BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram of the method used in practicing the preferred embodiment of the present invention;
FIG. 2 is a schematic side elevational view representing a simplified air classifier to illustrate the general function of an air classifier in practicing the invention;
FIG. 3 is a graph of the constructed line representing the relationship between the grain size of nepheline syenite and its abrasive characteristics;
FIG. 4 is a graph comparing the distribution profile obtained between an experimental sub-5 micron product and the sub-5 micron product of the present invention; and,
FIG. 5 is a schematic view of the method and equipment used in practicing the preferred embodiment of the invention as shown in FIG. 1.
THE INVENTION
The showings are for the purpose of illustrating the preferred embodiment of the invention and not for the purpose of limiting same, FIG. 1 is a block diagram of a method 100 wherein a particulate nepheline syenite is processed to obtain an ultra-fine grain size less than 10 microns and preferably less than 5 microns. The method is used to control the grain size of the nepheline syenite where at least 99% of the nepheline syenite is below a set selected ultra-fine particle size. Furthermore, the distribution profile is quite narrow, i.e. in the range of 4-5 microns. The invention does not produce particulate nepheline syenite with a large range of particle sizes that merely includes a mixture of ultra-fine particles and larger particles because the abrasive characteristic of the nepheline syenite particles increases drastically with increased particle size. Consequently, the invention involves at least 99% of the particle size being less than a set value, which value is preferably 5 microns. This is a different product than nepheline syenite wherein the particle size distribution profile is in the range of between 2 microns and 11 microns. It has not been practical to obtain a nepheline syenite having substantially greater than 99% of the particles less than 5 microns with a narrow distribution profile. This objective has been accomplished only in experimental environments utilizing a wet milling procedure. Such procedures result in agglomerations of the ultra-fine particles due to surface activity of the small particles. A substantial amount of process energy is required. These limitations have heretofore bode against obtaining such small ultra-fine particles, even though it is known that such particles reduce the Einlehner abrasive value or number.
For the purposes of reducing abrasive properties of materials containing nepheline syenite particles to a low Einlehner Abrasion Value, the nepheline syenite particles must have a grain size less than 10 microns and preferably less than 5 microns. The present invention is a method of processing nepheline syenite which involves the combination of a dry ball mill and an air classifier. A representative method 100 employing the invention is illustrated in FIG. 1 where nepheline syenite in granular form is supplied at first process step 110. The mined particulate material is ground in a dry grinder 112 using standard mechanical equipment so the resulting particles can be within a certain particle size using grading step 114. In the grading step, which can be done by a screen such as a 16 mesh screen, the particles exiting along outlet line 114a have a first given value. The first value is in the general range of about 1,000 microns. The use of a mechanical 16 mesh screen in the grading step allows the particles flowing along output line 114a to have a size forming optimum feed stock for ball mill 120. If the size of the particles from the dry grinder 112 is greater than the mesh size at step 114, the larger particles are transported along output line 114b to sorter 116. At the sorter, larger unusable particles are ejected along output line 116a and smaller particles are redirected to the grinder 112 through. return line 116b. Thus, the inlet portion of method or system 100 produces a given first grain size which is conductive to subsequent processing according to the present invention. This grain size is selected to be 1,000 microns; however, this is only representative and the particles from output line 114a can have any particular given particle size. This is the first given grain size in method 100. In practice the graded nepheline syenite at outlet line 114a has a grain 25 mesh size (600 micron). Steps 110, 112 and 114 comprise a primary jaw and cone to reduce the mined product to clumps less than 6 inches, rotary kiln to dry the material, a cone crusher to reduce the rock to less than one inch and a tertiary crusher in the form of a vertical shaft impact crusher. The material is then graded to pass a 25 mesh screen and is provided at outlet line 114a.
Nepheline syenite having a particular given size in output line 114a is directed to a feed stock ball mill process step 120 operated to produce ultra-fine particles, without the addition of a liquid to slurry the particles. Thus, ultra-fine particles are ejected from ball mill of step 120 along output line 122. Any standard ultra-fine ball mill can be used for step 120 of the inventive method. Ultra-fine particles from the ball mill of step 120 exit through output line 122 and are processed by a standard air classifier. This air classifier is adjusted by the process air velocity from blower 132. The blower directs high velocity air through line 132a into a standard air classifier step 130. The air classifier step removes particles less than 5 microns by directing such ultra-fine particles through output line 134. These particles can accumulate in collector 136. In accordance with standard air classifier procedure, particles having a maximum grain size of a given second value are separated and directed to collector 136. In accordance with the invention these particles are less than 10 microns and preferably less than 5 microns. In practice, over 99% of the particles have a grain size of about 5 microns in the preferred embodiment of the invention. Of course, air classifiers remove ultra-fine particles with a distribution profile. In the invention, the profile is 5 microns to about 1 micron. The dust with a size less than about 0.5 micron is carried by air from blower 132 through line 138 to be collected in dust receptacle or collector 140. Air classifier 130 also has a large particle discharge line 150 directed to collector 152. From this collector, larger particles are recycled through line 154 back into the input of the ball mill of step 120. Feed stock from line 114a and returned particles from line 154 are processed by the dry ball mill step 120 and are directed through output line 122 into standard air classifier 130. The air classifier separates the desired particles for accumulation in collector 136. It also discharges unacceptable small particles into collector 140. Larger particles are recycled through collector 152. Thus, a continuous in-line method 100 accepts mined nepheline syenite and outputs nepheline syenite with ultra-fine particles of less than 10 microns and preferably less than 5 microns. The distribution of particles of nepheline syenite produced by method 100 is in the general range of 1 to 5 microns in the preferred embodiment of the invention. Consequently, a specific low value for the particle size is obtained for the natural mined material nepheline syenite. The distribution profile is less than about 4 microns and has a maximum size in the general range of 5 microns. A distribution profile of 4-5 microns with an upper value less than 10 microns and a lower value of at least 1 micron defines the output material of method 100.
The invention involves the combination of a dry ball mill to produce ultra-fine particles without wet grinding in combination using an air classifier, which is a device that removes particles with a certain size range from air borne fine particles. A schematic representation of an air classifier is illustrated functionally in FIG. 2. The particles are discharged directly as feed stock in line 122 into the air classifier 130. Thus, a combination of a dry operated ball mill and an air classifier produces the desired small particle size for the nepheline syenite of the present invention. As illustrated in FIG. 2, a functional representation of an air classifier is shown. Air classifier 130 has an air inlet represented as inlet tunnel 200 for blower 132. Blower 132 can include fan 204 powered by motor 206. Screen 202 prevents large particles of extraneous material from being drawn by the high flow of air in inlet or tunnel 200. In practice, the classifier speed is generally about 4,000 RPM with a total flow of about 6,000 CFM. Such high air velocity through inlet tunnel 200 is directed to an area below hopper 210 for accepting feed stock from line 122. Nepheline syenite is dropped from hopper 210 through inlet tunnel 200 where it is entrapped and carried by air through controlled baffle 220. Larger particles above a given value to be extracted by classifier 130 are discharged by gravity through line 222 which is outlet 150 of method 100 shown in FIG. 1. Such large particles are collected on conveyor 230 where they are transported to collector inlet funnel 232 for discharge into collector 152 for return to the ball mill by way of line 154, as schematically shown in FIG. 1. Air transport currents 240 pass through tunnel or tube 200 into a larger volume hood 242, where the pressure differential and carrying capacity of the air is controlled by the size of the hood compared to the velocity of the particle transporting air. This combination of air and hood allows the transporting air 240 to drop particles of a given size to be extracted in area 250 into outlet line 134 for depositing in collector 136. Thus, large particles are discharged by gravity into collector 152. Particles having the desired distribution range are deposited in collector 136 and other fines or dust smaller than the desired material to be separated by classifier 130 are carried through tube 260 to discharge 138 in the form of funnel 138a for discharging the fines or dust into collector 140. Air is discharged from line 262 as schematically represented in FIG. 2. Thus, the functions of an air classifier are illustrated in FIG. 2 where classifier 130 receives ultra-fine feed stock from line 122. This is the output produced by a dry ball mill used in step 120. The combination of a dry ball mill and an air classifier to provide a selected tight range of ultra-fine particle size for nepheline syenite has not been accomplished before discovery of the present invention.
By processing nepheline syenite in accordance with the method of the present invention, it has been found that the Einlehner Abrasive Value (EAV) is less than 100 for a maximum grain size of 10 microns and a value of about 50 for the preferred embodiment wherein the material has a maximum grain size of 5 microns. In FIG. 3, line 300 is the linear regression of points 302, 304, 306, 308 and 310 which are samples of nepheline syenite having maximum particle size of 3 microns, 10 microns, 20 microns, 35 microns and 60 microns, respectively. The abrasion number or value (EAV) for material using these various samples determine the points shown on FIG. 3 to construct line 300 by linear regression. As can be seen, with a maximum grain size of 5 microns, an Einlehner Abrasion number or value of 50 is obtained. At 10 microns, the value or number is 100. Tests have indicated that the lower the abrasion number or value the less wear there is on equipment processing viscous material using nepheline syenite. It is desirable to have a value less than 100 and preferably about 50. This value is obtained by the preferred embodiment wherein the grain size of the processed nepheline syenite is less than 5 microns and generally in the range of 1-5 microns. This is a very small range for the distribution profile and ultra-fine grain size. This produces an improved nepheline syenite heretofore not obtained economically in commercial quantities.
After producing the product in accordance with the invention as described in the flow chart or diagram of FIG. 1, the resulting product had a maximum grain size of 5 microns and a minimum grain size of about 0.5 microns. The distribution of the finished product is show in graph 400 in FIG. 4 wherein substantially all of the particles are less than 5 microns. The tested distribution indicates that the minimum grain size is 0.5 microns and only about 10% of the particles had this small size. To obtain a comparison of the distribution obtained by practicing the invention with distribution obtained only by an experimental laboratory process. A sub-5 micron nepheline syenite was produced in a laboratory environment. The distribution curve 402 was obtained for this experimental material having a grain size range of 1-5 microns. This product used a wet process to provide a comparison vehicle. As can be seen, the mass produced high volume commercial application of the present invention illustrated in FIG. 1 produces a distribution curve quite similar to the curve 402 of the experimental material where the particle size are controlled between 5 microns and 1 micron. The only difference is that the mass produced commercial method 100 has a few particles with a lesser diameter than is possible by an experimental, laboratory controlled process for producing a representative sub-5 micron nepheline syenite. Method 100 produces nepheline syenite with an ultra-fine particle size in the range of 0.5-5.0 micron. The method is equally useful for usable quartz free particulate igneous rock with at least orthoclase and microcline constituents. This type of material is used for fillers, extenders and sources of aluminum without the disadvantage of crystalline silicon dioxide.
In practice the method of the present invention is performed by system 500 shown in FIG. 5. Nepheline syenite graded to 25 mesh size is provided at line 114a to input mechanism 510. Mechanism 510 comprises hopperorfeed bin 512 with output 514 for loading weight feeder 516 from which fresh feed stock is provided by tube 518 to feed box 520. Conventional pebble mill 530 is mounted on a stand having load cell 532 to create a weight signal in line 534 indicating the load weight in mill 530. The rotor of mill 530 includes ceramic particles so the mill grinds the incoming nepheline syenite with a ceramic media. Other media can be used in mill 530, which is referred to as a dry “ball mill.” Screw conveyor 540 circulates material from box 520 into mill 530 where the first incoming size is reduced to a substantially smaller size and is moved to output compartment 542 with outlet 544. Forced transport airfrom line 550 passes through pickup nozzle 552 so material from mill 530 is directed by air into ultrafine air classifier 560 by air line 562. Secondary air from suction line 566 is drawn into the classifier by blower 564. This air, together with transport air from line 562, is the primary air of the classifier and conveys particles upwardly through exhaust 568. Small particles (less than 10 microns and preferably less than about 5 microns) are separated and directed by line 570 to product filter 580. The filter drops the particles into collector 136 by line 582 and expels small particles of dust through line 584. The nepheline syenite from filter 580 has the desired small size less than 10 microns with a range of about 4 microns. Preferably the size is less than 5 microns. With a 4 micron range, the particles are about 1 to 5 microns with the majority closer to 5 microns.
Mill 530 has a circulating load. Larger particles from classifier 560 are directed back to feed box 520 through line 590. Load cell 532 provides a weight signal in line 534. When this signal is indicative of a weight below a set amount, weight feeder 516 provides the needed fresh feed to box 520. In this manner the circulating load is maintained generally constant so the fresh feed equals the discharged small particles.
System 500 is shut down to change product grades. On start up, classifier 560 is operated at 3900 RPM or about 98% of maximum speed and blower 564 is operated at 1500 cfm. The size of the particles is tested as mill 530 is operated, first at low weight and then gradually increased. When the weight is steady at a set value, the system commences automatic control and line 566 is opened to give more primary air. The speed of the classifier is increased as samples are taken periodically until the desired specification is reached. Then the system is operated steady state.
The entire mill has a circulating load measured by cell 532, which is the ratio or percentage of mill discharge versus the fresh feed rate. In practice the circulating load is set to 11-15 TPH. The weight of the mill controls the fresh feed ratio. In steady state, the primary air in line 570 is the sum of secondary air at line 566 and transport air in line 562. Air from line 566 is used to mix the material within the classifier so it is a homogeneous mixture. Air flow is also the opposing force on the classifier wheels and the balance of these forces causes the particle size to exhaust 568. Classifier 560 consists of six parallel ceramic “squirrel cage” like wheels which spin at the same speed. All product must pass through the wheels and the speed of the wheels balanced with the air determines the size of product at collector 136. These parameters are adjusted to obtain the desired particle size. Mill 530 is adjusted to control the set circulating load. Other equipment can be used to perform the invention as claimed. The claims are incorporated by reference as part of this description.
Patent Application
20080015104
