Abstract:
A test bench for testing a hammer and hammer tool comprising: a bench frame; a load cell assembly mounted on the bench frame for absorbing the impact delivered by the hammer; and a movable mounting deck for securing the hammer to the bench frame and for moving the hammer with the hammer tool into a test firing position against the load cell assembly and delivering an impact force against the load cell assembly. The load cell assembly comprises a pneumatic air bag assembly constructed to dissipate the impact force of the hammer. Other aspects include a load cell assembly for testing a hammer and hammer tool and a method for test firing a hammer tool. Hydraulic hammers generating forces between 200 ft-lb and 12,000 ft-lb can be adequately test fired.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/190,449 filed Aug. 28, 2008, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a test bench for test firing industrial hammers, such as large industrial hammers and, in particular, to hydraulic hammers without the hammer being fired in actual field use. 
       BACKGROUND INFORMATION 
       [0003]    Large industrial hammers are, for example, percussion tools or impact vibrators and include pneumatic hammers, which are powered by compressed air, and hydraulic hammers, which are powered by a liquid. 
         [0004]    Pneumatic hammers tend to be of smaller size and striking force than hydraulic hammers. An example of a typical pneumatic hammer is a jack hammer which is hand-held while in use, is approximately two to three feet in length and may weigh up to approximately 60 pounds. A jack hammer may deliver between approximately 900 to 1,600 blows per minute and the force of the blow is approximately 45 to 100 ft. lb. per blow. 
         [0005]    Hydraulic hammers, by contrast, come in a variety of sizes and are usually much larger than a typical pneumatic hammer. Hydraulic hammers are often used as accessory units or attachments for construction machinery, such as excavators, loaders or other basic equipment for purposes of breaking or crushing rock, concrete or some other relatively hard material. A small hydraulic hammer may weigh approximately 265 pounds and deliver approximately 1,000 to 1,500 blows per minute with the force per blow being approximately 162 ft. lb. or 200 Joules. A very large hydraulic hammer can weigh approximately 16,000 pounds and deliver approximately 500 blows per minute with the force per blow being approximately 9,500 ft. lb. or 13,000 Joules. 
         [0006]    Industrial hammers are generally driven by a percussion piston which moves inside a housing and alternately performs an operating stroke in a hammering direction and a return stroke in the opposite direction. During operation, the kinetic energy of the percussion piston when it strikes a tool is introduced via the tool and the tool tip into the material to be processed and the kinetic energy is converted into destructive actions. Depending on the hardness of the material to be processed, only a portion of the kinetic energy is converted to destructive action. The remaining, non-converted energy is reflected via the tool back into the percussion piston. Thus, percussion tools represent highly stressed devices that typically need frequent servicing. 
         [0007]    Prior art testing devices have been directed towards test benches for hand operated pneumatic hammers. However, these test benches by virtue of their scale of size and component design generally are not suitable for testing the larger industrial hammers and, in particular, hydraulic hammers because of the massive size and force generated by hydraulic hammers in comparison to hand held pneumatic hammers. Most notably, these prior art devices employ an impact dissipating device that is insufficient to withstand the impact force of a large hammer and if used with a large industrial hammer the impact of the blow would not only cause the dissipating device to fail within a few blows but would also reflect the impact energy backwards through the frame of the test bench and the hammer securing mechanism so as to cause failure of the apparatus. 
         [0008]    Examples of such prior art testing devices include, for example, U.S. Pat. No. 4,235,094 which discloses a vibration safety test bench for hand held riveting hammers wherein the riveting hammer is secured in a vertical position and the hammer is fired against a dummy work rigidly secured to the test bed and most preferably comprised of a duralumin plate. Similarly, U.S. Pat. No. 2,389,138 discloses a pneumatic hammer testing machine wherein the cutter piece of a pneumatic chipping hammer is held in place against a slab or plate of material by a pulley and weight mechanism. U.S. Pat. No. 1,576,465 discloses yet another test bench for a pneumatic rock hammer wherein the tool end of the drill is held against a testing block resiliently supported by a number of rubber blocks by a means exerting a constant force, such as a weight hanging from a chain. 
         [0009]    Other prior art testing devices employ fluid-containing dissipating devices to receive the impact of the tool. For example, U.S. Pat. No. 4,901,587 discloses a test fixture for an air feed drill and U.S. Pat. No. 5,277,055 discloses a test stand for a hand held impact or impact-rotary tool, both of which impact the tool against a hydraulic pressurized cylinder. However, fluid-containing dissipating devices are not well suited for the repetitive and strong impact force of large industrial hammers because fluid rebounds relatively slowly and also would develop friction which would cause the unit to become hot and possibly fail. 
         [0010]    Hydraulic hammers cannot be “dry fired” or test fired without impact against a resisting surface without causing damage to the mechanism. For this reason, it has not been possible to test fire a hydraulic hammer after servicing the unit without returning it to the field for actual in-service testing. Thus, there is a substantial need for a test bench which can accommodate the size and operating force of large industrial hammers so as to determine under test conditions whether the hammer is functioning properly. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides a hammer test bench and a method for testing large industrial hammers and, in particular, hydraulic hammers which may be of massive size and operating force. In accordance with an embodiment of the present invention, there is provided a test bench with a movable mounting deck assembly for securing a large industrial hammer on the test bench and mechanically moving and securely holding the hammer into a firing position with the tool of the hammer against a load cell assembly, which is capable of dissipating the repetitive impact force of the hammer upon test firing. The load cell assembly is comprised of an impact receptor mounted to a pneumatic air bag assembly secured within a support carriage which allows the pneumatic air bag assembly to contract upon impact of the hammer tool on the impact receptor and then rebound to expand to its original configuration to dissipate the impact force of the hammer. The pneumatic air bag assembly is equipped with a gauge regulator assembly that allows the air pressure within the air bag assembly to be adjusted to accommodate the size of the hammer being tested and with pressure relief valves that protect the air bag assembly from being over inflated. The support carriage allows the pneumatic air bag assembly to contract and expand but holds the air bag assembly in a linear position so as to keep the impact receptor aligned with the hammer tool to preserve the structural integrity of the pneumatic air bag assembly. The height of the load cell assembly may be adjusted by raising or lowering the support carriage to align the hammer tool with the center of the impact receptor. The energy needed for movement of the mounting deck assembly and the energy needed for the firing of the hammer are generally supplied separately by a power unit which can be operated by remote control. 
         [0012]    An aspect of the present invention provides a test bench for testing a hammer and a hammer tool, comprising: a bench frame; a load cell assembly mounted on the bench frame for absorbing the impact force delivered by the hammer; and a movable mounting deck for securing the hammer to the bench frame and for moving the hammer and hammer tool into a test firing position against the load cell assembly for delivering an impact force against the load cell assembly; the load cell assembly comprising a pneumatic air bag assembly constructed to dissipate the impact force of the hammer. 
         [0013]    Another aspect of the present invention provides a load cell assembly for testing a hammer and a hammer tool, comprising: an impact receptor for receiving the hammer tool of the hammer during testing and for absorbing the impact force delivered by the hammer tool against the impact receptor; a pneumatic air bag assembly connected to the impact receptor and constructed to dissipate the impact force; and a support carriage for securing the pneumatic air bag assembly to the load cell assembly and for holding the pneumatic air bag assembly in a position for maintaining the impact receptor in alignment with the hammer tool. 
         [0014]    A further aspect of the present invention provides a method of test firing a hammer and a hammer tool, comprising: providing a load cell assembly comprising a pneumatic air bag assembly constructed to dissipate the impact force delivered by the hammer tool and to expand to its original configuration after each test firing cycle of the hammer; and reciprocating the hammer into a test firing position with the hammer tool of the hammer impacting against the load cell assembly to absorb the impact force delivered by the hammer and to contract the pneumatic air bag assembly, and with the hammer moving away from the load cell assembly to allow the pneumatic air bag assembly to expand to its original configuration after each test firing cycle of the hammer 
         [0015]    These and other aspects of the present invention will be more apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a plan view of a hammer test bench of the present invention. 
           [0017]      FIG. 2  is a side elevation view of the hammer test bench of  FIG. 1 . 
           [0018]      FIG. 3  is an enlarged perspective right side view of a load cell assembly mounted on the hammer test bench of  FIG. 1 . 
           [0019]      FIG. 4  is an enlarged perspective front view of the load cell assembly of  FIG. 3 . 
           [0020]      FIG. 5  is an enlarged perspective view of a mounting deck assembly of the hammer test bench of  FIG. 1 . 
           [0021]      FIG. 6  is an enlarged perspective left side view of a tailstock for mounting the load cell assembly of  FIG. 1 . 
           [0022]      FIG. 7  is a plan view of a hammer test bench of the present invention supporting a hammer to be test fired. 
           [0023]      FIG. 8  is a side elevation view of the hammer test bench and the hammer of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring first to  FIGS. 1 and 2 , there is illustrated, in general, a hammer test bench  10  for test firing large industrial hammers, and in particular, hydraulic hammers without the hammer being fired in actual field use. Hammer test bench  10  comprises a bench frame  12  with an open center  14  ( FIG. 1 ), a load cell assembly  16  attached to the rear end  20  of bench frame  12  by a tailstock  22  which is fixedly mounted on the bench frame  12 ; and a mounting deck assembly  26  which positions the hammer and hammer tool for making contact with the load cell assembly  16  by operation of a hydraulic positioning cylinder assembly  28  located within mounting deck assembly  26  as shown in  FIG. 2 . Mounting deck assembly  26  secures a hammer to be tested. As better shown in  FIG. 2 , hydraulic positioning cylinder assembly  28  is attached to the fore end  30  of bench frame  12  and to the rear end  32  of mounting deck assembly  26  for reciprocating mounting deck assembly  26  toward and away from load cell assembly  16  for testing of the hammer. 
         [0025]    Still referring to  FIGS. 1 and 2 , bench frame  12  is constructed of materials suitable for supporting the weight of the other components of the hammer test bench  10  and the weight of the hammer (not shown) being tested, the total weight of which can range up to approximately 20,000 pounds. In a non-limiting embodiment of the present invention, and as better shown in  FIG. 2 , bench frame  12  is comprised of an open bench top comprised of two opposed side frames  34  and  36 , and two opposed end frames  38  and  40 . Side frames  34  and  36  and end frames  38  and  40  may be comprised of rectangular steel tubing which may be welded together to form bench frame  12 , and which bench frame  12 , in turn, is supported by a plurality of bench legs  42 , three of which are clearly shown in  FIG. 2 . Bench legs  42  may also be comprised of rectangular steel tubing and are attached, for example, by welding, to side frame  34 . Even though three bench legs  42  are shown in  FIG. 2 , it is to be appreciated that an additional three bench legs  42  are provided on the opposite side of bench frame  12  and are attached, for example, by welding, to side frame  36  of bench frame  12 . As clearly shown in  FIG. 1 , mounting deck assembly  26  further comprises a headstock  44  for bracing a hammer (not shown) to be test fired, and ratchets  46  and  48  which cooperate with opposed ratchets  50  and  52 . Ratchets  46 ,  48 ,  50  and  52  receive straps (not shown) which are wrapped around the hammer for tightening and securing the hammer to be test fired to mounting deck assembly  26 . 
         [0026]      FIGS. 3 and 4  more clearly illustrate the load cell assembly  16  which receives the hammer tool of the hammer to be test fired.  FIG. 3  shows an enlarged perspective right side view of the load cell assembly  16  and  FIG. 4  shows an enlarged perspective front view of load cell assembly  16 . Load cell assembly  16  comprises an impact receptor  54  ( FIG. 4 ) mounted to a pneumatic air bag assembly  56  ( FIG. 3 ) which is secured within a support carriage assembly  58 . Support carriage assembly  58  comprises spaced-apart front carriage plate  60  and rear carriage plate  62 ; a first front supporting foot assembly  64  and a second front supporting foot assembly  66  as better shown in  FIG. 4 ; a plurality of supporting guide rod assemblies, some of which are indicated in  FIGS. 3 and 4  by reference numerals  68 ,  70 ,  72 ,  74 , and  76  for interconnecting carriage plates  60  and  62 ; a hand wheel adjustment assembly  78 ; a plurality of lifting eyelets, two of which are indicated in  FIGS. 3 and 4  by reference numerals  80  and  82 , and which lifting eyes  80  and  82  are attached at various locations on the top end surface of front carriage plate  60  and rear carriage plate  62 ; and a first rear supporting assembly  84  and a second rear supporting assembly  86  attached to rear carriage plate  62 . 
         [0027]    As shown in  FIG. 3 , front carriage plate  60  is located between the first front supporting foot assembly  64  and the second front supporting foot assembly  66 , and rear carriage plate  62  is positioned between the first rear supporting assembly  84  and the second rear supporting assembly  86 . 
         [0028]    Referring particularly to  FIG. 4 , impact receptor  54  comprises a receptor base plate  88 , a cylindrical impact receptacle  90  mounted on the receptor base plate  88 , which houses a replaceable impact plate  92  and a rubber disc  91  (shown by the dotted lines), which is concealed from view by the replaceable impact plate  92 . Rubber disc  91 , which is housed in the cylindrical impact receptacle  90 , is used generally for localized shock absorption purposes. The diameter of replaceable impact plate  92  is slightly less than the internal diameter ID of the impact receptacle  90  and is held in place by a close tolerance fit. Receptor base plate  88  is mounted to the external front side of the front carriage plate  60  as shown in  FIG. 4  by a plurality of threaded screws, some of which are shown by reference numeral  100  positioned around the perimeter of receptor base plate  88 . Impact plate  92  in some non-limiting embodiments, may be a disc shaped plate made of a hard metal material, such as, steel that the hammer tool is brought to bear against. This impact plate  92  rests in the bore of cylindrical impact receptor  90  to conceal the rubber disc  91 , described herein above. In some instances, impact plate  92  and rubber disc  91  may be sacrificial in nature so as to prevent premature failure of one or more components of the load cell assembly  16 . 
         [0029]    Still referring to  FIGS. 3 and 4 , and as better shown in  FIG. 3 , front supporting foot assembly and rear supporting assembly  64  and  66  each comprises an adjustable vertical support arm  102 , which, for example, may be welded to the top surface  104  of a horizontal foot base plate  106 . Horizontal foot base plate  106  is reinforced with a plurality of triangular foot base gusset plates  108 , which are for example welded to the sides of the adjustable vertical support arm  102  and to the top surface  104  of the horizontal foot base plate  106 . Adjustable vertical support arm  102  is secured to the front carriage plate  60  by a plurality of bolt and nut fasteners, one of which is indicated by reference numeral  110  fitted through a center slot  112  in the support arm  102 . The height of both front supporting foot assembly  64  and rear supporting foot assembly  66  relative to front carrier plate  60  can be adjusted by loosening the bolt and nut fasteners  110  and moving the vertical support arm  102  up or down in a vertical direction with reference to  FIGS. 3 and 4 . 
         [0030]    As shown in  FIGS. 3 and 4 , foot base plate  106  of the first front supporting foot assembly  64  rests upon the top surface  114  of side frame  34 ; whereas, the foot base plate  106  of the second front supporting foot assembly  66  rests upon the top surface  116  of side frame  36 . The foot base plate  106  of foot assembly  64  and the foot base plate  106  of foot assembly  66  are slideable along their respective top surfaces  114 ,  116  of side frames  34 ,  36  towards and away from rear carriage plate  62  of support carriage assembly  58  for adjustment of load cell assembly  16  relative to side frame  34  and  36 . It is to be appreciated that the bottom surface of each foot base plate  106  of each supporting foot assembly  64 ,  66  will comprise a frictionless surface. In a non-limiting embodiment, the foot base plate  106  may be coated with a smooth, plastic coating to facilitate movement along the top surface  114 ,  116  of side frames  34 ,  36 . 
         [0031]    Still referring to  FIGS. 3 and 4 , front carriage plate  60  is connected to rear carriage plate  62  by a plurality of guide rod assemblies, such as those shown at reference numerals  68 ,  70 ,  72 ,  74  and  76 . Each guide rod assembly  68 ,  70 ,  72 ,  74  and  76 , as particularly indicated for guide rod assembly  70  in  FIG. 4 , comprises a support guide rod  118  which passes through a bushing  120  ( FIG. 3 ) on an internal side of front carriage plate  60  and through an aperture  122  in front carriage plate  60 . Even though not shown in  FIG. 4 , bushings similar to bushings  120  may be provided with respect to the guide rod assemblies and rear carriage plate  62 . Each guide rod assemblies  68 ,  70 ,  72 ,  74  and  76  are secured to the external side ( FIG. 4 ) of carriage plate  60  by a nut fastener  124  affixed to the threaded end of the support guide rod  118 . Nut fastener  124  comprises at least two nuts  126 ,  128 , a metal washer  130 , for example steel, and a resilient washer ring  132  fixed to the threaded end of the support guide rod  118 . Resilient washer ring  132  may be made of any suitable resilient material, for example, rubber, and has a substantial thickness for shock absorption purposes. It is to be appreciated that even though five guide rod assemblies are shown in the figures, that there are at least six guide rod assemblies. All guide rod assemblies are secured to rear carriage plate  62  by internal threads that fix each guide rod assembly to the rear carriage plate  62  in a rigid, non-permanent manner. 
         [0032]      FIG. 5  illustrates in detail the mounting deck assembly  26  for securing a hammer to be test fired and  FIG. 6  illustrates in detail the tailstock  22  which secures the load cell assembly  16  to the top of hammer test bench  10  of  FIGS. 1 and 2 . 
         [0033]    With particular reference to  FIG. 6 , tailstock  22  comprises a vertical face plate  136  attached to a horizontal base plate  138 ; a plurality of triangular gusset plates  140 ,  142  and  144  ( FIG. 1 ) attached, for example, by welding, to the top surface of base plate  138  and to the back surface of face plate  136 ; a hollow tube  146  attached, for example, by welding, to the bottom surface of face plate  136 ; and a plurality of lifting eyelets  82  and  148 . As discussed herein above, lifting eyelet  82  is attached, for example, by welding, to face plate  136 . Lifting eyelet  148  as shown in  FIG. 6  is attached, for example, by welding, to base plate  138 . As shown in  FIG. 6 , the width of face plate  136  is less than the width of base plate  138  and the bottom section of face plate  136 , and face plate  136  extends below base plate  138  to fit between the interior surfaces  148 ,  150  of side frames  34 ,  36  respectively, where face plate  136  is secured to test bench  10  by means of removable pin  152 . Removable pin  152  passes through an aperture  154  which is bored in side frame  34 , through the tailstock tube  146 , and through an aperture  156 , which is bored in side frame  36 . Additional apertures such as those shown by reference numerals  156  and  158  in  FIG. 4  may be provided along the length of side frames  34  and  36 , respectively so that tailstock  22  can be secured along test bench  10  at different locations in order to accommodate the testing of different length hammers. 
         [0034]    Referring again to  FIG. 3 , rear carriage plate  62  of the support carriage assembly  58  is affixed to and supported by tailstock  22  by the first and second rear supporting assemblies  84  and  86  which are an integral part of rear carriage plate  62 . As shown in  FIG. 3 , supporting assemblies  84  and  86  have an internal notched section  160  which fits around the back side of face plate  136 . Rear carriage plate  62  along with supporting assemblies  84  and  86  may be raised or lowered relative to face plate  136  of tailstock  22  by using the hand wheel adjustment assembly  78  mounted over the top surface of rear carriage plate  62 . More particularly, hand wheel adjustment assembly  78  comprises an adjustment base plate  162 , which extends over the top surface of rear carriage plate  62  and the top surface of face plate  136 . A hand wheel  164  is attached to a threaded shaft  166  which passes through nut  168  mounted to the top surface of adjustment base plate  162  and through an aperture (not shown) in base plate  162  to rest against the top surface of face plate  136 . As hand wheel  164  is rotated, shaft  166  pushes against the top surface of face plate  136  to raise rear carriage plate  62  away from the top surface of face plate  136 . A lowering of rear carriage plate  62  is accomplished by a reverse action. Once a desired height is reached, rear carriage plate  62  along with supporting assemblies  84  and  86  may be affixed to face plate  136  by fixing bolt assemblies  170 ,  172 ,  171 , and  173  which are equipped with handles  174 ,  176 ,  175  and  177  respectively that operate fixing bolt assemblies  170 ,  172 ,  171  and  173  which pass through apertures (not shown) in supporting assemblies  84  and  86  and engage face plate  136 . Even though fixing bolt assemblies  170 ,  172 ,  171  and  173  are shown in  FIG. 3  associated with supporting assembly  84 , similar bolt assemblies may be provided for supporting assembly  86 . 
         [0035]    Referring again to  FIGS. 3 and 4 , the guide rod  118  of each supporting guide rod assembly  68 ,  70 ,  72 ,  74 , and  76  extends through an aperture in rear carriage plate  62  and are secured to rear carriage plate  62  by a nut fastener  124  (better shown in  FIG. 3 ) fixed to the threaded end of guide rod  118  similar to that described herein above for the nut assemblies  124  associated with front carriage plate  60 . Similarly, nut fastener  124  associated with the guide rod  118  of each supporting guide rod assembly  68 ,  70 ,  72 ,  74  and  76  and rear carriage plate  62  comprises at least two nuts fixed to the thread end of the supporting guide rod  118 , a metal washer, and a resilient washer which is provided for shock absorption purposes. 
         [0036]    Referring particularly to  FIG. 3 , the pneumatic air bag assembly  56  comprises a rubber body  178  having a plurality of rubber volutes  180 ,  182  and  184 , and which rubber body  178  is a cast one-piece construction. Pneumatic air bag assembly  56  is attached at its one end to the internal surface of front carriage plate  60  by a steel bead ring  186  and is attached at its other end to a rear bag support assembly  188  by a steel bead ring  190 . The rear bag support assembly  188  comprises a base plate  192  attached, for example, by welding, to a cylindrical port station  194 . A gauge regulator assembly  197  is attached to the cylindrical port station  194  and allows compressed air from shop air compressors (not shown) to fill and maintain pressure in the rubber body  178  during test firing of the hammer. Cylindrical port station  194  is also equipped with at least two pressure relief valves  193  and  195  to protect the pneumatic air bag assembly  56  from being over pressurized. Gauge regulator assembly  197  may be quickly attach to and disconnected from load cell assembly  16  via quick disconnect fittings, in a manner well known to those skilled in the art. Gauge regulator assembly  197  is set up to continually adjust air pressure such as to match the pressure in rubber body  178  to the size of the hammer which is being test fired. Larger hydraulic hammers in most instances, will required more pressure than smaller hammers. Two pressure relief valves  193  and  195  located in cylindrical port station  124  provide primary and redundant over-pressure protection for pneumatic airbag assembly  56 . Each relief valve  193 ,  195  is designed to handle the volume of air in the pneumatic air bag assembly  178  and to limit the maximum pressure in rubber body  178  so as not to exceed the manufacturer&#39;s limitations for rubber body  178 . Even though only one relief valve may be used for this latter purpose, a second relief valve is added as a back-up safety device. 
         [0037]    A suitable pneumatic air bag assembly for use in the invention is available from Firestone Industrial Products Co., a Division of Firestone Tire and Rubber Company, Manufacturers Part Number W01-358-7761, known as Firestone Model Number 312C Air Spring Assembly. The maximum pressure allowable in this pneumatic air bag assembly is published by Firestone as being 100 PSI based on a two-ply construction of rubber body  178 . The burst pressure of this pneumatic air bag assembly may be three times the published maximum pressure, that is, 300 PSI. Suitable pressure relief valves for the invention may be Part Number 159-SN-50-100 available from Watts and factory preset to 100 PSI. The inventors have found favorable performance of the pneumatic air bag assembly  56  when gauge regulator assembly  196  is adjusted between 25 and 60 PSI, depending on the size of the hammer being tested, the larger hammers requiring higher air pressures. 
         [0038]      FIGS. 7 and 8  clearly illustrate a hammer  196  with hammer tool  198 , which is to be test fired in test bench  10 . Hammer  196  is positioned in mounting deck assembly  26 , as more clearly shown in  FIG. 5 . With particular reference to  FIG. 5 , mounting deck assembly  26  in addition to head stock  44 , ratchet assemblies  46 ,  48 ,  50  and  52  and positioning cylinder assembly  28 , further comprises straps  200  and  202  secured to ratchet assemblies  46  and  48 , respectively, buffer  204 , upper deck plate  206  and lower assembly  208 . Lower assembly  208  is a carriage structure made from steel plates, which in some non-limiting embodiments, are welded together and comprises a plurality of C-shaped members, one located at each of the four corners of top plate  206 . Three such C-shaped members are indicated in  FIG. 5  by reference numerals  210   212 , and  214 , but it is to be appreciated that a fourth C-shaped member is mounted to the upper left hand corner of top plate  206 . Lower assembly  208  further comprises a central bracketed member  216  connected to the C-shaped members and a lower deck plate  218 . Upper deck plate  206 , the four C-shaped members, and central bracketed member  216  are structurally connected together, for example, by welding as shown in  FIG. 5 , with the lower deck plate  218 , in some non-limiting embodiments, being connected to the bracketed member  216  by threaded fasteners (not shown). The bottom surface of each C-shaped member is frictionless, and in some embodiments, may be coated with a smooth plastic coating to facilitate reciprocation of mounting deck assembly  26  along the top surface of side frames  34  and  36  so that mounting deck assembly  26  may slidably move via positioning cylinder assembly  28  in the direction of the load cell assembly  16  to bring hammer tool  198  into contact with impact receptor  54  of load cell assembly  16  ( FIGS. 7 and 8 ) for testing and to return mounting deck assembly  26  via positioning cylinder assembly  28  to its original positioning along test bench  10  after testing the hammer  196 . 
         [0039]    Still referring to  FIG. 5 , ratchet assemblies  46 ,  48 ,  50  and  52  are mounted to the top surface of upper deck plate  206  on each of the upper edges of upper deck plate  206  via elongated brackets  220  and  222  and are slidably adjustable along the length of brackets  220  and  222  in a manner well known to those skilled in the art in order to adjust ratchet assemblies  46 ,  48 ,  50  and  52  along mounting assembly  26  to accommodate the length and/or size of the hammer being tested. Suitable ratchet assemblies  46 ,  48 ,  50  and  52  and straps  46  and  48  may be those commercially available and operate in a manner well known to those skilled in the art. When a hammer to be tested is positioned within ratchet assemblies  46 ,  48 ,  50  and  52  on upper deck plate  206 , straps  46  and  48  are brought across the hammer and are fastened and secured in their respective ratchet assembly  50  and  52 . 
         [0040]    With reference to  FIGS. 5 ,  7  and  8 , as will be appreciated, alignment blocks (not shown) may be used to position test hammer  196  on mounting deck assembly  26  and in alignment with load cell assembly  16 . Head stock  44  bears the repelling force of the hammer  196  fire during the testing process. As more clearly shown in  FIG. 5 , buffer  204  which may be in a cylindrical configuration to coincide with the configuration of the hammer, in general may be provided between the headstock  44  and the hammer  196 . Buffer  204  may be made of a resilient material, for example, rubber. Buffer  204  is generally provided to protect the several components of the system, especially the bolts used to secure the several components together throughout the mounting deck assembly  26  from shearing during the live fire testing of the hammer.  FIGS. 7 and 8  show mounting deck assembly  26 , headstock  44 , buffer  204 , ratchet assemblies  46 ,  48 ,  50  and  52 , and straps  200 ,  202 , and the manner in which mounting deck assembly  26  is captive within the test bench frame  12 , yet slides to bring the hammer tool  198  into contact with the load cell assembly  16 . It is to be further appreciated that  FIGS. 7 and 8  do not contain all of the reference numerals of the other figures for simplicity sake. 
         [0041]    Referring again to  FIG. 4 , pneumatic air bag assembly  56  is supported and mounted between front carriage plate  60  and rear carriage plate  62 , which are supported by the guide rod assemblies shown at  68 ,  70 ,  72 ,  74  and  76 , and the first front supporting foot assembly  64  and the second front supporting foot assembly  66 . Each of the guide rods of the guide rod assemblies  68 ,  70 ,  72 ,  74  and  76  are supported by bushings  120  ( FIG. 3 ). Supporting foot assemblies  64  and  66  are adjustable up and down in a vertical direction relative to  FIG. 3 . The impact point of the hammer tool (not shown) requires that it be centered into the impact receptor  54  ( FIG. 4 ). Supporting foot assemblies  64  and  66  can then be adjusted in a vertical direction relative to impact receptor  54  ( FIG. 4 ) in accordance to the overall dimensions of the hammer to be tested. Supporting foot assemblies  64  and  66  are also necessary to support the weight of the front end of load cell assembly  16  so as to maintain the alignment of the support rods of supporting guide rod assemblies  68 ,  70 ,  72 ,  74  and  76  While proper setting of supporting foot assemblies  64  and  66  holds the front carriage plate  60  in alignment with the tool of the hammer to be tested, handles  172 ,  174 ,  175  and  177  allow fixing their respective screws ( FIGS. 3 and 4 ) to hold the load cell assembly  16  in place on the tailstock  22 . Hand wheel assembly  78  via hand wheel  164  and threaded shaft  166  allows for fine adjustment of the load cell assembly  16  relative to the centering of the hammer tool. Front carriage plate  60  and the remaining components of the load cell assembly  16  must be kept closely in alignment with the hammer tool to be tested in order to avoid any misalignment stresses on the guide rods  118  of guide rod assemblies  68 ,  70 ,  72 ,  74  and  76  and bushings  120 . When being tested, the impact of the hammer tool will in effect compress the rubber body  178 , which acts as a spring and rebounds to meet the next blow of the hammer tool  198 . If a 312C air spring assembly from Firestone, as discussed herein above, is used, it generally will have a minimum compressed length of 4.5 inches overall, a maximum extended length of 14.75 inches overall, with an optimum design length of 13.0 inches overall. This particular air spring assembly gives a net compression range of 8.5 inches. Some hammers may have a maximum tool stroke length of approximately 6.0 inches. In practice, it has been found by the inventors that the length of travel of the hammer tool averages between 2.0 inches and 5.0 inches. As for the air pressure in the pneumatic air bag assembly  56  of the invention, gauge regulator assembly  196  maintains a relatively constant setting in rubber body  178  throughout the test session. It is to be appreciated that the tailstock  22  and the load cell assembly  16  supported by tailstock  22  can be positioned relative to each other and relative to the test bench  10  by using the several eyelets  80 ,  82 , and engaging the several eyelets  80 ,  82  with a hoisting device provided in the testing area. 
         [0042]    Referring particularly to  FIG. 4  the center of impact plate  92  of load cell assembly  16  is impacted by the tool bit of the hammer that is test fired. As explained herein above, the load cell assembly  16  via the pneumatic air bag assembly  56  dissipates the energy from the blow of the hammer and rebounds before the next blow from the hammer is given. The rate of blows is also referred to as cycles and the energy dissipated is measured in ft. lbs. or joules. As stated herein above, in an embodiment of the present invention, bench frame  10  is constructed of materials and components suitable for supporting up to approximately 20,000 pounds. In an embodiment of the invention, test bench  10  may be capable of operating between 350 cycles and 520 cycles, and the energy dissipated may range from about 200 ft.-lb (271 joules) to about 12,000 ft.-lb. (16,269 joules). 
         [0043]    The energy needed for movement of positioning cylinder assembly  28  (attached to the mounting deck assembly  26 ) toward and away from load cell assembly  16  and the energy needed for the firing of the hammer are supplied by a hydraulic power unit (not shown). In this example, this power unit is an arrangement comprised of an electric motor, a hydraulic pump, a reservoir containing hydraulic oil, and a control valve assembly. The control valve assembly of this arrangement responds to electrical inputs from the operator via a remote control pendant attached to a control cable. While this remote control pendant is generally hard wired to the power unit, one could integrate another control version that works on a radio frequency (RF-wireless) technology. This power unit provides the hydraulic energy necessary to position the mounting deck  26  and the supported impact hammer during testing and also provides the power (hydraulic pressure and flow) to the hydraulic hammer being tested. 
         [0044]    In a non-limiting embodiment of the invention, this power unit (not shown) of test bench  10  described in the preceding paragraph may produce a hydraulic oil flow of approximately 23 GPM at pressures up to 2500 PSI from a variable displacement piston pump coupled to a 25 horsepower electric motor. The hydraulic oil flow is controlled by a valve package that allows the operator of the test bench  10  to simultaneously fire the hammer and adjust the positioning of the mounting deck assembly  26  to maintain contact of the hammer tool  198  and the impact receptor  54  of the load cell assembly  16 . The maximum pressure supplied to the hammer may be controlled by the operator at a panel (not shown) on the front of the power unit (not shown) which features two pressure gauges, which receive pressure from two pressure circuits. That is, two hoses (for one reversible circuit) for delivering pressurized oil generally will be provided and attached to the hammer to be tested and two hoses (one reversible circuit) for delivering pressurized oil will be provided and attached to the positioning cylinder assembly  28  attached to the mounting deck assembly  26 . The pressurized oil for the test hammer and the pressurized oil for the mounting deck assembly  26  will be provided from a single pressure source that is controllable as two separate reversible circuits. 
         [0045]    Hammer test bench  10  of the present invention allows live fire testing of the repairs that were made to the hammer before the hammer is returned for field operations. This testing is performed to correct any operational and/or leakage problems that may be associated with the hammer. As can be appreciated from the above, mounting deck assembly  26  secures hammer  196  and reciprocates hammer  196  into a test firing position via hydraulic positioning cylinder assembly  28  and against load cell assembly  16 , which absorbs the impact force delivered by hammer tool  198  against the impact receptor  90 . Load cell assembly  16 , along with the pneumatic air bag assembly  56 , via support carriage  58  is maintained in a linear position in alignment with impact receptor  90 . Gauge regulator assembly  197  adjusts the air pressure in the pneumatic air bag assembly  56  according to the size of the hammer being tested; while one or more pressure relief valves  193 ,  195  prevent over-inflation of the pressure in the pneumatic air bag assembly  56 . Pneumatic air bag assembly  56  is constructed to dissipate the impact force delivered by the hammer tool  198  by contracting when the hammer tool  198  hits against replaceable impact plate  92  and impact receptor  90 , and by expanding to its original configuration after each cycle of the test firing of hammer  196  and into a non-firing position when hammer  196  is moved away from load cell assembly  16 . In dissipating the impact force delivered by hammer tool  198 , a sufficient amount of compressed air is assured within the expandable pneumatic air bag assembly  56 , by and with pressure regulator  197  maintaining the air pressure in the pneumatic air bag assembly  56  while at the same time replacing the air that may have escaped over the two pressure relief valves  193 ,  195  during the compression of the pneumatic air bag assembly  56 . 
         [0046]    Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.