Patent Publication Number: US-10307930-B2

Title: Guide bar for a saw chain having a reduced-wear direction-reversing section

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority of German patent application no. 10 2013 013 956.2, filed Aug. 21, 2013, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     A known guide bar includes an elongate, flat base body made of a base body material. The base body extends along a longitudinal center axis and, in order to guide a saw chain, has a running surface formed on an outer periphery of the base body and a guide groove formed in the outer periphery of the base body. The guide groove has a groove base. Formed at one end of the base body is a direction-reversing section for the saw chain, wherein the direction-reversing section includes at least one add-on component having a running surface made of more wear-resistant material than the basic material of the base body. The add-on component is secured to the base body of the guide bar by at least one weld seam. 
     The connection of the add-on component made of wear-resistant material to the base body material of the base body can result in high local stress peaks in the base body material or in the weld seam, and this can result in damage when the guide bar is subjected to mechanical loads. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a guide bar of the generic type such that, while the guide bar has a simple structure, a firm, durable connection between the add-on component and the guide bar is established without excessive material stresses occurring as a result of the welding operation. 
     The guide bar of the invention is for a saw chain. The guide bar defines a longitudinal center axis and includes: an elongated, flat base body made of a base body material and extending along the longitudinal center axis; the base body having an outer periphery and having a guide track formed on the outer periphery for the saw chain; the guide track including a guide groove configured in the periphery and the guide groove having a groove base; a direction-reversing section for the saw chain configured on one end of the base body; the material of the base body being a wear-resistant material; the direction-reversing section being configured as an add-on component made of a material having a wear resistance greater than the wear resistance of the base body material; and, the add-on component being fixed to the base body by a weld seam having a length (S) and running between the add-on component and the base body and arranged to lie spatially below the groove base of the guide groove over a major part of the length (S). 
     The weld seam extends between the add-on component and the base body in the front region of the guide bar and is located—at least over a major part of its length—spatially beneath the groove base of the guide groove for guiding the saw chain. The weld seam is at a distance, measured in the plane of the guide bar, from the running surface of the guide bar of less than about 1.5 times to 3 times the depth of the guide groove. As a result of the weld seam being moved—as seen in the viewing direction toward the open guide groove or the groove base—to under the groove base of the guide groove, the material stress in the region of the groove base can be significantly lowered. This ensures that the add-on component is secured permanently to the base body of the guide bar and also resists high mechanical operating loads. 
     According to a feature of the invention, a segment of the guide groove is formed together with the groove base in the add-on component, such that an even larger spatial distance can be established between the weld seam and the groove base. 
     Advantageously, the main body of the guide bar engages over the add-on component such that the base body overlaps the add-on component. The weld seam is in this case arranged such that it forms an outer boundary of the overlap region, that is, is located in the edge region of the overlap region. 
     Expediently, the add-on component is fixed in its position on the base body. Advantageously, to this end, a finger-like, flat projection is formed on each flat side of the base body and this projection extends in the direction of the longitudinal center axis of the base body and forms the end of the base body. The add-on component is fixed in its position on the base body by the projections. 
     According to another feature of the invention, a recessed region for accommodating the projection, which is formed in particular in a flat manner, is provided in the outer side of an add-on component, such that the add-on component is located in an oriented manner in the plane of the guide bar. Expediently, for precise position fixing, the projection engages in the recessed region of the add-on component largely without play. 
     If the add-on component is formed with a slight excess thickness with respect to the distance between the projections, the add-on component—even when it consists of a plurality of add-on component halves—can be kept clamped between the projections. This is advantageous during preassembly in the manufacture of the guide bar. 
     The weld seam is guided such that it extends, at least along a segment of its length, along a longitudinal edge of the projection. 
     The add-on component preferably consists of a sintered material, in particular of Stellite®. In particular a cobalt-base alloy with 29 percent by weight of chromium, 8 percent by weight of tungsten and 1.3 percent by weight of carbon is advantageous as the material. 
     Expediently, the add-on component is composed of two add-on component halves which abut one another at a partition plane. If the add-on component halves are formed as identical parts, the add-on component halves are easy to manufacture and assemble. 
     The base body of a guide bar has two flat sides, wherein a weld seam is formed on each flat side of the base body in order to connect the add-on component non-detachably to the base body. According to another feature of the invention, the add-on component can have a partition plane, wherein the weld seams arranged on each flat side merge into one another in the region of the partition plane and ensure an intimate connection also of the add-on component halves of the add-on component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the drawings wherein: 
         FIG. 1  is a schematic side view of a motor-driven chain saw; 
         FIG. 2  is a perspective view of a guide bar for a motor-driven chain saw according to  FIG. 1 ; 
         FIG. 3  is a side view of the guide bar according to  FIG. 2 ; 
         FIG. 4  is a plan view of the outer periphery of a longitudinal edge of the guide bar according to  FIG. 3 ; 
         FIG. 5  is an enlarged view of the detail V in  FIG. 3 ; 
         FIG. 6  is a section view taken along line VI-VI in  FIG. 5 ; 
         FIG. 7  is an enlarged partial view of the add-on component made of more wear-resistant material; 
         FIG. 8  is a section view taken along line VIII-VIII in  FIG. 5 ; 
         FIG. 9  is a partial view of a further embodiment of the direction-reversing section of a guide bar having an add-on component; 
         FIG. 10  is a section view taken along line X-X in  FIG. 9 ; 
         FIG. 11  shows a perspective view of a guide bar before the add-on component is attached to the base body; 
         FIG. 12  shows a side elevation view corresponding to the perspective view of  FIG. 11 ; and, 
         FIG. 13  is a section view taken along line XIII-XIII of  FIG. 12 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
       FIG. 1  schematically illustrates a motor-driven chain saw  1 . Arranged in the housing  2  is a drive motor for driving a saw chain  4  that runs around a guide bar  3 . The drive motor can be a combustion engine, an electric motor, a compressed air motor or similar motor. In the rear housing region, the motor-driven chain saw  1  has a rear handle  5 , extending in the longitudinal direction of the housing  2 . The handle  5  has operator-controlled elements  6 . A bale handle  7  is provided in the front region of the housing  2 . The bale handle straddles the housing  2  transversely to the longitudinal direction thereof. Arranged in front of the bale handle  7  is a hand guard  8  which, by pivoting, triggers a safety braking unit (not illustrated in more detail). 
     The guide bar  3  extends from the front region of the housing  2  in the longitudinal direction of the motor-driven chain saw  1 ; at the rear clamping end  9  of the guide bar  3 . The guide bar is secured in a clamped manner between a sprocket wheel cover  10  and the housing  2 . 
     In the exemplary embodiment shown, the guide bar  3  includes an elongate, flat base body  11 . A direction-reversing section  13  for the saw chain  4  is formed at that end  12  of the base body  11  that is opposite the clamping end  9 . The direction-reversing section  13  comprises an add-on component  14  which (at least in the region of its outer periphery, which forms a running surface  17  ( FIG. 2 ) for the saw chain) is formed from a more wear-resistant material than the base body material of the base body  11 . 
     The base body  11  extends along a longitudinal center axis  15  in the longitudinal direction of the motor-driven chain saw  1 . A running surface  17  is formed on the outer periphery  16  ( FIG. 2 ) of the base body  11 . A guide groove  18 , which has a groove base  19  ( FIG. 6 ,  FIG. 10 ), is furthermore provided centrally in the outer periphery  16 . The running surface  17  extends on both sides of the guide groove  18 . 
     The add-on component  14 , which forms the direction-reversing section  13  at the front end  12  of the guide bar  3 , is firmly connected to the base body  11  by at least one weld seam  20  ( FIG. 5 ,  FIG. 9 ), wherein (as  FIGS. 5 and 9  show) the weld seam  20  extends between the add-on component  14  and the base body  11  of the guide bar  3 , and is thus located at the front end  12  of the guide bar  3 . Along a major part of its length S, the weld seam  20  extends spatially between the longitudinal center axis  15  of the guide bar  3  and the groove base  19  ( FIGS. 5 and 9 ) of the guide groove  18 . The weld seam  20  between the add-on component  14  and the base body  11  is thus located (perpendicularly to the open guide groove  18  or the groove base  19  in the viewing direction  40 ) beneath the groove base  19 . 
     As is illustrated schematically and in a greatly enlarged manner in  FIGS. 5, 6 and 10 , the weld seam  20  is located at a distance A from the groove base  19  of the guide groove  18  of preferably less than about twice the depth T of the guide groove  18 , in particular less than half the depth T of the guide groove  18 . The weld seam  20  is thus at a distance, measured in the plane of the guide bar  3 , from the running surface  17  of the guide bar  3  of less than about three times the depth T of the guide groove  18 , in particular less than twice the depth T of the guide groove  18 ; the distance of the weld seam  20  from the running surface  17  corresponds to the sum of the distances A plus T. In particular, the distance A of the weld seam  20  from the groove base  19  is in the range between 0.3 mm and 10 mm, preferably in a range from 0.5 mm to 5 mm, in particular about 0.77 mm. The depth T, measured from the running surface  17  to the groove base  19 , of the guide groove  18  is in the range between 2 mm and 20 mm, preferably between 3 mm and 10 mm, in particular 5.05 mm. 
     As  FIGS. 2 and 3  show, the guide bar has, in the region of the clamping end  9 , a greatest height H, measured transversely to the longitudinal center axis  15 , that decreases continuously as far as the direction-reversing section  13  at the free end  12 . Such a guide bar is also known as a carving bar. 
     In the exemplary embodiment according to  FIGS. 3 to 8 , the add-on component  14  comprises two add-on component halves ( 14   a ,  14   b ) ( FIG. 6 ), wherein the add-on component halves ( 14   a ,  14   b ) are preferably identical parts, that is, are formed in an identical manner. 
     As can be seen in particular from  FIG. 6 , the guide groove  18  of the base body  11  continues in the add-on component  14 .  FIG. 6  shows that not only the guide groove  18  but furthermore also the groove base  19  of the guide groove  18  is formed in the add-on component  14 . 
     In the exemplary embodiment shown, the guide bar  3  is a built-up guide bar  3 ; its base body  11  comprises a center plate  30  which is covered by side plates  31 . The outer sides of the side plates  31  furthermore form flat sides  32   a  and  32   b  of the base body  11  of the guide bar  3 . One side plate  31  forms the first flat side  32   a  and the other side plate  31  forms the second flat side  32   b . Alternatively, the guide bar  3  can also be formed from a solid material. 
     Each side plate  31  has a finger-like extension in the form of a projection  33 , wherein the projection  33 , which is formed in a substantially flat manner, extends in the direction of the longitudinal center axis  15  and forms the end  12  of the base body  11 . In the direction of the longitudinal center axis  15 , the projection  33  engages in the add-on component  14  in order to fix the latter in its position on the base body  11 . In this case, provision is made for the projection  33  to be held in an approximately play-free manner in the add-on component  14 , while the abutment edges  35  located in the root region of the projection  33  have slight play (u) with respect to the edge  22  of the add-on component  14 . This avoids static redundancy of the support of the add-on component  14  on the projection  33 . 
     In the exemplary embodiment according to  FIGS. 2 to 8 , the projection  33  of the base body  11  of the guide bar  3  engages over the add-on component  14 ; in other words, the projections  33  overlap the add-on component  14 . In this case, provision is made for the weld seam  20  to be positioned such that it delimits the overlap region  34 . 
     The add-on component  14  is fixed in its position at the front end of the base body  11  preferably in a form-fitting manner, for which purpose it interacts in a suitable manner with the projections  33 . Thus, a projection that extends in the direction of the longitudinal center axis  15  can be formed on the base body  11  of the guide bar  3  on each flat side ( 32   a ,  32   b ) in the region of the direction-reversing section  13 , the projection  33  being received in a recessed region  23  of the add-on component  14 . The recessed region  23  is formed in the outer side  21  of an add-on component  14   a  or  14   b  and receives the projection  33  substantially along its entire length that extends in the direction of the longitudinal center axis  15 . Preferably, a projection  33  is received in the recessed region  23  largely without play to lie in contact engagement with support surface  23   a  as shown in  FIG. 8 . The recessed region  23  is advantageously deeper than the material thickness of the projection  33 . The depth of the recessed region  23  is selected such that the outer side  21  of the add-on component  14  is located approximately in the same plane as the flat side  32   a  or  32   b  of the guide bar  3 . 
     In the exemplary embodiment, the add-on component is composed of two add-on component halves  14   a  and  14   b  which rest against one another in a partition plane  38 ; the projections  33  are in this case each located in a recessed region  23  of one add-on component half  14   a  and  14   b , such that the add-on component halves  14   a  and  14   b  of the add-on component  14  are held between the projections  33 . Preferably, the add-on component halves  14   a  and  14   b  of the add-on component  14  are dimensioned such that the material that remains in the region of the recessed regions  23  has a thickness (d) which corresponds approximately to the distance (a) between the projections  33  of the two side plates  31 . Preferably, the thickness (d) is formed with a slight excess thickness such that the add-on component  14  composed of the add-on component halves  14   a  and  14   b  is held in a clamped manner between the projections  33 . This can be advantageous in the preassembly of the guide bar. 
     Once the add-on component halves ( 14   a ,  14   b ) of the add-on component  14  have been plugged onto the end  12  of the base body  11  of the guide rail  3 , the add-on component  14  is fixed preferably by means of welding. Laser welding is particularly suitable for this purpose, wherein the weld seam  20  is configured such that it extends along the contour of the projection  33 . The weld seam extends advantageously along a segment  24  of its length S along the longitudinal edges  36  and  37  of the projection  33 . As illustrated in  FIG. 5 , the weld seam  20  extends along the two longitudinal edges  36  and  37  of the projection  33 , wherein the segments  24  of the weld seam  20  are connected together at the longitudinal edges via an arc segment  25  of the weld seam  20 . The arc segment  25  of the weld seam  20  corresponds to the shape of the free end of the projection  33 . As  FIG. 5  shows, the weld seam  20  extends over the entire edge of the projection  33 . The edge of the projection  33  is formed by the longitudinal edges  36  and  37  and the arc segment  39 , connecting the longitudinal edges  36  and  37 , of the free end of the projection  33 . 
     As  FIG. 5  shows, the weld seam  20  continues over a run-out segment  26  in the base body  11  of the guide bar  3 . The length of the run-out segment  26  corresponds approximately to the length L, measured in the direction of the longitudinal center axis  15 , of the projection  33 . 
     As can be seen from  FIGS. 6 and 8 , the projections engage on both flat sides ( 32   a ,  32   b ) of the base body  11  of the guide bar  3  into in each case one add-on component half ( 14   a ,  14   b ) of the add-on component  14  and fix the latter in position on the base body  11 . The weld seam  20  is executed on each of the flat sides  32   a  and  32   b  of the guide bar  3 , as the sectional illustration in  FIG. 8  shows. In this case, a weld seam  20  passes to such a depth that the weld seam  20  on the one, first flat side  32   a  and the weld seam  20  on the other, second flat side  32   b  merge into one another or come into contact with one another in the region of the partition plane  38  of the add-on component  14 . As a result, not only is each add-on component half ( 14   a ,  14   b ) of the add-on component  14  firmly connected to the respective side plate  31  of the base body  11 , but the add-on component halves ( 14   a ,  14   b ) are also connected together cohesively in the region of their partition plane  38 . 
     In the exemplary embodiment according to  FIGS. 9 and 10 , the add-on component  14 ′ consists of two add-on component halves  14 ′ a  and  14 ′ b  which are each connected individually to a side plate  31 . An add-on component half  14 ′ a  or  14 ′ b  rests with its inner edge  41  against the longitudinal edges  36  and  37  and against the arc segment  39 , connecting the longitudinal edges together, of the free end of the projection  33 , preferably without play. The abutment edge  35  of the add-on component has in this case—as also illustrated in  FIG. 5 —slight play (u) with respect to the edge  22  of the base body  11  of the guide bar  3 , the edge extending on both sides of the projection  33  in the root region of the projection. As a result of the play (u), static redundancy of the add-on component  14 ′ on the base body  11  of the guide bar  3  is avoided. 
       FIG. 11  shows a perspective view of the guide bar before the add-on component ( 14   a ,  14   b ) is welded to the base body  11 .  FIG. 12  shows a side elevation view corresponding to the perspective view of  FIG. 11  and  FIG. 13  is a section view taken along line XIII-XIII of  FIG. 12 . 
     As  FIG. 10  shows, in the exemplary embodiment according to  FIGS. 9 and 10 , the center plate  30  projects in between the add-on component halves  14 ′ a  and  14 ′ b  of the add-on component  14 ′. The edge  41  of an add-on component half  14 ′ a  and  14 ′ b  is thus located lower than the groove base  19  perpendicularly to the groove base  19  of the guide groove  18  in the viewing direction  40 . 
     The weld seam  20  is guided along the longitudinal edges  36  and  37  and along the arc segment  39 , connecting the longitudinal edges, of the projection  33 , wherein the run-out segments  26  of the weld seam  20  extend, in continuation of the longitudinal edges  36  and  37 , into the base body  11  of the guide bar. 
     Since the center plate  30  projects in between the add-on component halves  14 ′ a  and  14 ′ b , the groove base  19  is located higher—in the viewing direction  40  onto the groove—than the edge  41  of the add-on component; the weld seam  20  is thus located beneath the groove base  19 . 
     The weld seam  20  extends in the region between the edge  41  of the add-on component  14 ′ and the side plates  31  of the base body  11  of the guide bar  3  and is thus located, along a majority of its length—in the exemplary embodiment along its entire length—beneath the groove base  19  in the add-on component  14 ′; in other words, the weld seam  20  is located, as seen in the—preferably perpendicular—viewing direction  40  onto the groove base  19 , beneath the groove base  19 . The weld seams  20  executed on both flat sides  32   a  and  32   b  of the guide bar  3  in order to secure the add-on component halves  14 ′ a  and  14 ′ b  of the add-on component  14 ′ are expediently produced by laser welding; the depth of the weld seam  20  can preferably be set such that the weld seams  20  applied to the opposite flat sides  32   a  and  32   b  of the guide bar  3  come into contact and/or are connected cohesively together at the depth. 
     The add-on component  14  or  14 ′, or the add-on component halves ( 14   a ,  14   b ,  14 ′ a ,  14 ′ b ) of an add-on component ( 14 ,  14 ′), preferably consist of a sintered material, expediently of Stellite. A material known under the designation Stellite  12 , which is based on a cobalt-base alloy with 29 percent by weight of chromium, 8 percent by weight of tungsten and 1.3 percent by weight of carbon, can be used as Stellite. 
     The add-on component or its add-on component halves can also consist of different materials, it being essential that at least the running surface for the saw chain is formed from a wear-resistant material such as Stellite or the like. 
     In the exemplary embodiments shown, the weld seam  20  is shown as a continuous weld seam; it may be expedient, rather than a continuous weld seam, to provide welding spots which are located in a row one after the other and form a dotted weld seam. 
     In the exemplary embodiments shown, the projection  33  extending as an extension in the direction of the longitudinal center axis  15  is formed such that—starting in the root region of the projection—it forms two longitudinal edges  36  and  37  which are substantially straight and run toward one another ( FIG. 5 ). A longitudinal edge ( 36 ,  37 ) of a projection  33  forms, in continuation, an angle α of about 5° to 15°, in particular 10°, with the longitudinal center axis  15 . The continuations of the two longitudinal edges  36  and  37  thus enclose an angle of about 10° to 30°, in particular an angle of 20°. The two longitudinal edges  36  and  37  are connected together via an arc segment  39  of the free end of the projection  33 . The arc segment  39  is a circular arc segment with a circumferential angle of less than 180°, in particular 160°. 
     It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.