Large hydraulic turbine blade casting process research and development
Large hydraulic turbine blade casting process research and development
Jul 30, 2025
Introduction In recent years, along the development line of energy saving, professionalism and high efficiency, China's hydraulic turbine generator set industry is booming towards industrialization, high efficiency and scale. Various types of hydraulic turbine supporting products produced by the industry have gained a certain degree of competitiveness in the international market, both in terms of quality and price. With the continuous expansion and growth of the demand for hydraulic turbine generator sets as well as the export volume, China's hydraulic turbine industry has ushered in unprecedented opportunities and challenges. Hydraulic turbine runner is the core component of hydraulic turbine, which needs to bear the impact of water flow constantly, and is the main component to convert the potential energy of water flow into mechanical energy . The hydraulic turbine runner is mainly composed of upper crown, lower ring and blades, in which the shape of the blades is more complicated, the curvature of the main body is irregular, the degree of torsion is large, and the wall thickness of the inlet side as well as the outlet side varies greatly. The blades are also the core components of the hydraulic turbine, and the manufacturing of hydraulic turbine blades is often a key challenge to be overcome in the industry. At present, the most common hydraulic turbine blades are axial-flow and mixed-flow blades, as shown in Fig. 1, which are characterized by large curvature change, thin wall and large warpage. The traditional casting program is generally for the solid sample modeling (flat bumping vertical casting modeling method) or core modeling (vertical bumping vertical casting modeling method) program, as shown in Figure 2.
Among them, the defects of the flat collision vertical casting program are:
the need to process the actual sample mold and support the tire plate;
the need to assemble the sand box with sand/core after the formation of the sand core turned up, the operation is difficult;
low productivity, sand-iron ratio (the ratio of the weight of the casting sand to the weight of the casting) is large.
There are the following defects in the standing collision casting modeling method:
the cavity consists of two sand cores with two sides of the blade, and the cost of the mold is high;
due to the limitations of the design of the core box of this type of product, the core needs to be turned over during the process, and it is difficult to form the core;
the production efficiency is low, and the ratio of sand to iron is large.
In order to overcome the technical defects, this paper researches a new casting process scheme to improve the product quality and production efficiency and reduce the production cost of hydraulic turbine blade castings through the optimized design of modeling scheme.
1 Determination of process program 1.1 Analysis of structure and difficulties The casting studied in this paper is shown in Fig. 3, the casting profile size is 2315*1532*611mm, the maximum wall thickness is 310 mm, the minimum wall thickness is 8 mm, the net weight is 2456 kg, the gross weight is 3243 kg, and the material is ASTMA743 Grade CA-6NM.The product has a large degree of warping, the wall thickness is extremely thin, and the casting is very easy to flush the sand during the casting process, which will produce sand trapping, slag trapping, and so on. defects. 1.2 Process program design 1.2.1 Determination of modeling scheme Comprehensive structural characteristics of this type of blade, the number of orders and technical quality standards and other factors, taking into account the small weight of the casting, the casting of a box of multiple pieces of the casting program, the design of a blade with a positive pressure surface and the negative pressure surface of the two sides of the characteristics of the sand core, the parting surface to take a vertical with the molding parting surface, as shown in Figure 4. 1.2.2 Design of casting shrinkage, counter-deformation and make-up quantities Cast steel parts in the solidification of three shrinkage processes, they are liquid shrinkage, solidification shrinkage and solid shrinkage, solidification shrinkage and solid shrinkage occurs when the line shrinkage (i.e., shrinkage), the shrinkage will be based on the material of the castings and different degrees of the castings affect the size of the reference to the previous production of the structure and material and the casting similar to the actual shrinkage of the casting, the casting shrinkage of the casting in the range of 1.6% to 2.0% The casting shrinkage is between 1.6%~2.0%, and there is a tendency of “flattening” deformation of the bottom warped edge during solidification and heat treatment. Considering that the casting bottom edge wall thickness is thin and large warpage, in this part of the design of a certain amount of anti-deformation to prevent deformation of the casting in the casting and heat treatment process, as shown in Figure 5. 1.2.3 Design of risers and allowances for castings The location of the risers and allowances is usually determined according to the structure of the casting, the size of the thermal joints and the direction of casting of the casting, according to the size of the casting module, the length of the horizontal shrinkage distance to determine the type and number of risers, and to check whether the liquid steel provided by each riser can meet the amount of liquid steel that can meet the loss of shrinkage of casting in the area that it is shrinking. The design of the riser is usually calculated using the modulus method to determine a theoretical model, and then through the checking of the amount of make-up shrinkage liquid and Magma simulation riser safety distance to determine the final size of the riser, the fundamental purpose of the riser design is to ensure that it is able to solidify at last, and give the casting a constant supply of sufficient amount of make-up shrinkage liquid, to ensure that the casting of the casting organization is homogeneous, dense, as little as possible, casting defects and to meet the customer requirements for the quality of casting . quality requirements of customers. Casting subsidies and cold iron design is to ensure that the casting organization is dense and does not produce two key factors, in addition to casting engineers to carry out modulus calculations, but also the application of advanced Magma software simulation to assist in the verification of the distribution of hot joints and shrinkage gradient and other factors to determine the most reasonable size of the risers and the most appropriate subsidy position. According to the shrinkage distance and casting wall thickness, increase the cold iron in the end area of the shrinkage, clear shrinkage area, adjust the solidification sequence, to ensure the internal organization of dense and no shrinkage, to meet the requirements of non-destructive flaw detection. The use of Magma simulation casting modulus, as shown in Figure 6, the hot joints are mainly distributed in the water inlet edge and the bottom two warped edge part, because of the increase in the casting shrinkage efficiency can improve the production rate, reduce the ratio of sand to iron, in the process design, will be the two blades into one group, the hot joints out of the water edge of the centralized part of the common a dark risers, the process as a whole using the upper and lower two-layer riser design concepts, and the reasonable use of the cold iron, the blades solidified! The area is divided. For each area of the riser design, to realize the stepped shrinkage. The final formation of blade casting specific casting process design as shown in Figure 7. 1.2.4 Design of the pouring system The pouring system is the channel to introduce the steel in the ladle into the casting cavity, the design of the pouring system is an extremely important step in the design of the casting process, which must ensure that the liquid steel can safely, smoothly and quickly into the cavity, and to ensure that slagging, exhaust smoothness. Considering the large impact force when pouring a single blade in large ladle and the consistency of the pouring parameters of each blade, a box of ten pieces of modeling and pouring is adopted. This casting finally adopts open pouring system, in order to avoid steel impacting the cavity and steel sand entrapment, the inner gate is set right below the dark riser, so that the steel flows smoothly from the dark riser. Through calculation, the size and number of inner gates are determined by controlling the pouring speed and pouring time according to the casting weight. In addition, in view of the casting surface inspection requirements are high, in order to avoid the ladle steel inclusions into the cavity caused by the casting slag, process design in each inner gate to increase the filter and the end of the cross sprue to increase the collection pipe to ensure the purity of the liquid steel into the cavity, and at the same time, set up a riser filler system to increase the loss of temperature of the liquid steel at the risers, to reduce the bottom of the inner gate at the liquid steel into the flow of the continuous brought about by overheating, and to further enhance the sequential solidification filler system. Further strengthen the conditions for sequential solidification. Using Magma simulation software, the casting system is simulated and optimized and improved according to the problem to design the most suitable casting system, as shown in Figures 8 and 9. 1.2.5 Core design Design a sand core with two sides of the blade, as shown in Figure 10, this sand core front core head can be completely matched with the reverse core head, and at the same time in the design of the sand core on the positioning table to ensure that the size of the two neighboring sand core with each other. When the box will be sand core linear array, according to the sand core on the positioning table combination can get the required blade cavity, general use of N +1 sand core can be produced N blade required cavity, as shown in Figure 11: 2 Product Quality Verification According to the casting dimensions and NDT NDT results, the casting wall thickness dimensions [9-10] meet the design requirements and satisfy the customer specifications. The overall surface of the casting is clean, the organization is dense, no shrinkage loosening is detected, and all the properties meet the customer's requirements, so the overall quality of the casting is very good. The site operation is convenient, reduce labor intensity, while the molding method and process design methods to make the sand-iron ratio greatly reduced, the output rate increased significantly, can reduce the cost of about 25% for the company, the casting process is feasible. 3 Conclusion In this paper, through the study of the structure of hydraulic turbine blade castings and make-up shrinkage gradient, using Magma simulation inspection assistance, the optimal casting process is determined, and the comprehensive design of the pouring system strictly controls the quality of the castings. The new molding scheme design ensures the reliability of the process, realizes the mass production of multiple pieces in one box, solves the problems of uneven pouring parameters and sand flushing in small pieces, improves quality and efficiency, and further reduces the cost. The conclusion is as follows:
Two blades are designed as a group to make the hot joints merge and share the risers, which can improve the process yield rate of the castings; multiple blades are cast together, and the use of the same pouring system can homogenize the pouring parameters, reduce the inlet speed of the inner gate, and prevent the impact of the liquid steel on the cavity.
The use of the dichotomous pouring system+filter+cross sprue the first liquid steel collection pipe can be used to reduce the sand and slag inclusions and deficiencies on the surface of the casting effectively.
For the large cast steel parts with bottom pouring, the use of supplementary pouring system can effectively improve the heat preservation of the riser area, prevent the steel slag from entering into the cavity at the end of pouring, strengthen the sequential solidification conditions, and reduce the slagging defects of the products.
The use of double-sided core molding method can reduce the sand-iron ratio to less than 5, and reduce the labor intensity of molding, and the modeling of multiple pieces in one box can multiply the efficiency.
