Why a flexible coupling? A flexible coupling exists to transmit power (torque) from one shaft to some other; to compensate for minor amounts of misalignment; and, using cases, to provide protective functions such as for example vibration dampening or performing as a “fuse” in the case of torque overloads. Therefore, industrial power China Pulley transmission often demands flexible instead of rigid couplings.

When enough time involves specify replacements for flexible couplings, it’s human nature to take the simple path and find something similar, if not really identical, to the coupling that failed, probably applying a few oversized fudge factors to be conservative. Too often, nevertheless, this practice invites a repeat failure or pricey system damage.

The wiser approach is to start with the assumption that the prior coupling failed since it was the incorrect type for that application. Taking period to look for the right type of coupling is definitely worthwhile actually if it just verifies the prior design. But, it might lead you to something completely different that will are better and go longer. A different coupling style may also extend the life of bearings, bushings, and seals, preventing fretted spline shafts, minimizing sound and vibration, and slicing long-term maintenance costs.

Sizing and selection
The rich selection of available flexible couplings provides a wide variety of performance tradeoffs. When choosing among them, resist the temptation to overstate services factors. Coupling assistance factors are designed to compensate for the variation of torque loads standard of different powered systems and also to give reasonable service existence of the coupling. If chosen too conservatively, they are able to misguide selection, raise coupling costs to unnecessary levels, and even invite damage somewhere else in the system. Remember that correctly selected couplings generally should break before something more expensive will if the machine can be overloaded, improperly managed, or somehow drifts out of spec.

Determining the right kind of flexible coupling starts with profiling the application the following:

• Prime mover type – electrical motor, diesel engine, other

• Genuine torque requirements of the driven aspect of the machine, instead of the rated horsepower of the primary mover – be aware the range of adjustable torque resulting from cyclical or erratic loading, “worst-case” startup loading, and the amount of start-stopreversing activity common during normal operation

• Vibration, both linear and torsional

• Shaft sizes, keyway sizes, and the desired suit between shaft and bore

• Shaft-to-shaft misalignment – take note degree of angular offset (where shafts are not parallel) and amount of parallel offset (length between shaft centers if the shafts are parallel but not axially aligned); also be aware whether driving and driven systems are or could be sharing the same base-plate

• Axial (in/out) shaft movement, End up being range (between ends of generating and driven shafts), and any other space-related restrictions.

• Ambient conditions – generally heat range range and chemical substance or oil exposure

But actually after these fundamental technical information are identified, other selection criteria is highly recommended: Is ease of assembly or installation a account? Will maintenance problems such as for example lubrication or periodic inspection end up being acceptable? Are the components field-replaceable, or does the entire coupling need to be changed in the event of failing? How inherently well-balanced may be the coupling design for the speeds of a particular application? Will there be backlash or free of charge play between your parts of the coupling? Can the gear tolerate much reactionary load imposed by the coupling because of misalignment? Understand that every flexible coupling style provides strengths and weaknesses and connected tradeoffs. The main element is to find the design suitable to the application and budget.

Application specifics
Originally, flexible couplings divide into two primary groups, metallic and elastomeric. Metallic types make use of loosely installed parts that roll or slide against each other or, alternatively, nonmoving parts that bend to take up misalignment. Elastomeric types, however, gain versatility from resilient, non-moving, rubber or plastic elements transmitting torque between metallic hubs.

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Metallic types are suitable to applications that want or permit:

• Torsional stiffness, meaning very little “twist” happens between hubs, in some instances providing positive displacement of the driven shaft for every incremental motion of the traveling shaft

• Operation in relatively high ambient temperatures and/or presence of certain oils or chemicals

• Electric motor drive, seeing that metallics generally aren’t suggested for gas/diesel engine drive

• Relatively continuous, low-inertia loads (metallic couplings aren’t recommended for generating reciprocal pumps, compressors, and other pulsating machinery)

Elastomeric types are best suited to applications that require or permit:

• Torsional softness (allows “twist” between hubs so that it absorbs shock and vibration and will better tolerate engine get and pulsating or relatively high-inertia loads)

• Greater radial softness (allows more angular misalignment between shafts, puts less reactionary or part load on bearings and bushings)

• Lighter weight/lower cost, in terms of torque capacity relative to maximum bore capacity

• Quieter operation

Thoroughly review the suggested application profile with the coupling vendor, getting not merely their recommendations, yet also the reasons behind them.

Failure modes
The wrong applications for every type are those characterized by the circumstances that a lot of readily shorten their life. In metallic couplings, premature failing of the torque-transmitting element frequently results from metal fatigue, usually because of flexing caused by excessive shaft misalignment or erratic, pulsating, or high-inertia loads. In elastomeric couplings, breakdown of the torque-transmitting element most often results from extreme warmth, from either ambient temperature ranges or hysteresis (inner buildup in the elastomer), or from deterioration because of connection with certain oils or chemicals.

Standards
For the most part, industry-wide standards usually do not can be found for the normal design and configuration of flexible couplings. The exception to this is the American Gear Producers Assn. standards relevant in North America for flangedtype equipment couplings and the bolt circle for mating both halves of the couplings. The American Petroleum Institute provides specifications for both standard refinery assistance and unique purpose couplings. But other than that, industry specs on flexible couplings are limited to features such as bores/keyways and matches, balance, lubrication, and parameters for ratings.

Information for this article was provided by Tag McCullough, director, marketing & program engineering, Lovejoy, Inc., Downers Grove, Ill., and excerpted from The Coupling Handbook by Lovejoy Inc.