
The complete Industry News section from the March/April 2013 issue of Gear Technology.
Universal tractor transmission oil (UTTO) is multifunctional tractor oil formulated for use in transmissions, final drives, differentials, wet brakes, and hydraulic systems of farm tractors employing a common oil reservoir. In the present work, the gear protection properties of two formulated vegetable-based UTTO oils, one synthetic ester-based UTTO oil, one synthetic ester gear oil, and one mineral based UTTO oil are investigated.
In this paper a thermal network model is developed to simulate the thermal behavior of a high-speed, one-stage gear unit which is jet-lubricated.
The complete product news section from the September / October 2014 Issue Gear Technology.
A reader asks: While I have read a reasonable amount of the literature on the pros and cons of anti-wear and anti-scuff additives, I find that the more I read, the more confused I become. I could use some clarity in my life.
Historically, wind turbine gearbox failures have plagued the industry. Yet an effective oil analysis program will increase the reliability and availability of your machinery, while minimizing maintenance costs associated with oil change-outs, labor, repairs and downtime. Practical action steps are presented here to improve reliability.
When it comes to purchasing gear lubricants, many people on both the sales and purchasing side decide to play the numbers game. The person with the most numbers, or the biggest numbers, or the lowest numbers, must have the best product - right? Wrong; gear oil selection is not a game, and numbers alone cannot determine the right product for an application.
Design Problem: Develop a gear drive for a pedal-powered water craft that will be easy to manufacture, use and maintain; that will be lightweight enough for the boat to be portable; and that will eliminate the environmental risk of lubricants leaking into the water.
Most research on micropitting is done on small-sized gears. This article examines whether those results are also applicable to larger gears.
We talked energy efficiency with some major players in the lubricants industry— but with a focus on their products’ impact regarding energy efficiency of gears and gearboxes in wind turbines.
A very direct and effective way of increasing power transmission efficiency is a changeover from mineral-oil-based lubricants to synthetic lubricants.
Mineral-oil-base lubricants show a significant decrease of kinematic viscosity with rising temperature, as exemplified in Figure 1 by lubricants for vehicle gears. An important attribute of lubricants is their viscosity index (VI), according to DIN/ISO 2909 (Ref. 4). Viscosity index is a calculated coefficient, which characterizes the change of viscosity of lubricants as a function of temperature. A high viscosity index represents a low variation of viscosity due to temperature and vice versa. A low viscosity-temperature-dependence is required for lubricants that are operated at significantly varying temperature conditions, such as vehicle engine and gear lubricants in summer and winter time. This way, the oils remain flowing and pumpable at low temperatures on the one hand; and on the other hand, sufficiently thick lubricant films can be formed at higher temperatures for a safe separation of the surfaces.
On gear drives running with pitch line velocities below 0.5 m/s so called slow speed wear is often observed. To solve some problems, extensive laboratory test work was started 10 years ago. A total of circ. 300,000 h running time on FZG back-to-back test rigs have been run in this speed range.
The following article is concerned with the analysis of the wear-reducing effect of PVD-coatings in gearings. Standardized test methods are used, which under near-real conditions enable statements to be made about the different forms of damage and wear (micropitting, macropitting, scuffing).
The Integral Temperature Method for the evaluation of the scoring load capacity of gears is described. All necessary equations for the practical application are presented. The limit scoring temperature for any oil can be obtained from a gear scoring test.
This article summarizes the use of laboratory fatigue data for bearings and gears coupled with probabilistic life prediction and EHD theories to predict the life and reliability of a commercial turboprop gearbox.
This paper will present data from both laboratory and field testing demonstrating that superfinished components exhibit lower friction, operating temperature, wear and/ or higher horsepower, all of which translate directly into increased fuel economy.
Gears are currently run at high speed and under high load. It is a significant problem to develop lubricants and gears with high load-carrying capacity against scoring. The particles of molybdenum disulfide have been considered to increase the scoring resistance of the gears. The wear characteristics and the scoring resistance of the gears lubricated with MoS2 paste and MoS2 powder have been investigated. (1) However, there are few investigations on the performance of the gears coated with MoS2 film with respect to scoring.
Aircraft transmissions for helicopters, turboprops and geared turbofan aircraft require high reliability and provide several thousand hours of operation between overhauls. In addition, They should be lightweight and have very high efficiency to minimize operating costs for the aircraft.
During the last decade, industrial gear manufacturers, particularly in Europe, began to require documentation of micropitting performance before approving a gear oil for use in their equipment. The development of micropitting resistant lubricants has been limited both by a lack of understanding of the mechanism by which certain lubricant chemistry promotes micropitting and by a lack of readily available testing for evaluation of the micropitting resistance of lubricants. This paper reports results of two types of testing: (1) the use of a roller disk machine to conduct small scale laboratory studies of the effects of individual additives and combinations of additives on micropitting and (2) a helical gear test used to study micropitting performance of formulated gear oils.
Okay, so you want to make some high quality gears for your customers, and you want to make a profit for your company, but you don't want to make a mess of the environment. What can you do?
The last decade has been a period of far-reaching change for the metal working industry. The effect of higher lubricant costs, technical advances in machine design and increasing competition are making it essential that manufacturers of gears pay more attention to testing, selecting and controlling cutting fluid systems. Lubricant costs are not a large percentage of the process cost relative to items such as raw materials, equipment and labor, and this small relative cost has tended to reduce the economic incentive to evaluate and to change cutting fluids.
How do we know when the gear material we buy is metallurgically correct? How can we judge material quality when all gear material looks alike?
The cost of teaching salesmen the ins and outs of gearing has proven to be expensive. Your journal is Just what we have been looking for. We found your article on lubrication analysis on gearing very interesting. More on the basics and more on lubrication would be appreciated.
Not long ago, many manufacturing managers thought sensitivity to environmental protection standards meant additional expenses, decreased productivity, and a plethora of headaches and hassles.
Editor's Note: The following article details the advantages of synthetic lubricants in certain applications. However, the user should be aware of certain design issues arising from the extract chemistry of the synthetic. For example, some synthetics may have low solvency for additives. Others may not be compatible with mineral oils or nonmetallic components such as seals and paints. Some synthetics may absorb water and may not have the same corrosion resistance as mineral oils. Finally, the user should consider biodegradability or toxicity before switching to any new lubricant. Many of these concerns are present in petroleum-based lubricants as well, so consult a lubrication specialist before specifying a lubricant.
By increasing the number of gears and the transmission-ratio spread, the engine will run with better fuel efficiency and without loss of driving dynamics. Transmission efficiency itself can be improved by: using fuelefficient transmission oil; optimizing the lubrication systems and pumps; improving shifting strategies and optimizing gearings; and optimizing bearings and seals/gaskets.
"Going green" and energy efficiency are goals that all industries -- especially in Europe and the United States -- are working on, in such sectors as electric motors, lubrication, gears and on and on. Drumroll here please for magnetic gearing
This article offers an overview of the practical design of a naval gear for combined diesel or gas turbine propulsion (CODOG type). The vibration performance of the gear is tested in a back-to-back test. The gear presented is a low noise design for the Royal Dutch Navy's LCF Frigate. The design aspects for low noise operation were incorporated into the overall gear system design. Therefore, special attention was paid to all the parameters that could influence the noise and vibration performance of the gearbox. These design aspects, such as tooth corrections, tooth loading, gear layout, balance, lubrication and resilient mounting, will be discussed.
The use of plastic gearing is increasing steadily in new products. This is due in part to the availability of recent design data. Fatigue stress of plastic gears as a function of diametral pitch, pressure angle, pitch line velocity, lubrication and life cycles are described based on test information. Design procedures for plastic gears are presented.
The search for greater gear life involves improvement in cost, weight and increased power output. There are many events that affect gear life, and this paper addresses those relating to fatigue, gear tooth pitting, fatigue strength losses due to the heat treating processes and shot peening technique. The capability of shot peening to increase fatigue strength and surface fatigue life eliminate machine marks which cause stress risers, and to aid in lubrication when properly controlled, suggests increased use and acceptance of the process.
The phenomena of deterioration of surfaces are generally very complex and depend on numerous conditions which include the operating conditions, the type of load applied, the relative speeds of surfaces in contact, the temperature, lubrication, surfaces hardness and roughness, and the compatibility and nature of materials.
The cutting tool industry has undergone some serious changes in the last couple of years in both technology and the way the industry does business. The emerging technology today, as well as for the foreseeable future, is dry cutting, especially in high volume production settings. Wet cutting continues to be as popular as ever with lubrication advances making it more economical and environmentally friendly. There has also developed a process called "near dry cutting." this process offers many of the benefits of fluids while eliminating many of hte associated problems.
News Items About lubrication
1 Cimcool Introduces Insol Lubrication (September 2, 2014)
Cimcool Fluid Technology is pleased to introduce InSol lubrication. This new technology coupled with unique surfactants and inhibitors pr... Read News
2 Oelheld Introduces Water-Based Lubrication Line (April 3, 2013)
Oelheld U.S. introduces its water based lubrication line. AquaTec 5001 is a high performance, synthetic metalworking fluid specifically d... Read News
3 Person Joins Klϋber Lubrication (March 15, 2013)
Klϋber Lubrication announces that Ron Person has joined its North American operations as director of business development for oil an... Read News
4 Klϋber Lubrication Appoints Kraemer as CEO (February 14, 2013)
Klϋber Lubrication, a worldwide manufacturer of specialty lubricants, announces the appointment of Ralf Kraemer as chief executive o... Read News
5 Two Publications from Society of Lubrication and Tribology Available (February 8, 2007)
The completely revised and updated Handbook of Lubrication and Tribology, Volume I: Application and Maintenance, Second Edition, is now a... Read News
6 Kluber Lubrication Receives European Ecolabel Approval (November 21, 2013)
Klϋber Lubrication, a worldwide manufacturer of specialty lubricants, announces that its Klüberbio EG 2 gear oil for thrusters ... Read News
7 Lubrication Engineers Introduce Monocal GP Grease (February 26, 2014)
Lubrication Engineers, Inc. recently introduced Monocal GP Grease (1499), a versatile general purpose lubricant for use in severe conditi... Read News
8 Oelheld Introduces AirForge 4027 Clean Lubrication (April 29, 2015)
Oelheld U.S. recently introduced AirForge 4027, a newly developed protective lubricant for hot forging of steel and alloys. It'... Read News
9 Klüber Lubrication Introduces Synthetic Grease for Extreme Climatic Conditions (April 10, 2015)
Klϋber Lubrication recently introduced Klübersynth EM 94-102, a fully synthetic lubricating grease incorporating a calcium comp... Read News
10 Klϋber Lubrication Receives ISO 21469 Certification (July 23, 2014)
Klϋber Lubrication, a worldwide manufacturer of specialty lubricants, has received the National Sanitation Foundation (NSF) ISO 2146... Read News
11 Kluber Lubrication Gluberlub and Kluberplex Solutions Designed for Offshore Industry (April 21, 2016)
Klϋber Lubrication will feature its multi-purpose oils and greases for offshore applications at booth #2923 during the Offshore Tech... Read News