Study On Preparation Of High Solid Rate Semi-solid Slurry By Swirling With Medium Cooling Cylinder

In view of the problem that the melt reaches the thermal equilibrium state in the existing SEED technology,which leads to the long preparation time for preparing high solid rate semi-solid slurry and the complicated supporting equipment,a new method is proposed to break the thermal equilibrium state between the barrel and the melt in the rotating stage by setting a closed cooling channel inside the barrel,using the medium to continuously cool the barrel and dissipate heat,improving the undercooling and promoting the nucleation,Thus,a scheme for rapidly preparing high solid rate semi-solid slurry is proposed.Through the mechanical design and development of the structure of the medium cooling cylinder,eccentric gyration structure,turnover structure and other parts,the test platform is built;Combined with PLC programming and configuration,it can realize the on-off of cooling medium,the tilting pouring of barrel platform,the control of rotational speed and mixing time of rotary mixing,and the automatic control of the horizontal flipping discharging process at the end of pulping;Under the condition of medium cooling cylinder and swirling,the effects of medium cooling conditions(natural cooling,air cooling and water cooling),pouring temperature and swirling conditions on the solid fraction and solidification structure of the melt during the preparation of semi-solid slurry were studied;The nucleation and growth rule and influence mechanism of melt in thermal equilibrium state under gas cooling condition are analyzed and discussed,which provides theoretical and practical basis for further research on the preparation technology of high solid rate semi-solid slurry and industrial practice,and has good reference value.The specific conclusions are as follows:The swirling conditions change the supercooling gradient of traditional dendritic solidification.On the one hand,the temperature field of the whole melt is in a uniform supercooled state,and the disturbance of cyclotron swirling promotes the collision of atomic clusters,which contributes to the massive supercooled nucleation of the melt;On the other hand,the melt near the side wall of the barrel has a higher degree of supercooling,which makes it easier to nucleate by chilling.At the same time,the melt is subject to the strongest cyclotron swirling and scouring effect,resulting in grain free and promoting nucleation.The pouring temperature represents the superheat of the melt.Proper lowering of the pouring temperature is conducive to obtaining greater undercooling of the melt under the same conditions,promoting the nucleation of grains and increasing the nucleation rate;Compared with natural cooling for a long time,properly prolonging the cyclotron swirling time under the air cooling condition can effectively improve the degree of supercooling,increase the number of nucleation and promote grain growth,rapidly prepare high solid rate semi-solid slurry,shorten the swirling time and improve the efficiency;Under the condition of near liquidus pouring(620 ℃),rotating speed of 120 rpm,and heat dissipation of gas cooled cylinder,the more appropriate preparation time of high solid rate semi-solid slurry is 30 seconds.If the time is too short,the proportion of solid phase in semi-solid slurry is low and the fluidity is good,so it is a low solid rate semi-solid slurry;If the swirling time is too long,the proportion of solid phase in the semi-solid slurry will increase significantly,leaving the subsequent forming time short,which is easy to cause process stability problems.Combined with the thermocouple’s melt temperature data,calculated solid rate data and solidification structure change under natural cooling,gas cooling and water cooling conditions,it can be determined that the melt enters the thermal equilibrium state about 30 s after rapid cooling under natural cooling conditions,and then the melt slowly cools down,requiring a long time of swirling to improve the solid rate of semisolid slurry;The air cooling method is adopted to strengthen the heat dissipation of the barrel.The melt has a faster cooling speed,and enters the thermal equilibrium state in about 25-30 s.Because the barrel has a continuous heat dissipation capacity,the same high solid rate semi-solid slurry preparation effect can be achieved in a short time;Air cooling improves the heat dissipation of the barrel,breaks the thermal balance of the melt,and strengthens the cooling of the melt.With the swirling,the melt increases the degree of supercooling at a controllable rate,promoting the generation of new primary grains,and the growth of existing grains,rapidly reducing the liquid phase,rapidly making high solid rate semi-solid slurry,which can greatly reduce the pulping time and improve the efficiency;By configuring cooling medium,the problem of long time swirling and complicated supporting equipment for preparing high solid rate semi-solid slurry by rotary thermal balance method can be effectively solved.