Haimin Long

Evaluation of distortion of castings

Abstract Displacement results are usually used as the criterion for distortion of castings during casting and heat treatment processes. However, the displacement results consist of both contraction and distortion. Contraction is a kind of uniform volume change, which can be solved by enlarging the castings by a contraction coefficient. However, the actual distortion has to be deleted by giving inverse distortion or by mechanical correction method. In this paper, algorithms are presented to evaluate the distortion of castings. One method is to subtract the uniform contraction from the displacement results. The other is to calculate the deflection angle between the normal direction of the discretised surface triangle of the original casting shape in stereolithography format and that of the simulated casting shape. The third one is the application of actual machining allowance in the evaluation of distortion. These methods are validated by three case studies, including a heavy hydroturbine blade casting.

Observation of the Mold-Filling Process of a Large Hydro-Turbine Guide Vane Casting

The mold-filling process has a determining effect on the quality of castings, and it has always been a hot but difficult research topic. The authors developed a wireless monitoring system for the mold-filling process of castings based on a contact time method and an observation system based on heat-resistant high-speed cameras. By using these two systems, the filling process of a turbine guide vane casting with a stepped gating system was investigated. The filling profile of the casting was recorded, and the filling time of nine typical positions was acquired. These results show that at the beginning, the liquid steel flowed out from the top ingate, which was designed to be the last to fill. The numerical simulation of the filling of the guide vane was performed, and the outflow from the top ingate were predicted. Finally, the gating system of the casting was improved with enlarged sprue. The new design features bigger sprue to ingate ratio; therefore, it could avoid the overflow from the top ingate and realize stable filling.

Reply to Discussion of “Observation of the Mold Filling Process of a Large Hydro-Turbine Guide Vane Casting”

We appreciated Professor John Campbell’s comments very much. The mold filling of liquid metals is very important, especially as the first step of making a casting. Therefore, the filling system design is a very serious work. The melt filling process has been a 1000year mystery because it cannot be directly observed because of the mold obstacle. So, researchers have resorted to water analogy system. However, the analog results have been always doubted. In recent years, the X-ray observation method unveiled the filling process for specimens or small castings in laboratories. But, still some problems need to be solved such as dealing with the complicated and large castings. In our paper, we highlighted the effective direct observation system of mold filling and its successful application in a 10 t heavy steel casting, i.e., the using of high temperatureresisted camera to directly observe the filling process of heavy steel castings weighing in tons, which is affordable and the liquid steel flow can be directly watched at real time. It is a very valuable method for foundries, especially for the production of heavy castings, the direct observation means optimization of filling system and finally reducing waste and improving casting quality. Up to now, this method have been used in seven new heavy castings in the foundry of Harbin Electric Machinery Co., Ltd., and some observation results approve the experience, while some are in contradiction with the experience. As to the gating system design related to my paper, I agree with Professor John Campbell about the avoidance of the free fall of the melt in air or in the sprue to prevent inclusions and turbulence. However, in foundries, the filling system design is by theories with the consideration of the factors such as experience, cost, pouring ladle, and easy-going with on-site workers. Years ago I watched a bottom nozzle of a ladle was hardly opened till the end of filling of a heavy steel casting. Thus, in foundries, all these factors have to be considered, especially, in the production of heavy steel castings. Counter-gravity filling by using pressurized furnaces or pumps has been successfully applied in the production of aluminum castings; however, it is still hard to be adopted in steel castings up to date. The viewpoint about steady fluid flow in mold filling is easy to understand, but its importance in foundrymen minds varies. I will surely recommend these filling system design ideas and principles to foundries and assure them of their significance and effectiveness.

Intensive riser cooling of a turbine blade steel casting after solidification

To improve the production efficiency and reduce residual stress and deformation, a new method-Post Solidification Intensive Riser Cooling (PSIRC) was proposed for heavy steel castings. Risers are cooled by forced air from its top surface as the solidification of a casting finishes, so, the risers are turned into cooling passages during the cooling process of a casting with contrast to their function of feeding passages during the solidification process. This method was applied to a hydro turbine blade with 0.9 ton melt. Its cooling speed increased apparently meanwhile with improved temperature distribution uniformity and the hot spot was pushed almost to the casting bottom. The cooling efficiency was improved 40% before shakeout and its residual stress was reduced meanwhile.

Measurement and Observation of the Filling Process of Steel Castings

The filling process is significant for the quality of castings, and it has always been a hot but hard topic. The author develops a wireless measurement system for the filling process of casting based on contact time method and an observation system for the filling process of casting based on high speed camcorders working under high temperature. By using these two systems, the filling process of a turbine blade and a hub casting were measured and observed. And the filling situation of the castings with bottom gating system was obtained and the filling time of a number of typical positions was recorded. The result showed that liquid steel flows through the forward ingates at first. The velocity of the liquid steel in the mold was obtained by the calculation of the filling time. The study also shows that these two systems operate conveniently and reliably. They are effective tools for monitoring of the filling process of castings and future optimizing of gating system, and have broad prospect in casting production.

Experimental study on the filling process of the lost foam casting process of a cast iron plate

Lost foam casting owns a series of advantages, however, EPS pattern burns while the liquid metal fills, which makes the filling process complicated and directly leads to defects in castings. A measurement system of the liquid metal filling based on a modified contact time method (MCTM) was established. The filling of measured points is illustrated by a LED pattern, and the filling time of all the points is obtained by the analysis of the recorded movie. This method is free of limitation of signal acquisition channels. The system was applied into the experimental study of the filling of a vertical plate-shaped specimen of cast iron. The filling of one hundred positions was measured, and the filling profiles and filling velocity during filling process were obtained, which reflected the features of its filling process. The influence of some parameters including the metastatic head, the density of the EPS pattern, the thickness of coating and the permeability of sand mould on the filling process were investigated.