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The image given below shows a bolster with a series of riser and runner. What I really do not understand is which is the riser and which is the runner. Also a detailed explanation to why multiple risers and multiple runners are being used will be highly appreciated. In general what is the distinguishing feature between a riser and a runner? Out of the two rods in the periphery why is one relatively thick and the other one thin?


1 Answer 1


A riser is a static reserve volume of metal available to flow into the casting to compensate for shrinkage as the liquid freezes. Risers are relatively large because they should not freeze until after the casting has frozen. Risers may be "hot topped", exothermic material is put on to provide extra heat to keep the riser liquid as long as possible. A runner is a pathway in the mold for liquid metal to flow from the sprue to reach all parts of the casting . One reason for runners is that if all molten metal enters the mold at one location it will overheat the mold . Locations where the mold has been heated more than others can cause shrinkage porosity and cracks. There may be some small features to permit venting of air and steam from the mold.

  • $\begingroup$ Just curios, would it be correct, or wrong, to say the "riser" is the vertical runs in a piping system, and the "runner" is the horizontal runs? $\endgroup$
    – r13
    Mar 20, 2021 at 16:45
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    $\begingroup$ The difference is in the function , not the orientation. $\endgroup$ Mar 20, 2021 at 18:35
  • $\begingroup$ I think I can understand what you mean. But this is what I got from QUORA.com, "The main difference is that runner is a horizontal pathway into the mould cavity whereas riser is a vertical pathway . Riser is of two types open riser and blind riser " I am stuck on what is the function of the blind riser? $\endgroup$
    – r13
    Mar 20, 2021 at 18:50
  • $\begingroup$ @r13 blind risers are not open to the air at the top, so they retain heat longer than open risers. On the other hand, there may be air trapped in the blind riser which prevents it completely filling with molten material. "Runners" are where the liquid runs into the mold when you pour the casting. "Risers" are where the excess liquid rises up above the shape of the part you want to case, to make sure the mould is completely full. $\endgroup$
    – alephzero
    Mar 20, 2021 at 22:34
  • $\begingroup$ Thanks. Here is a brief explanation of "Blind Riser" - "Blind risers are located in the lower section of castings, or just hidden at a level below the top risers, and like open risers, they act as reservoirs that supply liquid metal into a casting as it contracts on solidification. Open risers break through the cope to the top of the mold and are entirely exposed to the outside atmosphere." $\endgroup$
    – r13
    Mar 20, 2021 at 22:54

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