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Aluminium International Today November/December 2013

UK-based MQP claims that its Opticasttechnology makes it possible to study andquantify all the factors affecting grainrefinement, including grain refiner potency,melt nucleation level, growth restrictionfactors, grain refiner recovery and in linetreatments. According to the company, itallows rapid and reliable results to begenerated so that accurate conclusions canbe made regarding implementation ofoptimised grain refining practice.

Grain refiner variability is an importantfactor in achieving a fully optimisedpractice and this has led to thedevelopment of Optifine, which is a grainrefiner.

Integrated aluminium productionEti Aluminyum, a member of CenzigHolding, is located at Seydisehir in Turkey,and is one of a very small number ofaluminium producing facilities in the worldthat is fully integrated. It has its own bauxitemines near to its factory and this is thestarting point for a total process of oreextraction, primary aluminium smelting andcasthouse processing to billet.

The casthouse at Seydisehir producesaround 65kt/yr of 6063 billet. Castingequipment comprises two 45Mt holders, anAlpur inline degasser, a filter box with 40ppiceramic foam filters and a Wagstaff billet

casting table. The majority of the furnacecharges contain a large proportion of itsown primary aluminium and the currentgrain refinement is with 2.2kg/tonne ofstandard commercial 5/1 TiBAl.

Casthouse trialsA series of trials was carried out in theSeydisehir casthouse by MQP. The firstobjective was to demonstrate the ability ofOptifine to achieve a minimum 50%reduction in grain refiner additioncompared with the standard TiBAl grainrefiner being used. A second objective wasto reduce consumption by 70%. Theseobjectives would mean initially reducingaddition rates from 2.2kg/tonne down to1.1kg/tonne and then down to0.65kg/tonne.

The work began by taking samples ofmetal from the furnace spout and carryingout Opticast crucible tests with standard5/1 TiBAl grain refiner and Optifine addedat 0.5kg/tonne,1.0kg/tonne and2kg/tonne.

The aim was to establish that it waspossible to reduce the addition rate to1.1kg/tonne using Optifine and still meetthe required grain size specification.

The Opticast curves, which resulted fromthe trial, revealed a large difference inefficiency between the standard

commercial TiBAl grain refiner (blue line)and Optifine (red line) as shown in Fig 1.

The horizontal hatched line at 146 µmindicates the grain size obtained insamples taken in the launder when thestandard TiBAl grain refiner was used at anaddition rate of 2.2 kg/tonne. The redcurve for Optifine additions indicates thatthe same grain size can be achieved withan addition of 0.5 kg/t of Optifine.

Based on these results it was decided tocarry out a second trial with Optifine at anaddition rate of 1.1 kg/tonne. The resultsfrom this showed an average grain sizemeasured at 135 µm in the Opticastsamples, which confirmed the predictionmade in the first trial.

After homogenisation, a billet slice fromthis trial was examined and the grainstructure was as shown in Fig 2.

The next step was to produce fiveproduction casts with a 50% reduction inthe addition rate down to 1.1kg/tonne.The normal practice at Eti is to assure atitanium level of 50 ppm in the furnacebefore casting in order to assure a highenough growth restriction. The base levelof titanium in charges may vary from aslow as 5 ppm to 100 ppm in the furnace,depending on the ratio between puremetal and scrap. This means that if theanalysis shows less than 50 ppm, Ti waffles

Optifine brings Turkish delightUK-based MQP carried out a series of tests at Eti Aluminyum in Turkey to demonstrate the ability of itsOptifine product to achieve a minimum 50% reduction in grain refiner addition compared with the useof standard TiBAl grain refiner. A second objective was to reduce consumption by 70%. By Michael Bryant*

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Fig1 Opticast grain refinement curves from the first trial Fig 2 Micrograph of billet cast from second trial with Optifine added at 1.1kg/tonne. Grainsize after homogenisation was 65 µm compared to the 135 µm measured in the Opticastsamples

*Marketing director, MQP Ltd

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24 CASTHOUSE www.aluminiumtoday.com

November/December 2013 Aluminium International Today

are added to increase the concentration to50 ppm.

In two of the production casts, thetitanium content was increased by Tiaddition, but in the other three casts notitanium additions were made as a meansof evaluating if Optifine could performacceptably even if the growth restrictionconditions were not optimised. The resultsfrom the tests are shown in Fig 3.

The Opticast results indicate that toensure a small grain size an adequate Tilevel is essential to provide optimumgrowth restriction conditions. The twocasts without Ti addition hadextraordinarily low Ti levels of roughly 2ppm, which resulted in grain sizes around210 µm. Two other casts to which Ti hadbeen added to around 20-30 ppmproduced grain sizes just above 160 µm.The other cast without a Ti addition, but abase Ti concentration well above 50 ppmdue to a large proportion of scrap in thecharge, showed a very small grain size of110 µm.

Having determined that a satisfactorygrain size can be produced with anOptifine addition of 1.1kg/tonne, providedthat the Ti content is adequate, a furtherproduction cast was made with a lowerOptifine addition in conjunction with a Tilevel adjusted to 50 ppm. Crucible testswere made with Optifine additions rangingfrom 0.86kg/tonne down to 0.56kg/tonne.

The results showed that grain sizeprediction works well when the Ti level inthe furnace is adjusted to 50 ppm. It alsoindicates that it would be possible to castthis alloy with an Optifine addition even aslow as 0.56 kg/tonne, a decrease of 75 %from the original level of 2.2 kg/tonne. Abillet slice from this cast with a0.65kg/tonne Optifine addition showed,after homogenisation, a grain size 110 µmas in Fig 4.

It is worth noting that in these trials,none of the 6063 billets cast from metaltreated with Optifine experienced cracking,even when the measured grain size in theOpticast samples was over 200µm. In fact

a 200µm grain size in an Opticast samplecorresponds to about a 100µm grain sizein a billet. This puts it well within theallowable maximum 176µm grain sizecorresponding to ASTM Grade 2.0, whichEti Aluminium uses to avoid billet cracking.

The results have confirmed thatalthough in the case of smelter metal thegrowth restriction factor is substantiallyless than in a remelt operation, this can beovercome by increasing titanium levels to0.005%. Optifine was successfully used forthe casting of 6063 billets on a productionbasis with the addition rate being reducedby 70% compared to standard grainrefining practice – provided the titaniumlevel was increased to 0.005%.

The Seydisehir casthouse is now in theprocess of converting its grain refiningpractice to Optifine. This will involveproduction of 6063 billet and ananticipated production of rolling slab. �

Contact:www.mqpltd.com

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Fig 4 Billet micrograph from cast with Optifine added at 0.65 kg/t Fig 3 Grain sizes in Opticast samples for five production casts with Optifine addition rate of1.1 g/t

ETI ALUMINYUMEti Aluminyum, located at Seydisehir, isTurkey’s only producer of liquidaluminium and it is the country’s onlyfully integrated producer, which takes inuntreated ore downstream and then hasthe capacity to fulfil every processrequirement to the finished product. Thecompany has its own bauxite mineslocated 20km from the factory and this isthe starting point of its operations.

ETI’s level of integration gives it theadvantage of better control of rawmaterial quality, cost and supply. Thecompany holds only minimal raw materialstocks, which makes it easier to forecastraw material and final product costs.

However, there are disadvantages.“There are more inputs and factors

affecting our profitability in this style ofoperation. As we have seen recently,energy costs have spiralled and so havesome vital raw material costs, like causticsoda, petroleum coke, natural gas, andelectricity. To manage such a highlyintegrated plant with its many processesrequires a bigger and more complexorganisation. Today more than 1,300people work here,” a companyspokesman said.

Producing aluminium is an energy-intensive process and many plants havebeen brought to the brink by risingenergy costs – it is estimated that arounda third of plants around the world areoperating at a loss – but Eti Aluminyumhas avoided the full impact of these

increases by using its own hydro-electricpower plant.

The plant in question has the capacityto process 460kt of bauxite annually andcurrently produces 60kt of aluminium peryear. There is also an on-site castingfacility with a capacity of 75kt/yr.

Eti Aluminyum produces primary andcast aluminium products as well as wetand dry aluminium hydroxide, calcinedalumina and a small quantity of high Mg-alloyed plates.

MQP is grateful to Eti Aluminyum for itsco-operation in this work at the Seydisehirplant and for its permission to publish theresults. Special thanks to Bader Saglamfor her participation in the programme.

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