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  Metal Forming

Foundry work is the process of making a metal casting of an object by pouring molten metal into a mould. The mould is made using a pattern of the article required. In some cases, the mould contains a core that determines the dimensions of any internal cavities.There are two types of foundries. Ferrous foundries produce iron and steel castings. Non-ferrous foundries produce castings of copper-based alloys (brass, bronze and copper), aluminium-based alloys (lead, zinc, nickel, magnesium) and other alloys.

Process

Pattern Making

The pattern shop area involves the making, assembly and storage of patterns for use in moulding and core-making foundry processes.Pattern making is the process of forming a likeness of the final casting so that a mould can be made. The pattern is not identical to the final casting because allowances have to be made for the shrinkage of the metal in the mould.

The pattern maker is a craftsperson who translates two-dimensional design plans to a three dimensional object. Some "high tech" pattern shops utilise the use of CADCAM (Computer Aided Design-Computer Aided Manufacture) technology. The computer electronically designs or models the pattern and also determines the cutting path of the cutting router.

Traditionally, patterns were made of wood but they are now commonly made of metal, plastic or foam. Traditional wooden patterns and core boxes are made in a workshop using hand tools and woodworking machinery, such as bench saws, circular saws and planers.

Sand mould and core making

The core shop is primarily concerned with processing and curing cores. Tasks include core moulding, blowing/shooting, painting and stoving.Cores are moulded sand shapes which may be placed inside moulds to define a cavity inside the final casting. Cores must be mechanically strong (as molten metal flows around the core during pouring). However, the cores must also be easy to break down to allow the removal of the sand and casting after pouring and cooling.

Cores are produced by blowing, ramming or in heated processes, investing sand into a core box. The finished cores, which can be solid or hollow, are inserted into the mould to provide the internal cavities of the casting before the mould halves are joined. Sand cores are also widely used in die casting, where permanent metal moulds are employed.

Sand casting is the most common production technique, especially for ferrous castings. Sand is mixed with clay and water or with chemical binders and then packed or rammed around the pattern to form a mould half. The two halves are joined together to make the mould - a rigid cavity that provides the required shape for the casting.

Variations on this technique include the use of plaster in place of sand and the recently invented patternless process, where the mould is machined directly out of a sand block without the need for a pattern.

Other casting techniques

Although sand casting is the predominant production technique, other methods are used, as described below.Metal moulds are used for certain types of production including centrifugal casting techniques and diecasting. Centrifugal (spun) casting involves pouring the metal into a rotating mould and is used for making pipes, rolls and cylinder liners. Die-casting is commonly used for production of aluminium and zinc castings.

For investment processes, expendable pattern replicas are made in wax or polystyrene and then coated with a ceramic refractory material to make a hard shell. Wax is removed from the shell by steam and polystyrene removed by firing. The shell is then fired at 1000 C to set the ceramic bond. For casting, the shells are sometimes embedded in vacuum packed or chemically bonded sand to provide support and enable a thinner shell to be employed.

Lost foam casting is another variation involving the use of polystyrene pattern replicas. In this process, the pattern replica is coated with a single coat of refractory paint and embedded in a box of sand, which can be chemically bonded or stiffened by vacuum. The molten metal is poured directly onto the replica resulting in vaporisation of the polystyrene.

Loss Exposure

Lost foam casting is another variation involving the use of polystyrene pattern replicas. In this process, the pattern replica is coated with a single coat of refractory paint and embedded in a box of sand, which can be chemically bonded or stiffened by vacuum. The molten metal is poured directly onto the replica resulting in vaporisation of the polystyrene. Also a large number of plant and machinery is used in foundry work.

This includes

wood cutting and finishing machines in pattern shop automatic and semi-automatic machinery in moulding and core-making mechanical handling devices, cranes, hoists, monorails, conveyors, forklifts, trucks, electromagnets grinders

Continuous vibration of some equipment results in increased mechanical stress on nuts, bolts, chains and cables, which may eventually lead to equipment failure. This in turn may result in major explosions or fires. In respect of core making, there is high exposure to hazardous substances used in the core preparation and painting e.g. amines and formaldehyde. The sand binder system ingredients include toluene, phenol and furfuryl alcohol. These can cause combustion and explosion.

Hazards associated with the moulding shop include hazardous substances used in the mould preparation e.g. esters, solvents, isocyanates, phenol, formaldehyde, furfuryl alcohol and atmospheric contaminants e.g. sulphur dioxide, acid mist

Molten Metal

Molten metal is a major hazard in foundry melting and pouring areas. Workers who perform tasks with or near molten metal may come into contact with metal splashes and be exposed to electromagnetic radiation.

The following situations may increase the risk of hot metal splashes

  • Charging a furnace with contaminated or moist scrap metal and alloys using
  • Moist tools, moulds or other material when contacting molten metal
  • Tapping or pouring the molten metal into a holding furnace, tundish or ladle
  • Slagging or raking operations
  • Pouring molten metal from ladles into moulds
  • Oxy-boiling of carbon
  • Liquid sintering (a process for hardening of the lining with molten metal)

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