Gang Nie

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.

A New Method for Ultrasonic Treatment on the Melt of Steel

Ultrasonic treatment of the melt metals is a hot research topic; however, it is hard to introduce ultrasound into liquid steel because of the requirement of resistance to high temperature and erosion in the melt. In this paper, a new method, unit piece method (UPM), is proposed to introduce ultrasound into liquid steel. The metal to be treated is cast together with amplitude transformer as free end. During the experiment the transformer is placed upward and its free end is melt by induction coils. Then the amplitude transformer powered by ultrasound acts on the melt pool. The effect of ultrasound on the melt of 304 stainless steel is studied. The microstructure of the treated area is significantly modified and equi-axed grains are obtained. The effect of power of ultrasound is discussed. This method is proved to be effective.

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.

Water analogue experimental study on the filling process of a steam turbine housing casting

Mould filling is of determining effect on the quality of castings. Numerical simulation is widely used for the study of mould filling, but the result is necessary for validation. Water analogue experiment used to be a main way for mould filling research before, but it was hard to simulate the mould filling of real castings. In this paper, a new water analogue system for real castings was established. The casting cavity was shaped by assembling transparent organic glass slices cut by laser, with each slice exactly representing the geometry of each casting section. Therefore, the shape of the mould cavity is guaranteed. The system was applied to study the filling process of a heavy steam turbine housing casting weighing 70.3 tons. Its filling process was observed and analysed. It is found that there is alternating flow in the gating system because of the height difference of the ingates. That also resulted into the uneven filling during the process. Therefore, the design was improved and it was proved to be more effective through experimental study. This water analogue method is proved to be applicable for research on the filling process of castings.

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.

Active and Passive Deformation of Large Thin-Walled Workpiece in Heat Treatment Process

Displacement is traditionally deemed to be equivalent to deformation. However, displacement is not exactly deformation, for example, the tip of a workpiece illustrates big displacement, but, it caused by the deformation of main body. In this paper, theory of active and passive deformation is proposed for the evaluation of the deformation of workpiece during heat treatment process and the corresponding algorithm was established. The deformation consists of active and passive deformation; the former is the actual deformation, while the latter is caused by the deformation of other areas. This algorithm was applied to the deformation analysis of a hydraulic turbine blade which is a large thin-walled workpiece. And the real deformation area of the blade is found.