Sprue base well
This is a reservoir China precision machining for metal at the bottom of the sprue to reduce the momentum of the molten metal. The molten metal as it moves down the sprue grains in velocity some of which is lost in the sprue base well by which the mould erosion is reduced.
This molten metal changes direction and flows into the runners in a more uniform way.
It is generally located in the horizontal plane (parting plane) which connects the sprue to its ingates, thus letting the metal enter the mould cavity. The runners are normally made trapezoidal in cross section. It is a general practice for ferrous metals to cut the runners in the cope and the ingates in the drag. The main reason for this is to trap the slag and dross which are lighter and thus trapped in the upper portion of the runners.
For effective trapping of the slag, runners should flow full. When the amount of
molten metal coming from the down sprue is more than the amount flowing through the ingates, the runner would always be full and thus slag trapping would take place. But when the metal flowing through the ingates is more than that flowing through the runners, then the runner would be filled only partially and the slag would then enter the mould cavity.
The runner is extended a little further after it encounters the ingate. This
extension is provided to trap the slag in the molten metal. The metal initially comes along with the slag floating at the top of the ladle and this flows straight, going beyond the ingate and trapped in the runner extension.
Riser Most of the foundry alloys shrink during solidification. Table 10.1 shows the various volumetric shrinkages for typical material. As a result of this volumetric shrinkage during solidification, China precision machining voids are likely to form in the castings unless additional molten metal is fed into these places which are termed as hot spots since they remain hot till the end. Hence a reservoir of molten metal is to be maintained from which the metal can flow readily into the casting when the need arises. These reservoirs arecalled risers.
As shown in Table 5.6, different materials have different shrinkages
and hence the riser requirements vary for the materials. In grey cast iron, because of graphitization during solidification, there may be an increase in volume sometimes. This if course, depends on the degree China precision machining of graphitization in grey cast iron which is controlled by the silicon content.
In order to make them effective, the riser should be designed keeping the following in mind.
1. the metal in the riser should solidify in the end.
2. the riser volume should be
sufficient for compensating the shrinkage in the casting.
Table 5.6 volumetric liquid shrinkages
Medium carbon steel 2.50 to 3.50
High carbon steel 4.00
Aluminum alloy (11-13% Si) 3.50
Aluminum bronze 4.10
70-30 brass 4.50
Bearing bronze 7.3
Grey cast iron 1.90 to negative
White cast iron 4.00 to 5.75