Define Design Aspects of Pot Bearing?
Basic elements of a POT bearing are:
- POT or a shallow cylinder
- An elastomeric pad
- A set of sealing rings
- A piston
POT bearings are fixed against all translation unless they are used with a PTFE sliding surface. The POT may either be one piece construction shaped by machining or fabricated by welding ring on to the base plate. The elastomer pad inserted into the POT is restrained from being squeezed out of the annular gap between the side wall and the piston by means of a set of two or three flat brass rings. The circular rings have traditionally been brazed into a closed circle, whereas the flat ones are usually bent from a strip and the ends are not joined. Brass rings are placed in a recess on the top of the elastomeric pad.
PTFE rings have been tried, but have been abandoned because of their poor performance. The cover piston which fits into the POT is placed in contact with the elastomer pad. In the POT type sliding bearing the cover/piston is mounted by a sliding assembly. The upper surface of the piston is recessed and filled with the PTFE disc. The upper sliding plate is provided with a sheet of stainless steel or chrome nickel alloy steel. The PTFE disc is provided with small cavities (lubrication pockets) containing a special lubricant which ensure lifelong lubrication of the sliding surface. An all around seal is provided to prevent ingress of moisture and dust on the contact surface as well as inside the POT. Generally four holes are drilled in the top plate as well as the plate on which POT is mounted to facilitate attachment of the POT bearings to the girders and bed block. The PTFE-steel contact surface can also be in the form of two hemispheres in which case the bearing provides for rotation as well as translation.