DE3307586A1 - Injection mold arrangement and method for injection molding plastic parts - Google Patents

Description

Henkel, Pfenning, Feiler, Hänzel & Meinig *, Patent attorneys

European Patent Attorneys Admitted to the European Patent Office

Dr Phil G Henkel. Munich Dtp! -Ing J Pfenning Berlin Dr. rer. nat L Feuer, Munich Dipl -Ing W. Hänzel. Munich

Emhart Industries, Inc. D.pi.-Phys κ Meinig Berlin

Dr. Ing.A Butenschon. Berlin

Farmington, Conn., V.St.A.

Mohlstrasse 37

D-8000 Munich 80

Tel 089 / 982085-87 Telex 0529802 hnkld Telegrams ellipsoid

1530 / W.G.

March 3, 1983

Injection mold assembly and method of injection molding

Plastic parts

The invention relates to a Spritzdüsenventi1- and storage arrangement with cylinder and plasticizing or kneading screw which is usually used for simultaneous Production of a number of parisons in an injection mold for subsequent blow molding to containers, such as bottles, type used. In particular, the arrangement is designed so that in A holding pressure is maintained while the injection unit (injector) processes the next batch of the mold space Plastic melt plasticizes or kneads, the Storage (accumulator) after each work cycle and before refilling with new plastic melt is cleaned and the mold space during its charging with melt for the purpose of reducing a Mold part shrinkage an appropriate holding pressure is maintained in order to ensure uniform wall thickness and temperature of the molded part.

The invention also relates to a method for injection molding plastic (mold) parts.

In recent times, developments have been directed more and more towards the production of plastic bottles as a partial replacement for glass bottles.

These developments are based on the knowledge that Plastics such as polyethylene terephthalate (PET), if they are molecularly stretched or stretched, tougher, but are lighter than glass, as well as on the methods and devices known in the glass industry for stretching and blowing glass both lengthways and crossways.

When manufacturing a plastic container, one must start from a parison, which then heat-treated and stretched to the plastic container or blow molded. The plastic container produced, e.g. a bottle, should expediently be a

Uniform wall thickness without unsightly flaws both in terms of wall strength and appearance to the end user. To produce a bottle with uniform wall strength (thickness) and without the appearance Detrimental errors must be assumed to be an absolutely error-free parison.

JO Such parcels must therefore not deviate from Have wall thickness or have defects such as those that occur when forming the parison The form used contains voids or the parison due to an insufficiently filled form, a Shrinkage in the form or the like. is faulty.

Furthermore, for reasons of competition, the speed is also important critical in the manufacture of the tubs and the plastic bottles. This production speed requires the continuous and simultaneous molding of a number of parisons using a single injection molding mechanism.

There are a large number of protective rights on devices for injection molding materials, whereby a memory [accumulator) is provided in the spray assembly. These devices are provided in order to produce molded parts, such as parisons, that are free from defects and in a multiple mold Deliver molded parts of uniform wall thickness. All previous spray nozzle valve and accumulator arrangements however, there are shortcomings in terms of operating speed and / or defects in the molded parts due to the impossibility of a complete one Cleaning (purging) the storage cylinder after each work step. This will be done in the next Operation old plastic melt in the mold injected so that wall defects arise and / or a more expedient when supplying new melt

Holding pressure on the mold space cannot be guaranteed. If there is no holding pressure, this can result of shrinkage in the mold space, a molded part of uneven wall thickness or the like. form.

The object of the invention is in particular to provide a spray mold arrangement, i.e. a Spray nozzle valve and accumulator assembly for the continuous and simultaneous manufacture of a Number of molded parts, such as parisons, in an injection mold, whereby due to the arrangement of the mechanical Components and their cyclical work sequence, the entire spray material from the previous cycle driven out of the arrangement and the storage cylinder with it again during the injection cycle filled with fresh plastic (injection material) and then, in conjunction with the screw pressure, a holding pressure is applied while the rotary valve closesj in this way, loss is compensated and ensures a uniform wall thickness of the molded part produced.

This object is achieved by the features characterized in the attached patent claims.

The subject of the invention is therefore a spray nozzle valve and storage arrangement with a rotary slide valve and a plastic collecting or storage cylinder between the injection mold and the discharge end of the kneading screw. The mold space into which the plastic is injected contains a shut-off valve to interrupt the flow of plastic. A compressed air cylinder with piston actuates the rotary valve in the plastic (melt) stream immediately behind the screw. A storage cylinder is located between the rotary valve and the mold distributor

Piston to maintain pressure on the plastic in the mold during the hold pressure period during which the plastic shrinks and freezes. The accumulator piston is actuated by a hydraulic cylinder to the to maintain the necessary holding pressure. To compensate the storage cylinder has a displacement for shrinkage van about 5% of the total injection mold volume. The accumulator piston end and the associated one Cylinder head insert have one Shape that all of the remaining plastic is expelled from the cylinder when the piston hits the end has reached its stroke, leaving only one passage for the flow of plastic.

A feature of the invention thus consists in the combination of the mechanical components described and the cyclical order in which the storage piston takes all of the sprayed material from the previous one Injection cycle drives out, the cylinder is charged with fresh injection material again during the injection cycle and then, in conjunction with the injection screw pressure, exerts the holding pressure while the rotary valve closes. During this time, the injection screw starts the next batch of plastic melt to plasticize or to knead, while the storage piston to compensate for shrinkage of plastic melt into the mold space. During this time, the holding pressure creates a steady Wall thickness and a uniform cooling of the plastic molding ensured and one Maintain uniform wall temperature. After the holding pressure period has elapsed, the accumulator pistons are withdrawn and the plastic located in the mold distributor is relieved of pressure, so that the Fcrm shut-off valve can close without back pressure.

The holding and curing cycle is in accordance with the invention for perfect heat regulation from the screw return <j recovery cycle separated.

The arrangement according to the invention enables the continuous Batch manufacture a number of items, such as tubs, with uniform wall JQ thick and without defects that would show up in the finished molding. The following is the invention in connection with the production of parisons for bottle manufacture.

The following are preferred embodiments the invention explained in more detail with reference to the drawing. Show it:

Fig. 1 is a partially broken away view of a Külbel injection mold arrangement with injection

nozzle valve and storage arrangement according to the invention,

FIG. 2 shows a section along the line 2-2 in FIG. 1, kept on an enlarged scale

schematic representation of the pressure medium system,

Fig. 3 is kept on a further enlarged scale Cut along line 4-4 to the

Representation of the accumulator piston in its fully retracted position,

4 shows a representation similar to FIG. 3, showing the storage piston in its extended position

or withdrawn position, and

Fig. 5 is a timing diagram for the injection molding process .

According to FIG. 2, a cylinder which can be set in rotation by a hydraulic motor and a hydraulic cylinder is used (both not shown) displaceable, working in a heated cylinder 12 Injection screw 10 for plasticizing or kneading the injection material in a chamber 14 Cylinder 12 is connected to a heated spray nozzle body 16, which has a passage 1B and a Has rotary valve 20, in turn by a solenoid-operated air valve 24 controlled pressure medium motor 22 is actuated. The rotary valve 20 is a collecting 1 or storage chamber 26, which is closed by a cylinder head insert 30. A piston 26 and

_{2ft of} the insert 30 are designed so that they define a passage 32 when the piston and insert are in mutual contact as shown in FIG. The continuous passage 18 guides the plastic to a manifold with heated webs via a

__ Passage 36 to a valve chamber 38. A form-closing valve 40 controls the flow of plastic in a mold space 42. The closing valve 40 is via a Plate 44 operated by a hydraulic cylinder 46 which in turn is operated by a solenoid operated valve

on 48 is controlled.

The collecting or storage piston 26 is drivingly with a piston 52 of a hydraulic cylinder 50 connected. The extension speed of the piston gg 26 is controlled by a flow valve 54.

A directional control valve 56 driven by a solenoid 58 is actuated, leaves the piston 26 for the

Run in cleaning and holding pressure cycle or cycle. A solenoid 60 leaves the piston 26 during

of the decompression or pressure relief cycle ο

move out.

A pressure reducing valve 62 is used to adjust the Cleaning pressure level by means of an adjusting element 64. A solenoid valve 66, when actuated, controls the pressure reducing valve 62 through a pressure relief valve 66 with setting element 70 for setting the size of the holding pressure (hold pressure). A check valve 72 prevents a ._ escape of pressure medium from the system during the Sphere flask refilling cycle.

The arrangement operates according to the timing diagram according to Fig. 5 ,. which the working order resp.

«Λ illustrates the clock operation of the arrangement. to At the beginning of the injection cycle, the screw 10 has plasticized or kneaded the injection material in the chamber 14. The passages 18 and 36 and the chamber 38 are filled with plastic while

_o _ the mold closing valve 40 is closed.

When the mold space 42 is closed, the Injection nozzle rotary slide valve 20 and the mold closing valve 40 by their respective actuators, gejQ opens.

The screw 10 drives the plastic through the passages into the molding space 42. Simultaneously The accumulator piston 26 translates under the control of valve 56 and solenoid 58 and 58 inward under a pressure set on the pressure reducing valve 62 to remove the remaining plastic by dBn the chamber 28 to drive out. When the piston 26

abuts the cylinder head insert 30, the plastic flows through the passage, so that the rest

_ The spray material is expelled.
ο

When the solenoid 58 is de-energized, the direction control or reversing valve 56 can move into the middle position return, in which the plastic,

j «i.e. the melt, the storage chamber 28 again can fill and the piston 52 at a speed determined by the flow valve 54 shifts outwards. At the end of the injection cycle, the plastic is expelled from the chamber 14

jg, where he has the storage chamber 2Ö and the mold space 42 fills in. At this time, the directional control valve operated by the solenoid 58 permits 56 the application of the holding pressure by actuating the valve 66 and the pressure relief valve

68. The mold space is now under both the screw 1G and the storage piston 26 Pressure set. The rotary valve 20 is returned to the closed position, so that the injection or Kneading screw 10 set in rotation again for plasticizing or kneading the next batch can be.

The accumulator piston 26 continues to exert the holding pressure on the (injected) plastic to make volumetric To compensate for shrinkage in the mold space 42 and to ensure a uniform wall thickness and temperature control on the molded part C injection molding). At the end of the memory hold time, the Directional control valve 56 controlled by solenoid 60 the pistons 52 and 26 retract so that the plastic in the valve chamber 38 is depressurized will. The mold closing valve 40 is now against a minimal resistance of the plastic

closed. After the curing time determined by the temperature of the molded part, the

Mold space opened to remove the molded part. The ο

Screw 10 can move during the demolding period keep turning until the material to be sprayed has been plasticized or kneaded as required.

_in the inventive arrangement provides the following VorteiIe:

1. In the arrangement described, the accumulator piston can exert the holding pressure while the

.The next batch for each injection or kneading screw plasticized. This enables a longer plasticizing or kneading time, whereby the Injection material is exposed to lower shear stress and heat because the screw does not move rotates at a lower speed and requires a lower drive torque.

2. The storage cylinder is used in every working cycle cleaned and then again with fresh art

2 * j material melted j this ensures that that no residual material remains in the system.

3. By maintaining an appropriate holding pressure and the constant supply of material to the Mold space, mold shrinkage is largely reducedj in this way are uniform Wall thickness and temperature of the molded part guaranteed.

4. The curing time in the mold is determined by

the residual heat of the (molded part) wall j the molded part must therefore at a precisely defined time

being taken out of the mold This period of time is neither limited by the plasticizing cycle still determined.

5. The arrangement described is particularly advantageous in applications in which the molding temperature must be regulated to the further processing of the molded part, such as training and conditioning of a parison, before a to allow subsequent blow molding.

Further advantages of the arrangement result from its overall structure or its simple construction and working method.

Various changes and modifications to those described are of course available to those skilled in the art Embodiment possible without the framework of the Invention is deviated.

Claims (7)

Claims / Ί .J Injection mold assembly for injection molding of plastic parts, characterized in that a cylinder (12) and a plasticizing or Kneading screw (10) having injection unit for Plasticizing or kneading a plastic melt and for spraying the same, an injection mold with (At least) one molding space (42) for molding plastic molded parts and one the discharge end of the cylinder; (12) with the mold space (42) connecting passage means are provided, the series according to a 10 that can be controlled for opening and closing Rotary valve (20) in the vicinity of the cylinder (12), a collection or storage unit (26, 26) with a Storage chamber (28) and an element (26) for controlling the amount and pressure of the in the. _ "Storage chamber (2Θ) located plastic as well as in the vicinity of the mold space (42) a valve chamber (38) with a valve unit (40) cooperating therewith for controlling the flow of the plastic melt to the mold space (42). 2. Arrangement according to claim 1, characterized in that that the rotary slide valve (20) can be actuated by a pressure medium motor (22) which in turn is driven by a solenoid operated air valve (24) control OQ . is cash 3. Arrangement according to claim 1, characterized in that that the valve unit (40) cooperating with the valve chamber (38) is a closing or shut-off valve is, which can be actuated by a hydraulic cylinder (46) which in turn is controllable by a solenoid-controlled valve (48). 4. Arrangement according to claim 1, characterized in that that the storage unit has a cylinder (50) Has piston (52).
5 5. Arrangement according to claim 1, characterized in that that the injection mold has several injection molds and a corresponding number of valve chambers (38) associated with it Valve units (40) comprises that the Valve chambers (38) via a distributor (e.g. 36) are connected to the injection unit and the storage unit (26, 28) and that the various Valve units (40) simultaneously by a plate (44) can be actuated, which are operatively connected to an Io actuatable by a solenoid controlled valve (48) Hydraulic cylinder (46) is connected. 6. Arrangement according to claim 4, characterized in that that a device for continuous operation of the injection mold assembly and for clock control (Timing) of the working sequence is provided in such a way that the storage piston (26) the entire, from a previous work cycle __ remaining plastic melt from the accumulator Cylinder (25) drives out and the latter during the Injection cycle charged with fresh plastic melt and then in connection with the plasticizing screw pressure a holding pressure is applied when the rotary valve (20) closes. 7. Process for injection molding plastic molded parts in an injection mold with (at least) one mold space and a device for closing the Injection mold, characterized in that a moldable Plastic in a plastic injection unit with a cylinder and an injection or Plasticizing screw plasticized or kneaded is that the plasticized plastic van der Injection unit in a latter with the mold space the injection mold connecting passage device, the one next to the cylinder of the injection unit arranged, for opening and closing controllable rotary valve, a collection or storage unit with a storage chamber and a control unit for controlling the amount and pressure of the in the Storage chamber located plastic and a valve with valve chamber next to the mold space has, and is then injected into the mold space that the storage chamber simultaneously with the The plastic is introduced into the mold space (by plastic expulsion), cleaned and then refilled that the arranged in the passage device next to the cylinder of the injection unit Rotary valve closed and while the plastic injection pressure is being maintained in the mold space via the storage chamber and the control unit a second batch of plastic for injection in the mold space is plasticized so that the Plastic molded parts (e) removed from the injection mold will (become) and that the above operations are repeated.