DE102007030704A1 - Plasticator of injection molding machine for manufacturing plastic melt, has units for inserting fluid in screw with incorporated bore, and fluid is led to discharge duct, which is provided in axial end area of screw - Google Patents

Abstract

The plasticator (1) has a screw cylinder (2), in which a screw (3) is movably arranged in swiveling and axial manner. Units are provided for inserting a fluid (G) into the plastic melt. The screw cylinder has a space (7) in front of the screw, in which plastic melt is collected for injecting into an injection molding tool. The units for inserting a fluid in the screw has incorporated bore (4). The fluid is led to a discharge duct (5), which is provided in the axial end area of the screw close to the space in front of the screw. An independent claim is also included for a method for manufacturing a plastic melt in a plasticator of an injection molding machine.

Description

The The invention relates to a plasticizing unit of an injection molding machine for producing a plastic melt, wherein the plasticizing unit a worm cylinder, in which a worm rotatable and is arranged axially displaceable, wherein the plasticizing unit Having means for introducing a fluid in the plastic melt and wherein the screw cylinder has a screw antechamber, in which molten plastic for injection into an injection mold can collect. Furthermore, the invention relates to a method for producing a plastic melt.

For the production From plastic moldings made of foamed plastic, it is procedurally required in the manufacture of plastic melt for the purpose of injection molding a fluid, usually a gas, to introduce into the plastic melt, in the form of small and smallest bubbles in the plastic melt triggers, so that a foam material is formed. It is between the introduction a physical and a chemical blowing agent distinguished.

at the physical foaming process can the fluid either during plasticizing the material or during the injection of the melt in an injection mold be introduced. To one as possible homogeneous foam structure in the plastic melt and thus in the finished molded part it is necessary to reach the fluid as possible evenly in the Melt to dissolve. In this case, the melt in the areas where a solution of Fluid in the melt should form, be kept under pressure, for a premature frothing to prevent. At the same time it must be ensured that no Fluid from the screw cylinder in the direction of the filling opening for the plastic granules escapes. If the fluidized melt then in an injection mold injected, it comes because of the associated pressure drop for foaming of the fluid, d. H. for foaming.

Known is it about the fluid over to feed the screw cylinder at a feeding point of the melt. there it can be local to education high fluid concentrations come. One reason for this is that the entry point for the fluid mostly not contour adapted to the screw cylinder accomplished is and thus in the zones where no adequate rinsing effect is present (so-called dead water zones) a higher fluid concentration can. In the case of a gas as a fluid are already forming in the Plastic melt in this way disadvantageously larger gas bubbles, which is after injection of the melt into the cavity of the injection mold find. Such big bubbles adversely affect the mechanical strength of the plastic material out.

Farther is the speed of the melt on the inner wall of the screw cylinder Zero, which means that the onward transport of the fluid-laden Melt immediately at the insertion of the screw cylinder must be made by diffusion and only when the fluid into areas with higher Speed has arrived, a distribution and a transport of Fluids in the melt by the much more effective convection can be done. diffusion processes in the plastic melt, however, only relatively slowly take place.

in addition comes that by passing the Schneckensteges or the Webs of mixing and shearing elements of the screw at the Fluideinbringstelle in the worm cylinder, the fluid flow is not uniform. Every time while the plastification of the screw web at the point of introduction of the fluid passes by, rises locally the pressure on, leaving a higher Resistance for the entry of fluid into the melt is present. When using of augers, as is typical in injection molding of the Case is shortened the effective screw length during the Dosing. The introduction of fluid therefore takes place in different ways processed areas of the melt. At the beginning of dosing is the snail still in its foremost position, d. h the contribution the fluid in this case is relatively far from the screw tip away. If, however, the screw has reached the end of the metering path, the fluid is already introduced near the screw tip. Therefore it is with larger Dosierwegen required, several points of introduction for the fluid at different provide axially offset points of the worm cylinder to the Degree of homogeneity to increase. However, this represents a relatively large amount of equipment.

Of the Invention is based on the object, a plasticizing a injection molding machine and to provide a method for producing a plastic melt, the one or the other Brings improvements. It should therefore be achieved in a simple manner be that a high homogeneity of the solution the fluid is present in the plastic melt, so that qualitatively high quality foamed plastic moldings can be sprayed. The concentration of the fluid in the melt should be as local as possible be equal; Concentration differences should be largely avoided become.

The solution of this problem by the invention is characterized in that the means for introducing a fluid comprise at least one hole machined into the screw over that a fluid can be passed to at least one outlet channel, which is located in the axial end of the screw near the Schneckenvorraums.

The at least one bore extends preferably coaxial with the axis of rotation of the screw. The at least An outlet channel can be considered perpendicular or at an angle to the Bore extending bore may be formed. It can at least an outlet channel can be arranged in the screw tip.

Of the At least one outlet channel may be on the surface of the Snail be designed as a hole or slot. To the exit to allow fluid however, to prevent the entry of melt, has the bore or the slot preferably has a diameter or a width, which is between 0.01 mm and 0.25 mm.

It may alternatively be provided for controlling the fluid flow, the at least one outlet channel has valve means, with a fluid flow back can be prevented in the hole.

A another alternative solution provides that in the at least one outlet channel a material used with high porosity is. In this case, the material with high porosity is preferably sintered metal.

One well-distributed fluid leakage is favored when in accordance with a Further development is provided that a plurality of outlet channels are provided. The exit channels can while equidistant around be arranged around the circumference of the screw. Furthermore, the outlet channels be arranged offset in the axial direction of the screw.

A Particularly preferred embodiment of the invention provides that in the bore in the screw, a piston is arranged, at least temporarily can be arranged axially immovable. In the piston can be incorporated a bore through which the fluid to the at least an outlet channel can be passed. This hole in the piston is preferably arranged coaxially to the center line of the piston. In the hole in the piston can Valve means may be arranged, with which a return flow of fluid from the at least an exit channel can be prevented in the bore. These Valve means are preferred as a spring-biased check valve educated.

in the Area of the at least one outlet channel is preferably at least a mixing and / or shearing element, in particular a screw flight, arranged.

The Means for introducing a fluid can also be multiple, in particular Twice, to be present to two different fluids in the plastic melt to contribute. The funds can at least two coaxial with the axis of rotation of the screw arranged Pipes for comprise at least two different fluids.

The inventive method for producing a plastic melt in a plasticizing unit an injection molding machine provides that while the melting of plastic material by rotation of the screw in the worm cylinder at least one fluid through at least one is passed into the screw incorporated bore, wherein the Fluid from the at least one bore to at least one outlet channel passed in the axial end of the screw near the Schneckenvorraums will, over it enters the plastic melt.

The The worm can be coaxial to the axis of rotation of the worm and having fluid-rolled bore in which the piston arranged is while being the melting of plastic melt (dosing) and their accumulation in the worm antechamber the worm axially away from the worm antechamber is moved while during this axial screw movement of the piston is held axially, so that in the bore existing fluid through the relative axial Displacement of the piston in the bore via the at least one outlet channel is introduced into the plastic melt.

In This case provides a preferred embodiment of the method before that the piston is positioned so that it is furthest in the from the screw antechamber remote axial position of the screw in essentially inserted to the end of the bore.

Preferably is before the beginning of the axial withdrawal movement the screw bore with fluid in the desired amount and / or pressure filled.

With the proposed plasticizing unit and the corresponding method for the production of plastic melt is achieved that in apparativ relatively simple way (at least) a fluid of the plastic melt while fed to their plasticization can be, with the fluid distributed very evenly in the melt. Accordingly, concentration differences of the fluid in the melt largely avoided. The result is a homogeneous plastic melt, with the high quality foamed Plastic moldings can be injected.

In the drawing is an embodiment of Invention shown. The single figure shows the cut through a plasticizing unit of an injection molding machine, wherein from the plasticizing unit a worm cylinder with a screw in it is shown.

The plasticizing unit 1 for the production of plastic melt has a screw cylinder 2 in which, in a known manner, a snail 3 is arranged. The snail 3 has as usual snail bars 10 on, which are indicated only very schematically and knead the plastic material to be plasticized and homogenize. The snail 3 is designed as a screw conveyor, ie it is not only rotatably arranged in the screw cylinder, but it can also be moved axially. In the left end area in the area of an outlet opening 12 for melt is a Schneckenvorraum 7 present, can be cumulated in the melt, before this also axial movement of the screw 3 (to the left) over the exit opening 12 can be driven into the cavity of an injection molding tool, not shown.

The plasticizing unit 1 is designed to add a fluid G, which may be a propellant. In the present case, a gas is used as the fluid, which consists of a source, not shown, of the plasticizing unit 1 is supplied, so that with her a melt-gas mixture can be produced. The gas G should be present in finely divided form homogeneously in the plastic melt.

So that the gas G can be introduced as homogeneously as possible in the plastic melt, the following gas supply is provided: The screw 3 has a bore concentric with its axis of rotation 4 on, near the snail tip 13 ends. In the end of the hole 4 are exit channels 5 present, of which only one is shown. The exit channels 5 are here designed as bores, which are perpendicular to the axis of rotation of the screw 3 , ie extend radially and on the cylindrical outer surface of the screw 3 lead. The outlet is designed circular or slot-shaped. In this case, the diameter or the slot width of the outlet is selected so that although the low-viscosity fluid G can escape, but not higher-viscosity melt in the outlet channels 5 can occur. In this way, an entry of melt and thus a clogging of the outlet channels 5 prevented.

In the hole 4 is a piston 6 arranged, in its interior a bore 8th Has. This hole 8th is in the right end of the snail 3 connected to a fluid source via the gas G in the bore 8th The connection to the fluid source is indicated only schematically, so that gas G from the fluid source via the bore 8th into the hole 4 and continue via the exit channels 5 and the plastic melt can enter, but the reverse approach is not possible, is in the (left) end region of the piston 6 a valve means 9 arranged in the form of a spring-biased check valve.

The hole 4 has an end 11 up to which the piston 6 can be inserted.

The introduction of fluid G thus takes place via the screw 3 , The advantage of this is that on the surface of the screw 3 in the movement of which the plastic melt has both a velocity component in the direction of the screw channel and transversely thereto. As a result, the introduced fluid G on the one hand evenly in the screw channel in the direction of the antechamber 7 promoted, on the other hand, it comes through the cross-flow to a good mixing of melt areas, which already have a corresponding load of fluid, with the screw areas, which still have little or no loading with fluid.

The introduction of the fluid G preferably takes place in suitably prepared melt, in particular directly behind the metering zone or behind a shear and mixing zone of the screw 3 , In this "solution formation zone", diffusion and convection processes lead to the formation of a homogeneous solution of fluid G in the melt.

Since the solubility and the diffusion rate of fluid and melt usually increases with the temperature of the melt, by external heating of the screw cylinder in this area or by an upstream shear element (such as the screw flight 10 or by an additional shear element) the melt temperature can be raised. Thereafter, the mixing of the introduced fluid with the melt takes place in a mixing zone of the screw. In a subsequent zone, the melt temperature is reduced again to achieve short cooling times of the molded part and rapid stabilization of the foam structure during injection into the mold cavity. This cooling zone may also be part of the nozzle of the plasticizing cylinder.

The supply of the fluid G takes place - as explained - from the screw shaft over the bore 4 and the exit channels 5 , The end of the exit channels 5 are formed either as a fine holes or slots, these insertion points are geometrically designed so that the fluid escape due to the low viscosity, but can not get a melt in the fluid supply lines.

Alternatively, a valve mechanism in the outlet channels 5 be provided, which may be either by the fluid pressure itself or positively controlled, so that the fluid can flow only in the melt. The closing of these valves can be done either by a spring mechanism (spring-biased check valve) or positively controlled.

Another way to allow the discharge of fluid into the melt, but no melt back, is that the fluid through a sintered metal insert from the outlet channel 5 exit. Due to its structure, the sintered metal insert has very fine channels through which the fluid can flow, but into which no melt can enter.

Advantageously, a plurality of outlet openings are provided for the fluid (although only one such outlet opening is provided in the figure), which are arranged offset in the circumferential direction and also in the axial direction. It is also possible that the fluid at the screw tip 13 exit.

Not shown in the figure is the possibility to provide for the achievement of particular properties of the foam structure, the supply of two or more fluids, preferably at different locations of the screw 3 enter the melt. The supply of fluids may be either by concentrically arranged tubes or by adjacent holes in the screw 3 respectively.

In the exemplary embodiment, the introduction of the fluid G into the melt takes place during dosing by the piston 6 , This is - at least during the dosing - arranged axially fixed (indicated in the figure by the right end of the piston 6 ). When dosing it will be in the hole 4 located fluid G through the piston 6 out of the hole 4 due to the worm retraction movement.

The volume of the hole 4 is filled with fluid G during or after the injection of the plastic melt into the cavity of the tool. The check valve 9 in the hole 8th in the piston 6 prevents fluid G from being forced back into the fluid supply line during dosing. By choosing the length of the piston 6 it is ensured that at the Dosierwegende the entire amount of fluid is forced into the melt, ie the piston 6 reaches the end 11 the bore 4 ,

By the pressure with which the volume of the bore 4 is prefilled with fluid G, the amount of fluid to be supplied to the melt can be adjusted.

The valve means 9 and optionally also valve means in the outlet channels 5 can be opened and closed by active control or actuation so that process variations are possible and fluid G is injected into the melt in a specifically predetermined time sequence.

1

plasticizing

2

screw cylinder

3

slug

4, 5, 6

medium for introducing a fluid

4

drilling

5

outlet channel

6

piston

7

the screw

8th

drilling

9

valve means (Check valve)

10

mixing and / or shear element (screw flight)

11

The End the bore

12

outlet opening

13

screw tip

G

fluid (Gas)

Claims (24)

Plasticizing unit ( 1 ) of an injection molding machine for producing a plastic melt, wherein the plasticizing unit ( 1 ) a worm cylinder ( 2 ), in which a screw ( 3 ) is arranged rotatable and axially displaceable, wherein the plasticizing unit means ( 4 . 5 . 6 ) for introducing a fluid (G) into the plastic melt and wherein the screw cylinder ( 2 ) a worm anteroom ( 7 ), in which plastic melt can collect for injection into an injection mold, characterized in that the means ( 4 . 5 . 6 ) for introducing a fluid (G) at least one into the screw ( 3 ) incorporated hole ( 4 ), via which a fluid (G) to at least one outlet channel ( 5 ) can be guided, which in the axial end of the screw ( 3 ) near the snail's anteroom ( 7 ) is located. Plasticizing unit according to claim 1, characterized in that the at least one bore ( 4 ) coaxial with the axis of rotation of the screw ( 3 ) runs. Plasticizing unit according to claim 1 or 2, characterized in that the at least one outlet channel ( 5 ) as perpendicular or at an angle to the bore ( 4 ) extending bore is formed. Plasticizing unit according to one of claims 1 to 3, characterized in that the at least one outlet channel ( 5 ) is arranged in the screw tip. Plasticizing unit according to one of claims 1 to 4, characterized in that the at least one outlet channel ( 5 ) on the surface of the screw ( 3 ) is formed as a bore or slot. Plasticizing unit according to claim 5, characterized in that that the hole or slot has a diameter or a width which is between 0.01 mm and 0.25 mm. Plasticizing unit according to one of claims 1 to 4, characterized in that the at least one outlet channel ( 5 ) Valve means, with which a fluid flow back into the bore ( 4 ) can be prevented. Plasticizing unit according to one of claims 1 to 4, characterized in that in the at least one outlet channel ( 5 ) a material with high porosity is used. Plasticizing unit according to claim 8, characterized in that that the material with high porosity sintered metal is. Plasticizing unit according to one of claims 1 to 9, characterized in that a plurality of outlet channels ( 5 ) are provided. Plasticizing unit according to claim 10, characterized in that the outlet channels ( 5 ) equidistant around the circumference of the screw ( 3 ) are arranged around. Plasticizing unit according to claim 10 or 11, characterized in that outlet channels ( 5 ) in the axial direction of the screw ( 3 ) are arranged offset. Plasticizing unit according to one of claims 1 to 12, characterized in that in the bore ( 4 ) a piston ( 6 ) is arranged, which can be arranged at least temporarily axially immovable. Plasticizing unit according to claim 13, characterized in that in the piston ( 6 ) a hole ( 8th ) is incorporated, via which the fluid (G) to the at least one outlet channel ( 5 ) can be directed. Plasticizing unit according to claim 14, characterized in that the bore ( 8th ) in the piston ( 6 ) coaxial with the center line of the piston ( 6 ) runs. Plasticizing unit according to claim 14 or 15, characterized in that in the bore ( 8th ) in the piston ( 6 ) Valve means ( 9 ) are arranged, with which a backflow of fluid (G) from the at least one outlet channel ( 5 ) into the hole ( 8th ) can be prevented. Plasticizing unit according to claim 16, characterized in that the valve means ( 9 ) are formed as a spring-biased check valve. Plasticizing unit according to one of claims 1 to 17, characterized in that in the region of the at least one outlet channel ( 5 ) at least one mixing and / or shearing element ( 10 ), in particular a screw land, is arranged. Plasticizing unit according to one of claims 1 to 18, characterized in that the means ( 4 . 5 . 6 ) for introducing a fluid (G) several times, in particular twice, are present in order to bring two different fluids (G) in the plastic melt can. Plasticizing unit according to claim 19, characterized in that the means ( 4 . 5 . 6 ) at least two coaxial with the axis of rotation of the screw ( 3 ) arranged tubes for at least two different fluids. Process for producing a plastic melt in a plasticizing unit ( 1 ) of an injection molding machine, wherein the plasticizing unit ( 1 ) a worm cylinder ( 2 ), in which a screw ( 3 ) is arranged rotatably and axially displaceable, wherein the plasticizing unit further comprises means ( 4 . 5 . 6 ) for introducing a fluid (G) into the plastic melt and wherein the screw cylinder ( 2 ) a worm anteroom ( 7 ), in which plastic melt can collect for injection into an injection mold, characterized in that during the melting of plastic material by rotation of the screw ( 3 ) in the screw cylinder ( 2 ) at least one fluid (G) through at least one in the screw ( 3 ) incorporated hole ( 4 ), wherein the fluid (G) from the at least one bore ( 4 ) to at least one exit channel ( 5 ) in the axial end region of the screw ( 3 ) near the snail's anteroom ( 7 ), through which it enters the plastic melt. A method according to claim 21, characterized in that the screw ( 3 ) one to the axis of rotation of the screw ( 3 ) coaxial and filled with fluid (G) bore ( 4 ), in which a piston ( 6 ) is arranged, wherein during the melting of plastic melt and their accumulation in Schneckenvorraum ( 7 ) the snail ( 3 ) axially from the antechamber ( 7 ) is displaced away, wherein during this axial screw movement of the piston ( 6 ) is held axially, so that in the bore ( 4 ) existing fluid (G) by the relative axial displacement of the piston ( 6 ) in the hole ( 4 ) via the at least one outlet channel ( 5 ) in the plastic melt is introduced. Method according to claim 22, characterized in that the piston ( 6 ) is positioned so that it is furthest from the anteroom ( 7 ) remote axial position of the screw ( 3 ) essentially until the end ( 11 ) of the bore ( 4 ) is inserted. A method according to claim 22 or 23, characterized in that before the start of the axial retracting movement of the screw ( 3 ) the bore ( 4 ) is filled with fluid (G) in the desired amount and / or pressure.