Alüminyum ekstrüzyon kalıpları için kullanılan dağlama çözeltilerine alternatif yüksek performanslı yeni ürün eldesi = Obtaining high performance new product alternative to etching solutions used in aluminum extrusion molds

Abstract

Küresel ölçekte artan alüminyum ekstrüzyon profil ihtiyacı ve üretime dair oluşan zaman baskısı ile çevrim sürelerinin kısaltılması adına ekstrüzyon prosesi için kullanılan kalıpların yeniden üretime kazandırılması için hazırlık işlemleri gerekmektedir. Alüminyum ekstrüzyon prosesinde çevrim süresinin arttıran ve darboğaz oluşturan kullanılmış kalıbın yeniden üretime kazandırılması incelediğinde, ekstrüzyon sonrası kalıp içerisinde kalan artık alüminyumun öncelikle giderilmesi gerekmektedir. Bu işlem için ekstrüzyon endüstrisinde sodyum hidroksit esaslı çözücüler yaygın olarak kullanılmaktadır. Alüminyum amfoterik bir metal olması ve sodyum hidroksit çözeltileri içerisinde hızla reaksiyona girebilme özelliği ile, uygun sıcaklık ve konsantrasyon şartları sağlandığında çözünerek, kalıplar yeni bir ekstrüzyon üretimine hazır hale getirilmektedir. Bu çalışma, sodyum hidroksit esaslı dağlama çözeltilerine ilişkin en verimli koşulların belirlenmesi için Taguchi deneysel tasarım yöntemi kullanılarak uygun konsantrasyon, sıcaklık, alüminyumun çözünme hızını simule edebilecek en uygun parametrik koşullar belirlenmiştir. Yapılan metot çalışması sonrasında, ekstrüzyon kalıpların içerisinde kalan alüminyumun çözünme hızını etkileyecek, işlem süresini kısaltacak ve ekstrüzyon kalıplarının üretime daha hızlı kazandırılmasını sağlayacak sodyum hidroksit esaslı çözeltilere farklı kimyasal katkıların etkilerinin incelenmesi ve yenilikçi ürün elde edilmesi amaçlanmıştır. Sodyum hidroksit esaslı çözeltileri şelatlama ajanı, yüzey aktif madde ve peroksit katkıları eklendi. Çözünme reaksiyonu sırasında belirli zaman aralıklarında numuneler alındı. Çözeltilerin 6XXX serisi alaşımlı alüminyum parçalar üzerinde çözünme reaksiyonu ile birlikte, titrasyon yöntemi kullanılarak, sodyum hidroksit ve alüminyum konsantrasyonların zamana karşı değişimleri ile Ph ve İletkenlik ölçümleri yapılarak çözeltilerin zamana karşı değişimleri takip edildi. Reaksiyon tamamlandıktan sonra, her çözeltiden belirli bir miktar numune alınarak kurutma işlemine tabi tutuldu. Kurutulmuş toz haline getirilen numunelerde çeşitli karakterizasyon teknikleri uygulandı. Numunelerin görsel olarak oluşturdukları yapıların analizi için SEM yöntemi kullanıldı. Yapıların oluşturdukları bağların tanımlanması ve kıyaslaması adına FTIR yöntemi kullanıldı. Numunelerin yapılarında oluşan oksit birleşiklerinin ağırlıkça derişimlerini belirmek için XRF tekniği ile kimyasal kompozisyon ölçümleri yapıldı. Parça alüminyum yüzeyin de kimyasal aşındırma sonrası oluşabilecek yüzey porozitesi ve yüzey şekilleri Optik Mikroskop altında incelendi. Tüm bu yöntemler kullanılarak sonuçlar değerlendirilmiş ve prosese uygun bir çözelti tavsiye edilmiştir.

Aluminum extrusion is a method that aims to produce profiles from aluminum and its alloys by applying plastic deformation. Molds made of steel are preferred to produce designs specific to the geometry targeted by aluminum extrusion production. these molds are expressed as commonly used solid or tenoned. While solid molds are mostly preferred in the production of solid flat profiles tenoned molds are preferred in the production of profiles with spaces inside. When we look at today, aluminum takes its place with its value-added products in many sectors such as automotive, defense industry, aviation, rail systems and maritime. Aluminum is occours approximately the thirdly element in the earth's crust. The reason why aluminum cannot be found in pure form in the earth's crust is its desire to bond with oxygen. General properties of aluminum and reasons for preference, Different mechanical strength values can be obtained with the alloying process. Due to the affinity of aluminum for oxygen, its corrosion resistance is high thanks to the natural oxide layer formed on its surface. Aluminum has the ability to reflect most of the heat and light waves falling on it. Although there is a 39% loss in conductivity compared to copper, aluminum is approximately 70% lighter than copper. That is, an aluminum wire with the same electrical resistance is twice as light as a copper wire. Through the electrolyte and mechanical processes applied to the surface with its natural color and shine, an elegant appearance can be obtained by adding color and pattern. Aluminum is also widely recognized as one of the most energy efficient metals. The contribution of many factors to energy saving, such as the use of environmentally friendly building materials, the durability of aluminum, high strength-to-weight ratio and design flexibility, has made it a product that can be preferred by architects and designers. In addition to alloying and sizing, it is used in many automotive parts, door-window frames, engines, tanker and truck body panels, computer chips, and is among those who prefer aluminum in many international markets. Extruded aluminum profiles are preferred in doors, windows and industrial applications, roof, facade, panel, ceiling and many other building construction materials sector. When the sectoral markets are evaluated, when the aluminum usage areas in the world are examined, it is known that the construction sector has the largest usage area with 25%, followed by the automotive and railway sectors with a wide range of uses. In this case, it actually shows the demand for aluminum profiles.The aluminum extrusion process is carried out at high temperatures. For the aluminum alloys produced, 304 H11 hot work steel molds are preferred. These molds are cooled and then annealed at high temperature. With global increase of need in aluminum extruded profiles there is pressure building up on the production of extruded profiles with this dies that are used in extrusion needs preparation in order to be used again. When the investigation about reprocessing of dies which increases the cycle time and creates bottleneck in producion is done, it can be seen that there is aluminum inside the die that is needed to be ridded in order to use the die again. For this process sodium hydroxide-based solvents are widely used in aluminum industry. Since the aluminum is amphoteric and reacts easily in sodium hydroxide solution with the proper temperature and concentration conditions are met, sodium hydroxide solution can dissolve aluminum thus making die ready for new extrusion production. During the cleaning process of the dies in sodium hydroxide-based solutions, the different diameters and sizes dies are exposed to cleaning. The aluminum die cleaning process is a demand for rapid cleaning of the molds required for production and to ensure the continuity of extrusion production, rather than a planned and desired process. Considering these situations, it is possible to go beyond the standard conditions during the mold cleaning process. These conditions are exothermic heating that occurs naturally during the dissolution reaction of aluminum in aqueous sodium hydroxide solution. Continuous temperature increase is not a very desirable situation, and when the data revealed in previous studies are examined, it is necessary to provide an optimum reaction temperature. In cases where there are sudden temperature increases and the temperature does not remain constant, there is a decrease in the volume of the solution with evaporation. In fact, this situation can indirectly reduce the reaction rate as it affects the balance of water amount that should be in the environment in the reaction of aluminum with sodium hydroxide. Separate from the temperature increase, another parameter that affects the dissolution process of aluminum in alkaline baths and the reaction rate is the amount of dissolved sodium hydroxide present in the aqueous solution. The amount of dissolved sodium hydroxide should be in balance with the amount of aluminum with which it will react. In die cleaning baths, the sodium hydroxide concentration initially present tends to decrease over time as the treatment time increases. As a result of the decrease in the concentration and the prolongation of the processing times, the operators working in the process can go beyond the standard job description. Additional liquid sodium hydroxide solution is added to the cleaning baths by the operators during the cleaning process so that the molds can be quickly removed from the bath and reprocessed. Although this situation seems to be a desirable situation in terms of the continuity of the production and the effectiveness of the cycle times, it is actually an undesirable situation for the die cleaning process. By increasing the amount of sodium hydroxide added to the solution, it creates much more waste environmentally and provides a cost disadvantage. During the mold cleaning process, the molds of different sizes thrown into the cleaning baths generally contain different amounts of aluminum by weight. This situation theoretically reveals that small diameter molds can be cleaned more quickly and gained into production than a large diameter mold during the process period. As a requirement of the processes, the cleaning levels of the dies are checked during the cleaning process between the average usage periods of 4 hours. Due to the different diameters of the dies, the duration of the cleaning process for each dies and how long it will be kept in the bath are not clear. While this situation of uncertainty may seem like standard business, it means that a die that has been cleaned to a processable level is still subject to cleaning in bath solutions. In this situation, the sodium hydroxide concentration cannot be used effectively in the solution, and subsequently, less number of molds are cleaned in the same time instead of the number of molds that can be cleaned in a shorter time. All measurements that can simulate real conditions were made in the laboratory environment as a prototype in order to have a new formula that will increase the optimization and then the process performance of the sodium hydroxide solution for all these parameters involved in the process and extending the processing time. First of all, Taguchi method has been used to identify the most efficient condition for sodium hydroxide based etching solution. The parametric conditions of most appropriate concentration and temperature to achieve simulate the aluminum's dissolving rates has been defined. With this methodic work we have aimed to investigate the effects of the different additives that are added to the sodium hydroxide solutions and to attain an innovative product for effecting the aluminum's dissolve rates those are left in the dies, shortening the process times and making the dies ready for production faster. Chelation agents, surface active matter and peroxide additives were added. Comparison of dissolution reaction and reaction rates on 6xxx series aluminum has been investigated. Time variation of sodium hydroxide and aluminum concentrations using the titration method with the dissolution reaction of solutions on 6XXX series alloyed aluminum parts together the variation of the solutions against time was monitored by pH and conductivity measurements. After the reaction was completed, a certain amount of sample was taken from each solution and subjected to drying process. Various characterization techniques were applied to dried powdered samples. SEM method was used to analyze the structures visually formed by the samples. FTIR method was used to define and compare the bonds formed by the structures. Chemical composition measurements were made with the XRF technique to determine the weight concentrations of the oxide compounds formed in the structures of the samples. Surface porosity and surface shapes that may occur after chemical etching on the part aluminum surface were examined under an Optical Microscope. Using all these methods, the results were evaluated and a suitable solution was recommended for the process.