US 3161485 A
Description (OCR text may contain errors)
1964 E. BUHRER 3, 6 85 SAND COOLING PLANT Filed Feb. 28, 1958 4 Sheets-Sheet 1 LL lull 1/11 1L1 I A INVENTOR mm 0mm BY WWW ATTORNEYf) Filed Feb. 28, 1958 4 Sheets-Sheet 2 Int EN 72R; zen/w Eli/m7 Dec. 15, 1964 E. BUHRER 3,161,485
SAND COOLING PLANT Filed Feb. 28, 1958 4 Sheets-Sheet 3 IN V! 7:02 F 5 ATM/Al emm-w Dec. 15, 1964 E, U R R' 3,161,485
SAND COOLING PLANT Filed Feb. 28, 1958 4 Sheets-Sheet 4 F I Iv 1 4-0708:
1? a l/v aux/m? United States Patent 3,161,485 SAND COOLING PLANT Erwin Biihrer, Schaffhausen, Switzerland, assignor to Georg Fischer Aktiengesellschaft, Schaifhausen, Switzerland, a company of Switzerland Filed Feb. 28, 1958, Ser. No. 718,273 Claims priority, application Switzerland, Dec. Ztl, 1957, 54,6969; Jan. 30, 1958, 55,276 3 Claims. (U. 34236) The present invention relates to the cooling of molding sand and more particularly to the cooling of used molding sand to recondition such sand for subsequent molding operation.
If castings are produced in a continuous cycle the duration of each cycle may be reduced to about 20 minutes or even less. During each pouring operation the molding sand will be heated in accordance with the amount of molten iron poured into the molds. However, the temperature in the sand may rise to an already unpermissible level during the first pouring operation and cooling of the molding sand after each pouring operation may therefore become an absolute necessity.
The cooling of relatively hot molding sand, e.g., sand having a temperature above 100 C., does not present serious difficulties because a sufiicient amount of water can be added to cool the sand upon evaporation of this water. It is evident that such sand may have a relatively high moisture content.
It has, however, been found that difficulties arise when sand of relatively low temperature is to be cooled because the amount of moisture, which may safely be added to this sand prior to cooling is very small. In this case the permeability of the sand is very low and thus the quantity of air which may penetrate the sand for cooling purposes is insufficient to reduce the temperature to the desired level. If the pressure of the air is increased in order to increase the air volume passing through the sand, this air may cause a break-through in the sand layer. As a consequence practically the full amount of air will flow through this break-through, while the adjacent portions of the sand layer will no longer be penetrated by the air and therefore the remainder of the sand will not be cooled.
The aim of the present invention is to avoid the above mentioned problems in cooling of molding sand and it is therefore a primary object of the present invention to provide means contributing to an eflicient and uniform cooling of used molding sand of relatively low temperature down to a temperature which will permit reusing the sand for subsequent molding and pouring operations.
Another object of the present invention is to provide means facilitating cooling of molding sand for its reuse in a manner permitting the maintenance of predetermined properties of said sand, or to re-condition said sand to regain said properties.
A further object of the present invention is to provide means affording cooling of said sand in layer formation in such a manner as to avoid any danger of the cooling air breaking through said layer in uncontrollable fashion.
Still another object of the present invention is toprovide means ensuring controlled distribution of the cooling air through a layer of sand resting on a support.
It is a further object of the present invention to pro vide means ensuringsupport ofa layer of molding sand for the purpose of cooling said sand by means of pressurized air and permitting a degree of control upon the pressure of said air acting on said layer.
A still further object of the present invention is to provide-means rendering the possibility of cooling molding sand in a continuous operation by penetration of cooling air through a layer of sand in a simple and reliable manner.
These and other objects of the invention will become further apparent from the following detailed description. Reference is now made to the accompanying drawings showing several embodiments of the invention:
In the drawings,
FIG. 1 shows a section along line II in FIG. 2 through a device for cooling molding sand and embodying the present invention.
FIG. 2 is a cross-section along line II-II of the device shown in FIG. 1.
FIG. 3 shows a cross-section through a joint between two adjacent members of the supporting means, the section being taken along line III-III in FIG. 4 and drawn to a larger scale.
FIG. 4 is a plan view of a portion of the supporting means shown in FIGS. 1, 2 and 3.
FIG. 5 is a graph showing the air volume passing through the supporting means in accordance with the present invention, and through the sand layer resting .on said supporting means, in function of the pressure of the cooling air and the moisture contentof the sand.
FIG. 6 shows a detail of a modified supporting means in a section taken along line VIVI in FIG. 7 and drawn to a largerscale.
FIG. 7 is a plan view of the detail shown in 'FIG. 6.
FIG. 8 is a schematic representation showing a part of a supporting member in plan view in accordance with FIGS. 6 and 7.
Referring to FIGS. 1-4 showing a first and preferred embodiment of the invention: a mixing trough 1 includes a plurality of inclined paddles 2 rotatably arranged therein. The paddles are operatively connected with a driving motor 4 and are used to agitate the molding sand 3 contained in the trough. This sand is delivered from a conveyor 5 arranged above the trough and may be given a predetermined degree of moisture by a spray nozzle 31. After being agitated continuously the molding sand will leave the trough through the opening 6 therein and enter a pivotably arranged, suspended oscillating tube 7, which distributes the sand in a uniform manner over the full width of a vibrating support 8, driven by eccenter means 9. From the vibrating support the sand will move in loose formation downwardly until it reaches an air permeable support 10 which is designed as a conveyor. This conveyor comprises a plurality of sections 30 which are hinged together. As will be seen from FIG. 3, the joints between the individual adjacent sections are sealed by means of rubber strips 34 in a manner well known in the art. Each section 30 contains a plurality of openings or ports '25 for the passage of cooling air, the ports being evenly spaced over the full area of the section, as for instance shown in FIG. 4. The conveyor 10 is moved in the direction of arrow 33 in FIG. 1 and will entrain the sand falling thereon from the vibrating support, in the form of a loosely heaped layer of continuous even depth and width. Below the upper portion of the conveyor is a plenum chamber-11, the side walls or rims 17 of which are arranged in sealing relation with the conveyor. The width of the plenum chamber corresponds substantially to the width of the conveyor 10 as will be seen from FIG. 2, while its length is such that it will extend from near the discharge end to at least below the location 35 where the sand from the vibrating support is received by the conveyor 10. Above the conveyor a hood'13 is arranged, which essentially covers the 'full length and width of the conveyor. Compressed air is fed through pipes 12 into the plenum chamber 11 by means of a blower 16. The compressed air will, after flowing through the ports 25 in the conveyor, penetrate the sand layer while cooling the latter through evaporation of the moisture contained therein and will subsequently be collected in the hood 13 and removed by means of suction. When, during movement of the conveyor, the sand reaches the end thereof, the cooling process will be practically completed. The sand will then be discharged onto a conveyor 14, which will transport the sand to a further station either for additional conditioning thereof or for direct reuse.
In FIG. 2 further air supply means are shown comprising a delivery pipe 18, branching off at 19 into two pipes 20 and 21. The two pipes 20 and 21 extend across the width of the lower portion of the cooling conveyor 10 and are provided with nozzles 23 designed to direct compressed air against both surfaces of the cooling conveyor for the purpose of removing adhering sand particles from this cooling conveyor it). A sheet metal enclosure 24, arranged below and laterally of the cooling conveyor, directs any sand particles falling from the cooling conveyor onto the conveyor 14.
FIGS. 6 and 7 show a port 25 on an enlarged scale. from these figures it can be seen that above each port 25 a cover member 26 may be arranged which is connected to the conveyor 10 by means of riveting or other means of attachment.
The crosses shown at 28 schematically show the locations where the cooling air will enter the sand layer resting on the cooling conveyor 10 when the cover members 26 are in place. While the cover members 26 shown in FIGS. 6 and 7 provide for two entry openings of the cooling air into the sand, it is self evident, that cover members may be provided having a larger number of entry openings.
FIG. 8 shows a portion of the conveyor 10 in plan view and indicates schematically the arrangement of the cover members 26 thereon and situated above the ports 25. From FIG. 8 it will be noted that the cover members 26 are arranged in a substantially uniform pattern.
It will be realized that the ports 25, whether covered or not, have the functions of conducting the compressed air from the plenum chamber 11 into the layer of sand resting on the cooling conveyor, and also of limiting the flow of air through any one of the ports, at any location of the conveyor 10 to a predetermined value. To this end the dimension or size of the ports 25 is chosen to obtain a positive pressure drop in the air flowing through each port opening. While this pressure drop should at least be A of a mm. water column, it will in most cases be considerably higher.
The graph shown in FIG. indicates the conditions under which air flows through supporting means or conveyor constructed in accordance with the present invention and through a layer of sand resting thereon.
In this graph the amount of air passing through conveyor support and sand layer has been indicated as a function of the pressure of this air. The amount of air passing through the device is computed in m. per hour per m? of cooling surface. In practice these values generally range between 50 and 300 m. per hour per m. As will be understood the cooling surface is the etfective area of the conveyor or supporting means for receiving sand thereon. The values of air passage in m. per hour per m? have been plotted in the direction of arrow 38. Arrow 39 indicates increasing values in airflow resistance, expressed in mm. water column pressure drop within the support means in accordance with the invention.
Arrow 40 indicates increasing values in air flow resistance, expressed in mm. water column pressure drop for a sand layer of 100 mm. depth and for varying moisture contents of the sand.
The lower portion of the above graph, relating to the conditions in the support means in accordance with the invention by the resultant curve clearly indicates that turbulence exists in the flow of cooling air through the ports in the supporting means. This is the case within substantially the entire range of the air volumes and air velocities needed for the practical operation of the device.
As is well known with turbulent flow, the pressure drop varies with the square of flow velocity. Consequently the curve shown in the lower portion of FIG. 5 has a parabolic character. On the other hand, the flow of air through the sand layer is, at corresponding values of pressure velocities, of laminar character in which case the pressure drop therein varies in direct proportion to the velocity of the cooling air. Thus, the lines shown in the upper portion of the graph of FIG. 5, indicating various moisture contents of the sand, are straight lines.
In order to show more clearly the effect of a supporting means constructed in accordance with the invention, i.e., having ports causing turbulence in the air flowing therethrough, an example has been indicated in the graph of FIG. 5. The dash lines 41 show that at 140 m. per hour air passage through each m. of cooling area and with a 3.5% moisture content of the sand the pressure drop through the support means and through the sand layer of mm. depth corresponds to a total of mm. water column. Thus the pressure drop in the supporting means is approximately 70 mm. water column and the pressure drop in the sand layer approximately 75 mm. water column. As will be clear to those skilled in the art, the permeability of the sand layer may vary due to factors other than the moisture content of the sand. Thus, variations in permeability may be caused for instance by irregularities of the sand layer either in depth or structure thereof, caused when depositing the sand upon the supporting means. For the example indicated in dashand dot-lines 42, it has been assumed that the pressure drop in a portion of the sand layer has been reduced to 50 mm. water column. As a consequence thereof the air volume passing through the supporting means and the sand layer will tend to increase, and when it reaches a certain critical value, will tend to blow off the sand resting on this particular portion of the supporting means. However, measurements show, as indicated by dashand dot-line 42, that under this condition such excessive increase of the throughflowing volume of air is prevented due to the fact that the pressure drop in the supporting means, i.e., the ports of this particular location, not only increases as a linear function, but with the square of the increase in air volume. Thus, it will be seen that the ports 25 effectively prevent an excessive amount of air passage and also prevent a disturbance or destruction of the sand layer. At the same time therefore these ports also prevent the fines in the sand from being carried away by the flow of air.
The device described in connection with FIGS. 14 operates as follows:
Molding sand to be cooled is transported to the mixing trough 1 by means of the conveyor 5.
In the mixing trough the sand is continuously agitated by means of rotating paddles 2, and cooling water may be added if necessary to increase the moisture content of the sand. The molding sand, still hot, leaves the mixing trough through opening 6 and will be deposited by passing through tube 7 and over vibrating support 8, in a loosely heaped continuous layer onto the supporting means 10 which is built in the form of a conveyor. The oscillating tube 7 and the vibrating support 8 insure that a layer of substantially uniform depth and structure will be formed, the sand in this layer being loosely arranged, since during deposition thereof on the supporting means, no compaction occurs.
The operation of a cooling device of this type including mixing and sand distributing means has been described in greater detail in my co-pending US. Patent application, Ser. No. 483,703, filed January 24, 1955 (now Pat. No. 2,863,190, issued December 9, 1958).
The blowers 16 will feed air into the plenum chamber 11 through the pipes 12. From the plenum chamber 11 this air, having a certain pressure, will enter the ports 25 in the supporting means 10 during movement of the latter across the plenum chamber and will pass through the sand layer resting thereon as indicated by upwardly directed arrows 45.
The pressure in the plenum chamber 11 will be chosen so that a pressure drop of 10-50 mm. water column in the supporting means is available per 100 mm. of depth of the sand layer.
For all practical cases the pressure drop occurring in the support means will be at least between and 25% of the total pressure drop. It will be understood that this pressure drop in the supporting means is present at all times, i.e., also when the sand layer resting on the supporting means is of entirely uniform structure. The pressure drop increases however when the amount of air flowing through the supporting means increases at any particular location. Due to the non-linear increase of the pressure drop, in the supporting means the amount of cooling air passing through the corresponding port or ports may not increase in proportion to the reduced pressure drop in the sand layer.
The ports 25, due to their even distribution over the area of the supporting means and due to their relatively small size, also effect a fine distribution of the air passing through the sand layer.
In a practical example of the construction of the supporting means in accordance with the invention, the diameter 36 (FIG. 4) of the ports 25 will for instance be 1.5 mm. In this case the distance 37 may be approximately 16 mm.
The modified device shown in FIGS. 6-8 operates similarly to the device shown in FIGS. 1-4. However, in deviation with respect to the first described embodiment, the cooling air in this modified device will not enter the molding sand immediately after leaving the ports 25, but will first pass below the cover members 26 which deflect the flow of air and provide an even finer distribution thereof before entering the sand layer at the locations 28.
It will be seen that a device has been described which will permit effective cooling of not only relatiiely hot molding sand, but also of molding sand of a reduced temperature generally prevailing when pouring thin walled castings. With a device of the type described it is possible to cool about three tons of molding sand per m? of cooling area, without removing the fines therefrom.
Various changes and modification may be made without departing from the spirit and scope of the present invention and it is intended that such obvious changes and modifications be embraced by the annexed claims.
Having thus described the invention, which is claimed as new and desired to be secured by Letters Patent, is:
1. In a cooling system for treating a granular mass, in particular for cooling molding sand from a foundry mold; a conveyor provided with horizontally spaced apart sections interconnected with each other, said sections being provided with perforations for the passage of cooling air therethrough for contact with a layer of sand when supported thereupon to facilitate cooling thereof, air supply means located below the surface of said conveyor, so that the latter carries said sa'nd layer and cooling air may be forced through the perforations of said conveyor sections at a pressure in accordance with the thickness of said sand layer While a drop in said pressure takes place during the passage of said cooling air through the perforations of said sections and through said sand layer, whereby the position of said layer remains substantially unaltered during passage of air therethrough, means flexibly and extendably interconnecting said sections, and means for removing air after its passage through said sand layer, the munber and size of said perforations being such that the cooling air passes through said perforations under turbulent flow conditions and said perforations cause a pressure drop in said airflow which is about between 5-25% of the total pressure drop occurring during the flow of the air through said perforations and said layer.
2. In a cooling system as in claim 1, said air supply means including a plenum chamber, means above said conveyor for strewing the sand onto said sections, said plenum chamber having a longitudinal extension which extends at least to a location below said strewing means.
3. In a cooling system for treating granular masses, in particular for cooling molding sand from a foundry mold; endless conveyor means provided with spaced apart perforations for the passage of cooling air therethrough, said conveyor means being provided with horizontally spaced apart sections, means for flexibly and extendably interconnecting said spaced apart sections, covering means substantially arcuately shaped and connected to said conveyor means above said perforations, said covering means deflecting flow of air through said perforations toward a layer of sand supported upon said conveyor means, air supply means located below said conveyor means, means sealing said supply means adjacent the ends of said conveyor means, so that cooling air directed by said supply means passes through said perforations of said conveyor means and through the sand layer at a predetermined air pressure and against said covering means while a drop in said pressure takes place during the passage of said cooling air through the perforations and through said sand layer, thereby to leave the position of said sand layer on said conveyor means substantially unaltered during the passage of air therethrough, and exhaust means for said air located above said conveyor means for removing air after passage thereof through said perforations arid said sand, the number and size of said perforations being such that the cooling air passes through said perforations under turbulent flow conditions and said perforations cause a pressure drop in said airflow which is about between 5-25% of the total pressure drop occurring during the flow of air through said perforations and said sand layer.
I References Cited by the Examiner UNITED STATES PATENTS 1,235,027 7/17 Harrison 34-236 X 1,800,432 4/31 Buck 198-195 1,844,782 2/32 Mittag 34-62 X I 2,041,142 5/36 Norvig 34-20 2,098,786 10/37 Flint 34-164 2,514,204 7/54 Cummings 34-25 X 2,672,412 3/54 Burrows et a1 -5 2,735,535 2/56 Ness 198-195 2,863,190 12/58 Buhrer 22-217 X 2,863,191 12/58 Dietert et al 28-89 FOREIGN PATENTS 542,135 11/55 Belgium.
NORMAN Y'UDKOFF, Primary Examiner.
GEORGE D. MITCHELL, BENJAMIN BENDETT,
CHARLES OCONNELL, Examiners.