The foundry process

Starting from foundry scrap (selected scrap according to a certain chemical composition) or ingots, the foundry produces finished castings. Usually these are components which will require further treatment or assembly to yield a final product. 

On the moulding side, a basic distinction is made between permanent and lost moulds. Foundries casting in permanent moulds, buy these metal moulds (dies) externally, but typically operate an in-house mould repair and maintenance shop. Foundries casting in lost moulds, often buy wooden, metal or plastic patterns (for their mould design) and operate an in-house pattern maintenance and repair shop. Moulds, cores and lost models are generally produced as part of the foundry process. 

Superalloys with a high content of alloying elements, such as nickel, will also be discussed. 

Foundries utilise mechanisation and automation depending on the need for reproductivity and on the series sizes. The most flexible installation is typically the jobbing foundry. This produces a variety of products in small numbers ( 100). In general, this type of foundry applies manual moulding techniques with resin-bonded sand moulds. The melting furnace works batch wise to allow an easy change of alloy. This implies the use of induction or rotary furnaces. 

Specific casting techniques, such as full mould casting, centrifugal casting and continuous casting are applied where the product type requires it. 

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Dust and particles releases are a general issue in all stages of the foundry process, and for all processes used. Dust is generated in the production and processing of sand moulds and cores, as well as in the finishing of the castings (both from lost moulds and permanent moulds). 

In the foundry process, emissions to air are not limited to one (or several) fixed point(s). The process involves various emission sources (e.g. from hot castings, sand, hot metal). A key issue in emission reduction is not only to treat the exhaust and off-gas flow, but also to capture it. 

A general flow chart of the foundry process is depicted in Figure 2.1. The process can be divided into the following major activities ... 

The general mass stream overview for the foundry process is given in Figure 3.1. This scheme generally applies for ferrous and non-ferrous foundries. Specific aspects of the various process steps and types will be woiked out below. 

Figure 3.1 Mass stream overview for the foundry process...

Microwave drying also brings pol mierisation reactions to a further completion. This reduces the gaseous emissions in the proceeding stages of the foundry process (i.e. pouring, cooling, shakeout). 

The foundry process contains various point sources of noise. These include scrap handling furnace charging burners... 

The foundry process involves the use, consumption, combination and mixing of various material types. BAT requires the minimisation of raw materials consumption and the furthering of residue recovery and recycling. Therefore, BAT is to optimise the management and control of internal flows. 

A general overview of the inputs and outputs of the foundry process is given in the figure below. The Casting step mentioned in the centre of the picture covers also all necessary moulding operations. The major input streams are metal, energy, binders and water. The key emissions are dust, amines and VOCs, and for specific furnace types also SO2, dioxins and NOx. 

Among the foundry processes, the shell molding or Croning process has evolved into an accepted production method using both shell molds and shell cores. Invented in Germany in 1943 by J. Croning, this process has been industrially adapted because it offers high production rates. A scheme of the process is described in Fig. 9.16. Its principles are as follows ... 

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