Torsionally stiff coupling
Torsion- resistant couplings are, in addition to the vibration-damping couplings, representatives of the group of high-precision couplings. In mechanical engineering, they are a typical application in the field of machine elements. They are used to transmit torque from the drive shaft to the output shaft. There they simultaneously compensate for shaft offsets (e.g. in the axial or lateral direction). Normally, these misalignments are so-called misalignments, for example caused by thermal expansion or assembly inaccuracies, which are compensated for by the torsionally rigid coupling systems. The Schmidt coupling is predestined for large, variable radial misalignments that can be found in profiling systems, coating systems, roller drives and calenders . The shafts can be adjusted radially in all directions within the permissible values, both at rest and during operation and under load. A constant angular speed of the input and output side is guaranteed.
Use and execution
Compared to the vibration-damping couplings, the torsionally stiff couplings are characterized by the fact that they counteract impressed torques with very little ( twisting ). This makes them interesting for drives where small angular differences have to be transmitted, e.g. B. with stepper drives. Typical representatives of torsionally rigid couplings are, for example, metal bellows couplings or spring bar couplings . The materials used are typically steel or aluminum. In the meantime, plastics such as PEEK are also used for couplings in the food industry or in the aerospace industry. Of course, due to their lower density, aluminum and PEEK have the advantage that the entire component has a lower mass moment of inertia .
The angle of rotation that is created by the applied torque is normally not more than 0.1 °. With a given torsional rigidity, it is directly proportional to the drive torque.
The so-called Flexlink coupling, a flexurally elastic, torsionally rigid steel coupling, is a fatigue-free, special shape made entirely of high-quality steel for maximum torques. It is used to compensate for radial, axial and angular misalignments between two shafts with low reaction forces. Tangentially arranged spring bars serve as elastic connecting elements in the coupling. The ends of the spring bars are fixed to the inner part and the outer part of the coupling. If a shaft displacement occurs, the inner part of the coupling is bent in relation to the outer part of the coupling. The flexion capacity of the coupling is determined by the number of pairs of spring rods.
The latest developments in the industrial sector, especially where high speeds are required with high performance, are moving in the direction of fiber-reinforced composite materials. Application examples for this are, for example, ship propulsion systems, decentralized power plants or wind power plants.
With the help of these modern materials it is possible to avoid the fatigue behavior of rubber couplings and still enable angular compensation. The cardanic principle is usually achieved here via a corrugated membrane designed with FEM on each side. The advantages of this composite coupling principle are:
- Very high rigidity
- Low mass, therefore quick response and little inertia
- Minimal, almost linear displacement reaction forces
- Excellent vibration and electrical insulation properties: soundproofing and avoidance of leakage currents from the generator to the motor
- no electrical corrosion
Torsionally stiff couplings fall under the category of torsionally stiff and flexible couplings. The so-called parallel crank coupling (Schmidt coupling - source: Roloff / Matek machine elements) occupies an exceptional position. The compensation of, for example, radial displacements does not take place on the basis of a flexurally elastic behavior, but rather through a pure, force-free pivoting movement of needle-bearing parallel link pairs.
Torsion-proof couplings are used in a wide variety of applications in which rotary movements and / or torques have to be transmitted precisely. The focus here can be on the transmission of high torques. This is the case when used in mechanical engineering such as printing machines, packaging machines, conveyor systems or sheet metal forming. There are other requirements in the area of sensor technology. Here an encoder coupling has the task of protecting measuring instruments from mechanical overstressing and ensuring the exact transmission of the rotary movement according to the resolution of the encoder.