Gravity die casting

Gravity die-casting is the simplest and most versatile of the diecasting methods. The molten metal is poured into the die, using the force 

This process provides castings of greater accuracy than sand casting, due to the use of metal moulds which can be used to produce thousands of castings before they require replacement. The most commonly used material for the manufacture of dies for gravity die- 

Workshop Processes, Practices and Materials. DOI 10.1016/B978-0-08-089064-7.000I8-I 

Copyright 2010 Bruce J. Black. Published by Elsevier Ltd. All rights of reproduction in any form reserved. 

To allow for rurmers and risers, the volume of material required can amount to over twice the volume of the actual component. Although the surplus can be recovered, it is stUl wasteful in its removal, dressing the component (or fettling using a hand-held grinder), and the energy required in remelting. 

Material utilization moderate to high (10-40 per cent lost in scrap, but can be recycled). 

If accuracy and surface finish not an issue, can use sand cores instead of metallic or graphite for greater economy. 

Production volumes of 500-1000 may be viable, but suited to higher volume production. Tooling costs moderate. 

Finishing costs low to moderate. Gates need to be removed. 

Shape complexity limited by that obtained in die halves. 

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GRAVITY DIE CASTING PROCESS CAPABILITY MAP FOR IRON AND COPPER AND ZINC ALLOYS... 

Gravity die cast ZA alloy test plates and 99.99% pure rolled zinc samples were exposed at a waste water treatment plant in Detroit, Michigan, USA. The results after one year are summarised in Table 4.38 . 

The quantities of SFe used in various operating conditions are given in Table 3.26 (pressure diecasting) and Table 3.27 (gravity die-casting). These concentrations need to be maintained close to the melt surface [191, IMA, et al.]. The tabled values are the recommended practice for the use of SFe from the International Magnesium Association (IMA). In practice, higher concentrations are sometimes used (e.g. 99.4 % CO2, 0.6 % SFg) [202, TWG, 2002]. 

For gravity die-casting and centrifugal casting, post combustion, chemical washing and adsorption to activated carbon are used in order to reduce organic emissions and odour. These systems have already been described above. 

Metaalgieterij Giessen, Hoboken (B) aluminium foundry using HPDC and gravity die-casting. 

The dies are cheaper than for high-pressure methods since they can usually be made of cast iron, but they are sometimes more expensive than for gravity die-casting. The capital ouday for machines is higher than for gravity but lower than for the high-pressure method. 

For example, if the component under consideration is to be made from aluminium alloy and only 2000 per year are required, the choice would be limited to gravity die-casting. If, however, the quantity required was 50000 per year then the high-pressure cold-chamber method would be appropriate. 

Low pressure die casting uses low-pressure (1 bar) air to force the molten metal into the die cavity. Less popular than gravity die casting, and tends to be used purely for the production of car wheels. Gives lower production rates. 

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