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Materials Science
Prompt Description
Schematic illustrating the synergistic lubrication mechanisms observed on 15 µm textured CrN coatings. (a) VG100: Predominant micro-hydrodynamic film thickness (100% ECR) is achieved due to the high viscosity of the lubricant. (b) 5W50/5W30: A transition to boundary/mixed lubrication occurs, where the CrN surface facilitates the adsorption of chemical additives, resulting in the formation of a stable tribofilm. This tribofilm compensates for the reduced fluid film thickness. In all cases, the high hardness of CrN prevents deformation of the texture edges, thereby preserving the geometric integrity of the micro-dimples.
![2.3.1 Control of Roasting Temperature and Time
The roasting temperature is the most critical factor determining the final consolidation strength of the pellets. An appropriate roasting temperature (typically between 1200-1250°C) promotes the recrystallization of magnetite (Fe₃O₄) into hematite (Fe₂O₃) within the pellets, forming a dense interlocked crystal structure, thereby imparting sufficient mechanical strength to the pellets. If the temperature is too low, consolidation is insufficient, leading to inadequate pellet strength. If the temperature is too high, over-melting may occur, causing liquid phase adhesion of the pellets, which deteriorates the permeability of the burden, increases energy consumption and FeO content, and reduces the reducibility of the pellets.
Temperature control is primarily achieved by directly adjusting the gas flow rate and indirectly by adjusting the combustion air volume and the temperature and air volume of each wind box. However, strong coupling relationships exist between these variables, and adjusting one parameter often affects others. This requires the control system to have a high degree of coordination and precision, a process that often relies on various data analysis methods. For example, Liu Piliang et al. studied the roasting temperature of a Baotou Steel 624m2 D-L type belt roasting machine and found, through correlation analysis using SPSS and regression analysis using MATLAB, that the factors significantly affecting the roasting temperature were the temperature of the 14# hood and the temperature of the 14# wind box. In actual production, the temperature of each burner is adjusted to ensure that each process section of the pellet roasting process reaches the required temperature and temperature gradient. Therefore, accurate and stable control of the roasting machine temperature is crucial for improving the roasting process and the quality of the pellets. [1] Yu Haizhao, Liao Jiyong, Fan Xiaohui. Application and Research Progress of Pellet Technology in Belt Roasting Machine [J]. Sintering Pellet, 2020, 45(04):47-54+70. DOI:10.13403/j.sjqt.2020.04.054.
The roasting time is determined by the length of the belt roasting machine and the running speed of the trolley. The faster the machine speed, the higher the output, but the shorter the residence time in each process section. The machine speed must be matched with the thermal regime to ensure that the pellets complete all necessary physical and chemical changes within a limited time. Frequent adjustments to the machine speed indicate production instability. Ideally, a constant machine speed is maintained under a stable thermal regime. The roasting machine transmission system typically includes a motor, reducer, and drive shaft. The reliability of each component directly affects the smooth operation of the trolley, including the conveyor belt and drive drum. Equipment failures can cause fluctuations in operating conditions and, in severe cases, can lead to the shutdown of the entire transmission system.
2.3.2 Setting of Furnace Atmosphere, Air Speed, and Air Volume
The process air system is the "respiratory system" of the belt roasting machine, responsible for transporting heat, controlling the atmosphere, and removing exhaust gas. Therefore, the failure and shutdown of any fan will have a very serious impact on the entire roasting process. In particular, problems with the cooling fan and main induced draft fan are likely to cause the roasting machine temperature to become too high, leading to serious equipment damage. [1] Chang Tao. Functional Overview of Process Air Fans in Belt Roasting Machine [J]. Shanxi Metallurgy, 2016, 39(04):116-117. DOI:10.16525/j.cnki.cn14-1167/tf](/_next/image?url=https%3A%2F%2Fpub-8c0ddfa5c0454d40822bc9944fe6f303.r2.dev%2Fai-drawings%2FDDH0qyRcjYzIyMRRkKUIJcdlgPmgPMHT%2Ff3d19d20-94a8-4c09-8e14-d71fe09abb08%2F193d559a-d99c-43db-acd7-15de7b277e53.png&w=3840&q=75)