Metal Casting Technologies : MCT-MARCH-2014
26 www.metals.rala.com.au Beckwith Macbro Resin Coated Sands Contact : Rob Dalla Via 30 Devon Road Devon Meadows, Melbourne Telephone: +61 3 5995 4244 Mobile: 0417 332 723 Fax: +61 3 5995 5030 E-mail: email@example.com Website: www.beckwithmacbro.com.au All grades of resin coated sand used for shell molding and shell cores for ferrous and non-ferrous applications PRODUCTS n Range of resin strengths from 1.0% to 5.0%. n Silica, Zircon, Chromite coated sands or blended mixes. n Coated Sands of different AFS typically from 50-90 AFS. n Thermal Reclaimed Coated Sands. n Frac Sand. SERviCES n Full technical and trouble shooting service. n On-site shell core and shell molding facility to evaluate the product applications. n Laboratory facility to ensure product quality. FORSALESHELLCOREMACHiNESSHELLMOULDMACHiNES METAL casting Technologies March 2014 27 TEcHNicAL fEATURE TEcHNicAL fEATURE isers are provided in castings to produce sound castings free from shrinkage defects. These risers feed liquid metal to the sections of castings during its solidification. Each riser can feed liquid metal up to certain distance. This feeding distance is defined as the distance from the edge of riser to the edge or corner of casting up to which liquid metal is fed from the riser before and during solidification such that the section remains free from visible shrinkage porosity, i.e. radiographically sound casting section. The development of feeding distance rules for steel castings began in the early 1950s. The results of initial works showed that  the feeding distance for plate castings (plate is defined as W/T≥3) is equal to 4.5T, where T is the thickness of the section of a casting and W is its width. This feeding distance of 4.5T is composed of two regions. 2.5T is sound by the chilling effects of the edges of the plate casting, due to comparatively more heat loss to the mould at the edges including the effect of corners. The remaining 2T (adjacent to riser) is sound by the temperature gradient of the riser. These two zones are referred to as end zone and riser zone respectively. Chills are provided either in the mould to enhance directional solidification and to increase temperature gradient in the casting [1-3]. The feeding distance of 4.5T from a riser is resulted, when no chills are used in casting. Placing chills in suitable locations in the mould not only promote directional solidification, it also increase the feeding distance. It is established that the feeding distance for plate castings with an end chill is 4.5T + 2 inches. This value of feeding distance is applicable when the thickness of the chill is equal to T for plate castings. The thickness is taken as equal to T based on experiments that indicated that increasing the chill thickness beyond this value did not significantly increase the feeding distance. The end chills increase the feeding distance by increasing the length of end zone; they have no effect on the riser zone. Earlier work on use of extensive chill in plate casting has shown that  the hot spot gradually reduces as a chill is placed at the end and at the end as well as top and bottom near the edge of a plate casting of constant length. In the present work, simulation has been carried out on a plate casting with varying lengths without and with chills placed at different locations to find the solidification time and Niyama criterion. The Niyama criterion is a local thermal parameter which is defined as G/√T, where G is the temperature gradient and T is the cooling rate . Extensive trial of plate castings has been carried out in other works and the soundness of the castings were compared with the corresponding Niyama criterion values computed from simulations. It was determined from these comparisons that if the Niyama criterion value of a casting section is greater than 0.1 K1/2S1/2mm-1, the section will be radiographically sound. Therefore the simulation has been carried out in the present work on several plate castings without and with chills to plot solidification time and Niyama criterion values using MAGMASOFT version 5.2.0 to determine the feeding distance of riser attached to the plate casting. To study the effect of chills on feeding distance, the length of the plate casting was varied in simulation. A plate casting of 25 mm thickness, 100 mm wide was selected for the work. The drawing of the plate casting is shown in Fig.1. Effect of extensive chill in plate casting on solidification behaviour and feeding distance Ajay Tripathi1, Nandita Gupta2 and P. C. Maity3 1Emirates Techno Casting FZE, UAE 2Associate Professor, Foundry Technology Department, National Institute of Foundry and Forge Technology, Ranchi, India 3Metal Casting and Materials Engineer r Figure 1. drawing of the plate casting showing placement of chills. All dimensions are in mm. a protective thermal barrier against gas temperatures of up to 1450oC [5-7]. For turbine blades which do not require coatings or cooling systems and which can withstand higher operating temperatures alternative materials such as Mo-Si-B alloys must be developed . In most non-aerospace applications above 550oC, and up to around 1100-1150oC, austenitic (FCC) heat resistant high alloy Cr-Ni cast steels are used. Plain C steels can only be used up to 350oC and low alloy martensitic Cr-Mo steels are limited to 600-650oC . A range of casting grade compositions for 25%Cr - (10-20)%Ni and 17%Cr – (25-35)%Ni austenitic steels, some of which contain additional elements such as Mo, Co, Nb, W and N, have been developed for use in the as-cast condition [1, 10-12]. As in Ni base alloys compositions must be selected to avoid the formation of damaging second phases such as sigma during service which cause severe reductions in toughness and corrosion resistance. For higher performance in automotive turbocharger housings and exhaust manifolds the composition of 18%Cr-10%Ni cast stainless steel has been modified to significantly improve creep resistance . The Ni content is raised to 12.5% together with additions of 4%Mn and 0.25%N. This avoids as-cast-ferrite in the as-cast microstructure, reduces the tendency to form sigma phase and promotes the formation of nanometer sized nitrides to provide precipitation hardening. Where required this steel may be used in place of the Si-Mo ductile irons which are normally used for exhaust components . In the martensitic (ferritic) steels improved creep and higher temperature capability compared to low alloy 2%Cr-1%Mo grades has been achieved in 10-12%Cr steels alloyed with Mo, Co, W, V, Nb, B and N [15-17]. Improved performance was needed to increase efficiency in power generation plant by enabling the use of higher superheated steam temperatures [6, 16]. These steels are air hardened after austenitising and then tempered at 650-750oC to produce a tempered martensite structure with a high dislocation density and which contains fine strengthening precipitates of carbides, nitrides and carbonitrides of V and Nb. Mo and W provide solid solution hardening in the ferritic matrix. Large castings weighing up to 60 tonne such as inner casings for pumps are produced in the steels which were mainly developed by collaborative research in Europe during the 1990s. n ReFeReNCeS: 1. J.T.H. Pearce. “Ferrous casting alloys for heat resistance”. Metal Casting Technologies (2009) Vol.55 pp.36-41. 2. F. Abe et al (ed.) “Creep-resistant Steels” (2008) Woodhead Publishing 667pp. 3. D.R . Askeland. “The Science and engineering of Materials” (1988) Van Nostrand Reinhold pp.139-140. 4. L . engel & H. Klingele. “An Atlas of Metal Damage” (1981) Wolfe/Hanser pp. 52-61. 5. http://www.grc.nasa.gov/WWW/StructuresMaterials/AdvMet/research/turbine_ blades.html. 6. J. Knott. “energy – materials and mechanisms”. energy Materials (2008) Vol. 3 pp.11-19. 7. K . Harrison. “Advancing aero-engines”. Materials World (2010) Vol.18 pp.18-21. 8. R .C . Reed. “The Superalloys: Fundamentals & Applications”. (2008) Cambridge University Press. 9. J.A . Lemberg & R.O. Richie. “Mo-Si-B Alloys for Ultrahigh-Temperature Structural Applications”. Advanced Materials (2012) Vol.24 pp.1445-1480. 10. “Steel Castings Handbook - Supplement 9: High Alloy Data Sheets Heat Series”. (2004) Steel Founders’ Society of America. 11. “Heat and Corrosion Resistant Castings: Their engineering Properties and Applications”. Publication No. 266, The Nickel Development Institute, 52pp. 12. G .J. Cox. “Some effects of composition on the properties of cast austenitic heat resisting steels”. British Foundryman (1980) Vol.73 pp.1-21. 13. J.P. Shingledecker et al. “Creep Behaviour of a New Cast Austenitic Alloy”. International J. of Pressure Vessels and Piping (2007) Vol.84 pp.21-28. 14. S.H. Park et al. “Development of a heat resistant cast iron alloy for engine exhaust manifolds”. SAe Transactions (2005) Vol.114 pp.777-783. 15. P.J. ennis et al. “Recent Advances in Creep Resistant Steels for Power Plant Applications”. Operational Maintenance and Materials Issues (2002) Vol.1 No.1 28pp. 16. R . Vanstone et al. “Manufacturing experience in an Advanced 9%CrMoCoVNbNB Alloy for Ultra-Supercritical Steam Turbine Rotor Forgings and Castings”. J. eng. Gas Turbines Power (2013) Vol.135 8pp. 17. R .F. Hanus. “Heavy steel casting components for power plants “mega - components” made of high Cr – steels”. Proceedings of the 9th Liege Conference: Materials for Advanced Power engineering, (2010) Liège, pp.286-295. 18. For further reading on dislocations, plastic deformation and strengthening mechanisms: “Modern Physical Metallurgy & Materials engineering” 6th edition (1999). R .e, Smallman and R.J. Bishop, Butterworth-Heinemann 427pp.
Whos who September 2012