DE102009012481B3 - Injection molding machine for processing e.g. plastic to produce foamed material, has storage chamber connected with lock chamber by valve unit, where storage chamber and lock chamber are vented by another valve unit - Google Patents

Abstract

The machine has a dosing unit (3) for dosing and supplying a material and including a pressure chamber lock with a lock chamber (31) and a storage chamber (30). A driving fluid supply (7) has a supply network with driving fluid connections (37, 38) at the lock chamber and the storage chamber. The driving fluid supply is shiftably connected with the storage chamber by a first valve unit (51), and the storage chamber is shiftably connected with the lock chamber by a second valve unit (52). The storage chamber and the lock chamber are vented by a third valve unit (53).

Description

The The invention relates to an injection molding machine for processing of plastics and other plasticizable masses such as powdery or ceramic masses for the production of physical fuels frothed Materials according to the preamble of claim 1.

In the field of injection molding, there are various special processes besides compact injection molding. One of these special processes is foam injection molding, which enables the production of foamed structural foam parts. Such molded parts have in contrast to compact moldings a sandwich-like structure, that is, a more or less compact outer skin with a closed-cell core. An injection molding machine for the production of foamed with physical fuels materials is from the WO 2006/136609 A1 whose structure will be discussed in more detail below.

The foam injection molding In contrast to injection molding of compact molded parts has some essential Advantages. These are, for example, a density reduction of Molding, an increased specific Stiffness due to displacement of the area moments of inertia in the surface layers of the component and an increased insulation effect, for example against heat. The production of moldings with large wall thicknesses is possible, which greater freedom allowed in the design. The process also allows molded parts with lower Residual stresses, low distortion and often more favorable manufacturing tolerances and produce smaller sinkholes.

For the production frothed Moldings can essentially distinguish two different types of blowing agent are: physical blowing agents and chemical blowing agents. The physical blowing agents have chemical blowing agents Often decisive advantages. Because of their mostly stable chemical compounds is in their use no increase in Degradation of the material to be processed to fear. Physical blowing agents are relatively inexpensive blowing agents. Furthermore By using physical blowing agents larger foaming degrees can be achieved. This physical Propellants are also referred to below as physical propellants referred to several forms of aggregate state from liquid to gaseous to supercritical to take into account.

The mode of action of physical blowing agents, which are added directly to the material to be foamed, is based firstly on the change in the state of matter of these substances, such as the evaporation of a liquid (eg CFC), or on the supersaturation of the material with respect to one previously dissolved in the material fluid. As part of the injection molding process, the supersaturation of the polymer and thus the foaming is initiated in almost all cases solely due to the pressure drop at the outlet of the melt from the nozzle of the plasticizing unit or upon entry into the cavity. A generic state of the art is made EP 0 952 908 B1 known.

Chemical blowing agents, by contrast, are substances which only split off gas during the processing process due to a chemical reaction, usually initiated by the application of heat, and thus enable the production of a foam structure in the material. The cause of the gas separation can be either the thermal decomposition of the blowing agent or a chemical reaction of various substances contained in the blowing agent. The resulting gas is usually N ₂ , CO ₂ or CO.

The physical blowing agents include, for example, in addition to the hydrocarbons Water, nitrogen and carbon dioxide. However, hydrocarbons either not environmentally friendly are (HCFC) or due to their flammability only to considerable Safety requirements can be processed (eg pentane), win Propellants such as carbon dioxide and nitrogen are becoming increasingly important.

The foam injection molding let yourself in principle divided into two process variants, with respect to the pressure that during the processing in the tool is effective, can be differentiated.

Low pressure process:

Of the foaming Material is initially used in the low-pressure process in a screw cylinder plasticized (Schneckenvorplastifizierung). If a chemical blowing agent to be used, this must be the Material previously be added in a treatment step. In the case of using a physical blowing agent, this becomes to be frothed Material, for example, added after plasticizing in the screw cylinder (2-stage screw). The screw then conveys the polymer / blowing fluid mixture at high speed into the cavity. The dosed and into the cavity injected polymer volume is less than the volume of the cavity, a hallmark the low pressure method. Only by the foaming of the melt is the Mold nest completely refilled. The foaming process is triggered by the pressure drop of the melt along the flow path.

The Low pressure processes for the production of foamed moldings are distinguished depending on the degree of foaming through cavity pressure less than 70 bar. For example, aluminum tools are often enough with low complexity the requirements. In addition, working with low clamping forces possible. The disadvantages of the low-pressure method are mainly in the often bad Surface quality of the molded parts produced.

High pressure process:

A Improvement of the surface quality of foamed components let yourself through the use of a so-called high-pressure process for the production foamed Achieve moldings. Here, the entire mold cavity with the melt / blowing fluid mixture filled, the tool volume is smaller than the volume of the molded part to be produced. In a Be following the injection phase subsequent emphasis phase the marginal layers of the molding compressed to a closed To achieve edge layer. Foaming is caused by the magnification of the Mold cavity initiated. This can be done by using a dipping edge tool or by pulling the core. Such a tool will also as a "breathing" tool designated. Alternatively, the need for foaming pressure reduction by retreating the injection piston can be realized, wherein the excess melt in the injection cylinder back foamed. High pressure processes work with cavity pressures, the values on the order of magnitude as with compact casting can.

variants Both methods each have a further improvement in the surface quality of the foamed components to the goal. In particular, measures like cyclic heating and cooling of the Tool (eg Variotherm method) or injection at gas back pressure (Gas back pressure method) are for the improvement of the surface quality of special Importance.

At the cyclic heating and cooling of the tool causes heating the mold wall after the injection process to a temperature melting above the softening temperature of the material the molding surface. Thus, surface defects, that come from injecting, eliminated. Thereafter, the mold wall must be cooled to a solidification to allow the material. Disadvantages of the process are long cycle times that are complicated Tool technology and a high specific energy consumption.

At the Gas back pressure method is a foaming of the polymer / blowing fluid mixture during the Injection thereby avoided that previously a gas pressure of about 20 to 30 bar is generated in the tool. Thus, the pressure drop leading to blistering occurs not on anymore. A disadvantage of this method are the high tooling costs because the tool halves must be made gas-tight and with a high surface quality.

These activities be used individually or combined in both the low pressure and the high pressure process applied, so a variety of different methods used becomes. The low pressure processes include the TSG process (thermoplastic foam casting), the UCC process (Union Carbide Corporation) and the Variotherm process. To the high pressure procedures belong the TM method, the TAF method (Toshiba-Asahi-Foam) or DOW method, the USM method (United Shoe Machinery) and the TFM process (Thermoplastic Foam Molding).

So far is a cost savings in foam injection molding is not always possible because in the calculation of raw material savings additional costs for propellants, longer Prevent manufacturing times or any subsequent treatment of the surface. The production of foamed materials requires the use of specially designed for this purpose or heavily modified machines such. B. low-pressure injection molding machines, that by a screw pre-plasticization with piston injection characterized by special plasticizing units, via the the gas is mixed in and homogenized. Furthermore, there are versions known between the injector and Plasticizing unit are mounted. Also for this are special investment techniques necessary, by special sealing techniques of the driving fluid over the melt-shaped material besides the additional need from Treibfluiddosierstationen a high cost and procedural Mean effort.

The WO 2006/136609 A1 proposes to overcome the disadvantages of the prior art already to use a metering unit with two chambers on a plasticizing, wherein in the one chamber material nachgefördert, while the material directly on the plasticizing cylinder with the driving fluid via a pressure-tight lock chamber and the plasticizing in whose catchment area is supplied. This ensures that no driving fluid can escape uncontrollably. This dosing unit can be easily mounted on conventional injection molding machines and retrofitted. In the lock chamber, a nearly constant pressure can be maintained.

adversely However, it has turned out that the ventilation times relatively long and icing may occur.

outgoing from this prior art, the present invention is the Object to overcome the disadvantages of the prior art and a reliable one Dosing unit for an injection molding machine to accomplish.

These Task is by an injection molding machine with the features of claim 1 solved.

Of the injection molding machine and the dosing unit are assigned valve means which ensure that the ventilation times be reduced and icing problems are reduced. This can a pressure drop both in the store and in the lock chamber sustainably reduced or avoided, which also leads to uniform processing and to obtain a uniformly closed-celled Foam contributes. In conjunction with the known dosing unit can thus be a fast, reliable and easy-to-use dosing unit to be created any injection molding machines retrofitted can be.

Further Advantages emerge from the subclaims and the following Description of several embodiments.

in the Below, the invention will be described with reference to several in the figures embodiments explained in more detail. It demonstrate:

1 a schematic representation of an injection molding machine with a metering unit according to the prior art,

2 to 4 Circuits for supplying the dosing unit with drive fluid,

5 a section through a metering unit

6 a schematic overall view of the dosing unit with control unit and pressure transducers.

Before the invention is described in detail, it should be noted that they do not affect the respective components of the device as well the respective process steps is limited, since these components and methods may vary. The terms used herein are intended only to particular embodiments describe and are not used restrictively. If moreover in the description or in the claims the singular or indefinite Articles are used, this also applies to the majority of these elements, as long as the overall context is not clear makes something else clear.

1 shows a schematic representation of an injection molding unit on an injection molding machine 1 for the processing of plastics and other plasticizable materials such as powdery or ceramic materials for the production of foamed with physical fuels materials. The injection molding machine 1 consists of a plasticizing unit 21 , a static mixer 22 and a needle valve nozzle 23 , The plasticizing unit 21 has a plasticizing cylinder 15 in which a conveying means such as a screw is arranged. The plasticizing cylinder 15 has heating bands 17 to provide the thermal energy necessary for the molten material.

At the rear end with respect to the main conveying direction of the screw, the screw 19 a drive device 16 on. At the catchment area 20 the snail 19 is over a filler neck 40 a metering device 3 for feeding material to be plasticized and foamed 5 at the plasticizing unit 21 arranged.

The dosing unit 3 has a material supply 24 and a motive fluid inlet 37 on. The drive fluid inlet 37 is via a Treibfluidzuleitungssystem 11 , which is preferably a pressure reducer 9 has, with a gas cylinder 7 connected. Of course, the motive fluid supply may be to the motive fluid inlet 37 also be done elsewhere, for example via a Treibfluiddosierstation.

In relation to the main conveying direction of the screw 19 rear area or in other words on the drive side area of the screw 19 is between the snail 19 and the plasticizing cylinder 15 a seal 13 arranged. The seal 13 is radial to the screw 19 arranged and seals in the axial direction. Through the seal 13 it is guaranteed that in the plasticizing cylinder 15 located propellant fluid in the drive-side region of the screw 19 not from the plasticizing cylinder 15 can escape. In relation to the main conveying direction of the screw 19 front area of the plasticizing machine 1 ensures the needle valve nozzle 23 in the closed state, that the driving fluid is not removed from the plasticizing unit 21 or the plasticizing machine 1 can escape.

The dosing unit 3 for dosing and feeding the material to be plasticized and foamed in the plasticizing cylinder 15 has a pressure chamber lock with a lock chamber 30 and a storage chamber 31 with at least two locks before and after the storage chamber. The lock chamber is also opposite the material supply 24 also by means of a lock pressure-tight lockable. The propellant fluid supply 7 is via a supply network with Treibfluidanschlüssen 37 . 38 , at the lock chamber 30 and at the storage chamber 31 connected. In the supply network valve means are provided to lock chamber 30 and / or storage chamber 31 If necessary, to put under pressure or to be able to keep under pressure.

5 shows such a dosing unit in section. In waiting mode, ie when there is enough material in the plasticizing unit, both are poppets 70 . 71 closed and both the lock chamber 31 as well as the storage chamber 30 are under pressure, usually carbon dioxide or nitrogen is used as gas. In both chambers, the material to be foamed, z. B. granules. From the lower storage chamber 30 cyclically trickles material into the catchment area 20 for the funding 19 , Does the level in the storage chamber 30 below a limit, the valve cone becomes 71 opened between lock chamber and storage chamber, allowing material from the lock chamber 31 in the storage chamber 30 can trickle. Once the lock chamber 31 is empty, the valve cone 71 closed between lock chamber and storage chamber. To the lock chamber 31 To refill with new material, it must first be vented, ie the pressure in the chamber must be reduced to ambient pressure. This is the Treibfluidanschluss 37 ( 2 to 4 ) with the vent 28 in order to keep the time for venting as short as possible.

Once the pressure in the lock chamber 31 degraded, what about a pressure transducer 43 can be detected, the refilling process begins. This will be a in 5 drawer, not shown, opened, so that the range of material supply 24 between gate valve and upper valve cone 70 can fill with granules. The gate valve is then closed and the upper valve plug 70 open. This material comes from the material supply 24 into the lock chamber 31 , The upper valve cone 70 will be closed again. This process is repeated until the refilling process of the lock chamber 31 is completed. The number of repetitions depends on the ratio of the usable volume in the lock chamber to the volume between the gate valve and the upper valve cone 70 from. This procedure prevents the lock chamber from running in an uncontrolled manner and closing the upper valve plug 70 becomes impossible.

When the refilling process is finished, the lock chamber becomes 31 again "ventilated", ie filled with propellant fluid, so that the pressure in the lock chamber 31 and the pressure in the storage chamber 30 are essentially the same. The lock process is now complete and the system is in wait mode.

The 2 to 4 show different circuits for gas connection of the pressure locks. Basically, the Treibfluidversorgung 7 with the storage chamber 30 via a first valve means 51 and the storage chamber 30 with the lock chamber 31 via a second valve means 52 (or via the first valve means 51 and the fifth valve means 55 in 4 ) connected switchable. storage chamber 30 and lock chamber 31 are at least a third valve means 53 (or via the third valve means and a fourth valve means 54 in 3 ) can be vented. The second valve means 52 is in the embodiment of 2 a 3/2-way valve, via which the lock chamber 31 at the same time in the direction of the vent 28 is vented. That with the storage chamber 30 connected third valve means 53 is a 2/2-way valve. The embodiment is characterized mainly by a simple piping, since the valve means 51 . 52 . 53 via separate connections or lines 61 . 62 . 63 and on a common line 60 with the storage chamber 30 are connected.

The first valve means 51 behind the propellant fluid supply 7 is always open during operation of the injection molding machine, so that the storage chamber 30 always under pressure. The 3/2-way valve (second valve means 52 ) is in waiting mode so that the line between storage chamber 30 and lock chamber 31 is open, so that the lock chamber is under pressure. When refilling the lock chamber, the second valve means 52 closed and in the second position of the 3/2-way valve is via the Treibfluidanschluss 37 the lock chamber 31 towards the vent 28 vented. Depending on the cross section may result in a relatively long venting time. After the end of the dosing process, ie after the umpteenth repetition in the refilling process, the lock chamber is 31 to re-aerate, ie the gas pressure is to rebuild. For this purpose, the second valve means switches 52 back to the starting position. With opening of the second valve means 52 the pressure drops in the storage chamber 30 as the gas enters the non-pressurized lock chamber 31 flows. This can lead to expansion of the gas and to cooling of the storage chamber and thus to icing. The third valve means 53 serves to vent the storage chamber and is open when the system is switched off.

In the embodiment of 3 is the lock chamber 31 via an additional fourth valve means 54 in the form of a 2/2-way valve in the direction of the vent 28 vented. This valve is closed in the waiting mode and open during refilling. This valve carries with it to a significant reduction of the venting time. A pressure drop in the storage chamber after the filling process of the lock chamber 31 but still occurs.

According to 4 becomes a fifth valve means 55 provided that the lock chamber 31 with the propellant fluid supply 7 and with the storage chamber 30 switchable connects. This supplies the first valve means 51 the storage chamber 30 with motive fluid, while the fifth valve means 55 the lock chamber 31 supplied with propellant fluid. The first valve means 51 is basically always open during production. The fifth valve means 55 is idle but closed during refill. The separate supply of the two chambers can be a pressure drop in the storage chamber 30 and thus avoid the cooling in the storage chamber. For bleeding the lock chamber 31 can now use a 2/2-way valve instead of the 3/2-way valve 52 ' be used. The 2/2-way valve 52 ' becomes like the 3/2-way valve (second valve means 52 ) in the embodiments in the 2 and 3 opened before refilling and then closed again. By using the 2/2-way valve 52 ' Can the pressure in the lock chamber 31 be reduced much faster, which significantly shortens the entire refilling process.

The pressure control in the lock chamber can be passive (by venting or connecting to the storage chamber) or actively by means of pressure regulation. Pressure transducer 43 capture according to 6 the pressure in the storage chamber 30 and in the lock chamber 31 , The signals thus detected are sent to the control unit 42 transmitted, this information to control the valve means 51 to 55 used.

1

injection molding machine

3

dosing

5

plasticizable material

7

Propellant fluid supply

9

pressure reducer

11

management

13

poetry

15

plasticizing

16

Drive unit for 19

17

Heating tapes

19

Auger

20

catchment area

21

plasticizing

22

static mixer

23

shut-off

24

Material supply

28

vent

30

storage chamber

31

lock chamber

37, 38

Propellant fluid port

40

connecting pieces

42

control unit

43

Pressure transducer

51

first valve means

52 52 '

second valve means

53

third valve means

54

fourth valve means

55

fifth valve means

60

common management

61, 62, 63

management

70 71

shuttle

Claims (7)

Injection molding machine ( 1 ) for the processing of plastics and other plasticizable materials, such as powdery or ceramic materials, for the production of materials foamed with physical fuels, comprising - a plasticizing unit ( 21 ) with plasticizing cylinder ( 15 ) and the funds received therein ( 19 ), - a dosing unit ( 3 ) for metering and feeding the material to be plasticized and foamed into the plasticizing cylinder ( 15 ), the dosing unit ( 3 ) a pressure chamber lock with a lock chamber ( 31 ) and a storage chamber ( 30 ) with at least two locks before and after the storage chamber ( 30 ), - a drive fluid supply ( 7 ) with a supply network with Treibfluidanschlüssen ( 37 . 38 ) at the lock chamber ( 31 ) and at the storage chamber ( 30 ), - Valve means in the supply network to put under pressure or under pressure holding lock chamber (as required) 31 ) and / or storage chamber ( 30 ), characterized in that the drive fluid supply ( 7 ) with the storage chamber ( 30 ) via a first valve means ( 51 ) and that the storage chamber ( 30 ) with the lock chamber ( 31 ) via a second valve means ( 52 ) is connected switchable and that storage chamber ( 30 ) and lock chamber ( 31 ) via at least one third valve means ( 53 ) are vented. Injection molding machine according to claim 1, characterized in that the second valve means ( 52 ) is a 3/2-way valve, via which the lock chamber ( 31 ) at the same time can be vented. Injection molding machine according to claim 1 or 2, characterized in that the with the storage chamber ( 30 ) connected third valve means ( 53 ) is a 2/2-way valve. Injection molding machine according to one of the preceding claims, characterized in that the first, second and third valve means ( 51 . 52 . 53 ) via separate connections or lines ( 61 . 62 . 63 ) with the storage chamber ( 30 ) are connected. Injection molding machine according to one of claims 1 to 3, characterized in that the first, second and third valve means ( 51 . 52 . 53 ) via a common line ( 60 ) with the storage chamber ( 30 ) are connected. Injection molding machine according to one of the preceding claims, characterized in that the lock chamber ( 31 ) via an additional fourth valve means ( 54 ) is vented. Injection molding machine according to one of the preceding claims 1, 3 to 6, characterized in that the lock chamber ( 31 ) via a fifth valve means ( 55 ) with the driving fluid supply ( 7 ) and with the storage chamber ( 30 ) is connected switchable.