US3210131A - Conveying system for particulate materials - Google Patents

Description

Oct. 5, 1965 w. M. BOOTH ETAL CONVEYING SYSTEM FOR PARTICULATE MATERIALS 2 Sheets-Sheet 1 Filed Jan. 31, 1963 INVENTORQ W/ZHAM M. BOOTH BET/V44 0 6'. k/lff ATTORNEY United States Patent 3,210,131 CONVEYING SYSTEM FOR PARTICULATE MATERIALS William M.'Booth, Grand Haven, and Bernard G. Witte, Newaygo, MiCh., assignors to Newaygo Engineering Company, Newaygo, Mich., a corporation of Michigan Filed Jan. 31, 1963, Ser. No. 255,242 3 Claims. (Cl. 302-53) This invention relates to a pneumatic conveying system for particulate materials, and more particularly for foundry sand.

This application is a continuation-in-part of application Serial No. 58,550 filed September 26, 1960, now abandoned, of William M. Booth entitled Conveying System for Particulate Materials.

Usually, foundry sand is conveyed from one point to another in a foundry by conveyor belts. However, conveyor belts are slow and are unable to handle the large amounts of sand necessary to supply the needs of a modern high-capacity foundry. It has therefore been proposed in the past to convey sand pneumaticall from one foundry station to another. Prior installations of this type have used pressure-tight transporter hoppers which were charged with sand. Compressed air under high pressure was then introduced into the top of the hopper to push the sand downward into a conveying tube. This system had several drawbacks; first, foundry sand, particularly after it has gone through the muller, is very adherescent and therefore tended to compact in the transporter hopper and clog the conveyor tube.

For the same reason, it was necessary to provide large conveyor tubes with very gradual bends in them. The necessity for gradual bends in the tube often required considerable excavation in prior art installations because the transporter hopper could not be mounted high enough above the floor of the foundry to lead the conveyor tube away from it at the required radius without going below the floor level. When the system did operate, the friction of the sand against the outside walls of the tube in the gradual bends would cause such substantial abrasion of the conveyor tube that expensive repairs had to be undertaken at frequent intervals. Furthermore, a considerable amount of compressed air was required to transport the sand in these prior art applications; a typical such installation would, for example, transport three to four pounds of sand per cubic foot (at atmospheric pressure) of compressed air. Finally, the rapid transport of the sand in these prior installations, as compared to conveyor belt installations, did not permit the used sand to cool to handling temperatures before being delivered back to the molding station, so that expensive cooling devices were required.

It was next proposed in US. Patent No. 2,794,686 (now Re. 24,716) to improve the flow of sand through the conveying pipe by providing the base of the transporter hopper with a ring of air jets to continuously stir the sand in the hopper during transportation and by providing boosters at intervals along the conveying pipe in which similar rings of jets theoretically imparted a helical motion to the sand to prevent clogging during the conveying process. This system, however, reduced friction of the sand against the pipe Walls only partially, and the discreteness of the air jets caused heavy turbulence and severe abrasion of the equipment in the vicinity of the jets. Also, the abrasion caused by centrifugal forces in bends of the pipe still caused heavily unilateral wear of the pipe on the relatively weak outside wall of the bend.

The present invention overcomes all these problems by providing for the introduction of the compressed air into both the hopper and the pipe in a continuous, uniform, spirally rotating laminar flow in such a manner that the sand is in effect held in suspension throughout the system away from the Walls of the system and is simul taneously maintained in sufficient agitation to prevent its compacting. This improvement results not only in considerably less wear by greatly reducing sand friction against the hopper and conduit walls, but it also permits a much more efficient utilization of the compressed air. For example, a typical installation according to this invention can transport six to eight pounds of sand per cubic foot of air. The suspension action which reduces abrasion and prevents compacting of the sand furthermore makes it possible to use much smaller conveying pipes with sharp bends. This in turn has two advantages: first, excavations are no longer necessary because the conveying pipe can be laid entirely above ground; second, experience has shown that pads of compacted foundry sand from along the outside walls of the conveying pipe in the sharp bends. These sand pads absorb the impact of the conveyed sand particles and greatly reduce the abrasion of the pipe at the bend.

The sudden expansion of the compressed air as it leaves the annular jets causes this air to become highly chilled. Due to the much greater quantity of air delivered by the annular jet of this invention as compared to the discrete jets of the prior art, the air in the present system cools the sand to a considerable degree, thus dispensing with the necessity for special cooling apparatus.

It is therefore the primary object of this invention to provide a fast, efficient, wear-resistant pneumatic conveying system for foundry sand having a high sand-to-air ratio.

It is a further object of this invention to provide a pneumatic conveying system for particulate materials which requires no special excavations or other construction measures.

It is another object of this invention to provide a foundry sand handling system in which the sand is substantially suspended by a rotating, laminar air cushion in spaced relation to the walls of the conveying components during the conveying process.

It is yet another object of the invention to provide for rotation of the sand-supporting laminar conveying air film in a direction compatible with the forces arising from the earths rotation.

It is yet a further object of the invention to provide for discharge of the conveying air at an angle to adjacent walls of the conveying components so as to combine maximum conveying efiiciency with minimum wear.

It is a still further object to provide a pneumatic foundry sand handling system which is free from bridging even when highly adherescent sand is used.

It is still another object of this invention to provide a foundry sand handling system which makes it possible to cool the sand while it is being conveyed.

These and other objects of this invention will become apparent from a perusal of the following specification, taken in connection With the accompanying drawings in which:

FIG. 1 is a diagrammatic elevation of a system constructed according to this invention;

FIG. 2 is a fragmentary vertical section through one form of transporter hopper which can be used in the system of FIG. 1;

FIG. 3 is a horizontal section along line IIIIII of FIG. 2;

FIG. 4 is a detail vertical section of the impeller manifold along line IV1V of FIG. 3;

FIG. 5 is a vertical section through the conduit jet; and

FIG. 6 is a vertical section along line VI-VI of FIG. 5.

Basically, the system of this invention uses a pressuretight hopper (generally referred to hereinafter as the transporter hopper) into which charges of particulate material,

such as foundry sand, are intermittently introduced. (The resulting intermittent operation of the system can be eliminated by providing two transporter hoppers connected to the same conveying conduit by switch means such as that disclosed in the copending application Serial No. 236,930 filed November 13, 1962 and entitled Switch for Pneumatic Conveyors. In such an installation, one transporter hopper can be charged while the other is conveying.) Pressure means such as compressed air are provided to create a pressure in the transporter hopper so as to bias the particulate material toward the conveying conduit. The compressed air is introduced into the transporter hopper in a generally tangential direction so as to provide a continuous, swirling laminar air flow along the walls of the transporter hopper which in effect suspends the sand in spaced relation to the walls of the hopper during the conveying process. This effectively reduces adhesion of the material to the sides of the hopper, bridging of the material across the conveying conduit, and abrasion of the hopper walls. In accordance with one aspect of the invention, abrasion is further reduced by discharging the air stream into the hopper at an acute angle to the hopper walls, rather than parallel thereto.

Jet means are provided in the conveying conduit near the transporter hopper to draw the particulate material out of the transporter hopper, thus assisting the action of the pressure means in the transporter hopper itself. Compressed air is introduced tangentially into the conduit jet means so that it exits from the jet in a continuous, spiraling laminar stream forming a revolving cylindrical air cushion which keeps the particulate material away from the inner walls of the conveying conduit. The particulate material is thus substantially suspended in the center of the conveying conduit. Unlike the individually oriented, discrete jets of the prior art, the laminar jet of this invention creates a distinct vacuum (about ten pounds per square inch) in the transporter hopper when the conduit jet is operated alone. This vacuum effect considerably increases the transporting power of the impeller. The sudden expansion of the compressed air as it leaves the jets also chills the air so that the particulate material is cooled thereby during the conveying process.

For the same reason as mentioned above in connectionwith the hopper, and also because of the desirability of avoiding discontinuities in the conveying conduit, the air stream of the conduit jet is introduced into the conduit at an angle to the conduit walls.

In both the impeller and the conduit jet, another aspect of the invention teaches that counterclockwise rotation of the laminar air cushion, in the direction of conveying, materially improves the performance characteristics of the system. This improvement is due to the action of the earths rotational forces in the Northern Hemisphere on the revolving air cushion.

It the system is used to convey foundry sand, sharp bends may be purposely formed in the conveying conduit to cause the formation of pads of compacted foundry sand along the walls of the conveying conduit on the outside of the bend. These sand pads absorb the impact of the sand particles as they go around the bend and thus reduce abrasion of the conveying conduit at the bend.

At the end of the conveying conduit, the particulate material is tangentially introduced into a cylindrical receiving hood which slows the particles down by friction against the walls of the hood. The slowed particles then are allowed to drop by gravity into a receiving container such as a bin.

' Referring now to FIG. 1, foundry sand 20 coming, for example, from a muller (not shown), arrives by any suitable transportation means such as conveyor belt 22 and is dumped into the storage bin 24. A transporter hopper 26 is located underneath the storage bin 24 and is adapted to receive sand therefrom when the cover 28 of transporter hopper 26 is opened. Suitable means for accomplishing this are shown in the copending application Serial No. 175,993 filed February 27, 1962, and entitled Valve for Pressurized Hopper.

A compressor 31) cooperating with an air tank 32 and a pressure regulator 34 supplies compressed air at a constant pressure of e.g. one hundred pounds per square inch to the air system 36 which supplies compressed air to the impeller 46) and jet 42 through control valves 44, 45, respectively. If desired, the top of hopper 26 may also be pressurized. An atomizer 46 may be provided in the jet air line 48 to introduce a finely dispersed treating agent into the conveying conduit or pipe 50 is desired.

Sand pads 52 which form in the portions 54, 56, and 58 of the conveying pipe 50 provide abrasion resistance to the (normally thin) outer portions of the bends of the conveying pipe 51).

One end 60 of the conveying pipe 50 is connected to the impeller 41? at the bottom of the transporter hopper 26, while the other end 62 of the conveying pipe 50 is tangentially connected to a cylindrical receiving hood 64 in which the arriving sand is slowed by rubbing against the side walls 66 of hood 64 under the influence of centrifugal force. The slowed particles 68 then fall under the effect of gravity into the receiving bin 70 which may be positioned, for example, at a molding station 72.

FIG. 2 shows the frustoconical bottom or funnel portion 76 of the transporter hopper 26. The impeller 40 is mounted between the bottom hopper flange 106 and the conveying pipe entrance flange 110 by bolts 108. Seals 112 and 113 keep the impeller pressure-tight. In order to create the previously mentioned swirling or suspension action, compressed air is introduced into the impeller manifold chamber 114 by tangential air intakes 116 (FIG. 3). Air escapes from the impeller manifold chamber 114 into hopper 26 through the annular nozzle 118. The effective air discharge area of nozzle 118, and hence its air flow characteristics, can be adjusted by an appropriately size nozzle ring 120. To prevent sand from falling into the impeller manifold chamber 114, a resilient seal 122 is provided adjacent the nozzle ring 118 to act as a check valve which permits compressed air to travel upward but prevents sand from traveling downward. The resilient seal 122 and the nozzle ring are fastened to the impeller 41 by a retaining ring 124 and screws 126. The impeller 40 has a central opening 128 through which the sand in the transporter hopper 26 can pass into the conveying pipe 50.

As will be best seen in FIG. 4, the walls of the nozzle 129 are inclined about fifteen degrees with respect to the inner, preferably polyurethane-lined wall 84 of the frustoconical hopper section 76. This inclination takes into account the fact that the air emerging from the nozzle 129 is decompressed as it enters the hopper 26 and therefore forms a divergent pattern whose angle of divergence d has been empirically determined to be about fifteen degrees on each side of the surface of the imaginary cone 0 defined by the parallel walls 80, 82 of the nozzle 129. The inclination of the nozzle 129 with respect to the walls 84 not only produces a more uniform laminar air flow along the wall 84, but also eliminates the serious abrasion effects by which unavoidable impurities in the compressed air previously scored the anti-adherescent polyurethane lining 78 and even the steel wall 84 so badly that the useful life of the hopper 26 was greatly shortened.

A preferred form of conduit jet according to this invention is best shown in FIGS. 5 and 6. In FIG. 5, 130 is the downstream end of the portion of conveying pipe 50 which was designated by the numeral 54in FIG. 1. The jet 42 is inserted between the pipe end 130 and the upstream end 132 of the pipe section leading to element 56 in FIG. 1 and fastened thereto by appropriate means such as 134. The jet 42 includes a pair of end pieces 135, 137 held together by bolts 139. The end pieces 135, 137 clamp between them a manifold assembly composed of three rings 141, 143, which are secured together by b ll 147 and define an annular manifold chamber 136.

Compressed air is tangentially introduced into the manifold chamber 136 by tangential air intakes 138. The walls 148, 150 of the rings 141, 145 define between them a frustoconical nozzle 140 which opens into the conduit 50. It will be noted from FIG. 5 that the jet 42 is so constructed that there is no discontinuity in conduit 50 throughout the jet 42 except for the actual discharge opening of the nozzle 140 itself. This construction significantly reduces the turbulence at jet 42 and aids in the rapid creation of a smooth air cushion downstream of jet 42. Air is discharged in a spiraling laminar pattern from the annular nozzle 140 and expands in the conveying pipe 50 into a divergent pattern similar to that discussed herein-' above in connection with the impeller 40. The rapid forward motion and large quantity of the air discharged from nozzle 140 creates a vacuum upstream of jet 42 which draws sand out of the portion 54 of pipe 50 and hence out of the transporter hopper 26.

In order to compensate for the convergence of the air stream at the exit from the nozzle 140, the surface of the imaginary cone 0' defined by the nozzle 140 is disposed at a fifteen degree angle to the conduit wall 152. The rapid spinning motion of the air stream as it travels downstream in the conduit 50 quickly causes the convergence forces to be overcome by the centrifugal forces acting on the air molecules, so that the air stream quickly settles into a cylindrical air cushion spiraling forward along the wall of the conduit 50.

In accordance with one aspect of the invention, the air is so introduced (FIG. 6) into the manifold 136 by intakes 138 as to cause counterclockwise (looking downstream) spinning of the air emerging from nozzle 140. This is the natural spin direction in the northern Hemisphere, and it has been found that if this spin direction is not observed, a reversal of the spin direction occurs in the pipe 50 at some distance from the jet 42, and clogging of the pipe is apt to result at that point, particularly if the conveyed sand is very humid. By using a counterclockwise spin, no such reversal occurs, and the necessity for boosters at intervals along the pipe is eliminated for all practical purposes.

For a like reason, the impeller 40 is arranged, as best shown in FIG. 3, to produce a counterclockwise (look ing downward in FIG. 3) rotation of air. It has been found that this feature greatly reduces short-circuits, i.e. air flow directly from the impeller into the pipe while a bridge of compacted sand remains intact above the air current in the hopper.

Assembly The system is assembled as shown in FIG. 1. The valves 44, 45 may, if desired, be connected to an appropriate control system adapted to operate them in the proper sequence for automatic operation as hereinafter described. If two transporter hoppers are used, a switch such as that shown in FIG. 6 of the aforesaid copending application Serial No. 236,930 may be provided in the conveying pipe 50 either ahead of or beyond the jet means 42.

Operation When it is desired to convey sand from the storage bin 24 to the receiving bin 70, the cover 28 is opened and a charge of sand is introduced into the transporter hopper 26 from storage bin 24. When the transporter hopper 26 is almost completely filled, the cover 28 is closed and the valve 44 is operated to supply compressed air to the impeller 40. This causes the sand to become suspended within the transporter hopper 26 and the pipe 50. When the air pressure within the hopper 26 reaches approximately twenty pounds per square inch, the sand begins to move into the pipe 50. At that pressure, valve 45 is operated to power the jet 42, and the material is thereupon conveyed a considerable speed out of the transporter hopper 26 and through the pipe 50 due to the dual action of the pressure created by impeller 40 and the vacuum created by jet 42. The delaying of the actuation of jet 42 until conveying pressure has been built up in the transporter hopper 26 reduces the possibility of short-circuiting the air flow in the hopper 26 by withholding the vacuum effect from jet 42 until the suspension of the material in hopper 26 has become complete.

If desired, the atomizer 46 may be filled with an appropriate treating liquid, and the sand passing by jet 42 will then be treated with this liquid in fine dispersion. In any event, the cooling of the air as it expands upon entering pipe 50 causes a considerable cooling of the sand as it travels through pipe 50. The sand is eventually discharged at the other end 62 of conveying pipe 50 into the cylindrical receiving hood 64. There, it is thrown against the walls 66 of hood 64 by centrifugal force and is thus slowed down until gravity causes it to drop into the receiving bin 70.

It will be seen that this invention provides a highcapacity pneumatic conveying system which can be installed in low space, i inexpensive to install, operate, and maintain, and which permits a highly efiicient utilization of the pneumatic medium and permits the cooling and treating of the conveyed material in transit. Obviously, the invention can be carried out in numerous ways of which the illustrative embodiment shown is merely one example. Consequently, the invention is not intended to be limited by the embodiment shown herein, but solely by the scope of the following claims.

We claim:

1. A pneumatic hopper assembly for particulate materials comprising: a pressure-tight hopper; controllable inlet means into the top portion of said hopper for material to be conveyed; said hopper having a generally frustoconical, downwardly convergent bottom wall and an outlet at the base thereof; conveying conduit means connected to said outlet; an annular pressure manifold around said frusto-conical bottom wall adjacent the base thereof; pressurized fluid inlet means into said annular chamber, tangentially thereto; a continuous annular outlet slit in said bottom wall, communicating with said manifold, and directed upwardly into said hopper along said frustoconical wall, causing the pressurized gases introduced tangentially into said annular manifold to swirl out of said slit in a continuous spiraling laminar film along said hopper wall to suspend the particulate materials thereagainst; and means to form a pressure differential between said conveying conduit means and the top of said hopper to force the suspended materials through said outlet.

2. The assembly in claim 1 in which said tangential fluid inlet means to said manifold is arranged to create counterclockwise spiraling toward said conduit means from said hopper.

3. The assembly in claim 1 including an annular nozzle around said outlet and adjacent said frusto-conical wall to form said annular slit, and having between them an angle generally equal to half the divergence angle of the pneumatic fluid stream discharged from said slit.

References Cited by the Examiner UNITED STATES PATENTS 2,027,697 1/36 Nielsen 302-5 3 2,794,68 6 6/5 7 Anselman 303-5 3 FOREIGN PATENTS 707,791 7/ 41 Germany. 325,544 2/30 Great Britain.

SAMUEL F. COLEMAN, Primary Examiner.

ANDRES H. NIELSEN, ERNEST A. FALLER,

Examiners.

Claims (1)

1. A PNEUMATIC HOPPER ASSEMBLY FOR PARTICULATE MATERIALS COMPRISING: A PRESSURE-TIGHT HOPPER; CONTROLLABLE INLET MEANS INTO THE TOP PORTION OF SAID HOPPER FOR MATERIAL TO BE CONVEYED; SAID HOPPER HAVING A GENERALLY FRUSTOCONICAL, DOWNWARDLY CONVERGENT BOTTOM WALL AND AN OUTLET AT THE BASE THEREOF; CONVEYING CONDUIT MEANS CONNECTED TO SAID OUTLET; AN ANNULAR PRESSURE MANIFOLD AROUND SAID FRUSTO-CONICAL BOTTOM WALL ADJACENT THE BASE THEREOF; PRESSURIZED FLUID INLET MEANS INTO SAID ANNULAR CHAMBER, TANGENTIALLY THERETO, COMMUNICATING ANNULAR OUTLET SLIT IN SAID BOTTOM WALL, COMMUNICATING WITH SAID MANIFOLD, AND DIRECTED UPWARDLY INTO SAID HOPPER ALONG SAID FRUSTOCONICAL WALL, CAUSING THE PRESSURIZED GASES INTRODUCED TANGENTIALLY INTO SAID ANNULAR MANIFOLD TO SWIRL OUT OF SAID SLIT IN A CONTINUOUS SPIRALING LAMINAR FILM ALONG SAID HOPPER WALL TO SUSPEND THE PARTICULATE MATERIALS THEREAGAINST; AND MEANS TO FORM A PRESSURE DIFFERENTIAL BETWEEN SAID CONVEYING CONDUIT MEANS AND THE TOP OF SAID HOPPER TO FORCE THE SUSPENDED MATERIALS THROUGH SAID OUTLET.

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