Types
Risers are categorized based on three criteria: location, if it is open to the atmosphere, and how it is filled. If the riser is located on the casting then it is known as a top riser, but if it is located next to the casting it is known as a side riser. Top risers are advantageous because they take up less space in the flask than a side riser, plus they have a shorter feeding distance. If the riser is open to the atmosphere it is known as an open riser, but if the risers is completely contained in the mold it is known as a blind riser. An open riser is usually bigger than a blind because the open riser loses more heat to mold through the top of the riser. Finally, if the riser receives material from the gating system and fills after the mold cavity it is known as a live riser or hot riser. If the riser fills with material that has already flowed through the mold cavity it is known as a dead riser or cold riser. Live risers are usually smaller than dead risers. Note that top risers are almost always dead risers and risers in the gating system are almost always live risers.
Note that the connection of the riser to the molding cavity can be an issue for side risers. On one hand the connection should be as small as possible to make separation as easy as possible, but, on the other, the connection must be big enough for it to not solidify before the riser. The connection is usually made short to take advantage of the heat of both the riser and the molding cavity, which will keep it hot throughout the process.
There are risering aids that can be implemented to slow the cooling of a riser or decrease its size. One is using an insulating sleeve and top around the riser. Another is placing a heater around only the riser.
Read more about this topic: Riser (casting)
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