Will precision casting insulation cotton become black spots when dropped into the mold shell?

Will precision casting insulation cotton become black spots when dropped into the mold shell?

Will the insulation cotton in investment casting become polished black spots if it falls into the mold shell? Today, precision casting manufacturer Tianyao Metal will discuss this issue in detail for everyone. Firstly, no matter what falls into the mold shell, it is not acceptable as it can affect the quality of castings, especially polished parts.

Generally speaking, when the shell is placed in a roasting furnace, regardless of whether the pouring cup of the shell is facing up or down, it must be ensured that nothing can be drilled inside the shell. So, the environment for shell baking is not well done, and solving the problem must be done from the source. In fact, there is no problem with the sprue cup facing up or down during shell baking. A friend said that when roasting in an electric furnace, the sprue cup should be facing upwards, while when roasting in a gas or oil furnace, the sprue cup should be facing downwards, which can basically ensure that there is no drilling inside the mold shell. In fact, there is a certain truth, but not entirely. The best way is to add a lid to the sprue cup area, just like dust prevention measures should be implemented for molds that cannot be immediately produced after waxing or roasting.

Actually, insulation cotton is made of aluminum silicate fiber. Since it can be used online to block slag, we have also used it in actual production. It floats on top of the molten metal, which is relatively light. Even if it falls into the molten metal, it cannot penetrate into the interior of the molten metal. It must float on the surface of the molten metal and come into contact with the mold shell or the top of the riser. This is the first situation; In the second scenario, the thermal corrosion of insulation cotton by molten metal is also quite severe. Generally, after using two to three furnaces, a complete insulation cotton cannot be used anymore. The side of the insulation cotton in contact with the metal will burn black and coke. What will happen when drilling into the interior of the molten metal in this situation?

In an article titled "Analysis of Defects and Quality Control in Stainless Steel Investment Casting" published in Volume 28, Issue 8 of 2008 in the magazine "Special Casting and Nonferrous Alloys", it was analyzed that the black spots on stainless steel castings mainly come from external sources, such as sand and impurities brought in by metal furnace materials, fragments peeled off from the refractory material of the furnace lining, and crushed sand washed down by the molten steel during the pouring process. There are also oxides generated inside the melt, such as the oxidation of elements in the molten steel. The silicates in the non-metallic inclusions mentioned above, such as iron silicate, manganese silicate, and ternary oxides, oxidize Si in the molten steel into silicon dioxide, which then forms low melting point inclusions with manganese oxide, ferrous oxide, and aluminum oxide. In the molten steel, it is liquid and difficult to separate, but it is not wet with the steel, resulting in black spot defects From this perspective, it is completely impossible for insulation cotton to become black spots in stainless steel melt, as it can withstand high temperatures of 1600 ℃ and is by no means a low melting point.

We cannot determine whether the insulation cotton will turn into polished black spots after falling into the metal liquid. We are discussing here whether the insulation cotton will become black spots when drilling into the metal liquid. Why don't we find a way to completely prevent it from entering the metal liquid? This is the fundamental way to solve the problem.

Precision machining