Bakır-gümüş esaslı alaşımların fiziksel ve mekanik özellikleri

Abstract

Oksijenli elektrolitik bakır filmaşin üretiminde kullanılan Sürekli Döküm Sisteminin kalite ve ekonomikliğini etkileyen en önemli parametresi hareketli döküm kalıbı olarak kullanılan döküm tekerleğidir. Döküm tekerleği malzemesi olarak uygulamada tarihsel gelişim içinde çelik, bakır, bakır-gümüş alaşımı, bakır- kromzirkonyum alaşımı gibi çeşitli malzemeler kullanılmış tır. Halihazırda döküm tekerleği olarak genellikle bakır- kromzirkonyum alaşımı kullanılmaktadır. Bu araştırma, döküm tekerleği olarak kullanılan bakır esaslı alaşımlar içinde, amaca uygun en iyi özelliklere sahip alaşımların geliştirilmesi düşünülerek yapılmıştır. Bu maksatla daha önce kullanılmış malzemelerden biri olan bakır-gümüş alaşımı esas alınarak, bu alaşıma farklı miktarlarda gümüş, titanyum, nikel, wolfram ve molibden ele mentlerinin ilavesi ile elde edilen alaşımların, termomekanik işlemler uygulandıktan sonra farklı durumlar ındaki mekanik özellikleri, elektrik iletkenliği ve yeniden kristalleşme davranışları incelenmiştir. Yapılan çalışmalar sonucunda incelenen alaşımların mekanik özellikler, iletkenlik ve yeniden kristalleşme davranışlarına göre bu alaşımlar sınıflandırılmıştır. En iyi öze 1 1 iklere sahip olan alaşımların, bakı r -gümüş ( % 0.3) ve bakır-gümüş (% Ö. 3 ) -titanyum(% 0 k 1 ) malzemeleri olduğu tesbit edilmiştir.

The efficiency of a continuous rod casting system depends on opt imüm des ign of the melting units for producing a high quality melt, satisfactory operation of the rod rolling line and last not least on behaviour of the casting wheel, that means' the quality of the casting wheel material. The function o( the casting wheel is to shape the melt into a solidified bar and to cool the bar down to ensure a sufficient stability as it leaves the casting wheel for inline processing cm the rolling mill. That kind of function has a major effect on the overall economics of a continuous rod casting plant. Factors in the economic equation include the cost of fabricating the casting wheel and its working life, that means the total tonnage that a wheel lasts. The SCR process is a combination of continuous melting, casting, roiling, pickling and coiling operations. Copper cathode is melted in a vertical shaft furnace and continuously trasferred to a cylindrical holding furnace which provides f low stabi 1 izat ion of the molten metal to the tundish located directly above the casting machine. The tundish is equipped with an automatic flow control system for the pouring of molten copper into the casting machine. The heart of the SCR system is the casting machine. It consists of a wheel having at its periphery a groove closed by an endless steel belt which in effect becomes the fourth side of the continuous mould. This mould is water spray cooled on all sides, solidifying the bar in less than thirty seconds. The bar is then guided through an in-line bar preperation unit which removes the belt side corners. High pressure water sprays are also provided to remove any surface scale or oxide. The bar then enters the rolling mill where it is reduced to the final rod size by means of a series of -VIII- Relative performance and lifetimes of each of the different wheel materials only apply with regard to one particular casting machine as well as indentical operating conditions. Actual service life at a casting wheel, that is, achievable total tonnage of sound bar or rod, depends not only on rod caster design and contribution but on a multiplicity of specific operating variables as well. Cast cross-section: Development of fatigue cracks depends both on the amplitude and the number of thermal cycles. The latter being identical with the number of wheel revolutions. This quite independent of the fact that larger size sections require more time to solidify arid, beicause of that, are cast using larger diameter wheels. Wheel shape: Wheel shape influences both the achivable rate of cooling and thus microst ructure of the cast bar, and the number of times a wheel can be machined and re-used. Wheel temperature: There is a direct link between casting wheel working temperature and the number of thermal cycles completed before the development of fatigue cracks Cooling: The manner and quality of cooling not just determine microst ructural quality of the cast bar, but also working life of the casting wheel. Cooling water quality: Along with optimum adjustment of the cooling segments, quality of the cooling water is another major factor which helps assure satisfactory caster operation Lubrication of casting groove: Unlike deposits on the outer surface which raise wall temperature of the wheel, lubrication of the casting groove has a beneficial effect; the layer acts as an insulant which lowers heat flux between the melt and the wheel, thus reducing wheel temperature. Starting and re-starting conditions: Thermal stresses in the wheel are highest at the start of a cast, requiring particular care in operational handling. There is a risk of overheating and resultant development of cracks that shorten wheel life during.XI every start and re-start of a wheel - Hot spots: Occasional breakdown of the energy supply of continuous rod casters while in operation leads to standstillof the aspouring continuous. Overheating of the wheel section between metal entry and start of the cooling, causing a local drop in strength together with an increase in conductivity in Elbrodur G, and a change in stress distribution in the wheel. Re-nulchining of casting wheels: Actual wheel life is determined by the timing of the re-machining of cast i ng grooves. After a certain time in service, fatigue cracks develop even in materials having high fatigue strength such as Elbrodur G. Once they exists such minute cracks very quickly expand. To prevent this, the wheel should be machined as early as possible, that is, just as soon as there are any incipient cracks. The aim of this study is to determine a suitable copper-base alloy which can be used for casting wheel material at the SCR System. For this purpose silver bearing copper alloy is used as a base material. Different amounts of silver, titanium, nickel, wolfram and molibdenium elements were added into silver bearing copper alloy. After casting of these allays ( Table 1. ), t hermo-mechani ca 1 treatments were applied to the alloys and mechanical properties, electrical conductivities, recrysta 1 1 i zat i on behaviours and metal lographic structures of these alloys were investigated. -XII- Relative performance and lifetimes of each of the different wheel materials only apply with regard to one particular casting machine as well as indentical operating conditions. Actual service life at a casting wheel, that is, achievable total tonnage of sound bar or rod, depends not only on rod caster design and contribution but on a multiplicity of specific operating variables as well. Cast cross-section: Development of fatigue cracks depends both on the amplitude and the number of thermal cycles. The latter being identical with the number of wheel revolutions. This quite independent of the fact that larger size sections require more time to solidify arid, beicause of that, are cast using larger diameter wheels. Wheel shape: Wheel shape influences both the achivable rate of cooling and thus microst ructure of the cast bar, and the number of times a wheel can be machined and re-used. Wheel temperature: There is a direct link between casting wheel working temperature and the number of thermal cycles completed before the development of fatigue cracks Cooling: The manner and quality of cooling not just determine microst ructural quality of the cast bar, but also working life of the casting wheel. Cooling water quality: Along with optimum adjustment of the cooling segments, quality of the cooling water is another major factor which helps assure satisfactory caster operation Lubrication of casting groove: Unlike deposits on the outer surface which raise wall temperature of the wheel, lubrication of the casting groove has a beneficial effect; the layer acts as an insulant which lowers heat flux between the melt and the wheel, thus reducing wheel temperature. Starting and re-starting conditions: Thermal stresses in the wheel are highest at the start of a cast, requiring particular care in operational handling. There is a risk of overheating and resultant development of cracks that shorten wheel life during.XI every start and re-start of a wheel - Hot spots: Occasional breakdown of the energy supply of continuous rod casters while in operation leads to standstillof the aspouring continuous. Overheating of the wheel section between metal entry and start of the cooling, causing a local drop in strength together with an increase in conductivity in Elbrodur G, and a change in stress distribution in the wheel. Re-nulchining of casting wheels: Actual wheel life is determined by the timing of the re-machining of cast i ng grooves. After a certain time in service, fatigue cracks develop even in materials having high fatigue strength such as Elbrodur G. Once they exists such minute cracks very quickly expand. To prevent this, the wheel should be machined as early as possible, that is, just as soon as there are any incipient cracks. The aim of this study is to determine a suitable copper-base alloy which can be used for casting wheel material at the SCR System. For this purpose silver bearing copper alloy is used as a base material. Different amounts of silver, titanium, nickel, wolfram and molibdenium elements were added into silver bearing copper alloy. After casting of these allays ( Table 1. ), t hermo-mechani ca 1 treatments were applied to the alloys and mechanical properties, electrical conductivities, recrysta 1 1 i zat i on behaviours and metal lographic structures of these alloys were investigated.