Difference between revisions of "Mine hoisting systems"
(→Head Frame Construction)
|Line 96:||Line 96:|
A comparison of steel and concrete structures can be found below
A comparison of steel and concrete structures can be found below
[[image:Comparison_of_Concrete_and_Steel_Headframes.|thumb|center|c| Comparison of Concrete and Steel Headframes (Butler & Schneyderberg, 1981) <ref name="Butler">Butler, D., & Schneyderberg, A. (1981). Headframe selection: steel vs concrete. Mining Congress Journal, 15 - 19.</ref> ]]
Revision as of 13:20, 11 February 2011
The following article is regarding the design of underground mine hoisting systems
Mine hoisting systems are comprised of five major components: hoists, conveyances, wire ropes, shafts, and headframes. Each of these components requires extensive design considerations.
- 1 Types of Hoists
- 2 Types of Conveyances
- 3 Rope Construction
- 4 Head Frame Construction
- 5 References
Types of Hoists
Divided Single Drum (Balanced)
Balanced single drum hoists have one rope winding from the top of the drum and one winding on the underside of the drum. This rope configuration is what gives this setup the ‘balanced’ name. This type of drum hoist is good for two skips operating from the same level or for a cage and counterweight from multiple levels
Single Drum (Unbalanced)
This type of drum hoist is very simple and has only one conveyance attached to a single rope . This setup is extremely energy intensive in comparison to other drum setups.
Split differential hoists are very similar to divided single drum hoists. They are balanced hoists. What makes this type of hoist advantageous is that the differential portion of the hoist allows a smaller counter weight to be attached. This is an example of a mechanical advantage.
Double Drum (One Clutched)
The double drum setup with one drum clutched is very useful. It is very effective where multi level hoisting is required. Adjustments can be made after installation to change the rope length and allow for any rope stretching.
Double Drum (Both Clutched)
The double drum setup where both drums are clutched is also very useful. This setup is good for operations where conveyances are controlled in each shaft compartment independently. This setup is commonly used for shaft sinking operations.
The Blair hoist is by far the most complex layout. In this setup there are two drums each of which are divided. While the increased complexity of this system make maintenance issues more serious it has its advantages. This setup has the capability to run four compartments independently. There is one rope in each of the compartments and each is used for single conveyance. This setup has significantly increased capacity and can carry greater loads at depth than any other setup.
Friction hoists or Koepe hoists are the second main type of hoist. Instead of a drum located some distance away for the shaft, as in drum hoisting, the drum is directly above the shaft itself. Rope passes over the wheel during hoisting operations. This type of hoist is synonymous with low initial capital cost and high reliability. In operations that use this type of hoist rope guides are often used. The low inertia and the balance ropes which run from the bottom of the conveyance reduce the power requirements. This type of conveyance only uses a single compartment. The wheel at the top of the shaft is grooved to keep the rope in place. The wheel is lined with a high friction surface in order to resist slipping as the rope is not attached to the wheel at any point. This type of hoist is characterized by a push button elevator feel. While there are no different distinct types of friction hoists there is one variation that can be made. The number of ropes passing over the wheel can be increased. In general, the deeper the hoisting goes the more ropes required. 
Types of Conveyances
In general there are two types of conveyance. Cages are used to transport labour and materials and skips are used to transport either ore or waste. In some cases a counter weight is required to balance a cage or a skip.
There are many different variations of cages but the general construction of them is similar. They are constructed with a headframe and a travel compartment. The size of the cage depend on the personnel requirements for the mine and the size of the constructed shaft. In many shaft configurations there are separate compartments for cages and skips, as well as, compartments for mine services, ventilation and possible man raises.
There are several different types of skips depending on the requirements of the mine.
Overturning or Kimberly
The overturning or Kimberly skip has both positive and negative aspects associated with it. It is able to handle large sized muck with low spillage. Some of the negative aspects are that is often has material that sticks to the bottom during the unloading of the ore or waste. It is constructed with a large head frame because of the high stresses incurred. This often results in a small payload relative to the size of the skip.
Swing Out Body or Front Dump
The swing out or front dump skip has both positive and negative aspects associated with it. This type of skip has the ability to handle a large payload. It has a relatively small head frame and is easy to empty. Some problems that often arise with this type of skip are a build-up of muck at the hinge point and slimes drip out of the bottom. Also the door mechanism is complex and occasionally makes maintenance issues difficult to fix in a timely manner.
The fixed bottom dump is the most versatile type of skip. It easily can convert from a skip to a cage. While in skip form it can carry a large payload and has a relatively small head frame. In the dumping mechanism no scrolls are needed. With this type of conveyance fixed guides or rope guides are often required.
The construction and selection of ropes in mine hoisting systems is an important design aspect.
Please see the Mine hoisting ropes article for more information.
Head Frame Construction
Headframes support the sheave wheel that the hoist ropes pass over to reach the drum hoist or the friction hoist itself. Their height above the surface allows for material to be dumped on surface. Headframes can potentially be made from steel, timber or concrete but modern technical requirements have made wood almost obsolete. A comparison of steel and concrete structures can be found below
Headframes must be able to support numerous loads:
- Dead load is the headframe, sheave wheels, conveyances and their contents.
- Live load occurs when hoisting at maximum capacity
- Braking load which arises as the conveyances stop in the shaft and the forces transfer to the sheave
- Wind load and snow load which depend on the dimensions and location of the structure
- The effects of temperature and seismic stresses in the area
The headframe design should allow for the placement of mine services nearby.For example, a lamp room, waiting area, first aid room, dry, maintenance, and administrative offices. The skip dumping area should be located in close proximity to the waste storage and handling facilities. There should be adequate access for installation maintenance and removal of conveyances and the hoists & sheaves. During shaft sinking the headrames are generally made from wood or steel. Prefabricated hollow steel gives strength and allows for easy set up and take down. The installation of a permanent headframe tends to be more economical and time saving. The permanent skeleton is designed to support the installation of the sinking sheaves. As the shaft is sunk the headframe and surrounding services can be fully installed.
- McIsaac, G. (2006). 2.3 Hoisting Systems. In Mine 244 - Underground Mining (pp. 19-24). Kingston: Queen's University.
- Edwards, F. A. (1992). Chapter 17.5 Hoisting Systems. In SME Mining Engineering Handbook (2nd ed., Vol. 1, pp. 1646-1678). Littleton: Society for Mining, Metallurgy, and Exploration, Inc.
- De Souza, Euler (2010). Lecture 7: Hoisting Systems. In Mine 244 - Underground Mining Course Notes. Kingston: Queen's University.
- Butler, D., & Schneyderberg, A. (1981). Headframe selection: steel vs concrete. Mining Congress Journal, 15 - 19.