Manufacturers install flexible shaft couplings in rotary equipment and machinery in order to connect rotary equipment to shafts and transfer torque. Examples of such machinery and equipment components include driveshafts, line shafts, power transmissions, wheels, and more. They also do things like isolate propeller pulse, dampen driveline vibration, and quiet gear chatter.
Flexible shaft couplings are also found in boats, hydraulic pumps, wind turbines, tube shafts, automobiles, paper making machines, printing machines, compressors, roll formers, and blowers.
Some of the many industries that rely on flexible shaft couplings include aerospace, automotive, construction, metal processing, mining, mineral processing, power general, quarry, and cement.
The earliest flexible couplings were used first by the Greeks around 300 BC and later by the Chinese around 25 AD.
Jerome Cardan invented the modern flexible coupling in the 1500s. His model featured a cross, two yokes, and four bearings. Then in 1650, Robert Hooke came up with the first practical application for the Cardan joint (Cardan shaft), which for this reason is sometimes called the Hooke joint. Hooke used the coupling to assist rotating shafts in clock drives.
In 1821, Irishman John Oldham invented the Oldham coupler. His goal was to fix an issue with paddle steamers, but we still use his coupler to this day.
The next advances in flexible couplings happened in 1886, when F.M. Roots theorized that he could modify a rigid coupling to make a more flexible coupling that would stop the shaft from failing. His theory is the basis for modern diaphragm couplings.
During the early 1900s, particularly the 1920s, flexible couplings use spread rapidly, and shaft coupling manufacturers popped up all over the United States. Their new popularity was due to the young and booming auto industry; couplings were and are important components of vehicles. One of the most important flexible couplings to early automobiles was the metallic disc coupling. However, until the 1940s, flexible metallic disc couplings were only functional with applications featuring low speeds, low torques, and low levels of misalignment.
Between 1930 and 1945, engineers developed a wide variety of coupling types that we still use today, such as jaw couplings, disc couplings, gear couplings, chain couplings, slider block couplings, and grid couplings. During the late 40s and on through the 50s, manufacturers made tons of improvements in the area of coupling misalignment allowance and power. This was largely in response to the introduction of new equipment, such as rotary equipment, that required lighter weight couplings, couplings that could move faster, and couplings that could accommodate for misalignment.
Today, manufacturers continuously update couplings to accommodate ever-changing technology. While the concept of couplings is basically the same, couplings made now may come in materials, shapes, and sizes that were never possible before. They are also more precise and better made, thanks to CNC technology.
To construct flexible shaft couplings, processes like electroforming, chemical deposition, mechanical forming, and welding can all be used.
Electroforming is a process during which manufacturers add layers of metal to a piece of a mandrel until the couple reaches the perfect thickness.
Chemical deposition is a similar process, except that manufacturers deposit the materials through electrodeposition.
Roll-forming is a continuous shaping process that involves shaping metal via contoured forming rolls. It is quite common.
Extrusion is another common machining technique for manufacturers who perform mechanical forming. It involves feeding metal stock through a shaped die so that it takes on the shape of that die.
Welding of couplings involves welding together a series of rings or washers from the outside and the inside for maximum strength.
Most often, manufacturers make flexible couplings using aluminum or stainless steel. Aluminum flexible couplings offer the advantages of a low price and a light weight, while stainless steel flexible couplings offer the advantages of superior strength, increased corrosion resistance, and improved torque capacity.
Flexible shaft couplings can be divided into three primary categories based on their flexibility and intended use: mechanical, elastomeric, and metallic membrane. Besides these, a number of manufacturers also create various types of shafts for custom or specialized applications.
Mechanical Flexible Couplings
Mechanical flexible couplings are composed of a number of fitted parts that loosely slide or roll by one another. Though they require periodic lubrication and maintenance, they are good investments. They allow high degrees of angular misalignment while maintaining high torsional rigidity.
Jaw couplings, also known as spider couplings, are composed of two metal hubs pressed into an elastomeric part called the spider. They are used for applications where vibration must be limited. In addition to vibration dampening, jaw couplings offer many advantages, such as their resistance to moisture, dirt and sand, and grease and oil. Also, they do not need lubrication to work. The main disadvantage of this type coupling is the fact that they struggle with misalignment.
Oldham couplings are compact couplings that offer extra leeway for nonlinearly aligned shafts. They feature three discs; one is coupled to the input shaft, one is coupled to the output shaft, and one is coupled to the others using a tongue and groove on each side. The tongue and groove sets are perpendicular to one another. The input and output shafts and the middle disc all move at the same rpm speed.
Servo couplings are couplings that transfer torque with low inertia, no backlash, and high torsional stiffness.
Uniflex couplings are one-piece couplings designed to tackle high shaft misalignment, high temperatures, and space constraints. They are used for applications in a variety of industries, including textiles, robotics, printing, conveying, packaging, agriculture, and more.
Encoder couplings are couplings that manufacturers attach to connect encoder shafts with rotating shafts.
Spacer couplings are couplings installed in between a pump shaft coupling hub and a motor shaft coupling hub. Used in pumps, they create enough space for the user to remove the seal during maintenance without damaging or moving anything.
Elastomeric Flexible Couplings
Elastomeric flexible couplings are lightweight couplings that transmit torque between metallic hubs using material like rubber or plastic. In addition to their light weight, elastomeric flexible couplings offer high vibration dampening, an inexpensive price, tolerance to high degrees of misalignment, resilience, and shock absorption. Also, they don’t require lubrication.
Bellows couplings are one of the most popular types of elastomeric flexible couplings. Bellows couplings connect shafts that need more flexibility or are not linear in their alignment.
Bush pin flange couplings are elastic couplings with shafts that are only slightly misaligned. They feature a rubber bushing that absorbs vibration and shock.
Metallic Membrane Flexible Couplings
Metallic membrane couplings are somewhat expensive flexible couplings that, unlike most, do not usually permit offset misalignment. They are, however, low maintenance and do not require lubrication. Typically, metallic membrane flexible couplings offer flexibility via bendable membranes.
Fluid couplings are couplings that work alongside flexible couplings, though they are not necessarily flexible couplings themselves. They work by transferring energy through oil by way of a pump. They are often used as motor couplings, offering the ability to start with a low load, shock absorption and overload protection. They gain an allowance for misalignment when manufacturers pair them flexible couplings.
Universal joints, or universal couplings, work in a similar manner to provide a full range of motion. They allow the shaft to rotate and bend while still providing torque to the wheels. The central hub of the universal joint is where the shaft is joined to the third element. This allows for more bending than in a flexible shaft coupling.
Gear couplings are also used in similar applications, and transfer rotary motion at a 90-degree angle. A gear coupling is designed like a sprocket and it connects shafts while providing torque at the same time. If equipment is designed with more than 5 degrees of misalignment, manufacturers use universal joints or gear couplings for maximum flexibility.
One of the biggest advantages of flexible shaft couplings are their ability to function in the face of different types of misalignment.
Misalignment occurs during operation when the shaft’s axis of rotation becomes skewed. This can happen because of movement, vibrations or bumps during motion. Parallel misalignment occurs when the shafts’ rotational axes become parallel to each other. Angular misalignment is when the shafts intersect at an angle, and skewed misalignment occurs when both axial and angular misalignment take place at once.
Axial Displacement Accommodation
Besides accommodating misalignment, flexible shaft couplings have other important functions in mechanical equipment. End float, another term for axial displacement, is the result of the shafts moving away from or towards each other on their axes. Flexible shaft couples can help to accommodate this by absorbing shocks and dampening vibrations.
Examples of flexible shaft coupling accessories that you may require include coupling grease/lubricant, fitting kits, coupling encoder attachments, keyway connections, nuts and bolts, repair kits, and more.
The standard requirements and certifications to which flexible shaft couplings must adhere depend on your application, industry, and location. For example, ISO (International Standards Organization), which puts out standards for items used around the world, offers a number of standard recommendations for couplings used in a number of different settings. ISO 14691:2008 is an ISO standard that details requirements for mechanical power transmission flexible couplings used in the petroleum, petrochemical, and natural gas industries.
Industry leaders often use ISO standards as their own. Learn what standard adherences your application requires by checking with your industry leaders and applicable government offices.
Choosing the Right Manufacturer
To get the best flexible shaft couplings for your application, you need to work with an experienced coupling manufacturer. To aid you in your search for such a manufacturer, we have listed several shaft coupling suppliers that we know and trust. You will find their information on this page. Before checking them out, we recommend you spend some time writing down your specifications and requirements. That way, when you go to look at the manufacturers, you will be able to more quickly sift through them and determine which ones might work best for you. Also, when you go to talk to your top picks (we recommend three or four), your specifications list will help you focus your conversation.
The right manufacturer will not only offer the products you seek but will also offer them at a high quality within your budget and offer acceptable delivery options. Also, note that some manufacturers create couplings for many different applications, while others specialize in couplings for automotive use (e.g. flywheel couplings, torque limiters, driveshafts, tyre couplings, etc.) or industry-specific equipment. The right type of manufacturer for you in this regard will depend on the details of your application. Bearing all of this in mind, get to looking, and happy hunting!