SURFACE LEVELLING

Post 291 — by Gautam Shah

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Surface-levelling is a major category of surface finishing technologies. Surface-levelling is done by THREE major systems, 1 Removal of excess material, 2 Deposition of additional material, and 3 Refashioning the surface sections.

REMOVAL OF EXCESS MATERIAL

To remove the excess material surfaces are re-cut, ground and polished. Stone surfaces are chiselled or axed to level out the surface and to remove the weathered crust. Freshly mined and weathered stones are re-cut or chiselled to expose a fresh surface. Rough cut or split (sedimentary) stones are spliced into two, by a smooth saw cut. Leather surfaces are shaved for thinning and to remove the surface hair. Leathers are split to make uppers and soles. The palm leaves are shaved to remove the stems and make them smoother for writing. Barks of the trees are removed by axes and choppers. Timbers are re-cut or planned with finer tools to achieve a smoother surface. Timbers are split very finely to create veneers.

Grinding and Polishing, are the two finer processes for surface-levelling of hard materials such as building stones, metals, glass, and precious and semiprecious gems, ivory, bones, leathers, timbers, pottery products, cement concrete and other cement products. Hard materials such as marble and granite, take a high gloss, whereas others like sand stones, are too coarse-grained to be polished, and can only be smoothed to a granular finish. Surface-levelling is done by sharp tools that chip away very thin section off the surface.

Grinding is done by rubbing down with a graded series of coarse and fine abrasives, such as Carborundum, sandstone, emery, pumice, and whiting. Grinding wheels usually consist of particles of a synthetic abrasive, such as silicon carbide or aluminium oxide, mixed with a vitrified or resinoid bonding material. Grinding can be coarse or fine, depending on the size of the grit used in the grinding wheel. Polishing uses extremely fine abrasive substances, such as jewellers’ rouge, Tripoli, whiting, putty powder, and emery dust, to rub or burnish an extremely smooth and glossy finish on the surface of a material. Metal and glass can be ground to a mirror finish. Polishing is done by tumbling and vibratory mass-finishing media, sandblasting, pulp-stones, ball-mills etc. The polishing materials are coated on the surface of cloth, felt, or leather wheels. One special type of polishing wheel is made of soft rubber or plastics with the abrasive grains moulded into it.

Honing and Lapping, are used for very fine level of polishing by material removal process. Honing improves the accuracy and finish of motor car cylinder bores, hydraulic cylinders, and similar parts. There are four types of precision grinding machines: Center-type grinders, Center-less grinders, Internal grinders, and Surface or flat bench grinders.

Other processes include singeing, washing, bleaching, etching, etc. Textiles, paper leather, leaves, wood, etc. are some of the materials that can be singed. High temperature singeing removes surface fibres or hair, de-oxidize impurities and in case of metal harden the surface. Synthetic or composite textiles are selectively or locally singed to fuse the fibres or filaments, and create transparency, opacity, etc. Wood surfaces on sintered create a dehydrated, old shrivelled, or shrunk surface similar to an old wood. Metal surfaces also burnt to harden the top surface and to remove oily residues, dehydrate, and descale the surface. Reverse of metal plating process removes the surface molecules to achieve matt finish.

DEPOSITION OF MATERIALS

Deposition of material could be casing, cladding, layering, or lamination, lapping, molecular deposition and coating. Cladding is common in masonry work for a new surface, insulation, water proofing, etc. Casing is done to metal structures for rust inhibition, static discharge and fire protection. Layering or lamination is common in composite formation through co-extrusion processes. Molecular deposition of metal compounds or ceramic forming (non-metal) materials achieve a very thin body deposition. Polyester metalized films offer solar radiation cut-off. Metal plating through anodic transfer also creates very thin body layering. Metal deposition over plastics, ceramics and filaments provide dual qualities. Coating is very vital field of material addition. Coatings are applied in a liquid phase or get converted to it at the time of application (such as in case of powder coatings). Coating deposition is aided by electrical charge, pressure or spluttering. Many of the surface addition processes are intermediary treatments for the next lot of surface treatments. Alkaline or acidic washes or solvent wetting leaves substances that are beneficial for other subsequent applications. In medical field skins, tissues and muscles are planted to encourage fresh growth.

REFASHIONING THE SURFACE SECTIONS

The most important treatments in these sections are annealing and hardening. Heat treatment followed by controlled cooling changes the molecular arrangements within the entire body or surface sections. In case of polymers, chain linking alters the quality of materials. Textiles become de-creased or creased on pressurized with heat treatment. Burnishing of a metal surface achieves a smoother surface, through hard pressing up to yield-point. Woods, papers and Fabrics are burnished to achieve a compacted mass. Surfaces are refashioned by pressing or embossing textures and patterns.

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SPRAYING

Post 290 – by Gautam Shah

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Spraying is a method of throwing or projecting atomized liquid by adding several times more volume of gas. Spraying was known to primitive humans as a way of adding air to water for gurgling the mouth, and to project it to a defined place with pressure. The technique was useful to ignite as well as douse the fires, with respectively, oil or water.

Hand Prints by mouth spray -Primitive art

Spraying involves two processes, first atomization of liquid with a gas and secondly pushing through an orifice to exert pressure. The mouth with closing in lips, and caved or hollowed tongue formed a dynamic orifice, whereas the pressure was caused by breathed air. Primitive atomization was also caused by blowing air over a thin body of liquid. Vibrating bristles or shaking fingers dipped with liquid, also causes, the spread.

Spraying was used for many purposes. Oils were sprayed over fires and cooking foods. Colours were sprayed over body, ceramics, leather and clay floors. Colours were sprayed to achieve even mass tones and diffused edge effects. Colours were sprayed within marked boundaries or stencils.

Spraying with bristles

Stencil Printing

One of the simplest ink spraying tool was an L bent tube, with a small aperture on the outer curve. The tube was thin enough to allow liquid to rise through capillary action, and the other tube was used to blow air. The blown air spayed the rising up liquid. A similar process is used in old style home-use insecticide pumps.

L tube spraying from ink bottle

A varied form of L tube spraying -home insecticide pump

Spraying is used to create instant cooling and spread of oily substances (as carried with water or other solvents or through emulsification). Scents and medicines are sprayed to provide instant effect over a large area. Asthma sprays reach deep sections of throat to provide relief. Skin sprays create a thin coating over bleeding wound or painful muscle.

In India during the colour festival of Holi, coloured water is sprayed with a nozzle drum pump. This simple device is now being replaced with multi nozzle plastic guns. Home bath showers and garden sprinklers distribute the water into very fine strands or droplets.

Textile plants cotton spinning and weaving sections require high level of humidity. Similarly in very cold weather, chances of humidity being stripped out of the indoor air are very high. This requires addition of moisture in the air. Operation theaters need to be sterilized with formaldehyde vapour. All these spaces use water atomization technology.

Ultrasonic Humidifier

Mist creators

Spraying mechanisms are used in industrial burners and automobile combustion engines. By spraying fuels in burners, larger volume of oxygen is made available, which in turn minimizes the pollutants. Hot water spraying with heavy pressure is used for cleaning-washing without using any detergents or chemicals in many sensitive production areas like foods and pharmaceuticals. Water-sprays are used in chimney stacks to remove particulate and dissoluble matters. One of the most important uses of spray technology is in agriculture. Spray applications in agriculture include spread of herbicides, insecticides, pesticides and fertilizers.

Aerosol spray cans have become part of our life. These are used for spraying fluids like scents, deodorants, paints, waxes, hair-oils, whipped creams, food dressings, chemicals, medicines etc. These cans or packs have some form of propellant, ‘a general name for liquid chemicals that can readily be vaporized and so used for creating thrust or pressure. In 1939, American Julian S. Kahn received a patent for a disposable spray can, but its commercial success came much later.

It was found that chlorofluorocarbons (CFCs), used as propellants in aerosol sprays, depletes of Earth’s ozone layer. These were sought to be replaced with mixtures of volatile hydrocarbons, such as propane, n-butane and isobutane. Di-methyl and Methyl ethers. These replacement materials have a disadvantage of being flammable. Nitrous oxide and Carbon dioxide are also used as propellants to deliver foodstuffs (e.g. whipped cream, food dressings). Medicinal asthma inhalers use hydrofluoroalkanes (HFA).

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RAMPS

Post 289 – by Gautam Shah

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Ramps are inclined passages for smooth transfer people, vehicles and goods between elevations. Ramps have a pitch lower than stairs, and are physically easier to ascend or descend than stairs. Ramps occupy more floor space compared to any other gravity transfer system.

Ramps require less force than lifting a load straight up though at an increase in the distance moved. An inclined plane allows the same work to be done with a smaller force exerted over a greater distance. A ramp is an inclined plane, one of the six classical simple machines defined by Renaissance scientists. Inclined planes have been used to move up an object along its inclined plane or by for lifting loads straight up from wells and mines. Indian leather water bags (mashaq) were pulled up by bullocks moving down a ramp.

Inclined slopes as simple machines have been used in many different conditions. A wedge is an inclined machine. A screw, is an inclined narrow spiral wrapped around a cylinder. Inclined planes have been used by people since prehistoric times to move heavy objects. Heavy stones used in Stonehenge or Dolmens were set in place with inclined planes made of earth. Egyptian pyramids, Ziggurats and Inca temples were constructed with inclined planes. Greeks constructed Diolkos, a paved ramp 6 km long, to drag ships overland across the Isthmus of Corinth. Ramps have been used to move heavy guns to fortification tops, to negotiate hills and mountains, and to draw water from wells and minerals from deep mines.

Ramps have been used to move a mass of people in public buildings and places. Ramps have been used by Le Corbusier as an indicative of democracy and ceremony. Ramps are used in place of stairs or steps. Wheeled items like trolleys, perambulators, chairs, vehicles are easy to move on ramps than stairs.

Inclined slopes, using the Earth or soil’s capacity to remain stable in inclined form has been used for constructing causeways. The stable angle of friction or angle of repose, is the maximum angle at which a soil mass remains stable and ‘at which loads can rest motionless on an inclined plane due to friction, without sliding down’.

Ramps when steeper than 10 %, require a non slip flooring and a grip-able handrail. Ideal pitch for a ramp is below 8.33 % (1:12), however most codes accept pitches up to 16.66 %, some labour laws allow 25 % pitch for very short runs (2mts). Ramps for wheel chair users and patient trolleys should not be steeper than 5 % (1:20). Length of a ramp must not be more than 6 mts, after which a break in gradient in the form of a level landings or rests should be at least 1650 long. Straight line layout of multiple ramp units (even with adequate provision of mid landings, must be avoided, instead a secondary ramp unit at right angle or U turn is advisable. For physically normal users, a ramp, per lap lengths of maximum 25 mts or 2 mts climb, are ideal. Width requirements: for single lane traffic 750 mm, furniture passage 900 mm, for drama or cinema aisles minimum 900 mm, increasing 35 mm for every 1500 mm of run.

Continuous ramps tend to accelerate the movement speed in descent and so become hazardous. Multi-directional ramps require additional elements to cut-off descent speeds at the change junctions. Circular ramps generate concentric force during rapid descents. Circular ramps of clock-wise or counter-clock movement have relevance (if any) in either the decent or accent.

Ramps are negotiable by wheel-chaired patients, as assistive devices for mobility, if they can break-retard the speed during decent, or have muscle power to turn the wheel for accent. Alternatively some assistance is needed for both.  Long ramps (even with mid breaks or rests), or a stack of multiple ‘flights’ are not advisable. It is cheaper and far efficient to install-operate elevators, or moving walkways.

Factors that define the utility of a ramp are: Texture of the floor, gripping power of the handrail, height of the handrail, distance between two handrails (in narrow ramps), configurations of the ramp structure, angle, movement to ascend/ descend, age profile of the users, orthopaedic functionality of the user, etc. It is very difficult and hazardous to move on a ramp with any type of hand, shoulder or head loads (railway porters), as the weight disturbs the nominal centre of gravity of the body. This is the reason why people stoop forward while climbing up steep slopes, and backward while moving down a ramp slope.

Ramps along with steps provide a dual system, however to match the gradient of the ramp, such steps have a wide tread and very low height riser, making them very difficult to use. In hospital areas such steps between or on one, or both sides of the ramp help the person to push the chair or trolley up or down the slope with better control. The same configuration is used in industrial warehouses to move large barrels or wheeled items. Ramp and stair combination is also used in inclined elevators often called a funicular railway. The slope accommodates the rails or the guides of the inclined elevator and the steps are used by the service personnel. Here the gradient is usually very acute so the tread is very narrow while the riser very tall.

Parabolic ramps are used in places like Amusement parks, water games parks etc. A parabola has two sets of inclinations. The short radius curvature of the parabola, if at the lower end, helps in retarding the speed of descent, while the larger curvature of the parabola, if at the lower part, the initial acceleration gets a sudden boost at the end. This later version is very hazardous, and is used if only sufficient fore space or speed absorption mechanism (sand pit, water pool) is provided for beyond the parabola. Ice-skating tournaments where a skater needs very high speed start to accomplish the required twists, turns, lump before landing, have such slopes. A roller coaster rides makes extensive use of ramps structures to create very intensive centripetal and centrifugal forces with high accelerated speeds that almost defy the gravity. Cycling Velodrome uses double curvature ramps.

Inclined planes are widely used in the form of loading ramps to load and unload goods on trucks, ships, and planes. Wheelchair ramps are used to allow people in wheelchairs to get over vertical obstacles without exceeding their strength. Escalators and slanted conveyor belts are also forms of inclined planes. Aircraft slides and fire evacuation tubes allow people to rapidly and safely reach the ground.

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BURNISHING

Post 288 – by Gautam Shah

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Burnishing is a surface material finishing process. It polishes and hardens the surface, so that the endowed finish lasts longer. Surfaces that depend on the smoothness for reduced friction, and take lots of wear, need to be burnished. A burnishing rubs the rough surface texture and makes it shinier, but it is not intended as a polishing process. Polishing removes all excess (protruding) materials to level out the surface, whereas Burnishing removes minimum surface material and hardens the surface. It is true that a well polished or a smooth surface takes better burnishing.

Burnishing and Peening, are two most popular cold-work finishing operations. These are post-machining operations for improving the surface roughness, hardness, wear resistance, load-bearing characteristics, fatigue strength and resistance to corrosion. Burnishing machines press rollers or balls against a surface to mechanically deform and refine surface finishes. Burnishing and peening, are used for bearings, rotating shafts and turbine blades. Burnishing redefines micro sizing like the tolerances and geometry like quality of roundness.

Burnishing is mainly a Metal surface alteration process. It is used in various versions for Ceramics, Wood, Leather Paper Cement, Textiles and Artwork. Burnishing occurs on a surface, where another surface sliding on it creates a contact stress which locally exceeds the yield strength of the material. It induces plastic deformation of the surface component, hardens the surface by generating compressive stresses.

Burnishing is not always desirable process for all metal items. It affects the behaviour quality of the surface significantly and often unpredictably. A burnished face, visually seems smoother but with repeated sliding marks grooves over the surface in the sliding direction. Heavy burnishing forces separation of top layer causing peeling of it. Burnishing generates heat which is greater than rubbing or polishing. This excess heat deforms thin body parts. A part deformed due to heavy burnishing, takes greater friction, creating a ‘runaway’ situation where the part fails.

Ceramics burnishing are a treatment in which the green mass of the pot (before drying for baking) is polished and compressed. Compressing the mass and allows excess water to come to the surface, increases the density of the mass and provides a glossy surface. Burnishing is also done after coating the raw item with the slip. As part of surface compaction, sometimes patterns are embossed on the surface. Hard smooth surfaces like wood, bone, glass, metal, or ceramics are rubbed on the surface.

Wood Burnishing is done by rubbing hard grained wood piece along the surface of the wood. Burnishing generates heat, to dry out the surface, melt and fuse the resinous substances or additive substances such as oils, wax etc. Burnished surfaces retain the natural feel (grain and colour) of the wood, and is more natural looking then any coating treatment. Lacquer coated woods are burnished with wool fabrics to gain a natural sheen. Sometimes rubbing compounds that have very fine abrasive grains, wax, oils, lubricants like silicone oil and colouring dyes are used.

Leather Burnishing is used for top and under surfaces as well as edges of leather products. Hard wood pieces are rubbed over leather with or without rubbing materials like oil or wax to achieve a compressed mass and glossy face. The heat also facilitates penetration of rubbing material. The process is also conducted at leather sheet and product formation level. At a leather sheet level-heated roller with pattern compresses the leather. A process, reverse of burnishing is done to produce suede surfaces.

Paper Burnishing is a post paper forming process. It is done to compact the grain-mass and provide sheen, by heavy calendaring. Calendaring is accompanied by bodying with starch, minerals or resins. It is done to emboss textures or patterns. Photographic mount-boards have such ingrained textures.

Cement Burnishing is done to plasters and cast concrete surfaces. Cement plasters are re-trovelled after the initial setting of the cement. Trowels of wood or metal sheets are rubbed to compress the mass, bring the excess water to the surface and polish it. In case of Tri-mix concrete floors, post setting vibration compacts the surface bringing out the excess water, which is than suctioned out.

Textile Burnishing is a fabric finishing and texturizing process. Fabrics are hot pressed and passed through rollers. Sized and chemical treated fabrics get a sheen and smoother surface. Fabrics are singed during the process to burn standing or loose fibres and to compact the mass. Shrinking also reduces the mass.

Art-Work Burnishing involves applying colours and than rubbing them to level the surface. Frescoes =applying colours on fresh;y coated plaster, uses burnishing for two purposes 1, to press-in the surface with pigments in high saturation, and 2 to achieve a sheen on the surface.  The technique was used for Encaustic or wax colour painting. Wax colours were rubbed and polished to achieve a saturated effect. Tempera paintings were also treated or touched with same techniques. Modern day application uses wax crayons or pencils to fill in colours, which are then rubbed with smooth glass or stone. The surface gets warm to melt and fuse the colours.

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QUALITY MANAGEMENT SYSTEM STANDARDS: QMS

Post 287 –by Gautam Shah

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ISO 9000 standards form Quality Management System QMS. Organizations need to do lot of preparatory work to align with these systems. The process involves redefining many notions that exist as ephemeral concepts by stating them distinctly and making them available transparently in public domain. 

Organizations wishing to follow ISO 9000 systems must carry out certain reforms within the organization, before calling in a recognized auditor for the validation process. The prime requirement is to frame the goals of the organization. Many times this are informal ideologies, with the top level of a management team. These must therefore be formally documented, and every single participant (current and others joining in future) in the organization is made aware of it.

Participation

The goals or the policy of the organization will cover:

• Nature of business being conducted
• Future changes envisaged in business nature
• Define clear roles and responsibilities for policy determination, implementation, preview and reporting
• Define the external ‘clients’ who sustain the organization, nature of return or the benefit gained, and other beneficiaries
• Define the internal or departmental ‘clients’ for products and services
• Define products, services and other inputs required to serve external and internal clients or other beneficiaries.
• Define processes that occur within each of the departments, and necessary conditions for them to be sustained (including human resources, health & safety requirements, environmental concerns)
• Define likely scale of affectations to ‘third parties’ and other stack-holders due to the business activities
• Form and place (public domain and documents) where these data (as listed above) will be available, frequency of revision, and process of accepting feedback on it.

These exercises help define various processes operative in the organization and the nature of dependency among it. The organization is seen here as a large complex system consisting of several sub systems few of which are fairly independent, but most others are interpolating subsystems. The structured perception of the organization helps in developing a sharper quality control regime.

Verification – Validation – Accreditation

On completion of the ground work (as listed above) a request is made to any of the recognized registrar to specific requirements to be ISO compliance worthy. The requirements are defined in various standards of the series. One may also remain in compliance without being registered by an accredited Auditor, but cannot have the benefit of declaring itself to be an ISO 9000 accredited organization.

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EMPLOYMENT

Post 286 – by Gautam Shah

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In an organization people worthy to be employed, come through many processes of elimination. The selection is substantially a discriminatory procedure. The eliminations occur on many grounds like sex, race, region of origin, age, language, social status, etc. Some selection methods though scientific, are not tenable under normal laws. Constitutions of many democratic nations, however overtly or discreetly override, provide, dictate or recognize ‘the reservations in employment’. This is due to certain historical effects and time delayed efforts to eliminate and correct them.

Elimination processes have TWO basic functions: FIRST, reduce the lot from which to choose, TWO select the most appropriate person out of the remaining manageable lot. The first function is so subtly carried out that often the applicants for jobs are never aware of it. As for example, an advertisement that appears in a language newspaper or media being accessed in particular town or region, would generate replies from that set of people, eliminating all others.

elimination processes

Selection of an employee based on following aspects:

1. Objective requirements (intellectual): Skill, experience, training, work related abilities.
2. Subjective requirements: Personality traits, initiative, speed of reaction, temperament, memory, power of reasoning.
3. Physical requirements: Age, height, muscle power, health history, abnormality of body limbs and sense-abilities
4. Other requirements: Past record, references, readiness to accept the terms of employment.

Tompkins square riot of unemployed 1874 NY

An Employer sees performance as a tool for future efficiency to be gained at a specific cost, whereas an Employee perceives performance as immediate compensation, personal fulfillment, future promotion and skill gain. Organizations relate the performance of an employee with the profitability. Management of the organization continuously monitor the performance of the employed person. This is more so in Design organization where human resources are very important assets, unlike in manufacturing units where productivity of machines and raw material costs have greater significance.

Performance of an employee is a product of many factors such as individual ability, personality traits, input effort, sincerity, perception of the role, motivating factors, etc. Yet, performance can be conditioned as the enhanced capacity to deal with more complex or new problems, share of responsibility, greater authority, etc. An employee can be motivated for gain, comfort, increased learning, or even enhanced motivation.

Job Discharge

The relationship between the employer and employee continues to evolve. The original conditions of employing a person such as the technological relevance, nature of projects, economics of resources deployment, personal efficiencies, work-culture, all change with passage of time. The employer and the employee begin to see each other very differently after a period of time. The employment -the process of being employed is reassessed by both. This has TWO facets: an employee wishes to cease working with the employer, or the employer wants to terminate the employee.

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DRAWN ARCHITECTONIC ELEMENTS

Post 285 – by Gautam Shah

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Architectonic elements over openings are mainly of carved, sculpted or formed nature, and occasionally drawn objects. The first set are exploited on the exterior face, whereas the second types are more preferred on interior surfaces.

Exterior elements get the advantage of strong and directional sun light and natural colour-textures of the materials. The interior elements have very subdued illumination and often rendered over plastered surfaces.

Interior elements of drawn objects like paintings, mosaics, and other surface renderings must use colour to convey the depth by contrast and delineation of outlines. Patterns and subject themes are also used for reinforcing the architectonic nature of the elements.

Drawn elements were not possible on exterior faces. Fresco, Tempera or Encaustic techniques of painting used materials that did not weather well. Mosaic work with variegated colour stones, ceramic or glass pieces, were fixed with lime or such cementing materials that gave uncertain results over ageing. Interior renderings, however, in many instances have surpassed the sculpted work.

Interior renderings in post middle ages began to draw shadows of thematic presentations, and these had to match the directions of natural shades within the interior space. For the directional illumination and shadows, contrasting colours and tonal variations were used but sense of perspective was not fully matured.

At other end in Middle East buildings were being converted to Islamic faith. Here instead of drawn stories plain bands of stones were over painted with decorative motif, calligraphic writings, or clad with metal sheets of bronze or gold. In many instance such treatments did not match with the original architecture but were of appliqué nature.

Patterns and themes were used to supplement the functional and decorative character of the opening. The openings, for structural reasons have been narrower in width, then their measures in height. Openings’ treatments were articulated to enhance the perceived width.

‘The Greeks, consciously or unconsciously, practiced extreme simplicity in art, and the fine-grained marble that they worked also encouraged the tendency to leave purity of an outline to speak for itself. Thus, whether on the grand scale of a temple building like the Parthenon or in the single human figure as the Hermes of Olympia, they were content with beauty unadorned by distracting ornament’.

‘The Romans never seem to have been satisfied till they had loaded their monumental buildings with every possible ornamental addition. Here too again the influence of material is apparent; for concrete demanded a disguise, and coarse limestone did not permit of delicate purity of line and thus called for extraneous ornament, so the Romans completed the magnificence of their monuments by a wealth of decoration’. –From: History of Architecture by Sir Banister Fletcher

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ABS PLASTICS

Post 284 –   by Gautam Shah

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ABS (Acrylonitrile-butadiene-styrene) has been described as wonder or Industrial plastic. Styrene Acrylonitrile copolymers were available since 1940’s, but introduction of a Butadiene as a third component in the 1950s created a range of ABS plastics.

ABS high impact resistance cover

ABS polymers are not affected by water, salts, inorganic acids, food acids and alkalis, alcohols and animal, vegetable and mineral oils. ABS plastics are soluble in ketone, swell or soften in some chlorinated hydrocarbons, esters, aromatics and aldehydes.

ABS in home goods

ABS can be moulded, extruded, vacuum-formed, blow moulded, rotational moulded and chrome plated. Moulding at a high temperature improves the gloss and heat resistance; however, high impact resistance and strength, are available by moulding at low temperature. ABS plastics are used largely for mechanical purposes, they also have remarkable electrical properties that are fairly constant over a wide range of frequencies and unaffected by temperature and atmospheric humidity. ABS is damaged by sunlight, causing a widespread and expensive recall of automobiles in US history.

Automobile Interior trims of Plain and Chrome plated ABS

ABS is used for brief cases, suit cases, printer bodies, remote control bodies, television bodies, hair dryers, textile bobbins, toys including Lego and Kre-O bricks, plated car linings and trims, bumpers, bars, furniture, protective headgear, hardware, water-taps, sanitary ware, golf-club heads. ABS raw material colour is ivory to white, but can be pigmented. ABS plastic ground down to a dia. of less than one micrometer is used as the vivid colourant in some tattoo inks.

ABS LEGO bricks

Its glass transition temperature is 105 °C. ABS. It is amorphous and therefore has no true melting point. ABS can be used between -20 and 80 °C, though its mechanical properties vary with temperature. ABS plastics are self-extinguishing, but flammable at high temperatures. It melts, then boils, when its vapours may burst into flames. On burning ABS does not produce any organic pollutants except carbon monoxide and hydrogen cyanide.

Automobile parts

ABS is a Terpolymer (three-way polymer) made by polymerizing styrene and acrylonitrile in the presence of poly-butadiene. It is formed of a long chain of poly-butadiene crossed with shorter chains of poly-styrene-co-acrylonitrile, but in varying proportions (from 15-35% acrylonitrile, 5-30% butadiene and 40-60% styrene), to achieve quality variants. The Acrylonitrile imparts chemical resistance and surface hardness, Butadiene contributes the impact strength and over all toughness, and Styrene helps in processing. ABS combines the strength and rigidity of acrylonitrile and styrene polymers with the toughness of poly-butadiene rubber.

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FLOOR SPREADS –TYPES, SIZES and SHAPES

Post 283 –  by Gautam Shah

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The words ‘Carpets, Rugs, Durries, Floor Spreads and Heavy Tapestries’ are often used synonymously. The quality, the sizes and the uses differentiate one from the other.

Early (pre 1900s) Carpets, Rugs, Durries, Floor Spreads and Heavy Tapestries were traditionally made for specific purposes and clientèle. Some of these were used as table covers, and floor spreads were hung. With industrial revolution, looms were automated and users increased manifold. The sizes, yet varied from country to country, and for the niche markets being served. The carpets and other items were earlier sold at places of production to tourists, but now vast quantities were sold in major commercial centres of the world.

Carpets are larger, nearly cover the room space or are extended ‘wall to wall’. Modern day carpets are made heavier, stiffer and softer, by the backing materials system. Some backing systems are fixed to the back face of the carpet, whereas others such as soft padding are laid on the floor. Backing system often include a static discharge network with earthed wires. Some of the pile and tufted carpets can have very heavy body construction, and may not require backing. Carpets either remain on the floor due to gravity, non skidding backing surface, or the large extensive surface. Most carpets are, however, affixed with carpet tacks or hooks at the periphery or by adhesives.

Rugs are smaller and nearly similar to carpets in terms of constitution. Rugs are simply spread on the floor, without backing or padding. Rugs being thinner and smaller can be rolled up. Rugs are also called throw-rugs because by throwing up in air one can unroll and spread it on the floor. Rugs are floor-spreads placed at specific locations within a room. Rugs are chiefly used for under the feet comfort. Rugs are also used to create places of interest or focus. Rugs are often laid over the carpet for the same reason. Rugs are spread over railings or parapets or hung on the walls. Rugs are thinner and simply reversing it dust can be removed. Rugs are formed as circular, elliptical and diamond shaped. The material is cut from larger woven material, and the edges are seamed with stitches, often with additional borders.

Durries are thinner than rugs. Durries can be folded up to 4/6 folds. Durries have tied weft ends or stitched edges. Durries have a simple weave and patterns are generally identical on both the faces. Traditional durries were made from waste, carded or combed wool, cotton or jute of small length or staple fibres. The coarseness of the yarn provides a dull finished surface. Durry could be very small 500x 500 mm (in India called Aasan), for one person to seat during religious ceremonies. Durries with finer cotton fibres are called Shetrunjees -Satranji (India). These are small enough for a person to sleep (800x1800mm) and larger enough (2700x4500mm) to seat 20 people.

Floor Spreads are made from cotton yarns, thin grasses and reeds, and synthetic flat yarns (such as polyester or Polypropylene). Floor-spreads are used for floor level dining, seating and sleeping. Reed floor-spreads, are called Chatais. Chatais are used as under spreads for mattresses, as prayer mats, dead body covers for burial and as hung screens over passages and openings. Modern day floor-spreads are non-woven mats of polypropylene fibres. Foamed base Rexine and other extruded composites.

Carpets of Asian countries came to Europe after 11^th C. These were very rare and precious items to be placed under the feet. Carpets were display items as table covers and wall hangings. Persian carpets are categorized as for Farsh or floors, (5500x2500mm) are the larger units placed at the centre. This is flanked by two runners or strip carpets called Kanarehs, (5000x900mm) used for walking. The end piece of three carpet arrangement is called Kellegi, (3700x1800mm). Other then these are nomadic-rug (Qa-licheh=small rug) or carpets (called Klim or Saumak), and prayer spreads called Namazik.

Modern loom carpets are 12 Feet (3.7 m) and 15 feet (4.6 m) in the USA, and 4.0 and 5.0 Mts in Europe. Carpet tiles are cut from woven material or non-woven pressed fiber sheets. The edges are seamed by stitching, adhesives or heat-fused. Commercial sizes are 400x400mm. For very large spaces like halls (greater than 3.5mts) pieces of carpets are seams joined by stitching or adhesives.

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PLASTICS -the beginnings

Post 282 – by Gautam Shah

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Plasticity of Clay

Man had Clay as the first material that could be formed to desired shape. Clay gains ‘plasticity’ -moulding or shaping capacity, due to its grain shape, size and distribution and addition of water. A natural metal nodule or a purified one from the ore, on heating also became, ‘plastic’. This property was unavailable with materials like wood and stone. Materials like Bamboo or Cain, have the capacity to bend but cannot be shaped or moulded.

Historically there were few natural materials that exhibited the plastic behaviour. Bitumen was used as a water proofing material for boats and also as a joint material for masonry. Plant-based starch materials on being cooked showed flow behaviour.

Bitumen

A plastic material can ‘flow’, is ductile and so can be moulded or shaped, with application of pressure or heat. Plasticity is a property of material to be deformed repeatedly without rupture by the action of a force, and remain deformed after the force is removed. Materials commonly known as ‘plastics’ are polymeric compounds that show elastic and viscous components.

Natural Rubber

Several natural plastic materials were known from ancient times, but without clear perception of categorical behaviour. Lac, an insect exudate was used as gum or joining material in India. The lac was used for cast mouldings since 1868. Rubber, a plant exudate was used since 1535, as water proofing material and for shoe making. Cattle’s horns were used for Lanterns during middle ages, however, materials with similar properties of horns were developed by treating casein -milk-proteins with lye. Casein was also used as gum material. During 1851 Rubber was combined with sulphur to form Ebonite. Several natural oils, such as Linseed, Castor, etc., was polymerised to form longer chain products.

The development of plastics actually began with formation a cellulose nitrate plasticized with camphor, as a substitute material for than widely used ivory balls for billiards in 1860. The product was patented under the trademark Celluloid. It was also used later in the manufacture of objects ranging from dental plates to men’s collars. Celluloid was commercially successful, despite its flameability and capacity deteriorate when exposed to light. Cellulose used for manufacturing the Celluloid was of plant origin. The first totally synthetic plastic was the phenol-formaldehyde resin, Bakelite. Other plastics introduced during this period include modified natural polymers such as a rayon, made from cellulose products.

Bakelite electrical switches were part of early electrification. These were black to dark chocolate brown electrical switches mounted on ceramic base and had brass internal fittings. Bakelite was used for garment buttons, telephones and electric current proof handles. Celluloid films were part of early reels of movies. These were highly combustible and required extra ordinary protection in cinema projection rooms. Celluloid films were later replaced with polyester films. Celluloid white balls were used in Table tennis or ping-pong, as it was known in 1940-50s.

The development of plastics has evolved from the use of natural plastic materials such as shellac to chemically modified natural materials such as the Rubber, Nitrocellulose, etc. to completely synthetic materials such as Bakelite, etc. During 1800s, Goodyear developed a process of vulcanization of natural rubber, accelerating the development of plastics.

Natural Rubber crafts

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