CORROSION OF ALUMINUM - Aluminum develops a thin oxidation layer immediately upon exposure to the atmosphere. This tough oxide film protects the surface from further oxidation. The alloying elements alter the corrosion resistance of the aluminum. The alloys used for airplanes are usually given extra protection by painting or “cladding” with a thin coat of a corrosion-resistant alloy. Painting is generally not needed for medium-strength alloys used for structural applications. Stress Corrosion Cracking (SCC) - is a form of intergranular corrosion that can result in total failure of aluminum parts. Three conditions need to be fulfilled for this corrosion to occur. A susceptible alloy is the first of them. Not all aluminum alloys are equally prone to SCC. High yield strength alloys are more likely to suffer from stress corrosion cracking. The second condition is that the service environment must be humid or wet. The third condition is the existence of tensile stress in the material. TYPES OF ALUMINUM CORROSION • Atmospheric Corrosion • Galvanic Corrosion • Pitting Corrosion • Crevice Corrosion • General Corrosion • Intergranular corrosion • Stress Corrosion Cracking • Corrosion Fatigue • Filiform Corrosion • Erosion corrosion • Microbiological Induced Corrosion Corrosion Fatigue - It is a well-known fact that fatigue can cause complete failure of a product if left unchecked. In the case of aluminum, fatigue cracks can act as initiation sites for pitting corrosion. Corrosion fatigue in aluminum occurs when it is repeatedly subjected to low stress for long periods of time. Atmospheric Corrosion - The most common form of aluminum corrosion. Atmospheric corrosion of aluminum occurs as a result of exposure to natural elements. Galvanic Corrosion - This type of corrosion is also known as dissimilar metal corrosion. It can affect aluminum when it is physically or through an electrolyte connected to a noble metal. Pitting Corrosion - is a surface corrosion phenomenon of aluminum metal characterized by small holes (pits) on the surface. Usually, these pits do not affect the strength of the product. Crevice Corrosion - is a form of localized corrosion process in materials. Overlapping materials or unintentional design mistakes can lead to the formation of crevices. Uniform or General Corrosion - When corrosion takes place almost uniformly on an aluminum product surface, it is uniform or general corrosion. This type of corrosion can happen with products constantly exposed to a highly acidic medium. It may also occur in the presence of high electrochemical potential while the product is in an electrolyte. A typical example is rusting of an aluminum plate in acidic solution. Intergranular Corrosion - When it comes to aluminum, the grain boundary is electrochemically different compared to the alloy microstructure. This causes an electrochemical potential set up between the two and an exchange of electrons takes place. Filiform Corrosion - Filiform or wormtrack corrosion is initiated as pitting corrosion. It starts at points where the paint has peeled off the surface of the aluminum. The reason could be scratches or bruises on the surface that expose the underlying metal surface. - occurs and spreads easily in the presence of chloride anions and high humidity. Though it initiates as saltwater pitting corrosion, the mode of propagation is that of crevice corrosion. Microbiological induced Corrosion - is corrosion caused due to microorganisms/fungi. This type of corrosion is noticed in fuel and lubrication oil tanks. Aluminum - is widely used in building because of its intrinsic properties of lightness and corrosion resistance. Aluminum is used in external facades, roofs and walls, in windows and doors, in staircases, railings, shelves, and other several applications. Aluminum frame used for structural support of a building - The properties of pure aluminum are not suitable for structural applications. Some industrial applications require pure aluminum, but otherwise, alloying elements are almost always added. These alloying elements, along with cold working and heat treatments, impart characteristics to the aluminum that make this product suitable for a wide range of applications. ADVANTAGES OF ALUMINUM • has one-third the density of steel • • • • • • • • • • • has good thermal and electrical conductivity has high strength-to-weight ratio can be given a hard surface by anodizing and hard coating will not rust has high reflectivity can be die cast has alloys that are weldable is easily machined has good formability is nonmagnetic is nontoxic Aluminum METALLURGY - Aluminum has a face center cubic (FCC) lattice structure. It is very malleable, with a typical elongation over a 50-mm gauge length of over 40%. It has limited tensile strength, on the order of 28 mpa. The modulus of elasticity of aluminum is about 69 gpa. Commercially pure aluminum (i.E., More than 99% aluminum content) is limited to nonstructural applications, such as electrical conductors, chemical equipment, and sheet metal work. CASTING METHODS FOR ALUMINUM PRODUCTS • SAND CASTING - Sand with a binder is packed around a pattern. The pattern is removed and molten aluminum is poured in, reproducing the shape. Produces a rough texture which can be machined or otherwise surfaced if desired. • PERMANENT MOLD CASTING - Molten aluminum is poured into a reusable metal mold. Economical for large volume production. • DIE CASTING - Molten aluminum is forced into a permanent mold under high pressure. Suitable for mass production of precisely formed castings. FORMING METHODS FOR ALUMINUM PRODUCTS EXTRUSION - Aluminum heated to 425 to 540°C is forced through a die. Complex cross sections are possible, including incompletely or completely enclosed voids. ROLLING - Rollers compress and elongate heated aluminum ingots, producing plates (more than 6 mm thick), sheets (0.15 to 6 mm) thick, and foil (less than 0.15 mm). ROLL FORMING - Shaping of sheet aluminum by passing stock between a series of special rollers, usually in stages. BRAKE FORMING - Forming of sheet products with a brake press. Uses simpler tooling than roll forming but production rates are lower and the size of the product is limited. CUTTING OPERATIONS - Production of outline shapes by blanking and cutting. In blanking, a punch with the desired shape is pressed through a matching die. EMBOSING - Shaping an aluminum sheet by pressing between mated rollers or dies, producing a raised pattern on one side and its negative indent on the other side. DRAWING - Shaping an aluminum sheet by drawing it through the gap between two mated dies in a press. SUPERPLASTIC FORMING - An aluminum sheet is heated and forced over or into a mold by air pressure. Complex and deep contour shapes can be produced, but the process is slow. TEMPER DESIGNATIONS FOR ALUMINUM ALLOYS FABRICATED - No special control over thermal conditions or strain hardening is employed. ANNEALED - Wrought product ~ annealed to the lowest strength temper - Cast products ~ annealed to improve ductility and dimensional stability. STRAIN HARDENED - Wrought products only. Strength is increased by strain hardening, with or without supplemental thermal treatments. PHYSICAL PROPERTIES OF ALUMINUM - Aluminum has a lower density than any other commercial metal except magnesium. Given the right type of surface, aluminum makes an excellent reflector, especially for ultraviolet light - Aluminum is an odourless, tasteless, silvery-white metal. With increasing silicon and ductile and quite soft. The aluminum crystal has a face-centred cubic structure. - The concentration of the lattice in the less pure metal results from the formation of impurity segregations. Purity also affects most other physical properties. - Aluminum has a lower density than any other commercial metal except magnesium. - Aluminum may also be used as a selective cold or hot wall or as a body approximating the effect of a black body. In the infrared region, the reflectivity of aluminum is exceeded only slightly by that of gold and silver. Welding and fastening - Aluminum pieces can be joined either by welding or by using fasteners. Welding requires that the tough oxide coating on aluminum be broken and kept from reforming during welding, so arc welding is generally performed in the presence of an inert gas that shields the weld from oxygen in the atmosphere. - The two common processes by which aluminum is welded are Gas Metal Arc Welding, GMAW, and gas tungsten arc welding, GTAW. In the GMAW process, the filler wire also serves as the electrode. that GTAW uses a tungsten electrode and a separate filler wire. - Welding can alter the tempering of the aluminum in the area of the weld. In addition to welding, either bolts or rivets can join aluminum pieces. Bolts can be either aluminum or steel. When steel bolts are used, they must be either galvanized, aluminized, cadmium plated, or made of stainless steel to prevent the development of galvanic corrosion. - Rivet fasteners are made of aluminum and are cold driven. Both bolt and rivet joints are designed based on the shear strength of the fastener and the bearing strength of the material being fastened. 9 Steps of Casting Glass 1. Design your glass piece 2. Make a plaster mold 3. Remove the mold 4. Melt out wax 5. Measure out the glass 6. Pour the glass into the mold 7. Allow it to cool down 8. Remove the final product 9. Polish the final product Characteristics & Properties of Glass As A Building Material According to ‘James Stevens Curl & Susan Wilson’ (Authors of The Oxford Dictionary of architecture), “glass is a semi- or fully transparent hard, brittle, lustrous material made by igneous fusion of silica (usually sand) with an alkaline sodium or potassium salt and added ingredients. According to ‘Laufs Wilfried & Luible Andreas’ (2003) (Published in Introduction on use of glass in modern buildings), Glass is a magical building material as it has various applications in doors, windows and building façades depending on its characteristics & properties. Characteristic of Glass as a Building Material 1. Hardness and Brittleness - It is a hard material as it has great impact resistance against applied load. 2. Weather Resistance - It is weather resistant as it can withstand the backlash of rain, sun and wind. 3. Insulation - It is an excellent insulator against heat, electricity and electromagnetic radiation because of its good insulating response against visible light transmission. 4. Chemical Resistance - It can withstand the effect of the chemical reaction under different environment conditions or acidic effects. 5. Color and Shape Varieties - It can be blown, drawn and pressed to any colour, shape, and variety and is available in the market depending upon their use, dimensional requirements, and safety requirement. 6. Transparency - The transparency is one such property of glass which creates a visual connect with the outside world. With the advent of technology, clear glass can also be altered, making it opaque. 7. Fire Resistance Glazing - Modern glazing products allow fire protection up to 120 minutes. The transparent glazing is protective by becoming opaque if it is subjected to above 120°C. This is achieved with the help of special transparent gels. Property Modification - It is also possible to change some of its properties to suit different purposes. List of Surface Modification Process of Glass a) Anti-Fog Coating b) Anti-Reflective Coating c) Chemically Strengthened Glass d) Anti-Corrosion Coating e) De-Alkalization Coating f) Hydrogen Darkening Layer g) Insulated Coating h) Sand Blasting and Acid Etching Process (Fosted Glass) i) Low Emissivity Coating j) Pyrolytic Coating k) Self-cleaning Coating l) Sandwichable Film or Smart Film m) Water Repellent Coating n) Sol-Gel Coating Glasses - can be used to transmit or shield radiation. More over photosensitive glasses for fluidic devices are used in machine controls. TYPES OF GLASS USED IN CONSTRUCTION Laminated Glass - is among the most effective types of glass used in building construction. In order to manufacture laminated glass, two plies of normal glass are usually bonded together (strongly) with interlayers to form strong, permanent bonds. Shatterproof Glass - This type of glass is highly resistant to breakage due to the inclusion of plastic polyvinyl butyral during manufacture. The added element prevents the glass from forming sharp-edged pieces that lead to further breakage during impact. Tinted Glass - a highly convenient form of glass that is characterized by its unique colors. To produce tinted glass, manufacturers introduce color-producing ingredients that help to add a bit of color without affecting other properties of the glass. Tempered Glass - Also called hardened glass, tempered glass is a common type of glass used in construction for its strength. To ensure the final product is strong, manufacturers tend to process normal glass with chemical or thermal treatments, which introduce strength-enhancing properties, thus making the glass tough. Glass Wool - a well-known insulating material made from melted glass as the primary raw material. In addition to melted glass, other significant constituents of glass wool include silica sand and fixing agents. This type of construction glass is usually available as superfine wool and loose wool. Insulated Glass Unit - also known as insulated glass unit, is recommended in areas with high air conditioning costs. This glass type is made when a cavity separates two or more glass panes before the edges are carefully sealed. For increased insulation effectiveness, the cavity is usually filled with nonconducting gas like argon or dehydrated air. Wired Glass - mainly used as a safety glass due to its impressive fireresistant properties. The glass is carefully reinforced with strong wire mesh during production to enhance its durability and resistance to large impacts. SAFETY GLAZING Required in all areas. Such glass must satisfy test requirements. Glazing Materials Used in Buildings, Safety Performance Specifications and Methods of Test. Typically, acceptable materials include laminated glass, fully tempered glass, wired glass, and certain plastics. GLASS FIBERS Made essentially by flowing molten glass through tiny holes in dies. Two very important types of glass are in wide use for reinforcements: E glass, which is essentially a borosilicate glass named for electrical and electronic applications, and high strength S glass which is a magnesiaalumina-silica material with higher tensile strength than E glass. GLASS CASTING A technique of shaping glass objects. The process starts with melting glass—glass frit, glass powder, glass stingers/noodles, so on—to the point where it becomes soft and malleable. • • • COMMON GLASS TECHNIQUES GRAPHITE CASTING - Available in a variety of shapes and designs, graphite mold can withstand high temperatures and help you achieve a higher degree of dimensional accuracy and tolerances. PATE DE VERA - It is a French team that refers to using a glass plate to design desired glass shape. The process involves the mixing of colorants, enamels, gum arabic, and water and combined with minuscule glass pieces. KILN CASTING - Kiln casting is the process of placing cold glass pieces into, through, or over the kiln casting mold inside a kiln. Heat it to a temperature where the glass becomes liquid and takes the required shape. • • SAND CASTING - Sand casting art is one of the most common and economical processes to cast glass. It involved placing or craving a design into the sand to create a mold. Then, pour hot liquid glass into the molds and wait for it to cool down. LOW CAST CASTING - This technique requires a mold that is surrounded by a sacrificial wax model. During the process, the wax is melted out and replaced by molten glass. This type of casting is the best for creating detailed glass structures. EQUIPMENT NEEDED FOR GLASS CASTING Safety Equipment - is highly important to protect yourself during the glass casting process. Below- mentioned is the required safety equipment. Wax - Create your design in wax before building a mold around it. Shape it with texturing tools, a soldering iron, and a heat gun. Many experienced wax sculptors swear by repurposing dental tools in order to effectively sculpt and carve unique designs in wax. Molds - You can make your own molds using a combination of plaster and silica. Mix equal parts by weight of plaster, silica, and water together until it has the consistency of heavy cream. Plaster gives the mold support and silica has a high refractory, so it can withstand a lot of heat. Scale - A gram scale is necessary for making your investment and calculating how much glass you will need. Wallpaper Steamer - A gram scale is necessary for making your investment and calculating how much glass you will need. Kiln and Kiln Furniture - A kiln large enough to fit your mold is necessary for melting the glass into your mold and annealing. Kiln furniture is used inside of the kiln during firing to ensure that the molds and components do not deform or stick to one another. Coldworking Tools - In the final stage of this process, you will use a grinder, belt sander, and more to polish and finish your piece.
