MATERIALS HANDLING TECHNIQUES

From ancient times THREE different classes of materials have been handled by human beings.

1. Materials like Clay with important quality of plasticity that allowed the shaping at ambient temperature.

2. Materials like Wood and Stone were re-shaped by removal of the mass.

3. Metals were workable in both the manners, shaped by heating and beating (forging) and removal of the mass.

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One may include Weaving as a different class of ‘material formation process’. Though, weaving is often categorised as a method of ‘material composition’ rather then a ‘forming-shaping’ process.

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Needle Craft tools

Many Techniques of Materials handling in use today are essentially the same as those employed in ancient times. Several of the material handling techniques have originated from day to day living such as cooking, farming, home building, storage management and rituals.

Over the ages the techniques of materials handling have been refined in terms of the tools used, and rationalized in terms of procedures. Many processes are now highly mechanised saving time and energy, and some even are fully automatized, using programmed automats and robotics that allows faster, accurate and safer production.

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Ancient stone tools

Some important techniques of associated with material handling are briefly discussed in following FOUR groups.

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1          Techniques for material handling by reshaping the form such as plastic moulding, casting, extruding, pressing, shaping, embossing, reforming, deforming, removal of material, stretching, compressing and forging.

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2          Techniques for material handling by application of foreign materials or material deposition such as alloying, embellishing, cladding, layering, fixing, etc.

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3D Printing Material Deposition

3          Techniques of for materials handling by composition, such as assembling, entwining, joining, tying, bracing, weaving, embroidery, stitching, etc.

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Industrial multi tasking Robots

4          Techniques of for materials handling by ‘composite’ forming through the Matrix and Filler concept, such as layering, particle composites, etc.

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Composite forming- corrugated boards

Cutting is the oldest of all techniques of material finishing. First cutting tools were made of sharp edged flint stone chips. These helped in cutting meats for food and for cleaning the hides. Later cutting stone chips were tied to wood or bone handles for better tool holding and leverage greater force. Cutting Axes were reasonable for medium strength materials like wood, but, for harder materials like stones, cutting and beating actions were separated into hammer and chisel. Hammering was also used for grinding food, breaking and crushing nuts and compressing leather. Cutting was used for fast division of materials and quicker removal of parts of materials (skinning, shaving, debarking, chopping, mining). Cutting was the crude but primary technique of material processing.

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Hammer - Material deformation

Carving is a controlled cutting technique requiring use of a chisel and only occasional pounding by a hammer. Carving is associated with fine but soft grain materials like ivory, horn, bones and wood. Carving is also done to pliable metals like copper, silver-based alloys, and also hard but fracture-able materials like stones.

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Wood turning Lathe

Engraving like the carving is a material removal process, but more delicate and shallower. It was done with sharper and narrower points and with only hand pressure or very light pounding of the hammer. Engraving is today done by fine rotary tools similar to the dentist’s pneumatic drill. A computer controlled, diamond bit engraving is now also done to ultra thin materials. In Intaglio, or Gravure, printing, the image to be printed is etched or incised into the surface of the printing plate or cylinder. Gramophone records and Computer disks have engraved and embossed grooves. Engraving is now, carried out by laser process rather then sharp points.

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Chasing is engraving, but in small length linear-strokes or in continuous linear patterns. The material is either depressed or displaced by a fine tool as dots. Historically wet ceramic pieces and plastered-surfaces (writing tablets- Cuneiform) were rendered by chasing. Braille writing on a thick paper sheet is a form of chasing. Engraving and chasing techniques are frequently used to provide a matt finish, onto normally very glossy stainless steel surfaces. Chasing techniques are also used for relieving as well as introducing stresses at the surface section, for facilitating greater moisture or heat transfer, and to improve the ductility of the material.

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Embossing is a technique of form deformation or mass reshaping of a sheet like material. It introduces a texture through pounding, beating or by pressing of the surface. The pressure may be applied from one face or both faces of a sheet, locally as spots, or continuously under a plate or roller, creating repeat patterns or random designs. Pounding or beating compacts, the surface-sections of the material, and thereby increases its density and integrity. Embossing techniques are used to reduce the gloss by matting the surface. Embossing is done to increase the thickness bulk of very thin surface materials and make them apparently stiffer. Synthetic fabrics and fibres are emboss-deformed and permanently set (perma-set and texturizing) through heat or chemical treatments.

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Repousse is a method of raising a design in relief from the reverse side. There are three essential types of tools used: -for tracing, -for bossing, -for chasing. Ornaments in relief are also produced by mechanical means. A thin, pliable sheet of metal is pressed into moulds, between set of dies, or over the stamps. Embossed utensils of copper and brass, statuettes of gods formed of thin silver and gold plates are very much part of every Indian house. Today Aluminium craft pieces are similarly embossed and black anodized.

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The design is first drawn on the surface of the metal and the motifs outlined with a tracer, which transfers the essential parts of the drawing to the back of the plate. The plate is then embedded face down in an asphalt block and the portions to be raised are hammered down into the soft asphalt. Next the plate is removed and re embedded with the face on top. The hammering is continued, this time forcing the background of the design into the asphalt. By a series of hammering and re embedding, followed finally by chasing, the metal sheet attains the finished appearance.

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Traditional Indian Brass and copper utensils have hammered finish on the outside. The same is often copied on aluminium utensils but reducing the strength due to ‘cold working’ of the metal. Leather and paper surfaces are rolled embossed to create textured patterns. Timber veneered surfaces are pressed for texture creation. Rendering of a wet plaster face by variety of pressing and chasing tools is very common. Chasing is very common with copper and brass pots (e.g. Peshwai Lotas and glasses).

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Matting is mainly used for creating textured surfaces. Matting is a mechanical technique compared to etching where a chemically active substance is used. Mating and etching can also be done by chemical metal removal processes (such as by reversing the metal deposition by changing the cathode charge) in the final stage of plating. Parallel, crossed, irregular, concentric, circular and other geometric configurations are carved or embossed on the surface. In matting process very fine lines or dots are created. Matted areas contrast with other glossy areas.

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Matting of Surface

Etching is usually done by an active or reactive chemical substance that will either erode away part of the surface or change its colour quality. Acid and alkali treatments also provide etched surfaces. Etching is also an artwork technique of Hydrofluoric acid over Glass surfaces.

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Concrete surface levelling

Surface levelling is a major field of material handling. Surfaces are levelled by chipping away very thin sections off the surface. The material must have layered formation (e.g. Kotah -Ladi stones, bamboo, cane) or fracturable or brittle constitution (e.g. stones). Surfaces are ground and polished for a levelling. Surface levelling is done as plastering with materials like clay, lime, gypsum, etc. 

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Shaving is done to remove material’s components such as outward hair or fibres, layers, etc. Leather surfaces are shaved to remove the surface hair and also for thinning. Leathers are also surface split to separate leather suitable for uppers and soles. The palm leaves are shaved to remove the stems and make them smoother for writing. Tree-barks are removed by axes and choppers to retard insect attack and increase moisture removal. Timbers are re-cut or planned with finer tools to achieve a smoother surface. Timbers are split very finely to create veneers. Wood planning is also a shaving technique. Carpets and rugs require close shearing by scissors to shave of protruding fibres.

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Grinding removes material from the surface to roughen a normally glossy surface like glass, or polish a rough surface like stone. Grinding requires material of higher hardness than the surface material, and is done by rubbing down with a graded series of coarse to fine abrasives, such as Carborundum, sandstone, emery, pumice, sand, glass and diamond powders. Where a material constitution permits, very fine grinding may polish the surface. Grinding is a cutting operation in which each grit that comes in contact with the material cuts out a minute chip, or swarf. 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. Metal and glass can be ground to a mirror finish and an accuracy of 0.0000025 cm. 

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Abrasives are used as grinding wheels, sandpapers, honing stones, polish, cutoff wheels, tumbling and vibratory mass-finishing media, sandblasting, pulp-stones, ball mills, and many other tools and products. Stone surfaces are chiselled to split the material into thinner sections, to remove the weathered crust and also to level out the surface. Grinding and polishing is done to: Hard materials such as building stones, marbles, granites, metals, glass; Precious and Semiprecious stones like gems, diamonds; Animal products like ivory, bones, horns, teeth, leather; Plant products like timbers, seeds; Ceramics like pottery products, bricks, cement concrete and other cement products.

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Polishing, Honing, Lapping, Buffing: 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 brilliant finish on the surface of a material. The polishing materials are coated on the surface of cloth, felt, leather, rubber pr polymer wheels or as belts. Metal surfaces are levelled and finished by honing and lapping. Honing removes less than 0.0125 millimetres of material from the surface to eliminate micro scratches and machine marks from ground machine parts. It is done with bonded abrasive sticks or stones that are mounted in a honing head. Lapping is a process in which a soft cloth (wool, linen and chamois-leather) impregnated with abrasive pastes (rubbing compounds), is rubbed against the surface of a workpiece.

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Buffing is a term used for polishing of metals. Buffing is done with polishing compounds and brushes of various shapes, and abrading materials, like: (animal hair, synthetic fibres, plant fibres -coir), flex, wool and leather. Barber polishing the razor on a leather stripe is a buffing process that levels out small nicks on the blade. Utensils are buffed for a polished surface.

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There are four types of precision grinding machines: Centre-type grinders used for tiny valve spools to steel mill roles. Centre-less grinders used for bowling balls, surgical sutures, and tapered roller bearings. Internal grinders are employed for inside diameters of gears, bearing races, and similar parts. Surface grinders are used for die tops, bench surfaces.

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Lapping is used to produce a high-quality surface finish or to finish a workpiece within close size limits. Dimensional tolerances of 0.00005 millimetres can be achieved in the hand or machine lapping of precision parts such as gauges or gauge blocks.

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Burnishing is controlled burning (or a heat treatment) at the surface section to remove part of the material and to change the colour or texture properties of the surface. Burnishing is both a process of surface finish and surface cleaning. Most of the organic materials can be surface-treated directly with fire or indirectly with high heat to achieve a burnished or ironed effect. Textiles, paper, leather, leaves, wood, etc. are some materials that can be burnished. High temperature burnishing removes the surface fibres and hair, and chars or burns (sinter) the top part of the surface, creating a burnt colour + texture effect. Textiles are Ironed, i.e. decreased or perma-set, i.e. creased with pressurized heat treatment. Synthetics or composite textiles are selectively or locally burnished to fuse the fibres or filaments, create textured effects and also alter the transparency, opacity, etc. Wood surfaces on burnishing, creates a dehydrated or an old shrivelled or shrunk surface, similar to an old wood.

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Metal surfaces also burnished not only to harden or anneal the top surface but to burn the oily residues, dehydrate, and descale the surface. Burnished metal surfaces often attain peculiar colour and pattern effects.

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