German HOFMANN coupling HOFMANN model HOFMANN price

HOFMANN couplings consist of components such as an internal gear ring with the same number of teeth and a flanged half-coupling with external teeth. External teeth are available in two tooth profiles: straight teeth and crowned teeth. Crowned teeth refer to external teeth machined into a spherical surface, with the center of the sphere on the gear axis. The backlash is larger than that of standard gears. Crowned tooth couplings allow greater angular misalignment (compared to straight-tooth couplings), improve tooth contact conditions, increase torque transmission capacity, and extend service life. During operation of gear couplings, relative displacement occurs between the two shafts, and the tooth surfaces of the internal and external gears periodically slide axially relative to each other, inevitably resulting in tooth surface wear and power loss. Therefore, gear couplings must operate under good lubrication and sealing conditions.

HOFMANN Coupling Structure and Applications

Universal couplings have various structural types, such as: cross-axis type, ball cage type, ball fork type, block type, ball pin type, ball joint type, ball joint plunger type, three-pin type, triple-yoke type, triple-ball-pin type, hinge-yoke 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 magnitude of transmitted torque. They are mechanical components used to connect two shafts (drive shaft and driven shaft) in different mechanisms, causing them to rotate together to transmit torque. In high-speed, 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, connected to the drive shaft and driven shaft respectively. Most prime movers are connected to working machines via couplings.

HOFMANN 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 drive shaft and driven shaft are collinear during machine operation. Alignment accuracy affects whether the machine can operate normally, which is especially critical for high-speed machinery. Achieving absolutely accurate alignment of the two shafts for cross-type universal couplings is difficult, and maintaining accurate alignment continuously for continuously operating machines is even more challenging. Uneven thermal expansion of components in cross-type universal couplings, 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 when installing the coupling. From an assembly perspective, as long as the coupling can transmit torque safely and reliably, the larger the allowable deviation of the two shaft centers, the easier it is to meet 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.

HOFMANN Coupling Measurement Sequence

Misalignment of universal couplings may be radial displacement, angular misalignment, or both. Coaxiality measurement should be performed at four evenly distributed positions on the end face and circumference of the universal coupling. For pump sets connected by cross-axis universal couplings, coaxiality adjustment is inevitable during installation to ensure the coupling halves are both concentric and parallel; otherwise, it will affect pump efficiency 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. Measurement 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, adjustment must be made. During adjustment, first adjust the pump levelness, then use the pump's universal coupling as the reference to measure and adjust the motor coupling half to ensure the motor and pump are coaxial and concentric. When adjusting coupling concentricity, adjust face gap first, then 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 axial gap to make the two halves parallel, then adjust 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 universal couplings 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 perform alignment, which can greatly improve the speed of universal coupling alignment.

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