Method and moulding system for manufacturing a fibre-reinforced polymer object via a feedback system for controlling resin flow rate

Abstract

A method of manufacturing a fibre-reinforced polymer object by means of vacuum-assisted resin transfer moulding (VARTM), wherein fibre material is impregnated with liquid resin in a mould cavity comprising a rigid mould part having a mould surface defining an outer surface of the object, is described. One or more pressure sensors are connected to resin inlets of the VARTM system. A control unit is used for controlling a polymer supply unit based on measured resin pressure and is adapted to adjusting a resin flow rate, if pressure measured by the pressure sensors is below a lower threshold level or above a higher threshold level.

Claims

1. A method of manufacturing a fibre-reinforced polymer object by means of vacuum-assisted resin transfer moulding (VARTM), wherein a fibre lay-up is impregnated with a liquid resin in a mould cavity comprising a rigid mould part having a mould surface defining an outer surface of the object, said method comprising the steps of: a) arranging the fibre lay-up on the mould surface, wherein the fibre lay-up includes a plurality of fibre layers; b) arranging at least one resin inlet above the fibre lay-up; c) attaching one or more pressure sensors to the at least one resin inlet, above the fibre lay-up; d) arranging a vacuum bag on top of the rigid mould part and sealing the vacuum bag to the mould part to define the mould cavity; e) evacuating the mould cavity; f) supplying the liquid resin to the mould cavity via the at least one resin inlet to impregnate the fibre lay-up, the liquid resin being supplied at a resin flow rate; g) monitoring a pressure with the one or more pressure sensors and generating a signal indicative of said pressure; h) feeding said signal to a control unit that controls the resin flow rate supplied to the at least one resin inlet, wherein the control unit is configured such that the resin flow rate of the liquid resin is increased if the pressure monitored by the one or more pressure sensors, in step g), at the at least one resin inlet drops below a lower pressure threshold, wherein the control unit is further configured such that the resin flow rate of the liquid resin is decreased if the pressure monitored by the one or more pressure sensors, in step g), at the at least one resin inlet is above a higher pressure threshold, and wherein the higher pressure threshold is higher than the lower pressure threshold; and j) curing the resin to form the fibre-reinforced polymer object, wherein a further pressure sensor measures the pressure of a plurality of separate segments of the mould cavity via a respective resin outlet of each of said segments, said control unit configuration factoring in the measured pressure from said further pressure sensor.

2. The method according to claim 1, wherein the at least one resin inlet comprises a plurality of resin inlets, the mould cavity being divided into the plurality of separate segments with each having a respective one of the plurality of resin inlets, wherein steps f)-i) are carried out separately for each of said segments, and wherein a resin inlet pressure is monitored for each of said segments.

3. The method according to claim 2, wherein the resin flow rate is controlled separately for each of said segments.

4. The method according to claim 1, wherein the at least one resin inlet comprises a plurality of resin inlets, the mould cavity being divided into the plurality of separate segments with each having a respective one of the plurality of resin inlets, wherein the one or more pressure sensors comprises at least a single pressure sensor connected to both a first resin inlet of a first segment of said plurality of separate segments and a second resin inlet of a second segment of said plurality of separate segments, and wherein in step g) a maximum pressure of each of the first resin inlet and the second resin inlet is monitored and fed to the control unit in step h).

5. The method according to claim 1, wherein the at least one resin inlet comprises a plurality of resin inlets, the mould cavity being divided into the plurality of separate segments with each having a respective one of the plurality of resin inlets, wherein the resin is supplied directly into one of the plurality of separate segments, or alternatively, the resin is supplied to one of the plurality of separate segments indirectly via another one of the plurality of separate segments.

6. The method according to claim 1, wherein the fibre-reinforced polymer object forms part of a load carrying structure of a blade shell part.

7. The method according to claim 6, wherein the blade shell part forms a blade shell half of a pre-bent wind turbine blade comprising two blade shell halves being interconnected along a leading edge and a trailing edge of the pre-bent wind turbine blade, said wind turbine blade having a root region, an airfoil region with a tip region, and optionally a transition region between the root region and the airfoil region.

8. The method according to claim 1, wherein each of the at least one resin inlet comprises a resin inlet channel and an inlet box, each respective one or more pressure sensors of step c) being connected to a respective one of the resin inlet channel or inlet box by a connection part integrated into the respective resin inlet channel or inlet box.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in details below with reference to an embodiment shown in the drawings in which

(2) FIG. 1 is a schematic view of a wind turbine provided with three pre-bent blades, at least one of these blades having a blade shell half being produced according to the method according to the invention;

(3) FIG. 2 is a side schematic view of one of the blades shown in FIG. 1;

(4) FIG. 3 is a schematic, longitudinal, sectional view of a rigid mould part for forming the pressure side, i.e. the upwind side of a blade shell half;

(5) FIG. 4 is a schematic top view of the mould part shown in FIG. 3, the width of said mould part being enlarged for illustrative purposes;

(6) FIG. 5 is a schematic top view of the encircled area A in FIG. 4;

(7) FIG. 6 is a schematic top view of the encircled area B in FIG. 4;

(8) FIG. 7 is a schematic cross-sectional view along the lines VII in FIG. 4,

(9) FIGS. 8a and 8b illustrates resin levels in a non-segmented and a segmented mould cavity, respectively,

(10) FIG. 9 shows a first embodiment of the feedback loop according to the invention,

(11) FIG. 10 shows a second embodiment according to the invention,

(12) FIG. 11 shows a resin inlet box and a pressure sensor connected to the resin inlet box,

(13) FIG. 12 shows an embodiment, where resin is supplied directly into each segment,

(14) FIG. 13 shows an embodiment, where resin is supplied into segments via intermediary segments,

(15) FIG. 14 shows an embodiment, where a single pressure sensor senses the resin pressure in a plurality of separate segments, and

(16) FIGS. 15a and 15b show a cross-section of a part of a pressure sensor and an exploded view of the pressure sensor, respectively.

DETAILED DESCRIPTION OF THE INVENTION

(17) The upwind wind turbine schematically shown in FIG. 1 comprises a tower 1, a nacelle 2 arranged rotatably on top of the tower 1, a main shaft 3 extending essentially horizontally from the nacelle 2 and being provided with a hub 4 from which three blades 5 extend radially. Each blade comprises a root region 6, an airfoil region 7 with a tip region 8, a transition region 9 between the root region 6 and the airfoil region 7, and a centre line P being defined by the centre line of the normally cylindrically shaped root region. This axis often corresponds to a pitch axis of the blade. The tip region 8 of the airfoil region 7 ends in a tip 10. The different regions of the blades are also shown in FIG. 2.

(18) The blade 5 is a pre-bent blade extending forwardly against the wind in a forwardly curving manner so as to place the tip 10 at distance a in front of the centre line P as seen in the wind direction W. The blade 5 comprises two blade shell halves 11, 12 connecting along a leading edge and a trailing edge of the blade. The blade shell half 11 forms the pressure side, also called the upwind side, of the blade, as it faces the wind during operation of the wind turbine. The blade shell half 12 forms the suction side, also called the downwind side, of the blade, as it faces away from the wind during operation of the wind turbine.

(19) FIG. 8a shows the problem of infusing resin into mould cavities with height differences and wherein fibre material has previously been arranged. The resin supply forms a reservoir and due to the height differences in the mould cavities, the resin level will have a first height h.sub.1 in a first part of the mould, and a second height h.sub.2 in a second part of the mould. The resin level or pressure is therefore set as a trade-off to accommodate for the height differences. Thus, due to the gravity acting on the resin, a too high fibre/resin ratio tends to be formed at the highest positioned areas of the mould, and a too low fibre/resin ratio tends to be formed at the lowest positioned areas of the mould as seen in the longitudinal direction thereof. By segmenting the mould cavity into separate cavities as shown in FIG. 8b, it is possible to individually control the resin level or resin pressure in the separate cavities so that the resin level in the first part of the mould may be set to h.sub.1, and the resin level in the second part of the mould may be set to h.sub.2, thereby ensuring that the fibre/resin is kept close to the optimum for the entire finished structure.

(20) In the following and with reference to FIGS. 3-7, it will be described how segmentation of the infusion areas and the mould cavity may be used for minimising the effect of gravity acting on the resin when moulding forwardly curved wind turbine blade shell halves. The embodiment described refers to the production of a blade shell half 11 forming the upwind side of the blade 5.

(21) For manufacturing the blade shell half 11, a rigid mould part 13 is provided, said mould part 13 having a mould surface 14 forming the outer surface of the shell half, i.e. the pressure side of the blade. The mould part 13 is provided with an upper rim 15, as clearly seen in FIG. 7. As it most clearly appears from FIG. 3, the mould for moulding the upwind shell half 11 is arranged so that the line of the mould part corresponding to the centre line P of the root region of the blade is arranged to tilt slightly upwards relative to horizontal from the root region towards the tip region. In the present embodiment the lowermost portion of the mould surface in the root region and in the tip region is arranged at the same level, as shown in FIG. 3. As a result, the height difference between the highest and the lowest point of the lowermost portion of the mould surface when seen in the longitudinal direction is minimised.

(22) A lay-up 16 comprising a number of fibre layers is placed on the mould surface 14. In the embodiment shown the fibre lay-up 16 comprises first fibre layers 17 arranged directly on the mould surface. On the first fibre layers a large number of fibre layers are placed in a longitudinally extending zone of the mould so as to provide a load-bearing structure 18 of the blade shell half.

(23) As seen in the transverse direction of the mould the zone forming the load-bearing structure 18 is provided in the lowermost area of the mould surface. In the longitudinal direction the zone comprising a large number of fibre layers extends essentially from the root region to the tip region, as shown by dotted lines in FIG. 4. Additionally a plurality of fibre layers is arranged on the first lower fibre layers 17 at a region corresponding to the region of the leading edge and the trailing edge, respectively, of the blade shell half to provide a leading edge fibre reinforcement 20 and a trailing edge fibre reinforcement 19. A first core material 21 is arranged between the load-bearing structure 18 and the leading edge fibre reinforcement 19 and a second core material 22 is arranged between the load-bearing structure 18 and the trailing edge fibre reinforcement 20. The core material can be a hard polymer foam or balsawood. The fibre lay-up 16 is completed by arranging second fibre layers 23 on top of the load-bearing structure 18, the leading edge fibre reinforcement 19, the trailing edge fibre reinforcement 20, the first core material 21 and the second core material 22.

(24) Next a distribution layer 24 is arranged on the second fibre layers 23. The distribution layer is divided into three distribution layer segments 24A, 24B, 24C by providing two flow barriers 25, 26 in the distribution layer 24 in areas thereof above the load-bearing structure 18. The flow barriers 25, 26 have a transverse extent so that they are provided only in the area of the distribution layer above the load-bearing structure 18 and not in the adjacent area of the lay-up 16. In the present embodiment the flow barriers 25, 26 are formed by a formable substance, such as a so-called tacky tape, and restrict longitudinal resin flow between the distribution layer segments.

(25) As especially shown in FIG. 3, the flow barriers 25, 26 are arranged where the height difference between the lowest and the highest point of the mould surface 14 is within a pre-determined range, such as below 1 m. A first longitudinally extending feed channel (or resin inlet) 27 is arranged on top of the distribution 24. The feed channel 27 is formed as a tube with an omega profile being opened towards the distribution layer 24, as shown in FIG. 7.

(26) The first feed channel 27 extends from the root region to the tip region, as shown in FIG. 4. It is divided into three feed channel sections 28, 29, 30 which are arranged in respective distribution layer segments. Longitudinally adjacent sections of the first feed channel 27 are interconnected by means of a connection line 31, 32 to provide resin communication between adjacent feed channel sections. A valve 33, 34 is arranged in each connection line 31, 32 to allow for an interruption of the resin flow between the adjacent feed channel sections. The connection lines 31, 32 provided with the valve 33, 34, respectively, most clearly appear from FIGS. 4-6.

(27) Finally, it should be noted that an inlet box 35 to the first feed channel is provided in the feed channel section and preferably at or in the highest area thereof which is also the highest area of the mould surface as seen in the longitudinal direction thereof.

(28) Further, additional substantially longitudinally extending feed channels 36-42 are arranged above the fibre distribution layer 24 on either side of and laterally spaced apart from the longitudinally extending first feed channel 27. As seen in FIG. 4, the additional feed channels are continuous feed channels, i.e. they are not divided into sections, and the transversely extending flow barriers 25, 26 are not provided in the distribution layer below the additional feed channels. Further, the additional feed channels 36-42 are placed laterally outside the load-bearing structure 18. Inlet boxes 46-52 to the additional feed channels are arranged in line with the inlet box 35 to the first feed channel as seen in the transverse direction of the mould.

(29) A vacuum bag 43 is arranged on top of the distribution layer 24 and the feed channels and sealed to the rim 15 of the mould part to form a mould cavity 44 between the vacuum bag 43 and the mould surface 14 of the mould part 13. The mould cavity is then evacuated and resin is supplied to the mould cavity.

(30) Resin is supplied to the mould cavity through the inlet boxes 35 to the mid section 29 of the first feed channel 27 and through the inlet boxes 46-52 to the additional feed channels 36-42. First, resin is supplied to the first feed channel 27, the valves 33, 34 in the connection lines 31, 32 being opened so that all three sections 28, 29, 30 of the first feed channel 27 are supplied with resin.

(31) When the resin flow front towards the leading edge has passed the feed channel 38, resin is supplied to the feed channel 38 through the inlet box 48. Correspondingly, resin is supplied to the feed channel 39 through the inlet box 49 when the resin flow front towards the trailing edge has passed the feed channel 39.

(32) Then, the valve 33, 34 is closed to stop the resin supply to the sections 28, 30 of the first feed channel 27. Resin supplied to the highest positioned section 29 of the first feed channel 27 is continued. Resin is then supplied in sequence to the feed channel 40, the feed channel 37, the feed channel 41, the feed channel 36, and the feed channel 42 through the respective inlet boxes 50, 47, 51, 46, 52. During the sequential resin supply to the above feed channels, the resin supply to the feed channels 39, 38, 40, 37, 41, 36, 42 is stopped at pre-determined points in time so as to obtain the desired resin impregnation of the lay-up. After the resin supply to all the additional feed channels has been stopped the resin supply to the inlet 35 to the first feed channel 27 continues until the desired fibre/resin ratio has been obtained in the fibre lay-up, especially in the zone of the fibre lay-up forming the load-bearing structure 18.

(33) The provision of the flow barriers 25, 26 restricts or prevents resin flow through the distribution layer from the distribution layer segment 24B to the distribution layer segments 24A and 24C being positioned at a lower level than the distribution layer segment 24B during the continuous supply of resin to the channel section 27 being positioned above the distribution layer segment 24B. As a result, a resin surplus in the lay-up below the distribution layer segments 24A and 24B is prevented.

(34) A resin surplus in said distribution layer segments 24A and 24B is further prevented by disconnecting the resin supply to the feed channel sections 27, 29 arranged above these the distribution layer segments 24A and 24B.

(35) When the supply of resin is completed, the resin is allow to cure and the finished blade shell half forming the upwind side of the blade is connected to a finished blade shell half forming the downwind side of the blade, thereby forming a wind turbine blade.

(36) However, even in the manufacturing setup described in reference to FIGS. 3-7, it has proven difficult to control the fibre/resin ratio of the separate areas of the wind turbine blade shell to a high degree. Therefore, according to the invention, the pressure level of each segment is controlled via a feedback loop, which is described in the following.

(37) FIG. 9 shows a first embodiment utilising the feedback loop according to the invention. Resin is supplied from a polymer or resin supply unit 64 via a resin supply line 65 to the inlet box 35, which in turn distributes resin to first resin inlets 27, 27. A pressure sensor 60 is connected to the inlet box 35 and senses the pressure of the resin supplied to the first resin inlets 27, 27. The pressure sensor 60 generates a signal indicative of the resin pressure and sends this signal to a control unit 62, which is adapted to control the polymer supply unit 64 based on the signal received from the pressure sensor and to increase or decrease the flow rate, if pressure measured by the pressure sensors is below a lower threshold level or above a higher threshold level, respectively. The system of course also comprises a vacuum source (not shown) connected to the mould cavity and adapted for evacuating and drawing resin into the mould cavity.

(38) FIG. 10 shows a part of a second embodiment utilising the feedback loop according to the invention. The second embodiment differs from the first embodiment in that the pressure sensor 60 is connected directly to the first resin inlet 27, optionally via a hose (not shown).

(39) FIG. 11 shows a cut-out of the inlet box 35 with a pressure sensor connected directly to the inlet box 35, which provides a simple way of implementing the pressure sensing.

(40) Resin may be fed to each segment via separate supply lines as illustrated in FIG. 12. In such an embodiment each segment is provided with a pressure sensor and a feedback loop to control the pressure of the resin supplied to the segments. In an alternative embodiment shown in FIG. 13, the resin is supplied to at least some of the segments via intermediary segments. A resin supply line is connected to the intermediary segment and resin is then supplied to other segments by opening a valve 34. Conversely, the resin supply to the end segment can also be cut off by closing the valve, similar to the embodiments described with reference to FIGS. 3-7.

(41) In one advantageous setup shown in FIG. 14, it is possible to use a single pressure sensor 60 to measure the pressure of a plurality of segments. Thus, the various segments each comprise an outlet 67, 68, 69 that leads resin to the pressure sensor 60. Thus, the pressure sensor 60 measures the maximum pressure of the various segments. This setup is particular advantageous to the setup utilising indirect resin supply as shown in FIG. 13. The setup makes it possible to use a reduced number of pressure sensors and still be able to control the resin pressure in each segment by the feedback loop according to the invention.

(42) FIGS. 15a and 15b show a cross-section of a part of the pressure sensor 60 and an exploded view of the pressure sensor, respectively. The pressure sensor 60 is a differential diaphragm pressure transducer. A tube or cap 80 is connected to a pressure sensor body 90 via a threaded connection 86. The cap 80 is sealed against the pressure sensor body 90 by use of an o-ring 82 and forms a chamber 88 in front of a diaphragm 88 of the pressure sensor. The cap 80 has an opening whereby resin can be fed into the chamber 88, and the pressure on the diaphragm 84 can thereby be measured, e.g. by probing the deflection of the diaphragm.

(43) Finally, it should be noted that the invention also relates to a wind turbine blade having at least one blade with at least one shell half being produced according to the method according to the invention, and a wind turbine being provided with such a blade.

(44) The invention has been described with reference to advantageous embodiments. However, the scope of the invention is not limited to the described embodiment and alterations and modifications may be carried out without deviating from the scope of the invention. The feedback loop may for instance be used for non-segmented mould cavities as well.

LIST OF REFERENCE NUMERALS

(45) 1 tower 2 nacelle 3 main shaft 4 hub 5 blades 5 root region 7 airfoil region 8 tip region 9 transition region 10 tip 11,12 blade shell halves 13 mould part 14 mould surface 15 upper rim 16 fibre lay-up 17 first fibre layers 18 load-bearing structure 19 leading edge fibre reinforcement 20 trailing edge fibre reinforcement 21 first core material 22 second core material 23 second fibre layers 24 distribution layer 24A distribution layer segment 24B distribution layer segment 24C distribution layer segment 25,26 flow barriers 27, 27 first feed channel/first resin inlet 28-30 feed channel section/resin inlet section 31, 32 connection line 33, 34 valve 35 inlet box 36-42 additional feed channel 43 vacuum bag 44 mould cavity 45 leading edge 46-52 inlet box 53 trailing edge 60 pressure transducer 62 control unit 64 resin/polymer supply unit 65 resin supply line 66 resin/polymer supply nozzle/connector 67-69 outlets 80 tube/cap 82 o-ring 84 diaphragm 86 threaded connection 88 chamber 90 pressure sensor body a distance P centre line W wind direction