Structures like bridges and pipes move due to atmospheric agents and seismic activity, requiring expansion joints and bearing surfaces to minimize frictional damage. Skid plates, made of low-friction materials, are used to create bearing surfaces that require little maintenance. They can also be used in pipe supports and to separate buildings from foundations in earthquake zones. Different slide plate designs are used for high loads and temperatures. Sliding plates can also be used as wear surfaces for moving parts like drawbridges.
Bridges, footbridges and overhead pipes move due to expansion and contraction due to atmospheric agents and also to seismic movement, or movement of the earth. These structures contain expansion joints to allow for movement and bearing surfaces or skid plates to minimize frictional damage. A skid plate is a combination of a flat steel plate and a low friction material that allows movement with little wear on the structure.
Bearings are used to reduce wear in most moving equipment, but buildings, bridges or other structures, static or non-moving, also need to be moved. The weight of traffic passing over a bridge or changes in temperature can cause the bridge structure to move in different directions. Metal beams in direct contact and under load may not move properly, or the high friction may cause sudden movement or release which can damage the structure.
Adding a skid plate between the beams creates a low-friction bearing surface that allows for smooth movement of the structure. A common plate coating is a slippery fluoropolymer fused to the bearing surface on both beams. The result is two polymer surfaces in contact, resulting in a low friction bearing that requires no lubrication and little maintenance.
Skid plates can also be used in pipe supports, used to support pipes where they are raised above the ground. Pipes can expand and contract due to temperature changes and a skid plate can be added to the pipe support beam. The support surface does not move, but allows the movement of the pipe resting on it.
Geological conditions can also cause buildings and bridges to move. In an earthquake zone, bearing surfaces may be installed underneath buildings to separate the structure from the underlying foundation. During an earthquake, the skid plate design allows the building to move very little as the ground shifts underneath it.
Some applications are not suitable for polymer bearings due to high loads or operating temperatures. A different slide plate design uses bronze or other metals that contain graphite carbon or lubricating oil. Graphite is often contained in the metal in the form of small buttons that are slightly higher in profile than the plate. Oil-filled bearings and plates are formed from tiny beads fused together, called sinters, which contain many oil-filled channels and voids.
Sliding plates can also be used as wear surfaces for moving parts. Drawbridges open and close repeatedly to allow ship traffic to cross rivers and canals. The end of the drawbridge can rest on a sliding plate which minimizes wear on the bridge. It also provides a bearing surface for any thermal expansion or contraction of the bridge when closed.
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