Abstract:
A crack repair method includes forming a pair of holes into a surface of a structural workpiece on opposite sides of the crack, forming a slot into the surface of the structural workpiece to connect the holes on opposite sides of a crack, installing the cammed drawbolt assembly into the holes and slot, drawing said crack closed by actuating the cammed drawbolt assembly into a closed position and securing the drawbolt into the closed position.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to repairing cracks in workpieces, and more particularly, to a method for repairing cracks in structural workpieces using a cammed drawbolt approach. 
     Cracks occur in structural materials during manufacturing processes such as casting of metal or ceramic objects and molding of synthetic material objects. Cracks also occur during use of structural objects due to causes including stress, fatigue, aging or other conditions of use. The material of the structural object and the conditions of its use are taken into account in determining the most practical repair technique. X-ray, fluorescent penetrant or various other inspection techniques are used to evaluate the characteristics of cracks and the need and practicality for repair. Some cracks may be small enough that they represent no risk to performance, but others will require repair to allow safe and compliant operation of the machine, such as a power generator, locomotive, ship propulsion engine or other system. Many cracks may best be repaired by a technique not requiring extreme heating as occurs with, for example, welding or soldering. Extreme heat may induce stresses in the structural workpiece material which may be difficult or expensive to remedy. Bonding using chemical agents which soften a portion of a structural workpiece may be undesirable, because solvents or other softening agents may damage the material of the structural workpiece surfaces or require expensive or complex treatments to remove solvent residue. Large structural components, for example, diesel engine cast components, such as frames and engine blocks, are expensive to manufacture. Maintaining a spare engine in a user&#39;s inventory is rarely done due to the associated inventory costs, and waiting to re-engine a power generator, locomotive, ship or other industrial user may create considerable cost and inconvenience for the user. A technically sound, low-cost crack repair method is needed to facilitate reliable repair of cracks to minimize downtime and overall life cycle cost. Some materials other than metals have characteristics, such as limited temperature tolerance or corrosion, which make repair by techniques using heat or chemical bonding difficult or impossible. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A crack repair method includes forming a pair of holes on opposite sides of a crack, forming a slot into the structural workpiece to connect the holes on opposite sides of a crack, installing a cammed drawbolt assembly into the holes and slot, drawing said crack closed by actuating the cammed drawbolt assembly into a closed position and securing the drawbolt into the closed position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, partial cross-sectional side view of a structural workpiece including a crack to be repaired; 
         FIG. 2  is a schematic, partial cross-sectional view of a structural workpiece as shown in  FIG. 1  prepared for repair; 
         FIG. 3  is a schematic, plan view of a structural workpiece as shown in  FIG. 2 ; 
         FIG. 4  is schematic side view illustrating a cammed drawbolt assembly; 
         FIG. 5  is a schematic, partial cross-sectional view of a structural workpiece prepared for repair with a cammed drawbolt assembly positioned for installation into the structural workpiece; 
         FIG. 6  is a schematic, partial cross-sectional view of a cammed drawbolt in place after actuation to close the crack in the structural workpiece; 
         FIG. 7  is a schematic, partial plan view of a structural workpiece and a cammed drawbolt assembly positioned to close a crack in the structural workpiece; 
         FIG. 8  is a schematic, partial plan view including a partial cut-away illustration of a cammed drawbolt in its closed position; 
         FIG. 9  is a schematic partial cross-sectional view of an alternative structural workpiece repair; and 
         FIG. 10  is a schematic plan view of the another type of structural workpiece repair. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  schematically illustrates a structural workpiece  10  containing a crack  12 . One step in a method of repairing structural cracks is shown schematically in  FIGS. 2 and 3 . A first hole  14  is formed into surface  13  of structural workpiece  10  on a first side  15  of crack  12  and a second hole  16  is formed into surface  13  on the opposite side  17  of crack  12 . A slot  18  is formed into the structural workpiece  10  of sufficient length to join the first hole  14  and second hole  16 . Although the surface  13  is schematically illustrated as a planar surface, the surface may be of other shapes, so long as the holes  14 ,  16  and slot  18  penetrate the structural workpiece to extend below the surface  13 . The diameter  20  and depth  22  of the holes  14  and  16  and the width  24 , see  FIG. 3 , and depth  26  of the slot  18  necessary to accomplish a repair are selected based upon the structural workpiece material and the length, width and depth of crack  12 . The position of the first hole  14  and the position of the second hole  16  are selected so that the slot  18  crosses the crack  12  at a predetermined orientation relative to crack  12 , typically approximately perpendicular to said crack  12 , but at other angular orientations where the shape of the surface  13  requires force to be applied at an angle other than perpendicular. The technique used to form the holes and the slot is selected to be appropriate for use on the material of the structural workpiece. For example, for cast metals and ceramics the holes would typically be drilled and reamed, and the slots would be milled using cutting tools suited for the material. For structural plastics and composite materials, other material removal techniques, such as chemical etching, would be employed. 
     A cammed drawbolt assembly  30  for repairing the structural workpiece  10  is shown in  FIG. 4 . The cammed drawbolt assembly  30  includes a dowel  32  having a thread  34  to receive a drawbolt  36  at thread  38  at one end  40  and a shaped head  42  at the other end  44 , and a cammed dowel  46  having a through-hole  48  and cam slot  50  shaped in a complementary shape to receive the shaped head  42  of the drawbolt  36 . The dimensions and materials of the dowels  32 ,  46  and the drawbolt  36  are selected to provide the leverage required for a particular structural workpiece to be repaired and to be compatible with the operating conditions, such as heat, vibration, lubricants and other factors, in which the structural workpiece  10  operates. For example, a drawbolt assembly used to repair a cast metal structural workpiece  10  would typically be a metal drawbolt assembly. 
     As shown schematically in  FIG. 5 , the dimensions of the dowels  32 ,  46  and the drawbolt  36  are selected so that each of them will fit the respective holes  14 ,  16  and slot  18  in the structural workpiece  10 . The cammed drawbolt assembly  30  is assembled by threading the drawbolt  36  into the thread  34  of dowel  32  and inserting the shaped head  42  into through-hole  48 , so that the exposed length  52  of drawbolt  36  matches the spacing  54  between holes  14  and  16 . The cammed drawbolt assembly  30  is placed into the holes  14 ,  16  and slot  18  and a hex-headed tool  60  is inserted into the cammed dowel  46 . The drawbolt  36  is actuated by rotation of the cammed dowel  46  in the direction shown by arrow  62  in  FIG. 7  to pull shaped head  42  of the drawbolt  36  into the cam slot  50  to draw the shaped head  42  into the cammed dowel  46  and thereby to close crack  12 . 
     As shown in  FIGS. 6 and 8 , after the crack  12  is closed by rotation of hex-headed tool  60 , drawbolt  36  and cammed dowel  46  are bonded together, for example by a tack weld  64 , to secure the cammed dowel  46  from rotation. This will create a “stitch” to secure the material of the structural workpiece  10  from further cracking. Although a single stitch is illustrated and described, it will be understood that many cracks are deep enough or long enough to require more than one stitch to repair. The operator will evaluate the condition of the structural workpiece and select the number of stitches to be installed in a material to provide adequate strength for the application for which the structural workpiece is used. 
     In an alternative embodiment of the method of crack repair, as shown in  FIG. 9 , a structural workpiece  80  may be repaired from either or both sides if necessary, for example, where a crack  82  extends through the structural workpiece  80  and the operational location and application of structural workpiece  80  allows access to both sides  85  and  93  of structural workpiece  80 . Hole  86  is formed into surface  85  of structural workpiece  80  on a first side  87  of crack  82  and hole  88  is formed into surface  85  on the opposite side  89  of crack  82 . Slot  90  is formed into surface  85  to connect holes  86  and  88 . Hole  94  is formed into surface  93  of structural workpiece  80  on a first side  95  of crack  82  and hole  96  is formed into surface  93  on the opposite side  97  of crack  82 . Slot  98  is formed into surface  93  to connect holes  94  and  96 . A first drawbolt assembly  84  is assembled and inserted into holes  86  and  88  and slot  90 , and a second drawbolt assembly  92  is assembled and inserted into holes  94 ,  96  and slot  98 . As crack  82  may be of different size and shape on one side of structural workpiece  80  from the crack on the other side of structural workpiece  80 , drawbolt assembly  84  and the dimensions of holes  86 ,  88  and slot  90  are sized to apply the needed pressure on one side of structural workpiece  80  and drawbolt assembly  92  and the dimensions of holes  94 ,  96  and slot  98  are sized to apply the needed pressure on the other side of structural workpiece  80 . 
       FIG. 10  is a schematic plan view illustrating a repaired structural workpiece  100  showing that the shape, width and depth of the crack  102  shown in hidden line at particular locations may be taken into account in selecting the details of the stitching to perform the repair. As shown, cammed drawbolt assemblies  104 ,  106 ,  108  and  110  of varying sizes are used to close crack  102  to a line  112 . Where the crack is an irregular shape and irregular width, the number, spacing and size of individual stitches used for the repair are selected by the operator to provide the necessary reinforcement. The holes and slot for each of the cammed drawbolt assemblies  104 ,  106 ,  108  and  110  are formed so that each drawbolt of the cammed drawbolt assemblies  104 ,  106 ,  108  and  110  is oriented generally perpendicularly to the crack  102 . Where the shape of the workpiece surface and the shape and size of the crack require, other orientations relative to a crack to be repaired may be selected for the drawbolt position. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.