Non-Metalli( Bearings Handle Big Loads on Self-Unloading Barges
Self-unloading Great Lakes barges, equipped with long booms that stockpile material on docks alongside, are using non-metallic bearings to support the huge cylinders that position the booms as they unload tons of taconite, gravel, calcite or other bulk mineral cargo. The self-lubricating bearings are designed to simplify maintenance by reducing the amount of lubrication needed to prevent corrosion of the large diameter shafts.
The self-unloading barges are part of the tug-barge concept that is emerging more often in Great Lakes shipping. Instead of a traditionally powered ship, a giantbarge is constructed with a notch at the stern, into which a tugboat is locked hydraulically, enabling the two vessels to function as a single ship. The automated barge contains the self-unloading system and performs all cargo transfer operations, while the tugboat provides the power and navigation capabilities. Unlike the flat-ended barges that are tied together and pushed along inland waterways, these barges have the hull of a Great Lakes ship. This allows them to handle rough seas that can develop on the Great Lakes but which would capsize a river barge. On a self-unloader, a belt conveyor travels the length of a vessel's hold, running beneath large hoppers with bottom-discharge gates that can be controlled to empty onto the belt. At one end of the vessel, the conveyor elevates the material it is carrying to the deck, where it discharges onto a boom conveyor. Often, the cargoelevating function is accomplished by a second belt conveyor installed over the top of the first so the entire assembly can be configured into a horizontal "J" shape, with the top conveyor holding the material in place during the inversion.
Topside, the material is discharged to a conveyor carried on a boom that may be several hundred feet long, which transports it to stockpiles on shore. Generally, the material is stockpiled in rows, as the ship moves slowly alongside the dock while the conveyor continues to discharge material. The pivoting boom allows discharge either to port or starboard side.
