WO2004050324A1

WO2004050324A1 - Method and installation for the production of injection-molded parts

Info

Publication number: WO2004050324A1
Application number: PCT/CH2003/000122
Authority: WO
Inventors: Robert Weinmann
Original assignee: Netstal-Maschinen Ag
Priority date: 2002-12-04
Filing date: 2003-02-19
Publication date: 2004-06-17
Also published as: AU2003203128A1

Abstract

The invention relates to a method and an installation for producing injection-molded parts (12), especially preforms, in which the liquid molten material is received directly from a chemical production plant (1) and is continuously fed to an injection-molding machine (3). At least two injection cylinders (21, 22) which comprise controlled or regulated injection pistons (24, 25) and via which the cyclical injection cycle is carried out in alternation with the charging cycle, are alternately charged with the continuous flow of melted material. The inventive installation is used for producing injection-molded parts, particularly preforms, the liquid molten material being received directly from the a chemical plant (1) and being continuously fed to an injection-molding machine (3) so as to cyclically produce the injection-molded parts in injection molds.

Description

Process and plant for the production of injection molded parts

Technical field

The invention relates to a process for the production of injection molded parts, in particular preforms, the liquid melt being taken over directly from a chemical production system and being fed continuously to the injection molding process; furthermore a system for the production of injection molded parts, in particular preforms, the liquid melt being taken over directly from a chemical plant and being continuously fed to an injection molding machine, for the cyclical production of the injection molded 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, like any bulk goods, can be obtained from the injection molder for his specific needs. The chemical production facility is capable. 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 of all textiles are yarns or threads, which are either made from natural materials such as wool or silk or the so-called 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. When filaments are produced, the peculiarity of the continuous process comes into play, since the endless 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 usually in the manufacture of filaments the chemical plant and the spinning process belong together.

As stated at the beginning, an injection molding machine works strictly cyclically. The material flow is interrupted between each cycle. This helps to ensure that granules are kept ready for the injection molding process in a small storage container above the machine and drawn in periodically via the metering screw, heated and injected into the cavities of the mold in a metered amount. 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.

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

Presentation of the invention

The method according to the invention is characterized in that with the continuous melt flow at least two injection cylinders with controlled or regulated injection pistons are alternately charged, via which the cyclical injection molding process is carried out in counter-clocking with the charge.

The system according to the invention is characterized in that the injection molding machine has at least two injection cylinders with injection pistons and control / regulating means, 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 adopted and via the corresponding activation the injection piston, the injection cylinders work as an injection unit and the injection molded parts can be produced cyclically.

At the center of the new invention is the transfer of a continuous melt flow via a controlled / regulated charge from two alternating injection cylinders, which are used for the charging process in push-pull of the injection molding cycle. Various studies have shown that the productivity of large injection molding machines is so great 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 finding the link between the continuous melt supply and the discontinuous injection process.

The new invention allows a number of particularly advantageous configurations, for which reference is made to claims 2 to 6 and 8 to 15.

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

Through the synchronous cooperation of at least two injection cylinders in push-pull, either as a charging station or as an injection unit, the basic problem of converting a continuous melt flow into a cyclical melt flow is solved and a given volume flow is taken over exactly.

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 injection piston movement is 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. Overcoming flow losses by the melt pump or by the pressure energy applied by it. The energy for the acceleration and the mechanical friction losses is applied by regulating the injection piston accordingly. The piston movement should 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 placed between the injection cylinders and the injection molds. 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 the respective opening or closing position is subordinate to the switchover phase and cannot trigger any interference. 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 unloading 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 regulation 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.

Brief description of the invention

In the following, the invention is illustrated 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.

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 (5) 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 directly over the piston rod 28 connected to the hydraulic drive 26. The drive piston 29 is acted upon on both sides with oil. The changeover takes place via a hydraulic valve 50, which is controlled via an output interface 51. 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 loaded. The shut-off valve 36 is in the closed position. The shut-off valve 37, on the other hand, is in the open position, so that the injection cylinder 22 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 Figure 8, the injection cylinder 22 works 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 opposite 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 piston 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 100 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 a constant shot weight is obtained.

Claims

claims

1. A process for the production of injection molded parts, in particular preforms, the liquid melt being taken over directly from a chemical production system and continuously being fed to an injection molding machine, characterized in that at least two injection cylinders with controlled or regulated injection pistons are alternately charged with the continuous melt flow , over which the cyclical spray cycle is carried out in push-pull of the charge.

2. The method according to claim 1, characterized by the fact that the loading of the at least two injection cylinders is carried out strictly synchronously, such that a constant mass flow of the melt is taken over by the loading process.

3. The method according to claim 1 or 2, characterized by the fact that the charging movement of the injection pistons is actively controlled in such a way that mechanical friction losses and acceleration losses are compensated for and there is no disruptive effect on the mass flow of the continuous melt flow.

4. The method according to any one of claims 1 to 3, dad u rch ge ken nzeichn et that 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 ,

5. The method according to any one of claims 1 to 3, adu rc hge ke nn zeic hn et that the respective switchover from one injection cylinder to the next is controlled via valves, the charging current being successively reduced to zero in a transition region and at the same time the charging current for the next one is increased in a coordinated manner so that there is no retroactive disturbing effect on the continuous melt flow.

6. The method according to any one of claims 1 to 5, characterized by the fact that a heated valve block is arranged between the injection cylinders and the injection mold, via which liquid melt can be discharged for the set-up phase or in the sense of an emergency exit in the event of instantaneous faults.

7. Plant for the production of injection molded parts, in particular preforms, the liquid melt being taken over directly from a chemical plant and being continuously fed to an injection molding machine for the cyclical production of the injection molded parts in injection molds, characterized in that the injection molding machine has at least two injection cylinders with injection pistons and control means such that the at least two injection cylinders can be operated alternately as controlled / regulated loading cylinders, such that a continuous melt flow can be accepted 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.

8. System according to claim 7, characterized in that it has a feed line for the liquid melt and a valve arrangement via which liquid melt can optionally be supplied to one of the at least two injection cylinders.

9. Plant according to claim 7 or 8, characterized in that the valve arrangement is part of a valve block which is placed between the injection cylinders and the injection molds.

10. System according to one of claims 7 to 9, characterized by the fact that the valve arrangement has a changeover valve, via which the one injection cylinder can alternately be connected to the feed line and the other injection cylinder can be connected to the cavities of the injection molds.

11. System according to one of claims 7 to 9, d ad u rc hge ke n nze I net that the valve arrangement for each injection cylinder has a changeover valve, via which alternately one injection cylinder with the feed line and the other injection cylinder with the cavities of the Injection molds can be connected.

12. System according to one of claims 7 to 11, that the injection cylinders and the valve arrangement form a heatable structural unit with a connection for the feed line and at least one connection point for the injection mold.

13. System according to one of claims 7 to 12, that the charging process can be carried out by active control of the injection piston with unchanged static melt pressure in the feed line, with the aim of a constant loading volume.

14. System according to claim 13, so that the piston retraction speed and / or the piston retraction path can be determined anew for each loading process.

15. System according to one of claims 13 or 14, d ad u rc hge ke n nze I net that the control / regulation of the piston travel for each loading and spraying cycle recorded and the loading volume, with the aim of a constant loading quantity, can be corrected across cycles is.