Device for expanding hollow bodies

[0001] The present invention relates to a device for expanding hollow bodies, especially pipe ends, having a plurality of sector-shaped expansion jaws disposed in a distributed manner around the axis "AA" in the fastening element and radially sliding relative thereto and comprising segments with cylindrical surfaces whose radius corresponds to the radius expanded hollow body, wherein the protrusions and depressions are arranged alternately in the gaps between the expansion jaws, and the outer surfaces of the protrusions extend radially inward relative to the cylindrical surfaces at least at their ends.

[0002] Such devices are also referred to as "expanders" or expander heads, respectively, and, among other things, serve as tools for use in sanitary engineering. Winding can be carried out manually, e.g. using a hand lever, but also using a motor with a threaded rod or using hydraulic devices.

[0003] As is known from EP 0 725 908 B1 and the corresponding DE 694 14 721 T2, when expanding plastic pipes to produce pipe joints, other dependencies should also be considered than for expanding metal pipes. Plastic pipes, especially those made of cross-linked polyolefins, including cross-linked polyethylene, have so-called shape memory, also called memory effect. This leads to the fact that the pipes return to their previous shape after expansion, which is time-dependent, and makes it necessary to use appropriate working speeds. In addition, plastic pipes have significantly higher wall thicknesses, as opposed to metal pipes with the same diameters, which means that radial stretching must at least correspond to these wall thicknesses.

[0004] Based on these assumptions and bearing in mind the limiting impressions with sharp edges caused by the edges of the expansion jaws, which leads to leaks in the places of future pipe joints, in these documents it is suggested to conduct the expansion in step and return the expansion jaws to the basic position after execution each step and then, push them deeper towards the end of the pipe and repeat pulling many times or continuing it accordingly. For this purpose, the stairs should have radii much smaller than the thickness of the walls of the pipes. The radial movement is carried out by means of a stretching mandrel with a tapered tapered surface, which slides into a set, for example, six expansion jaws. Each of these expansion jaws has two outer cylindrical surfaces between which each one conical surface is arranged in the axial direction, these surface geometries corresponding to the extended jaw position. For this purpose, the conical surfaces can also be equipped with fine gear teeth on their outer sides.

[0005] On the one hand, it is therefore possible to select larger peripheral surfaces of the jaw sectors at the expense of the gap width between the jaws, but on the other hand this design requires a lot of work using tools for each of the pipe connections, which is time consuming - also due to the looseness caused by shocks - and tedious for technical staff considering the energy requirements due to the weight of the tool. In addition, the stretched end of the pipe maintains its funnel shape, even when sliding on the last surface of the cylinder, which leads to a partial loss of directionality of the pipe end.

[0006] From DD 221 936 A1 and DE 43 39 993 C1 corresponding to, for example, the preamble of claim 1, it is known that in tools enabling one-stage stretching, it is possible to use staggered projections and alignments in the gaps between the jaws in the axial direction to reduce leaks in the walls of hollow bodies as the radial movement of the expansion jaws increases. To this end, the assumption that the outer surfaces of the expansion jaws, the so-called working surfaces, should be placed in a radial end position on the cylindrical surface, plays a role. However, the effect has been shown to be accompanied by undesirable deformations. Thus DE 43 39 993 C1 suggests chamfering the ends of the projections relative to the partially cylindrical working surfaces inside, in such a way that the outer surfaces of the projections will not at least largely extend beyond the cylindrical partial surfaces defined by the working surfaces when the expansion jaws are retracted.

[0007] However, it has been shown that edges formed between cylindrical surfaces and bevelled edges leave angular imprints at the beginning of stretching, which can no longer be completely removed during further stretching. It is presumed that the reason for this is the bending caused by the edges, and therefore the increased material efficiency, as a result of which the material stability is locally excessively increased and it may no longer be possible to balance it when stretching continues. This effect is known as crushing hardening in metallurgy (see "the Great Brockhaus" 1983, p. 138). As a result, a defective seal at the joints of the pipe ends, which leads to leaks.

[0008] As is known from EP 0 718 057 A2, a method is known for breaking or rounding axially parallel longitudinal ends, as well as peripheral sectorally shaped front edges of dilating jaws with a minimum angle of 2.0 mm. However, in practice, it has turned out that such rounding of the front edges is not sufficient to avoid any damage due to breaking of the plastic pipe under mechanical pressure, both during expansion, when connecting the sections by deforming the pipe during assembly or at high internal pressures, as in for drinking water and heating lines.

[0009] Against this background, the object of the present invention is to provide a stretching device and method of operation for plastic pipes, thanks to which it is possible to obtain a pressure-resistant extension with large radial paths along the entire length of the connection of the two ends of the pipe in one working step to obtain solid cross-sections, yet limiting the formation of sharp-edge prints on the stretched pipe ends, which reduces the causes of leaks.

[0010] This object is achieved by means of the device according to the invention described above, characterized in that

a) Cylindrical surfaces pass rounded to the outer surfaces of the projections

(b) the dilating jaws are radially narrowed inwards towards their free ends, and

c) cavities and protrusions are continuous in a radially inwardly narrowed area.

[0011] In this way, the goal is fully achieved in that tensile devices and a method of operation for plastic pipes are provided, with which it is possible to achieve pressure-resistant, gradual expansion with large radial paths along the entire length of the connection two ends of the pipe in one working step, obtaining constant cross-sections in the axial direction, and yet reducing the formation of prints with sharp edges on the stretched ends of the pipes, thanks to which the causes of leaks are reduced. To this end, a special role is played by the fact that the dilating jaws are radially inwardly narrowed in the area of ​​their free ends, and that the recesses and protrusions are continuous in the radially inwardly narrowed area. In this way, plastic deformation of the pipe is obtained, which occurs in the longer section of the transition area between the original pipe diameter and the expanded pipe diameter, in such a way that the occurrence of point, three-axis deformations with high brittleness is reduced.

[0012] In accordance with further embodiments of the present invention, it is particularly preferred that • on the one hand, the radially tapered inward region passes smoothly around the periphery into cylindrical surfaces, and on the other hand it is rounded with respect to the front surfaces.

• the outer surfaces of the inwardly narrowed area were placed at the end of the strut in the area of ​​the cone, • the angle of opening of the cone-shaped surface area was between 30 and 45 degrees, • the length of the area narrowed inside was and between 3 and 30 mm, and / or that • the radius of curvature at the transition points between the cylindrical surfaces and the outer surfaces of the projections is at least 1 mm.

[0013] In the following, one exemplary embodiment of the object according to the invention and the method of its handling are presented in more detail as well as its additional advantages with reference to Figures 1 to 3. They show:

Figure 1 perspective view of five expanding jaws of the expansion head in the extended position,

Figure 2 axial top view of the six dilating jaws in the retracted position, and

Figure 3, an axial top view of the object of Figure 2 having six expansion jaws in a predetermined end position at the end of the pipe expansion.

[0015] For better clarity, the fastening nut on the driving tool in Figure 1 is omitted, as is one of the expansion jaws 1 which are supported in the usual way by a nut with guide pins that have radial longitudinal holes in which the pins can be moved leading. To this end, the flange sectors 2 have axially parallel openings 3. The tension springs, which are not illustrated, are also inserted into the peripheral groove sections 4. Also omitted is the expansion mandrel cooperating with the drive, which may have a cone or pyramid-shaped surface coaxial to the axis "AA", depending on the geometry of the complementary sliding surface on the inner sides of the expansion jaws 1.

[0016] The extension 5 having a cut out from the cylindrical surface 6 extends parallel to the axis "AA", the radius of which corresponds to the radius of the predetermined inner radius of the stretched hollow body 10. This position is shown in Figure 3. The recesses 7 protrude from the cylindrical surfaces 6 from both pages that change in the direction of the "AA" axis in the projections 8. As shown especially in Figure 1, the recesses 7 and the projections 8 are located on both sides of the expansion jaws 1, or respectively on the cylindrical surfaces 6 in positions relatively offset from each other and have dimensions chosen in such a way that all the expansion jaws 1 are shaped in this way. the same way and work together so that only one type of expansion jaw is required for each size

1. The stop surfaces 9 for the end surfaces of the hollow bodies 10 to be stretched are positioned between the cylindrical surfaces 6 and the flange sectors 2.

[0017] At this point, the invention begins to work: as shown in Figures 1 to 3, the cylindrical surfaces 6 extend partly along the length of the projections 8 at the same radius. Then, however, the radius of curvature decreases, in that the ends of the projections 8 are located further from the inside than the cylindrical surfaces 6. As shown in Figures 2 and 3, the protruding ends are neither shaped in the closed position of the expansion jaws 1 (Figure 2) nor in the position in which they are most open (Figure 3), which can leave permanent impressions and sharp-ended and hardened bends due to the high material efficiency of the hollow bodies 10. This material is generally only required for tangential machining.

[0018] Figure 1 further shows that the expansion jaws 1 have a radially inwardly narrowed form at the free ends in a certain area and that the depressions 7 and the projections 8 are continuously present in the area 11. In the stretched state the outer surfaces of the area 11 are located on a cone-shaped surface area at an apex angle of, for example, 35 degrees, as indicated by two dashed lines that intersect the AA axis. In this way, sector-shaped front surfaces 12 having a smaller outer circumference than the outer circumference of cylindrical surfaces 6 are limited. Transitions of area 11 to cylindrical surfaces 6 on the one hand and to the front surfaces 12 on the other hand are well rounded to avoid any pressure on the ends. The rounding is shown in Figure 3 using bundles of thin concentric circles with center points on the AA axis.

[0019] Figure 2 clearly shows that there are only well-rounded surfaces on the outside of the zigzag-shaped slots and on the outside of the projections 8, and Figure 3 also shows that this geometry is also preserved in the position of maximum spreading of the expansion jaws 1 , and that the base with the slit-shaped grooves is overloaded by the stretched material of the hollow body 10 in a straight line, as shown in the upper half of Figure 3. The internal cross-section of the hollow body 10 therefore only slightly diverges from the cylindrical surface, which significantly improves the cohesion of the resulting pipe connection.

[0020] The production of individual expansion jaws 1 can advantageously be carried out by sintering metal particles to obtain a complementary and heated form.

[0021] List of references:

jaws expanding sectors flanges holes circumferential groove extension cylindrical surface recesses protrusions stopping surfaces hollow bodies narrowed area front surfaces "AA" axis

Rothenberger Aktiengesellschaft

Proxy:

PL-PAT-2012-63

EP 2 467 220 B1