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Disc Couplings Dump Downtime
Disc Couplings Dump Downtime
Kevin Remack
Want to expand coupling life? Who doesn’t? You may want to look into advanced-design disc couplings.
These couplings feature discs with optimized profile and thickness to provide a higher torque-to-outside-diameter ratio, higher service factors and up to 50 percent greater misalignment capability. All this provides for smaller reactionary forces on bearings compared to conventional disc couplings, which helps achieve infinite coupling life in properly specified applications.
The advanced-design variety utilizes high-grade stainless steels for strength and resistance to hostile environments, and provides the torsionally rigid, no-backlash operation characteristic of disc couplings. Typical applications of disc couplings are on high-speed machinery where non-lubricated, low-maintenance and long-life couplings are desired. However, with its benefits, disc couplings are replacing other coupling styles in redesigns and retrofits.
Benefits of Disc Couplings
Disc couplings offer plants the benefit of reduced downtime through maintenance-free operation and running inspection.
By design, a disc coupling has no moving parts and requires no lubrication, reducing equipment maintenance costs associated with shutdown, motor/equipment removal and labor. Without having to remove a motor or reposition the equipment side, which are typical risks of realignment, breakage and safety concerns are eliminated.
Inspection of disc couplings is also plant-friendly. They can be inspected for condition, wear and performance without disassembly.
Additionally, you can inspect them while the equipment is running with the use of a strobe light. Under a strobe, you can see the discs flex and move. You can also see any damage. In the event that a disc pack needs replacement, certain coupling styles allow for a center section (containing the disc packs) to be removed without removing either shaft hub.
The versatility of disc couplings is shown in a paper plant application. Heavy industry use as shown in a coal pulverizer application.
Installation Tips
A flexible disc coupling is designed for long life when operated within the torque and alignment limits as set forth in the manufacturer’s catalog and installation instructions.
The installation of a flexible disc coupling is critical. Various problems can arise during mounting of the hubs and the coupling assembly process.
Burrs, dirt and grit on either the shaft or in the bores can cause the hubs to gall during mounting. Poorly fitted keys can also gall and not seat correctly. Concentrated heat on the hubs will cause distortion.
The coupling must be properly assembled and the locknuts tightened in accordance with the installation instructions. Loose bolts will cause elongation of the disc bolt holes and eventual failure of the discs or bolts.
The most common form of failure in disc couplings is fatigue due to excessive disc flexure. This is usually caused by poor initial alignment of the connected machines. Operational conditions can also be factors.
Axial misalignment: This is the variation in the distance between the machinery shafts in relation to the neutral length of the coupling.
Angular misalignment: This is the effective angle between the two machinery shafts and is usually quantified by measuring the angle between the center lines of the shafts if they were extended to intersect.
Radial (parallel) misalignment: This is the transverse distance between the two machinery shafts and is quantified by measuring the distance between the center lines of the shafts if they are extended to overlap.
Misalignment may result from: the practical tolerance in machining; initial alignment of the machines or movement; settlement; or, operating thermal variations of the machinery. In practical applications, all misalignment types are likely to be present as a result of the causes.
Applications determine disc size. A wide spectrum of sizes are available.A wide selection of disc coupling configurations are available to fit application requirements.
Flexible Solution
Disc couplings handle misalignment by deflection of the flexible discs. The discs are bolted on a set bolt circle diameter, being fastened alternately to the “driving” and “driven” flanges. The deflection takes the form of a bending/twisting of the link between the adjacent bolts.
In practice, a single flexible disc will only accommodate axial and angular misalignments. Radial misalignments are accommodated by using two flexing discs. The radial misalignment is the total amount of radial displacement divided by the distance between the centers of the flexing discs. Since the disc coupling only identifies radial misalignment as an angular misalignment at each flexing disc, any angular and radial misalignment must be evaluated as a “combined angular/parallel” misalignment.
Since the level of acceptable misalignment is stress related, there is an effect due to both the torque being transmitted and the rotational speed of the coupling. The axial thrust generated in a disc coupling under axial misalignment is related to the bolting arrangement of the coupling. It’s also influenced by the speed of operation and, being of a non-linear stiffness, is dependent on the actual axial deflection experienced.
When the axial growth of machinery shafts during operation is known, it’s acceptable to introduce an axial predilection to the coupling. This involves adjusting the length of the coupling components between the flexing elements so they are “pre-stretched” or “pre-compressed” on installation to an amount that compensates for the known axial growth. This permits the coupling to run at its neutral position during operation.
Electrical systems are grounded to limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and to stabilize the voltage to earth during normal operation. Electrical systems can be grounded in several ways. There are induction grounded systems, resistance grounded systems, and high impedance grounded systems among others. The most common grounded system is the solidly grounded system, where there is no intentional grounding impedance in the earthing or grounding circuit.
Electrical systems are grounded to limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and to stabilize the voltage to earth during normal operation. Electrical systems can be grounded in several ways. There are induction grounded systems, resistance grounded systems, and high impedance grounded systems among others. The most common grounded system is the solidly grounded system, where there is no intentional grounding impedance in the earthing or grounding circuit.
The secret to making and keeping reliable electrical connections is contained in two elements: start with clean contact surfaces, and apply high force. Clean contact surfaces are a function of cleaning procedures, including joint compounds, and will be covered in a future article. Application of high force is the subject here. The trouble comes about because the terms "torque" and "force" are incorrectly used interchangeably. Force is NOT torque. Force is a function of torque.
The secret to making and keeping reliable electrical connections is contained in two elements: start with clean contact surfaces, and apply high force. Clean contact surfaces are a function of cleaning procedures, including joint compounds, and will be covered in a future article. Application of high force is the subject here. The trouble comes about because the terms "torque" and "force" are incorrectly used interchangeably. Force is NOT torque. Force is a function of torque.
It's hard to imagine belt conveyors anywhere playing a more important role than at South Africa's Kendal Power Station. Here, the world's largest black-coal-fired electrical generating complex converts up to 1.4 million tons a month into more than 4100 megawatts, enough to supply three cities the size of nearby greater Johannesburg.
It's hard to imagine belt conveyors anywhere playing a more important role than at South Africa's Kendal Power Station. Here, the world's largest black-coal-fired electrical generating complex converts up to 1.4 million tons a month into more than 4100 megawatts, enough to supply three cities the size of nearby greater Johannesburg.
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So you want to be a leader! Your leadership career is a journey, and just like any journey, it requires a driver. The question is, who is driving your leadership career? Is it you, or are you letting external forces take the wheel? Taking control of your career is essential for your personal and professional growth. In this article, I will explore the importance of you taking control and offer some insights from my 45 years in the world of work that may help you steer your career in the right direction.
The world is increasingly turning towards renewable energy solutions to combat climate change and create a sustainable future. Solar engineering, one of the most promising fields in this energy transition, taps into the inexhaustible power of the sun. This comprehensive FAQ will delve into the key aspects of solar engineering, answering common questions and shedding light on this pivotal technology.
The world is increasingly turning towards renewable energy solutions to combat climate change and create a sustainable future. Solar engineering, one of the most promising fields in this energy transition, taps into the inexhaustible power of the sun. This comprehensive FAQ will delve into the key aspects of solar engineering, answering common questions and shedding light on this pivotal technology.
Whether it's turning off lights, idling back process equipment and fixing compressed air leaks to energy audits and installing compressed-air management systems-reducing utility costs can take several forms. As with any project, the return on investment should guide you on the projects that you select.
Whether it's turning off lights, idling back process equipment and fixing compressed air leaks to energy audits and installing compressed-air management systems-reducing utility costs can take several forms. As with any project, the return on investment should guide you on the projects that you select.
I was recently engaged by a client to conduct failure analysis on a large (and expensive) double-acting cylinder off a hydraulic excavator. This cylinder had been changed-out due to leaking rod seals after achieving only half of its expected service life. Inspection revealed that apart from the rod seals, which had failed as a result of the 'diesel effect', the other parts of the cylinder were in serviceable condition. The diesel effect occurs in a hydraulic cylinder when air is drawn past the rod seals, mixes with the hydraulic fluid and explodes when pressurized.
I was recently engaged by a client to conduct failure analysis on a large (and expensive) double-acting cylinder off a hydraulic excavator. This cylinder had been changed-out due to leaking rod seals after achieving only half of its expected service life. Inspection revealed that apart from the rod seals, which had failed as a result of the 'diesel effect', the other parts of the cylinder were in serviceable condition. The diesel effect occurs in a hydraulic cylinder when air is drawn past the rod seals, mixes with the hydraulic fluid and explodes when pressurized.
