The hottest flexible coupling overcomes the nightm

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Flexible couplings overcome the nightmare of vibration

like any other mechanical equipment that consumes energy, pumps need an energy source to drive them. They require mechanical energy to perform the task of transferring liquids from one location to another, which is provided by internal combustion engines or electric motors. The energy source drives the pump through an energy transmission system, which usually consists of a series of gearboxes, drive shafts and couplings. All this may seem quite simple, but to operate the pump safely and efficiently, there are several inherent terrible forces in the system that need to be suppressed. The first nightmare appears in a rather secretive form, called torsional vibration. Unless effectively handled, torsional vibration may destroy an energy transmission system and the pump it is driving. It may completely damage the solid steel drive shaft, causing the pump to twist itself and loosen from the base, and may even pose a threat of injury to nearby people. So what is torsional vibration? What do we do with it

in the early 20th century, torsional vibration was the most terrible nightmare of energy transmission engineering. In the industrial field, it will cause aircraft crashes, car breakdowns and common failures of drive systems. It is caused by almost unpredictable pulses in torque, which is inherent to internal combustion engines. Each time the compressed fuel and air mixture is ignited, it expands rapidly and drives the piston to fall onto the cylinder within its power stroke. Each power stroke produces a pulse or peak in the torque, which will cause the drive shaft to distort imperceptibly

people may think that something as strong as a steel drive shaft will obviously twist without scissors, but when a force is applied, any piece of metal will bend. When a large amount of energy is generated, the energy contained may be huge. In addition, the influence of torsional vibration will be amplified by another terrible thing in the system, that is, a related phenomenon called torsional resonance

if we consider the pumping system driven by diesel engine, every diesel engine has inherent resonance, which is a bit like the sound of ringing or vibrating guitar. If this torsional resonance is consistent with the natural frequency of the pump, the consequences will be disastrous, or at least, it will greatly shorten the service life of the system and force a higher degree of maintenance

in the first 25 years of the 20th century, torsional vibration was unobservable for simple equipment, because the torsional vibration of the drive shaft overlapped with the stable average rotation rate. Professor Edward Miller, a former head of the Department of mechanical engineering at MIT, made an observation and found the shear failure force of torsional vibration. In the original test of the diesel driven pump, he mentioned that the shaft connecting the engine and the pump began to glow "cherry red" before it completely failed. The number of destructive energy phenomena is only the consequence of torsional vibration. At that time, torsional vibration can not be truly visible until failure occurs

engineering knowledge has developed greatly. Since then, torsional vibration is no longer as mysterious as before. The manufacturer can provide details of torsional resonance of each engine, and the design engineer can ensure that the torsional vibration level in the system is within the allowable range. The new solution is to install a flexible or torsional flexible coupling between the diesel engine and the pump shaft to isolate the harmonic of the engine from the system. There are two types of flexible couplings commonly used for this purpose, one is compression rubber coupling, and the other is internal shear rubber coupling

louis crosset invented the compressed rubber coupling when working for WC Holmes, which provides the damping and tuning characteristics necessary to protect the components of the diesel engine drive transmission system. Crosset chose "hol" from Holmes and "set" from its own name, and founded Holset engineering in 1952. The company's compressed rubber coupling soon achieved success, and later he continued to develop a series of turbochargers. Its coupling department was acquired by reonold in 1996. Since then, the company has carried out sales activities under the name of Renold hi Tec couplings (RHC) and benefited a lot from the new investment

Figure 1: the exploded view of the compressed rubber coupling shows its structure and the rubber block installed between the metal blades with different levels of experimental performance to meet different requirements. The basic principle of the invention of crosset is essentially the same as that at that time, and may be just a little more refined. Essentially, the two round metal parts are connected by something that looks like the paddles of a Ming Lun steamboat, protruding inward from the outside and outward from the inside. The rubber piece is placed in the gap between the blades. When the external parts are rotated by the engine, it drives the internal parts through this rubber piece. In this way, the rubber is compressed, so the word "internal pressure rubber" comes into being

Figure 2: compressed rubber coupling is usually used in pumping system to solve and prevent problems

Figure 3: universal joint coupling, used in the case of deviation between pump and diesel engine

when the rubber is compressed, it behaves like a compressible fluid, which is stronger than the optional rubber internal shear technology or tension technology. Here, the slightest scratch in the rubber can lead to catastrophic tearing and complete connection failure. The compressed rubber coupling of RHC has failure protection performance in essence, because even if the most unlikely situation occurs (such as film vaporization), the solid metal blades will participate in providing driving force. Where possible, high vibration loads may cut the fire and tear the rubber sheet. At this time, the coupling will continue to operate with little loss of efficiency. In many applications, such as fire fighting, pump failure cannot be selected, and compressed rubber couplings are usually designated for this application because of their failure protection characteristics

the compressed rubber coupling is maintenance free and does not need lubrication or any form of adjustment, which means that in all applications of the pump, it has the lowest life cycle cost. In this kind of coupling, only the rubber sheet plays a role. In most cases, the rubber sheet has a service life of more than 10 years. The compression rubber coupling is also very durable, especially suitable for applications with worse conditions, such as pump loosening of large granular sand or sand. In harsh application environment, stronger vibration will occur. The rubber sheet in the coupling can reduce the vibration load and reduce the vibration torque of the power transmission system

another alternative to diesel drive systems is variable frequency motor (VFD), which is becoming more and more common in pumping applications. VFD can make more economical use of motor, but because of its special nature, it will produce pulse output, which requires flexible coupling to also carry out stacking experiments requiring constant pressure. The shaft device can control torsional synchronous torque load and rotational vibration. The rubber in the coupling will weaken the pulse and change the natural frequency of the engine system, making it lower than the running speed of the pump

Figure 4: compressed rubber coupling installed between diesel engine and centrifugal pump

flexible coupling is also used to withstand varying degrees of deviation. For applications in clutch housings, the coupling must withstand small deviations due to manufacturing tolerances. However, for applications that do not require support, the degree of deviation depends on the accuracy of the pump to engine calibration. It is quite common that the pump and engine are firmly installed on a shockproof base, which is a bit like the suspension system of an automobile. The different deviation depends on the amount of movement on the base. These deviations can be adjusted by using two flexible couplings and a shaft between them. In this way, when the pump and engine move relatively, the shaft can be hinged

each pumping system is different, but what they have in common is the need for safe operation, reliability and the lowest possible maintenance cost. Compressed rubber couplings meet all challenges and appear in pumping applications around the world. Since each system is unique, RHC engineers use their own software to analyze the dynamic performance of the system before proposing the correct connection solution

contact information

alan Dean, Renold hi Tec couples

112 Parkinson lane

halifax HX1 3qh uk

:01422 255103

email: an@

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