Mould and core-making

1 Exhaust capture of dust from green sand preparation (sand plant) 

The exhaust air from the green sand preparation is saturated with water. Therefore, wet systems (often of the low pressure type) seem to be most suitable for exhaust capture. However, the wet system is widely being replaced by dry dust abatement. The latter has the advantage that part of the dust may be recirculated and that no waste water stream is generated. Additionally, the wet systems are prone to internal eorrosion and the build-up of dust and oxidation products. The wet separation of exhausted air impurities can result in problems for the waste water cleaning. Dust contains bentonite which is difficult to dispose of due to its anti-sedimentable effects. [225, TWG, 2003] 

When applying fabric filters, condensation problems need to be prevented. Condensation may cause a deposition of dust, clogging and/or a tearing of the filter. The addition of cooling water to the sand needs to be done in a controlled way in order to minimise steam formation. The dew point of the airflow may be increased through heating with gas burners. 

One benefit is that the collected dust is dry and so can be easily transported. After size separation, the coarse fraction and part of the fine fraction may be recirculated into the sand mixing. 

The use of wet systems cause the production of a waste water flow. Which needs to be treated, a sludge fraction, which needs to be a disposed of. Some systems work without producing waste water. The sludge is thickened and, if it contains a sufficient amount of bentonite, is re-used in the moulding-sand cycle. 

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Olivine sand is produced by crushing natural rocks, which explains its diverse characteristics. It is usually used for moulding and core-making in manganese steel casting. The presence of manganese prohibits the presence of silica as these two components react to give a very fusible compound. The reported purchase price in Spain is EUR 130/tonne (2002). 

Moulding and core-making with chemically-bonded sand... 

This process is used to a minor extent for moulding and core-making, with restrictions for steel casting, as cracks or pinholes may occur. These can be prevented however, by the addition of iron oxide and by dr3dng the moulds and cores. In some countries (e g. Sweden) this type of binder has not been used for 25 years, mainly because of its effect on the working environment. 

This process is the only one among all moulding and core-making processes that can use precoated sand, directly available from suppliers and ready for use, although pre-coating of the sand may also be performed at the foundry. 

Table 3.37 Example dust emissions and particle size for mould and core-making [202, TWG, 2002]...

The use of chemical binders results in the production of various compounds during mixing, mould- and core-making, storage, pouring and cooling, as indicated in Table 3.35. Some indicative emission factors for several processes are given in Table 3.40 and Table 3.41. 

Mould- and core-making, including sand preparation... 

Moulding and core-making with chemically-bonded sand 4.3.3.1 Minimisation of binder and resin consumption... 

Modem mould and core-making machines allow the production parameters of the various product types to be saved in an electronic database. This allows easy change-over to new products, without the loss of time and materials from finding the right parameters by simply using trial and error. For new products, the settings for similar products may be used to shorten the optimisation time. 

Chemically-bonded sand mould and core-making... 

Regeneration ratio the ratio between the mass of regenerated sand and the total mass of sand used in mould and core-making, expressed as a percentage... 

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