Dewaxing is the removal of wax impurities from oil, molds, and injection molds. Petroleum dewaxing uses solvents to extract waxes, which can cause gelling and affect combustion. Propane can be used as a wax remover. Investment casting and sinter mold casting use wax molds that are removed through heating. Injection molding uses release agents that can be removed with soap and water.
Dewaxing is a process of introducing a solvent into an oil stream to remove wax impurities from the desired product. It is also a term used in investment casting and metal casting for the removal of waxes or binders from molds. A third definition is any solvent-based system used to remove mold release agents from injection molds and parts.
Petroleum dewaxing is used to extract high molecular weight components, often referred to as waxes, from a petroleum stream. These impurities cause gelling or solidification of petroleum products at higher temperatures. They can also affect the combustion performance of diesel and gasoline fuels. Different solvents can be used, but the desired effect is to separate the waxes in the solvent for later extraction, or to cause the waxes to separate and float to the top for removal.
Gases such as propane are useful as wax removers. When propane is injected into the fluid stream, it flashes or becomes a gas; this effect, called automatic chilling, causes the fluid to cool rapidly. Waxy materials will turn from liquids to solids and can be strained or skimmed off the top of the tank.
In investment casting or investment casting, wax molds of the desired part are first made. The wax mold is covered with a plaster shell by repeatedly dipping the mold in liquid plaster. As the mold is heated slowly, the wax melts and is removed, leaving an internal void in the plaster of the part shape. This type of casting is sometimes referred to as investment casting. The plaster mold is then fired at a very high temperature to form a ceramic, which can contain the hot metal used to make the part.
Sinter mold casting is a slightly different type of dewaxing process. The molds are made from a mixture of sand or ceramic powder with a waxy binder and compressed under high pressures to form a solid mold. The mold is then heated in a furnace to burn off the wax and sinter, or bond, the powder together. It can then be used for metal casting in the same way as a plaster mold.
Injection molding can also use sintered mold mix differently. The mixture is heated until the wax component softens and the mixture is injected into a prepared mold. When the part is removed from the mold, it is dewaxed as if it were a sintered mold.
Plastic parts are often made in injection molds, using thermoplastic resins that melt at reasonably low temperatures. A release agent is sprayed onto the mold surfaces to prevent the plastic parts from sticking together. Dewaxing refers to the removal of release agent, much of which can be removed with a soap and water rinse.
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