Device for producing pipes made of thermoplastic

A device for producing pipes made of thermoplastic with annular transverse profilings with a cross section in the form of undulation peaks and undulation troughs has half-molds, which complete one another pairwise along a straight mold section to form a closed mold, which can be moved in a movement direction. Projecting into the mold is an extrusion tool, which has a nozzle support body. To produce an adequate seal between the half-molds and nozzle support body, the latter is covered with exchangeably attached hollow half-shells, which form a cylindrical external face.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 10 2010 043 786.7, filed Nov. 11, 2010, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.

FIELD OF THE INVENTION

The invention relates to a device for producing pipes made of thermoplastic with annular transverse profilings with a cross section in the form of undulation peaks and undulation troughs, with half-moulds, which complete one another pairwise along a straight mould section to form a closed mould, which is moveable in a motion direction, with a central longitudinal axis, which is transportable in the circuit counter to the movement direction of the mould to an upstream end of the mould section and which have an annular internal profiling, which is loadable with a partial vacuum, with a smallest internal diameter D39to produce the transverse profiling, and with an extrusion tool, which has a nozzle support body with one of an external diameter D33and D33′ with at least one channel for plastic melt, which has a nozzle with a diameter D19, which is connected by means of a channel end portion widening toward the nozzle to the channel, which has an inner nozzle ring and an outer nozzle ring, which between them limit the channel end portion and which are fastened to the nozzle support body,

BACKGROUND OF THE INVENTION

Devices of this type known, for example, from EP 2 116 352 B1 or U.S. Pat. No. 5,320,797 have been extraordinarily successful in practice. In the configuration of devices of this type for producing pipes with a nominal width ≧400, the problem emerges that the extrusion tool, also designated a pipe head, becomes very heavy, which leads to not inconsiderable additional structural outlay and additional costs resulting from this.

SUMMARY OF THE INVENTION

The invention is based on an object of configuring a device of the generic type in such a way that even in a configuration for large nominal widths, the weight of the extrusion tool is as small as possible, without endangering the sealing of the mould to the outside to maintain the partial vacuum.

This object is achieved according to the invention by the external diameter D33or D33′ being smaller than the internal diameter D19, wherein the nozzle support body—in relation to the movement direction—upstream of the outer nozzle ring, is covered with exchangeably attached hollow half-shells, which form a cylindrical external face with a diameter D37and wherein a narrow annular gap with a gap width a is formed between the cylindrical external face and the internal profiling with the smallest internal diameter D39. Between the cylindrical external face formed by the half-shells and the internal profilings of the smallest diameter generally formed by mould webs, only a narrow annular gap is limited, which acts as a restrictor point and therefore prevents an increase in pressure relevant to the process in the region of the partial vacuum. One or more annular gaps of this type are generally sufficient to maintain the partial vacuum; in addition, however, by the seals projecting outwardly over the external face, which is bringable into sealing abutment with the internal profiling with the smallest internal diameter D39, being provided on the half-shells, an additional seal can also be achieved, with a plurality of seals being provided at a spacing c in the direction of the centre longitudinal axis such that at least one seal always rests in a sealing manner on an internal profiling with the smallest diameter D39being particularly advantageous.

Further features, advantages and details emerge from the following descriptions of two embodiments of the invention with the aid of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

AsFIG. 1allows it to be seen, a device for producing plastics material composite pipes with transverse grooves has two extruders1,2, which are connected to an extrusion tool3, which in practice is also called a pipe head. From the extrusion tool3, two tubes of plastics material melt are coextruded within one another, from which the composite pipe mentioned is molded. Used for this purpose is a mould machine4, in practice also called a corrugator, which is formed from half-moulds6,6a, which are provided with an internal profiling5, are set against one another pairwise on a mould section7and are located tightly against one another in a movement direction8of the mould9thus formed. The composite pipes mentioned are molded in the mould9. This method is generally known in practice and shown and described, for example, in U.S. Pat. No. 5,693,347, to which reference may be made for explanation.

The extruder1is a so-called side extruder, because it opens by means of a lateral melt line10into the extrusion tool3, while the other extruder2opens centrally, i.e. concentrically with respect to the centre longitudinal axis11of the mould9into the extrusion tool3.

The extrusion tool3has an internal nozzle mandrel12, which is screwed together from a plurality of parts and is arranged concentrically with respect to the axis11. The internal nozzle mandrel12is surrounded by an internal nozzle jacket13, which is also multi-part and is also in turn surrounded concentrically with respect to the axis11by an external nozzle mandrel14. The latter is in turn surrounded by an external nozzle jacket15. An internal channel16configured concentrically with respect to the axis11is limited between the internal nozzle mandrel12and the internal nozzle jacket13, while an external channel17is limited between the external nozzle mandrel14and the external nozzle jacket15. The internal channel16opens by means of an internal nozzle18out of the extrusion tool3, while the external channel17opens by means of an external nozzle19out of the extrusion tool3. Extruded from the two nozzles18,19are the internal tube20mentioned and the external tube21mentioned, which are connected to one another to form a composite pipe in a manner known, for example, from U.S. Pat. No. 5,320,797. The internal nozzle mandrel12, the internal nozzle jacket13, the external nozzle mandrel14and the external nozzle jacket15are fastened with the interposition of an internal star distributor22and an external star distributor23and a sleeve tool24to a support part25. In the region of this support part25, the extrusion tool3is supported by means of a support construction, not shown, on a base, also not shown, as is conventional in practice. The melt line10from the side extruder1opens into the sleeve tool24, as can be inferred fromFIG. 1. The details of the star distributors22,23and the sleeve tool24are shown and described in detail, for example, in EP 2 116 352 B1, to which reference is made.

The internal nozzle18is limited by an inner internal nozzle ring26and an outer internal nozzle ring27, which limit an internal channel end portion28connecting the internal channel16to the actual internal nozzle18and widening in a funnel shape to the internal nozzle18. The external nozzle19is limited by an inner external nozzle ring29and an outer external nozzle ring30, which also limit an external channel end portion31widening outwardly in a funnel shape, specifically toward the external nozzle19. The inner internal nozzle ring26is attached to the internal nozzle mandrel12. The outer internal nozzle ring27is attached to the internal nozzle jacket13. The inner external nozzle ring29is attached to the external nozzle mandrel14. The outer external nozzle ring30is fastened to the external nozzle jacket15. A cooling and calibrating mandrel32is attached to the inner internal nozzle ring26.

The internal nozzle18has a diameter D18, while the external nozzle19has a diameter D19. The portion of the extrusion tool3surrounded by the external nozzle jacket15and designated the nozzle support body33has an external diameter D33, which is significantly smaller than D18and D19. The external nozzle jacket15is surrounded by heating devices34configured in the form of heating strips. The outer internal nozzle ring27can also be surrounded by a corresponding heating device35.

The nozzle support body33is surrounded by thin-walled half-shells36made of aluminum, which surround the nozzle support body33with a continuous cylindrical external face37. The diameter D37of this cylindrical external face37substantially corresponds to the diameter D19of the external nozzle19. If tubes with a larger diameter D18and D19are to be extruded, the nozzle rings26,27,29,30are exchanged. Accordingly, the half-shells36are replaced by half-shells with a larger diameter. The remaining nozzle support body33remains unchanged. The nozzle support body33can thus remain unchanged, in each case, even when producing pipes with a different nominal width. It is adapted to the pipe to be produced with the smallest possible nominal width.

As can be inferred fromFIG. 2, the internal profiling5of the half-moulds6,6aconsists of annular mould recesses38, between which likewise annular mould webs39with the smallest internal diameter D39are also configured, in each case. The external tube21is formed into undulation peaks40in the mould recesses38, while the external tube21is formed into undulation troughs41of the external tube21by the mould webs39.

The internal tube20is welded to the external tube21on the cooling and calibrating mandrel32in the region of the undulation troughs41. This method is known in detail, for example, from U.S. Pat. No. 5,320,797, already mentioned. The mould recesses38are loaded with a partial vacuum by vacuum channels42, which are configured in the half-moulds6,6aand are connected by vacuum slots43to the respective mould recesses38. Either support air with the required excess pressure relative to the atmospheric pressure is introduced into the space44between the tubes20,21or else this space44is vented to the outside. Both take place by means of a gas channel45. If a pipe socket51is to be formed at fixed intervals in a composite pipe to be continuously produced, half-moulds46having a corresponding socket recess47are then used, which is also shown inFIG. 2. These half-moulds46are also provided with corresponding vacuum channels42, from which vacuum slots43lead into the socket recess47. The forming of the external tube21into undulation peaks40or pipe sockets51takes place as described above. It can thus—as shown above—take place by the so-called vacuum method or else the combined blow molding-vacuum method.

As can be inferred fromFIG. 2, only a narrow annular gap48with a gap width a of 2 mm to 10 mm exists between the mould webs39of the half-moulds6,6aand the cylindrical external face37of the half-shells36. Configured between the two mould webs39a, which—in relation to the movement direction8—directly follow the socket recess47, and the cylindrical external face37is, in each case, an annular gap48awith the gap width b, to which there applies: 2 mm≦b≦5 mm. The reason is that the undulating portion of the pipe directly adjoining the pipe socket51is cut out after production. The restriction can therefore be increased, without the composite pipe being weakened in the undulation trough41. The internal diameter D39aof these mould webs39ais thus generally slightly smaller than the internal diameter D39. In addition, seals49projecting radially slightly outwardly and made of a suitable plastics material can be attached to the half-shells36and in each case engage with the mould webs39upon movement of the mould9in the direction8, thereby forming a complete seal. If a plurality of lamellar-like seals49of this type is provided, it is expedient to select the spacing c thereof in the movement direction8in such a way that at least one seal49in each case always rests on a mould web39or39a. Independently of these seals49, the annular gaps48or48acan be selected to be so narrow that the partial vacuum built up by means of the vacuum channels42and the vacuum slots43between the mould recesses38or the socket recess47and the external tube21is also maintained. The external tube21is thus reliably held on the internal profiling5of the mould9or placed there in the course of the pipe production.

As soon as the internal tube20is placed against the external tube21at least partially preformed in the socket recess47for the pipe socket51, the pair of half-moulds6,6afollowing the pair of half-moulds46having the socket recess47is already placed on the pair of half-moulds46. An adequate number of restrictor points is thus produced as soon as the venting between the external tube21and the internal tube20begins.

So that the mould9is already closed off with an adequate spacing upstream of the external nozzle19and therefore also of the internal nozzle18, in other words can maintain the partial vacuum in the manner described, it is expedient if the half-moulds6,6aor46are transported after removal from the mould section7and back to the upstream end50of the mould section7in the manner indicated inFIG. 1. The respective half-moulds6,6aand, accordingly, the half-moulds46, after the return transport, are returned transverse to the movement direction8of the mould back into the mould section7, whereby the corresponding seal relative to the cylindrical external face37formed by the half-shells36is immediately achieved. The details of this transportation are shown and described in U.S. Pat. No. 5,693,347 A and U.S. Pat. No. 4,212,618 A, to which reference may be made.

As emerges, in particular fromFIG. 3, two respective half-shells36,36aare positioned and centered with respect to one another by means of adjusting pins52and connected to one another by means of screws53, whereby two half-shells36and36ain each case extend over the full periphery, in other words form a type of pipe portion.

The half-shells36and36ain each case have flanges54,54a,54bat their ends, two flanges54,54aresting against one another in the direction of the axis11in each case being connected to one another by means of screws55. The entirety of the half-shells36,36ais supported by means of the individual flanges54,54a,54brelative to the nozzle support body33in the radial direction and mounted by means of the screws53on the external nozzle ring30.

The seals49are in each case arranged in the joint between two flanges54or54aresting against one another in the axial direction and clamped by means of the screws55and56.

The embodiment according toFIG. 4differs from that according toFIG. 2only with respect to structural details. Structurally identical parts are therefore provided with the same reference numerals as inFIG. 2. If the parts are functionally the same but structurally slightly different, the parts are designated by the same reference numerals as inFIG. 2but with an apostrophe. Reference can therefore entirely be made to the above description.