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METAFRAM couplings utilize their mechanical characteristics to enable continuous rotation of the connected shafts and reliably transmit torque and motion, even when the two shafts are not on the same axis and an angular misalignment exists. The most significant feature of universal couplings is their substantial angular compensation capability, compact structure, and high transmission efficiency. The angle between the axes of universal couplings varies with different structural types, generally ranging from 5° to 45°.

Introduction to METAFRAM couplings

Gear couplings have small radial dimensions and high load-carrying capacity. They are commonly used for shaft transmission under low-speed, heavy-load conditions, such as in the metallurgy, mining, and lifting/transport industries, and are also suitable for the petroleum, chemical, and general machinery industries. High-precision gear couplings that have undergone dynamic balancing can be used for high-speed transmission, such as in gas turbine shaft systems. Since drum-tooth gear couplings offer greater angular compensation than straight-tooth gear couplings, drum-tooth gear couplings are widely adopted both domestically and internationally, while straight-tooth gear couplings should be avoided where possible. Gear couplings are a type of movable rigid coupling. They transmit torque and rotational motion between the two halves of the coupling through the meshing of internal and external teeth, making them suitable for connecting coaxial shaft systems and providing certain compensation for relative displacement between the two shafts. Its structure is shown in Figure One. It mainly consists of an internal gear ring, a gear sleeve, and end covers. For smaller-sized gear couplings, the end cover and internal gear ring can be formed as a single unit. Due to their compact structure, high load-carrying capacity, wide operating speed range, and reliable operation, gear couplings are widely used in various mechanical industries, including metallurgy, mining, lifting/transport, petroleum, and shipbuilding.

METAFRAM coupling classification

Gear couplings can be divided into three types based on the axial tooth profile of the external gear sleeve: straight-tooth gear couplings, drum-tooth gear couplings, and special drum-tooth gear couplings. Regardless of the type, the internal gear ring and the involute straight internal gear are identical, except for differences in the selection of the tip clearance coefficient. The axial tooth blank of the external gear sleeve in straight-tooth gear couplings can be machined into two shapes: straight and arc-shaped, while the pitch circle and root circle remain straight. The meshing form of this coupling is exactly the same as that of involute cylindrical gear internal and external teeth. Relative displacement between the two shafts is compensated by increasing the side clearance between the internal and external teeth, but the compensation amount is limited. In drum-tooth gear couplings, the tooth tips of the external gear sleeve are machined into an arc shape, meaning the tooth blank is machined into a spherical surface. In the cross-section at the tooth center plane and tangent to the pitch cylinder, the teeth form a drum shape, hence the name drum-tooth coupling. Its features are: 1) High load-carrying capacity. Based on bending strength calculations, the torque transmitted is increased by 15 to 30% compared to straight-tooth gear couplings under the same conditions; 2) Rational structure and reliable performance. The drum-shaped tooth sides improve contact conditions at certain axis angles, thereby reducing contact stress and eliminating load concentration at the tooth ends of straight-tooth couplings (i.e., eliminating edge crushing), which improves operational performance. 3) Good compensation performance. The drum-shaped profile of the external gear sleeve teeth increases the allowable relative offset between the connected shafts. The maximum allowable inclination angle can reach 6 degrees, with a general recommendation of 1.5° to 2.5°.

METAFRAM coupling troubleshooting

1) Misalignment of gear couplings: Coupling misalignment is classified into angular misalignment, parallel misalignment, and combined misalignment. Angular misalignment occurs when there is face runout on the coupling faces, and the centerlines of the two half-couplings form an angle. This generates excitation forces during rotation, inducing vibration responses. Parallel misalignment occurs when the centerlines of the two half-couplings are not collinear, but remain parallel at a certain distance, generating vibration responses during rotation. Combined misalignment is the most common misalignment phenomenon in actual rotating machinery, involving both angular misalignment and parallel misalignment, representing a combination of both. During the manufacturing process, the coupling face may not be perpendicular to the centerline, or the centerline of the face bolt holes may not be concentric with the journal, due to process or measurement issues. During the installation process, tightening the connection bolts (gear sleeve bolts) causes deformation of the shaft, resulting in significant runout at the journal. Sometimes, differences in the tightening force of the circumferential connection bolts of the coupling can also cause conditions similar to face runout of the coupling. During operation, if operating conditions change drastically, such as during load application, when the load reaches a certain value (i.e., the shaft system torque increases to a specific level), mutual dislocation of the coupling occurs, changing the alignment state of the shaft system, and causing a sudden change in the vibration response of the rotor connected by the coupling. A large instantaneous change in shaft system torque impacts the coupling transmitting the torque, causing mutual dislocation of the coupling and changing the alignment state of the shaft system. 2) Torsional vibration: The torsional vibration of gear couplings has been analyzed and studied, mainly using Fourier series solutions, with clearance, damping, and excitation force as parameters, A nonlinear analysis was conducted on the torsional vibration of shaft systems connected by gear couplings; Extensive tests were carried out on the axial vibration of shaft systems connected by gear couplings, and the main causes of axial vibration were qualitatively explained, indicating that axial vibration is mainly caused by misalignment and friction on the tooth surfaces, and significant axial displacement will occur when there is no axial restoring force or thrust bearing. Vibration analysis is one of the techniques for predicting coupling misalignment, as it can determine the gradual trend of changes in equipment condition, but when determining whether a piece of equipment is in a misaligned state, it is necessary to refer to a large amount of historical data and cases, and to distinguish whether the issue lies with the bearings, lubricating oil, or coupling, or with the connection and fixation, so it has certain limitations. Infrared thermography can, when equipment condition is poor, differentiate overheated areas such as bearings, motor housings, and couplings, and determine the alignment error of the coupling, and when combined with other predictive techniques such as vibration analysis, the effect will be better. Tests were conducted on high-speed rotating turbine generators and blowers, providing a brief explanation of the bending vibration caused by gear couplings; Bending vibration tests were performed on shaft systems connected by gear couplings under different parameter conditions such as unbalance, lubrication conditions, clearance, errors, and load; In addition, Yamauchi, Someya, and others conducted a nonlinear analysis of the bending vibration of half-coupling systems under the action of dry friction on the tooth surfaces, The vibration of gear couplings is mainly related to the misalignment between the internal and external gears and tooth surface friction, and special attention must be paid to the lubrication of tooth surfaces in high-speed rotation conditions.

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