1. Field of the Invention
The invention relates to an apparatus of continuously producing a composite pipe with a pipe socket,
2. Background Art
An apparatus of this type is for example known from U.S. Pat. No. 7,238,317 B1. The greater the nominal widths of corrugated pipes, the more grow the elevations and thus the increase in size of the pipe socket in relation to the inside diameter of the composite pipe. This is due to the fact that the standard composite pipe is very often used as a spigot, meaning that a composite pipe is inserted by its elevations into the socket. The transition portions between the composite pipe disposed upstream during in-line production and the pipe socket on the one hand, and the pipe socket and the downstream composite pipe on the other, possess considerable radial extension. In particular the transition portion between a composite pipe and socket, which remains after separation of the extruded continuous run of pipe, must possess pronounced radial extension i.e., must be directed steeply outwards in relation to the central longitudinal axis, so that, upon insertion of the spigot into the socket as far as to the transition portion, there will be no dead space, nor considerable dead space, where dirt might deposit. The greater the nominal widths and/or the higher the production rate, the greater the risk that the internal tube does not adhere by its full face to the external tube in the vicinity of the transition portion and at the beginning and end of the socket. In the apparatus disclosed in U.S. Pat. No. 7,238,317 B1, these problems were solved by providing a recess in the at least one annular rib for connecting the transition area with the adjacent annular mold recess. This provides for evacuation of the space between the internal tube and the external tube in the vicinity of the transition portion, strictly speaking at the transition between the composite pipe and the pipe socket, to ensure that the pressure exerted on the internal tube from outside causes the entire surface of the internal tube to be pressed against the corresponding region of the external tube to which it is welded. This solution proved to be exceptionally suitable. In particular in the case of very large nominal pipe widths, problems may still occur when molding the pipe socket for twin-wall composite pipes.
Thus it is the object of the invention to develop an apparatus of the generic type such that even in the case of large nominal widths, a good molding of the pipe socket is achieved.
This object is attained according to the invention in that the distance a of the inner die from the outer die with respect to the extension b of the socket recess in the conveying direction is such that a≧b. The gist of the invention is that the apparatus is designed such that the molding of the pipe socket from the internal tube leaving the inner die does not start until the external tube leaving the outer die is in full contact with the socket recess in the vicinity thereof and this contact with the two annular ribs defining the socket recess is well sealed. In the vicinity of the pipe socket to be molded, the external tube already has its defined shape when the portion of the internal tube is extruded which is used for molding the pipe socket. The distance of inner die and outer die may naturally be increased even more so that the external tube already covers several upstream and downstream annular ribs when the extrusion of the internal tube, which is to be molded into the pipe socket, starts.
Further features, advantages and details of the invention will become apparent from the following description of an exemplary embodiment by means of the drawing.
The installation shown in
Downstream of the extruders 1, 2 as seen in the conveying direction 4, provision is made for a molding machine 6, a so-called corrugator, which is followed by an aftercooler 7. A crosshead 8, which projects into the molding machine 6, is mounted on the extruder 1 which is in alignment with the molding machine 6 and the aftercooler 7. The other extruder 2, by the side of the extruder 1, is connected to the crosshead 8 by way of an injection channel 9 which discharges laterally into the crosshead 8. As diagrammatically outlined in
The design of the molding machine 6 is known and common practice. It is described for example in U.S. Pat. No. 5,320,797, to which reference is made explicitly. It substantially comprises a machine bed 11 with half shells 12, 12′ disposed thereon, which are joined to each other, constituting two so-called chains 13, 13′. These chains 13, 13′ are guided along deflection rollers (not shown) at the upstream inlet 14 and the downstream outlet 15 seen in the conveying direction 4. When circulating in the conveying direction 4, they are guided such that every two half shells 12, 12′ are united into a pair, with pairs of shells closely succeeding to each other in the conveying direction 4. A drive motor 17 serves for actuation of the half shells 12, 12′ which are united on a molding path 16, forming pairs of shells.
The crosshead 8 comprises two melt channels which are concentric of a joint central longitudinal axis 18, namely an inner melt channel 19 and an outer melt channel 20 which, seen in the conveying direction 4, terminate downstream in an inner die 21 and outer die 22. The inner melt channel 19 is connected to an injection channel 23 of the extruder 1 which is in alignment with the molding machine 6, whereas the outer melt channel 20 is connected to the injection channel 9 of the other extruder 2. Between the inner die 21 and the outer die 22, a gas duct 24 discharges from the crosshead 8, the gas duct 24 on the one hand being connectable by way of a valve to a source of compressed gas for so-called stabilizing air to be blown in or on the other hand to atmosphere.
A calibrating mandrel 25, which is also concentric of the axis 18, is mounted on the extrusion head 8 at the downstream end thereof seen in the conveying direction 4. It has cooling channels 26 for cooling water which is supplied via a cooling-water flow pipe 27 and led off via a cooling-water return pipe 28. Further provision is made for an air pipe 29 connected to a gas gap 30 which serves as an additional gas duct and, as seen in the conveying direction 4, is located directly downstream of the inner die 21 between the extrusion head 8 and the calibrating mandrel 25. The pipes 27, 28, 29 pass through an approximately tubular supply channel 31 which is provided in the extrusion head 8 concentrically of the axis 18.
The half shells 12, 12′ have annular mold recesses 32, 32′ that succeed to each other at regular distances, each of them being connected to partial-vacuum channels 33. Upon arrival of the half shells 12, 12′ on the molding path 16, the partial-vacuum channels 33 reach partial-vacuum supply sources 35 and 36 so that partial vacuum is applied to the mold recesses 32.
The plastic melt, which is supplied by the extruder 2 through the injection channel 9 and to the extrusion head 8, flows through the outer melt channel 20 to the outer die 22 where it is extruded, forming an external tube 37. Owing to the partial vacuum, this tube 37 gets seated in the mold recesses 32, 32′, forming a tube that is provided with annular elevations 38. Plastic melt is supplied from the extruder 1 through the injection channel 23 to the extrusion head 8, flowing through the inner melt channel 19 towards the inner die 21 where it discharges as an internal tube 39 that approaches the calibrating mandrel 25. The calibrating mandrel 25 expands slightly outwards from the inner die 21 on in the conveying direction 4 until the internal tube 39 bears against the corrugation troughs 40 of the external tube 37 where both of them are welded together. Once cooled and solidified, the internal tube 39 and the external tube 37 constitute the composite pipe 10.
As in particular shown by
As far as described hereinbefore, the apparatus is substantially known from U.S. Pat. No. 6,458,311 B1 and U.S. Pat. No. 7,238,317 B1 which are expressly referred to.
As seen in
As illustrated by
As illustrated by
By locally defined allocation to the socket recess 42, a rod-shaped switch member 55 is connected to the corresponding half shell 12, operating a switch 56 by means of which to modify the speed and thus the extrusion rate of the extruders 1, 2 and by means of which to supply the gas duct 24 and the gas gap 30. To this end, an arm 57 is mounted on the molding machine 6, running in the conveying direction 4 above the half shells 12, 12′. This is where the switch 56 is mounted which is operated by the switch member 55. As seen in
Upon manufacture of the standard corrugated composite pipe 10 in the way seen in
When the aforementioned low over pressure is applied to the gas duct 24, a partial vacuum or a low over pressure is simultaneously applied to the gas gap 30. A partial vacuum is in particular applied to the gas gap 30 if the plastic material used for the hoses 37, 39 is a polyethylene or a polypropylene material. The partial vacuum at the calibration mandrel ensures that a smooth inner surface of the internal tube 39, and ultimately of the internal pipe 39′, is maintained. This process is referred to as the so-called vacuum calibration. When PVC is used as plastic material for the production of the hoses 37, 39, it is suitable to apply a low over pressure of 0.05 to 0.15 bar above atmospheric pressure to the gas gap 30. This pressure is thus lower than the one which is applied to the gap 58 between internal tube 39 and external tube 37 via the gas duct 24. When the aforementioned plastic material is used, the low over pressure in the internal tube 39 prevents the internal tube 39 from adhering to the calibration mandrel 25 before it is welded with the external tube 37.
When the standard corrugated composite pipe 10 is produced as described above, the extruders 1, 2 are operated at a defined speed, in other words they extrude in each case a constant mass flow of plastic melt per unit time.
When the transition area 44 moves into the vicinity of the outer die 22 at the instant seen in
When the transition area 44 reaches the inner die 21, corresponding approximately to the illustration of
At the same time, the over pressure is removed from the gas duct 24 which is then connected to atmosphere for evacuation of the gap 58 between internal tube 39 and external tube 37 in the vicinity of the socket recess 42. The internal tube 39 is pressed outwards against the external tube 37. As also shown in
As can be seen from
When the transition area has passed the inner die 21, the drive motor 3 of the extruder 1 is being triggered in such a way that for instance its speed rises, which means that the flow rate per unit time of the plastic melt is increased. Consequently, more plastic melt per unit length is supplied to the internal tube 39 in the vicinity of the produced socket 41 than in the vicinity of the standard corrugated composite pipe 10 where only the smooth internal pipe 39′ is made from it.
When the transition area 47 of the socket recess 42 passes the outer die 22, the extrusion rate of the extruder 2 that delivers the external tube 37 is being set back to the original rate. The extruder 2 again supplies the amount per unit time of the plastic melt that is necessary for producing the elevations 38. The external tube 37 rests on the transition area 47 and the connecting grooves 53 formed therein, thus producing connecting passages 62 in the external tube. Then the external tube bears against the annular rib 49 and is molded into the slotted recesses 51, forming overflow channels corresponding to the overflow channels 59.
When the transition area 47 reaches the inner die 21, then the gas pressure that acts at the gas gap 30 is again reduced and compressed air and so-called stabilizing air is applied to the gas duct 24, which means the process returns to conditions that prevail upon manufacture of the standard composite pipe 10. When the transition area 47 has passed the inner die 21, the drive motor 3 is being triggered, whereby the extrusion rate of the extruder 1 is reduced to the original rate so that again the amount of plastic melt per unit time is extruded that is needed for manufacture of the smooth internal pipe 39′.
The endless, in-line molded composite pipe 10 shown in
Number | Date | Country | Kind |
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20 2007 016 630.3 | Nov 2007 | DE | national |