Search results
Results from the WOW.Com Content Network
Silicones also exhibit good chemical resistance and high-temperature resistance (205 °C, 400 °F and higher). For this reason, silicone molds are suitable for casting low-melt metals and alloys (e.g. zinc, tin, pewter, and Wood's metal). RTV silicone rubbers are, however, generally expensive – especially platinum-cure.
c = specific heat of the mold (in [J·kg −1 ·K −1]), ρ m = density of the metal (in [kg·m −3]), c m = specific heat of the metal (in [J·kg −1 ·K −1]). It is most useful in determining if a riser will solidify before the casting, because if the riser solidifies first then defects like shrinkage or porosity can form. [5] [6]
Closed shrinkage defects, also known as shrinkage porosity, are defects that form within the casting. Isolated pools of liquid form inside solidified metal, which are called hot spots. The shrinkage defect usually forms at the top of the hot spots. They require a nucleation point, so impurities and dissolved gas can induce closed shrinkage defects.
There are two main types of RTV silicone used for making molds. Platinum cure, which is the most expensive but has a very long shelf life for cured molds and can be formulated to have essentially zero shrinkage. Platinum cure is also compatible with the widest variety of resins.
In directional solidification growths of single crystals, spurious grains nucleate when molten metal flowed into a gap between the mold/seed gap and solidified. [10] This is catastrophic to mechanical properties of Ni-based superalloys such as CMSX4, and can be minimized by keeping the tolerance of <001> from the local surface normal. [ 11 ]
Shrinkage and Contraction can again be classified into liquid shrinkage and solid contraction. Liquid shrinkage is the reduction in volume during the process of solidification (liquid to solid), the liquid shrinkage is accounted for by risers. Solid contraction is the reduction in dimensions during the cooling of the (solid) cast metal.
Draft angle design is an important factor when designing plastic parts. Because of shrinkage of plastic material, injection molded parts have a tendency to shrink onto a core. This creates higher contact pressure on the core surface and increases friction between the core and the part, thus making ejection of the part from the mold difficult.
Silicone rubber is an elastomer (rubber-like material) composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations.