GB2061770A - Improvements in or relating to the separation of granular mixtures - Google Patents

Abstract

As part of a reclaiming process of chemically bonded sand after use in foundry moulds, carbonaceous and sand fines are separated by apparatus 1 which comprises a casing 2 and an impeller disc 3 rotatable about a substantially vertical axis 4, disposed within the casing 2 so as to define an annular space 5 therewith. An extraction fan 7 is used for drawing air through the annular space 5 in an upward direction, and a tubular member 18 is used to feed granular mixture on to a central part of the impeller disc 3 whereby it is discharged into the path of the upwardly flowing air and the fines carried away. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the separation of granular mixtures This invention relates to the separation of granular mixtures.

The invention is particularly concerned with the reclamation, by separation, of,chemicallybonded sand after use in foundry moulds.

For economical reasons it is advantageous to reclaim the sand. To this end, however, the large lumps of sand have to be reduced to grain size and residual bonds and carbonaceous and sand fines removed.

The present invention provides a simple and inexpensive method of removing the fines.

According to one aspect of the invention, a method of separating granular mixtures comprises the use of centrifugal force to discharge the mixture into the path of a flow of fluid whereby the components of the mixture divide-out under the influence of the centrifugal force and whereby the lighter components are carried away by the fluid.

According to another aspect of the invention, apparatus for separating granular mixtures comprises means for subjecting the mixture to centrifugal force whereby the components of the mixture divide out and means for causing fluid to flow over the divided components whereby the lighter components are carried away.

Bn a preferred form the apparatus comprises a casing, an impeller disc rotatable about a substantially vertical axis disposed within the casing so as to define an annular space therewith, extraction fan means for drawing air through the annular space in an upward direction, and means for feeding granular mixture on to a central part of the impeller disc whereby it is discharged into the path of the upwardly flowing air.

As used herein, the term "lighter components" applies not only to components of lower specific gravity but also to those of small mass.

The various aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein Figure 1 is a side view, in medial section, of a preferred form of apparatus, and Figure 2 is a fragmentary view taken on the lines ll-ll of Fig. 1.

With reference to the drawings, apparatus 1 for separating unwanted fines out of a granular mixture comprising the fines and grains of foundry sand comprises a circular casing 2 and an impeller disc 3 rotatable about a substantially vertical axis 4 disposed within the casing so as to define an annular space 5 therewith. The apparatus further comprises extraction fan means 6, including an extraction fan 7, for drawing air through the annular space 5 and in an upward direction, (as indicated by arrows 8), and means generally indicated at 9 for feeding the granular mixture on to a central part of the impeller disc 3 whereby it is discharged into the path of the upwardly flowing air.

In further detail, the disc 3 is saucer-shaped having a convex upper surface and a concave under surface. The disc 3 is releasably clamped to the bottom end of a drive shaft 1 5 by an attachment 16. The shaft 1 5 is rotated about the axis 4 by a variable-speed electric motor 17.

The shaft 1 5 is disposed in a tubular member 18 which forms part of the means 9. The member 1 8 is disposed substantially co-axially with the rotational axis 4. The casing 2 supports an air extraction duct 1 9 extending substantially normal to the axis 4. One end of the duct 1 9 houses the extraction fan 7, which is driven by a variable speed electric motor 20. The other end of the duct 1 9 is blanked off by a plate 25. Adjacent that end the duct 1 9 is cut away to allow the tubular member 1 8 to extend lengthwise into the duct where it is slidably supported by a tubular guide 26.

The tubular member 18 is movable, in an axial direction, relative to the impeller disc 3 so as to define a variable gap 27 between the lower end of the former and the adjacent convex surface of the latter. Once positioned, the tubular member 1 8 is secured in place by a locking bolt 28 carried by the tubular guide 26.

The upper end of the tubular member 1 8 carries a branch duct 29 extending at an angle to the axis 4.

A skirt-like member 35 is disposed below and substantially co-axial with the disc 3. The upper periphery of the member 35 extends inwardly, beneath the periphery of disc 3.

The member 35 is disposed substantially centrally within the casing 2 by equi-spaced and radially-extending arms 36 supported by tubes 37 carried by the casing 2.

Slots 38, (see Fig. 2), are formed between the tubes 37 so as to define atmospheric air inlets.

The casing 2 is lined with heavy grade rubber 39.

In operation, the apparatus 1 is used in the final stage of the reclamation of chemically bonded sand after use in foundry moulds. The large lumps of sand are reduced down to grain size by well-known methods, for example by crushing, and any tramp metal removed.

The granular mixture, which comprises unwanted fines of carbonaceous material and sand, at least some of which is held together by static electricity, is then discharged into the tubular member 1 8 by way of the branch duct 29. The mixture then falls from the lower end of the member 1 8 on to the centre of the impeller disc 3. (The rate of feed on to the disc 3 is adjusted by varying the gap 27).

At the same time, air entering the casing 2 by way of the slots 38 is drawn upwardly through the annular space 5 by the extraction fan 7.

The granular material falling onto the spinning disc 3 is subjected to centrifugal force, which force compels the relatively light and heavy components of fines and sand to divide out as they pass over the convex upper surface of the disc and into the path of the air flowing upwardly through the space 5.

As the divided particles enter the air in the flowpath encircling the periphery of the impeller 3, the lighter fines are carried away from the apparatus 1 by way of the duct 19, leaving the heavier sand to fall into a collecting vessel 40 or to pass through a cooler (not shown) for subsequent re-use.

The rubber lining 39 protects the inner surface of the casing 2 from damage by erosion.

In use, the speeds of the electric motors 1 7 and 20, and the size of the gap 27 are carefully adjusted so as to obtain efficient separation of the fines and sand.

The invention provides a simple and inexpensive method of achieving the desired separation.

An example of the apparatus 1, using an impeller disc 3 of about 22" diameter, achieved a through-put of 1 2 tons per hour.

Claims (14)

1. A method of separating granular mixtures comprising the use of centrifugal force to discharge the mixture into the path of a flow of fluid whereby the components of the mixture divide-out under the influence of the centrifugal force and whereby the lighter components are carried away by the fluid.

2. The method claimed in Claim 1, wherein the mixture is discharged by an impeller into fluid flowing along an annular path encircling the periphery of the impeller.

3. The method claimed in Claim 1 or 2, wherein the fluid is air.

4. The method claimed in Claim 1, 2 or 3, when applied to the reclamation of chemically bonded sand.

5. A method of separating granular mixtures substantially as hereinbefore described, with reference to the accompanying drawings.

6. Reclaimed sand obtained by the method claimed in any one of Claims 1 to 5.

7. Apparatus for separating granular mixtures comprising means for subjecting the mixture to centrifugal force whereby the components of the mixture divide-out and means for causing fluid to flow over the divided components whereby the lighter components are carried away.

8. Apparatus as claimed in Claim 7, wherein the means for subjecting the mixture to centrifugal force comprises an impeller.

9. Apparatus as claimed in Claim 7 or 8 wherein the means for causing fluid to flow over the divided components comprise fluid suction means.

10. Apparatus as claimed in Claim 9, wherein the fluid is air and the last-mentioned means comprise an extraction fan.

11. Apparatus as claimed in any one of Claims 7, 8, 9 or 1 0, comprising a casing, an impeller disc rotatable about a substantially vertical axis disposed within the casing so as.

to define an annular space therewith, extraction fan means for drawing air through the annular space in an upward direction, and means for feeding granular mixture on to a central part of the impeller disc whereby it is discharged into the path of the upwardly flowing air.

1 2. Apparatus as claimed in Claim 11, wherein the means for feeding granular material on to the impeller disc is adjustable so as to control the rate of feed.

1 3. Apparatus as claimed in Claim 11 or 12, wherein the means for feeding granular material on to the impeller disc comprise a tubular member disposed substantially co-axially with the rotational axis of the disc and movable relative to the disc so as to define a variable gap between the lower end of the tubular member and the adjacent surface of the disc.

14. Apparatus for separating granular mixtures substantially as hereinbefore described, with reference to the accompanying drawings.