Study On Naturally Pressurized Running System

Casting under the condition of gravity is a general and economic foundry method.Many of gravity casting defects are easily formed during pouring and mould filling of molten metal,in which severe.surface turbulence of molten metal leads to metal re-oxidization and air entrapment. Recent research results both at home and abroad showed that bi-film formed after fold-over of re-oxidized metal film may be the important reason for these defects,such as precipitating gas holes,shrinkages,shrinkage porosities and so on.At present,the molten metal flow is still not controlled well in most of sand gravity casting running systems,which are widely used in our country' s foundries,and this affects the improvement of our casting quality.Therefore,to look for a better running system design method is very important for improving casting quality of gravity casting and the foundry process design level.Naturally pressurized running system(NPRS) is a new one based on the concept of designing the flow channels in the mould so as to follow the natural form that the flowing metal wishes to take,and it takes the continuity of fluid flow as design principles,and the main purpose is to control the molten metal being close to 'turbulence-free' during mould filling.Based on the concept of NPRS,and chose ZL114A as mould filling test material,authors study the design method details of the new running system, designing different running systems and same feeding systems for one plate sample,validating and analyzing the superiorities of NPRS over the traditional running system according to the test results,and exploring the feasibility of putting this new running system design methods into foundry practice.The mould filling process is simulated by using of numerical simulation software Z-CAST in this study.According to the analysis for the numerical simulation results,it is found that the molten metal flow through the naturally pressurized system is very steady,and with reasonable speed slowing down measures,the whole mould filling process in the naturally pressurized system is controlled well,and the surface turbulence is limited and mould filling status is desirable.The X ray scanning and mechanical test examinations proved that,compared with samples produced by using of traditional running system,the samples produced by using of NPRS have a higher reproducibility and better synthetically mechanical properties.These study results showed that,in the way of limit the surface turbulence during mould filling and improve the reproducibility and interior quality of samples,NPRS has more valuable contribution compared with traditional running system.Further studies may be carried out in other cast alloys.