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排序方式: 共有102条查询结果,搜索用时 31 毫秒
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浸入式水口燃烧式烘烤预热温度场研究 总被引:4,自引:2,他引:4
浸入式水口在浇钢以前必须进行充分预热 ,利用燃烧的煤气烘烤水口是常用的预热烘烤方式。本工作运用有限元技术对浸入式水口燃烧式烘烤预热的瞬态传热过程进行了研究 ,得到了水口烘烤预热后的温度场分布和水口的升温曲线。研究结果表明 ,在燃烧式预热烘烤方式下 ,水口沿轴线方向的温度变化梯度较大 ,水口颈部预热后的温度较低 ,是导致水口颈部频繁断裂和较易出现竹节样裂纹的主要原因。欲提高水口颈部的预热温度 ,必须改进水口的预热烘烤方式 相似文献
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Cladding is the process of depositing a superior built-up layer by fusion on a substrate. In blown powder laser cladding process, the powder travels across the laser path, gets heated up by absorbing laser energy, and finally melts on the substrate under the intense laser beam; as the substrate moves away this melt pool solidifies to form a continuous built-up layer. The laser energy is partly absorbed by the solid powder during its flight path (termed preheating) and partly by the top surface of the melt pool. In the present study a two-dimensional conduction heat transfer equation has been solved using finite-volume method to model the cladding process. It is observed that preheating allows higher scanning speed resulting in thin clad layer with low dilution. Preheating also permits high powder feed rate resulting in thick cladding with low dilution. 相似文献
4.
《International Journal of Hydrogen Energy》2021,46(56):28686-28699
Thermal energy storage systems based on metal hydrides can be a solution for preheating fuel cells (FCs). They can provide thermal energy at temperatures below −20 °C during startup, while heat at 50 °C during operation is sufficient for regeneration. The challenge of such a system in mobile applications is the final weight specific thermal power. In this study, a reactor design based on additive manufacturing techniques for ~300 g of metal hydride is presented. Here, a reactor (passive) to hydride (active) mass ratio of 0.97 is realized, still reaching high weight specific thermal power of up to 2.1 kW/kgMH at −20 °C and 8 bar (LmNi4.91Sn0.15). Considering the example of preheating a FC from −20 °C in ~120 s, the performance of LaNi5 and LmNi4.91Sn0.15 is studied. While LaNi5 requires higher regeneration temperatures than LmNi4.91Sn0.15 (>40 °C compared to >20 °C), its performance is less sensitive to operative variations due to its nearly ideal thermodynamic characteristic. 相似文献
5.
An overlapping composite track coating was produced on a steel surface by preplacing a 0·5 mm thick layer of TiC powder and then melting using a tungsten inert gas torch of constant energy input. The influence of the overlapping operation on preheating of the substrate, the dissolution of TiC particulates and the subsequent depth and hardness of the composite layer was analysed. The melt microstructure consisted of both undissolved and partially dissolved TiC particulates, together with a variety of morphologies and sizes of TiC particles precipitated during solidification. Preheating, resulting from the overlapping operation, occurred, producing additional melting of the TiC particulates and deeper melt depths but with a reduced volume fraction of TiC precipitates in the subsequent tracks. A maximum hardness of over 800 HV was developed in the composite layer. The high hardness was unevenly distributed in tracks melted at the initial and final stages, while it varied across the melt depths in other tracks. 相似文献
6.
Long processing cycle makes vacuum assisted resin infusion molding (VARIM) only suitable for low and medium volumes of production, and shortening of curing time is critical to improving the processing efficiency of automotive composite parts. In this paper, unidirectional carbon fiber reinforced composite laminates were fabricated by VARIM. Three different processes (namely quick, quick-post and preheating) were employed, in which a kind of rapid curing epoxy resin is used. The preheating of mold and fiber was conducted to shorten the filling time compared with that of quick process. Quick-post process with a post cure stage was investigated to verify the composite properties fabricated by quick process. The cycle time was 16 min for preheating process, about 30% shorter than that of quick process, simultaneously, flexural strength and interlaminar shear strength (ILSS) were respectively improved by 29% and 7% compared with those of quick process. The non-uniformity of mechanical properties at different positions along resin flow direction under preheating process was found, but the processing quality of composite was good. The preheating process is confirmed to be suitable for the improvement of processing efficiency of VARIM with good mechanical properties. In addition, the composite fabricated by quick-post process has better mechanical properties, which is attributed to the alleviation of residual stress during post curing process. 相似文献
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基于零件切片的选择性激光烧结预热温度控制方法 总被引:5,自引:0,他引:5
选择性激光烧结(Selective laser sintering,SLS)系统是通过加支撑或采用人工调节预热温度的方法来减少成形件的翘曲变形,它劳动强度大、SLS材料浪费多、成形效率低,且预热温度难以精确控制。基于以上情况,提出一种新的控制方法,使预热温度能随零件断面几何形状的变化而自动调节。以华中科技大学开发的SLS设备为研究对象,验证这种新型控制方法的可行性。试验结果和实际应用表明:与原有控制方式比较,根据文中所提出的方法成形的零件表面质量、尺寸精度和形状精度等都有较大幅度改善,并且真正实现了SLS成形过程的自动化。 相似文献
9.
Magnesium is one of the lightest structural metals that has been used in different industries such as automobile, aerospace and electronics. However, in fusion joining of magnesium alloys, porosity is one of the main drawbacks to achieve a weld with desirable properties. The oxide layer existing on the surface of magnesium alloy is one of the causes of pore formation in the weld bead. In the current study, a fiber laser with a power of up to 4 kW is used to weld samples in a zero-gap lap joint configuration. Two groups of samples are studied: as-received (AR) surfaces (where an oxide layer remains on the surface) and treated surfaces. The surface treatment includes two techniques: mechanically removed (MR) and the use of a plasma arc (PA) as a preheating source. Also, a separate set of experiments are designed for preheating samples in a furnace for comparison with the PA-treated results. To reveal the chemical compositions of the welds and metal sheet surfaces, an energy dispersive spectroscopy (EDS) is performed. Surface chemical compositions are tested by X-ray photoelectron spectroscopy-reflected electron energy loss spectroscopy (XPS-REELS) to characterize the surface composition on AR and PA-treated samples. The dynamic behavior of the weld pool and laser-induced plasma plume is monitored in real-time using a high speed CCD camera to investigate the stability of the laser welding process. The presence of the oxide layer at the faying surface of two overlapped sheets results in an unstable process. The obtained results reveal that the preheating procedure can effectively mitigate pore formation at the interface of the two overlapped sheets. 相似文献
10.
本文简介了邯钢7#高炉热风炉的工艺状况,重点描述了基于Quantum PLC的热风炉本体仪控系统、基于西门子S7-400PLC(软件配置按PCS7系统模式)的热风炉热油预热控制系统和基于西门子S7与S5系列PLC混合配置的热风炉换炉电控系统的构成、软硬件配置、工作原理、主要控制功能和应用效果。 相似文献