Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an injection moulding tool with at least one central feed conduit, including one or more plates which are arranged over one another, at least one hot runner feed conduit with a branching point or with several branching points, in which a direction change and/or a division of the hot runner feed conduit is effected, for the feed of the hot injection moulding mass to two or more cavities. 
     2. Discussion of Related Art 
     Injection moulding tools are tools, by way of which plastic parts are manufactured. They are applied in injection moulding machines, in which an injection moulding mass is heated and in the molten condition is led via so-called hot runner feed conduits to the cavities, in which the respective plastic parts are moulded. Cooling channels which cool the region around the cavities so that the liquid plastic solidifies run in the region of these cavities. 
     Injection moulding tools must be regularly overhauled, since a certain erosion occurs, which however is relatively low. Deposits which occur in the hot runner feed conduits are more of a problem. These deposits occur to a more or less frequent extent, depending on the type of plastic. Deposits however generally occur with all plastics, independently of whether it is thereby the case of thermoplastics or duroplasts. Generally, it can however be said that the higher the processing temperature, the more deposits occur. Of course all regions of the injection mould which come into contact with the hot injection moulding mass are considered. However, it is known that deposits in the injection mould cavity tend to be inherent of a poor bleeding of the injection mould and tend to indicate a design fault, whereas deposits in the hot runner feed conduits unavoidably occur with certain plastics, even if no overheating is present. 
     As a result, one can assume that one main problem of the deposits occurs in the hot runner feed conduits, in the case of a correct design and temperature control. The cleaning of these hot runner feed conduits however requires a considerable amount of effort. The course of the hot runner feed conduits in the injection moulds is not at all in simple straight lines, but within the injection mould runs from one direction change point to the next in a straight manner or also from one branching point to the next branching point or from one direction change point to a branching point in a straight line. 
     An injection moulding tool of the state of the art is shown in  FIG. 3 . In the present embodiment, it includes two plates, specifically an upper base plate A and of a lower base plate B. On the one hand, the central hot runner feed conduit C is located in the upper plate A, and different hot runner feed conduits E lead from a branching point D in the horizontal direction. These hot runner feed conduits E are realized by a continuous horizontal bore and these bores are then closed by plugs G up to the direction change point F. The hot injection moulding mass via an injection valve J finally gets into a cavity H via a further section of the hot runner feed conduit F. 
     If the hot runner feed conduits need to the cleaned, then the plugs G need to be drilled out, the conduits cleaned and new plugs inserted thereafter. This effort cannot be carried out at the injection moulding business itself, and the respective injection mould must be sent back to the mould construction company where this service work is then carried out. A production interruption of at least several days, but mostly of several weeks thus arises. 
     Although different documents, such as Great Britain Patent Reference GB 1 299 094 or German Patent Reference DE 10 2008 045701-A or also EPO Patent Reference EP 2 263 845 B show injection moulding tools with hot runner feed conduits, these documents however concern themselves with other problems, for example with a special feed of these hot runner feed conduits, in order with this to reduce the build-up of deposits. 
     SUMMARY OF THE INVENTION 
     As a result, it is one object of this invention to provide an injection moulding tool which is designed so that its hot runner feed conduits are significantly simpler to clean, and as a result the interruption times for the cleaning of the tool and the costs which this entails are reduced. 
     This object and others are achieved by an injection moulding tool of the initially mentioned above, which is characterized by the hot runner feed conduits in each plate of the injection mould running in a straight line from the upper surface to the lower surface of this plate and inclined to the upper or lower surface, and at least at one side run out into exchangeable inserts, in which the distribution or the direction change of a hot runner feed conduit is affected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the subject matter of this invention is represented in the drawing, and is explained wherein: 
         FIG. 1  is one embodiment of an injection moulding tool which is designed according to this invention; 
         FIG. 2  shows the same injection moulding tool as in  FIG. 1  again represented identically, for relieving the figure of too many reference numerals; and 
         FIG. 3  is a simplified diagram showing an injection tool of a conventional construction manner, as already described above in a detailed manner. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The description of an injection moulding tool according to the state of the art, as is represented in a simplified manner in  FIG. 3 , is not repeated. 
     A section of an injection moulding tool according to this invention is represented in  FIGS. 1 and 2 . The injection moulding tool in its entirety is indicated at numeral  1 . At the very top, one recognizes a central feed conduit  2  which is shaped into a sprue bushing  20 . The sprue bushing  20  is held in a fixation plate  21 . The sprue bushing  20  with the central feed conduit  2  which is connected to an extruder or injection moulding assembly of the injection moulding machine, which are not shown here, rests on an upper plate  3 . The plate  3  in turn lies on a lower plate  4 . The individual plates here are releasably connected to one another by means which are not explained further. 
     Heating means are arranged in the individual plates. The heating means can be electrically insulated heating rods or also hot runners, through which a heating fluid is pumped. A further explanation of the heating means is omitted since these are conventional and are independent of this invention with regard to their design. 
     Each plate  3 ,  4  of an injection moulding tool  1  has an upper surface  7  and a lower surface  8 . The number of the required plates  3 ,  4  increases depending on the complexity of the injection moulding tool  1 . The terms upper plate  3  and lower plate  4  are to be seen as relation details of two adjacent plates. As the case may be, with an injection moulding tool  1  with three respective plates, for example, the middle plate with regard to the plate lying therebelow forms the upper plate or with regard to the plate lying thereabove forms the lower plate. 
     Each plate however has an upper surface  7  and a lower surface  8 . 
     The central feed conduit  2  in the sprue bushing  20  runs out into an exchangeable insert  10  of the upper plate  3 . For this, a recess  30  is formed in the upper surface  7  of the upper plate  3 . In the example represented here, the sprue bush  20  partly engages into the recess  30 . The sprue bush  30  practically forms the upper side of the hot runner feed conduits  5  which connect below the central feed conduit  2  and which branch from here. Whereas here, the lower halves of the branching hot runner feed conduits  5  are formed by the respective exchangeable insert  10 , here the upper halves of the branching hot runner feed conduits  5  are formed by the parts of the sprue bushing  20  which engage into the recess  30 . 
     This design however is not compelling and the hot runner feed conduits  5  can also be completely formed in the exchangeable insert  10 . 
     Basically, one differentiates between different types of inserts, specifically on the one hand manifold (distribution) inserts which are indicated at  11 , and on the other hand deflection inserts which merely serve to realize a direction change of the hot runner feed conduit  5 . As already mentioned, the manifold (distribution) inserts are indicated at  11 , the deflection inserts are indicated at  12 . However, it is always the case of exchangeable inserts  10  in both cases. 
     The exchangeable inserts  10 ,  11 ,  12  are preferably designed so that these taper in a closure direction, in order to simplify their exchangeability. These exchangeable inserts in the normal case are designed in a polygonal manner in a plan view, and that surface of the exchangeable inserts  10 , into which the hot runner feed conduit  5  runs out, is indicated at  13 . These run-out or exits surfaces  13  are preferably inclined so that these run perpendicularly to the running direction of the hot runner feed conduit which runs out, which is to say exits there. 
     Basically, the exchangeable inserts can be cubic, cylindrical with perpendicular walls or truncated-cone-like or truncated-pyramid-like with inclined walls. 
     If with regard to the exchangeable insert  10 , it is the case of a manifold insert  11 , then this has at least two exit surfaces  13 . Basically, the manifold inserts can be polygonal and not only two hot runner feed conduits can branch therefrom without any problem, but these hot runner feed conduits can be arranged in a star-like manner, so that a multitude of hot runner feed conduits can branch off. Two to maximally eight such branching hot runner feed conduits are usually present. With injection moulding tools of the type considered here, and which in technical terms are called hot-runners, one designates the injection moulding tool according to the number of cavities  9  provided therein. The cavities are the hollow spaces which are to be filled with the hot injection moulding mass. If, for example, one has a tool with sixteen cavities, then one speaks of a 16-cavity tool or mould. In such a case, one would mostly incorporate four hot runners  5  in the upper plate  3  from the manifold insert  11 , which are then recessed into deflection inserts  12  in the upper plate  3  at its lower side. The deflection inserts  12  then in turn run out in manifold inserts  11  in the upper surface of the lower plate  4 , wherein again four hot runners feed conduits  5  branch away from each manifold insert  11  and these then, for example, run out into sixteen cavities via sixteen deflection inserts  12 . Then only deflection inserts  12  continue to be present in the lower surface of the lowermost plate which is in connection with the cavities  9 . 
     Although the exchangeable inserts  10  with the preferred embodiment are represented here tapering from the upper side of the plate to the base of the recess  30  and thus running inclined to the upper or lower surface  7 ,  8  of the respective upper or lower plate  3 ,  4 , it is also possible to design the side surfaces of the exchangeable inserts running perpendicularly to the upper or lower surfaces of the respective plate. This is possible not least since one preferably incorporates a bore  14  in each case from the surface lying opposite the recess  30 , perpendicularly to the plate surface, the bore has a suitable inner thread in which screws can be inserted, and by which a pressure can be exerted onto the respective exchangeable inserts  10 ,  11 ,  12 . With this, the inserts can be fastened to the respective surface in an aligned and highly precise manner, and in particular the inserts can be easily ejected for cleaning. Accordingly, the bores are indicated as ejection bores  14 . The respective ejection screws  15  which are mounted therein have a corresponding outer thread which matches the threaded bore  14 . These screws serve for the fastening as well as disassembly of the exchangeable inserts  10 ,  11 ,  12 . 
     If deposits occur on the hot runner feed conduits, then this leads to these deposits forming an insulation layer, and as a result the heat of the injection moulding tool can no longer be led correctly to the injection moulding mass. The temperature of the injection moulding mass as a result is too low on entry into the cavity, and this can be recognized on the finished parts by the plastics technician. This can be briefly compensated by one increasing the temperature of the injection moulding tool, but deposits or combusted which is to say carbonized particles are thus increasingly formed. These particles are visible in the injection moulded part and lead to aesthetic and mechanical shortcomings, which cannot be tolerated. A person skilled in the art and in injection moulding technology knows that the injection moulding tool must now be cleaned. The person can now carry out this itself without having to send the injection moulding tool back to the mould manufacturer. For this, he separates the different plates of the injection moulding tool according to this invention, in order remove the various exchangeable inserts by way of ejection screws and to then clean the respective hot runner feed conduits  5 . 
     For this, the person does not need to drill out a plug and insert a new one again. Of course, the person can also clean the exchangeable inserts itself. However, the tool manufacturer can indeed also co-deliver a complete set of exchangeable inserts for the respective injection moulding tool, in order however to reduce the stoppage time of the tool, so that the injection moulding business merely needs to clean through the conduits and then exchange the set of co-delivered, exchangeable inserts. It then assembles the injection moulding tool again thereafter. 
     A mould manufacturer, who manufactures the injection moulding tool of the type according to this invention, would standardize the exchangeable inserts. Basically, hot runner conduits, which is to say hot runners, with only three to four different diameters are required for example, depending on the tool size. Thus with this, it is conceivable for business to manufacture the exchangeable inserts for example of sintered material in a large scale manufacture or also, with regard to moulding technology, to have such metallic exchangeable inserts manufactured, for the common sizes of injection moulding tools. However, one would always manufacture such inserts in a self-produced and machining manner, for more sophisticated injection moulding tools. 
     The bores must be led through from the one surface to the other surface in a complete manner, so that one can clean the hot runner feed conduits which run is a straight, but inclined manner in the respective plate, without any problem. The recesses, into which these bores run out however, do not need to be so large that the exit surface of this continuous bore runs out completely in the region of the recess. This indeed can be recognized in  FIG. 2 , for example. Thus in  FIG. 2 , one can recognize that the hot runner feed conduit  5  although running out completely within the recess  30 , however basically crosses this recess and exits again at  16 . The exchangeable insert  10  however does not close off this bore exit region  16 , and as a result it is of no significance as to whether the exit surface of the bore lies completely within the base surface of the recess  30  or extends out of this. The exchangeable inserts are not a hindrance on cleaning the hot runner feed conduits since the exchangeable these inserts  10  are removed for the cleaning.

Technology Category: b