DE102013101353B3 - Plasticizing device for e.g. injection molding machine, has inlet openings that are provided to introduce inert gas into feed zone, and housing openings that are gas-tightly closed during operation of plasticizing unit - Google Patents

Abstract

The plasticizing device has a worm shaft (32) of the plasticizing screw (12) of the plasticizing cylinder (10) is led out to the rear direction of the drive unit (L,M) and is connected to a drive element (18) of the drive unit. A connection region (V) of the worm shaft and drive element is arranged in a separate housing or a housing portion (22a) of drive unit. The inlet openings (34b) are provided to introduce an inert gas into the feed zone of the plasticizing unit. The housing openings (50) are gas-tightly closed during operation of the plasticizing unit.

Description

The present invention relates to a plasticizing unit for a plastic processing machine according to the preamble of claim 1, in particular a plasticizing unit for an injection molding machine or an extrusion plant.

Injection molding machines conventionally comprise a plasticizing and injection unit and a closing unit, wherein in the latter one or more molds are provided, each with one or more cavities. In contrast, in the plasticizing and injection unit, a plastic starting material is melted - that is, a plastic state is transferred - and then injected through corresponding sprue channels into the cavity of a closed tool received in the closing unit.

In the plasticizing and injection unit embodiments are known in which the plasticization and the injection takes place in separate units. One speaks in these cases of a screw pre-plasticization with downstream injection piston-cylinder unit or "shot-pot unit".

Furthermore, embodiments are known in which a so-called auger is used, which is arranged in a plasticizing cylinder and can be acted both rotationally and in the axial direction and driven. During the rotation of the plasticizing screw, a plastic material is melted, inter alia, by the introduction of shearing energy and externally supplied heating energy. The melt material collects in a worm antechamber in front of the screw tip. With increasing metering, the screw is thereby pushed back or process. If sufficient melt has been plasticized, the screw is pushed forward by a drive in order to introduce the melt material via the runner channels into a closed cavity.

When operating plasticizing units, it may u. a. In the catchment area of the plasticizing unit material degradation of plastic granules occur, by oxidation with the air present in the catchment area. In order to avoid such an oxidation, it is known to flood the catchment area of the plasticizing unit via the funnel or the funnel block with a protective gas.

From the DE4233541A1 It is known to carry out the processing under protective gas in the processing of hydrolysis and / or oxidation-sensitive polymers, wherein the funnel is filled with argon, for example, and this argon also floats the plasticizing unit. During injection molding, a gas flow of about 1 liter per minute is maintained.

From the US6187229B1 It is known to introduce a protective gas such as nitrogen (N ₂ ) via the hopper block in the plasticizing cylinder and downstream out of the plasticizing cylinder via a suction port connected to a vacuum pump. In addition to the inert gas, other volatile substances can be removed and removed from the plasticizing cylinder via this suction opening.

While from the two aforementioned publications embodiments are known in which there is a constant supply of inert gas and thus a protective gas flow is maintained, it is also known from the prior art, the catchment area only to flood and perform the plasticizing gas-tight, so it does not is required to maintain a protective gas flow. For this purpose, for example, on the WO2009100473A1 directed. From the WO2009100473A1 a fumigation of the feed zone of a plasticizing unit is known, wherein the housing of the plasticizing screw is made gas-tight in the direction of the drive. The melt seals in the direction of the screw tip. In order to make the housing of the plasticizing screw gas-tight in the direction of the drive, it is known to provide the bearing of the worm shaft in the rear end wall of the worm cylinder with a suitable seal. The worm or the worm shaft is thus sealed against the cylinder.

The DE6610094U discloses an extruder for the preparation of polyamides with residual moisture for monofilament production. The hopper can be hermetically sealed by a hopper lid. The polyamide to be processed is introduced into the funnel without any pre-drying or consideration of existing moisture, the funnel is then hermetically sealed and the funnel contents are superimposed with an inert gas, for example nitrogen. So that the feed zone of the extruder is well sealed, is also in the DE6610094U (as well as in the aforementioned WO2009100473A1 ) provided the bearing of the worm shaft in the rear end wall of the worm cylinder with a suitable seal.

The DE 11 2007 000 216 T5 discloses an injection device in which a drying gas is introduced into the catchment area of the plasticizing screw. The dry gas supply passage for the supply of dry gas may also be located behind the material supply opening, via which plastic material is supplied to the plasticizing screw. In this case, a sealing member may be provided between the plasticizing screw and the cylinder.

However, such a seal has a number of disadvantages. On the one hand, the seal can be permanently deformed due to imbalances of the worm or the worm shaft. On the other hand, a significant abrasion occurs at the seal due to the rotation of the worm or the worm shaft, so that the seal must be replaced from time to time. Incidentally, leaks can occur with increasing wear of the seal and protective gas can escape at this point. It is therefore necessary to constantly monitor whether sufficient protective gas is still present in the catchment area and it is necessary from time to time to top up shielding gas in order to compensate for the leakage losses. In the long term, this can lead to a considerable consumption of protective gas. This known type of gas-tight design of a plasticizing unit can thus not be convincing in terms of energy and resource efficiency.

Based on the aforementioned prior art, the present invention seeks to provide a plasticizing, seen in the permanent and even over longer periods of operation of the plasticizing seen no or almost no losses of supplied inert gas.

This object is achieved by the features mentioned in claim 1. Advantageous embodiments and further developments can be found in the subclaims.

Due to the fact that that region of the plasticizing unit is gas-tight, in which the connecting region of the worm shaft and a drive element of the drive unit is, for the first flooding with protective gas compared to the aforementioned prior art, a larger amount or a larger volume of inert gas required, but the plasticizing unit remains permanently gastight. In particular, the operation of the plasticizing unit does not adversely affect the tightness. Therefore, it does not usually occur over longer operating times of the plasticizing unit to losses of supplied inert gas. The once made flooding of the catchment area of the plasticizing unit remains.

The aforementioned connection region is located in a separate housing or in a housing component of the drive unit, wherein the housing or the housing component has one or more closable housing openings, in particular mounting openings and viewing windows. According to the invention, these housing openings should be closed gas-tight. Furthermore, these housing openings should be closed or covered gas-tight during operation of the plasticizing unit.

In an advantageous embodiment of the invention, the housing openings can be covered and thus closed by means of cover elements, wherein suitable sealing means can be provided between the cover elements on the one hand and the housing or the housing component on the other hand. For example, the sealing means may be formed as a sealing cord or sealing loop, which rotate around the housing openings around. The sealing means may be provided on the housing or the housing component. But they can also be provided on the cover elements. Of course, sealing means can be provided both on the cover elements and on the housing or the housing component. In this case, identical, identical or even different or different sealing means can be used. For example, the sealing means on or on the cover elements could have a different shape than the sealing means on the housing or the housing component. With regard to the material of the sealant, it should be ensured that these are made of a sealing material, for example EPDM, in particular with regard to the protective gas used.

Depending on the intended use of the housing openings, the cover elements can be permanently or detachably connected to the housing or housing component. If the cover elements are durable, d. H. can not be detachably connected to the housing or the housing component, it may also be an adhesive in the sealing means, d. H. the cover elements can be glued over the housing openings covering the housing or the housing component. But it is also possible to dimension the cover so that they can be inserted into the housing openings and glued there.

A housing opening, which must be accessible from time to time for assembly purposes, sometimes also referred to hereinafter as a mounting opening, is usually covered and sealed with a cover plate which removably and removably attaches the housing opening to or on the housing or housing component is, for example by means of a screw connection. A housing opening, which merely serves to allow an operator an insight into the interior of the housing or the housing component, hereinafter occasionally also referred to as a viewing opening can be permanently covered or closed with a viewing window, ie not necessarily one detachable connection can be provided. Thus, the viewing window can be glued onto the housing or the housing component so as to cover the viewing opening. It is also it is possible to dimension the viewing window so that it can be inserted into the viewing opening and glued in there.

The sealing means for gas-tight construction of the housing or the housing component may thus also be an adhesive. Of course, depending on the material of the cover, another cohesive connection may be considered as an adhesive.

Furthermore, the drive element connected to the worm shaft can be led out of the housing or the housing component in the direction of the drive unit with a suitable seal. If a hydraulic linear or axial drive is provided, the drive element may be the piston rod of the hydraulic drive and the seal may be the already existing sealing ring sealing the piston rod with respect to the hydraulic fluid. Otherwise, other suitable seals may be provided.

The protective gas can preferably be introduced via the material supply unit, via which the plastic material to be processed and in particular present in granular form is entered into the plasticizing unit. In this case, the protective gas can be introduced into the catchment area via the funnel and / or via the funnel block of the material supply unit. As an inlet opening for introducing the protective gas in the catchment area can thus serve the funnel itself or its lower outlet opening. However, it is also possible for one or more inlet openings to be provided in the funnel block, which can be connected to a protective gas source.

An embodiment of the present invention will be described below with reference to FIGS 1 and 2 explained. It shows the 1 a schematic representation of the plasticizing and injection unit in side view and in sectional view (predominantly). The 2 shows a perspective view of a plasticizing and injection unit according to the invention.

In the 1 is a plasticizing and injection unit with a plasticizing cylinder 10 represented in which a plasticizing screw 12 rotatably and axially slidably received in a known manner. At the top of the plasticizing unit 14 is an injection port 16 provided, via which a plastic melt located in the screw antechamber can be transferred into a cavity of an injection mold. Furthermore, the plasticizing screw 12 at its front end via a Rückströmsperre 30 , At the rear end of the plasticizing cylinder 10 is on a funnel block 34 a hopper 36 attached. The funnel block 34 has a vertical bore 34a , via which the usually in granular form plastic material from the hopper 36 in the plasticizing cylinder 10 reach and the catchment area of the plasticizing screw 12 can be supplied. Furthermore, in the funnel block 34 a hole 34b provided via the a suitable protective gas such as argon or nitrogen in the plasticizing 12 or in the catchment area of the plasticizing screw 12 can be supplied. The rear part of the plasticizing cylinder 10 is with a drive housing 22 in particular, the axial drive L for the plasticizing screw 12 is realized. On its upper side has the housing section 22a via a housing opening 50 (see also 2 ). In a chamber of the housing 22 is a double-acting injection piston 20 slidably received back and forth, this chamber in a first hydraulic chamber 24 and a second hydraulic chamber 26 divided. The hydraulic piston 20 has a central piston stem 18 on, whose front end is fixed to the worm shaft 32 the plasticizing screw 12 connected is. The worm shaft 32 is through a pivot bearing 38 through the rear end wall of the plasticizing cylinder 10 passed. In the piston shaft 18 Coaxially a bore is provided, whose inner surface is formed with a splined groove, in the form-fitting a splined toothing of an output shaft received therein 29 a rotary drive M is added. Due to the combination of splined and splined, the output shaft is 29 while axially in the piston skirt 18 slidably, but rotatably recorded. Via cables 40 and 41 can a hydraulic fluid in the hydraulic chambers 24 and 26 be added and removed. In this case, with a corresponding admission of the second hydraulic chamber 26 the plasticizing screw 12 Move forward, which is injected into the cavity vortex material in a cavity. When applying the first hydraulic chamber 24 the snail can be actively withdrawn.

The housing 22 has a housing section 22a in which the worm shaft 32 with the piston shaft 18 of the axial drive L is connected. The housing section 22a Can also be used as a separate case 22b be executed as in the 2 is shown, which will be described in more detail below.

The 2 shows an injection unit according to the invention in a perspective view. For a better overview, the hopper is 36 omitted and the axial drive L is shown only in part. In contrast to 1 are still heating cables 71 . 72 . 73 and 74 shown, the plasticizing cylinder 10 surround.

In the case 22b are housing openings 50 . 60 present, which are closed during operation of the injection unit with suitable cover elements. For example, at the top of the case 22b a comparatively large housing opening 50 intended. It is a so-called mounting opening, through which one has access to the connection or coupling between the worm shaft 32 and the piston shaft 18 of the axial drive L. In operation, this housing opening 50 closed by a suitably large cover. For example, a suitably large cover plate 54 be provided by means of screw on the top of the housing 22b can be releasably attached. Furthermore, the housing 22b on one side, in particular on the operating side of the injection molding machine, a further housing opening 60 have, via which an operator in the interior of the housing 22b can look into it. This case opening 60 can also be referred to as a viewing opening and is in operation with a suitable large viewing window 64 locked. According to the invention, it is now provided that the housing 22b is designed gas-tight. These are the case openings 50 and 60 around suitable seals 52 and 62 provided so that when fixing cover plate 54 and lens 64 the housing openings 50 and 60 are sealed gas-tight. For example, around the mounting hole 50 around a sealing cord are laid before the cover plate 64 to the housing 22b is screwed on.

Of course, the cover plate 54 also have yourself a suitable sealing cord. The term "sealing cord" is in no way limiting, but it is intended to mean all sealing means or sealing elements which are suitable for fastening the cover plate 54 on the case 22b a gas-tight seal the mounting hole 50 to effect. The sealing of the housing opening 60 or the viewing opening 60 can be done in the same way as the sealing of the mounting hole 50 , Because the lens 64 but not necessarily solvable with the housing 22b can be connected, the lens can 64 also by means of suitable adhesive gas-tight to the housing 22b glued on or - with appropriate dimensioning of the lens 64 - in the viewing opening 60 used and with the housing 22b be glued. In the direction of the axial drive L is the housing 22b anyway tight because of the piston skirt 18 through a seal 80 anyway sealed for the hydraulic fluid. In the direction of the injection opening 16 automatically results in a gas-tight seal through the plastic melt in the plasticizing 10 , Will now over the inlet opening or bore 34b a protective gas in the catchment area of the plasticizing screw 12 fed, this protective gas flows on the one hand in the direction of the Schneckenvorraums until it is stopped by plastic melt, and on the other to the rear towards the rear end of the plasticizing 10 , Through the pivot bearing 38 enters the protective gas in the gas-tight housing 22b and gradually fill its interior with protective gas until the interior of the housing 22b completely filled with protective gas at the end. Because of the seals 52 and 62 also no protective gas in the area of the housing openings 50 and 60 out of the case 22b escape.

The invention has been described herein with reference to a plasticizing and injection unit with a screw conveyor. Of course, the invention can also be implemented in a plasticizing and injection unit with screw pre-plasticization and ShotPot. Furthermore, extrusion systems can also be equipped with a plasticizing unit according to the invention.

• • Wird Stickstoff als Schutzgas verwendet, ist dieses geringfügig leichter als Luft und kann daher über den Trichter entweichen. In diesem Fall kann ein Nachdosieren von Stickstoff nach Bedarf (z. B. über das Messen und Überwachen der Sauerstoffkonzentration) und/oder in einem definierten Zeitabstand vorgesehen werden (z. B. immer zu Beginn des Plastifizierens oder am Ende der Nachdruckphase bis zum Ende des Plastifizierens).
• • Wird Argon als Schutzgas verwendet, ist dieses schwerer als Luft und sollte somit im Gehäuse verweilen. Ein Nachdosieren sollte somit nicht erforderlich werden. Aber auch dies kann über das Messen und Überwachen der Sauerstoffkonzentration an geeigneter Stelle im Gehäuse überwacht werden, so dass im Bedarfsfalle auch ein Nachdosieren von Argon vorgenommen werden kann.
• • Beim Befüllen des Gehäuses mit Schutzgas kann ein Entlüften des Gehäuses durchgeführt und durch geeignete Sensoren überwacht bzw. geregelt werden.

With regard to the protective gas, the following should be noted:

• • When nitrogen is used as a shielding gas, it is slightly lighter than air and can therefore escape through the funnel. In this case, replenishment of nitrogen may be provided as needed (eg, by measuring and monitoring the oxygen concentration) and / or at a defined time interval (eg, always at the beginning of the plasticizing or at the end of the holding phase until the end plasticizing).
• • Argon used as a shielding gas, this is heavier than air and should therefore remain in the housing. A re-dosing should therefore not be required. But even this can be monitored by measuring and monitoring the oxygen concentration at a suitable location in the housing, so that in case of need also a post-dosing of argon can be made.
• • When filling the housing with protective gas, the housing can be vented and monitored or regulated by suitable sensors.

LIST OF REFERENCE NUMBERS

10

plasticizing

12

plasticizing

14

Tip of the plasticizing unit

16

Injection opening

18

piston shaft

20

Injection piston

22

Housing for the injection piston

22a

Housing section with openings

22b

own housing

24

First hydraulic chamber

26

Second hydraulic chamber

29

output shaft

30

backflow

32

worm shaft

34

funnel block

34a

Drilling for granules

34b

Inlet opening or hole for inert gas

36

hopper

38

pivot bearing

40

Hydraulic line to the first hydraulic chamber

41

Hydraulic line to the second hydraulic chamber

50

Housing opening (mounting opening)

52

Seal around mounting hole

54

Cover plate

60

Housing opening (view opening)

62

Seal around sight opening

64

Window

71, 72,

Heating tapes

73, 74

80

poetry

L

Linear or axial drive

M

rotary drive

Claims (7)

Plasticizing unit ( 10 . 12 ) for a plastic processing machine, in particular for an injection molding machine or for an extrusion plant, comprising a plasticizing cylinder ( 10 ) with a plasticizing screw ( 12 ) and a drive unit (L, M) with at least one rotary drive (M) for generating a rotary movement of the plasticizing screw ( 12 ), whereby the worm shaft ( 32 ) of the plasticizing screw ( 12 ) from the plasticizing cylinder ( 10 ) led back towards the drive unit (L, M) and with a drive element ( 18 ) of the drive unit is connected or connectable, wherein the connection region (V) of worm shaft ( 32 ) and drive element ( 18 ) in a separate housing ( 22b ) or a housing component ( 22a ) of the drive unit (L, M) is arranged, wherein the housing ( 22b ) or the housing component ( 22a ) one or more closable housing openings ( 50 . 60 ), and wherein one or more inlet openings ( 34b ) are provided in the plasticizing unit, in order to introduce a protective gas into the catchment area of the plasticizing unit ( 10 . 12 ), characterized in that the housing openings ( 50 . 60 ) are gas-tight, and that the housing openings ( 50 . 60 ) are sealed gas-tight during operation of the plasticizing unit. Apparatus according to claim 1, characterized in that; that the housing openings ( 50 . 60 ) by means of cover elements ( 54 . 64 ) are coverable, wherein the cover elements ( 54 . 64 ) the housing openings covering the housing ( 22b ) or the housing component ( 22a ) are attachable, and wherein between the cover elements ( 54 . 64 ) and the housing ( 22b ) or the housing component ( 22a ) Sealing means are provided. Apparatus according to claim 2, characterized in that the sealing means as a sealing cord or sealing loop ( 52 . 62 ) are formed, which around the housing openings ( 50 . 60 ) are circumferentially formed around, wherein the sealing means ( 52 . 62 ) on the one hand to the housing ( 22b ) or the housing component ( 22a ) and / or on the other hand on the cover elements ( 54 . 64 ) are provided, and wherein the sealing means consist of a sealing material with respect to the protective gas, for example EPDM. Device according to claim 1 or 2, characterized in that the sealing means are an adhesive. Device according to one of the preceding claims, characterized in that the drive element ( 18 ) with a seal ( 80 ) out of the housing ( 22b ) or the housing component ( 22a ) is led out in the direction of the drive unit (L, M). Device according to one of the preceding claims, characterized in that a material feed unit ( 34 . 36 ) is provided, which an outlet opening ( 34a ), which at an inlet opening in the plasticizing cylinder ( 12 ) is connected, so that by means of the material supply unit ( 34 . 36 ) in the plasticizing cylinder ( 12 ) material to be processed into the catchment area of the plasticizing unit ( 10 . 12 ), and that the protective gas is supplied via the material supply unit ( 34 . 36 ) can be fed. Apparatus according to claim 6, characterized in that the material feed unit ( 34 . 36 ) a hopper ( 36 ) and a funnel block ( 34 ), and that the inert gas through the hopper ( 36 ) and / or over the funnel block ( 34 ) in the plasticizing cylinder ( 10 ) can be fed.

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