To save energy and raise molding and coremaking productivity, the synthetic procedure of novolaks for the shell process was investigated. The study indicated that it was difficult to obtain fast curing novolaks under ...To save energy and raise molding and coremaking productivity, the synthetic procedure of novolaks for the shell process was investigated. The study indicated that it was difficult to obtain fast curing novolaks under strongly acidic conditions alone. A novel synthetic procedure was proposed for preparing novolaks in a two-step manner, a divalent metal salt catalyzed novolak preparation followed by a strong acid catalyzed novolak preparation. The optimum conditions for the two-step procedure were determined by orthogonal experiment design. The results showed that it was easy to prepare fast curing novolaks with cure time in the range of 20 s to 30 s and softening point in the range of 80℃ to 90℃ under complex catalysis conditions.展开更多
In this paper, the characteristics of the preparation of novolacs for the shell process under microwaveirradiation are investigated. Both polymerization and dehydration of the resins under microwave irradiation are co...In this paper, the characteristics of the preparation of novolacs for the shell process under microwaveirradiation are investigated. Both polymerization and dehydration of the resins under microwave irradiation are comparedwith those under conventional heating and further analysis is made. The results show that compared with those underconventional heating, the polymerization and dehydration time under microwave irradiation are shortened by 85.2% and80.7% respectively; On the other hand, the polymerization and dehydration under microwave irradiation lead to aremarkable increase in flow distance of the resins. Furthermore, the polymerization under microwave irradiation leads toreduced cure time, while the dehydration under microwave irradiation causes a slight increase in cure time.展开更多
The development of montmorillonite modified phenolic resin under microwave irradiation heating was investigated.The effect of montmorillonite content and stirring time on the structure and morphology of synthetic resi...The development of montmorillonite modified phenolic resin under microwave irradiation heating was investigated.The effect of montmorillonite content and stirring time on the structure and morphology of synthetic resin was analyzed.The optimum processing procedure was found to be 45 min stirring time with 5.4% montmorillonite addition.Further,the platelet spacing increases with stirring time till montmorillonite exfoliated to nanoscales platelet.When montmorillonite is exfoliated,layered structure at nanoscale can be uniformly distributed in the resin.The overall performance of montmorillonite modi fied phenolic resin is improved remarkably,such as flow ability,tensile strength and toughness property of resin coated sand.However,the gelation speed decreased slightly by adding montmorillonite.展开更多
Fine-grained BaTiO3-based X7R ceramic materials were prepared and the effects of milling process on the core-shell structures and dielectric properties were investigated using scanning electron microscope, transmissio...Fine-grained BaTiO3-based X7R ceramic materials were prepared and the effects of milling process on the core-shell structures and dielectric properties were investigated using scanning electron microscope, transmission electron microscope, and energy dispersive spectroscopy （EDS）. As the milling time extends, the dielectric constant of the ceramics increases, whereas the temperature coefficient of capacitance at 125℃ drops quickly. The changes in dielectric properties are considered relevant to the microstructure evolution caused by the milling process. Defects on the surface of BaTiO3 particles increase because of the effects of milling process, which will make it easier for additives to diffuse into the interior grains. As the milling time increases, the shell region gets thicker and the core region gets smaller; however, EDS results show that the chemical inhomogeneity between grain core and grain shell becomes weaker.展开更多
Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was f...Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting.The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting;and the formation mechanism of the gas pore,and shrinkage porosity defects were analyzed.The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment,insufficient feeding and non-sequential solidification.Subsequently,through changing the position of risers,adding a connecting channel between the risers,and setting blind risers at the U-shaped brackets,an optimized gating and feeding system was established to improve the quality of the casting.After optimization,the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated.The experiment results with the optimized casting process are in good agreement with the numerical simulation,which verifies the validity of the finite element model in the shell mould casting.展开更多
文摘To save energy and raise molding and coremaking productivity, the synthetic procedure of novolaks for the shell process was investigated. The study indicated that it was difficult to obtain fast curing novolaks under strongly acidic conditions alone. A novel synthetic procedure was proposed for preparing novolaks in a two-step manner, a divalent metal salt catalyzed novolak preparation followed by a strong acid catalyzed novolak preparation. The optimum conditions for the two-step procedure were determined by orthogonal experiment design. The results showed that it was easy to prepare fast curing novolaks with cure time in the range of 20 s to 30 s and softening point in the range of 80℃ to 90℃ under complex catalysis conditions.
文摘In this paper, the characteristics of the preparation of novolacs for the shell process under microwaveirradiation are investigated. Both polymerization and dehydration of the resins under microwave irradiation are comparedwith those under conventional heating and further analysis is made. The results show that compared with those underconventional heating, the polymerization and dehydration time under microwave irradiation are shortened by 85.2% and80.7% respectively; On the other hand, the polymerization and dehydration under microwave irradiation lead to aremarkable increase in flow distance of the resins. Furthermore, the polymerization under microwave irradiation leads toreduced cure time, while the dehydration under microwave irradiation causes a slight increase in cure time.
文摘The development of montmorillonite modified phenolic resin under microwave irradiation heating was investigated.The effect of montmorillonite content and stirring time on the structure and morphology of synthetic resin was analyzed.The optimum processing procedure was found to be 45 min stirring time with 5.4% montmorillonite addition.Further,the platelet spacing increases with stirring time till montmorillonite exfoliated to nanoscales platelet.When montmorillonite is exfoliated,layered structure at nanoscale can be uniformly distributed in the resin.The overall performance of montmorillonite modi fied phenolic resin is improved remarkably,such as flow ability,tensile strength and toughness property of resin coated sand.However,the gelation speed decreased slightly by adding montmorillonite.
基金supported by the National Science fund for Distinguished Young Scholars (No.50625204)the National Natural Science Foundation of China (Science Fund for Creative Research Groups)(No.50621201)+1 种基金the Major State Basic Research Development Program of China (No.2009CB623301)the National High-Tech Research and Development Program of China (No.2006AA03Z0428), and Samsung Electro-Mechanics Co., Ltd.
文摘Fine-grained BaTiO3-based X7R ceramic materials were prepared and the effects of milling process on the core-shell structures and dielectric properties were investigated using scanning electron microscope, transmission electron microscope, and energy dispersive spectroscopy （EDS）. As the milling time extends, the dielectric constant of the ceramics increases, whereas the temperature coefficient of capacitance at 125℃ drops quickly. The changes in dielectric properties are considered relevant to the microstructure evolution caused by the milling process. Defects on the surface of BaTiO3 particles increase because of the effects of milling process, which will make it easier for additives to diffuse into the interior grains. As the milling time increases, the shell region gets thicker and the core region gets smaller; however, EDS results show that the chemical inhomogeneity between grain core and grain shell becomes weaker.
基金financially supported by the Major Science and Technology Projects in Anhui Province (No. 18030901097)the Natural Science Foundation of Anhui Province (No.1908085QE197)the Fundamental Research Funds for the Central Universities (JZ2018HGBZ0133, JZ2019HGTA0043)
文摘Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting.The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting;and the formation mechanism of the gas pore,and shrinkage porosity defects were analyzed.The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment,insufficient feeding and non-sequential solidification.Subsequently,through changing the position of risers,adding a connecting channel between the risers,and setting blind risers at the U-shaped brackets,an optimized gating and feeding system was established to improve the quality of the casting.After optimization,the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated.The experiment results with the optimized casting process are in good agreement with the numerical simulation,which verifies the validity of the finite element model in the shell mould casting.
