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LEMO coupling connects several sets of diaphragms (thin stainless steel plates) to the two half-couplings with bolts in an alternating arrangement. Each set of diaphragms consists of multiple stacked layers. Diaphragms are classified into link-type and one-piece types of various shapes. The diaphragm coupling compensates for the relative displacement between the two connected shafts through the elastic deformation of the diaphragms. It is a high-performance flexible metallic element coupling that requires no lubrication, has a compact structure, high strength, long service life, no rotational backlash, is unaffected by temperature and oil contamination, and features acid, alkali, and corrosion resistance. It is suitable for shaft transmission in high-temperature, high-speed, and corrosive media environments.

LEMO Coupling Structure and Applications

Universal couplings come in various structural types, such as: cross-axis type, ball cage type, ball fork type, cam type, ball pin type, ball joint type, ball joint plunger type, three-pin type, triple-fork type, triple-ball pin type, hinge rod type, etc.; the most common is the cross-axis type, followed by the ball cage type. In practical applications, they are classified into heavy-duty, medium-duty, light-duty, and small-sized based on the transmitted torque. They are mechanical components used to connect two shafts (driving shaft and driven shaft) in different mechanisms, enabling them to rotate together to transmit torque. In high-speed and heavy-load power transmission, some couplings also provide buffering, vibration damping, and improved dynamic performance of the shaft system. A coupling consists of two halves, each connected to the driving shaft and the driven shaft respectively. Generally, prime movers are connected to working machines via couplings.

LEMO Coupling Alignment Process

Alignment of universal couplings is one of the important tasks in machine installation. The purpose of alignment is to ensure that the centerlines of the driving shaft and the driven shaft are on the same straight line during machine operation. Alignment accuracy affects whether the machine can operate normally, which is especially important for high-speed rotating machinery. Achieving absolutely accurate alignment of the two shafts for cross-axis universal couplings is difficult, and maintaining accurate alignment for continuously operating machinery is even more challenging. Uneven thermal expansion of components, shaft deflection, uneven bearing wear, machine displacement, and uneven foundation settlement are all reasons why it is difficult to maintain shaft alignment. Therefore, an allowable deviation value for the two shaft centers is specified during machine design, which is also required during coupling installation. From an assembly perspective, as long as the coupling can safely and reliably transmit torque, the larger the allowable deviation of the two shaft centers, the easier it is to meet the requirements during installation. However, from an installation quality perspective, the smaller the deviation of the two shaft centerlines, the more precise the alignment, the better the machine operation, and the longer the service life. Therefore, the allowable deviation for shaft alignment during universal coupling installation should not be regarded as a margin left by careless construction by installers.

LEMO Coupling Measurement Sequence

Misalignment of universal couplings may be radial displacement, angular misalignment, or both. Concentricity measurement should be performed at four evenly distributed positions on the end face and circumference of the universal coupling. Machine pumps connected by cross-axis universal couplings inevitably require concentricity adjustment during installation to ensure the coupling halves are both concentric and parallel; otherwise, it will affect the efficiency of the machine pump or cause equipment operation accidents. For some large high-temperature equipment, factors such as increased equipment base height due to thermal linear expansion should also be considered during coupling alignment. Measurements can be performed in the following order: 1) Temporarily connect half universal coupling A and B, and set up special tools. 2) Rotate half couplings A and B simultaneously, causing the special tool or alignment line to rotate sequentially through the four positions. At each position, measure the radial values (or gaps) and axial values of the two half couplings. Install BJ. If the universal coupling is found to be misaligned or non-parallel, adjustments must be made. During adjustment, first adjust the levelness of the machine pump, then use the universal coupling of the machine pump as a reference to measure and adjust the motor coupling half to ensure the motor and machine pump are coaxial and concentric. When adjusting the concentricity of the coupling, adjust the face gap first, then the shaft gap. When adjusting the motor, shims of different thicknesses can be used under the motor base according to d and mouth values. First adjust the axial gap to make the two halves parallel, then adjust the radial gap to make the two halves concentric. If the equipment manufacturer has no specific requirements, for shaft speed 2980rmin, the shaft gap (concentricity) and face gap (parallelism) errors of general universal couplings shall not exceed 0.03mm; for shaft speed 1500rmin, the shaft gap and face gap errors of the universal coupling shall not exceed 0.05mm. During coupling alignment, the principle of similar triangles can be used, taking into account the influence of shaft gap adjustment on face gap, to calculate and align, which can greatly improve the speed of universal coupling alignment.

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