Device for expanding hollow bodies

p0001The invention relates to a device for expanding hollow bodies, in particular tube ends, with a plurality of sector-shaped spreader jaws, which are distributed in a holder about an axis "AA" and are radially movable therewith and have cutouts from cylindrical surfaces whose radii correspond to the radii of the expanded hollow body , Wherein projections and recesses are alternately arranged in the separating gaps between the spreader jaws, and wherein the outer surfaces of the projections extend radially inwardly at the end opposite the cylinder surfaces.

p0002Such devices are also referred to as "expanders" or expander heads and serve, among other things, as tools for use in sanitary engineering. The drive can be done manually, eg by hand lever, but also by motorized spindles or by hydraulic machines.

p0003Through the <patcit id="pcit0001" dnum="EP0725908B1"><text>EP 0 725 908 B1</text></patcit> And the corresponding ones <patcit id="pcit0002" dnum="DE69414721T2"><text>DE 694 14 721 T2</text></patcit> It is known that during the expansion of plastic pipes for the production of pipe connections, other relationships must be observed in addition to the expansion of metal pipes. Plastic pipes, in particular those of crosslinked polyolefins, including the crosslinked polyethylene, have a so-called memory memory, which is also referred to as a memory effect. As a result, the tubes contract again after the expansion in a time-dependent manner, so that corresponding working speeds are to be applied. In addition, plastic tubes have much greater wall thicknesses compared to metal pipes of the same diameter, so that the radial expansion must correspond at least to these wall thicknesses.

p0004On the basis of these considerations and against the background of suppressing sharp-edged impressions by the edges of spreader jaws which lead to leakages of the later pipe connection, the mentioned documents propose to carry out the expansion in several steps, and the spreader jaws after each step are returned to the And then pushing them deeper into the end of the pipe and repeatedly repeating or continuing the expansion. The steps should be significantly smaller than the wall thickness of the pipes. The radial movement is effected by an expanding mandrel with a slender conical surface, which is inserted into a set of, for example, six spreader jaws. These spreader jaws each have two outer cylindrical surfaces between which a conical surface is arranged in the axial direction, these surface geometries corresponding to the expanded jaw position. The conical surfaces can also be provided with fine toothing on their outside surfaces.

p0005On the one hand, this makes it possible to select the peripheral surfaces of the baking seams to the detriment of the gap widths between the jaws. On the other hand, however, this construction necessitates multiple tool operations for each pipe connection which, due to the jogging, And also because of the weight of the tool. Furthermore, the expanded pipe end also retains its funnel shape when pushed over the last cylinder surface, as a result of which the guiding properties of the pipe end are partly lost.

p0006Through the <patcit id="pcit0003" dnum="DD221936A1"><text>DD 221 936 A1</text></patcit> and the <patcit id="pcit0004" dnum="DE4339993C1"><text>"DE 43 39 993 C1</text></patcit>, Which corresponds, for example, to the preamble of claim 1, in single-stage expansion tools, it is known to arrange alternating projections and recesses in the dividing lines between the spreader jaws in the axial direction in order to alleviate the sinking of the wall of the hollow bodies with increasing radial movement of the spreader jaws. In this case, the consideration plays a role that the outer surfaces of the spreader jaws, the so-called work surfaces, are to lie in a cylindrical surface in the radial end position. However, it has been shown that the effect is accompanied by undesirable deformations. In the<patcit id="pcit0005" dnum="DE4339993C1"><text>"DE 43 39 993 C1</text></patcit> It is proposed that the ends of the projections be inclined inwards towards the partially cylindrical work surfaces in such a way that the outer surfaces of the projections in the contracted state of the spreader jaws at least do not substantially protrude beyond the cylinder partial surfaces defined by the working surfaces.

p0007However, it has been found that the edges formed between the cylindrical surfaces and the bevels leave edged impressions at the beginning of the expansion, which can no longer be completely eliminated in the course of the further expansion. The reason for this can be assumed to be that bending is caused by the edges and thus a reinforced flow of the material, by which the strength of the material is locally excessively increased and can no longer be compensated when the expansion is continued. This effect is referred to as cold hardening in metallurgy (see the "<nplcit id="ncit0001" npl-type="s"><text>Grosse Brockhaus ", 1983, p. 138</text></nplcit>), The result are leaks at the connecting points of pipe ends, which lead to leaks.

p0008Through the <patcit id="pcit0006" dnum="EP0718057A2"><text>EP 0 718 057 A2</text></patcit> It is known to break or round the axially parallel longitudinal edges and also the circular-shaped front edges of the spreader jaws, with a maximum radius of 2.0 mm. However, it has been found in practice that such roundings at the front edges are not sufficient to prevent brittle fractures of plastic pipes under mechanical stresses, whether by expanding, by joining pipe sections, by pipe deformation during assembly or by high internal pressures Water pipes for drinking water and heating.

p0009Against this background, the invention is based on the object of specifying an expansion device and an operating method for plastic tubes, by means of which it is possible to produce single-stage pressure-resistant expansions with large radial paths over the entire connecting length of two pipe ends in a work with a constant cross- Impressions in the expanded pipe ends to suppress and thus the causes for leaks.

p0010According to the invention, the above object is achieved by the fact that<ol><li>A) the cylinder surfaces rounded off into the outer surfaces of the projections,</li><li>B) the spreader jaws are designed to be radially inwardly tapered in the region of their free ends, and that</li><li>C) the recesses and the projections are continued in the radially inwardly tapered region.</li></ol>

p0011The object of the present invention is to provide an expansion device and an operating method for plastic tubes, by means of which it is possible to produce single-stage pressure-resistant expansions with large radial paths over the entire connecting length of two pipe ends in an operation with a cross section which remains the same in the axial direction Nevertheless suppress the formation of sharp-edged impressions in the expanded pipe ends and thus the causes for leaks. In particular, it plays a role in the fact that the spreader jaws have a radially inwardly tapered configuration in the region of their free ends, and that the recesses and the projections are continued in the radially inwardly tapered region. As a result, the plastic deformation of the pipe in the transition region between the original pipe diameter and the expanded pipe diameter is distributed over a longer distance, so that three-axial deformations with punctiform embrittlement effects are suppressed.

p0012It is particularly advantageous in further embodiments of the invention if <ul><li>The radially inwardly tapered region on the circumference on its circumference on the one hand transitions without edge to the cylinder surfaces and, on the other hand, is also rounded towards the end faces,</li><li>The outer surfaces of the inwardly tapered region at the end of the spreading stroke lie in a conical envelope surface,</li><li>* The opening angle of the conical envelope surface is between 30 and 45 degrees,</li><li>* The length of the inwardly tapered area is between 3 and 30 mm, and / or when</li><li>* The radius of curvature at the transition points between the cylinder surfaces and the outer surfaces of the projections is at least 1 mm.</li></ul>

p0013An exemplary embodiment of the subject matter according to the invention and its effects and other advantages are described below with reference to FIGS <figref idrefs="f0001 f0002">Figures 1 to 3</figref> In more detail.

p0014Show it:<dl id="dl0001"><dt>FIG</dt><dd>5 shows a perspective view of five spreader jaws of an expansion head in the spread state,</dd><dt>FIG</dt><dd>An axial plan view of six spreader jaws in the contracted state and,</dd><dt>FIG</dt><dd>An axial plan view of the article of FIG <figref idrefs="f0002">FIG</figref> With the six spreading jaws in the predetermined end position at the end of a spreading operation of a tube.</dd></dl>

p0015In <figref idrefs="f0001">FIG</figref> The transfer nut for mounting on a drive tool has been omitted for the sake of clarity as well as one of the spreading jaws 1 which are mounted in the usual manner by means of guide pins in the transfer nut which have radial longitudinal holes in which the guide pins are displaceable. For this purpose, the flange sectors 2 have axially parallel bores 3. In sections of circumferential grooves 4 tension springs (not shown) are also inserted here. Furthermore, the expansion mandrel which belongs to the drive, which may have a conical or pyramidal surface which is coaxial with an axis "AA", depends on the geometry of the sliding surfaces which are complementary thereto, on the inner sides of the expansion jaws 1.

p0016A continuation 5 extends parallel to the axis "AA" from each flange sector 2 with a section of a cylindrical surface 6 whose radius corresponds to the predetermined inner radius of the expanded hollow body 10. This position is in<figref idrefs="f0002">FIG</figref> shown. Into the cylinder surfaces 6, recesses 7 extend from both sides, which alternate with projections 8 in the direction of the axis "AA". How specifically the<figref idrefs="f0001">FIG</figref> The recesses 7 and the projections 8 are arranged offset relative to each other on both sides of the spreader jaws 1 and the cylinder surfaces 6 and are dimensioned in such a way that all the spreader jaws 1 are identically shaped and interlocked so that only one type of spreader jaws is used for each size 1 is required. Between the cylinder surfaces 6 and the flange sectors 2 there are also abutment surfaces 9 for the end faces of the hollow bodies 10 to be expanded.

p0017At this point, the invention begins: Like the <figref idrefs="f0001 f0002">Figures 1 to 3</figref> The cylinder surfaces 6 extend over a partial length of the projections 8 with the same radius. However, a reduction of the radius of curvature then takes place, so that the ends of the projections 8 lie radially farther inward than the cylindrical surfaces 6. As the<figref idrefs="f0002">Figures 2 and 3</figref> , Neither in the closed state of the spreader jaws 1 (<figref idrefs="f0002">FIG</figref>), Nor in the most open state (<figref idrefs="f0002">FIG</figref>), Which could leave permanent impressions and sharp-edged and solidified bends due to a strong flow of the material in the material of the hollow bodies 10. This material is then essentially only subjected to tangential flow.

p0018The <figref idrefs="f0001">FIG</figref> Furthermore shows that the expansion jaws 1 are designed to be tapered radially inwards at their free end in a region 11, and that the recesses 7 and the projections 8 continue in the region 11. In the expanded state, the outer surfaces of the region 11 lie in a conical envelope surface, with an opening angle of, for example, 35 degrees, which is indicated by the two dashed lines intersecting on the axis AA. As a result, sector-shaped end surfaces 12 with a smaller outer circumference are delimited than the outer circumference of the cylinder surfaces 6. The transitions of the region 11 into the cylinder surfaces 6 on the one hand and into the end surfaces 12 on the other hand are well rounded in order to avoid edge pressing. The roundings are in<figref idrefs="f0002">FIG</figref> By means of flares of thin concentric circles with center points on the axis AA.

p0019The <figref idrefs="f0002">FIG</figref> Shows very clearly that only well-rounded surfaces are present on the outer side of the zigzag-shaped separating gaps and on the outsides of the projections 8, <figref idrefs="f0002">FIG</figref> Also makes it clear that this geometry is maintained even in the maximally spread state of the spreader jaws 1 and that the notch-shaped groove base is spanned rectilinearly by the stretched material of the hollow head 10, which in the upper half of FIG <figref idrefs="f0002">FIG</figref> Is shown. The inner cross-section of the hollow body thus deviates as little as possible from a cylindrical surface, which substantially improves the sealing of a subsequent pipe connection.

p0020The individual spreader jaws 1 can advantageously be produced by sintering suitable metal particles in a complementary and heated form.

<u>Reference list:</u>

p0021<dl id="dl0002" compact="compact"><dt>1</dt><dd>spreading jaws</dd><dt>2</dt><dd>Flange Sectors</dd><dt>3</dt><dd>drilling</dd><dt>4</dt><dd>Circumferential groove</dd><dt>5</dt><dd>progress </dd><dt>6</dt><dd>cylinder surface</dd><dt>7</dt><dd>recesses</dd><dt>8th</dt><dd>projections</dd><dt>9</dt><dd>contact surfaces</dd><dt>10</dt><dd>hollow body</dd><dt>11</dt><dd>rejuvenated area</dd><dt>12</dt><dd>end faces</dd></dl><dl id="dl0003" compact="compact"><dt>"AA"</dt><dd>axis</dd></dl>