An gray iron foundry or ductile iron foundry manufactures metal castings through the process of melting metals into a liquified substance in order to pour it in a mold that contains a hollow cavity of the required product. After the metal has been solidified by the coolling process, the mold material gets removed and a casted product is finished. The solidified product is called a "casting". Casting is an economical technique to produce complex shapes and products compared to other methods. Our steel foundry works with aluminium and cast iron mostly, but we can also work with metals such as zinc, bronze, magnesium, brass, steel and ductile iron. Our cast iron foundry and workshop manufactures mostly low tech products in medium to high quantities.
The melting process is done with a furnace, which is charged with: virgin materials, internal scrap, external scrap and alloying elements. Virgin materials are pure forms of the primary metal that we use to form an alloy. External scrap is material from other forming processes such as machining, forging or punching whereas internal scrap refers to defective castings, risers, gates and other metal surplusses produced within the casting foundry. The charge is melted, refined, the melt chemistry is adjusted and then tapped into a transport vessel. To avoid defective castings, deleterious gasses and elements is removed by refining. Materials are added during the melting process to reach a specific product requirement specified by industry standards. Sometimes, certain fluxes are used to seperate metal from slag and to remove dissolved gas from metals that dissolve certain gasses, we use degassers.
A casting manufacturer melts the metal with special furnaces. These are large vessels to hold the materials and provide energy for the melting process. Modern furnaces types are: crucible, reverberatory, cupolas, induction and electric arc furnaces. Crucible and reverberatory furnaces are common for the production of aluminium, bronze and brass castings, while electric arc furnaces, cupolas and induction furnaces are often used for ferrous materials. Designing and setting up a furnace is a complex process and can be any size dependant on your requirements. Furnaces of casting manufacturers range from small ones to melt precious metals to large furnaces weighing several tons, capable of melting hundres of pounds of scrap at one time. The design of the furnace is according to the type of metals that need to be melted.
Furnaces used by iron foundries or metal foundries also need to be designed based on the fuel that is used to produce the desired temperature. Zinc or tin for example have a low melting point and in this case melting furnaces reach around 500° C. To reach 500° C, electricity, propane or natural gas are used. Steel or nickel based alloys that have high melting points even require furnaces that reach temperatures over 1600° C. To achieve high temperatures, such as these, electricity or coke is used by casting foundries. So depending on the type of metals a foundry is working with or specializing in, different types of furnaces setups are used. A grey iron foundry for cast iron may use: a cupola, induction furnace or an electric arc furnace. A steel foundries will use an electric arc furnace or induction furnace. Induction furnaces or crucible furnaces are often used by brass or bronze foundries. Gas heated crucible furnaces, electric resistance or reverberatory furnaces are commonly used by aluminium foundries.
Degassing processes in an iron casting foundry are necessary to reduce the amount of hydrogen that is dissolved in the liquid metal substance, especially when working with aluminium alloys. A casting wil end up to be porous if the hydrogen concentration is too high, as the hydrogen comes out of the solution when the aluminium cools down and solidifies. Porosity has serious impacts on the quality of the product. By bubbling argon or nitrogen through the melt, it is possible to remove hydrogen from the melt. When bubbles in the melt move upwards, the dissolved hydrogen are brought to the top surface. The amount of hydrogen can be measured with special equipment. It is also possible to check the amount of hydrogen dissolved by calculating the density of the aluminium sample. If porosity still is a problem after degassing, a process called metal impregnating is used to accomplish porosity sealing.
Foundry companies work with patterns made in the required shape of the product. If the design is simple, we can use a single piece pattern or sold pattern. Complex designs are made in two parts, also called split patterns. Split patterns have an upper section (cope) and a bottom section (drag). Split and solid patterns both can have cores inserted. The function of these cores is to create hollow areas in the mould. The parting line is where the cope and the drag separate. A good practice when making a pattern is to taper the edges, in order to remove the pattern without breaking the mould. Materials that are used to make a pattern are: wax, wood, plastic or metal. Molds are constructed by several different processes depending on: the type of foundry, the type of metal that is poured, quantity of parts that must be produced, the size of the casting and the complexity of the casting. The mold processes are: sand casting, lost-foam casting, investment casting, ceramic mold casting, V-process casting, die-casting, billet (ingot) casting.
Pouring, Shakeout and Degating
The molten metal is then poured into the mold, either by hand using ladles or by automatic pouring machines. When the product has solidified, it is removed from the mold. Sand based molds are removed by shaking or tumbling. At this point the foundry castings are still attached to the runners and gates. These are the channels in which the metal travels to reach inside the mold. After that, the runners, heads, gates, and risers are removed by the steel casting foundry from the casting using bandsaws, cutting torches or ceramic cutoff blades. This removal process is also called degating. Depending on the metal type and design of the gating system, the sprue, runners and gates can be easily removed by breaking them away with a sledge hammer or special knockout machinery. Risers are usually removed with a cutting method but modern methods use knockoff machinery that allow the riser to break off at the right place. The gating system yields leftover material, including risers, head and sprue, which are sometimes called sprue all together, that could even exceed more than half of the metal required to pour a full mold.
Grinding or Blasting
After the casting is degated, there may still be sand or other molding material attached to the casting. As such, a blasting process is used to clean the surface. Normally, in this blasting process, tiny granular media or grinding balls are propelled against the surface to blast away the sand and other unwanted materials. These grinding balls are either blown with compressed air or are hurled by a shot wheel. Materials that could be used as grinding media are: iron, steel, aluminium oxides, glss beads, other metal alloys, walnut shells or baking powder. Blasting media is selected to develop the reflectance and te color of the cast surface. This blasting process is also referred to as: cleaning, bead blasting or sand blasting. Afterwards a process called shot peening could be used to finish the surface.
A final steps in the casting process are: grinding, sanding or machining the products in order to achieve the required dimensions, shapes or surface finishing. Products that require tight dimensional control are machined in CNC milling centers. It is, however, not uncommon for many compononents to be used without machining processes. Our foundry also offers other services such as painting the products to prevent corrosion and to improve the visual appeal. We could also weld wrought metals together to form a completed product.