WO1997049542A1

WO1997049542A1 - Method for molding fiber-reinforced resin composite container

Info

Publication number: WO1997049542A1
Application number: PCT/US1997/011080
Authority: WO
Inventors: Rikard Karl Haraldsson
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1996-06-27
Filing date: 1997-06-25
Publication date: 1997-12-31
Also published as: TW358771B

Abstract

A method of constructing large, unitary, fiber-reinforced polymer composite containers using a vacuum-assisted resin transfer molding process. The method allows for the construction of container systems with only two separately molded parts - an open box consisting of a base (i.e., floor), 2 sidewalls and 2 endwalls, and a cover (i.e., roof). The method results in a structure which maintains the continuity of the reinforcement fibers across the junction between the floor, side, and endwall corners. This method can be applied to very large composite structures such as railcar bodies, intermodal containers, and shelters.

Description

METHOD FOR MOLDING FIBER REINFORCED RESIN COMPOSITE CONTAINER

Cross-Reference to Related Application

This application is a continuation-ir.-part of application Serial No. 08 =72,17= filed June 2", 1996, which is a continualion-iπ-part of application Serial No. 08/609,671 filed March 1, 1996 which in cum claims the benefit: of U.S. Provisional Application Y.z . 60/~C0584 filed June 25 , 1995.

Background of the Invention

This invention relates to a T.ethod cf constructing unitary fiber reinforced resin ccr.posite containers using a vacuum assisted resin transfer -.oiάing process.

Fiber reinforced compcsice ccntainers such as raiicar bodies, intermodal containers, anc truck bodies which incorporate materialΞ such as foarr. and balsa cores are desirable because they are iightweigr.c, corrosion resistance, and provide excellent thermal insulation. To make these ccntainers competitive with rr÷cai structures, the manufacturing costs muse be c.mimizec without sacrificing structural performance. Typically, high stress levels are generated in the corners of these containers due to large bending r.cments . For applications such as raiicar bodies, higr. compressive stresses in the fleer are experienced due to fork lift truck wheel loadinc. Composite containers can oe proαuced m severa. ways One metnoα consists of assemoling a series of f a_t panels (e.g , pultrusions) using a secondary adnesive Donding approach This manufacturing approach results in joints at the corners of tne structure and a discontinuity of fiber reinforcement This invention eliminates fiber discontinuities at the corners and adhesive bonding of multiple panel sections.

Typically, composite parts and structures wnich are exposed to tne environment need to De protected from UV degradation and weatnermg, as we_^- -x as being made aestneticaily pleasing The effects cf UV and weatneπnα are currently reduced or eliminated by: incorporating UV absorbers into the resin, incorporating fillers into _tne resin, pigmentmg the outer resin layers of the composite part; gel coating the surface prior to melding, and_/or painting the finished surface Of these metnods, gel coats twhich are applied prior to tne composite fabrication process/ , and paint iwπich is applied as a secondary operation after tne composite fabrication process are the most effective However, tne application of gel coats or paints results m the emission of VOCs Both gel coating and painting operations also require a large capital expenditure both in spraying and ventilation systems and equipment. Gel coated parts must be layed up and molded within a reasonable time after the gel coat is applied, in order to obtain a good bond between the gel coat and the part being melded. However, large, structural parts may ta.<e several days to lay up, many more curing the prototyping stages. Automation and process improvements will speed up the lay-up time, out this time will probably still be toe long for a gel coating operation. Aesthetically ^* pleasing surfaces are usually accomplished by either gel coating or painting.

Summary of the Invention

This invention defines an approach for constructing large composite containers using a vacuum assisted resin J-0 transfer molding process. The method is applied to larσe composite containers such as rail car bodies which may be as large as 68 feet long by 10 feet wide by 12 feet high. The approach consists of molding only two (2¹ individual parts which are subsequently joined. An open box with 2 15 or 4 sides and a floor is fabricated in one molding step with the top or roof melded in a separate operation.

The materials (e.g. , fabric and cores; are initially positioned on three ,'2; or five (5, separate molds which are supported by casters and oriented horizontally. 20 After the individual sections are laid-up, the two (2} sidewalls and optionally two (2) endwalls are attached to the base floor mold. The sidewalls and endwall molds are then rotated into a vertical position and belted together. The hinging mechanism allows for the mold 25 segments to be attached to the base mold and rotated freely into a vertical position. The hinge also provides for a seconαary lateral movement to seat the siaewall molds to the case mold.

The sidewall and endwall molds are designed so chat a small portion of the floor is included. This allows the entire corner geometry to be incorporated and creates a vertical joint with the floor mold This section of the mold also provides a lip which effectively contains the lay-up during mold rotation At the interfaces between molds, a seal is provided to maintain the vacuum integrity of the assembled meld because if air leaks along the mold, surface finish defects and possibly structurally weakened areas

on the intensity and location of the leak) will occur. Indexing keyways are also provided to ensure alignment between sections.

This invention relates to the material lay-up metnod used to maintain the fiber continuity across the corners of the composite container. Although the five sections are laid up separately, fiber continuity is maintained by the inclusion of additional material m each lay-up beyond the size of the section. This added material is initially folded back on itself and then unfolded after the molds are assembled. The layers of unfolded fabric extend the required distance and are interleaved (overlapped) with fabric in the adjacent section to effectively transfer the load around the corner. Metal caul plates may be positioned over the inside of the lay-up to improve surface definition and smoothness. These caul plates are held in place by retainers at the top cf each section to prevent movement during the rotation of tne molds .

After the molds are assembled and the fabric is unfolded m each corner, the entire lay-up is vacuum bagged. A pre-seamed vacuum bag is used which replicates the inside of the box. A continuous seal is created at the top edge of the sidewalls and endwalls . A resin matrix is then infused into the box using a vacuum assisted resin transfer molding process . Once the resin has cured the box is now a unitary structure.

The sidewalls can have openings within the sidewalls of the size and shape suitable for accommodating structural elements, such as doers and windows, or suitable for the installation of miscellaneous systems and/or equipment, sucn as mechanical refrigeration units. The composite box can comprise means for supporting ancillary structures appendabie to the composite box, such as metal attached plates, mounting studs/threaded attachments, bearing plates, brackets, beams, fittings, hinges, lateral beams, transverse beams, floor stringers, corner rails, and/or posts. The composite box can further integrate internal co-molded hollow elements integrated within the walls of the composite box suitable for running utilities, such as co-molded ducting and/or conduits for air flew, water, and miscellaneous systems, such as electrical wiring.

The method of forming a composite box having end, side, and bottom walls comprises forming a plurality of cores, eacn having a peripheral surface, iengtn and wictn dimensions extending end-to-end and side-to-side, respectively, positioning said cores end-to-end and side-by-side in respective mold segments that define said end, side, and bottom walls while encapsulating the cores in faPric material; assembling the moid segments to interface with one anotner form a box, said fabric material overlapping with fabric material in adjacent moid segments, sealing the interface oetween the mold segments enclosing said molds m a hermetically sealed

Pag having inlets and outlets,- connecting a source of uncured resm to saiα inlets evacuating said molds through said outlets; forcing said uncured resm through said inlets to said outlet to fill the meld between said core and said mold to impregnate said fioer material; curing said resm to form a Composite box; ana removing the mold segments. Preferably, the resin is vinyl ester or polyester.

In forming the composite box of the present invention, openings can be included within tne wails of the composite box of a size and shape suitable for accommodating structural elements . The cores can be positioned m order to create an opening within the sidewalls suitable for accommodating structural elements. Means for supporting ancillary structures to the walls within the composite box can be appended to the walls of the composite box. Hollow elements having endings at the surface of the walls of the composite box can be co- molded within tne composite box, and the endings of tne ncliow elements can oe filled with an easily-removaole substance, such as clay, preventing the hollow openings from filling with resin during the process of filling the z molds.

The composite box structure comprises end, side, and bottom walls, each of said walls, including a plurality of cores having a peripheral surface, length and width dimensions; the cores are positioned end-to-end and

,Λ side-oy-side to define said end, side, and bottom walls: a layer of fiber material encapsulates the cores and bridges the adjacent edges of said end, side, and bottom walls; and a cured resm material saturates said layer of fiber material to form a unitary composite box structure.

. The composite box also includes fiber material caps along the length of said cere side-by-side positioning cf said cores, and resin saturated fiber material form I beam reinforcements m said end, side, and bottom walls and said top.

_Λ The composite box can be constructed with a co- molded layer molded to the top and side and bottom wails.

The co-molded outer surface would protect against UV degradation and weathering, and therefore will have enhanced UV stability and enhanced abrasion, impact, and wear resistance. The co-molded layer can be either a 25 film cr sheet of material which will bond chemically and/or mechanically with the resin system used in fusing tne composite portion of the box. Co-molded layer could be, in ter al ia , a sheet made of acrylic or polwmylidene fluoride. The co-molded surface should, in addition, guard against fiber print-through and offer an aesthetically pleasing surface with multiple color options, which should not fade over the expected oroduc ^" life.

A railroad car may be built comprising a box, as defined above, mounted to a wheeled frame structure reinforced with steel I beams that interact with the I beam reinforcements in said bottom wail. The ccmcos"ⁱt_° box can also be used for cargo and shipping containers, truck trailer bodies, modular housing, and insulated refrigeration rail cars.

Brief Description of the Drawings

Fig. 1 shows five separate molds containing materials positioned for forming a box.

Fig. 2 shows the five separate molds of Fig. 1 in the shape of a box.

Fig. 3 is a cross-sectioned view of Fig. 2 taken along line 3-3 with tne addition of vacuum baggmσ and its relationship to a roof section.

Figs. 4a and 4b are enlarged partial views of Fig. 3 showing alternate embodiments of the improved seal of this invention.

Fig. 4 is a cut away view of a mold.

Fig. 5 shows a cross section of a mold.

Fig. 6 shows the incorporation of co-molded openings within the walls of the composite box. Fig ⁿ shows a cross section of tne walls of tne composite box

Fig. 8 snows a cross section of a moid navmg a co- molded ς hollow element.

Fig. 9 shows a cross-section of a typical composite lay-up m a mold, including the co-molded film or sheet

Fig. 10 shows a cross-section of the fabric lay-up co-molded to a plastic sheet. in Detailed Description of the Preferred Embodiment

Referring to Figs. 1. 2, 3 and 3, five separate molds are shown to include two end walls 10, 12, two side walls 14, 16 and a floor 18 These molds contain cores covered with fabric as best shown on Fig. 3. For ■,.- example, cores 20 are placed m a mold, witn fabric 22 covering the cores. Since a key to this invention is to maintain the continuity across the junction between the floor side and end wall corners of the box additional material 22a is included in each lay up which is beyond the size of the mold This material is initially folded back on itself and then unfolded after tne molds are assembled and interleaved with material in adjacent molds to transfer loaα around corners 'Figs. 1, 2 , and 3) .

Fig. 4 is a cut away view of the floor mold 18 showing the cores 20 assembled within the mold. The cores can be of various materials suitable for the particular use being made of the composite box. A preferred material for the cores is foam which has the added feature of providing insulation where the box is used as a refrigerated rail car

After the molds are assembled and sealed at their interfaces, the entire box is vacuum bagged. A pre-seamed vacuum bag 30 is used, and a continuous seal 32 is created at the top edges of the end wall and side walls. At the interface between mold sections a chemical barrier seal 34 is provided (Fig. 3 and 4A; to provide vacuum integrity of the assembled meld sections.

Referring now to Figs. 3 and 4, a vacuum cutlet 40 is connected to a vacuum source (not shown) and to the interior of the bag 30. A source 44 of uncured resin 46, such as tank 44 containing vinyl ester or polyester, is connected through bag 30 via tubing 45 and T shaped fittings 43 placed in channels 50 of cere 20. Channels 50 are connected to a distribution network either m or on the surface of cere 20.

In operation, the bag 30 is evacuated forcing uncured resin 46 through channels 50 and grooves 52 to fill the moid and the bag 30 to impregnate fiber material 22, 22a and 24. The resm is allowed to cure.

After removing the vacuum bagging materials and the connections between mold segments, the side and endwall molds are removed. After the molds are separated, they are rotated back to their horizontal position (the molded walls remain vertical) . The box is removed from the base moid.

A roof structure 51 is molded separately in one piece using the same method as tne box. The roof is molded as a 'tub' which incorporates a small portion of both the side and end wails This allows for the melding of the entire corner of the roof and creates a single horizontal seam between the box and roof . The reef may- include a vertical flange 52 which fits inside the interior surface of the box sidewalls. This flange helps align the roof to the box during assembly and allows for the installation of a mechanical fastener into the 0 sidewall .

As best shown in Figs. 4A and 4B, a typical moid section joint consists of a flange 16A tnat is normal to the mold surface extending along the entire edge. This flange provides a mating surface to which seals, indexing -,- features, and clamping mechanism may be attached. There exists a pressure differential between the mold surface (low pressure; and the back of the mold (high atmospheric pressure) . In order to maintain this pressure differential, a "system" cf seals (i.e., a chemical

90 barrier seal 34 and a vacuum seal 60 Fig. 4A; are attached to one or both flanges. The main seal or vacuum seal consists of a closed loop gasket which in the cross section shown in Fig. 4A and 4B is designated 60. A- vacuum is applied within this closed loop through vacuum port 62. If the one or both cf the active seals should

25 fail, the leak path will follow the path of least resistance and is intercepted by the vacuum source. The mam seal 60 needs to be verv compliant so that the initial seal can be provided with a relatively light clamping force. Once tne vacuum is applied and the "loop" is evacuated through vacuum port 62, the seals will be compressed by the atmospheric pressure that exists on the back side of the flange. This provides an additional benefit of requiring minimal external clamps to hold the mold segments in position as we now have available to us a clamping mechanism that provides a verv uniform clamping pressure along the entire length of the flange area. The embodiment shown as Fig. 4B can provide a satisfactory seal without the need for a chemical barrier seal . This force can oe considerable and is a product of the area of the closed loop and the atmospheric pressure (app 14.7 PSD . Some of the materials that may be used for the Active Seal include closed cell foam extrusions of Neoprene, ΞPDM, Silicone, etc.

The cores are shown in Fig. 4 with C-clamps 24 and 26 around the ends of the cores. Fig. 5 shows a cross section of the cores 20 separated by C-ciamps 26 and Fig. 8 shows a cross section of the cores 20 separated oy a hollow element 27 co-molded and integrated within the walls of the mold suitable for running utilities within the mold. Shown in Fig. 6 are two openings co-molded into the walls. The larger opening 86 is suitable for a door or larger system and/or equipment such as a mecnamcai refrigeration unit, and the smaller opening 84 is suitable for a window or smaller system or equipment

Supporting ancillary structures can oe appended tc the walls of the composite box such as the metal attach plate 94 shown m Fig. 7. In addition, hollow elements 5 92, naving endings at the surface of the walls of the composite box can be filled with a removable substance (not shown) such as clay to prevent the nollow openings from filling during the process of filling the melds.

A typical mold lay-up as shown m Fig. 9 consists of in a mold 70, a film or sheet of surfacing material 72, the fabric lay-up 74, a core material 76, a caul plate ⁿ B and a vacuum bag 80. The surfacing material 72 is placed in the mold during the composite lay-up and prior tc infusion, and is co-molded with the fabric ⁷4 and cere 76 , _r into the final composite structure.

A thermosetting resm typically bonds to the plastic sheet by chemical means (it attacks the surface of the plastic, thereby forming a good bond when the resin cures) . If the bond strength between the plastic sheet

_0A and the cured floerglass/resm laminate is not

2 J satisfactory by this method lenemical bond; alone, a fabric layer can be imbedded into the plastic sheet prior to the molding operation. This gives the resm something to lock into during the molding process, thus forming a mechanical bond as shown in Fig. 10 between the plastic 25 sheet 72 and the cured fiberglass/resin laminate 82 (m addition to any chemical bond which may also exist) .

Claims

What is Claimed is:

1 A method of forming a composite bcx having end, side, and bottom walls said method comprising- forming a Plurality of cores each having a ς peripheral surface, length and widtn dimensions extending end-to-end and side-to-side, respectively; positioning said cores end-to-end and side-by-side in respective mciα segments that define said end, side, and bottom wails and said top while

,_Λ encapsulating the cores in faoric material; assembling the moid segments to interface with one another to form a bcx, said fabric material overlapping with fabric material m adjacent mold segments;

. sealing the interface oetween tne moid segments; enclosing the assemcied molds m a hermetically sealed bag having inlets and outlets; connecting a source of uncured resin tc said inlets evacuating said molds tnrough said outlets; 2o forcing said uncured through said inlets to said outlet to fill the mold between said core and said mold to impregnate said fiber material; curing said resm to form a composite box; and 25 removing said mold segments . 2. The method of claim 1, wnerem said resm is vinyl ester

3 The method of claim 1, wherein said resm is polyester.

4. The method of claim 1, wherein sealing tne interface between the mold segments is provided by a vacuum seal .

5. A composite box structure comprising: end, side, and bottom wails, eacn cf said walls and said top including a plurality of cores having a peripnerai surface, iengtn and width dimensions, said cores being positioned end-to-end and side-by-side tc define said end, side and bottom walls; a layer of fiber material encapsulating saiα cores and bridging the adjacent edges of said end, side and bottom walls ^• and a cured resin material saturating said layer of fiber material tc form a unitary composite POX structure .

6. The composite box of claim 5, wherein said resm is polyester.

7. The composite box of claim 5, wherein said resin is vinyl ester.

8. A two piece insulated composite box structure comprising: a first structure having side and bottom walls and a second structure being a top for said first structure, each of said walls and said top including a plurality of cores having 3 peripheral surface length, ana width dimensions said cores being positioned end-to- end and side-by-side to define said top, side, and bottom walls, 5 a layer of fiber material encapsulating said cores and bridging the adjacent edges of said side and bottom walls; and a cured resm material saturating said layer of fiber material to form a unitary composite box ι_g first structure having two side wails and a bottom wail and a separate second structure top.

9. The composite DOX of Claim 8 further comprising said first structure having two end walls each including a plurality of cores having a peripheral

1 r surface, length, and width dimension, said cores being positioned end-to-end and sιde-oy-sιde to define said end walls .

10 The composite box of Claim 8 wherein said side wails have openings withm said side walls of a size

_7Q and shape suitable for accommodating a structural element .

11. The composite box of Claim 9 wherein said walls have openings withm said walls of a size and shape suitable for accommodating a structural element . __ς 12 The composite box of Claim 8 further comprising a co-molded surface layer melded to said top and side and pottom walls. 13. The composite bcx of Claim 9 further comprising a co-molded surface layer molded to said top and side and bottom walls.

14. The composite box of Claim 12 wherein said co-molded layer has enhanced UV stability and enhanced abrasion, impact, and wear resistance.

15. The composite box of Claim 14 wherein said co-molded layer is an acrylic sheet.

16. The composite box of Claim 14 wherein said co-molded layer is made of polyvmylidene fluoride.

17. The composite POX of Claim 8 further comprising means for supporting ancillary structures appendable to said composite box, within said side wails.

18. The composite box of Claim S wherein said cured resin material is a phenolic resm.

19. The composite box of Claim IC further comprising co-molded composite structural elements integrated withm the walls of such composite box.

20. The composite box of Claim 10 further comprising co-molded hollow elements integrated withm such walls, suitable for running utilities withm said hollow elements.

21. A method of forming a composite box having side and bottom walls, said method comprising: forming a plurality of cores, each having a peripheral surface, length, and widtn dimensions extending end-to-end and side-to-side, respectively; positioning said cores end-to-enα and side-oy-side in respective mold segments tnat define said side and bottom walls and said top while encapsulating the cores m fabric material; 5 assembling the mold segments to interface with one another to form a box, said fabric material overlapping with fabric material in adjacent mold segments; sealing the interface between the mold I_Q segments; enclosing the assembled molds in a hermetically sealed bag having at least one inlet and outlet; connecting a source of uncured resin to , -. said inlet; evacuating said molds through said outlet; forcing said uncured resin through said inlet to said outlet to fill tne moid between said core and said meld to impregnate said fiber material; curing said resm tc form a composite box; and

20 removing said moid segments . 22. The method of forming the composite box cf Claim 21 wherein said first structure also includes two end walls each including a plurality of cores having a peripheral surface, length, and width dimension, said

25 cores being positioned end-to-end and side-by-side to define said end walls. 23. The method of forming the composite box of

Claim 21 wherein said walls have openings withm said walls of a size and shape suitable for accommodating a structural element .

24. The method of forming the composite box of Claim 21 further comprising a co-molding a surface layer to said walls.

25. The method of forming the composite box of Claim 21 wherein said co-molded layer has enhanced UV stability and enhanced abrasion, impact, and wear resistance .

26. The method of forming the composite box of Claim 21 wherein said co-moided layer is an acrylic sheet .

27. The method of forming the composite box of Claim 21 wherein said co-molded layer is made of polyvinylidene fluoride.

28. The method of forming the composite bcx of Claim 21 further comprising appending means for supporting ancillary structures to said walls within said composite box.

29. The method of forming the composite box of Claim 21 wherein said cores are positioned in order to create an opening within said wails suitable to accommodate a structural element .

30. The method of forming the composite box of Claim 21 further comprising co-molding hclicw elements, within the walls of said composite box, having endings at the surface of saiα walls ana filling the endings of saia holiow elements with an easily removable supstance, preventing said hollow openings from filling with resin during the process of filling the molds.

31 The method of forming the composite box of Claim 21 wherein the easily removable substance is clay.

32. A method of for making insulated rail cars having side and bottom walls, said method comprising: forming a plurality of cores, each having a peripheral surface, length, and width dimensions extending end-to-end and side-to-side, respectively, positioning said cores end-to-enα and side-by-side in respective moid segments that define said side and bottom walls and said top while encapsulating tne cores in fabric material; assembling the molα segments zo interface with one another to form a box, said fabric material overlapping with fabric material m adjacent mold segments; sealing the interface between the mold segments; enclosing the assembled molds m a hermetically sealed bag having at least one inlet and outlet; connecting a source of uncured resm to said inlet; evacuating said molds through said outlet, forcing said uncured tnrougn said inlet to said outlet to fill the mold between said core and said moid to impregnate said fiber material; curing said resm to form a composite box,- and removing said mold segments. 33 A method for making truck trailer bodies having side and bottom wails, said method comprising: forming a plurality cf cores, each having a peripheral surface, length, and width dimensions extending end-to-end and side-to-side, respectively; positioning said cores end-to-end and side-by-side in respective moid segments that define said side and bottom walls and said top while encapsulating the cores m fabric material; assembling the mold segments to interface with one another to form a box, said fabric material overlapping with fabric material m adjacent mold segments; sealing the interface between the mold segments,- enclosing the assembled molds in a hermetically sealed bag having at least one inlet and outlet; connecting a source of uncured resm to said mlet; evacuating said molds through said outlet; forcing said uncured through said inlet to said outlet to fill the meld between said core and said mold tc impregnate said fiber material; curing said resin to form a composite box; 3 and removing said moid segments. 34. A method for making modular housing having side and bottom walls, said method comprising: forming a plurality of cores, each having T_Q a peripheral surface, length, and width dimensions extending end-to-end and side-to-side, respectively; positioning said cores end-to-end and side-by-side in respective mold segments that define said side and bottom walls and said top while encapsulating

15 the cores in fabric material .- assembling the mold segments to interface with one another to form a bcx, said fabric material overlapping with fabric material in adjacent mold segments;

20 sealing the interface between the mold segments; enclosing the assembled molds in a hermetically sealed bag having at least one inlet and outlet;

25 connecting a source of uncured resin to said inlet; evacuating said molds through said outlet; forcing said uncured through said mlet to sa_id outlet to fill the moid between said core and said mold _to impregnate said fiber material^; curing said resin to form a composite box; and removing said moid segments.