Abstract:
A concrete dispensing boom for stationary and mobile concrete pumps has a plurality of boom arms, connected to one another at joints, and a concrete conveying line consisting of a plurality of pipe segments preferably connected to one another in an articulated manner via pipe bends and rotary couplings. Said pipe segments run along the individual boom arms and are attached to these boom arms. At least one of the boom arms has a hollow chamber profile which has at least two hollow chambers separated from one another by a separating wall, at least one of which chambers is a closed chamber and one is open at the periphery. The pipe segment allocated to the boom arm concerned is disposed on the opening side outside, partially inside or inside the open hollow chamber.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT/EP2013/065468, filed Jul. 23, 2013, which claims priority to DE 10 2012 213 729.7, filed Aug. 2, 2012, both of which are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a concrete dispensing boom for static and mobile concrete pumps, having multiple boom arms which are connected to one another at joints, and having a concrete delivery conduit which is composed of multiple pipe segments which are articulatedly connected to one another preferably by way of pipe bends and rotary couplings and which are guided along and fastened to the individual boom arms. 
         [0003]    Known concrete dispensing booms have boom arms which are designed with a closed box profile or tubular profile (DE 196 44 410 A1). With a box profile or tubular profile of said type, it is possible to ensure good stability and torsional rigidity of the boom arms with a relatively low weight. A box profile or tubular profile has the disadvantage, however, that a concrete delivery conduit arranged in the interior of a profile of said type can be made accessible, for maintenance of the concrete delivery conduit, only with considerable outlay in terms of construction. However, if the concrete delivery conduit is led outside the boom arms, cumbersome pipe brackets are required in order to hold the concrete delivery conduit on the boom arms. Said pipe brackets entail additional weight which must be taken into consideration in the design of concrete dispensing booms. 
       SUMMARY 
       [0004]    The present invention provides a concrete dispensing boom which exhibits good stability and torsional rigidity while having a simultaneously low inherent weight. 
         [0005]    This is achieved by means of a concrete dispensing boom in which at least one of the boom arms has a hollow chamber profile with at least two elongate hollow chambers which are separated from one another by a partition and of which at least one is closed and one is circumferentially open, and wherein the pipe segment associated with the respective boom arm is arranged on the opening side outside, partially within or entirely within the open hollow chamber. 
         [0006]    This disclosure is based on the concept that a boom arm which has a box profile, that is to say which has a rectangular cross section, can be produced, by joining together flange plates and side wall or web plates, with very high stability and in inexpensive fashion by virtue of the respective plates being welded together. A further concept of this disclosure is that a closed profile offers the advantage that the boom arm can be painted with only little outlay, and rust problems owing to ingress of water are avoided. A boom arm in box form can in particular also, with little outlay in terms of manufacture, be of cranked design, that is to say configured so as to be singly or multiply angled toward its sides. In the case of a concrete dispensing boom, said cranked configuration is necessary in the case of certain boom arms in order that these can move past one another during operation. 
         [0007]    The concrete delivery conduit held on a boom arm, and the angled structural form of boom arms, have the result that the boom arms in a concrete dispensing boom are subject to considerable torsional moments. In the case of conventional concrete dispensing booms, such torsional moments are high inter alia because the cantilever construction of the pipe brackets increases said moments. 
         [0008]    It is therefore a concept of this disclosure to adapt the cross section of the boom arms in a concrete dispensing boom to the local load on a boom arm. According to this disclosure, it is therefore proposed that, in the case of a boom arm of box-shaped form for a concrete dispensing boom, at least one of the side walls be set back. In this way, a circumferentially open cavity is created as additional structural space for the concrete delivery conduit, such that the concrete delivery conduit can be guided more closely along the boom arm. With these measures, it is possible in particular to reduce the lever forces with which the load of the concrete delivery conduit acts on a boom arm via the pipe brackets. 
         [0009]    In the context of this disclosure, it is proposed in particular that the boom arm which has the hollow chamber profile be configured as a box with an upper flange and a lower flange, which box has a first side wall which is set back in relation to the upper flange and the lower flange and which has a second side wall which is spaced apart from the first side wall, wherein the upper flange and the lower flange together with the first side wall and the second side wall define the at least one closed hollow chamber, and the first side wall together with the upper flange and the lower flange form the circumferentially open hollow chamber. Said circumferentially open hollow chamber may for example have a trapezoidal, in particular rectangular or triangular cross section. 
         [0010]    The second side wall, too, may be arranged so as to be set back in relation to the upper flange and the lower flange, and thus define a further circumferential hollow chamber. The cross section of said further circumferentially open hollow chamber may also be trapezoidal, in particular rectangular or triangular. The upper flange and the lower flange are preferably parallel to one another. The first side wall and/or the second side wall are/is in this case perpendicular to the upper flange and/or the lower flange. To optimize the torsional load profile in a boom arm, it is advantageous if the spacing of the first side wall from the second side wall varies across the boom arm. 
         [0011]    The upper flange and/or the lower flange in a boom arm according to this disclosure may also protrude to different extents beyond the side wall of a boom arm in different regions, that is to say the upper flange and/or the lower flange may have a flange edge, the spacing of which from the first side wall and/or from the second side wall assumes different values in the longitudinal direction of the boom arm. 
         [0012]    The first side wall and/or the second side wall may have an attachment section which can be pre-mounted on the upper flange and/or on the lower flange. With the attachment section that can be pre-mounted, it can be achieved that the side wall can be equipped with an attachment structure which can be screwed to the further boom arm sections. 
         [0013]    A reduction of the torsion loading of a boom arm provided with a cranked configuration can be attained in particular if the concrete delivery conduit is led from one side of the boom arm to the opposite side of the boom arm through the first side wall and through the second side wall in the cranked section. 
         [0014]    In this case, the concrete delivery conduit is fixed to the first side wall or to the second side wall by means of one or more pipe brackets, and may be arranged partially within or entirely within the open hollow chamber. 
         [0015]    A boom arm with a hollow chamber profile may be composed at least partially of fiber-reinforced plastic (fiber composite plastic) or of metal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
           [0017]      FIG. 1  shows a side view of an automotive concrete pump with a concrete dispensing boom; 
           [0018]      FIG. 2  shows a cross section through a boom arm in the concrete dispensing boom with a concrete delivery conduit; 
           [0019]      FIG. 3  shows a section of a further boom arm for a concrete dispensing boom, which has a cranked section and bears a concrete delivery conduit; 
           [0020]      FIG. 4  shows a torsion load generated in the further boom arm by the concrete delivery conduit; 
           [0021]      FIG. 5  to  FIG. 8  show, in cross section, further boom arms of alternative construction for a concrete dispensing boom; and 
           [0022]      FIG. 9  and  FIG. 10  show plan views of further boom arms for a concrete dispensing boom. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure. 
         [0024]    In this disclosure, terms such as “vertical,” “perpendicular,” “parallel,” “horizontal,” “longitudinal,” “central,” “rectangular” and the like are used to describe the orientation, position or general shape of structural elements disclosed herein. As would be readily recognized by one of ordinary skill, it shall be understood for purposes of this disclosure and claims that these terms are not used to connote exact mathematical orientations or geometries, unless explicitly stated, but are instead used as terms of approximation. With this understanding, the term “vertical,” for example, certainly includes a structure that is positioned exactly 90 degrees from horizontal, but should generally be understood as meaning positioned up and down rather than side to side. Other terms used herein to connote orientation, position or shape should be similarly interpreted. Further, it should be understood that various structural terms used throughout this disclosure and claims should not receive a singular interpretation unless it is made explicit herein. By way of non-limiting example, the terms “chamber,” “conduit,” “boom arm,” to name just a few, should be interpreted when appearing in this disclosure and claims to mean one or more. All other terms used herein should be similarly interpreted unless it is made explicit that a singular interpretation is intended. 
         [0025]    The automotive concrete pump  10  in  FIG. 1  has a chassis  12  with a substructure  14  which bears a concrete dispensing boom  18 . The concrete dispensing boom  18  is mounted on the substructure  14  at a boom pedestal  16  and has rotary joints  34 ,  34 ′,  34 ″ and  34 ′″ in which the boom arms  22 ,  22 ′,  22 ″ and  22 ′″ can be moved about a horizontal axis of rotation. The concrete dispensing boom  18  is formed with a concrete delivery conduit  20  which has pipe bends  50  and pipe segments  30  which are articulatedly connected to one another by way of pipe couplings  32  and rotary couplings  52 . 
         [0026]      FIG. 2  shows the boom arm  22  in cross section along the line II-II in  FIG. 1 . The boom arm  22  has a hollow chamber profile which has a closed, elongate hollow chamber  24  and a circumferentially open hollow chamber  26  which extends in the longitudinal direction. In other words, chamber  26  has an opening extending along its length or is open on one side, as is depicted in  FIG. 2 . The hollow chamber profile of the boom arm  22  is in the form of a box which has an upper flange  28  and a lower flange  36 . The box has a first side wall  38  and a second side wall  40 . The first side wall  38  is a partition in the hollow chamber profile. The upper flange  28  and the lower flange  36  are parallel to one another, wherein the first side wall and/or the second side wall are/is perpendicular to the upper flange and/or to the lower flange. The first side wall  38  is positioned so as to be set back in relation to the upper flange  28  and the lower flange  36 . 
         [0027]    That pipe segment  30  in the concrete dispensing boom  18  which is associated with the boom arm  22  is arranged outside the hollow chamber  26  on the opening side thereof. That is, pipe segment  30  is arranged outside of the opening extending along the length of chamber  26 . It is pointed out that it is however basically also possible for the pipe segments  30  of the concrete delivery conduit  20  to be arranged partially within or even entirely within the open hollow chamber  26 . 
         [0028]    The pipe segment  30  is held on the boom arm  22  by means of a pipe bracket  42  which projects into the hollow chamber  26  and is fixed to the first side wall  38 . By means of this measure, it can be achieved that the torsional moment introduced into the boom arm  22  via a pipe bracket  42  by the load of the concrete delivery conduit  20 , which acts in accordance with the arrow  46 , is minimized. The boom arms  22 ′,  22 ″ and  22 ′″ in the concrete dispensing boom  18  shown in  FIG. 1  also have a construction corresponding to the construction of the boom arm  22 . 
         [0029]      FIG. 3  shows a section of a further boom arm  62  for a concrete dispensing boom with a concrete delivery conduit  80 . The boom arm  62  has a hollow chamber profile which has a closed elongate hollow chamber  64  and which comprises two circumferentially open hollow chambers  66 ,  68  which extend in the longitudinal direction. The hollow chamber profile of the boom arm  62  is also in the form of a box which has an upper flange  70  and a lower flange  72 . The box has a first side wall  74  and a second side wall  76 . The two side walls  74 ,  76  are partitions in the hollow chamber profile. The upper flange  28  and the lower flange  36  are parallel to one another, wherein the first side wall  74  and/or the second side wall  76  are perpendicular to the upper flange  70  and to the lower flange  72 . It is however also possible in the case of a boom arm according to this disclosure to provide an upper flange and a lower flange which taper toward one another in conical fashion. 
         [0030]    By contrast to the boom arm  22  shown in  FIGS. 1 and 2 , the boom arm  62  has a cranked section  78 . The concrete delivery conduit  80  is fixed to the boom arm  62  by means of the pipe brackets  82 ,  84  on the first side wall  74  and by means of the pipe brackets  86 ,  88  on the second side wall  76 . In the cranked section  78 , the concrete delivery conduit is led from one side of the boom arm  62  to the opposite side of the boom arm  62  through the first side wall  74 , the closed hollow chamber  64  and through the second side wall  76 . 
         [0031]    In the section  92 , the spacing A of the first side wall  74  from the second side wall  76  is constant. In the section  78 , the spacing between the first side wall  74  and the second side wall  76  decreases. In the section  94 , the spacing B of the first side wall  74  from the second side wall  76  is defined by B&lt;A. With this measure, the torsional resistance of the boom arm cross section is adapted across the boom arm  62  to the load thereof. 
         [0032]      FIG. 4  shows, in relation to the line  90  of the common center of area of the upper and lower flanges  70 ,  72  in the boom arm section  92 , the torsional load T introduced into the boom arm  62  by the load of the concrete delivery conduit  80 . By virtue of the fact that the concrete delivery conduit  80  is led through the side walls  74 ,  76  of the boom arm  62 , it can be achieved that the torsional moment T introduced into the boom arm  62  after the cranked section  78  at least partially compensates the torsional moment introduced into the boom arm  62  before the cranked section  78 . 
         [0033]    In the case of the boom arm  62 , the side walls  74 ,  76  are designed for attachment to the upper flange  70  and the lower flange  72  by way of an attachment structure. Said attachment structure is designed such that, in the set-back position of the side walls  74 ,  76 , a high-quality connection to the upper flange and lower flange  70 ,  72  is made possible. The sections of the side walls  74 ,  76  are then fixed to said attachment structure by screw connection or by welding. 
         [0034]      FIG. 5  shows a further boom arm  122 , constructed alternatively to the boom arm  22 , for a concrete dispensing boom in a cross section corresponding to the view of  FIG. 2 . 
         [0035]    The boom arm  122  also has a hollow chamber profile which has a closed elongate hollow chamber  124  and a circumferentially open hollow chamber  126  which extends in the longitudinal direction. The hollow chamber profile of the boom arm  122  is likewise in the form of a box which has an upper flange  128  and a lower flange  136 . The box has a first side wall  138  and a second side wall  140 . 
         [0036]    The upper flange  128  and the lower flange  136  are parallel to one another, wherein the first side wall and/or the second side wall  138 ,  140  are perpendicular to the upper flange and/or to the lower flange. In this case, the first side wall  138  is positioned so as to be set back in relation to the lower flange  136 , and has the spacing D UI  from the flange edge  137  on the side of the first side wall  138 . By contrast, the flange edge  129  of the upper flange  128  on the side of the first side wall  138  has the spacing D O1 &lt;D U1 . 
         [0037]    The first side wall  138  is a partition in the hollow chamber profile. The second side wall  140  is also a partition in the hollow chamber profile. The second side wall  140  is positioned so as to be set back in relation to the upper flange  128  and has the spacing D O2  from the flange edge  131  on the side of the first side wall  138 . By contrast, the flange edge  139  of the lower flange  136  on the side of the second side wall  140  has the spacing D U2 &lt;D O2 . 
         [0038]    The upper flange  128  and the lower flange  136  together with the first side wall  138  form a circumferentially open hollow chamber  128  which has a cross section  127  in the form of a convex trapezoid. Together with the second side wall  140 , the upper flange  128  and the lower flange  136  define a further hollow chamber  148  with a cross section  154  in the form of a convex trapezoid, said further hollow chamber likewise being circumferentially open. 
         [0039]    The pipe segment  130 , associated with the boom arm  122 , of the concrete delivery conduit in the concrete dispensing boom  118  is arranged outside the hollow chamber  126  on the opening side thereof, and is fixed to the first side wall  138  by means of one or more pipe brackets  142 . It is pointed out that it is however basically also possible for the pipe segments  130  of the concrete delivery conduit to be arranged partially within or even entirely within the open hollow chamber  126 . It is furthermore possible for the pipe segments of the concrete delivery conduit to also be arranged on the side of the circumferentially open hollow chamber  148  of the boom arm  122 , specifically either within or only partially within or else outside the circumferentially open hollow chamber  148 . 
         [0040]    It is furthermore pointed out that, in a further alternative embodiment of the boom arm, the first side wall  138  may be flush with the upper flange  128 , or the second side wall  140  may be flush with the lower flange  136 . In this case, the cross section  127  of the circumferentially open hollow chamber  126  has the form of a right-angled triangle. A corresponding situation applies to the circumferentially open hollow chamber  148 . 
         [0041]      FIGS. 6 to 8  show further boom arms  122 ′,  122 ″,  122 ′″ of alternative construction to the boom arm  22  for a concrete dispensing boom in a cross section corresponding to the view in  FIG. 2 . In this case, elements which functionally correspond to one another are denoted in  FIGS. 5 to 9  using reference signs with the same numerals. 
         [0042]    In the case of the boom arm  122 ′ shown in  FIG. 6 , the upper flange  128 ′ and the lower flange  136 ′ are positioned symmetrically in relation to the axis of symmetry  155 ′ of the hollow chamber  124 . That is to say, for the spacing D U1  of the flange edge  137 ′ of the lower flange  136 ′ and the spacing D O1  of the flange edge  129 ′ of the upper flange  128 ′ from the first side wall  138 ′, and for the spacing D U2  of the flange edge  137 ′ of the lower flange  136 ′ and the spacing D O2  of the flange edge  129 ′ of the upper flange  128 ′ from the first side wall  138 ′, the following applies: D O1 =D O2 &gt;D U1 =D U2 . 
         [0043]    In the case of the boom arm  122 ″ shown in  FIG. 7 , the flange edge  137 ″ of the lower flange  136 ″ and the flange edge  129 ″ of the upper flange  128 ″ have the spacing D U1 &gt;D O1  from the first side wall  138 ′. The flange edge  131 ″ of the upper flange and the flange edge  139 ″ of the lower flange  136 ″ have in this case the spacing D U2 &gt;D O2  from the second side wall  140 ″. In this case: D O1 =D O2 &lt;D U1 =D U2 . 
         [0044]    The boom arm  122 ′″ shown in  FIG. 8  has a circumferentially open hollow chamber  126 ′″ with a pipe segment  130 ′″ of a concrete delivery conduit arranged therein. In the case of the boom arm  122 ′″, the flange edge  137 ′″ of the lower flange  136 ′″ and the flange edge  129 ′″ of the upper flange have the spacing D U1 =D O1  from the first side wall  138 ′″. The flange edge  137 ′″ of the lower flange  136 ′″ and the flange edge  129 ′″ of the upper flange have in this case the spacing D U2 &lt;D O2  from the second side wall  140 ′″. 
         [0045]      FIG. 9  shows a further boom arm  222  which is of alternative construction in relation to the boom arm  22  in  FIG. 2  and which has a hollow chamber profile of box form with a circumferentially open hollow chamber and with a first and a second side wall  238 ,  240 . In the case of the boom arm  222 , the flange edge  237  of the upper flange has, over the longitudinal direction, the varying spacing D O1  from the first side wall  238  corresponding to the values D O1   (1) , D O1   (2) , D O1   (3) . The spacing of the flange edge  231  of the upper flange from the second side wall  240  is in this case constant over the longitudinal direction. 
         [0046]    In an alternative embodiment according to this disclosure of the boom arm  222 , it is possible for also the spacing D U1  of the flange edge of the lower flange on the side of the first side wall  238 , or only the spacing D U1  of the flange edge of the lower flange, to assume different values along the longitudinal direction of the boom arm  222 . 
         [0047]    In the case of the boom arm  322  shown in  FIG. 10 , the upper flange and the lower flange together with a first and a second side wall  338 ,  340  likewise form a hollow chamber profile of box form, wherein in this case, the spacing D U2  or D O2  from the flange edge  331  of the upper flange to the second side wall  340  assumes different values D O1   (1) , D O1   (2) , D O1   (3)  . . . over the longitudinal direction of the boom arm  322 . It is pointed out that, in this case too, in an alternative embodiment according to this disclosure of the boom arm  322 , the spacing D U1  or D O1  of the flange edge  337  of the lower flange or upper flange, respectively, on the side of the first side wall  338 , the spacing D U1  of the flange edge  331  of the lower flange on the side of the second side wall  340 , or only the spacing D U1  of the flange edge of the lower flange, may assume different values along the longitudinal direction of the boom arm  322 . 
         [0048]    With the embodiments for a boom arm in a concrete dispensing boom described above on the basis of  FIG. 5  to  FIG. 10 , it can likewise be achieved that the torsional moment introduced into the boom arm by the load of the concrete delivery conduit via a pipe bracket is low. 
         [0049]    It is pointed out that the hollow chamber profiles of the boom arms described above may be composed not only of metal but at least partially also of fiber composite plastic. 
         [0050]    It is also pointed out that this disclosure also encompasses further modifications and refinements of concrete dispensing booms which arise from combination of different features of the exemplary embodiments described above. 
         [0051]    In summary, the following can be stated: a concrete dispensing boom  18  for static and mobile concrete pumps has multiple boom arms  22  which are connected to one another at joints  34 , and has a concrete delivery conduit  20  which is composed of multiple pipe segments  30  which are articulatedly connected to one another preferably by way of pipe bends  50  and rotary couplings  52  and which are guided along and fastened to the individual boom arms  22 . At least one of the boom arms  22  has a hollow chamber profile with at least two hollow chambers  24 ,  26  which are separated from one another by a partition  40  and of which at least one is closed  24  and one  26  is circumferentially open. In this case, the pipe segment  30  associated with the respective boom arm  22  is arranged on the opening side outside, partially within or within the open hollow chamber  26 . 
         [0052]    While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 
       LIST OF REFERENCE SIGNS 
       [0053]      10  Automotive concrete pump 
         [0054]      12  Chassis 
         [0055]      14  Substructure 
         [0056]      16  Boom pedestal 
         [0057]      18  Concrete dispensing boom 
         [0058]      20  Concrete delivery conduit 
         [0059]      22 ,  22 ′,  22 ″,  22 ′″ Boom arms 
         [0060]      24  Closed hollow chamber 
         [0061]      26  Circumferentially open hollow chamber 
         [0062]      28  Upper flange 
         [0063]      30  Pipe segment 
         [0064]      32  Pipe coupling 
         [0065]      34 ,  34 ′,  34 ″,  34 ′″ Rotary joint 
         [0066]      36  Lower flange 
         [0067]      38  First side wall 
         [0068]      40  Second side wall 
         [0069]      42  Pipe bracket 
         [0070]      44  Line 
         [0071]      46  Arrow 
         [0072]      50  Pipe bend 
         [0073]      52  Rotary coupling 
         [0074]      62  Boom arm 
         [0075]      64  Hollow chamber 
         [0076]      66  Hollow chamber 
         [0077]      68  Hollow chamber 
         [0078]      70  Upper flange 
         [0079]      72  Lower flange 
         [0080]      74  First side wall 
         [0081]      76  Second side wall 
         [0082]      78  Cranked section 
         [0083]      80  Concrete delivery conduit 
         [0084]      82  Pipe bracket 
         [0085]      84  Pipe bracket 
         [0086]      86  Pipe bracket 
         [0087]      88  Pipe bracket 
         [0088]      90  Line 
         [0089]      92  Section 
         [0090]      94  Section 
         [0091]      118  Concrete dispensing boom 
         [0092]      122 ,  122 ′,  122 ″,  122 ′″ Boom arm 
         [0093]      124 ,  124 ′,  124 ″,  124 ′″ Closed, elongate hollow chamber 
         [0094]      126 ,  126 ′,  126 ″,  126 ′″ Open hollow chamber 
         [0095]      127 ,  127 ′,  127 ″,  127 ′″ Cross section 
         [0096]      128 ,  128 ′,  128 ″,  128 ′″ Upper flange 
         [0097]      129 ,  129 ′,  129 ″,  129 ′″ Flange edge of the upper flange 
         [0098]      130 ,  130 ′,  130 ″,  130 ′″ Pipe segment 
         [0099]      131 ,  131 ′,  131 ″,  131 ′″ Flange edge 
         [0100]      136 ,  136 ′,  136 ″,  136 ′″ Lower flange 
         [0101]      137 ,  137 ′,  137 ″,  137 ′″ Flange edge 
         [0102]      138 ,  138 ′,  138 ″,  138 ′″ First side wall 
         [0103]      139 ,  139 ′,  139 ″,  139 ′″ Flange edge 
         [0104]      140 ,  140 ′,  140 ″,  140 ′″ Second side wall 
         [0105]      142 ,  142 ′,  142 ″,  142 ′″ Pipe bracket 
         [0106]      148 ,  148 ′,  148 ″,  148 ′″ Circumferentially open hollow chamber 
         [0107]      154 ,  154 ′,  154 ″,  154 ′″ Cross section 
         [0108]      155 ′,  155 ″ Axis of symmetry 
         [0109]      222 ,  322  Boom arm 
         [0110]      231 ,  331  Flange edge 
         [0111]      237 ,  337  Flange edge 
         [0112]      238 ,  338  First side wall 
         [0113]      240 ,  340  Second side wall 
         [0114]    D U1  Spacing 
         [0115]    D U2  Spacing 
         [0116]    D O1  Spacing 
         [0117]    D O2  Spacing