Reclamation of ester-cured phenolic resin bonded foundry sands
A method of preparing a particulate refractory composition for use in the manufacture of foundry moulds and cores from spent foundry moulds or cores formed of refractory material and an ester-cured phenolic resin binder, the method comprising the steps of breaking up the spent foundry moulds or cores, mixing the resulting broken material with a particulate pozzolan additive and subjecting the mixture to a heat treatment at a temperature in the range 450 to 900° C.
1 . A method of preparing a particulate refractory composition for use in the manufacture of foundry moulds and cores from spent foundry moulds or cores formed of refractory material and an ester-cured phenolic resin binder, the method comprising the steps of breaking up the spent foundry moulds or cores, mixing the resulting broken material with a particulate pozzolan additive and subjecting the mixture to a heat treatment at a temperature in the range 450 to 900° C.
2 . A method as claimed in claim 1 in which the pozzolanic additive is selected from volcanic ash, pulverised fuel ash, fly ash, ground granulated blast-furnace slag, condensed silica fume, amorphous silica and calcined bauxite.
3 . A method as claimed in claim 1 in which the pozzolanic additive is pulverised fuel ash.
4 . A method as claimed in any preceding claim in which the pozzolanic additive has a particle size substantially less than 0.5 mm.
5 . A method as claimed in any preceding claim in which the pozzolanic additive is present in an amount of from 0.1 to 3% by weight based on the weight of solids.
6 . A method as claimed in claim 5 in which the pozzolanic additive is present in an amount of from 0.3 to 1.3% by weight based on the weight of solids.
7 . A method as claimed in any preceding claim in which the pozzolanic additive is added to the spent foundry sand as a slurry with water.
8 . A method as claimed in claim 7 in which the slurry has a solids content of from 20 to 50% by weight.
9 . A method as claimed in any preceding claim in which the heat treatment is at a temperature in the range 450 to 750° C.
10 . A method as claimed in any preceding claim in which the mixture is subjected to heat treatment for a period of from 20 minutes to 12 hours.
11 . A method as claimed in claim 10 in which the mixture is subjected to heat treatment for a period of from 30 minutes to 2 hours.
12 . A method as claimed in any preceding claim in which the heat treatment is effected in a fluidised bed.
13 . A method as claimed in any preceding claim which additionally comprises the step of removing dust and/or fines during and/or after the heat treatment.
14 . A foundry moulding composition comprising a mixture of the particulate refractory composition obtained by a method as claimed in any preceding claim with a liquid curable binder in an amount of from 0.5 to 5% by weight based on the weight of the particulate refractory composition.
15 . A foundry moulding composition as claimed in claim 14 in which the liquid curable binder is an ester-curable phenolic resin.
16 . A foundry moulding composition as claimed in claim 15 in which the ester-curable phenolic resin is an aqueous alkaline phenol-formaldehyde resole resin.
17 . A method of making a foundry mould or core comprising preparing a composition as claimed in any one of claims 14 to 16 forming the composition into the desired pattern or shape and allowing the ester-curable binder to undergo cure.
18 . A method as claimed in claim 17 comprising the step of gassing the formed composition with a gaseous ester to bring about cure of the binder.