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Low carbon alloy steel 20CrNiMo is a kind of high strength surface hardening material which was commonly used as high-quality gears. After surface nitriding, carburizing or carbonitriding quenching treatment, it has good tooth surface hardness and tooth root toughness. According to the relevant national standards, a number of material test bars had been designed and carried out, the tensile strength and tensile fatigue strength date of material had been obtained. The lognormal distribution and two parameters Weibull distribution were used to fit and test the testing data, and the R-S-N curves of materials with the different confidence levels were obtained by calculating the probability distribution function. The fatigue life data of the material was more suitable for the lognormal distribution.

According to the space meshing theory, the mathematics model of conjugate surfaces is constructed. Based on the coordinate transformation of this model, the mathematical solution of the wheel and pinion tooth surfaces is obtained. On the basis of surface synthesis, the construction method of gradient surface (Ease-off) for tooth modification is given. Taking the rotating projection plane of the tooth surface as the coordinate plane, the normal deviation of the modified tooth surface from the conjugate tooth surfaces for pinions is calculated, and the Ease-off surface of the spiral bevel gear is obtained. Based on analysis of the Ease-off surface, the complete contact morphological characteristics of tooth surface are obtained: the contact line-off, contact path, transmission error, etc., which are highly consistent with the actual contact pattern of the tooth surface. The above findings provide an accurate and feasible method for the topology design and meshing simulation of complex tooth surfaces.

In recent years, China has paid more and more attention to ecological and environmental protection, and the treatment of solid waste during industrial production has become more important. For example, stainless steel production industry, electroplating industry, chromium salt production industry, etc., will produce a large amount of chromium-containing solid waste. Long-term accumulation will not only occupy land resources but also cause serious harm to the environment. Therefore, it is particularly important to develop more effective methods for recycling and processing chromium-containing solid waste. This article summarizes the current situation of chromium ore resources in China, predicts the demand for chromium ore in the next few years, expounds the current situation and hazards of chromium-containing solid waste, and summarizes the new domestic and foreign chromium-containing solid waste treatment technologies in recent years. Research and progress in the recycling of chromium-containing solid waste, introducing the advantages and disadvantages of different treatment methods, in order to find a better way to recover and treat chromium-containing solid waste in the future. [ABSTRACT FROM AUTHOR]

A gas chromatography-mass spectrometry (GC-MS) method has been developed for the determination of dibutyltin (DBT), tributyltin (TBT) and triphenyltin (TPhT) in textile auxiliaries. The sample was first extracted with n-hexane in acetate buffer solution (pH 4.0) under ultrasonication (for hydrophobic sample) or oscillation extraction (for hydrophilic sample) and then derivatized with sodium tetraethylborate in tetrahydrofuran. The derivative was determined by GC-MS in selected ion monitoring (SIM) mode. The separation and quantification were achieved using a Rxi-5 ms silica capillary column (30 m x 0.25 mm x 0.25 microm). The linear ranges were 0.1-8.0 mg/L for both DBT and TBT, and 0.1-4.0 mg/L for TPhT. There were good linear relationships between the peak area and concentration in the linear ranges and the correlation coefficients (r2) were 0.9994-0.9998. The detection limits (LOD) were from 0.003 mg/L to 0.005 mg/L. The average recoveries of these organotin compounds at the three spiked levels of 4.0, 10.0 and 40.0 mg/kg were 92.6%-108.0% with the relative standard deviations (RSDs) of 2.5%-10.2%. The method is simple and accurate for simultaneous analysis of the DBT, TBT and TPhT in textile auxiliaries.