Adaptive system and method for the production of thermosetting matrix composites

Abstract

An adaptive system for the production of thermosetting matrix composites by resin infiision / inj ection comprises at least one mold (2) having a cavity suitable for containing a fibrous preform designed to define the reinforcement of the composite, at least one container or buffer (4) for the containment of a thermosetting resin, feed ing means for feeding the resin from the container (4) into the mold (2) and which comprise at least one vacuum generator (9) adapted to provide a depression or vacuum degree sufficient to promote the passage of the thermosetting resin from the container (4) into the mold (2) and which are also provided with a compressor (10) adapted to be selectively fluidically connected to the container (4) to provide the thermosetting resin with an overpressure.

Description

[0001] ADAPTIVE SYSTEM AND METHOD FOR THE PRODUCTION OF THERMOSETTING MATRIX COMPOSITES

[0002] Description

[0003] Technical Field

[0004] The present invention finds its application into the technical field of systems and methods for the processing of plastic materials and particularly has as its object an adaptive system for the production of thermosetting matrix composites by infusion / inj ection of a resin.

[0005] The invention also relates with an adaptive method for the production of thermosetting matrix composites suitable to be carried out with the above system.

[0006] State of the art

[0007] In the production processes of composite materials formed by a thermosetting resin matrix with fibrous reinforcement in the form of fabric or mat, it is possible to use various techniques which differ in particular in the ways in which the resin is fed.

[0008] For example, one of the most widespread classes of Out-Of-Autoclave (00 A) processes used to produce composite material components is that referred to as Liquid Composite Molding (LCM).

[0009] This expression refers to a class of manufacturing processes for the production of components in composite material wherein a fibrous reinforcing preform, in the form of fabric or mat, is placed in the inner cavity defined by a rigid mold and from the relative countermould, rigid or flexible, and then impregnated with a flow of resin.

[0010] The passage of the resin inside the preform is allowed thanks to a pressure gradient by applying vacuum in the cavity with the aid of a vacuum pump.

[0011] The impregnation phenomenon is well described by the well-known Darcy’s law (equation 1) which correlates the speed of the resin flow, v, to the pressure gradient VP through the viscosity of the resin, p, and the permeability of the porous medium, K.

[0012] In particular, from this law it can be deduced that to increase the speed of the flow, with given pressure gradient VP and permeability of the porous medium K, the viscosity p has to be decreased.

[0013] The viscosity of the resin decreases as the temperature increases up to a certain value, strictly linked to the type of resin.

[0014] This trend is reported in a qualitative manner in Fig. 1 which shows that after a starting decrease of viscosity as the temperature increases until a minimum value, a step follows wherein, by further increasing the temperature, the polymerization reaction of the resin begins with the formation of macromolecules (gelation) and a consequent increase in viscosity.

[0015] Therefore, to reduce impregnation times and therefore increasing the production speed, a possible solution is to reduce the viscosity of the resin by providing thermal energy thereto with the aid of heating systems, such as microwaves or electrical resistors.

[0016] This methodology is typically applied to RTM (Resin Transfer Molding) processes, where the resin is pushed by overpressure.

[0017] Instead, the systems wherein the resin is moved by vacuum, such as in VARTM (Vacuum Assisted Resin Transfer Molding) technologies, provide for preheating the mold or preform, if it is composed of conductive fibres, for example carbon.

[0018] Fig- 2 shows a second-known system for LCM production based on infusion, wherein the system comprises a vacuum pump P connected to a trap T which, due to the vacuum effect, allows the resin to flow from the container R to the mold S to impregnate the dry preform placed thereinto. In some cases, there is a heating system H of the mold or fibers.

[0019] The demand for resin during the impregnation step shows the qualitative trend reported in Fig- 3, from which it can be observed that it is possible to identify two steps, i.e. a first step wherein the demand for resin is high, due to the need to fill the ducts that bind the buffer to the mold, the diffusion channel and the first part of the preform, and a second step wherein the flow must pass through the rest of the preform and is therefore reduced.

[0020] A drawback of the known techniques is made up from the difficulty in obtaining complete impregnation of the reinforcing fibers at any level, both micro and macro. Therefore, the need is felt for a technique that allows to improve the flow of the resin in LCM processes in order to obtain an impregnation that is almost complete or in any case improved compared to known techniques.

[0021] Scope of the invention

[0022] The object of the present invention is to overcome the above-mentioned drawbacks by providing a system for the production of thermosetting matrix composites which is characterized by particular effectiveness and relative cost-effectiveness.

[0023] A particular object is to provide a system for the production of thermosetting matrix composites which allows to obtain a higher degree of resin impregnation of the fibrous reinforcement compared to the known LCM techniques.

[0024] Yet another object is to provide a system for the production of thermosetting matrix composites which allows obtaining more precise control of the resin flow during the whole process.

[0025] Not the least object is to make available a method for the production of thermosetting matrix composites which allows to obtain a higher degree of resin impregnation of the fibrous reinforcement compared to the known LCM techniques.

[0026] These objects, as well as others which will become more apparent hereinafter, are achieved by an adaptive system which, according to claim 1, comprises at least one mold having a cavity suitable for containing a fibrous preform adapted to define the reinforcement of the composite, at least one container for the containment of a thermosetting resin, feeding means for feeding said thermosetting resin from a container into said mold, wherein said feeding means comprise at least one vacuum generator suitable of producing a depression suitable for promoting the passage of said thermosetting resin from said container to said mold.

[0027] Advantageously, said feeding means further comprise a compressor adapted to be selectively fluidically connected to said container to provide said thermosetting resin with an overpressure possibly suitable to cooperate with the depression generated by said vacuum generator.

[0028] In this way, the cooperation between overpressure and depression, which will preferably be simultaneous but which may possibly be subsequent and / or alternated with each other, will allow the desired effect of optimal impregnation to be obtained, thanks to their combined effect.

[0029] According to a further aspect of the invention, an adaptive method is provided for the production of thermosetting matrix composites in accordance with claim 14.

[0030] Advantageous embodiments of the invention are obtained in accordance with the dependent claims.

[0031] Brief disclosure of the drawings

[0032] Further features and advantages of the invention will be more apparent in light of the detailed description of a preferred but not exclusive embodiment of an adaptive system for the production of thermosetting matrix composites, shown by way of non-limiting example with the aid of the attached drawing tables wherien:

[0033] FIG. 1 is a typical qualitative graph relating to the trend of the viscosity of a resin as a function of temperature;

[0034] FIG. 2 is a schematic view of a vacuum LCM system according to the prior art;

[0035] FIG. 3 shows a typical qualitative graph relating to the resin flow rate as a function of time during the impregnation step;

[0036] FIG. 4 is a schematic view of the adaptive system according to a preferred embodiment;

[0037] FIG. 5 is a schematic view of a detail of the system of Fig. 4 in a first operating mode; FIG. 6 is a schematic view of the above detail of the system of Fig. 4 in a second operating mode.

[0038] Best modes of carrying out the invention

[0039] Fig- 4 shows a preferred embodiment, exemplifying but not limiting for the invention, of an adaptive system operating according to the present invention and designed for carrying out a method or process for the production of thermosetting resin compounds reinforced by reinforcing fibers, usually in form of fabric or rug (mat).

[0040] For the purposes of the present invention, the type of resin and reinforcing fibers are irrelevant, as they may be selected from those commonly used in the field, and therefore the used materials will not be indicated below. First of all, the illustrated system, globally referred with 1, comprises a mold 2 suitable for appropriately interacting with a counter-mold 3 to define a closed inner cavity suitable for containing a fibrous preform designed to define the reinforcement of the composite.

[0041] The mold 2 is connected to a container 4 for containing and feeding the cavity with a thermosetting resin.

[0042] According to the illustrated embodiment, the container 4 acts as a buffer and will allow the resin to be fed into the mold 2 by means of special feeding means.

[0043] By way of a non-limiting example, the buffer 4 and the feeding means will be sized to guarantee a volumetric flow rate of thermosetting resin between 0.01-20 L / min.

[0044] The buffer 4 may also house a stirrer 5 equipped with a suitable impeller, such as a marine, radial, anchor or similar type impeller, driven by a rotary motor 7 provided with a mechanical transmission 8 to mix the thermosetting resin, avoiding the occurrence of an early polymerization due to premature activation of the resin, ensuring its homogenization from a thermal point of view and thus reducing the possibility of blocking the resin flow.

[0045] The resin feeding means may be divided into two sections, i.e. a first section comprising a vacuum generator 9 suitable to provide a depression or vacuum degree sufficient to promote the passage of the thermosetting resin from the buffer 4 to the mold 2 and a second section which, in turn, comprises a compressor 10 suitable to be fluidly connected to the buffer 4 to provide the thermosetting resin with overpressure. In this way, when the two sections are both operational, the overpressure will cooperate with the depression generated by the vacuum generator 9 to increase the flow rate of thermosetting resin that flows from the buffer 4 to the cavity of the mold 2.

[0046] In detail, the vacuum generator 9 could be a suction pump for generating vacuum fluidly connected to the cavity of the mold 2 by means of a suction duct 11 through which air may be drawn from the cavity to facilitate the entry of the resin, which can be supplied from the container / buffer 4 or directly from another tank. Conveniently, it will be possible to insert a trap 12 between the vacuum pump 9 and the mold 2 to recover any excess resin that may be sucked in, preventing it from reaching the pump 9.

[0047] The resin from the container or buffer 4 to the cavity of the mold 2 will flow through a suction duct 13 which connects the outlet 14 of the buffer 4 to the inlet of the cavity of the mold 2.

[0048] The second section of the feeding means is instead provided with a reservoir 15 for the resin connected to the compressor 10 by means of a first solenoid valve 16 whose opening / closing will allow the reservoir 15 to be connected to the buffer 4 or to exclude it from the resin feeding circuit.

[0049] The reservoir 15 may also be provided with a second solenoid valve 17 adapted to place it in communication with the outside when the resin is withdrawn only due to the effect of the depression generated by the vacuum pump 9.

[0050] Conveniently, control means, not shown, of a mechanical, electronic or electromechanical type may be provided, suitable to control the two solenoid valves 16, 17 so as to close the first solenoid valve 16 when the second solenoid valve 17 is opened and vice versa, and thus connect the buffer 4 to the compressor 10 or exclude the latter from the feeding circuit.

[0051] The reservoir 15 is fluidly connected to the buffer 4 via a supply duct 18 provided with an end section 19 inserted inside the buffer 4.

[0052] Conveniently, the mold 2 may also be associated with heating means 20, preferably selected from the group of systems operating by heating fluid, electrical resistance, induction or similar, whose task will be to make the resin more fluid to optimize the filling of the cavity.

[0053] Furthermore, the reservoir 15 may also be associated with preheating means 21 for preheating the thermosetting resin which are suitable for bringing the resin to a preheating temperature lower than the respective polymerization temperature.

[0054] By way of a non-limiting example, the preheating means 21 may comprise a microwave preheater element suitable to provide a power between 50-10000 W. According to a further particularly advantageous aspect, the end section 19 of the supply duct 18 inserted in the buffer 4 will be associated with moving means 22 suitable for moving it between a first raised position, corresponding to the condition in which the reservoir 15 communicates with the compressor 10 to feed the resin under overpressure, and a second lowered position corresponding to the condition wherein the compressor 10 is excluded from the resin feeding circuit in the cavity and wherein the reservoir 15 is possibly in communication with the outside through the second solenoid valve 17 to always keep it at atmospheric pressure.

[0055] Figs. 5 and 6 show in greater detail the structure of the buffer 4 and the different configurations assumed depending on the condition of insertion or exclusion of the compressor 10 from the feeding circuit.

[0056] From these figures it can be observed that the buffer 4 is constrained to a fixed base 23 via two pairs of guide shafts 24 which will allow the vertical movement of part of the elements of the buffer 4.

[0057] In particular, the buffer 4 is integral with a movement structure movable along the two guide shafts 24 and which comprise one or more double-acting cylinders 26 which will allow the vertical translation, in both directions, of the end section 19 of the supply duct 18, so as to allow buffer 4 to assume two distinct configurations depending on the process step.

[0058] In the first step of the process in which the resin is pushed by the pressure generated by the compressor 10, exclusively or with the aid of the vacuum generated by the vacuum pump 9, the buffer 4 is found in the configuration of Fig. 5.

[0059] In this configuration, the end section 19 of the supply duct 18 is raised with respect to the dispensing hole 14 of the buffer 4 so as to discharge the resin inside it and allow the dispensing of the resin due to the combined effect of depression and overpressure, In the second phase of the process, when the compressor 10 is removed from the circuit and the reservoir 15 is placed in communication with the external environment, the buffer 4 is found in the configuration of Fig. 6, wherein the outlet 27 of the end section 19 is in direct contact with the dispensing hole 14 of the buffer 4, so that the resin is withdrawn due to the depression directly from the reservoir 15. The movement of the elements of the buffer 4 occurs thanks to the presence of the guides 28 which, sliding on the respective guide shafts 24, allow the inner end section 19 fixed to the upper disk, through the thrust of the double-acting cylinders 26, to insert into the suction duct 13 connected to mold 2.

[0060] The end section will slide in the hollow shaft 30 of the agitator 5 thanks to appropriate bushings. There is also a valve 31 to allow the discharge of the remaining resin and the washing of the buffer 4 during the second step of the process.

[0061] Operationally, we will first proceed to insert the reinforcing fibers inside the cavity of the mold 2 and then to close it using the countermold 3, according to known techniques which are not restrictive of the present invention.

[0062] At this point, the buffer 4 will be fed by activating the compressor 10 which will take the resin, catalysed or not, from the reservoir 15, generating an overpressure in it such as to guarantee the flow rate of resin necessary to satisfy the request in the first step of the process.

[0063] The resin will flow through the preheating element 21 adapted to guarantee the desired temperature increase for the resin, without reaching the value that activates polymerization.

[0064] At the same time, in this first step the vacuum pump 9 may also be activated so that the resin enters the mold 2 due to the combined effect of depression and overpressure, impregnating the reinforcement fabric.

[0065] In this step of the production process, the buffer 4 is in communication with the mold 2 according to the operation mode of Fig. 5.

[0066] In the second step of the production process, when there has been a partial impregnation of the reinforcing fabric with the resin and the required resin flow rate can be reduced, the compressor 10 will be excluded by closing the first solenoid valve 16 and the possible opening of the second solenoid valve 17 which will put the reservoir 15 in communication with the outside.

[0067] Therefore, the resin contained in the reservoir 15 will flow into the mold 2 as a result of the decompression set by the vacuum pump 9 alone. In this phase, the buffer 4 will be in communication with the mold 2 according to the operation mode of Fig. 6. It will be possible to have both a variant in which the production system operates in VARTM mode, i.e. with an active vacuum pump 9, and a variant in which it operates in RTM mode, i.e. with not active vacuum pump 9 and wherein the constant flow rate of the resin will be guaranteed by the feeding and / or injection system. From the above it is clear that the object of the present invention achieves the intended objects.

Claims

Claims1. An adaptive system for the production of thermosetting matrix composites by infiision / inj ection of resin, comprising: at least one mold (2) having an inner cavity adapted to contain a fibrous preform designed to define the reinforcement of the composite; at least one container or buffer (4) for containing a thermosetting resin; feeding means for feeding said thermosetting resin from said container (4) to said mold (2); wherein said feeding means comprise at least one vacuum generator (9) suitable to promote a depression or vacuum degree sufficient to promote the passage of said thermosetting resin from said container (4) into said mold (2); characterized in that said feeding means further comprise a compressor (10) suitable to be selectively fluidically connected to said container (4) to supply said thermosetting resin with an overpressure suitable for promoting the passage thereof into said mold (2).

2. System as claimed in claim 1, characterized in that said container (4) has a buffer function.

3. System as claimed in claim 1 or 2, characterized in that said feeding means comprise a reservoir (15) for the resin connected to said compressor (10).

4. System as claimed in claim 3, characterized in that said reservoir (15) is connected to said compressor (10) by means of a supply duct (18) provided with a first solenoid valve (16).

5. System as claimed in claim 4, characterized in that said reservoir (15) is provided with a second solenoid valve (17) suitable to placed it in communication with the outside, control means being provided for closing said first solenoid valve (16) upon opening of said second solenoid valve (17) and vice versa.

6. System as claimed in claim 4 or 5, characterized in that said container or buffer (4) is fluidically connected to said cavity of said mold (2) by means of a suction duct7. System as claimed in any preceding claim, characterized in that said mold (2) is associated with heating means (20).

8. System as claimed in claim 7, characterized in that said heating means (20) are selected from the group of devices operating by means of electric resistance, induction or similar heating fluid.

9. System as claimed in any preceding claim, characterized in that said reservoir (15) is associated with preheating means (21) for preheating said thermosetting resin suitable for bringing said resin to a preheating temperature lower than the respective polymerization temperature.

10. System as claimed in claim 9, characterized in that said preheating means (21) comprise a microwave preheater element suitable to supply a power ranging from 50- 10000 W.

11. System as claimed in any preceding claim, characterized in that said container or buffer (4) and said feeding means are sized to guarantee a volumetric flow rate of said thermosetting resin comprised between 0.01-20 L / min.

12. System as claimed in any claim 6 to 11, characterized in that said container or buffer (4) is provided with a dispensing hole (14) in fluidic communication with said inner cavity of said mold (2) through said suction duct (13) for feeding it with said resin, said supply duct (18) in turn having an end section (19) inserted in said container or buffer (4) and associated with translation means (22) suitable for move it between a first raised position corresponding to the condition wherein said reservoir (15) is in communication with said compressor (10) and wherein said supply duct (18) supplies said resin into said container or buffer (4) and a second lowered position corresponding to the condition wherein said reservoir (15) is in communication with the outside and wherein said supply duct (18) supplies said resin directly into said suction duct (13).

13. System as claimed in any preceding claim, characterized in that said container or buffer (4) houses a motorized stirrer (5) for mixing said thermosetting resin.

14. An adaptive method for manufacturing thermosetting matrix composites by infusion / inj ection of resin, comprising the following steps: a) providing at least one mold (2) having an inner cavity;b) inserting a fibrous preform into said inner cavity to define the reinforcement of the composite; c) feeding said thermosetting resin into said mold (2); wherein said feeding step comprise a feeding step of said thermosetting resin by effect of the application of a vacuum; characterized in that said feeding step provides for a further step of feeding said thermosetting resin into said mold (2) by applying an overpressure.

15. Method as claimed in claim 14, characterized in that said feeding step by applying overpressure is carried out at least partially simultaneously with said feeding step with application of vacuum.

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