Cat paw gap

The sliding pin system is a device that ensures the cylinder can expand freely in a directed manner while maintaining its axis center unchanged. During startup and load increase, the temperature of the cylinder in a steam turbine gradually rises, resulting in thermal expansion. Since the temperature rise of the base plate is lower than that of the cylinder, if there is a fixed connection between the cylinder and the base plate, the cylinder will not be able to expand freely. Therefore, various sliding pins should be installed between the cylinder and the base plate as well as between the cylinder and the bearing housing, and appropriate gaps should be left in the bolts that fix the cylinder, thereby creating a complete sliding pin system that ensures the cylinder can expand freely while maintaining the center of the unit unchanged. Sliding pins can be classified into six types based on their installation location and functions: cross pins, longitudinal pins, vertical pins, cat’s paw cross pins, corner pins (pressure plates), and inclined pins. Cats’ paws are generally installed on the horizontal joint surfaces between the front bearing housing and the intermediate bearing housing of double-cylinder steam turbines; they consist of cat’s paws that protrude from the ends of the lower or upper cylinder, as well as special pins and bolts. The cat claw serves as a cross-pin and also provides support for the cylinder. The function of the cat’s paw cross sell is to ensure the free expansion of the cylinder in the transverse direction. At the same time, as the cylinder expands and contracts axially, it pushes the bearing housing forward or backward in order to maintain the axial relative position between the rotor and the cylinder.