Ester Ester curedcured sodiumsodium silicatesilicate

1 Ester Ester curedcured sodiumsodium silicatesilicateA A valid valid processprocess forfor sandsandreclamationreclamation5959ththIn dianIndian FoundryFoundry CongressCongressFebFeb 1111--13, 201113, 2011 ChandigarhChandigarh -- IndiaIndiaAuthorAuthor Ing. Cozzi CarloIng. Cozzi CarloSales Manager Sales Manager Sogemi EngineeringSogemi EngineeringMilan Milan -- ItalyItalySodiumSodium silicatesilicate binderbinder It s a binder based on a module with SiO2-Na2O ratiovarying from 2 to The most popular application method consists ofhardeningmouldsandcoresbyinjectionofCO 2gashardeningmouldsandcoresbyinjectionof CO2gas Another possibility is the addition of a liquid hardener, generally organic esters , in a normal continuous mixer In the presence of aqueous silicate, CO2gas, or acid, released by hydrolysis of Ester causes precipitation of a silica gel that, due to a further loss of water.

2 Solidifies the sand to make the required ofof sodiumsodium silicatesilicateLow incidence of gas defectsVery low incidence of cracks in castingsVery low incidence of cracks in castingsNo sulphur, phosphorus and nitrogenSafety for operators and environmentNegative Negative factorsfactors whichwhich effectedeffectedsodiumsodium silicatesilicate useuse Low strength and break-down capacity Short preservationLow flow ability of the sand mix Low flow ability of the sand mix High shake-out time-bench life ratio (in case of silicate/liquid hardener) Difficult sand reclamationStregthStregth dependsdepends onongrowing application percentagesgrowing silicate modulegrowing silicate moduletype of silicateBreakBreak--downdown capacitycapacity dependsdepends ononpercentage of the applied bindersilicate modulesilicate moduletype of silicateBreakBreak--downdown relationsrelationsbinderadditionsbreak-d ownbreak-downsoda contents(higher module)

3 RemediesRemedies saccharine dextrose wood flour graphiteAddition ofbetter break-down capacityloss of strength and core preservationuse of specialorganic materialSandSand mix flow mix flow abilityability percentage of the applied silicate silicate viscosityDepends on:Development of products with low viscosity modified byspecial additives and which allowed to reduce considerablythe percentage life and shake-out time A short bench life means high module and, in caseof silicate/hardener, a higher setting velocity. the higher the sand/ambient temperature, theshorter the bench life and, in case ofsilicate/liquidhardener,thehigherthese ttingsilicate/liquidhardener, of hardener which influences setting velocitySandSand reclamationreclamation wet sand reclamation with high yields requires very large volumes of sand to justify the high investment involvedplant dimensions have to be very large and in plant dimensions have to be very large and in addition washing water must be treatedDry sand reclamation seems to be the only economically acceptable solutionSandSand reclamationreclamation.

4 ProblemsproblemsThe following problems have been found during the development of this process due to its increased accumulation, residual binders inthesandinterferewiththehardeningreacti onthesandinterferewiththehardeningreacti onreducing the bench life of the sand mixtures to apoint where regular production of moulds and cores iscompromised accumulation of residual material also increases thecontent of soda in the sand, continuously reducingsand reclamationreclamation: target: targetREMOVING THE ELASTIC REMOVING THE ELASTIC FILM OF SILICATE FROM SAND GRAINSSandSand reclamationreclamation: : solutionssolutionsFrom chemical poinf of view: use of propylene carbonate ( Ester ) which, when incontact with silicate, hydrolyse, causing theprecipitation of silica without leaving any residue toeffecttheplasticityofthesilicafilmeffe cttheplasticityofthesilicafilmFrom installation poinf of view: Use of a thermo-mechanical reclamation becauseheating the silicate film which covers the sandgrain greatly helps the removing of the elastic filmof silicateSandSand reclamationreclamation.

5 Topicstopics sand heating in a fluid bed dryer with a temperature of 150 C where sand looses the main part of its incorporated water, therefore the silicate film which covers the sand grains the silicate film which covers the sand grains becomes stiff and fragile. mechanical attrition to remove the silicate film sand cooling, classification and dedusting in a fluid bed machine pneumatic conveying of sand to storage silosCrushershake-outSand fluid-bedheaterSand fluid-bedcooler/classifierAttrition mill for mechanical treatmentReclaimedReclaimed sandsand: : typicaltypical resultsresults at at 550 ,6% max0,6% max AlkalinityAlkalinity0,3% 0,3% maxmax (NA(NA220 0 content content)) FinesFines < 100 < 100 maxmaxBench life and shake out time at 20 C aredoubled if compared to new sandYield of reclamation is 90-95% with only5-10% addition of new sand, mainly withcoresToTo keep keep thesethese resultsresults constantconstant.

6 % of binder and hardener in use ( % of sand for binder, 10% of binder for hardener).. it is necessary to check the following .. it is necessary to check the following parameters:parameters:sand for binder, 10% of binder for hardener) chemical and physical features of the sand working conditions of the reclamation plant, with special attention to sand temperature inside the drier, wear of the friction mill and dust collection of the Case studystudy: : FaremFarem foundryfoundryRemanzaccoRemanzacco (Italy)(Italy) Steelmaking foundry producing valves, castings formechanic industry Weightfrom10 to5000 kg Weightfrom10 to5000 kg 4000 ton/year production Ester cured sodium silicate as binder Use of silica sand and chromite sand Thermo-mechanic reclamation plant Chromite separation from silica sandTypicalTypical castingscastings producedproduced bybyFaremFaremReclaimedReclaimed silicasilica sandsandanalysisanalysis ,33%0,33% NANA220 0 content content0,08%0,08% FinesFines< 100 < 100 < 100 < 100 CompressionCompression resistanceresistance7 kg/cm7 kg/cm22(1 (1 hrhr))

7 33 kg/cm33 kg/cm22(4 (4 hrs hrs))43 kg/cm43 kg/cm22(24 (24 hrshrs)) BenchBench lifelife13 min13 minSandSand benchbench life life graphgraphkg/cm2 Safety valueResistancekg/cmHardening time (hrs)Bench life (min)ReclaimedReclaimed chromitechromite sandsandanalysisanalysis ,33%0,33% NANA220 0 content content0,15%0,15% FinesFines < 100 < 100 CompressionCompression resistanceresistance8 kg/cm8 kg/cm22(1 (1 hrhr))34 kg/cm34 kg/cm22(4 (4 hrs hrs))42 kg/cm42 kg/cm22(24 (24 hrshrs)) BenchBench min SilicaSilica sandsand benchbench life life graphgraphkg/cm2 Safety valueResistancekg/cmHardening time (hrs)Bench life (min)ResultsResults 100% use of reclaimed sand formoulding (backing) 100% useofreclaimedchromitefor 100% useofreclaimedchromiteformoulding (facing) Only 5% addition of newsand/chromie through coresAdditionalAdditional remarksremarks The process can be applied using differenttypes of sand, such as.

8 Chromites, silica,olivineApproximately30%ofsandhard enedbyC0 Approximately30%ofsandhardenedbyC02does not create any problem Latest sodium silicate gives good bench life andcompression strength with high roomtemperature tooConclusionsConclusions Low moulding costs due to a lower use of binders and higher sand process has given the following advantagesThis process has given the following advantagesand higher sand reclamation. Very good castings with good surfaces and impressive reduction of defects caused by gas. Healthier working environment and no dangerous gas a a lotlot forfor youryourattentionattentionattentionatten tionForFor more more detailsdetails.