Enhanced volatile removal for composite layup

Abstract

A composite article lay up comprising a first layer of resin impregnated fiber material and a second layer of resin impregnated fiber material. An open cell material is layered between the first layer and the second layer. The open cell material has no resin during a first stage of a resin cure cycle. The open cell material has passages configured to flow volatiles formed during the first stage of the resin cure cycle. The open cell material is configured to fill with the resin during a second stage of the resin cure cycle. The open cell material is configured to form an integral structure with the first layer and the second layer as part of the composite article at the completion of the resin cure cycle.

Claims

1. A method comprising: forming a laminate of fabric impregnated with resin; layering an open cell material in the absence of said resin within at least one layer of said laminate to form a composite article layup; wherein layering said open cell material includes placing layers of open cell material between plies of said fabric; encapsulating said composite article lay up in a vacuum device to facilitate removal of volatiles from said composite article layup; vaporizing volatiles from said resin; transporting said volatiles through said open cell material from said resin away from said composite article layup; flowing said resin into said open cell material; filling open cells of said open cell material with resin after said volatiles have transported through said open cell material out of said vacuum device; consolidating said resin and said fabric and said open cell material; and curing said resin in said composite article layup.

2. The method of claim 1, further comprising: applying a compaction vacuum to said composite article layup in said vacuum device.

3. The method of claim 1, further comprising: degassing said resin in said composite article layup.

4. The method of claim 1 wherein said resin comprises a polyimide material.

5. The method of claim 1 further comprising: forming transport passages through said open cell material from said resin to an exterior of said composite article layup.

6. The method of claim 5 wherein said transport passages are formed in a predetermined pattern from a first location proximate said resin within said laminate to a second location proximate an outlet of said vacuum device.

7. The method of claim 1 wherein said open cell material comprises a braided tube.

8. A method comprising: forming a laminate of fabric impregnated with resin; layering an open cell material in the absence of said resin within at least one layer of said laminate to form a composite article layup; wherein said open cell material comprises a braided tube; encapsulating said composite article lay up in a vacuum device to facilitate removal of volatiles from said composite article layup; vaporizing volatiles from said resin; transporting said volatiles through said open cell material from said resin away from said composite article layup; flowing said resin into said open cell material; filling open cells of said open cell material with resin after said volatiles have transported through said open cell material out of said vacuum device; consolidating said resin and said fabric and said open cell material; and curing said resin in said composite article layup.

9. The method of claim 8, further comprising: applying a compaction vacuum to said composite article layup in said vacuum device.

10. The method of claim 8, further comprising: degassing said resin in said composite article layup.

11. The method of claim 8 wherein said resin comprises a polyimide material.

12. The method of claim 8 further comprising: forming transport passages through said open cell material from said resin to an exterior of said composite article layup.

13. The method of claim 12 wherein said transport passages are formed in a predetermined pattern from a first location proximate said resin within said laminate to a second location proximate an outlet of said vacuum device.

14. The method of claim 8 wherein layering said open cell material includes placing layers of open cell material between plies of said fabric.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a partial cross-section schematic of a composite article lay up.

(2) FIG. 2 is a plan view schematic of a composite article lay up.

(3) Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

(4) FIG. 1 shows a vacuum manufacturing assembly layup or assembly 10 for forming a composite article 12. The assembly 10 includes a base plate tool 14 that forms a shape or mold for the composite article 12. The plate 14 is rigid and impermeable and forms an air tight portion of the assembly 10. A laminate of fabric impregnated with resin or first layer 16 impregnated with resin 18 of the composite article 12 is positioned on the plate 14. A permeable fabric sheet 20 can be placed between the first layer 16 and the plate 14. An open cell material 22 made up of a porous media is laid onto the first layer 16. A second layer impregnated with resin 18 is positioned over the open cell material 22 to form the composite article 12. A release membrane 26 can be used in the manufacturing assembly 10. The release membrane 26 can be laid over the composite article 12 to allow for gases to pass through while preventing the flow of liquids past the membrane 26. A breather layer 28 covers the composite article 12 and provides open passages for gases to escape from the exterior of the composite article 12. An impermeable vacuum sheet 30 is situated over the breather layer 28 and on top of the composite article 12. The sheet 30 is sealed to the base plate 14 via sealant 32 such that there is no infiltration of exterior atmosphere and so that a vacuum can be pulled within the space formed between the vacuum sheet 30 and base plate 14 for the purpose of removing any gases formed during the resin 18 cure. A vacuum coupling 34 is attached to the impermeable vacuum sheet 30 and configured to attach to a vacuum device (not shown) for drawing a vacuum inside the space covered by the vacuum sheet 30.

(5) During the process of manufacturing the composite article 12, the resin 18, impregnated in the first layer 16 and the second layer 24 of the composite article 12, is heated and undergoes distinct steps of curing before forming into the finished composite article 12. The resin 18 is heated to a point that allows for volatile materials to change phase into a gas or vapor. The resin produces water vapor and gases including gaseous alcohol and the like, known as volatiles 36 and shown as arrows. The volatiles 36 are drawn out of the composite article 12 due to the vacuum applied to the vacuum manufacturing assembly 10. As discussed earlier above, the volatiles may be trapped in the first and second layers' resin 18 and may form voids (not shown) in the composite article 12.

(6) In an exemplary embodiment, with a resin 18 of polyimide, during cure the preimpregnated reinforcement material releases the solvent used to preimpregnate the layers 16, 24. In a typical release up to about 8 weight percent of material is released. The solvent is usually alcohol, such as ethanol or methanol for a polyimide. Other solvent, such as methyl ethyl ketone, acetone and methylene chloride have been used or made present as volatile impurities in the resin 18 manufacturing process. The resin monomers react to form the cured or vitrified resin and release water and alcohol, typically ethanol or methanol, as a product of reaction.

(7) The composite article 12 illustrated herein, is not subjected to the same problems caused by the formation of voids by the volatiles 36. The unique structure of the open cell material 22 allows for the evacuation of the volatiles 36 from within the structure of the composite article 12. The nature of the open cell material 22 creates multiple passages capable of permitting the flow of gases and vapor through the open cell material 22 and out of the composite article 12. The open cell material 22 is laid out between the first layer 16 and the second layer 24 in a fashion that allows for transport of the volatiles 36 from within the composite article 12 along the plane of the open cell material 22 in a lateral direction. In an exemplary embodiment, the volatiles 36 can flow in the plane of the laminate structure of the composite article 12 as well as through the plane in the transverse direction. The size and location of the pockets and open cells of the open cell material 22 allow for the evacuation of the volatiles 36 via shorter pathways out of the layers 16, 24.

(8) The open cell material 22 can include an Astroquartz scrim, braided tubes, filaments and the like. The open cell material 22 in another embodiment can be made of other fibers such as E glass and S glass. The open cell material 22 can be placed in layers between the plies of the composite article 12. The open cell material 22 can be placed in any variety of alternating combinations between the layers of the composite article 12. The open cell material 22 can be laid out in whole sheets, in strips, as braided tubes, in crossed lattice patterns, and the like.

(9) The open cell material 22 allows for resin 18 to fill in the open cells at the proper time in the curing process. Ultimately, creating a strong integral structure without voids. The open cell material 22 remains stable at the elevated temperatures required to cure the resin 18 in the layers 16, 24. The open cell material 22 allow the volatiles 36 to escape early in the cure cycle. When the resin 18 flows during the cure cycle, the open cell material 22 becomes filled with resin 18 at a later stage of the cure cycle after the volatiles have been removed. Ultimately as the resin 18 that has filled the open cell material 22 cures completely, the open cell material 22 becomes solid and part of the composite article 12. The resin 18 filled open cell material 22 has the same material properties as the other portions of the composite article 12.

(10) The resin 18 can be a polyimide resin, which can be a mixture of suitable aromatic diamine(s), the half ester of suitable aromatic half ester, such as, the phenyl ethynyl group. During the curing reaction the solvent used in the prepregnation operation is removed by heat and vacuum. The aromatic amine and the half esters from the tetraacid and the end cap initially react to form amic acid, which then further react to form an imidized molecule with up to approximately ten repeat units. Imidization is essentially complete at approximately 175 degrees Celsius. The imidized resin is further heated under vacuum and held at a temperature where the resin undergoes a melt with minimal crosslinking at about 225 degrees Celsius to about 315 degrees Celsius. The melt facilitates the reaction of unreacted materials and allows for the removal of remaining volatiles. The assembly 10 can be heated at a temperature sufficient to cause the endcap groups of the resin to react by an addition reaction with no volatile byproducts). The cured assembly 10 lay up is then cooled and removed from the base plate tool 14 and the processing materials removed.

(11) The exemplary embodiment in FIG. 2 includes a composite article 12 with multiple pathways 38 formed by use of the open cell material 22. In some composite article 12 designs, the size, shape and form of the composite article 12 create intrinsically long and difficult to vent and degas areas of the composite article 12 during the manufacturing process. The areas that are difficult to remove the volatiles 36 (shown as arrows) can be more prone to void formation due to trapped volatiles 36 in the layers 16, 24 during the curing process. The addition of the open cell material 22 in patterns 40 that extend from areas that may not vent volatiles 36 well to areas that have better volatile 36 removal properties, such as holes or open portions 42 in the composite article 12 or sections that are open, allows for the volatiles 36 to be removed early in the cure cycle as described above. The volatiles 36 are less likely to be trapped and cause voids. The patterns 40 of the open cell material 22 can shorten the pathways for the volatiles 36 to escape and be removed during degassing phases of manufacturing. When the vacuum is applied to the manufacturing assembly 10, the volatiles 36 flow through passages of the open cell material 22 exiting the composite article 12 and being evacuated from the assembly 10. The patterns 40 can include shapes and sizes that maximize the removal of volatiles 36 from the layers 16, 24 including sheets, strips, lattice and the like.

(12) The patterns 40 made of the open cell material 22 are configured to be open to the flow of the volatiles 36 during the degassing phase of the resin curing. The patterns 40 are configured to be filled with resin 18 after degassing and allow for the resin 18 to flow into the open voids and ultimately fill the open cell material 22 and form as an integral structure with the layers 16, 24 in the composite article 12.

(13) One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, the open cell material 22 can consist of various alternate fibers. Accordingly, other embodiments are within the scope of the following claims.