Flexible couplings, especially gear couplings, can exert substantial axial and radial loads, sufficient in some cases to fail bearings or to damage gears. Gears based on their rotational motion and the heavy amount of load they carry are subjected to fatigue. Beyond that its a bit unusual for a gear tooth coupling to fail except for two reasons. Every failed coupling provides some evidence about what caused the failure. International journal for research in applied science. Once the stresses in a flexible disc exceed the endurance limits, failure occurs within a short period without alarm of failure 1. Coupling description the mt gear coupling is a steel doublejoint coupling. A fractured spline gear coupling for a motor shaft was received for analysis to investigate the cause of failure. The mt coupling is torsionally stiff and formed by two crowned hubs which engage two flanged sleeves with internal straight parallel teeth see coupling parts at. The 37 mw gearbox had broken pinion teeth after several thousand operating hours. How to diagnose gear failures neale consulting engineers. Clean out old lubricant and inspect seals and gear teeth. The only way to improve coupling life is to understand what caused the failure and to correct it prior to installing a new coupling.
Due to this mechanical motion, these couplings must be lubricated. While failures caused by a combination of factors occur. Fortunately, gear couplings often provide signature failure modes that. Main function is to transmit torque and at the same time accommodate the misalignment between two shafts. The causes of gear coupling failure mainly include the following two aspects. Falk couplings are common components in any mechanical drive system. The oem was proceeding with a tooth profile redesign to make the gear more tolerant of the misalignment to which other consultants had attributed the tooth failures. Analysis of a cracked spline gear failure analysis and.
Poor lubrication between the gear teeth generates higher friction between these teeth, resulting in gear coupling wear, heat generation and high axial loads to mating equipment bearings. Bending moments and radial forces arise from the friction forces between the coupling teeth when operating normally. The lovejoy coupling handbook lovejoy a timken company. If practical, record tooth contact patterns under either loaded or unloaded conditions. The 37 mw gearbox had broken pinion teeth after several thousand operating hours the oem was proceeding with a tooth profile redesign to make the gear more tolerant of the misalignment to which other consultants had. Abnormal wear of gear couplings a case study sciencedirect. Gear coupling teeth do not need full height because the torque load is carried at the pitch line of the tooth and many teeth are in contact with each other in the hub and the sleeve to carry the load.
When a failure arises from this cause there are often other adjacent teeth showing cracks at an earlier stage of development. Misalignment of gear coupling shafts due to assembly errors results in uneven distribution of clearance between meshing teeth of the hub and sleeve and eventually nonequal tooth load sharing which may result in cyclic loading and failure due to fatigue. Type curvedtooth gear coupling allsteel gear coupling geometries design compact short compact mass moment of inertia low average shaft distance dimension very low very low types extract shiftable coupling type sd, sd1, sdd, sdd3 sd flange type fa, fb, fab, fh, fr cover type da, db, dab, dh, dr. Falk lifelign gear couplings triplecrowned teeth are crowned on the root, tip and face to articulate freely and minimize wear caused by misalignment. May 29, 2018 the typical failure mode of gear couplings is that the teeth wear away from improper lubrication andor excessive misalignment until there is excessive backlash and tooth tip clearance leading to high vibration, or they become so thin they can no longer support the torque and roll over, an example which is a hub spinning inside a sleeve. If it is grease lubricated, then a common cause is poor maintenance with respect to lubrication. Spiral bevel teeth are at an angle so more than one is in mesh, similar to a helical gear hypoid a variation on spiral bevel with the pinion centerline moved. However, under unusually poor op erating or lubricating conditions, the teeth can become so thin that total failure occurs. Failures are a result of excessive cyclic bending stresses applied to teeth in.
The gear teeth in a gear coupling have high backlash to allow for angular misalignment. Worm unlike involute gears in that the action only involves sliding. Instantaneous failure of the diaphragm type coupling permitting machine runaway, is the greatest risk in this design. Gear type coupling runaway can result from loss of gear teeth due to wear which is gradual and normally gives warning. Fortunately, gear couplings often provide signature failure modes that can be quickly identified and diagnosed. Coupling answers where the world turns for coupling knowledge.
Complete this step before disassembling gearbox components for inspection. Figure 1 provides an overview of the coupling as received for analysis. Due to the application of load on the gear teeth, the gear tooth is subjected to bending. Gear couplings a gear coupling figure 1 accommodates misalignment and shaft end float by the misalignment and sliding of the gear teeth on the hub in the sleeve figure 2. Usually only one or two teeth are affected and, apart from the broken teeth, the others are in good condition with no sign of cracks. Jan 30, 2015 evaluating gear tooth wear and being able to root cause and address coupling failure are both critical to ensuring maximum reliability and uptime for a given mechanical power transmission system. The gear coupling is assembled with a slight interference on the major diameter, balanced, disassembled, ground at the tooth tips and reassembled for use in the application. The coupling hub can have typical gear coupling teeth with crowning or can have four to six crowned dogs. These joints are often connected by a third shaft called the spindle. Evaluating gear tooth wear and being able to root cause and address coupling failure are both critical to ensuring maximum reliability and uptime for a given mechanical power transmission system. Failure was found to be occurring in the form of rapid wear of teeth. Grindhonepolish gear teeth superfinish, coat, or smooth bearing rings or elements avoid shotpeened flanks make hardest gearbearing element as smooth as possible make pinion 2 hrc points harder than gear use oil with high micropitting resistance keep lubricant.
Clearance distribution of misaligned gear coupling teeth. The gear grip coupling is a threepiece highly flexible design which includes two hubs and an elastic sleeve. The way in which mating gear teeth contact indicates how well they are aligned figure 1. Bevelsimilar to a spur gear but designed for a right angle drive, tends to be rough and noisy. Seal will be forced out of one end during this operation. If a good grease is 11,1 available, then any high viscosity oil is preferable.
The gear ring of the gear coupling has a large axial displacement and can not even mesh. The load is shared among multiple teeth around the coupling circumference, resulting in higher load. Gearbox typical failure modes, detection and mitigation methods. Pictures of gear couplings are included, as well as selection charts and an explanation of how the charts are used. Biswas a number of failures occurred in the gear coupling transmitting the torque from a steam turbine rotating at 7500 rrain to a 1. Gearbox reliability collaborative gearbox 1 failure. Since gear coupling tooth wear is generally related to the lubricant, it is necessary to determine the reason for lube. This article covers constructional features of the gear coupling, tooth profiles and crowning of teeth in a gear coupling, allowable degrees of misalignment, and selection and service procedures for gear couplings. Gearbox typical failure modes, detection and mitigation. The fatigue in the gears induces the formation of cracks in the root of the gear tooth which propagates with each rotational cycle of the gear and. The tooth surface of gear coupling is seriously damaged. Coupling answers where the world turns for coupling.
The most likely failure mode of a gear coupling tooth is that which comes. A gear coupling is a mechanical device designed to transmit torque between two shafts that are not collinear. Mechanically flexible couplings, such as gear and chain couplings, provide a flexible connection by permitting coupling components to move or slide over each other. Flexible gear coupling installation and maintenance. Extend gear coupling life extended service of gear couplings can be achieved by understanding the principles of wear, how lubricants function and proper maintenance. Jun 21, 2007 assessing gear damage can be a challenge, especially in industrial equipment. Some failures can be seen readily, while others require some investigation. Gearbox reliability collaborative gearbox 1 failure analysis. Couplings tracking the causes of coupling failure plant.
Jgma 7001011990 terms of gear tooth failure modes jis b 0160. How to achieve gear coupling reliability lubrication. Select a gear coupling to connect a 500 hp, 1170 rpm electric motor to a drive high speed shaft of a maneuvering winch. Msi was contracted by the oem to perform testing and analysis to determine the root cause of gear tooth failures on an aeroderivative gas turbine power generation drivetrain. Where tooth wear progresses rapidly, eventual disengagement of the gear coupling can occur when either external or internal teeth roll or bend over. The original tooth form followed the spur gear form with modification.
Gear grip shaft collars, flywheel coupling, jaw coupling. By eliminating tiploading while reducing backlash and radial clearances, lifeligns triplecrown teeth can help protect equipment from damaging loads. That can include things like a failure of an end seal allowing the grease to fly out of the coupling due to centrifugal force. The wear pattern indicates the hs gear mesh was misaligned causing a higher load at the rotor end of the teeth. The primary failure mode of the sun spline was severe fretting corrosion. Later improvements included tooth crowning that increased misalignment capability and coupling life. The root cause of the failure was probably lubricant starvation.
When the same is repeated for a very huge number of cycles bending fatigue failure of the gear sets in. The first gear couplings had straight teeth, and depended purely on backlash to accommodate misalignment. Couplings require periodic maintenance, and regular inspection will provide clues to help improve the life of a falk coupling. The primary failure mode of the hs gearset was severe scuffing. Gear couplings are torsionally rigid and consist of hubs with multi crowned teeth at flank, tip and chamfering on teeth, gaskets, sleeve and orings. Grindhonepolish gear teeth superfinish, coat, or smooth bearing rings or elements avoid shotpeened flanks make hardest gear bearing element as smooth as possible make pinion 2 hrc points harder than gear use oil with high micropitting resistance keep lubricant cool, clean, and dry use highviscosity lubricant. Jan 30, 2015 a gear coupling has a backlash and loose fit between the teeth so it cannot be spun on a balance machine while assembled without modification. The crowning accommodates a limited amount of angular misalignment while transferring torque from the element to the hub.
The gear coupling tooth geometry has evolved over many years. Therefore, it is not easy to figure out solutions to causes. Nakandakar involute splines are commonly used in gearboxes to connect gears and shafts, especially when high torque is transmitted through the coupling. Unlike lab tests designed to isolate a particular failure mode, field failures may combine several modes. The failure starts as a crack which is usually at the root of the tooth and proceeds across the base of the tooth until the complete tooth breaks away from the gear. Universal joints are capable of higher misalignments. The main types of failure encountered with gear couplings are worn teeth. Gear tooth failure where fractured surfaces show a single brittle break with no sign of fatigue marking.
Many gear coupling designs use the tips of the hub teeth to pilot the floating member. Interchangeable half for half with series h, waldron coupling and other competitive couplings. Gear couplings are generally limited to angular misalignments, i. Some minor misalignment is provided by the clearances between gear teeth and chain and sprocket teeth respectively, however shafts should be aligned to less than 0. The coupling typically consists of two flexible joints, one fixed to each shaft. The typical failure mode of gear couplings is that the teeth wear away from improper lubrication andor excessive misalignment until there is excessive backlash and tooth tip clearance leading to high vibration, or they become so thin they can no longer support the torque and roll over, an example which is a hub spinning inside a sleeve.
A variety of falk couplings are available, including gear, grid, disc, elastomeric, fluid and composite. Assessing gear damage can be a challenge, especially in industrial equipment. Axial forces occur when the coupling is worn, with steps in the teeth. Gear damage are defined by the following standards. Dec 01, 2008 mechanically flexible couplings, such as gear and chain couplings, provide a flexible connection by permitting coupling components to move or slide over each other. A gear coupling has a backlash and loose fit between the teeth so it cannot be spun on a balance machine while assembled without modification. Gear grip applications the gear grip product is a general use coupling best suited for applications with a large degree of misalignment and is rated up to 50 hp. Apr 20, 2016 the gear teeth in a gear coupling have high backlash to allow for angular misalignment. However, the gear type coupling is not immune to runaway. This is why the gear coupling lubricant plays such a critical role in the reliability and life of a gear coupling. The lovejoy coupling handbook the lovejoy coupling handbook. It was reported that the coupling was installed near the top of the filter shaft and was inserted into a gearbox motor.
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