Why can blind risers be smaller than opentop risersSolutionA

Why can blind risers be smaller than open-top risers?

Solution

ANSWER:
As we know risers are employed as reservoirs for a casting in regions where it is expected that there will occur a shrinkage in metal, i.e, areas which are the last to solidify. Thus, risers must be made large enough to ensure that they are the last to solidify. If a riser solidifies before the part (it is to feed) does, it is useless. Consequently, an open riser (which is in contact with air) must be larger to ensure it will not solidify first. A blind riser is less prone to this phenomenon, as it is in contact with the mould on all surfaces. Thus, it is slower to cool since the mould increases in temperature and the riser can be located in an area that will cool more slowly; thus, a blind riser may be made smaller.