The term hoisting rope is used in mining to designate ropes that are used to raise and lower loads in a mainly vertical direction in shafts , dies and the like. Hoisting ropes used in mining must be manufactured in accordance with the recognized rules of technology.
In the case of aerial ropeways , hoisting ropes are a combination of a pull rope and a carrying rope . Only by using hoisting ropes could gondola realized -Seilbahnen. Driving equipment (armchairs, gondolas, load suspension systems) are either clamped firmly with screws or variably clamped and disconnected in the stations.
The development from the direct extraction of raw materials close to the surface via Schurfpingen to pits required the possibility of load conveyance without the time-consuming direct transfer from hand to hand or via load carriers . Ropes made of plant fibers , twisted leather or the like were used very early on to raise and lower the vessels for conveyed goods or water , which are also constantly specializing . In many mines , the miners moving in and out on a rope was an everyday sight. The miner sat either on a toggle or in a rope loop . While hoisting ropes were undoubtedly moved directly by hand at the beginning, the development of rope drives also rapidly progressed via hand reels , gopels and water wheels to increasingly specialized hoisting machines .
In the late Middle Ages, the practicable depth of a hoisting shaft was mainly limited by the quality of the available ropes and therefore by their unfavorable ratio of dead weight to tensile strength in addition to the performance of the mainly used hand reels, the development of evenly forged chains and mainly wire ropes enabled previously unimagined usable depths continuous shafts and the resulting ever-increasing demands on the conveyor systems used and their drives.
Today in mining almost exclusively wire ropes consisting of a large number of cold-drawn strands are used, with the average strand diameter being around 2.5 mm.
As before, the haul rope breaks greatly feared. Conveyor ropes are therefore subject to regular, strict controls. In the past, rope breaks before special load-bearing devices were used across the board, often leading to sometimes serious mining accidents.
In 1834 Oberbergrat Albert invented the first wire rope in Clausthal, this type of rope gradually replaced the hemp rope that had been used in mining until then.
Types of rope
A distinction is made between the following ropes based on their external shape:
- Round strand ropes
- Lang lay ropes
- Ordinary lay ropes
- Triangular strand ropes
- Flat ropes
On the basis of the intended use, conveyor ropes are divided into:
- Upper ropes
- Lower ropes
Depending on the use of the hauling rope, various criteria must be taken into account when selecting the rope:
- Number of ropes (single or multi-rope conveyance)
- Risk of corrosion
- Twist properties of the different types of rope
- necessary rope diameter
The number of ropes required results from the limit depth or the limit load.
Suitable ropes must be used in shafts where there is a risk of corrosion.
The necessary rope diameter is determined from the rope load to be calculated.
Breaking strength of the hoisting rope
So that the rope load can be correctly determined, the breaking force of the hoisting rope must be verified. In technology, a distinction is made between three types of rope breaking force determination:
- determined breaking force
- calculated breaking strength
- real breaking force
The determined breaking force is formed from the sum of the actually determined individual breaking forces of the wires.
The calculated breaking force is a quantity that serves as the basis for the choice of rope in planning. The calculated breaking force is the product determined from the metallic cross-section ( ) and the nominal strength of the individual wire ( ).
The following formula applies:
For safety reasons, the calculated breaking force of the hauling rope (minimum breaking force ) must be greater than the greatest static rope load by the rope safety factor .
The real breaking force is the actual breaking force of the hoisting rope determined on the test stand.
A so-called rope binding is attached to the rope ends so that conveyor ropes are protected as much as possible at the rope ends . This allows a reliable fastening of the rope. The rope binding can be designed in different ways, there are the following options for the design of the rope binding:
- Use of rope clamps
- Splicing the rope
- Braiding of the rope ends with subsequent potting in conical sockets ( sleeves )
Round ropes are predominantly used as upper ropes in shaft hoisting systems. Since these ropes are exposed to particularly heavy loads, they must meet certain safety criteria. The load-bearing capacity of the ropes must correspond to 9.5 times the nominal load in rope systems. In the case of pure material shafts, the load capacity must correspond to 7.5 times the nominal load. The nominal load corresponds to the payload plus the dead weight of the cages and ropes. The hoisting rope is not connected directly to the hoisting cage, but via a so-called intermediate harness .
The following safety-related requirements are placed on hoisting ropes:
- sufficient service life
- sufficient and at the same time limited driving ability
- reliable recognizability of discard
In the case of traction sheave conveying, the hoisting rope is guided over the traction sheave (Koepe disc ) to the hoisting cages, which are attached to the hoisting rope. To compensate for the weight of the rope, a lower rope must be attached under the baskets. Without this, the upper rope would slip on the traction sheave due to its own weight.
In drum winding machines , one rope is wound on each drum and the other is unwound. With drum conveyors, the conveyor ropes are loaded differently than with traction sheaves.
For reels , the great advantage is the complete absence of lead of the ropes, which is why this type is especially used in shaft sinking. The disadvantage is the high level of stress and wear and tear on the ropes.
When setting up the hoisting machine as a so-called floor hoisting machine next to the shaft, the hoisting ropes must be diverted over the sheaves , which are located in the conveyor frame of daytime shafts. Sheaves are grooved wheels through which the hoisting ropes coming from the hoisting machine are guided to the hoisting cages. When setting up the hoisting machine above the shaft as a tower hoisting machine, all that is required is a deflection disk to increase the angle of wrap on the traction sheave and to reduce the lateral distance between the conveyor fragments .
Effect of the rope diameter
The rope diameter has a direct effect on the size of the sheave and the pulley. The nominal diameter of sheaves and deflection sheaves on round ropes must be at least forty times the nominal rope diameter, but at least 0.6 meters. With locked ropes, the nominal diameter of the sheaves and deflection sheaves must be at least one hundred and twenty times the nominal rope diameter. With flat ropes, the nominal diameter of the sheaves and deflection sheaves must be at least sixty times the nominal rope thickness. These requirements also explain why sheaves have dimensions of more than five meters.
Since larger nominal rope diameters are required with increasing depth and higher payload, rope sheaves with larger nominal diameters must also be used. However, the pulley diameter cannot be increased at will. That is why conveyor systems are often equipped with multi-rope conveyors. If certain limit loads or limit depths are exceeded, the transition to the multi-rope technique is mandatory.
From a payload of 28 tons or a limit depth of 2000 meters, in many cases even at 1400 meters, multi-rope hoisting must be used. The main reasons are the rapidly increasing rope cross-section and the resulting larger bending radii of the haul rope. Due to the larger bending radii, rope supports and sheaves with a larger nominal diameter must be used. Larger cable carriers, in turn, require a higher torque and only allow lower speeds . For higher torques you need more powerful electric motors , and the entire construction must be reinforced. All of this leads to increasing investment costs.
Problems with multi-rope conveyance:
- Rope deflection between sheave and traction sheave
- the load distribution between the individual ropes
- Work such as B. Changing or shortening the rope
- special requirements for intermediate harnesses
Multi-rope conveyors can only be used for traction sheave conveyance and drum conveyance; for reel conveyance, only single-rope conveyance is possible.
Upper ropes are exposed to a wide variety of loads during operation. Due to the different grooves in the rope carrier and in the deflection sheaves, the rope deformations of the hoisting rope vary. Since the rope wires and fibers can be moved relative to one another, the conveyor rope can easily run. Nevertheless, with unfavorable groove combinations (e.g. V-groove in the traction sheave and round groove in the deflection pulley), varying ovalization stresses occur in the ropes, which have an impact on the service life of the hoisting ropes. Another stress is the slip that occurs between the traction sheave and the hoisting rope . Another stress on hoisting ropes is the presence of damp shafts, where galvanized ropes must be used. Bare steel ropes can also be used if the hoisting ropes are subject to high mechanical stress and the associated shorter lay-up times.
Since the economic operation of a shaft hoisting depends to a great extent on a relatively even capacity utilization, the possibility of counterbalancing the weight of the conveying vessels was recognized very early on by not winding and unwinding a rope with an attached vessel on one side, but automatically lifting one vessel and lowering the other while the rope ran through .
However, if one vessel is at its lowest level and the other at its highest level, the weight of the rope itself causes very different forces to act on the rope's suspension point. This difference can be eliminated by a more or less freely hanging rope below the two and connecting them, the lower rope.
Flat ropes are mainly used as lower ropes. Discarded upper ropes may still be used as lower ropes under certain conditions. In addition to compensating for the weight of the rope, the lower rope also reduces the risk of a zip line .
If lower ropes have fallen below 5 times the safety factor compared to their own weight, or if there are signs that the calculated breaking strength has been reduced by more than 30%, they may no longer be used for safety reasons.
Regular and reliable inspections are an absolute must to ensure the safety of hoist ropes. For safety reasons, hoisting ropes in mining must be checked by a competent person every working day. In addition, the rope must be checked by an expert at regular intervals . The ropes are monitored by visual and tactile tests during the inspections . Visible wire breaks are counted per reference length. The rope diameter is checked and, if necessary, the lay length. Another check is the qualitative assessment with regard to rope deformation , corrosion and wear . For the purpose of recognizing the readiness for discard , the lay time of the hoisting rope is also taken into account. For higher safety requirements, hoisting ropes are examined at regular intervals for internal rope damage, depending on the requirement, using special measuring methods (e.g. magnetic-inductive rope testing). Visual and tactile tests are not sufficient for this.
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