Method of improving the properties of reclaimed sand used for th

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

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524445, 524447, 524591, 524593, 524594, B22C 118

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active

060158468

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BRIEF SUMMARY
The use of ester-cured alkaline phenolic resins for the production of foundry moulds and cores has had a major influence on the industry due to the improvements in the casting finish possible and in the environmental benefits achieved. The techniques were first developed commercially by Borden (UK) Limited. Examples of such techniques are disclosed in EP-A-085512 and EP-A-086615.
Despite the advantages gained by the use of ester-cured phenolic resins, a serious disadvantage is that the rebond strengths obtained with sands reclaimed from moulds and cores made with ester-cured phenolic resins are generally far inferior to the strengths obtained with new sand or sand reclaimed from other processes. This is also true of ester- and CO.sub.2 - cured silicate resin systems. For environmental and commercial reasons it is desirable to recycle as much reclaimed sand as possible and thereby limit, as far as possible, the dumping of waste sand.
Various treatments have been proposed which seek to improve the rebond strength of ester-cured phenolics on reclaimed sand. The most common treatments are mechanical attrition and thermal reclamation though other processes, such as wet scrubbing and the use of additives, have been used. One of the most successful additives employed is that described in EP-A-336,533.
Procedures which employ thermal reclamation of the sand (which reduces loss on ignition due to a build up of organic residues) can result in a higher rebond strength than sand treated by simple mechanical attrition. There is some evidence (e.g., Sedlak et al, Cast Metals, Vol 3, 2, 1990) which suggests that the poor rebond strengths on reclaimed sand correlate with the level of elutable alkali in the sand. Thermal treatment alone does not reduce the level of elutable alkali. In fact, it can increase it by releasing metal salts from the organic matrix. Furthermore, the presence of the alkali metal can cause fusion of the sand particles through glass formation which precludes the use of certain thermal treatment processes, such as those employing fluidised beds.
We have now discovered that by using certain inorganic additives the levels of elutable alkali metal in particulate refractory aggregates containing elutable alkali can be dramatically reduced. The invention which is based on this discovery is particularly applicable to reducing the level of elutable alkali in sand recovered or reclaimed from spent foundry moulds and cores that had been produced using alkaline binder systems to bind the sand together. Furthermore, the problem of silicate fusion, associated with the presence of these materials during thermal reclamation, may be eliminated according to the invention.
An object of the present invention is to provide a novel treatment of particulate refractory aggregate containing elutable alkali, such as is recovered or reclaimed from spent foundry moulds or cores, to improve its usefulness in the production of new foundry moulds and cores.
A further object is to provide a foundry moulding composition which contains particulate refractory aggregate recovered or reclaimed from spent foundry moulds and cores.
A yet further object is to provide a method of making foundry moulds and cores using particulate refractory aggregate recovered or reclaimed from spent foundry moulds and cores.
The present invention provides a particulate refractory composition for use in the manufacture of foundry moulds and cores which comprises a mixture of a particulate refractory aggregate containing elutable alkali with, as an additive thereto, a particulate active clay having a particle size of less than 0.5 mm.
The use of the particulate active clay additive in the composition has the effect of improving the strengths of foundry moulds and cores that are produced using the composition compared to the case where no particulate active clay additive is incorporated into the particulate refractory.
By the term "particulate active clay additive" we mean particulate clay having a particle size of less than 0.5 mm which is capable of reactin

REFERENCES:
patent: 5043412 (1991-08-01), Chandramouli et al.
patent: 5190993 (1993-03-01), Iyer
Hawley's Condensed Chemical Dictionary, 12ed. pp. 288, 668, 1993.
Cast Metals, vol. 3, Nov. 2, 1990, pp. 62-67.

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