US3093418A - Fluidising and feeding of finely divided materials - Google Patents

Description

FLUIDISING AND FEEDING OF FINELY DIVIDED MATERIALS Filed Sept. 22, 1960 2 Sheets-Sheet l VACUUM PUMPR 38 COMPRESSOR V as r35 1 W I if 1 I 374 s i/l. I 1 z 2 INVENTOR. ALLA/v MACKENZIE Dosuz June 11, 1963 A. M. DOBLE 3,

FLUIDISING AND FEEDING OF FINELY DIVIDED MATERIALS Filed Sept. 22, 1960 2 Sheets-Sheet 2 INVENTOR. ALLA/v MACKENZIE 00515 nited States Patent 3,093,418 FLUIDISING AND FEEDING F FINELY DIVIDED MATERIALS Allan M. Doble, 206 Poath Road, Melbourne, Victoria, Australia Filed Sept. 22, 1960, Ser. No. 57,792 2 Claims. (Cl. 302-17) This invention relates to the fluidizing and feeding of powdered, finely-ground and other finely divided materials and refers especially, but is not limited to, the feeding of abrasive material to blast guns and the like.

In the abrasive blasting art a system was proposed for fluidizing and feeding finely-divided abrasive material from a closed container havinga horizontal porous bottom which provided for the entry of atmospheric air to fluidize the material when the interior of the container was connected to a vacuum pump or the like. This system employed a vertical discharge pipe extending upwardly through the porous bottom into the body of abrasive material in the chamber an'd this pipe, open at its upper end, was connected at its lower end to an intermediate portion of an air pipe which extends from the upper end of the closed container to a blast gun. The gun was arranged Within a sealed cabinet having a hopper bottom connected to the vacuum pump through a cyclone separator. The solid material consisting of the abrasive material and of particles removed from the workpieces within the cabinet, was returned from the cyclone to the container for re-circulation.

Thus, in the above described apparatus when the vacuum pump was operating and the valve of the gun was open, air was continuously withdrawn from the top of the sealed container and replaced by air which entered through the porous bottom of the latter and which passed upwardly through and so fluidized the abrasive material therein. Also, the fluidized material continuously entered the upper end of the vertical discharge pipe and gravitated therefrom into the air pipe, whereby it was conveyed by the air stream to the blast gun.

In all such abrasiveblasting operations, the debris removed from the workpieces, and which consequently becomes miXed wtih the abrasive, is generally of comparatively coarse particle size and thus it is undesirable that this material should be re-circulated. For this reason, in the aforesaid prior art system, the discharge pipe had its upper end located some distance above the bottom of the container, whereby when the bed was fluidized, it was intended that the coarser particles gravitate to the bottom of the container where they could not enter the discharge pipe.

However, the aforesaid system proved to have several disadvantages, one problem being that the coarse abrasive material or debris was not separated to the desired extent within the closed container. Thus, during the operation of the apparatus a large number of the coarse abrasive particles and debris entered the vertical discharge pipe and were re-circulated to the blast gun, and this seriously reduced the quality of the surface treatment in these fine particle abrasive systems.

Another disadvantage of the prior art devices of the aforementioned type was that they did not provide an effective means to regulate the rate of feed of the abrasive material. Such feed regulation is essential in order to provide an efficient blasting operation under various conditions including the type of material being treated and the surface finish desired.

Therefore, one principal objective of the present invention is to provide na improved fluidizing and feeding apparatus for finely divided materials which completely separates out the coarse abrasive particles and debris and re-circulates only the fine particles to the blasting gun.

. 3,093,418 Patented June 11, 1963 -or alternatively, by connecting the interior thereof to a source of reduced pressure.

Another important object of my invention is to provide a novel arrangement of components wherein a simple yet reliable means can be utilized to regulate the rate of feed of the abrasive particles in the air stream.

In carrying out the aforementioned objects, my invention includes apparatus comprising a storage chamber having a porous bottom, and a novel upstanding partition therein separating the storage chamber to form a feed chamber that is closed at its upper end and open at its lower end. The lower edge of the partition is spaced above the bottom of the storage chamber so that the coarse abrasive particles and debris may gravitate there- -below. .A discharge passage communicates with an upper portion of the feed chamber and restricted air passage connecting the storage chamber above the material therein to an upper part of the feed chamber.

' Thus, when air or other gas enters the storage chamber, it passes upwardly through the porous partition and fluidizes the abrasive material, and some of the air then the highest within the feed chamber and an effective separation of coarse particles is thereby obtained. When the upper surface of this colurnn is disposed sufiiciently close to the entrance to the discharge passage, the fiuidized material is then swept thereinto by an air stream which flows substantially across the top of the column. "The problem of regulating the rate of feed of the abrasive material has been solved in my invention by varyirig' the position of the upper end of the column relatively to the discharge opening and thisis preferably effected by means of a valve for regulating the flow of air through the restricted passage. Alternatively, provision may be made whereby the said discharge opening 'may be raised or lowered to regulate the flow of abrasive p t c e v v According to a preferred arrangement of the present invention, the novel feed chamber is formed by a more or less vertical duct which is arranged centrally within the storage compartment. The vertical duct is preferably of a tapered formation so that it converges upwardly whereby the velocity of the material increases as it rises up the duct. i 1

Other objects and advantages of the invention will appear from the following description of a preferred embodiment and description of the operation thereof, given in accordance with 35 USC 112.

In the following description of preferred forms of the invention reference is made to the accompanying drawings wherein:

FIG. 1 is a view in elevation and in section showing apparatus according to one form of the invention;

FIG. 2 is a view in cross section taken along the line .22 of FIG. 1; and

FIG. 3 is a view in elevation and in section of apparatus according to a modified form of the invention.

The apparatus illustrated in FIGS. 1 and 2 of the drawings is directed to one form of my invention for fluidizing and feeding finely divided abrasive particles. As shown, the apparatus 10 comprises a storage chamber 11 having an upper part of elongated vertical cylindrical form and a lower part of downwardly convergent conical shape. Attached to the lower end of the storage chamber 11 is an integral flange 12 of annular formation. Near the bottom of the storage chamber 11 are fixed diametrically opposite lugs 13 which carry bolts 14 that are pivotally connected thereto. The bolts 14 carry wingnuts 15 and serve to retain in position a filter box 16.

The filter box 16 comprises a plate 17 which is slotted to receive the bolts 14, and a ring 18 fixed to the plate 17 so as to define a circular space within the filter box. The ring 18 has a flange 19 adapted to engage the flange 12 with a gasket 20 interposed. A spacing ring 21 is inserted within the filter box, and a disc 22 of porous stone or some other suitable porous material such as a resin bonded quartz filter, is supported by the ring 21 so that its upper surface is flush with the upper surface of the flange 19. An inlet pipe 23 is provided to admit air into the filter box below the porous disc 22. It will be evident that the filter box 16 is readily detachable to unload the storage chamber 11 and provide access thereto. If desired, an opening (not shown) may be provided in the side of the chamber 11 immediately above the filter 22, and provided with closure means which can be removed to permit the periodic removal of coarse particles which tend to settle on the porous disc 22.

To perform the novel columnating action the fluidized abrasive particles within the storage chamber 11, I utilize a novel vertical duct or feed chamber 25 which constitutes an important feature of the invention. The feed chamber 25, as shown in FIG. 2, is preferably a rectangular shape in cross section and is arranged centrally within the chamber 11 with its upper end disposed above the normal level of the abrasive material within the chamber 11, while its lower end is disposed a substantial distance above the top of the porous disc 22. The duct 25 is closed at its upper end, while its lower end is open so as to communicate freely with the interior of the chamber 11.

A discharge pipe 26 is arranged above the level of the material in the storage chamber 11, and it extends through one wall of the feed chamber 25 through the storage chamber 11 and out one wall thereof. An air inlet hole 27 is formed in the wall of the feed chamber 25 at approximately the same height as the discharge pipe 26 so as to connect the feed chamber 25 to the upper portion of the storage chamber 11. A needle-type regulator valve 28 extends through the wall of the storage chamber 11 so as to provide for regulation of the effective size of the air hole 27 by turning the handle 29 thereof. Thus the flow of air through the hole 27 may be restricted to any desired extent.

As indicated in the drawings, the duct 25 is of oblong shape in plan view as shown in FIG. 2; and the discharge pipe 26 extends centrally into one of the end walls thereof, while the air hole 27 is arranged in one of the side walls adjacent to the opposite end wall and on the opposite side of a shallow transverse baffie 30 which depends from the closed upper end 31 of the duct and has its lower edge arranged slightly below the level of the discharge pipe 26. Thus the air must pass below the baflie 30 in flowing from the air inlet hole 27 to the discharge pipe 26.

The apparatus 10 illustrated in FIGS. 1 and 2 would normally be used for supplying powdered abrasive material to a blast gun in a system similar to the type described above. Thus, to illustrate my invention as it would be employed in a complete blasting system, I have shown the storage chamber 11 arranged below a cyclone separator 32 or other equivalent means, from which the abrasive and other solid material descends into the storage chamber 11. A vacuum pump 33 is connected to the cyclone separator 32 by a duct 34. A blast gun 35 of the conventional ejector type wherein a high velocity compressed air jet induces a secondary flow of abrasive-laden air is located within a blast gun cabinet 37 which is connected by a suction line 38 to the cyclone separator 32. Accordingly, the blast gun 35 is connected to the discharge pipe 26 and to a source of compressed air controlled by a valve '36. The air inlet pipe 23 is preferably connected to a silica-gel moisture trap 39 to dry the air entering the storage chamber 11.

In the operation of the apparatus 10 when used in the abrasive blasting system shown in FIGS. 1 and 2, a partial vacuum is maintained in the blast gun cabinet 37 by means of the suction pump 33 connected to the blast gun cabinet 37 through the cyclone separator 32 located above the storage hopper 11. When the valve of the blast gun 35 is open, air is induced to flow into the cabinet 37 from the discharge pipe 26 through the gun 35. Thus the pressure in the feed chamber 25 is reduced to cause a flow of air thereinto from the upper part of the surrounding storage chamber 11, but due to the restriction of the air hole 27, there is an appreciable pressure drop from the storage chamber 11 to the feed chamber 25.

The reduction in the air pressure due to the vacuum pump 33 within the storage chamber 11 causes air to pass into the bottom thereof through the inlet pipe 23 and the porous disc 22 and then upwardly through the abrasive material which is thereby fluidized in the usual way.

Due to the reduced pressure within the feed chamber 25 and to the fluidized condition of the abrasive material, this material now rises within the chamber 25 in the form of a column as portrayed in FIG. 1 and when the surface of this column reaches a suflicient height, the air in flow ing across the chamber 25 and around the bafile 30 from the aperture 27 to the discharge pipe 26, sweeps over and erodes the surface of the column, so that the abrasive material is carried at a corresponding rate into the pipe 26. The position of the upper surface of the column may be varied, by controlling the pressure within the upper end of the feed chamber 25 by means of the regulating needle valve 28, and thus the rate of feed of the material may be regulated as desired.

As the lighter and smaller particles tend to rise higher than the heavier and coarser particles, a classifying action takes place. That is to say, the coarser particles do not rise to the top of the column, so that an effective separation is produced. Thus the coarse particles tend to sink to the bottom of the storage chamber 11 and accumulate on the top of the filter box 16 in the form of a layer as indicated in FIG. 1. This layer assists in uniformly distributing the incoming air in the body of the finely divided material. However, if the amount of accumulated coarse material becomes excessive, it may be removed manually through the opening referred to above.

Reference is now made to FIG. 3 of the drawings which illustrates, partly in schematic fashion, abrasive blasting apparatus including fluidizing and feeding means according to another form of the invention. The apparatus shown in FIG. 3 comprises a sand blasting cabinet 40 to the bottom of which there is connected a conical storage chamber 41. At the bottom of the storage chamber 41 a filter box 42 is mounted with a porous block 43 of the type previously described located therein.

The storage chamber 41 is provided with a central feed chamber 44, but instead of being of uniform cross section the feed chamber 44 is made of conical or pyramidal form so that its cross section diminishes towards the top. The upper end of the feed duct or chamber 44 is connected to a discharge pipe 45 which may extend outwardly through the wall of the chamber 41 or may be connected directly to a sand blasting gun 46 as shown in FIG. 3. The junction of the feed chamber 44 with the outlet pipe 45 is effected by means of a T-joint 47, and a pivot tube 48 is mounted within the T-joint 47 so that it faces towards the outlet pipe 45. A pipe 49 provided with a control valve 50 leads from the interior of the cabinet 40 and is connected to the other arm of the T-piece 47. The valve 50 operates in a similar manner to the needle valve 28 shown in FIGS. 1 and 2, i.e. it serves to control the pressure differential between the chamber 41 and the top of the feed duct '44 and so controls the height of the column of fluidized material in the feed duct 44.

The apparatus also includes a pressure air-line 51 having one branch 52 which is connected to the filter box 4 2 through a valve 53, and a second branch 54 which is connected to the blast gun 46 through a valve 55.

In the operation of this form of the invention, compressed air supplied by a compressor 57' and admitted through the valve 53 to the filter box 42 causes the material within the chamber 44 to be fluidized, while the compressed air admitted through the valve 55 to the blast gun 46 induces a flow of air and suspended material through the outlet pipe 45 to the blast gun 46. The blasting gun 46 may be manipulated manually within the cabinet 40 using a flexible protective shield 58 in the wellknown manner.

By closing the valve 50 to restrict the fiow through the pipe 49 and by opening valve 53 to increase the flow of fluidizing air, the amount of abrasive particles carried through the pipe 45 can be increased, whereas if the valves 50 and 53 are operated in the reverse manner the amount of abrasive particles in the air carried through the pipe 45 can be reduced.

An important feature of the construction of FIG. 3 is that at the bottom of the duct 44 the vertical travel of the abrasive particles is comparatively slow whereas at the top of this duct the speed of travel of the particles is considerably greater in view of the smaller cross sectional area. It is found in practice that this arrangement leads to an even rate of feeding at both high and low concentrations of the abrasive particles in the air stream.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. Apparatus for fluidizing and feeding finely divided materials comprising: a storage chamber having a porous bottom; a feed chamber mounted within said storage chamber, said feed chamber comprising a vertically ex tending duct open at its lower end and closed at its upper end, said duct having a frusto-conical form with a cross section that diminishes towards its upper end; the lower edge of said duct being spaced above the bottom of said storage chamber whereby the material may gravitate therebelow; a restricted air passage connecting the storage chamber above the material therein to an upper part of said feed chamber; and a discharge passage communicating with an upper portion of said feed chamber.

2. Apparatus for fiuidizing and feeding finely divided materials comprising: a storage chamber having a porous bottom; a feed chamber mounted within said storage chamber, said feed chamber comprising a vertically extending duct open at its lower end and closed at its upper end, said duct having a cross section that diminishes towards its upper end and a lower edge spaced above the bottom or" said storage chamber whereby the material may gravitate therebelow; a T-joint conduit having a stem and two branches, said stern being connected to the upper end of said duct; a pipe having a restricted air passage connecting the storage chamber above the material therein to one said branch of the T-joint; and a discharge conduit connected to the other said branch and thereby also communicating with an upper portion of said feed chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,707,132 Baresch Apr. 26, 1955 2,758,564 Randall Aug. 14, 1956 2,924,489 Beckmann Feb. 9, 1960

Claims (1)

1. APPARATUS FOR FLUIDIZING AND FEEDING FINELY DIVIDED MATERIALS COMPRISING: A STORAGE CHAMBER HAVING A POROUS BOTTOM; A FEED CHAMBER MOUNTED WITHIN SAID STORAGE CHAMBER, SAID FEED CHAMBER COMPRISING A VERTICALLY EXTENDING DUCT OPEN AT ITS LOWER END AND CLOSED AT ITS UPPER END, SAID DUCT HAVING A FRUSTO-CONICAL FORM WITH A CROSS SECTION THAT DIMINISHES TOWARDS ITS UPPER END; THE LOWER EDGE OF SAID DUCT BEING SPACED ABOVE THE BOTTOM OF SAID STORAGE CHAMBER WHEREBY THE MATERIAL MAY GRAVITATE THEREBELOW; A RESTRICTED AIR PASSAGE CONNECTING THE STORAGE CHAMBER ABOVE THE MATERIAL THEREIN TO AN UPPER PART OF SAID FEED CHAMBER; AND A DISCHARGE PASSAGE COMMUNICATING WITH AN UPPER PORTION OF SAID FEED CHAMBER.

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