engineering

Coupling

Coupling is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Coupling rather than just read about it. In short: A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both.

Key takeaways

Coupling belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Coupling to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Coupling from memory before moving on to harder problems.

Reference excerpt

A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. In a more general context, a coupling can also be a mechanical device that serves to connect the ends of adjacent parts or objects. Couplings do not normally allow disconnection of shafts during operation, however there are torque-limiting couplings which can slip or disconnect when some torque limit is exceeded. Selection, installation and maintenance of couplings can lead to reduced maintenance time and maintenance cost.

Uses Shaft couplings are used in machinery for several purposes. A primary function is to transfer power from one end to another end (ex: motor transfer power to pump through coupling). Other common uses:

To alter the vibration characteristics of rotating units To connect the driving and the driven part To introduce protection To reduce the transmission of shock loads from one shaft to another To slip when overload occurs

Types

Beam

A beam coupling, also known as helical coupling, is a flexible coupling for transmitting torque between two shafts while allowing for angular misalignment, parallel offset and even axial motion, of one shaft relative to the other. This design utilizes a single piece of material and becomes flexible by removal of material along a spiral path resulting in a curved flexible beam of helical shape. Since it is made from a single piece of material, the beam style coupling does not exhibit the backlash found in some multi-piece couplings. Another advantage of being an all machined coupling is the possibility to incorporate features into the final product while still keeping the single piece's integrity. Changes to the lead of the helical beam provide changes to misalignment capabilities as well as other performance characteristics such as torque capacity and torsional stiffness. It is even possible to have multiple starts within the same helix. The material used to manufacture the beam coupling also affects its performance and suitability for specific applications such as food, medical and aerospace. Materials are typically aluminum alloy and stainless steel, but they can also be made in acetal, maraging steel and titanium. The most common applications are attaching rotary encoders to shafts and motion control for robotics. Beam couplings can be known by various names depending upon industry. These names include flexible coupling, flexible beam coupling, flexible shaft coupling, flexure, helical coupling, and shaft coupling. The primary benefit to using a flexible beam coupling to join two rotating shafts is to reducing vibration and reaction loads which in turn will reduce overall wear and tear on machinery and prolong equipment life.

Bush pin flange Bush pin flange coupling is used for slightly imperfect alignment of the two shafts. This is modified form of the protected type flange coupling. This type of coupling has pins and it works with coupling bolts. The rubber or leather bushes are used over the pins. The coupling has two halves dissimilar in construction. The pins are rigidly fastened by nuts to one of the flange and kept loose on the other flange. This coupling is used to connect shafts which have a small parallel misalignment, angular misalignment or axial misalignment. In this coupling the rubber bushing absorbs shocks and vibration during its operations. This type of coupling is mostly used to couple electric motors and machines.

Constant velocity

There are various types of constant-velocity (CV) couplings: Rzeppa joint, Double cardan joint, and Thompson coupling.

Clamp or split-muff In this coupling, the muff or sleeve is made into two halves parts of the cast iron and they are joined by means of mild steel studs or bolts. The advantages of this coupling is that assembling or disassembling of the coupling is possible without changing the position of the shaft. This coupling is used for heavy power transmission at moderate speed.

Diaphragm Diaphragm couplings transmit torque from the outside diameter of a flexible plate to the inside diameter, across the spool or spacer piece, and then from inside to outside diameter. The deforming of a plate or series of plates from I.D. to O.D accomplishes the misalignment.

Disc Disc couplings transmit torque from a driving to a driven bolt tangentially on a common bolt circle. Torque is transmitted between the bolts through a series of thin, stainless steel discs assembled in a pack. Misalignment is accomplished by deforming of the material between the bolts.

Elastic

An elastic coupling transmits torque or other load by means of an elastic component. One example is the coupling used to join a windsurfing rig (sail, mast, and components) to the sailboard. In windsurfing terminology it is usually called a "universal joint", but modern designs are usually based on a strong flexible material, and better technically described as an elastic coupling. They can be tendon or hourglass-shaped, and are constructed of a strong and durable elastic material. In this application, the coupling does not transmit torque, but instead transmits sail-power to the board, creating thrust (some portion of sail-power is also transmitted through the rider's body).

Flexible Flexible couplings are usually used to transmit torque from one shaft to another when the two shafts are slightly misaligned. They can accommodate varying degrees of misalignment up to 1.5° and some parallel misalignment. They can also be used for vibration damping or noise reduction. In rotating shaft applications a flexible coupling can protect the driving and driven shaft components (such as bearings) from the harmful effects of conditions such as misaligned shafts, vibration, shock loads, and thermal expansion of the shafts or other components. At first, flexible couplings separate into two essential groups, metallic and elastomeric. Metallic types utilize freely fitted parts that roll or slide against one another or, on the other hand, non-moving parts that bend to take up misalignment. Elastomeric types, then again, gain flexibility from resilient, non-moving, elastic or plastic elements transmitting torque between metallic hubs.

Fluid

Gear

… excerpt ends here. Continue reading the full article.

Illustrations

Coupling: Rotating coupling — Rotating coupling

Worked examples

Example 1 — a first encounter with Coupling

Start with the simplest possible case. Write down what Coupling claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Coupling before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Coupling ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Coupling

In research: Coupling appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Coupling in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Coupling is common in secondary-school and first-year university syllabi. It links to neighbouring topics Household hardware, Mechanisms (engineering), Rotating shaft couplings, so understanding it makes those chapters shorter.
In everyday life: Look for Coupling outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Coupling in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Coupling means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Coupling out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Coupling in simple terms?

Why does Coupling matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Coupling?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Coupling.