US2618013A - Apparatus for forming pellets - Google Patents

Description

mf W11] 504M411 INVENTOR-i I a; ATT RMEYi Filed Aug. 2, 1949 S A WEIGAND ETAL APPARATUS FOR FORMING PELLETS Patented Nov. 18, 1952 UNITED S'lTES PATENT ()FFICE AtPARATUS FOR FORMING PELLETS tion of Ohio [application August 2, 1949, Serial No. 108,207

4 Claims.

stream against the surfaces of metal objects such as castings which are to be cleaned thereby.

In recent years metallic particles of an abrasive nature have been used extensively in grit blasting operations in preference to finely divided sand which was commonly used in the past. Such metal grit has been produced heretofore by crushing metal of a frangible nature or by dropping molten particles of metal into a bath of water which chills them promptly so that the particles retain their integrality. In other instances molten metal is subdivided by slinging it from the face of a rotating disk. However, the shot produced by any of these methods has varied sub-' stantially in particle size, a large percentage of the grit being either too large or too small to be used extensively for grit blasting operations. Hence, extensive screening of the yield shot has been required to separate the fines and over-sized materials, and the yield of particles of the desired size has been relatively low in relation to the Whole amount of comminuted metal. Small particles cannot be used effectively and usually are wasted as impalpable dust, while particles which are too large produce an undue rough or peened efiect upon the work which has been grit blasted by them.

The principal objective of this invention has been to provide an apparatus for producing metallic shot particles or pellets which are adapted particularly for blast cleaning and which, as produced, bear a greater uniformity, from particle to particle, than the shot or grit prepared by the past methods. The objective of the invention also has been to provide apparatus which is controllable to produce shot of given particle size with a minimum yield of particles which are smaller and larger than the particles intended to be produced.

In the practice of this invention various metals may be comminuted but the invention is disclosed particularly in relation to the manufacture of pellets of copper alloy suited for use in the cleaning of copper base castings according to the method disclosed and claimed in the copending United States application of Bolton and Weigand of the native metal of the casting and which retains its original grit blasted appearance during processing or storage to much better advantagethan the surfaces of similar castings which have been cleaned by the use of the common sand or metal abradants. The shot disclosed in the aforesaid patent application which has been found to possess this peculiar property, typically but not necessarily, may consist of an alloy of approximately 82 /2 copper, 14% zinc and B /2% silicon; it preferably ranges in particle size from 20 to AFA sieve mesh and displays a Brinell hardness of substantially 50 to 100.

Shot of this nature, when impacted in a velocity stream against the surface of a casting fabricated of steam or valve bronze, bronze of the Navy M specification, or of alloy A. S. T. M.-D61 or D62, While dislodging any dirt, adherent sand or oxide film that may be present, imparts a surface skin or film having the appearance of the native metal, but this surface does not tend to become smudged or to accumulate dirt as does the surface of a commonly grit blasted casting. Hence, castings treated by the process of the aforesaid patent application retain the pleasing appearance that they possess on leaving the grit b asting machine. Since large quantities of shot of suitable alloy are utilized in the surface finishing of cuprous alloy castings of the type described, in the form of valve bodies, steam fittings, plumbing fixtures and the like, this invention is disclosed particularly in relation to a process for producing suitable alloy abradant in a convenient manner, with a minimum yield of off-size particles. However, though the invention is disclosed in this environment, the apparatus of the invention is suited for the production of grit particles from metals other than the alloys mentioned specifically.

Briefly, a method using the apparatus of the invention comprises dropping the stream of molten metal, at a given rate, upon a splash plate, sweeping the splashing molten metal from the splash plate by a velocity stream of air substantially coincidental to the spattering of the molten metal on the splash plate and thereby subdividing v the splash particles, then freezing and collecting the particles which are so produced. This method has, peculiarly, been found to produce a high yield of particles of given size, even though the particles of spatter as produced by the mere falling of the molten metal are not apparently of uniform size or shape. In any event, through the control of the temperature of the molten metal, the height of fall, the rate of flow of the molten metal on the splash plate, and the velocity of the sweep stream, finished particles of remarkably uniform size within a given range may be produced. Therefore, the process enables maximum production of shot of substantially uniform size in a given range-or size to be obtained.

Apparatus adapted for the practice of the method asdescribed" may be simple and inexpensive. A typical production unit is shown, somewhat diagrammatically, in the drawings in which Figure 1 is a cross section and Figure 2 is a top plan view.

In the apparatus shown in the drawings; a

splash plate I is mounted over a: tank or. con-' tainer 2. The splash plate whichmay'be made of steel is inclined toward the inside of the container which is partly filled with water, as indicated by the level 3. A stream ofmolten metal is furnished to the splash plate from a crucible 4, or other suitable sources, which is constructed and arrangedv to provide' a: stream of relatively uniformsize or. rate ofefiow, and the source ofmoltenmetal is-high enough above the splash plate-tocause the stream-to-spatter upon-impact withithe splash-plate. Side plates 55-b0und the area-.of impactof-the-streamof moltenmetal on the splashiplate to prevent side escapeof moltenparticles and to-facilitate in their disintegration.

as-discussed ata-later point in the specification.

Adjacent the areapof impact of the moltenstream of; metal upon the splash-plate I- an air nozzle 8' is'arrangedto causea-streamof air of substan-* tial velocity to sweep overthe surface of the splash plate ina direction substantially parallel to fit: such-that metal fallingupon the splashsurface,-, including the spatter, isblown from the plate over thesurface of-the tank-2 Belowthe: lower edgeof thesplash plate; but above the watcr level in the container, a second steel plate I'- is mounted, this one being angulatedslightly upwardlyin relation to the waterlevel, the planzof configuration of this. second plate. beinginthepath ofparticles which are swept 01f ofthe splash plate by the air stream so that. metal particles.- proceedingdown the splash plate, substantially in parallelismwith it, will? bedeflected from. their path when striking the plate. In Beyond plate 1 the tankis provided-.with abafile B-Whichmay bein the form of.a sheetof metal ofsemi-circular. configuration stood onendvertically in the. tank-2. Thus particles projectedfrom plate 'I,- as-wellas other metalparticles:whichleave splash plate'l but never hitv the deflector. Tare all caught by the baffie andfall in the. water in thetank. A cover plate 9 may-beextended'across thetop of bafile 8- to.prevent:.escape upwardly of theparticles.

The splash plate iscoo1ed and spattered with molten metal which is facilitated by-maintaining a..film-of water. upon its surface. This is-providedthrou-ghthe jet 1 il' which delivers the water toapoint just-aheadof the-air nozzle fi. The

side. plates 5'I5'are also flushedwithwater from The "surface of this baffiethus has a thin film ofwatermaintained over all of the areas of its'surface against'which' hot'or molten. particles are blown-fromthesplashpiate:

Water is supplied to tank 2 by a jet tube l5 having a regulating valve It, and is discharged by a drain line communicating with the tank on the side opposite to the tube l5, the rate of drainage being regulated by the valve ll. The jet from the tube l5 prevents undue accumulation of pelletsinthe water directly adjacent the baille E! by washing themto other portions of the tank. The drain valve may be adjusted to prevent the water level in the tank from rising due to the water being drained into it from splash plate I and heme i and if necessary, the water stored inthetank maybe cooled and agitated by projecting into-ita stream of fresh water through jet tubel5; either constantly or intermittently.

When the stream of molten metal from the crucible or supply source hits the splash plate it spatters'vigorously, especially in the presence of thewater' film which is maintained upon its surface. The exact nature of the process of subdivision-which occursis difficult to determine sincetlie atmosphereisbe clouded-by steam and:

- ditional particles moving: downwardly in subwhich is struck by a particle ofmoltenmetaltends: to subdivide the particle. The heavier globules-striking plate I are subdivided upon impactand tlie smaller subdivided particles are projected. by the. air stream directly to the baffle 8 while the larger andheavier ones tend to deflect downwardly upon plate. I. Hence, the heavier subdividedparticlsstriking the nearer surface Production of shot particles of a'given size iscontrolled by adjustment of the size of the stream of moltenmetaland rateof fall as governed by the height'of l'thesource of supply over the splash plate, as well as by the pressure or velocity of the airissued from the nozzle 6 and the relative distancesand angles of disposition'of the splash plate I and plate 1.

As one example, inproducing shot from the alloy of" copper, zinc and silicon adapted. to be used in the process'of the aforesaid pending patent application, wehave found that the alloy may" fall from a'height of approximately in a stream which is apparently. in the neighborhoodof /a in diameter. The angle of incline ofthe splash plate may-be approximately 25"tothehorizon'tal whilethe angle of incline of plate I may be approximately 5. With air supplied to the nozzle 6 at a pressure at 90 lbs. per square inch, substantially two-thirds of the product collected in the tank 2 will be constituted by rounded pellets which will pass a 20 mesh screen but will not pass a 70 mesh screen. In producing pellets from a cuprous alloy of the type described it is preferably to blanket the molten metal in the crucible or container from which it is supplied with a flux consisting of approximately equal parts of borac and sodium carbonate to which by weight of lead oxide is added. The flux apparently reduces the surface tension of the molten metal to permit the desired subdivision of particles. Without the flux, the stream of metal does not disintegrate properly upon impact and tends to form a relatively high percentage of elongated particles or particles of fibrous nature.

The foregoing data is given by way of illustration but not by way of limitation. Particles of larger size than those indicated, but having similar uniformity, may be produced by increasing the rate of flow or decreasing air blast pressure. On the other hand, the size of the particles may be decreased by increasing the height of the fall or the air blast pressure or both. Our tests have shown that rounded pellet-like shot containing 50% or more capable of passing 20 mesh screen is desirable for final cleaning of small castings or castings having relatively delicate surface configurations and, in our experience, the height of fall of approximately 80" yields such product in large percentage.

Large quantities of shot of the desired configuration may be furnished with simple apparatus of small size and low cost.

Having described our invention, we claim:

1. An apparatus for manufacturing metal pellets suitable for use in grit blasting operations comprising; a tank adapted to contain a water bath, a bafile at one end of said tank, a splash plate mounted angularly with respect to an end of the tank, in spaced relation to said baflle means mounted above said splash plate adapted to drop a stream of molten metal upon the splash plate from a height sufficient to cause spatteringof the stream upon impact with the plate, means for maintaining a film of water upon the surface of the splash plate, means for supplying a blast stream of air across the plate to propel spatter globules from the plate, a deflector plate interposed between the splash plate and baiiie at a plane below the splash plate, the deflector plate being angulated in a direction to deflect to below the splash plate, the deflector plate being angulated from a horizontal plane toward the splash plate, supply means above said splash plate adapted to drop a stream of molten metal upon the plate to spatter the stream and form globules, means for supplying an air blast across the spatter zone to blow a portion of the globules directly to the vertical baflle and another portion of the globules from the splash plate to the deflector plate and to the baflle by deflection, the concave surface of the baffle being adapted to deflect into the tank the particles propelled at various angles from the splash plate and deflector plate.

3. Apparatus for forming pellets suitable for grit blasting from molten metal, which comprises the bafile globules which are projected from the splash plate.

2. An apparatus for manufacturing rounded metal pellets for grit blasting operations comprising; a tank adapted to contain a water bath, a relatively flat splash plate mounted over a portion of the tank, the plate being angulated from a horizontal plane toward the opposite end of the .tank, a baflie disposed at the opposite end of the tank and having a configuration vertically which presents a concave surface toward the splash plate, a relatively flat deflector plate disposed between the splash plate and baiile at a plane a water tank having a collector bafiie at one portion thereof and a splash plate spaced from the bafile over another portion of the tank, said splash plate being inclined on an angle so as to deflect molten metal falling upon it toward the bafiie, the said splash plate bein adapted to cause a stream of molten metal falling upon it to spatter into globules, means for providing a blast of air over the surface of the splash plate to sweep spatter therefrom generally in the direction of the baffle, and a secondary impact plate which is disposed above the tank intermediate the said splash plate and the bafile, in position to deflect and coincidentally subdivide relatively larger particles of spatter which are swept from the said splash plate by the air stream.

4. Apparatus for forming pellets suitable for grit blasting from molten metal, which comprises a water tank having a collector baiile at one portion thereof and a splash plate spaced from the bafile over another portion of the tank, said splash plate being inclined on an angle so as to deflect molten metal falling upon it toward the baffle. the said splash plate being adapted to cause a stream of molten metal falling upon it to spatter into globules, means for spraying water over the collector surface of said baflle, means for providing a blast of air over the surface of the s splash plate to sweep spatter therefrom generally in the direction of the baflie, and a secondary impact plate which is disposed above the tank intermediate the said splash plate and the bafiie, in position to deflect and coincidentally subdivide relatively larger particles of spatter which are swept from the said splash plate by the air stream.

SYLVESTER A. WEIGAND.

ANTHONY B. MONNIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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