• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to a method for producing injection-molded parts made of plastic with an injection molding tool, wherein the plastic melt in the form of at least one strip-shaped melt strand is injected through a nozzle slot (2) into a cavity (15) of the injection mold before the injection molded part is removed from the mold after solidification of the plastic melt becomes. In order to ensure advantageous process conditions, it is proposed that heat is supplied to the plastic melt during the solidification in the cavity (15) in the sprue area and that the sprue during demoulding of the injection molded part due to the temperature gradient between the solidified injection molded part and the plastic melt in the sprue of the nozzle slot (2) is torn off.
    公开号:AT520389A2
    申请号:T50960/2018
    申请日:2014-09-10
    公开日:2019-03-15
    发明作者:
    申请人:Haidlmair Holding Gmbh；
    IPC主号:
    专利说明:

    Summary
    The invention relates to a method for producing injection molded parts made of plastic using an injection molding tool, the plastic melt being injected in the form of at least one ribbon-shaped melt strand through a nozzle slot (2) into a cavity (15) of the injection molding tool before the injection molded part is removed from the mold after the plastic melt has solidified becomes. In order to ensure advantageous process conditions, it is proposed that characterized in that heat is supplied to the plastic melt during solidification in the cavity (15) in the sprue area and that the sprue during demolding of the injection molded part due to the temperature gradient between the solidified injection molded part and the plastic melt along the sprue area the nozzle slot (2) is torn off.
    (Fig. 2) / 14
    41850 (II)
    The invention relates to a method for producing injection molded parts made of plastic with an injection molding tool, the plastic melt being injected in the form of at least one ribbon-shaped melt strand through a nozzle slot into a cavity of the injection molding tool before the injection molded part is removed from the mold after the plastic melt has solidified.
    So that the plastic melt in the injection molding nozzle does not cool down in injection molding tools, it is known (DE 26 07 644 A1) to use a heatable nozzle core which is coaxial with the nozzle opening and which ends in a conical tip, so that the housing of the injection molding nozzle has a circular nozzle opening between the housing and the conical tip of the nozzle core there is an annular channel for the plastic melt which tapers in the direction of flow and opens out in the circular nozzle opening of the housing. A disadvantage of such injection molding nozzles is that the melt throughput that can be achieved is limited because an increase in the flow rate leads to greater shear stress on the plastic melt in the nozzle channel and thus to additional heating of the plastic melt with the risk of material damage. If, on the other hand, the nozzle opening is enlarged, higher melt temperatures in the center area of the nozzle opening with the consequence of an uneven solidification of the melt flow introduced into the cavity of the mold can be expected, which can not only result in a loss of quality of the injection molded part, but also difficulties in the tear-off behavior of the sprue , For these reasons, several injection molding nozzles are used for the production of large-volume injection molded parts, which are comparatively complex
    2.14
    Control and possibly the risk of the occurrence of
    Joined seams in the joint area within the cavity meet more
    Increase melt flows so that on the one hand with material damage in the
    Area of the weld lines and on the other hand with an impairment of the optical
    Appearance of the injection molded parts must be expected.
    In order to be able to inject the plastic melt for plate-shaped injection molded parts into the cavity of the molding tool in a flow that is matched to the shape of the injection molded parts, the plastic melt is introduced into the cavity via a film sprue in a ribbon-shaped strand. The film gate includes a nozzle channel that widens to the length of a nozzle slot opening into the cavity. With the help of such film sprues, the melt throughput through the nozzle opening can be increased, but the film sprue solidifies with the plastic melt in the cavity, so that the film sprue demolded with the injection molded part has to be subsequently separated from the injection molded part.
    In the case of a hot runner nozzle with a slot-shaped nozzle opening, it is known (DE 41 25 975 A1) to heat the housing by means of an external heater, which creates heat conditions in the area of the nozzle slot which make it impossible to tear off the sprue along the nozzle slot when the injection molded part is removed from the mold , Since the housing for receiving the nozzle core forms a cylindrical bore and the nozzle core in the area of this cylindrical bore is designed as a rotating body with a crosspiece, the annular area of the outlet cross section of the distributor channel is equal to the remaining annular area between the nozzle core and the housing, which in connection with the fact that that the crossbar of the nozzle core divides the nozzle slot in the housing into two separate slots located opposite one another and leads to changing flow and temperature conditions over the longitudinal extent of the nozzle slot.
    Finally, nozzle probes with three melting channels open to the outside are known (EP 0 162 438 A1), which are arranged around a heatable core forming a tip. These nozzle probes are not in the area of their tip, but in the area of theirs
    3/14 flat end connected to the cavities of an injection molding tool, in each case via only a single passage opening, which is located in the area of coolant lines. Since there are therefore no nozzle slots for forming band-shaped melt strands, the disadvantages associated with such melt strands, particularly with regard to the tearing off of the sprue when the injection molded part is removed from the mold along the nozzle slot, do not occur at all.
    The invention is therefore based on the object of designing a method for injecting a plastic melt into a cavity in such a way that, even at higher melt throughputs, an advantageous gate break can be ensured without fear of impairing the quality of the injection molded part.
    Starting from a method of the type described at the outset, the invention achieves the object in that heat is supplied to the plastic melt during solidification in the cavity in the sprue area and that the sprue during demolding of the injection molded part due to the temperature gradient between the solidified injection molded part and the plastic melt in The sprue area along the nozzle slot tears off.
    The invention is based on the finding that the shear stress of a plastic melt injected through a slot nozzle into a cavity is comparable to the shear stress in a round nozzle, the diameter of which approximately corresponds to the slot width. The melt throughput can consequently be increased at will by the choice of the width of the band-shaped melt strand without having to fear an increased shear stress with the disadvantageous consequences of an increase in the temperature of the plastic beyond the permissible melt temperatures. A prerequisite for the sprue tear-off when the injection molded part is removed from the mold is, however, that a corresponding temperature gradient can be ensured between the plastic melt solidified in the cooled cavity and the sprue over the entire longitudinal extent of the slot nozzle, so that the mechanical, which is dependent on the temperature
    4.14
    The strength of the plastic in the transition area from the sprue to the injection molded part when it is removed from the mold causes the sprue to tear off in the area of the nozzle opening without pulling threads. Such a setting of the temperature gradient in the transition area from the sprue to the solidified injection molded part is achieved by supplying heat to the sprue, in the area of which the plastic then remains molten in the cooled cavity during the solidification of the injection molded part. The nozzle area that otherwise forms the sprue is therefore part of the hot runner of the injection molding nozzle. The transition from the liquid melt to the solidified plastic body resulting in a thin layer in the area of the nozzle opening leads to a sprue tear-off in the surface of the nozzle opening and thus to a tear along a narrow surface area of the injection molded part, which makes reworking of the tear-off point unnecessary.
    It is essential for an advantageous introduction of the plastic melt into the cavity of an injection mold via a nozzle slot that the melt flow is divided over the length of the nozzle slot from a rheological point of view, because only then can an increase in the melt throughput that is dependent on the slot length be ensured. A simple way of dividing the melt flow over the length of the nozzle slot is by throttling the melt flow. Such a throttling zone can be achieved by narrowing the flow cross section, but also by other measures to increase the flow resistance.
    The temperature of the injection mold is preferably controlled in accordance with the solidification temperature of the plastic used in each case, so that the plastic melt injected into the cavity solidifies to the injection molded part while maintaining short cycle times. The solidification process of the plastic melt in the area of the nozzle slot is of particular importance with regard to the sprue break-off. For this reason, the housing forming the nozzle slot can be cooled in the area of the nozzle slot with the effect that a
    5/14 sets the desired temperature gradient between the solidified injection molded part and the molten sprue in the area of the nozzle slot.
    The method according to the invention is described in more detail with reference to the drawing. Show it
    1 is a partially broken diagram of an injection molding nozzle according to the invention for performing the method according to the invention,
    2 shows this injection molding nozzle in a cross section perpendicular to the nozzle slot, FIG. 3 shows a section along the line III-III of FIG. 2,
    4 shows the nozzle core in a side view,
    Fig. 5 shows the nozzle core of FIG. 4 in an end view
    6 shows a variant of an embodiment of an injection molding nozzle inserted into an injection molding tool in a schematic cross section.
    The injection molding nozzle according to FIGS. 1 to 5 comprises a housing 1, which forms a nozzle slot 2, and a nozzle core 3 accommodated by the housing 1, between which and the housing 1 a nozzle channel 4 tapers in the flow direction, which preferably completely completes the nozzle core 3 encloses. To apply a plastic melt to this nozzle channel 4, the nozzle core 3 has a central feed channel 5, to which the distributor channels 6 provided on the two long sides of the nozzle core 3 connect. However, it would also be possible to feed the two distribution channels 6 separately, not via a branch 7 of a common feed channel 5, for example in order to be able to inject different plastics in layers.
    The distribution channels 6 starting from the branch 7 of the central feed channel 5 each form two symmetrically formed channel branches tapering in the direction of flow, which are flow-connected at their ends to the corresponding channel branches of the opposite distribution channel 6, so that the constructive requirements for advantageously meeting the rheological requirements Flow formation of the
    6/14
    Plastic melt can be created over the entire area of the nozzle slot 2. According to the exemplary embodiment, the distributor channels 6 are designed in the form of a recess which is open towards the housing 1, which not only brings about simple manufacturing conditions, but also good heat transfer from the heated nozzle core 3 to the plastic melt in the region of the distributor channels 6 due to the enlargement by the recesses Ensures surface of the nozzle core 3.
    In order to be able to ensure a desired flow distribution over the longitudinal extent of the nozzle slot 2, the nozzle channel 4 can be supplied with the plastic melt supplied via the distributor channels 6 via a throttle zone 8, via which the distributor channels 6 are connected to the nozzle channel 4. The throttle zone 8 is generally defined by constrictions in the flow cross section, each of which extends over the length of the section of the nozzle slot 2 associated with the distribution channel 6, so that the plastic melt is exposed to predetermined pressure ratios over the entire area of extension of the nozzle slot 2. The throttling effect can differ in order to influence the flow distribution over the flow cross section.
    In order to improve the flow conditions for the plastic melt emerging from the nozzle slot 2, the nozzle core 3 in the region of the nozzle channel 4 can form an inlet section 9 adjoining the throttle zone 8 and a downstream outlet section 10 which has a smaller angle of inclination than the inlet section 9 with respect to the nozzle outflow direction , as can be seen in particular from FIGS. 1 and 5. Due to the smaller angle of inclination of the outlet section 10, the plastic melt undergoes an additional deflection in the direction of the nozzle slot 2.
    A prerequisite for a sprue tear-off when an injection molded part is removed from the mold is that the plastic melt in the nozzle channel 4 does not solidify. The nozzle core 3 must
    7/14 can therefore be heated accordingly in order to be able to supply heat to the plastic melt in the area of the nozzle duct 4 as well. Although heating of the nozzle core is also possible via the housing 1, more favorable heating conditions result if the nozzle core 3 is heated directly. For this purpose, according to the illustrated embodiment, 3 electric heating cartridges 11 are used in the nozzle core, which ensure controlled heating of the nozzle core 3. According to the exemplary embodiment, the heating cartridges 11 run perpendicular to the nozzle slot 2 because the space available makes the heat input into the tapering end section of the nozzle core 3 easier. However, this arrangement of the heating cartridges 11 is not mandatory. 6 shows a nozzle core 3 with heating cartridges 11 running parallel to the nozzle slot 2. Needless to say, the electric heater can also be replaced by a heater using a heat carrier flowing through the nozzle core 3.
    In order to reduce heat losses due to heat transfer from the plastic melt to the housing 1, the housing 1 can be shielded from the nozzle core 3 by thermal insulation 12, which advantageously forms the wall of the distributor channels 6 on the housing at least in sections. This thermal insulation, which surrounds the nozzle core 2 in the form of a jacket, does not itself have to be produced from a heat-insulating material. It is entirely possible to hinder the heat transfer from the plastic melt, which in itself forms a poor heat conductor, to the housing 1 by a region-wise air gap between the thermal insulation 12 and the housing 1, for example by providing the outer surface of the thermal insulation 12 with corrugation.
    In contrast to the embodiment according to FIGS. 1 to 5, according to the embodiment according to FIG. 6, the nozzle core 3 is displaceably mounted in the housing 1 for closing the nozzle slot 2. An actuator 13 is used to move the nozzle core 3 into the closed position shown in FIG.
    8/14 which is designed in the embodiment in the form of a wedge gear 14.
    In addition, the housing 1 is formed by a mold plate 16 delimiting the cavity 15 of an injection molding tool, so that a separate plate 16 is integrated into one
    Form plate 16 to be used housing for the injection molding nozzle.
    Due to the introduction of the plastic melt into the cavity 15 of an injection molding tool via a nozzle slot 2, the shear stress of the plastic melt can be kept comparatively small in relation to the possible melt throughput, which is an essential prerequisite for a material-friendly injection of the plastic melt into the cavity 15.
    The break-off of the sprue depends on the strength properties of the plastic in the area of the nozzle slot 2, which is solid within the cavity 15 during demolding, but is molten in the gate area, so that a high temperature gradient within a thin area occurs in the transition area from the cavity 15 to the nozzle channel 4 Layer in the area of the nozzle slot 2 results, whereby the conditions for a tear-off of the sprue along the surface determined by the opening of the nozzle slot 2 are given. For this purpose it is recommended to cool the housing in the area of the nozzle slot 2. 1,2 and 6, cooling channels 17 are indicated for this purpose. With an appropriate choice of the influencing parameters, the demolition surface can thus be moved into the molding surface of the respective injection molded part without the need to postprocess the sprue demolition. The sprue is thus moved to the area of the hot runner.
    Particularly advantageous demolding conditions arise in this context according to FIG. 6 if there is the possibility of closing the nozzle slot 2 with the aid of the nozzle core 3.
    9.14
    patent attorneys
    Dipl.-Ing. Helmut Hübscher
    Dipl.-Ing. Gerd pretty
    Dipl.-Ing. Karl Winfried Hellmich
    Spittelwiese 4, 4020 Linz (41850) II
    权利要求:
    Claims (3)
    [1]
    claims
    1. A method for producing injection molded parts made of plastic using an injection molding tool, the plastic melt being injected in the form of at least one band-shaped melt strand through a nozzle slot (2) into a cavity (15) of the injection molding tool before the injection molded part is removed from the mold after the plastic melt has solidified, characterized in that heat is supplied to the plastic melt during solidification in the cavity (15) in the sprue area and that the sprue is torn off along the nozzle slot (2) when the injection molded part is removed from the mold due to the temperature gradient between the solidified injection molded part and the plastic melt in the sprue area.
    [2]
    2. The method according to claim 1, characterized in that the melt flow is restricted for distribution over the length of the nozzle slot (2).
    [3]
    3. The method according to claim 1 or 2, characterized in that the housing (1) forming the nozzle slot (2) is cooled in the region of the nozzle slot (2) for setting the temperature gradient between the solidified injection molded part and the molten sprue.
    10/14
    u.
    11/14
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    同族专利:
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    引用文献:
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
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