In cases where porosity still remains present after the degassing process, porosity sealing can be accomplished through a process called metal impregnating. Alternatively, the presence of hydrogen can be measured by determining the density of a metal sample. There are various types of equipment that can measure the presence of hydrogen. Carbon monoxide is typically used for iron and steel. Chlorine, nitrogen, helium and argon are often used to degas non-ferrous metals. When the bubbles go up in the melt, they catch the dissolved hydrogen and bring it to the surface. Porosity often seriously deteriorates the mechanical properties of the metal.Īn efficient way of removing hydrogen from the melt is to bubble a dry, insoluble gas through the melt by purging or agitation. ![]() If the hydrogen concentration in the melt is too high, the resulting casting will be porous the hydrogen will exit the molten solution, leaving minuscule air pockets, as the metal cools and solidifies. It forms as a result of material reactions or from water vapor or machine lubricants. Hydrogen is a common contaminant for most cast metals. by chemical reaction in the cast material.by physical entrapment during the casting process or.Gases can form in metal castings in one of two ways: Most aluminium foundries use either electric resistance or gas heated crucible furnaces or reverberatory furnaces.ĭegassing is a process that may be required to reduce the amount of hydrogen present in a batch of molten metal. Bronze or brass foundries use crucible furnaces or induction furnaces. For example, an iron foundry (for cast iron) may use a cupola, induction furnace, or EAF, while a steel foundry will use an EAF or induction furnace. The majority of foundries specialize in a particular metal and have furnaces dedicated to these metals. The fuel used to reach these high temperatures can be electricity (as employed in electric arc furnaces) or coke. For high melting point alloys such as steel or nickel-based alloys, the furnace must be designed for temperatures over 1,600 ☌ (2,910 ☏). Electricity, propane, or natural gas are usually used to achieve these temperatures. For low temperature melting point alloys, such as zinc or tin, melting furnaces may reach around 500 ☌ (932 ☏). Furnaces must also be designed based on the fuel being used to produce the desired temperature. They are designed according to the type of metals that are to be melted. Furnaces in foundries can be any size, ranging from small ones used to melt precious metals to furnaces weighing several tons, designed to melt hundreds of pounds of scrap at one time. Reverberatory and crucible furnaces are common for producing aluminium, bronze, and brass castings.įurnace design is a complex process, and the design can be optimized based on multiple factors. For ferrous materials EAFs, cupolas, and induction furnaces are commonly used. Furnace choice is dependent on the alloy system quantities produced. Modern furnace types include electric arc furnaces (EAF), induction furnaces, cupolas, reverberatory, and crucible furnaces. ![]() Furnaces are refractory-lined vessels that contain the material to be melted and provide the energy to melt it. ![]() Several specialised furnaces are used to heat the metal. During the tap, final chemistry adjustments are made. Certain fluxes may be used to separate the metal from slag and/or dross and degassers are used to remove dissolved gas from metals that readily dissolve in gasses. Material is added during the melting process to bring the final chemistry within a specific range specified by industry and/or internal standards. Refining is done to remove harmful gases and elements from the molten metal to avoid casting defects. The process includes melting the charge, refining the melt, adjusting the melt chemistry and tapping into a transport vessel. Internal scrap consists of gates, risers, defective castings, and other extraneous metal oddments produced within the facility. External scrap is material from other forming processes such as punching, forging, or machining. Alloying elements are either pure forms of an alloying element, like electrolytic nickel, or alloys of limited composition, such as ferroalloys or master alloys. Virgin material refers to commercially pure forms of the primary metal used to form a particular alloy. Virgin material, external scrap, internal scrap, and alloying elements are used to charge the furnace. A metal die casting robot in an industrial foundry
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