Broken rope

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A rope breakage or rope tear refers to the tearing of a steel rope due to material fatigue or overload. Especially with hoisting ropes in seigeren or tonnlägigen shafts a rope break can have serious consequences. The rope break usually occurs between the rope pulley and the cage . In the case of steel ropes used for horizontal conveyance, the consequences of a rope break are usually not as serious.

Basics and history

In the first half of the 20th century, rope breaks on shaft hoisting systems were still very common. Often these broken ropes resulted in the hoist cage falling and the miners on it having a fatal accident. In March 1907, for example, 22 miners were killed on a regular cable trip at the Gerhard mine due to a broken cable and the subsequent crash of the cage. In March 1913, the cage occupied by 14 miners crashed on the Belgian coal mine Maurage after a rope broke, killing all 14 miners. In the period from 1940 to 1952 there were a total of 20 cases of rope breaks in mining. Due to the dangers of broken ropes, special safety devices were required at that time for the conveyance of ropeway systems, which should protect the cage from falling in the event of a broken rope. After the quality of the hoisting ropes improved from around 1950, the safety gears were abolished again. Despite the improved rope quality and the improved testing and monitoring methods, there were still six broken ropes in shaft hoisting systems between 1960 and 2010. In 2001, a 76 millimeter thick hoisting rope broke after a loaded hoisting vessel could not be braked sufficiently due to a defect in the hoisting machine's brakes and when the hoisting machine was switched off, it began to drift towards the sump . The empty bucket then hit the bumper beam with such great force that the rope broke. At the Fürst Leopold / Wulfen mine , the unoccupied auxiliary car got stuck on a rail joint in the shaft guide , and since the cage monitoring did not trigger, a hanging rope formed. After a short time, the basket suddenly came loose and fell into the hoisting rope. The hoisting rope broke and the basket fell into the swamp.

Signs of wear

Steel ropes are loaded in different ways during their use, which gradually reduces their load-bearing capacity. In the course of the operating time, structural changes lead to a reduction in the rope diameter. When operating in a corrosive atmosphere and with wire ropes that are left in place for a long time, corrosion occurs over time. Due to the corrosion, the reduction in the rope diameter leads to a reduction in the static breaking strength. In addition, rust pockets can form, which also weaken the rope. The movement of the strands leads to abrasion of the rope material, the so-called internal abrasion. Movements between the pulley chuck and the rope, e.g. B. when braking or grinding the rope on objects, it comes to so-called external abrasion. Both forms of abrasion reduce the rope diameter at the stressed points and thus lead to a reduction in the load-bearing capacity. Due to the changing strain, there are also individual wire breaks which, depending on the load, can be so concentrated in one place that entire rope strands break.

Wire breaks

Wire breaks occur mainly due to material fatigue or material wear. Wire breaks always occur where the load on the rope is greatest. If the wire material is already damaged, this damage can lead to wire breaks after a short period of use. Such pre-damage can already arise during wire production if the wire has high internal stresses due to the production process. A study from 1996 showed that wire breaks also occur as a result of wire breaks that have already occurred. However, individual wire breaks do not have a major impact on the load-bearing capacity of the rope. In a study from 1997 it was found that in the event of wire breaks in a rope, the broken wires already have their full load-bearing capacity in the rope after one and a half times the rope lay length. Only when these wire breaks occur concentrated in a short section of the rope will the load-bearing capacity of the rope be reduced.

overload

Conveyor ropes are specially dimensioned for each conveyor system. Each rope must have a very specific breaking force. This is determined on the basis of rope break tests of the individual wires with subsequent calculation and tearing of test pieces. The rope withstands the determined values ​​under normal operating conditions. Under certain conditions, these values ​​are exceeded by abrupt braking or jerky pull on the rope. In the case of hoisting ropes in mine conveyor systems, impact loads are more than three times as high as with normal elevator systems. This is due to the high conveyor speeds at which the conveyor baskets are moved. Due to the great depth , the hoisting ropes used have a very large dead weight, which in the event of malfunctions means that in the worst case, the hoisting ropes are subjected to six times the load. In the event of an abrupt stop, e.g. B. by blocking the conveyor or disproportionate emergency braking, these values ​​are still exceeded, so that the breaking force of the hoisting rope is exceeded and the hoisting rope breaks. Such an overload can occur if the conveyor gets stuck on the downward journey and the rope continues to drift. In such a case, a rope loop known as a suspension rope is formed by the drifting rope. If the conveyor suddenly loosens, it suddenly falls several meters until the suspension rope is pulled taut again. The load on the rope can exceed the breaking force of the rope and tear the rope. Rope breaks due to hanging rope can occur in drum hoists.

prevention

In the German mining industry, no conveyor rope has broken due to wear and tear for around 50 years. This is mainly due to the increased controls on the hoisting ropes. For example, hoisting ropes have to be checked regularly by competent persons and responsible persons . In addition, there are regular reviews by recognized experts. If the inspections reveal that the breaking strength of the rope is more than 15 percent lower, the ropes may no longer be used for the rope journey. Signs of wear due to corrosion or abrasion are usually detected by visual inspections. External wire breaks can be recognized by the fact that the rope is slightly prickly. However, internal wire breaks cannot be determined by external inspection. In order to obtain a precise overview of the degree of weakening of the hoisting rope, these ropes are checked by means of non-destructive testing procedures if necessary. Magnetic devices are used to measure the stray field to check the cross-section reduction of the hoisting rope due to corrosion, abrasion or wire breakage.

Individual evidence

  1. ^ A b Julius, Ritter von Hauer: The conveyors of the mines. 2nd edition, published by Arthur Felix, Leipzig 1874
  2. ↑ K. Bax: The operational safety of triggering conveyor cage catching devices. In: Glückauf, Berg- und Hüttenmännische magazine. Association for mining interests in the Oberbergamtsiertel Dortmund (ed.), No. 43, 69th year, October 28, 1933, pp. 1005-1009.
  3. ↑ a b c d e Winfried Sindern, Olivier Gronau: Steel wire ropes - proven service providers for shaft hoisting systems. In: Ring Deutscher Bergingenieure eV (Hrsg.): Mining. Volume 61, No. 4, Makossa Druck und Medien GmbH, Gelsenkirchen April 2010, ISSN  0342-5681 , pp. 155-164.
  4. ↑ a b Adolf Heilandt: A contribution to the calculation of wire ropes. Printed and published by R. Oldenbourg, Munich and Berlin 1916
  5. ↑ Hans Bansen (ed.): The mining machines . Third Volume, The Shaft Carriers. Published by Julius Springer, Berlin 1913, pp. 76–84.
  6. ↑ a b c Drahtseilwerk Dietz: Spezialdrahtseile Diepa Online ( Memento from March 17, 2007 in the Internet Archive ) (PDF; 4.3 MB)
  7. ↑ a b H. Herbst: Damage to hoisting ropes. In: Glückauf, Berg- und Hüttenmännische magazine. Association for mining interests in the Oberbergamtsiertel Dortmund (Ed.), No. 12, 59th year, March 24, 1923, pp. 285–288.
  8. ^ Karl-Heinz Wehking: Running ropes . 3rd completely revised edition, Expert Verlag, Renningen 2005, ISBN 3-8169-2497-2 , pp. 100–130.
  9. ↑ Richard Meebold: The wire ropes in practice. Springer-Verlag Berlin Heidelberg GmbH, Berlin 1938, pp. 54-59.
  10. ↑ Andreas Klöpfer: Investigation of the service life of wire ropes subjected to tensile swell. Dissertation at the Institute for Materials Handling and Logistics at the University of Stuttgart, June 2002
  11. ↑ Rope safety worldwide. From Durchblick No. 10, autumn 2010, information magazine of the DSK
  12. ↑ a b Technical requirements for shaft and inclined conveyor systems (TAS). Verlag Hermann Bellmann, Dortmund 2005
  13. ↑ A. Siemieniec S. Wolny: Analysis of the working conditions of a conveyor system during an emergency braking. Clausthal University of Technology, Institute Communication No. 24 Online (accessed on July 29, 2011; PDF; 152 kB)
  14. ↑ Thuringian Mining Ordinance for Shaft and Inclined Conveyor Systems (ThürBVOS) of November 1, 2004
  15. ↑ Hugo Bethmann: The hoists, elements of the hoists, pulleys, winches and cranes. Second improved and increased edition, printed and published by Friedrich Vieweg and Son, Braunschweig 1908
  16. ^ Klaus Feyrer: Wire ropes. Dimensioning, operation, safety. Springer-Verlag Berlin Heidelberg, Berlin 1994, ISBN 978-3-662-06770-3 , p. 388.

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