Method Of And Device For Continuous Preparation Of Granular Material, Such As Foundry Sand

Abstract

A method and device for mixing, loosening, aerating and cooling granular material is disclosed where the material to be treated is introduced into two axially arranged cylindrical containers spaced at a small distance one from another to provide a discharging gap therebetween. At least one of the containers is rotated by a driving motor so that the contacting grain layers in the gap will rub together and subsequently are discharged by centrifugal forces from the gap.

Description

BACKGROUND OF THE INVENTION:

The present invention relates generally to the treatment of granular materials. More particularly, this invention relates to a method of an a device for the preparation, such as mixing, loosening, dispersing and cooling of granular materials, especially of foundry sands.

Methods and devices already known in which a combined assembly of mixing, loosening, and cooling devices is employed. Conventional mixing devices are provided with a container for receiving the material to be mixed, and with rotatary mixing members or agitators arranged in the container. The loosening devices or the so called aerators are provided with a sand centrifuge for loosening and cooling the granular material. In order to expedite the cooling action of the granular material to be mixed, blowers for directing an air stream into the mixed material are frequently employed. The air stream from the blower produces an increased temperature exchange with the relatively hot molding granular material delivered from a foundry plant.

The disadvantage of such prior art combination of separate processing devices for the preparation of foundry sands is in the necessity to employ separate feeding devices for connecting respective partial processing devices one to another. As a consequence, relatively considerable construction costs result and, in addition, the entire combined assembly requires considerable floor space.

It is, therefore, an object of this invention to avoid the aforementioned disadvantages of prior art methods and devices for the treatment of granular materials.

More particularly, an object of this invention is to provide a method and device which simplifies the preparation process for granular materials.

Another object of this invention is to provide a single compact device for performing all stages of the preparation process.

Still another object of this invention is to provide a method and device which substantially reduce operative and construction costs.

SUMMARY OF THE INVENTION

According to this invention, the above objects are attained by providing a method where two quantities of the granular material to be treated are brought into contact in a planar area, at least one of the quantities is rotated and/or vibrated to produce mutual friction at the area of contact and subsequently to discharge by centifugal forces the abraded grains from the contact area.

The device for carrying out the above described method comprises feeding means for continuously delivering granular material to be processed, into a pair of containers. The two containers are oxially arranged and spaced one from the other about an adjustable distance to create a discharging gap there between. The facing ends of both containers are provided with openings through which the fed material enters the discharging gap. At least one of the containers is coupled with a driving motor which can be provided with additional means to impart to the container a rotary or a compound rotary and vibratory movement; due to the rotation, the contacting surfaces of respective quantities of granular material in both containers start rubbing together and by centrifugal force the processed material is discharged from the gap.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of this invention, together with further objects and advantages thereof, reference is made to the following detailed description of the accompanying drawing wherein:

FIG. 1 is a sectional, elevation view of an embodiment of the device for preparation of granular material according to this invention;

FIG. 2 is a sectional elevation view of another embodiment of the device according to this invention;

FIG. 3 is a sectional elevation view of still another embodiment of the device according to this invention;

FIG. 4 is a cut-away elevation view, partly in section of agitating and mixing means of the device of this invention; and

FIG. 5 is a cut-away elevation view, partly in section, of another modification of agitating and mixing means of FIG. 4.

DETAILED DESCRIPTION

In the embodiment of the device for preparing granular materials, as illustrated in FIG. 1, a vertical container is affixed to a stationary supporting frame 2. Above a top opening 3 of the container 1, there is disposed a conveyor 4 for feeding granular material 5 to be prepared, such as foundry sand, for example, into the container 1. It is advantageous to make the container of a frustoconical configuration as to allow the granular material to pass downwardly with minimum friction. This can be done preferably by slightly inclining the inside wall 13 of the container 1 and by increasing the diameter of bottom opening 8. Agitating and mixing members 7 are fixedly mounted on a vertical shaft of a driving device 6. The shaft projects coaxially into the container 1 and is rotated by a driving device 6 which, as it will be explained later with reference to FIGS. 4 and 5, can also bring the agitating and mixing members 7 into horizontal or vertical vibrations. The shape arrangement of the agitating and mixing members 7 can be variously modified according to required operative conditions. For example, it is possible to make those members 7 in the form of horizontally projecting rods, or rake-shaped projections or in the form of a spiral conveyor. Opposite to the bottom opening 8 of the container 1 there is located at a certain small distance from the bottom rim of the wall 13 a dish-shaped second container 10. The second container 10 is firmly connected to a driving shaft 15 of a motor 14. The motor 14 is provided with laterally projecting swivel rods which are movably supported for tilting the motor 14 about a horizontal axis. In addition to a rotary movement, the driving shaft 15 is thus adapted for importing a vibratory movements in horizontal and vertical planes to the second container 10 as it is indicated by dashed lines in FIG. 1. The top opening 9 of the second container 10 faces the bottom opening 12 of the first container 1, and respective side walls 11 and 13 are spaced one from the other to form a circular discharging gap 12 between the container 1 and the container 10. The clearance of the gap 12 is adjustable by means of oblong vertical holes 34 in the wall of discharging chamber 17 in which the bearings for the swivel rods of motor 14 are fastened by bolts and nuts 16. The top of the cylindrical discharging chamber 17 is provided with cover 19 having an annular passage 21 adjacent to the periphery of the wall 13 of the container 1. The annular passage 21 communicates through a ring-shaped conduit 22 with an air blower 23. The discharging chamber 17, conduit 22 and air-blower 23 are suspended on the supporting frame 2. The bottom of the discharging chamber 17 open into a storage bin (not shown).

In accordance with the method of this invention, the operation of the device for the preparation of granular material is as follows:

The material to be treated, for example foundry sand 5, is first fed by conveyor 4 through the inlet top opening 3 of the first container 1 and falls there through to the bottom of the second container 10 where it piles up as high as to reach the interior of the first container 1. As soon as the sand in container 1 reaches a predetermined level, the mixing action is started by the actuation of agitating and mixing members 7. Subsequently, the motor 14 is switched on and the shaft 15 thereof which is connected a little excentrically to the bottom of the second container 10 starts rotating and the second container 10 is driven at a relatively high speed.

Simultaneously, due to the excentricity of the mounting of the shaft 15, the second container 10 vibrates in a horizontal plane. Due to this compound motion, the granular mixture 5 is centrifugally jetted out against the inside wall of the discharging chamber 17. Simultaneously, the air blown through the annular passage 21 in the direction of arrow 24 cools the jetted layer 33 of the sand mixture and disperses respective particles. The inside wall of the discharging chamber 17 can be with advantage provided with an elastic coating, such as of a plastic material.

Due to the dish-shaped configuration of the second container 10, the accumulated granular material during the rotation of the container 10 causes rubbing or friction in the area of the discharging gap 12 between the bottom layer of the granular material in the stationary first container 1 against the rotating and top layer in the second container 10. In this frictional area of the gap 12, the mixing action is most effective since due to the direct friction of one granular layer against a plurality of grains in the adjacent layer, the activating motion is attained in addition to and irrespective of the motion of the agitating and mixing members 7. As a result, the initially added binding material and other additives are disintegrated and uniformly coat surfaces of individual grains. In the course of the centrifugal discharge of the relatively highly tempered granular mixture coming from the foundry plant, there occurs a temperature exchange with the cool air in the discharge chamber 17. To increase the cooling effect, the blower 23 can be set into operation for blowing cool air through the sand veil 33 jetted-out from the circular discharge gap 12, as shown by arrow 24.

In the preparation of granular substances such as, for instance, molding and grain sands, ceramic masses and similar materials, the homogenizing stage of the preparation process is of decisive importance. In this stage the treated mixture which consist of grains of different sizes, is not only homogenized but also very frequently mixed with powdery, liquid or pesty binders and additives whereby as it is required in molding sands, there must be also provided in as short time as possible a uniform envelop of the added binder around the grains. The binder is added very frequently in minute quantities only. For this reason, the kneading and frictional processes within the granular mixture itself are essential since the energy introduced into the mixture is thereby most effectively distributed and the resulting motion provides the optimum homogenization of grains and coating of their surfaces.

If there are employed additives and binders which produce, due to mere upper surface tension only or due to inherent adhesive forces, a more or less strong cohesion in the prepared material so the latter material may not be processed in a clotty condition but it must be prepared for a further processing in as loose condition as possible, i.e. uniformly separated into individual grains. These requirements are fully met by the above described method of and device for the preparation of granular mixtures of this invention.

Further modifications of the invention are illustrated in FIGS. 2 and 3. With reference to FIG. 2, there is schematically shown an embodiment in which two devices of FIG. 1 are operatively coupled in a vertical arrangement so that the outlet of the upper device communicates with the inlet of the lower device. In this manner, the mixing, homogenizing and dispersing actions are repeated and thus optimized.

In the device as illustrated in FIG. 3, the granular material 5 to be processed is fed to the discharging gap 12 from two opposite directions. One stream of the material to be processed is fed by means of a conveyor, preferably a screw conveyor 26, into a first cylindrical or tube-shaped container 24. Another stream of material 5 is fed from the opposite direction by means of a second screw conveyor 27 into a second cylindrical or the tube shaped container 25. The two containers as well as the coaxially disposed screw conveyors 26 and 27 may be arranged horizontally, spaced by a small, adjustable distance one from the other, so that a vertical discharging gap 12 will result. Instead of screw conveyors, it is possible, of course, to apply other conveying means such as plungers, membranes, pressure air and the like. By contrast to the embodiment of FIG. 1, both cylindrical containers 24 and 25 are supported for rotary and/or excentrically vibrating movements from opposite directions, as indicated by arrows 28 and 29. The amplitude of the range of vibrations of containers 24 and 25 is indicated by dashed lines 30. By means of the resulting counter-directed movements of the granular mixture in containers 24 and 25, the contacting grains in the gap 12 are subject to centrifugal and frictional forces similarly as in the previous embodiments.

The processed grains rub together and, at the same time are jetted outwardly by centrifugal forces against the wall of discharging chamber 17, where the discharged sand layer 33 is dispersed and aerated in an analogous manner as it has been explained with reference to FIG. 1. Cooling air delivered from a blower 23, is conducted through vertical ring-shaped conduit 31 and passes through an annular passage 21 into the interior of the discharging chamber 17, as indicated by arrows 32. From the discharging chamber 17, the processed granular material falls into a storage bin (not illustrated).

In a modification of the embodiment according to FIG. 3, the two facing containers 24 and 25 can be arranged at a certain angle one to another, instead axially, in this case, the intermediate discharging gap 12 will have unequal clearance around its periphery. The inclined position of the containers 24 and 25 enables that the two opposite streams of granular material 5 may be conveyed to the area of the discharging gap by force of gravity only which can also be applied for the creation of the frictional or rubbing pressure. As it has been already mentioned, the clearance of the gap 12 can be adjusted by axial displacement of the containers 24 and 25.

FIG. 4 illustrates a modification of drive means 6 for rake-shaped agitating and mixing members 7. The drive means 6 rotates the shaft of members 7 over an excentricnot illustrated of any suitable design so that those members 7 exercise in addition to their rotary movement vibrations in horizontal plane, as indicated by dashed lines.

FIG. 5 shows another variation of the drive means 6 for rod-shaped agitating and mixing means 7, where the supporting shaft of members 7 performs, in addition to its rotary movement, vibrations in a vertical plane, as indicated by dashed lines. The vertical vibrations can be produced by a can shaft driven by drive means 6.

It is possible, of course, to design drive means in such a manner as to perform, in addition to a rotary movement, vibrations both in horizontal and in vertical planes. Further modification may also be made in the spirit of the invention. It is possible, for example, to avoid the application of auxilliary parts of the device such as of the blower 23 for cooling the discharged material, or of the agitating and mixing members 7 which, even if useful for cooling or mixing process, may under certain operational circumstances occur as unnecessary.

The device according to this invention is suitable for the preparation of sands of heterogenous composition such as of the so called "Cold Box" or "Hot Box" Sands as well as sands which contain chemically hardening binders, especially synthetic resins, water glas, cement and similar binders.

The invention may be embodied in various other constructions and various changes may be made as come within the scope of the accompanying claims.

Claims

What Is Claimed Is:

1. A method of the preparation of granular material, especially of the mixing, separating and cooling of foundry sand, comprising the steps of providing two quantities of said granular material, feeding one quantity against the other quantity to an area of their mutual contact, producing a rotary movement of one quantity relative to the other quantity to cause a friction there between in said contact area, and discharging centrifugally a layer of said granular material from said contact area.

2. A method according to claim 1 further comprising a step of producing a vibratory movement in at least one of said quantities in addition to said rotary movement.

3. A device for the preparation of granular material, especially for the mixing, separating and cooling of foundry sand, comprising in combination, two container means axially arranged at a closely spaced relation one to another to provide a discharging gap there between, the facing ends of said container means being provided with openings respectively, to allow the flow of said granular material into said gap, and drive means coupled to at least one of said container means to produce a rotary movement of one container means relative to the other one.

4. A device according to claim 3 further comprising means for vibrating at least one of said containers.

5. A device according to claim 3 wherein one of said container means is in the form of a vertically arranged tube, the other container is disposed beneath said tube and has a dish-shaped configuration.

6. A device according to claim 5 wherein said tubular container has a frustoconical configuration.

7. A device according to claim 5 further comprising agitating and mixing members disposed within said tubular container means.

8. A device according to claim 3 wherein both container means have tubular form.

9. A device according to claim 8 wherein said tubular container means are arranged at an angle one to another.

10. A device according to claim 3 further comprising a discharge chamber surrounding said gap and directing the prepared granular material upon its discharge from said gap to a storage container.

11. A device for the preparation of granular material, especially for the mixing, separating and cooling of foundry sand,

comprising in combination

two container means axially arranged at a closely spaced relation one to another to provide a discharging gap there between, the facing ends of said container means being provided with openings respectively, to allow the flow of said granular material into said gap, and

drive means coupled to at least one of said container means to produce a rotary movement of one container means relative to the other one, said container means having tubular form, and

conveyor means disposed in each of said container means for conveying said granular material from opposite directions to said discharging gap.

12. A device for the preparation of granular material, especially for the mixing, separating and cooling of foundry sand, comprising in combination, two container means axially arranged at a closely spaced relation one to another to provide a discharging gap there between, the facing ends of said container means being provided with openings respectively, to allow the flow of said granular material into said gap, and drive means coupled to at least one of said container means to produce a rotary movement of one container means relative to the other one,

a discharge chamber surrounding said gap and directing the prepared granular material upon its discharge from said gap to a storage container, and

blower means, an annular passage disposed on top of said discharge chamber, and conduit means for directing air from said blower means through said annular passage to aerate the jetted layer of said granular material.