The main measure to eliminate cold barriers or flow marks is to use the correct pouring system to prevent two or more metal flows from converging, or turbulence and interruption when filling the mold with liquid titanium. In gravity casting, it is recommended to use bottom casting system as much as possible, so as to avoid or reduce the occurrence of cold separation or flow marks on the casting surface.
In order to obtain a casting with a smooth surface and a complete filling, centrifugal casting is usually used. At this time, the flow velocity of liquid titanium from the bypass into the cavity is very large, and it is easy to produce strong splashes. It is difficult to completely avoid cold partitions or flow marks. In this case, more attention should be paid to the process design of the casting, using a reasonable casting process, a correct casting system, avoiding reverse metal flow in the cavity, eliminating metal splashes as much as possible, and improving metal liquids where possible. Pouring temperature.
Effect of wall thickness of titanium castings on microhardness (degree of surface contamination) of the surface layer. Castings cast in the same mold, the thicker the casting, the more contaminated the surface layer. For castings with a wall thickness (greater than 10mm), it is not advisable to preheat the mold to too high temperature before pouring. Some literature pointed out that when the wall thickness of the casting is below 10mm, the effect of the wall thickness of the casting on the surface roughness of the casting is not very obvious. The contamination layer on the surface of the casting is mainly caused by the mutual reaction between titanium and the mold and the adsorption of gas on the surface of the mold, among which oxygen is the most harmful.
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