German KWD coupling KWD model KWD price

KWD couplings transmit motion by welding or bonding a thin-walled corrugated tube (bellows) directly to the two half-couplings. 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 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 completed 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 control over the precision of the bellows wall thickness and can achieve thinner walls than bellows made 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.

KWD coupling introduction

Gear couplings have small radial dimensions and high load capacity. They are commonly used for shaft transmissions under low-speed, heavy-load conditions, such as in metallurgy, mining, and lifting/transport industries. They are also suitable for petroleum, chemical, and general machinery industries. High-precision gear couplings that have undergone dynamic balancing can be used for high-speed transmissions, such as 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 two half-couplings through the meshing of internal and external teeth, 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 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.

KWD 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. For straight-tooth gear couplings, the axial tooth blank of the external gear sleeve can be machined into straight and arc shapes, while the pitch circle and root circle are 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. For drum-tooth gear couplings, the tooth tip of the external gear sleeve is machined into an arc, meaning the tooth blank is machined into a spherical surface. In the cross-section at the tooth center plane tangent to the pitch cylinder, the teeth form a drum shape, hence the name drum-tooth coupling. Its characteristics are: 1) High load 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) Reasonable structure and reliable performance; since the tooth sides are drum-shaped, contact conditions are improved when the shaft 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 tooth profile of the external gear sleeve 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°～2.5°.

KWD 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 manufacturing, process or measurement issues may cause the face to be non-perpendicular to the centerline, or the centerline of the face bolt holes to be non-concentric with the journal. During installation, tightening the connection bolts (gear sleeve bolts) can deform 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), the coupling becomes mutually displaced, the alignment state of the shaft system changes, and the vibration response of the rotor connected by the coupling changes abruptly. A large instantaneous change in shaft system torque impacts the torque-transmitting coupling, causing mutual displacement 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, primarily 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 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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