How to choose the coupling What should I pay attention to when using the coupling

How to choose the coupling? What should I pay attention to when using the coupling?

Couplings belong to the category of general mechanical parts, which are used to connect two shafts (a driving shaft and a driven shaft) in different mechanisms and rotate them together to transmit torque. In high-speed and heavy-load power transmission, the coupling also has the functions of buffering, damping and improving the dynamic performance of the shafting. When choosing a coupling, it is necessary to consider various factors according to the actual situation and requirements of the chooser, and select the coupling variety, type and specification that best suits your needs from the existing standard couplings. In general, the existing standard coupling can basically meet the needs of different working conditions.

Due to the unstable driving torque of the power machine and the load moment of the working machine, as well as the impact caused by the manufacturing error of the transmission parts and the dynamic load caused by the unbalanced centrifugal inertia force of the parts, the transmission shaft system is under variable load (periodical variable load and Non-periodic impact load) will produce mechanical vibration, which will affect the service life and performance of the machine, destroy the normal working conditions of instruments and meters, and cause additional dynamic stress to the shafting parts. When the total stress or the alternating stress are respectively When the allowable limit is exceeded, the parts will be damaged or fatigued. When designing or selecting couplings for torque and motion transmission, torsional vibration analysis and calculation should be carried out. The purpose is to find the natural frequency of the shaft system to determine the critical speed of the power machine, so as to calculate the torsional vibration of the shaft Additional loads and stresses generated by the system and transmission. When necessary, adopt vibration damping and buffering measures. The basic principle is to reasonably match the quality, stiffness, damping and interference force of the system and the frequency, so that the transmission device does not operate within the speed range of the resonance zone, or does not appear within the operating speed range Strong resonance phenomenon. Another effective method is to use highly flexible elastic couplings in the shafting system, referred to as high-elasticity couplings, to reduce the natural frequency of the shafting system and use its damping characteristics to reduce the torsional vibration amplitude .

How to choose the coupling? What should I pay attention to when using the coupling?

There are many types, types, and specifications of couplings. Based on the correct understanding of the concepts of varieties, models, specifications, etc., according to the needs of the transmission system, choose the coupling from the standard couplings. At present, our country has formulated more than ten national standards and industry standards. Most of these standard couplings are universal couplings. Only when the coupling design has multiple requirements, designers can meet the usual requirements. Standard couplings are easy to purchase, and the price is more than that of non-standard couplings designed by ourselves. Among the many standard couplings, accurately choosing the best coupling that suits your needs is related to a series of issues such as performance, reliability, life, vibration, noise, energy saving, transmission efficiency, transmission accuracy and economy. It is also related to the quality of mechanical products.

When selecting the coupling, the designer should select the coupling according to the needs of the shaft transmission system, avoiding intuitively considering the coupling between the driving end and the driven end. When the power machinery is working, the driving end and the driven end are connected by one or more couplings of different varieties or models and specifications to form a shaft transmission system. In mechanical transmission, power machinery is nothing more than electric motors, internal combustion engines and steam turbines. As the working principle and structure of power machinery are different, their mechanical characteristics are also slightly different. Some of them operate stably, and some have an impact on the transmission system.

The mechanical characteristics of power machinery have a certain influence on the entire transmission system. Different types of power machinery have different mechanical characteristics, so the corresponding power machinery coefficient kW should be selected, and the best coupling suitable for the system should be selected. The type of power machinery is the basic factor for selecting the type of coupling. Power of the power machinery is one of the main basis for determining the size of the coupling, and its size is proportional to the torque of the coupling.

Most of the power machinery in the transmission system of a specific mechanical product is an electric motor. Most of the power machinery in the transmission system of mechanical products, such as ships and various vehicles, are mostly internal combustion engines. When the power engine is an internal combustion engine with different cylinder numbers, the influence of torsional vibration on the transmission system must be considered. This influencing factor is related to the number of cylinders of the internal combustion engine and whether each cylinder works stably. At this time, an elastic coupling should be selected to adjust the natural frequency of the shaft system, reduce the torsional vibration amplitude, thereby reducing vibration, buffering and protecting the components of the transmission device, improving the alignment performance, and improving the stability of the output power.

In the transmission system of various mechanical products, due to the difference in structure and material, the difference in carrying capacity is very small. The load category is mainly due to impact, vibration, forward and reverse rotation, braking, violent starting and other reasons to form a different type of load on the working load of the working machine. In order to facilitate selection and calculation, the load of the transmission system is divided into four categories.

The load category of the traditional system is the basic basis for selecting the coupling type. In order to improve the performance of the transmission system, flexible couplings with elastic elements should be used to cushion, reduce vibration, and compensate for shaft deviation. The torque during vigorous starting, forward and reverse rotation and braking is several times the torque during stable and stable operation, which belongs to overload operation and will inevitably shorten the service life of the coupling elastic element. The coupling only allows short-term overload, and short-term overload usually does not exceed 2-3 times the rated torque, that is, [Tmax]≥2-3tn.

Under low-speed and heavy-load conditions, avoid using couplings that are only suitable for small and medium power, such as elastic sleeve pin couplings, core-type elastic couplings, polygonal rubber couplings, tire couplings, etc.; For shafting systems that require overload safety protection, safety couplings should be selected; for shafting systems with small load changes, small impacts, and small vibrations, flexible couplings with elastic elements and poor damping and vibration reduction effects should be selected. The load-bearing capacity of the metal elastic coupling is higher than that of the non-metal elastic element elastic coupling; the reliability of the squeezing elastic element elastic coupling is higher than that of the stress elastic element elastic coupling.

The allowable speed range of the coupling is calculated and determined according to the minimum outer edge size of the allowable linear speed of the coupling of different materials. Couplings with different materials, varieties, and specifications allow different speed ranges. Changing the coupling material can increase the allowable speed range of the coupling.

Relative displacement of the two shafts of the coupling

The relative displacement of the two shafts of the coupling is caused by many factors such as manufacturing error, assembly error, installation error, shaft deformation caused by load, base deformation, bearing wear, temperature change, and relative movement of the component building. Generally speaking, the relative displacement of the two shafts is inevitable, but the direction of ecological equilibrium displacement produced by the shafting transmission under different working conditions is different, that is, the axial, radial angular direction and displacement. Only the flexible coupling can compensate the relative displacement of the two shafts. Therefore, a large number of flexible couplings have been selected in practical applications. Rigid couplings are not compensated, and their application range is huge, so the amount of rigid couplings is very large. Universal couplings should be used for shafting transmissions with large angular displacement; diaphragm couplings should be used for shafting transmissions controlled by axial displacement and axial displacement; rigid couplings should be used when the alignment accuracy is low.

For shaft transmission with large torque and small transmission motion, low transmission accuracy is required, and flexible couplings with metal elastic elements should be used. The shaft transmission of high torque and high power transmission also has requirements for transmission accuracy. At high speeds, avoid using non-metal elastic components. The flexible coupling with a gap between the flexible coupling and the movable parts should be selected, and the diaphragm coupling with low transmission accuracy should be selected.

How to choose the coupling? What should I pay attention to when using the coupling?

The outer dimensions of the coupling, that is, the maximum radial and axial dimensions, must be within the installation space allowed by the machine and equipment. Choose a coupling that is convenient for assembly and disassembly, does not require maintenance, has a long maintenance period or is convenient for maintenance, replaces wearing parts without moving the two shafts, and is easy to adjust the coupling.

It is difficult to adjust the alignment of the two shafts for large machinery and equipment, so you should choose a coupling that is durable and easy to replace wearing parts. Flexible couplings with metal elastic elements generally have a longer service life than flexible couplings with non-metal elastic elements. The need for sealing and lubrication and the use of non-durable couplings will inevitably increase maintenance workload. For occasions with long-term continuous operation and high economic benefits, such as the high end of the rolling mill transmission system of Chinese metallurgical enterprises, gear couplings are currently commonly used. Although gear couplings theoretically transmit large torque, they must be Durable work can only be done under the conditions of good lubrication and sealing, and frequent inspections of the sealing conditions and lubricating oil are required to maintain a large amount of work, increase auxiliary working hours, reduce effective working time, and affect production efficiency.