Research and development for industry: Advanced ... - CSIR

TOWARDS A NEW TITANIUM SECTOR| 32 |Producing titanium castings:A new South African opportunityThe few companies around the world that produce titanium castings using an investment casting process keep their cards closeto their chests. For this reason South Africa had to develop its own process, while ensuring that it is both cost-effective andcommercially viable.CSIR technical assistant Sam Papo removing casting moulds from the wax melting oven.The CSIR’s investment casting team. From left are Sam Papo, Nonjababuiliso Mazibuko,Pierre Rossouw, Peter Malesa and William Tefu.A wax mould of an aircraft part. A face coat as well as a refractory stucco, followed by layers ofback-up refractory coats, will cover the final wax assembly. It will be dried completely before thewax can be removed from the formed shell, into which titanium will be cast.The investment castingof titanium is one of thetechnology building blocksthat South Africa needs in itsstrategy to develop an entiretitanium value chain for a newindustry sector. With investmentcasting, it is possible to castparts with intricate shapes andthin walls into a near-net shape,meaning that the parts will notneed expensive and difficultmachining after the castingprocess.“Because of the metal’s highlyreactive nature, the investmentcasting of titanium is a greatdeal more intricate than theusual investment castingprocess,” says Pierre Rossouw,principal technologist withthe CSIR’s metals and metalsprocesses group. “Also, very littlehas been published about theprocess, as the companies thatare able to do it prefer to keepthis as proprietary information.”Rossouw’s job is to see if CSIRproducedtitanium powder canbe used in a casting processfor industrial components. TheCSIR’s goal with the investmentcasting of titanium is not onlyto do castings, but to optimiseevery step in the process sothat the technology, equipmentand everything needed for theprocess, can be successfullytransferred to industry.The team started byidentifying and thenmastering each of four criticaltechnologies needed for theprocess. The first was theface coat, the first layer ofthe investment mould thatreduces the reaction betweenthe titanium and the mouldmaterial during the castingprocess. There is always anoxygen-rich reaction layerafter casting, referred to as analpha case. The second stageinvolved the development ofintricate melting techniques.This was followed by thechemical milling process toremove the alpha case thatformed due to the limitedreaction with the face coatduring casting. Lastly, atechnique called HIPing(Hot Isostatic Pressing) hadto be mastered, which closesand fuses any internal microporositythe cast componentmight have.The market for titanium lies mainly with aerospace, medical,oil and gas, power generation, high-end automotive, sportand jewellery industries. The demand for it is growing rapidly,both internationally and locally.Rossouw explains that eachof these techniques had to beoptimised, with cost savingsfor industry always top ofmind. He also had to look atthe mechanical properties ofthe castings, where especiallyfracture toughness and fatigueresistance proved to be themost important requirement forclients.While the CSIR has nowdeveloped the capacity tocommercially cast titaniumparts, the organisation is stillcontinuing with research andthe transfer of the technology.The overall goal is to maintain adevelopment base for the futurethat can support industry withnew techniques and problemsolving.“We plan to be running withthe process commercially by2015, but we are not sure inwhich format this will be,” saysRossouw. “We might be settingup a completely different plant,use the existing one with anindustrial partner or look atother ways to implement it.Either way, the plan includesall the infrastructure, humanresources development and thetechnology of the process.”Pierre Rossouw,principal technologistat the CSIR, believesthat the investmentcasting of titaniumrepresents a wonderfulopportunity for thelocal manufacturingindustry.Apart from perfecting andoptimising the investmentcasting process for titanium,the CSIR is also working withthe Department of Scienceand Technology on a three tofour-year plan that includesa market evaluation; thetechnology’s industrialisation;a plan for human resourcesrequirements and training;and a commercially viablebusiness plan for itscommercialisation.“I believe that the investmentcasting of titanium representsa wonderful opportunityfor the local manufacturingindustry,” concludes Rossouw.“The industry will have accessto locally produced materialsand techniques that previouslyhad to be imported at a veryhigh premium. We havealready had some interest init, and we are working withthe international aerospaceindustry to ensure that wemeet its rigorous standards.”– Petro LowiesEnquiries:Pierre Rossouwprossouw@csir.co.zaAbout titanium• Titanium never occurs in nature as a metal.It is found in mineral form and to get to metal,the mineral must first become titanium oxide ortitanium dioxide, after which it can be convertedinto titanium ore and finally into metal.• The complex process of converting titanium oreinto metal has only been commercially viable fora little more than 50 years.• The use of titanium has since then expanded byan average of 8% per year.• The largest deposits of ilmenite sands and rulite(from which titanium is derived) are found inAustralia, South Africa and Canada.• Despite its abundant deposits, South Africa doesnot have a titanium industry.• Titanium is stronger than steel but 45% lighter.• Titanium is 30% more elastic than steel.• Titanium has an extremely high melting pointof 1 660 ˚C and is cast at temperaturesof 1 750 - 1 800 ˚C.• Titanium is a very reactive metal.It spontaneously forms a hard, protective oxidefilm when it comes into contact with oxygenat elevated temperatures. This necessitates allthermal processes to be done under a very goodvacuum or protected gas (in the case of lowertemperature operations).• When the process of investment casting is usedto manufacture parts from titanium, less of thevaluable titanium alloy is wasted. This is becauseinvestment casting produces parts in a near-netshape that requires very little and often nomachining thereafter. Investment casting is alsosuitable for the production of parts that haveextremely intricate shapes and/or thin walls.| 33 |