Rope transmission

A cable drive or cable transmission is a device for transmitting a rotary movement from one shaft to another by means of cables . Today, this technology is only used where the electrical current for corresponding electrical devices is not available and in pulley applications .

functionality

Change of drive direction

Round belt drive / deflection

Each of the shafts carries a pulley with a groove on the circumference , and a self-contained rope is looped around both pulleys, which is carried along by the one pulley through the friction in the groove and the other pulley also rotates with the help of the friction offset. The friction requires a pressure of the rope against the circumference of the pulley, which is generated either by pulling the rope tightly ( cotton and hemp rope operation , cord operation ) or by the weight of the rope hanging down between the pulleys ( wire rope drive ).

The hemp and cotton rope drive has often replaced the belt drive for transmitting large forces (up to 1000 horse forces). With him, the force is mostly distributed over a number of ropes (up to 30) with a diameter of 30-50 mm, which run at high speed (10-40 m and above per second) next to and below each other, with each pulley with a corresponding number of Grooves with a wedge-shaped cross-section must be provided.

The hemp and cotton rope drive is used in particular to transmit the power of a larger motor to the main transmission shafts and has a lower space requirement, slightly lower operating costs and greater security against operational disruptions in front of the belt drive, but does not, like the belt drive, allow disengagement by means of loose or Blank disk. In rooms with high levels of humidity or very variable temperatures, the tension in the ropes is influenced too much.

Jarolimek replaces the hemp or cotton ropes with so-called steel cords (steel cord drive), ie coil springs made of steel wire , the clear diameter of which only corresponds to the wire diameter, so that their springiness is only slight when there is a high tensile force. The cord drive is generally in use when less power is required, especially in machines with hand and foot operation. A cord (cord without end, driving cord) made of hemp or twisted leather strips (twisted straps) or intestines ( gut strings , peesen) is used here.

Long splice on the rope

The ends of hemp cords are joined by splicing and twisted straps and gut strings by iron hooks and eyes . The wire rope drive, invented by the “Brothers Hirn” around 1850, has ropes of 5–32 mm diameter made of iron or steel wire with a diameter of 0.5–2.2 mm and is used to transmit forces of any magnitude over great distances (20 to 2000 m), for which straps or hemp ropes are unfavorable and completely useless in the open air. Given the large distance between the sheaves, the rope must hang down between the sheaves in an arc of relatively great arrow height so as not to tear under its own weight. The tension created in it by the weight of the rope creates the friction on the pulleys for transmission.

If the two sheaves are very far apart, the rope is supported by rollers every 100 to 200 m, because otherwise its depression and the resulting height of the sheaves (pillars) support would be too great. In such a case, the so-called. composite rope transmission by switching on intermediate stations with two-track pulleys, which are connected from station to station by an endless rope.

If the rollers are unevenly high, the so-called crooked rope drive is obtained. Distractions or branches of the rope run are to be managed by means of changing stations with bevel gears . Idler pulleys are less recommended because they impair the durability of the rope. The disc diameters change between 1.5 and 5.5 m at a peripheral speed of 10–30 m per second.

Famous plants of this type were:

the rope drive of the Schaffhausen waterworks,
the rope drive of the Société des eaux et des forêts in Freiburg im Üchtland ,
the cable drive of the Compagnie générale de Bellegarde,
the Zurich rope drive

literature

Keller, calculation and construction of the engines (2nd edition, Münch. 1881);
Meißner, The power transmission (Jena 1882–87, 2 vols.)