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Shaft
This document discusses shaft design and sinking methods. It defines different types of shafts and their purposes. Shaft design involves selecting materials and considering stresses, strength, deflection and vibration. Common materials are steel alloys. Shafts are sunk using various methods like drilling and blasting, wood/steel piling, open caisson, cementing or freezing processes. Factors in choosing a vertical or inclined shaft include the ore body geometry and depth. The document provides details on shaft sinking and construction.
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Shaft
- 1. PRESENTATION TOPIC SHAFT DESIGNAND SINKING Presented By Under guidance of Pramoda G Dr. Balasubramanian A 2nd semester, Geology Professor
- 2. Shaft Definitions Shaft- Arotating member used to transmit power. Axle- A stationary member used as support for rotating elements such as wheels, idler gears, etc. Spindle- A short shaft or axle (e.g., head-stock spindle of a lathe). Stub shaft- A shaft that is integral with a motor, engine or prime mover and is of a size, shape, and projection as to permit easy connection to other shafts Line shaft- A shaft connected to a prime mover and used to transmit power to one or several machines Jackshaft- (Sometimes called countershaft). A short shaft that connects a prime mover with a line shaft or a machine Flexible shaft- A connector which permits transmission of motion between two members whose axes are at an angle with each other
- 3. What does itmean “shaft design”? shaft design ? 1. Material selection 2. Geometric layout 3. Stress and strength: static and fatigue 4. Deflection and rigidity: bending defl., torsional, twisting, slope at bearings and shaft- supported elements, and shear deflection due to transverse loading on short shafts. 5. Vibration: critical speed Material selection • Many shafts are made from low carbon, cold-drawn or hot-rolled steel. • Alloy steel: Nickel chromium and vanadium are steel Nickel, some of the common alloying materials. However alloy steel is expensive. • Shafts usually don’t need to be surface hardened unless they serve as the actual journal of a bearing surface. • Hardening of surface (wear resistant): case hardening and carburizing ; cyaniding and nitriding.
- 4. Purpose of aShafts • To access an ore body . • To transport men and material to from underground workings . • For hoisting ore and waste from underground. • Storage of nuclear waste Shaft Cross Sections 1. Rectangular Shafts Most shafts that were constructed in the 1900’s were of a rectangular cross- section because of the shape of the pieces of equipment that were taken down the shaft i.e. cages, skips, and counterweights were all square or rectangular in nature and so it made a lot of sense to sink or mine rectangular shafts. Breaking a square / rectangular shutter was however problematic and this slowed down the rate of sinking.
- 5. 2 Circular Shafts Almostall the hard rock mines now have circular shafts because the cross section provides good geometry for airflow and good rock support characteristics. The circular shutter is ease to move when doing concurrent lining resulting in faster work progress during sinking operations. This is an important aspect when it comes to the cash flow of the project. 3 Elliptical Shafts Elliptical shafts were designed as an alternative to large circular shafts by simply adding half moons along the main axis. This had the effect of reducing the circular excavation and therefore the cost of sinking the shaft.
- 6. • Identify possiblemining layouts • Define standard mining block (stope or panel size) per layout • Calculate steady state conditions per level • Define steady state inputs/outputs requirements per level • Determine minimum access dimensions to cater for equipment and ventilation • Calculate development requirements to get to steady state • Simulate full level production from start of block to ore body extremity • Determine the maximum number of levels that will operate simultaneously Determining the rate of mining can be as follows:
- 7. 1 Criteria forchoosing a Vertical Shaft A vertical shaft should be chosen under the following conditions: • Ore body should be steep dipping • Ideal for deep ore bodies • Provides quick access to ore body • Most economic hoisting method for depths exceeding 500m • Quicker return on capital investment 2 Criteria for choosing a Decline or Inclined Shaft A decline or inclined shaft should be considered under the scenarios: • Flat dipping ore body • Shallow ore bodies • Require high throughput • Require low initial capital costs • Want to avoid some of the environmental concerns (headgear)
- 8. Choosing the RightShaft The size or dimensions of each shaft will differ according to the intended duty for each unit. There are three types, namely: vertical, decline and inclined shafts. a) Narrow tabular deposits (steep & flat dipping – gold, platinum, etc) b) Wide tabular deposits (coal, potash) c) Massive deposits (copper, nickel, iron ore)
- 9. Different types ofshafts Shaft type Diameters (m) Depths (m) Mining ventilation 1-6 50-1500 Mining ore passes 3-7 50-1500 Mining access shafts 5-10 50-1500 Water treatment shafts 1-3 20-100 Tunnel access shaft 5-20 10-50
- 11. Objectives Introduction Definition Shaft collar Shaft sinkingmethods Down-the-hole shaft sinking method Wood/steel piling Open caisson Cementing process Freezing process Types of shafts
- 12. Introduction shaft sinking, excavationfrom the surface of an opening in the earth. Shafts, which are generally vertical, are usually distinguished from tunnels, which are horizontal. Little difficulty is experienced in shaft sinking through solid rock, which contains little water. Shafts sunk in loose water-bearing soils and lined with cast iron or with concrete masonry 1 to 2 ft (30-61 cm) thick, built in sections as the work advances. Shaft sinking through rock is generally accomplished by blasting. Diameter and depth depends upon the type of the shaft Shafts are usually circular or rectangular.
- 13. Definition Shaft: A verticalor inclined tunnel from surface for the conveyance of men, materials, hoisting ore, pumping water and providing ventilation. Sinking: The work in excavating a shaft. Shaft sinking: It may be described as an excavation of vertical or inclined tunnel from surface for conveyance of men, materials, ventilation, pumping water, in addition to hoisting ore and waste rock. It is also called Shaft Construction or Shaft Mining.
- 14. Shaft collar On thesurface of an underground mine, a collar is required for a shaft or raise entry, Collars are also required For ventilation shafts, service shafts, and for all raises that reach surface. collars are normally lined with concrete Methods of shaft sinkingThere are different methods of shaft sinking/construction. Actually three possible methods allowing a shaft to me sunk through highly weathered over burden on the basis of Excavation and Wall support. These are; Down-the-hole Shaft sinking Methods Remote Shaft sinking Methods Raiseboring Method
- 15. Down-the-hole-Shaft sinking method 1. Rockbolting & meshing 2. cast-in-place lining 3. pre-cast lining 1. Drilling & blasting 2. shaft-boring mucking 3. V-mole with pilot hole
- 16. Excavation method Drilling &blasting: A shaft is constructed by drilling holes and filling them with explosives. Using this method, drilling and blasting can sink around 5-10 metres in one blast. This is very labour-intensive, unsafe and has high running costs. The most viable alternative for shafts up to 100m in length.
- 17. Mucking: The operation ofloading broken rock by hand or machine, usually in shafts tunnels. Note: Muck, any useless material produced in mining. mucking out cuttings from the bottom of the shaft. Usually this would require some skip-hoisting, bucket-hoisting or clam- grab equipment.
- 19. V-mole with pilothole The V-mole is an improvement on the concept of the shaft boring machine. Before boring, a pilot-hole is drilled, to assist in both cuttings removal and guiding the machine along the correct path. The V-mole uses grippers to hold on to the side of the shaft . The V-mole is a costly machine not suited for drilling short shafts.
- 20. Wall supporting methods Rockbolting and meshing A wire mesh is fastened to the walls with evenly spaced rock bolts. Rock bolting is a commonly used, cheap method. The rock-bolts increase normal stresses on joints so that shear failure along joints becomes more difficult. Often rock bolts and mesh are used as a basis for shotcreting. Water in-flow during shotcreting severely reduces the quality of shotcrete.
- 22. Cast-in-place lining It ispossible to cast concrete rings as the shaft sink progresses. This method provides a smooth, watertight and permanent lining for the shaft. The casing can be reinforced to cope with horizontal stresses (i.e. ring- shaped reinforcement) making the casing elements more economical.
- 24. Pre-cast lining segments Insands, mudstone and sandstone, steel, pre-stressed concrete or composite liners with a smaller diameter (i.e. up to the 4.5 dia: )than the shaft are lowered after drilling out the hole. Concrete can then be poured behind the walls to create the lining.
- 25. Shaft sinking methods a)Wood/Steel Piling The first set of piles, forming a circle around the shaft site is started at the surface. As the piles are driven down, the ground is excavated, and a circular crib is put in every few feet. In this way the shaft is sunk in a series of short wooden cylinders. b) Open Caisson In this method the shaft is started by digging a shallow excavation and placing a cutting shoe on the bottom of the pit. The ground inside and just under the shoe is excavated and the lining is built up as the shoe sinks.
- 26. c) Cementation Process Cavitiesand fissures are filled with quick-setting cement under high pressure then allowed to set. Cement pumps are designed for pressure as high as 5000 lb/sqin. d) Freezing Process This method was first used in 1883. The wet round is artificially frozen and then blasted and excavated as though it were solid rock. From 20 50 holes are drilled on the circumference of a circle. Circulating pipes placed in the holes and a calcium or magnesium chloride solution is pumped through the pipes to freeze the ground.
- 27. CONCLUSION • Shafts fora newly founded ore body or indeed existing ore reserves. • The methodology is cannot be avoid the optimization process to come up with best economic option. • Shaft must have adequate torsional strength to transmit torque and not be over stressed. • Shafts are mounted in bearings and transmit power through devices such as gears, pulleys, cams and clutches. • Shaft must sustain a combination of bending and torsional loads
- 28. REFERENCE 1. J.E Shigleyand C.R Mischke , Mechanical Engineering Design , McGraw Hill Publication, 5th Edition. 1989. 2. M.F Spotts, Design of Machine Elements, Prentice Hall India Pvt. Limited, 6th Edition, 1991. 3. Khurmi, R.S. and Gupta J.K., Text book on Machine Design, Eurasia Publishing House, New Delhi. 4. Sharma, C.S. and Purohit Kamalesh, Design of Machine Elements, Prentice Hall of India, New Delhi, 2003.