Device for expanding hollow bodies

DESCRIPTION

DEVICE FOR ENLARGING HOLLOW BODIES

The invention relates to a device for widening hollow bodies, in particular pipe ends, with a plurality of sector-shaped expandable jaws disposed on a support, distributed about an AA axis and which are radially movable throughout. and comprising segments of cylindrical surfaces whose radii correspond to the radii of the enlarged hollow body, wherein the projections and notches are arranged alternately at the separation joints between the expandable jaws, wherein the outer surfaces of the projections extend radially inwardly with respect to the cylindrical surfaces at least at their ends.

Such devices are also referred to as expanders or expansion heads and, among other applications, are used as tools in the sanitary installation technique. They can be actuated manually, for example by means of a lever, but also motorized by means of spindles or by hydraulic machines.

It is known from EP 0 725 908 Bl and its corresponding document DE 694 14 721 T2 that during the expansion of plastic pipes for the production of pipe connections other correlations other than those taken into account during the expansion of plastic pipes must be considered. the expansion of metal pipes. Plastic tubes, in particular cross-linked polyolefin tubes, including those of

ΕΡ2467220Β1 cross-linked polyethylene, feature a so-called shape memory effect, which is also known as memory effect. The result is that, after expansion and depending on time, the pipes shrink back to their original shape, so that the work must be performed at a speed that takes into account the time factor. In addition, the plastic tubes have substantially greater wall thicknesses than metal tubes of the same diameter, so that the radial expansion should correspond at least to these wall thicknesses.

In view of these considerations and the background to the suppression of sharp edge impressions caused by the expandable jaw edges and which may cause leakage at the rear pipe connection, The aforementioned documents suggest stepwise expansion and that the expandable jaws are retracted to their initial position after each phase to re-insert them deeper into the tube end and repeat or continue the expansion several times. For this, the phases should be significantly smaller than the pipe wall thickness. 0 Radial movement occurs through an expandable mandrel with a narrow tapered surface which is introduced into a set of, for example, six expandable jaws. These expandable jaws respectively have two external cylindrical surfaces, between which are respectively arranged a conical surface in the axial direction, wherein these surface geometries correspond to the position of the expandable jaws when they are expanded. The conical surfaces may comprise thin teeth on their outer sides.

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On the one hand, this larger circumferential allows to select surfaces for the expandable jaw sectors rather than the opening widths between the expandable jaws, on the other hand this construction assumes the operation of different tools for each pipe connection, which is very time consuming - including time spent shaking movements to release the tool - and require the use of a lot of force, making it fatiguing for the operator, even due to the weight of the tool. In addition, the expanded end of the tube retains its funnel shape even when it is slid over the cylindrical where the tube end properties are partially lost, the last orientation surface of the

It is known from DD 221 936 A1 and DE 43 39 993 Cl, which correspond, for example, generally to claim 1, that single-phase expansion tools alternately comprise projections and recesses in the separation joints between the expandable jaws in the axial direction. to minimize sinking of the hollow body wall during increased radial movement of the expandable jaws. Another consideration is that the outer surfaces of the expandable jaws, the so-called work surfaces, should be based on a cylindrical surface in the radial end position. However, the effect has been shown to be accompanied by unwanted deformations. In DE 43 39 993 Cl it is therefore suggested that the ends of the projections be chamfered inwardly with respect to the partially cylindrical work surfaces so that the external surfaces of the projections with the jaws in their retracted position are not stand out from the partially cylindrical surfaces defined by the work surfaces.

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However, it has been shown that the edges formed between the cylindrical surfaces and the chamfers leave angular impressions at the beginning of the expansion, which throughout the remaining expansion will not completely disappear again. The reason for this may be due to edge bending and increased material flow, which causes a localized excessive increase in material strength and when expansion continues, it cannot be compensated for. In metallurgy this effect is called hardening (see Grosse Brockhaus, 1983, p 138). The results of this are leaks at the pipe end joints that can lead to leaks.

From EP 0 718 057 A2 it is known to break or round the longitudinal edges parallel to the axis and also the circular sector front edges of the expandable jaws so that the maximum radius is 2.0 mm. However, in practice it has been shown that such rounding of the front edges is not sufficient to prevent fragile fractures in plastic tubes when mechanical stresses occur, either during expansion or when joining sections of tubes, or due to deformations that occur. in pipes during assembly, whether due to high internal pressures, such as in drinking water or heating system pipes.

In view of this background, the present invention has for its task the provision of an expansion device and an operating procedure for plastic tubes, which allows the production in one step of compression-resistant expansions with large radial pathways. along the entire length of

62467220Β1 joining two pipe ends carried out in a single working process and maintaining a constant cross section while preventing the formation of sharp edges on the expanded pipe ends and thereby suppressing the causes of leaks.

The task described herein is solved by the device according to the invention presented initially, characterized by

(a) the cylindrical surfaces are rounded to transition to the projection surfaces;

(b) the expandable jaws consist of a radially inwardly reducing section in the area of ​​their free ends and in which

c) the notches and projections extend into the radially inwardly reducing section area.

In this way, the task is solved to its full extent by means of an expansion device and an operating procedure for plastic pipes, which allow the production in one step of compression-resistant expansions with large radial paths over along the entire joint length of two pipe ends carried out in a single working process and maintaining a constant cross section in the axial direction, preventing the formation of sharp edge impressions at the ends of the expanded pipes and thereby suppressing the causes of leaks. Of central importance is the fact that the expandable jaws are made up of a section that

ΕΡ2467220Β1 reduces radially inwardly in the area of ​​its free ends and notches and projections extend in the area of ​​the radially inwardly reducing section. Thus, the plastic deformation of the pipe in the transition area between the original diameter of the pipe and the expanded diameter of the pipe will occur over a longer distance so that triaxial point deformations with a strong effect are suppressed. brittle.

Within other embodiments of the present invention, it is particularly advantageous if, in the circumference, the radially inwardly reducing area on the one hand is border-free to the cylindrical surfaces and on the other hand if it is also rounded in relation to the front surfaces, * the outer surfaces of the inwardly reducing area are arranged as a conical hemispherical surface at the end of the expansion stroke, * the opening angle of the conical hemispherical surface is between 30 and 45 degrees, * the length of the inward reducing area is between 3 and 30 mm and / or, if * the radius of curvature of the transition points between the cylindrical surfaces and the external surfaces of the projections is greater than or equal to 1 mm.

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An embodiment of the object of the invention and its modes of action and other advantages will be explained below in detail with reference to Figures 1 to 3.

They are shown:

Figure 1 shows a perspective view of five expandable jaws of an expansion head in its extended state,

Figure 2 shows an axial top view of six expandable jaws in their retracted state and,

Figure 3 shows an axial top view of the object of the

Figure 2 with six expandable jaws at the predetermined end position at the end of a tube expansion process.

For a clearer arrangement, the blank nut for fastening to a drive tool, such as one of the expandable jaws 1, which is typically installed by means of guide pins in the blind nut having radial grooves, has been omitted in Figure 1. the guide pins can move. For this, the sectors of the ftanges 2 have holes 3 parallel to the shaft. In the circumferential groove sections 4, spring springs are inserted which are not shown here either. Also not shown is the expandable mandrel of the drive, which may have a conical or pyramidal surface coaxial to the AA axis, depending on the geometry of the complementary sliding surfaces within the expandable jaws 1.

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From each sector of the flanges 2 extends, parallel to the axis AA, an extension 5 with a section of the cylindrical surface 6, whose radius corresponds to the predetermined internal radius of the expanded hollow body 10. This position is shown in Figure 3. The cylindrical surfaces 6 insert notches 7 on both sides alternately with projections 8 towards the axis AA. As specifically shown in Figure 1, the notches 7 and projections 8 on either side of the scalable jaws 1 or offset misaligned cylindrical surfaces such that all expandable jaws 1 are formed identically and can engage between so that in any case only one type of expandable jaws is required 1. Between the cylindrical surfaces 6 and the flange sectors 2 are further stopping surfaces 9 for the end surfaces of the hollow bodies 10 to be expanded.

to others are willing and are

At this point, the invention will be presented: As shown in Figures 1 to 3, the cylindrical surfaces 6 extend beyond the partial length of the projections 8 with the same radius. However, a reduction in the radius of curvature then occurs, so that the ends of the projections 8 are located radially further inwardly than the cylindrical surfaces 6. As shown in Figures 2 and 3, thus, no protruding edges appear either in the closed state of the expandable jaws 1 (Figure 2) or in the more open state (Figure 3), which could leave permanent imprints and sharp, sharp edge flexions. to the intense flow of material within the hollow body material 10. This material is then essentially requested

ΕΡ2467220Β1 with tangential flow only.

Figure 1 further shows that the expandable jaws 1 are constituted by a radially inwardly reducing section in an area 11 of its free ends and that the notches 7 and the projections 8 continue in that area 11. In an expanded state, the outer surfaces of the area 11 are on a conical hemispherical surface with an opening angle of, for example, 35 degrees, indicated by the two dotted lines intersecting the AA axis. Thus, the sector-shaped front surfaces 12 with a smaller outer circumference are defined as the outer circumference of the cylindrical surfaces 6. Both the transitions from area 11 to the cylindrical surfaces 6 and the front surfaces 12 are well rounded to avoid too here compressions on the lips. Rounding is indicated in Figure 3 by thin concentric circles with center points on the AA axis.

Figure 2 shows very clearly that on the outside of the zigzag separation joints and on the outside of the projections 8 only well-rounded surfaces are present. Figure 3 also clearly shows that this geometry is maintained even at the maximum open state of the expandable jaws 1 and that the bottom of the notch-shaped groove extends in a straight line through the hollow body expanded material 10, which is visible. at the top of Figure

3 The inner cross section of this hollow body 10 has a minimal deviation from the cylindrical surface, which significantly improves sealing of a subsequent pipe joint.

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Production of the individual expandable jaws 1 may advantageously be accomplished by the appropriate sintering process of metal particles in a complementary or heated mold.

Reference List:

Expandable Jaws

Flange Sectors

Holes

Circumferential slot

Extension

Cylindrical surface

Carvings

Projections

Stopping surfaces

Hollow body

Beveled area

Front surfaces AA axis.

Lisbon, January 3, 2013

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