Baode Sun

Wear resistance of a Cr3C2-NiCr detonation spray coating

Coatings can be applied to surfaces to improve the surface characteristics over those of the bulk properties and are widely used in tribological applications either to reduce wear and/or to modify friction during contact. One of the foremost coating methods for combating wear is thermal spraying. To prolong the life of steel slab continuous casting rolls, Cr3C2-NiCr detonation spray coating was processed on the roll surface in a steelmaking plant in China. This article studies the mechanical properties and wear resistance of this coating. The abrasive and dry frictional wear testing were performed using a pin-on-disk tester. Experimental results show that the wear resistance of the coated samples, i.e., coating reduces the risk of seizure compared to uncoated samples, is much better than those of the uncoated steel at room and elevated temperatures with any load and sliding velocity. The coating wear mechanisms under different test conditions are discussed.

Numerical Simulation of the Wax Injection Process for Investment Casting

The dimensions of the wax pattern overwhelmingly determine the final quality of an investment casting component, therefore its very important to know the deformation and local dimension changing of the wax pattern, and as a result, learn how to modify the tooling design. As the most promising way with the advantages in cost and period, numerical simulation learns what exactly happens inside the tooling when the wax is injected, and how the pattern will change with the cooling and demolding. This article achieved some material properties by some measures used for application in polymer study, and then constructed a thin-walled 3D model of the wax injection process. The predicted results, like filling time, shrinkage, etc., were compared with those of experimental data. A qualitative agreement between them with an acceptable difference in shrinkage was reported, and the optimization of location of the injection gates was discussed as well.

Cavity Pressure and Dimensional Accuracy Analysis of Wax Patterns for Investment Casting

The dimension error of an investment casting always begins at the injection of the wax pattern, and the knowledge on this stage will help to decide the proper pattern shrinkage allowances, and finally understand the dimensional variations of the casting. This study investigated the influence of the process parameters on the cavity pressure and dimensional variations of the wax patterns with different thicknesses by both simulative and experimental methods. A commercial simulation code, three-dimensional (3D) laser scanner, and the pressure sensor were used. Simulated and measured cavity pressure and diameters were compared and found to be matched very well. It was found that the holding time and packing pressure affect the thickness stability of the wax pattern greatly. However, changes in injection temperature did not affect the magnitude of cavity pressure and contraction greatly. The cavity pressure is more sensitive to packing pressure. There was no notable effect on the shrinkage of the wax pattern when holding time greater than the gates sealing time. The shrinkage of the thickness increases with the increase of the thickness. The work presented here is significant to model the deformation of wax pattern and understand the effect of the process parameters and geometry variables on the wax pattern shrinkage allowances.

The Influence of Injection Processing on the Shrinkage Variation and Dimensional Stability of Wax Pattern in Investment Casting

The accuracy of the wax patterns used in the investment casting process has a direct bearing on the accuracy of the final cast part. Wax injection process plays a key role in production of nearly net shape wax pattern. Dimension shrinkage is one of the most significant problems of a wax pattern in terms of dimensional stability in the wax injection molding. This study aimed to determine the effects of injection parameters on the dimensional accuracy of the wax patterns. Linear contractions normal to flow direction and weight of wax patterns were measured and dimensional variations were evaluated. The results highlight it is important that when dealing with thick gates, short packing time appears to be the best way to avoid gate area over packing and dimensional variations, high packing pressure appears to increase expansion and dimensional variation of wax pattern.