**6.5 Melt contamination by reusable sprue**

An effort to bring down overall system costs have led to the use of re-usable sprues. These are usually in the form of metallic pipes. Re-usable sprues must however be used with caution because of the tendency of accumulated impurities in the sprue channel to contaminate the melt.

Fig. 12. Premature solidification of melt inside the sprue due to inadequate pre-heat
