| Because of their higher strength and fluidity,better collapsibility and lower gas evolution,resin-coated sands have been widely used in steels and aluminum alloys casting.However,in order to meet the higher requirements of special casting on the performance of resin-coated sand,further improve the strength and reduce gas evolution.In this paper,the effects of the basic composition of resin-coated sand system such as the type of raw sands and their praticle sizes,the kind of phenolic resin and their addition aomunt on the properties of resin-coated sand were studied.And the effects of modification treatments such as adding silane coupling agents into the system,high-temperature roasting and pickling to the raw sands on the properties of resin-coated sands were also investigated.Using Y91 type of thermoplastic phenolic resin as binder,the ceramic sand and silica sand with praticle size of 50/100 mesh?70/140 mesh and 100/200 mesh were used as raw sand respectively,the resin-coated sands were prepared under the same thermal coating process.The results show that the strength of resin-coated sands prepared by ceramic sand is 1.2-1.6 times of those by silica sand,and the loss on ignition of the former is 0.2-0.3%lower than the latter.Mixing ceramic sand into silica sand can greatly improves the strength of resin-coated sand,and the strength enhances with the increasing amount of ceramic sand.The strength of resin-coated sands prepared by ceramic sand increases with the decreasing praticle size within the range of 50-200 mesh.The strength of resin-coated sand can be improved by mixing the raw sand with different particle size.And the better strength appears when the raw sand is evenly distributed in the four or five sieve meshes.Using 70/140 mesh ceramic sand as raw sand,four types of phenolic resin(Y91,Y80,S901 and S902)were used as blinder to prepare resin-coated sands respectively.It is found that the strength of resin-coated sands get better with the increasing addition amount of resin,while the specific tensile strength and bending strength at room temperature decrease.And the resin-coated sand prepared by S902 resin is proved to be the best.The specific tensile strength and bending strength at room temperature are 1.92MPa and 4.10MPa,respectively.The loss on ignition of resin-coated sand is 2.69%when the addition amount of resin is 2.5 mass%of raw sand.The kinds of resin have little influence on the loss on ignition of resin-coated sand and each 1%increase of resin results to 1.04%increase of loss on ignition.Using ceramic sand as raw sand,the strength of resin-coated sands is improved at around 10%by adding silane coupling agent(KH-550?KH-560?KH-570?KH-792?BTSE)and the BTSE is confirmed to have the greatest impact.With 2.5 mass%resin of raw sand and 0.6 mass%silane coupling agent of resin,the tensile strength and bending strength at room temperature are 5.97MPa and 10.22MPa,respectively,about 1.45 times and 1.14 times of the untreated resin-coated sands.However,silane coupling agents have little influence on the loss on ignition.After the high-temperature roasting treatment to the raw sands,the strength of resin-coated sands prepared by ceramic sand show poorer performance.The tensile strength and bending strength at room temperature decrease by 24%and 27%,respectively.However,the strength gets significant improvement after the pickling treatment to ceramic sand with diluted sulphuric acid solution.When the acid solution concentration is 10w%and pickling time is 5min,the tensile strength and bending strength at room temperature are 5.31MPa and 10.11MPa,respectively,about 1.29 and 1.13 times of the untreated.Improving the pickling solution concentration or extending the pickling time can both effectively improve the strength of resin-coated sands. |
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