Post 291 — by Gautam Shah
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.