US 3377660 A
Description (OCR text may contain errors)
pril 16, 1968 D. w. MARSHALL ET AL 3,377,660
APPARATUS FOR MAKING CRYSTAL ABRASIVE Original Filed April 20, 1961 Inventors. DOUGLAS 14/. MARSHALL EDGAR A. PETT :5 M/
' :fH-korneg/ United States Patent 4 Claims. (CI. 18-46) ABSTRACT OF THE DISCLOSURE An apparatus utilizing a trough for flowing molten abrasive material from a furnace onto a cool rotating casting cylinder, rapidly solidifying it into a thin semisolid curved sheet, densifying the semisolid material with a pressure roll, and then partially fracturing the strip of semi-solid material by reversing its curvature by pulling it away from the cylinder with a driven rapidly cooled conveyor means whereupon the partially fractured strip is deposited onto collecting means in the form of large fragments which upon being rapidly cooled and solidified break up into smaller fragments well adapted to be reduced in size to form conventional abrasive particles.
Related cases This application is a division from application S.N. 104,317 filed Apr. 20, 1961, now abandoned.
Background 0 the invention Currently, aluminous abrasive is made from a suitable mixture of bauxite ore fused in to ton batches and allowed to cool for a period of a week or more in the form of large pigs. These pigs are then broken up with sledge hammers and the resulting fragments sorted to separate the high-grade product from the impurities and reclaims. This method is expensive, arduous and time consuming and, because ofthe length of the time required to effect cooling, the crystal size is generally coarse to intermediate. Alumina cooled slowly in large batch-type water-cooled furnaces has, for example, a crystal size of from between 50 and 80% monocrystalline in 24 grit while a similar aluminous abrasive poured into a 300 pound ingot mold will vary from 25 to 70% monocrystalline in a 24 grit.
Summary An object of this invention is to provide an apparatus for making very fine crystalline alumina abrasive having a crystal size in the order of less than 1% monocrystalline in 24 grit and containing as little as 4 to 14% monocrystalline in 80 grit and, by reason of this fineness, to provide a grain which withstands impact and wear a great deal better than the coarse grain material now produced and which, therefore, is superior to coarse grain crystal for snagging operations. 1
The apparatus, as herein disclosed, for carrying out the foregoing method, comprises a quenching cylinder mounted for rotation about its longitudinal axis, a trough arranged above the upper part of the quenching cylinder for flowing molten material onto the upper surface of the quenching cylinder as it rotates, means for cooling the surface of the quenching cylinder partially to solidify the material as it is spread on the surface, and means for effecting rotation of the quenching cylinder gravitationally to dolf the partially solidified strip at its lower side. A conveyor is disposed subjacent the quenching cylinder having a horizontal surface, and there is means for effect ing movement of the surface away from the downwardly moving side of the quenching cylinder to assist in pulling 3,377,660 Patented Apr. 16, 1968 the strip away from the surface of the cylinder to effect further fragmentization and cooling. A squeeze cylinder of smaller diameter than the quenching cylinder is arranged parallel to the quenching cylinder with its surface closely adjacent the surface of the quenching cylinder, and there is means for varying the pressure between the surfaces of the cylinders. There is also means for spraying a coolant interiorly of the quenching cylinder and on the surfaces of the conveyor.
The invention will now :be described in greater detail with reference to the accompanying drawing which is a diagrammatic illustration of the apparatus shown in side elevation.
Description of the preferred embodiment The apparatus, as herein illustrated, comprises a standard tapping furnace 10 from which the fused product of which the abrasive is to be made is discharged through a spout 12 into a horizontally disposed graphite trough 14, the latter being supported at its opposite ends, subjacent the spout 12, by transversely spaced, inverted V- shaped frames 16-46, each of which has vertically disposed and inclined legs Ida-46a and 16b-16b. The forward side of the trough 14 is open and a quenching cylinder 20, having a diameter in the order of 28", is mounted below the trough for rotation about its longitudinal axis on a shaft 22, the latter being journaled at its ends on the inclined legs Nib-16!) of the frames -16-16. A squeeze cylinder 24, which has a diameter in the order of 20", is mounted in a horizontal position forwardly of the cylinder 20 on a shaft 26 parallel to the shaft 22. The opposite ends of the shaft 26 rest on transversely spaced, horizontally disposed tracks 28-48, the rear ends of which are fastened to the inclined legs lob-4612 and the forward ends of which are supported by the upper ends of vertically disposed legs 3[l-3ii. The lower ends of the legs 30-30 are fixed to the inclined legs 16b-16b. The cylinder 24 is thus free to move bodily toward the cylinder 20 and its surface is held in contact with the surface of the cylinder 20 by weights WW suspended from the rear ends of the flexible cables 32-32, connected at their forward ends to the ends of the shaft 26 and extending rearwardly therefrom over the pulleys 3434, the latter being mounted on brackets 36-36 fixed to the legs 16b-16b.
Below the cylinders 20 and 24 there is a conveyor in the form of a continuous belt 37 entrained at its end about horizontally disposed drums 38--38, one of which is supported at its ends by the legs 16a-16a and the other of which is supported at its ends by legs 4040. The upper surface of the belt 37 is situated about 14" below the line of contact between the cylinders 20 and 24.
The legs 40--40 also support a motor M and drive shaft 42 on which there are multiple sheave sprockets 44-44 about which are entrained roller chains 46-46 and 48-48. The opposite ends of the roller chain are entrained about pulleys 50-50 and 52--52 mounted, respectively, on the ends of the shaft 22 supporting the cylinder 20 and the shaft supporting the drum 38. The cylinder 20 is driven at about 10 to 15 revolutions per minute and the upper run of the conveyor is driven at a speed of about feet per minute.
A spray head 54 in the form of a pipe is disposed within the cylinder 20 parallel to its axis of rotation in a position to direct jets of water against the inner side of the cylinder near the top. By this means, the temperature of the cylinder may be kept well below that of the melting point of the steel which is 1350" C. A spray head 56 is mounted parallel to and adjacent the rear one of the drums 38 at the level of the upper run of the conveyor, so as to project jets of water along the upper surface of the belt toward the area upon which the material falls from the quenching cylinder 20, and additional spray heads 60 are disposed beneath the underside of the upper run of the conveyor for directing jets of water against its underside.
In accordance with the method herein described, the product is 95% alumina produced from bauxite ore by reduction with coke or coal in the furnace and discharged therefrom at a temperature of about 2000 C. into the graphite trough 14 from which it flows forwardly onto the upper surface of the rotating quenching cylinder 20, spreading out thereon in the form of a strip of about 12" wide and A to /8 thick. Since the quenching cylinder 20 is kept at a temperature well below the melting point of the steel (1350 C.) by the water cooling, the strip commences to solidify as it contacts the cylinder and hence to take the shape of the outwardly convex surface of the cylinder. The strip, however, is still plastic when it reaches the squeeze cylinder 24 so that, when it passes between the surface of the quenching cylinder 20 and the squeeze cylinder 24, it is compressed thus reducing the macroporosity. As the strip leaves the line of contact between the cylinders 20 and 24 it commences to break away from the surface of the cylinder 20 by reason of its own weight and fall to the upper surface of the conveyor 37, however, since the strip is still somewhat plastic, it retains enough continuity so that the part resting on the conveyor, at any time, and moving forwardly therewith, assists in pulling the part still on the cylinder from the surface of the cylinder. The dead-weight of the suspended strip, that is, the part hanging down from the cylinder, plus the forward pull which reversibly bends the strip as it leaves the cylinder initiates breaking it into fragments about 12 square. As these fragments move forwardly on the conveyor further cooling breaks then into still smaller pieces.
When examined in cross-section the product discloses a dark dense fine crystal structure of 1 to 30 microns containing some macropores in contrast to furnace Alundum which is brown to pink in color, waxy in appearance, and has a crystal size of 500 microns 1100 in length. State-d according to another method of indicating crystal size, the product has a count of less than 1% in 24 grit and 4 to 14% in 80 grit. The term monocrystal refers to the percentage of whole crystals in any grit size. Crystals produced according to the method are much stronger than coarsely crystal materials and have a superior resistance to wear.
Although the product therein described has a 95% alu mina content, it is to be understood that abrasive products of from 94% to 100% are within the scope of the invention, and that the fine crystal structure improves the properties of the product at all levels within the above-mentioned range.
The principal advantages of the apparatus and method described reside in that the product is finely crystalline; that the time required for making it is drastically reduced; for example, within 10 to 15 minutes after it is poured, it can be crushed for shipment or use in making grinding wheels; and that it can be made much chaaper because it can be more easily crushed and requires less handlin-g and labor.
In the apparatus and method carried out thereby, as described above, the strip of semisolid or plastic alumina is squeezed between the quenching cylinder and squeezing cylinder for the purpose of reducing macroporosity, that is, the pores visible to the unaided eye. It is quite possible, however, to omit the squeezing cylinder and still obtain much finer crystals than with conventional methods of furnace casting due to the fact that quenching can be effected rapidly enough so that the crystals do not have time to grow. Moreover, although the molten material is deposited on the external surface of a cylinder for quenching, it could be deposited on the internal surface of a cylinder, doifed therefrom by rotation, and spilled axially from one end, for example, by inclining the cylinder.
It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.
1. Apparatus for making fine crystal abrasive comprising:
(a) a cylinder mounted for rotation about its horizontal axis;
(b) a trough arranged above the upper part of the cylinder for flowing molten material onto the downwardly moving face of the cylinder to form a layer of substantially uniform thickness thereon as it rotates, means for cooling the surface of the cylinder for effecting rapid partial solidification of the material in a curved shape conforming to the shape of the surface of the cylinder and for controlling crystal growth; 'a conveyor disposed subjacent the cylinder having a surface traveling in a direction away from the downwardly moving face of the cylinder for collecting, engaging and pulling the layer of material in a continuous strip away from the cylinder whereby the curvature of the partially solidified layer of material is reversed with respect to the curvature formed on the cylinder whereby to partially fracture but not fragmentize the layer of material; and
(c) means for cooling the surface of the conveyor to complete solidification of the strip of material thereon and to furthermore completely partially fracture the layer of material whereby to break the material into fragments while being so conveyed, said fragments being suitable for immediate crushing and screening to produce abrasive particles.
2. Apparatus for making fine crystal abrasive acc-ording to claim 1 comprising:
(a) means adjacent the rotating cylinder for pressing against the layer of material on the cylinder for densifying the partially solidified abrasive material.
3. The apparatus of claim 2 wherein said pressing means takes the form of a pressure roller mounted to rotate about an axis parallel to the axis of the cylinder.
4. The apparatus of claim 1 wherein means are provided to rotate said cylinder to have a surface speed within a range of about 470 to 880 inches per minute, and means are provided to drive said conveyor at about 960 inches per minute.
References Cited UNITED STATES PATENTS 1,445,004 2/ 1923 Cowles 18-155 2,071,035 2/1937 Jenett 18-155 2,576,317 11/1951 Toulmin 18-155 3,001,232 9/1961 Martinals 18-155 3,076,999 2/ 1963 Washburn 18-1 1,586,187 5/1926 Ferngren -184 1,818,153 8/1931 Nobbe 65-99 2,624,164 l/l953 Donofrio 18-26 2,659,948 11/1953 Properzi 18-26 3,119,146 1/1964 Crandall et al 18-1 3,187,379 6/1965 Rahm 18-1 3,193,888 7/ 1965 Rochester 18-26 WILLIAM J. STEPHENSON, Primary Examiner.