Manufacture of carbon-bonded alumina based on a lactose-tannin binder system via slip casting

Binders play an important role in the manufacture of carbon-bonded alumina (Al₂O₃-C) refractory materials. To diminish the currently used coal tar pitch binder Carbores® P, which could release hazardous polycyclic aromatic hydrocarbons during operations, environmental-friendly lactose and tannin are applied as the main binders in this study. Compact cylinders of fine-grained Al₂O₃-C based on the lactose-tannin (16 wt%) binder system with significantly reduced pitch content (4 wt%) are successfully prepared via slip casting for the first time. The lactose to tannin mass ratio is systematically varied from 5:1 to 1:5 in the raw material formulation. The specimens based on the new binder system are less dense, more porous and contain less residual carbon than the pitch-based reference. Mechanical tests show that the specimens with lactose-tannin ratio of 5:1, 4:1 and 3:1 have considerable cold crushing strengths, although the splitting tensile strengths are low. In contrast to the well-established pressing route, the slip casting route for compact Al₂O₃-C is more comparable to the replica route for Al₂O₃-C foam filter due to the pressureless shaping process.     

Towards a new generation of environmentally-friendly ceramic foam filters: contribution of graphene nanoadditives in calcium aluminate-rich coatings

In this contribution, the widely used non-ecological production process of ceramic foam filters was modified into an environmentally friendly procedure, in which no hazardous materials are involved. Firstly, a large number of carbon-bonded ceramic foam filters were prepared by this approach. In the next step, a thin coating consisting of graphene-doped, carbon-bonded calcium aluminate was applied over these filters. Reference samples as well as coated samples were analyzed in detail with a focus on the phase composition, microstructural analysis, and mechanical as well as thermal properties. The results confirmed that the application of the developed coating improved the cold crushing strength of the ceramic foam filters. In addition, by application of graphene nanoadditives, it is also possible to vary the surface microroughness which will subsequently enable improved efficiency of inclusions elimination from metal melts during the filtration process.     

Carbon-bonded alumina foam filters produced by centrifugation: A route towards improved homogeneity

An alternative route for producing carbon-bonded alumina filters was analyzed and compared with the state of the art, both based on the replica method. The latter comprises a dip coating and subsequent rolling and spraying steps (R+S). The proposed route is based on dip coating and centrifugation (CF-T1). Aiming to investigate the influence of an additional thermal treatment on the ceramic coating homogeneity, a modified centrifugation route was analyzed (CF-T2). Computer tomography (CT) analyses provided a targeted evaluation of the spatial material distribution after each processing step. It was found that log-normal functions fitted well the wall thickness values attained for all investigated filters. Qualitative surface evaluation was conducted using a digital (optical) microscope. The R+S and CF-T1 filters exhibited surface macro-cracks and hollow struts, due to the release of the polyurethane foam template during firing. The CF-T2 presented partly filled struts with a high amount of micro-cracks on the surface, being a potential alternative to increase the filtration efficiency, as the filter surface area was raised. However, in preliminary mechanical tests, the surface micro-cracks seemed to considerably reduce the cold crushing strength of the CF-T2 filters. Based on the CT data, it was possible to conclude that the centrifuged filters presented a more homogeneous material distribution, as a consequence of higher automation level of the process.     

Innovative carbon-bonded filters based on a new environmental-friendly binder system for steel melt filtration

New carbon-bonded alumina filters for steel melt filtration were developed. The carbonaceous matrix was based on a new, environmental friendly binder system based on lactose and tannin. The filter preparation was analogous to the production of conventional foam filters according to the Schwartzwalder process. The processing as well as the rheology of the slurries was investigated. An addition of n-Si increased the carbon yield and the cold crushing strength (CCS) of the samples. Higher values of CCS were obtained after coating of the filters with alumina. The material was characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The applicability of these new filters was assessed in impingement tests with a steel melt, in which three out of four recipes survived the thermal shock.     

Additive manufactured polyamide foams with periodic grid as templates for the production of functional coated carbon-bonded alumina foam filters

For the industrial production of metal melt filters, the replica technique is established since several decades. The polyurethane foams used as templates show a rather random structure with several defects which are transferred into the final filter structure after the replication. In order to generate filters with periodic structure and low amount of defects, a periodic foam model was used and open cell foams were produced by selective laser sintering of aged polyamide 12 (PA12). The PA12 foams were then used as sacrificial templates for the replica technique in the production route of Al₂O₃-C filters with functional coatings based on a cold sprayed Al₂O₃-C coating or a flame sprayed coating based on Al₂O₃. The differences in geometry between the computer-generated model foam, the sacrificial PA12 foam, the foam after carbonization, and the additional functionalized filters with the cold and hot coating were analyzed by computed tomography. Based on CT-data isosurfaces of the foams were generated to virtualize and distinguish the differences. Preliminary mechanical tests showed a higher cold crushing strength for the filters coated via flame-spray technique than the cold coating.     

连铸用功能耐火材料的发展

新的冶炼技术和连铸新工艺的发展使连铸用功能耐火材料面临前所未有的挑战。研制开发多功能、高性能和长寿命的连铸用耐火材料是今后主要的研究课题。本文讨论了影响浸入式水口、长水口及整体塞棒使用寿命的主要因素 ,并阐述了改善性能、延长使用寿命的措施     

连铸水口密封剂的研制与应用

通过对连铸水口接缝处热状态的分析 ,提出了水口接缝密封剂合理的工作温度区间。由此研制的密封剂用于水口接缝处 ,水口内负压测定和钢样分析结果表明 ,密封剂对钢流保护作用显著 ,达到了氩气保护效果。     

Nano-functionalization of carbon-bonded alumina using graphene oxide and MWCNTs

This paper focused on the nano-functionalization of carbon-bonded alumina using graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs). GO was prepared according to the modified Tour's method. The rheology of suspensions containing GO, CNTs and both substances were analyzed and discussed. Xanthan proved to be a suitable stabilizer for the three systems. The spraying process of the suspensions was investigated with the aid of a high-speed camera. Al₂O₃-C filters and flat samples were spray coated, for investigations in contact with steel. The ceramic foam filters as well as the starting suspensions were analyzed by several analytic techniques to investigate the microstructure and other properties. Moreover, the hot stage microscope was used to study the steel/coating wetting behavior during operation at high temperatures. The results showed that the formulation containing both GO and CNTs delivered the best performance in contact with the melt. Similar coatings based on these nano-sized materials may offer an innovative route to improve purification of steel melts by filtration.     

中碳钢连铸保护渣显微结构的研究

为优化设计连铸保护渣,更有效地满足连铸 生产工艺的要求,采用偏光显微镜和扫描电子显微 镜,针对两种粘度不同的连铸保护渣在不同温度 (1150℃、1200℃、1250℃保温1h和1350℃保温 0.5h)处理后的显微结构进行了研究。结果表明:这 两种保护渣的结晶相主要是枪晶石和硅灰石;低温时 以枪晶石为主,随着处理温度的升高,硅灰石晶体数 量增多,晶体发育程度也越来越明显。粘度低的中碳 钢保护渣,在1250℃时枪晶石晶体发育比较明显,硅 灰石的数量比较少而且发育不完整。粘度高的保护 渣中,枪晶石在1200℃时结晶程度较为明显;而硅灰 石在1200℃时明显出现,数量比较多,且晶体发育较 明显,在1350℃下其结晶程度最为明显。     

TZP(Al_2O_3)质泡沫陶瓷过滤器

研究了TZP（A12O3）材质泡沫陶瓷过滤器的制备工艺。结果表明，泡沫陶瓷过滤器的烧结滞后于普遍压制成型的试块，于1550℃左右烧成的过滤器强度可达1．5MPa；过滤器加热至1100℃保温数分钟空冷后，强度有回升现象。产生上述现象的机理有待于进一步分析。     

泡沫陶瓷过滤器的研究现状和发展趋势

本文阐述了国内外铸造用泡沫陶瓷过滤器的材料成分、生产工艺和结构特点 ,着重介绍了它们的技术性能及其在液态铸造合金过滤净化中的应用效果 ,同时探讨了铸造用泡沫陶瓷过滤器在新世纪的市场前景和发展趋势。     

铸钢用高通量复合水口的开发

随着铸钢工艺技术的发展,要求铸钢用水口在使用条件下具有安全可靠性和高的使用寿命。本实验通过研究不同材质铝碳、镁碳及尖晶石-碳的性能,成功地开发出高通量复合水口,它在大型钢包上使用后安全可靠、寿命高。     

连铸用复合式整体塞棒

整体塞棒的棒体部位以特级高铝熟料、电熔刚玉和鳞片状石墨为主原料；塞头部位以电熔刚玉、特级高铝熟料和鳞片状石墨、碳化硅为主原料。选用液体树脂为结合剂并加入适量的添加剂。该制品在８ｔ连铸中间包使用，可连浇８炉。     

钢液对连铸用含碳耐火材料的侵蚀作用研究

采用中频炉的实验室模拟试验(试验条件:钢液温度1600℃,浸入时间30min,气氛分别为空气和真空)和通过对用后耐火材料的显微结构分析,研究了钢液对3种连铸用含碳耐火材料(Al2O3-C、MgO-C和ZrO2-C)的侵蚀作用。结果表明,脱碳层的形成及钢液中夹杂物与脱碳层中耐火氧化物的反应是材料蚀损的主要原因。因此,在含碳耐火材料接触钢液的表面形成致密耐火层,能有效抑制钢液对连铸用含碳耐火材料的侵蚀。     

提高连铸钢包内衬寿命的措施

本文分析了攀钢钢包内衬损毁的原因。从提高耐火材料性能和使用技术两方面采取了改进措施,使钢包一次性平均使用寿命从72次提高到90次,最高达115次,取得了显著的经济效益。     

Porous alumina ceramics for slip casting molds

Although a slip cast process using a gypsum mold enables large and complicated dense green body to be made, the green body is contaminated with calcium and sulfur impurities from the gypsum mold. In the case of a resin mold, external pressure must be applied due to its poor water wettability. Porous alumina ceramics are used as a mold material for the first time to overcome these problems. The porous alumina ceramics show higher water wettability than gypsum or resin. The porous alumina molds have submicron pores, and provide larger penetration pressure and higher casting rate than gypsum molds.     

Impact of spinel forming systems (Fe-/Mg-/Mn-Al-O) as functional coating materials for carbon-bonded alumina filters on steel melt filtration

Since solid, non-metallic inclusions influence considerably the quality of casted steel products, carbon-bonded alumina foam filters are used in secondary metallurgical treatments to remove these particles from steel melts. In order to attain a significant improvement of the filtration process, five different carbonaceous spinel compounds from the Fe-/Mg-/Mn-Al-O systems are applied on carbon-bonded alumina filters in this study and investigated with regard of their filtration efficiency. However, these spinel compounds decompose partially during sintering at 1400?°C under reducing atmosphere, wherefore the resulting coatings contain not only spinel compounds, but also oxidic and metallic components. The subsequent interaction with molten steel leads to the development of multicrystal structures on the filter surface, which stem from interfacial reactions between coating materials, molten steel, and inclusions. As a result of this procedure, a reduction of almost 60% alumina inclusions is measured with the aid of an automatic SEM, whereby spinel compounds from the Fe-Mn-Al-O system achieve highest filtration efficiencies.     

连铸用滑板的发展概况及其损毁机理

着重介绍了连铸用滑板的发展概况以及滑板的分类,概括了各类滑板的制备工艺及其使用过程中的优缺点。在滑板的使用过程中,其损毁主要原因是热机械损毁和热化学损毁,并根据滑板损毁的主要原因简单介绍了防止滑板损毁的主要措施。     

铝用泡沫陶瓷过滤器现状与应用趋势

简述了过滤净化对于铝及铝合金熔铸的重要意义,通过国内外现有铝用泡沫陶瓷过滤器(CFF)的对比分析,提出了国内铝用CFF在性能与应用方面存在的问题以及面临的竞争,并从材料、制备工艺、效用评价等方面提出了改善铝用CFF性能的若干措施。     

连铸中间包透气上水口的研制与应用

介绍了连铸中间包透气上水口的性能和种类及连铸工艺对透气上水口性能的要求。利用合成莫来石颗粒、α-Al