German MURTFELDT coupling, MURTFELDT model, MURTFELDT price

MURTFELDT couplings leverage their mechanical design to enable continuous rotation of two shafts not on the same axis, even when an angular misalignment exists, while reliably transmitting torque and motion. The key feature of universal couplings is their significant angular compensation capability, compact structure, and high transmission efficiency. The angle between the two shaft axes varies by universal coupling design, typically ranging from 5° to 45°.

Introduction to MURTFELDT couplings

Gear couplings feature a small radial dimension and high load capacity. They are commonly used for shaft transmission in low-speed, heavy-load applications, such as in metallurgy, mining, and lifting/transport industries, and are also suitable for petroleum, chemical, and general machinery sectors. High-precision gear couplings that have undergone dynamic balancing can be used for high-speed transmission, such as in gas turbine shaft systems. Since crowned gear couplings offer greater angular compensation than straight-tooth gear couplings, crowned 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, suitable for connecting coaxial shaft systems and providing certain compensation for relative shaft displacement. Their structure is shown in Figure One, consisting mainly 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 integrated into a single unit. Due to their compact structure, high load capacity, wide speed range, and reliable operation, gear couplings are widely used in various mechanical industries, including metallurgy, mining, lifting/transport, petroleum, and shipbuilding.

MURTFELDT coupling classification

Gear couplings are classified into three types based on the axial tooth profile of the external gear sleeve: straight-tooth gear couplings, crowned gear couplings, and special crowned 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 straight or arc shapes, while the pitch circle and root circle remain straight. The meshing form of this coupling is identical to that of involute cylindrical gear internal and external teeth. Compensation for relative shaft displacement is achieved by increasing the side clearance between the internal and external teeth, but the compensation amount is limited. In crowned gear couplings, the tooth tip of the external gear sleeve is machined into an arc shape, meaning the tooth blank is spherical. In the cross-section at the tooth center plane tangent to the pitch cylinder, the teeth form a drum shape, hence the term "crowned" coupling. Its features are: 1) High load capacity: calculated based on bending strength, the torque transmitted is 15–30% higher than that of straight-tooth gear couplings under the same conditions; 2) Rational structure and reliable performance: the crowned tooth profile improves contact conditions at certain shaft angles, reducing contact stress and eliminating load concentration at the tooth ends of straight-tooth couplings (i.e., edge crushing), thereby improving operational performance. 3) Good compensation performance: the crowned shape 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°.

MURTFELDT coupling troubleshooting

1) Gear coupling misalignment: 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; it is a combination of both. During the manufacturing process, 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 the installation process, tightening the connection bolts (gear sleeve bolts) causes deformation of the rotating 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 coupling face runout. 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 undergoes a sudden change. 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, mainly using the Fourier series solution method, 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 many past data points 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 supply fans, 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 the tooth surfaces in the case of high-speed rotation.

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