JPH0348851B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a closed-needle nozzle for injection molds, in particular multi-molding molds, in the area of the transition to the mold in the feed path for liquid plastics or the like. A closure needle is disposed at the closure needle for axial reciprocating movement toward a closed position and an open position, the closure needle having a cylindrical shape at its closed end having a small diameter compared to the rest of the closure needle. The sealing area is preferably of the type in which the transition from the large diameter section to the small diameter section is preferably tapered and/or rounded.

A closed-needle nozzle of this type is known from DE 26 44 670 A1. In the closed position, the end of the closed needle, which is cylindrical with a reduced cross section, rests in a correspondingly sized hole in the injection wall of the mold behind it and prevents further flow of the injection molding material into the mold. do. The closing movement of the closing needle can be effected in various ways, for example by a pressure spring or, in particular, via a pivot lever driven by a hydraulic or pneumatic piston. Disadvantages of this known needle closure device include the following. That is, in the open position of the needle and in particular during the closing process, the closure needle is laterally deflected by the injection-molded material, preferably plastic, so that the cylindrical closure part of the closure needle may be displaced accordingly. The needle does not enter the aperture accurately and hits the aperture edge, causing damage to the needle tip and the aperture edge over time.

Therefore, a number of needle-closed nozzles are known which have a tapered closed end that enters a correspondingly tapered opening.

Furthermore, the Federal Republic of Germany patent application publication no.
A closing needle with a cylindrical end, which is known from US Pat. No. 2,832,877, is held against deflection by a guide body. Since this guide surrounds the needle in close proximity, the flow of hot plastic or similar injection molding material must be deflected laterally around the same guide and thus against the nozzle wall. reaches the normal temperature range and around the nozzle wall. This causes a sudden change in the viscosity of the injection molding material, which causes significant flow changes and resistances, which can in some cases result in insufficient filling of the mold. Even if the mold is completely filled, if the injection molding material, especially the plastic, is cooled too strongly during injection, the final product may be visually, mechanically or dimensionally unsatisfactory. It may be caused.

It is therefore an object of the present invention to improve a closed-needle nozzle of the type mentioned at the outset so that it can be produced in a very compact and rapid manner by means of a cylindrical addition at the end of the needle that cooperates with corresponding holes in the mold wall. While retaining the advantages of a secure closure, it is nevertheless possible to avoid the need to expose the plastic or similar injection molding material to the ambient temperature range, while at the same time avoiding damage in the area of the needle end and/or hole edge. The object of the present invention is to provide a needle-closed nozzle that can avoid the above problems.

In order to solve this object, a first embodiment of the invention provides that in a closed-needle nozzle of the type mentioned at the outset, a precentering body for the closing needle is provided in the front needle region, and the closing needle is has at least one channel for allowing the injection molding material to flow through during the centering process, and the precentering body is tapered in the needle closing direction, and the precentering body has at least one channel that allows the injection molding material to flow through the needle. an imaginary joining line connecting the leading edge of the cylindrical sealing area and the next largest step of the closing needle through a joining point located on a parallel diameter with a cone angle relative to the axis;
It is a small or acute angle compared to the angle formed by the needle axis.

With this arrangement, even in the event of a deflection of the closing needle, the large-diameter step rests against the inside of the precentering body, so that the sensitive cylindrical sealing surface at the front of the needle comes into contact. That will no longer be the case. At the same time, the passageway also eliminates the need for the injection molding material to be deflected into the outside ambient temperature range. On the contrary, the injection molding material can also flow in the region of the precentering body between the precentering body and the needle.

In any case, the difference between the cone angle on the inside of the precentering body and the angle of the imaginary bond line on the outside of the needle is in this case somewhat larger than the maximum possible deflection angle of the needle. Contact of the cylindrical sealing surfaces of the needles is avoided.

It is also advantageous if the contact area at the step of the transition from the maximum diameter of the closing needle to the sealing area during any possible deflection of the needle is rounded. In this way, the frictional forces between the front centering body and the closing needle itself are kept low during contact at the front centering body.

It is particularly advantageous if a plurality of channels, preferably three, are distributed evenly over the entire circumference of the precentering body. In this way, the forces due to the material pressure are distributed as evenly as possible on the closing needle, so that deviations due to the material are largely avoided. In this case, it is advantageous if the channels open radially inwardly into the central needle guide. With this embodiment, a good transfer of material directly into the injection opening takes place before the injection opening is closed by the cylindrical closing part of the needle.

The hole through which the sealing area of the closing needle enters is tapered in the first entry area and only cylindrical in the lower area close to the mold, the hole first tapering in the closing direction of the needle. It is especially advantageous if you are familiar with it. With this configuration, it is furthermore possible to prevent the cylindrical sealing area from colliding with the hole edge and damaging it, as well as from subjecting the cylindrical sealing area itself to undesired loads and deformations. be avoided.

In this case, it is advantageous if the clearance of the centering body is smaller than the clearance of the sealing area or closing part, since the sealing area can be arranged in the bore without contact in the position of use. This avoids damage to the needle-closed nozzle in this area, which is critical for sealing. It has been found that a sufficient sealing effect is obtained even for relatively high plastic pressures if the distance between the outside of the sealing area and the inner wall of the hole is approximately 1/100 mm. This small distance between the needle end and the wall of the hole in which it is received allows for a burr-free release during demolding. In this case, it is also advantageous if the end end of the needle lies flush with the mold surface in the closed position, as is known per se.

It is particularly advantageous if the precentering body is made of a wear-resistant material. Nevertheless, sufficient heat can be supplied to the channels for the plastic or similar injection molding material in the precentering body to avoid problematic viscosity fluctuations.
This is because only a relatively short portion of the injection molding material flow path extends through the precentering body;
This is because the injection molding material remains in the passage provided within the centering body and does not need to be deflected into the normal temperature range.

Furthermore, it is advantageous if the heat-conducting nozzle, which is arranged around the entire needle area, is uninterrupted and consists of a material with high thermal conductivity and also surrounds the precentering body. This also provides a uniform temperature over the entire nozzle area. In this case, short interruptions or interval increases in the heat supply in the area of the centering body are less problematic due to the flow rate of the injection molding material. In this case, the heat-conducting nozzle can be maintained at the desired temperature electrically from the outside in a manner known per se, for example with a heating zone.

In order to avoid as much as possible from the beginning or to keep the deflection of the closing needle as low as possible and thus also to significantly prevent wear in the area of the precentering body or to keep it as low as possible, the second invention provides In a construction, in a closed-needle nozzle of the type mentioned at the outset, a front centering body for the closing needle is provided in the front needle region, so that the closing needle also prevents the flow of injection molding material during the centering process. the precentering body is tapered in the needle closing direction, and the cone angle of the precentering body with respect to the needle axis lies on parallel diameters. smaller or more acute angle than the angle formed by the needle axis and an imaginary joining line connecting the leading edge of the cylindrical sealing area and the next largest step of the closing needle through the joining point and at the end of the needle opposite the sealing area,
At least one piston rod of a drive piston or the like is arranged to be moved coaxially and directly relative to the closing needle.

With this arrangement, if there is a temperature difference between the drive piston and its piston rod and the hot passage, lateral movements that may cause the needle end and thus the closing needle to move laterally are avoided. can be avoided from being transmitted to the needle end.

It is indeed already known to move the closing needle by means of a piston, however, in this case the piston is adapted to move laterally parallel to the closing needle, and the movement of the piston causes a pivoting lever to be moved. The pivoting movement of the pivoting lever must be converted into a reciprocating motion of the closing needle (as disclosed, for example, in DE 26 14 911). Since such a pivoting movement always has a movement component in the transverse direction, the risk of undesired needle deflection is increased in such pivoting lever drives. By constructing it in accordance with the second aspect of the invention, the above-mentioned deflection forces that can be caused by the movement of the pivoting lever are avoided.

Furthermore, a further advantageous embodiment of the second invention is provided in that at least two or more pistons are arranged one after the other in a space-saving manner and are adapted to interact with each other. Aspects are possible. Since only a relatively small piston diameter is required with this arrangement, it is possible to arrange a large number of separate molds located in close proximity within the multiple mold. Furthermore, such a piston drive can be operated with the compressed air available during normal operation, for example from 4 to 6 bar, and can generate sufficient pressure. By choosing a suitable diameter ratio and increasing the number of pistons per closing needle, the required e.g. 100 Kg or Kp at the needle end can be reduced.
can be achieved without difficulty in extremely narrow spaces.

In particular, by using the previously described configurations and measures individually or in combination, the
A needle-closing nozzle for injection molds is obtained which can be installed in narrow spaces and which allows a precise and tight closure without risk of damage, especially in the sealing area of the needle tip. At the same time, viscosity fluctuations in the injection molding material are also avoided.

Next, embodiments of the present invention will be described with reference to the drawings.

The closed-needle nozzle, designated as a whole by 1 (hereinafter simply referred to as nozzle), may be provided in plural numbers, in particular for filling a plurality of injection molds, in particular multiple molds. The main part of this nozzle 1 is a feed channel 2 for a liquid plastic or similar injection molding material 3.
A closing needle 4 is disposed in the housing and is capable of reciprocating between an open position and a closed position. In FIGS. 1 and 2, the closure needle 4 is shown in the open position.

At its closed end, the closing needle 4 has a cylindrical sealing region 6, which has a smaller diameter than the rest of the closing needle 4. The transition section 7 from the large diameter section to the small diameter section is tapered in the illustrated embodiment.

According to the invention, a precentering body 8 for the closing needle 4 is provided in the front needle region, which precentering body 8 allows the injection molding material 3 to flow through it even during the centering process. At least one, in this embodiment three passages 9 (see FIG. 3)
have. The precentering body 8 tapers in the needle closing direction, the cone angle of the precentering body 8 relative to the needle axis being the outer point of the front edge 10 of the cylindrical sealing region 6. and the outer point located on the parallel diameter of the next largest step 11. This ensures that even if the needle is deflected, as shown in broken lines in FIG. The large-diameter step portion 11 comes into contact with the inner wall 12. That is, the precentering body 8 cooperates in an advantageous manner with the relatively insensitive step 11 of the closing needle 4 and seals the sealing area 6, which is desired to have a high degree of precision.
cannot be harmed under any circumstances. It is advantageous in this case for the above-mentioned angular difference to be somewhat larger than the maximum possible deflection angle of the closing needle 4, so that the sealing area 6 lies on the inner wall of the precentering body 8. 12 is reliably avoided.

In particular, as you can clearly see from Figure 3, there are three passages 9.
are evenly distributed over the entire circumference in the inner region of the precentering body 8. This ensures that the forces exerted on the closure needle 4 by the injection molding material are evenly distributed, so that deflections of the closure needle 4 are further avoided.

The hole 13 for the closing needle is also clearly shown in FIG.
The position of the closure needle at 3 is also shown.
The first entry area 13a of the bore 13 has a conical shape, and the bore 13 first becomes cylindrical in the lower area 13b, close to the mold, to receive the front edge area of the sealing area 6 of the closing needle 4. do. As a result, the original seal location (range 13b) is restored once more.
An entry hopper is formed, so that the needle end face is prevented from resting on the edge of the bore 13 in any case. In this case the lower range 13
There is a slight play of approximately 1/100mm in b.
As a result, damage to the sealing area 6 and the hole 13 can be avoided without impairing the sealing effect. In this way, the wall of the area 13b of the hole 13 and the sealing area 6
If the distance between the two is small, separation can be performed without creating burrs during demolding. As can further be seen in FIG. 2, the end face of the sealing area 6 of the closing needle 4 lies flush with the mold surface 14 in the final closing position.

As can be seen from FIG.
This open point of the channel 9 is closed in the use position in which the closing needle 4 has been moved downwards.

Since the precentering body 8 occupies only a relatively short area of the flow path of the injection molding material 3, even if the precentering body 8 is made of a wear-resistant material, the injection molding material heat conduction is not impeded. Therefore, the thermally conductive nozzle 15, which is made of a material with high thermal conductivity and is provided in the entire needle area, is virtually free from wear.
A uniform temperature can be produced in this relatively critical region of the injection molding material feed, so that fluctuations in the viscosity can be avoided. FIG. 1 also shows a heating element 16 for the heat-conducting nozzle 15.
is shown, and the heat-conducting nozzle 15 also surrounds the area of the precentering body 8 . The heating element 16 is, for example, electrical and consists of an electrical heating band.

FIG. 1, which shows the main configuration of the present invention, further shows:
A drive device for the lowering movement of the closing needle 4 is designated as a whole by 17. This drive device 17
The lateral force which deflects the closing needle 4 when there is some play in the guide 19 is caused by the same drive device 17.
The needle shaft 18 is configured so that it cannot be affected by the needle shaft 18. In this embodiment, instead of a pivot lever acting on the end 20 of the needle shaft 18, a piston rod 21 cooperating with the associated piston 22 is arranged directly coaxially with the closing needle 4. A piston rod 23 of a second piston 24, which is also arranged coaxially, acts on the piston 22. Furthermore, as shown in FIG. 1, an air inlet opening 25 is assigned to both pistons 22, 24, which are normally loaded with compressed air. A stopper 26 is provided below the lower piston 22 at an interval of height H, and the interval (height H) of this stopper 26 from the lower side of the piston is similarly within the lower range of FIG. exactly equal to the closing stroke distance H of the closing needle 4, shown in FIG. The opening 27 serves for the return movement of the piston 24 and for the return movement of the piston 22. The return movement of the closing needle is effected in a known manner by the pressure of the injection molding material 3 applied to a valve-shaped enlargement 28 provided at the lower end of the needle shaft 18.

at least two pistons 2 acting on each other
2, 24 makes it possible to provide the necessary closing force for the closing needle 4 against the injection molding pressure in a relatively small space, so that it is possible to provide the necessary closing force for the closing needle 4 against the injection molding pressure, so that it is possible It becomes possible to arrange a large number of closing needles 4 of the octopus type in a small space. It is also possible to attach a significant number of separate molds to a multiple mold. Furthermore, the compressed air pressure used in normal production operations is sufficient to provide a relatively large force for the closing movement of the closing needle 4.
A further advantage here is that no space is required on the side of the closing needle 4 for driving the closing needle. At the same time, however, it is possible to dispense with a closing spring acting in the axial direction of the closing needle, which always exerts a closing pressure even when the closing needle is opened and can therefore perform a piston-like precise closing movement.

[Brief explanation of drawings]

1 is a longitudinal sectional view showing the area of the needle-closing nozzle and its piston drive; FIG. 2 is an enlarged longitudinal sectional view showing the front area of the closing needle; FIG. FIG. 3 is a top plan view of the conduction nozzle. DESCRIPTION OF SYMBOLS 1... Nozzle, 2... Supply path, 3... Injection molding material, 4... Closed needle, 5... Closed end, 6
... Seal range, 7 ... Transition part, 8 ... Front centering body, 9 ... Passage, 10 ... Front edge, 11 ... Step section, 12 ... Inner wall, 13 ... Hole, 13a ... Approach range, 13b... Range, 14... Mold surface, 15...
... Heat conduction nozzle, 16 ... Heating body, 17 ... Drive device, 18 ... Needle shaft, 19 ... Guide, 20 ... End part, 21, 23 ... Piston rod,
22, 24... Piston, 25... Air inflow opening, 26... Stopper, 27... Opening, 28...
Enlarged section, H...height.

Claims (1)

[Scope of Claims] 1. A closed-needle nozzle for an injection mold, in the feed channel for liquid injection molding material, in the region of the transition to the mold, with a shaft pointing towards the closed position and the open position. of the type in which a closing needle reciprocating in the direction is arranged, the closing needle having at its closed end a cylindrical sealing area having a small diameter compared to the rest of the closing needle; , a front centering body 8 for the closing needle 4 is provided in the front needle area, the closing needle 4 having at least one channel 3 through which the injection molding material 3 can flow even during the centering process. , the precentering body 8 tapers in the needle closing direction, and the connection point at which the cone angle of the precentering body 8 with respect to the needle axis lies on parallel diameters. a small or acute angle compared to the angle formed by the needle axis and an imaginary joining line connecting the leading edge 10 of the cylindrical sealing area 6 and the next largest step 11 of the closing needle 4 through A needle-closed nozzle for an injection mold, characterized in that: 2. The difference between the cone angle of the front centering body 8 and the angle of the imaginary connecting line connecting the front edge 10 and the step 11 is such that the step 11 comes into contact with the inner wall 12 of the front centering body 8. 2. A needle-closing nozzle according to claim 1, wherein the needle-closing nozzle is larger than the maximum possible deflection angle of the closing needle. 3. The needle-closing nozzle according to claim 1 or 2, wherein the contact area at the stepped portion 11 in the transition portion from the maximum diameter portion of the closing needle 4 to the sealing area 6 is rounded. 4. Needle-closed nozzle according to one of the claims 1 to 3, in which the three passages 9 are evenly distributed over the entire circumference of the precentering body 8. 5 The passage 5 is directed radially inwardly and opens into the central needle guide.
The needle-closed nozzle according to any one of items 1 to 4. 6 Hole 1 for sealing area 6 of closure needle 4
5. The needle according to claim 1, wherein 3 is tapered in the first entry region 13a and cylindrical in the lower region 13b close to the mold. Closed nozzle. 7. Claims in which the clearance of the front centering body 8 is smaller than the clearance of the sealing area 6 in the hole 13, and the sealing area 6 is arranged in the use position without contacting the inside of the holes 13, 13b. The needle-closed nozzle according to any one of items 1 to 6. 8. Needle closure according to any one of claims 1 to 7, wherein the distance between the outside of the sealing area 6 and the wall of the area 13b close to the mold of the hole 13 is approximately 1/100 mm. formula nozzle. 9. Needle-closing nozzle according to one of the claims 1 to 8, wherein the front edge 10 of the closing needle 4 lies flush with the mold surface 14 in the closed position. 10. A closed-needle nozzle according to claim 1, wherein the precentering body 8 is made of a wear-resistant material. 11 The heat conduction nozzle 15 provided in the entire needle range is made of a material with high thermal conductivity,
11. A closed-needle nozzle according to claim 1, which also surrounds the precentering body. 12. A closed-needle nozzle according to any one of claims 1 to 11, wherein the heat-conducting nozzle 15 is electrically heated from the outside. 13 Needle-closing nozzle for an injection mold, in the feed channel for liquid injection molding material, in the region of the transition to the mold, the closure reciprocates axially towards a closed position and an open position. a front needle region in those types in which a needle is arranged and the closing needle has at its closed end a cylindrical sealing region having a small diameter compared to the rest of the closing needle; is provided with a precentering body 8 for the closing needle 4, the closing needle 4 having at least one channel 3 allowing the injection molding material 3 to flow through it even during the centering process, The defining body 8 tapers in the needle closing direction so that the cone angle of the centering body 8 with respect to the needle axis creates a cylindrical sealing area through the connection point lying on parallel diameters. The sealing range 6 is smaller than the angle formed by the needle axis and the imaginary joining line connecting the front edge 10 of the closing needle 6 and the next largest step 11 of the closing needle 4. Injection molding, characterized in that, at the opposite needle end, a piston rod 21 of at least one drive piston 22 or the like is arranged, which is moved coaxially and directly relative to the closing needle 4 Needle closed nozzle for molds. 14 at least two pistons 22, 24 are arranged one after the other and act on each other,
A closed needle nozzle according to claim 13. 15. Needle-closing nozzle according to claim 13 or 14, in which a stop 26 is arranged below the piston 22 closer to the closing needle 4 at an interval of the needle travel distance to the closed position. 16. Needle-closing nozzle according to any one of claims 13 to 15, wherein the piston drive 17 of the closing needle 4 is supplied with compressed air of 4 to 6 bar.