US 3460766 A
Description (OCR text may contain errors)
Aug. 12, 1969 E. SARAPUU 3,460,766
ROCK BREAKING METHOD AND APPARATUS Filed June 13, 1966 2 Sheets-Sheet 1 ATT NE'Ys I NVENTOR 12, 1969 I E. SARAPUU 3,460,766
ROCK BREAKING METHOD AND APPARATUS I Filed June 13, 1966 2 Sheets-Sheet 2 yog'g gah' mmmu m/ 1/5! 63 6/ 74 INVENTOR .9. Em'c/v 54/ 0 000 #5504) ATTORNEYS United States Patent 3,460,766 ROCK BREAKING METHOD AND APPARATUS Erich Sarapuu, Kansas City, Mo., assignor, by mesne assignments, to Small Business Administration, Kansas City, Mo., an independent agency of the United States Government Filed June 13, 1966, Ser. No. 556,948 Int. Cl. B02c 19/00, 23/00 US. Cl. 241-1 17 Claims This invention relates to methods of and apparatus for fracturing rock by the use of electrical means.
In recent years, several new techniques of rock breaking have been under development and testing. Therefore, one might expect that fracturing of rock by blasting and mechanical forces would be supplemented, more extensively in the future, by new rock-breaking principles like:
( 1) jet piercing and flame cutting;
(2) electromagnetic fracturing;
(3) electrical disintegrating drilling;
(4) breaking of rock by high frequency electric energy and current impulses;
(5) microwave heating;
(6) plasma jet heating;
(7) sonic drilling;
(8) impulse jet monitor;
(9) electrohydraulic crushing;
(10) drilling by explosives Some of these methods are already in use and the others are undergoing further testing.
Taconite is a very hard silicious rock containing fine quartz (chert), hydrous iron silicates, greenlite, minnesotait, stilpnomelane, magnetic and nonmagnetic iron oxides. These minerals are distributed throughout the matrix and are sometimes concentrated in irregular roughly parallel bands in the mass of ore. The electric conductivity of taconite is due primarily to the magnetite minerals and their distribution pattern in the matrix.
The fracturing of taconite by means of electrical conduction and electrically generated thermal stresses has been demonstrated by my developments. Energy transfer in the process of fracturing of rock may be accomplished by multi-contact electrodes at comparatively low voltages using 60-cycle alternating current or direct current. I have demonstrated that large scale use of electrical fracturing technique is feasible with ores such as taconite. The fracturing of taconite and other ores described in this specification is based on the electrical conductivity of rocks and iron ore and the transfer of electrical power into a rock or ore by means of multi-contact electrodes.
The heating of rock by electrical current is mentioned in the literature before. However, the high resistivity of rock has caused many research people to generate induced conductivity of rock in the form of a fused zone between electrodes. This has been accomplished by means of high frequency current or at very high potential (dielectric breakdown). My new study and resulting findings have been based on the natural conductivity of ores, either metallic or electrolytic, or both.
It is known from petrographic studies of metallic ores, especially those related to the treatment of taconite, that the mineralized zones are dispersed in the silicious matrix and very often these zones are not connected in a manner which is suitable to form a path of electric conductivity between mineralized zones. Secondly, the electrical contact resistance of a point electrode is very high. Therefore, when point electrodes are used, the latter two factors cause difiiculties in the transfer of electrical power into the rock.
In order to analyze the transfer of electrical energy into a rock or taconite, it is valuable or necessary to "Ice evaluate variables affecting the total electrical resistance of the circuit. Much of this electrical resistance is in the form of contact resistance at the electrodes. This resistance can be described in the following mathematical terms:
(1) Contact resistance of a point electrod (half sphere) r=radius of point electrode S=resistivity (2) Contact resistance of plate electrode 5' l Pi r 4=radius of plate These theoretical considerations show that the contact resistance can be reduced by increasing the diameter of electrodes and by decreasing the resistivity of the rock or taconite.
If one were to visualize a hypothetical case presented involving the application of two spaced point electrodes to a three-dimensional body placed against two spaced points of a silicic matrix or rock, the two electrodes connected by an AC or DC power circuit, the contact resistance of this arrangement would be very high. In changing the structure of the circuit to involve a pair of disc electrodes placed against two flat surfaces of a three-dimensional rock or taconite body, a marked lowering of contact resistance would be obtained by increasing the diameter of the electrodes. Such electrodes would cover more surface area of the rock and probably or possibly connect electrically a much larger number of conductive zones. Such reduction of resistance between the electrodes and the rock, the iron ore therein, or mineralized zones therein, might make it possible to fracture the rock at a relatively low voltage.
Unfortunately, in attempts to fracture or break up rock bodies of considerable size and mass in place in the earth, quarries, mines or the like, plane or flat conveniently located, contact zones for the use of disc or plate electrodes of regular surface are not readily available. The preparation and provision of such zones is not only impossible in most cases, but would be time consuming, difficult and often hazardous.
An object of the invention is to provide methods of and apparatus for utilizing multi-point electrodes in a process of rock fracturing and breaking.
Another object of the invention is to provide methods of and apparatus which make rock breaking possible utilizing natural electrical conductivity of the rock.
Another object of the invention is to provide suitable multi-point electrodes operative and adapted to connect large numbers of independent mineralized zones in rocks whereby the passage of electrical current between the multi-point electrodes results in volume heating of the rock at relatively low voltage and high amperage.
Another object of the invention is to provide multipoint electrode structures of such type that the areal extent thereof can be freely increased whereby the heating effect of FR): (where I=amperage and Rx=electrical contact resistance) can be made very effective by lowering Rx and increasing I by means of an electrode design.
Another object of the invention is to provide applications of multi-point electrodes in rock fracturing which make the distance effect between electrodes relatively negligible in that the contact resistance involved in the use of the multi-point electrodes remains constant regardless of distance therebetween.
Another object of the invention is to provide a new departure in rock breaking wherein the natural conductivity (electrical) of rock is utilized rather than induced conductivity. Induced conductivity is the process or effects utilized when single point or low surface area electrodes are employed and a conductivity pattern is forced upon the rock by the use of high frequency current or very high voltage. The utilization of natural conductivity, on the other hand, does not require high frequency or relatively higher voltage, particularly as electrode spacing increases, because a relative maximum number of natural conductivity channels and patterns in the rock being fractured are utilized.
Another object of the invention is to provide electrode structures and rock fracturing methods wherein the rock surfaces or surface areas utilized for electrode contact are saturated with potential electrical current input points whereby to effectively minimize the electrical contact resistance when current is applied and thus minimize the voltage requirements of the process and apparatus being used.
Another object of the invention is to provide methods of and apparatus for volume heating of rock rather than limited zone heating from an induced conductivity zone.
Another object of the invention is to provide methods of and apparatus for simultaneously generating many complementary micro and macrofractures in the rock by volume electrical heating therethrough whereby to greatly increase the internal effect of thermal stress patterns and also make the rock much more susceptible to simultaneously or sequentially applied mechanical crushing and grinding effects.
In the application of point electrodes or localized area electrodes to rock masses in the attempts to fracture same, if one is fortunate, one may get a zone of low resistivity or low contact resistance whereby, when current is applied, with high frequency, or high voltage, heat will be transmitted into the rock along a limited current channel. The highest heating at local zones is at the electrodes. This process only serves to fracture the smallest rocks.
Other and further objects of the invention will appear in the course of the following description.
In the drawings, which form a part of the instant specification and are to be read in conjunction therewith, embodiments of the invention are shown and, in the various views, like numerals are employed to indicate like parts.
FIG. 1 is a view showing a large rock mass to be fractured by application of suitable electrical current (AC as shown or DC if desired), same applied to the rock through two multi-point electrodes, here shown in the form of piled chain masses, the latter attached to two electrical power input connections. One connection and electrode chain mass is positioned to the left in the view on the top of the rock, the other to the right underneath the rock.
FIG. la is a detail of the electrical power input connection between the chain masses of FIG. 1 and the electric power lines.
FIG. 2 is a three-quarter view from above of multipoint electrode structures positioned prior to fracturing a rock, said electrodes comprising tWo chain mats, each having an electrical connection to an electrical power circuit, one chain mat positioned on top of the boulder or rock mass, the other positioned thereunder.
FIG. 3 is a view taken along the line 3-3 of FIG. 2 in the direction of the arrows.
FIG. 4 is an end view of a vibrating electrical frame construction adapted to receive large rock masses or boulders, the frames carrying chain mats of the type seen in FIG. 2 whereby to give large area multiple electrode contacts with the boulder.
FIG. 5 is a side view of the apparatus of FIG. 4.
FIG. 6 is a plan view from above of a moving apparatus for handling large rock masses or boulders, same comprising two endless chain electrode mats mounted on powered drive rollers or shafts in such manner as to be movable in the same direction and receive vertically thereupon a rock mass to be carried forwardly thereby.
FIG. 7 is a front view (upwardly in the view of FIG. 6) of the apparatus of FIG. 6 from the boulder discharge end thereof.
FIG. 8 is a three-quarter perspective view from above of a cylindrical housing or tank adapted to receive rock masses therewithin, the tank or cylinder revolving whereby to tumble or move the rock masses about within the vessel and obtain multi-point or large area electrode contact therewith.
FIG. 9 is a view of a continuous conveyor assembly involving multi-point electrodes for continuously handling inputs of large rock masses thereto and breaking same down by application of electrical force through chain mat electrodes above and below into smaller and smaller segments. The view is taken from the side and is schematic with the large rocks moving from the right downwardly to the left with discharge down onto a lower conveyor of the lesser size rock fragments.
In a specific example of the electrical fracturing of taconite, experiments were carried out with a 10 kvA. autotransformer. This unit was equipped with recording voltmeter, ammeter and wattmeter. The sequence of tests was programmed to measure and evaluate the parameters treated in the theoretical discussion of electrical fracturing of taconite. (Point electrodes, plate electrodes, etc.)
The sample of taconite used for the first test was ap proximately 10 cm. by 6 cm. by 5 cm. and weighed 1100 grams. The measurements of contact resistance of point electrodes were made with an ohmmeter. Values of contact resistance on the surface of taconite vary over a wide range; for example, typical values recorded were 300,000 ohms, 8,000 ohms, 5,000 ohms, 200 ohms, 70 ohms, etc.
The same sample was used for electrically generated fracture demonstration. A plate electrode of one inch diameter was utilized in this experiment. The initial contact resistance of the electrode was 15 ohms. There were two prime objectives to be studied. One was to establish the possibility of fracturing taconite by the application of electrical current. Second was to determine the energy requirements and specific surface energy of fracture. The sample under test was coated with temperature-sensitive paint in order to show the isotherms on the surface of the taconite and also obtain some indication of the distribution of current flow in the sample. It was found possible to fracture the taconite by this method.
Data from this test are presented:
The time interval between power cycles was about one minute. The effect of heating was noticeable after the third cycle. The temperature of the sample was about F. at two locations on the surface of the taconite. Such heated locations were visible as dark shaded areas. A second high temperature zone developed. Fractures developed after the fourth application of electrical power. The isotherms at two locations showed maximum temperature of 290 F. and the average surface temperature of the rock reached about 150 F. The total energy requirements of this experiment was 21,960 watt-seconds. There were also micro-fractures developed in the taconite. This was proved by applying a slight compressive force to break up the test sample.
In an experiment on a larger scale, a 70-pound sample of taconite was selected for crushing. Large diameter electrodes (7 inches) were used, which were made of steel chain. The application was almost exactly like that seen in FIG. 1 of the instant specification. The sample was fractured by 0.033 k-wh. of energy input; the taconite separated along major fractures. The rock was dropped from a height of two feet and fractured into many small fragments. Using the principles developed and experiments along the lines described above, fracturing of taconite boulders weighing several hundred pounds has been accomplished.
Referring back to the discussion of point contact electrodes, if steel electrodes are employed, once the current density exceeds 100 amperes per square centimeter into the 100 ampere power range, the said steel electrodes melt. If graphite electrodes are employed, the rock melts without any measurable success in breaking the rock.
Referring back to the taconite boulder fractured with electrodes 7 inches in diameter, the boulder had dimensions of 11 x 9 x 7 inches. The electrodes were made up of one-half inch chain, same coiled and forming a flat and disc-like electrode. Each link may be considered as a point electrode in the system. The flexibility of chain permits individual links to fold over the rock surface contours and make excellent contact with the rock. An even more ideal contact may be achieved in such situations wherein graphite cloth or felts may be positioned on the rock zones desired to be utilized for electrode contacts and the chain or chain mat electrodes of the type utilized in the instant experiments or disc-like large area metal electrode contacts may be applied thereto or thereover.
The use of such large area contact electrodes suffices to put sufiicient power into the rock to break same. It is desirable to move the power into the rock as quickly as possible to avoid the necessity of heating the whole mass. The desired effect is to create a plurality of simultaneous current channels resulting in the creation or growth of a plurality of simultaneously exerted thermal stress lines and channels. Thus there are provided two sets (one at each electrode zone or area) of plural electrode contact points each simultaneously active in transmitting electrical energy through the rock. The process involves the problem of putting energy into rocks through a multiplicity of current flow channels. There results from this a multiplication of distributed thermal stresses. Once there has been created a plurality of simultaneous electrical current flows into the rock from a plurality of electrode contact points, it may be observed that the most varied flow patterns of current passage through the rock or boulder are created, depending upon the mineralized zones therein and paths of least resistivity and greatest conductivity. When the boulder or rock is painted with temperature sensitive paint, numerous surface areas displaced in varied manner from the electrode contact areas or zones will display discoloration, each thus indicating that a current channel has been created which reaches the surface at that particular point. Fracturing of the boulder or rock thereafter along planes of cleavage, same induced to a greater or lesser extent by the heat created by the current passage or the combined effects of mechanical action and heating action of the current, show that the planes, lines, channels and routes of passage of electrical energy through the rock are quite varied. A higher voltage is required for lesser conductive material and larger contact area electrodes.
If a steady flow of electrical current can be maintained in the rock sample and a swift heating process generated deeply into the rock, ultimately the thermal stresses Will break the rock or permit relatively easy breaking thereof by application of additional mechanical forces thereto. The rock may be considered as a prestressed material and the creation of a multitude of heating zones, lines, volumes, planes, etc. which penetrate into the rock effect stress releases inside of the rock volume and physical failures and changes result in breaking of the rock.
In a specific example utilizing a conductive rock (taconite) utilizing electrodes consisting of chain linkages in the manner of FIGS. 1 and 1a, such electrode was used on a specimen of approximately 10 x 8 x 4 inch size. Fractures developed in this sample. The electrical variables during such rock breaking included a time of twelve secconds, a voltage of 114, amperage 72, killowatts 9.0 and impedance 1.6 ohms. Thus it was demonstrated that workable rock breaking mechanism was feasible using 60-cycle AC current. It is additionally feasible to employ DC variable frequency current effects.
Referring to FIGS. 1 and 2, therein is shown a rock mass or boulder 20, to be fractured by application of electrical current thereto. The apparatus for accomplishment of the latter comprises a source of electrical power, which may be a 60-cycle AC source, for example, or any suitable commercial source adapted to furnish the power level required. Locally generated power from conventional power generating equipment of sufficient capacity may be also employed. A DC power source of pulsing or constant character may additionally be employed. The main criterion for the successful application of my technique is the availability of suflicient total power to meet the fracture requirements of the rock mass involved, that is, to sufficiently overcome the contact resistance utilizing the electrodes involved and taking into account the electrical characteristics of the specific boulder. Also, preferably, there is suflicient current flow available with ample voltage to effect multi-channel penetration of the current into the rock in a relatively short time. The latter parameters may vary considerably from rock to rock and sequentially with a given rock, but it is desirable to have sufiicient available power and potential difference that there is a relatively high velocity input of power flow into the rock along any natural conductive channels available, whereby the passage of currents from one electrode mass or zone toanother involves a large number of definite lanes, paths and passages of current flow which are themselves strongly locally heated, rather than a slow, diffused leakage of current into the rock. When the former eifect is created, the thermal stresses and thermal expansions of these paths of current travel result in localized zones of weakness, and fracturing or cleavage thereof, whereby the rock itself may readily fall into numerous pieces or fragments or quickly does so when subjected to relative minimum of applied external mechanical stress, such as striking with a hammer, a swinging impact ball, a bulldozer blade, or the like. Since every rock is unique in its individual gross and microphysical structure, chemical makeup, electrical conductivity, distribution of mineralization, shape, temperature, moisture content, etc., it is impossible to precisely calculate or estimate the exact quantity of power to be required, the contact resistances, the optimum positions for the electrodes, the pattern and variation of the electrical power input variables as the rock heating commences and proceeds, etc.
However, numerous observations have been made. If a very large rock mass is to be fragmented, depending upon the power available, sections or portions thereof which are relatively isolated or more readily available to application of the technique may be fragmented or broken olf first by judicious electrode emplacement. In all cases, the electrodes should preferably be placed on opposite sides of portions of a rock mass rather than closely adjacent one another on the same surface. The rougher the rock surface is or the more irregular, the more care that must be exercised in making sure that a large multiplicity of positive effective electrode contacts are achieved with a relatively large surface area of the rock at each electrode contact zone. By utilizing chain mat of the character of FIGS. 2 and 3, a very good operating contact can be achieved on rocks where relatively fiat surfaces are available, these types of electrodes holding up very well under long use and stress. Where the surface is more greatly irregular, the elongate free chain electrodes of FIGS. 1 and 2 are often preferable as the chain can be draped or hung on or around various parts of the rock and massed in hollows or over protuberances.
Furthermore, in rocks exposed to weathering or having earth or organic covering or partial covering, same should be cleaned off or broken off to provide a good raw contact surface, if possible, say by sledgehammering, pickaxing, jackhammering or the like in order to avoid loss or minimizing of maximal electrode rock surface contact through interposition of insulating or dielectric type materials such as earth, vegetation or the like. Oxidized zones are also not optimal and should be scaled off if possible to give good contact. In quarries, mines or the like, this is generally not a problem. Generally speaking, the amount of current required is roughly proportional to the total mass of the rock involved. However, this may very well not be the case as rock samples of like shape or configuration and almost identical mass may have extraordinarily different mineralization, even in the same bed or strata or available conductivity and one rock may fracture easily and swiftly, the other being considerably more resistant. Additionally, the presence of actual internal physical stressing from some reason, potential fault lining, or the like, throughout individual rocks or strata may have a good deal to do with the ultimate breakage pattern and total current required and how it is drawn from the power source.
At any rate, referring to FIG. 1, in fragmenting or fracturing of a typical boulder, a first mass of chain, preferably steel, with, say, one-half inch diameter steel rod making up the links 21 thereof, is piled or looped in a mass on one side of the rock. The steel electrode, comprising merely a steel, highly conductive rod 22 with an insulating hand grip 23 for handling, and connected to a typical insulated electric cable or line 24 is linked the power source, here indicated as a typical commercial AC generator or power line from a commercial source 25. The other side of the circuit is provided by insulated cable or line 26 passing through insulated hand grip 27 to steel electrode or rod 28, same welded or connected to another chain mass 29. The latter is positioned under the rock, in this view, thus on the other side of the rock from chain mass 21. Good, indeed hard, wedging, physical contact between the chain masses 21 and the rock is most desirable and necessary. Thus, a second rock might be piled on top of chain mass 21 and rocks wedged under the second chain mass 29 to assure close physical contact.
If desired, and often in most cases most optimal, quantities of graphite cloth or felt or other suitable highly conductive means, softly flexible and compactible, may be placed on the rock surfaces to be contacted by the electrodes before same are applied. Such, particularly when the chain masses are piled thereon or wedged thereagainst, may yet give even more intimate electrical current carrying contact between the broad conductivity zones and the'power current. This may be particularly so if the rock is furrowed, grooved or pitted whereby even the chain links do not provide the desired maximum number of operative electrical contacts. It must be kept in mind that only a few fractions of an inch in extent may represent the only available highly conductive and low contact resistance areas in a large zone several square feet in extent. Thus, small spots on the surface of a rock immediately next to one another may drastically differ in conductivity and contact point resistance. This is demonstrated concretely from the impedance and resistivity data which I have collected, the contact resistivity of point electrodes on a specimen taconite being given, supra.
Once the desired electrode positioning and placing is achieved, power is fed to the rock at the maximum rate acceptable and effects observed. If the rock does not take the current at the rate desired or no immediate discernable heating, fragmenting and fracturing effects are discerned or in a very short period of time, one or both of the electrodes may be shifted, graphite felt applied, the rock surface abraded or scored, etc., and the current reapplied until the desired result is obtained.
FIG. 1a shows a detail of the connection of the electrode 28 into the chain mass 29, namely, by welding the steel rod 28 as at 30 to one of the chain links 29a. Such chain link may be at any position along the chain, preferably substantially centrally thereof. A typical length of chain utilized here would be some 12 to 20 feet in length. More or less may be employed, depending upon the size of the rocks, the total current available, etc.
FIGS. 2 and 3 show the use of a chain mat in fracturing boulders wherein a plurality of elongate chain segments 31-36, etc., each independent of the other, but each having a series of connected links, preferably the same number, are cross-connected by elongate metal rods 37 whereby to form a rigid, yet flexible structure. The rods 37 may be replaced by flexible steel cable segments which will give yet greater dimensional flexibility transversely of the mat. Likewise, smaller diameter chains could be employed. The object is to provide a mattress, blanket or mat of electrically conductive material, preferably steel, of great durability and strength, convenient handling characteristics, providing a very large number of potential, concrete, contact points with a rock surface. The chain links are admirable for this purpose. An interwoven mat of cables has proven fairly suitable, but it is occasionally desirable to hammer or beat against the mat when positioned on the rock to provide positive contacts. The inherent weight of a steel structure of this sort makes for good contact, as well. Same also admirably beds against and holds in place conductive steel wool, wire felts, graphite cloths and felts or the like.
Rods 37 have enlarged heads 37a on one end thereof and threaded ends to receive nuts 38. Thus chain segments may be added or subtracted as desired by utilizing shorter or longer rods. The input electrode 39 comprises a steel rod having the usual insulating protective grip 40 and cable attachment 41 of insulated sort. Rod 39 is welded or otherwise fixedly attached to one or more links of chain segments 33-35, inclusive. Such connection may be to one link of one chain, two links of two chains, etc. Both the physical contact of adjacent chain links and the conductive steel rods 37 or cables makes every link of the entire mat a potential electrode or set of electrodes in contact with the surface of the rock.
In the view of FIG. 2, a second mat of like character to that seen on top of boulder 42 is illustrated at 43 with power line 44 leading through insulating grip 45 to welded electrode contact 46. If desired, the current input from cables 41 and 44 may be split into two electrodes welded to two portions of the mat, or the like.
Referring to FIGS. 4 and 5, therein is shown a device for combining electrical current and physical or mechanical effects. A pair of rectangular (alternatively oval, circular, square, triangular, etc.) steel frames, hollow centrally thereof, are provided as at 47 and 48. These frames are mounted in the manner shown, namely, inclined, say, 30 from the vertical and in planes facing one another and angled toward one another in the lower portion thereof. Any suitable supporting frame structures, such as legs, arms, sheets, or the like, may be utilized to support these rectangular frame members 48 and 47 with respect to one another on a vehicle, on the earths surface, in a factory, over a concrete floor or slab, or the like. Such support members, not shown, are preferably of electrically insulating material or insulated where connected to the frame. Means may be provided to vary the angle of the frames with respect to one another, draw them closer to one another in the same or different angle postures, move them apart from one another or the like. All of these would be essentially conventional in character and thus not detailed, but the essence of successful use and application of same is that they would be insulated or dielectric, when two members connect or engage both frames 47 and 48. Frames 47 and 48 are here shown as rigidly connected to one another and spaced from one another by members connected centrally to lengths of insulating substance 49 and 50.
A vibrator mechanism of any conventional sort, commercially available, is schematically indicated at 51 with a connection to one of the frames also schematically indicated by line 52. Such a vibrator could merely involve an oscillating or reciprocally moving shaft connected to any sort of rotating shaft or wheel, with the two frames mounted in a spring cradle for shaking purposes or same could involve an impact device on the frames for transmitting shock into the rock carried thereby, etc.
The hollow centers of frames 47 and 48 are filled by a plurality of elongate interconnected chain masses generally designated 53, individual adjacent links of the chains preferably connected by steel rods or cable segments as in FIGS. 2 and 3. The chain links are welded or otherwise fixedly connected to the frame vertical walls or end members, while the rods or cable segments 54 may or may not be welded or othewise connected to the upper and lower wall members or frames 47 and 48. In the case of rods, such connection is preferably not made as the mesh then tends to be too rigid. In the case of cables, such connection may be more feasibly made. In the latter case, such cable interlinks may be of greater length than the distance between the upper and lower frame members whereby to provide more give. The rigidity of the chain lengths themselves may be varied to give a nesting effect with the rock with thus greater electrode contact. Power cable inputs 55 and 56 pass to electrodes 57 and 58 welded or otherwise fixedly attached to steel frames 47 and 48, whereby to feed electrical current in large quantities into the frames themselves and the webworks or meshworks of chain links and rods provided in the hollow centers thereof.
Thus, when a large boulder or rock or series of same as at 59 is emplaced down between the frames, wedging itself by its own weight against the screens of chain mesh, the current feed into the frame passes into the mesh and thence into the rock through the contact areas thereon. The vibration action then serves to wedge the rock more securely into the mesh. Current application heats the rock and the vibration action may be increase-d as desired whereby, as the rock becomes heated in portions thereof, fragments and pieces fall olf, thereby permitting the motion of the rock downwardly in the wedging frames, current application continuing. Such may continue until the entire rock mass has disintegrated due to the combined effects of heating and mechanical action. The distance apart of the bottom of the frames 47 and 48 determines the ultimate size of the particles leaving the frame, as all rock pieces in contact with the frames themselves or the mesh thereof will continue to receive current and be heated, as well as the impacts of the vibrator 51.
The construction of FIGS. 6 and 7 differs primarily from that of FIGS. 4 and 5 in that a moving chain mesh belt or the equivalent thereof is provided which, when a rock or boulder is received upon the downwardly in clined, wedging, moving chain mats, the assembly moves the boulder along from an input zone to an output zone. Pieces of the fracturing or fractured boulder may fall down between the lower edges of the chain belt and any boulder mass residual is ultimately discharged from the other end of the belt. It should be noted that, if the apparatus of FIGS. 4 and 5 or of FIGS. 6 and 7 is positioned over a drop zone of concrete, metal or the like, the passage of fragments through the frames or belts onto such surface from a height may serve to further or finally fracture or fragmentize same or the discharge of large hunks or masses from the output end of the apparatus of FIGS. 6 and 7 onto a hard surface may effect the desired breaking and fracturing if sufficient electrical current heating has been provided in passage through the assembly. Velocity of movement may be regulated to character or weight of the boulder.
Thus referring to FIGS. 6 and 7, endless chain belts 60 and 61 are driven and supported by each of a plurality of rods, drums, shafts or drive cylinders 62 and 62a in the case of belts 60 and 63 and 63a in the case of belt 61. Drums 62 and 63 are mounted on rotatable drive shafts 62' and 63'. Shafts 62' and 63' and like drive shafts on drums 62a and 63a, if desired, carry pulleys or sheaves 65 and 66 fixedly attached thereto and rotatable therewith, the latter driven by belts 67 and 68 conneted to the drive shafts and pulleys of conventional electric motors 69 and 70 or other suitable power sources.
It should be noted that the mat, web and belt structures of the apparatus of (1) FIG. 2, (2) FIGS. 4 and 5 and (3) FIGS. 6 and 7 are basically similar in the makeup of the means which contact the boulders, namely, same are composed of pluralities of intermeshed chain link segments. the latter interconnected transversely thereof by cables or rods as most clearly seen in FIGS. 2, 3 and 5. The drums, cylinders or the like 62, 62a, 63 and 63a may be ridged or grooved on the surfaces thereof to provide optimum drive connections and support of the chain belt and are preferably of electrically conductive material themselves, such as steel. Electrode connections 71 and 72, comprising elongate steel rods or shafts extend upwardly from drums 62 and 63 and have any suitable electrical power connections thereto 73 and 74. The power lines 73 and 74 may be connected to shafts 71 and 72 by sliding fittings, brush contacts, or the like, anything conventional and suitable to pass the current from the static conductor 73 and 74 to the rotating rods 71 and 72. At 75 is shown a large rock or boulder which is received upon the chain mats and moves, slowly or swiftly, along the terminal input chain drive support drums 62a and 63a. The belt segments or links 60 and 61 may be any desired length and any desired number of power or follower rotating chain drum supports, not shown, may be positioned between say, drums 62 and 62a. Indeed if desired, the drum support of the chain may be almost continuous, one to the other.
Certain of the drums may be of dielectric or insulating material or surfaced with such, while the current input may be to several pairs or sets of drums with each belt. The object is to provide a continuous current flow of minimum resistance and impedance from conductors 73 and 74 into the drums 62 and 63 and thence to the endless chain mats 60 and 61. The drive shafts for the drums must be received in suitable bearings and frames, same conventional, for supporting the belts and their driving and supporting members and may incorporate vibrating means, means for moving the belts toward or away from one another, canting the angle of the belts with respect to one another, absorbing shock, etc. These are not shown in detail as many varieties of conventional devices may be utilized for these purposes.
As in the case of the previously described modifications, particularly FIGS. 4 and 5, steel wool, wire felts, graphite cloths or felt, etc. (fine texture conductors) may be overlaid on the chain belts or meshes before the receipt of the rocks thereon to aid in communication of electrical impulses into the rocks. In the apparatus of FIGS. 4 and 5 and FIGS. 6 and 7, such are not generally as needed as in the apparatus of FIGS. 1 and 2, as the wedging weight of the boulders and rocks onto the chains provides more and better electrical contacts than a mere more or less free lay-on contact as in the earlier described version.
In FIG. 8, there is shown, schematically, an elongate steel cylinder 80, centrally hollow, which is driven in rotation by one or more external rollers 81 and 82 in physical contact with the outside surface of the shell. Gear interengagement, rubber-steel engagement, with the cylinders or rods 81 and 82 being rubber or dielectric coated (or the like) may be employed to provide a suitable drive. The velocity of revolution is variable as desired, depending upon the size and masses involved, power available, etc. Centrally suspended, but rigidly positioned there is an elongate steel slab or bar 83 which, alternatively, may be a rectangular mesh of the type seen in FIG. 5.
Boulders, rocks or rock masses are fed into one end of cylinder 80, positioned in the direction of rotation on one side of bar or slab 83. This side, in the apparatus shown, would be in the zone designated 84, whereby the rotation of cylinder 80 would tend to move the rocks upwardly and round in a clockwise direction, same rolling back to impact repeatedly against the side of the bar 83. The space below the bar is to permit relatively small fragmentized rock portions to pass under the bar or aggregate toward the center of the shell 80 whereby to fall out downwardly between the rollers 81 and 82. Angling or slanting the shell 80, rollers 81 and 82 and slab or bar 83 slightly downwardly with a fall from the input and to the output end moves the boulders and fractured rock masses gradually from one end to the other with the smaller pieces then ejecting from the end of the cylinder. Brush contacts 85 and 86, the former riding over the outside surface of steel cylinder 80, the latter connected or contacting one end of slab 83, serve to input power respectively to the cylinder shell 80 and the slab 33. Power input lines 87 and 88 connect to any suitable AC or DC source of sufficient power. There being no physical contacts between slab 83 and shell 80, the current therebetween is transmitted by rocks simultaneously contacting the surface of slab 83 and the cylinder shell 80. The rolling and moving action of the shell and the impacting of the rocks repeatedly against the steel slab 83 furnish both electrical and physical action to effect rock fragmenting.
Referring to FIG. 9, therein is illustrated a variation or modification of the relatively simple apparatus of FIGS. 6 and 7. Herein, in essence, there are provided a plurality of sets of electrically conductive chain or cable mesh belts which receive, therebetween, in conveyor fashion, relatively large rock masses, apply electrical current thereto of sufficient magnitude and duration to effect shattering, fragmenting or breaking down of the rock masses into lesser size pieces, certain minimum size pieces being passed out of the current applying zone, the larger remaining fragments passing into the lesser sized current applying zone until the entire body of rock has reduced to a certain minimum size.
Thus, in the upper right-hand corner of FIG. 9, there is provided a conveyor of any suitable material (nonconductive, if desired) generally designated 90, the belt therof mounted on rollers of suitable conventional type 91. Rock or ore masses of relatively large size 92 and 93 are passed along and off the end of this most elevated conveyor 90. Immediately past the discharge end of conveyor 90 and positioned slightly therebelow, there is provided a chain mesh or cable mesh belt 95 or conductive type previously described. Belt 95 is mounted on rollers 96 and 97 operative to drive same in positive forward drive in the direction of the arrows shown, suitable follower and idler rollers or powered rollers (not seen) positioned between rollers 96 and 97 being provided to adequately support and move whatever rock mass may be provided on top thereof. Electrical input cable 98 is connected in conventional manner by sliding contact or brush contact with drum or drive cylinder 96 whereby to transmit electrical current into belt 95. Positioned above belt 95 is a second chain or cable mesh electricity conducting belt 99, same mounted on drive and support rollers or cylinders 100 and 101. There is schematically indicated on the frame structure 102 the vertical adjustability of the entire belt and roller complex of belt 99.
The other side of the electrical current input to this first double chain belt system is provided by cable 103 electrically connecting to the drum 101. The drum and drive structure, as well as support structure, of the upper belt, in all of the cases described, need not be as rugged as the ones relatively therebelow, as the weight carried, etc. is less. Impacting or vibrating means may be provided on either the above or below belts, or both. None of the support framework or the like is shown, as this may be conventional. It may be seen that the large boulders, such as 104, just entering the system of belts 95 and 99 are broken down into numerous relatively smaller fragments generally designated 105 and larger remaining pieces such as 106 and 107.
Immediately following the discharge end of belt 95, there is provided a receiving chute 108 having thereabove and across the input surface thereof, a plurality of powered rollers 109, same bridging the input chute, but permitting the passage therebetween of relatively smaller size fragments, the latter seen at 110. These fragments pass downwardly onto an elongate conveyor receiving belt 111 received on driven and follower rollers 112-114, etc. Belts 95 and 99 preferably wedge inwardly, down wardly.
Past chute 108, there is provided a second set of vertically spaced, downwardly wedging chain belts, numbered 115 and 116, respectively, having, for the lower belt, rollers 117 and 118, and for the upper, rollers 119 and 120. With respect to the latter, the vertically adjustable frame 121 is again provided with power current inputs through cables 122 to the lower system and 123 to the upper system. The upper end of belt 115 is positioned below the lower end of belt 95 whereby, in addition to the belt drives and roller drives, the downward action of gravity aids the motion of the heavy rock masses. The falls of the rock masses from, for example, belt 95 onto rollers 109, aids in breaking up partially fractured or incipiently fracturable rock and ore mass bodies. It may be seen that the rock masses 122 and 123 are diminishing in size and the frame 121 must be adjusted to maintain heavy contact of the upper belt 116 therewith.
Following the discharge end of belt 115, there is again provided a discharge chute 124 having rollers 125 positioned thereabove with rock fragments 126 moving downwardly onto conveyor belt 111.
There is thereafter shown a third and optionally final set of chain mesh belts 127 and 128 driven by rollers 129 and 130 with current feed cables 131 and 132 provided in previously described manner. The upper belt may or may not be adjustable in this last instance, the final ejection from lower belt 127 being directly onto the surface of conveyor 111. Thus it is seen that, through a series of staged steps and phases of application of electrical current to very large rock masses, a more or less uniformly sized quantity of rock or ore fragments may be provided on belt 111 for ultimate discharge to further treatment of chemical, physical or even electrical means.
In a specific example of rock breaking wherein 60-cycle AC current from a commercial line, three-phase, was utilized to drive a DC generator providing a steady DC current for electrical power input to the rock, a five ton (approximate) rock comprising iron ore consisting largely of magnetite, in a mine near Sullivan, Missouri was fractured. Utilizing chain pad electrodes of the type seen in FIGS. 2 and 3, approximately one square foot in area, the initial voltage requirement was volts, with a current flow of 500 amperes, thus indicating an initial resistance of 0.36 ohm. After a short period of time, approximately two minutes, a rise in the indicated current flow at the initial voltage indicated a fall in the internal resistance of the rock. Due to limits of the available power capacity, progressive voltage reductions were made as the cur-rent flow increased. After some ten minutes, the voltage level had been reduced to some 90 volts at a current flow of 1200 amps. In the particular mine involved, with the said particular type of ore, I have discovered that approximately two killowatt hours per ton of rock will result in sutficient internal fracturing thereof that the rock can be fractured by physical contact with the loading machines involved in the mine. Also in this particular ore, as is the case in most rocks and ores, the appearance of fine visible surface fractures indicates the successful progression of the internal heating and fracturing process. The quantity and extent of these fractures vary considerably, but, in a multi-ton rock, the appearance of a relatively small number of elongate fine fractures indicate the availability of the rock for fracturing by various available physical means.
Once the multiplicity of fine visible surface fractures has appeared, the rock may additionally be sprayed with water, same penetrating the surface fractures and resulting in a marked opening of the fractures throughout the rock. The rock or ore mass, generally, in most cases, audibly works and sounds during the application of the current indicating the development of the stresses, fractures and cleavages Within the rock. Arcing between electrode portions and the rock surface should be rninimized by keeping the full electrode area in contact with the rock.
The techniques and apparatus herein disclosed are generally more successful with the relatively conductive rocks and ores, that is, the numerous and highly varied metallic ores. However, for example, the technique has proved successful in fracturing rocks of the characters of shale having therewithin recoverable some one percent of copper. In rocks with this relatively low mineralization, very high initial resistivities are encountered, such as, for example, 4000 volts with /2 ampere current flow utilizing small area electrodes.
In the fracturing of ore masses and rocks in a magnetite ore of the type above mentioned, a 500 volt generator or transformer with a capacity of 200 kva. would handle and fracture rocks of the order of ten tons. In rocks of this sort, namely, iron ore consisting largely of magnetite, one cubic foot of rock weighs approximately 250 pounds. Therefore, an 8-foot cube would weigh of the order of 12 tons.
A common problem of the process is size reduction of very large rocks and ore masses to fit loaders, skips or to go through certain sized openings. This apparatus and process as described is quite successful in this stage. Such rocks are of the order immediately described above and most often the results of blasting processes. Thus, coarse crushing of quite large boulders, rocks and ore masses may be involved. Generally, most rocks or ores are going to be greatly fragmentized in the milling process. Therefore, any micro-fracturing put into a rock, whether or not same results in major fractioning of the total size or not aids the general process of milling and fragmentizing. Thus, the current and power requirements are not too critical in coarse crushing by electrical means as all power put into the rock generally is useful somewhere along the milling or crushing line.
Thus, very generally speaking, one would expect to use the apparatus of FIGS. 1-3, inclusive, on very large, multi-ton boulders in situ in mines or quarries, same generally considered too large to move and lift, per se. The two forms of apparatus seen in FIGS. 4-7, inclusive, would be working with the fragments resultant from the apparatus and processes of FIGS. 1-3, inclusive. Thereafter, a further refining process would be seen in the apparatus of FIG. 8 which would work with fragments and pieces resultant from the apparatus of FIGS. 4-7, or smaller. FIG. 9, on the other hand, shows several stages of coarse crushing, which would take one down, say, to apparatus of the character of FIG. 8. Each stage of milling, typically, is generally considered to involve a factor of 4 in size reduction.
From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the process.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.
As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
Having thus described my invention, I claim:
1. A process in aid of fracturing rocks comprising contacting two spaced apart zones of a rock mass with a pair of relatively large yet limited area multi-point contact electrodes against the rock within said area and flowing suflicient electrical power into said rock to effect heating of a plurality of internal channels of relatively high conductivity in said rock, thereby creating a multiplicity of thermal stresses within said rock.
2. A process in aid of fracturing rocks comprising contacting two spaced apart zones on opposite sides of a rock mass with a pair of relatively large yet limited area multiple point contact electrodes against the rock within said area and flowing sufficient electrical power into said rock to effect marked heating of a plurality of internal channels of relatively high conductivity within said rock.
3. Apparatus for aiding the fracturing of rocks comprising an electrode structure made up of a conductive metallic rod fastened to one side of a chain pad, said chain pad involving a plurality of sets of interconnected chain links, a plurality of individual links of each set interconnected with individual links of other sets.
4. Apparatus for electrically treating rock fragments and boulders comprising a pair of opposed screens of electrically conductive material adapted to receive a rock fragment or boulder in spaced wedging fit therebetween and an electrical power cable connection to each of said opposed screens.
5. Apparatus for flowing electrical current into rock fragments and boulders comprising a pair of spaced, drive belts of electrically conductive material adapted to receive in Wedging contact therebetwen rock fragments and boulders and an electrical power cable connection to each of said belts of conductive material.
6. A process of coarse crushing of rocks and boulders comprising passing a boulder between a first pair of vertically spaced, opposed, boulder surface contacting, electrically conductive conveyors and passing sufiicient electrical power into said boulder from said conveyors to internally heat portions thereof, passing said internally heated boulder over a first rock fragment discharge conduit whereby to remove fragments of same, then passing the attrited boulder between a second pair of vertically spaced, opposed, boulder surface contacting electrically conductive conveyors and passing sutficient electrical power thereinto to internally heat additional portions thereof and passing said internally heated boulder over a second rock fragment discharging conduit whereby to remove additional fragments of same.
7. A process as in claim 6 including the step of collecting the rock fragments from the first and second discharge conduits on another conveyor running therebelow.
8. Apparatus for coarse crushing rocksand boulders comprising a first pair of vertically spaced, opposed, boulder surface contacting electrically conductive conveyors adapted to pass suflicient electrical power therefrom into a boulder simultaneously contacted by both of same to internally heat portions thereof, a rock fragment discharge conduit, vertically oriented, following said first pair of conductive conveyors having powered roller means to pass said boulder over same, a second pair of vertically spaced, opposed, boulder surface contacting, electrically conducting conveyors positioned passed said first conduit adapted to engage the residual boulder in such manner as to pass electrical power therein whereby to internally heat additional portions thereof and a second rock fragment discharging conduit positioned passed said second pair of electrically conductive conveyors.
9. Apparatus as in claim 8 including a second set of powered rollers over said second conduit.
10. Apparatus as in claim 9 wherein the first set of said conveyors, the first discharge conduit, the second set of conveyors and the second discharge conduit are all positioned at least slightly below one another, in succession.
11. Apparatus for electrically fragmenting and fracturing rock fragments and masses comprising a revolving cylinder of electrically conductive material and an elongate body of electrically conductive material positioned inwardly of said revolving cylinder, said elongate body extending substantially axially of said cylinder and spaced inwardly from the sides thereof and electrical power cables with electrode means contacting said shell and body to transmit electrical power thereinto.
12. Apparatus for aiding in the fracturing or rock masses comprising a pair of electrical power cable links, said links attached at one end to relatively large area multi-contact electrodes.
13. Apparatus as in claim 12 wherein said electrodes comprise multi-link chain masses.
14. Apparatus as in claim 12 wherein said electrodes comprise multi-link chain pads, said links interconnected with one another.
15. Apparatus for flowing electricity into a rock mass having a plurality of electrically conductive channels or zones therein and surfaces of varying electrical contact resistance comprising relatively large area multi-contact zone electrodes of electrically conductive material, said electrodes flexible and dimensionally resilient whereby to permit electrical contact of a plurality of portions of a given electrode with a plurality of rock surface points of lesser contact resistance simultaneously.
16. A process of preparing a rock for fracturing same comprising flowing electrical current into said rock at a plurality of points in each of a pair of limited spaced apart zones on the rock surface of relatively reduced contact resistance from relatively large area multi-contact point electrodes against the rock within said area.
17. The process of aiding the flow of electrical current into a rock in preparation of same for fracturing comprising flowing electrical current into a plurality of points of relatively low contact resistance on the rocks surface through an electrically conductive textural material of the character of graphite cloth, same contacted on the side thereof away from the rock by a multi-contact point relatively large area electrode of electrically conductive material.
References Cited UNITED STATES PATENTS 2,007,383 7/1935 Opp.
475,191 5/1892 Burton et a1 219-119 2,959,364 11/1960 Anderson et al. 24l200 3,208,674 9/1965 Bailey 24l-1 FOREIGN PATENTS 939,784 10/1963 Great Britain.
ANDREW R. JUBASZ, Primary Examiner US. Cl. X.R.
--16; 2l9ll9; 241200, 291, 301; 299l4