Service of the magnesia-spinellide lining of a melting furnace roof

Conclusions On the basis of a study of the magnesia-spinellide roof of a melting furnace it was established that the refractory consists of four zones, the least changed, the working, the zone of contact with the lining slag, and in the lining slag. A nonuniform distribution of the components in specimens of lining slag taken from different portions of the roof was observed.The lining slag and the zone of contact with the lining slag consist of crystals of picrochromite, ferrite, and magnesioferrite, between which there is located a silicate binder including forsterite, hedenbergite, and the impurity phases bunsenite, hematite, and magnetite. The working zone consists of chromite, picrochromite, monticellite, and the introduced melting products copper, chalcosite, and cuprite.On the basis of analysis of the data on failure of refractories as the result of chemical interaction with the melting products, penetration of the low-melting components, and thermomechanical cracking at the boundaries of the zones it was established that one of the methods of protection of the roof is cooling.Translated from Ogneupory, No. 2, pp. 51–55, February, 1989.     

Use of zirconia refractories for lining high-temperature induction furnaces

Conclusions A lining was prepared from zirconia (sectors) which can guarantee the induction heating of refractory alloy blanks up to temperatures of 2300°C in a protective atmosphere. The zirconia sectors placed in the working zones showed the maximum wear. The sectors failed due to splitting, cracking, and scaling of the working surface.The service life of the lining depends on the number of heatings of the blank, the variations in temperature, and the degree of cooling in the lining between heatings. It can be determined only by using refractories in industrial induction furnaces.Translated from Ogneupory, No. 3, pp. 32–36, March, 1971.     

裂解炉看火孔损坏原因及改进措施

对不同材质看火孔衬里的损坏原因进行剖析，找出了看火孔损坏的主要原因。并针对模块结构衬里的看火孔，提出含锆模块现场切割，形成整体看火孔，有效解决了看火孔裂纹，损坏及外壁钢板过热变形等问题。     

双轴压缩下混凝土预制双裂纹扩展与应力应变关系研究

对混凝土预制双裂隙板试件进行了双轴压缩试验,研究了裂隙倾角以及岩桥倾角对双裂隙的扩展演化影响.通过在裂隙尖端贴放应变片,分析了裂隙扩展与应力应变关系,探讨了裂隙尖端应变集中对裂隙扩展演化的作用规律.试验结果表明,裂隙倾角以及岩桥倾角对裂隙的扩展、贯通有较大影响.实验结果共观测到7种裂纹贯通模式(T1和T2;S1和S2;TS1、TS2和TS3)及两种贯通失败模式(剪切失败和拉伸-剪切失败),且随着岩桥角的增加,裂纹贯通模式由剪切裂纹贯通到翼型-剪切复合式贯通,然后再到翼形裂纹贯通逐渐转化.应力应变曲线与裂隙扩展贯通密切相关,拉应变集中是翼形裂纹产生的原因,而压应变集中则是引起剪切裂纹产生的原因.     

Novel Composite Microstructure and Mechanical Behavior of Mollusk Shell

Preliminary investigations of the microstructure/mechanical properties relationship in a mollusk shell—the large conch, Strombus gigas —are reported. Strombus gigas has the well-ordered "crossed lamellar" microstructure and, in four-point bending, is remarkably tough in certain orientations, permitting noncatastrophic ("graceful") failure. Fractography indicates that several toughening mechanisms are acting in concert, including crack bridging, microcracking, fiber pullout, and microstructurally induced crack arrest branching. Microindentation studies show that this material is very resistant to cracking; the damage zones around the indents strongly reflect the lamellar character of the microstructure.     

复合材料筋混凝土梁裂缝开展试验分析及宽度计算

分析了光圆GFRP筋混凝土梁和螺纹状表面粘砂CFRP筋、GFRP筋混凝土梁的开裂机理、裂缝开展过程、开裂形态、配筋率等因素对裂缝宽度和裂缝间距的影响,同时对AC1440．1R-01推荐的裂缝宽度计算公式与其他公式进行了对比和验证。结果表明：AC1440．1R-01公式预测值与试验值吻合较好,并推荐了该公式有关参数的取值。     

Designing a band for a detachable unit of an induction channel furnace

Conclusions The calculations carried out indicate that a metal cylinder applied with a tolerance to the lining of the longitudinal channel creates stresses that are inverse in sign to the tensile forces at the danger site of the lining. This excludes the development of tensile forces in the danger zone of the lining, both during short-term heating and during prolonged service, i.e., it eliminates one of the main causes of cracking in the lining of the longitudinal channel of a detachable unit.During the development of microcracks in the lining, when the induction furnace is working, the band, tightening the lining, prevents microcracking. Moreover, the metal cylinder prevents penetration of melt into the heat-insulating layer through the pores of the lining, especially during vacuum melting.Translated from Ogneupory, No. 6, pp. 14–16, June, 1992.     

Key Technologies for Energy Efficient Al(OH)_3 Dilute Phase Fluidized Bed Roasting Furnaces

Research on new types of castables, pre-cast assembly parts and thermal insulation materials with good resistance to wear, thermal shock and erosion, and low thermal conductivity, was done to solve problems of high system energy consumption, cracking and spalling of partial lining and mismatch of furnace top material and hanging material and so on, caused by unreasonable design of China's Al(OH)3 dilute phase fluidized bed roasting furnace lining. Several difficult problems such as the matching of different materials, preservation of expansion joints among different zones and reasonable mechanical distribution of lining were solved. "Integrated furnace" concept was established including refractories R D, lining structure design, construction optimization, furnace warming technology, initial operation and lining maintenance technology. The key technologies of high-efficiency and energy-saving for furnaces were developed. These achievements have been applied to China's Al(OH)3 dilute phase fluidized bed roasting furnaces to reduce energy consumption by 1 000 MJ per ton alumina, enhance the capacity and reduce the exhaust gas emission.     

The possibility of repair of metallurgical ladle lining

Metallurgists have always dreamed of an “eternal ladle”, i.e., the possibility of repairing a metallurgical ladle without removing its old lining. However, the use of thick mixtures for this purpose is problematic, whereas thinner mixtures are prone to cracking under cooling. The author demonstrates that the reason for such cracking is the temperature contraction of the surface layer, which is the first to be cooled, as a consequence, a larger volume becomes enclosed in a shell of a smaller capacity, which leads to its cracking. A method is proposed for cooling the inner volume of lining to remove temperature stresses from the outer layers and prevent their cracking. __________ Translated from Novye Ogneupory, No. 7, pp. 59–62, July, 2007.     

Temporal Characteristics of Desiccation Cracking and Resistivity of Lateritic Soil in Drying Process

To describe and measure the initiation and development of desiccation cracks in lateritic soil and to discuss the relationship between crack ratio and resistivity, three parallel specimens are prepared and dried under different temperatures and humidity. The geoelectrical resistivity technique combined with image processing method is applied. Water content, surface crack ratio, and electrical resistivity are monitored during the drying path. Results indicate that the calculated surface crack ratios can be identified on the basis of five distinct stages. The occurrence of the first crack in three specimens indicates that the first cracking time occurs earlier with increasing temperature and decreasing relative humidity. The time that crack ratios stabilize indicates that environmental parameters significantly influence crack evolution. The temporal characteristics of resistivity can also be identified on the basis of five distinct stages. The resistivity and crack ratio can be effectively described by a mathematical equation, which is considered as the basis for the use of the geoelectrical technique for the assessment of the temporal variability of soil desiccation cracking.     

Contact Damage in Single-Crystalline Silicon Investigated by Cross-Sectional Transmission Electron Microscopy

Cross-sectional transmission electron microscopy (TEM) is demonstrated as a powerful tool for investigating subsurface damage in the micrometer and submicrometer ranges in brittle materials, and applications to a wide variety of contact damage in silicon are discussed and illustrated with TEM images. Regions of plasticity and different types of cracking are identified and characterized for various contact situations: indentation, scribing, solid-particle impacts, and polishing/grinding. Most single-point contact situations result in similar types of damage in silicon, although transitions between different damage mechanisms occur between different load levels. Normally, the crack geometry is governed by the principal stress directions and is only weakly influenced by the lattice orientation. Grinding with metal-bonded abrasives results in fairly deep subsurface damage zones, but the main mode of material removal is superficial lateral cracking. Polishing with small-size free abrasives results in very superficial damage zones and mirror-like surface finish.     

Thermally Induced Failure of Copper-Bonded Alumina Substrates for Electronic Packaging

Although copper-bonded alumina substrate has been used for some power electronic devices, its use has been rather limited because of lack of information on the thermally induced failure of the substrate. The phenomenology of thermal cracking was experimentally studied in this work. Interface debonding occurred at the side edge of copper chips and grew inwardly along the interface. Subsequently, the interface crack deviated into the alumina after propagating up to approximately 200 μm. The curving of the interface crack was caused by a mixed Mode I and Mode II loading near the edge. The cracking was widespread, whereby small cracks coalesced with one another to form a long, shallow crack along the perimeter of the copper chips. The cracking sensitivity was influenced by such design factors as edge sharpness, nickel plating, and copper backing. Annealing the substrate above 700 K before testing promoted the cracking considerably. The substrate cracking is discussed in terms of stress conditions near the edge.     

Study of thermal shock resistance of fired and unfired zirconia refractories

Conclusions Comparative studies were made of fired and unfired refractories based on zirconium dioxide. The fired refractories are more resistant to cracking. However, the unfired materials possess a higher resistance to the development of cracking which is noted during the registration of surface deformations in the process of destruction of the specimen; and this is confirmed by analytical criterial evaluation.The determination of the destructive drop in temperatures before the development of the first crack in specimens based on granular bodies should not be considered as a reliable evaluation of the thermal shock resistance of the refractories.A new method was developed for observing the nature of the failure in specimens during thermal loading.Translated from Ogneupory No. 1, pp. 52–56, January, 1973.     

Pitting and stress corrosion cracking behavior in welded austenitic stainless steel

The effect of microstructural changes in 304 austenitic stainless steel induced by the processes of gas tungsten arc welding (GTAW) and laser-beam welding (LBW) on the pitting and stress corrosion cracking (SCC) behaviors was investigated. According to the in situ observations with scanning reference electrode technique (SRET) and the breakdown potentials of the test material with various microstructures, the GTAW process made the weld metal (WM) and heat-affected zone (HAZ) more sensitive to pitting corrosion than base metal (BM), but the LBW process improved the pitting resistance of the WM. In the initiation stage of SCC, the cracks in the BM and HAZ propagated in a transgranular mode. Then, the crack growth mechanism changed gradually into a mixed transgranular + intergranular mode. The cracks in the WM were likely to propagate along the dendritic boundaries. The crack initiation rate, crack initiation lifetime and crack propagation rate indicated that the high-to-low order of SCC resistance is almost the same as that for pitting resistance. High heat-input (and low cooling rate) was likely to induce the segregation of alloying elements and formation of Cr-depleted zones, resulting in the degradation in the corrosion resistance.     

Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus.     

Flaw-Insensitive Ion-Exchanged Glass: II, Production and Mechanical Performance

A two-step ion-exchange process that introduces strengthening and multiple cracking into glasses has been developed. The experimental parameters in the second step must be carefully controlled to avoid spontaneous cracking, because the compressive stress is reduced in the surface region. Control of the near-surface stress gradient is an important role of the second ion-exchange step. Double ion exchange leads to strength values as high as those that are obtained after the first ion-exchange step but remarkably produces multiple cracking on the specimen surface on loading. The multiple cracking, which acts as a failure warning, is initiated at 300 MPa, and the crack spacing decreases as the applied stress increases. The multiple cracking is shown to be a result of the crack stability that is induced by the designed residual-stress profiles. This behavior has been confirmed, using the measured residual stresses to calculate the apparent-toughness curves for surface cracks. The duration of the first ion-exchange step has been shown to be important in determining the degree of strengthening; however, the duration of the second step controls the extent of the crack stability.     

The nature of the destruction and method of increasing the resistance of electric furnace linings

Conclusions During service, abundant saturation of the lining by components of the melting region is observed. The amount of silicates in the slag belt reaches 40–60% and in the high-lying lining — 10–15%.In regard to composition of the silicate bond in the working zones the lining is divided in height into two zones: the slag belt and the high-lying part. In the slag belt the bond is composed chiefly of cuspidine and fluorite; in the high-lying part — of dicalcium silicate and glass.Formation in the silicate bond of cuspidine and fluorite is due to the high rate of wear of the lining of the slag belt.In refractories of high density there is a smaller zone impregnated with reagents of the melting region, and so there is less wear during service.Further increase in the life of the lining can be obtained by using refractories with a minimum porosity in the slag belt and opposite the hot-phase arc; such refractories include fusion-cast blocks.     

Progressive cracking mastercurves of the transverse ply in a laminate

In this study, progressive cracking of a transverse layer in a cross‐ply composite laminate subjected to tensile loading is considered. Using the results of a probabilistic cracking model, approximate relations for crack density as a function of stress are derived for initiation‐controlled and propagation‐controlled cracking. It is shown that the crack density evolution in the transverse ply can be represented by a mastercurve in suitably normalized coordinates. The mastercurve approach is applied to progressive cracking in glass/epoxy laminates. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Innovative approach to simulating the biodeterioration of industrial cementitious products in sewer environment. Part II: Validation on CAC and BFSC linings

The development of a new test method for evaluating the resistance of manufactured cementitious products to biogenic acid attack, labeled BAC-Test for Biogenic Acid Concrete Test, was reported in Part I of this paper. The performance of the test in terms of sulfur-oxidizing bacteria selection and acid and sulfate production has been validated previously. In this second part, the representativeness of the degradation mechanisms of the cementitious materials is explored. Two segments of industrial pipes – ductile cast iron coated with cementitious linings (blast furnace slag cement (BFSC) and calcium aluminate cement (CAC) mortars) – were exposed to the test for 107 days. Then linings were analyzed by SEM coupled with EDS, EPMA, and XRD. Significant differences between BFSC and CAC linings were highlighted. Abundant cracking of the BFSC lining was observed, caused by precipitation of secondary ettringite, while no cracking was observed in the CAC lining. The CAC outer layer was composed mainly of AH₃ gel. The decalcification front was deeper in the BFSC matrix than in the CAC one.     

Using Periclase-Carbon Converter Linings at the Magnitogorskii Iron-And-Steel Works (MISW) Joint-Stock Co.

Results of a repair-and-maintenance program aimed at increasing the durability of the converter lining in an oxygen converter shop at the MISW JSC are reported. The program includes a single-round placement of the lining, the use of high-resistance PUPK-1-grade refractory components in high-wear zones, advanced methods for lining maintenance, development of high-resistance mixtures and taphole blocks, improvement of the converter process parameters, and introduction of advanced methods for lining wear monitoring.