EP0718057A2 - Device for flaring hollow workpieces - Google Patents

Abstract

Hollow bodies, partic. the ends of pipes, are enlarged with more than two expanding jaws (7) of sector shape, arranged about an axis (A). The jaws are separated by gaps (14) and have partly cylindrical working faces (13). On either side of each gap, edges (7c) of the jaws running parallel to the axis are broken, pref. by bevels. Pref. the sector-shaped end edges (7f) are also broken. The opening angle between two adjacent jaws is 40-90 deg., pref. 50-70 deg. Jaws are pref. precision cast and are expanded by a mandrel (4).

Description

The invention relates to a device for expanding hollow bodies, in particular pipe ends, with more than two identical, essentially sector-shaped expanding jaws arranged about an axis "A", which are separated from one another by parting lines and have partially cylindrical working surfaces and by means of a drive device in the radial direction are arranged movably to the axis "A" in a holder.

The parting lines are limited by the side surfaces of the expansion jaws and can be opened between the distance 0 and a predetermined maximum value.

In such a device, known from DE-PS 42 02 348 C1, the parting lines are formed by plane-parallel gaps which have sharp edges to the work surfaces. This was already due to the classic manufacturing process, in which a rotary body was divided into six sectors, for example by three diametrical saw cuts. The working strokes of the said expansion jaws run in the radial direction to axis "A", so that the joints or gaps widen with increasing working stroke. Although the work surfaces are in the most open position of the expanding jaws in one or more cylinder surfaces, the support of the hollow body in the area of the separating joints is increasingly lacking as a result. As a result, the shape of the expanded hollow bodies, which consist, for example, of tubes made of copper or plastic, deviates from the exact cylindrical shape, and the sharp edges on the gap edges form on the inner surface of the tube. The sharp edges result from the manufacturing process of the expanding jaws: a rotating body is broken down into sections by sawing processes that form the expanding jaws.

The expansion takes place in most cases for the purpose of being able to insert another hollow body into the expanded hollow body and to be able to connect it to the expanded hollow body. So if pipes of the same origin diameter and the same wall thickness are to be connected to one another, the working stroke of each expanding jaw must necessarily correspond to the wall thickness of the pipe, if necessary plus a so-called "capillary gap" for accommodating a solder or an adhesive. It is desirable for the capillary gap to have a gap width that is as constant as possible over the entire circumference of the connection point. This requirement is opposed by the gap or the joint between the individual expanding jaws.

Plastic pipes generally have a greater wall thickness than metal pipes of the same outside diameter. As a result, the working stroke of the expansion jaws must be adapted to this wall thickness, which necessarily also increases the gap width of the parting lines at the end of the expansion process.

This process leads, in particular in the case of plastic pipes, to the disadvantage that the sharp edges meet at the transition lines between the sides and impress the work surfaces into the pipe material. This process is reinforced by the properties of some plastics that contract after the expansion process, so that part of the plastic penetrates into the gaps in the joints. This process complicates the sealing between the hollow bodies to be connected considerably. In addition, the plastic is slightly overstretched on the sharp edges, which manifests itself in transparent or translucent plastics by a white discoloration, the so-called "whitening". Whitening can easily become the starting point for fractures (Stoeckhart "Kunststoff-Lexikon", 1981, p. 556).

From DE-C-519 535 it is known to round off the circular-arc-shaped end edges of the base jaws and of additional top jaws in the case of pipe expanding pliers with two expanding jaws. Nothing is said about the formation of the axially parallel edges of the expanding jaws. With such a tool, cylindrical widenings can only be produced by rotating them gradually and actuating the expanding pliers step by step. If there was a large expansion path that was not up for discussion on the day of issue of the publication due to the lack of suitable pipe materials, there would be sharp-edged impressions in the pipe material on the axially parallel edges.

Even with the expanding mandrel according to DE 42 20 794 A1, chamfers are provided only at the free ends of the expanding jaws, so that the same problems arise with respect to the axially parallel edges.

WO 84/00120 discloses a tube expander with partially frustoconical expansion jaws which have only short cylindrical surfaces and which are designed as sectors and which perform pivoting movements when expanding. In order to avoid deviations from the cylindrical shape of the tube and drawing grooves in the inner surface of the tube, sectors of different shape and length, which are referred to as main and secondary jaws, are provided alternately, by any Fill in the gap between the expander jaws. The construction of such expander heads and their control is complicated because the different expander jaws have to perform axial relative movements against one another at times. All expanding jaws have bevels only at their arcuate ends, not at the longitudinal edges which are at least partially parallel to the axis. Expansion heads of this type can only be used in connection with specially designed expander tongs specially designed for this purpose, but not as retrofit elements for expander tongs already on the market. Above all, however, the expansion process must be carried out progressively by pulling the expanded expander jaws out of the tube in order to produce a somewhat cylindrical expansion. Before the expansion process, the tube with the expander jaws must be pushed against the expander pliers against a spring force in order to put the device in working order. This makes the device complicated to set up and the process takes time getting used to.

The invention is therefore based on the object of specifying a simply constructed and easy-to-use device of the type described at the outset, with which the hollow body can be expanded as gently as possible and which can be used in conjunction with conventional expander pliers.

In the device described at the outset, the object is achieved in that the expanding jaws on both sides of each parting line are broken at the axially parallel edges.

Such identical expanding jaws are present more than twice, preferably at least four times, usually six times or eight times.

The edges can be broken by any geometric shape, for example by chamfering, rounding, or by chemical etching or precision casting. It has surprisingly been found that even slight deviations from a sharp angle of 90 ° between the gap wall and the working surface facilitate the flow of the material and prevent the edges from "mapping" on the inner pipe surface and the dreaded whitening of plastics.

A so-called expanding mandrel is usually used as the drive device for the expanding jaws, which has a frustoconical or truncated pyramid-shaped end and is inserted in the axial direction into a correspondingly shaped cavity between the expanding jaws. As a result, the axial movement of the expanding mandrel is converted into a single, exclusively radial working stroke of the expanding jaws via appropriately designed sliding surfaces.

A plier-shaped expansion tool with a tool body, in which an expanding mandrel is mounted, is described in DE-PS 40 71 404. The expanding mandrel is driven by an arcuate link which acts on a rolling element in the expanding mandrel. However, the use of the device according to the invention is not limited to such an expansion tool; rather, pliers-like expansion tools with a cam drive or with a rack and pinion drive are also suitable. Threaded spindles or hydraulic drives in which the expanding mandrel is driven by a hydraulic piston can also be used as drive devices.

The invention also relates to devices in which each expanding jaw has a plurality of stepped, partially cylindrical working surfaces, as is described, for example, in DE-PS 42 02 348 C1. The number of diameter gradations can be increased even further, so that in this way a universal expansion tool for different Diameter is obtained. It is only necessary that each work surface on both sides of all the joints passes into the gap walls by means of broken edges.

Advantageous refinements of the subject matter of the invention emerge from the subclaims.

Three exemplary embodiments of the subject matter of the invention are explained in more detail below with reference to FIGS. 1 to 4.

Figur 1

in perspektivischer Darstellung in der linken Hälfte eine Außenansicht und in der rechten Hälfte einen teilweisen Axialschnitt durch einen Expansionskopf, und die

Figuren 2 bis 4

stirnseitige Ansichten von Spreizbacken mit unterschiedlichen Kantenbrechungen.

Show it:

Figure 1

in a perspective view in the left half an external view and in the right half a partial axial section through an expansion head, and the

Figures 2 to 4

end views of expanding jaws with different edge breaks.

In Figure 1, an expansion head 1 is shown, the supporting part of which is a union nut 2 with an internal thread 3, with which the expansion head 1 can be screwed onto a tool base body, not shown here. This basic tool body includes a broken mandrel 4 with a conical expansion surface 5. The union nut has an annular inner flange 6 on the end facing away from the internal thread 3, which serves to support and hold a total of six expansion jaws 7.

Inner flange sectors 8, which are parts of the expanding jaws 7 and have grooves 9 on their outer surfaces, in which an annular tension spring 10 is mounted, cooperate with the inner flange 6 on its inner circular ring surface. The flange sectors 8 are each connected to the inner flange 6 by a rivet 12 pressed into corresponding bores 11, the axis of which runs parallel to the axis AA of the expansion head. The Rivet 12 also penetrates the inner flange 6, which for the purpose of radial movement of the expanding jaws with the rivet has elongated and radially extending recesses, which are not particularly emphasized here. Figure 1 shows the expanding jaws 7 in their most outward position.

The spreading jaws 7 have working surfaces 13, which are parts of a common cylindrical surface, the diameter of which corresponds to the final diameter of the widening to be produced. Since the initial position of the expansion jaws is shifted radially inwards, 7 expansion joints 14 are formed during the expansion process between the expansion jaws, which are delimited by side surfaces 7a and 7b, which form the so-called gap walls.

The edges 7c, which form the transitions between the side surfaces 7a, 7b and the working surfaces 13, are broken over their entire length, ie between the end surfaces 7d and the widenings 7e, of the expanding jaws 7, which is explained in more detail with reference to FIGS. 2 to 4 becomes:

In Figures 2 and 3 chamfers are shown, which include opening angles of 60 ° or 90 ° between them, i.e. the side surfaces are chamfered on their axially parallel outer edges at angles of 30 ° and 45 °, respectively. The angles between these chamfers and the work surfaces 13 are therefore obtuse angles, which differ significantly from 90 °, that this spatial shape is already sufficient to solve the task at hand!

FIG. 4 shows rounded edges 7c which are more difficult to manufacture by machining, but which are very inexpensive to manufacture by precision casting or chemical etching.

The chamfers or roundings form, as it were, "notches" as long as the expanding jaws are not expanded. It has been shown that the notch depth and width is not particularly critical and can be found by trial and error can, keeping in mind that the work surfaces 13 should be as large as possible. It can be seen from all the figures that the edge breaks are present on both sides of all separating joints 14, ie the “notches” are mirror-symmetrical to the radial center planes of the separating joints 14. In any case, the radial working stroke of the expanding jaws is also greater than the maximum wall thickness of the pipes to be expanded .

Finally, it is particularly advantageous if the expanding jaws are also broken at the end edges 7f in the shape of a sector of a circle, which almost complement each other to form a circle. As a result, the flow of the material is also promoted at these end edges 7f and the "white break" is suppressed in the case of plastics. Analogous considerations apply to the geometric shapes of these end edges 7f as for the axially parallel edges 7c.

With the device according to the invention it is possible, for example, to expand plastic pipelines with an outer diameter of 28 mm and a wall thickness of 3 to 4 mm by about 10 mm in diameter in order to be able to insert a correspondingly dimensioned counterpart with a cylindrical surface of corresponding diameter.

Claims (8)

Device for expanding hollow bodies, in particular pipe ends, with more than two, essentially sector-shaped expansion jaws (7) arranged around an axis "A", which are separated from one another by parting lines (14) and have partially cylindrical working surfaces (13) and by means of a Drive device (expanding mandrel 4) are arranged in a holder (union nut 2) movable in the radial direction to the axis "A", characterized in that the expanding jaws (7) on both sides of each parting line (14) on the axially parallel edges (7c) of the working surfaces ( 13) are broken. Device according to claim 1, characterized in that the expanding jaws (7) are broken at the end edges (7f) in the shape of a sector of a circle. Device according to claim 1, characterized in that the expanding jaws are provided with chamfers on the axially parallel edges (7c) of the working surfaces (13). Device according to claim 3, characterized in that the opening angles between two adjacent expanding jaws (7) are between 40 ° and 90 °, preferably between 50 ° and 70 °. Device according to claim 1, characterized in that the width of the bevels is between 0.3 and 3 mm, preferably between 0.5 and 1.0 mm. Device according to claim 1, characterized in that the axially parallel edges (7c) of the working surfaces (13) are rounded. Apparatus according to claim 6, characterized in that the radius of the roundings is between 0.2 and 2.0, preferably between 0.4 and 1.5 mm. Device according to claim 1, characterized in that the expanding jaws (7) are designed as investment castings.

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