The apparatus described herein relates generally to a gib shim. More specifically, the apparatus relates to an adjustable gib shim.
A gas turbine is mounted to its base by vertical supports at multiple locations. A forward support may be placed at the lower half vertical flange of the forward compressor casing, and two more supports may be placed on either side of the turbine shell. The forward support is a flexible plate that permits axial expansion of the turbine. The turbine shell supports are fixed and mounted to pads on each side of the base frame, and extend up to each side of the exhaust frame of the turbine shell. The turbine shell supports permit radial expansion, but control the axial and vertical position of the unit horizontal centerline to assure proper casing alignment.
Gib keys and blocks are used to prevent or limit lateral or rotational movement of the turbine casings while permitting axial and radial movement resulting from thermal expansion. A gib key may be machined on, or attached to, the lower half of the turbine shell. The gib key fits into a guide block which is welded to the turbine's base frame. In some applications, a specific gap between the gib key and block is desired. To obtain this gap the gib key must be machined until the desired gap is obtained. The machining operation is basically an iterative process that is typically repeated many times. For example, the gap is measured, the gib key is ground down and installed, the gap is re-measured and the process repeats until the desired gap is obtained. The gap may change based on various parameters, for example, shipping the turbine may require one gap, operation of the turbine may require a different length gap, and extended use of the turbine may require yet another gap. Measuring, machining and installing all these different gib keys is a time consuming and labor intensive process.