Abstract:
A chisel bit of a percussion tool for penetrating hard surfaces includes a shaft having a mounting end, a working end and upper and lower protuberances formed along its length. The upper protuberance provides for retaining the mounting end of the shaft within a body of the percussion tool. The lower protuberance forms a retaining collar beyond the body of the percussion tool against which a resilient extractor is mounted along the shaft. The resilient extractor includes an elastomeric member that is positioned by the retainer collar along the shaft to contact the hard surfaces penetrated by the chisel bit and exert a resilient bounce back force against the hard surfaces when the chisel bit has penetrated to a given depth to prevent the chisel bit from becoming stuck in place.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/783,647, filed May 20, 2010 of which is herein incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO A “SEQUENCE LISTING” 
       [0003]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The invention relates to bits for demolition tools. It particularly relates to demolition bits for air powered percussion hammers. 
         [0006]    2. Description of Related Art 
         [0007]    In the construction and demolition industries, the use of air powered percussion hammers to break up existing concrete is well known. Such hammers use a chisel that is hammered into the existing concrete and causes the concrete to crack and break up so that it can be removed by loading equipment. One difficulty with the percussion air hammer and chisel bits is that the bits may become trapped in the concrete if it does not crack. Then it is difficult for the operator to withdraw the bit and slows down the demolition. 
         [0008]    U.S. Pat. No. 4,993,894 to Fischer discloses a masonry drill bit that includes a stop to control hole depth. The drill stop also has a resilient element that serves as an anti-vibration element. 
         [0009]    U.S. Pat. No. 6,609,860 to Wanek also discloses a stop that limits the hole depth of a masonry drill. 
         [0010]    U.S. Pat. No. 4,548,279 to Zaruba discloses a demolition tool that is provided with an extractor for pulling the chisel from the work surface when it becomes difficult to remove. 
         [0011]    There remains a need for an apparatus and method to allow rapid release of a demolition chisel from concrete. There remains a need for a method of removing demolition chisels from concrete that does not delay demolition. There remains need for a method of removing chisels from concrete that is not tiring to the operator of the percussion demolition tool and does not cause delays. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    The invention relates to a demolition tool comprising a chisel comprising a bounce back feature. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0013]      FIG. 1  is a prospective view of a percussion air hammer with the bounce back element installed. 
           [0014]      FIG. 2  is a view of a chisel that is provided with the bounce back element of the invention. 
           [0015]      FIG. 3  is a view of the assembling of the chisel with the bounce back element. 
           [0016]      FIG. 4  and  FIG. 5  are top and bottom views of the elastomeric member used in forming the bounce back element. 
           [0017]      FIG. 6  and  FIG. 7  are top and bottom perspective views of the elastomeric member that may be used in the bounce back element. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The invention has numerous advantages over prior practices in the art. The invention removes the chisel from the concrete without requiring additional energy to be expended by the operator of the percussion demolition device. Further, as the invention extracts the chisel a larger hole is created which aids in further demolition. The invention device, while creating the advantages as set forth above, does not require extra physical effort by the operator in operating the air hammer. In fact, the effort required is less as the operator does not need to wrestle with the percussion hammer to remove the chisel from holes. The invention also extends the life of the hammer bits as they are not abused during extraction from the concrete. These and other advantages will be apparent from the detailed description below. 
         [0019]    In  FIG. 1 , a percussion air hammer  10  is illustrated. The air hammer  10  is provided with grips  12  and air hose  14 . The air hose  14  is connected to an air compressor, not shown, to supply high-pressure air to the hammer  10 . The air hammer  10  drives a bit or chisel  20  that is provided with the resilient bounce back bit extractor element  15  of the invention. 
         [0020]      FIG. 2  is a perspective view of a chisel  20  with the resilient extractor element  15  mounted on the chisel  20 . The chisel  20  is provided with two protuberances  22  and  24  separated by area  23 . Protuberance  22  is provided for engaging the chisel shaft with the air hammer in the conventional way. Protuberance  24  is shown as a retainer collar that serves as a stop for the bounce back element  16 . Washer  26  is provided between retainer collar protuberance  24  and resilient member  16 . The bounce back element  15  is held to the chisel by strap  28 . It is noted that the chisel  20  is not round in the cross-section but it is provided with a series of lands  32  and ridges  34  leading to the chisel point  36 . Chisel portion  21  extends into the hammer and the working chisel portion  25  is below the retainer collar  24 . 
         [0021]      FIG. 3  is a perspective view of the chisel and resilient bounce back element  15  prior to assembly. In assembling the invention, the washer  26  is placed on the chisel  20  and moved up against the retainer collar protuberance  24 . The elastomeric member  16  is moved up against the washer  26 . The elastomeric member is then fastened to the chisel  23  by tightening the strap  28  in the groove  36 . 
         [0022]      FIGS. 4 and 5  are top and bottom views, respectively, of the elastomeric member  16  utilized in the invention.  FIGS. 6 and 7  provide perspective top and bottom views of the elastomeric member  16  utilized in the invention. The elastomeric member  16  is provided with a channel  42  where the chisel will pass through the elastomeric member. The elastomeric member further is provided with cutouts  44  that extend to below the groove  36  where the fastening strap  28  will be located. By providing these grooves  44 , the top of the elastomeric member  16  will collapse and deform when the fastening band  36  is tightened causing the elastomeric member  16  to be tightly held to the chisel. 
         [0023]    The protuberances  22  and retainer collar  24  on the chisel are each shown as a continuous annular addition to the chisel. The protuberances would not need to be continuous around the chisel shaft and could be formed in separated portions. It is preferred that the protuberances be formed by forging the chisel with the protuberances integral with the rest of the chisel. The protuberances may be welded to the chisel but are more likely to break both at the protuberance holding the elastomeric member and at the protuberance that fastens the chisel to the percussion hammer. The protuberance  22  for fastening to the percussion hammer may be any design to fit the particular percussion hammer being utilized. The protuberance  24  may be any shape that will stop washer  26  and not break during usage. A retainer collar is, as illustrated, preferred as it is less likely to break than other shapes of protuberances. A chisel with an integral forged protuberance is much more reliable than a welded protuberance, which is more subject to breakage during use. 
         [0024]    The chisel generally is about 19″ long. Typically, about 6″ of the chisel will extend above the protuberance  22  for placement into the hammer. The lower collar  24  is generally between 2.5″ and 3.5″ below the protuberance  22 . The chisel bit then extends about 9″ below the retainer collar protuberance  24 . In one preferred embodiment, the chisel  20  has an overall length of 19″. The hammer portion  21  is 6″ long; the work bit portion  25  is 9⅛″ long; and the portion  23  between the protuberances  22  and  25  is 2⅜″ long. The protuberances are each ½″ on the shaft, which is 1⅛″ in diameter. 
         [0025]    While the bit or chisel illustrated herein has a hexagonal cross-section, it is possible to use chisels of other cross-section such as round. It is also possible that the bit or chisel could have a star shape or point rather than the chisel end illustrated. The term chisel as used herein is intended to include bits provided with other than chisel points unless specifically indicated. 
         [0026]    The strap  28  holding the elastomeric member  16  in place may be any strap convenient to use. The strap needs to be able to be tightened quickly and not loosen during use. Typical of such straps are hose clamps, plastic clamps such as for electrical ties, and metal clamps, which are semicircular with two of the clamps bolted to each other to compress the elastomeric member  16 . The washer  26  generally would be formed of steel and of diameter sufficient to spread the compression load on the elastomeric member  16  so it is less likely to crack or deform at the upper side. 
         [0027]    The size of the elastomeric member  16  may be any effective length and width that does not interfere with the operation of the chisel. The size will vary depending on the properties of the elastomeric member and the size of the jack hammer. The elastomeric member generally is of such size as to not need to greatly deform to provide the rebound or bounce back required to remove a chisel from a hole. Not having excessive deformation will prolong the elastomer&#39;s life. It is generally desirable that compression of the elastomeric member be less than 50% to cause rebound of the chisel and have long life of the elastomer. Any suitable width and length of elastomeric member may be utilized that is effective. Generally, the width would be between about 3″ and 4″ and the length (along the central hole) between about 3″ and 5″. A length of about 4″ is preferred for good rebound without interfering with the working depth of the chisel. The washer would have a diameter of about an inch and a half. A chisel is typically about 1.1″ in diameter. 
         [0028]    The elastomeric member  16  should be abrasion resistant, particularly at the end that contacts the concrete, blacktop, or other hard surface. It is known to increase abrasion resistance of elastomers by embedding fiberglass, fiberglass cloth, metal wire, metal particles, or ceramic particles in the elastomeric member  16 . The durometer should be such that the elastomeric member  16  has properties that will allow good bounce back when the chisel contacts the concrete. Generally, the durometer would be between about 40 and 80. A preferred durometer property would be between 55 and 65 to provide a good bounce back element and sufficient toughness to survive the use with the chisel of the percussion hammer. The tensile strength of the elastomeric member  16  should be sufficient to provide long life to the elastomeric member that provides the bounce back element for the chisel. A tensile strength of between 800 and 1500 pounds per square inch (psi) has been found to be suitable. A preferred tensile strength is about 1000 psi for good bounce back and long life. The elongation of the elastomeric member may be any suitable amount that results in an elastomer with good bounce back or rebound elements. An elastomeric member with an elongation to breaking of between 250% and 350% has been found to be preferred for long life and good bounce back. The elastomeric member also should maintain bounce back properties over the temperature range where the percussion hammer may be used. This typically would be between −25° F. and 175° F. 
         [0029]    The elastomeric member  16  may be formed of any suitable polymer composition that results in suitable properties for the bounce back feature and long life. Suitable compositions are elastomeric polymers and blends of synthetic and natural elastomers. A preferred elastomeric composition has been found to be a styrene butadiene rubber for long life and desirable bounce back properties. The resin is preferably reinforced with material such as fiberglass cloth to aid in preventing wear where it contacts the concrete. Other reinforcement materials for elastomerics are steel wires and ceramic particles that may be used in the invention. 
         [0030]    The cutouts  44  in the top of the elastomeric member may be any size that provides for achieving a good grip on the chisel when the strap is tightened, but does not weaken the elastomer such that it will deteriorate in that area. Typically, the cutouts would be between ⅛″ and ⅜″ wide and extend down about an inch from the top of the elastomeric member. 
         [0031]    While described as the elastomeric member, it is also possible that other materials could be used to create the bounce back feature for a percussion chisel. For instance, springs could be utilized instead of the elastomer. The springs would be mounted on the chisel such as they are mounted around a central Pogo stick shaft such that when the chisel enters into a certain depth of the concrete it would compress the spring on the shaft of the chisel and cause rebound. 
         [0032]    While discussed with use of a pneumatic percussion hammer, it is also possible that the invention can be used with other types of percussion hammers powered by electricity or hydraulics.