LEATHER FINISHING

LEATHER FINISHING

Post 350 ⇒   by Gautam Shah 

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First preparation for leather begins when raw hides are washed to clean the blood and other tissue materials. After the tanning, the leather is treated for specific surface qualities. The leather passes through several wet processes for colouring and oiling. After drying the hide is mechanically processed for specific look or feel.

Suede Leather

Commercially available leathers are of basic four classes.

1 Full-grain leather is a hide without sanding, buffing, etc., nominally employed to remove or level out the natural surface imperfections. The grain structure nearly remains intact allowing to breathe while retaining the strength and durability. Some furniture upholstery, shoe soles, leather shuttle buffers (such as in weaving looms), belting, etc. use the full-grain leather.

2 Top-grain leather Many of the hides are split and shaved (at certain sections) to level out the surface to even thickness, before and after tanning, but for better quality the process is redone. The repeat process makes the leather thin, soft and pliable. Its surface may have less breath-ability.

3 Imprinted grain leather is a product over which grains are embossed or pressed. The surface imperfections are corrected by splitting, sanding, and then grains are embossed. After these processes the leather is dyed. Heavy pigmentations also cover up micro irregularities of the surface.

4 Split leather is created by separating the layers (process similar to veneering of wood) of leather. The top layer, if too thin, the bottom is reinforced with synthetic materials, woven or knitted fabrics or other splits of leathers. The splits are also top layered with synthetic polymer products. Splits are also used to create suede leathers. By-cast leather is a split leather with a layer of polyurethane lamination that is then embossed. It is a leather in only look aspect (and not the feel); otherwise, its surface is completely layered in plastic.

Textures on Leather

LEATHER TREATMENTS

Heavy leathers are finished by coating the grain surface with a finishing compound, and finally by brushing it under a revolving, brush-covered cylinder. The grain surface of light leathers is buffed, or sandpapered, to correct imperfections in the skin. Buffing the flesh side of leather raises the nap and produces the popular leather known as suede. For smooth finishes, most light-leather is seasoned, or treated with a mixture of such materials as waxes, shellac or emulsified synthetic resins, dyes, and pigments. Pigments are used sparingly to avoid a painted look.

rawhide consisting of rough untanned skin

Leathers are surface treated in many different ways. Impregnation is achieved by padding, dipping, brushes coating, spraying, rolling, screen printing etc. Impregnation systems are water or solvent based, and help strengthen the crust while saturating the colouring and coating. Fillers are also water and solvent based, used to for achieving surface uniformity of colour and gloss while adjusting the feel. Auxiliaries are many different types, used to optimize the performance of the finishing systems and for special effects. Modifiers improvise the feel quality of leathers, while altering physical qualities of the leather. Dulling agents help adjust the gloss at the top coat. Topcoats are surface covering systems applied to leathers to impart specific transparent, translucent or opaque (solid) colour, shade, or decorative (metal, pearl, etc.) effects.

Book Binding with coloured embossed Morocco leather.

Leathers are surface altered by chemical and mechanical treatments. Chemical surface treatments include bleaching, staining, and other coatings. Leathers are infused with such materials as Epsom salts, oils, and then lubricated with hot emulsions of soap, grease, and sometimes wax. Mechanical surface treatments are: pressing -for levelling and compacting, rolling -for firmness and gloss, and embossing -to achieve granular or wrinkled textures.

Embossed leather

Leather Substitutes, are synthetic substances that look, feel or behave like a leather due to its one of the dominant qualitative advantage, cost, uniformity or easy availability. Replacement products are also used by people who do not wish to use an animal product. These synthetics include such plastics as polyvinyl chloride and non woven fiber impregnated with binders. These materials lack leather’s porous quality, pliable nature, and resilience.

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CALICO

CALICO

Post 349 ⇒   by Gautam Shah 

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The word Calico derives from Caliyans, a community of weavers from Kozikode or modern Calicut city of Kerala state in South India. Calico, all cotton fabric in plain or tabby weave ordinary cloth, was manufactured since 11th C., or perhaps earlier. It was later manufactured at several coastal locations like Surat and Cambay of Gujarat, indicating its export value. The exported Calico was floral patterned printed fabric, sometimes called Chintz. By 17th and 18th C., when European traders and colonists established trade-posts in India, it was as important a commodity as the spices traded between India and Europe. The European interest in the fabric was for the unprocessed or Grey fabric as well as for the printed version of it.

Printed Calico dress

Hemachandra, an Indian writer, of 12th C., mentions chhimpa, or calico prints, decorated with chhapanti, or a printed lotus design. The earliest fragments of exported fabric of 15th C., have been ‘found at Fustat near Cairo’. It shows resist dyed fabric. During the Mughal period block printed cotton fabrics were manufactured in Ahmedabad, Surat, Cambay of Gujarat, Rajasthan, and in Burhanpur, in the Khandesh region of Central India. All these centers were surrounded by cotton growing lands.

Grey Cotton print for Razai (cotton filled blanket)

Grey Cotton print for Razai (cotton filled blanket)

In India, Calico processing and printing, both, were improvised to suit the European market requirements. For home use simpler geometric patterns and motifs of small flowers were used whereas for the Europe needs larger patterns or ‘all-over’ designs were produced. Calico prints, procured by the East India Company from India, were comparatively cheap (compared to wool-cotton combinations) and popular. It affected the English weavers, so an act was passed (1700s) preventing import of dyed or printed fabrics from India, China or Persia. The importers shifted, to Grey (non-processed) fabrics. These were processed and printed in England. Local weavers also began to import raw cotton, and produced grey cloth with linen warp and cotton weft, known as fustian. This was not enough to satisfy the expectations of local projectionists. A law now banned the use (wearing) of any printed or stained calico, muslin, etc. except the local fustians. These laws made India just a supplier of low cost raw material, rather then an exporter of a value-added commodity, the Calico.

printed cotton designed by William Morris

In Europe calicoes were generally used for hangings, curtains, bed-covers, and dresses. The fabrics were bleached, base or ground dyed and then printed through rollers or screens. Block printing was not common in European factories. Indian-made chintz or calico fabrics were with darker ground colours compared to very light base in European fabrics. Early Indian chintzes, the glazed calicoes, were blocks mark printed with large floral patterns. But Europe, in later periods preferred patterns with smaller motifs.

print cotton

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ZONING of SPACES

ZONING of SPACES

Post 348 ⇒   by Gautam Shah 

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Spaces are characterized by the activity occurring in it. The activity takes the domineering position for the time slot, and so has a natural tendency to be singular and focal. Multiple activities in the same time slot do not have specific spatial character.

Prayer area -Core zone shift to opaque periphery

To remain relevant and focused the main activity of the space, must remain at the core zone of the space. In other words the main activity must stay away from the peripheral zones. The peripheral areas of the space are vibrant due to strong external effects. The strong external bearing can be curtailed by opaque edges. The core area, to retain its consistency begins to shift towards the protected edge. The shift to the edge may also occur due the architectural form of the space, local environmental conditions, overpowering functional needs, available facilities, amenities and enrichments. A dominant enclosure on one or few sides of a domain creates an inviolable shield, an identity of belonging, or a sense of orientation.

Extensive space -diffused periphery zones

Core zones gain strength by the architectural form. Spaces forms like concentric, conical, angular, circular, pyramidal, etc., are focused and so enhance the focus of the core zone. Very extensive domains lack an effective focus.

Akshardham Temple NewDelhi India

A core zone can be formed by the dimensional and cognition reach extent of the occupants. Such core zones are very personal, affirmed by the user rather than the architectural form. The reach extent scales the domain space.

Off centric core zone

Core zone of a space is a work setting, and so it is maintained free of permanent facilities. Amenities are also pushed to the opaque edge to source, the services like power, supplies, disposals, etc. The amenities in core zones need to be demountable, relocatable, handy-mobile, multipurpose equipments, plug in tools, wireless gadgets, miniaturized appliances and modular in design. Compared to these, the amenities in the peripheral zones are strongly dependent on the architectural and structural systems, and so are static.

Historically a core zone of the ‘Home’ was the ‘hearth’ (literally meaning a focus). It was considered safe, intimate and interactive for the family. The hearth was created often without any abutting elements like the cave wall or a rock face. The ambit of the core zone was determined by the climate, the scale of the space, number of participants and level of interaction, and the degree of personalization required. There was only one such zone in the dwelling. The home in charge -the mother was master of the core zone. Her role and presence had become so obvious that ‘the hearth, the mother and home’ were synonymous. In tribal and aboriginal homes the core area is a female domain. The core zone was the natural center of metaphysical spread, ‘the home’, as much as the mother was de-facto guardian of culture. Today, however the hearth is not an inevitable element for safety, security or comfort. It is the quality of barriers and other gadgets that provide this. Dwellings now have many sub domains each belonging to an individual, smaller group, or configured for a set of tasks. Very few activities of the family occur at the one place and are scheduled in the same time slot. But the family members do share a lifestyle developed through metaphysical markings like beliefs (customs, taboos, etc.) and the metaphoric means.

Groups forming multiple core zones

MULTIPLE CORE ZONES

Multiple core zones occur in very extensive domains. Such domains have weak central command and so allow formation of groups. The groups separate out primarily due to needs like physical accommodation, need for social intimacy and reach of communication. The groups may not seek a distinct territory or qualitative space segment. However, frequent such occurrences, show the existence of multiple qualitative space segments.

Large spaces allow multiple core zones

Multiple core zones also emerge where several overlapping or closely spaced domains operate within a larger built space entity. Such core zones share the same spatial segment simultaneously or are programmed in same time schedules. Here the consistent elements are: spatial characteristics, environmental features, participants, amenities, facilities, tasks and activities. Multiple core zones tend to remain together, but often get separated by strong peripheral areas.

Bedouin tent -two core zone space Male + Female areas

Arab tents had dual core areas within the basic form of the tent, one occupied by the women and used for main cooking, and the other half is used by men and for preparing coffee, etc. These two sections are divided by a mass of stored elements, such as mattresses, floor spreads, etc. The side flaps of the tent are stretched out to create peripheral zones of various sizes. The stretched width and the angle of the flap are conditioned by the sun’s position, wind direction, nature of tasks to be conducted and the need for privacy.

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Cooking and dining once (and still do in many societies) belonged to a single core zone, but were separated as two concurrent core areas. These two core areas were further separated by a pantry area that was a peripheral zone to both. Entrance is buffered by a lobby, foyer, entrance hall, or vestibule from other sections of the house. Yards, verandahs, porches are used to separate out the building from the street.

Single room dwelling units

Small or one room, houses have multiple core zones. These zones exist in terms of activity space spreads, which often overlap in time. The multiple core zones match the space layout characteristics, such as four corners, the area near the door or window, the area abutting the wall, the axis formed between two opposite side opening. Traditional Sarai rooms are two and half man width = 5 Mts or 16.5 Ft. This allows two families or their men or women to occupy a side. The depth of the room is of less important.

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POSTURES and BEHAVIOUR

POSTURES and BEHAVIOUR

Post 347 ⇒   by Gautam Shah 

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Postures are very important tools of behaviour for task facilitation and intentional as well as unintentional expression. Postures required for conducting tasks primarily provide change, relaxation, transition, exercise and reach. Postures for communication and interaction may gain from the spatial ambiance but depend on external amenities, facilities.

Different Postures depending on nature of task, reach, person

Postures have many variations within a basic theme or purpose. The variations are micro changes of the body that help in sensorial perceptions and manifestations. Postures have empathetic and confirming images for the society as these are closely linked to the local terrain, climate, environment. Postures directly and abstractly convey the state of interpersonal relationships, social standing, personality traits such as confidence, submissiveness, and openness, current emotional state and temperament. Certain body positions, patterns and movements suggest specific emotions, that are readable by the clan or group.

Posture variations

Posturing is using own body, its limbs and sensorial nodes in coordinated manner vis-á-vis another individual, groups of persons, or the elements of the space. In case of social encounters one perceives the sensorial and bio-manifestations and accordingly improvises own responses. Space, environment and the objects are used as tools for posturing. One can also reshape the space, reformat the environment and rearrange the objects and thereby economize or avoid some degree of posturing.

Flirtation and Jealousy -postures

Posturing, is primarily for own well being, or sustenance of life. Secondly, it is to resist or follow the gravity, by exploiting or overcoming its effects. Posturing is used for privacy and intimacy. Posturing helps one to control incursions by others into the personal domain of behaviour, as much as it allows one to project a participating personality.

A person takes on postures with several intents. First purpose is to gain and maintain it. Gaining a posture is to transit over from some other posture, and maintenance is readiness to change over to another one. It also includes the scope of micro posturing for blood circulation, muscle relaxation, fluid balancing, making gestures, and micro tuning the reach and handling capacities.

US President Reagan holds a oval office staff meeting -posture and interaction

Postures are axially balanced or skewed. Balanced postures are mirror-image (congruent) postures, such as equally posed two feet, two hands, etc., or are normal ones like the frontal face, upright torso, erect neck, straight eye level, etc. Skewed postures reflect a readiness to transfer to another posture, due to shift in interest or boredom. Both, the balanced and skewed postures, cannot be maintained for a very long period. Good designs include other support systems. The supports are casual, subtle, imperceptible, or very obvious ones.

Expression of anger posturing

Designers design for postures as important poses of behaviour sequences. Some flexibility within the postural poses is perceived or left to the individual to extemporize. A chair that is slightly wider or lower, a bar stool with a foot support ring, a seat with multi flexural (revolving, tilting, rotating) adjustability, TV or monitor swiveling stands are some of the examples that allow flexibility. Office executive chairs allow great many postures, due to the width of the seat, height of the seat, height of the handles from the seat, depth of the handles (elbow or arm accommodation), inclination of the back (tilting), height of the back (mid spine, shoulder support, neck and head support), swiveling, etc. Other postural options are provided by the table top height from the ground and seat level of the chair, depth and width of the table, nature of foot rest, task being handled, mobility of the chair (depending on the quality of wheels and flooring surface), etc. The site and its environmental conditions also play their role, such as the chair close against a wall, against an open space, facing a barrier or an open area, the source of illumination and air handling devices, one sided or multi directional interaction, communication devices being used and duration of work.

Identical Train seats -different postures

Similarly ordinary people need to exploit the situational conditions for behavioural setting. Where possible a person would choose an appropriate seat with reference to the host or other participants, own social status, own psychological make-up, presence or absence of intervening elements, angle, level and distance of the encounter, level of comfort and formality desired. Next strategy would be for macro or micro shifting of the seat. Where such devices are lightweight mobile, micro shifting for angular and distance adjustments are done, but such choices are usually limited. Other strategies will include body or postural accommodation, such as seating by fully drawing back or upright, leaning on, one of the arm rest rather then a balanced posture, keeping arms on armrest, lap or any other front side device, placing the legs under the seat, straight-up, seating with cross feet or leg, seating frontally but looking sideways.

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METAL-MATRIX COMPOSITES

METAL-MATRIX COMPOSITES

Post 346 ⇒   by Gautam Shah 

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Composite materials have at least two materials, with distinct roles. One acts as MATRIX and the other functions as a FILLER. The structure and properties of the filler-matrix interface play a major role in the mechanical properties of composite materials. The stresses acting on the matrix are transmitted to the fillers across the interface. A series of strips held together offers strength equal to one strip but when clamped together all layers take the load.

Metal matrix composite components

Some engineering parts have to operate at temperatures high enough to melt or degrade a polymer, so a polymer matrix is not useful. In such a situation Metal matrices offer high-temperature resistance, and strength and ductility, or bend-ability. The main problem with metal-matrix composites (MMC) is that even the lightest metals are heavier than polymers, and they are very complex to process.

MMC can be used in such areas as the skin of a hypersonic aircraft, and Space shuttle, commercial airliners, electronic substrates, bicycles, automobiles, golf clubs, and a variety of other applications. Metal matrix composites have good thermal conductivity, high shear strength, very high abrasion resistance, high-temperature bearing capacity, non-flameability, not affected by solvents. These composites can be machined or processed further through conventional engineering tools and equipments.

Air craft shell -metal matrix composites

Majority of commercially used metal matrix composites have Aluminum as the matrix, but in specialty metal sections, large number of applications employ matrix properties of super-alloys, titanium, copper, magnesium, or iron. Aluminum-matrix composites are not a single material, but a group of materials whose stiffness, strength, density, and thermal and electrical properties can be defined. The matrix alloy, the reinforcement material, the volume and shape of the reinforcement, the location of the reinforcement, and the fabrication method can all be varied to achieve required properties. Regardless of the variations, however, aluminum composites offer the advantage of low cost over most other MMCs.

Aluminum MMCs are produced through several routes such as casting, powder metallurgy, in situ development of reinforcements, and foil-and-fiber pressing techniques. For Metal matrix composites fillers as reinforcements are like, continuous fibers, discontinuous fibers, whiskers, particulates, and wires. With the exception of wires, which are metals, reinforcements generally are ceramics. Metal wires include tungsten, beryllium, titanium, and molybdenum. Metal matrix composites are typically made by infiltrating liquid metal into a fabric or a prearranged fibrous configuration called a preform.

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RUBBER and VULCANIZATION

RUBBER and VULCANIZATION

Post 345 ⇒   by Gautam Shah 

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Vulcanization is a cross or inter linking process between individual polymer chains. Raw rubbers have little elasticity, stability, and are deformable but with interlinking the flexible polymer molecules get entangled. The interlinked entanglement can be temporary as such molecules can again disentangle and flow under stress.

'Dry' divers suit

‘Dry’ divers suit

Rubber dam gate

The interlinking is carried out by addition of sulfur, or other equivalent curatives or accelerators. The term vulcanization also refers to other process where cross linkage is encouraged, as for example cellulose treated in a zinc chloride solution to cross-link the cellulose fibers.

Non Vulcanized raw rubber sheets

Some form curing of rubber was carried out since prehistoric times. Ancient Mesoamericans, extracted latex from a rubber tree Castilla elastica, and mixed with juice of a local vine, Ipomoea alba, to create processed rubber as early as 1600 BC. Modern process of ‘curing’ the rubber, the vulcanization, was named after Vulcan, the Roman god of fire, metalworking and forge, in the 19th C.

Hephaestus at the Forge by Guillaume Coustou the Younger (Louvre) Roman equivalent of Vulcan

First rubber products remained stable during winter period, but with summer heat became liquid gum like mass. The process of vulcanization corrected that defect while offering many stable products such as tyres, shoes, soles, hoses, and conveyor belts. Uncured rubber is used for adhesives, insulating and friction tapes, coatings, etc.

Rubber Boots

Neoprene Diving suit

Rubber foams

Rubber has good resistance to abrasion and so used for tyres, industrial belts and conveyor belts. It is flexible and elastic so used for gaskets, bendable pipes, foundation packing as vibration absorber, stretchable threads, bands and stripes. Rubber is relatively impermeable to water and gases, and so useful for hoses, balls, rain-wear, diving gears, and balloons, cushions. Rubber is used for inner lining of chemical storage vessels. It is a poor conductor, so used for insulation as well as for electrical insulation. Vulcanized rubber is used to make articles such as clarinet and saxophone mouth pieces, bowling balls and hockey pucks.

Air port conveyer belt of reinforced rubber composite

Vulcanization affects properties of rubber on several fronts: such as better strength, stiffness, hardness, fatigue and abrasion resistance, chemical stability, reduced deformations superior behaviour in temperature variations. Vulcanization is made agents like sulfur, sulfur donors, peroxide, thiazole and sulfonamide accelerators, metal oxides, polyvalent metal ions. Curing is heat treatment, usually after a product is formed. The product is heated and maintained at the required temperature under steam pressure. Many articles are vulcanized in moulds that are compressed by hydraulic presses.

Rubber under keys of keypad

The optimum amount of sulfur to be added to the rubber is about 10% by weight. Adding an excess of sulfur produces a very brittle and inelastic substance called Ebonite. Man-made or synthetic rubber can also be vulcanized, and the process is similar. Vulcanized rubber is about 10x stronger than natural rubber and is also about 10x more rigid. Polymers that are elastic are sometimes called elastomers.

Rubber roof coating

It is often difficult to distinguish a covalently interlinked Elastomer from one that is merely tangled or one that is held together by strong intermolecular associations. One means of distinguishing is to test whether the polymer dissolves in a compatible solvent or merely swells without dissolving. Covalently interlinked molecules do not dissolve. Interlinking is therefore necessary for good solvent resistance or for use at high temperatures.”

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METALS TREATMENTS for CORROSION RESISTANCE

METALS TREATMENTS for CORROSION RESISTANCE

Post 344 ⇒   by Gautam Shah 

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Corrosion is oxidation of metals in reaction with an oxidant such as oxygen. Rusting is formation of iron oxides through gradual destruction of the material by chemical reaction with the environment. Corrosion or degradations as a process of wearing away of the mass also occurs in ceramics (efflorescence of bricks and terracotta), stones, glass and polymers. Corrosion can be local or more widespread affecting the entire surface. Corrosion is a diffusion process and occurs on the exposed surfaces. One of the main methods of preventing such destruction is to isolate the surface from its environment, including the atmosphere and contact with other passive materials.

Glass disease or corrosion

Acid rain damaged gargoyle

Bishnupur W Bengal, India Corroded Brick work

Both, Ferrous and Non ferrous metals, have a tendency to corrode that is the atom lose electrons and become ions. This is called an anodic reaction, and for the corrosion process to proceed there must be a corresponding cathodic perceptor that adsorbs the electrons.

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Reasons for corrosion could be:

External (environmental)

Internal (constitutional)

Structural (joint system)

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There are several ways prevent, reduce or terminate the corrosion.

Metals get corroded by the environment. In most cases, to create an ideal environment for surrounding the metal will require a very large and extensive system, and possibly large quantity of energy to maintain it.

Corrosion occurs due to the discharge of electrons. Metal electrons migrate due to electrical potential that builds up amongst different metals and between the metal and an electric conductive substance, of an assembly. If cathodic polarity is imposed by supplying an electric DC current to reverse the direction or by attaching sacrificial anodes such as aluminium or magnesium, whose atomic relationship with steel is such that a current is generated without external assistance (the anodes are earthed and have electrolytic continuity with the structure).

Next course is to isolate the metal from corrosion conducive aspects of environment (such as moisture, water, acidic fumes, chlorides etc.). Coatings and plating provide the required isolation. The most appropriate way would be to place the isolating element as close to the metal surface, as possible, and if feasible even integrate it into the metal itself. Electroplating, metalizing etc., are some of the techniques that are on the verge of integration.

Copper roof on the Minneapolis City Hall, coated with patina

Corrosion can also be controlled by constitutionally upgrading the metal, by one of the following techniques.

Mechanical -stress induction and relief techniques at Normal, Hot and Cold temperatures,

  Chemical -additive and subtractive treatments

  Alloying – solid solution, precipitation, amalgamation.

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