METHOD AND DEVICE FOR MIXING AND SUPPLYING PLASTIC INTO A MOLD FOR A VACUUM INFUSION

Abstract

A method and device for mixing plastic from liquid components in a mixer (8) and conveying it through a line (10) into a mould (12), in particular for vacuum infusion, characterised in that the components are each pumped by means of a pump (24) from their own respective component container (22) into a mixer (8) and are mixed therein, that these volume flows are controlled by a controller (26) in such a manner that they supply the components to the mixer (8) in a specific ratio, that the pressure loss in the line (10), between a pressure sensor in one of the component supply lines (32) leading to the mixer (8) and the mould (12), is determined, and that the pressure is measured by the pressure sensor and supplied to a controller (26) which, taking into consideration the determined pressure loss, controls the volume flows such that the pumps (24) supply the components to the mixer (8) at a pressure that is greater than the ambient pressure or than another specific pressure that should not be exceeded in the mould (12) by at most the pressure loss.

Claims

1. A method for mixing plastic from liquid components in a mixer and conveying the plastic through a line into a mould, in particular for vacuum infusion, at a pressure below ambient pressure or below another specific pressure that should not be exceeded in the mould, the method comprising acts of: (a) pumping each of the components using a pump from a respective component container into a mixer and mixing the components therein, (b) controlling volume flows using a controller in such a manner that the components are supplied to the mixer in a specific ratio, (c) determining pressure loss in the line, between a pressure sensor in a component supply line leading to the mixer and the mould, and (d) measuring the pressure in the component supply line using the pressure sensor and supplying the pressure to a controller which, taking into consideration the determined pressure loss, controls the volume flow of the component in the component supply line of the pressure sensor such that the pump supplies the component to the pressure sensor at a pressure that is greater than the ambient pressure or another specific pressure that should not be exceeded in the mould by at most the pressure loss.

2. A device for mixing plastic from liquid components in a mixer and conveying the plastic through a line into a mould, in particular for vacuum infusion, at a pressure below ambient pressure or below another specific pressure that should not be exceeded in the mould, the device comprising: at least one pump that is configured to pump the components from a respective component container into a mixer that is configured to mix the components, a controller that is configured to control volume flows in such a manner that the components are supplied to the mixer in a specific ratio, a device that is configured to input and/or measure pressure loss in the line between a pressure sensor in a component supply line leading to the mixer and the mould, and a controller that is configured to control, taking into consideration the determined pressure loss, the volume flow in the component supply line of the pressure sensor such that the component is supplied to the pressure sensor and from the pressure sensor to the mixer at a pressure measured by the pressure sensor that is greater than the ambient pressure or another specific pressure that should not be exceeded in the mould by at most the pressure loss.

3. The device according to claim 2, wherein the line includes a line strand from the mixer to a line manifold and a plurality of local lines leading from the line manifold into the mould.

4. The device according to claim 3, wherein the amount of pressure loss in the local lines is determined as the amount of pressure loss in the local line with the lowest pressure loss and is supplied to the controller to be taken into consideration when controlling the pumps.

5. The method according to claim 1, further comprising an act of degassing at least one of the components in the component container prior to performing acts (a) to (d).

6. The method or device according to claim 2, wherein the mixer is a mixing head with a drive device for a dynamic mixer insert.

7. The method according to claim 1, wherein the line includes a line strand from the mixer to a line manifold and a plurality of local lines leading from the line manifold into the mould.

8. The method according to claim 7, wherein act (c) includes determining the amount of pressure loss in the local lines as the amount of pressure loss in the local line with the lowest pressure loss and supplying the pressure loss to the controller to be taken into consideration when controlling the pumps.

9. The method according to claim 1, wherein the mixer is a mixing head with a drive device for a dynamic mixer insert.

Description

[0032] Further advantages, configurations and details of the invention are described in the following in the description of embodiments and with reference to the enclosed figures. The drawings show the following:

[0033] FIG. 1 shows a schematic flow diagram of a method according to the invention with members of a device system according to the invention, and

[0034] FIG. 2 shows a sectional side view of a mixing head of a device system according to the invention.

[0035] FIG. 1 shows a flow diagram 2 of a method for mixing a thermosetting plastic from two liquid components 4, 6 in a mixer 8 and conveying it for vacuum infusion through a line 10 into a mould 12 at a pressure lower than the ambient pressure.

[0036] The plastic is applied whilst still in liquid form to the rigid mould 12 that corresponds in a complementary manner to an outer side of the component, according to FIG. 1 to a side of a wind turbine blade (not shown). The plastic is applied to the rigid mould surface 14 underneath a film 16, the intermediate space 18 being placed under “vacuum”, i.e. subjected to negative pressure 20. In this intermediate space 18, the plastic impregnates fibre layers (not shown; for example woven fabric and/or laid fabric, in particular of glass) so that the component of fibre-reinforced plastic (namely, according to FIG. 1, a wind blade half-shell) is formed once the plastic has cured, since only the side formed by the rigid mould 12, 14 as the outer side of the future wind blade, and not the film side, can be reproduced in a dimensionally accurate manner. The vacuum 20 in the intermediate space 18 in the mould ensures that pockets of air which might otherwise form weak points later on are extracted—and in particular also that the liquid plastic is drawn into the fibre layers as a matrix. However, the pressure in the mould in the intermediate space 18 underneath the “vacuum film” 16 may not exceed the ambient pressure, not least because otherwise the film side 16 of the mould would be “blown up”.

[0037] The method now includes the steps of pumping the components from their own respective component container 22, by means of a respective pump 24 in each of the component containers 22, into the mixer 8 and mixing them therein. By means of a programmable logic controller 26, these volume flows (measured in volumetric flow meters 25) are controlled (by controlling the pumps 24—signal lines are shown as dashes) in such a manner that the components 4, 6 are supplied to the mixer 8 in the ratio required to produce the thermoset.

[0038] The volume flows are furthermore controlled by the controller 26 (again by controlling the pumps 24, namely with a priority inferior to the control of the mixing ratio) in such a manner that the components 4,6 are supplied to the mixer 8 at a pressure that is greater than the ambient pressure—namely greater by at most the pressure loss in the line from the mixer 8 to the mould 12.

[0039] The pressure in the mixed, liquid plastic is measured prior to mixing in the mixer 8 by a pressure sensor 30 in one of the two component supply lines 32 to mixer 8 (i.e. upstream of the mixer 8 with respect to the component flow direction) in the mixing head 28 (FIG. 2; more details below). The pressure sensor 30 is therefore only exposed to one of the more harmless, not yet mixed liquid components 4, and not, as is the case in the prior art, to the already mixed, already reacting, curing plastic that regularly renders the sensors at the sensitive measurement points inaccurate and unusable. The pressure at the sensor 30 in the component supply line 32 of the component 4 immediately upstream of the mixer 8 in the mixing head 28 is supplied to the controller 26. In the shown example, the configuration of the mixing head 28 and the arrangement of its components, including the sensor 30, is based on its construction for other methods for mixing two-component plastics.

[0040] The pressure loss in the line between the pressure sensor 30 and the mould 12 (or, for example, in a section 34 of the line 10 that is important for pressure loss, according to FIG. 1 up to a manifold 34; see below) can be measured (i.e. offline, for example determined in a preliminary test) before the actual manufacturing process is carried out, but can in particular also be calculated. The pressure loss occurs due to known laws of fluid mechanics, and thus the measurement and in particular also the calculation thereof are possible and objective, and are in particular not subject to any human discretion. According to the method, rheological, dynamic pressure losses, such as those due to fluid viscosity, line geometry and fluid friction in the line are, for example, taken into consideration in the calculation, but in particular also hydrostatic conditions, i.e. pressure loss (or increase) due to the amount of rise (or fall) between pressure measurement points 30 and the mould 12.

[0041] After inputting the line pressure loss into an input device 35 (and/or data supply line), the controller 26 controls the component volume flows in the lines 32 in particular in such a manner that the components 4, 6 are supplied to the mixer 8 at a pressure that is greater than the ambient pressure by at most the line pressure loss between the pressure sensors 30 and the mould 12. It is therefore ensured according to the invention that the film side 16 of the mould 12 is not blown up—namely even without having to measure the pressure in the intermediate space 18 of the mould, and in particular without having to measure it anywhere at all in the already mixed, still liquid plastic (for instance at the introduction points 36 into the mould 12, as according to the prior art; not shown).

[0042] As already indicated, the line 10 has a line section 34 or main line strand 34 from the measurement points 30 to a line manifold 38, as well as a plurality of local lines 40 (of varying lengths) leading from the line manifold 38 into the mould 18. This allows the mixed plastic to be guided from the mixer 8 to the manifold 38 through the main line strand 34 and, from the manifold, is introduced via branches into the intermediate space 18 of the mould 12 at a plurality of points 36 under the film 16. The amount of pressure loss in the local lines 40 is then preferably determined (i.e. measured and/or calculated) as being the amount of pressure loss in the local line with the lowest pressure loss and is supplied to the controller 26 to be taken into consideration when controlling the volume flows. Since these local lines run structurally parallel to one another from manifold 38 into mould 12, taking into consideration only one of the local lines, in particular the one with the lowest pressure loss, logically ensures that the pressure balance in each of the introduction points 36 from the local lines 40 into the mould 12 results in a pressure that is lower than the ambient pressure. Even taking into consideration the pressure loss in just one line section, for example in just the main line strand 34, will reliably ensure this according to the invention. The reason for this is that due to its logically shorter length than the whole line 10, a lower pressure loss will also be determined (in particular calculated and/or measured) in the line section 34. Since the volume flow is controlled according to the invention in such a manner that the pressure upstream of the mixer 8, measured at the sensors 30, is greater than the ambient pressure by (at most) the pressure loss, the liquid pressure at the inlets 36 into the mould 12, 18 will, given an actually even higher whole line pressure loss, accordingly be more significantly below ambient pressure.

[0043] By employing the shown device, a conventional so-called mixing head 28 is, as already stated, used in the shown method 2, such as is also used for other methods for mixing two-component plastics:

[0044] For the production of plastic prior to further processing, for example prior to introduction into the sprue of an injection mould, it is also the case for many plastics, in particular thermosets such as epoxy, that at least two liquid components, also in the prior art, are normally mixed together such that the resulting, in particular liquid (or also viscous, paste-like) mixture crosslinks. The component mixture is commonly forwarded for processing through a tubular passage (not shown), the—static— mixing insert, with turbulators in the interior thereof that deflect, divert and/or locally accumulate the fluid flowing therethrough, generate turbulence and/or swirl and thus mix the fluid flowing therethrough, possibly locally immediately before processing of the plastic. As is known, supply lines lead into this mixer, in particular in the same number as liquid components. A pressure sensor is in most cases arranged in at least one of the supply lines, which measures the fluid pressure in the still unmixed, i.e. not yet reacting, component.

[0045] In the method 2, production (mixing of the components 4, 6) takes place locally at a considerable distance from the processing of the plastic, vacuum injection thereof into the intermediate space 18 between the mould 14 and the film 16. However, in the method 2, such a conventional mixing head is also suitable as a mixer within the meaning of the invention and, optionally, its (at least one) pressure sensor 30 as a sensor within the meaning of the invention. This also applies to the so-called dynamic mixer 8 and mixing head 28 (shown in FIG. 2):

[0046] To ensure that the components 4, 6 are mixed as uniformly and completely as possible, it has proven to be advantageous and become established to configure the turbulators 42 in the tubular passage 44 such that they rotate. Mixing heads 28 then have at least two component supply lines 32 as well as a rotary drive 46 with a drive shaft 47. Such a device 28 is then adjusted to place the tubular passage member 44 (mixer tube) in fluid-tight conducting connection with the component supply lines 32, and to place a rotary drive connecting structure 48 in rotary drive connection 48 with a mixer insert 50 (typically comprising a number of turbulators 42 and being configured for use in the passage member 44) when the mixer insert 50 is inserted into the passage member 44 and the passage member is placed in conducting connection with the component supply lines. In known mixer inserts 50, such a rotary drive connecting structure is often an opening (not shown) lying substantially radial to the axis of rotation, into which a hook (not shown) at the end of the drive shaft is hooked in order to create the drive connection—shown, however, is a self-tapping thread 48 at the end of the drive shaft 47 in a bore 48 at the start of the mixer insert 50. The mixer tube 44 and mixer insert 50, which together are also called mixer 8, as well as the above-described static mixers (not shown) may (also according to the invention) be single-use or disposable articles.

[0047] A stirrer 52 (for example to homogenise the component) and/or a heater 54 (for example to keep the component temperature constant) may be provided in the component containers 22.

LIST OF REFERENCE NUMBERS

[0048] Flow diagram 2 of a method according to the invention for mixing plastic [0049] Two liquid components 4, 6 [0050] Mixer 8 [0051] Supply line 10 [0052] Mould 12 [0053] Mould surface 14 [0054] Film 16 [0055] Intermediate space 18 [0056] “Vacuum”; negative pressure 20 [0057] Component container 22 [0058] Pump 24 [0059] Volumetric flow meter 25 [0060] Programmable logic controller 26 [0061] Mixing head 28 [0062] Pressure sensors 30 [0063] Component supply lines 32 to the mixer 8 in the mixing head 28 [0064] Section important for pressure loss; main line strand 34 of line 10 [0065] Input (device) 35 of the line pressure loss [0066] Introduction points 36 into the mould 12 [0067] Line manifold 38 [0068] Local lines 40 [0069] Turbulators 42 [0070] Tubular passage; mixer tube 44 [0071] Rotary drive 46 [0072] Drive shaft 47 [0073] Rotary drive connecting structure 48 [0074] Mixer insert 50 [0075] Stirrer 52 [0076] Heater 54