The Technique of FURNITURE MAKING
PROPERTIES OF METAL Age-hardening
A slow hardening process which takes place in certain alloys, particularly those of aluminium when allowed to stand at room temperature after annealing. If you wish to work the material after it has become age-hardened, it must be reannealed. Duralumin age-hardens after five days.
Brittleness
Liability to break under a sharp blow. White cast iron and heat-hardened high-carbon steels are extremely brittle.
Conductivity
Capacity to transmit heat and electricity. Copper, silver and pure aluminium are good conductors.
Ductility
Ability to be stretched into fine wire without fracture; copper is highly ductile.
Elasticity
Ability to regain original shape after deformation. Lead is very malleable but has little elasticity—it does not spring back when bent.
Fusibility
Property of becoming liquid when heated. Different metals have different melting points.
Hardness
Resistance to deformation, bending and cutting.
Malleability
Capacity to be extended in all directions without fracturing by rolling, hammering or beating. Gold is the most malleable metal, and can be beaten into leaf 1/25000 in thick.
Tenacity or cohesion
Resistance to a pulling force—the opposite to ductility.
Work-hardening
Hardening of metal while it is being hammered or bent. The hardening causes the metal to become more brittle, and it must therefore be annealed to prevent it from cracking.
PROCESSES IN WORKING METAL Annealing
Heating metal to restore it to its softest possible working state.
Bluing
Treating steel to improve its corrosion - resistance. The metal is heated to create an oxide skin, then quenched in oil.
Casting
Production of metal shapes by pouring molten metal into moulds.
Drawing
Pulling ductile metals through holes in a plate, to reduce their cross-sectional areas.
Extruding
Forcing malleable materials through holes to produce bars, sections or tubes.
Forging
Shaping hot metal by hammering.
Hardening
Producing maximum hardness in high carbon steel by heating it to bright cherry red, then quenching it in water or brine. This process makes metal brittle and is usually following by tempering.
Pressing
Forming sheet metal to shape with a press tool.
Spinning
A process in which a fast revolving sheet of ductile metal is forced over a wood or metal form. Much aluminium alloy kitchenware is produced in this way.
Tempering
Removing some of the brittleness from steel after it has been hardened. The tempering is done by heating the steel, then cooling it— temperatures and speed of cooling vary with the types of steel. Steel cannot be tempered without being hardened.
METAL FINISHES IN FURNITURE PRODUCTION
Many metals and alloys readily corrode and tarnish when exposed to the atmosphere and therefore have to have a form of protective covering. These can be broadly classified as follows:
Metallic coatings
Chrome plate (the most common) Nickel plate Bronze plate
Silver plate Zinc plate
Process of applying a thin coating of an expensive anti-corrosive metal. In furniture production, used predominantly on mild steel.
Non-metallic coatings
Enamelling—stove and spray—has the advantage of giving colour to metal furniture. Lacquering—process of applying a thin transparent lacquer to decorative metals such as brass, to seal them from the atmosphere.
Plastic and nylon coating—becoming
increasingly popular, especially for restaurant furniture; can be in bright colours and gives a warm feeling to cold metal.
Chemical processes
Chemical colouring—used to alter the colour of the existing metal as well as to protect it; used chiefly on brass and copper.
Anodizing—used for aluminium alloys; consists of a hard film (anobic film) which can be dyed to various colours.
