| Super large cylinder liner has the characteristics of large cylinder diameter,variable wall thickness and complex structure,which is mainly used in the engines of large ships.With the development of marine engine,the requirements for the strength,stroke,explosive force,effective pressure and output power of the engine become higher.Therefore,three requirements are put forward for the performance of super large cylinder liner: high strength,high wear resistance and uniform component.But this kind of cylinder liner casting is difficult,the process yield rate is very low,which greatly limits the development of Chinese ship business.In this paper,we had a thorough understanding of the current production situation of factories,started with the numerical simulation of super large cylinder casing,designed and established a model of the super large cylinder casing casting process.We simulated temperature field,flow field and pressure field by coupling calculation,and explored the influence of centrifugal speed,pouring temperature,casting temperature and pouring time on casting filling and solidification,and analyzed its influence mechanism.Through orthogonal experiment,each parameter was optimized comprehensively to guide the numerical simulation calculation of larger cylinder liner.The software Procast was used to design the horizontal centrifugal casting process of the super large cylinder liner.First,the three-dimensional model of the casting was divided into finite element mesh,the initial conditions and boundary conditions in the casting process were set,the rotation parameters of the casting mold were set,and the reasonable pouring time was set.Through the analysis and comparison of the numerical simulation results,the possible defect distribution of the casting was predicted.Finally,the optimal casting process parameters were obtained and the rationality of the casting process was verified.The flow process of metal liquid was divided into gravity flow stage and centrifugal flow stage.Coupling calculation of temperature field,flow field and pressure field in horizontal centrifugal casting process of cylinder liner was conducted.By analyzing the flow field,the liquid metal starts to expand axially at the gate and then rotates against the inner wall of the casting mold in the same direction as the casting mold.The metal liquid first fills the left cavity,then the metal liquid layer continuously thickens and spreads to the right until the cavity was filled,which took 90.3s.The analysis of the temperature field shows that the liquid metal moves forward in a layered flow form after entering the casting mold,and the temperature of the liquid metal at the front end is about 100? lower than that at the end.Radial and axial screenshots of any section are taken.The temperature of the casting is low at the axial ends and high in the middle,and the temperature gradient is about 100°C higher than the radial temperature gradient.The temperature of the outer surface of the casting is always lower than the temperature gradient of the inner surface.The temperature of the metal liquid near the inlet is higher than that far away from the inlet,and the cooling rate is faster at first and then slower.Due to the release of latent heat of crystallization,a temperature platform appears.In the final solidification position of the metal liquid,it is easy to appear shrinkage cavity and porosity.The solidification sequence of the casting is layer by layer from the outside to the inside,and the final solidification position is in the middle of the thick-walled end of the casting.Mold temperature increases first and then decreases,and the temperature distribution in the casting is similar,so the calculation results are accurate.The pressure field was analyzed.The pressure field showed a gradient distribution in the radial direction.The maximum pressure difference between the outer surface and the inner surface is 3.17 bar.The pressure at the thick-walled part of the casting is 0.97 bar higher than that at the thinwalled part.The maximum pressure of the metal liquid reaches 5.063 bar,and the metal liquid has strong feeding capacity.Process parameters have great influence on casting quality.When the speed is500r/min,the thickness of the upper end of the casting is thinner than that of the lower end,the phenomenon of rain occurs,the inner surface is rough,and defects are easy to appear;At 800r/min and 900r/min,liquid metal flow is chaotic and even splashes appear.The outer wall of the casting is prone to crack under excessive pressure,which increases energy consumption and produces defects such as bubbles and segregation.When the centrifugal speed is 700r/min,the metal liquid flow is continuous and uniform,and the filling effect is better.The casting temperature has almost no effect on the filling rate,but it affects the motion state of the metal liquid.The casting temperature determines the superheat of the metal liquid.When the casting temperature is 1430?,the filling mold is relatively stable.At 1370? and 1410?,the metal liquid has the phenomenon of splitting,and it is easy to produce cold separation and other defects after solidification.But at1450?,the metal liquid viscosity is small,it is easy to produce the phenomenon of splashing.The higher the casting temperature is,the slower the solidification rate is.The mold temperature affects the solidification rate and cooling time of the casting.With the increase of the mold temperature,the solidification time of the casting becomes longer and the solidification rate slows down.There is a linear relationship between the cooling time and the mold temperature.The cooling time of the casting increases with the increase of 50?,but the increasing range is decreasing continuously.The pouring time determines the inflow velocity of the molten metal.With the increase of pouring time,the feed flow width decreases slightly at first and then increases.In order to make the casting filling process more uniform and stable,the pouring time should be moderate.The influence of each parameter on temperature field and flow field was measured through temperature difference and flow field.Orthogonal tests were designed to determine the primary and secondary order of influence on the temperature difference as follows: pouring temperature,pouring time,centrifugal speed,mold temperature;The main and secondary order of influence on the distribution time is as follows: centrifugal speed,casting time,casting temperature,casting temperature;The orders are not consistent.We analyzed the centrifugal rotational speed,casting temperature,pouring temperature,pouring time for the influence law of temperature field,flow field,used the comprehensive evaluation index membership degree of each parameter for the temperature difference and the distribution time to determine the final comprehensive influence factors of the primary and secondary order of pouring time,pouring temperature,centrifugal speed,mold temperature;The optimal solution was determined as follows:pouring time is 70 s,pouring temperature is 1370?,centrifugal speed is 700r/min,casting temperature is 100?;The optimized scheme is used to guide the numerical simulation of centrifugal casting of larger cylinder liner,and the casting filling is complete.With the increase of diameter,the temperature field distribution of molten metal becomes more and more uneven,and the filling process of molten metal is not stable,which indicates that castings with large diameter are more likely to form defects such as cold separation and segregation. |
PDF Full Text Request