Experimental Study On Solidification Process Of Strand With Internal Cold Source

With the rapid development of national economy and the gradual improvement of people’s living standards,processed products from casting strand had come into our daily life,which had put forward new requirements for strand quality.There were many problems in the solidification process of strand,and shrinkage cavity was a very typical problem.In order to improve the loose shrinkage defects in the solidification process of the strand,an experimental scheme is proposed in which an internal cold source is added during the solidification process.In this paper,an alloy-like liquid is used to simulate the strand solidification process with an internal cold source.The alloy-like liquid in this paper is NH4C1-70%H2O solution,and the cooling medium is anhydrous ethanol solution.Selecting a mold with a plexiglass material as the main body.The cooling solution circulation pump will pass a fixed temperature cooling medium into the mold chamber,and use K-type thermocouples to monitor the temperature variation during the solidification process.The collected temperature data is converted into a computer through a data acquisition module and stored in a computer Capturing a solidified tissue image during coagulation with a camera.The effects of cooling temperature,solution temperature,internal cold source insertion time,and internal cold source insertion concentration on the solidification process were considered.After the experiment,the experimental data was processed using Imagej and Origin software.The higher the temperature of the solution is,the greater the percentage of mushy zone is.When the temperature of the solution is 65℃,it is 20%higher than that of 45 ℃.When the solution temperature is 45℃,a large area of equiaxed crystal collapse occurs,and the problem of dendrite bridging will occur for the other two conditions,which eventually leads to the problem of loose shrinkage.Compared with the temperature of the solution,the cooling temperature has a greater effect on the mushy zone,and the percentage of the mushy zone is as high as 76%when the cooling temperature is-20 ℃.During the solidification process,the area of dendritic fragments first increased and then decreased.The maximum area of dendritic fragments was 0.94 mm2,and the maximum total area of dendritic rain was 93.46 mm2.The area of dendritic rain on both sides of the mold was larger than the central area.The temperature of the mushy zone on both sides of the mold is lower than that of the central zone,and the temperature difference at the time of solidification for 30 minutes under the cooling temperature of-20℃ is 13.9℃In the solidification experiment with internal cold source,the dendrite fragments dissolved by heat from the internal cooling source are all equiaxed,so the increase in the percentage of the mushy zone is the increase in the percentage of equiaxed crystals.The internal cold source with a concentration of 15%is 13%higher than the mushy zone during the solidification process without the internal cooling source,and it is 6%higher than the internal cooling source with a concentration of 5%.At the same time,the percentage of the mushy zone of the internal cold source was increased by 9%when the dendritic rain area.was the maximum.The dendritic rain inhibited the growth of columnar crystals.The temperature of the solution near the supercooled internal cold source dropped sharply,the lowest temperature was 7℃,and more dendritic fragments were generated.The maximum area of the dendritic fragments was 0.68 mm2,which was very small compared to the area without the internal cold source.The maximum area of dendrite rain during the dissolution of the internal cold source was 1021 mm2.Dissolved dendrite fragments in the internal cooling source are constantly moving,and the ultimate trend is to move to the center of the mold with the fluid.The use of an alloy-like solution can systematically understand the change law of the slab during solidification.The insertion of an internal cold source can effectively improve the problem of loose shrinkage in the slab during solidification.The dendritic fragment changes after the internal cooling source has dissolved new understanding.