Jiujun Xu

Analysis of non-uniform thermal behaviour of special steel during slab continuous casting

A full-scale finite-element model of a slab and its mould was developed to reveal the complex thermal behaviour of special steel in a vertical caster during slab continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mould. The model was validated by comparing the calculated temperature with the measured ones. The temperature distribution of the slab is not symmetric, reflecting the non-uniform nature of heat transfer and hence the necessity of formulating a full-scale model. It will provide a helpful tool for further improving the casting parameters and operations for special steel.

Experimental research and numerical analysis in thin film lubrication of point contact

Purpose – The purpose of this paper is to establish a rapid and effective numerical model of thin film lubrication with clear physical conception, in which viscosity variation along the direction of film thickness was used instead of average viscosity, and continuous Reynolds equation was used in the calculation of thin film lubrication. Design/methodology/approach – Based on rheology and thin film lubrication with point contact and considering features of shear thinning and like-solidification of lubricant oil in the thin film lubrication state, a modified formula with overall average equivalent viscosity was proposed by combining numerical calculation and experiment data. Findings – It is a fast and efficient method for film lubrication state simulation. Research limitations/implications – Thin film lubrication research on a nanoscale is very popular, and a variety of thin film lubrication models are proposed. Due to the complexity of thin film lubrication, it is still in the stage of revealing law and ...

Study on the non-uniform slab shrinkage of special steel during slab continuous casting

ABSTRACT A full-scale finite-element stress model of a slab and its mould was developed to analyse the non-uniform slab shrinkage of special steel in a vertical caster during slab continuous casting. The stress model was based on the heat transfer model which was validated by comparing the calculated temperature with the measured ones. According to the shrinkage calculation, the single linear taper is not suitable for the continuous casting of this special steel, and the narrow face taper need to be calculated and optimised. It will provide a helpful tool for further improving the casting parameters and operations for special steel.

Tribological performance of three surface-modified piston rings matched with chromium-plated cylinder liner

Purpose The paper aims to investigate the friction and wear properties of three surface-modified piston rings matched with a chromium-plated cylinder liner. Design/methodology/approach Samples were taken from the chromium-plated cylinder liner, Cr-Al2O3 ring, CrN ring and Mo ring. Tribo-tests were conducted on a reciprocating sliding tribometer under fully formulated engine oils. Friction coefficients and wear depths of three friction pairs were tested. Surface morphologies of cylinder liners and piston rings before and after test were analyzed. Findings Experimental results show that in the Cr-Al2O3 piston ring, scuffing occurred easily when matched with the chromium-plated cylinder liner; compared with the Mo ring, the CrN ring could decrease the wear depth of the piston ring from 2.7 to 0.2 μm, and the wear depth of cylinder liner remained; however, the friction coefficient increased from 0.113 to 0.123. The tribological performances of three surface-modified piston rings were significantly different when they matched with chromium-plated cylinder liner. Originality/value Chromium-plated cylinder liner and the three kinds of surface-modified piston rings have excellent friction and wear properties, respectively. However, according to the systematic characteristics of internal combustion (IC) engine tribology, only the appropriate cylinder liner–piston ring can improve the tribological performance of the IC engine. This paper reports the tribological performance of three surface-modified piston rings matched with a chromium-plated cylinder liner. The results can be used as reference for the design of high-power-density diesel engine.

Synthesis of high viscosity index base stock and study on the lubricating properties

Purpose – This paper aims to address the polymerization of 1-decene by [Emim]Cl/AlCl3 ionic liquid and the film-forming properties of the product compared with commercially available base stocks. Design/methodology/approach – Experiments were carried out to investigate the influence of [Emim]Cl/AlCl3 mole ratio, catalyst dosage, reaction temperature, reaction time and water on the polyreaction. Poly alpha-olefin (PAO) is prepared under optimal reaction condition. Film-forming properties of PAO have been compared with those of Group I, Group II and Group III base stocks, which are selected with approximately the same viscosity. Findings – Experimental results show that after a 4-h reaction time, yield of PAO can be higher than 85 per cent and viscosity index can be up to 160 with [Emim] Cl/AlCl3 mole ratio of 2:1, catalyst dosage of 3 per cent wt. and water content of 20 ppm. A strong influence of water on reaction is observed. With approximately the same viscosity, PAO shows the superiority in film thickn...

Lubrication film thickness calculation from contact resistance measurement in point contact

Purpose – The purpose of this study is to solve this problem. Different lubrication states play a huge role in friction, wear and service life of parts. To ensure the reliability and power of the internal combustion engine, it is necessary to ensure that the friction pair has been in the best lubrication state. One of the key problems of lubrication state and transformation characteristics is to achieve real-time measurement of lubrication state. Design/methodology/approach – Previous studies show that the contact resistance method is very effective in the qualitative analysis of lubrication state test. The circuit is simple and does not require expensive test equipment. But this method could not accurately reflect the film thickness ratio. Through a combination of experimental and theoretical analysis methods, the limitation of the contact resistance method could be overcome. Findings – The relationship between the point contact film-thickness ratio and contact resistance was established, then the film-t...

Effect of surface chemical etching on the lubricated reciprocating wear of honed Al–Si alloy

To improve the wear resistance of the honed Al–Si alloy cylinder liner, the chemical etching was applied on the surface of the Al–Si alloy samples. The effect of the etching time on the wear behaviors of the etched surface was investigated using an in-house designed reciprocating wear machine with oil lubrication. Meanwhile, the tribological properties were related to the changes in the surface morphology of the Al–Si alloy samples before and after the wear tests to analyze the associated underlying wear mechanisms. Results show that 5% NaOH solution is an effective chemical agent to etch the surface of Al–Si alloy samples. The 2 min etched Al–Si alloy samples exhibits low friction coefficient and small weight loss, indicating a good wear behavior of the properly etched surface. The insufficiently etched surface was found when the etching time was less than 2 min. Rare silicon particles are exposed due to the little removal of the aluminum on the surface, such that aluminum will be in direct contact with the piston ring during friction, causing adhesive wear. In contrast, overetching leads to the even more seriously worn out surface as observed in the samples etched for more than 3 min. The silicon particles tends to debond from the matrix with the increase of etching depth, then serve as the abrasive grains in the friction, resulting in the considerable increase of the friction coefficient and weight loss.

Wear behavior of the aluminum-silicon alloy cylinder liner wear against Chrom–Keramik–Schicht piston ring:

The aluminum–silicon alloy cylinder liner shows great potential for engine cylinder liner applications as its excellent castability, light weight, and good thermal conductivity. In order to improve the capability of the whole friction system further, the friction performance of the piston rings wear against cylinder liner should be discussed in details. In this paper, the wear behavior of the aluminum–silicon alloy cylinder liner wear against Chrom–Keramik–Schicht (CKS) piston ring was carried out by the contraposition reciprocating test rig under lubrication. The surface morphology was characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. When CKS piston ring wears against aluminum–silicon alloy cylinder liner, comparing with sprayed molybdenum piston ring, the friction coefficient reduced nearly 10%. Besides, the weight loss of cylinder liner and piston ring reduced nearly 95%. In the process of friction, aluminum was rolled repeatedly on the surface of cylinder liner. And the honing roads were still visible clearly on the worn surface. The coating of CKS piston ring is dense, lower roughness and higher hardness, and not easy to fall off. While the worn surface of CKS piston ring was smooth in the process of adhesive wear. When the aluminum–silicon alloy cylinder liner wears against CKS piston ring, the matched pair presents an excellent wear behavior.

Investigation of non-uniform slag films and air gap during slab continuous casting

ABSTRACT Based on an inverse algorithm and a full-scale heat transfer model of slab/mould, the non-uniform temperature fields of mould and slab are obtained. Considering the formation mechanism and heat transfer characteristics of the slag films and air gap, a mathematical model of the heat transfer between the liquid/solid slag films and air gap is further developed. According to the model, the non-uniform distributions and evolution of liquid/solid slag films and air gap are comprehensively revealed, which proposes a theoretical foundation for exploring the complex heat transfer of mould/slab and provides a helpful tool for further improving the casting parameters and operations.

Wear behavior of Al-Si alloy cylinder liner prepared by laser finishing

Laser finishing tests were carried out using a 1000 W, CO2 continuous transverse-flow laser, with a defocusing value of 2 mm, and at different scanning speeds (200 mm/min, 400 mm/min, 600 mm/min, 800 mm/min, and 1000 mm/min). When the laser scanning speed was 600 mm/min, an Al-Si alloy cylinder liner gave the lowest friction coefficient and weight loss. Laser finishing could completely remove the aluminum layer and at the same time increase the silicon particles’ exposure with rounded edges. This microstructure improved the lubrication and bearing capacity, while it reduced adhesion and the friction force. Therefore, the friction coefficient and weight loss were lower with laser finishing than without.