Zipline

In mining, rope slip is the term used to describe the slipping of the hauling rope in the traction sheave , which can occur when the vehicle is started or braked sharply. Zipline occurs mainly when an overload is attached. Unlike zipline hiking , zipline doesn't happen all the time.

Basics

In the case of traction sheave conveyors, the driving force for moving the conveying cages must be created by means of friction, with the rope slipping under certain conditions. This rope slip can be so pronounced during acceleration phases, for example, that the hoisting rope slips considerably over the traction sheave (rope slip). This zip line is mostly undesirable because it has unpleasant side effects. The zip line can result in the hoisting machine operator or, in the case of automatic operation, the control system, no longer being able to stop the hoist cage in the prescribed position. A very strong zip line can even cause the baskets to enter the safety gear . In certain situations, the zipline is partially intentional and required. If the conveyor cage jams or the counterweight rests, the rope must slip so that it is not damaged or even torn.

Types of rope slip

The rope slip (rope slip) can be divided into three main groups: sliding slip, running radius slip and stretching slip. When starting and braking, the inertia of the masses causes sliding slip . Slippage occurs in particular when the inertia cannot be fully compensated by the rope elongation. The running radius slip is caused by the different rope forces. Depending on the rope force, the penetration depth of the hauling rope into the groove of the traction sheave and thus the running radius changes. Since the path of the hoisting rope must be the same on both sides of the sheave, there is a relative movement between the hoisting rope and the drive groove, the run-radius slip. The elongation slip is caused by the different strengths of the rope forces and that exist on both sides of the traction sheave. As a result of these different rope forces, there is a change in the elastic expansion between the point of contact and the point of departure of the hoisting rope. The resulting relative movement between the hoisting rope and the drive groove leads to rope slip. ${\displaystyle S_{1}}$ ${\displaystyle S_{2}}$

Origin of the zip line

Zipline is caused by dynamic forces when decelerating or starting. According to the Euler-Eytelwein formula , the force possible without a zip line depends on the force in the slack side . The difference between the two rope tensile forces and at the traction sheave, at which a rope slide is just avoided, is called the rope slide limit. The circumferential force transmitted by frictional engagement between the hoisting rope and the drive pulley has a significant influence . The coefficient of friction µ is of great importance here. ${\displaystyle F_{1}}$ ${\displaystyle F_{2}}$ ${\displaystyle F_{1}}$ ${\displaystyle F_{2}}$ ${\displaystyle F_{u}}$

Wrap angle α

The following applies to the transferable circumferential force: ${\displaystyle F_{u}=F_{1}-F_{2}\,}$

However, if the critical rope force ratio, which characterizes the traction, is exceeded, a rope slip occurs. The sliding of the hoisting rope over the traction sheave is physically characterized by the fact that the state of static friction changes into the state of sliding friction. This then leads to relative movement between the hoisting rope and the traction sheave. The angle of wrap of the hauling rope around the traction sheave has a major influence on the suppression of the zip line. The rule here is that the zip line is a function of the wrap angle α and is not conditioned by the different locations of the hoisting machine.

Countermeasures

In order to avoid a zip line under normal conditions, particular care must be taken to ensure that there is always sufficient friction between the traction sheave and the hoisting rope. This is first achieved by using suitable materials that have a high coefficient of friction and are used as pulley linings. The rope must be lubricated with a suitable agent that is sticky and may only be applied to the hauling rope with a thin layer. It is even better to process the rope with rope lacquer. The rope core must also never be lubricated with grease. Another possibility to counteract the zip line is the appropriate wrap angle.

The following minimum conditions must be met:

For tower hoists: ${\displaystyle {\frac {F_{\text{u}}}{F_{2}}}=1{,}66}$

For floor conveyors: ${\displaystyle {\frac {F_{\text{u}}}{F_{2}}}=1{,}19}$

Source:

Individual evidence

1. ↑ ^{a b c} H. Herbst: Results of the negotiations of the Prussian Ropeway Commission. I. In: Glückauf, Berg- und Hüttenmännische Zeitschrift. Association for mining interests in the Oberbergamtsiertel Dortmund (Ed.), No. 2, 61st year, January 10, 1925, p. 34.
2. ^ Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary. 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .
3. ↑ ^{a b c} Richard Meebold: The wire ropes in practice. Springer-Verlag Berlin Heidelberg GmbH, Berlin 1938, p. 63.
4. ↑ ^{a b} Patent No. 77289 of the German-Austrian Patent Office: Device to stop the operation of traction sheave hoisting machines in the event of a rope slip .
5. ↑ Wolfram Vogel: Requirements for suspension elements in today's elevator technology. University of Stuttgart, Institute for Materials Handling and Logistics.
6. ↑ Oliver Berner: Service life of wire ropes in traction sheave elevators when combining grooved profiles. Institute for conveyor technology and logistics.
7. ↑ Technical requirements for shaft and inclined conveyor systems (TAS) . Verlag Hermann Bellmann, Dortmund 2005.
8. ↑ Patent DE 102006042909A1 from October 11, 2007 from TSG Technische Dienst Service Gesellschaft mbH Erfurt. Title: Dynamic determination of the traction capability in traction sheave-driven elevator systems .
9. ↑ ^{a b c} Hans Bansen (Ed.): The mining machines . Third Volume, The Shaft Carriers. Published by Julius Springer, Berlin 1913.