Pressing tool for press-fitting of a plastic pipe socket

Abstract

The invention relates to a pressing tool for press-fitting of a plastic pipe socket which is cooled below the hot deformation temperature after being fitted and has an oversize in relation to a predefined final cross section, the pressing tool comprising two pressing jaws (1) which can be pressed against each other perpendicular to their separation plane (2) and, when closed, have an undersize opening cross section in relation to the predefined final cross section. In order to create advantageous pressing conditions, according to the invention the opening cross section of the closed pressing jaws (1) is oval at least in an axial portion of the pressing jaws (1), deviating from a circular shape (3), with a longer main axis (4) lying in the separation plane (2).

Description

[0001] Press tool for undersized pressing of a plastic pipe socket

[0002] Technical field

[0003] The invention relates to a pressing tool for undersized pressing of a plastic pipe socket which, after being cooled below the hot forming temperature after being fitted, has an oversize in relation to a predetermined final cross-section and has two pressing jaws which can be pressed together perpendicular to their parting plane and which, in the closed state, have an opening cross-section that is undersized in relation to the predetermined final cross-section.

[0004] State of the art

[0005] To fit thermoformable plastic pipes with an end socket, it is known (WO 94 / 08772 A1) to heat the pipe end in the area where the socket will be located above its forming temperature and expand it to a diameter that exceeds the specified final diameter of the socket. After cooling, the socket is pressed at a temperature below its forming temperature to a slight undersize below the specified final diameter, so that after elastic expansion following the pressing process, the socket has the specified final dimension. Pressing the socket undersize at a temperature below its forming temperature creates molecular forces that counteract the shrinkage of the socket due to a memory effect that would otherwise occur due to heating or long-term creep, thus preventing the thermoformed sockets from shrinking.To ensure that the desired effect on the long-term behavior of the finished pipe sleeves is achieved by pressing them undersized after they have cooled below their deformation temperature, a specific duration of the pressing forces on the pipe sleeve must be observed. This duration depends on the dimensions of the pipe sleeve, the properties of the plastic, and the operating conditions, particularly the temperature profile, and is therefore determined based on these parameters. However, this limits the cycle times of the pressing tools and thus the number of pipe sleeves that can be processed in a given time using these tools.

[0006] Description of the invention

[0007] The invention is therefore based on the objective of designing a press tool for undersized pressing of a plastic pipe sleeve that has an oversize in relation to a predetermined final cross-section after being cooled below the hot forming temperature, in such a way that cycle times can be shortened without having to accept disadvantages with regard to the long-term behavior and the dimensional accuracy of the pipe sleeves.

[0008] Starting from a press tool of the type described above, the invention solves the problem by having the opening cross-section of the closed press jaws be oval in at least one axial section of the press jaws, deviating from a circular shape, with a longer main axis lying in the division plane.

[0009] The invention is based on the understanding that the two pressing jaws of the pressing tool exert a longer influence on the pipe socket in the area of ​​the parting plane during the closing and opening of the pressing jaws than in the intervening apex areas. As a consequence, a greater effect of undersize pressing is to be expected in the area of ​​the parting plane, which, among other things, affects the final cross-section of the pipe socket, which, deviating from a circular shape, has an oval shape with the longer main axis perpendicular to the parting plane. Therefore, if an opening cross-section is selected for the closed pressing jaws that is oval with a longer main axis lying in the parting plane, the uneven pressing load on the pipe socket around the circumference during the closing and opening of the pressing jaws, which is particularly significant with comparatively short cycle times, can be compensated for, and a pipe socket with a circular final cross-section can be obtained.The press load on the pipe sockets, which is largely balanced across the circumference of the socket as a result of these measures, also has a beneficial effect on the long-term behavior of the pipe sockets, so that the cycle time for the press tool can be significantly reduced by means of press jaws designed according to the invention, and thus production can be increased accordingly, without having to fear any loss of quality for the manufactured pipe sockets.

[0010] Since only certain manufacturing tolerances need to be observed in the production of pipe sockets, it is often sufficient to provide the oval opening cross-section of the closed press jaws, which deviates from the circular shape, only in an axial section of the press beams, e.g. outside the ring groove area usually provided in the socket for receiving a sealing ring, although an oval opening cross-section extending over the axial length of the press jaws naturally provides the best conditions for pipe socket production that meets high quality requirements.

[0011] The effects of undersized pipe socket pressing also depend on the temperature conditions under which the pressing is carried out. This means that a heating device, which can be controlled with varying temperatures across the circumference of the pressing jaws, can further influence the final cross-section of the pipe socket. Cooler sections of the pressing jaws result in larger final diameters of the pipe socket in those areas.

[0012] Brief description of the invention: The invention is illustrated by way of example in the drawing. It shows...

[0013] Fig. 1 shows a pressing tool according to the invention for undersized pressing of a pipe socket in a schematic longitudinal section through the closed pressing jaws and

[0014] Fig. 2 shows this pressing tool in a section along line 11-11 of Fig. 1.

[0015] Ways to implement the invention

[0016] A pressing tool according to the invention for undersized pressing of a pipe socket has two pressing jaws 1 in the form of half-shells, which are pressed together perpendicular to a parting plane 2. The opening cross-section of the closed pressing jaws 1 deviates from a circular shape 3 indicated by dashed lines in Fig. 2 and has an oval shape with a longer main axis 4 in the parting plane 2 and a shorter main axis 5 perpendicular to the parting plane 2.

[0017] To produce a pipe socket at the end of a plastic pipe, the plastic pipe is first heated to a suitable deformation temperature in the area of ​​the future pipe socket. Then, in a socketing station, the pipe end is expanded to a cross-section exceeding the specified final cross-section, forming a pipe socket that is typically designed with an annular groove to accommodate a ring seal. Regarding the oversized or undersized cross-sections relative to the respective final cross-section, it is important to note that for comparison purposes, these cross-sections must be referenced to a uniform temperature level, taking into account their respective thermal expansion.

[0018] The oversized pipe sockets from the socketing station are cooled below the forming temperature before being pressed between the press jaws 1 to an undersize determined by the opening cross-section of the closed press jaws 1. Due to the ovality of the opening cross-section of the press jaws 1, a uniform processing of the pipe sockets can be achieved, compensating for the varying pressing loads on the pipe sockets in the area of ​​the parting line and in the intervening apex areas during the closing and opening of the press jaws 1. This allows for shorter cycle times without compromising the quality of the manufactured pipe sockets.

[0019] As can be seen in Fig. 1, the fitted pipe sockets must also be subjected to undersize pressing in the area of ​​the annular grooves for the ring seal after cooling. For this purpose, the press jaws 1 have an annular recess 6 into which the wall sections of the annular grooves of the pipe sockets, which bulge outwards during the fitting process, engage. If, for example, the circular cross-sectional shape is maintained in the area of ​​these annular recesses 6, this has only a minor influence on the final cross-section of the pipe sockets following the annular groove for the ring seal, so that, despite the measures according to the invention only extending to an axial section of the press jaws in such a case, a required tolerance range can be maintained.

Claims

Patent claims 1. Pressing tool for undersized pressing of a plastic pipe sleeve, which has an oversize in relation to a predetermined final cross-section after being cooled below the hot forming temperature after being fitted with a sleeve, comprising two press jaws (1) which can be pressed together perpendicular to their dividing plane (2) and which, in the closed state, have an opening cross-section that is undersized in relation to the predetermined final cross-section, characterized in that the opening cross-section of the closed press jaws (1) is formed in at least one axial section of the press jaws (1) as being oval with a longer main axis (4) lying in the dividing plane (2), deviating from a circular shape (3).

2. Pressing tool according to claim 1, characterized in that the oval opening cross-section extends over the axial length of the press jaws (1).

3. Pressing tool according to claim 1 or 2, characterized in that the pressing jaws (1) have a heating device which can be controlled with a temperature different over the circumference of the pressing jaws (1).

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