German GKN Service coupling GKN Service model GKN Service price

GKN Service couplings transmit motion by welding or bonding a thin-walled corrugated tube (bellows) directly to the two coupling halves. This type of coupling has a simple structure, small overall dimensions, is easy to machine and install, and offers high transmission accuracy. It is mainly used in low-power precision machinery and control mechanisms that require compact structures and high transmission accuracy. The coupling consists of two hubs and a thin-walled metal tube, connected by either welding or bonding. Although many other materials are available, stainless steel and nickel are the most commonly used materials for the metal tube. Nickel tubes are produced using electrodeposition. This method first involves machining a solid mandrel into a corrugated shape, electroplating nickel onto the mandrel, and then chemically dissolving the mandrel to obtain the nickel bellows. This method allows for precise control of the bellows wall thickness and can achieve thinner walls than those produced by other methods. These thin-walled bellows give the coupling high sensitivity and rapid response, making it ideal for applications in extremely small and precise instruments.

GKN Service Coupling Introduction

Gear couplings have small radial dimensions and high load-carrying capacity. They are commonly used in shaft transmissions under low-speed, heavy-load conditions, such as in the metallurgy, mining, and lifting/transport industries. They 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 transmissions, 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 coupling halves through the meshing of internal and external teeth. They are suitable for connecting transmission shaft systems with two concentric axes and have a certain ability to compensate for relative displacement between the two axes. 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.

GKN Service Coupling Classification

Based on the different axial tooth profiles of the external gear sleeves, gear couplings can be divided into three types: 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 a straight-tooth gear coupling can be machined into two shapes: straight and arc-shaped, while the pitch circle and root circle are both straight. The meshing form of this coupling is exactly the same as the internal/external tooth meshing of involute cylindrical gears. 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; that is, 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 characteristics are: 1) High load-carrying capacity. Calculated based on bending strength, the torque transmitted is increased by 15～30% compared to straight-tooth gear couplings under the same conditions; 2) Rational structure and reliable performance. The drum-shaped tooth sides improve contact conditions when the axes are at a certain angle, 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 two connected shafts. The maximum allowable inclination angle can reach 6 degrees, with a general recommendation of 1.5°～2.5°.

GKN Service 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, causing the centerlines of the two half-couplings to 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) can cause shaft deformation, resulting in significant wobble 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 trend of gradual changes in equipment condition, but when determining whether a piece of equipment is in a misaligned state, it is necessary to have a large amount of historical data and cases for reference, 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 of internal and external gears and tooth surface friction, Special attention must be paid to the lubrication of tooth surfaces in high-speed rotation conditions.

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