Cast Impellers Research Articles

Numerical Simulation on Impeller Casting Defects and Optimization

The numerical simulation is similar to the experimental research, which uses the computer. 3D printing is an experimental study, which is compared with simulation. 3D printing and precision casting of impellers are frequently used in industrial scenarios. To address the problem of low casting yield of aluminium alloy impellers in gypsum‐type casting, three‐dimensional modelling by magics, casting simulation, and parameter optimization method by applying ProCAST software are used to improve the casting yield of impellers. The results show that the optimized structure of the casting system is more reasonable, so that the shrinkage and shrinkage defects are concentrated in the location of the riser; the maximum stress value of the casting and the casing during the solidification stage is 2.71 MPa, which is much smaller than the stress limit of the casing; the maximum horizontal displacement of the casting along the X and Y axes after solidification is completed at 0.025 mm and 0.022 mm, respectively, and the maximum displacement along the Z axis due to the presence of the riser is 0.009 mm, which greatly improves casting accuracy and molding quality.

Evolution of microstructure and hardness in shell moulded impeller casting

ABSTRACT To remain competitive in this growing field of the manufacturing industry, there is a need to reduce the lead times in the development of a component. The virtual simulation environment tool can be utilised for minimising production time as well as assure defect-free casting. This technique is based on heat transfer and volumetric calculations for prediction of possible defects. In this paper, analysis of automobile impeller casting is explored. The modelling of the casting and feeding system is done using the CATIA software. The CAD model of the impeller is imported into the simulation environment for solidification simulation. The simulation is performed using SolidCAST software which is based on the Finite Difference Method. The simulations are performed to ensure proper feeding for achieving sound casting. The melting trials are performed in jobbing foundry. The hardness and microstructure analysis of simulated and experimental casting is performed so as to correlate. The section thickness and cooling rates in casting were analysed and used for formulating hardness and microstructure in the experimental castings. The statistical predictions based on simulated and experimental results are presented for formulating Brinell hardness and amount of pearlite phase in particular section of shell moulded ductile iron casting.

Corrosion Resistance of Selected Cast Iron Grades Under Deposit Mining Conditions

The paper analyzes two types of alloyed cast iron used for pump impellers operated in mine working conditions. The research on corrosion resistance of two cast iron grades resistant to abrasive wear was presented. Tests were performed for chromium cast iron (HCCI) grade EN-GJN HV600 (XCr18) (acc. to EN 12513) and high-silicon cast iron HSCI Grade 1 (acc. to ASTM A 518/ A 518M - 99). Deposit mining is characterized by variable working conditions. Both types of cast iron are resistant to abrasive wear and are suitable for loaded elements (e.g. pump impellers). The paper presents a metallographic analysis of selected cast iron grades based on light microscopy. The chemical composition of the tested cast irons was determined with the Leco GDS 500 spectrometer; C and S content was determined with the CS125 Leco Carbon–Sulfur Determinator. The Si content for HSCI Grade 1 was determined by gravimetric method. Corrosion tests were performed under laboratory conditions. In-service tests of cast impellers were performed under real conditions (working mines applications). Corrosion resistance tests were measured with VoltaLab® Potentiostat (PGP 201). Performed tests resulted in the determination of the usefulness of materials used for dewatering pump impellers in mine working conditions. The results of laboratory tests were verified under the operating conditions of cast impellers. In the conditions of transporting a liquid-solid mixture at the moment of appearance of impurities (e.g. chlorine impurities) in the liquid, the impellers from cast iron HCCI revealed a tendency to pitting corrosion, which explains the exploitation results collected in the mining. After laboratory tests for sample from HCCI, the low value of breakdown potential Eb and repassivation Ecp was concluded which says about the absence of pitting corrosion resistance.

Casting process design and practice for coolant pump impeller in AP1000 nuclear power station

The coolant pump impeller casting is the only rotating component in the nuclear island of an AP1000 nuclear power station, and is required to have a 60-year service time, which requires advanced materials and processing technologies to guarantee. In this paper, the casting process was studied, designed and modifed by means of numerical simulation. The gating system was distributed symmetrically and the runner diameter was a little bigger for avoiding sand wash and turbulence; the feeding system focused on the solution of blades feeding, as some parts of which should reach Severity Level 1 radioactive testing standard. Therefore, upper and lower plates cooperating with chillers acted as feeding method besides additional 2–3 times thickness; in addition, lowering sand core strength, decreasing pouring temperature and increasing dimension allowance would be adopted to avoid crack defects. Finally, the pilot impeller was cast. The results show that the casting process design is reasonable, as the liquid rises very smoothly when pouring, and no volume defects are found by means of 100% radioactive testing. Based on this casting process, 16 coolant pump impellers have been successfully produced and delivered to customers.

Rapid casting of complex impeller based on 3D printing wax pattern and simulation optimization

Rapid casting is the product of digital, information, and optimization of casting technology. It mainly includes rapid prototyping and virtual manufacturing. In order to shorten the production cycle of a stainless steel closed impeller casting, the wax pattern was made by high impact polystyrene (HIPS) with a selective laser sintering and photosensitive resin with stereolithography (SL). In order to prevent the formation of shrinkage defects, different gating systems designed to examine the molten metal flow and solidification behavior during the pouring and solidification process. The results show that pouring temperature is 1550 °C and pouring speed is 0.75 m/s, which is favorable for filling impeller castings, and can avoid casting defects. The optimized gating system prevented surface shrinkage and interior defects. The optimized gating systems have been verified by experiment, and the rapid casting has been realized based on 3D printing wax pattern and simulation optimization. This rapid casting can reduce processing time and costs, and enhance casting quality in the foundry industry.

STRUCTURAL PHASE STATE AND TRIBOTECHNICAL PROPERTIES OF CASTINGS FROM HIGH-CHROME STEEL 20Cr15Mn3, OBTAINED BY TECHNOLOGY OF PRECISION SOL-GEL CASTING IN CERAMIC FORMS

The structure, phase composition and tribotechnical properties of the impeller casting for oil and centrifugal pumps made from high-chromium steel 20Cr15Mn3, obtained by the technology of precise casting, were studied. It was concluded that impeller casting made from high-chromium steel 20Cr15Mn3, obtained by the technology of exact casting of Sol-Gel in ceramic molds, had improved properties and can serve as a replacement for the traditionally used material – cast iron.

Optimization to Develop Multiple Response Microstructure and Hardness of Ductile Iron Casting by using GRA

Ductile irons are important engineering materials because of its high strength to weight ratio and castability. The ductile iron castings are used widely for automobile applications due to their wide spectrum of property range. Weight reduction is important in automobile to improve its fuel efficiency which can be achieved by thinning down the casting sections without altering its functionality. Generally, automobile castings are having varying section thickness. Varying thickness castings offers different cooling rates while solidification of the casting. The solidification cooling rate decides the final microstructure of the cast components. Cooling rate was found to affect directly the amount of pearlite and ultimately the as cast properties in varying thickness ductile iron castings. In view of this, the automobile impeller casting is selected for study in the present work as it consists of varying section thickness in which small sections are connected to central hub. The casting solidification simulations were performed and analyzed. The solidification cooling rates were analyzed further to correlate the experimental processing parameters. The samples from poured castings were analyzed for microstructure and hardness at different section thickness. Multiple response optimization of microstructure and hardness was carried out by combined Taguchi and Grey Relational Analysis (GRA). Contribution of input variables on the output variables is attained using ANOVA.

Anti-carburizing Coating for Resin Sand Casting of Low Carbon Steel Based on Composite Silicate Powder Containing Zirconium

This paper studied the structure and properties of anticarburizing coating based on composite silicate powder containing zirconium by X-ray diffraction analyzer, thermal expansion tester, digital microscope and other equipment. It is introduced that the application example of the coating in the resin-sand casting of ZG1Cr18Ni9Ti stainless steel impeller. The anti-carburizing effect of the coating on the surface layer of the cast is studied by using direct reading spectrometer and spectrum analyzer. The change of the micro-structure of the coating after casting and cooling is observed by scanning electron microscope. The analysis of anti-carburizing mechanism of the coating is presented. The results indicate that the coating possesses excellent suspension property, brush ability, permeability, levelling property and crackresistance. The coating exhibits high strength and low gas evolution. Most of the coating could be automatically stripped off flakily when the casting was shaken out. The casting possesses excellent surface finish and antimetal penetration effect. The carburizing layer thickness of the stainless steel impeller casting with respect to allowable upper limit of carbon content is about 1mm and maximum carburizing rate is 23.6%. The anticarburizing effect of casting surface is greatly improved than that of zircon powder coating whose maximum carburizing rate is 67.9% and the carburizing layer thickness with respect to allowable upper limit of carbon content is greater than 2mm. The composite silicate powder containing zirconium coating substantially reduces the zircon powder which is expensive and radioactive and mainly dependent on imports. The coating can be used instead of pure zircon powder coating to effectively prevent metal-penetration and carburizing of resin-sand-casting surface of low carbon steel, significantly improve the foundry production environment and reduce the production costs.

Anti-carburizing Coating for Resin Sand Casting of Low Carbon Steel Based on Composite Silicate Powder Containing Zirconium

This paper studied the structure and properties of anticarburizing coating based on composite silicate powder containing zirconium by X-ray diffraction analyzer, thermal expansion tester, digital microscope and other equipment. It is introduced that the application example of the coating in the resin-sand casting of ZG1Cr18Ni9Ti stainless steel impeller. The anti-carburizing effect of the coating on the surface layer of the cast is studied by using direct reading spectrometer and spectrum analyzer. The change of the micro-structure of the coating after casting and cooling is observed by scanning electron microscope. The analysis of anti-carburizing mechanism of the coating is presented. The results indicate that the coating possesses excellent suspension property, brush ability, permeability, levelling property and crackresistance. The coating exhibits high strength and low gas evolution. Most of the coating could be automatically stripped off flakily when the casting was shaken out. The casting possesses excellent surface finish and antimetal penetration effect. The carburizing layer thickness of the stainless steel impeller casting with respect to allowable upper limit of carbon content is about 1mm and maximum carburizing rate is 23.6%. The anticarburizing effect of casting surface is greatly improved than that of zircon powder coating whose maximum carburizing rate is 67.9% and the carburizing layer thickness with respect to allowable upper limit of carbon content is greater than 2mm. The composite silicate powder containing zirconium coating substantially reduces the zircon powder which is expensive and radioactive and mainly dependent on imports. The coating can be used instead of pure zircon powder coating to effectively prevent metal-penetration and carburizing of resin-sand-casting surface of low carbon steel, significantly improve the foundry production environment and reduce the production costs.

Property Optimization of Impeller Casting Using GRA

Ductile irons are important engineering materials because of its high strength to weight ratio and castability. The ductile iron castings are used widely for automobile applications due to its wide spectrum of property range. Weight reduction is important in automobile to improve its fuel efficiency which can be achieved by thinning down the casting sections without altering its functionality. Generally automobile castings are having varying section thickness. Varying thickness castings offers different cooling rates while solidification of the casting. The solidification cooling rate decides the final microstructure in cast components. Cooling rate was found to be affect directly the amount of pearlite and ultimately as cast properties in varying thickness ductile iron castings. In view of this, the automobile impeller casting is selected as it consists of varying section thickness in which small sections are connected to central hub. The casting solidification simulations were performed and analyzed. The solidification cooling rates were analyzed further to correlate the experimental processing parameters. The samples from poured castings were analyzed for microstructure and hardness at different section thickness. Multiple response optimization of microstructure and hardness is carried out by combined taguchi and Grey Relational Analysis (GRA). Contribution of input variables on the output variables is attained using ANOVA.

Study of Forming Mechanism of Non-Filling Holes in Blades of Semi-Solid Cast Impellers

The semi-solid casting process has a lot of advantages in controlling casting defects. High quality impellers have been produced successfully by the semi-solid process for several years. The semi-solid processed impellers have uniform microstructure and premier mechanical properties, and therefore excellent durability. Further improvement of performance of the impellers is demanded and achieved by increasing curvature and length of blades of impellers. These changes create potential trend of casting defects in blades of impellers, such as non-filling holes. In our recently work, castings were made in different conditions, including two-step plunger velocity and one-step plunger velocity. The experimental results show that the change of plunger velocity played a decisive role in the forming of non-filling holes. Entrapped gas is the direct reason of the non-filling holes. With the increasing of plunger velocity, the area of non-filling holes increased. The non-filling holes in blades could be avoided by eliminating the plunger velocity’s changing during filling blades.

Optimization of Aging Cycle of Stainless Maraging Steel Using Dilatometric and Differential Scanning Calorimetric Analysis to Improve its Strength

04X13H5M5К9Л is a stainless maraging steel with high strength and excellent toughness. This alloy has been selected for making Impeller casting which is subjected to localized stresses reaching as high as 700 MPa at the tip of its vanes. The impeller rotates at 19000 RPM for 253 seconds.This alloy comprises of austenitic – martensitic dual phase at room temperature, in which martensite exhibits Body Centered Cubic (BCC) structure with moderate hardness (HRC 30) and high toughness. The required strength is achieved by precipitation of second phase particles in soft martensite matrix at suitable aging temperature. There is always a chance of reversion of martensite to austenite on heating either for extended period or at higher temperature. Thus optimization of aging temperature and time becomes highly critical keeping in mind the functional stress requirements of the component. The optimization has been done using Differential Scanning Calorimetric (DSC) analysis, dilatometric studies and experimental iterations of heat treatment temperatures and aging time.Different combination of strength and ductility could be achieved by varying heat treatment parameters. Martensite start and finish temperatures and austenitic reversion temperatures were established through DSC and dilatometric studies. Effect of subzero temperature on properties and microstructure of this steel is also presented here. Scanning Electron Microscopy and Energy Dispersive Spectroscopy were also carried out to analyze phases in different heat treatment conditions.

Casting and Heat Treatment of Turbocharger Impellers Thixocast from Alloy 201

Commercial semi-solid cast impellers are produced from Al-Si-Cu alloys heat treated to the T6 temper. The study described in this paper involved the identification of casting and heat treatment parameters to produce semi-solid processed turbocharger impellers from a silicon-free, higher strength 201 alloy. Casting parameters were identified which minimized hot tearing in the alloy 201 impellers. A series of heat treatment studies were performed to determine optimum heat treatment parameters. The T71 temper was identified as the preferred heat treatment condition to produce high strength as well as superior elongation. The results from mechanical property measurements conducted on the T71 heat treated impellers are reported. Optical and scanning electron microscopy (SEM) were also used to characterize the microstructure of alloy 201 impellers before and after heat treatment, and representative microstructures are presented.

Development of Complex Patterns: Scope and Benefits of Rapid Prototyping in Foundries

The quality through frugal engineering concepts has gained prime importance to the foundries around the world. Although simulation packages have been used as a tool to achieve quality and productivity, the use of Rapid Prototyping (RP) is not yet fully practiced in foundries in this concern. This paper provides a detailed study of the fabrication of a complex master pattern (impeller casting) using rapid prototyping technique besides presenting its scope and benefits compared to the current practices. The main objective of this work is to enlighten the foundry engineers to make use of rapid prototyping technology (fused deposition modeling) to eliminate the material wastage in pattern production, reduce the cost and lead-time in the production of accurate complex castings of an acceptable surface quality.

High-quality aluminum turbocharger impellers produced by thixocasting

The thixocasting process was chosen to produce the impellers as it is capable of producing castings with extremely high internal quality. Slugs cut from the DC cast bars are re-heated to the semi-solid casting temperature, and a specially-designed runner and gating system is used to prevent oxide from the surface of the slugs from becoming incorporated into the impeller. The technology used to produce the semi-solid impellers is described in detail. The semi-solid cast impellers, produced from an Al-Si-Mg-Cu alloy, are heat treated to the T6 temper. Results from testing are presented demonstrating that the impellers are free of porosity and other internal defects. Both mechanical property and fatigue data are presented showing that the semi-solid impellers have better properties than impellers produced by conventional casting and similar properties to forged and machined impellers. A short study is also described which identified suitable processing parameters to minimize hot tearing in the complex-shaped turbocharger impellers semi-solid cast from alloy 201. The surfaces of the impellers were examined using penetrant testing, and the results of modifying processing parameters on the propensity for surface cracking are presented. An aging study was performed to identify optimum mechanical strength.

Casting product–process–producer compatibility evaluation and improvement

The manufacturability of a cast product depends on process capabilities, which in turn depend on the facilities of the producer (foundry). Selecting the right combination of the product, process, and producer to simultaneously optimize functionality and manufacturability considerations is a challenging task. This paper presents a multi-criteria methodology that integrates the hitherto separate problems of process and producer selection, by introducing the concept of an ideal foundry. A set of 25 common criteria (11 objective and 14 subjective type) grouped under six headings (geometry, quality, production, delivery, facility, and other), have been identified to evaluate the process and the producer. Objective criteria are assessed using a fuzzy logic approach, whereas a rating method has been employed to accommodate subjective criteria. An analytical hierarchy process has been used to obtain the relative importance of the evaluation criteria. The methodology is also useful for benchmarking of foundries, and feedback for improving product–process compatibility. This is illustrated with an industrial example of a steel impeller casting.

Numerical Analysis of Blade Geometry Generation Techniques for Centrifugal Compressors

It is a known fact that machined impellers result in improved compressor performance compared to cast impellers of the same design. The performance improvements can be attributed to better surface finish, more accurate geometric definition (tighter dimensional tolerances), well-defined edges, and the lack of blade tip fillet on shrouded impellers. In addition, it has been observed through experimental investigations that the construction method of the impellers has an impact on performance. This paper presents computational fluid dynamic investigations of two types of impellers, with blade surfaces generated using straight-line elements (SLEs) and CAD arbitrary definitions. Because there are many different mathematical definitions that CAD tools employ for curves, the resulting arbitrary blade surface is not unique. The numerical results will help understand the causes of the performance differences as well as the effects of SLE blades on the flow through the impeller. Input conditions for computational dynamic simulations are based on experimental results. All references to experimental data in the present paper are for cast impellers. Therefore, the differences in performance are attributed to blade definition (SLE versus other) and not to differences resulting from manufacturing methods.

One-piece cast impellers for axial pumps

One-piece cast impellers for axial pumps