High throughput pultrusion system and process

Abstract

Embodiments of the present disclosure are directed towards a pultrusion system and process for forming a continuous fiber-reinforced polyurethane (CFRP) composite structure. The pultrusion system and process include reinforcement fibers (102); a polyurethane mixing and dispensing unit (104) to form a reaction mixture of polyurethane resin; an injection box (106) for forming reinforcement fibers wetted out with the reaction mixture; a curing die assembly (108) to provide heat and a predefined shape to the wetted out reinforcement fibers; one or more of a post curing heating block (110) to provide additional heat to the curing process of the reaction mixture to form the continuous fiber-reinforced polyurethane composite structure in the predefined shape; one or more of a cooling block (112) to remove heat from the continuous fiber-reinforced polyurethane composite structure in the predefined shape; and a pulling system (114) to pull the continuous fiber-reinforced polyurethane composite structure at a predefined rate.

Description

HIGH THROUGHPUT PULTRUSION SYSTEM AND PROCESSField of Disclosure

[0001] Embodiments of the present disclosure are directed to a pultrusion system and process for preparing a continuous fiber-reinforced polymer composite structure.Background

[0002] Pultrusion is a manufacturing process used to create continuous lengths of composite materials with a constant cross-sectional shape. Pultrusion involves preparing continuous reinforcing fibers, such as fiberglass (glass fibers) or carbon fiber, which are pulled through a series of guides and tensioning devices to ensure they are aligned and free from tangles. The prepared fibers are then wetted with a resin by passing them through a resin bath or a resin injection system. The resin used is usually a thermosetting polymer such as polyester, polyurethane, vinyl ester, or epoxy. Unlike epoxy or vinyl ester resins, which can be processed using a resin bath, polyurethanes require a resin injection system. This is due to the fact that the polyol and isocyanate start to react immediately after being mixed together, even at ambient temperature. The resin-saturated fibers then pass through a shaping die, which determines the cross-sectional shape of the final composite product.

[0003] Once shaped, the composite structure enters a curing die assembly that provides the necessary heat to initiate the curing process of the resin. Curing can be achieved through heat, ultraviolet (UV) light, or a combination of both, depending on the resin system used. This stage allows the resin to harden and form a rigid composite structure. As the composite structure cures, it is continuously pulled through the die by a pulling mechanism. This pulling force ensures uniformity and helps in maintaining the desired shape and dimensions of the final product. Once the composite structure has fully cured, it is cut into desired lengths using a saw or other cutting methods.

[0004] Composite structures are typically used for structural applications. For example, composite structures made with carbon fibers and epoxy resins are being used commercially to make spar caps on modern wind turbine blade designs. The growing wind turbine blade market, however, requires a fast and efficient pultrusion process where linear production speeds of composite structures is an important consideration. While multiple factors can affect the pultrusion processing speed, it is currently accepted that epoxy resins are limited to a production speed of only around 0.6-0.8 m / min due to its intrinsic low conversion rate and high pulling force. On the other hand, polyesters and vinyl esters have good resin conversion degree and low pullingforces at high speeds, but mechanical properties are not at the level of epoxy resins or polyurethanes. So, there is need in the art to increase production speed with a focus on polyurethane.

[0005] Increasing production speed, however, brings substantial processing challenges. One challenge is that the residence time in the curing die assembly decreases with increasing production speed, which can affect the extent to which the resin is able to cure (or “convert”) by the time it reaches the exit of the curing die assembly. Making the resin chemistry more reactive (e.g., by means of more reactive building blocks or increasing the level of catalyst) is one way to help maintain the resin conversion in the curing die assembly, but increasing the resin system’s reactivity also accelerates the reaction speed at ambient temperature, with an increase of resin viscosity having a negative impact on fiber impregnation at the open bath or close injection box. Another approach to compensate for an increase in speed is to increase the temperature of the curing die assembly. This, however, has limits on the maximum possible curing temperature so as not to damage the resin and the composite structures, and additionally requires increased energy consumption. Another possible approach would be to use a longer pultrusion die, but pultrusion dies longer than one meter have markedly increased tooling costs. Another issue that arises is that with increasing production speeds the composite structure will arrive at the pulling mechanism with too high of a temperature. The hotter the composite structure the higher the wear of the gripping blocks of the pulling mechanism and / or the chances that the composite structure will stick to or be deformed by the pulling mechanism. Therefore, there is a need for an improved pultrusion method for preparing composite structures.Summary

[0006] The present disclosure provides various embodiments, including addressing the above shortcomings by addressing the thermal treatment of the continuous fiber-reinforced polymer (CFRP) composite structure in the pultrusion system and pultrusion process.Embodiments of the present disclosure provide for a CFRP composite structure that uses polyurethane as a thermoset resin in a high speed pultrusion system and process. The CFRP composite structure can be used as a component of wind blade spar caps, among other applications. The pultrusion system and process of the present disclosure allows for a proper conversion level of the polyurethane thermoset resin without compromising open time while keeping the tooling cost and machining complexity within reasonable boundaries.

[0007] The embodiments of the present disclosure provide for, among other things, a pultrusion system for forming a continuous fiber-reinforced polyurethane (CFRP) compositestructure. The system includes reinforcement fibers, a polyurethane mixing and dispensing unit, an injection box fluidly coupled to the polyurethane mixing and dispensing unit, a curing die assembly attached to the injection box, one or more of a post curing heating block, one or more of a cooling block and a pulling system to pull the CFRP composite structure. For the various embodiments, the polyurethane mixing and dispensing unit include an A-part and a B-part to form a polyurethane resin, where the A-part and the B-part mix to form a reaction mixture for the polyurethane resin. For the various embodiments, the injection box receives the reinforcement fibers and the reaction mixture that is injected into the injection box to form wetted out reinforcement fibers. For the various embodiments, the curing die assembly can include a cooling zone as thermal bridge to avoid heat propagation backwards from the curing die to the injection box. The curing die assembly also includes a first heating zone having a first predefined temperature to provide heat to promote a curing process of the A-part and the B-part of the reaction mixture, and surfaces defining a cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass and solidify to provide a predefined shape to the wetted out reinforcement fibers. The curing die assembly further includes an exit from the curing die assembly.

[0008] For the various embodiments, each of the one or more of the post curing heating block has a passageway through which the wetted out reinforcement fibers in the predefined shape and undergoing the curing process passes. For the various embodiments, the one or more of the post curing heating block is spaced apart and separate from the exit of the curing die assembly such that the wetted out reinforcement fibers in the predefined shape and undergoing the curing process exit the curing die assembly and enter the one or more of the post curing heating block having a predefined temperature to provide additional heat to the curing process of the reaction mixture to form the CFRP composite structure in the predefined shape. For the various embodiments, the one or more of the post curing heating block are dimensioned such that they do not modify the predetermined shape at or beyond the exit of the curing die assembly. In other words, there are no post molding operations at or beyond the exit of the curing die assembly. To that end, for the various embodiments the CFRP composite structure does not apply substantial pressure against the passageway of the one or more of a post curing heating block to cause a change in the predefined shape of the CFRP composite structure. Each of the said post curing heating blocks can have uniform of different temperature setting provided by the different heating zones, where the heating zones can have different temperature set points as to provide a certain heating temperature profile, as discussed herein. According to the present disclosure, the post cure heating block can contact the CRFP composite as it passes through thepost cure heating block to ensure heat transfer from the post cure heating block to the CRFP composite by conduction, where any pressure is from the gravity weight of the CRFP composite on the post cure heating block.

[0009] For the various embodiments, each of the one or more of the cooling block has a passageway through which the CFRP composite structure in the predefined shape passes. For the various embodiments, the one or more of the cooling block is spaced apart and separate from the curing die assembly and the one or more of the post curing heating block such that the CFRP composite structure exits the one or more of the post curing heating block and enters the one or more of the cooling block having a predefined temperature to remove heat from the CFRP composite structure in the predefined shape. Each of the said cooling block can have a uniform or different temperature settings for the cooling zones in the cooling block to provide a certain predefined cooling temperature profile, as discussed herein. The one or more of the cooling block are dimensioned such that they do not modify the predetermined shape of the CFRP composite structure. For the various embodiments, the CFRP composite structure does not apply substantial pressure against the passageway of the one or more of the cooling block to cause a change in the predefined shape of the CFRP composite structure. According to the present disclosure, the cooling block can contact the CRFP composite as it passes through the cooling block to ensure heat transfer from the CRFP composite to the cooling block by conduction, where any pressure is from the gravity weight of the CRFP composite on the cooling block. The pulling system pulls the CFRP composite structure at a predefined rate through the pultrusion system.

[0010] Embodiments of the present disclosure also include a pultrusion process for forming the CFRP composite structure. The pultrusion process includes forming wetted out reinforcement fibers with reinforcement fibers and the reaction mixture of the A-part and the B- part used to form the polyurethane resin and passing the wetted out reinforcement fibers through the curing die assembly. As discussed herein, the curing die assembly provides a first heating zone having a first predefined temperature to provide heat to promote a curing process of the A- part and the B-part of the reaction mixture, and surfaces defining a cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass and solidify to provide a predefined shape to the wetted out reinforcement fibers. The process further includes passing the wetted out reinforcement fibers in the predefined shape undergoing the curing process through the passageway of one or more of the post curing heating block. The one or more of the post curing heating block can have, as discussed herein, a uniform temperature setting or different heating zones having different temperature settings as to provide a certain predefined heating temperature profile to deliver additional heat to the curing process. The one or more of the postcuring heating block is spaced apart and separate from the exit of the curing die assembly such that the wetted out reinforcement fibers in the predefined shape undergoing the curing process exit the curing die assembly and enter the one or more of the post curing heating block that has the predefined temperature to provide additional heat to the curing process of the reaction mixture to form the CFRP composite structure in the predefined shape and are dimensioned so that the CFRP composite structure does not apply substantial pressure, as discussed herein, against the passageway of the one or more of the post curing heating block to cause a change in the predefined shape of the CFRP composite structure. The process further includes passing the CFRP composite structure in the predefined shape through a passageway of one or more of the cooling block, where the one or more of the cooling block is spaced apart and separate from the curing die assembly and the one or more of the post curing heating block such that the CFRP composite structure exits the one or more of the post curing heating block and enters the one or more of the cooling block. As discussed herein, the one or more of the cooling block can have a uniform temperature setting or different cooling zones having different temperature settings as to provide a certain predefined cooling temperature profile. The one or more of the cooling block remove heat from the CFRP composite structure in the predefined shape. For the various embodiments, the one or more of the cooling block are dimensioned such that the CFRP composite structure does not apply substantial pressure, as discussed herein, against the passageway of the one or more of the cooling block to cause a change in the predefined shape of the CFRP composite structure. The process further includes pulling the CFRP composite structure at a predefined rate.Brief Description of the Drawings

[0011] These and other features of the disclosure will become more apparent from the following description in which reference is made to the appended drawings wherein:

[0012] FIG. 1 shows a schematic diagram of a pultrusion process in accordance with an embodiment of the present disclosure.Detailed Description

[0013] The present disclosure provides various embodiments that address the thermal treatment of a continuous fiber-reinforced polymer (CFRP) composite structure in a pultrusion system and pultrusion process. Embodiments of the present disclosure provide for a CFRP composite structure that uses, for example, polyurethane as a thermoset resin in a high speed pultrusion system and process. The CFRP composite structure can be used as a component ofwind blade spar caps, among other applications. The pultrusion system and process of the present disclosure allows for a proper conversion level of the polyurethane thermoset resin without compromising open time while keeping the tooling cost and machining complexity within reasonable boundaries.

[0014] Referring now to Fig. 1 , the embodiments of the present disclosure provide for, among other things, a pultrusion system 100 for forming the CFRP composite structure. The pultrusion system 100 includes reinforcement fibers 102, a polyurethane mixing and dispensing unit 104, an injection box 106 fluidly coupled to the polyurethane mixing and dispensing unit 104, a curing die assembly 108 attached to the injection box 106, one or more of a post curing heating block 110, one or more of a cooling block 112 and a pulling system 114 to pull the CFRP composite structure. As discussed herein, the pultrusion system 100 also includes a cutting system, as discussed herein, to cut the CFRP composite structure to a desired length, where it is possible to wind the CFRP composite structure on a coiling unit as are known in the art. As discussed herein, the pultrusion system 100 and process uses polyurethane in the CFRP composite structure. Using polyurethane in the CFRP composite structure provides for fast reactivity and low pulling force through the pultrusion system 100, which can lead to high processing speeds (e.g., production speeds higher than 2 m / min). The one or more of the post curing heating block 110 and the one or more of the cooling block 112 also help to meet the conversion target for the curing of the polyurethane resin of at least 90% conversion, while providing for a pick-up temperature of the CFRP composite structure at the pulling system of less than 55 °C, well below the glass transition temperature for the polyurethane resin so as to avoid permanent deformations and wear of the puller grips.

[0015] The reinforcement fibers 102 are located upstream from the injection box 106 and curing die assembly 108 and can be supplied by one or more spools (not shown). For the various embodiments, the reinforcement fibers 102 are pulled from the one or more spools and can pass through one or more carding plates and / or tensioning mechanisms, as are known in the art, to arrange and / or position the reinforcement fibers 102 in a desired orientation and arrangement.

[0016] For the various embodiments, the reinforcement fibers 102 constitute about 55 to 85 percent by weight (wt.%) of the CFRP composite structure. All individual values and subranges from about 55 to 85 wt.% are included; for example, the reinforcement fibers 102 can constitute from a lower limit of 55, 60 or 65 wt.% to an upper limit of 85, 80 or 75 wt.% of the CFRP composite structure. For the various embodiments, the reinforcement fibers 102 can be formed from glass, carbon, or polyaramid, however there are a variety of other reinforcementfibers, which can be used for the reinforcement fibers 102. For example, these include, but are not limited to, synthetic and natural fibers or fibrous materials, for example, but not limited to polyester, polyethylene, nylon, quartz, boron, metal, basalt, ceramic and natural fibers such as fibrous plant materials, for example, jute and sisal. Combinations of the above discussed reinforcement fibers can also be used for the present disclosure. For the various embodiments, the reinforcement fibers 102 can have a filament diameter on the order of 5 to 25 pm.

[0017] The pultrusion system 100 further includes the polyurethane mixing and dispensing unit 104, having and supplying both an A-part and a B-part (the isocyanate reactive component) to form a polyurethane resin. Both the A-part and the B-part are individually dispensed from their respective vessels (e.g. A-part 1 16, and B-part 1 18) under pressure and at predetermined flow rates to a mixer 120. For the various embodiments, the A-part includes, among other things, at least one of an isocyanate containing compound, while the B-part includes at least one of a polyol containing compound, among other things. For the various embodiments, the predetermined flow rates can be based on the desired isocyanate index for the reaction mixture. As known in the art, the isocyanate index is the ratio of the number of isocyanate functional groups present in a formulation (e.g., the reaction mixture) to the number of hydroxyl functional groups (Isocyanate Index = (NCO groups) I (OH groups)), which determines the stoichiometry of the reaction between isocyanates and hydroxyl-containing compounds during the polyurethane formation process.

[0018] The mixer 120 can be a static or active mixer as are known in the art. In the mixer 120, the A-part and a B-part mix to form a reaction mixture for the polyurethane resin of the CFRP composite structure. The polyurethane mixing and dispensing unit 104 pumps and delivers the reaction mixture from the mixer 120 under pressure to the injection box 106 for wetting out the reinforcement fibers 102 prior to them entering the curing die assembly 108. As used herein, “wetting”, “wetting out”, “wet” and “wetter” means to saturate the voids and interstices within and between the reinforcement fibers 102 with the reaction mixture for the polyurethane resin as provided herein.

[0019] For the various embodiments, the A-part may comprise the polyisocyanate component and the B-part may comprise the polyol component. By the term “polyol” means a composition that contains a plurality of active hydrogen groups that are reactive towards the polyisocyanate component under the conditions of processing (e.g., hydroxyl groups, amine groups, etc.).

[0020] Examples of such polyols include polyether polyols that may be prepared by polyaddition of alkylene oxides (alkoxylation) onto an initiator ( / .e., a polyhydroxy functionalstarter compound) in the presence of catalysts known in the art that can shape the proportion of primary and secondary hydroxyls in the resulting polymer or oligomer.

[0021] The initiator includes one or more compounds having a low molecular weight and a numerical hydroxyl functionality of at least 2. The initiator can be an organic compound that is to be alkoxylated in the polymerization reaction. The initiator may contain as many as 10 hydroxyl groups. For example, the initiator may be a diol or triol. Mixtures of initiators may be used. The initiator will have a hydroxyl equivalent weight less than that of the polyether product, e.g., may have a hydroxyl equivalent weight of less than 500 g / mol equivalence, less than 300 g / mol equivalence, greater than 20 g / mol equivalence, from 20 to 300 g / mol equivalence, from 20 to 200 g / mol equivalence, or from 30 to 150 g / mol equivalence by way of example.Exemplary, initiator compounds such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,8- octanediol, cyclohexane dimethanol, bisphenol A, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, sugars and sugar alcohols such as sorbitol and sucrose, and / or alkoxylates of any of these that have a weight average molecular weight less than that of the product of the polymerization.

[0022] The polyether polyols may have a functionality of at least 2 or more such as ranging from 2 to 6, or 2 to 4. The preferred polyether polyols has 100% secondary OH groups.

[0023] Polyurethane compositions may include an isocyanate-reactive component containing at least one polyether polyol, and optionally one or more hydroxy functionalized (meth)acrylates. As used herein, use of “(meth)” in conjunction with various acrylate species indicates that the scope of the specification covers both the acrylate or methacrylate variations of the referenced compound . As such the isocyanate-reactive component or B-part may include one or more hydroxy functional (meth)acrylate monomers that react with the isocyanate component and / or polymerize in the presence of a free radical initiator to produce a polyurethane acrylate hybrid composition. Hydroxy functional (meth)acrylate monomers may have the general structure:

[0024] wherein R1 is selected from hydrogen, methyl or ethyl; R2 is selected from alkylene groups having 2-6 carbon atoms, 2,2-bis(4-phenylene) propane, 1 ,4- bis(methylene)benzene, 1 ,3-bis(methylene)benzene, 1 ,2-bis(methylene) benzene; and n is an integer selected from 1 -6. Hydroxy functional (meth)acrylate monomers may include hydroxyC1 -10 alkyl (meth)acrylate monomers, such as hydroxyethyl acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate monomer, and the like.

[0025] Hydroxy functional (meth)acrylates may be added at a percent by weight (wt.%) of the polyurethane acrylate hybrid composition in a range of 15 wt.% to 40 wt.%, from 20 wt.% to 38 wt.%, from 25 wt.% to 35 wt.%, or from 27 wt.% to 32 wt.%.

[0026] The described polyether polyols and hydroxy functional methacrylate monomer may be used in the polyurethane resin compositions described herein. The term “polyisocyanate” means a composition that contains a plurality of isocyanate or -NCO groups that are reactive towards the polyol component under the conditions of processing. Examples of such polyisocyanates can include di- or polyisocyanate compounds, as are known in the art. Compositions disclosed herein may be substantially free of water ( / '.e., max content in the formulation is 0.1 % or less) and produce negligible amounts of foam upon combination of the reactant components.

[0027] Examples of other polyurethane resins that are useful with the present disclosure include, but are not limited to, those provided in WO 2023 / 035262, incorporated herein by reference. WO 2023 / 035262 provides examples of what is referred to as hybrid polyurethane compositions, where such compositions include at least one of (a) a first polyisocyanate compound; (b) a first prepolymer that is formed by reacting a second polyisocyanate compound and a first polyol having an average equivalent weight of 30 to 200 g / eq and an average functionality of 2 to 3 and where the first prepolymer has an NCO content of 21 to 25 % based on the weight of the first prepolymer; and (c) a second prepolymer prepolymer formed by reaction of a third polyisocyanate compound and a second polyol, where the second polyol has an average equivalent weight of from 250 to 3000 g / eq and an average functionality of 2-3 and the second prepolymer has a NCO content of 10 to 20 % based on the weight of the second prepolymer. The total amount of the first prepolymer and the second prepolymer can be 10 to 70 wt.% based on the total weight of the isocyanate component. The hybrid polyurethane composition further includes an isocyanate-reactive component comprising a third polyol, an isocyanate reactive (meth) acrylate monomer and a free radical initiator. Other polyurethane compositions can include those polyether and polyester-based compositions seen in, for example, U.S. Pat. No. 11 ,142,616 B2 and U.S. Pat. Pub. 2018 / 214914A1 , both of which are incorporated herein by reference.

[0028] Isocyanate components may contain one or more isocyanate compounds, such as polymeric isocyanates, aromatic isocyanates, or carbodiimide-modified isocyanates.Isocyanate compounds may be monomeric, oligomeric, prepolymers, and the like. The isocyanate component can include, for example, one or more isocyanate and / or polyisocyanate compounds. Isocyanate components may include isocyanate compounds having a nominal functionality of 1 .5 or greater, or > 2.0 or greater, more precisely 2.2 to 2.8

[0029] The isocyanate component may include an isocyanate compound having a number average molecular weight of 150 g / mol to 750 g / mol. In some cases, the isocyanate compound can have a number average molecular weight from a low value of 150 g / mol, 200 g / mol, 250 g / mol or 300 g / mol to an upper value of 350 g / mol, 400 g / mol, 450 g / mol, 500 g / mol or 750 g / mol. The number average molecular weight values reported herein are determined by end group analysis, gel permeation chromatography, and other methods as is known in the art. The isocyanate compound can be monomeric and / or polymeric, as are known in the art.

[0030] The isocyanate component may include on or more of aliphatic polyisocyanate, cycloaliphatic polyisocyanate, araliphatic polyisocyanate, aromatic polyisocyanate, and the like. Examples of isocyanates include, but are not limited to, polymethylene polyphenylisocyanate; toluene 2,4- / 2,6-diisocyanate (TDI) ; methylenediphenyl diisocyanate (MDI, including its isomers); polymeric and prepolymeric MDI; triisocyanatononane (TIN); naphthyl diisocyanate (NDI); 4,4’-diisocyanatodicyclohexyl-methane; 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI); tetramethylene diisocyanate; hexamethylene diisocyanate (HDI); 2-methyl-pentamethylene diisocyanate; 2,2,4-trimethylhexamethylene diisocyanate (THDI); dodecamethylene diisocyanate; 1 ,4-diisocyanatocyclohexane; 4,4’- diisocyanato-3,3'-dimethyl-dicyclohexylmethane; 4,4’-diisocyanato-2,2-dicyclohexylpropane; 3- isocyanatomethyl-1 -methyl-1 -isocyanatocyclohexane (MCI); 1 ,3-diisooctylcyanato-4- methylcyclohexane; 1 ,3 -diisocyanato-2-methylcyclohexane; and combinations thereof, among others. In addition to the isocyanates mentioned above, partially modified polyisocyanates including uretdione, isocyanurate, carbodiimide, uretonimine, allophanate or biuret structure, and combinations thereof, among others, may be utilized.

[0031] Isocyanate compounds may include isocyanate prepolymers resulting from reaction of an isocyanate- reactive compound with a molar excess of an isocyanate compound or polymeric isocyanate compound under conditions that do not lead to gelation or solidification. Isocyanate prepolymers disclosed herein may have an isocyanate index, defined as the equivalents of isocyanate divided by the total equivalents of isocyanate-reactive hydrogen containing materials, multiplied by 100) in a range of from 30 to 400, 40 to 300, or 40 to 200. Isocyanates components disclosed herein may include one or more isocyanate compoundshaving an NCO content at a percent by weight of above 20 wt.%, such as in a range of 20 wt.% to 75 wt.%, or 20 wt.% to 60 wt.%.

[0032] PU compositions disclosed herein may include an isocyanate component at a percent by weight (wt.%) ranging from 15 wt.% to 80 wt.%, 20 wt.% to 80 wt.%, or 20 wt.% to 70 wt.%.

[0033] An example of suitable polyol and isocyanate combination for the reaction mixture of the present disclosure includes VORAFORCE™ TP1270EU / 1300 (DOW), which is a blend of polyols and isocyanate that can achieved a low initial viscosity.

[0034] The two component polyurethane resin once the A-part and the B-part are mixed together has a viscosity at 25 °C of about 200 to 800 cP. The time to triple that initial viscosity at 25 °C is in about 15 minutes or more. This allows for a thorough mixing of the A-part and the B-part in the mixer 120, and wetting the fibers in the Injection box 106, before substantial polymerization occurs. Other additives may also be included in the A-part, and / or B-part, such as fillers, pigments, plasticizers, curing catalysts, UV stabilizers, internal mold release agents, antioxidants, microbiocides, algicides, dehydrators, thixotropic agents, wetting agents, water scavengers, antifoaming agents, antistatic agents, flow modifiers, matting agents, deaerators, extenders, molecular sieves for moisture control, dyes, UV absorber, light stabilizer, fire retardants and smoke suppressants.

[0035] For the various embodiments, the injection box 106 is fluidly coupled to the polyurethane mixing and dispensing unit 104. The injection box 106 receives the reinforcement fibers 102 and the reaction mixture from the polyurethane mixing and dispensing unit 104 under pressure. For the various embodiments, the injection box 106 facilitates the controlled injection of the reaction mixture into the reinforcement fibers 102 to form wetted out the reinforcement fibers 102 prior to their entry into the curing die assembly 108. Such controlled injection of the reaction mixture into the reinforcement fibers 102 helps to ensure a thorough impregnation and consistent distribution of the reaction mixture throughout the reinforcement fibers 102 and the CFRP composite structure. To achieve this, the injection box 106 includes one or more of an inlet port through which the reaction mixture is injected. In addition, the injection box 106 can include distribution channels or pathways that help to guide the reaction mixture from the intake port to various sections where the reinforcement fibers are introduced into the injection box 106. The channels can help ensure an even and controlled flow of the reaction mixture into and on to the reinforcement fibers 102 so as to wet out the reinforcement fibers 102.

[0036] The injection box 106 can further include a pressure control unit to control and regulate the pressure of the reaction mixture being injected into and wetting out thereinforcement fibers 102. Such pressure control helps to prevent either over-saturation or under-saturation of the reinforcement fibers 102. In addition, the injection box 106 can be temperature controlled (e.g., heated or cooled) to maintain the reaction mixture at a desired temperature to better achieve a desired viscosity and / or curing behavior for the reaction mixture. The wetted out reinforcement fibers 102 then exit the injection box 106 and proceed to the curing die assembly 108. Residence time for the reinforcement fibers 102 in the injection box 106 can be typically less than one minute.

[0037] As illustrated in Fig. 1 , the curing die assembly 108 is attached to the injection box 106. The curing die assembly 108 includes a first heating zone 122 having a first predefined temperature to provide heat to promote a curing process of the A-part and the B-part of the reaction mixture, and surfaces defining a cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass and solidify to provide a predefined shape to the wetted out reinforcement fibers (e.g., a die). As discussed herein, the curing die assembly 108 can include more than the first heating zone 122. For example, the curing die assembly 108 can include in addition to the first heating zone 122, a second heating zone 124 and a third heating zone 126. For the various embodiments, the cross-sectional shape of the die(s) provide the eventual cross-sectional shape of the CFRP composite structure. In other words, the die(s) of the curing die assembly 108 impart the cross-sectional shape or geometry to the CFRP composite structure and heat to cure the resin.

[0038] For the various embodiments, each of the first heating zone 122, the second heating zone 124 and third heating zone 126 of the curing die assembly 108 can have different temperature set-points that are individually controlled. So, in one embodiment, each of the heating zones 122, 124 and 126 could have the same predetermined temperature.Alternatively, two of the heating zones 122, 124 and / or 126 could have the same predetermined temperature, while the third of the heating zones 122, 124 or 126 could have a different predetermined temperature. In addition, each of the heating zones 122, 124 and 126 could have a different predetermined temperature as compared to the each of the other heating zones. This allows for more precise temperature distribution along the length of the curing die assembly 108, accommodating variations in the reaction mixtures curing rates and better ensuring uniform shaping and curing.

[0039] For the various embodiments, the predetermined temperature of each of the heating zone(s) temperature set-points can independently be set from 150 °C to 250 °C. All individual values and subranges from 150 °C to 250 °C. are included; for example, the predetermined temperature of each of the heating zones can have a lower limit of 150 °C, 160°C, 170 °C or 180 °C to an upper limit of 250 °C, 240 °C, 230 °C, or 220 °C. For the various embodiments, the residence time of the wetted out reinforcement fibers passing through the curing die assembly 108 can be from about 4 minutes to about 5 seconds.

[0040] The curing die assembly 108 can further include a cooling zone 128, which provides a thermal bridge to the curing die assembly 108 so as to avoid back propagation of heat to the injection box 106. For the various embodiments, the cooling zone 128 does not add heat to the curing process of the A-part and the B-part of the reaction mixture but provides surfaces defining the cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass and solidify to provide the predefined shape to the wetted out reinforcement fibers (e.g., a die). As discussed herein, a cooling fluid (e.g., chilled water) can be circulated through the cooling zone 128 to create the thermal bridge, where the arrows in Fig. 1 illustrate the movement of the cooling fluid. For the various embodiments, when present the cooling zone 128 precedes the first heating zone 122 and, when present, any of the second heating zone 124 and / or third heating zone 126.

[0041] For the various embodiments, the cooling zone 128 is equipped with a cooling element and temperature control mechanism that can maintain the predefined temperature for the cooling zone 128. For example, the cooling zone 128 can include a continuous conduit within and throughout the cooling zone 128 which the cooling fluid (e.g., water) is circulated to create the thermal bridge. The temperature control mechanism can, in addition, control the flow rate and / or inlet temperature of the cooling fluid to the cooling zone 128.

[0042] For the various embodiments, the curing die assembly 108 with each of the heating zones 122, 124 and 126, and the cooling zone 128 can be formed from a heat-resistant material, such as steel, stainless steel or other alloys, that can withstand the high temperatures required for the pultrusion process. The curing die assembly 108 along with each of the heating zones 122, 124 and 126, and the cooling zone 128 can consist of one or more portions (e.g., two halves) that are joined together and / or on the curing die assembly 108 so as to provide the heating and cooling as described herein along with the cross-sectional shape provided by the curing die assembly 108 that aligns and encase the reinforcement fibers 102 wetted out with the reaction mixture. For the various embodiments, curing die assembly 108 can also include one or more mandrels depending on the geometry of the cross section being pultruded. For example, a mandrel may be used to produce a hollow cross-section.

[0043] According to the present disclosure, the wetted out reinforcement fibers 102 are compressed into the cross-sectional shaped as they pass through the curing die assembly 108. The compressive force applied in the curing die assembly 108 helps to further force the reactionmixture into and between the reinforcement fibers 102 during the curing process. This action helps to ensure that the reinforcement fibers 102 conform precisely to the desired shape, resulting in a CFRP composite structure that mirrors the die's intricate configuration.

[0044] For the various embodiments, the surfaces defining the cross-sectional shape discussed herein can include cylindrical shapes, such as rods, tubes, beams, rectangular (including square) or other geometric cross-sectional shapes are known. For example, the cross-sectional shape discussed herein can be used to provide the predefined shape of the CFRP composite structure with a rectangular cross section having a thickness of 2 to 6 millimeters and a width of 50 to 300 millimeters. The curing die assembly 108 can have a length from 0.5 to 2 meters. Other dimensions and shapes are of course possible as will be appreciated by one skilled in the art.

[0045] For the various embodiments, the curing die assembly 108 also includes an exit 130, through which the CFRP composite structure of the present disclosure exits the curing die assembly 108 to then enter the one or more of the post curing heating block 110.

[0046] Upon exiting the curing die assembly 108, the wetted out reinforcement fibers 102 in the predefined shape and undergoing the curing process enter one or more of a post curing heating block 110. As illustrated, the one or more of the post curing heating block 110 is spaced apart and separate from the exit 130 of the curing die assembly 108 such that the wetted out reinforcement fibers 102 in the predefined shape and undergoing the curing process exit the curing die assembly 108 and enter the one or more of the post curing heating block 110. Each of the one or more of the post curing heating block 110 has a passageway through which the wetted out reinforcement fibers 102 in the predefined shape and undergoing the curing process pass. In addition, each of the one or more of the post curing heating block 110 has a predefined temperature to provide additional heat to the curing process of the reaction mixture to form the CFRP composite structure in the predefined shape. However, in contrast to their interaction with the curing die assembly 108, including the heating zones 122, 124 and 126 discussed herein, the one or more of the post curing heating block 1 10 is dimensioned such that the CFRP composite structure does not apply substantial pressure against the passageway of the one or more of a post curing heating block 110 that would cause a change in the predefined shape of the CFRP composite structure. Rather, the passageway of each of the one or more of the post curing heating block 1 10 is dimensioned such that while it at least partially or completely surrounds the CFRP composite structure as it passes therethrough, it does not provide any substantial resistance or pressure against the CFRP composite structure. For the various embodiments, the one or more of the post curing heating block 110 can have surfacesthat define essentially the same cross-sectional shape through which the wetted out reinforcement fibers from the injection box passed, but where the area of the cross-sectional shape for the one or more of the post curing heating block 110 is larger (e.g., 5 to 20 percent) than the area of the cross-sectional shape for the die(s) of the during die assembly 108, including the first heating zone 122 and optionally heating zones 124, 126 and cooling zone 128. In other words, the one or more of the post curing heating block 110 act to provide additional heat to the curing process of the reaction mixture to form the CFRP composite structure and not as a die to provide the predefined shape of the CFRP composite structure.

[0047] For the various embodiments, the one or more of the post curing heating block 110 can include a first post curing heating zone 134. For the various embodiments, the first post curing heating zone 134 is the initial post curing heating zone that the wetted out reinforcement fibers 102 in the predefined shape and undergoing the curing process enter after leaving the curing die assembly 108. For the various embodiments, the one or more of the post curing heating block 110 can further include additional post curing heating zones, as discussed herein, where the additional post curing heating zones can include a last post curing heating zone 136, which is the final post curing heating zone that the now formed CFRP composite structure passes through before exiting the post curing heating block 110. For the various embodiments, each of the first post curing heating zone 134 and the last post curing heating zone 136 have a passageway, as discussed above, through which the reinforcement fibers 102 and the reaction mixture in the predefined shape pass. For the various embodiments, the passageway of each of the one or more of the post curing heating block 110 can be from 0.3 to 2.0 meters long.

[0048] As illustrated in Fig. 1 , the first post curing heating zone 134 is spaced apart and separate from the curing die assembly 108 and the last post curing heating zone 136 such that the reinforcement fibers 102 and the reaction mixture in the predefined shape exit the curing die assembly 108 and enter the first post curing heating zone 134 and the last post curing heating zone 136. Each of the first post curing heating zone 134 and the last post curing heating zone 136 have a predefined temperature to provide additional heat to the curing process of the reaction mixture to form the CFRP composite structure in the predefined shape. As discussed above, the CFRP composite structure does not, however, apply pressure against the passageway of either of the first post curing heating zone 134 or the last post curing heating zone 136 (or any intervening post curing heating zones) to cause a change in the predefined shape of the CFRP composite structure.

[0049] For the various embodiments, the predefined temperature of the post curing heating zone(s) can be the same (e.g., uniform) or profiled. As used herein, profiled means that the predefined temperature of two or more of the post curing heating zones have a different temperature than each other and / or the predefined temperature(s) of the post curing heating zone, which further enable thermal optimization. So, in one example the predefined temperature of the first post curing heating zone 134 is different than the predefined temperature of the last post curing heating zone 136. This temperature control allows for the possibility of having different amounts of heat provided in the zones within the post curing heating block 110, which is an advantage of the present disclosure.

[0050] For the various embodiments, each post curing heating zones of the one or more of the post curing heating block 110 is equipped with a heating element and temperature control mechanism that can maintain the predefined temperature for the respective post curing heating zone. For example, the heating element of each post curing heating zone of the one or more of the post curing heating block 1 10 can be an electrical heating element or a heated fluid passing through a conduit in the respective heating zone of the post curing heating block 110. The heating provided by the post curing heating zones of the post curing heating block 1 10 can be through a conduction mechanism, where heat is not transferred through infrared, convection or microwave.

[0051] For the various embodiments, the predetermined temperature of each of the post curing heating zones can be independently set from 150 °C to 250 °C. All individual values and subranges from 150 °C to 250 °C. are included; for example, the predetermined temperature of each of the post curing heating zones can be independently set from a lower limit of 150 °C, 160 °C, 170 °C or 180 °C to an upper limit of 250 °C, 240 °C, 230 °C, and 220 °C. For the various embodiments, the residence time of the CFRP composite structure passing through each post curing heating zones can be from about 4 minutes to about 5 seconds.

[0052] The post curing heating zone(s) of the one or more of the post curing heating block 110 can be formed from a metal or a metal alloy or other thermally conductive material. Each of the post curing heating zones can consist of two or more portions (e.g., two halves) that are joined to the post curing heating block 110 and / or together so as to provide the passageway discussed herein. For the present disclosure, each zone can have a heating element that can be an electrical plate clamped to the post curing heating block 110 (e.g., top and bottom of the post curing heating block 110). Alternatively, the heating zone can be formed by an internal coil with a thermal fluid connected to a thermal control unit. Each plate can deliver heat to keep ontarget the desired temperature in the zone through a control system. For example, in one embodiment each of the post curing heating zones consists of two parts, with a bottom part that is fixed to the pultrusion line frame, and the top part held in place with releasable fasteners (e.g., screws) so that the only pressure applied against the CFRP composite structure in the predefined shape is due to its own weight (e.g., due to gravity acting on the CFRP composite structure as it passes through each passageway of the post curing zones of the one or more of the post curing heating block 1 10. In other words, the one or more of the post curing heating block 110 acts only as a heating station, and not as a die, for the CFRP composite structure.

[0053] For the various embodiments, the residence time of the CFRP composite structure in the post curing heating block 110 is sufficiently long to under the predetermined temperature(s) to ensure complete and uniform curing of the polyurethane throughout the CFRP composite structure. The residence time and temperature profile in the post curing zones of the post curing heating block 110 can be determined based on the characteristics of the polyurethane resin, the dimensions of the CFRP composite structure, and the desired mechanical properties of the CFRP composite structure. This profile can vary depending on factors such as resin formulation, thickness, and the final application of the CFRP composite structure.

[0054] Upon exiting the post curing heating block 1 10, the CFRP composite structure enters the one or more of the cooling block 112. As illustrated, the one or more of the cooling block 112 is spaced apart and separate from the curing die assembly 108 and the one or more of the post curing heating block 110 such that the CFRP composite structure exits the one or more of the post curing heating block 110 and enters the one or more of the cooling block 112. Each of the one or more of the cooling block 112 has a passageway through which the CFRP composite structure passes. In addition, each of the one or more of the cooling block 112 has a predefined temperature to remove heat from the CFRP composite structure. However, in contrast to their interaction with the curing die assembly 108 with heating zone 122 and optionally heating zones 124 and 126, and cooling block 128 as discussed herein, the one or more of the cooling block 1 12 is dimensioned such that the CFRP composite structure does not apply substantial pressure against the passageway of the one or more of a cooling block 112 that would cause a change in the predefined shape of the CFRP composite structure. Rather, the passageway of each of the one or more of the cooling block 112 is dimensioned such that while it at least partially or completely surrounds the CFRP composite structure as it passes therethrough, it does not provide any substantial resistance or pressure against the CFRP composite structure. For the various embodiments, the one or more of the cooling block 1 12can have surfaces that define essentially the same cross-sectional shape through which the wetted out reinforcement fibers from the injection box passed, but where the area of the cross- sectional shape for the one or more of the cooling block 1 12 is larger e.g., 5 to 20 percent) than the area of the cross-sectional shape for the die(s) of the during die assembly 108, including the first heating zone 122 and optionally heating zones124, 126 and cooling zone 128. In other words, the one or more of the cooling block 1 12 act to remove heat from the CFRP composite structure and not as a die to provide the predefined shape of the CFRP composite structure.

[0055] For the various embodiments, the one or more of the cooling block 112 can include a first cooling zone 140. For the various embodiments, the first cooling zone 140 is the initial cooling zone of the one or more cooling block 112 that the CFRP composite structure enters after leaving the one or more of the post curing heating block 1 10. For the various embodiments, the one or more of the cooling block 112 can further include additional cooling zones, as discussed herein, where the additional cooling zones can include a last cooling zone 142, which is the final cooling zone that the CFRP composite structure passes through before exiting the one or more of the cooling block 112. For the various embodiments, each of the first cooling zone 140 and the last cooling zone 142 have a passageway, as discussed above, through which the CFRP composite structure passes. For the various embodiments, the passageway of each of the one or more cooling block 112 can be from 0.3 to 2.0 meters long.

[0056] As illustrated in Fig. 1 , the first cooling zone 140 is spaced apart and separate from the post curing heating block 110 including the last post curing heating zone 136, and the last cooling zone 142 such that the CFRP composite structure exits the post curing heating block 110 and enter the first cooling zone 140 and the last cooling zone 142 of the cooling block 112. Each of the first cooling zone 140 and the last cooling zone 142 have a predefined temperature to remove heat from the CFRP composite structure. As discussed above, the CFRP composite structure does not, however, apply pressure against the passageway of either of the first cooling zone 140 or the last cooling zone 142 (or any intervening cooling zone) to cause a change in the predefined shape of the CFRP composite structure.

[0057] For the various embodiments, the predefined temperature of each of the cooling zones can be the same (e.g., uniform) or profiled. As used herein, profiled means that the predefined temperature of two or more of the cooling zones have a different temperature than each other. So, in one example the predefined temperature of the first cooling zone 140 is different than the predefined temperature of the last cooling zone 142. This temperature control allows for the possibility of having different amounts of heat removed in the different zones within the cooling block 112, which is an advantage of the present disclosure.

[0058] For the various embodiments, each of the one or more of the cooling zones in the cooling block 112 is equipped with a cooling element and temperature control mechanism that can maintain the predefined temperature for the respective cooling zone. For example, the cooling element of each of the cooling zones of the one or more of the cooling block 112 can be a cooling fluid (e.g., water) passing through a conduit in the cooling block 1 12 for the respective cooling zone. The cooling provided by the cooling zone can be through a conduction mechanism.

[0059] For the various embodiments, the predetermined temperature of each of the cooling zones of the one or more of the cooling block 112 can be independently set from 0 °C to 50 °C. All individual values and subranges from 0 °C to 50 °C are included; for example, the predetermined temperature of each of the cooling zones can be independently set from a lower limit of 0 °C, 5 °C, 10 °C or 15 °C to an upper limit of 50 °C, 40 °C, 35 °C, or 30 °C. For the various embodiments, the residence time of the CFRP composite structure passing through each cooling zones can be from about 4 minutes to 5 seconds. For the various embodiments, the reaction mixture can have a conversion of at least 90 percent before passing the CFRP composite structure in the predefined shape through the passageway of the last cooling zone 142. For the various embodiments, the CFRP composite structure exiting the last cooling zone 142 can have a temperature of no greater than 55 °C.

[0060] The one or more of the cooling block 112 that include the cooling zones discussed herein can be formed from a metal or a metal alloy or other thermally conductive material. Each of the cooling block 112 can consist of two or more portions (e.g., two halves) that are joined together so as to provide the passageway discussed herein. In one embodiment, each of the cooling block 112 consists of two parts, with a bottom part that is fixed to the pultrusion line frame, and the top part held in place with releasable fasteners (e.g., screws) so that the only pressure applied against the CFRP composite structure in the predefined shape is due to its own weight (e.g., due to gravity acting on the CFRP composite structure as it passes through each passageway of the one or more of the cooling zones of the cooling block 112. In other words, the one or more of the cooling block 112 act only as a heat removal station, and not as a die, for the CFRP composite structure.

[0061] For the various embodiments, the residence time of the CFRP composite structure in the cooling block 112 is sufficiently long to cool the CFRP composite structure to a temperature below the glass transition temperature (Tg) of the polyurethane of the CFRP composite structure. For example, the cooling block 112 can help to stabilize the CFRPcomposite structure prior to entering the pulling system 1 14. Cooling of the CFRP composite structure can also help to prevent deformation or warping of the CFRP composite structure due to residual heat in the CFRP. In addition, cooling of the CFRP composite structure can also help to prevent damage to the gripper or puller wheels of the pulling system, as discussed herein. For the various embodiments, the cooling block 112 helps to actively cool the CFRP composite structure below its Tg before arriving at the pulling system 114. Such a structure allows for the conversion levels of the polyurethane resin of the CFRP composite structure to be maintained at greater than 90% along with a take up temperature at the puller system 114 of less than 55 °C.

[0062] At the exit of the one or more cooling block 112, the CFRP composite structure is pulled through the pultrusion system 100 at a predefined rate using the pulling system 114. The pulling system 1 14 can be one of either a caterpillar puller or a reciprocating puller, both as are known in the art. The pulling system 114 can pull the CFRP composite structure from the cooling block 112 at the predefined rate of 0.5 to 4 meters / minute. The pulling system 114 maintains the continuous movement of the CFRP composite structure through the various stages of the pultrusion system 100, as discussed herein, while maintaining the desired tension and speed. For the various embodiments, the pulling system 1 14 can include a set of motorized puller wheels or grippers that grip the CFRP composite structure and exert a controlled pulling force. The pulling force is regulated to maintain consistent tension on the CFRP composite structure as it moves through the system 100. Tension control units, including tension sensors, can be used to maintain consistent and uniform properties of the CFRP composite structure. The motorized puller wheels or grippers and the tension sensors can adjust the pulling force on the CFRP composite structure in real-time, which helps to ensure uniformity in the CFRP composite structure dimensions and properties. The pulling system 114 can also be synchronized with the other stages of the pultrusion system 100, as discussed herein. Proper coordination ensures that the continuous fiber-reinforced polyurethane composite structure enters each stage at the right time and with the appropriate tension. For instance, the pulling speed might need to be adjusted to accommodate the curing time required for the specific polyurethane resin being used.

[0063] For the various embodiments, the number and design of the puller wheels of the pulling system 1 14 can vary depending on the specific requirements of the pultrusion process. The puller wheels or grippers used in the pulling system 1 14 can be formed from a variety of materials to ensure effective grip, durability, and resistance to wear and heat. Examples of suitable materials for the puller wheels or grippers include rubber or elastomeric materials suchas polyurethane, and other polymeric materials such as nylon, polyether ether ketone (PEEK), or acetal. The puller wheels or grippers can also include metal or metal-coated materials, such as the ones discussed herein.

[0064] The pulling system 1 14 can also include a cutting mechanism. The cutting mechanism can also be coordinated with the pulling speed to ensure that the CFRP composite structure is cut into individual pieces of the desired length. The cutting mechanism can include saws, blades, or other cutting tools as are known in the art.

[0065] The produced CFRP composite can be cut to desired length through a proper cutting saw system, as discussed herein, or coiled on a coiling device, as known in the art, at certain coil lengths as for example 50 meter (m), 100 m, 200 m, 300 m up to 400 m for each single coil. The advantage of producing coils is that they can be shipped as is to the end user where it can then be uncoiled and cut to the desired length, for example in the production of spar caps for wind blades.

[0066] Embodiments of the present disclosure can further include a pultrusion process for forming the CFRP composite structure. The process can include forming wetted out reinforcement fibers with the reinforcement fibers and the reaction mixture of the A-part and the B-part used to form the polyurethane resin, as discussed herein. The wetted out reinforcement fibers are then passed through the curing die assembly, as discussed herein, where the curing die assembly provides at least the first heating die having the first predefined temperature to provide heat to promote a curing process of the A-part and the B-part of the reaction mixture, and the surfaces defining the cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass to provide the predefined shape to the wetted out reinforcement fibers. The wetted out reinforcement fibers in the predefined shape undergoing the curing process are then passed through the passageway of the one or more post curing heating block, as discussed herein. As discussed herein, the one or more of the post curing heating block is spaced apart and separate from the exit of the curing die assembly such that the wetted out reinforcement fibers in the predefined shape undergoing the curing process exit the curing die assembly and enter the one or more of the post curing heating block. The one or more of the post curing heating block have the predefined temperature to provide additional heat to the curing process of the reaction mixture to form the CFRP composite structure in the predefined shape, as discussed herein. As discussed herein, the wetted out reinforcement fibers in the predefined shape undergoing the curing process can pass through the passageway of each of the first post curing heating zone and the last post curing heating zone of the one or more of the post curing heating block to form the CFRP composite structure. The CFRPcomposite structure does not, however, apply pressure against the passageway of the one or more of the post curing heating block to cause a change in the predefined shape of the CFRP composite structure, as discussed herein.

[0067] The CFRP composite structure in the predefined shape then passes through the passageway of one or more of a cooling block, as discussed herein. The one or more of the cooling block is spaced apart and separate from the curing die assembly and the one or more of the post curing heating block such that the CFRP composite structure exits the one or more of the post curing heating block and enters the one or more of the cooling block having the predefined temperature to remove heat from the CFRP composite structure in the predefined shape, as discussed herein. As discussed herein, the CFRP composite structure can pass through the passageway of each of the first cooling zone and the last cooling zone to cool the CFRP composite structure to a temperature of no greater than 55 °C (e.g., well below the Tg of the polyurethane resin). The CFRP composite structure does not, as discussed herein, apply pressure against the passageway of the one or more of the cooling block to cause a change in the predefined shape of the CFRP composite structure. The CFRP composite structure is pulled through the system at a predefined rate, as discussed herein.EXAMPLES

[0068] The Examples (EX) and Comparative Examples (CE) are based on model predictions using Abaqus Standard (Dassault Systemes). Abaqus Standard was used to simulate the pultrusion system by finite elements and the curing kinetics / thermal analysis using the boundary conditions as provided herein for the EX and CE found below. Curing kinetics and finite element analysis using Abaqus Standard were calibrated versus process data and used for prediction on speeds and cure degree under different conditions provided herein. The curing kinetics for supplying internal (volumetric) heat generation as a function of the degree of conversion were based on the Kamal and Sourour model.

[0069] Regarding the development of the model, only one quarter of the pultrudate and curing die assembly was modeled as per experimental setup with suitable symmetry boundary conditions. Controlled temperature boundary condition were used to represent heater section in the curing die assembly. Steady state time, pull time, pulling speed, mass fraction, volume fraction, material properties, material / unit conversion equations, output interval requests are parametrized in the numerical model. In the end, there was established a conductive base line numerical model (CE A) for different speeds (CE A - 0.5 m / min, CE B - 2.0 m / min) for the pultrusion process.

[0070] To investigate the effect of heating and cooling (CE C, EX 1 , EX 2, EX 3), subsequent conductive heating / cooling blocks were added with suitable boundary conditions and adjusted overall gaps / length. The numerical curing model used for the EX and CE of each fiber / polyurethane system in which resin-impregnated bundles of fibers (rovings) are drawn into a curing die assembly with different speed to achieve a degree of cure of greater than 90% and a take-up temperature less than 55 °C.

[0071] For the simulation the following parameters were used for the polyurethan resin. VORAFORCE™ TP1300 Isocyanate (DOW), VORAFORCE™ TP1270EU Polyol (DOW) and a mold release agent additive VORAFORCE™ TM3700 (DOW) are used in all the modelling simulations. The ratio of mold release to polyol was 5.3 parts to 96 parts by weight. The polyol and mold release blend is commonly referred to as B-Part. The isocyanate constitutes A-Part. The ratio A-Part to B-Part was 1 15:100 (A-Part:B-Part) by weight, as to have an Isocyanate Index of 1 10. The reinforcement fibers were modeled as glass fibers having a nominal filament diameter of 17pm, where the CFRP composite structure contained 70% of glass fiber in volume.

[0072] Fig. 1 illustrates the novel pultrusion process 100, as discussed herein, that was used in the simulated system, which includes a polyurethane mixing and dispensing unit 104 that provides both the A-Part and the B-part for the polyurethane chemistry. The polyurethane mixing and dispensing unit 104 is connected to the injection box 106 that also receives reinforcement fibers 102, where the reaction mixture of the A-part and B-part of the polyurethane impregnate the reinforcement fibers 102. The impregnated reinforcement fibers 102 next enter the curing die assembly 108 to provide the desired cross-sectional shape to the CFRP composite structure. The curing die assembly 108 includes the first heating zone 122, the second heating zone 124 and the third heating zone 126, each set to a temperature of 190 °C. The total length of the curing die assembly 108 was 1 meter. The pultrusion process 100 further included one or more of a post curing heating block 110 and one or more of a cooling block 112, as provided in T able 1 . Each of the post curing heating block 110 was 1 meter long and each post curing heating zone (as provided in Table 1 below) was set to a temperature of 190 °C. Each of the cooling block 112 was 1 meter long and each cooling zone (as provided in Table 1 below) was set to a temperature of 35 °C. The CFRP composite structure 110 was advanced through the pultrusion system 100 by the pulling system 114.

[0073] Table 1 provides the simulation results. As seen, EX 1 -3 differed from the CE A- C in terms of reaching the processing targets of at least a 90 % conversion of the polyurethane resin and a take up temperature at the pulling system 1 14 of less than 55 °C due to thepresence of the post curing heating block 110 and the cooling block 112, with their associated zones, after the curing die assembly 108.Table 1 - EXAMPLES (EX) and Comparative Examples (CE)

[0074] CE A shows that that a pultrusion line that works at low speed, even without a post heating block or cooling block, will be able to meet the conversion target requirement: in fact, the low pultrusion speed implies a longer time during which the reacting material is inside the die, at 190 °C (at 0.5 m / min, the residence time is about 2 minutes for 1 m length die), thus leading to good conversion. However, the pultruded article then reaches the pullers (positioned at five (5) meters distance from the curing die assembly) with a temperature of 77.5 °C, which is higher than desired.

[0075] CE B is similar to CE A, with the difference that the line speed is now 2 m / min: as a consequence, the residence time inside the die is reduced to only 30 seconds, which is not enough to reach sufficient degree of reaction at the die exit (the conversion percent is only 52.2%). Also, due to the higher speed, the pultruded item reaches the pullers when it is at 162.2 °C, which is much hotter than desired.

[0076] CE C is similar to CE B, but with a heating block positioned after the die: this results in improved degree of conversion at the exit from the heated zone reaches (90.3 %), however the temperature at the puller entry is even higher than before, at 164.1 °C.

[0077] EX 1 and EX 2 describe similar lay outs, with a post curing heating block of one (1 ) meter length, positioned after the curing die assembly, followed by three cooling blocks of one (1 ) meter length each, positioned immediately after the post curing heating block: the post curing heating block allows for a high degree of conversion even at pultrusion speed of 2 m / min (EX 1 ) or at pultrusion speed of 2.5 m / min (EX 2), while the cooling blocks (see in Table 1 ) make sure that the pultruded article reaches the pullers at a sufficiently low temperature. EX 1 and EX 2 clearly shows that at high speed post heating and post cooling are both needed.

[0078] EX 3, characterized by faster pultrusion speed (3 m / min) using additional heating and cooling to achieve the desired conversion and temperature at the pullers: this modelling example is characterized by having two post curing heating blocks of 1 m length each with four cooling blocks of 1 m each. This example proves the flexibility of the innovative approach that enable to add multiple heating and cooling blocks depending on the speed, to ensure proper level of resin conversion and cooling of the composite material.

Claims

What is claimed is:1 . A pultrusion system for forming a continuous fiber-reinforced polyurethane composite structure, comprising: reinforcement fibers; a polyurethane mixing and dispensing unit having an A-part and a B-part to form a polyurethane resin, wherein the A-part and the B-part mix to form a reaction mixture for the polyurethane resin; an injection box fluidly coupled to the polyurethane mixing and dispensing unit, wherein the injection box receives the reinforcement fibers and the reaction mixture to form wetted out reinforcement fibers; a curing die assembly attached to the injection box, wherein the curing die assembly includes: a first heating zone having: a first predefined temperature to provide heat to promote a curing process of the A-part and the B-part of the reaction mixture; and surfaces defining a cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass and solidify to provide a predefined shape to the wetted out reinforcement fibers; and an exit; one or more of a post curing heating block having a passageway through which the wetted out reinforcement fibers in the predefined shape and undergoing the curing process pass, wherein the one or more of the post curing heating block is spaced apart and separate from the exit of the curing die assembly such that the wetted out reinforcement fibers in the predefined shape and undergoing the curing process exit the curing die assembly and enter the one or more of the post curing heating block having a predefined temperature to provide additional heat to the curing process of the reaction mixture to form the continuous fiber- reinforced polyurethane composite structure in the predefined shape and is dimensioned such that the continuous fiber-reinforced polyurethane composite structure does not apply substantial pressure against the passageway of the one or more of a post curing heating block to cause a change in the predefined shape of the continuous fiber-reinforced polyurethane composite structure;one or more of a cooling block, wherein each of the one or more of the cooling block has a passageway through which the continuous fiber-reinforced polyurethane composite structure in the predefined shape pass, wherein the one or more of the cooling block is spaced apart and separate from the curing die assembly and the one or more of the post curing heating block such that the continuous fiber-reinforced polyurethane composite structure exits the one or more of the post curing heating block and enters the one or more of the cooling block having a predefined temperature to remove heat from the continuous fiber-reinforced polyurethane composite structure in the predefined shape and is dimensioned such that the continuous fiber- reinforced polyurethane composite structure does not apply substantial pressure against the passageway of the one or more of the cooling block to cause a change in the predefined shape of the continuous fiber-reinforced polyurethane composite structure; and a pulling system to pull the continuous fiber-reinforced polyurethane composite structure at a predefined rate.

2. The pultrusion system of claim 1 , wherein each of the one or more of the post curing heating block include a first post curing heating zone and a last post curing heating zone, wherein each of the first post curing heating zone and the last post curing heating zone have a passageway through which the reinforcement fibers and the reaction mixture in the predefined shape pass, wherein the first post curing heating zone is spaced apart and separate from the curing die assembly and the last post curing heating zone such that the reinforcement fibers and the reaction mixture in the predefined shape exit the curing die assembly and enter the first post curing heating zone and the last post curing heating zone each having a predefined temperature to provide additional heat to the curing process of the reaction mixture to form the continuous fiber-reinforced polyurethane composite structure in the predefined shape and dimensioned such that the continuous fiber-reinforced polyurethane composite structure does not apply substantial pressure against the passageway of either of the first post curing heating zone or the last post curing heating zone to cause a change in the predefined shape of the continuous fiber- reinforced polyurethane composite structure.

3. The pultrusion system of claim 2, wherein the predefined temperature of the first post curing heating zone is different than the predefined temperature of the last post curing heating zone.

4. The pultrusion system of claim 2, wherein the passageway of each of the one or more of the post curing heating block is from 0.3 to 2.0 meters long.

5. The pultrusion system of any one of claims 1 -4, wherein the one or more of the cooling block include a first cooling zone and a last cooling zone wherein each of the first cooling zone and the last cooling zone has a passageway through which the continuous fiber reinforced polyurethane composite structure in the predefined shape pass, wherein the first cooling zone is spaced apart and separate from the post curing heating block and the last cooling zone such that the continuous fiber-reinforced polyurethane composite structure exits the post curing heating block and enters the first cooling zone and the last cooling zone each having a predefined temperature to remove heat from the continuous fiber-reinforced polyurethane composite structure in the predefined shape and are dimensioned such that the continuous fiber-reinforced polyurethane composite structure does not apply substantial pressure against the passageway of either the first cooling zone or the last cooling zone to cause a change in the predefined shape of the continuous fiber-reinforced polyurethane composite structure.

6. The pultrusion system of claim 5, wherein the predefined temperature of the first cooling zone is different than the predefined temperature of the last cooling zone.

7. The pultrusion system of claim 5, wherein the passageway of each of the one or more of the cooling block is from 0.3 to 2.0 meters long.

8. The pultrusion system of any one of claims 1 -7, wherein the predefined shape of the continuous fiber-reinforced polyurethane composite structure has a rectangular cross section with a thickness of 2 to 6 millimeters and a width of 50 to 300 millimeters.

9. The pultrusion system of any one of claims 1 -8, wherein the reinforcement fibers constitute about 55 to 85 percent by weight of the continuous fiber-reinforced polyurethane composite structure.

10. The pultrusion system of any one of claims 1 -9, wherein the pulling system pulls the continuous fiber-reinforced polyurethane composite structure from the cooling block at the predefined rate of 0.5 to 4 meters / minute.

11. A pultrusion process for forming a continuous fiber-reinforced polyurethane composite structure, comprising: forming wetted out reinforcement fibers with reinforcement fibers and a reaction mixture of an A-part and a B-part used to form a polyurethane resin; passing the wetted out reinforcement fibers through a curing die assembly, wherein the curing die assembly provides: a first heating zone having: a first predefined temperature to provide heat to promote a curing process of the A-part and the B-part of the reaction mixture; and surfaces defining a cross-sectional shape through which the wetted out reinforcement fibers from the injection box pass and solidify to provide a predefined shape to the wetted out reinforcement fibers; and an exit; passing the wetted out reinforcement fibers in the predefined shape undergoing the curing process through a passageway of one or more of a post curing heating block, wherein the one or more of the post curing heating block is spaced apart and separate from the exit of the curing die assembly such that the wetted out reinforcement fibers in the predefined shape undergoing the curing process exit the curing die assembly and enter the one or more of the post curing heating block that has a predefined temperature to provide additional heat to the curing process of the reaction mixture to form the continuous fiber-reinforced polyurethane composite structure in the predefined shape and dimensioned such that the continuous fiber- reinforced polyurethane composite structure does not apply substantial pressure against the passageway of the one or more of the post curing heating block to cause a change in the predefined shape of the continuous fiber-reinforced polyurethane composite structure; passing the continuous fiber-reinforced polyurethane composite structure in the predefined shape through a passageway of one or more of a cooling block, wherein the one or more of the cooling block is spaced apart and separate from the curing die assembly and the one or more of the post curing heating block such that the continuous fiber-reinforced polyurethane composite structure exits the one or more of the post curing heating block and enters the one or more of the cooling block having a predefined temperature to remove heat from the continuous fiber-reinforced polyurethane composite structure in the predefined shape and dimensioned such that the continuous fiber-reinforced polyurethane composite structure does not apply substantial pressure against the passageway of the one or more of the coolingblock to cause a change in the predefined shape of the continuous fiber-reinforced polyurethane composite structure; and pulling the continuous fiber-reinforced polyurethane composite structure at a predefined rate.

12. The pultrusion process of claim 1 1 , wherein the one or more of the post curing heating block includes a first post curing heating zone and a last post curing heating zone, wherein each of the first post curing heating zone and the last post curing heating zone have a passageway, and the process further includes passing the wetted out reinforcement fibers in the predefined shape undergoing the curing process through the passageway of each of the first post curing heating zone and the last post curing heating zone, wherein the last post curing heating zone is spaced apart and separate from the curing die assembly and the first post curing heating zone such that the wetted out reinforcement fibers in the predefined shape undergoing the curing process exit the first post curing heating zone and enter the last post curing heating zone that has a predefined temperature to provide additional heat to the curing process of the reaction mixture to form the continuous fiber-reinforced polyurethane composite structure in the predefined shape and dimensioned such that the continuous fiber-reinforced polyurethane composite structure does not apply substantial pressure against the passageway of the one or more of the post curing heating block to cause a substantial change in the predefined shape of the continuous fiber-reinforced polyurethane composite structure.

13. The pultrusion process of any one of claims 11 -12, wherein the one or more of the cooling block includes a first cooling zone and a last cooling zone, wherein each of the first cooling zone and the last cooling zone have a passageway, and the process further includes passing the continuous fiber-reinforced polyurethane composite structure in the predefined shape through the passageway of each of the first cooling zone and the last cooling zone, wherein the last cooling zone is spaced apart and separate from the first cooling zone such that the continuous fiber-reinforced polyurethane composite structure exits the first cooling zone and enters the last cooling zone that has a predefined temperature to remove heat from the continuous fiber-reinforced polyurethane composite structure in the predefined shape and dimensioned such that the continuous fiber-reinforced polyurethane composite structure does not apply substantial pressure against the passageway of the one or more of the cooling block to cause a change in the predefined shape of the continuous fiber-reinforced polyurethane composite structure.

14. The pultrusion process of any one of claims 11 -13, wherein the reaction mixture has a conversion of at least 90 percent before passing the continuous fiber-reinforced polyurethane composite structure in the predefined shape through the passageway of the last cooling zone.

15. The pultrusion process of any one of claims 11 -14, wherein the continuous fiber- reinforced polyurethane composite structure exiting the last cooling zone has a temperature of no greater than 55 °C.

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