Stone, Clay, and Glass Products
This group deals with materials taken principally from the earth. Establishments are
concerned with producing goods, and even mining and quarrying these materials, as long as
additional processes follow. The major group's
industries include:
-Flat Glass
-Glass and Glassware, Pressed or Blown
-Glass Products
-Cement (hydraulic)
-Structural Clay Products
-Pottery and Related Products
-Concrete, Gypsum, and Plaster Products
-Cut Stone and Stone Products
-Abrasives, Asbestos, and Miscellaneous Nonmetallic Mineral Products
Material Production: Most of the material formation for this group consists of actual mining. Stone is usually cut into usable sections (for stone products) or ground up for other uses. Again, establishments in this group that do mine and quarry are concerned with all of the processes required to take raw materials and turn them into products. Establishments concerned with mining and quarrying only, are classified elsewhere.
CERAMICS consist of combinations of metallic and non-metallic elements. Compounding is the process used to produce ceramics. They are brittle materials used extensively for their resistance to electricity, wear, and high temperatures. Most ceramics have crystalline structures and can display polymorphism (many crystalline states). For example, silica can exist in three forms; quartz, tridymite, and cristobalite. Clay, in its raw form, is used to produce ceramics used in a wide variety of applications including bricks and pottery.
COMPOSITES are heterogeneous solids consisting of two or more components that are mechanically or metallurgically bonded. There are three basic types of composites; laminar, particulate, and fiber reinforced. Common methods of producing composites include; compression molding, filament winding, pultrusion, autoclave curing. Quite often, there are no names for composite construction that simply puts two separate materials together in one shape or form. It is advantageous to add strengthening materials to a material that is often too weak when left pure. A good example of a particulate composite is cement, while an example of a fiber reinforced composite is steel reinforced cement.
Forming: Forming is this major group is limited to glass and clay products. Stone is either crushed or machined, and concrete is only produced to the point of being ready to "mix."
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. Glass is occasionally formed in specialized casting processes.
Hot working forming processes require that the material be mechanically worked or deformed when heated. In this major group, glass and other ceramics are the only materials that can be hot worked. 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.
EXTRUSION requires that the material be compressively forced to through a suitable shape (called a die) to form a product with reduced cross section. The extrusion process is like squeezing toothpaste out of a tube. The two types of extrusion used in hot working are direct and indirect. In direct extrusion, a ram pushes the material through the die. In indirect extrusion, the ram pushes the die back around the material. Blowing glass is considered a form of extrusion.
DRAWING is a plastic forming process in which a flat sheet or plate of material is formed into a recessed, three-dimensional part with depth several times the thickness of the material. Hot drawing is used, primarily, for forming thick-walled parts of simple geometry.
Other hot working processes include HOT SPINNING, and PIERCING. Hot spinning is the plastic forming of parts from a flat rotating disk of clay. Piercing is the production of thin walled, seamless tubing by center punching solid, circular stock with a bullet like tool. Piercing is used to produce glass tubing.
Machining: All of the industries in this major group use machining processes. Machining deals with removing material (usually in the form of chips) so as to obtain a finished product of desired size, shape, and finish. Machining that does not produce chips is classified as non-traditional machining.
SAWING produces chips by a succession of small cutting edges or teeth arranged in a narrow line on a saw blade. Sawing processes include cutting off sections of stone to notching glass. Saws can be classified into three distinct types; reciprocating, band, and circular.
WATER JET machining removes material through erosion effects of a high velocity, small diameter jet of water. It is commonly used for cutting and slitting of wire, and for cable stripping. Abrasives can be added to the water to handle stronger materials.
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 wood removal. However, it can provide extremely smooth surfaces. With coarser abrasive, ground and frost glass may be obtained.
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.
Assembly: The actual putting together, joining, and additional finishing of components constitutes assembly. Not many processes define a fashion in which parts and components are put together; it's just done in (hopefully) the fastest, most efficient manner. Once together, there has to be a means of joining the components. In this major group, materials other than those considered in this group are used to finish products. As long as the majority of the product is stone, clay, or glass, it still belongs in this group.
ADHESIVE BONDING uses composite systems with several compounds to join two surfaces together. The bonding material may exist as liquids, pastes, solids, tapes, or films. Common types of adhesives include:
The surfaces of all components to be joined must be clean and dry to insure proper bonding. A good example is the joining clay or stone based abrasives to paper to create "sand paper."
MECHANICAL FASTENING requires that a joint be formed by mechanically interlocking or interfering with no fusion or bonding present. Fastener types include integral and discrete. Integral fasteners are machined areas of wood such as tabs and seams that fit into other parts. Discrete fasteners are separate pieces such as nails, bolts, screws, rivets, and wires.
COATING is performed to impart certain properties to surfaces such as resistance to weather and wear, different colors, and smoother finishes. Coatings can be classified into organic and inorganic types. Common coatings include paint, enamel, anodization, and plastic laminations.
Inspection and Testing: Most of the processes already described in the stone, clay, and glass group occur at only one point in the overall manufacturing path. Inspecting and testing, however, are performed numerously throughout all processes. It can consist of a simple check to see if a piece is present, or a minute measurement of the surface of a finished part. Inspection and testing tell whether or not a particular process was performed adequately.
DESTRUCTIVE TESTING does not allow for use of the tested part after inspection because it imparts some type of mechanical deformation. An example is the stress testing of safety glass windows. This type of testing is done on a sampling basis. Other types of destructive testing include fatigue, impact, creep, torsion, and shearing.
NON-DESTRUCTIVE TESTING allows for use of the part after inspection. It includes a wide range of optical and mechanical techniques. Mechanical techniques using instruments such as calipers, micrometers, and scales may contact the part, but they leave no significant mechanical deformation. Optical techniques include structured light, triangulation, holography, and interferometry. An example of a NDT application using fourier optics to detect impurities in glass products.