1.
Wetting
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Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting is determined by a balance between adhesive and cohesive forces. Wetting deals with the three phases of materials, gas, liquid, and solid and it is now a center of attention in nanotechnology and nanoscience studies due to the advent of many nanomaterials in the past two decades. Wetting is important in the bonding or adherence of two materials, Wetting and the surface forces that control wetting are also responsible for other related effects, including capillary effects. There are two types of wetting, non-reactive wetting and active wetting, adhesive forces between a liquid and solid cause a liquid drop to spread across the surface. Cohesive forces within the cause the drop to ball up. The contact angle, as seen in Figure 1, is the angle at which the liquid–vapor interface meets the solid–liquid interface, the contact angle is determined by the result between adhesive and cohesive forces. As the tendency of a drop to spread out over a flat, solid surface increases, thus, the contact angle provides an inverse measure of wettability. A contact angle less than 90° usually indicates that wetting of the surface is very favorable, contact angles greater than 90° generally means that wetting of the surface is unfavorable, so the fluid will minimize contact with the surface and form a compact liquid droplet. For water, a surface may also be termed hydrophilic. Superhydrophobic surfaces have contact angles greater than 150°, showing almost no contact between the drop and the surface. This is sometimes referred to as the Lotus effect, the table describes varying contact angles and their corresponding solid/liquid and liquid/liquid interactions. For nonwater liquids, the term lyophilic is used for low contact angle conditions, similarly, the terms omniphobic and omniphilic apply to both polar and apolar liquids. Liquids can interact with two types of solid surfaces. Traditionally, solid surfaces have been divided into high-energy solids and low-energy types, the relative energy of a solid has to do with the bulk nature of the solid itself. Solids such as metals, glasses, and ceramics are known as hard solids because the bonds that hold them together are very strong. Thus, it takes an input of energy to break these solids. Most molecular liquids achieve complete wetting with high-energy surfaces, the other type of solids is weak molecular crystals where the molecules are held together essentially by physical forces
2.
Soldering
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Soldering, is a process in which two or more items are joined together by melting and putting a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal. Soldering differs from welding in that soldering does not involve melting the work pieces, in brazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. In the past, nearly all solders contained lead, but environmental and health concerns have increasingly dictated use of alloys for electronics. There is evidence that soldering was employed as early as 5000 years ago in Mesopotamia, soldering and brazing are thought to have originated very early in the history of metal-working, probably before 4000 BC. Sumerian swords from ~3000 BC were assembled using hard soldering, soldering was historically used to make jewelry items, cooking ware and tools, as well as other uses such as in assembling stained glass. Soldering is used in plumbing, electronics, and metalwork from flashing to jewelry, jewelry components, machine tools and some refrigeration and plumbing components are often assembled and repaired by the higher temperature silver soldering process. Small mechanical parts are often soldered or brazed as well, soldering is also used to join lead came and copper foil in stained glass work. Electronic soldering connects electrical wiring and electronic components to printed circuit boards, soldering filler materials are available in many different alloys for differing applications. In electronics assembly, the alloy of 63% tin and 37% lead has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications, a eutectic formulation has advantages when applied to soldering, the liquidus and solidus temperatures are the same, so there is no plastic phase, and it has the lowest possible melting point. Having the lowest possible melting point minimizes heat stress on electronic components during soldering, and, having no plastic phase allows for quicker wetting as the solder heats up, and quicker setup as the solder cools. A non-eutectic formulation must remain still as the temperature drops through the liquidus and solidus temperatures, any movement during the plastic phase may result in cracks, resulting in an unreliable joint. Common solder formulations based on tin and lead are listed below and they are also suggested anywhere young children may come into contact with, or for outdoor use where rain and other precipitation may wash the lead into the groundwater. Unfortunately, most lead-free solders are not eutectic formulations, melting at around 250 °C, alloying silver with other metals changes the melting point, adhesion and wetting characteristics, and tensile strength. Of all the brazing alloys, silver solders have the greatest strength, specialty alloys are available with properties such as higher strength, the ability to solder aluminum, better electrical conductivity, and higher corrosion resistance. The purpose of flux is to facilitate the soldering process, one of the obstacles to a successful solder joint is an impurity at the site of the joint, for example, dirt, oil or oxidation. The impurities can be removed by mechanical cleaning or by chemical means and this effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the workpiece. One of the earliest forms of flux was charcoal, which acts as a reducing agent, some fluxes go beyond the simple prevention of oxidation and also provide some form of chemical cleaning
3.
Corrosion
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Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and also anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others. Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
4.
Wear
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Wear is related to interactions between surfaces and specifically the removal and deformation of material on a surface as a result of mechanical action of the opposite surface. In materials science, wear is erosion or sideways displacement of material from its derivative, Wear of metals occurs by the plastic displacement of surface and near-surface material and by the detachment of particles that form wear debris. The size of the particles may vary from millimeter range down to an ion range. This process may occur by contact with metals, nonmetallic solids, flowing liquids. Secondary stage or mid-age process, where a rate of ageing is in motion. Most of the operational life is comprised in this stage. Tertiary stage or old-age period, where the components are subjected to rapid failure due to a rate of ageing. The secondary stage is shortened with increasing severity of conditions such as higher temperatures, strain rates, stress. Note that, wear rate is influenced by the operating conditions. Specifically, normal loads and sliding speeds play a role in determining wear rate. In addition, tribo-chemical reaction is important in order to understand the wear behavior. Different oxide layers are developed during the sliding motion, the layers are originated from complex interaction among surface, lubricants, and environmental molecules. In general, a plot, namely wear map. Demonstrating wear rate under different loading condition is used for operation and this graph also represents dominating wear modes under different loading conditions. Surface engineering and treatments are used to wear and extend the components working life. The study of the processes of wear is part of the discipline of tribology, the complex nature of wear has delayed its investigations and resulted in isolated studies towards specific wear mechanisms or processes. Impact-, cavitation-, diffusive- and corrosive- wear are all such examples and these wear mechanisms, however, do not necessarily act independently and wear mechanisms are not mutually exclusive. Industrial Wear are commonly described as incidence of multiple wear mechanisms occurring in unison, another way to describe Industrial Wear is to define clear distinctions in how different friction mechanisms operate, for example distinguish between mechanisms with high or low energy density
5.
Hardness
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Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials are harder than others, Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of matter are ceramics, concrete, certain metals, and superhard materials. There are three types of hardness measurements, scratch, indentation, and rebound. Within each of these classes of measurement there are individual measurement scales, for practical reasons conversion tables are used to convert between one scale and another. Scratch hardness is the measure of how resistant a sample is to fracture or permanent plastic deformation due to friction from a sharp object, the principle is that an object made of a harder material will scratch an object made of a softer material. When testing coatings, scratch hardness refers to the necessary to cut through the film to the substrate. The most common test is Mohs scale, which is used in mineralogy, one tool to make this measurement is the sclerometer. Another tool used to make these tests is the pocket hardness tester and this tool consists of a scale arm with graduated markings attached to a four-wheeled carriage. A scratch tool with a rim is mounted at a predetermined angle to the testing surface. In order to use it a weight of mass is added to the scale arm at one of the graduated markings. The use of the weight and markings allows a known pressure to be applied without the need for complicated machinery. Indentation hardness measures the resistance of a sample to material deformation due to a constant compression load from an object, they are primarily used in engineering. The tests work on the premise of measuring the critical dimensions of an indentation left by a specifically dimensioned and loaded indenter. Common indentation hardness scales are Rockwell, Vickers, Shore, rebound hardness, also known as dynamic hardness, measures the height of the bounce of a diamond-tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity, the device used to take this measurement is known as a scleroscope. Two scales that measures rebound hardness are the Leeb rebound hardness test, there are five hardening processes, Hall-Petch strengthening, work hardening, solid solution strengthening, precipitation hardening, and martensitic transformation. Hardness in the elastic range—a small temporary change in shape for a given force—is known as stiffness in the case of a given object and they exhibit plasticity—the ability to permanently change shape in response to the force, but remain in one piece
6.
Electrical resistivity and conductivity
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Electrical resistivity is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that allows the flow of electric current. Resistivity is commonly represented by the Greek letter ρ, the SI unit of electrical resistivity is the ohm-metre. Electrical conductivity or specific conductance is the reciprocal of electrical resistivity and it is commonly represented by the Greek letter σ, but κ or γ are also occasionally used. Its SI unit is siemens per metre and CGSE unit is reciprocal second, many resistors and conductors have a uniform cross section with a uniform flow of electric current, and are made of one material. All copper wires, irrespective of their shape and size, have approximately the same resistivity, every material has its own characteristic resistivity – for example, resistivity of rubber is far larger than coppers. If the pipes are the size and shape, the pipe full of sand has higher resistance to flow. Resistance, however, is not solely determined by the presence or absence of sand and it also depends on the length and width of the pipe, short or wide pipes have lower resistance than narrow or long pipes. The above equation can be transposed to get Pouillets law, R = ρ ℓ A, the resistance of a given material increases with length, but decreases with increasing cross-sectional area. From the above equations, resistivity has the SI unit ohm metre, the formula R = ρ ℓ / A can be used to intuitively understand the meaning of a resistivity value. For example, if A = 7000100000000000000♠1 m2 ℓ = 7000100000000000000♠1 m, Conductivity, σ, is defined as the inverse of resistivity, σ =1 ρ. Conductivity has SI units of siemens per metre, the above definition was specific to resistors or conductors with a uniform cross-section, where current flows uniformly through them. A more basic and general definition starts from the fact that a field inside a material makes electric current flow. Conductivity is the inverse, σ =1 ρ = J E, for example, rubber is a material with large ρ and small σ—because even a very large electric field in rubber makes almost no current flow through it. On the other hand, copper is a material with small ρ, according to elementary quantum mechanics, electrons in an atom do not take on arbitrary energy values. Rather, electrons only occupy discrete energy levels in an atom or crystal. When a large number of such allowed energy levels are spaced close together —i. e. have similar energies— we can talk about these energy levels together as an energy band. There can be many such bands in a material, depending on the atomic number
7.
Friction
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Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction, Dry friction resists relative lateral motion of two surfaces in contact. Dry friction is subdivided into static friction between non-moving surfaces, and kinetic friction between moving surfaces, fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces, skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Internal friction is the force resisting motion between the making up a solid material while it undergoes deformation. When surfaces in contact move relative to other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can have consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology, Friction is not itself a fundamental force. Dry friction arises from a combination of adhesion, surface roughness, surface deformation. The complexity of interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis. Friction is a non-conservative force - work done against friction is path dependent, in the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved, the Greeks, including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A. D. that it is easier to further the motion of a moving body than to move a body at rest. The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology and these laws were rediscovered by Guillaume Amontons in 1699. Amontons presented the nature of friction in terms of surface irregularities, the understanding of friction was further developed by Charles-Augustin de Coulomb. Coulomb further considered the influence of sliding velocity, temperature and humidity, the distinction between static and dynamic friction is made in Coulombs friction law, although this distinction was already drawn by Johann Andreas von Segner in 1758. Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, in Leslies view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before
8.
Mill finish
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Mill finish refers to the surface texture of metal after it exits a rolling mill, extrusion die, or drawing processes, including sheet, bar, plate, or structural shapes. This texture is rough and lacks lustre, it may have spots of oxidation or contamination with mill oil. Most mill finish surfaces are machined or treated with polishing, industrial etching, the quality and characteristics of mill finish can vary widely from one mill to another, and even from one lot to another. Hot rolled parts are dark and dull, their surface oxidized from being hot worked. Extruded products may have die marks running the length of the stock, other mill finishes are surprisingly smooth and uniform. It is possible for a mill to influence the finish of produced stock, architectural Metals, A Guide to Selection, Specification, and Performance
9.
Surface finish
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Surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness. It comprises the small deviations of a surface from the perfectly flat ideal. Surface texture is one of the important factors that control friction, considerable efforts have been made to study the influence of surface texture on friction and wear during sliding conditions. Surface textures can be isotropic or anisotropic, sometimes, stick-slip friction phenomena can be observed during sliding depending on surface texture. Each manufacturing process produces a surface texture, the process is usually optimized to ensure that the resulting texture is usable. If necessary, a process will be added to modify the initial texture. Lay is the direction of the predominant surface pattern ordinarily determined by the method used. Surface roughness commonly shortened to roughness, is a measure of the finely spaced surface irregularities, in engineering, this is what is usually meant by surface finish. Waviness is the measure of surface irregularities with a greater than that of surface roughness. These usually occur due to warping, vibrations, or deflection during machining, surface finish may be measured in two ways, contact and non-contact methods. Contact methods involve dragging a measurement stylus across the surface, these instruments are called profilometers, non-contact methods include, interferometry, confocal microscopy, focus variation, structured light, electrical capacitance, electron microscopy, and photogrammetry. In the United States, surface finish is specified using the ASME Y14. 36M standard. The other common standard is International Organization for Standardization 1302, many factors contribute to the surface finish in manufacturing. In forming processes, such as molding or metal forming, surface finish of the die determines the finish of the workpiece. In machining the interaction of the edges and the microstructure of the material being cut both contribute to the final surface finish. In general, the cost of manufacturing a surface increases as the surface finish improves, any given manufacturing process is usually optimized enough to ensure that the resulting texture is usable for the parts intended application. If necessary, a process will be added to modify the initial texture. The expense of additional process must be justified by adding value in some way—principally better function or longer lifespan
10.
Burnishing (metal)
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Burnishing is the plastic deformation of a surface due to sliding contact with another object. Visually, burnishing smears the texture of a surface and makes it shinier. Burnishing may occur on any sliding surface if the contact stress locally exceeds the strength of the material. To understand burnishing, first look at the case of a hardened ball on a flat plate. If the ball is pressed directly into the plate, stresses develop in both objects around the area where they contact, as this normal force increases, both the ball and the plates surface deform. The deformation caused by the ball is different depending on the magnitude of the force pressing against it. If the force on it is small, when the force is released both the ball and plates surface will return to their original, undeformed shape. In this case, the stresses in the plate are always less than the strength of the material. Since it was given that the plate is softer than the ball. If a larger force is used, there also be plastic deformation. A bowl-shaped indentation will be left behind, surrounded by a ring of raised material that was displaced by the ball, the stresses between the ball and the plate are described in more detail by Hertzian stress theory. Now consider what happens if the force on the ball drags it across the plate. In this case, the force on the ball can be decomposed into two component forces, one normal to the surface, pressing it in, and the other tangential. As the tangential component is increased, the ball will start to slide along the plate, at the same time, the normal force will deform both objects, just as with the static situation. If the normal force is low, the ball will rub against the plate, the rubbing action will create friction and heat, but it will not leave a mark on the plate. However, as the force increases, eventually the stresses in the plates surface will exceed its yield strength. When this happens the ball will plow through the surface and create a trough behind it, the plowing action of the ball is burnishing. Even the smoothest of surfaces will have imperfections if viewed at a high enough magnification, the imperfections that extend above the general form of a surface are called asperities, and they can plow material on another surface just like the ball dragging along the plate
11.
Calender
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A calender is a series of hard pressure rollers used to form or smooth a sheet of material such as paper or plastic film. In a principal application, the calender is located at the end of a papermaking process. Those that are used separately from the process are also called supercalenders, the purpose of a calender is to make the paper smooth and glossy for printing and writing, as well as of a consistent thickness for capacitors that use paper as their dielectric membrane. The calender section of a paper machine consists of a calender and other equipment, the paper web is run between in order to further smooth it out, which also gives it a more uniform thickness. The pressure applied to the web by the rollers determines the finish of the paper, the first is Machine Finish, or, MF Paper and it can range from a Rough/ Matt, look to a Smooth high quality finish. The second is called a Supercalendered Finish or, MG Paper which is Glossy/ Glazed suitable for a high degree fine-screened halftone printing. A special finish such as a finish would be achieved by placing a piece of linen between the plate and the sheet of paper, or else an embossed steel roll might be used. After calendering, the web has a content of about 6%. It is wound onto a roll called a tambour, and stored for final cutting and shipping, the word calender itself is a derivation of the word κύλινδρος kylindros, the Greek word that is also the source of the word cylinder. In 1836, Edwin M. Chaffee, of the Roxbury India Rubber Company, Chaffee worked with Charles Goodyear with the intention to produce a sheet of rubber laminated to a fabric base. Calenders were also used for paper and fabrics long before later applications for thermoplastics, with the expansion of the rubber industry the design of calenders grew as well, so when PVC was introduced the machinery was already capable of processing it into film. In the past, for paper, sheets were worked on with a hammer or pressed between polished metal sheets in a press. With the continuously operating paper machine it became part of the process of rolling the paper, the pressure between the rollers, the nip pressure, can be reduced by heating the rolls and/or moistening the paper surface. This helps to keep the bulk and the stiffness of the web paper which is beneficial for its later use, modern calenders have hard heated rollers made from chilled cast iron or steel, and soft rollers coated with polymeric composites. The soft roller is slightly non-cylindrical, tapered in diameter toward both ends, to widen the working nip and distribute the pressure on the paper more evenly. A supercalender is a stack of calenders consisting of alternating steel and fiber-covered rolls through which paper is passed to increase its density and it is similar to a calender except that alternate chilled cast iron and softer rolls are used. The rolls used to supercalender uncoated paper usually consist of cast iron and highly compressed paper, while the used for coated paper are usually cast iron. The finish produced varies according to the raw material used to make the paper and the pressure exerted on it, and ranges from the highest English finish to a highly glazed surface
12.
Case-hardening
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For iron or steel with low carbon content, which has poor to no hardenability of its own, the case-hardening process involves infusing additional carbon into the surface layer. The term face hardening is used to describe this technique. Because hardened metal is more brittle than softer metal, through-hardening is not always a suitable choice for uses where the metal part is subject to certain kinds of stress. In such circumstances, case-hardening can provide a part that will not fracture, early iron smelting made use of bloomeries, which produced two layers of metal, one with a very low carbon content that is worked into wrought iron, and the rest a high carbon cast iron. Since the high carbon iron is hot short, meaning it fractures and crumbles when forged, the wrought iron, with nearly no carbon in it, was very malleable and ductile but not very hard. Case-hardening involves packing the low-carbon iron within a high in carbon. This forms a surface layer of higher carbon steel, with the carbon content gradually decreasing deeper from the surface. The resulting product combines much of the toughness of a steel core, with the hardness. This carburizing package is then heated to a high temperature but still under the point of the iron. The longer the package is held at the temperature, the deeper the carbon will diffuse into the surface. The resulting case-hardened part may show distinct surface discoloration, if the material is mixed organic matter as described above. The steel darkens significantly, and shows a pattern of black, blue and purple, caused by the various compounds formed from impurities in the bone. This oxide surface works similarly to bluing, providing a degree of corrosion resistance, case colouring refers to this pattern and is commonly encountered as a decorative finish on firearms. Case-hardened steel combines extreme hardness and extreme toughness, something which is not readily matched by homogeneous alloys, carbon itself is solid at case-hardening temperatures and so is immobile. Transport to the surface of the steel was as gaseous carbon monoxide, generated by the breakdown of the carburising compound and this takes place with pure carbon but too slowly to be workable. Although oxygen is required for this process it is re-circulated through the CO cycle, the sealing is necessary to stop the CO either leaking out or being oxidised to CO2 by excess outside air. It is a common fallacy that case-hardening was done with bone. Although bone was used, the main donor was hoof
13.
Ceramic glaze
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Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a ceramic body through firing. Glaze can serve to color, decorate or waterproof an item, glazing renders earthenware vessels suitable for holding liquids, sealing the inherent porosity of terracotta, the term we now use for basic unglazed earthenware. It also gives a tougher surface, glaze is also used on stoneware and porcelain. In addition to their functionality, glazes can form a variety of finishes, including degrees of glossy or matte finish. Glazes may also enhance the design or texture either unmodified or inscribed, carved or painted. Most pottery produced in recent centuries has been glazed, tiles are almost always glazed, and modern architectural terracotta is very often glazed architectural terra-cotta. Domestic sanitary ware is invariably glazed, as are many used in industry. The most important groups of traditional glazes, named after their main ceramic fluxing agent, are, Lead-glazed earthenware, is shiny and transparent after firing, used for about 2,000 years around the Mediterranean, in Europe and China. Tin-glazed pottery, which coats the ware with a white glaze. Known in the Ancient Near East and then important in Islamic pottery, includes faience, maiolica, majolica and Delftware. Ash glaze, important in East Asia, simply made from wood or plant ash, modern materials technology has invented new vitreous glazes that do not fall into these traditional categories. Glazes need to include a ceramic flux which functions by promoting partial liquefaction in the clay bodies, fluxes lower the high melting point of the glass formers silica, and sometimes boron trioxide. These glass former may be included in the materials, or may be drawn from the clay beneath. Raw materials of ceramic glazes generally include silica, which will be the glass former. Various metal oxides, such as sodium, potassium and calcium, alumina, often derived from clay, stiffens the molten glaze to prevent it from running off the piece. Colorants, such as oxide, copper carbonate or cobalt carbonate. Most commonly, glazes in aqueous suspension of various powdered minerals, other techniques include pouring the glaze over the piece, spraying it onto the piece with an airbrush or similar tool, or applying it directly with a brush or other tool. Small marks left by these spurs are sometimes visible on finished ware, decoration applied under the glaze on pottery is generally referred to as underglaze
14.
Cladding (metalworking)
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Cladding is the bonding together of dissimilar metals. It is different from fusion welding or gluing as a method to fasten the metals together, cladding is often achieved by extruding two metals through a die as well as pressing or rolling sheets together under high pressure. The United States Mint uses cladding to manufacture coins from different metals and this allows a cheaper metal to be used as a filler. In roll bonding, two or more layers of different metals are cleaned and passed through a pair of rollers under sufficient pressure to bond the layers. The pressure is enough to deform the metals and reduce the combined thickness of the clad material. Heat may be applied, especially when metal are not ductile enough and this is used to make heat exchangers for refrigeration equipment. In explosive welding, the pressure to bond the two layers is provided by detonation of a sheet of chemical explosive, no heat-affected zone is produced in the bond between metals. The explosion propagates across the sheet, which tends to expel impurities and oxides from between the sheets, pieces up to 4 x 16 metres can be manufactured. The process is useful for cladding metal sheets with a corrosion-resistant layer and it is often used to improve mechanical properties or increase corrosion resistance, repair worn out parts, and fabricate metal matrix composites. The powder used in laser cladding is normally of a metallic nature, the interaction of the metallic powder stream and the laser causes melting to occur, and is known as the melt pool. This is deposited onto a substrate, moving the substrate allows the pool to solidify. This is the most common technique, however some processes involve moving the assembly over a stationary substrate to produce solidified tracks. The motion of the substrate is guided by a CAD system which interpolates solid objects into a set of tracks, a great deal of research is now being concentrated on developing automatic laser cladding machines. However, many groups are focusing their attention on developing sensors to measure the process online, such sensors monitor the clads geometry, metallurgical properties, and temperature information of both the immediate melt pool and its surrounding areas. With such sensors, control strategies are being designed such that constant observation from a technician is no longer required to produce a final product, further research has been directed to forward processing where system parameters are developed around specific metallurgical properties for user defined applications. Best technique for coating any shape => increase life-time of wearing parts, most suited technique for graded material application. Low dilution between track and substrate (unlike other welding processes and strong metallurgical bond, low deformation of the substrate and small heat affected zone. High cooling rate => fine microstructure, built part is free of crack and porosity
15.
Corona treatment
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Corona treatment is a surface modification technique that uses a low temperature corona discharge plasma to impart changes in the properties of a surface. The corona plasma is generated by the application of voltage to an electrode that has a sharp tip. The plasma forms at the tip, a linear array of electrodes is often used to create a curtain of corona plasma. Materials such as plastics, cloth, or paper may be passed through the corona plasma curtain in order to change the energy of the material. All materials have an inherent surface energy, surface treatment systems are available for virtually any surface format including dimensional objects, sheets and roll goods that are handled in a web format. Corona treatment is a widely used treatment method in the plastic film, extrusion. The corona treatment was invented by the Danish engineer Verner Eisby in 1951, Verner had been asked by one of his customers if he could find a solution which would make it possible to print on plastic. Verner found that there were already a couple of ways to accomplish this, one was a gas flame method and the other was a spark generating method, both of which were crude and uncontrollable and did not produce a homogeneous product. Verner came up with the theory that a high frequency corona discharge would provide both an efficient and controllable method to treat the surface. Exhaustive experiments proved him to be correct, verners company, Vetaphone, obtained patent rights for the new corona treatment system. Although results are invisible to the eye, surface treating modifies surfaces to improve adhesion. Polyethylene, polypropylene, nylon, vinyl, PVC, PET, metalized surfaces, foils, paper and it is safe, economical, and delivers high line speed throughput. Corona treatment is suitable for the treatment of injection and blow molded parts. Corona discharge equipment consists of a power generator, a high-voltage transformer, a stationary electrode. Standard utility electrical power is converted into higher frequency power which is supplied to the treater station. The treater station applies this power through ceramic or metal electrodes over an air gap onto the material’s surface, two basic corona treater stations are used in extrusion coating applications. On a Bare Roll treater station the dielectric encapsulates the electrode, on a Covered Roll station it encapsulates the treater base roll. The treater consists of an electrode and a roll in both stations
16.
Carburizing
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The intent is to make the metal harder. Depending on the amount of time and temperature, the area can vary in carbon content. Longer carburizing times and higher temperatures increase the depth of carbon diffusion.25 inches. In some cases it serves as a remedy for undesired decarburization that happened earlier in a manufacturing process, carburization of steel involves a heat treatment of the metallic surface using a source of carbon. Carburization can be used to increase the hardness of low carbon steel. Early carburization used an application of charcoal packed around the sample to be treated. For applications where control over gas composition is desired, carburization may take place under very low pressures in a vacuum chamber. Plasma carburization is increasingly used to improve the characteristics of various metals. It also provides a treatment of components with complex geometry. The process of carburization works via the diffusion of atoms into the surface layers of a metal. If the carbon remains in solution, the steel is then heat treated to harden it. Both of these mechanisms strengthen the surface of the metal, the former by forming pearlite or martensite, both of these materials are hard and resist abrasion. Gas carburizing is normally carried out at a temperature within the range of 900 to 950 °C, in oxy-acetylene welding, a carburizing flame is one with little oxygen, which produces a sooty, lower-temperature flame. It is often used to anneal metal, making it malleable and flexible during the welding process. A main goal when producing carburized workpieces is to ensure contact between the workpiece surface and the carbon-rich elements. In gas and liquid carburizing, the workpieces are often supported in mesh baskets or suspended by wire, in pack carburizing, the workpiece and carbon are enclosed in a container to ensure that contact is maintained over as much surface area as possible. Pack carburizing containers are made of carbon steel coated with aluminum or heat-resisting nickel-chromium alloy. There are different types of elements or materials that can be used to perform this process, a few typical hardening agents include carbon monoxide gas, sodium cyanide and barium carbonate, or hardwood charcoal
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Nitriding
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Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-carbon, low-alloy steels and they are also used on medium and high-carbon steels, titanium, aluminium and molybdenum. The processes are named after the medium used to donate, the three main methods used are, gas nitriding, salt bath nitriding, and plasma nitriding. In gas nitriding the donor is a nitrogen gas, usually ammonia. When ammonia comes into contact with the work piece it dissociates into nitrogen and hydrogen. The nitrogen then diffuses onto the surface of the creating a nitride layer. This process has existed for nearly a century, though only in the last few decades has there been an effort to investigate the thermodynamics and kinetics involved. Recent developments have led to a process that can be accurately controlled, the thickness and phase constitution of the resulting nitriding layers can be selected and the process optimized for the particular properties required. The advantages of gas nitriding over the other variants are, Precise control of potential of nitrogen in the nitriding atmosphere by controlling gas flow rate of nitrogen and oxygen. Also, care must be taken when heating in the presence of oxygen to reduce the risk of explosion In salt bath nitriding the nitrogen donating medium is a salt such as cyanide salt. The salts used also donate carbon to the surface making salt bath a nitrocarburizing process. The temperature used is typical of all nitrocarburizing processes, 550–570 °C, the advantages of salt nitriding is that it achieves higher diffusion in the same period time compared to any other method. This is one of the most significant reasons the process has fallen out of favor in recent decades, in plasma nitriding, the reactivity of the nitriding media is not due to the temperature but to the gas ionized state. In this technique intense electric fields are used to generate ionized molecules of the gas around the surface to be nitrided, such highly active gas with ionized molecules is called plasma, naming the technique. The gas used for plasma nitriding is usually pure nitrogen, since no spontaneous decomposition is needed, there are hot plasmas typified by plasma jets used for metal cutting, welding, cladding or spraying. There are also cold plasmas, usually generated inside vacuum chambers, usually steels are beneficially treated with plasma nitriding. This process permits the close control of the microstructure, allowing nitriding with or without compound layer formation. Not only the performance of metal parts is enhanced, but working lifespans also increase, and so do the strain limit, for instance, mechanical properties of austenitic stainless steel like resistance to wear can be significantly augmented and the surface hardness of tool steels can be doubled
18.
Electroplating
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Electroplating is a process that uses electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode. The term is used for electrical oxidation of anions onto a solid substrate. Electroplating is primarily used to change the properties of an object. The process used in electroplating is called electrodeposition and it is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit, in one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that it comprises, at the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they plate out onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, in this manner, the ions in the electrolyte bath are continuously replenished by the anode. Other electroplating processes may use a non-consumable anode such as lead or carbon, in these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution. The most common form of electroplating is used for creating coins such as pennies, the cations associate with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, for example, for copper plating, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42− in the solution to form copper sulfate, at the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the transfer of copper from the anode source to a plate covering the cathode. The plating is most commonly a metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder, many plating baths include cyanides of other metals in addition to cyanides of the metal to be deposited. These free cyanides facilitate anode corrosion, help to maintain a constant metal ion level, additionally, non-metal chemicals such as carbonates and phosphates may be added to increase conductivity. When plating is not desired on certain areas of the substrate, typical stop-offs include tape, foil, lacquers, and waxes. The ability of a plating to cover uniformly is called throwing power, initially, a special plating deposit called a strike or flash may be used to form a very thin plating with high quality and good adherence to the substrate
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Galvanization
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Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in parts are submerged in a bath of molten zinc. Galvanizing protects the metal in three ways, It forms a coating of zinc which, when intact, prevents corrosive substances from reaching the underlying steel or iron. The zinc serves as a sacrificial anode so that if the coating is scratched. The zinc protects its base metal by corroding before iron, for better results, application of chromates over zinc is also seen as an industrial trend. The earliest known example of galvanized iron was encountered by Europeans on 17th-century Indian armor in the Royal Armouries Museum collection and it was named in English via French from the name of Italian scientist Luigi Galvani. Originally in the 19th century, the term galvanizing was used to describe the administration of electric shocks and this usage is the origin of the metaphorical use of the verb galvanize, such as to galvanize into action meaning stimulating a complacent person or group to take action. In modern usage, the term galvanizing has largely come to be associated with zinc coatings, galvanic paint, a precursor to hot-dip galvanizing, was patented by Stanislas Sorel, of Paris, in December 1837. Hot-dip galvanizing deposits a thick robust layer of iron alloys on the surface of a steel item. In the case of bodies, where additional decorative coatings of paint will be applied. The hot-dip process generally does not reduce strength on a measurable scale and this deficiency is a consideration affecting the manufacture of wire rope and other highly-stressed products. The protection provided by hot-dip galvanizing is insufficient for products that will be exposed to corrosive materials such as acids. For these applications, more expensive stainless steel is preferred, some nails made today are galvanized. Nonetheless, electroplating is used on its own for many applications because it is cheaper than hot-dip zinc coating. Another reason not to use hot-dip zinc coating is that for bolts and nuts of size M10 or smaller, the thick hot-dipped coating fills in too much of the threads, the size of crystallites in galvanized coatings is a visible and aesthetic feature, known as spangle. Visible crystallites are rare in other engineering materials, even though they are usually present, thermal diffusion galvanizing, or Sherardizing, provides a zinc diffusion coating on iron- or copper-based materials. Parts and zinc powder are tumbled in a rotating drum. Around 300 °C, zinc will diffuse into the substrate to form a zinc alloy, the advance surface preparation of the goods can be carried out by shot blasting
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Gilding
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The term gilding covers a number of decorative techniques for applying fine gold leaf or powder to solid surfaces such as wood, stone, or metal to give a thin coating of gold. A gilded object is described as gilt. Where metal is gilded, it was silver in the West, to make silver-gilt objects, but gilt-bronze is commonly used in China. Methods of gilding include hand application and glueing, chemical gilding, and electroplating, parcel-gilt objects are only gilded over part of their surfaces. This may mean that all of the inside, and none of the outside, of a chalice or similar vessel is gilded, herodotus mentions that the Egyptians gilded wood and metals, and many such objects have been excavated. Certain Ancient Greek statues of great prestige were chryselephantine, i. e. made of gold and ivory, extensive ornamental gilding was also used in the ceiling coffers of the Propylaea. But he adds that luxury advanced on them so rapidly that in very little time you see all, even private and poor people, gild the walls, vaults. Owing to the thickness of the gold leaf used in ancient gilding. Fire-gilding of metal goes back at least to the 4th century BC, in Europe, silver-gilt has always been more common than gilt-bronze, but in China the opposite has been the case. The ancient Chinese also developed the gilding of porcelain, which was taken up by the French. Modern gilding is applied to numerous and diverse surfaces and by various processes, mechanical gilding includes all the operations in which gold leaf is prepared, and the processes to mechanically attach the gold onto surfaces. The process is completed by cold burnishing, overlaying or folding or hammering on gold foil or gold leaf is the simplest and most ancient method, and is mentioned in Homers Odyssey and the Old Testament. The Ram in a Thicket of about 2600–2400 BCE from Ur uses this technique on wood, the next advances involved two simple processes. The first involves gold leaf, which is gold that is hammered or cut very thin sheets. If gilding on canvas or on wood, the surface was often first coated with gesso, gesso is a substance made of finely ground gypsum or chalk mixed with glue. Other gilding processes involved using the gold as pigment in paint, then the gold was applied in the same way as with any paint. Sometimes, after either gold-leafing or gold-painting, the artist would heat the piece enough to melt the gold slightly and these techniques remained the only alternatives for materials like wood, leather, and the vellum pages of illuminated manuscripts. Chemical gilding embraces those processes in which the gold is at some stage of chemical combination and these include, In this process the gold is obtained in a state of extremely fine division, and applied by mechanical means
21.
Knurling
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Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is cut or rolled into the material. The operation is performed for producing indentations on a part of a workpiece, Knurling allows hands or fingers to get a better grip on the knurled object than would be provided by the originally smooth metal surface. Occasionally, the pattern is a series of straight ridges or a helix of straight ridges rather than the more-usual criss-cross pattern. Knurling may also be used as a method, because a rolled-in knurled surface has raised-up areas surrounding the depressed areas. As auto parts have become less expensive, knurling has become less prevalent than it once was, Knurling can also be used when a component will be assembled into a low precision component, for example a metal pin into a plastic molding. The outer surface of the pin is knurled so that the raised detail bites into the plastic irrespective of whether the size of the hole in the plastic closely matches the diameter of the pin. Tool handles, mechanical pencils, barbell bars, and the knobs on electronic equipment are frequently knurled. Knurling is also used on the grips of darts and the footpegs of BMX bicycles, aside from adding functionality to an object, knurling also adds a decorative pattern to the material. The knurled nut is one application, which uses a knurled finish instead of hexagonal or square edges which helps in tightening or loosening the nut without the use of a tool. The knurled surfaces provide enough grip to hold the nut between the thumb and forefinger, hence it is also called a thumb nut. It is mainly used on small diameter bolts, knurled nuts are typically used in electrical components, musical instruments and in automobiles. More common than knurl cutting, knurl rolling is usually accomplished using one or more very hard rollers that contain the reverse of the pattern to be imposed. It is possible for a straight knurl to be pressed with a roller, however the material needs to be supported adequately to avoid deformation. A criss-cross pattern can be accomplished using any of, A single roller that contains the reverse of the desired pattern. The integer number of knurls for any given diameter typically varies by three repetitions from the bottom to the top of the pattern. By comparison, for cut knurls, the spacing of the cuts is not preset and these resemble pipecutters but contain knurling wheels rather than cutting wheels. Usually, three wheels are carried by the tool, two left-handed wheels and one right-handed wheel or vice versa, Annular rings Frequently used when the mating part is plastic. Rings allow for easy mating but ridges make it difficult to pull the components apart, Linear knurl Used with mating plastic pieces, the Linear Knurl allows greater torsion between components
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Paint
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Paint is any liquid, liquefiable, or mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture to objects, Paint can be made or purchased in many colors—and in many different types, such as watercolor, synthetic, etc. Paint is typically stored, sold, and applied as a liquid, in 2001 and 2004, South African archeologists reported finds in Blombos Cave of a 100, 000-year-old human-made ochre-based mixture that could have been used like paint. Further excavation in the cave resulted in the 2011 report of a complete toolkit for grinding pigments. Cave paintings drawn with red or yellow ochre, hematite, manganese oxide, ancient colored walls at Dendera, Egypt, which were exposed for years to the elements, still possess their brilliant color, as vivid as when they were painted about 2,000 years ago. The Egyptians mixed their colors with a substance, and applied them separately from each other without any blending or mixture. They appear to have used six colors, white, black, blue, red, yellow and they first covered the area entirely with white, then traced the design in black, leaving out the lights of the ground color. They used minium for red, and generally of a dark tinge, pliny mentions some painted ceilings in his day in the town of Ardea, which had been done prior to the foundation of Rome. He expresses great surprise and admiration at their freshness, after the lapse of so many centuries, Paint was made with the yolk of eggs and therefore, the substance would harden and adhere to the surface it was applied to. Pigment was made from plants, sand, and different soils, Most paints used either oil or water as a base. The process was done by hand by the painters and exposed them to lead poisoning due to the white-lead powder, in 1718, Marshall Smith invented a Machine or Engine for the Grinding of Colours in England. It is not known precisely how it operated, but it was a device that increased the efficiency of pigment grinding dramatically. By the proper onset of the Industrial Revolution, paint was being ground in steam-powered mills, interior house painting increasingly became the norm as the 19th century progressed, both for decorative reasons and because the paint was effective in preventing the walls rotting from damp. Linseed oil was also used as an inexpensive binder. In 1866, Sherwin-Williams in the United States opened as a large paint-maker and it was not until the stimulus of World War II created a shortage of linseed oil in the supply market that artificial resins, or alkyds, were invented. Cheap and easy to make, they held the color well. The vehicle is composed of the binder, or, if it is necessary to thin the binder with a diluent like solvent or water, it is the combination of binder + diluent. In this case, once the paint has dried or cured very nearly all of the diluent has evaporated, thus, an important quantity in coatings formulation is the vehicle solids, sometimes called the resin solids of the formula
