Abstract:
A method and apparatus for the removal of rivets from steelwork employs a high velocity narrow stream of water, containing abrasive particles, to cut through the head of the rivet in a circular path that produces a ring. The remainder of the rivet is then easily extricated from the steelwork. The apparatus includes a cutting head assembly having a nozzle that is driven in a circular path. A mounting device removable anchored to the steelwork supports the cutting head assembly.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to the removal of rivets from bridges or other structures by using apparatus having a cutting tool mounted so as to make the removal process efficient, safe, reliable and easy.  
         [0003]     2. Description of the Prior Art  
         [0004]     Rivets are not generally used in constructing modern bridges because it has been observed that over time, rivets lose strength and tension due to stress and vibration on the bridge structure, and undergo corrosive deterioration. However, rivets were widely used in the recent past to build bridges and other structures. Since these are enormously expensive structures to build, and since structural integrity is critical, it is common practice to remove rivets from older bridges and replace them with tension-controlled bolts or high strength fasteners that can be tensioned and maintained over time.  
         [0005]     Rivets typically employed in securing abutting steel beams are fabricated of iron and comprised of a circular cylindrical shaft terminating in a first or manufactured head. The rivet is usually heated to a red heat in preparation for insertion through aligned holes in the beams. Following insertion, an opposite second head is produced by hammering.  
         [0006]     Up until now, the removal of rivets from bridges or other structures has been accomplished using jackhammers, grinding tools, milling tools, drills, torches, and other implements. This is a difficult task, and tends to disturb the protective paint on and around the rivets. Said paint generally contains lead and/or chromate compounds intended to inhibit corrosion. If dispersed as particulate matter into the ambient air or water, such compounds present toxicity concerns.  
         [0007]     Improper use of prior tools can introduce heat, which can damage surrounding metal. Such methods are physically demanding, dangerous, and time-consuming, often requiring from ten minutes to three hours to remove each rivet. A particularly challenging aspect of the rivet-removing operation is to accurately position and secure the usually heavy cutting tool upon the rivet, particularly on vertical side surfaces. Although the use of a high velocity jet of water containing suspended abrasive particles is known as a cutting modality, its application to the specific requirements of rivet removal has not heretofore been suggested.  
         [0008]     It is accordingly an object of the present invention to provide a process for the rapid removal of rivets from structural steel forms.  
         [0009]     It is another object of this invention to provide a process of the aforesaid nature which employs a high velocity jet of water which contains suspended abrasive particles.  
         [0010]     It is a further object of the present invention to provide a process of the aforesaid nature which removes minimal amounts of metal and protective paint from the area contiguous to said rivet.  
         [0011]     It is a still further object of this invention to provide a process of the aforesaid nature which minimizes the release of said paint in particulate form into the ambient environment.  
         [0012]     It is yet another object of the present invention to provide apparatus for accomplishing the aforesaid process features.  
         [0013]     It is an additional object of the present invention to provide apparatus of the aforesaid nature which accurately positions and secures a cutting tool upon a rivet.  
         [0014]     These objects and other objects and advantages of the invention will be apparent from the following description.  
       SUMMARY OF THE INVENTION  
       [0015]     The process of the present invention comprises cutting through at least one head of a rivet in a circular path congruent with the cylindrical surface of the rivet shaft, thereby removing as a ring the portion of the outer extremity of the head that extends outwardly beyond the shaft, then pushing upon the remaining center portion of said head to dislodge the rivet, said cutting being accomplished by a high velocity narrow stream of water containing suspended abrasive particles.  
         [0016]     The apparatus of the present invention is comprised of: 
    a) an ultra-high pressure pump capable of providing water pressurized to at least 35,000 PSI,     b) water filtration means for supplying filtered water to said pump,     c) means for entering particulate abrasive material into said pressurized water,     d) a cutting head assembly, including a nozzle which receives said abrasive-containing pressurized water and directs it as a narrow, high velocity stream capable of cutting through steel,     e) mounting means for supporting said cutting head and achieving accurate positioning thereof with respect to a rivet targeted for removal,     f) drive means associated with said cutting head assembly for causing said nozzle to move in a circular path congruent with the cylindrical surface of the rivet shaft, and     g) collection means disposed in spaced apart relationship with said nozzle for receiving debris produced by the interaction of said high velocity stream with said rivet.   
 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0024]     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing forming a part of this specification and in which similar numerals of reference indicate corresponding parts in all the figures of the drawing:  
         [0025]      FIG. 1  is a perspective schematic view showing a conventional rivet which secures abutting steel beams, and a cutting tool performing the removal process of this invention.  
         [0026]      FIG. 2  is a side view of the embodiment of  FIG. 1 .  
         [0027]      FIG. 3  is a schematic side view of a cutting head assembly useful in the embodiment of  FIG. 1 , with portions broken away to reveal interior details.  
         [0028]      FIG. 4  is a perspective side view of a first embodiment of mounting means useful in the apparatus of the present invention, shown in operative association with the cutting head assembly of  FIG. 3 .  
         [0029]      FIG. 5  illustrates a second embodiment of mounting means useful in the apparatus of this invention.  
         [0030]      FIG. 6  is a perspective view of a third embodiment of mounting means useful in the apparatus of the present invention.  
         [0031]      FIG. 7  is a schematic view of a truck-mounted embodiment of the apparatus of this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Referring to  FIGS. 1 and 2 , a rivet  10  of conventional configuration is shown comprised of first head  11 , second head  12 , and intervening circular cylindrical shaft  13 . The rivet, serving to secure together abutting flat structural steel members  14 , is shown as it would appear following the cutting process of this invention.  
         [0033]     A cutting head assembly  15  operatively secures nozzle  16  and causes it to travel in a circular path above first head  11  while emitting a high velocity narrowly collimated stream  17  of water containing suspended abrasive particles, said stream having the ability to cut through steel. Said circular path is congruent with the cylindrical surface of shaft  13 , thereby removing as a ring  18  the portion of the outer extremity of head  11  that extends outwardly beyond the shaft. In the illustrated, preferred embodiment, stream  17  is caused to continue upon a path tangent to shaft  13  and emerge through second head  12 , thereby producing second ring  19 . Once the aforesaid cutting of at least first head  11  has been achieved, the remainder of the rivet may be pushed away from engagement with said steel members. The removal of the rivet has been found easier when the cutting stream penetratively acts upon both heads. This is presumably because any corrosive bonding between the shaft of the rivet and the steel members is removed. The removed rivet is quickly replaced with a new fastening device.  
         [0034]     The stream is preferably of circular configuration, having a diameter such as to produce a kerf width (cutting path) between about 0.03 and 0.04 inch. The stream has a linear velocity of between mach 1 (1090 feet/second) and mach 2, and is caused to complete its circular path within 1 to 15 minutes, representing a travel rate between 2.75 and 0.183 inches/minute, depending upon the depth of cut and diameter of rivet shaft. The stream contains between 10 and 15 weight percent of abrasive particles, said particles having a size between 16 and 500 microns. Suitable abrasive particles include corundum, silicon carbide, garnet, silica, aluminum oxide, copper slag and particulate carbon dioxide. The distal tip  66  of nozzle  16  is positioned between 1 and 2 mm. from the first head  11  of the rivet.  
         [0035]     Cutting head assembly  15 , as best shown in  FIG. 3 , is further comprised of drive motor  24  interactive with drive pulley system  25  and drive shaft  26  terminating in offset adjustment means  27  which sets the diameter of the circular path of nozzle  16 . Said components of cutting head assembly are enclosed within a box-like housing  58  having external electrical connector terminal  59 . A coiled conduit  28  conveys a pressurized flow of abrasive-containing water to delivery head  29  which feeds nozzle  16 . The coiled configuration of conduit  28  accommodates the movement of delivery head  29  and nozzle  16  in the course of their circular path. The upper, inlet extremity  62  of conduit  28  preferably joins with an electrically controlled valve  65  which may be positioned atop housing  58 . A quick-release fluid coupling  68  may be associated with valve  65  to expedite releasable joinder with an upstream conduit that conveys the cutting fluid to said valve.  
         [0036]     The cutting head assembly  15  is accurately secured in proper position with respect to the rivet workpiece by adjustable mounting means  31 . A first embodiment of such mounting means, suitably used when a horizontally extending ledge component  32  of the steelwork structure can be employed for support, is shown in  FIG. 4 . Said embodiment comprises a receiving bracket  33  which adjustably engages cutting head assembly  15 , and base assembly  34  having anchoring means in the form of bi-polar electromagnets  35  controllably interactive with ledge  32 . A catching enclosure  36 , extending forwardly from base assembly  34  embraces nozzle  16  and the underlying rivet workpiece for the purpose of confining debris produced by the cutting operation. A vacuum port  37 , extending rearwardly from said base assembly, communicates with catching enclosure  36  for the purpose of removing said debris. Auxiliary catching enclosure  60  and interactive vacuum removal means  53  may be positioned beneath ledge  32  for receiving debris emergent from the second head of the rivet.  
         [0037]      FIG. 5  illustrates a second embodiment of said mounting means, designated by numeral  38 , and intended for controlled attachment to a vertical steel member  39  adjacent the rivet workpiece. The components of mounting means  38  are generally the same as those for mounting means  31 . However, catching enclosure  36  and vacuum port  37  are re-arranged to be located downwardly from base assembly  34 .  
         [0038]     A third embodiment of said mounting means, designated by numeral  40 , and including an articulated arm  41 , is illustrated in  FIG. 6 . Said mounting means  40  includes a base assembly  42 , which may be equipped with anchoring means in the form of electromagnets or clamping devices for controlled attachment to a suitable steel surface adjacent the rivet workpiece. Arm components  43  of adjustable length terminate in bearing-equipped pivot hubs  44 . Distal hub  45  supports a positioning hub  46  mounted for rotational movement in a plane orthogonal to the plane of rotation of said distal hub. Positioning hub  46  is attached to a cutting head assembly  15  secured within the receiving bracket  33  of mounting means  31 . Support means, in the form of air cylinders  47  support the combined weight of the arms, associated components, mounting means  31 , and cutting head assembly  15 . By virtue of the adjustable support provided by the air cylinders  47 , and other features of construction, the cutting head assembly has freedom of movement over a wide range of motion, and is caused to be weightless to the operator, thereby facilitating easy manipulation. In alternative embodiments, the supporting air cylinders may be replaced by springs or hydraulic cylinders. Braking means, in the form of drum or disc brakes operated by air cylinders  50  are interactive with each pivot hub. Activation of said braking means locks the entire assembly into a particular configuration which accurately positions nozzle  16 . Articulated arm assemblies similar to that shown in  FIG. 6  are available from the Midwest Speciality Company of Wapakoneta, Ohio.  
         [0039]     A pump suitable for pressurizing water to 35,000 to 55,000 psi is Jet Edge model 55-260DXUHP mobile pump powered by a diesel engine made by the Jet Edge Company of St. Michael, Minn. Other suitable pumps may be powered by diesel, gasoline or natural gas engines.  
         [0040]     The cutting operation may be manually controlled, or may be computer-aided in its operation, including start/stop, depth of cuts and positioning during local and remote operation. The cutting head may be positioned over the rivet manually using mechanical indicators, optical devices involving triangulating lasers, or other alignment means.  
         [0041]     The various operating components of the apparatus of the present invention are preferably assembled upon a portable vehicle such as a truck, as shown schematically in  FIG. 7 . Other vehicles include barges and railway units. The truck-mounted assembly of  FIG. 7  includes a pump unit  54 , abrasive supply vessel  55  and industrial vacuum unit  56 . Various appropriate electrical and fluid connecting means are associated with the several truck-mounted components.  
         [0042]     When in use, the operator will adjust offset adjustment means  27  to the sought diameter of travel of the nozzle. Then, the operator releases the braking means and positions the cutting head. The brake system is re-engaged. The auxiliary catching/vacuuming means is positioned on the opposite head of the rivet and locked in place by magnetic or mechanical means, and a start button is pushed. The system will automatically cycle to turn on the abrasive and water delivery systems, and will shut the system off at completion of the cut.  
         [0043]     While particular examples of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broadest aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.