Primary Metals Industry
This group deals with smelting and refining ferrous and non-ferrous metals from ore, pig or scrap. Establishments are also concerned with the alloying and formation of these metals. This groups industries include:
-Steel Works, Blast Furnaces, and Rolling Mills
-Iron and Steel Foundries
-Primary Smelting and Refining of Nonferrous Metals
-Secondary Smelting and Refining of Nonferrous Metals
-Rolling, Drawing, and Extruding Nonferrous Metals
-Nonferrous Foundries
-Miscellaneous Primary Metal Products
Material Production: This group's primary function is to produce metals that can then be formed and eventually machined into durable goods.
CHEMICAL REDUCTION refer to the overall process of breaking metallic-oxide bonds to produce pure metal. It is done in a blast furnace which uses a hopper to feed ore mixtures. Metals produced from reduction include iron, aluminum, titanium, magnesium, and zinc.
OXIDATION decreases the amount of carbon, silicon, manganese, phosphorous, and sulfur in a mixture of molten pig iron and scrap to form steel. The Bessemer, open-hearth, basic-oxygen, and electric furnace are specific oxidation processes used to make steel. Most steel (and iron) is produced in the form of ingots to be used in future forming processes. Ingots are large, thick cylindrical bars that tend to vary in size based upon the application.
SMELTING is a process used to produce nonferrous metals. In the case of copper, crushed sulfides and oxides are melted in a reverberatory or electrical furnace. During the melt, lighter impurities, known as slag copper, float to the top. Pure copper, iron, and sulfur sink to the bottom to form a product known as matte. Matte may then be oxidized to obtain pure copper.
ALLOYING requires the addition of elements to metals for the purpose of altering their properties. Strength, ductility, toughness, and resistance to corrosion are examples of properties affected by alloying. Alloying elements include:
Alloying is often a very expensive process. While it produces very important materials, it can sometimes be replaced with other processes such as heat treatment.
HEAT TREATMENT uses controlled heating and cooling of metals for the purpose of altering their properties. The three basic heat treatment processes are; annealing (furnace cool), normalizing (air cool), and quenching (liquid cool). Typically, the slower processes (annealing and normalizing) sacrifice strength for greater ductility. Faster processes (quenching) sacrifice ductility for greater strength. More specific hardening processes include:
Heat treatment can also be confined to surfaces only. Common techniques include carburizing, ionitriding, and nitriding.
Forming: Forming processes are common to the primary metals group because once metal is made, something has to be done with it! Whether it's the forming of simple ingots, or the casting of precision engine blocks, formation must occur. However, only basic formation processes and little mechanical working of material are done within this group.
CASTING is one of the oldest and most common methods of forming. It requires the melting of a solid, heating it to the proper temperature, treating it to produce a desired chemical composition, and then pouring it into a cavity or mold for solidification. A wide range of sizes and shapes are possible with casting including large and bulky to small and detailed products. Some common casting processes include:
Some machining is required in casting processes to remove cores, gates, fins, left by air holes in the molds. Casted parts offer the best resistance to working stresses because they are melted for forming and not mechanically worked. Common casted parts include ingots and engine blocks.
POWDERED METALLURGY is a material formation process that is similar to casting in that some type of mold is used. Fine metal powders are blended, pressed within a mold, and then heated or sintered. Powdered metallurgy is used for its ability to produce many complex shapes in one step. Machining is many times unnecessary for a part produced with powdered metallurgy. Melt atomization and electrolytic deposition are the most common processes used to produce the often expensive metal powder. The extent of powder metallurgy in the primary metals group is the production of the powder, only.
Hot working forming processes require that the material be mechanically worked or deformed when heated. Hot working is attractive because it is very easy to shape materials at higher temperatures. Massive deformation is available without sacrificing much strength. Some disadvantages include the need for machining after the process and the presence of poor dimensional accuracy.
ROLLING is usually the first step in converting cast products (such as ingots) into finished wrought products. It consists of passing heated metal between two rolls that revolve in opposite directions, the space between the rolls being somewhat less than the thickness of the entering metal. Rolled products have minimum directional properties; this means that they aren't strong in one direction and weaker in another. Heat treatment can also be performed along with rolling; this is referred to as controlled rolling. The most common rolled product is sheet metal.
Machining: The extent of the machining done in the primary metals group is minimal. The only need for machining is light and often after casting to take off sprues used for air and for cleaning up surface defects. At this point, primary metal establishments are done and the bulk parts are shipped out to establishments that specialize in more detailed machining and assemblies.
FILING requires cutting teeth arranged in succession along the same plane on the surface of a file to remove material chips. Types of files include; single-cut, double-cut, vixen-cut, and rasp-cut. Files are also classified by coarseness and construction. Filing is important to many industries in easily removing sharp edges that could cause injury in finished products.
ABRASIVE machining uses very small cutting edges that are integral parts of abrasive particles to produce chips from the material. A good example is using sandpaper to smooth a rough surface. Types of abrasives include; quartz, aluminum oxide, silicon carbide, and diamond. Some common types of abrasive processes include grinding and lapping. Grinding uses a wheel of some shape on which abrasives are bonded. Lapping requires that fine particles be embedded into a soft material (like paper) which serves to finish the part. Abrasive machining is limited to small amounts of metal removal. However, it can provide extremely smooth surfaces.
ABRASIVE JET machining removes material through the action of a focused stream of abrasive laden gas. Common abrasives include; aluminum oxide, silicon carbide, sodium bicarbonate, and glass beads. AJM is used to debur plastic parts, deflash small castings, and touch up molds. AJM is very cheap and good for difficult to reach areas. It can machine very hard materials, but it has a slow material removal rate. Stray cutting may occur, along with the embedding of particles in the workpiece.
CHEMICAL machining is classified as non-traditional machining in that it doesn't produce chips. It employs some type of chemical reaction (sometimes enhanced by electrical or thermal energy) to remove material. Chemical machining often take the place of processes such as deburring, grinding, and polishing.
ULTRASONIC machining is a material removal process used to erode holes and cavities in
hard workpieces. It uses shaped tools and high frequency mechanical motion. Another form
of ultrasonic material removal is the stripping of finishes via underwater ultrasonic wave
emission.