大型整体铸钢轧辊无流浇注工艺研究

在浇注辊身长径比≥2．5时，辊身易出现探伤超标，冒颈缩孔、疏松等品质缺陷。为解决此问题，采取无流浇注工艺，以实现整个浇注过程的顺序凝固，减少上述品质缺陷的发生几率，从而提高产品的内在品质。     

Birch wood particle shrinkage during rapid pyrolysis

A study of the shrinkage of cubic (∼5 mm) birch wood particles during pyrolysis is presented. The particles were rapidly injected into a preheated furnace with a constant temperature in the range 350-900°C. The size of the particles in longitudinal, tangential and radial directions was measured until no further mass loss occurs. The volume shrinkage was found to be 45-70% and the shrinkage in the different directions 5-25, 25-40 and 15-40% for longitudinal, tangential and radial directions, respectively. Longitudinal shrinkage commenced after about 60% mass loss and is not strongly dependent on heating rate or on cellulose chain scission. A maximum shrinkage was found for tangential and radial directions at 400 and 500-700°C, respectively, and above these temperatures the shrinkage decreases. The char yield decreases and the char structure becomes more deranged with increasing temperature. Empirical models of shrinkage as a function of conversion are presented.     

Maturation of fresh cement paste within 1- to 10-m-large formworks

The objective of this research was to examine the maturation of early-aged cement paste through the survey of the evolutions of the total lateral pressure exerted by cement paste against formworks and of the pore water pressure. The experimental device was specially developed for this purpose. Three types of cement paste mixtures with a water/cement (W/C) ratio of 0.30, 0.36 and 0.45, respectively, have been tested. In addition, temperature and setting kinetics were also examined. The results have shown that the kinetics of the pore water pressure and the total lateral pressure were strongly affected by the W/C ratio, the vibration and the level of stress, to which the fresh cement paste is subjected. The confrontation of these results with the theory currently available as regards setting of cement makes it possible to identify the physicomechanical phenomena, which occur within formworks.     

Calcium silicate structure and carbonation shrinkage of a tobermorite-based material

Carbonated autoclaved aerated concretes (AACs) show no shrinkage at a degree of carbonation approximately less than 20%. The ²⁹Si MAS NMR spectrum showed that at a degree of carbonation less than 25%, the typical double-chain silicate anion structure of tobermorite-11Å was well maintained and interlayer Ca ions were exchanged with protons. This corresponded to the absence of carbonation shrinkage at a degree of carbonation less than 20%. When the degree of carbonation increased from 25% to 50% up to 60%, the double-chain silicate anion structure of tobermorite-11Å was decomposed and Ca ions in the Ca-O layers were dissolved, showing a possible mechanism of carbonation shrinkage.     

EPS保温砂浆干燥收缩性能研究

本文主要研究了聚合物、外加剂和纤维对EPS保温砂浆干燥收缩性能的影响,以改善其收缩性能,使之能够减少因收缩而出现的开裂情况。     

桓仁矿北岔区低品位矿及表外矿开采方案研究

论证了采用浅孔留矿法对桓仁矿北岔区的低品位矿及表外矿进行综合回收的可行性。本回收项目的实施,可回收铁精矿28 6万t、铜精矿6332t,回收铁金属18 58万t、铜金属475t,使国家的宝贵资源得到充分利用,并可延长矿山的服务年限1 6年。     

Prediction and measurement of welding distortion of a spherical structure assembled from multi thin plates

A spherical structure assembled from 14 thin bent plates and two circular polar plates was taken as the research object and its welding distortion was investigated in this study. Firstly, the welding distortion due to each welding line is measured by experiment. Then, the spherical structure was modeled by shell element and its welding distortion produced by each welding line was evaluated using the inherent deformation method proposed by authors. The computational process requires a short time when the inherent deformation method is employed. To determine the inherent deformation existing in the welding lines, a computed model with 3D solid element for a typical butt welded joint was applied and one case of the detail transient analysis by Thermal Elastic Plastic Finite Element Method was performed.     

模拟夏季施工环境下混凝土早期收缩试验研究

对夏季高温日晒、风吹的施工环境进行了模拟,考察了采取两种养护措施和掺加三种特殊材料对混凝土在此模拟环境下早期收缩性能的影响.通过复掺聚丙烯纤维和膨胀剂,研制了一种在夏季施工环境下10d内几乎不产生收缩的混凝土,并对在夏季环境下混凝土的养护提出了具体的建议.     

Early development of properties in a cement paste: A numerical and experimental study

This paper presents the results of an experimental and numerical study of the properties of a high-performance Portland cement paste (w/c ratio 0.37; 5% silica fume) cured at 20 °C in sealed conditions for 5 days. Properties such as electrical conductivity, strength, stiffness, porosity, Vicat penetration, and autogenous deformation were measured and modelled. The kinetics of hydration was studied by means of isothermal calorimetry. The numerical simulations were performed with CEMHYD3D, developed at the National Institute of Standards and Technology, and HYMOSTRUC, developed at the Delft University of Technology. The results of the simulations were compared with experimental data, and the match was good. Clear correlations were found among electrical conductivity, autogenous shrinkage, and connectivity of solids.     

Simultaneous Heat and Mass Transfer in Shrinkable Apple Slab During Drying

The goal of the study was to determine the influence of drying shrinkage on the kinetics of convection apple slab drying. The arbitrary Lagrange-Eulerian (ALE) method was used to enter a problem with moving boundaries. It was found that drying shrinkage had a major influence on the both simulated temperature and water content in the material. The lower the moisture content in particles during drying, the more pronounced the effect of shrinkage on simulation of heat and mass transfer. It was found that application of the arbitrary Lagrange-Eulerian method for shrinkage modeling leads to a relatively simple mathematical model of the drying kinetics of shrinkable materials.