RHETORIC in DESIGN -issues for design -16

Post 653 -by Gautam Shah

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Rhetoric is the ‘art of speaking or writing effectively’. (Webster’s Definition) Aristotle describes it as ‘the ability or means of persuasion’. He describes three forms of rhetoric: Ethos (distinctive spirit of a people or an era), Logos (the logic and supportive evidence behind an argument or a reasoned discourse), and Pathos (represents an appeal to the emotions of the audience, and elicits feelings that already resides in them). Rhetoric is used in literary and verbal expressions, by using things that are familiar, but less acknowledged in common usage. In literary and verbal expressions rhetoric is exploited by construction (of the language form) and reinforced through the means of delivery such as rendering diction and graphics.

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Literary and verbal expressions generate instant and consistent impression over their audience or followers. Designed objects like arts, crafts, architecture, graphics, products, etc. however, do not carry an immediate or intense message of persuasion. A design has a persistent delivery, but very variable in content. It gets actualized in many different scenarios.

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Emotions through rhetoric ‘have specific causes and effects’ (Aristotle -book 2.1.2–3). Such dialogues however, do not exist between designers and connoisseurs. ‘Aristotle posits that along with the pathos (an appeal to the emotions of the audience), a speaker must also deploy good ethos (distinctive spirit of a people or an era) in order to establish credibility’. Philo distinguishes between two different types of logos 1 Prophorikos (the uttered word) and 2 Endiathetos (the word remaining within). In case of design-objects, the later one is relevant, as the rhetoric of design is always latent or potential.

640px-Henri_Rousseau_(French)_-_A_Centennial_of_Independence_-_Google_Art_ProjectRhetoric is means of expression or conveyance. In Literature and utterances it gets reinforced through linkages or examples, and altered through feedback from the audience. Such immediate response is not possible for Art, craft or architecture, and if any, it arrives as feed-forward in the make up (training and experience) of the creator. The design feed-forward chiefly relies on the visual rhetoric like books, site visits, media images, etc. But, it is impossible to perceive here ‘one cause to one effect pattern’. Other sensorial inputs like touch, smell, taste, aural, etc., historically had alogical legitimacy. Once a design actualizes, the feedbacks may arrive as historical realizations, but in different time and context. So designs can ‘have traceable past, but uncertain future.

Interior_of_a_revolving_space_station_(artwork)

It is often claimed that visual literacy is of recent origin, when we ignore the mediums of expression and conveyance, which have been with us since primitive age. Wall murals’ images were visual rhetoric, well ‘read’ and capable of arousing Aristotelian pathos (an appeal to the emotions of the audience). Some examples of visual means are charts, graphs, diagrams, photographs, movies, printed media, etc. but though these arouse the pathos but not always as instant response.

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Visual Literacy

The study of visual rhetoric is different from that of visual or graphic design, in that it emphasizes images as sensory expressions of cultural meaning, as opposed to purely aesthetic consideration. (Kress, Gunther, and Theo van Leeuwen. Reading Images: The Grammar of Visual Design. New York: Routledge, 1996.).

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The Design objects like architecture poses a statement only after their making, or on being used as an ‘artifact. Vitruvius stated that a work of architecture is a matter of ‘invention, arrangement, memory, delivery, and style’, and the process was perceived to be similar, to the Aristotelian way of putting together a speech. Design creation is very circumstantial, meant for a client, functions, site, regulatory framework, financial restraints, etc. It, however, needs to be tempered by arrangement, assimilation or composition of many different elements and considerations. These, together offer a holistic character, but realizable only after the creation. Rhetoric in design, if any, is in the design feed-forward, and after its avatar through the feedback. The feed back spreads over a very long period, sometimes after the original entity is destroyed. The Aristotelian depiction of Rhetoric as ‘the ability or means of persuasion’, for designed objects like architecture remains vague or conjectural.

Bidri_craft,_craftmen_at_work

The ability or means of persuasion were reasonable for artefacts conceived and made by the same person. But modern designers generate designs through surrogates or representations, and transmitted to makers or assemblers as schema or specifications. The communication through a schema is an order for execution, but certainly not for persuasion or concurrence. The instructions, if, any are non-personal and distanced in time. Some designs are too involved with the clients or stake-holders, but many others are panoptic. Designers are self-absorbed to care for persuasion or confirmation of anyone. Rhetoric exists, but as statement of non-confirmation.

Deconstruction Ways by Isidro Blasco

Design disciplines are categorized in four major domains: Graphic Design (Real and abstract -symbols communication), Products Design (objects, artefacts, craft-items), Services Design (software, interaction, stake holders) and Empathetic Design (social concerns).

McKeon, Buchanan state the understanding of design, as of symbols and images1, physical artifacts2, actions and activities3, and environments or systems4.

Architecture Confluence Lyon Deconstruction

Build-Designs are perceived at Two levels. First level consists of assembly of elements like signs, patterns, or images, and the organizational discipline. At another level, there is holistic form that is conceived without any elemental identities.

Kirtimukha_sculptures_on_shikhara_(tower)_of_Amrutesvara_temple_at_AmruthapuraThere are few characteristics common to both the congregated and totalitarian forms. Design, in part or as a whole is an allusion to something separated in time and space, and formed through analogy (comparison) or antithesis (contrast). Antiphrasis is an impressionistic expression to convey non-conventional meaning used for sarcasm. Build-forms or the constituents are given magniloquence by way of exaggerated scale, contrasts, precarious shape and intensive vibrancy.

Bilbao,_Euskal_Herria_-_panoramio_(1)

There are few features that rhetorize composite forms due to multiplicity of constituents elements. The sub-elements occur as microcosm, recurrence, as directional move, evolution-devolution and support-contrast. These rhetoric elements manifest in scaling, sequencing or within a perceptible domain of time or spatial reference.

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Design objects like architecture, fashion, products, are created for stake-holders and for personal gratification. Objects for personal gratification often result from intense desire to go out of the box as a non-conformal creative activity. This attitude, though very radical, resulting into unusual approaches and solutions, is tied to reality. All worldly creations are governed by factors like gravity, terrain and environment. Arguments of persuasion, justification or acceptance.

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Out of the Box thinking: It is believed, the term for unconventional perspective in thinking, has come from British mathematician Henry Ernest Dudeney. In this, nine dots are to be interconnected by using four lines drawn without the pencil leaving the paper. The puzzle required one to go beyond the dot array boundaries that is move out of the box.

9Dot puzzle

 

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This is the 16 th article of 20 topics series on ISSUES for DESIGN

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MEANING of CRAFTS -5 -TOOLS

Post 651 -by Gautam Shah

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Villeneuve_d'Ascq_Eté2016_Asnapio_(35)

Tools are implements used by a person in manual operations for production or processing, like manipulation materials, craft-work, building construction, cultivation, food processing, offense-defence, handling, carriage, measurement and expression (writing, drawing, enacting). Tools have been used for making better tools. Tools are for doings things in an easier manner, as well as for doings things that otherwise would not have been possible by hands. There are few conditions where instead of the tools, the supports and other facilitatory structures and arrangements help in creative efforts and productivity.

Stone Age Caveman Ancestor Hunting Neanderthal

Tools are universal implements, used over different tasks and materials. Over a time, though, an exclusive manner of handling develops. The manner of handling evolves a holding mechanism. The holding mechanism, an entity integral with the tool, allowed efficient use of the tool. The combination of a tool and its handling mechanism was a task (and material) specific facility. The tools and handling section, each served different purposes, and so were shaped accordingly. Both faced different stresses and required different composition. But a combination of diverse forms and materials need to be compatible, coordinated and well joined.

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Handled tools extend and modify the reach of the body. The extended reach helps remote access, adds to leverage and allows torque or twisting. For cutting, breaking, beating, copping and such other jobs need leverage for impact or percussive forces.

Stone Age Tomahawk Blue Archaic Close Hoe Sky

A lever amplifies an input force to provide a greater output force. The lever arm is defined as the perpendicular distance from the axis of rotation to the line of action of the force.

Recognizing objects that can work more efficiently was the first craft. Refining by reshaping natural objects for a specific purpose has been one of the oldest craft industries. Some of the basic craft tools were for food preparation, and personal safety and security. Early tools were fragile and often got consumed in the use-processes. And so, the search for new tools was everlasting, alternatively new tools had to be fashioned from old ones. Redefining the tools necessitated search for better materials, sharpening the edge, and tying a handle.

640px-Adzes_from_New_GuineaTools were now of three basic classes: hand-held tools, percussive tools and projectiles. Other sub-classes were like cutting, scrapping, hole making, vessels, holding, measuring, coating-spreading, digging, mixing, etc.

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Primary tool materials were stones, woods, bones, clays and perhaps metals. Some of these could be re-formed by downsizing. Clay and metals were plastic materials that could be re-formed by moulding and additive process.

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Holding tools became important for two main purposes, to hold fine-sized objects and tools and to hold fire or hot things. Fine items like beads, and precious-stones need to be held properly to work upon them. Tool bits like fine and fragile edges need support, whereas fine points for drilling and engravings require adequate gripping. Tools were required to initiate, and work with fire. These included fire-fuel management utilities (chulhas), air blowers, handle for hot tools and holders for vessels. Agriculture related tools like thresher boards, winnowing baskets, sieves, land tillers, etc. Spinning, knitting, and weaving utilities developed for threads and cordage, which were used for binding handles, roof and wall elements, fishing nets, etc.

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Tools, as said earlier, are handy things. But there are many utilities, facilitatory structures and arrangements that have helped creative efforts and productivity. In these, at certain level of detail tools like appendages or similar advantages are invested. One of the first ones was the fireplace that contained the fire, helped efficient use of the fuel and offered resting stands for things to be heated. Similarly structures were created as dwelling spaces, clothes or apparel, shoes, head caps, adornments, toys, totems, murals, shutter systems over openings, hangers for food to protect it from insects and rodents, sleeping mats, hammocks and cradles, lamps that evolved less heat but more light, food grinding stones, narrow neck pitchers for liquid storage, slide for transporting goods, etc.

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At some level the tools, utilities, facilitatory structures and arrangements were merged as devices, machines, apparatuses, equipments or plants. These were integrated with the built-forms, for support, location-based advantage or task setting. The tool, craft and technology were one seamless pursuit. The pursuit also integrated several materials into not only single purpose entities but very specialized task facilities. The task related specializations also created technology-based castes, guilds and communities. The craft communities are tied to terrains and climates. This allows them to develop acutely ethnic styles.

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COPPER -1

Post 477 –by Gautam Shah

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Pure copper nodule 40 mm across

Copper resources of the world are estimated at nearly 5.8 trillion pounds. Of these only about 0.7 trillion pounds have been mined to date. The recycling and recovery rates of copper are so high that of nearly all of the copper mined throughout history, is still in circulation today. This means nearly 80 % of all copper ever mined is still in use today.

Malachite, Zaire> Uploaded by JJ Harrison

Copper was discovered by prehistoric man, in search of shiny stones that when beaten did not break down but rather flattened out. This was sensational discovery leading to search of shiny nodules across lands. Pure Gold and Copper nodules were forged into items of adornments and tools. It was known that several nodules of such pure metals could be forged to form a larger piece. Such nodule findings were rare. But two forms of copper carbonates greenish malachite and bluish azurite were easy to identify and collect from the grounds. Malachite was also used as a gemstone. Similarly many other bright minerals were identified.

Neoclassical vase in malachite in the Hermitage Museum, St Petersburg Uploaded by Dezidor

Azurite 80 x 60 mm Azuritechessy.jpg Uploaded by Archaeodontosaurus

Copper was known around 10000 BC or even earlier. Earliest copper object, a pendant dating 8700 BC, was found Iraq. Copper, in natural nodules form, remained a prized material for a while, but soon became a metal of utility. Unalloyed copper is soft for tools and weapons, but fairly suitable for shaping of utensils. Mesopotamia and Egypt exploited copper for creating tools used in farming, wood working, cooking, etc. These were hoes, adzes, saws, combs , pots, dishes, chisels, harpoons, cloak-pins etc. By 6000 BC it was realized that, although copper was not amenable to casting, it could be worked by hammering, chasing, engraving, and cold-rolling. Sumerians used copper sheets to form sculptures over wooden forms and fastened on walls with copper nails or wires set in bitumen.

Imdugud (also Zu or Anzu), the lion-headed eagle; Sumerian metalwork (sheets of copper), Temple of Ninhursag at Tell al-‘Ubaid; ca. 2500 BC

The Roman supply of copper almost entirely came from Cyprus, and so was known as metal of Cyprus, shortened to cyprium, later corrupted to cuprum. Copper is found at many locations as a primary mineral in basaltic lavas and also as reduced form of copper compounds. It occurs in combination with many minerals, such as chalcocite, chalcopyrite, bornite, cuprite, malachite, and azurite. It is an extremely ductile and malleable metal with high tensile strength. It is an excellent conductor of heat and electric. It is a very noble metal and by acting as a cathode can corrode other contagious metals except stainless steel. It is resistant to most acids and sea water.

Bronze decoration

A Copper alloy with tin is known as bronze. Bronze is a stronger alloy, and harder than both the pure metals. Bronze can be cast. A copper with zinc is called Brass. It was also known that by hammering the copper became hardened, ideal for creation hard edged tools. Copper and its alloys, bronze and brass, mark the first science revolution of man. However, relative scarcity of tin in many regions of the world did not allow use Bronze equally everywhere. Tin-based bronzes were preferred due to the hazard of arsenic poisoning from fumes produced by the oxidation of arsenic-containing minerals. Copper-arsenic alloys, of superior properties to copper in both cast and wrought form, were produced in many regions. Arsenic contents varied from 1 to 7 percent, with up to 3 percent tin. In many civilizations the production of pure copper, arsenical copper, and tin bronze continued together for some time.

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ART COATINGS

Post 432 – by Gautam Shah

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Lascaux2

Coatings are thin surface finishing techniques. A thin film is achieved by using a material that is in a liquid state or is convertible into a liquid phase. A coating may or may not have a colourant, but on drying achieves various degrees of transparencies. Coatings are applied to entities to alter the appearance, improve the tangibility and to provide a protective cover. Historically, however, coatings have been used for illustration and decorative effects.

The discovery of mixing dishes suggests that liquid pigment mixed with fat was also used and smeared with the hand. The subtle tonal gradations of colour on animals painted in the Altamira and Lascaux caves appear to have been dabbed in two stages with fur pads, natural variations on the rock surface were exploited to create the effects of volume.

Sleeping_Antelope_Tin_Taghirt

The simplest way of marking cave walls was to make finger-traces in the soft layer of clay covering the rock. Lime stone walls were engraved and filled in with iron oxide (hematite, or ochre), or the black pigment as manganese or charcoal. These materials were usually available locally. Analyses of pigments, reveal the use of extenders such as talc or feldspar, to increase the bulk of pigments. It also shows traces of animal and plant oils, used for binding. The pigment in paste form was applied with fingers, and also tools like animal-hair brushes or crushed twigs. Lumps of pigment discovered on cave floors may have been used as crayons, but since they do not mark the rock well, they were more likely to be sources of powder. Colour was often sprayed, from the mouth or through a tube. A network of ladder, supports and scaffolding was used to reach the ceilings and upper portions of walls. Light was provided by hearths, or portable burning torches.

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Primitive coatings were daubing of clays, minerals, charcoal, lamp blacks often mixed with mediums such as water, tallow, vegetable excretion and juices, urine, blood, bitumen. Binding mediums were employed to fix the mineral or colourant particles on the surface. Some of the binding mediums were evaporative and worked only as a `leveller’ for particulate matter. By 6000 BC, in China, calcined (fired) mixtures of inorganic compounds and organic pigments and binding mediums (vehicles) were prepared from gum arabic, egg white, gelatin, and beeswax.

Some oily mediums though superior in fixing and longer lasting, but collected dust on aging. Oil mediums became darker in colour due to oxidation, or just peeled off. Some of the mediums were destroyed due to fungus and algae. Later little more complex substances such as starches of rice and maize, pine wood extracts, egg albumin, bees wax, hydrated limes, gypsum, etc. were used.

PREHISTORIC ART FORMS

There are basic TWO sets of Arts. Fixed arts are built-forms, wall murals and architectural embellishments. These could have been part of either exterior and interior environments. Portable arts, comprise of objects or artefacts. These usually remained in protected environments. Fixed arts were largely painted and scratched or engraved, but portable arts had, at least in initial periods, natural finishes by way of selection and production processes.

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Portable arts consist of wide variety of object forms and material combinations. Compared to the fixed Arts the objects are smaller in size. The portable objects show all, the surface treatments, embellishments and coating applications. The objects of this category show greater integration of all the three interventions and greater detail or involvement. Large number and wide variety of objects have been preserved and recovered even from regions where Fixed Arts entities have not survived. Portable arts’ objects are smaller and personal hobby or a family craft creation. The colour and surface quality were matter of choice or discoveries through innovation in production.

Paulnabrone

Fixed Arts entities that have survived are surface treatments or renderings through show painting, scratching, engraving and daubing methods. On the other hand, the surviving built-forms, if considered as art-forms, represent technological milestones of material handling, supporting and construction planning. Fixed arts were large scale or important societal activities, involving entire community by way of voluntary participation or forced labour. The involvement of the community was for seasonal or occasional rituals. The leader, conductor or priest of the ritual and the team were the select few experts who initiated and updated the (art) entities over and over again. Such art-forms indicate occupation or interventions of several generations, as much as for more than 300 years.

Bradshaw rock paintings

Portable Art objects are incidental that is the availability, shape, size, colours, texture, etc. define the range of treatments. Many times the purpose it will serve evolves during the process of treatments. Such objects show material combinations. many different finishes were achieved, by change of forms and exploiting the tools. Material processes like heating, singeing, sintering, baking, beating, shaping, cutting, chopping, grinding, drilling, etc., were also used in farming and cooking. It was one seamless manner of learning.

Venus_of_Brassempouy

The materials were stones, precious stones, metal nodules, mineral and other colourants, woods, grasses, twigs, hides, leathers, skins, furs, hairs, shells, teeth, horns, bones, ivory, raw clay objects, baked clay ceramics, seeds, fruits, etc.

The objects formed were totems, body adornments, tools, implements, ritual and burial objects, cooking utilities, toys for children, amenities and dwelling embellishments.

Collier_de_Penne

These were exchanged, gifted to others or offered in rituals. The objects began to have consistent expressions. The varied metaphors, passing from one generation to other, ultimately became abstract. Coins, plaques, seals, etc. represent multiple conversions of expressions like a language.

Ggantija_Temples,_Xaghra,_Gozo

Fixed Art objects like built-forms, though functional utilities were built for community and for political purposes.

The public use entities were irrigation facilities, forest clearance, dykes, bridges, walks or passages, drinking water resources, community surround structures, security amenities and storage arrangements. These were not ‘decorative arts’ but symbolized technological innovations. Some like burial stones and dolmen had items of personalization.

Cave_Paintings_Bhembetika_(22)e

Fixed Arts objects like wall arts show skills of surface preparation, rendering or painting and surface finishing. These creations also show art of surface preparation by way of grinding, etching, daubing, engraving and colourant application. Wall-arts exist in odd narrow corners, at very high elevations, tall ceilings, day time dark corners and in nearly inaccessible places. The effort must have required support structures, bridges, scaffolds, illumination and ancillary works to protect the creations from moisture.

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WOOD RESOURCES

Post 217 – by Gautam Shah 

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Wood’s appearance, warmth to touch, its ability to be worked with simple inexpensive tools, wide range of tonal hues, grain patterns and textures make it, the most versatile craft material. The only drawback for using wood, is the effect of moisture on its structural properties and its susceptibility to decay. No two pieces of timber are similar, the great variations in structural properties, colour, texture etc., make it suitable for different uses. These wide variations in a quality put the timber to a disadvantage in comparison to many naturally available materials.

Wood products

Wood products

Wood products

Wood products

Trees can be basically classified into two groups – exogenous trees (exogens) and endogenous trees (endogens).

  • Trees may be broadly grouped into exogenous and endogenous trees according to the way in which their stem diameter increases.
  • Endogenous: are trees with inward growth, and have longitudinal fibres such as canes, bamboo, palms etc. Typically it is not possible to see any growth rings in this set of trees.
  • Exogenous: are trees with outward growth (such as additions of annual-seasonal rings), like Conifers (narrow leaves) (pine, fir), Deciduous trees (broad leaves) (teak, rose). These are used as engineering timbers.
Exogenous conifer

Exogenous conifer

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Endogenous plant Bamboo

Endogenous plant Bamboo

Exogenous plants as the name suggests grow outward. The stems are formed by successive additional layer on outside. Timber is essentially derived by the new mass formed in the cambium between the wood and the bark every year. Trees of cold climates and substantial numbers trees of warmer climates are exogenous. Rings in the trunk or branch section, and pith with medullary rays extending outwards to the bark are two distinguishing features of exogenous trees. Exogens yield timber for furniture and construction. Exogenous trees are subdivided into two main classes: broad-leaved trees and needle-leaved trees, or conifers. Broad-leaved Woods generally contain no resins, and the density or weight is greater. They are usually hard, and due to their irregular structure, net yield is lower.

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The other botanical group of endogenous trees or endogens or grow inward from a hard exterior shell or, more commonly, end-wise by the acquisition of a new joint. Endogenous trees grow by forming new fibres within the trunk interspersed with the old fibres. Old endogenous stems have older and harder wood near the surface, whereas younger and softer centre. Timber from these trees has very limited engineering applications. Examples of endogenous trees are Palms, bamboos, canes, etc. These are not broadly useful for furniture or construction work, yet have their specific advantages and uses.

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640px-Thonet_chairs_Wien_museum_Karlplatz

Commercial timbers of exogenous trees are classified as softwoods and hardwoods, though a very misleading nomenclature. Softwoods are timbers obtained from conifers, growing above certain altitude, and are supposed to be soft and lighter in colour. Hardwoods, are timbers that originate from the mainland and tropical areas are supposed to be hard and darker in colour. Many softwoods, though, are much harder and often of darker in shades than some of the hardwoods. Inversely many hardwoods are fairly soft and lighter in colour than some of the softwoods. Botanical names and commercial names of trees or timbers do not provide a true picture. There are multiple botanical names for the same specie adding to the confusion. Same timber is likely to be differently known commercially in various parts of the world.

Thanjavur_Palace'

Thanjavur Palace India

Timber is a very precious commodity. It takes decades to grow a commercially viable timber tree. Deforestation has become a prime issue from ecological points of view. Several countries have banned or severely curtailed and controlled the export of timber. Similarly many countries have banned import of timber to limit deforestation world wide. Many governments and local authorities discourage timber structures and other uses of timber. Government of India has enforced conditions, so that usage of timber as doors and windows and other structural purposes are nearly banned, in government schemes. Similar conditions are likely to be followed by state governments also. So over the years use of timber is likely to be severely curtailed not only due to legislation but also its difficult availability and consequent upward pricing.

Wood products

Wood Composite products

Timber grown in planned plantations is of consistent variety due to standard or a singular source of seedling or genetic derivation and grown in very controlled conditions. These results in trees with identical grain, colour and texture, belying the natural variations associated with woods.

wicker-furniture

Wood replacement products are of broadly two types. Wood-based composites such as plywood, block boards, chip and particle boards are likely to remain available, but only for a while. The availability of such products is also going to taper off in future. Wood ‘look-a-like’, make-believe, or pseudo wood products made of polymeric composites, painted, printed or layered materials are in the market.

Unlike a metal or plastic, wood is inherently a replenish-able resource, provided production and use are controlled and matched.

 

 

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METAL WORKING Processes

Post 151 -by Gautam Shah

Metals in cold and hot state can be deformed into useful shapes. The shape, function, and appearance of metal objects are largely determined by the type of metal used. Precious metals like the gold and silver is comparatively softer to work with, whereas base metals such as the copper, tin, lead, and iron and their alloys like bronze, brass, and pewter may differ widely in their characteristics.

Chinese metal working

The surface quality of a metal begins to emerge during the conversion processes like casting, forging or rolling. Even when some of the processes are cold working, there is a rise in temperature that affects the quality of the surface. In hot conversion processes the reheating conditions, in-line scale removal, rolling temperature, and cooling rate, all determine the surface quality of the product. All these also affect the atmospheric corrosion, paint-ability, and many other subsequent operations. Sometimes the final pass in hot-rolling generates specific surface patterns, such as with the protrusions on reinforcing bars or checkers on floor plates, ribs. In cold-rolling a specific surface, roughness is rolled into the strip at the tempering-mill to improve the deep-drawing operation, and to assure a good surface finish over the final product.

988px-Casting_pig_iron,_Iroquois_smelter,_Chicago

Literally hundreds of metalworking processes have been developed for specific purposes, but these can be divided into SIX broad groups: Casting, Rolling, Extrusion, Drawing, Forging, and Sheet-metal forming. The first five processes subject a metal to large amounts of strain. However, if deformation occurs at a sufficiently high temperature, the metal will re-crystallize, that is, its deformed grains will be consumed by the growth of a set of new, strain-free grains. For this reason, a metal is usually rolled, extruded, drawn, forged above its re-crystallization temperature. This is called hot working, and under these conditions there is virtually no limit to the compressive plastic strain to which the metal can be subjected. Other processes are performed below the re-crystallization temperature. These are called cold working. Cold working hardens metal and makes the part stronger. However, there is a definite limit to the strain that can be put into a cold part before it cracks.

Arts and Crafts Center

Frequent heating and graduated cooling anneal the metal mass more ductile or softer. Similarly sudden cooling by quenching in oil or water, causes the surface to cool much faster then the inner or core mass. This makes a surface of metal objects harder. Annealed and surface hardened materials have not only different structural properties but also have special surface qualities, (e.g. colour, hardness, etc.).

Surface Hardened parts

Metal grains or crystals are far from perfect. Due to the imperfect structure, metals are capable of taking shock loads and reversal of stress, unlike non metal compounds which have very regular crystal structure. When metals, such as steel is used at high temperatures and under uninterrupted stress as in case of boilers, jet engines, power house turbines, hot discharge nozzles, they yield very slowly, stretch, and eventually fracture. Metal components, which under go stress reversals very frequently, fail due to fatigue. These are more pronounced in bridges, crankshafts, etc.

Forging

 Metals are heated and cooled, without reaching to a melting stage, to provide hardening, strengthening, softening, improved formability, improved machinability, stress relief and improved dimensional stability. These thermo mechanical processes are known as annealing, normalizing, stress relief anneals, quench hardening, tempering, nitriding, martempering, austempering, carburizing, solution anneal, ageing, etc. All metals and alloys in common use are heat treated at some stage during processing. Iron alloys, however respond to heat treatment in a unique way because of the multitude of phase changes which can be induced.

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