Chapter 3 Mine operation 3.1 Drilling 3.2 Blasting 3.3 Overburden Removal 3.4 Loading 3.5 Haulage 3.6 Reclamation 3.7 Water and Air Management
3.1.1 Drilling Principles
3.1.2 Drilling application
Chapter 3 Mine Operation 3.1.1 Drilling principles 1. Introduction In virtually all forms of mining, rock is broken through drilling and blasting. Except in dimension stone quarrying, drilling and blasting are required in most surface mining. Only the weakest rock, if loosely consolidated or weathered, can be broken without explosives, using mechanical excavators (ripper, wheel excavators, shovels etc.) or occasionally a more novel device, such as a hydraulic jet.
In the mining cycle, drilling performed for the placement of explosives is termed production drilling. Drilling is also used in surface mining for purposes other than providing blast-holes. There are minor applications of rock penetration in surface mining other than drilling. In quarrying, dimension stone is freed by cutting, channeling, or sawing.
Usually mechanical means or sometimes a thermal jet is employed to produced a cut , outlining the desired size and shape of stone block. 2. Classification of methods A classification of drilling methods can be made on several bases. These include size of hole, method of mounting and type of power. The scheme that seems the most logical to employ is based on the form of rock attack or mode of energy application leading to penetration.
(1) Mechanical attack The application of mechanical energy to rock can be performed basically in only one of two ways: by percussive or rotary action. Combining the two results in hybrid methods termed roller-bit rotary and rotary-percussion drilling.
The mechanical category, of course, encompasses by far the majority (probably 98%) of rock penetration applications today. In surface mining, roller-bit rotaries and large percussion drills are the machines in widest current use, with rotaries heavily favored.
(2) Thermal attack The only thermal method having practical application today is flame attack with the jet pierce(刺穿). It penetrates the rock by spalling (削，割) ，an action associated with hard rocks of high free-silica content. Because of its ready capability of forming various shapes of openings, oxygen or air jet burners are used not only to produce blast holes but to chamber(禁闭) them as well and to cut dimension stone. Jet piercing of blast holes, however, has decreased in popularity in recent years as mechanical drills have improved in versatility and penetrability.
(3) Fluid attack While disintegration(分离) of rock by fluid injection is an attractive concept, the end result is more likely fragmentation than penetration. To produce a directed hole with pressurized fluid from an external source, jet action or erosion appears to be more feasible, but commercial application to date is limited.
Hydraulic monitors(水枪) have been used for over a century to mine placer(砂积矿床) deposits and to strip frozen overburden, and more recently, highpressure hydraulic jets have been applied successfully to the mining of coal, and other consolidated materials of relatively low strength.
Hydraulic and mechanical attack mechanisms assist and complement one another. For large holes, the hydraulic jet alone may be competitive with drilling.
(4)Sonic attack振动 Sometimes referred to as vibratory drilling, this method as presently conceived is a form of ultrahigh-frequency percussion.
Attractive but not presently commercial, actuation of sonic devices by hydraulic, electric, or pneumatic means is possible.
(5) Chemical attack Chemical reaction, because of the time element, may be more attractive as an accessory rather than a primary means of penetration. The use of explosives is a distinct possibility, however, and several alternative systems are under investigation. Additives to the drilling fluid, termed softeners, have shown some improvement in penetration rate in conventional drilling.
(6) Other methods of attack While some attempts to employ other forms of energy (electrical, light, or nuclear) have been made in experimental or hypothetical category at present.
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3.1.2 Drilling application 1. Percussion drills Percussion drills generally plays a minor role as compared with rotary machines in surface mining operations. Their application is limited to production drilling for small mines, second drilling, development work and wall control blasting控制爆破. There are two main types of drill mounting. The smaller machines utilize drifter-type(架式钻机) drills placed on self-propelled mountings designed to tow 拖the required air compressor. Typical hole sizes are in the 63 to 150mm range (Fig. 1).
The larger machines are crawler-mounted and selfcontained (Fig. 2). Drill towers 钻架permit single pass drilling 单根钻 杆from 7.6 to 15.2 m with hole sizes in the range of 120 to 229mm in diameter. These lager machines are almost exclusively专门地 operated using down-the-hole hammers潜孔钻头.
For many years these machines were exclusively operated using pneumatic气动hammers. ( pneumatic leg drill 气腿式钻机） Recently hydraulic machines(液压式) have been used in the smaller size range. The higher capital cost of these hydraulic drills is offset抵消 by lower operating costs and increased productivity compared with pneumatic machines.
Another aspect that is becoming increasingly more important is the reduced noise produced by the hydraulic drills.
(1) Percussion drill productivity Fig. 3 presents drill penetration rate plotted against hole diameter for percussive drills operating at low air pressures of up to 0.7Mpa, drilling in materials of two different compressive strengths. It will be observed that penetration rate decreases with both increasing hole size and increasing rock strength.
As the piston area and stroke length are fairly inflexible for a given hole size, one main thrust to help improve percussion drill productivity has been to improve the drill penetration rate by increasing the hammer operating pressure. A typical increase in penetration rate experienced when changing from 0.7Mpa to 1.7Mpa would be of the order of 200% with an approximate doubling in the actual hole production rate.
Some attempts have also been made to improve drill penetration rate using high frequency blow. However it has been found difficult, especially at the higher air pressures. The other option is to use hydraulic machines to improve the energy available at the drill bit. Table 1 presents a detailed test comparison between one hydraulic drill and eight pneumatic machines drilling a fine-grained, dense hornfels (角页岩) having a compressive strength of the order of 200Mpa.
The penetration rate for the hydraulic drill is shown to be from 20 to 100% higher than the pneumatic machines.
(1) Percussion drill costs Fig. 4 presents cost vs. blast-hole size for percussive drills operating up to 0.7Mpa air pressure in the same materials. the costs are dependent on both the blast-hole size and the strength of the rock.
Fig. 5 compares the costs for two sizes of hammer drill with a medium-sized rotary machine. This comparison is made for hammer drills operating with 0.7Mpa air pressure.
The high cost for hammer drilling is partly a result of lower penetration rates obtained as compared with rotary machines. The penetration rate of rotary machines is about 15m/hr, while the rate of hammer drilling is about 10m/hr. (Fig.6).
While an increase in operating air pressure has greatly improved blast-hole penetration rates, the drilling cost improvements have been less impressive because of higher maintenance costs, lower machine availabilities, etc. The results is that high pressure 178mm hammer drilling cost is approximately 100% higher than 250mm rotary drill per unit volume of material blasted.
A comparison between pneumatic and hydraulic surface mounted drill costs follows: Pneumatic hydraulic Investment cost 1.0 1.27 Energy cost 1.0 0.24 Drill steel cost 1.0 0.86 Overall operating cost 1.0 0.78 A complete operating cost comparison between the two drill types is presented in Table 2.
2. Jet-piercing drills（热力钻机） The jet-piercing process relies upon a characteristic of rock known as spallability. The rock is broken down, or spalled, as a result of differential expansion of the rock crystals by thermally induced stresses. The jet-piercing drill essentially consists of a burner fixed to a blowpipe that produces a high temperature flame (of the order of 43000F) by burning fuel oil in oxygen.
The drills have a typical drilling depth capacity of 15.2m. In addition to fuel oil and oxygen, water is also used to cool the burner and, in the form of steam, it helps eject the spalled rock cuttings from the blasthole. Hole diameters range from a minimum of approximately 229 mm up to 457 mm.
At present very few jet-piercer drills are in operation. One of the main problems with the system has been the high cost of oxygen and fuel oil which has helped to make the drill uneconomic.
俄罗斯、乌克兰大型露天铁矿应用火力扩孔技术。 CTP-600-20型火钻，装有两台32m3/min空压机、能扩孔至 600mm甚至更大直径,它 是目前独联体最大型的火力扩孔 钻机。 This paper presents the technique and equipments of the jet piercing and chamhering and it's application case in the largescale open-pit iron mines of Russia and Ukraine in the recent years. At present, Model CTP-600-20 jet piercer with chambering diameter of 600 mm and more is a largest one in Commonwealth of Independent States, which equipped with two compressors with capacity of 32 m3/min each.
3.Rotary drills In rotary drilling, the drill bit attacks the rock with energy supplied to it by a rotating drill stem. The drill stem is rotated while a thrust is applied to it by a pull-down mechanism using up to 65% of the weight of the machine, forcing the bit into the rock. The drill bit breaks and removes the rock by either a ploughing-scraping action in soft rock, or a crushing-chipping action in hard rock, or by a combination of the two.
Compressed air is supplied to the bit via the drill stem. The air both cools the bit and provides a medium for flushing吹 the cuttings from the hole. Water may be used in addition to the compressed air to suppress抑制，降尘 the effects of dust, however, this is normally found to have a detrimental effects on bit wear.
Blast hole sizes produced by rotary machines vary in the range of 100 to 445 mm diameter with the most common sizes being 200, 250, 311 and 381mm. These drills usually operate in the vertical position ， although many types can drill up to 25 or 300off the vertical. Drills are manufactured that can drill horizontal holes used in overburden stripping where hard bands of material are located low in the high-wall face.
(1) Rotary drill penetration rate One of the most important factors in drilling is how fast can drill hole be produced while the machine is actually drilling. This factor almost entirely influences productivity and has a strong influence on unit costs of the hole. The penetration rate of the rotary drill is about 15m/hr for the size of 250mm hole.
(2) Rotary drill rotation speed The rotary drive motor turns the drill tool string thus turning the drill bit at the bottom of the hole. As the rotary speed increases, so does the number of contacts and the penetration rate. The limit to rotary speed is hot bearings in the bit。 Current rotary speeds ranges from 60 to 90 rpm for hard materials with greater speeds for softer rocks
(3)Rotary drill pull-down weight轴压力 A portion of the machine weight is applied through the pull-down motor via the pull-down chain or chains, rotary head and drill stems to the drill bit. Fig 10 illustrates recommended bit loadings for different bit sizes. As the bit diameter increases, the bearing size increases thus allowing an increase in the tolerable load. Overloading the bit results in severe loss of bit life as illustrated in Fig. 11.
(4) Rotary drill bits Tri-cone rotary drill bit has evolved from the drag bit and two cone bits.
Fig. 12 illustrates the various components of a mill tooth bit. Mill, or steel tooth bits are used for soft rock with the cutoff being a medium-strength limestone. Fig. 13 and 14 illustrate the effect of rock strength on bit life for various bit sizes. The average footage per bit is about 800 for rock with compressive strength of 80MPa.
The larger bit sizes, incorporating larger bearings, etc. can be expected to give higher footages per bit. This has not always proved the case. Table 3 presents footages (400~600m)currently being experienced by a large Canadian iron ore operation. These footages are averages for the highest-grade tungsten carbide(钨碳合金钢) bit of different manufacture, the ore having variable compressive strengths approximately 204Mpa.
(5) Rotary drill air requirements Air is used to bail（解脱）the drill cutting from the hole as well as cool the bit bearings and, when used, roller stabilizer bearings. The air volume is the primary requirement for bailing cuttings from the hole. Air velocity up the hole is dependent on the air volume per minute as well as the hole annulus(环 带). The formula for calculating the air velocity can refers to the 《采矿学》 on page 403~411 .
The velocity of the drill cuttings in this air is dependent on the chip size, density, and shape At air velocity above this balancing value, the chip begins to move. A bailing velocity of 1800mpm is usually adequate to bail13mm chips.
Choosing the higher velocity has the following advantages: 1) Will bail larger chips; 2) Tend to give higher bit life 3) Will help cater for迎合hole cavities, etc. 4) May give higher penetration rates and possibly lower cost per ft 5) Reduce the volume of cuttings in the hole for a given penetration rate. But they will give increased stabilizer and pipe wear.
(6) Cold weather operation Drills to be used in cold climatic conditions should be purchased with a cold weather package. (7) Single pass drilling
Many new mining ventures selected bench height and drill equipment to utilize single pass drilling. Advantages of single pass are:
1) Eliminates adding stems 2) Reduces associated thread damage(丝扣损坏) 3) Reduces machine downtime for rod changing equipment and tool racks 4) Facilitates the cleaning of boreholes 5) Permits a continuous air flow through the bit at all times. This is especially important in wet holes as it eliminates the possibility of siphoning(虹吸作用)water and cuttings up into the bit.
Disadvantages: 1) High masts make the drill more unstable, back brace become almost mandatory, 2) Extra care needs to be taken when moving the drill over medium or long moves, 3) Pull-down chains become long and may require special attention.
For operations choosing to reduce bench height in order to attain single pass drilling, the following other benefits may also be experienced: 1) Multi-row blasts become easier to blast, 2) Drill cuttings volume is reduced (especially for the larger holes), 3) Contour areas are easier to drill and blast, 4) Ore grading is easier.
(8) Rotary drill productivity and costs Fig. 16 presents typical rotary drill productivity for different hole sizes drilling different material types. The larger the sizes of the hole, the greater the productivity of the rotary drill.
(9) Drilling trends Rotary drills have increased their dominance of blast-hole production in open pit mining. The trend has been to larger sturdier drills, to yield higher mechanical availability and operating performance. This increased availability has been achieved through improvement of crawler track frames, masts, propel chain, pull-down 向下压mechanisms, rotary head drives complete with automatic lubrication and greasing, on the new models of machine.
Fig 19 presents the drill penetration rate vs. hole size in a hard massive low-grade iron ore, and Fig. 20 shows the actual productivity obtained at one Canadian mine in going from 250 to 311 mm to 381mm diameter blast hole on the same size of drill. This represents a productivity increase of 73%.
Fig. 21 shows the total direct drilling and blasting costs, which were reduced from 32 to 27.5 c/ton. Machine capital cost savings also accrue(增加) due to the productivity increase.
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Table 2 pneumatic vs. hydraulic drill operating cost breakdown Labor Steels
13.5 10.1
12.7 11.2
Drill bits Compressed air/grease hydraulics
15.4 18.4
19.7 1.1
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3.3
Replacement/mainten 13.5 ance depreciation 29.1 total 100
17.3 34.2 100
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1号风 2号风 3号风 4号风 5号风 6号风 液压潜 动钻机 动钻机 动钻机 动钻机 动钻机 动钻机 孔钻机 20 ft/min
26 ft/min
18 ft/min
21 ft/min
26 ft/min
15 ft/min
31 ft/min
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