Abstract:
A hollow profile bar, preferably of extruded metal, comprises a tubular wall that is equally thick all around and is provided with salient outer webs evenly distributed about the outer circumference, which in pairs form undercut casing grooves with side walls, a radial salience of the outer webs from the tubular wall being substantially equal to the thickness of the tubular wall. To achieve tight packing of profile bars that are to be connected in one sectional plane of a hollow profile bar, the hollow profile bar is configured in such a way that slope lines of the side walls of an outer web intersect between the outer web and the axis of the bar.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a hollow profile bar, especially of extruded metal, comprising a tubular wall that is equally thick all around and is provided with salient outer webs, evenly distributed about the outer circumference, which in pairs form undercut casing grooves with side walls, a radial salience of the outer webs from the tubular wall being practically equal to the thickness of said tubular wall. 
     2. Description of the Prior Art 
     A hollow profile bar having the aforesaid features is known from DE U 296 15 208. The outer webs are broader at their outer circumference than at their circumference defined by the bottom of the casing grooves, thus forming a corresponding undercut. The degree of undercutting is determined, i.e., rendered minimal, by the fact that the slope lines intersect approximately within the axis of the tube. To make it possible to connect other hollow profile bars, links are used that can subsequently be “docked” at any point on the undercut outer webs. Because of the minimal undercutting of the outer webs, such links extend over a substantial circumference of the hollow profile bar and comprise in particular four coupling saliences, each of which engages in a respective casing groove. One result of this arrangement is uneven loading of the coupling saliences and thus the link; moreover, no more than four links can be used, thereby limiting the number of structures that can be connected to a hollow profile bar in one plane. 
     It is further known, for example from GB A 1 557 693, to realize sharply undercut outer webs on hollow profile bars having a tubular wall that is equally thick all around. The outer webs are T-shaped or have an anchor-shaped cross section. They form a polygonal outer circumference of the hollow profile bar. Its casing grooves are of large volume, resulting in substantial instabilities when elements are anchored to the outer webs to effect the force- or form-fitting connection of an additional hollow profile bar by means of a link. 
     Known from U.S. Pat. No. 3,969,031 are hollow profile bars comprising sharply undercut casing grooves of small volume. The outer webs forming the casing grooves in this case are only slightly salient, but are very wide in comparison to the casing grooves. A tubular wall that is equally thick all around is present in this case as well. However, the known tubular wall forms the bottoms of the grooves, portions of their side walls and regions of the outer web. The inner circumference of the hollow profile bar is therefore corrugated, and this corrugation causes the known tubular wall to exhibit instabilities when subjected to relatively high loads by hollow profile bars that are to be clamped thereon. 
     SUMMARY OF THE INVENTION 
     The object of the invention is, therefore, to improve a hollow profile bar having the features recited in the introduction hereto in such fashion that, despite possessing a tubular wall that is equally thick all around and thus is advantageously thin, it permits the stable clamped attachment of one hollow profile bar or additional hollow profile bars, particularly when plural hollow profile bars are to be coupled thereto within the same coupling plane. 
     This object is achieved by the fact that slope lines of the side walls of an outer web intersect between said outer web and the axis of the bar. 
     It is of significance for the invention that the slope lines of the side walls of an outer web, specifically of the same outer web, intersect between said outer web and the axis of the bar. The side walls thus are much more sharply inclined, and the undercuts correspondingly greater, than when the slope lines pass through the axis of the bar or embrace it without a prior point of intersection. In no case are the slope lines perpendicular to the outer circumference of the tubular wall, but instead form an acute angle therewith. The acute angularity makes it possible for a link of a to-be-coupled hollow profile bar to engage one of the two side walls of an outer web in a radially form-fitting manner. It is of importance in this regard that the coupling sites furnished by the outer webs are close to the tubular wall, thus eliminating the possibility of any especially high lever arms on the outer webs that might lead to deformation of the outer webs and/or the tubular wall. Due to the considerable slope of the side walls of the outer webs, links coupling profile bars are able to engage only a few outer webs, or in the extreme case, only one. The links therefore take up only a small portion of the outer circumference of the tubular wall. 
     The hollow profile bar can be improved in such a way that the slope lines of the side walls of an outer web have a point of intersection within the tubular wall. Such an embodiment is especially advantageous when the width of the outer webs at the outer circumference of the tubular wall is approximately equal to the thickness of said wall. The resulting structure in the area of interconnection between the outer web and the tubular wall is economical of material but still sufficiently strong. 
     To reduce notch stresses caused by loading of the outer web in the aforesaid area of interconnection between the outer web and the tubular wall and to avoid compromising the handling of the hollow profile bar by undesirable sharp edges during coupling and during the use of the finished structure, the hollow profile bar is configured so that the side walls of an outer web transition at predetermined radii to the outer circumference of the tubular wall and/or to a visible surface of the outer web that is practically parallel to the outer wall or is arched convexly with respect thereto. 
     It can further be advantageous if the smallest spacing between two outer webs is practically equal to or is greater than the outer circumferential length of one of said outer webs. This results in large widths for the grooves, especially in the area of the opening thereof. It is therefore possible to use links that are of comparatively broad construction in the circumferential direction of the tube. The links can be implemented with correspondingly sturdy cross sections. 
     If the hollow profile bar needs to be especially sturdy in the region where it is to be engaged by links for other hollow profile bars; it can be advantageous to configure the hollow profile bar in such a way that the outer circumferential length of an outer web is practically three times the smallest spacing between two outer webs. The tubular wall then has an especially massive and correspondingly sturdy cross section between two casing grooves. Such a cross-sectional configuration of the hollow profile bar can be integrated equally successfully into an otherwise differently realized cross-sectional configuration. 
     The hollow profile bar is advantageously configured so that the pitch of the outer webs on tubular walls having a circularly cylindrical cross section is 22.5 or 45 angular degrees. Given that the cross sections of hollow profile bars are normally dimensioned in the range of a few centimeters, this yields an outer circumferential shape that makes it possible to work with links for to-be-connected hollow profile bars that have normal cross sections with respect to strength requirements. 
     A significant improvement of a hollow profile bar can be considered to reside in providing an inner wall of a tubular wall having an equal thickness all around with more than two radially salient inner webs evenly distributed about the inner circumference of said inner wall. Such inner webs can assume multiple functions. One such function is to stabilize the hollow profile bar against bowing under load. In addition, it is possible to apply links to them that engage in an end of the hollow profile bar and are able to clamp onto the inner webs. In such cases, the inner webs must protrude only as far as is necessary for them to be gripped securely by the links. They do not need to span the entire interior space of the tube, creating uninterrupted transverse walls. 
     In a particular manner, the hollow profile bar can be realized so that the inner webs are aligned with the undercut casing grooves. In this case, the inner webs stiffen the inner webs of the tubular wall in a region between the two outer webs, particularly against inward collapse of the inner wall. This is especially advantageous when the links are applied across two outer webs that include a casing groove between them, thus subjecting the region of the tubular wall between the outer webs to particularly high stress. 
     The hollow profile bar can be configured so that the pitch of the inner webs is the same as or twice that of the casing grooves. If the pitch of the inner webs is the same as that of the casing grooves, the result is ideal stiffening of the tubular wall over its entire circumference, especially if inner webs are aligned with the undercut casing grooves. Doubling the pitch of the inner webs is indicated when hollow profile bars of comparatively small cross section are to be used with the most massive possible links to clamp inner webs inside the hollow profile bar. 
     It is possible to configure the hollow profile bar so that each inner web comprises a broad base and a thinner clamping strip extending radially therefrom. The broad base and the thinner clamping strip placed thereon form a shoulder. The broad base is sturdier than the clamping strip, thus enabling it to safely transfer any fastening forces or other external forces exerted on the clamping strip by the structure. Broad-based inner webs are especially advantageous when they stiffen the tubular wall in the area between two outer webs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described with reference to exemplary embodiments depicted in the drawing, wherein: 
     FIG. 1 is an end elevation of a first profile bar to which is coupled a second profile bar, shown in cross section, by means of a link, also shown in cross section, 
     FIG. 2 is an enlarged depiction of the first profile bar of FIG. 1, 
     FIG. 3 a  is a depiction similar to that of FIG. 1, with two profile bars to be coupled on, and 
     FIG. 3 b  a rear elevation of the link, shown in direction A of FIG. 3 a.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The figures provide cross sections and end elevations of hollow profile bars  10  to which hollow profile bars  31  of identical or different configuration are to be connected. This purpose is served by links  42  that can be of any desired design. 
     The first hollow profile bar  10  is realized as substantially circularly cylindrical. It is, therefore, a tube comprising a tubular wall  11 , whose thickness  16  is adapted to the loads expected to be exerted thereon. The hollow profile bar  10  is stiffened by outer webs  12 , evenly distributed about the outer circumference, that are salient radially and form casing grooves  14  between them. The salience  15  of the outer webs  12  from the tubular wall  11  is practically equal to the thickness  16  of tubular wall  11 . The visible surface  22  of outer webs  12  is arched convexly relative to tubular wall  11 , but could be arched to a greater or lesser extent, for example extending parallel to tubular wall  11 . Outer webs  12  are evenly distributed about the outer circumference of profile bar  10 , specifically at a pitch  25 . Two outer webs  12  include between them a casing groove  14 , realized in a swallowtail shape. The specific shape depends on the configuration of the side walls  13  and the outer webs  12 . The side walls  13  are predominantly straight, and a slope line can therefore be assigned to each of them. Side walls  13  in FIG. 2 have the slope lines  17 ,  17 ′, which intersect. The point of intersection  19  is shown in the area of tubular wall  11  in FIG.  2 . If the side walls  13  had a lower slope, it could also be located inside the tubular wall  11 , i.e., between the inner wall  26  thereof and an axis  18  of the bar. In any case, each side wall  13  forms an undercut  32 , so that the width of an outer web  12  at the outer circumference  21  of the tubular wall  11  is smaller than the outer circumferential length  24  of the outer web. This is also true of outer webs  12 ′, whose outer length  24 ′ is much greater, since outer webs  12 ′ are arranged at a pitch  28  that is twice the pitch  25  of outer webs  12 . Outer webs  12 ′ can be arranged about the entire circumference of the tubular wall at pitch  28  without thereby altering the coupling feasibilities, since the link  42  always grips over the same width, i.e., either over two outer webs  12  or over one outer web  12 ′. Outer webs  12 ′ increase the consumption of material for hollow profile bar  10 , which is not necessary for normal, relatively low stresses. 
     Accordingly, the outer circumferential length  24 ′ of an outer web  12 ′ is practically three times the smallest spacing  23  between two outer webs  12 . It is generally true of outer webs  12  that their smallest spacing  23  is practically equal to the outer circumferential length  24  of said outer webs  12 . This yields a casing groove  14  that is sufficiently capacious for the engagement of tong legs  34  of link  42 . 
     It should further be pointed out that the side walls  13  of an outer web  12  transition at a predetermined radius  20  to the outer circumference  21  of tubular wall  11 . This prevents notch stresses in the transition region, which can arise due to loads exerted on the outer webs  12 . The radius results in a corresponding shortening of the straight extension of a side wall  13 , which is especially noticeable in the case of planar outer webs. 
     Radii  20 ′ are further present at the transition from the side walls  13  to a visible surface  22  that is practically parallel to the outer wall or is arched convexly with respect thereto. As is apparent from FIG. 2, in particular, the aforesaid radii facilitate the engagement of tong legs  34  by tong ends  34 ′, especially when it is necessary to compensate for tilts caused either by tilting of the link  42  or by tolerances with respect to the link  42  or the stresses imposed on it. 
     The inner wall  26  of tubular wall  11  is occupied by inner webs  27  that are evenly distributed about the inner circumference of tubular wall  11 . Each inner web has a broad base  29 , which at one end is seated directly on the inner wall  26  and is radially salient therefrom, i.e., is oriented toward the axis  18  of the bar. At its other end, each broad base is provided with a clamping strip  30  that can be gripped by clamping jaws  6  of link  42 . It is not absolutely necessary for every clamping strip  30  to be provided with a broad base  29 . This depends, rather, on the width of the clamping jaws  6  used in the link  42 . If a hollow profile bar  10  is square, for example, the narrower clamping strips  30  will suffice, since the clamping jaws  6  of the link  42  can extend practically from wall to wall. On the other hand, the placement of the two clamping jaws  6  in hollow profile bar  10  of FIG. 1 reveals owing to the curvature of the circularly cylindrical hollow profile bar  10 , the clamping jaws  6  are unable to grip shorter clamping strips securely enough and thus appear to be unstable due to their distance from inner wall  26 , so that the broad base is appropriate. 
     The distribution of the inner webs  27  about the circumference depends on the technical object to be achieved. In the arrangements of FIGS. 1 and 2, the inner webs  27  are realized as comparatively long and are therefore merely disposed at a pitch of 45 angular degrees. Thus, comparatively massive and tall links  42  can still be mounted without colliding with the inner webs. The arrangement of the inner webs is such that they are aligned with the casing grooves  14 . They therefore stiffen the tubular wall  11  midway between two outer webs  12 . This is important when the link  42  laps two inner webs  12  with its tong legs  34 . In this case, a tubular wall  11  that was implemented as thin might collapse inward. The broad base  29  reliably prevents this. The pitch  28  of the inner webs  27  in this case is twice that of the outer webs  12 , but is as large as, i.e., identical to, that of the outer webs  12 ′. 
     FIG. 3 a  shows inner webs  27 ′ that can also serve to stiffen the tubular wall  11 . However, they are chiefly designed for a link that has a different mode of operation from that of FIGS. 1 and 2. 
     The links  42  in all the figures have in common the fact that they essentially comprise two clamping jaws  6  that are pressed together by means of a fixing element  41 , shown only in FIG. 3 a.  Link  42  is accordingly clamped onto hollow profile bar  10  by tong legs  34 . However, the jaws  6  are also clamped onto the second profile bar  31 . 
     The link  42  of FIGS. 1,  2  consists of two plate-shaped clamping jaws  6  (cf. the schematic placement shown in FIG.  1 ), which are essentially massively implemented. They clamp clamping strips  30  of inner webs  27  between them at their edges, where they are provided with suitable linear and/or planar clamping faces. The dimensioning of the clamping plates is such that it is impossible for the clamping jaws  6  to bow under load in the region of the fixing element  41 . This is counteracted by schematically indicated ribs  6 ′, which are present on each clamping jaw  6  and engage in slots (not shown in further detail) of the respective other clamping jaw  6 . Fixation by means of the fixing element  41  therefore ensures the desired linear and/or planar clamping of the clamping strips  30 . A positioning projection  43 , which is shown here on the lower clamping jaw  6  and which engages in a recess  44  in the upper clamping jaw, serves to position the clamping jaws  6  in the longitudinal direction thereof. A clip  45  serves to hold the two clamping jaws together before they are mounted to profile bar  31 , especially during the mounting of link  42  on hollow profile bar  10 . 
     Hollow profile bar  31  is spacedly disposed with respect to hollow profile bar  10 , so that a fixing element  41  is freely accessible and can readily be actuated as long as a cover  46  is not yet mounted. 
     FIG. 3 a  shows two links  42  applied at the same level of a first profile bar  10 . One link  42  has a formed-on element  37  on the inner surface  22  of one clamping jaw  6 . Said formed-on element  37  bears against a formed-on element  37  on the other clamping jaw  6 . The two clamping jaws  6  can be fastened together. This purpose is served by a fixing element  41 , which is realized as a screw and engages in a thread  35 . This is provided in the upper clamping jaw  6 , while the lower clamping jaw serves to receive a screw head in a countersunk bore. When fixing element  41  is tightened, tong legs  34  of clamping jaws  6  are pressed together and thereby engage in the undercuts  32  of casing grooves  14  of first profile bar  10 . Clamping on two outer webs  12  is effected as a result. The formed-on elements  37  divert the force of fixing element  41  and press clamping jaws  6  radially apart at an insertion end of the link  42 . This brings about a force fit of the outer circumference  40  of clamping jaws  6  with the inner wall  26  and/or with inner webs  27  of second profile bar  31 . The clamping jaws  6  are realized in this case as semicircular at the insertion end, rather than planar as shown in FIG.  1 . Outer circumference  33  therefore nearly corresponds to the inner circumference of tubular wall  11  and the spacing between inner webs  27  of the first bar  31 . In addition, the clamping jaws are provided with cutting edges  39  that press into the inner webs  27  when fixing element  41  is tightened, thereby preventing link  42  from being withdrawn from bar  31 . 
     In order to mount plural identical links  42  with their attached bars  31  on first hollow profile bar  10 , to achieve the tightest possible packing it is necessary that in addition to the cross-sectional configuration of profile bar  10  shown, a tong leg  19  of a clamping jaw  6  must occupy with its leg end  34 ′ no more than half of a casing groove  14 . Another tong leg  19  can then be fitted by its end  34 ′ into the other half. This is possible in particular if the link  42  and the end of the second profile bar  31  do not extend beyond the median planes  36  of two casing grooves  14  occupied by clamping jaws. The median planes  36  are defined by axis  18  and by a respective straight line  33  extending parallel to axis  18  and through the center of the casing groove  14 . This permits the tight packing of mutually abutting bars  31  whose longitudinal axes form an angle of about 45 degrees, thereby making it possible to assemble correspondingly acute-angled structures and/or for the outer circumference of the bar  10  to be occupied by up to eight elements in one plane of attachment. 
     FIG. 3 b  is a cross section through a link  42  according to FIG. 3 a.  The outer wall  40  of the clamping jaws  6  is semicircular, i.e., adapted to the shape of the inner wall  26  of second profile bar  31 . When fixing element  41  is tightened, the outer walls  40  of clamping jaws  6  are pressed by cutting edges  39  into short inner webs  27 . The resulting small contact area makes for a higher contact pressure and thus effective clamping.