LIST of METALS related BLOGS

 

Post 628 –by Gautam Shah

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  1. FORGING > https://interiordesignassist.wordpress.com/2015/06/11/forging/
  2. COATING of METALS – 1 > https://interiordesignassist.wordpress.com/2016/10/07/coating-of-metals-part-i/
  3. METAL COATINGS > https://interiordesignassist.wordpress.com/2015/06/01/metal-coatings/
  4. SHAPING of MATERIALS > https://interiordesignassist.wordpress.com/2015/07/03/shaping-of-materials/
  5. PROCESSING of MATERIALS > https://interiordesignassist.wordpress.com/2014/11/27/processing-of-materials/
  6. METALWORKING PROCESSES > https://interiordesignassist.wordpress.com/2014/09/02/metalworking-processes/
  7. METAL WORKING Processes > https://interiordesignassist.wordpress.com/2014/08/12/metal-working-processes/
  8. PERCUSSIVE TOOLS > https://interiordesignassist.wordpress.com/2016/05/07/percussive-tools/
  9. HAMMERS > https://interiordesignassist.wordpress.com/2014/07/20/hammers/
  10. DRILLING > https://interiordesignassist.wordpress.com/2014/06/17/drilling/
  11. PLATES, SHEETS and FILM MATERIALS -part I > https://interiordesignassist.wordpress.com/2016/02/07/plates-sheets-and-film-materials-part-i/
  12. IRON MAKING > https://interiordesignassist.wordpress.com/2015/11/03/iron-making/
  13. SMITHY > https://interiordesignassist.wordpress.com/2015/04/16/smithy/
  14. CARBON and STEELS > https://interiordesignassist.wordpress.com/2015/03/15/carbon-and-steels/
  15. WROUGHT IRON LATTICES > https://interiordesignassist.wordpress.com/2014/10/27/wrought-iron-lattices/
  16. STAINLESS STEELS > https://interiordesignassist.wordpress.com/2015/04/09/stainless-steels/
  17. IRON or STEEL -technologies through history > https://interiordesignassist.wordpress.com/2014/06/18/iron-or-steel-technologies-through-history/
  18. METAL CLEANING PROCESSES > https://interiordesignassist.wordpress.com/2016/01/11/metal-cleaning-processes/
  19. ALLOYS > https://interiordesignassist.wordpress.com/2016/01/05/alloys/
  20. FERROUS ALLOYS > https://interiordesignassist.wordpress.com/2015/05/11/ferrous-alloys/
  21. ALUMINIUM BRONZE alloys > https://interiordesignassist.wordpress.com/2015/02/03/aluminium-bronze-alloys/
  22. METAL EMBELLISHMENTS -PAINTED ENAMELS > https://interiordesignassist.wordpress.com/2015/08/20/metal-embellishments-painted-enamels/
  23. GILDING > https://interiordesignassist.wordpress.com/2015/07/12/gilding/
  24. FUSION JOINING SYSTEMS > https://interiordesignassist.wordpress.com/2015/04/11/fusion-joining-systems/
  25. METALS and ROOFS -Part – I > https://interiordesignassist.wordpress.com/2015/03/30/metals-and-roofs-%e2%97%8f-part-i/
  26. CORROSION PROOFING TREATMENTS > https://interiordesignassist.wordpress.com/2015/03/17/corrosion-proofing-treatments/
  27.  METAL TREATMENTS for CORROSION RESISTANCE > https://interiordesignassist.wordpress.com/2015/02/22/metals-treatments-for-corrosion-resistance/
  28. PATINA > https://interiordesignassist.wordpress.com/2015/03/08/patina/
  29. COPPER -1 > https://interiordesignassist.wordpress.com/2015/07/19/copper-1/
  30. COPPER -2 Copper Compounds > https://interiordesignassist.wordpress.com/2015/07/21/copper-2-copper-compounds/
  31. COPPER 3 -Bronze alloys > https://interiordesignassist.wordpress.com/2015/08/02/copper-3-bronze-alloys/
  32. TIN > https://interiordesignassist.wordpress.com/2015/03/02/tin/
  33. PEWTER > https://interiordesignassist.wordpress.com/2015/11/05/pewter/

enclume

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COATING of METALS -Part-I

Post 627 –by Gautam Shah

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A coating is a thin surfacing that is applied or attached to the surface with various degrees of ‘chemical’ integration or amalgamation. Metal coatings are of four types: ‘Organic’ coatings like paints, organosols or other polymeric compounds, Non-Organic coatings of metals, Coatings of metalloids reaching to ceramic states, and Gas reaction-deposition systems.

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Horses of Basilica San Marco > Wikipedia image by Author Tteske

Metals need a coating to alter the physical and chemical properties of a surface, such as to endow desired quality of texture, colour, patterns, electrical properties, surface reactivity, strength properties, etc. Often a surface treatment is in preparation for another treatment, as a temporary or permanent application. Maintenance of specific surface properties during sub-processing, transit, fabrication, installation and repairs require special coating systems.

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Copper Bronze spouted flagon 320 BC > Wikipedia image by Rosemania

Metal items require some form of ‘surface-deep’ preparatory ‘work’ to receive the coating, but such ‘work’ for small-or-thin-body entities like plates, sheets, foils, wires, threads may involve entire mass of the body. Post such preparatory work, involving heat leaves some stresses in the item. Small or thin body items have uniform stresses. But heavy items and assembled work can have differential stresses, which affects the final coating.

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Reclining Figure : Arched Legs 1969-1970 by Henry Moore > Flickr image by Pedro Ribeiro Simoes

One of the first Metal coating realized by Man was Patina. Metal rusting is nominally a crust like degradation products, but some metals like Bronze, acquire a surface layer over a period of time. Verdigris is the natural patina. Metal artifacts exposed to different environments such air, sea-water, soils acquire patina, a layer consisting of oxides, carbonates, sulfides, or sulfates. Patinas are products of surface mass degradation, and so etch or reduce thickness of the surfaces. Some patinas, however, curtail further degradation of the surface, and so are encouraged. Patinas are often visually appealing and so desired. Effects similar to patina can be achieved by designed exposure and by treating with various chemicals. Patinas are commonly green, but may vary in colour such as of red, brown, black, blue, or gray. Its surface may be smooth, glossy, or crusty. Newly made objects are deliberately patinated to simulate the antiquity in a process is often called distressing.

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Michelangelo’s Pieta in Bronze by Ferdinando Merinelli 1932 > Wikipedia image

Patina over copper alloys, such as bronze, due to the chlorides leads to green, while sulfur compounds are brown. The basic palette for patinas on copper alloys is blue-black due to ammonium sulfide, brown-black with liver of sulfur, blue-green for cupric nitrate, and yellow-brown due to ferric nitrate. For new artefacts accelerated patination carried out by applying chemicals with heat. Colours range from matte sandstone yellow to deep blues, greens, whites, reds and various blacks. Some patina colours are achieved by the mix of pigments and chemicals. The surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats. French sculptor Auguste Rodin used to instruct assistants to urinate over bronzes stored or buried in the yard. A temporary-washable patina, is produced on copper, by the vinegar (acetic acid).

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Bronze busts –with and without patina > Wikipedia image by MatthiasKabel

In architecture, metals, like copper, bronze, etc. have been used for a very long time, for wall cladding, door panelling, ceiling tiles, and roof covering. Copper provides excellent corrosion resistance. Copper surfaces form tough oxide-sulfate patina coating that protects underlying copper mass and resists further corrosion. Copper corrosion products are less toxic. Copper sheets have been used in many building to cover rounded domes, and articulated roof surfaces. Architectural copper is, though susceptible to oxidizing acids, heavy-metal salts, alkali, sulfur and nitrogen oxides, ammonia, sulfur and ammonium compounds. Brass, an alloy of copper and zinc, has good resistance to atmospheric corrosion, alkali, and organic acids.

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Thracian plaque > Wikipedia image by Ivorrusev

Metal to metal cladding systems were precursors to Plating technology. Such dual metal structures were created by beating, rolling, rivetting or co-forming. The chief purpose was to add strength to a weaker metal. Forging a metal over metal in some cases created partial homogeneity. It was easier to forge soft metals like tin, lead and copper over harder metals like Bronze, Iron etc. Tin and lead could be softened through heat and used for coating. Metal coating by cladding or sheathing, were useful for corrosion resistance, wear resistance, improved electrical/thermal conductivity and better handling (touch-feel).

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Gold foil processing at a workshop in Kanazawa Japan > Wikipedia image by Eckhard Pecher

Some of the simplest methods of sheathing used Gold, Silver and their amalgams with mercury. Gold, Silver, Tin and mercury based amalgams were used as liquidized coatings, where as Silver and Gold were fused as thin sheets or foils. Tin coatings were used for mirror making.

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METAL CLEANING PROCESSES

Post 571by Gautam Shah

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Metals parts need surface treatments and cleaning for conservation, restoration,  decoration, reflectivity (shine), dulling (removal of gloss), better hardness, surface integrity, prevention of corrosion and in preparation for the next treatment. Metal components get both organic and inorganic substances deposited from various lubricating oils, corroding environments and substances, and deposits from hard water etc. Metal surfaces need cleaning for removal of residual products from earlier processing, weathering, depositions during storage and transport and environmental contaminations. A cleaned metal is comparatively more active, and so may need, immediate next treatment, to prevent corrosion and contamination. So metal surfaces often receive simultaneously the processes of cleaning, surface activation and protection.

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Metal surfaces needs to be smoothed, scrubbed or scoured to receive next set of treatments. Cleaning processes are employed to discharge electrical ions from the component. Cleaning processes are designed to serve several purposes, such as cleaning, scoring and protective coating. Cleaning occurs at a raw material stage, product formation stage, in preparation to other finishes, or just prior to a marketable finish. But there are two distinct stages, at manufacturing plant and on-site applications.

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Center-less grinding  Wikipedia image by Wizard191

Alkali cleaning is typically done with caustic soda (NaOH) which removes all polar substances such as fats and oils. The vegetable and animal oils are converted to glycerol and soap, and the petroleum-based oils and grease are emulsified.

Acid cleaning, like alkali removes ionic deposits from the metal surface. Depending on the secondary products like salts determine the quality of acid to be used. Pickling process removes oxides from the surface by a dissolving liquid. For steel, a warm dilute sulphuric acid, and in some cases hydrochloric acid, hot or at normal temperature, is used. However, for some alloy steels nitric acid, is needed. Acid and alkali both processes require post treatment ph. balancing rinse or treatment.

Solvent cleaning: the articles are washed with a petroleum solvent or undergo cleaning (de-greasing) by vapour, in which a solvent such as tri-or tetra chloroethylene is heated in a closed system, and its vapours are condensed on the metal surface.

Emulsion cleaning: the metal parts are immersed in a warm mixture of kerosene, a wetting agent, and an alkaline solution.

Mechanical cleaning use force of air or water jet and sonar waves to remove partially attached particles. The process may include fine particles like sand, silica, metal grit etc. to blast the surface for the same purpose.

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Electrolytic cleaning: the articles are immersed in an alkaline solution and a direct current is passed between them and the other electrode which is usually steel.

Ultrasonic cleaning is used for blind holes or gears packed with soils etc. Small particles embedded in crevices get detached due to ultrasonic waves.

Plasma treatments bombard a surface with electron ions to break the surface level chemical bonds and change the chemical composition of the surface. Plasma treatments may also remove variety of material types such as paints, polymers, glass and ceramics.

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Statue of Perseus Piazza della Signoria Florence After cleaning Image by Jrousso at Wikipedia En

Metal cleaning Tools and Techniques

The metal products are small items like nails, rivets, long rolled sections, drawn items like wires, woven items like lattices, entwined items like ropes and barbed fencing, hollow pipes and tubes, or solid castings. Other products include assemblies like automobile bodies, boxes, cages, machine housings and structures like a truss. Metal components are single or multi-metal items, composites with polymers, ceramics, etc. Art restorers have to deal with metal objects of unknown composition, ageing, and coated with natural or applied substances. Art restorations require reversible processes, so if a treatment is found unviable it can be fully reverted. Metal products in continuous line productions are moved through several sets of electrodes, which, submerged in a cleaning liquid, electrolytically generate hydrogen gas at the steel surface for lifting residues off the material.

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Sand-blasting Wikipedia image by National Institute for occupational safety and health NIOSH USA

Hard substances like metal nodules or slags are removed by abrasion or high pressure air or water jet. Soft materials like soil etc. are removed by brushing. Brushing may be carried out dry or wet and with scrubbing and scourager agents. Brushes with natural hair, synthetic fiber, metal fibres and wires are used. Abrasive materials like A Carborundum, sand grit, metal particles etc. are blasted on the surface to clean up the surface. In some instances like manufacturing of nails, abrasive materials rotated in ball mills with nails, to achieve high polish. Ultrasonic sound waves are also used to remove particles.

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FORGING

FORGING

Post 445

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Forging is a process of shaping iron and other malleable metals by hammering or pressing. Forging is carried out above or below the re-crystallization temperature of the metal. A primary purpose of forging is to shape a metal, but it also redefines the grain size and arrangements. The forged metal becomes more ductile. Forging improves the structure of a metal like better resistance to fatigue and impact, compared to other shaping processes such as casting or machining.

Forging with machine-hammer

Forging is mainly a shaping process where the metal is Drawn-out, Upset or Squeezed or compressed. Forging is also used to join metal pieces.

1 Drawing-out: The length is increased by decreasing the cross-section, such as wires, rolled sections, etc.

2 Upsetting: The length decreases but cross-section increases, such as for forming nails, rivets, bolts and coin stamping.

3 Bending: It is done by hammering the work around a form, such as for pipes, plates or dished ends (top-bottom of vessels).

4 Joining: Two pieces of metal form a joint, by hammering them together at high temperature (such as for copper and brass items).

5 Punching: Forming small openings or slits in the metal by a punch of the proper shape, often over a hollowed section. Punching is also accompanied by forming of the edge profiles.

6 Cutting Forming or cutting large holes or shapes by punching, shearing, etc.

Forging swagging tools

7 Die Forming: Forging is also squeezing metals by producing multi-directional flow to fill in a shaped die through compression. Shaping dies are, open, closed or impression dies. It is usually done hot to increase the plasticity of metal and so reduce the required force. Open-die forging is used to form parts that are too big for a closed die, or where only a few pieces are required. Closed-die forging is used for items to be made to close tolerances and where no machining is required. Coins are formed with impressions on two sides and also with side-edge patterns. Scooter and other carburetors are formed by pressure die casting, a process of forging.

Forging is also called a smithy. The chief activities of iron workshops, since ancient times, have been to heat the metal and beat it to a shape, or Forging. Hand-held Hammer has been chief tool for forging, but in the last two centuries powered hammers and presses are used.

Forged Aluminum wheels

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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.

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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.

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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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