Post 504 by Gautam Shah
Surface Finishing is achieved by several processes such as:
1 Surface Levelling,
2 Surface Texturing,
3 Surface Property Modifications without resorting the first two,
4 Embellishment with other materials.
1 Surface Levelling is done by Removal of excess material, and Deposition of new materials.
Surface levelling is achieved by removing the texture or roughness forming excess material. For these surfaces are section re-cut, ground and polished. Stone surfaces are chipped with finer chisels, or wood faces are planned to level out the surface. Stone surfaces are dressed to remove the weathered crust. Rough cut or split (sedimentary) stones are spliced into two, by a smooth saw cut. Barks of the trees are removed by axes and choppers. Timbers are split very finely to create veneers. 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. Singeing or burning the surface section is used for fabrics, leather and paper. High temperature singeing removes surface fibres or hair, deoxidize 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. Metal surfaces are rolled over to flatten out the undulations or ‘turned’ or ground.
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 jeweller’s 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. A 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 surface levelling processes include singeing, washing, bleaching, etching, and ironing. Wood surfaces on sintering 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.
2 Surface Texturing is used to endow desired level of texture and in organized pattern format. This is done by chemical reactions with surface molecules and by mechanical means. Acid and Alkali etching are used for forming textures. Glass surfaces are etched with Hydrofluoric acid. Metals are acid etched and then neutralized with an alkali treatment. Water and solvents are used for surface making. High-speed jets of water are used to form surface patterns over partly set cement surfaces, Water used for washing out the top section of mosaic plasters to reveal the stone chips. Suctions are used to create textures in plaster surfaces. Paints are applied by roller to form granulated matt finish. Leathers, papers and plastics are hot pressed to imprint patterned textures. Recording media like CDs, DVDs have groves that store data.
3 Modifying or Refashioning the surface sections is done to change or equalize the surface properties of objects. Metal and glass surfaces are de-stressed by controlled radiation including heat treatment. Annealing and Hardening, are heating and cooling processes to change the molecular arrangements within the entire body, or just surface sections. In case of polymers heat treatments are used for chain linking. Textiles become de-creased or creased on pressurized with heat treatment.
4 Embellishment with other materials, are used in a superfluous or applique process or as an integrated process.
Applique processes are like casing, cladding, layering, or lamination, lapping, gilding and coating. Cladding is common in masonry work for a new surface, insulation, waterproofing, etc. Casing is done to metal structures for rust inhibition, static discharge, isolation and fire protection. Layering or lamination is common in composite formation through co-extrusion processes.
Integrative surface processes are surface molecular deposition or surface alloying systems. 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 systems form 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.