Application of insulation padding in a heavy turbine guide vane casting

To replace metal padding by insulation padding for castings can save the melt and reduce cleaning work of castings. The design of insulation padding was investigated. The equation of the modulus extension factor for insulation padding and the ratio of its thickness over the modulus of a casting were improved to determine the thickness of insulation padding. The insulation padding was designed for a turbine guide vane casting weighing 3. 5 t. A sound casting was obtained with 750 kg steel saved. On the other side, the casting obviously expanded at the interface with the insulation padding, which is perhaps the reason that the use of insulation padding has been suspended for many years. To avoid the expansion of insulation padding, a shielding layer made of a kind of material of good fire resistance was adopted to prevent the insulation layer from touching the melt. The shielding layer serves as a cushion of heat and expansion during solidification process so as to resist the expansion of castings and guarantee the feeding effect at the same time. Furthermore, insulation padding can be placed by a certain offset into the mold cavity so as to counteract the expansion of castings.