This paper presents the erosion results of the AISI H13 steel impinged by resin-bonded silica sand, using a testing rig that closely simulates the real blowing conditions during industrial core-making. Steel specimens...This paper presents the erosion results of the AISI H13 steel impinged by resin-bonded silica sand, using a testing rig that closely simulates the real blowing conditions during industrial core-making. Steel specimens were heat treated to obtain hardness of 294, 445 and 595 HV200 (29, 45 and 55 HRC). Erosion tests were carried out at impingement angles from 20° to 90° and air drag pressures of 1.38, 2.07 and 2.76 bar (20, 30 and 40 psi). The main results are summarized as follows:(i) The harder material, the lower erosion;(ii) the maximum erosion rate is at 30°;(iii) Little difference in erosion rate at impact angle of 60° and 90° for a constant pressure tested regardless of the hardness level;(iv) As the pressure increases, so does the erosion rate, being more sensitive for low impact angles. Finally, a differential form of the general erosion equation is applied on a practical core-making case to evaluate the erosion rate of the H13 steel at 30° and 90° impingement angles.展开更多
The temperature distributions of a prestressed concrete box girder bridge under the effect of cold wave processes were analyzed. The distributions were found different from those under the effect of solar radiation or...The temperature distributions of a prestressed concrete box girder bridge under the effect of cold wave processes were analyzed. The distributions were found different from those under the effect of solar radiation or nighttime radiation cooling and should not be simplified as one dimensional. A temperature predicting model that can accurately predict temperatures over the cross section of the concrete box girder was developed. On the basis of the analytical model, a two-dimensional temperature gradient model was proposed and a parametric study that considered meteorological factors was performed. The results of sensitivity analysis show that the cold wave with shorter duration and more severe temperature drop may cause more unfavorable influences on the concrete box girder bridge. Finally, the unrestrained linear curvatures, self-equilibrating stresses and bending stresses when considering the frame action of the cross section, were derived from the proposed temperature gradient model and current code provisions, respectively. Then, a comparison was made between the value calculated against proposed model and several current specifications. The results show that the cold wave may cause more unfavorable effect on the concrete box girder bridge, especially on the large concrete box girder bridge. Therefore, it is necessary to consider the thermal effect caused by cold wave during the design stage.展开更多
With modified water glass as binder and the introduction of micro silicon powders into the coremaking process,an improvement was made to the tensile strength and collapsibility of the sand core.The potassium hydroxide...With modified water glass as binder and the introduction of micro silicon powders into the coremaking process,an improvement was made to the tensile strength and collapsibility of the sand core.The potassium hydroxide,sodium hexametaphosphate and white sugar were applied as the modifiers of water glass.The optimum proportion of the modifiers was determined through the combination of single factor test and orthogonal test.The optimum proportion of water glass,potassium hydroxide,sodium hexametaphosphate and white sugar is 1000:40:5:5(wt.).In terms of weight,modified binder and micro silicon powders accounted for 2%and 0.6%of sand,respectively.The sand core was hardened by going through a warm core box process,in which the temperature of core box was 150°C,and the compressed hot air was blown at 120°C for 40 s under a pressure of 0.2 MPa.As for the sand core bonded with modified water glass,the tensile strength is 2.46 MPa at room temperature(σ0)and 2.49 MPa at 25°C and 40%RH for 24 h(σ24),which are 2 times more than that with unmodified binder.The bonded strengths of sand core are increased as a result of the reaction between-OH groups from addition of potassium hydroxide and SiO2 particles widely distributed in the sand core.Comparing with the sand core bonded with unmodified water glass,the high temperature residual tensile strength(σr)of sand core bonded with modified water glass under 600°C for 5 min,is sharply reduced from 0.20 MPa to 0.01 MPa.By the comparison with unmodified water glass,the dynamic viscosity of the modified water glass and the flowability of molding sand using modified water glass are increased from 74 mPa·s and 2.15 g to 80 mPa·s and 2.21 g,respectively.As revealed by FT-IR analysis,new groups including PO3-,PO43-,and Si-O-C appear in the molecular structure of modified water glass,which are beneficial to the collapsibility of sand core.展开更多
The cold box plus process it discussed in principle When the proper heating to the corebox is given (65℃±2℃). the binder lever can be saved, also the core strength and surface hardnessare imtroved, the moisture...The cold box plus process it discussed in principle When the proper heating to the corebox is given (65℃±2℃). the binder lever can be saved, also the core strength and surface hardnessare imtroved, the moisture-sensitvity is reduced. The mechanism of the cold box plus process isthat the proper heat increases the activity of resin function groups and promotes the crosslinking re-action The result of a scanning electron microscope analysis shows that the core surface strength isimproved by heat展开更多
基金financially supported by NEMAK S.A. and Industria Meccanica Bassi Luigi&Co
文摘This paper presents the erosion results of the AISI H13 steel impinged by resin-bonded silica sand, using a testing rig that closely simulates the real blowing conditions during industrial core-making. Steel specimens were heat treated to obtain hardness of 294, 445 and 595 HV200 (29, 45 and 55 HRC). Erosion tests were carried out at impingement angles from 20° to 90° and air drag pressures of 1.38, 2.07 and 2.76 bar (20, 30 and 40 psi). The main results are summarized as follows:(i) The harder material, the lower erosion;(ii) the maximum erosion rate is at 30°;(iii) Little difference in erosion rate at impact angle of 60° and 90° for a constant pressure tested regardless of the hardness level;(iv) As the pressure increases, so does the erosion rate, being more sensitive for low impact angles. Finally, a differential form of the general erosion equation is applied on a practical core-making case to evaluate the erosion rate of the H13 steel at 30° and 90° impingement angles.
基金Project(08Y60) supported by the Traffic Science’s Research Planning of Jiangsu Province,China
文摘The temperature distributions of a prestressed concrete box girder bridge under the effect of cold wave processes were analyzed. The distributions were found different from those under the effect of solar radiation or nighttime radiation cooling and should not be simplified as one dimensional. A temperature predicting model that can accurately predict temperatures over the cross section of the concrete box girder was developed. On the basis of the analytical model, a two-dimensional temperature gradient model was proposed and a parametric study that considered meteorological factors was performed. The results of sensitivity analysis show that the cold wave with shorter duration and more severe temperature drop may cause more unfavorable influences on the concrete box girder bridge. Finally, the unrestrained linear curvatures, self-equilibrating stresses and bending stresses when considering the frame action of the cross section, were derived from the proposed temperature gradient model and current code provisions, respectively. Then, a comparison was made between the value calculated against proposed model and several current specifications. The results show that the cold wave may cause more unfavorable effect on the concrete box girder bridge, especially on the large concrete box girder bridge. Therefore, it is necessary to consider the thermal effect caused by cold wave during the design stage.
文摘With modified water glass as binder and the introduction of micro silicon powders into the coremaking process,an improvement was made to the tensile strength and collapsibility of the sand core.The potassium hydroxide,sodium hexametaphosphate and white sugar were applied as the modifiers of water glass.The optimum proportion of the modifiers was determined through the combination of single factor test and orthogonal test.The optimum proportion of water glass,potassium hydroxide,sodium hexametaphosphate and white sugar is 1000:40:5:5(wt.).In terms of weight,modified binder and micro silicon powders accounted for 2%and 0.6%of sand,respectively.The sand core was hardened by going through a warm core box process,in which the temperature of core box was 150°C,and the compressed hot air was blown at 120°C for 40 s under a pressure of 0.2 MPa.As for the sand core bonded with modified water glass,the tensile strength is 2.46 MPa at room temperature(σ0)and 2.49 MPa at 25°C and 40%RH for 24 h(σ24),which are 2 times more than that with unmodified binder.The bonded strengths of sand core are increased as a result of the reaction between-OH groups from addition of potassium hydroxide and SiO2 particles widely distributed in the sand core.Comparing with the sand core bonded with unmodified water glass,the high temperature residual tensile strength(σr)of sand core bonded with modified water glass under 600°C for 5 min,is sharply reduced from 0.20 MPa to 0.01 MPa.By the comparison with unmodified water glass,the dynamic viscosity of the modified water glass and the flowability of molding sand using modified water glass are increased from 74 mPa·s and 2.15 g to 80 mPa·s and 2.21 g,respectively.As revealed by FT-IR analysis,new groups including PO3-,PO43-,and Si-O-C appear in the molecular structure of modified water glass,which are beneficial to the collapsibility of sand core.
文摘The cold box plus process it discussed in principle When the proper heating to the corebox is given (65℃±2℃). the binder lever can be saved, also the core strength and surface hardnessare imtroved, the moisture-sensitvity is reduced. The mechanism of the cold box plus process isthat the proper heat increases the activity of resin function groups and promotes the crosslinking re-action The result of a scanning electron microscope analysis shows that the core surface strength isimproved by heat
