Conveyors: power-driven – Conveyor section – Pusher conveyor and separate load support surface
Reexamination Certificate
1999-10-26
2002-06-11
Ellis, Christopher P. (Department: 3651)
Conveyors: power-driven
Conveyor section
Pusher conveyor and separate load support surface
C198S860300, C299S043000, C299S064000
Reexamination Certificate
active
06401912
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to endless conveyors for aggregate materials and, more particularly, to a conveyor pan assembly for an armored face conveyor for handling coal in a longwall mining system.
BACKGROUND OF THE INVENTION
Various types of conveyor pan assemblies for armored face conveyors are well known in the art. Typically, each pan assembly includes a deck plate positioned between and providing support for a pair of parallel sidewalls. The deck plate provides a conveying surface for the coal or other aggregate material being conveyed. The sidewalls form tracks for the longwall mining machine as it moves back and forth along the mine face.
Attachment of the sidewalls to the deck plate is attained by placing elongated structural welds along the upper and lower chamfered lateral edges of the deck plate. Usually, the sidewalls are cast in a sigma shape such that when the deck plate is placed between them, upper and lower troughs or runs are defined. Of course, the upper trough of each pan assembly serves to guide the flight bars pulled along by a drive chain for moving the aggregate material along the conveyor line to a takeaway conveyor; the inverted lower trough guiding the flights during the return. To form the conveyor line, a plurality of the pan assemblies are placed in an end to end relationship, usually by forming a welded joint between specially shaped mating faces on the ends.
One prevalent problem with known types of conveyor pan assemblies is that the structural welds between the deck plate and the sigma sidewalls are positioned both above and below the conveying surface, as shown in Westfalia's U.S. Pat. No. 4,484,677 to Berwald. There are several shortcomings in this design. The first is that placing two full length structural welds along the entire length of both lateral edges above and below the deck plate greatly increases the manufacturing time and expense. The second is that these above (or top) structural welds along the sidewalls are thus exposed to significant wear created by the flights and aggregate material moving over them along the upper run of the conveyor line. This deleterious wear on these critical structural welds is the single most important factor limiting the service life of the conveyor pan assembly. Forming the deck plate of hardened steel or other abrasion-resistant materials reduces wear on the conveying surface, but the structural welds holding the deck plate in place are softer and wear more quickly. If the structural welds on the deck plate holding the sidewalls in place are significantly weakened, the support of the mining machine is threatened. Deleterious production downtime is required while the mining operation is temporarily shut down to remove and repair the pan assembly, including replacing the deck plate. The complete failure of one of these structural welds can even lead to a total failure of the longwall mining and armored face conveyor system if the developing weakness is not detected in time.
A number of solutions have been proposed to eliminate the deleterious effects of wear on the structural welds created by the flights and aggregate material, as well as to reduce the amount of structural welding required to provide a strong, long-lasting conveyor pan assembly. One recent proposal is found in U.S. Pat. No. 5,131,724 to Bandy, Jr. et al., of which I am a co-inventor. A deck plate with outwardly projecting keys fit into mating slots formed in the sigma sidewalls. By placing the structural welds exteriorly of the sidewalls where the keys project through the slots (see
FIG. 2
of the '724 patent), the deleterious effects of wear created by the flights/aggregate material are eliminated.
While this pan assembly overcomes the wear problem and is a significant improvement over prior art proposals, one remaining limitation is that the upper deck plate is still attached directly to and provides the sole support for the sigma sidewalls. Thus, when the deck plate eventually wears out and is in need of replacement, the entire pan assembly must disassembled. This includes: (1) cutting the structural welds formed around the keys on the lateral edges of the deck plate where they project through the slots in the sigma sidewalls; (2) removing the worn deck plate; (3) making the necessary repairs; and (4) reinstalling a replacement deck plate. To do this, the sidewalls must be physically removed and separated apart from the deck plate. The spacing between the sidewalls is no longer set. The next step (5) thus involves the difficult and tedious step of realigning the sidewalls and resetting the spacing to receive the deck plate. Finally, step (6) involves proceeding to weld the deck plate back in place between the opposed sidewalls. This has thus proven to be a very time consuming and labor intensive operation.
While there have been improvements in this basic technology such as is found in the conveyor pan assembly shown and described in U.S. Pat. No. 5,871,261, of which I am also a co-inventor, these changes are directed to other features. For example, in this '261 patent, elongated bevels are added along the entire lower longitudinal edges of the deck plate to mate with similar bevels on the sidewalls. But, with this change in the structure, the same basic repair/replacement procedure as in the '724 patent is required.
To try to facilitate this repair of the pan assembly, including replacement of the deck plate, without disconnecting the sidewalls, others have proposed splitting the conveyor pan assemblies, including the sigma sidewalls, into separate upper and lower sub-assemblies that are mechanically fastened together by a connector bar. An example is found in Westfalia's U.S. Pat. No. 4,632,239 to Schoop et al., wherein external connector bars and fastener assemblies are used to secure the two sub assemblies together. While this arrangement permits removal of the upper sub-assembly with the deck plate for replacement, without the need for cutting structural welds, a different problem appears. These extra components are expensive and the fasteners are sometimes difficult to loosen for replacement due to the build-up of rust, corrosion and other debris. Furthermore, any kind of mechanical connection such as this, can over time loosen on its own due to the vibration of the mining machinery. Specifically, the connector bars/fasteners may loosen due to the significant jarring caused by the traversing mining machine supported on the sidewalls. Furthermore, loosening action can be aggravated by the vibrations created as the flights and aggregate materials move along the conveyor. Of course, even a slight misalignment of the upper sidewall section and the deck plate during the replacement effort, can make it difficult to reapply and tighten the connector bars/fasteners. Even when the sigma sidewalls are made integral, the connector bars/fasteners are required, and the full length side welds must be cut in order to replace the deck plate.
Thus, a need is identified for an improved conveyor pan assembly having a deck plate that is easier to install and remove, and is more economical in both initial cost and maintenance. The sigma sidewalls would remain assembled with a support plate so that the spacing is always maintained. All structural welds for holding the deck plate in place would be positioned away from the conveying surface. As an added advantage, the amount of structural welding required during fabrication of the conveyor pan assembly would be reduced without compromising its structural strength. Mounting the deck plate, but not the support plate, in an offset position in a longitudinal direction would also facilitate forming a secure overlapping joint with the next-in-line conveyor pan assembly. There would be no need for specially forming the ends of adjacent conveyor pans to fit together. Overall, the conveyor pan assembly would result in a significant improvement over prior art proposals, particularly in terms of ease and cost of manufacturing, service life, reliability, a
Ellis Christopher P.
King and Schickli PLLC
Tran Kohi H.
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