Frank A. Perret
The Siemens Brothers
Frank J. Sprague
It was where it was not a case of ascending to the heavens but of a descent to hell that the technology of vertical transport was revolutionized. Very early on, higher speeds were achieved for long vertical routes in the mining industry (a fact which has not changed even today) than were attained in high-rise buildings and in housing construction. However, as shaft depths increased, winding drums became unprofitable: they assumed enormous dimensions, with diameters reaching up to several metres. Due to the fact that the cable was wound onto the drum in rows, unequal loads were placed on the machine shafting. This increased the danger of the cable breaking, especially through intensive and continuous operation in 24-hour shifts. At certain pits the danger of cable breakage was so great that the miners preferred to descend the shaft by ladder.
In 1877 the mining engineer Friedrich Koepe (1835-1922) converted a drum machine into a friction-driven hoist for a shaft 234 metres deep (i.e. the equivalent of an eighty-storey building!). Instead of using a cable drum (onto which the cable was wound and fixed) as had hitherto been the case, Koepe loosely laid the cable over a disc which simultaneously served as a drive-wheel. The cable ran along a dovetailed groove and was driven solely by friction.
What appeared to be so incredibly
simple was, in fact, trailblazing, and has remained so up to the present
day, yet it completely failed to astonish the employers of Koepe, its
inventor. Unable to recognize its brilliant and novel character, the Friedrich
Krupp company did not have the friction drive system patented. As a result,
Koepe, the mining engineer, had the patent made out in his name. Once
it became successful beyond all doubt, Krupp demanded - in 1879 - that
he surrender the patent rights. This led to a conflict; a short while
later Friedrich Koepe quit his job.
<Friction as drive> was the critical point. Everyone was afraid of the cable slipping, resulting in an accelerated descent in the lift cage into the great depths of the shaft. Lift accidents in the mining industry were a three-fold source of torment for the miners travelling down into the pits:
- The height of fall is enormous, at the time it was well over 2000 metres. A lift cage plummeting down the shaft tore the shaft casing down with it.
- The pit water collected on the floor of the shaft, if the miner survived the fall, he drowned in the sludge.
- Being hit and killed by the lift cable constituted the third hazard. It fell behind the lift cage with the combined strength of Hercules and lashed anyone who might have survived with the force of an iron whip.
Friedrich Koepe's brilliant and courageous discovery solved several problems at once. The drive or Koepe disc demonstrated a number of advantages over the drum principle:
- multi-cable operation: the use of several cables over parallel discs increases safety in the case of cable breakage, each cable is also thinner and more flexible.
- The cable is only returned once, cable-wear is reduced and hazards caused by damaged cables are minimised.
- The cable always runs axially, the forces are simple to calculate. The danger of cable becoming slack is eliminated. This was a frequent cause of accidents with winding drums. During descent the platform got caught up, the cable continued to be lowered, the lift cage freed itself and fell with no means of support, the cable tore at the lift-cage suspension point owing to the increased tensile force:
- An equal distribution of tensile forces protects the cable, the drum and the motor; the difference in the cable weight is constantly balanced by a cable hanging loosely below.
- Being relatively light, the electric motor can be installed right at the top of the shaft; cable returns are thus eliminated.
From "A Cultural History of Vertical Transport" by Jeannot Simmen and Joseph Imorde (Available in ELEVATOR WORLD library in English)