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Patent Searching and Data


Title:
PROCESS AND APPARATUS FOR TREATING GRANULAR MATTER
Document Type and Number:
WIPO Patent Application WO/2005/099931
Kind Code:
A1
Abstract:
Disclosed is a rotary abrasion apparatus and method suitable for processing used sand-based moulds for metal casting, which may be contaminated with phenolic resins or the like, in order to reclaim said sand for re-use.

Inventors:
CARTER KEITH (AU)
Application Number:
PCT/AU2005/000529
Publication Date:
October 27, 2005
Filing Date:
April 13, 2005
Export Citation:
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Assignee:
CARTER KEITH (AU)
International Classes:
B22C5/04; B22C5/10; B22C5/18; (IPC1-7): B22C5/04; B22C5/10; B22C5/18
Foreign References:
US5439044A1995-08-08
US5520341A1996-05-28
GB2238741A1991-06-12
GB2238742A1991-06-12
Other References:
DATABASE WPI Week 199423, Derwent World Patents Index; AN 1994-188202
Attorney, Agent or Firm:
WATERMARK PATENT & TRADEMARK ATTORNEYS (Hawthorn, VIC 3122, AU)
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Claims:
CLAIMS:
1. Apparatus for the reclamation of used foundry moulding sand contaminated with moulding chemicals such as phenolic resins, said apparatus including: a moulding sand processing chamber, said chamber featuring: a moulding sand inlet and outlet; a classifying air inlet; a suction outlet for dust laden air; and a rotor positioned at the bottom of said chamber, said rotor being adapted to process moulding sand by imparting kinetic energy to said sand sufficient to cause abrasion between grains of said sand, wherein said abrasion substantially contributes to the removal of said moulding chemicals from the surface of said grains; and wherein said removed moulding chemicals form a dust cloud which exits said chamber via said outlet for dust laden air.
2. The apparatus of claim 1 , wherein said rotor features one or more blades which impart kinetic energy to the sand, said blades being mounted such that their leading face in the direction of rotation is angled upward and away from the direction of rotation at an angle of at least 39° from the horizontal.
3. The apparatus of claim 2, wherein said blades are angled at about 45° from the horizontal.
4. The apparatus of claim 3, wherein there are two said blades.
5. The apparatus of any preceding claim, wherein said classifying air inlet is adapted to release pressurised air in close proximity to the upper edge of said rotor.
6. The apparatus of claim 5, wherein the side walls of said chamber are defined by a substantially vertically oriented cylinder.
7. The apparatus of claim 6, wherein said cylinder has a diameter at least 0.8 times its height.
8. A method for reclaiming used moulding sand from sand moulds for metal casting operations, said method including the steps of: breaking down said casts into a freeflowing mass of contaminated sand, substantially coated with moulding chemicals; introducing this sand into the chamber of an apparatus as defined in any one of claims 1 to 7; causing the rotor to rotate for a predetermined time at a predetermined speed thereby to impart kinetic energy to the sand particles sufficient to cause the particles to abrade against one another, thereby to cause the moulding chemicals to be substantially removed from said particles; introducing air or other suitable gas into said chamber at a pressure sufficient to maintain the internal pressure of the chamber at least equal to the ambient air pressure, thereby to cause the moulding chemicals removed from the sand particles to be removed from the chamber via the suction outlet for dustladen air; and removing the sand particles from the chamber.
9. The process of claim 8, wherein said predetermined time is between 1 and 5 minutes.
10. The process of claim 9, wherein said predetermined time is approximately 2 minutes.
11. The process of any one of claims 8 to 10, wherein said predetermined rotor speed is approximately 200 rpm.
12. An apparatus for the reclamation of used foundry moulding sand contaminated with moulding chemicals substantially as herein described with respect to the figures.
13. A method for reclaiming used moulding sand from sandbased casts for metal casting operations substantially as herein described.
Description:
PROCESS AND APPARATUS FOR TREATING GRANULAR MATTER

FIELD OF THE INVENTION The present invention relates to a process and apparatus for treating granular matter. The invention has been developed primarily for use in processing chemically bonded moulding sand for the metal casting industry to reclaim the sand for further use in new moulds. However, it will be appreciated that the invention is not limited to this particular application. BACKGROUND OF THE INVENTION Foundries consume large quantities of sand to produce sand moulds for metal castings, and this consumption is increasing. The sand thus used by the foundry industry is a relatively costly resource, since it must conform to certain criteria relating to grain shape and size range distribution. In some jurisdictions the accessible supply of sand has been exhausted and, as a result, sand needs to be transported some distance to foundries, further increasing its cost. Foundry sand is typically blended with a combination of chemicals that, when cured, allow the sand to form a strong, well-defined mould. Chemical additions to the sand typically range between 1.9% to 4.5% of the sand mass. Significant environmental damage and resource wastage may be associated with the provision of new foundry sand. Firstly, large volumes of fresh water are used when washing raw sand and fossil fuels are used during the drying processes. Secondly, in some jurisdictions up to 90% of foundries using chemical sand bonding methods treat the used sand entirely as a waste product, dumping it in landfill. As the sand can contain toxic sand moulding chemicals such as phenolic resins, phenolic urethane resins, sodium silicate resins, acids, esters, iso-cyanides or other hazardous chemicals, significant environmental damage may occur if these chemicals leach from the landfills. Phenolic resins are in particularly common use in these applications. Further, smaller foundry operations are unlikely to find it feasible to simply dispose of this specialised material after a single use. An alternative strategy is to recycle or reclaim the sand, in particular by breaking down the sand moulds into individual grains and removing the above chemicals to re-expose the sand grain. Available sand recycling or reclaiming equipment tends to be expensive and is designed to process high volumes of sand, and is therefore best suited to large foundry operations. These systems require a substantial capital investment. Therefore, many small to medium sized foundry operations consider sand recycling physically and/or financially not viable. The systems used to break down the cast moulds, remove the castings, and the liberated moulding chemicals themselves, present a personnel health and safety issue which many smaller foundry operations are not equipped to handle. There are many proposed solutions, both existing and suggested, for providing a recycling service for used chemically moulded sand from foundries which are not in a position to use existing disposal or reclamation techniques. One solution involves establishing a central recycling plant where all foundries send used sand. However, as foundries treat used sand effectively as waste, it would be difficult ensure the delivery of the waste sand in a consistent condition for further reclamation processing. Another proposed solution is to incorporate the used sand into other products, such as pavers, bricks, mine-hole fills etc. This is already in practice in some foundries, however used chemically moulded sand is not always suitable for these applications. Therefore it is an object of the present invention to enable a process for the safe reclamation of foundry moulding sand by removal of at least phenolic resins, which is nevertheless suitable of installation in, and operation by, small- to medium-size foundry operations. SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided an apparatus for the reclamation of used foundry moulding sand contaminated with moulding chemicals such as phenolic resins, said apparatus including: a moulding sand processing chamber, said chamber featuring: a moulding sand inlet and outlet; a classifying air inlet; a suction outlet for dust laden air; and a rotor positioned at the bottom of said chamber, said rotor being adapted to process moulding sand by imparting kinetic energy to said sand sufficient to cause abrasion between grains of said sand, wherein said abrasion substantially contributes to the removal of said moulding chemicals from the surface of said grains; and wherein said removed moulding chemicals form a dust cloud which exits said chamber via said outlet for dust laden air. The invention described above has the advantage of relative simplicity and compactness, whilst providing an effective mechanism for removing a substantial proportion of the contaminating moulding chemicals, thereby allowing re-use of the sand. It has been found that a mixture of 50% reclaimed sand and 50% new sand provides excellent results in casting applications. It has also been found that acceptable results in casting applications can be achieved using up to 100% reclaimed moulding sand obtained via this apparatus. It is preferred that said rotor features one or more blades which impart kinetic energy to the sand, said blades being mounted such that their leading face in the direction of rotation is angled upward and away from the direction of rotation at an angle of at least 39° from the horizontal. Particularly good results have been obtained where there are two said blades, which are angled at about 45° from the horizontal. Without wishing to be bound by any theory, it is thought that this embodiment is effective as it causes the sand particles in front of the blade to be cyclically lifted and repositioned towards the wall of the housing and then to fall behind and substantially beneath the blade, which improves the abrasive interaction between the sand particles. In the above case, the horizontal is defined as being a plane perpendicular to the centre line of the shaft which drives the rotor. In an advantageous embodiment, said classifying air inlet is adapted to release pressurised air in close proximity to the upper edge of said rotor. This assists in the circulation of the sand grains above the blades, and allows the chamber to be maintained at a positive pressure relative to its environment. This assists in removal of the dust cloud of moulding chemicals. Particularly good results have been achieved where the side walls of said chamber are defined by a substantially vertically oriented cylinder, and where said cylinder has a diameter at least 0.8 times its height. According to another aspect of the invention, there is provided a method for reclaiming used chemical moulding sand from sand-based metal casting operations, said method including the steps of: breaking down said chemically-bonded sand moulds into a free-flowing mass of contaminated sand, substantially coated with moulding chemicals; introducing this sand into the chamber of an apparatus as described above; causing the rotor to rotate for a predetermined time at a predetermined speed thereby to impart kinetic energy to the sand particles sufficient to cause the particles to abrade against one another, thereby to cause the moulding chemicals to be substantially removed from said particles; introducing air or other suitable gas into said chamber at a pressure sufficient to maintain the internal pressure of the chamber at least at ambient levels compared with the ambient air pressure, thereby to cause the moulding chemicals removed from the sand particles to be removed from the chamber via the suction outlet for dust-laden air; and removing the remaining sand particles from the chamber. Particularly good results have been achieved where said predetermined time is between 1 and 5 minutes, preferably approximately 2 minutes, and where said predetermined rotor speed is approximately 200 rpm. Alternatively, it is anticipated that speed of up to 1 ,500 rpm may be used, with a commensurate reduction in said predetermined time. Now will be described, by way of a specific, non-limiting example, a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic side view of a plant for treating granular matter, incorporating an apparatus in accordance with a preferred embodiment of the invention; Figure 2 is a schematic side sectional view of a comminution apparatus for comminuting lumps of sand, being part of the embodiment of Figure 1 ; Figure 3 is a schematic end sectional view of the comminution apparatus of Figure 2; and Figure 4 is a schematic side sectional view of the reclamation apparatus according to a preferred embodiment, as incorporated in Figure 1 ; DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Figure 1 shows a plant 1 for treating granular matter comprising a comminution apparatus 3, and a reclamation apparatus 5 having a dosing means 7, a fluidising system 9, a dust extraction system 11 , and a transport system 13. The plant 1 is used to comminute lumps of bonded moulding sand and to remove moulding chemicals from the sand grains such that they are suitable for re-use as foundry moulding sand. The reclamation process involves the loading of lumps of foundry sand moulds, consisting of moulding sand and a moulding chemical such as a phenolic resin or similar, into the top of the comminution apparatus 3 using, for example, a bulk loader 15. The lumps form a pile in the comminution apparatus 3 on top of a grid 17. The grid is then vibrated by way of an unbalanced mass, driven by an electric motor 19. The grid includes a multiplicity of beams 21 having sharp upper edges 23 and lower shoulders 23a between which slots 24 are provided. As the grid 17 is vibrated, the upper edges 23 divide the lumps of bonded sand, fragmenting larger lumps into smaller lumps. At the same time, grains of sand are caused to be dislodged from the lumps, due to the interaction between the lumps and the vibrating grid 17, and the interaction between adjacent lumps. It has been found that to optimally facilitate the attrition process, the grid discharge slots 24 should be spaced by approximately 6mm. The comminution apparatus 3 may also beneficially include a classification screen 25 that does not allow oversized sand particles or sand lumps to pass therethrough. Once the sand grains have passed through the classification screen 25, it lands in a trough 27 from which it is discharged. Turning again to Figure 1 , sand leaving the comminution apparatus 3 is fed into the dosing device 7, which is in the form of a motorised auger elevator that moves the sand up to the entry chute 35 of the reclamation apparatus 5. The sand may then enter the reclamation apparatus 5 in batches, optionally at time intervals controlled by the dosing device 7 (i.e. by regulating the motor activator), and falls through chute 35 into the chamber 37 of the reclamation apparatus. Turning now to Figure 4, it will be noted that once the sand is in the chamber 37, it may be agitated by two blades 47 which rotate about the shaft 55 such that the sand grains in front of the blades 47 are cyclically lifted, thereby forming a 'cloud' of colliding grains above said blades 47. In order to facilitate this lifting effect, the leading face of the blades 47 in the direction of rotation is angled upward and away from the direction of rotation at an angle of at least 39° from the horizontal, optimally about 45°. In this case, the horizontal is defined as being a plane perpendicular to the centre line of the shaft 55. Optimally, the blades rotate at about 200 rpm for a period of between 1 to 5 minutes, preferably about 2 minutes. Other speeds, ranging up to and possibly beyond 1 ,500 rpm, are anticipated to be applicable, with a commensurately reduced rotation time. During this agitation, said grains may be repositioned towards a wall 49 of the chamber 37, and the sand grains behind the blade 47 may then fall substantially behind the blade 47. This agitation tends to cause grain-to-grain, grain-to-blade and grain-to-wall abrasion and/or impact, thereby to facilitate removal of the residual bonding agent from the sand and to form a dust thereof. In order to facilitate this turbulent mixing process, the chamber 37 optionally has an epi-spherical shaped bottom 51 and a substantially conical shaped top 53. Figure 4 also shows a drive shaft 55 powered by a motor 57, which drives the blades 47. The fluidising conduit 9 of Figure 1 splits into smaller conduits 9a, 9b shown in Figure 4, with the air entering these conduits being indicated by the arrows 59. The conduits 9a, 9b extend into the sand mass to maximise air-dust entrainment and separation from the sand grains, and to provide sufficient air pressure in of the chamber 37 relative to the ambient atmosphere to facilitate the removal of the dust-laden air from the chamber via the suction outlet 11 , as indicated by the arrow 62. While two such conduits are shown in the figures, any number of such conduits may be provided consistent with the invention. The sand entering and then leaving the chamber 37 is indicated by the arrows 61 and 63, respectively. The fluidising system 9 thus introduces pressurised air, supplied by a compressor 39 into the grain processing device 5. The pressurised air aids in fluidisation of the sand particles and dust in the chamber 37 such that the bonding agent dust, and any moulding sand dust, are caused to be extracted through the dust extraction system 11. The removed dust is then filtered from the air by a dust screen 41 which may incorporate a cloth screen. Once the sand has been agitated by the blades for the predetermined period, the batch of reclaimed sand is ejected from the chamber 37 through the outlet 43 in the bottom of the chamber 37. The sand may then be transported to a storage hopper 45 via a pneumatic sand transportation system for subsequent re¬ use or re-blending for use as moulding sand. An independent evaluation of the efficacy of the above-described apparatus and method was carried out by Pacific Rim Foundry Services (PRFS) of Sydney, Australia. The study found that the standard of moulding sand reclamation was excellent. A number of test batch runs were carried out on the above described plant, using the same mass of moulding sand. After each test, the reclaimed sand obtained was evaluated via a sieve analysis test, which produces a Grain Fineness Number (GFN) before moulding for the next test. In addition to this, a Loss on Ignition test (LOI) was conducted in order to benchmark the performance of the reclamation process. The GFN and LOI are standard measures of moulding sand performance which are familiar to those skilled in the art. One of the primary requirements of any sand reclaimer is that the grain size and distribution of the sand obtained via the reclamation process is the same as, or very similar to, the virgin sand used initially. In all of the tests conducted using the above described apparatus, the completed sieve analyses indicated that the degree of sand reclamation achieved was highly consistent throughout the duration of the multiple trial batches. The reclaimed sand was then used in casting operations involving a number of commonly casted metals. With regard to the testing of sand used in casting iron, the reclaimed sand GFN ranged from 46 to 50, having an average of 47.9, compared with a typical GFN for new sand of 47. Aluminium testing returned a GFN of between 48 and 49, brass testing returned a GFN of between 47 and 50 and steel testing returned a GFN of between 47 and 51. Regarding LOl testing, the accepted industry standard for LOI following sand reclamation is 2% to 2.5%. Preferably, LOI should be targeted below 2%, as this means that combustibles or organic residue on the sand grains are unlikely to cause casting defects such as gas porosity. The LOI achieved in the iron testing were at or below 1%; in aluminium testing they were close to 0.6%; in brass testing the average was 0.15% and for steel testing the results ranged between 0.08% to 0.25%. The difference in these results is due to the varying percentage of chemicals used in sand mouldings for different metals. In summary, the results indicate that the apparatus according to the invention, and the method of using the apparatus according to the invention, effectively produce reclaimed casting mould sand which can be incorporated in casting moulds at a rate of at least 50% combined with new sand, and potentially at up to 100% of sand-based casting moulds. Whilst the invention has been described with reference to a preferred embodiment, it will be appreciated by those skilled in the art that the invention can be embodied in other physical configurations, whilst retaining the spirit and scope of the invention as defined above.