Abstract:
In the production of a nozzle cartridge with a nozzle formed thereon in a hollow mold, in which a core ( 26 ) is located, a centering of the core ( 26 ) occurs in an injection phase by utilizing webs ( 40 ) provided on the hollow mold, with a conical centering surface ( 39 ) of the core ( 26 ) abutting against them. In a subsequent supplementary filling phase, the core ( 26 ) or an interior core ( 28 ) is withdrawn, the melt flowing over the webs ( 40 ) and forming a closed wall in the area of the nozzle base.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional U.S. application of Ser. No. 09/003,133 filed on Jan. 6, 1998, and now U.S. Pat. No. 6,033,615. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention refers to a method for producing a nozzle cartridge which can be used as a container for pressing out flowable or thixotrop materials, as well as a device for producing a nozzle cartridge, and finally also a nozzle cartridge. 
     BACKGROUND OF THE INVENTION 
     The cartridges used for pressing out flowable or thixotrop materials, e. g. sealing materials, have a cylindrical cartridge body limited at one end by an annular shoulder having an outlet connection projecting therefrom. As a separate part, a nozzle is screwed on the outlet connection provided with an external thread. There are also known nozzle cartridges in which the nozzle is an integral part of the cartridge and is produced integrally therewith. Such nozzle cartridges have the advantage that it is not necessary to mold a complicated thread. 
     The production of nozzle cartridges takes place by injecting a melt into a mold consisting of an exterior hollow mold and an interior core. In this process, the molten plastic is injected into the mold at a very high pressure, and the thermoplastic then becomes solid by cooling in the mold. A special problem is keeping the core centered in the mold. The core, which does not only fill out the interior of the future cartridge body but also the interior of the nozzle, extends from a core support like a cantilever and projects into the hollow mold. An even wall thickness of the cartridge is only achieved if the core remains exactly centered in the hollow mold. With the applied pressures and the resulting high forces, it is extremely difficult to maintain the central position of the core. A deviation of the core from its central position would result in an uneven distribution of wall thickness of the cartridge. 
     During production of cartridges comprising a threaded connection, the core is supported at the end of the threaded connection, and the melt is injected into the mold from this end. However, in the case of nozzle cartridges, because of the long structural shape of the nozzle and because of the small diameter at the end of the nozzle, it would not be sufficient to support the core at the end of the nozzle to center the core in an exact manner during the injection process. Therefore, it has been tried to inject nozzle cartridges in one piece by providing two injection locations in the area of the annular shoulder. However, this is not a satisfactory solution to the problem of centering. 
     SUMMARY OF THE INVENTION 
     The invention is based on the objective to provide a method for producing a nozzle cartridge by injecting a melt into a mold, in which an exact centering of the mold core is ensured. 
     The invention proposes a method for producing a nozzle cartridge comprising a cylindrical cartridge body ending in an annular shoulder and a tapering nozzle projecting from the annular shoulder, by injecting a melt into a mold comprising a hollow mold and a core, the core or a part thereof being supported, in a first injection phase, on the hollow mold in a centering area at the transition between annular shoulder and nozzle by conically centered webs and the core, or a part thereof, being supported, in a filling-up phase, at a distance from the centering area to fill up the areas kept free by the webs during the injection phase. 
     In the method according to the invention, the core (or a part thereof) is pressed in the transitional area between the annular shoulder and the nozzle against centering webs of the hollow mold, and thereby the core is centered relatively to the hollow mold. From this transitional area, the nozzle part of the core projects forward. Thus, the area in which the core is supported is not located at the end of the core but in the area of the annular shoulder. At this location, the diameter of the core is relatively large, so that an exact centering by simple measures is possible. The core is supported to be centered by appropriate webs provided either at the core or at the hollow mold in the area of support. The melt coming from the nozzle passes between these webs towards the cartridge body. Initially, the webs cause interruptions to be produced at the annular shoulder of the cartridge. Therefore, it is only in the injection phase that the webs are held against a centering surface. Then the counterpressure supporting the core during the injection phase is terminated so that the core withdraws a short distance under the pressure of the melt and the webs obtain a distance from the centering surface. In this process, the annular shoulder of the cartridge is completed by further advancing the melt due to the pressure of the melt during a supplementary filling phase. 
     By the method according to the invention, it is achieved to produce a nozzle cartridge by centering the core in particular in the area of the annular shoulder (base of the nozzle) so that a complete centering exclusively at the extreme end of the cartridge is avoided. 
     The invention further refers to a device for producing a nozzle cartridge. In this device, the core consists of two parts. Namely, it consists of an interior core for the nozzle portion and an exterior core for the cartridge body. The interior core is controlled such that it rests against the hollow mold during the injection phase in a central area at the transition between annular shoulder and nozzle and maintains a distance from the hollow mold during a supplementary filling phase. Thus, in this context, the position of the exterior core remains unchanged during the injection phase. The interior core serves to center the exterior core and as a shaping tool for the nozzle area. The centering core is axially displaceable in the exterior core to be able to assume different positions. 
     Finally, the invention also refers to a nozzle cartridge with a cartridge body ending in an annular shoulder and a tapering closed nozzle projecting from the annular shoulder. According to the invention, a conical nozzle base reinforced by ribs is arranged in the transition portion between the annular shoulder and the nozzle. The nozzle base forms a conical transition portion with a sufficient thickness to form a steam lock for a sufficient storage time of the future charge. The ribs reinforce the transition, keeping the nozzle in position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described with reference to the accompanying drawings, wherein 
     FIG. 1 shows a schematic longitudinal section of the mold during the injection phase, 
     FIG. 2 shows an enlarged segment of FIG. 1, 
     FIG. 3 shows the segment of FIG. 2 during the supplementary filling phase, 
     FIG. 4 shows a segment along the line IV—IV of FIG. 3, and 
     FIG. 5 shows a perspective representation of the nozzle cartridge produced. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Before the production method is explained, there at first is given a description of the nozzle cartridge represented in FIG.  5 . The nozzle cartridge comprises an elongated tubular cylindrical cartridge body  10  open at one end  11 , while the opposite end is limited by an end wall in the shape of an annular shoulder  12 . The annular shoulder  12  surrounds a conical nozzle base  13  having a wall surface inclined by about 400. The annular nozzle base  13  borders on the nozzle  14  consisting of an elongated, slightly conically tapering tube. The nozzle  14  ends in a nozzle tip  15  where it can be cut off to expose the nozzle opening with a choosable diameter. The nozzle tip  15  ends in a tip portion  16 . The entire cartridge consists of an integral part of plastic. 
     To produce the nozzle cartridge, the mold  20  represented in FIG. 1 is used. This mold  20  comprises a hollow mold  21  consisting of a main portion  22  and a head portion  23 . Main portion  22  and head portion  23  abut against each other along a separation surface  24 . The two portions  22  and  23  can be moved apart axially to eject the finished nozzle cartridge. The head portion  23  comprises a supply channel  25  axially extending towards the tip portion  17  and through which the melt is introduced to the mold cavity at a very high pressure to flow from the tip portion  17  to the rear end  11  of the cartridge body. 
     The mold  20  further contains a core  26  consisting of a tubular exterior core  27  and an interior core  28  extending through the exterior core. The exterior core  27  serves to shape the interior surface of the cartridge body  10  and the interior core  28  serves to form the interior surface of the nozzle  14 . The interior core  28  therefore comprises an extension  29  axially projecting from the exterior core  27  and shaping the nozzle  14 . Furthermore, the interior core  28  serves to center the exterior core  27 . 
     The exterior core  27  projects from a core support  30  pressed against the rear end of mold portion  22 , the separation line being referred to as  31 . The core support  30  can be pulled out of the hollow mold  21  together with the core  26 . It comprises a cylindrical space  32  in which a piston  33  connected to the interior core  28  is axially displaceable. The piston  33  is controlled as a function of the injection process. In FIG. 1, the piston  33  is represented in its advanced position in solid lines, while it is represented in its retracted position in dotted lines. The distance between the two positions can amount to about 2-3 mm. 
     As can be seen from FIG. 2, the interior surface of the annular shoulder  12  is formed by a slightly conical frontal surface  35  of the exterior core  27 , while the exterior core of the annular shoulder is formed by a slightly conical frontal surface  36  of the head piece  23  of the hollow mold. The frontal surfaces  35 ,  36  are parallel towards each other. The interior core  28  extends fittingly in a bore of the exterior core  27 . In the advanced state according to FIG. 2, a part  38  of the cylindrical longitudinal section of the interior core  28  projects beyond the frontal surface  35 . This part  38  borders on a conical centering surface  39  merging into the extension  29 . The cone angle of the centering surface  39  amounts to about 400. 
     In the injection phase, which is represented in FIG. 2, the centering surface  39  of the interior core  28  rests against conically arranged radial webs  40  projecting in a centering area  41  at the place of transition between annular shoulder  12  and nozzle  14  as extensions from an interior cone surface  42  of the hollow mold.. The interior cone surface  42  and the abutment surfaces of the webs  40  run parallel to the centering surface  39 . As can be seen from FIG. 4, there is a channel  43  between any two webs  40  through which the melt gets from the mold cavity of the nozzle  14  into the mold cavity of the annular shoulder  12 . 
     While the piston  33  is hydraulically held in its advanced position, the melt is injected at a very high pressure of 1500 to 2000 bars within a very short time (less than 0.4 sec.) from the supply channel  25  into the mold cavity of the nozzle cartridge. In this process, the melt at first gets centrically into the mold cavity for forming the tip portion  16  and then continues to flow in the annular space for forming the nozzle  14 . For centering the tip  45  of the extension  29 , there are provided on the head piece  23  three webs  46  projecting radially into the mold cavity, the tip  45  abutting against the webs in the injection phase. In this manner, the extension  29  is centered both at its base in the centering area  41  and at its tip  45 . In this process, the melt flows past the webs  40  and  46 . 
     After the melt has arrived at the rear end of the cartridge body  10  and fills the entire mold cavity, the piston  33  is relieved so that it withdraws together with the interior core  28  under the pressure of the amorphous melt. In this phase, the injection is already finished, and the supplementary filling phase takes place, during which the melt continues to flow into the mold. Now the interior core is no longer centered by the centering surfaces, but by the plastic already solidified in part. This state is represented in FIG.  3 . The centering surface  39  now is at a distance from the webs  40  and the tip  45  also is at a distance from the webs  46 . In the supplementary filling phase, additional melt is injected through the supply channel  25  before the melt injected in the first injection phase is solidified completely. That is why melt now gets under the webs  40  and  46 , thereby closing the wall is closed in the area of the nozzle base  13  and in the tip portion  16 . 
     After the supplementary filling phase has been finished and the melt has cooled off in the cooled mold  20 , the mold portions  22  and  23  are moved apart so that the nozzle  14  is exposed at the outside. Then the core  26  is pulled out of the mold  20  together with the nozzle cartridge, and the finished nozzle cartridge can be taken off the core. 
     Those locations which were kept free by the webs  40  during the injection phase form ribs  50  (FIG. 5) on the finished nozzle cartridge, which are raised on the conical nozzle base  13 . The conical nozzle base  13  consists of that surface which was formed in the supplementary filling phase by injecting melt behind the ribs  50 .