Abstract:
A dredge includes a primary grizzly with a sieve for separating dredged material initially into recoverable and discharge portions. A second or auxiliary grizzly and sieve are also provided on a chute extending from the primary grizzly to further remove remaining recoverable material from the portion of material discharged from the primary grizzly. A gate is provided for selectively opening and closing access to the auxiliary grizzly depending upon the make-up of the material discharged from the top of the primary grizzly. The combination of the primary and auxiliary grizzly provide for increased efficiency and effectiveness in recovering a larger percentage of recoverable material from a water-based dredging operation.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to dredges, and, more particularly, to grizzlies for such a dredge which separate recoverable material from material to be discharged or waste material. 
     Water-based and floating dredges typically include one or more bucket or clamshell-types grabs which are lowered into a waterway to collect sand, clay, gravel or the like from the bottom of the waterway. The grab typically deposits the collected material onto a grizzly which often includes a sieve having a plurality of generally parallel bars. The dredged material often contains components whose value justifies recovering them such as sand and gravel. Other components, such as clay, are not desirable for recovery and are simply collected for removal and disposal. Separating the recoverable material from the material to be discharged, however, in the past has been an inefficient and often time consuming process. Frequently, the dredged material includes a wide variety of materials. In other words, rarely does the dredged material include entirely recoverable material or entirely waste material to be discarded. 
     The time and expense involved in recovering useful material through a water-based dredging operation are very significant. Therefore, it is important to effectively and efficiently retain all of the available recoverable material from a given load. Currently, one common method for dredging is to deposit or dump the load of dredged material in the grab onto a primary grizzly for further processing. Once the dredged material is deposited onto the grizzly, smaller materials, such as sand and gravel, pass through the bars of the grizzly for recovery and further processing. The material remaining atop the grizzly is then discharged therefrom. 
     One manner of discharging the material remaining atop the grizzly is disclosed in U.S. Pat. No. 5,588,536 issued to the present inventor and hereby incorporated by reference in its entirety. In that patent, the dredge includes a bi-directional grizzly which includes a rake structure that can be operated in either of two opposite directions. If the material remaining atop the grizzly includes sufficient recoverable material for further processing, the rake is operated in a first direction to discharge that material directly into in a crusher or the like. However, if the material remaining atop the grizzly is not worthy of recovery, the rake is operated in a second opposite direction for discharge of the material down an inclined chute and onto a refuse barge, conveyor or the like. 
     However, the material remaining atop the primary grizzly often includes a mixed variety of components. For example, the remaining material may include larger rocks, gravel or the like which are too large to pass between the spaced bars of the primary grizzly but are still worthy of recovery for further processing. Nevertheless, the material remaining atop the primary grizzle often includes clay and/or other waste along with the recoverable components. The operator of the dredge then must decide whether to discard the entire contents of the material atop the primary grizzly or further process the waste material included therein in an effort to retain the available recoverable material. This dilemma often results in the discharge of a significant quantity of worthwhile recoverable material or processing of clay and other undesirable elements resulting in an inefficient and ineffective dredging operation. 
     SUMMARY OF THE INVENTION 
     A primary objective of this invention has been to provide an improved dredge and associated method which allows for the efficient and effective recovery of a larger percentage of the worthwhile recoverable material from a load of dredged material without the processing of waste material such as clay and the like. These and other objectives of the invention have been attained by a dredging station which includes a primary grizzly, as previously discussed in the background of this invention, for separating a load of material collected by the grab into a first recoverable portion which falls through the sieve of the primary grizzly and a first discharge portion which remains atop the sieve of the primary grizzly. 
     The primary or first grizzly includes a discharge mechanism for removing the discharge portion of the material remaining atop that sieve. In one embodiment, the discharge mechanism of the primary grizzly is a tipping grizzly in which one longitudinal end of the grizzly elevates relative to the opposite end so that the first discharge portion slides off of the grizzly and onto an inclined chute. One example of such a tipping grizzly is shown in U.S. Pat. No. 5,427,251, which is hereby incorporated by reference in its entirety. Alternatively, the discharge mechanism may comprise a rake or other arrangement as disclosed in U.S. Pat. No. 5,588,536. 
     The chute is inclined so that an upstream end is elevated relative to a downstream end. As the first discharge portion of material flows or falls down the chute, it encounters a second or auxiliary grizzly having a sieve which includes a number of generally parallel spaced bars for straining the first discharge portion of the material into a second recoverable portion of material and a second discharge portion. The second discharge portion of material remains atop the second grizzly on the chute and subsequently flows toward the downstream end of the chute and onto a barge, conveyor or the like for ultimate disposal. Advantageously, a crusher is positioned below the chute and in communication with the second grizzly for processing of the second recoverable portion of material which passes through the second grizzly and into a funnel connected to the crusher. 
     A movable gate is included on the chute for selectively opening and closing the second grizzly to permit or inhibit, respectively, access to the second grizzly as required depending upon the make-up of the first discharge portion of material discharged from the primary grizzly. Additionally, the sieve of the second grizzly includes a plurality of spaced bars which, in a present embodiment, are removable to provide for convenient access to the funnel and crusher therebelow for dislodging jams or other accumulations that may inhibit the flow of material. 
     As a result of this invention, material recovered from a waterway or the like can be more effectively and efficiently processed so that a higher percentage of recoverable material is retained and waste material such as clay or the like is ultimately discharged for disposal without being processed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objectives and features of the invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a side-elevational view of a dredge station including a chute and an auxiliary grizzly according to a presently preferred embodiment of this invention; 
     FIG. 1A is a top view of material being discharged from a primary grizzly shown in FIG. 1; 
     FIG. 2 is a cross-sectional top view of the chute and auxiliary grizzly taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view of a portion of the grizzly taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of FIG. 3; and 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  of FIG. 2 showing a portion of the chute of the auxiliary grizzly, a funnel and a crusher in communication therewith. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a floating gantry-type dredge  10  for use in a waterway  12  according to a presently preferred embodiment of this invention is shown. The dredge  10  may include one or more pontoons  14  for floating support, but it should be understood that the present invention is not limited to a pontoon supported or catamaran-type dredge, but includes other suitable waterway or nonwater-based dredges. The dredge  10  according to this invention includes a clamshell-type grab  16  which is suspended from a gantry (not shown). The grab  16  is suspended from the gantry and is movable as is well known in the art to a position directly over a primary grizzly  18 , as shown in FIG. 1, to a position (not shown) from which it is plunged into the waterway  12  for the collection and removal of sand, clay, gravel or the like from the bottom of the waterway  12 . 
     The primary grizzly  18  includes a grizzly hopper  20  positioned immediately below a sieve  22  comprised of generally parallel-spaced bars  24  defining gaps  25  therebetween. The sieve  22  screens, filters or strains out large material and prevents it from falling into the hopper  20 . The material that advances through the sieve  22  of the primary grizzly  18  and into the hopper  20  is directed to a material handling apparatus  27  and onto a conveyor  26  for further processing. The material which passes through the sieve  22  of the first grizzly  18  is referred to herein as a first recoverable portion. The dredge material which remains atop the sieve  22  of the first or primary grizzly  18  is referred to herein as the first discharge portion. The primary grizzly  18  and associated structure is supported by a support frame  28  extending between the grizzly  18  and the pontoon  14 . 
     A discharge mechanism  30  as shown in FIG. 1A is provided for removing the first discharge portion from the sieve  22  of the first grizzly  18  and onto a chute  32 . The discharge mechanism  30  may include a rake  31  and a tipping grid  33  such as that disclosed in U.S. Pat. No. 5,427,251 or may include a rake or other arrangement such as that disclosed in U.S. Pat. No. 5,588,536. Additionally, other arrangements for removing the first discharge portion from the sieve  22  of the primary grizzly  18  which are known to those of ordinary skill in the art are contemplated within the scope of this invention. 
     The chute  32 , which is particularly shown in FIGS. 1,  1 A and  2 , is inclined downwardly from an upstream end  34  toward a downstream end  36  thereof. At the downstream end  36  of the chute  32 , waste, referred to herein as a second discharge portion, falls onto a refuse barge  38  or other receptacle docked or positioned adjacent to the dredge  10  for disposal. The chute  32  includes a generally planar bottom wall  40  and a pair of upstanding lateral sidewalls  42  for containing the material falling by gravity from the upstream end  34  to the downstream end  36 . As shown particularly in FIG. 2, the chute  32  has a tapered configuration such that the upstream end  34  is wider than the downstream end  36 . Preferably, the upstream end  34  of the chute  32  is approximately 4,350 mm in width and the downstream end  36  is approximately 1,234 mm in width and each sidewall  42  is approximately 6,348 mm in length. 
     Advantageously, the present invention includes a second or auxiliary grizzly  44  which in one embodiment is located on the chute  32 , as shown particularly in FIGS. 1,  2  and  5 . The second or auxiliary grizzly  44  has a second sieve  46  for straining the first discharge portion of material flowing from the upstream end  34  of the chute  32  towards the downstream end  36 . The second sieve  46  strains the first discharge portion into a second recoverable portion which falls through gaps  48  formed between each pair of adjacent spaced bars  50  of the second grizzly  44 . A second discharge portion remains atop the bars  50  of the second sieve  46 . 
     The second recoverable portion falls through the second sieve  46  and a funnel  52  which in one embodiment projects downwardly from a bottom side of the chute  32  to direct the second recoverable portion of material into a crusher  54  located below the chute  32  and in communication with the second sieve  46 . The second recoverable portion of material falls through the funnel  52  and into a mouth  56  of the crusher  54  and is crushed between a pair of opposing crusher jaw members  58   a ,  58   b . In one embodiment, as is well known with crushers of this type, one jaw member  58   a  is stationary and an opposing jaw member  58   b  pivots toward and away from the stationary jaw member  58   a  to crush rocks, boulders or the like falling therebetween. The movable jaw member  58   b  is operably connected to a motor  60  and is driven via a belt  62  and a rotary drum  64 , as seen in FIG. 1. A second recoverable portion of material which passes through the crusher  54  is then deposited onto a conveyor  66  for subsequent processing and the like. 
     An upper end of the funnel  52  is connected to the bottom of the chute  32  to receive the second recoverable portion of material falling through the second sieve  46 . The funnel  52  includes a narrowed or tapered portion  68  at the bottom end thereof to direct the second recoverable portion of material into the crusher  54 . In one embodiment, the funnel  52  includes a door  70  which can be selectively opened and closed to provide access to the funnel  52 , the crusher  54  and adjacent components for servicing, replacement, cleaning or the like, as shown in FIG.  5 . 
     Referring to FIGS. 1-3 and  5 , this invention, in one embodiment, also includes a gate  72  to open and close the second grizzly  44  and to permit and inhibit, respectively, the flow of material through the second sieve  46 . As shown in FIG. 2, the gate  72  includes a generally rectangular plate which is captured on opposing lateral ends thereof in a pair of spaced channels  74  for reciprocal movement between a retracted open position, as shown in FIG. 2, and an extended closed position (not shown). The gate  72  is coupled at an upper edge thereof to a pair of pneumatic cylinders  76  or the like for reciprocal movement of the gate  72  to and between the open and closed positions (FIGS.  1  and  2 ). Each cylinder  76  is pivotally coupled through a collar  78  to the gate  72 , as shown in FIG.  5 . Plastic, Teflon or other appropriate material strips  80  may be mounted in conjunction with the channels  74  to provide for the easy translation of the gate  72  between the open and closed positions. 
     As such, if the first discharge portion of material appears to contain nothing but waste, the operator may actuate the cylinders  76  to close the gate  72  and thereby prevent any material from falling through the sieve  46  of the second grizzly  44 . As a result, all of the first discharge portion will then be dropped onto the waste barge  38  or the like for removal. Appropriate supporting beams  79  and braces  81  are required to support the chute  32  and the second auxiliary grizzly  44 . 
     Referring to FIGS. 2-4, the second sieve  46  of the second grizzly  44  includes a plurality of spaced bars  50  which define the gaps  48  between each adjacent pair of bars  50 . In one embodiment, the bars  50  are each selectively removable for repair, replacement and/or access to the funnel  52 , crusher  54  and other structures positioned below the chute  32 . Each bar  50  has a generally T-shaped cross-sectional configuration with an upper lateral member  82  and a downwardly extending lower member  84  forming the T-shaped configuration. In one embodiment, the width of the upper lateral member  82  of each T-shaped bar  50  is greater at an upstream end than at a downstream end, as shown in FIG.  2 . As a result of the tapered configuration of the upper lateral member  82 , the gap  48  provided between each pair of adjacent bars  50  is tapered such that there is a greater gap opening at a downstream end than at an upstream end thereof. Preferably, the gap  48  is approximately 380 mm at an upstream end and approximately 400 mm at a downstream end of the sieve  46 . As a result, boulders, rocks or the like which are too large to fit through the gap  48  proximate an upstream end of the sieve  46  are directed downwardly toward the larger portion of the gap  48  at the downstream end of the sieve  46  for passage into the funnel  52  and the crusher  54 . Each T-shaped bar  50  is held in place between the projecting legs  86  of a pair of spaced L-shaped brackets  88  mounted to the upstream and downstream ends of the sieve  46 , as shown particularly in FIGS. 2-4. Each bar  50  is approximately 1.2 meters in length for the second or auxiliary grizzly  44 . 
     As a result of a dredge  10  with the primary grizzly  18  and the auxiliary grizzly  44  on the chute  32 , a higher percentage of recoverable material from a load of dredged material is recovered and not discharged. Furthermore, the gate  72  of the second grizzly  44  is advantageously utilized to prevent clay other waste material from the first discharge portion of material from entering the crusher  54  of the second grizzly  44  when it is determined that there is not sufficient recoverable material in the first discharge portion. 
     The dredge  10 , according to this invention, can be constructed and utilized as original equipment. Moreover, an existing gantry-type dredge with a chute may be retrofit to include a second or auxiliary grizzly  44  positioned below the chute  32  and a crusher  54  installed in communication with the second grizzly  44  to achieve the benefits and advantages provided by this invention. 
     From the above disclosure of the general principles of the present invention and the preceding detailed description of at least one preferred embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, I desire to be limited only by the scope of the following claims and equivalents thereof.