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The 300-lb. ductile iron diaphragm casting goes in a steam turbine to help guide the infl ow of steam.


shape of the cast diaphragm is rela- tively simple. Bringing the core to life is a diff erent story. When the turbine diaphragm design was fi rst conceived and pro- duced, the core was diffi cult to make, requiring a burdensome manual pro- cess. T e initial design used a corebox with a spacer that was indexed to create the vane spacing. T e spacer was built in to a handle that was mounted in the center of the corebox. As each vane was placed, the handle was moved and secured into a hole with a dowel that was incorporated into the


handle. T e sand was packed by hand. Using this method to make the core required the foundry to use oil sand due to the long production process. T e biggest downfall to the corebox method was the required total area cal- culation was inconsistent and virtually impossible to achieve. Hand-packed sand meant there was nothing to maintain the spacing of the vanes after the spacer was indexed. Depending on how hard the core maker packed the sand, the vanes could easily shift both in position and angle. Since the surface area was always well over the defi ned limits, the vanes had to be bent back into position after the casting layout


was completed. T is caused more problems than the simple distortion of the vane throat area. Because it takes two diaphragm halves to create a full rotation, the castings have to be laid out to defi ne the split . T e fi rst vanes on each half must


be machined to marry up when assembled. With the issue of the vanes moving during coremaking, this was often very diffi cult to achieve. Surface machining was also often an issue because the surface was defi ned by the height of the highest vane and vane height tolerance exceptions were common. If the vane was too high, the material around it would


August 2017 MODERN CASTING | 27


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