Large thermal residual stresses in coatings during the coating deposition process may easily lead to coating delamination of coated carbide tools in machining. In order to reduce the possibility of coating delamination during the tool failure process, a theoretical method was proposed and a numerical method was constructed for the coating design of WC-Co cemented carbide cutting tools. The thermal residual stresses of multi-layered coatings were analytically modeled based on equivalent parameters of coating properties, and the stress distribution of coatings are simulated by Finite element method (FEM). The theoretically calculated results and the FEM simulated results were verified and in good agreement with the experimental test results. The effects of coating thickness, tool substrate, coating type and interlayer were investigated by the proposed geometric and FEM model. Based on the evaluations of matchability of tool substrate and tool coatings, the basic principles of tool coating design were proposed. This provides theoretical basis for the selection and design of coatings of cutting tools in high-speed machining.
The hydraulic system is the control center of aircraft, the performance of which is critically dependent on the purity of the oil that flows through it. Contamination of hydraulic system oil has been known to be the primary cause of catastrophic failure and accidents. A review of literature in the area of hydraulic oil contamination reveals three facts: (i) there is a dearth of effective methods to prevent intrusion of external contaminants into the hydraulic oil, (ii) there are no effective purification methods for liquid and gaseous contaminants of oil, and (iii) there is an absence of real-time monitoring for major contaminants. This work systematically reviews the hazards, sources, and removal methods of major contaminants, especially of gaseous contaminants. An active method to control oil contamination is proposed instead of the existing passive maintenance techniques that are ridden with problems. In a case study of aviation hydraulic system, our active control system comprises (i) a closed hydraulic circuit and a closed oil tank to prevent the intrusion of external contaminants, (ii) a vacuum centrifuge to efficiently remove contaminants without creating consumption costs, and (iii) monitoring devices installed to actively monitor the contaminant content in oil during operation. The results from the purification experiments and three-dimensional modeling indicate that the active control of hydraulic oil contamination can effectively remove 98.4% solid contaminants and reduce the water content below 50 ppm, and in particular reduce the gas content below 2%. It is obvious that this method can improve the continuous operation capability of aviation hydraulic systems and extend the intermaintenance period of aircrafts by reducing the contaminant content in oil. 相似文献
The electrical and dielectric properties of (1 ? x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–x(K0.5Na0.5NbO3) with x = 0, 0.03, 0.09, 0.18 have been investigated by impedance spectroscopy over a wide temperature range. The dc conductivity of the ceramics follows the Arrhenius law with an activation energy ranging from ~1.20 to 1.50 eV. Measurements under different atmospheres show the materials exhibit n‐type semiconducting behavior at elevated temperatures. The presence of a highly polarizable phase for all compositions is revealed by electric modulus (M″) spectra. The Burns temperature decreases with increasing KNN content. The change in temperature‐dependent permittivity with composition is explained by the difference in thermal evolution of polar nanoregions induced by the addition of KNN. 相似文献
To solve the problem of heavy metal pollution and agricultural wastes reclamation, spent substrate of pleurotus ostreatus (SSPO) was used as adsorbent to remove Zn2+ from aqueous solution. The biosorption of zinc ions on SSPO was studied as a function of the solution pH, temperature and initial Zn2+ concentration. The equilibrium sorption data were well represented by linear Langmuir isotherm models with R2 value of 0.9955 and non-linear Freundlich with R2 value of 0.9973. The BET surface area of SSPO can reach 51.16m2g?1. SEM-EDX and XRD revealed that (NH4)2Zn·H2O and Zn2PO4(OH) were the main compounds in metal-loaded SSPO. FTIR analysis indicated the governing functional groups such as O-H, N-H and P=O played an important role in biosorption. The desorption studies showed the reversibility of SSPO. The results indicate that SSPO is a potential adsorbent in wastewater treatment due to its great sorption capacity and low cost. 相似文献
合成了一种应用型钛系聚酯(PET)催化剂TY,考察了在PET合成中催化剂TY对酯化时间、缩聚时间、产品性能等的影响;并与传统锑系催化剂三氧化二锑(Sb2O3)的性能进行了对比。结果表明:钛系催化剂TY不仅能缩短酯化时间和聚合时间,而且催化剂用量少、催化活性高;钛系催化剂TY用量为20~25μg/g时,催化活性最佳,催化剂TY 20~25μg/g的催化活性相当于Sb2O3350~400μg/g的催化活性;钛系催化剂合成的PET切片的特性黏数达0.683 d L/g,与锑系PET相比,色相L值提高达71.68,b值相差不大,端羧基含量及二甘醇含量降低,结晶行为及热性能相当;钛系催化剂TY适合无重金属聚酯的工业生产,工业应用性强。 相似文献