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Flexible couplings are mechanical devices used to connect two shafts to transmit power while accommodating misalignments, vibrations, and shaft movements. They play a critical role in power transmission systems across various industries. Following are the common types of flexible couplings.
Elastic or flex rim couplings have long been used in power transmission industries because of their simple design and high performance. These flexible coupling types consist of two metal flanges separated by an elastic or flexible rim. The flexible rim, commonly made from rubber or other elastomeric materials, acts as a shock absorber and helps to compensate for minor misalignments between the connected shafts.
Elastic or flex-rim couplings are popular in low to medium power range applications. The flexible material dampens the vibrations and reduces noise transmission; therefore, it is mainly used in electric motor drives, pumps, fans, and other field machinery where there is little need for torsional stiffness but is needed for shock absorption and alignment compensation.
Jaw couplings are another elastic coupling that is quite popular in the power transmission industry. They consist of two metal hubs with jaw-like projections and an elastic or polyurethane insert between the hub jaws. These inserts are known as "spider" or "elastomer," which provide the necessary flexibility to absorb shocks and accommodate misalignments.
Jaw couplings are commonly used in applications with fluctuating loads, such as driving conveyors, mixers, and compressors. Their simple construction makes them easy to install and maintain. However, they are not suitable for high torsional vibration applications because of their limited torsional flexibility and stiffness.
Oldham couplings are specially designed to accommodate angular, axial, and parallel misalignments. These flexible coupling types comprise three components: two hubs and a center disc or slipway made of softer materials like plastic or non-metal. The center disc allows relative motion between the connected shafts, and the hubs provide a secure fit on the shafts.
Oldham couplings are primarily used in indexing systems, servo motors, and robotics, where precise control and minimal backlash are required. Their ability to accommodate misalignments makes them ideal for situations where alignment cannot always be guaranteed.
The cone and double-dome coupling was flexible coupling developed to meet the need for higher torque transmission and better misalignment compensation. The design consists of two conical hubs with a rubber or elastomeric insert shaped like a dome on either side. The conical shape allows for better grip and torque transmission, while the dome design helps absorb shocks and accommodate misalignments.
These couplings are predominantly used in heavy industries where high torque and power transmission is required, such as in mining, oil and gas extraction, and large machinery drives. Their robust design makes them suitable for extreme environments and loads.
Soft couplings are widely used and are an integral part of many industries, including motors, pumps, compressors, conveyors, fans, and other rotating machinery, and are commonly employed in the following application types.
In mechanical power transmission, flexible couplings bridge the gaps between different components. For instance, they connect electric motors to pumps, turbines, and compressors. Here, flexible couplings help compensate for any misalignment between the motor and the driven equipment, preventing any undue wear and tear, reducing vibration, and ensuring that power is transmitted efficiently. This means that if any of the two connected components were expanding or contracting, moving in different directions, or failing to align properly, the flexible coupling would absorb the consequences, and because of this property, flexible couplings are distinctly popular in industries that deal with heat and pressure changes.
Flexible couplings are primarily employed in the pump field to link the motor to the pump shaft. Here, the role of the coupling is to eliminate or reduce the misalignment effects that could otherwise affect the components. In pumps, for instance, flexible couplings help absorb the torque variations resulting from pumping fluid dynamical procedures. This property helps protect the pump and motor from damage and prolongs the interval between required maintenance and repairs. Flexible couplings also reduce the transmission of vibrations from the motor to the pump; thus, they are predominantly installed on hydraulic pumps that are usually very vibbly.
Flex couplings are commonly found in compressors where motors need to be coupled with the compressor drive shafts, particularly in centrifugal compressors. These couplings absorb the torsional vibrations that arise during the compression process, especially in reciprocating compressors, which also accommodate axial misalignment caused by thermal expansion or mechanical differential movement. This helps protect the wear and tear of the bearings and seals and helps improve efficiency by ensuring that more of the input power is directed toward useful work rather than being absorbed by vibrations or misalignments.
Flexible couplings are used to connect the motor and fan or blower shaft to compensate for misalignments in fan and blower applications. Because fans and blowers operate in different pressure and volume conditions, coupling is very vital in absorbing the resultant vibrations and ensuring power is transmitted efficiently. Flexible couplings also reduce noise and increase the risk of mechanical failure due to misalignment.
Elastic coupling spares parts in a power transmission system. Apart from providing flexibility and compensating for misalignments, they have certain characteristics that make them durable for a long time. These include the following.
Different materials are used to manufacture flexible couplings and their associated elastic components, and each material has a distinct effect on the durability of the flexible coupling. For instance, metals commonly used in making coupling bodies include steel, aluminum, and various alloys. These materials provide good tensile strength, thus enabling efficient torque transmission. Commonly used materials for the elastic components of flexible couplings include rubber and other elastomeric materials. These components dampen the absorption of vibrations and shocks and give flexibility. Although they are strong, their strength significantly reduces under extreme temperatures, exposure to various industrial fluids, and aging. These factors require careful consideration of the application environment and operating conditions when choosing coupling materials, as they directly affect the durability of the flexible coupling.
Sealing plays a vital role in the durability of flexible couplings. Seals prevent contaminants such as dust, dirt, water, and other particulates from getting into the coupling and affecting the elastomeric components. Additionally, it helps to prevent the escape of lubricants as well as protect the rubber components from chemicals. In environments where there is high contamination like construction, mining, or any processing industry, the use of seals to protect the coupling is imperative. Greased and sealed couplings have a longer lifespan due to the lower average exposure to contaminants and lubricants. This reduces the rate of wear on the elastomeric components.
Industrial applications involve coupling exposure to high heat, so having a heat-resistant flexible coupling is crucial in such applications. In such environments, flexible couplings with heat-resistant seals and elastomers should be used. Another alternative is to use metal flexible couplings where there is excessive heat. Metal flexible couplings come with the added advantage of being used in the industries where conventional rubber couplings have been banned due to the combustion of rubber in the area. They also have the added benefit of functioning properly in low-temperature areas as well.
Torsional stiffness is a measure of how much a material or component will twist under the application of torsional loads. In flexible couplings, higher torsional stiffness means that the coupling will resist twisting motion, which is kind of a disadvantage in some applications and vice versa in others. For instance, in engines, generators, and other rotating machinery, higher stiffness means better synchronization, whereas in machinery like compressors where excessive torsional vibrations could be detrimental to the machine, lower torsional stiffness would be better. It is this stiffness that needs evaluation when choosing a coupling for an application because it would affect both durability and performance.
Choosing the correct flexible coupling for an application in the power transmission industry is guided by several factors. Here are the basic considerations.
The coupling must be capable of withstanding the maximum torque and power levels within the application. Often, the coupling's power and torque ratings should exceed the application requirements as a safety measure. Power ratings indicate the coupling can transmit a given amount of power. Torque ratings say how much rotational force the coupling can withstand. Couplings rated for higher torque and power will last longer in higher-load applications.
Different applications can cause different types of shaft misalignments, and couplings are designed to compensate for these misalignments. For instance, if the application involves angular misalignment, one should look for a coupling designed to handle it, like a jaw or a disc coupling. On the other hand, if the application at hand will probably involve parallel misalignment, a coupling like a bushing or pin that can easily accommodate parallel misalignment would be ideal. For axial misalignment, a coupling such as a flexible or an Oldham coupling should be used.
Environmental factors such as temperatures, levels of contaminants, and exposure to harmful chemicals for the coupling components need to be considered. In this case, couplings with contaminants like seals and heat-resistant materials should be used in high contaminant or heat environments. In environments where the coupling is exposed to chemicals or hostile conditions, choose a coupling with corrosion-resistant materials like steel, aluminum, or special alloys. In environments like this, chemical-resistant seals and materials for the coupling are available.
Flexible coupling types include gear couplings, and each type has its own unique characteristics suitable for an application at hand. Gear couplings provide great torque and are usually used in applications requiring precision and high loads. Bellows couplings are suitable for high-precision applications in positioning systems because of their high torsional stiffness and elasticity. A disc coupling is often used in severe environments because of its rigidity, high torque absorption capability, and absence of flexible components. A spider coupling is often used in moderate load applications.
A1.Flexible coupling connects two shafts in hydraulic systems, helping to reduce misalignment between the pump and motor. By absorbing the small movements that may exist between the two components, a flexible coupling minimizes wear and tear, thus increasing the system's durability. In addition, it transmits hydraulic power efficiently from the motor to the pump, thus enhancing the overall operating efficiency.
A2.Following are some of the common signs indicating the need for flexible coupling replacement in a given application:
A3.Flexible coupling corrosion resistance totally depends on the materials used to fabricate them. For instance, stainless steel, special alloys, and aluminum couplings are ideal for high humidity, marine, and chemical processing environments. Besides, non-metallic couplings made from composites, rubber, or plastics are also corrosion-resistant. However, steel couplings are prone to corrosion unless protected by priming or painting.
A4.Like all mechanical machines, some flexible couplings also require lubrication. These include gear and metallic couplings. Lubrication prolongs the life of these couplings. Some flexible couplings are pre-filled with lubricant and sealed for life. This means these couplings do not require lubrication after they have been installed. However, some flexible couplings may also require lubrication to protect them from chemical contaminants and heat. It is this maintenance that makes flexible couplings a low-maintenance solution.
