WO2004050325A1

WO2004050325A1 - Method and installation for producing plastic parts

Info

Publication number: WO2004050325A1
Application number: PCT/CH2003/000724
Authority: WO
Inventors: Robert Weinmann
Original assignee: Netstal-Maschinen Ag
Priority date: 2002-12-04
Filing date: 2003-10-30
Publication date: 2004-06-17
Also published as: EP1567315A1; AU2003273716A1; CA2508466A1

Abstract

The invention relates to a method and an installation for producing injection moulded parts, especially preforms (12), the liquid melt being directly received by a chemical production installation (1) and continuously supplied to an injection moulding machine (13). If the melt is in a degassing state ready to inject, at least two injection cylinders (21, 22) comprising controlled or regulated injection pistons (24, 25) are alternately charged with the continuous melt flow, said pistons enabling the injection cycle to be carried out in a push-pull mode in relation to the charging of the cylinders. The continuously supplied melt flow is degassed as much as required on the machine side, e.g. in a degassing extruder, a degassing endless screw (60, 81) or a pre-accumulator (21, 22, 62, 90). The inventive installation is used to produce injection moulded parts, especially preforms (12), the liquid melt being directly received by a chemical installation (1) and continuously supplied to an injection moulding machine (3) for the cyclic production of injection moulded parts in injection moulds.

Description

Process and plant for the production of plastic parts

Technical field

The invention relates to a process for the cyclical injection molding of plastic parts, in particular preforms, the liquid melt being taken over directly from a chemical production system in the ready-to-spray degassing state or in the still insufficient degassing state and being fed to several processing stations with an injection screw or injection cylinder, and a system for the production of Injection molded parts, in particular of preforms, the liquid melt being taken directly from a chemical plant in the injection-molding degassing state or in the insufficient degassing state and being continuously fed to several injection molding machines for the cyclical production of the injection molding parts in injection molds.

State of the art

According to common practice, injection molding is a classic case of a cyclical production process. The raw material, mostly in granular form, is produced in specialized chemical plants in a wide variety of chemical compositions and colors and, as bulk goods, can be obtained by the injection molder in terms of quantity and quality for his specific needs. The chemical production facility is able to supply hundreds of small injection molding plants. The raw material is mostly transported in sacks across entire continents to the customer.

The situation in the textile field is different. The starting products, especially textiles, are yarns or threads that are either made from natural materials such as wool or silk, or from what is known as artificial silk. The basis of the artificial silk are filaments, which are produced from liquid melt via spinnerets. Many chemical process stages are required for the production process of the liquid melt. An important part is heat treatment and mixing, especially batch mixing. A certain minimum amount is mixed and processed continuously. If filaments are produced, that comes Peculiarity of the continuous process, because the continuous filaments require the constancy of the material flow. The endless filaments are produced via spinnerets and wound up after any intermediate treatments. This means that the chemical plant and the spinning process usually belong together in the production of filaments.

As stated at the beginning, an injection molding machine works strictly cyclically. The flow of material into the injection molds is interrupted between each cycle. This helps to ensure that granules are kept in sufficient quantities in a small storage container above the machine for the injection molding process and are drawn in periodically via the metering screw, heated and injected into the cavities of the mold in metered quantities. There has long been a desire to feed the hot melt directly from the chemical processing process to injection molding machines, i.e. without the intermediate process of cooling the melt and producing the granulate.

One of the first proposals for the direct supply of several injection molding machines from a polymerization plant is described in US Pat. No. 3,353,209. The liquid melt is fed from the polymerization system via a distribution system via a screw conveyor to, for example, three injection molding machines. Each injection molding machine also has its own screw conveyor, which cyclically feeds melt to a pre-tank of the injection molding machine via a pressure control. The melt pressure required for injection molding is built up via an injection cylinder with injection pistons and pressed into the molds in shots. The chemical processing in the polymerization plant is tied to a constant production flow due to the timing. Even with three injection molding machines, the constant production flow cannot be ensured for many reasons. With every injection molding machine, molds have to be changed, the injection process started and any faults stopped immediately. U.S. Patent 3,535,209 therefore proposes to supply the extrusion system to an extruder, e.g. when an injection molding machine fails.

The extruder took over the regular failures of the injection molding machines. In the event that all consumer points, i.e. the injection molding machines, such as the extruder, cannot take over the continuous melt flow, an emergency outlet is also actuated. As far as information is available, it has not been possible to implement the proposal of US Pat. No. 3,353,209 in industrial practice. Chemical production plants are so large that only a large number of injection molding machines can handle the production output. Even in the case of injection molding machines for PET production, which are among the largest, 10 to 20 injection molding machines are expected for a chemical production plant. A very special problem arises in the manufacture of preforms for PET bottles, since the PET bottles are primarily filled with liquid foods. These require maximum purity, so that foreign substances do not have a taste or even toxic effect. The toxic part is already taken into account in the procurement and processing of raw materials. A very special problem arises with the raw materials used for PET production, namely the formation of acetaldehydes.

U.S. Patent No. 5,597,891 proposes to lower the acetaldehyde content from initially 1 60 to 200 ppm to below the 5 ppm level prescribed for food containers. Gaseous agents are added to the liquid melt in the extruder and these are discharged again through a degassing point after a sufficient working time. The melt residence time is 10 to 15 minutes and the temperature is 260 to 300 ° C. Due to the long dwell time, it is a process step that typically belongs to the chemical plant.

W098 / 41 381 tries to solve the two central procedural steps in one unit. A gas is then added to the liquid melt from the chemical plant at high pressure in an extruder and the acetaldehyde content is reduced from 30 to 150 ppm to below 5, preferably below 3 ppm.

The exposure time of the gas is about 20 seconds. Since very specific temperatures of the melt and also a high precision of the melt pressure are required for the injection molding, the reduction of the acetaldehyde content is carried out in a first part of a processing unit and the injection molding preparation in a second part. A melt pump is provided between the two parts and feeds the melt to two or more injection molding units, controlled by valves, with the appropriate timing. The pressure build-up for each shot takes place via individual injection cylinders, which are each assigned to an injection molding unit. The major disadvantage of this proposed solution is that, on the one hand, all connected injection molding machines must be clocked in a strictly coordinated manner in the cycle, which is hardly achievable in real injection molding practice. By using the best possible control technology, the manufacturing process for the production of preforms in the With regard to cycle duration and quality, they can also be optimized with regard to different end products. This optimization would be sacrificed at least in part with the proposal according to W098 / 41381. Another theoretical proposal for direct preforming is described in US Pat. No. 5,656,719. The hot melt is fed to a post-condensation reactor with the addition of an inert gas. The post-condensation to lower the acetaldehyde content is achieved with a residence time of less than 60 minutes and a temperature of 260 to 285 ° C. The liquid melt is fed from the post-condensation reactor to a double-piston system and from the double-piston system alternately to an injection molding machine.

All the proposals described do not solve a central problem, namely the continuous transfer of the melt from the chemical production plant. It was recognized by the inventor that a continuous decrease in the melt mass is just as important as the preparation of the melt with regard to all the parameters required for injection molding. The central problem lies in overcoming the paradox, namely the conversion from a maximum of continuity to the highest precision of a strictly cyclical mass processing. Another increasingly major problem in melt processing is the fact that not only is there a much too high acetaldehyde content at the end of the chemical process stages, but that the melt has been in a hot and liquid state for so long and is mechanically processed. Attention is drawn to the 'not yet published international application for the preparation and processing of plastic melt from the granulate form.

The object of the invention was now to find ways and means of supplying the chemically continuously produced and heated plastic melt directly to the purely cyclical injection molding process, on the one hand economically and on the other hand in terms of production technology.

Presentation of the invention

The process according to the invention is characterized in that the liquid melt is taken over as a constant flow over time from each processing point by a chemical production system via a distribution system and transferred to cyclically controlled exact dosing quantities by each consumer, the processing points being injection molding machines. The system according to the invention is characterized in that each of the several injection molding machines can be connected to a feed line of a distribution system of the chemical plant, the individual injection molding machines having at least one pre-memory that can be activated via control / regulating means for the backflow-free transfer of the continuous melt flow into exact cyclical dosing quantities into the injection molds.

At the center of the new invention is the transfer of a continuous melt flow into cyclically controlled dosing quantities using at least one pre-store that can be activated via control / regulating means in the area of the injection molding machine. Various studies have shown that the productivity of large injection molding machines is so high that an economical solution can be achieved with miniaturization of the chemical system that is still portable. It is possible, at least in an initial phase, to process part of the production in a direct flow via injection molding machines and to process the rest conventionally into granules. In the case of direct preforming, the full production of a scaled-down chemical production system can already be carried out with 10 to 15 injection molding machines. Here, the new invention also enables technical implementation by solving the paradox between the continuous melt supply from the chemical production plant and the discontinuous or cyclical injection process on the part of the individual injection molding machine. A special aspect is that the residence time of the melt in the area of the injection molding machine is as short as possible in order to avoid temperature problems and segregation. It is very particularly preferably proposed that the pre-storage does not correspond significantly more than the amount required for one injection cycle, i.e. a maximum of 2 to 4 times.

Each individual injection molding machine solves the problem for itself, so that in the first approximation, an even better balance is created by a large number of injection molding machines. The new invention makes it possible to simplify the distribution system from the chemical plant without the need for actual distribution apparatus. Based on the machine control of the injection molding machine, it cycles the cyclical preparation of exact cyclical dosing quantities itself. In the classic state of the art, a sufficient amount of granules is kept in a storage container, the supply of a large container is usually ensured by level switches. It has been recognized by the inventor that an undetermined storage in a storage tank can lead to qualitative problems in the case of the continuous supply of melt. In the liquid melt Various chemical changes take place over time, which are not least dependent on inhomogeneities in relation to the melt temperature. By reducing the "storage container" for liquid melt to the size corresponding to a cyclically required metering quantity, corresponding temperature fluctuations can be virtually eliminated. As initial tests have shown, this achieves at least equal quality to classic injection molding technology, starting from a granulate shape. The new invention allows several particularly advantageous approaches. This depends above all on whether the melt flow is ready for injection from the degassing state or not. For the new solution, it is proposed that the large reduction in the acetaldehyde content in the chemical plant in the region be reduced below 30 ppm, so that the injection molding machine side only allows the remaining lowering without special gassing at higher temperatures. In the area of the injection molding machine, only the remaining reduction, for example to 1 to 2 ppm, then has to be carried out. For this, reference is made to PCT / CH03 / 0031 7.

The first solution for injection-ready melt allows a whole number of particularly advantageous configurations, for which reference is made to claims 2 to 12 and 14 to 21. At least some of the structural designs can also be used for the other possible solutions.

The loading process of the at least two injection cylinders is preferably carried out strictly synchronously, in such a way that a constant mass flow of the melt can be taken over by the loading process. The duration of an injection molding cycle is assumed. The theoretically maximum loading time for each injection cylinder corresponds to the duration of an injection molding cycle. During the loading time of one injection cylinder, the other is connected to the injection molding process, with the melt being injected in a first phase. The reprint phase then follows. There is a small reserve time until the end of the injection cycle. Each of the two injection cylinders therefore has a double function:

- Each injection cylinder is a charging station.

- Each of the injection cylinders is an injection unit.

The synchronous cooperation of at least two injection cylinders in push-pull, either as a charging station or as an injection unit, solves the basic problem of converting a continuous melt flow into a cyclical melt flow and exactly assumes a given volume flow. The charging movement of the injection pistons is very particularly preferably actively controlled / regulated in such a way that there is as little interference as possible on the mass flow of the continuous melt flow. It must be prevented that the ι

Injection piston movement is forcibly caused by the melt pressure in the feed line of the chemical production plant. The cycle time Tz for the injection cycle is specified. This allows the injection piston movement for charging to be controlled by means of position control over time. The charging process is influenced on the one hand by flow resistances of the viscous melt and on the other hand by mechanical friction losses of the drive, in particular of the injection piston. The flow pump is overcome by the melt pump or by the pressure energy it applies. The energy for the acceleration and the mechanical friction losses is applied by regulating the injection piston accordingly. The piston movement is to be controlled in such a way that resistances to the injection piston movement, in particular frictional resistances, are taken over by the controlled / regulated drive of the injection piston. The control takes place in such a way that the volume flow theoretically to be taken over is continuously taken over by the charging process.

According to a first embodiment, the respective switchover from one injection cylinder to the next is controlled via valves and is carried out as quickly as possible in such a way that there is no pressure surge on the melt flow supplied. According to a second embodiment, the respective switchover from one injection cylinder to the next is controlled via valves in such a way that the charging current is successively reduced to zero in a transition region and, at the same time, the charging current for the next is increased in a coordinated manner, thereby preventing a retroactive interference effect on the continuous melt flow. A heated valve block is advantageously arranged between the injection cylinders and the injection mold, via which, in the sense of an emergency exit, liquid melt can be drained off via a correspondingly controllable valve in the event of current faults. This additional valve is also required for the setup at the start of production in order to optimize the injection process to the required parameters regardless of the time.

In terms of the device, a feed line for the liquid melt and a valve arrangement are provided, via which liquid melt can optionally be supplied to one of the at least two injection cylinders, the valve arrangement being part of a valve block which is located between the injection cylinders and the injection molds is placed. The injection cylinder and the valve arrangement can be designed as a heatable structural unit, with a connection for the feed line and at least one connection point for the injection mold. The valve arrangement can have a changeover valve, via which alternately one injection cylinder can be connected to the feed line and the other injection cylinder can be connected to the cavities of the injection molds. It is also possible for the valve arrangement to have a changeover valve for each injection cylinder, via which the one injection cylinder can alternately be connected to the feed line and the other injection cylinder to the cavities of the injection molds. This has the great advantage that the valve switchover is carried out slowly and that the respective opening or closing position is subordinate to the switchover phase and cannot trigger any disruptive effects. In this phase, the injection pistons are steered away. The charging process is carried out by active control of each injection piston with the aim of an unchanged static melt pressure in the feed line and with the specification of a constant charging volume. This is especially true for the transition area from one injection piston to the next one. The piston retraction speed and / or the piston retraction path are preferably redetermined for each loading process. The influence of the melt pump and the system pressure and temperature fluctuations result in changes in mass due to fluctuations in density when controlled according to a constant volume. A shot-to-shot control keeps a minimal mass cushion constant and achieves a maximum shot weight consistency or processed mass per unit of time.

According to a further advantageous embodiment, the piston path for each loading and injection cycle is recorded via the control / regulation and the loading volume is corrected with the aim of a constant loading quantity across cycles. With the proposed solution, a melt flow with the maximum possible constancy can be implemented at a very high level into a cyclical dosing capacity with the maximum possible constant loading quantity. The previous continuous production process of the chemical plant is not disturbed. On the other hand, the injection molding process can be designed to the highest possible quality in every respect. According to a second approach to the method, it is proposed that the continuous melt flow be degassed prior to injection molding via a degassing extruder or a degassing screw and transferred to cyclical dosing quantities. In the case of a prior degassing, various configurations are possible in order to feed the melt to the spraying process as optimally as possible and with the least possible number of components. According to a first embodiment, the continuous melt flow is taken over by a degassing extruder with a continuously rotating screw conveyor and fed into a preliminary store designed as a cylinder with a controllable piston. Particularly preferably, the melt flow is cyclically valve-controlled transferred into a shot pot, the shot pot being filled with the full, continuous melt flow and additionally with the cyclically operable preliminary store. Various advantages result from this. The merging creates a very good mixing effect of the melt from the shot pot and the continuously supplied melt. The shot pot only needs a minimal size and delivers about half a shot quantity each.

According to a second embodiment, the continuous melt flow is taken over by a degassing extruder with a continuously rotating and linearly movable screw conveyor, part of the degassing extruder being designed as a cyclically activatable pre-storage device for generating cyclical metering quantities. The cyclical dosing quantities are transferred to a shot pot in a valve-controlled manner using the intrusion process.

According to a third embodiment, the continuous melt flow is taken over by a degassing extruder with a continuously rotating screw conveyor and the cyclical metering quantity is generated via two injection cylinders which can be controlled in parallel. Here the elements of the first solution are partially adopted.

According to a fourth advantageous proposal, the continuous melt flow is degassed in an accumulator as the supply pressure is released. The melt can be taken from the degassing storage device by a melt pump or an extruder and fed into a storage device with the required pressure build-up and a cylinder with a controllable piston. There are also two options here. In a first embodiment, the melt flow is cyclically valve-controlled transferred into a shot pot, the shot pot being filled with the full continuous melt flow and additionally with the cyclically operable preliminary storage.

In a second embodiment, the melt is taken over from the pre-degassing store by a melt pump or an extruder, after which the cyclical metering quantities are generated via two injection cylinders which can be controlled in parallel, with the required pressure build-up. According to the system, the new solution has a degassing extruder, a degassing screw or a degassing pre-storage. Depending on the specific requirements, one or the other component can be used. In the case of a degassing extruder or a degassing screw, these preferably have drive and control / regulating means for the purely rotary or rotary and linear movement of the screw conveyor. In all cases, the degassing extruder or the degassing screw can have a screw conveyor or two identical or counter-rotating twin screws. Furthermore, it is possible for the preliminary memory, in particular the preliminary memory designed as a shot pot, to be designed as a FiFo memory (first in, first out) or as a LiFo memory (last in, first out).

Brief description of the invention

In the following, the invention will be explained with the aid of a few exemplary embodiments

Details explained. FIG. 1 shows a schematic representation of an example of direct preforming with simultaneous granulation of part of the production quantity; 2 shows an example of the core components of the charging station and

Injection unit; 3 shows an example of control / regulation of the injection pistons; 4 schematically shows the alternate mode of operation of the charging station

Valve switching; 5 shows schematically an alternative with two valves and one controlled

Change for one charging station to the next; Figures 6 and 7 two examples corresponding to Figures 4 and 5; Figures 8, 9, 10 three situations of loading and changing from one

Charging station to the next; Figure 1 1 schematically shows the course of the entire injection molding process; the figure 1 2 purely schematically the preparation of the melt from the granulate form according to the classic state of injection molding technology; Figure 1 3 shows a first embodiment of the new invention with degassing of the liquid melt; Figure 14 shows a second embodiment with a special

Degassing extruder with built-in pre-storage; Figure 1 5 shows a third embodiment with degassing extruder and two

Injection cylinders corresponding to Figure 2; Figure 1 6 a further embodiment with an upstream

Degassing storage and a gear melt pump; 1 7 shows a very rough diagram for the formation of a memory filling process corresponding to FIG. 1 3.

Ways and implementation of the invention

Figure 1 shows schematically the new invention with a chemical plant 1 for the continuous production of liquid melt. The melt is transported directly to a number of injection molding machines 3 via a pressure-controlled melt pump with constant volume delivery via a heated line system 2. Each of the injection molding machines 3 is equipped with a charging station 4. Since malfunctions can never be completely excluded, the charging station 4 has an emergency outlet 6 for hot melt. The emergency outlet is also required for setting up the injection molding machine. The finished injection molded parts 1 2 are guided to a packaging device via a transport system.

1 shows a chemical plant 1 with four injection molding machines 3, which each take 1/8 of the continuous melt production of the chemical plant 1. The remaining production volume is fed directly via a heated line 9 into a granulating system 10, from which the cooled plastic granulate is filled into bags 11 and delivered to other injection molding plants. Figure 1 is a combined system and can possibly be an economical solution in a set-up phase. Of course, a combination of a chemical plant 1 with eight injection molding machines is also possible, which take over the entire production of the chemical plant. The number 4 or 8 was only chosen as an example. The optimum number in each case results from all practical factors.

Figures 2 and 3 show schematically and on a larger scale the transfer of the continuous melt flow in the line system 2 into the cyclical injection process for the injection molding process without a drive system for the charging station 20 with two injection cylinders 21 and 22, which are arranged directly on a valve block 23. In each of the injection cylinders there is an injection piston 24 or 25, which can be driven hydraulically. The hydraulic drive is only shown as an example. Of course, the injection pistons can also be driven differently, for example by an electric motor via servomotors. The two hydraulic drives 26, 27 are identical, so that only one is described below. The injection piston 24 is connected directly to the hydraulic drive 26 via the piston rod 28. The drive piston 29 is acted upon on both sides with oil. The reversal takes place via a hydraulic valve 50, which via a Output Interface 51 is controlled. The necessary information, in particular distance and pressure values, is transmitted to an input interface circuit 52, 52 'via the signal lines of the on-site sensors. The entire control / regulation takes place via a computer 53, which is connected to a data memory 54 and an input station 55 with a screen 56. The focus is on the control / regulation of the injection pistons 24 and 25 in function of the path over time, the melt pressure and the correspondingly coordinated control of the melt valves. In FIG. 3, the functional unit with the injection cylinder 21 is labeled A and the functional unit with the injection cylinder 22 is labeled B.

FIG. 4 shows the time sequence for the two functional units A and B. The time for an entire cycle is designated Tz. Tz is the cycle time given by the injection molding machine for a complete molding cycle. In the first assumption, the cycle time Tz is a fixed quantity. The four most important phases are only roughly indicated: E = injection, ND = holding pressure, RES = reserve time, and loading means the time for a single injection cylinder 21 or 22 to be loaded. A really critical point is the transfer of the charge from an injection cylinder to the following. The time period for the transition is designated by t. This should be as short as possible.

FIG. 5 shows another embodiment, as far as the transition is concerned. According to FIG. 5, the transition takes place by means of appropriate valve control and movement control of the injection pistons, in the transition phase. decreasing. In the takeover phase there is an exact displacement control of the two injection pistons, so that the decreasing loading volume Vab of one injection cylinder conversely corresponds to the increasing loading volume Vzu of the other injection cylinder.

FIG. 6 shows a first embodiment for a charging station in a somewhat more concrete but highly schematic manner. On the left side of the picture is an injection mold 3 with the two mold halves 31 and 32 and the melt feed with a distribution block 33. Preforms are shown as injection molded parts 1 2. The loading unit 20 comprises the injection cylinders 21, 22 with the injection pistons 24, 25 and an entire valve assembly , The valve assembly consists of a changeover valve 34, which, shown as a pressure slide, supplies the charging current from the supply line 35 to one or the other injection cylinder. In the situation shown, the injection cylinder 21 is loaded. The shut-off valve 36 is in the closed position. The shut-off valve 37, however, is in the open position, so that the injection cylinder 22 with is connected to the mold cavities. In the position shown, the injection piston 25 approaches the end position of the injection phase. The entire loading unit 20 is provided with a heating jacket 38, so that the melt temperature can be kept almost constant. The design according to FIG. 6 is based on the charging concept in FIG. 5. This presupposes that the changeover valve 34 can be changed over very quickly and that there are no setback effects on the continuous melt flow in the line system 2 or in the feed line 35.

FIG. 7 shows an embodiment in accordance with the loading concept of FIG. 5. Each of the two injection cylinders has its own shut-off valve 39 or, respectively, with respect to the feed line 35. 40 on. In the position shown, the injection cylinder 21 is loaded. Accordingly, the shut-off valve 39 is open and the shut-off valve 36 is closed. Conversely, the supply of melt in the injection cylinder 22 is blocked. The injection piston 25 is still shown in an injection movement according to arrow 41. An emergency outlet valve 43 is also shown in FIG. In the event of a fault on the side of the injection molding machine or the injection molding tool and / or for setting up, the emergency outlet valve 43 is opened. The corresponding pressure in the melt feed is constantly monitored, as indicated by reference numeral 45.

Figures 8, 9 and 10 show the three main situations for the charging station. In FIG. 8, the injection cylinder 22 operates completely separated from the supply line 35. The corresponding control, e.g. symbolized as speed control during injection and as pressure control during the holding pressure phase. The completely different pressure ratio during the injection molding cycle is shown in gray. The static pressure in the feed line 35 is shown in broken lines.

FIG. 9 shows the moment when the charging process is switched from the injection cylinder 21 to the injection cylinder 22. The tool side of the shut-off valves 36 and 37 is a depressurized state, unless the system pressure can be maintained with the shut-off valve 42.

Figure 10 shows the reverse situation. The injection cylinder 22 is shown in the loading phase and the injection cylinder 21 in the injection phase.

Figure 1 1 shows schematically the course of the entire injection molding process. In the following, reference is made to FIG. 1 1.

An injection cylinder of 40 to 50 mm and a stroke of approximately 200 mm are provided for a first test device, so that e.g. a volume of 300 cm3 or a shot weight of 300 to 400 gr. can be achieved. The hotrunner block is attached to the mold plate and has a direct connection to the mold cavities. On the other side, the hotrunner block has a direct connection to the injection units via a valve. Another valve can e.g. hot melt can be drained for setting up.

The two shot cylinders work alternatively and are also loaded alternatively. The change from a shot cylinder is controlled in less than half a second. The injection plunger moves backwards in a controlled speed ^' around the shot cylinder in order to load an exact volume during the cycle.

The casting process will

- speed controlled during injection and

- Pressure-controlled during the holding phase or holding phase.

The whole process is carried out strictly cyclically and alternately.

The loading of the shot cylinder is ensured by the pressure of the melt pump, e.g. with 1 00 to 200 bar. The controlled volume flow is constant over time and independent of the pressure. The shot weight is influenced by pressure fluctuations, especially pressure fluctuations from the melt feed system, so that the cushion varies at the end of the injection phase. This variation is corrected from shot to shot so that you can always work with minimal padding and maintain a constant shot weight.

The figure 1 2 shows schematically as prior art, as it were, a school example for the injection side of an injection molding machine. The centerpiece is an injection cylinder 100, into which raw material 103, usually in granular form, is fed via a hopper 102. In the injection cylinder 100 there is a screw conveyor or injection screw 104 which is mounted on the right side in a bearing point 105. The rotary movement of the injection screw 1 21 is generated by the axis A1 via a toothed wheel set 106 and the axial injection movement (axis A2) via a hydraulic piston 1 07, which is movable in an hydraulic cylinder 108 by an axial displacement. The axial displacement depends on the desired shot quantity for the injection of a part or the corresponding amount for multiple molds. On the far left, the injection cylinder 100 ends with a nozzle 1 1 0, through which the molten plastic mass 1 1 1 is injected into the cavities 138 of the two mold halves 1 36, 1 37. The injection cylinder 100 is surrounded by heating packages 1 1 2. The dimension SpH indicates the selectable spray stroke, with SptHmax. means the maximum spray stroke. The technology of the spraying process is assumed to be known. The “periphery” required for the hydraulics is only indicated by reference number 109. The reference number 1 13 marks a pressure sensor (P) and the reference number 1 14 a speed sensor (VE). The piston 107 is controlled via a servo or proportional valve 1 1 5. The required control pulses are given by a controller 1 1 6 or a machine control 1 1 7. The rotary movement of the injection screw 104 is actuated by a drive motor 11 (referred to as axis A1). The axial movement is triggered by the hydraulic piston 107 or the piston rod 1 1 9 (axis A2). The two axes A1 and A2 are completely independent of one another, but have in common the same output on the coupling piece 1 20 for the injection screw 104.

FIG. 1 3 shows a degassing screw 60. This has a drive stub 61 on the right in FIG. 2 with a cylindrical shaft part. A preliminary store 62 is located upstream of the feed area 63. The degassing screw 60 is formed over the entire length with different screw profiles and different pitches. The first zone 63 primarily has a conveying effect and is referred to as the feed zone. Adjacent to zone 63 is a degassing zone 64 with a low screw pitch. The degassing screw 60 has an abrupt reduction in diameter 65 at the transition from zone 63 to 64. As a result, the static pressure built up in the melt is reduced. As a result, the hot and liquid melt is degassed. Correspondingly, a connection piece 66 for the removal of the separated gas is arranged in the zone 64. The corresponding degassing is assumed to be known. Zone 64 is followed by a metering zone 65. The main task of the metering zone is to homogenize the melt and make it available for the next shot. An important characteristic of the degassing screw 60 is the double movement. The degassing screw 60 has hydraulic drive means 67 for a longitudinal movement (arrow 68) and drive means 69 for a rotational movement (arrow 70). Another important characteristic of the solution according to FIG. 13 is the preliminary storage 62. The continuous melt flow is fed directly into the preliminary storage 62 according to arrow 71. The pre-storage 62 has approximately the size SV, according to the largest possible amount of shots. In contrast to classic injection molding technology, there is a pre-metered amount of spray at the rear in the intake area of the degassing screw. According to FIG. 1 3, it is assumed that the continuous melt flow must be degassed. The metered quantity is withdrawn from the antechamber 62 by a return movement of the screw and conveyed forward for the next intrusion process. The injection piston 71 has a double function. The injection plunger moves backwards during the intrusion. The injection unit 72 has a hydraulic cylinder 73 and is moved in the cycle of the injection cycle via corresponding control means. This part is assumed to be known. In front of the injection piston 71 is a melt depot 74, which is injected in shots via a hot runner nozzle 75 into the cavities of the mold. A valve 76 is opened and closed in the rhythm of the injection cycle, so that either a shot quantity is transferred from the degassing screw 60 to the injection piston 71 or injection is injected into the cavities by the injection piston 71. The degassing screw 60 constantly rotates with a narrow band range with regard to speed variations and pushes one shot quantity at the front in the injection cycle from the back to the front, so that the continuously supplied melt flow is thereby transferred in cyclical portions. According to the method, the screw speed of the extruder screw 60 is very particularly preferably controlled / regulated by an automatic system in such a way that a predeterminable position range of the screw displacement path is achieved with continuous rotation and the lowest possible speed. The corresponding device has control means with computer and storage means as well as corresponding software for the continuous rotation of at least one extruder screw, the screw speed being controllable with an automatic system in such a way that with constant rotation and the lowest possible speed, a predeterminable position range of the Screw displacement path is accessible. Surprisingly, this allows the screw speed to be controlled both at the screw path and subsequently also at the drive torque for the rotary movement of the screw and the melt pressure at a much higher level in order to ensure the melt quality with the highest plasticizing performance. A particularly important point is that a dosing reserve can be dispensed with, the melt dwell time is particularly reduced in the pre-store and. given a specified cycle time, the worm can be operated with the lowest possible speed. It is possible, especially with the highest throughputs, to increase the capacity of existing machines by 1 5 to 20% and to reduce the AA values by around 0.5 ppm. The plasticizing screw can be operated approximately as with classic extruders. Advantageously, the cycle for controlling / regulating the screw is specified as the master by the preceding tool cycle time in automatic mode, the first option being to specify a starting speed either by hand or by a specified recipe from the control system and to automatic mode after two or more injection molding cycles is switched. When starting a new production batch or in the event of major deviations, a realistic screw speed can be determined for the control with the help of the screw number and this is used as a basis for one or more cycles. According to a further solution it is provided that the control system detects a tool cycle time extension or shortening, correspondingly determines a reduced or increased speed for the screw with the aid of the screw index and specifies the control system. A path measuring system is also assigned to the plasticizing screw. By specifying a travel range for the screw displacement, it can be ensured that the plasticizing screw does not move to the stop. By monitoring the position of the plasticizing screw and specifying a minimum slide-over residue or a bandwidth for a minimal transfer residue, the melt residence time can be kept to a minimum and metallic opening of the plasticizing screw can be avoided. According to another advantageous embodiment, the melt pressure in the screw antechamber can be monitored during the intrusion and optimized with regard to a gentle pushing over of the injection molding compound by controlling / regulating the screw displacement, for example in the range from 200 to 500 bar. A very particularly advantageous solution is characterized in that with the reduction of the screw diameter and the use of screws working in two or more synchronously and parallel to the injection piston, the melt can intrude into the injection piston in the same cycle. Two or more screws can be used. The machine becomes shorter, gives a small footprint and is therefore cheaper. The parameters listed above, which primarily determine the quality, remain optimally under control. The lifespan of all components of the screw units is increased, since at low speed the screw rotates almost constantly at a lower drive torque. It is also possible that two or more degassing screws operating in parallel are provided, by means of which melt mass can be intruded in shots in the same cycle onto a common injection piston. The control means are preferably designed for automatic operation, so that the screw position oscillates in the range of operating limits by cross-cycle and / or permanent speed adjustment. In the event of a malfunction with greater fluctuations, a new speed is determined for the following shot based on the screw index and for the following regulation / control process used. It is important that the device has sensor means for the screw speed and / or the screw path and / or the motor torque for the rotary movement of the screw and / or the pressure in the screw vestibule, so that the control programs are designed to optimize the melt quality can. Particularly in the case of the production of preforms, the device has a multiple mold and a removal robot for injection molded preforms for PET bottles, the injection molding cycle time being able to be determined in particular for fully automatic operation by the insertion movement of the removal robot into the opened mold halves. The control system is designed for cross-cycle speed tracking and / or for speed tracking during a single cycle. The plasticizing unit preferably has a hydraulic drive for the axial movement and an electric motor drive for the rotary movement of the screw. The melt is taken over cyclically from the preliminary container 62 and continuously transported via the degassing extruder. The transfer of the shot quantity takes place purely cyclically by corresponding linear movements of the screw and by transfer via a transfer channel 77 when the valve 36 is open.

Figure 1 4 shows another approach with an extruder, which is designed as a degassing extruder 29 and is driven only in rotation. The degassing screw 81 is of identical design, as is indicated in the solution according to FIG. 1 3 with the corresponding design of the screw geometry and of the screw shaft. FIG. 14 also shows the corresponding control and regulation of the individual parameters. In contrast to FIG. 13, in the embodiment according to FIG. 14, the extruder screw is driven only in rotation via a gear transmission 69 and an electric motor 82. The electric motor 82 is controlled by a machine computer 11. The degassing screw 81 takes over the melt flow supplied and passes it on essentially unchanged, which is indicated by the arrow 83. Another special feature of the solution according to FIG. 14 is the use of a preliminary storage 84, which can basically be configured in the same way as the injection unit 72 of FIG. 1 3. The continuous melt flow is converted into the cyclical metering required by the injection cycle via a preliminary storage 85 During which the valve 76 is closed, the entire melt flow is fed into the preliminary storage 85. The piston 73 is moved in a controlled manner in both directions of movement by a control 86. Venil 76 is opened for the intrusion phase. The continuous melt flow from the degassing screw is directed directly into the Shot / Pot 74. At the same time, the piston 71 makes an abutting movement and simultaneously transfers the entire amount of melt temporarily stored in the preliminary storage into the shot / pot 74 during an intrusion cycle. FIG. 1 7 shows the storage balance over an injection molding cycle time To. The pre-memory 85 is filled during the time T1 and emptied again during the time T2. For the phase of the intrusion, the two mass flows, indicated by arrows 87 and 88, are transferred to the shot / pot. The filling time for the shot / pot is reduced to a minimum.

Figure 15 shows another approach. The extruder part corresponds to the solution according to FIG. 14 and the injection part corresponds to FIG. 2. The shot-wise injection of the melt takes place alternately via the injection pistons 24 and. 25. The continuous melt streams are thereby converted into a cyclical one via the two controlled injection pistons 24, 25. Another interesting solution is shown in FIG. In the upper part of the picture there is a degasification reservoir 90, from which the continuous melt flow is passed on via a gear pump 91. The conversion of the continuous melt flow into a cyclic melt flow takes place in the same way as in the solution according to FIG. The pre-degasification store is dimensioned as small as possible, optimally not larger than the largest required shot quantity. The melt is drawn in by the gear pump 91 at very low pressure. The gear pump generates the pressure required for the intrusion process and for filling the pre-store 85.

Claims

claims

1. Process for the cyclical injection molding of plastic parts, in particular preforms, whereby the liquid melt is taken over directly from a chemical production system in the ready-to-spray degassing state or in the still insufficient degassing state and is fed to several processing stations with an injection screw or injection cylinder, so that it is characterized et that the liquid melt is taken as a constant volume flow over time from each processing point from a chemical production system via a distribution system and transferred to cyclically controlled exact dosing quantities by each consumer, the processing points being injection molding machines.

2. The method of claim 1, d ad u rc hge ke nnzeich net that a continuous melt stream ready for injection from the degassing state. From a first and a second injection cylinder with controlled or regulated injection pistons is alternately loaded by an injection molding machine, via which in push-pull mode the cycle, the cyclical injection cycle is carried out in the injection molding machine.

3. The method of claim 1 or 2, d ad u rch ge ke nnze ic h net that the loading of the at least two injection cylinders of each injection molding machine is carried out strictly synchronously, such that a constant flow rate of the melt is taken over by the loading process, with loading movement the injection piston is preferably actively controlled in such a way that mechanical friction losses and acceleration losses are compensated for and there is no interference with the mass flow of the continuous melt flow from the chemical production system.

4. The method according to any one of claims 1 to 3, d ad u rc hgeken nze that the respective switchover from a first injection cylinder to a second injection cylinder of an injection molding machine is controlled by valves and carried out as quickly as possible in such a way that no pressure surge on the melt flow fed to the injection molding machine.

5. The method according to any one of claims 1 to 4, d ad u rc hge ke n nze ic h net that the respective switchover from the first to the second injection cylinder is controlled via valves, the charging current being successively reduced to zero and in a transition region At the same time, the charging current for the next is increased in a coordinated manner, so that there is no retroactive interference effect on the continuous melt flow or the pressure of the melt flow.

6. The method of claim 5, d ad u rc hge ke nnzeich net that a heated valve block is arranged between the first and second injection cylinder and the injection mold of an injection molding machine, via which liquid melt is discharged for the set-up phase or in the sense of an emergency exit in the event of momentary faults can be.

7. The method of claim 1, dad u rc h g eke nnze ic hnet that a continuous, insufficiently degassed melt stream is degassed prior to injection molding via a degassing extruder or a degassing screw and transferred to cyclical dosing quantities.

8. The method of claim 1 or 7, ad u rc hge ke n nz eichn et that the insufficiently degassed melt flow is taken over by a degassing extruder with a continuously rotating screw conveyor and fed into a pre-store designed as a cylinder with a controllable piston, preferably the melt flow is cyclically valve-controlled transferred to a shot pot, and the shot pot is filled with the full continuous melt flow and additionally with the cyclically confirmable pre-storage.

9. The method according to claim 1 or 7, d ad u rc hgekenn ze I net that the continuous melt flow is taken over by a degassing extruder with a continuously rotating and linearly movable screw conveyor, with a part of the degassing extruder being designed as a cyclically activatable pre-store for generating cyclical dosing quantities and the transfer of the cyclical dosing quantities, in particular in a shot pot, are valve-controlled in the intrusion process.

10. The method according to claim 7, so that the continuous melt flow is taken over by a degassing extruder with a continuously rotating screw conveyor and the cyclical metering quantity is generated via two injection cylinders which can be controlled in parallel.

11. The method of claim 1, d ad u rc hge ke nnze ic hn et that the melt flow is cyclically valve-controlled transferred into a shot pot and the shot / pot is filled with the full continuous melt flow and additionally with the cyclically operable preliminary storage, the continuous melt flow with expansion of the supply pressure in a preliminary storage degassed and the melt is preferably taken over by a melt pump or an extruder from the degassing preliminary storage and is fed valve-controlled into the shot / pot from the preliminary storage.

12. The method according to claim 1 or 11, d adu rc h ge e n n e c e ic hnet that the melt is taken over in particular by a melt pump or an extruder from the degassing storage and with the required pressure build-up, the cyclical dosing quantities are generated via two parallel controllable injection cylinders of an injection molding machine.

13.System for the production of injection molding parts, in particular preforms, the liquid melt being taken over directly from a chemical plant in the injection-molding degassing state or in the still insufficient degassing state and being continuously fed to several injection molding machines, for the cyclical production of the injection molding parts in injection molds, d ad u rc hgekzeichenzeichen net, that each of the several injection molding machines can be connected to a feed line of a distribution system of the chemical plant, the individual injection molding machines having at least one pre-memory that can be activated via control and regulating means, for the backflow-free transfer of the continuous melt flow into exact cyclical dosing quantities into the injection molds.

14. System according to claim 13, ad u rc hge ke n nz eichn et that the individual injection molding machine has two injection cylinders with injection pistons and control / regulating means as a preliminary store, such that the at least two injection cylinders can be operated alternately as controlled / regulated loading cylinders , in such a way that a continuous melt flow can be taken over without backflow and the injection cylinders operate as an injection unit via the corresponding activation of the injection pistons and the injection molded parts can be produced cyclically.

15. System according to claim 13 or 14, d ad u rc hge ke nnzeichn et that the injection molding machine has a valve arrangement via which liquid melt can optionally be supplied to one of the at least two injection cylinders, the valve arrangement being part of a valve block which is located between the injection cylinders and placed in the injection molds.

16. System according to claim 15, ad u rc hge ke n nz eichn et that the valve arrangement has a changeover valve, via which alternately one injection cylinder can be connected to the feed line and the other injection cylinder to the cavities of the injection molds, the valve arrangement has a changeover valve for each injection cylinder, via which one injection cylinder can alternately be connected to the feed line and the other injection cylinder to the cavities of the injection molds.

17. System according to claim 15 or 16, so that the valve arrangement for each injection cylinder has a changeover valve, via which alternately one injection cylinder can be connected to the feed line and the other injection cylinder can be connected to the cavities of the injection molds is, the injection cylinder and the valve assembly form a heatable unit, with a connection for the feed line and at least one connection point for the injection mold.

18. System according to one of claims 13 to 17, d ad u rc hge ke nnze ic hn et that the charging process can be carried out by active control of the injection piston without retrospective change in the static melt pressure in the feed line, with the aim of a constant loading volume and the piston retraction speed and / or the piston retraction path can be determined anew for each loading process.

19. System according to claim 18, so that the control detects the piston travel for each loading and injection cycle and the loading volume can be corrected across cycles with the aim of a constant loading quantity.

20. System according to claim 13, d ad u rc hge ken nzeichn et that it has a degassing extruder or a degassing screw with a screw conveyor or two identical or opposite twin screws and drive and control / regulating means for purely rotary or rotary and linear movement of the screw conveyor or twin screws.

21. System according to claim 13, so that it has a preliminary memory, in particular a preliminary memory designed as a shot pot, which is used as a FiFo memory (first in, first out) or as a LiFo memory (last in , first out) is formed.