采矿专业毕业设计外文翻译Word文档下载推荐.docx

1、1 FRAGMENTATIONFragmentation is the breaking of coal, ore,or rock by blasting so that the bulk of the material is small enough to load, handle and transport.Fragmentation would be at its best when the debris is not smaller than necessary for handling and not so large as to require hand breaking or s

2、econdary blasting .Energy must be supplied to rock by direct or indirect means to fragment that rock and the type of loading system.Fragmentation energy is consumed by the main mechanisms: （1） creation of new surface area （fracture energy）, （2）friction （plasticity） and （3）elastic wave enegy dispersi

3、on.The loading method determines the relative proportions and the amount of energy consumed in fragmenting a given rock type. Unonfined tensile failure consumes the least energy with an increasing a,mount of energy required as the rock is more highly confined within a compressive stress field during

4、 fragmentation The way energy is applied by tools to cause rock or mineral fragmentation is important in determining fragmentation efficiency. To best design fragmentation tools and optimize fragmentation systems it would be desirable to know how rock properties influence breakage.The strength of ro

5、ck is influenced by the environmental conditions imposed on the rock.Those of most importance in rock are （1）confining pressure ,（2）pore fluid pressure, （3）temperature and （4）rate of load application .Increase in confining pressure, as with increasing depth beneath th earths surface or under the act

6、ion of a fragmentation tool, causes an increase in rock strength .Apparent rock strength decreases as porc fluid pressure increases, since it decreases the effect of confining pressure. Although chemical effects of pore fluids influence rock strength, they generally are small compared to the confini

7、ng pressure effect, except for a small minority of rock types .Increase in rock temperature causes a decrease in rock strength.This effect is very small because of the small ambient temperature changes found during mining. An increase in rate of load application causes an apparent increase in rock s

8、trength.Rock exhibits directional properties that in fluence the way it breaks. These are embodied in the concept of rock fabric ,which connotes the structure or configuration of the aggregate components as well as the physical or mechanical property manifestations. Rock fabric ont only relates to t

9、he preferred orientation of mineral constituents and their planes of weakness, but also to the configuration of discontinuities, microcracks and pores.Joints and bedding planes have great influence on fragmentation at field scale.Physical properties of rock （density,indentation,hardness,abrasivehard

10、ness and porosity ,）are frequently used in conjunction with mechanical properties to develop better empirical esti mations of rock fragmentation.2 BLASTHOLE CHARGING METHODSDrill hole charging can be carried out in different ways depending on whether the explosive used is in cartridges or in the for

11、m of loose material. The oldest charging method implies the use of a tamping rod and this system is still used to a very great extent .During the last 20years, compressed air chargers have been used and these machines provide both good capacity and also an improved level of charge concentration so t

12、hat the drill holes are utilized to a higher degree. During the last few years semi-automatic chargers have been taken into use, primarily in underground work. Compressed air chargers for blasting powder in the form of loose material have also come into use on a large scale. As far as slurry blastin

13、g is concerned, special pumping methods have been developed through which charging capacity in the case of large diameter drill holes is practically good.A tamping rod must be made of wood or plastic. It must not be too thick in relation to the drill hole diameter since this can crush and damage fus

14、e or electric detonator cables during charging work. If a good degree of packing is to be obtained during charging with a tamping rod then only one cartridge at a time should be charged and tamped. The detonator must be correctly fed into the drill hole during charging work.Compressed air chargers h

15、ave been in use is Sweden for about 20 years. The first type consisted of aluminum pipes connected together and the cartridges were blown into the hole with an air pressure of 42 pounds per square inch .since that time the charging tube has been replaced by anti-static treated plastic hose of a spec

16、ial design. A charger includes a foot-operated valve, reduction vavle with air hose, breech, connecting tube and charging hose.The semi-automatic charger permits the continuous insertion of explosive cartridge at the same rate as they are charged in the hole by the hose .Instead of a valve being use

17、d ,the cartridges pass through an air lock between two flaps. The air pressure in the charging hose is retained while cartridges are pressure in the charging hose is retained while cartridges are beins inserted .The semi-automatic charger permits considerably higher charging capacity than the normal

18、 type of charger.Explosives in the form of the form of loose material, usually ammonium nitrate explosives（ANFO）, require special chargers. Two types can be differentiated: pressrure vessel machines and ejector units. Pressure vessel machines are particularly suitable for crystalline An explosives w

19、ith good charging capacity. Ejector units are operate by an ejector sucking up explosive from a container through a charging hose. The explosive is then blown through the charging hose into the drill hole .There are, also combined pressure ejector machines. The charging hose used for ANFO charging o

20、perations must conduct electricity and have a resistance of at least 1K/m and max.30K/M.Nitro Nobel has developed a special pumping procedure which consists of a tanker vehicle which is used to pump explosive directly the drill holes. The charging capacity is very high in the case of large diameter

21、drill holes.3 CONTROLLED BLASTING TECHNIQUTES Controlled blasting is used to reduce overbreak and minimize fracturing of the rock at the boundary of an excavation. The four basic controlled blasting techniques are: line drilling, presplitting, cushion blasting and smooth blasting.Line drilling, the

22、earliest controlled blasting technique, involves drilling a row of closely spaced holes along the final excavation line, providing a plane of weakness to which to break. Line drill holes, 2or 4 diameters apart and contain no explosive. The blastholes adjacent to the line drillholes normally are load

23、ed lighter and are on closer spacing than the other blastholes. The maximum depth for line drilling is about 30 ft .Line drilling involves no blasting in the final row of holes, and thus minimizes damage to the final wall.Presplitting, sometimes called preshearing ,involves a single row of boreholes

24、 ,usually 2 to 4 in .in diameter ,drilled along the final excavation at a spacing of 6 to 12 borehole diameters .Dynamite cartridges 1to 1.5 in . in size on 1 to 2 ft .centers usually are string-loadde on detonating cord ,although special small-diameter cartridges with special couplers are available

25、 for total column loading .In unconsolidated formations ,closer spacings with lighter powder loads are required .The bottom 2 to 3 ft .of borehole usually is loaded somewhat heavier than the remainder .Stemming between and around the individual charges is optional .The top 2 to 3 ft . of borehole is

26、 not loaded ,but is stemmed. The depth that can bu presplit is limited by hole alignment ,with 50 ft .being about maximum .The presplit holes are fired before before the adjacent primary holes to provide a fracture plane to which the primary blast can break .In presplitting it is difficult to determ

27、ine the results until the adjacent primary blast is shot .For this reason ,presplitting too far in advance is not recommended .Presplitting seldom is done underground.Cushion blasting involves drilling a row of 2 to 6-in .diameter boreholes along the final excavation line ,loading with a light well-

28、distributed charge ,completely stemmed and firing after the main excavation is removed rather than before ,as in presplitting. The burden on the holes is slightly larger than the spacing .Wedges may be used to abut the charges to the excavation side of the borehole and minimize damage to the final w

29、all .Eeplosive loading is similar to that in presplitting .Cushion blasting has been done to depths near 100 ft .in a single lift with the larger-diameter boreholes because alignment is more easily retained .Cushion blasting seldom is done underground.Smooth blasting is the underground counterpart o

30、f cushion blasting .At the perimeter of the tunnel or drift ,closely spaced holes with a burden-to-spacing ratio near 1.5:1 are loaded with light well-distributed charges .Smooth blasting differs from cushion blasting in that （1） except at the collar ,the charges are not stemmed and （2） the perimete

31、r holes are fired on the last delay in the same round as the primary blast .Total column loading is most common ,although spacers may be used .The holes are stemmed to prevent the charges from being pulled out by the detonation of the previous delayed holes .Smooth blasting reduces overbreak in a dr

32、ift and also provides a more competent back requiring less support .It involves more perimeter holes than does normal blasting.Combinations of controlled blasting techniques are used .In unconsolidated rock,line drilling sometimes is desirable between presplit or cushion boreholes . Corners sometimes are presplit when cushion blasting is used.4 TUNNEL BLASTINGThe most common methed of driving a mining tunnel is a cyclic operation in three sequences:（1） Drilling shot holes ;charging them with explosives and blasting.（2） Removing the resulting muck pile.（3） Inserting the tun