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Metal Casting Technologies : September 2008
Avoiding titanium: The SinterCast® process and other developments In the patented SinterCast process the liquid base iron is deliberately under-treated with a Ti free Mg carrier alloy plus inoculant . The condition of this under-treated iron is then evaluated using computerized thermal analysis of the solidification behaviour of a sample of liquid metal. This enables a much more accurate measurement of cooling curve features such as undercooling when compared to the normal set up for CEL determination. The technique uses a specially coated sampling cup fitted with two thermocouples: one at the centre of the cup to predict start of casting behaviour and one at the bottom of the cup to predict end of casting behaviour, i.e. to predict Mg fading. On the basis of the analysis of the data from these two thermocouples the system predicts how much additional magnesium + inoculant must be added to the under-treated metal before pouring castings. The system then automatically controls a wire feed system to deliver the correct amount of extra treatment. It is claimed that, throughout the batch of castings being poured from a given treatment, nodularity can be kept within a 0-20% range and the formation of any flake graphite can be prevented. Many major motor manufacturers now use this process with current production of around 300,000 cylinder blocks per year . Large mass production automotive foundries can afford to invest in and pay technology licence fees for such a process. However such investment may be a barrier for smaller foundries that are interested in using CGI for low volume production such as pump and valve bodies. Research has continued towards developing improved Ti free treatments that may be successfully applied using conventional process control conditions in foundries who are experienced in making high duty FC and FCD grades. One new Ti free treatment which gives a sufficiently wide %Mg production window is a Mg-Ferrosilicon material containing 5-6%Mg + 5.5-6.5%RE + 1.8-2.3%Ca + 44-48%Si + a maximum of 1%Al . The increased Rare Earths content is said to widen the conditions under which compacted graphite is formed. It is recommended for use on low sulphur base irons (0.10 - 0.15%S as for FCD production) and can be used in sandwich or tundish ladle treatments or as an in the mould treatment. Normal addition rates are said to be 0.3- 0.4% compared to 0.5-1% for under-treatment with conventional Mg-Ferrosilicon or 1.5% for Ti containing Mg-Ferrosilicon. After treatment inoculation may be needed with addition rates of 0.1- 0.5% depending on circumstances. If the molten metal is correctly pre-conditioned before treatment then post-treatment inoculation may not be needed, especially if the steel scrap normally used in the sandwich (cover) process is replaced by a suitable inoculant material. Another approach [16-17] that may be suitable for smaller foundries is the use of a wire feeder to deliver a precise amount of conventional Mg-Ferrosilicon treatment alloy carried in 5mm diameter wire. Wire feeding rather than ladle treatment enables the ladle of liquid base iron to be accurately weighed before treatment thus allowing an exact amount of wire to be fed into the iron to meet the required narrow range of residual %Mg. ¦ REFERENCES 1. S. Dawson. “Compacted Graphite Iron – A Material Solution for Modern Diesel Engine Cylinder Blocks and Heads”. Proceedings of the 68th World Foundry Congress, 7-10th February 2008, Chennai, India. pp. 93-99. 2. D. Leslie-Pelecky. “The Physics of NASCAR”. (2008) ISBN 9780525950530, Dutton Books, US, 304pp 3. www.audioworld.com/news 4. S. Charoenvilaisiri and A. Iriapichart. “Development of Compacted Graphite Iron Castings in Thailand”. Proceedings of the 65th World Foundry Congress, 2002, Gyeongju, Korea, pp. 225-233. 5. G.F. Sergeant and E.R. Evans. “The production and properties of compacted graphite irons”. British Foundryman (1978) vol.71 pp.115-124. 6. I.C.H. Hughes and J. Powell. “Compacted graphite irons: high quality engineering materials in the cast iron family”. Proceedings of the SAE Earthmoving Industry Conference, April 9-11, 1984, Peoria, Illinois, US. 7. J. Powell. “A review of some recent work on compacted graphite irons”. The British Foundryman (1984) vol. 77 pp.472-483. 8. S. Dawson. “Process Control for the Production of Compacted Graphite Iron”. Proceedings of 106th AFS Casting Congress, May 4-7, 2002, Kansas City, US, 10pp. 9. C.M. Dunks and K.B. Turner. “Production of Compacted Graphite Iron Castings for Brake Systems”. Trans. AFS (1981) vol.89, pp. 575-586. 10. R.J. Warrick, G.G. Ellis, C.C. Grupke, A.R. Khamseh, T.H. McLachlan, & C. Gerkits. “Development and Application of Enhanced Compacted Graphite Iron for the Bedplate of the New Chrysler 4.7 Liter V-8 Engine”. SAE International Congress, March 1-4, 1999, Detroit, US, Paper 1999-01-0325, 9pp. 11. F.A. Mountford. “The Influence of Nitrogen on Strength, Soundness and Structure of Grey Cast Iron”. The British Foundryman (1966) vol. 59 pp.141-151. 12. H. Morrogh & W.J. Williams. “The production of nodular graphite structures in cast iron”. Journal of the Iron & Steel Institute (1948) vol. 158 pp.306- 322 13. J. Sissener, W. Thury, R. Hummer, & E. Nechtelberger. “Cast iron with vermicular graphite”. AFS Cast Metals Research Journal (1972) vol. 8, pp.178-181. 14. E.R. Evans, J.V. Dawson and M.J. Lalich. “Compacted Graphite Cast Irons and their Production by a Single Alloy Addition”. Trans. AFS. (1976) vol. 84, pp.215-220. 15. C.M. Ecob and C. Hartung. “An Alternative Route for the Production of Compacted Graphite Irons.” Proceedings of the Eighth Asian Foundry Congress, October 17-20, 2003, Bangkok, Thailand, pp. 146-159. 16. M.J. Fallon. “Experiments on the treatment of compacted graphite iron”. Foundry Trade Journal (2004) vol. 178, Jan/Feb., pp. 34-38. 17. M.J. Fallon. “The structures and tensile properties of irons containing mixtures of compacted and spheroidal graphite determined from step plates”. Foundry Trade Journal (2004) vol. 178: Part 1, April, pp. 123-129: Part 2, May, pp. 165-168. METAL Casting Technologies September 2008 63