Oxidation of compression annealed pyrolytic graphites

The reactivities of three highly crystalline, compression annealed pyrolytic graphites, designated APG142, G900, and G100 and differing in preferred orientation, crystallite size and defect content, were studied as a function of burn-off at 750°C and 20 Torr O₂ pressure. Large burn-off increments were achieved by oxidation at 900°C and about 30 Torr initial O₂ pressure. Measurements of bulk reaction anisotropy of the two principal surfaces (basal and edge) were found to correlate well with degree of preferred orientation and defect content. For two of the graphites, rate data taken on samples having wide variations in their basal surface to edge surface ratio could be normalized by expressing the rates in terms of an effective geometric edge area which takes into account the reaction anisotropy. However, the reactivity of APG142 samples, expressed in this same manner, was found to increase with increasing fraction of edge area, indicating a different mechanism for edge oxidation. Microscopic and macroscopic examination of oxidized specimens revealed a number of features including a high density (~ 10⁵/cm²) of non-basal defects in the G100 material. A number of samples of APG142 and G900 showed a pronounced terracing effect at the layer plane edges. This is consistent with a mechanism of edge oxidation involving the migration of reactive species over the basal surfaces. A principal feature observed in all these materials was the occurrence of non-uniform oxidation at the edges, resulting in the formation of slit shaped voids running parallel to the layer plane direction. The possible role of lattice vacancies, non-basal dislocations and grain boundaries in the overall oxidation process has been examined by developing idealized models involving preferential attack at these defect sites.     

Optimal thermal design of compression molds for chopped-fiber composites

Because heat is convected by the motion of material in the cavity of a compression mold, the time-averaged heating load on the cavity surface is nonuniform. In rapid production of large, thin parts, this can lead to large variations in cavity surface temperature when the mold is heated by the usual uniform distribution of heating lines. In this paper, a new method is developed for optimizing the mold heating design so that this nonuniform heating requirement can be satisfied with a minimum variation in cavity surface temperature. Oil heating is considered specifically, but the method can also be used for stream or electric heat. The optimal position and power supply for each heating line in the mold is determined by combining mathematical programming techniques with an analysis of the steady temperature field in the mold. The nonuniform heating load on the cavity surface is represented by a time-averaged steady heat transfer coefficient calculated from the transient temperature distribution in a polyester sheet molding compound as it fills the mold cavity. The design method is applied to an example mold for a large flat panel. At a one-minute cycle, the optimal heating design dramatically reduces nonuniformity in cavity surface temperature compared with a conventional distribution of heating lines. The optimal design is remarkably simple, uses only conventional equipment, and involves only half the customary number of heating lines. Nevertheless, it still has sufficient flexibility to adjust for changes in cycle time without sacrificing uniformity in cavity surface temperature.     

Thermal and cure analysis in sheet molding compound compression molds

Sheet molding compound (SMC) compression molding growth will benefit from faster cycles and more uniform cure so as to reduce in-plane thermal residual stress and resulting warpage in the molded part. These improvements require an in-depth study of the mold thermal design. Here we use a finite element model to analyze the quasi-steady temperature distribution in a plane perpendicular to the heating channels of a representative mold, and a finite difference model to investigate the cure dynamics at critical regions. Several changes in the mold heating system and operating conditions were considered and their effects on the temperature distribution and cure time were studied. It was assumed that the steam condensate is well drained and enough steam is supplied so that the steam tube walls are kept at a constant temperature. An important conclusion of the present study is that better insulation of the mold from the press does not help much in improving the uniformity of cavity surface temperature or cure. It was also found that reducing the distance between two consecutive steam tubes beyond the distance from the steam tube to cavity surface will not yield a significant change. The most practical way to give both more uniform cavity surface temperature and faster cure is to have higher steam temperature for the region where the charge is initially placed.     

Passivation of steel molds and parts of automated glass-forming machines

A passivation technique can be effectively used for improving the quality of the working surface of glass-shaping steel molds as well as for recovering used glass molds without recourse to mechanical finish grinding.Translated from Steklo i Keramika, No. 12, pp. 28–29, December 1996.     

钢丝帘线在轮胎加工和使用中的质量问题

探讨钢丝帘线质量对于轮胎质量的重要性。针对轮胎生产和使用中出现的胎体裂缝、缺线、跳线、外缠丝断裂以及钢丝抽出等质量缺陷，指出高强度、结构简单、开放型、全渗透型、密集型、高伸长率和高冲击型新结构钢丝帘线是目前钢丝帘线的发展方向。     

项目管理软件的重要性

系统地阐述了基于软件和网络的项目管理软件在项目管理中的重要性 ,项目管理软件只有以矩阵式管理模式为基础 ,运用网络计划技术与WBS(工作分解结构 )等先进技术 ,构筑于互联网上 ,实现协同管理 ,才能真正发挥作用 ,项目管理软件是项目管理理论与现代计算机技术的完美结合。     

浅谈钢丝帘布压延生产线的设计制造要点

介绍了钢丝帘布压延生产线的工艺流程、工作原理及主要部件的结构特点,阐述了钢丝整径装置、测厚装置及自动裁断装置等的主要特点。