The New Copper Casting-Machine: Experiences at ... - Pyro.co.za

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The importance of points c) and d) depends on the customer who receives the product. For example, insilicon metal these points are of great importance for a chemical-grade customer, who wants a veryhomogeneous material, and of less importance for an aluminium customer. The reason is that tramp elementsin silicon affect the reaction with CH 3 Cl in silicones production, and should be evenly distributed in thereactor. The tramp elements tend to solidify on the boundaries between the grains. With slow cooling, thesilicon crystals will be larger than the grains in the powder, and many grains will be essentially singlecrystals without grain boundaries. With smaller crystals the grain boundaries will be more evenly distributed,and most grains will contain some phases with tramp elements [3].In short, the standard system of casting needs the following operations:• Casting from the ladle to the casting mould or to the fines beds.• Waiting until the material is cold and solidified sufficiently.• Moving the material from the cooling area to the breaking up area.• Breaking up the material into the first sizes.• Breaking the material down to the customer’s requirements.• Picking up the fines and storing them in their own stock area.• Transporting the fines to the casting area and placing them into moulds.Figure 1. Conventional processing technology in a ferroalloys factory after metal tapping.Solidified ferroalloys need to be further crushed down to small lumps of up to 100 mm for use in customers’processes. This means it should go through two crushing processes and at least another two for sizing. Thefirst is normally done in jaw crushers and the second in roll crushers. These operations normally generatesignificant amounts of fines, which are undesirable for their bigger impurities content because the dominantfractures are transgranular. The production of fines is usually about 10%, taking into account that thematerial is under 5 mm.
These fines are either sold at a discount of about 20% to lumpy product, or are resmelted in the same factoryin the furnace, in the bed, or in the casting mould. Fines constitute the main part of the impurities andfrequently the customer, who is concerned about chemical purity, asks for the percentage of fines to beresmelted in the casting moulds to be minimal.From the point of view of capital investment, space is needed for all these intermediate stocks, coolingplaces, etc., also for transporting machinery, such as bulldozers, travelling cranes and the breaking upinstallations in its two stages. In general all this takes up 25% of the area of a factory, and in a new factorymeans 20% of the investment.Staff and maintenance costs for all these operations obviously depend on each factory. In silicon factories, anaverage figure of about 8% would be reasonable for the total cost for auxiliary works in the making of theproduct.Within this percentage there are two very important concepts, which are not included:• Losses of fines as a consequence of movements of stocks.• The loss of profits when the fines are sold at market prices, which are usually 20% below the commercialprices.In brief, all the treatments of the metal (from its molten state to its delivery to the customer) make up one ofthe most important costs for a ferroalloy factory. Many efforts have been made to reduce such costs and toimprove the quality and homogeneity of the product, for example water granulation. Casting onto copperplates is an existing solution, the same as continuous casting was for steel.2. REASONS FOR THE COPPER CASTING-MACHINEThe decision to set up a copper casting machine was taken when Ferroatlantica went into the chemical-gradesilicon market. The objective was to cast a thin layer (about 10/15 mm thick), to solidify this quickly, and notto use fines since they pollute part of the metal. Thus, a very pure and homogeneous metal would be obtainedboth in its liquid and solid states. Therefore, we got in touch with Dr. Anton More, who has a patent on thissystem and who had had previous experience with it when he worked for the Wacker-Chemie company inGermany before his retirement. Ferroatlantica I+D, the R&D company of the Ferroatlantica Group, reachedan agreement with him, and the design for a machine which would allow for the casting of all of the factoryproduction was begun. This machine would also cast at different layer thicknesses and so cater not only forthe chemical market, which requires thin layers, but also the aluminium one with thicker layers.The casting machine has been designed with enough capacity to cast all the production of the plant at acasting speed of around 150 kg/min. At Ferroatlantica (I+D), we have carried out, and are continuing to doso, many studies and improvements with the object of achieving the most automatic and safest installationpossible. The machine has been running at normal production level since some months ago, and although wehave still not reached the full level of casting from the three furnaces, our customers are being supplied withproducts cast using it.3. MAIN FEATURES OF THE FERROATLANTICA COPPER CASTING-MACHINEThe basic machine consists of one copper table and two iron tables. The width and length of these tableshave been calculated so that the cooling of the elements is very efficient and the copper, whose melting pointis somewhat more than 1000ºC can receive the molten metal which arrives at 1500 º C. The flow and speedof the water are very important parameters for the life span of the cooper plate and these were achievedthanks to a very adequate design of the refrigeration circuit. Thermocouples have been installed to measureboth the temperature of all the water circuits as well as of the copper plate where the metal falls onto it. Allthis data is controlled by a PLC, and one by one all the different operations have been changed over toautomatic.
Page 1: THE NEW COPPER CASTING-MACHINE: EXP
Page 5 and 6: 3.1 Safety and Video-Control System
Page 7 and 8: All this allows for an important re

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