Feasibility Of Standing Wave Ratio Method For Fast Measuring Moisture Of Green Sand

In casting production,the green sand quality is one of an important factor affecting the quality of the casting.In the large-scale production,the components of green sand remained essentially unchanged green sand water content can be considered one of the key factors that determine the quality of green sand.Thus,rapid and accurate measurement of the moisture content of green sand is important casting method to improving green sand quality and reducing the rejection rate,it has a very important practical significance.At first,this article discusses the green sand moisture content of the existing measuring methods and research status.Then,as a starting point to dielectric physics,the model of the dielectric physical properties of green sand is established,analyzed the microscopic dielectric mechanism and the characterization parameters of dielectric properties of green sand.Results show that under the action of electric field,to reduce the dielectric loss of green sand,must use the appropriate high frequency excitation source excitation.Based on the above analysis,this article puts forward a new method of rapid measurement of green sand moisture—standing wave ratio method and establish an equivalent electrical model of new method by mathematical analysis,in theory the standing wave ratio method for rapid measurement of green sand moisture is feasible.Based on the new method,the green sand moisture test system is set up which consists of green sand probe ? N5181 A signal generator ? DPO4054 digital oscilloscope?coaxial transmission line,It regard the voltage difference between the two ends of the transmission line as the macro parameters of dielectric properties of green sand.The impedance characteristics of green sand probe were analyzed,and an isomeric four-needle probe was designed and made by the 304 stainless steel.The needle length and diameter are 100 mm and 5 mm.A needle was taken as the center,and the other three needles were arranged at the circle of 25 mm diameter with an interval angle of 120 o.Analysis of the minimum size of sand sample that we used new methods to determine the standard sand which diameter of 110 mm and height of 160 mm and to design the sampler.Using the green sand moisture test system test frequency excitation source?amplitude excitation source?compactness of the green sand sample?clay content ? coal content and study the influence of these factors on the transmission line voltage difference.Finally,the relationship between specific component of green sand moisture and voltage difference of transmission line is given.The experiments show that suitable excitation source is the sine wave with the frequency of 115 MHz and the amplitude of 1000 m V.The voltage difference between two ends of the transmission line will increase with the increase of compactness,but the curve slope of 115 MHz is slightly less than that of 120 MHz and 125 MHz,which indicated the influence of compaction at 115 MHz on the voltage difference is relatively smaller.The clay content has a certain effect on the voltage difference between the two ends of the transmission line,with the increase of clay content,the absolute value of the voltage difference will decrease and clay content is greater than the impact compaction.The coal content have no influence on the voltage difference in the two endpoints.The components of green sand,with the increase of moisture,the voltage difference between two ends of the transmission line will increase,but the relationship between the voltage difference and the water content is not linear.