US2478461A - Apparatus and method for treating foundry sand - Google Patents

Description

Aug. 9, 1949. G. E. CONNOLLY APPARATUS AND METHOD FOR TREATING FOUNDRY SAND Filed March 16, 1946 INVENTOR.

GEORGE E. CON NOLLY.

BY M ATTORNEYS.

Patented Aug. 9, 1949 APPARATUS AND METHOD FOR TREATING FOUNDRY SAND George E. Connolly, New York, N. Y., assignor to Nichols Engineering & Research Corporation, New York, N. Y., a corporation of Delaware Application March 16, 1946, Serial No. 654,958

14 Claims.

This invention relates to methods and apparatus for treating sand and the like, and more particularly for reclaiming foundry sand for cores and dry sand molds.

In the manufacturing of metal castings, specially prepared silica sand is commonly used for molds into which impressions are made of the objects to be cast. It is customary in order to form cores and dry sand molds for casting purposes to mix the sand with binding agents such as oils or cereals which, for example, retain the sand in place until the core or mold is baked. The binding agent imparts to the sand a strength and rigidity which enables it not only to retain its shape while being originally formed but which enables it to withstand the hydrostatic head of the molten metal and the erosive action of the metal during pouring.

The silica sand must be held by the binder as above mentioned and also must be solidly packed to assist the binder to withstand said hydraulic pressure of the molten metal. and the washing effect thereof. Even though solidly packed it must be porous enough to enable gases from the metal and the mold to escape. Molds or cores which are not sufliciently porous to permit the escape of gases may cause the latter to remain in or to enter into the molten metal and thus to produce bubbles in the finished casting.

With new sand the desired porosity may readily be obtained but after using the sand a very few times it loses this characteristicbecause of an accumulation of clay and binder residues on the surface of the said grains.

In addition to the film of binding agent residue which clings to the sand grains, a problem is presented by the molding clay and other materials which become mixed with the sand when the molds are broken down in removing the castings therefrom. Flakes or films of the molding clay and other material adhere to many of the sand'grains and detract from the porosity and strength of subsequent molds or cores made with such sand. The usual steps heretofore employed to remove such a film involving agitation and removal of the fines from reclaimed sand have not proven to be entirely satisfactory. The film or flakes not only detract from the porosity of the sand but may render it unfit for further use as core and mold sand because the binding agents will not be able to form a suitable bond for the sand grains.

It has heretofore been the practice in some foundries to subject the sand to be reconditioned to a heating or roasting treatment at a temperature and under conditions causing the carbonaceous materials largely to be burned away.

The sand is thereafter cooled and the dust or fines removed, and the desired sand is passed into bins. It has been found, however, that with the above described process, and more particularly after the sand has been repeatedly used and reclaimed, many of the sand grains will become more or less coated with said film or flakes of molding clay and other materials as above discussed.

According to the present invention, a method and apparatus for reclaiming foundry sand is provided which will eliminate the above noted difficulties or minimize same to such an extent that the reclaimed sand may be repeatedly used many times.

Various further and more specific objects, features and advantages of the invention will clearly appear from the detailed description given below taken in connection with the accompanying drawings which form a part of this specification and illustrate by way. of example preferred arrangements of apparatus for carrying out, the invention. The invention consists in such novel methods and combinations of features and rn'eth- 0d steps as may be shown and described connection with the equipment herein disclosed.I

In the drawings:

Figure 1 is a schematic diagram partly in section and with parts broken away, of one form of apparatus for carrying out the invention; and

Fig. 2 is a view partly in section and with parts broken away showing an alternative embodiment of a scrubbing chamber illustrated in Fig. 1.

Referring to the drawings in further detail, suitable means are provided for roasting or heating the used sand comprising preferably a furnace it, which may be of a well-known type having a plurality of superposed hearths (not shown) surrounded and supported in the usual wayby a cylindrical furnace wall. The sand being treated is moved in a well-known manner, by means of a plurality of rotatable rabble arms (not shown), inwardly and outwardly over alternate hearths, discharge ports being provided in each hearth, the ports of alternate hearths being located respectively at the center and periphery thereof.

In the event that the above type of furnace is used for treating foundry sand of the types commonly available, it will ordinarily be found that the sand contains sufllcient carbonaceous matemanner in an amount suiiicient, when supplemented by the fuel value of the carbon content of the sand, to roast the sand at a temperature of from 1200 to 1500 F. as it passes through the furnace.

The furnace rabbling structure may be operated at a speed to provide a time of travel,

for example, of about one half to three quarters of an hour for the sand to pass from the furnace inlet over said successive hearths to a suitable outlet II. The temperature of the sand at the discharge, port is, for example, about 1200 F.

The sand on discharge from the furnace l will be substantially free of carbonaceous maing agent upon the sand may be diminished.

In order to disrupt this adhering non-carbonaceous material and also any residual carbonaceous material, and to facilitate the extraction thereof from the sand, the sand discharged from the furnace I0 is subjected to a novel interaction or scrubbing action in the presence of a suitable cooling gas such as air. Prior to the scrubbing, the hot sand may be cooled by mixing it with sand which has been cooled and scrubbed.

This air acts not only as a cooling medium but also as an entraining medium for imparting a high velocity to the sand grains, the air being directed through suitable conduits at a desired high velocity.

Jets of high velocity air with sandand other material entrained therein are directed against one another in order to break loose and remove the above mentioned undesired materials from thesurface of the sand grains by the interaction ofthe grains upon one another.

II are provided in legs II'- and II" respectively for regulating the flow therethrough, and for sealing the feed pipes against the pressure of air at the nozzle.

' In order to accomplish a desired initial cooling of the hot sand from furnace l0, and to provide for its gradual and controlled reduction in temperature, the hot sand discharged fromthe furnace may be initially cooled, for example, by mixing same in a predetermined ratio with cooled sand from chamber IS. The latter is provided preferably at the bottom thereof with a suitable outlet l3 having a valve 24 for controlling sand flow therethrough and through a conduit 25 connected thereto, to a mixing chamber or area 28 where cool sand is brought into contact with incoming hot sand from furnace l0, and from which the mixed hot and cool sand is carried to the scrubbing chamber via the conveyor l'9.

Means for removing the treated sand from chamber I3 are provided comprising, for example, a port or outlet 21 preferably at the bottom of said chamber. Connected to the outlet 21 is a suitable channel or conduit 28 having a gate 29 therein. A conveyor belt 30 may be employed for carrying the sand from channel 28 to bins (not shown).

The sand fines and other finely divided material is removed bysuitable classifying means 3| comprising, for example, a flue 32 preferably in the top of chamber l3. Flue 32 is connected by a conduit 33 to a suitable classifier 34 of known design.

The fines are directed to a receiving hopper (not shown) connected to the bottom portion 31 of the dust collector. A vent I8 is provided for the escape or withdrawal of exhaust air from the dust collector 34.

The means for accomplishing in a single apparatus the scrubbing, cooling and classifying actions may comprise, in the form shown in Fig. 1, a scrubbing chamber l3 having, for example, two opposed nozzle members II and li'having linings which are preferably constructed of suitable known abrasion resistant material in order to withstand the highly erosive action of the sandair stream flowing therethrough.

Suitable air'pump or fan means (not shown) are operatively connected to the conduits l6 and I! for pumping air at high velocity therethrough in order to entrain the sand which flows from' The furnace III is operatively connected to the scrubber I! by means of said discharge port l I,

a conduit II' which is in communication with a conveyor is through which sand is carried up to a conduit 20. The latter by means, for example. of an inverted Y shaped conduit 2| with legs'tl' and 2|" is in communication withjet conduits l0 and I1 respectively. Suitable valves 22 and The sides of the scrubbing chamber I3 which are in the path of the high velocity sand grains of the scrubbing chamber shown in Fig. 2 is similar to that of Fig. 1 with the exception that the walls of the chamber in the path of the jets from said nozzles are bulgedoutwardly at 39 and 40 in itself between the walls 43 and 44 and the airsand stream thereby providing protection against the above-mentioned erosive action of 'the high velocity sand. If desired the enlargement 39. 40

of the chamber may be of annular form.

In operation, sand is dischargedfrom furnace Ill through port I l at a rate, for example, of about 3 tons per hour or approximately 100 lbs. per minute at a temperature of about 1200 F. For

purposes of illustration assume that it is desired to subject the sand to four cycles of operation of the scrubbing, cooling, and classifying apparatus,

and that it is desired to reduce the sand to a final temperature of about F. in the reservoir of chamber ll.

Twelve tons'of sand per hour therefore must pass through nozzles M and I! or six hour for each nozzle.

tons per' '5 The apparatus preferably should be primed at the outset by filling the reservoir in chamber 13 with clean sand toa desired level at about 150 F. If it is desired, sand at room temperature may be used for priming purposes.

Sand is discharged from chamber I3 through where:

Sz=flow or rate of discharge from chamber I3 through 13'.

S1=flow or rate of discharge from furnace I0.

' n=number of cycles of operation.

' In connection with the temperature mentioned in the last paragraph, the general relationship between sand temperature in the conveyor IS with said sand discharge rates and temperatures is as follows:

.where T=sand temperature in conveyor l9. S1=rate of discharge from furnace l0. Sz=rate of discharge from I3 through l3.

Tl=temperature of discharged sand from furnace l0. Tz=temperature of discharged sand from chamber I3.

also

where:

Ty=temperature of the sand after passing through the jets.

A=airflow through the jets.

S1=rate of discharge from furnace l0.

S2=rate of discharge from It! through l3.

Te=sand temperature in conveyor l9.

In the mixing chamber 26, or the point of blending of hot and cool sand, 100 lbs. per minute of sand at about 1200 F. from the furnace join with, for example, 300 lbs. per minute of sand from chamber l3 at about 150 F. The hot sand is cooled at a desired rate and the resulting temperature is about 412 F. a a The mixture of sand flowing at approximately 400 lbs. per minute at about 412 F. is carried by the conveyor iii to the conduit. 20 and thence is distributed to the conduits l6 and I! through the Y shaped member 2i.

Air at high velocity, for example, at about 8000 F. P. M. is forced through each of said conduits l6 and I! thus producing a high suction at the respective connections of the conduits 2 i and 2 i therewith. Sand is thus drawn by gravity and sucked into conduits, l8 and Ill and is entrained by the air stream. When the sand reaches a velocity at which a substantial mutual abrasive action occurs at the point of impact, it has reached an abrasive velocity."

To cool 400 lbs. of sand per minute at about 412 F. down to the desired temperature of about 150 F. it is necessary to absorb about 21,000 B. t. u. In order to absorb this amount of heat by means of air, entering for example at 60 F.

6 and leaving the system at, for example, 144' F., the amount of air required is about 1000 lbs. per minute or about 13,000 cubic feet per minute at 60 F.

With an air velocity of approximately 8000 F. P. M. and with the nozzles l4 and I5 axially disposed at an angle of about 150, the jets of air-sand will be similarly angularly disposed and will produce a resultant relative velocity of the air-sand jets at the point of impact of about 13,850 F. P. M.

The sand grains thus violently strike and rub against one another at high velocity while undergoing the cooling action of the air. A scrubbing of the sand is thus accomplished by using the grains both as a target and a projectile in a mutual bombardment to remove any carbonaceous residue and non-carbonaceous film by attrition. The degree of attrition is a function of the velocity of the two air-sand streams, and of the number of cycles to which the sand is subjected.

Cooling is thus accomplished in two steps. First, the hot sand from the furnace is mixed intimately with treated sand at a lower tempera- .ture; and second, the air employed to provide perature reduction is thus fairly low. However,

it is possible to accomplish a cooling and scrubbing without pre-cooling by mixing hot sand and cool sand. Pre-cooling, for example, may be accomplished by a suitable cool gaseous substance. It is also possible to carry out a form of the invention by omitting the above described pre-cooling.

The large volume of air flowing through the nozzles I4 and I5 into the chamber I3 is sufficient to give velocity to and carry away the rejected sand fines or finer material and to maintain the same in suspension. Proper classification is assisted by selecting an appropriate size of the outlet flue.

vFrom the chamber l3 about 3 tons per hour of clean reclaimed sand may be taken through the gate -29. It is desirable and necessary to have the discharge rate through this gate approximately equal to the discharge rate of the furnace Ill. The gate 29 if desired may be controlled manually by the operator, who will note the height of the body of sand through window means such as at 46 or, if preferred, known devices either mechanical or photoelectric may be used at 4B which will act in response to the height of the sand and serve to actuate and control the gate 29 accordingly.

While the invention has been described with respect to certain preferred examples which have given satisfactory results, it will be understood by those skilled in the art after understanding the invention that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended therefore in the appended claims to cover all such changes and modifications.

What is claimed as new and is desired to be secured by Letters Patent is:

1. Method for treating sand to remove carbonaceous matter and other material, which comprises passing the sand through a roasting zone heated to a temperature sufllcient to cause combustion of the carbonaceous matter, then mixing sand at a lower temperature with the hot sand, the amount of sand at a lower temperature being sufiicient to produce a gradual cooling of the hot sand, hurling by means of opposed air streams the particles of sand at one another at a velocity sufilcient to cause disruption of undesired material adhering thereto, said air streams being at a temperature lower than that of the mixed sand, and finally separating the finer material from the sand.

2. Method for treating sand to remove carbonaceous material and clay, which comprises passing the sand through a burning zone heated to a temperature sufilcient to cause combustion of the carbonaceous material, mixing hot sand from the burning zone with scrubbed and cooled sand, and subjecting the sand so mixed to a scrubbing cooling action by entraining a portion of same in a cool stream of air, and entraining another portion of sand in another cool stream of air, the streams of air-sand being directed against one another.

3. Method for treating sand to remove carbonaceous material and clay, which comprises subjecting the sand to heat to burn away said carbonaceous material, and cooling and scrubbing. the heated sand by entraining same in a plurality of initially separate air streams which are directed against one another to provide mutually impinging cool air streams, the latter being at a temperature initially not greater than approximately 100 F.

4. Apparatus for reclaiming foundry sand, comprising a roasting furnace, a scrubbing chamber, a plurality of nozzles in said chamber, the jets from said nozzles being directed against one another, said nozzles being disposed at such angles that they are outside the path of jets from op posed nozzles, means for pumping gaseous substance through said nozzles, means for distributing sand from said furnace to said nozzles, and

' means for removing the fines from said chamber.

5. Method for treating sand to remove carbonaceous matter and other material, which comprises: passing sand through a roasting zone heated to a temperature sufilcient to cause combustion of said matter; then mixing sand at a lower temperature with the hot sand which has passed through theroasting zone, the amount of sand at a lower temperature being from one to three times the volume of the hot sand whereby a gradual cooling of the hot sand is effected; hurling by means of opposed air streams the particles of sand at one another at an abrasive velocity sufiicient to cause disruption of carbonaceous residue and non-carbonaceous material adhering thereto, said air streams being at a temperature lower than that of the mixed sand by at least about 300 F.; and finally separating the finer material-from the sand.

6. Method for treating sand to remove carbonaceous matter and other material therefrom,

which comprises: passing the sand through a roasting zone heated to a temperature of approximately 1200 F.; then mixing sand at approximately 150 F. with the hot sand; hurling, by means of opposed air streams, the particles of sand at one another at an abrasive velocity sufilcient to cause disruption of the carbonaceous residue and non-carbonaceous material adhering to the sand, said air streams initially being at a temperature of approximately 60 F.; and finally separating the finer material from the sand.

'1. Method for treating sand to remove carbonaceous matter and other material, which comfrom the burning zone with cool sand at a temperature not greater than about 150 F.; entraining a portion of the sand so mixed in astream of air at approximately room temperature; entraining another portion of the sand so mixed in another stream of air atapproximately room temperature, said streams of air being directed against one another and each having a velocity of the order of 5,000 to 10,000 F. P. M and finally separating the finer material therefrom.

8. Apparatus for reclaiming foundry sand, composing: a roasting furnace; a scrubbing chamber; a plurality of nozzles in said chamber, the Jets from said nozzles being directed against one another and the nozzles of said jets being obtusely angularly disposed; means for pumping fluid through said nozzles; means for distributing sand from said furnace to said nozzle; and means for removing the fines from said chamber.

9. Method for treating sand to remove carbonaceous matter and other material therefrom which comprises: passing the sand through a roasting zone heated to a temperature suflicient to cause combustion of the corbanaceous matter whereby the latter is burned away; then cooling the sand by entraining same in opposed streams of fluid initially at approximately room temperature, said streams impinging upon one another and travelling at a velocity sufllcient to cause disruption of a carbonaceous residue and of any non-carbonaceous material adhering to the sand; and finally separating the finer material from the same. e

10. Method for treating sand to remove carbonaceous material and clay, which comprises: passing the sand through a burning zone heated to a temperature sufiicient to burn away the carbonaceous material; mixing hot sand from the burning zone with sand which has been cooled and scrubbed; subjecting sand so mixed to a scrubbing-cooling action by entraining a part of same in a stream of fluid travelling at an abrasive velocity; entraining the balance of the sand so mixed in another stream of fluid travelling at a similar velocity; directing thestreams of fluidsand against one another within a reservoir; repeatedly recycling the sand from the reservoir by constantly mixing a predetermined flow therefrom with sand from said burning zone; and making constant withdrawals of treated sand from the reservoir at a rate whereby the rate of passage of sand from the reservoir is substantially equal to the rate of influx of sand in said fluid-sand streams.

11. Apparatus for reclaiming foundry sand, comprising: a roasting furnace; a scrubbing chamber; a plurality of nozzles in said chamber, the jets from said nozzles being directed against one another toward a region of mutual impact; means for conducting sand from said furnace to said nozzles; means for pumping a gaseous substance through said nozzles at a velocity sufllcient to entrain the sand and bring same to an abrasive speed; means for conducting a flow of sand from said scrubbing chamber to said first mentioned sand conducting means whereby sand is withdrawn from said chamber and mixed with sand flowing from said furnace to constitute an prises: passing the sand through a burning zone in-fiow of sand to said nozzles; and means for making constant withdrawals of sand from said chamber. repeated recycling of the sand being accomplished by constant additions of sand from the said scrubbing chamber to said in-fiow and by constant withdrawals of sand by said sand withdrawing means.

I 12. Apparatus for reclaiming foundry sand,

comprising: a roasting furnace, at scrubbing chamber, a plurality of nozzles in said chamber, jets from said nozzles being directed against one another, a conduit for conducting sand from said furnace to said nozzles, means for pumping a fluid through said nozzles for entraining sand and bringing same to an abrasive velocity, a passage member for interconnecting said chamber with said conduit whereby there is a continual flow of sand from the chamber into said conduit, the flow of sand from the furnace and from the chamber comprising the in-flow to said nozzles, and means for continually withdrawing sand from said chamber, the flow of sand out of the chamber through said passage member effecting a repeated recycling of the sand.

13. Method for treating sand to remove carbonaceous matter and other material therefrom which comprises: passing the sand through a roasting zone heated to a temperature sufficient whereby the latter is burned away; and cooling the sand by entraining same in mutually impinging streams of cooled fluid initially at a temperature substantially lower than that of the sand,

said streams travelling at a velocity suflicient to to cause combustion of the carbonaceous matter which comprises: passing the sand through a roasting zone heated to a temperature suflicient to cause combustion of the carbonaceous matter whereby the latter is burned away; cooling the sand by entraining same in opposed streams of cooled fluid initially at a temperature substantially lower than that of the sand, said streams impinging upon one another and travelling at avelocity sufiicient to cause disruption of carbonaceous residue and any non-carbonaceous material adhering to the sand; and finally separating the finer material from the sand;

' GEORGE E. CONNOLLY.

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

UNITED STATES PATENTS Number Name Date 238,044 Luckenbach Feb. 22, 1881 1,058,313 Luckenbach Apr. 8, 1913 1,935,344 Andrews Nov. 14, 1933 2,012,694 Runyan Aug. 27, 1935 2,226,330 Symons Dec. 24, 1940 2,326,218 Hartley Aug. 10, 1943 FOREIGN PATENTS Number Country Date 172,221 Great Britain Dec. 8, 1921

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