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Learn about the different types of metals, including ferrous and nonferrous metals, and their properties. Discover various methods of producing metal shapes and different finishing processes used with metals. Explore the characteristics and applications of aluminum, copper, iron, and stainless steel.
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Finish Surface Materials Metals: Read pages 185 – 205 in the textbook. Metals are generally categorized by their iron content. Ferrous (from the Latin ferrum) metals consist mostly of iron. Nonferrous metals contain little or no iron, generally have good corrosion resistance, and are non-magnetic. Nonferrous metals include copper, aluminum, silver, and gold. There are different ways to produce metal shapes. Casting: metal products are made by pouring molten metal into a mold. Extruding: shapes are produced by forcing semi-molten material through a die. Forged: shapes are hammered, pressed, or rolled into the desired shape. Wrought:one of the two forms of iron obtained through the smelting process. wrought iron is much less brittle than cast iron. When dissimilar metals are connected by an electrolyte, a current, called a galvanic current, flows from one to the other metal. An electrolyte is any liquid that conducts electricity, for example, water. This electric current causes one of the metals to deteriorate, and this reaction is called galvanic corrosion.
Table 7.13 (page 205 of the text) shows metals that are more easily corroded by galvanic corrosion, such as zinc, and aluminum, and those that are less easily corroded, such as stainless steel or copper. Metals that are higher on the galvanic scale will corrode when electrolytically connected to metals that are lower on the scale. Finishing processes used with metals Mechanical finishes: achieved by buffing, grinding, polishing, hammering, or otherwise texturing the metal surface for a specific appearance. Chemical finishes: various solutions applied to the surface of metals cause reactions that alter the surface character. Coatings: are either materials applied to the metal or formed by the metal itself through a chemical or electro- chemical process.
Aluminum The earth's most plentiful metal: about 8% of the earth's crust is composed of aluminum. Aluminum is never found as a free metal in nature. It is always chemically combined with other elements, and therefore must be 'extracted'. Aluminum is a soft, flexible metal, it is light in weight, and yet very strong. Aluminum is highly resistant to corrosion, it is an excellent thermal and electrical conductor. Aluminum is used for: door frames, windows, horizontal louver blinds, furniture, hardware, bicycle frames, and cases for a great variety of products, such as televisions, vcr's, and computers. Aluminum finishes Because aluminum is highly resistant to corrosion, it often does not require a special finish.
Finishes are often applied to aluminum for visual/decorative reasons. A list of mechanical (M), chemical (C), and Anodic Coatings (A) is presented in table 7.11 on page 198 of the text.
Anodizing is available in an infinite number of colors. The effect of volume on pricing of anodized colors is difficult to overstate. This is because an anodizer must procure enough dye to charge a tank in which he can completely submerge the parts. With large parts, say 24' long, dyeing can be very expensive. For example it can cost $10,000 to charge a 30' tank with a lightfast dye. The anodizer must recoup this cost in his pricing. Because of the potential for huge setup charges, most architectural anodizing is done with a $185 minimum charge in clear (silver), bronzes and black. (Shades of burgundy, green and blue are available through a process called "interference coloring." Contact your SAF sales representative for more information.) Small parts, in contrast, can be dyed with set-up charges as low as $400. We are also set-up to do Gold at our Charlotte plant which would require no set-up charge.
The most common finish that is applied to aluminum is anodizing. Anodizing involves passing an electrical current across a solution, (most commonly sulfuric acid) in which the aluminum is immersed. The coating provided by anodizing is thick enough (typically .03 mm) to withstand weathering and typical corrosion forces. Anodized coatings can be transparent, translucent, or opaque.
Copper Copper is a relatively soft, malleable, corrosion resistant non ferrous metal. Copper will develop a green patina if exposed to the weather. Copper can be made harder and stronger by adding small amounts of tin. copper + tin = bronze Copper and zinc combine to form brass copper + zinc = brass Brass is commonly used fordoor hardware, plumbing fixtures, small nails, and sculptures.
Iron About 5% of the earth's crust is composed of iron. Wrought iron is made from iron ore that is heated until it is soft but not melted . Cast iron contains large amounts of carbon, making it so hard and brittle that it cannot be worked into shapes, but must be cast into molds. Plumbing drainage pipes and ornamental rails for exterior use are often made from cast iron. Stainless Steel Stainless steel is an iron alloy that is inherently corrosion resistant because it contains chromium. Stainless steel alloys contain at least 50% iron and 10.5% chromium. Stainless steel finishes are described in table 7.3, (on page 189 of the text)
This poster shows aluminum extruded shapes. Aluminum extruded shapes
Powder Coating Liquid paint is composed of pigment, resin, and solvent. Powder paint is simply pigment encapsulated in a powdered resin and is thus simply thought of as “paint without the solvent.
Stainless steel door, perforated design
