**6.4 Vacuum control**

Proper control of vacuum pressure is paramount in countergravity casting. Too much vacuum will result in splatter of melt inside the moulding flask due to over-filling of the mould cavity. Loss of vacuum during casting is also a real problem for countergravity technique. This may be caused by improperly closed lid, damage to or cracks in the moulding flask, or a poor seal between the recess of the lock-nut and the conical connection

Aluminium Countergravity Casting – Potentials and Challenges 15

The possibility of more economical use of the melt is good for the bottom line of foundry operation and was actually the original goal of the countergravity technique. This has

The combination of precision near net shape and strength has resulted in countergravity die casting being used to produce parts formerly made of steel that required a significant

Net shape casting, particularly for thin sections is easily achievable in countergravity casting. Countergravity cast part may have walls as thin as 0.5 mm (National Institute of

In order to make the benefits of this casting technique more accessible, low-cost countergravity equipment have been developed. A low-cost design developed by the

The design utilizes a simplified vacuum control system and manual positioning of mould and moulding flask. Such low cost alternatives would be invaluable for small scale

Size restrictions have been tackled by many recent designs. Jie *et al* (2009) reported a system using compressed air to assist the up-flow of melt for large-sized castings. The Check Valve (CV) process is has been developed Hitchiner for larger sized casting. This allows for

motivated a growing list of companies and industrial sector to adopt the technology.

amount of secondary machining (Aurora Metals LLC, 2009).

Fig. 13. A low-cost machine for countergravity casting

Industrial Research, 2005).

operations.

authors is presented in figure 13.

point of the sprue on the mould. These non-ideal, but very real instances may require a more interactive vacuum system, wherein pressure feedback is used to constantly adjust the flask vacuum pressure.
