Patent Publication Number: US-8991515-B2

Title: Fail-resistant hammer assembly for a valveless percussive drill

Description:
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/887,742, filed Feb. 1, 2007, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to drills and, more particularly, to a percussive hammer assembly for use in connection with a hydraulic drill. 
     SUMMARY OF THE INVENTION 
     Various forms of percussive drills are known in the art. In one common form, the drill incorporates a hammer assembly comprising a tubular distributor that receives a piston in a telescoping fashion and allows it to reciprocate in order to perform the percussive drilling, such as in connection with the formation of boreholes in rock and the installation of roof anchors therein for mining applications. Pressurized fluid is introduced through radial inlets to cause the movement to and fro in connection with various circumferential passages formed in the exterior surface of the piston. An example of such a hammer assembly for use in connection with a valveless hydraulic percussive drill may be found in U.S. Pat. No. 4,550,785 to the present inventor, the disclosure of which is incorporated herein by reference. 
     Typically, the distributor and piston are made of steel hardened by way of heating. When assembled, the gap between the inner diameter of the distributor at the open end and the outer diameter of the piston is very small (usually thousandths of an inch), so as to form the desirable low friction fluid bearing. However, the presence of contaminants in the working fluid may “gall” and damage the piston. Even if damage does not result, the offset caused by the foreign object present one side of the annulus may cause the hard steel of the piston to engage the hard steel of the distributor frictionally, thus contributing to wear and early failure. 
     Accordingly, a need is identified for a hammer assembly for use in connection with a valveless hydraulic percussive drill that overcomes the foregoing limitations and is thus less resistant to failure. 
     SUMMARY OF THE INVENTION 
     In one aspect, the disclosed invention relates to an apparatus for forming part of a valveless percussive drill for use with a working liquid. The apparatus comprises a piston adapted for reciprocating movement in a longitudinal direction. The piston comprises an oversized head portion, a stem portion, a cushion portion, and at least one shoulder positioned at least partially between the head portion and the cushion portion. A tubular body is also provided for receiving the piston, which preferably includes at least an exterior surface that is generally symmetrical about a medial transverse plane. The body includes an interior surface resistant to galling due to the presence of any contaminant in the working liquid and a hardened end face for engaging the shoulder of the piston in the event of overtravel in the longitudinal direction. 
     In terms of materials, the interior surface may comprise bronze or ductile iron, while the body comprises a material harder than bronze, such as steel. The piston may comprise steel, including along an outer surface for engaging the interior surface of the body. As a result, the more lubricious and wear resistant material is adjacent the harder outer surface of the liner. 
     The tubular body preferably comprises a liner adapted for permitting at least the head portion of the piston to reciprocate. The end face of the body may be located adjacent an intake chamber for receiving the working fluid for causing the piston to move relative to the liner. A gap between the piston and at least the head portion of the tubular body defines an annulus for receiving the working fluid. The tubular body may further comprise a distributor adapted for receiving and permitting at least the stem portion of the piston to reciprocate. 
     Preferably, the liner for receiving the head portion of the piston contacts the end face of the distributor, such as along a shoulder. In the event of overtravel in the longitudinal direction, this engagement advantageously prevents the cushion portion of the piston from engaging a corresponding transverse face within the tubular body. As a result, the resistance to failure and accordingly the service life both increase. 
     Still a further aspect of the invention is a method of forming part of a valveless percussive drill for use with a working liquid. The method comprises providing a piston with an oversized head portion, a stem portion, a cushion portion, and at least one shoulder at least partially between the head portion and the cushion portion. The method further comprises positioning the piston at least partially in a tubular body having an interior surface resistant to galling and a hardened end face for engaging the shoulder of the piston. In the event of overtravel in the longitudinal direction, this engagement advantageously prevents the cushion portion of the piston from engaging a corresponding transverse face within the tubular body. As a result of practicing this method of manufacture, the resistance to failure and accordingly the service life both increase. In one embodiment, the providing step comprises providing a gap between the interior surface and an exterior surface of the piston, as well as a liquid in the gap. The method may further include the step of drilling using the valveless percussive drill. 
     A further aspect of the disclosure is a method of manufacturing a liner assembly for use in connection with a piston in a percussive drill. The manufacturing method comprises forming a tubular body of a first material for receiving the piston, the body having an interior surface and an end face, and providing a lining formed of a second material resistant to galling along at least a portion of the interior surface for engaging the piston. After the providing step, the method comprises hardening at least the end face of the body. 
     Preferably, the hardening step comprises heat treating the body to a temperature that does not impact negatively the second material of the lining. When the second material comprises bronze, and the heat treating does not cause the bronze to exceed a temperature of approximately 620° C. Preferably, the forming and providing steps comprise creating at least a portion of the body including the portion of the interior surface with the lining from a blank comprising the first and second materials. 
     In a related aspect, an apparatus for performing drilling is disclosed. The apparatus comprises a valveless percussive drill including: (1) a piston adapted for reciprocating movement in a longitudinal direction, the piston having an oversized head portion, a stem portion, a cushion portion, and at least one shoulder positioned at least partially between the head portion and the cushion portion; and (2) a tubular body for receiving the piston, the body having an interior surface resistant to galling and a hardened end face for engaging the shoulder of the piston in the event of overtravel in the longitudinal direction. 
     A further related aspect is an apparatus for forming part of a valveless percussive drill for use with a working liquid. The apparatus comprises a piston having an oversized head portion and at least one shoulder, and a tubular body having a bore for receiving the piston, the body including a cushion pocket. The shoulder engages a portion of the tubular body external to the cushion pocket if the piston overtravels within the bore. 
     Yet another aspect of the invention is an apparatus for forming part of a valveless percussive drill for use with a working liquid. The apparatus comprises a piston having an oversized head portion, and a tubular body having a bore for receiving the piston, the body including a cushion pocket. The piston includes means for engaging the tubular body external to the cushion pocket. Preferably, the means for engaging comprises an annular shoulder. 
     A further aspect of the disclosure relates to an improvement in a valveless percussive drill including a piston adapted for reciprocating movement within a tubular body formed of a first material and including a driving chamber associated with a port, a drain annulus, and a pressure seal annulus. The improvement comprises a lining formed of a second material resistant to galling along at least a portion of the interior surface and a hardened end face for engaging the piston in the event of overtravel. The tubular body may comprise a liner or a distributor. The piston may comprise an oversized head portion, a stem portion, a cushion portion, and at least one shoulder positioned at least partially between the head portion and the cushion portion and adapted for engaging the tubular body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross-sectional view of a hammer assembly constructed in accordance with the preferred embodiment of the invention; 
         FIG. 1   a  is an enlarged, cutaway view of a portion of the assembly of  FIG. 1 ; 
         FIG. 1   b  is a further enlarged, cutaway view of a portion of the assembly of  FIG. 1 ; 
         FIG. 2  is a side cross-sectional view of a hammer assembly constructed in accordance with the preferred embodiment of the invention; 
         FIG. 2   a  is an enlarged, cutaway view of a portion of the assembly of  FIG. 2 ; 
         FIG. 2   b  is a further enlarged, cutaway view of a portion of the assembly of  FIG. 2 ; 
         FIG. 3   a  is a side elevational view of one embodiment of a piston for use in connection with the disclosed hammer assembly; 
         FIG. 3   b  in an enlarged end view of the piston of  FIG. 3   a;    
         FIGS. 4   a  and  4   b  provide exemplary manufacturing techniques for the distributor and liner; 
         FIG. 5  illustrates a percussive drill; 
         FIG. 6  illustrates a liner for a valveless percussive drill and formed using the manufacturing technique forming part of the disclosure; and 
         FIG. 7  illustrates a distributor for a valveless percussive drill and formed using the manufacturing technique forming part of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1-3 , a hammer assembly  10  according to one possible embodiment is shown and will now be described in detail. In the illustrated preferred embodiment, and with initial reference to  FIG. 1 , this hammer assembly  10  includes an elongated annular liner assembly  12  comprising an elongated member or liner  14  and a mating elongated distributor  16 . As illustrated, the distributor  16  is coaxially disposed adjacent a rearward end of the liner  14 . Both the liner  14  and distributor  16  include various ports and inlets for receiving a working liquid or other non-compressible fluid. Other internal parts of an associated valveless percussive drill R (see  FIG. 5 ) are not shown for purposes of clarity, and specific details of its operation are not provided, but both of these are well-known in the art and can be found in the &#39;785 patent. 
     The coaxially communicating inner peripheries of the liner  14  and distributor  16  form a coaxial through bore  18  for receiving an elongated, stepped cylindrical piston  20  disposed for reciprocal movement in a longitudinal direction L. This bore  18  includes axially spaced forward and rearward bearing portions  22 ,  24 , which slidably support axially spaced forward and rearward stem portions  26 ,  26 ′ of piston  20 . An enlarged diameter intermediate portion  28  of the bore  18  between the respective bearing portions  22 ,  24  receives a generally stepped cylindrical intermediate or head portion  30  of piston  20 . Respective variable volume upstroke and downstroke (note action arrows U and D) piston driving chambers  32 ,  34  are formed adjacent respective forward and rearward ends of piston head  30  by axially spaced annular peripheral clearance spaces between the head  30  and bore portion  28 . Piston  20  cooperates with bore  18  to provide for porting of pressurized motive fluid alternately to and from driving chambers  32 ,  34  for self-excitation of the piston  20 , as described in more detail in the &#39;785 patent. 
     Generally, piston  20  is at least externally symmetrical about its medial transverse plane P-P, so only one axial half portion of the illustrated piston, i.e., the upstroke half, will be described. For purposes of this discussion, the remaining piston half portion, i.e., the downstroke half, may be considered substantially similar to the upstroke half. The reference characters applied to the downstroke half are primed characters to correspond to the hereinbelow described parts of the upstroke half of piston  20 . 
     With reference to  FIG. 1   a , the head portion  30  of piston  20  comprises a central, axially extending annular land  36 . This land  36  comprising the head portion  30  is axially slidable within bore portion  28  in cooperation with an exhaust annulus  38  to provide exhaust porting or valving during reciprocation of the piston  20 . 
     A second land  40  is formed with its largest diameter end portion, which is smaller than the diameter of land  36 , located adjacent the axial end of land  36 . This second land  40  tapers radially and inwardly therefrom along its axial extent at a taper angle with respect to the central longitudinal axis of piston  20 , As a result, land  40  provides controlled porting of exhaust fluid by uniformly increasing the outflow of pressure fluid to exhaust as the exhaust annulus  38  opens. Land  40  thereby reduces the possibility of undesirable fluid cavitation which might occur as a result of uncontrolled fluid pressure release to the exhaust. Additionally, the taper on land  40  tends to promote non-turbulent flow of pressurized fluid from the respective driving chambers  32 ,  34  to the exhaust chamber  38  as piston head  30  alternately moves therein during reciprocation so as to reduce any tendency of the fluid to retard piston movement. 
     Axially spaced in the longitudinal direction L from the outer axial end of land  40  is an annular land  42 . This land  42  cooperates with an annular cavity  43  formed adjacent the interface of bore portion  28  and forward bearing surface  22  to provide a fluid cushion for the piston. Extending axially intermediate the axially adjacent ends of lands  40  and  42  is an intervening portion  44 , which may be formed with a uniform or a tapering diameter, depending upon the respective diameters of the portions of lands  40  and  42  joined thereby. Land  42  extends axially in the longitudinal direction L to terminate adjacent the stem portion  26 . 
     In accordance with one aspect of the invention, and with reference to  FIGS. 1   a  and  1   b , an outwardly projecting shoulder  46  is provided on the piston  20 . Most preferably, this shoulder  46  is formed on the intervening portion  44  at least partially positioned and extending between first and second lands  40 ,  42 . Preferably, the shoulder  46  extends circumferentially about the piston  20  and provides an engagement face  48  extending generally transverse to the longitudinal direction L (that is, the direction of reciprocation). 
     In the event of excess over-travel of the piston  20  during reciprocation, this engagement face  48  contacts and mates with an end or “stop” face  50  of the liner  14  (or distributor  16  at the opposite end), which forms or defines part of the chamber for receiving the piston  20  and the associated working fluid forming the bearing. This engagement prevents a transverse end or “cushion” face  52  associated with land  42  from contacting the corresponding transverse end or “cushion” face  54  of the liner  14 . Together, this face  54  and the adjacent annular wall of the cavity  43  may be considered to define a cushion pocket for receiving a portion of the working fluid. The importance of this feature will be better understood upon reviewing the following description. 
     The liner  14  and distributor  16  are typically made of durable materials, such as hardened steel, in order to provide superior wear resistance against the reciprocating piston  20 . When assembled, the gap G between the inner diameter of the bearing portion  24  of the distributor  16  and the outer diameter of the corresponding surface of the stem  26 ′ of the piston  20  is very small (thousandths of an inch), so as to form the desirable low friction fluid bearing. However, the presence of contaminants in the working fluid or other foreign objects may “gall” and damage the piston  20 . Even if damage does not result, the resulting offset adjacent one side of the annulus formed between the structures may cause the hard steel of the piston  20  to engage the hard steel of the bearing portions  22 ,  24  frictionally, thus contributing to excessive wear and concomitant early failure. 
     To prevent this, a softer material, such as bronze or ductile iron, may be used to form the bearing portions  24  of the distributor  16  in which the piston  20  reciprocates. Such materials are more lubricious than steel, as well as relatively soft. Hence, they do not have the same problems with galling as the steel surface, even if the outer surface of the stems  26 ,  26 ′ for some reason engages the corresponding bearing surfaces  22 ,  24 . However, the use of such linings (and, in particular, the process used to form such a distributor  16  with a bronze surface along the bearing portion  24 ) prevents the steel distributor once formed from being fully hardened by way of heat treatment without potentially impacting the lining material (especially when formed of bronze). Thus, even with the use of a bronzed-lined distributor  16 , the “cushion” end face  54  of liner  14  (or end face  54 ′ of distributor  16 ) is not fully hardened and could fail upon being repeatedly engaged by a corresponding surface of the piston  20  as it reciprocates. 
     Reference is now made to  FIG. 2  to describe a possible solution to this problem forming an aspect of the disclosed invention. As should be appreciated, this figure shows the similar arrangement described above with respect to  FIG. 1  at the opposite end of the piston  20 , adjacent the distributor  16  that contacts the liner  14  along the end face  50 ′. The piston  20  is illustrated in the maximum upstream location (note action arrow D) relative to the liner assembly  12 . 
     With specific reference to  FIGS. 2   a  and  2   b , if the piston  20  over-travels rearwardly during reciprocation to this maximum position, the hardened engagement face  48 ′ of the annular shoulder  46 ′ formed on the piston  20  directly contacts and engages this end or stop face  50 ′ (which of course is external to the cushion pocket formed by the face  54 ′ and the annular wall of cavity  43 ). Unlike the “cushion” end face  54 ′, which cannot be easily hardened because of the desirability of providing a wear-resistant lining along the bearing portion  22  of the distributor  16 , the end face  50 ′ can be fully hardened, such as through induction hardening or like processes that do not in anyway impact the desired functionality of the lining. 
     Engagement between this stop face  50 ′ and the matching engagement face  48 ′ of the shoulder  46 ′ thus prevents the cushion face  52 ′ of the piston  20  from directly engaging the corresponding cushion face  54 ′ of the distributor  16 . This ensures that the desirable cushion is maintained (note the representation of fluid cushion C between faces  52 ′,  54 ′ in  FIG. 2   b ). This results in a hammer assembly  10  that is not only less resistant to failure as the result of contaminants in the working fluid, but also able to guard against over-travel in a more effective manner than in the prior art. Together, these features contribute to a substantially longer service life. 
     With reference now to  FIGS. 3   a  and  3   b , a particularly preferred embodiment of the inventive piston  20  is shown. As can be seen, the nominal diameter D 1  of the stem  26 ,  26 ′ is less than the nominal diameter D 2  of the cushion land  42 ,  42 ′ on either side of the piston  20 . The nominal diameter D 3  of the shoulder  46 ,  46 ′ is greater than the nominal diameter D 2  of the cushion land  42 , but preferably less than the nominal diameter D 4  of the head portion  30  (or, in other words, D 4 &gt;D 3 &gt;D 2 &gt;D 1 ). The two diameters D 3 ,D 4  could match, but the shoulder diameter D 3  should always be smaller in the illustrated embodiment to avoid any interference with the lined surfaces of the bearing portions  22 ,  24  within the bore  18 . 
     In accordance with another aspect of the invention, and referring to  FIGS. 4   a  and  4   b , a method of manufacturing a tubular body (either liner  14  or distributor  16 ) for use in connection with a hydraulic, piston-driven percussive drill or the like is described. The method comprises providing a first, preferably softer and more gall-resistant material along at least a portion of the interior of the different second harder material forming the body so as to form a bearing surface. The method further comprises the step of surface hardening an end face of the body for engaging the piston after the application of the material to form the bearing surface. Preferably, the softer material is bronze, in which case the step of hardening the end face involves heating the body without exceeding a temperature or otherwise being worked in a manner that might negatively impact the bearing material used. Most preferably, the bronze lining on steel is achieved by machining blanks comprising bronze bonded to steel (with the steel being a maximum hardness of about Rc=32), in which case this temperature limit is at or below the melting point of bronze (approximately 620° C.). Such blanks are available from Kugler Bimetal SA of Geneva, Switzerland. 
       FIGS. 6 and 7  illustrated a liner  14  and distributor  16  for a valveless percussive drill R including a softer and more gall-resistant material along at least a portion of the interior of the different second harder material forming the body so as to form the desired bearing surface. In a specific example, the softer material comprises bronze, and is provided along the bearing surfaces  22 ,  24  of the liner  14 , and distributor  16 , respectively. This may be accomplished using the above-described manufacturing technique(s). 
     Still more specifically, and referring to  FIG. 6 , the material may be applied to the bearing surfaces  22  of the liner  14  between the driving chamber  32  associated with a port  70 , a drain annulus  72 , and a pressure seal annulus  74 . These locations are of course remote from the cushion end face  54 , which would not include the softer material and could thus be surface treated and hardened in the desired manner (and thus potentially used in connection with a piston like the one shown in the &#39;785 patent that would engage this face in the event of overtravel in the downstream direction). 
     Similarly, referring to  FIG. 7 , the material may be applied to the bearing surfaces  24  of the distributor  16  between the driving chamber  34  associated with a port  76 , a drain annulus  78 , and a pressure seal annulus  80 . These locations are of course remote from the cushion end face  54 ′, which would not include the softer material and could thus be surface treated and hardened in the desired manner (and thus potentially used in connection with a piston like the one shown in the &#39;785 patent that would engage this face in the event of overtravel in the upstream direction). 
     The foregoing description of various embodiments of the present invention are presented for purposes of illustration and description. This illustration and description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments described provide the best illustration of the principles of the invention and its practical applications to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications suited to the particular use contemplated. All such modifications and variations are within the scope of the invention.