Key Engineering Materials Vols. 480-481

Abstract: Al2O3 reinforced Ti3A1C2 in situ composites have been fabricated by reactive hot pressing method from the mixture of Ti, Al, TiO2 and C. The phase formation and transformation regularity of samples during the process of hot pressing were investigated in detail by X-ray diffraction (XRD). The microstructures of the synthesized samples were observed by scanning electron microscopy (SEM). The results show that the reactions of powder mixture during the hot press sintering could be divided into three stages: firstly, Ti reacted with Al to form TiAl intermetallics, and Ti reacted with C to form TiC, respectively; and then TiO2 was reduced by Al to form Al2O3, TiAl intermetallics reacted with TiC to form Ti2A1C; finally Ti3A1C2 was formed through the reaction between Ti2A1C and TiC.

Abstract: Activated flux assisted tungsten inert gas (TIG) welding of austenitic 316L stainless steel was investigated. Autogenous TIG welding was used to produce a bead-on-plate weld. The FeO, FeS, and FeF2 were selected as the flux powders. The results showed that the FeS and FeO fluxes produced high aspect ratio welds, while the FeF2 flux produced a relatively low aspect ratio weld. The undercut defect was produced with use of the FeS flux. An experimental result suggested the constriction of arc column as a mechanism in improving activated TIG penetration. In addition, activated TIG process can increase the delta-ferrite content in austenitic stainless steel weld metal.

Abstract: The experiments were conducted based on the study of one kind of ultra fine-sized magnetite concentrate with nearly 85% of the material being less than 0.044mm in size. The preliminary study has shown that this iron concentrate has middle ballabitity(K=0.61) because the iron concentrate characterized with flaky and spherical particle shapes. Such features are detrimental to the granulation of green pellets. Much more research work was carried out on how to improve balling performance by processing this magnetite concentrate with high pressure roll grinding (HPRG). The results indicated that newly-created cracks and edges would appear. Specific surface area of iron concentrate would increase from 2161.72 cm2.g-1 (base case) to 2703.51cm2.g-1 and fine particles percentage (-0.044mm) would increase to 94.69%. For the balling performance experiment, the results revealed that the ballability would increase to 1.59. Drop strength of green pellets would increase from 6.1 times/0.5m to 14.7 times/0.5m. Compression strength of green pellets would increase from 10.5N.P-1 to 12.61N.P-1. But break down temperature would decrease from more than 600°C to 480°C. The whole experiments revealed that HPRG could improve the balling performance of ultra fine-sized magnetite concentrate.

Abstract: The following conclusion is drawn from detailed mechanical analysis of Diamond Saw Blade,The load on diamond is not significant in cutting. However, at the moment the blade starts in its working state, the impact on rock has significant destructiveness on diamonds. Higher linear velocity of the blade, higher rock hardness and higher feeding speed all contribute in greater impact force on the diamond from the rock. And it is also stated that the unstable quality of diamond saw blade is closely related to the selection of diamond without following the TT1 test result. When designing the diamond saw blade, the saw cutting performance of the rock should be taken into consideration, as well as the necessary analysis of the force on the blade.There are three forces exerted on the saw blade: ①vertical downward pressure;②horizontal feeding thrust;③tangential cutting force of the saw. They are discussed separately in the following.

Abstract: State education business institutes are believed as catalyst for the economic progress (especial for commerce) of any country. In China, many regional higher education institutes (mainly be regional university) have been founded from 1998. From 2006, most of those regional higher education institutes, such as regional university, promoted to be comprehensive regional higher education institutes (CRHEIs) in succession. Now more andmore students studying in those CRHEIs, and then the quality of teaching should be improved. In this paper, we analyses ICT (Information and communication technology)–based teaching and learning issues at CRHEIs level and old higher education institutes (ORHEs) level. Using normative Delphi method, we discussed ICT-based issues and get that ICT integration in CRHE need to be in lined with proper strategy in order to get their true benefits.

Abstract: The crystallinity of wood has an important effect on the physical, mechanical and chemical properties of cellulose fibers. Crystallinity of larch plantation wood was investigated with near infrared spectroscopy and multiple linear regression. Five typical wave lengths were selected to establish prediction model for wood crystallinity. Full-cross validation was applied to the model development. The model performance is satisfied with prediction correlation coefficient of 0.896 and bias of 0.0004. The results indicated that prediction of wood crystallinity with near infrared spectroscopy and multiple linear regression is feasible, which provides a fast and nondestructive method for wood crystallinity prediction.

Abstract: ZnO-based linear resistance ceramics were synthesized using Al2O3 doped ZnO-based system as raw materials by sintered at 1340 °C for 3 h. The effects of Al2O3 content ranged from 1 to 15 wt% on the microstructure and electrical properties of the ceramics were investigated in detail. The results show that the electrical properties such as nonlinear coefficient, resistivity and resistance temperature coefficient have been obviously influenced by Al2O3 doping. The optimal samples obtained by doping Al2O3 with 9 wt% have a nonlinear coefficient of 1.3, resistivity of 130 (Ω•cm) and resistance temperature coefficient of -5.4×10-3/ °C.

Abstract: It is stated that Diamond saw blades requires high embedding strength of the diamond, while diamond drill bits do not. It is necessary to improve the embedding strength of diamond in diamond saw blades, rather than in the diamond drilling bits. It is recommended to count the number of diamond particles on the matrix surface and get the embedding strength of diamond by calculation. Another recommendation is to use the compound powder of cobalt and tungsten carbide for pelletizing in order to improve the embedding strength of diamond and lower the cost of matrix. There are people studying how to raise embedding strength of diamond, for both diamond saw blades and diamond drilling bit. However, the requirements for embedding strength of diamond saw blades and diamond drilling bit are different. The following parts include the analysis for this problem.

Abstract: For the economic and reasonable application of high strength composite shaft lining of steel and concrete, the mechanical characteristic of this kind of structure were studied. First of all, according to the similarity theory, the shaft lining model is designed, then making the specimen and the loading test are put into effect. The results show that the combined action of inner and outer steel tube and middle concrete improves their respective performance. In shaft lining structure the stability of steel tube would be enhanced and the brittleness of high strength concrete would be improved also, so shaft lining structure shows fairly plastic feature when it is destroyed. Moreover, because of the restraint function of double-layer plate, the concrete in shaft lining structure completely is in triaxial compression stress state, the compressive strength can improve 1.53 ~ 1.90 times more than the concrete under uniaxial compression. The bearing capacity of shaft lining also increased greatly. Therefore, it is proposed that the improvement coefficient of the concrete’s compressive strength should be considered in the strength calculation of high composite shaft lining structure of steel and concrete.

Abstract: To reveal the jetting of fine drops, model of 2-phase flow between gas and liquid is offered based on volume of fluid method. Numerical simulation is launched for the droplet generation through narrow nozzle, and key factors are discussed. Aiming at the ink marking of defective dies in IC production, a jetting inker driven by piezoceramic stacks is developed. The actuation properties are derived; waveform of induced pressure at nozzle entrance is estimated, which coincides the numerical results. Performance of ink dot jetting is evaluated and simulation results are verified.