The design stage is where the most dramatic impact can be made on long term operational safety, and a review of all possible options is necessary to apply the most effective design in each case.
Consideration must be given not only to the effectiveness of the design but also to the health and safety aspects. Often only a little extra effort can reduce risks significantly.
There are several basic shaft and station layouts, which are shown generally on the attached sketches. These can be summarised as :
3.6.1 “over brow” design
The bank is a horizontal extension of the incline shaft, as shown diagrammatically in Fig 3.6.1. Cars must be pushed by hand over the brow into the incline while attached to the winding rope, and great care must be taken to avoid both physical damage to the rope and the development of a slack rope situation when a runaway car could cause rope damage or failure. Various safety devices such as the Marievale or “vula-vala” have been installed to assist in control of the cars.
This design is often used in situations where space is restricted, when the lower station is of similar layout to the bank ie a runaway car would exit straight onto the lower station.
Other pertinent issues include:
• care must be taken to prevent cars being shunted directly into the shaft;
• a small deviation from proper operational standards can cause a serious incident; and
• the mine risk assessment team saw this as the most hazardous design.
3.6.2 “station dropset” design of station access
The station is mined in the hanging wall above the incline shaft (see Fig 3.6.2), and a steel set is lowered into the shaft when required to support the material cars as they are moved from the shaft onto the station. This layout is used on steeper inclines, and can of course also be used at the bank and at the lower station. Other pertinent issues include:
• the dropsets should be interlocked with the winder to avoid a shaft accident. On one installation, consideration is being given to providing underwind and overwind limits linked to each station dropset;
• cars are pulled up from the bank into the shaft with the rope under tension; and
• a dead end can be provided in the shaft below the lower station.
3.6.3 “ramped” design of station access
The material cars are switched from the rail track in the shaft onto a short ramped section of track which is curved down to the station at the side of the shaft (see Fig 3.6.3). This design is used on shallower inclines, and can be applied to the bank and lower station as well as intermediate stations. Other pertinent issues include:
• the rail switch in the shaft can be set to the “straight through “ position, so reducing the chance of a runaway car coming out onto the station;
• cars are pulled up from the bank into the shaft with the rope under tension;
• a dead end can be provided in the shaft below the lower station;
• the chance of a car being shunted into the shaft is eliminated; and
• careful design is required of the ramped section onto the station.
3.6.4 Handling of material cars
Three different methods of handling material cars were noted:
• material cars attached to a pilot car or directly to the winding rope. The controls and shortcomings of this design have been fully reviewed in preceding sections;
• loading of material cars onto a large flatcar or “crocodile”, which is attached to the winding rope; and
• confinement of the material cars inside a frame or bridle which is attached to the winding rope.
The latter two options are used on “heavy duty” installations, and have the benefit of eliminating all the hazards associated with coupling slings and pins for connection of material cars. They have the following shortcomings:
◊ they require more space in the shaft and on stations; and
◊ they require the use of larger winders to handle the increased loads.
4. Discussions and Conclusions
Although only a relatively small sample of small winder sites were studied during this project, it was apparent that a significant variation in terms of the design, operation and maintenance standards applied to small winder systems currently exists. During
discussions with mine users and other interested parties (such as OEMs and the Inspectorate) the view that many small winders are not treated with the respect they deserve was often expressed. The project established that those small winders licensed for man winding tended to be well designed and maintained; however, the same cannot be said for many small unlicensed material winders. There appear to be several general factors that influence the quality of design, maintenance and operation of small winders.
These are:
• Mine size and large winder expertise. The studies indicated that standards of installation, operation and maintenance tended to be higher on the larger mines where there was a culture of licensed winder operation. In such situations it is relatively easy for staff involved with “small” winders to seek advice from their “large winder”
counterparts, and to use standards of design and operation that already exist; this comment is even more applicable where the standards originate from a central technical office. Staff on small mines do not have this facility.
• Duty and application. As is to be expected, winders that are important to mine operations are treated with more respect than others. However, an interesting comment from several sources was that the steeper an incline is, the more
“dangerous” it is perceived to be and so the more attention it receives.
• Nomenclature. Winding plants on the mines, whether large or small, are variously referred to as “winders” or “hoists”. The term “winch” is added to the variety for small winding plant. Use of the words “hoist” and “winch” tends to give the impression that these are not really important enough to earn the title of “winder”.
An attempt has been made to rationalise this terminology. Mesarovich (1991:13) suggested that the nomenclature should be based on the duty cycle, as is done for electric overhead travelling cranes, and proposed the following classification:
Class Name Duty
1 Hoist light duties, works less than 4 hours per day, does not always have a full load
2 Winch medium duties, works less than 8 hours per day
3 Winder heavy duties, works continuously, always carries a full load
This does however create problems in that a machine may be used on different duty cycles during its working life, and so may be classified differently at different times.
The use of this system could also result in a small man winder being classed as a
“winch” or “hoist” compared to a large “winder” being used for material. Standard nomenclature should be agreed by the users.