Alumina esaslı dökülebilir refrakterlerin geliştirilmesi
Başlık çevirisi mevcut değil.
- Tez No: 75333
- Danışmanlar: PROF. DR. SERDAR ÖZGEN
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Refrakter, Refractory
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Metalurji Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Üretim Bilim Dalı
- Sayfa Sayısı: Belirtilmemiş.
Özet
ÖZET Son yıllarda demir-çelik endüstrisinin ihtiyaçlarına paralel olarak gelişen refrakter endüstrisinin araştırmaları dökülebilir refrakterler üzerinde yoğunlaşmış ve bu tür kolloidal sistemlerin reolojik özelliklerinin gelişmesiyle birlikte mekanik etki uygulanmaksızın kalıpta yerleşen düşük poroziteli ve performansı en az dökülebilir refrakterler kadar yüksek yeni bir malzeme türü ortaya çıkmıştır. Bu malzemeler literatürde“kendi kendine akan dökülebilir refrakterler”,“serbest akan dökülebilir refrakterler”gibi ifadelerle tanıtılmaktadır. Kendi kendine dökülebilir ve reolojik özellikleri geliştirilmiş bu tür refrakter sistemleri günümüzde refraker tüketiminin en yoğun olduğu demir-çelik endüstrisinde ilgiyle karşılanmış olup özellikle Japonya' da tandiş ve pota astar örümlerinde pilot uygulamaları mevcuttur. Bu çalışmada kendi kendine akan refrakterler genel uygulama ve ürün özellikleri açısından incelenmiştir. Çalışma teorik ve deneysel kısımlardan oluşmaktadır. Teorik kısımda dökülebilir refrakterlerin dünyada gelişimi ve genel malzeme karakteristikleri anlatılmıştır. Deneysel kısımda serbest akış özelliğine sahip çeşitli kanşımlar karşılaştırmalı olarak değerlendirilmiştir. Karışımlar tane boyut dağılımının bir ifadesi olan q değerine göre saptanmıştır. Baz olarak alınan karışım q=0.25 olarak kabul edilmiş; akış özellikleri farklı hammadde ve katkılar kullanılarak geliştirilmiştir. Temel refrakter ürün özellikleri karşılaştırmalı olarak değerlendirilerek maksimum ürün özelliklerine ulaşılacak karışımın saptanması amaçlanmaktadır. XII
Özet (Çeviri)
SUMMARY DEVELOPMENT OF ALUMINA BASED CASTABLE REFRACTORIES The development of low-cement castables and ultra-low-cement castables reduced the consumption of refractories in steel industries and led to the production of high- quality unshaped refractories. There are four types of alumina according to their cement content;. Conventional (CaO>2.5%). Low cement (1.0%<CaO<1. 5%). Ultra low cement (0.2%<CaO<1.0%). Noncement (CaO<0.2%) In recent years the self flowing castables have been developed with high strenght, density, improved workabilitiy, easier installation. Flowability and reduced viscosity is the main characteristic of SFCs. When refractory aggregates, liquid and other components are mixed, the form a flowable adhesive composite. Improved flowability can be reached by optimum dispersion. Optimal particle packing is important to achieve good flow and high density at low water levels. The pores of the structure are filled by a viscous, liquid phase consisting of the fines, superfines and also cement. Particle size distribution is one of the most important parameters for self flow character. Several model has been presented in the literature on particle packing to obtain required density. In the following study the reological and some physical properties of self flowing castables were studied. Initially the castable composition of self flow castable was designed and tested, then the effect of reactive alumina type, q-value (distribution coefficient), microsilica addition and the use of spherical grains has been XIIIinvestigated. Particle packing was evaluated by the Dinger&Funk (Modified Andreassen) model according to q-value. The flowability properties are measured by flow test. 1. Experimental procedure 5x5x5 cm samples were prepared for the physical tests (apparent porosity, bulk density, cold crushing strenght). All tabular alumina components are mixed dry for 1 minute in the lab. mixer. After water addition wet mixing is continued for several minutes. The castable is then casted into moulds without vibration. After demoulding the samples is cured 24h at room temperature. Cured samples are made ready for tests after drying in 1 10°C/18h. To determine the flowability and water demand of self flowing castables, flow test was used. After wet mixing, metal flow cones are filled completely with self flowing castable without vibration. The flow cone is lifted up after 10, 30, 60 min The spreading of castable on the table is measured as an flow value of the castable. Self flowing castable should reach after 10 min. flow diameter of 200-250 mm and after 30 min flow diameter should be at least 190 mm. 2 Test results 2.1 Physical and reolojical properties of self flowing castables The flow test results of self flowing castables are given in Fig. 1. Flow properties of self flowing castables decreases with increasing time. It has seen that the self flowing castable was workable after 90 min. without hardening and available for easy installing of huge blocks, linings etc. The high plasticity of the castable makes the movement of the grains easy. When the flow-cone is lifted up the castable spreads on the flow table about 292 mm after 10 min. at approx. 12°C. XIV350 60 80 Time (m in) 140 Fig. 1 The flow test results of self flowing castables The apparent porosity (DIN 51056), bulk density (DIN 51065), cold crushing strenght (DIN 51067) are determined and all results are given in Table 1. Table 1 The apparent porosity, bulk density, cold crushing strenght values for SFC1 samples. The CCS and apparent porosity values increases due to sintering. At 1000°C the strenght of the castable decreased due to breakingdown of the hydrate phases. xv2.2 The effect of spherical grains The effect of spherical grains were investigated by the replacement of -45 micron tabular alumina particles with the spherical calcine alumina grains in same particle size. The ratio in the composition did not change for a meaningful comparison. The flowability increased with the addition of spherical grains. The flow diameter after 10 min. was 290 which was higher than that obtained from the first composition including angular tabular alumina grains. All the results are given in Table 2. Table 2 The test results with spherical grains in castable 2.3 The effect of reactive alumina type To observe the effect of reactive alumina type on flow and other physical properties two mixes with two different reactive aluminas were prepared. The reactive aluminas were classified according to their specific surface area. The flowability was higher in the castable including reactive alumina having high surface area. (Fig.2) 254“”“”rT SFC1 (BET= 4.3 m2/g) SFC3 (BET=3.8m2/g) MATERIAL Fig. 2 The effect of reactive alumina type on the flowability XVIThe physical properties obtained by tests are given in Table 3. Table 3 The effect of reactive alumina type on the physical properties Reactive alumina is a superfine component and strongly effective in sintering of the castable materials. The CCS values after sintering 1500°C obtained from SFC1 samples including reactive alumina with high specific surface area were the highest results. 2.4 The effect of q-value The effect of q-value measured according to Dinger&Funk equation was investigated. Higher q-values means higher content of coarser grains. The results of flow test are given in Fig. 3. 245 215 4 6 Microsilica content (%) 10 Fig. 3 The effect of q-value on flowability The flowability decreases in greater q-values due to increase in amount of coarser grains. XVIITable 4 The effect of q-value on physical properties for the samples sintered at1500°C *; slightly vibrated. The apparent porosity, bulk density and CCS values for the samples sintered at 1500°C obtained are given in Table 4 above. 2.5 The effect of microsilica By microsilica addition to the castable mix, the flowability increases generally. But too much addition of microsilica affects the flow properties negatively. (Fig.4) 245 240 220 215 4 6 Microsilica content (%) 10 Fig. 4 The effect of microsilica addition on flow properties The apparent porosity, bulk density and CCS values obtained are given in Table 5. XVIIITable 5 The effect of microsilica addition on physical properties for the samples sintered at 1500°C CCS values increases with the increasing microsilica addition. 3 Conclusion The flow properties developed with ? The use of spherical grains ? The use of reactive alumina having big specific surface area ? The low q-values. The use of superfines makes the mechanical strenght greater after sintering. The use of microsilica has an positive effect on the flow properties of the self flowing castables. After %6 addition the flow properties a significant drop was observed. When the distribution coefficient (q-value) is between 0.20-0.24, the castables give high free-flow. XIX
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