sandcasting

Background

Aluminium is a product with unique properties, making it a natural partner for the building industry. Thanks to its strength, durability, corrosion resistance and recyclability, it has become an essential product for the building industry and over the past 50 years its use in building applications has shown continuous and consistent growth.

Applications of Aluminium in Construction and Building

Aluminium extruded, rolled, and cast products are commonly used for window frames and other glazed structures ranging from shop fronts to large roof superstructures for shopping centres and stadiums; for roofing, siding, and curtain walling, as well as for cast door handles, catches for windows, staircases, heating and air-conditioning systems. Most recently, aluminium has played a significant role in the renovation of historic buildings. The characteristics and properties of aluminium as a material have lead to revolutionary and innovative changes in building techniques and architectural and engineering projects. Aluminium is leading the way into the future of the construction industry.

Recycling Aluminium Construction Materials

In addition to their particularly long service life, aluminium construction industry products can either be used after dismantling or indefinitely recycled, without any loss of the materials’ basic qualities and properties. The use of recycled aluminium also offers substantial energy benefits. Remelting used aluminium requires only 5 per cent of the energy needed to produce primary metal. Thus, rather then contributing to society’s growing waste problem, aluminium can be remelted and reformed to produce a new generation of building parts.

Reasons Why So Much Aluminium is Recycled

Aluminium in general has always been recycled at a higher rate than most other raw materials. Given the necessary infrastructure, it is possible to recycle all aluminium construction industry applications, for several reasons. First, there is a relatively high level of scrap aluminium available. Second, aluminium has a high scrap value which can contribute significantly towards covering demolition costs. Finally, the infrastructure required for the collection of scrap metals is already well-established and will continue to grow on its own economic merit as it has done in the past to provide an increasingly efficient recycling system.

Aluminium Recovery Rates

Nearly 40 per cent of all aluminium used today is remelted metal. However, this does not give a true picture of the recovery ratio that can be achieved in the construction industry, as the durability of aluminium building industry parts makes the material unavailable for recycling for many years.

Pretreating Aluminium Connected to Other Scrap

Aluminium scrap collected from construction applications is sometimes attached to other materials, such as resins or foam insulation products. The scrap is pretreated to eliminate such waste. Consequently harmful emissions produced by the burning of such waste materials during the remelting are minimised or avoided and the purity pf the remelted metal is therefore ensured. In general, however, aluminium construction products do not need to be protected by organic coatings used to safeguard some alternative materials. They therefore offer a source of good metal which can be recycled without any pre-processing.

Separating Aluminium from Other Scrap

Finally, aluminium is easily separated from other metal scrap. To facilitate this operation, the raw scrap is first broken down through cutting or crushing in fragmentation plants. Ferrous scrap can then be removed by magnetic devices, while non-magnetic scrap that differs in density from aluminium can be sorted in heavy liquor separation equipment. Alternatively, aluminium can be separated directly by using eddy-current sorting machines.
Energy Efficiency.

Sand Casting, Investment Casting, Die Casting, Green Sand Casting, Aluminum Sand Casting,

A sand casting or a sand molded casting is a cast part produced by forming a mold from a sand mixture and pouring molten liquid metal into the cavity in the mold. The mold is then cooled until the metal has solidified. In the last stage the casting is separated from the mold. There are six steps in this process:

   1. Place a pattern in sand to create a mold.
   2. Incorporate a gating system.
   3. Remove the pattern.
   4. Fill the mold cavity with molten metal.
   5. Allow the metal to cool.
   6. Break away the sand mold and remove the casting.

There are two main types of sand used for molding. "Green sand" is a mixture of silica sand, clay, moisture and other additives. The "air set" method uses dry sand bonded to materials other than clay, using a fast curing adhesive. When these are used, they are collectively called "air set" sand castings to distinguish these from "green sand" castings. Two types of molding sand are natural bonded (bank sand) and synthetic (lake sand), which is generally preferred due to its more consistent composition.

With both methods, the sand mixture is packed around a master "pattern" forming a mold cavity. If necessary, a temporary plug is placed to form a channel for pouring the fluid to be cast. Air-set molds often form a two-part mold having a top and bottom, termed Cope and drag. The sand mixture is tamped down as it is added, and the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold. Then the pattern is removed with the channel plug, leaving the mold cavity. The casting liquid (typically molten metal) is then poured into the mold cavity. After the metal has solidified and cooled, the casting is separated from the sand mold. There is typically no mold release agent, and the mold is generally destroyed in the removal process.[1]

The accuracy of the casting is limited by the type of sand and the molding process. Sand castings made from coarse green sand impart a rough texture on the surface of the casting, and this makes them easy to identify. Air-set molds can produce castings with much smoother surfaces. Surfaces can also be ground and polished, for example when making a large bell. After molding, the casting is covered in a residue of oxides, silicates and other compounds. This residue can be removed by various means, such as grinding, or shot blasting.

During casting, some of the components of the sand mixture are lost in the thermal casting process. Green sand can be reused after adjusting its composition to replenish the lost moisture and additives. The pattern itself can be reused indefinitely to produce new sand molds. The sand molding process has been used for many centuries to produce castings manually. Since 1950, partially-automated casting processes have been developed for production lines.

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