Method for producing a tube and injection-molding device

Abstract

The invention relates to a method for producing a tube by injection molding a thermoplastic molding compound by using an injection-molding device with an article cavity, which defines the outer contour of the tube, and with an injection device, which is designed to drive a profile through the article cavity filled with the thermoplastic molding compound and thereby displace a liquid core of the molding compound, wherein the method envisages closing an opening of the article cavity with a mould core, which with the article cavity forms a hollow mould space and which has a secondary cavity that can be filled with the molding compound. After the filling of the article cavity and the hollow mould space with the thermoplastic molding compound, a projectile is driven through the article cavity, wherein the projectile displaces the molding compound into the secondary cavity. Subsequently, the mould core with the filled secondary cavity is pulled, wherein the displaced molding compound is separated from the molding compound forming the tube. The invention also relates to an injection-molding device for carrying out the method.

Claims

1. A method for producing a tube by injection molding a thermoplastic molding compound while using an injection molding device having an article cavity which defines an external contour of the tube, having an injection device which is configured for driving a projectile through the article cavity that is filled with the thermoplastic molding compound while displacing a liquid core of the molding compound, wherein the method comprises introducing the projectile into a first opening of the article cavity; closing a second opening of the article cavity, disposed so as to be remote from the first opening, by way of a mold core which together with the article cavity forms a molding cavity and which has a secondary cavity that is fillable with the molding compound, wherein the molding cavity is formed partially in an area between the article cavity and the mold core; at least partially filling the article cavity and the molding cavity with the thermoplastic molding compound; driving the projectile from the first opening through the article cavity to the second opening while partially displacing the molding compound into the secondary cavity, wherein the projectile is driven toward or into the mold core, and a thin place or a predetermined breaking line is generated between the molding compound that forms the tube and the molding compound that is displaced into the secondary cavity; and pulling the mold core together with the filled secondary cavity, wherein, by the pulling of the mold core, the displaced molding compound is separated from the molding compound that forms the tube.

2. The method as claimed in claim 1, wherein the secondary cavity of the mold core is kept closed during the filling of the article cavity.

3. The method as claimed in claim 1, wherein the secondary cavity is opened immediately prior to the projectile being driven through the article cavity.

4. The method as claimed in claim 1, wherein the secondary cavity is opened with the aid of the melt pressure that is generated by the displaced molding compound.

5. The method as claimed in claim 2, wherein the mold core has a movable closure member which keeps closed the secondary cavity and immediately prior to the article cavity being filled, or while the article cavity is being filled, is moved into an opened position that releases the secondary cavity.

6. The method as claimed in claim 1, wherein the projectile is driven into the secondary cavity and in the terminal position closes the secondary cavity.

7. The method as claimed in claim 1, wherein the projectile is driven partially into the secondary cavity, wherein a shell area of the projectile is brought to bear against a pinch edge of the mold core, the projectile in this terminal position closing the secondary cavity.

8. The method as claimed in claim 1, wherein the projectile is driven partially into the secondary cavity, wherein an encircling shoulder of the projectile is brought to bear against an end side of the mold core, wherein the projectile in this terminal position closes the secondary cavity.

9. The method as claimed in claim 7, wherein the projectile has a perforated shell area in which the thermoplastic molding compound can accumulate, wherein the molding compound when curing connects to the projectile.

10. The method as claimed in claim 9, wherein an undercut blind bore is provided in the shell area of the projectile.

11. An injection molding device, in particular for carrying out the method as claimed in claim 1, for producing tubes, having a tool that forms an article cavity, having means for filling the article cavity with a thermoplastic molding compound, having an injection device for injecting a fluid toward a projectile that is to be driven from a first opening of the article cavity through the article cavity in the direction toward a second opening of the article cavity, having a secondary cavity for receiving the molding compound that is displaced by the projectile, having a mold core which is insertable into the second opening and which together with the article cavity forms a molding cavity that is capable of being filled with the molding compound, wherein the mold core encloses a volume which forms the secondary cavity, and that the volume of the secondary cavity has a cross section which is smaller than or approximately equal to the cross section of the projectile, wherein an internal delimitation wall of the secondary cavity is provided with at least one depression and/or an embossed feature.

12. The injection molding device as claimed in claim 11, wherein the secondary cavity is configured as a prismatic or cylindrical volume.

13. The injection molding device as claimed in claim 11, wherein the mold core has a closure member that is disposed so as to be adjustable in said mold core and in a first position closes the secondary cavity and in a second position releases the secondary cavity.

14. The injection molding device as claimed in claim 11, wherein the mold core at the end side has a wiper lip that projects into the secondary cavity.

15. The method as claimed in claim 1, wherein the thermoplastic molding compound is selected from the group comprising high-density polyethylene, polyamide, polyamide 6, polyamide 12, polyurethane, polycarbonate, acrylonitrile-butadiene-styrene-copolymer, polyketone, and polystyrene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained hereunder with reference to the exemplary embodiments illustrated in the drawings in which:

(2) FIG. 1 shows a partial sectional view of an injection molding device 1 according to the invention and according to a first exemplary embodiment;

(3) FIG. 2 shows a partial sectional view of an injection molding device according to the invention and as per a second exemplary embodiment; and

(4) FIGS. 3a and 3b show a partial sectional view of an injection molding device according to the invention and as per a third exemplary embodiment of the invention.

DETAILED DESCRIPTION

(5) The method according to the invention will be explained hereunder with reference to the figures that represent parts of an injection molding device 1.

(6) To this end, reference is first made to FIG. 1 which shows a partial section through an injection molding device 1 according to the invention. The injection molding device 1 comprises a tool 2 which is only indicatively illustrated in the figures and, for example, comprises two halves which in the closed state define an article cavity 3 which forms a negative of a tube 4 to be fabricated.

(7) The figures show an end of the article cavity 3 in the region of an end of the tube 4. In particular, the figures show that end of the tube 4 to be molded which is widened in the manner of a sleeve and has a connection geometry for receiving a connector component. That end of the article cavity 3 that is disposed so as to be remote from a sprue (not shown) and from a first opening having an injection device is illustrated in figures.

(8) The tool 2 of the injection molding device 1 is composed, for example, of two mold halves which define the article cavity 3, wherein the article cavity 3 is configured as the negative of a tube (3D tube) that is curved multiple times in space. The tool can have a plurality of movable components in the form of slides or the like, which are not illustrated in the drawing. An injection device for injecting a fluid toward a projectile 5 that is to be driven through the article cavity 3 is provided on that end of the tool 2, or of the article cavity 3, respectively, that is not illustrated, wherein the injection device comprises a projectile carrier having at least one injection nozzle and having at least one projectile receptacle for the projectile 5 as the displacement member for a thermoplastic molding compound that is to be filled into the article cavity 3.

(9) The article cavity 3 at the second end of the article cavity 3 that is illustrated in the figures is widened in the manner of a funnel or sleeve. The article cavity 3 in this region forms a second opening 6 into which a mold core 7 is inserted such that the latter seals the article cavity 3 in the region of the second opening 6.

(10) The mold core 7 in the position thereof that seals the article cavity 3 is shown in FIG. 1. The mold core 7 is capable of being demolded or pulled, respectively, from this position into a position that releases the article cavity 3. This position of the mold core 7 is not illustrated in the drawings.

(11) The mold core 7 is configured as a calibrating mandrel that is circular in the cross section. The mold core 7 in the region of the widening of the article cavity 3 forms a molding cavity which is configured as an annular space 8. The connection cross section of the tube 4 thus formed is configured as a sleeve that is circular in the cross section; however, the invention is to be understood such that this region of the tube 4 can have any other arbitrary shape, depending on the design of the article cavity 3 and of the mold core 7 in this region of the tool 2.

(12) The mold core 7 encloses a preferably cylindrical volume 9 which forms a secondary cavity of the tool 2. The volume 9 of the mold core 7 is dimensioned such that said volume 9, as will yet be described hereunder, can receive completely the molding compound that is displaced by the projectile 5. Only parts of the mold core 7 are illustrated in the figures; the size ratios are neither true to scale nor proportional; FIG. 1 shows only a schematic view of parts of the tool 2.

(13) The volume 9 of the mold core that serves as the secondary cavity is preferably configured so as to be cylindrical and forms an extension, or an appendage, respectively, of the article cavity 3. The volume 9 of the mold core 7 is oriented so as to be coaxial with and aligned to the article cavity 3 and in the case of the exemplary embodiments illustrated in FIGS. 1 and 2 has an internal diameter which corresponds to the internal diameter of the article cavity 3 and to the external diameter of the projectile 5. When the article cavity 3 and the volume 9 of the mold core 7 have a polygonal or prismatic internal contour, the external contour of the projectile expediently corresponds to the internal contour of the article cavity and of the secondary cavity.

(14) The volume 9 of the mold core 7 in all figures is illustrated in the open state; the projectile 5 in this state is in each case shown in the terminal position thereof.

(15) In the case of the exemplary embodiment illustrated in FIGS. 1 to 3 the mold core 7 comprises a movable and cylindrical closure member 10 which in FIGS. 1 to 3 is in each case shown in an opened position in which the closure member 10 in each case releases the volume 9 of the mold core 7.

(16) At the start of the method according to the invention, the closure member 10 is located in a position in which the latter terminates so as to be flush with an end face 11 of the mold core 7. The closure member 10 is disposed so as to be adjustable within the mold core 7; for example, the closure member 10 by way of a mechanism (not illustrated) is hydraulically or pneumatically adjustable between two terminal positions. In that position of the closure member 10 that is not illustrated, said closure member 10 in this position closing the volume 9 of the mold core, filling of the article cavity 3 with a thermoplastic molding compound is performed by way of a sprue that is disposed so as to be remote from the end of the article cavity 3 shown.

(17) Once the article cavity 3 has been completely or partially filled, the molding compound extends across the entire cross section of the article cavity and into the annular space 8. The closure member 10 thereafter is moved into an opened position illustrated in FIG. 1, in which the volume 9 of the mold core 7 is released, consequently forming a secondary cavity that is not filled.

(18) The projectile 5 thereafter is impinged with a fluid, for example with water, and is driven through the article cavity 3, wherein said projectile 5 displaces a liquid core of the thermoplastic molding compound that is filled into the article cavity 3 into the volume 9 of the mold core. FIG. 1 shows the projectile 5 in the terminal position thereof, in which said projectile 5 has been driven into the volume 9 of the mold core 7. The thermoplastic molding compound herein is shorn off on an internal encircling edge 12 of an opening 13 of the volume 9 of the mold core 7, wherein the projectile 5 between the latter and the internal enclosing wall of the volume 9 configures a thin film of molding compound. Part of the molding compound herein is displaced into depressions 14 on the internal delimitation wall of the volume 9 of the mold core 7.

(19) In a further method step, the mold core 7 is pulled out of the article cavity 3 in the direction of the arrow 15, wherein the molding compound which has been displaced into the depressions 14 and which in the meantime has at least partially solidified, resists said extraction movement of the mold core 7. As a result thereof, traction is exerted on the material film of the molding compound that has solidified in the meantime and projects into the volume 9 of the mold core 7. As a result thereof, the projecting material is torn off. The molding compound that has displaced into the volume 9 is thus separated from the molding compound that forms the tube 4 by way of the mold core 7.

(20) Further mold slides which protrude laterally into the article cavity 3 and toward the mold core 7 laterally generate windows in the sleeve of the tube 4 thus molded are identified by the reference sign 16.

(21) The exemplary embodiment of the injection molding device 1 according to the invention illustrated in FIG. 2 corresponds substantially to the exemplary embodiment of the injection molding device 1 illustrated in FIG. 1, wherein the same components are identified by the same reference signs. The exemplary embodiment illustrated in FIG. 2 differs from that exemplary embodiment illustrated in FIG. 1 in that the mold core 7 at the end side has a wiper lip 17 that projects into the opening 13 of the volume 9, the projectile 5 when being driven into the volume 9 shearing the thermoplastic molding compound between the projectile 5 and the internal delimitation wall of the volume 9 on said wiper lip 17.

(22) The exemplary embodiment illustrated in FIG. 3 corresponds substantially to that in FIGS. 1 and 2, wherein the same components are provided with the same reference signs.

(23) The projectile 5 in the case of the exemplary embodiment according to FIG. 3a has a perforated shell area in which thermoplastic molding compound can accumulate. The thermoplastic molding compound, when curing, connects to the projectile such that the projecting material is torn off when the mold core 7 is pulled. To this end, the shell area of the projectile 5 can have a blind bore 19, for example. The blind bore forms an undercut which causes the curing molding compound to be anchored.

(24) Moreover, the opening 13 of the volume 9 has a diameter that is slightly smaller than that of the article cavity 3 and than the largest diameter of the projectile 5, such that the encircling edge 12 that delimits the opening 13 forms a pinch edge on which the projectile 9 severs the thermoplastic molding compound.

(25) The invention is to be understood such that the particular design embodiment of the projectile and the configuration of the opening 13 of the volume 9 are measures which can be implemented in a mutually independent manner.

(26) The variant of the injection molding device shown in FIG. 3b differs from that in FIG. 3 in that the projectile 5 has an encircling shoulder 18 which impacts on the end face 11 of the mold core 7. The diameter of the opening 13 of the volume 9 is smaller than the diameter of the article cavity 3 also in the case of this exemplary embodiment.

LIST OF REFERENCE SIGNS

(27) 1. Injection molding device 2. Tool 3. Article cavity 4. Tube 5. Projectile 6. Second opening 7. Mold core 8. Annular space 9. Volume of the mold core 10. Closure member 11. End face 12. Edge 13. Opening of the volume 14. Depressions in the internal delimitation wall of the volume 15. Arrow 16. Mold slide 17. Wiper lip 18. Shoulder 19. Blind bore