DE20112525U1 - Injection unit of an injection molding machine - Google Patents

Description

.*.'·. . II .* . : &Ggr; : Telephone (02 02)2 59 06-0

Dipi.-ing. Harald Ostriga* ^email: ™ ^il@osw -p ^at - ^de

Dipl.-Ing. Bernd Sonnet*

Dipl.-ing. Jochen-Peter Wirths " ^address: _&Lgr;

^r ° Stresemannstr. 6-8

* Authorized by the European Patent Office 42275 Wuppertal-Barmen

Oslriga. Sonnei & Wirths ■ PO Box 20 16 53 ■ D-422 16 Wuppertal

W/he

Applicant: Prof.-Dr. Ing. Erich Schürmann

&iacgr;&ogr; Wittenberg 1

48324 Sendenhorst

Designation

of the invention: Injection unit of an injection molding machine

The invention relates to an injection unit of an injection molding machine with an injection device which is driven axially and rotatingly in a housing and is designed as a piston/screw and is provided with a non-return valve, wherein the injection device serves for plasticizing during the transport of the plastic granulate and functions as a piston during the pressing of the plastic melt through a nozzle into an injection mold, and a device for mixing and dosing the plastic melt and additives such as colorants, foaming agents, lubricants or the like.

The state of the art, which cannot be documented in printed documents, includes, for example:

Injection units for injection molding machines are known in which the additives are mixed into the plastic granulate before the screw.

It is also known to equip conventional piston screw injection molding units with separate dosing and mixing devices. However, these systems have considerable problems with the permanent sealing of the shaft

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Prof. Dr. Ing. Erich Schürmann

and piston feedthrough, since joining surfaces with relative movements must be sealed against melt leakage.

Based on the last-mentioned prior art, the object of the invention is therefore to create a new injection unit of an injection molding machine with an injection device designed as a piston/screw, which is driven axially and rotatingly in a housing, into which a separate metering and mixing device for additive metering is integrated, without moving parts protruding to the outside.

&iacgr;&ogr; must be sealed against melt leakage. Furthermore, the object of the invention is to simplify the structure and reduce the overall size of the device.

The solution to this problem arises from the features of claim 1, in particular the characterizing part, according to which a spacer element is arranged between the non-return valve of the screw and the piston, the length of which corresponds at least to the stroke of the injection unit and which has at least one flow channel, through which a fluidic connection is ensured in every position with a further flow channel which initially extends radially outwards and parallel to the movement and guide area of the piston into an area between the nozzle and the piston, and that the flow channel runs through the mixing and dosing device arranged adjacent to the movement and guide area of the piston.

The device according to the invention has numerous advantages over the prior art. On the one hand, no moving parts need to be sealed against melt leakage, which reduces the design effort. The coaxial design of the mixing and dosing device also results in a straight-line flow of force while at the same time reducing the size.

Prof. Dr. Ing. Erich Schürmann .* .'\

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Advantageously, the mixing and dosing device can move the piston

at least partially surround in a circular ring shape, whereby in this context it is basically possible for the mixing and dosing device to be connected to the spraying device with regard to its rotational movement.

The latter solution advantageously eliminates the need for an additional drive for the mixing and dosing device, so that the device as a whole has a simpler design.

In a particular embodiment of the invention, the mixing and dosing device is formed from mixing elements that are arranged on a rotatable pipe that is connected to the piston for rotation and on the inner diameter of the housing, as well as at least one additive feed. The mixing and dosing device is arranged very close to the movement path of the piston, but separate from it, which has a positive effect on the size, with the flow channel for the melt running through the mixing and dosing device around the movement space of the piston.

With such a mixing and dosing device, the

Mixing elements, for example, have different, opposing surface designs, in particular toothing, through which an intensive mixing of the melt with the additives added in the mixing and dosing device is achieved.

In a further embodiment of the invention, the spacer element is formed from a continuously tapered shaft, whereby the circular flow cross-section surrounding the shaft is completely available for transporting the melt from the screw to the mixing and dosing device. In this way, the necessary freedom of movement of the piston and screw can be created in a very simple manner without

Prof. Dr. Ing. Erich Schürmann

- regardless of the position of the spray device - the flow channel for the melt is interrupted.

Finally, a preferred embodiment of the invention is designed such that an additional intermediate component is arranged between the nozzle component and the housing component in front of the movement space of the piston, which represents an extended collection space for the melt in the x-direction, wherein the piston is provided on the nozzle side with a tapered shaft which serves to expel the melt.

This embodiment also has the advantage that the "first in - first out principle" is guaranteed, since the melt components that first enter the collection chamber are ultimately also the first to be injected through the nozzle into the injection mold.

It would also be conceivable in a further embodiment of the invention that the spacer element is formed from a tapered shaft, the cross section of which decreases slightly conically from the screw to the piston, wherein a diaphragm ring reducing the annular cross section is arranged in the housing at a short distance from the movement area of the piston, and wherein the shaft is provided with at least one through-bore running in the axial direction, which connects a flow channel leading out of the screw with an annular constriction of the shaft on the piston side, which creates a fluidic connection between the through-bore and the annular flow cross section.

This special solution has the advantage that even when the piston/screw arrangement (spraying device) is in the advanced position, no dead spaces are created in the flow cross-section available to the melt, so that the so-called "first in - first out principle" is also guaranteed here.

Prof. Dr. Ing. Erich Schürmann

Finally, the invention also relates to an embodiment in which the

An additional housing component having a nozzle is arranged in front of the movement space of the piston, which represents an extended collection space for the melt, wherein the piston is provided on the nozzle side with a tapered shaft which serves to eject the melt.

Here, too, the principle of "first in - first out" is ultimately advantageously ensured, since the melt components that first enter the area in front of the piston from the flow channel running through the mixing and dosing device are the first to enter the injection mold when the melt is later ejected, with the subsequently melted melt components following in the respective chronological sequence.

Further advantages of the invention will become apparent from the following description of several embodiments. They show:

Fig. 1 is a longitudinal section through a first embodiment of an injection unit after the ejection of the melt,

Fig. 2 is a longitudinal section through the injection unit according to Fig. 1 during the filling of the collecting space for the melt arranged in front of the piston,

Fig. 3 is a longitudinal section through the injection unit according to Figs. 1 and 2 with filled collecting space for the melt,

Fig. 4 is a longitudinal section through a second embodiment of an injection unit after the ejection of the melt,

Fig. 5 is a longitudinal section through the injection unit according to Fig. 4 during the filling of the collecting space for the melt,

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Prof. Dr. Ing. Erich Schürmann

Fig. 6 is a longitudinal section through the injection unit according to Figs. 4 and 5 with filled collecting space for the melt,

Fig. 7 is a longitudinal section through a third embodiment of an injection unit with an upstream housing component,

Fig. 8 is a longitudinal section through the injection unit according to Fig. 7 during the filling of the collecting space for the melt and

&iacgr;&ogr; Fig. 9 is a longitudinal section through the injection unit according to Fig. 7 and

8 with filled collecting space for the melt.

In the drawings, an injection unit of an injection molding machine is designated overall by the reference numeral 10.

The injection unit 10 has a housing 11, which is formed from the components 12 to 16.

A circular cylindrical guide channel 17 is arranged in the components 12 and 13, in which a screw 18 of a spray device S is arranged so as to be rotatable and axially displaceable. The screw 18 is provided with a thrust device at its free end in a manner not shown. At the other end of the screw 18 there is a non-return valve 19 and, connected to this, a tapered shaft 20 and a piston 21. The piston 21 is arranged so as to be longitudinally displaceable in a rotating tube 22, on the outer circumferential surface of which alternating circular ring-like mixing elements 23 of a mixing and dosing device 24 are arranged. Other mixing elements 25 are attached to the component 15 of the housing 11 at a distance from the mixing elements 23 in such a way that a circumferential circular ring-shaped flow channel 26 is formed between the mixing elements 23 and 25. The unit consisting of piston 21, tube 22 and mixing elements 23 is connected to the tapered shaft and

Prof. Dr. Ing. Erich Schürmann

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the screw 18 is firmly or positively connected and rotatably mounted via ring bearings 27 within the housing 11.

Finally, the mixing and dosing device 24 also has devices for feeding additives 28, which are arranged within the component 15 and whose outlet opens into the flow channel 26 of the mixing and dosing device 24.

The flow channel 26 of the mixing and dosing device 24 is

The radial flow channel regions 29 and 30 are connected on the one hand to a collecting space 31 for the melt located in front of the piston and on the other hand above the flow channel region 30 to an annular space-like flow channel 32 surrounding the tapered shaft 20.

Finally, the component 16 of the housing 11 has a nozzle bore 33 through which the melt located in the collecting chamber 31 can be injected into an injection mold (not shown) arranged upstream of the component 16.

Fig. 1 shows the position of the injection unit 10 or the injection device S immediately after the injection process. It can be seen that the injection device S has been advanced by a maximum stroke H in the direction x up to the nozzle bore 33 (see comparison of Figs. 1 and 3). As a result, the melt was almost completely pressed out of the collection chamber 31 into the injection mold (not shown). After the screw 18 has started rotating again, material is increasingly plasticized in the screw 18 and then transported via the non-return valve 19 into the annular space-like flow channel 32 and further via the flow channel areas 30, 26 and 29 into the collection chamber 31 for the melt. Since the mixing and dosing device 24 is rotationally connected to the piston/screw drive (drive of the injection device S), during the conveyance of the melt and simultaneous feeding

Prof. Dr. Ing. Erich Schürmann

of additives ensures complete mixing of the melt before the last one enters the collecting chamber 31.

As more and more melt is transported into the collecting chamber 31, the injection device S, consisting of the piston 21 of the tapered shaft 20 and the screw 18, simultaneously moves backwards in the y-direction. This process is only completed when the collecting chamber 31 is filled and the piston 21 hits a shoulder 34 during its movement in the y-direction. This is the point in time at which the pusher (not shown) moves the injection device S in the x-direction, with the non-return valve 19 preventing the melt from flowing back into the screw 18 during the injection process.

A further embodiment of the injection unit 10 is shown in Fig. 4 to 6. The changes essentially relate only to the spacer element arranged between the piston 20 and the screw 18, which in this case is also formed in the form of a tapered shaft 35, but which tapers slightly conically from the non-return valve 19 to the piston 21. This shaft 35 has a central through-bore 36 which begins in the area of the non-return valve 19 and ends at the piston-side end of the shaft 35 in an annular constriction 37 of the shaft 35, which creates a fluidic connection between the through-bore 36 and an annular flow channel 38.

In addition, a diaphragm ring 39 which reduces the flow cross-section of the annular space-like flow channel 32 is arranged in the housing component 13 at a short distance from the movement range of the piston 21. Between this diaphragm ring 39 and a surface of the shaft 35, a maximum gap s _max is created when the spray device S is moved when the collecting chamber 31 is filled (end position in the y direction, see Fig. 6) and a minimum gap s _min after the emptying of the collecting chamber 31 (end position in the x direction, see Fig. A) .

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Prof. Dr. Ing. Erich Schürmann

This special arrangement prevents flow dead spaces in every position of the injection device S because with increasing movement of the injection device S in the x direction, the flow resistance of the annular flow channel 32 increases due to the continuous reduction of the gap s, so that the longer flow path through the through hole 36, the annular constriction 37 and the return path (in the y direction) through the annular flow channel 32 to the flow channel 30 still has a similar flow resistance to the aforementioned shorter flow path. This ensures that the melt that first leaves the non-return valve 19 is actually the first to pass through the flow channel 30 and ultimately reaches the collection chamber 31, so that it is also the first to be pressed through the nozzle bore into the injection mold (first in - first out principle).

The individual positions of this previously described injection unit 10 are shown in Figs. 4 to 6.

Finally, Figs. 7 to 9 show a further embodiment of an injection unit 10 in which an intermediate component is arranged between the component 16 having a nozzle bore 33 and the component 15 of the housing.

40 is arranged, with which a significant extension of the collecting space 31 in the x-direction is achieved.

In addition, the piston 21 is provided with a wave-like ejection element

41, which has a smaller diameter than the piston 21 and thus an annular space 42 remains as a flow cross-section for the melt. After the melt has been expelled from the collecting space 31 (see Fig. 7), the spraying device S is set in motion again, as in the other embodiments, so that a rotating movement of the spraying device S begins. At the same time, melt is fed through the various aforementioned flow channels 32, 30, 26 and 29 into the annular space 42 and then into the

Prof. Dr. Ing. Erich Schürmann

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Collecting space 31 between nozzle bore 33 and a free end 43 of shaft 41. At the same time, due to the increasing accumulation of melt in the collecting space 31, the entire injection device S is continuously moved backwards in the y-direction until the end position in the y-direction shown in Fig. 9 is reached. The aforementioned "first in - first out" principle is also advantageously ensured in this injection unit 10 with a pre-installed intermediate component.

Claims (8)

1. Injection unit of an injection molding machine with an injection device, which is driven axially and rotatingly in a housing and is designed as a piston/screw, which is provided with a non-return valve, the injection device being used for plasticizing during the transport of the plastic granulate and acting as a piston during the pressing of the plastic melt through a nozzle into an injection mold, and a device for mixing and dosing the plastic melt and additives, such as colorants, foaming agents, lubricants or the like, characterized in that a spacer element ( 20 , 35 ) is arranged between the non-return valve ( 19 ) of the screw ( 18 ) and the piston ( 21 ), the length of which corresponds at least to the stroke (H) of the injection device (S) and which has at least one flow channel ( 32 , 38 ) through which a fluidic connection is established in each position with a radially initially outward and then parallel to the movement and guide area of the piston ( 21 ) up to a Area between nozzle ( 33 ) and piston ( 21 ) extending, further flow channel ( 30/26/29 ) is ensured, and that the flow channel ( 26 ) runs through the mixing and dosing device ( 24 ) arranged adjacent to the movement and guide area of the piston ( 21 ). 2. Injection unit according to claim 1, characterized in that the mixing and metering device ( 24 ) at least partially surrounds the piston ( 21 ) in a circular ring shape. 3. Injection unit according to claim 1 or 2, characterized in that the mixing and dosing device ( 24 ) is connected to the injection device (S) with regard to its rotational movements. 4. Injection unit according to claim 1, 2 or 3, characterized in that the mixing and metering device ( 24 ) is formed from mixing elements ( 23 , 25 ) which are arranged on a rotatable tube ( 22) which is rotationally connected to the piston (21 ) and on the inner diameter of the housing ( 11 ), as well as at least one additive feed ( 18 ). 5. Injection unit according to one of the preceding claims, characterized in that the mixing elements ( 23 , 25 ) have different, opposite surface designs, in particular toothings. 6. Injection unit according to one of the preceding claims, characterized in that the spacer element is formed from a continuously tapered shaft ( 20 ) and that the annular flow cross-section ( 32 ) surrounding the shaft ( 20 ) is completely available for transporting the melt from the screw ( 18 ) to the mixing and dosing device ( 24 ). 7. Injection unit according to one of claims 1 to 5, characterized in that the spacer element is formed from a tapered shaft ( 35 ), the cross section of which decreases slightly conically from the screw ( 18 ) to the piston ( 21 ), that a diaphragm ring ( 39 ) reducing the annular cross section ( 38 ) is arranged in the housing ( 11 ) at a short distance from the movement range of the piston ( 21 ), and that the shaft ( 35 ) is provided with at least one through-bore ( 36 ) running in the axial direction, which connects a flow channel leading out of the screw ( 18 ) to a piston-side, annular constriction ( 37 ) of the shaft ( 35 ), which creates a fluidic connection between the through-bore ( 36 ) and the annular flow cross section ( 38 ). 8. Injection unit according to one of the preceding claims, characterized in that an additional intermediate component is arranged between the nozzle component ( 16 ) and the housing component ( 15 ) in front of the movement space of the piston ( 21 ), which represents a collecting space ( 31 ) for the melt that is expanded in the x-direction and that the piston ( 21 ) is provided on the nozzle side with a tapered shaft ( 41 ) that serves to expel the melt.