CA2105983A1

CA2105983A1 - Composite structural element and process for making same

Info

Publication number: CA2105983A1
Application number: CA002105983A
Authority: CA
Inventors: Hartley Sandt
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-03-13
Filing date: 1991-03-13
Publication date: 1992-09-14
Also published as: EP0589872A4; AU658140B2; JPH06506406A; EP0589872A1; AU7555991A

Abstract

An elongated structural element includes an external tubular casing (11) with the hollow interior space filled with a plastic binder (12) containing a plurality of elongated parallel continuous strands of fiber reinforcement material (13) extending lengthwise of the element. A method for preparing such an element is provided by filling a preformed tubular casing (11) with a plastic binder (12) in liquid form in which is dispersed the fiber reinforcement material (13) and allowing the plastic binder to solidify. The element may be initially shaped prior to solidification or reheated into another shape such as a helical coil or spring. An internal casing (29) can also be used where the fiber reinforcement strands (13) are between the external and internal casings (11) and (29).

Description

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COMPOSIl~ STRUCTURAL E:LEMENT AND

BACKGROUND o~ r~Nr~ON
Structural elements such as rods, tubes, and beams are normally made by casting, extruding, or rolling techniques to produce plastic or metal tubing, sheets, rods, beams, and the like. These structural elements normally comprise a single material which is chosen for its combination of physical properties, e.g., strength and weight, as well as corrosion resistance, color, and texture. Plastic molding and extrusion procedures have provided the possibility of preparing plastic structural elements with selected combinations of physical properties, chemical properties, color, texture, etc. Fiber reinforcement of plastic materials has provided much higher .
physical s~rength properties than the plastic material alone could offer. In general, these fiber reinforced materials arë
made by extruding through a die a plastic melt having continu-ous strands of fiber distributed therein The extrudate is then solidified in the form of a continuous rod, beam, or strand and can be cut into whatever length is desired for use.
The disadvantages of the prior art procedures are (1) that the extrudate can not be made into a curved or non-linear , article, and (~) the surface properties at the;extrudate cannot be changed from that inherent in the extruded plastic.
It i9 an object of this invention to provide a novel structural element of fiber reinforced plastic material. It is another object of this invention to provide processes for manufacturing such structural elements. Still other objects will be apparent from the more detailed description which follows.
BRIEF SUMMARY OF TXE INVENTION
This invention relates to an alongated solid or tubular structural element having a subs~antially identical cross ~
section over its entire length, the element having a solid ~-core of thermoplastic or thermosetting re~in material em~
bedded in which is a plurality of elongated continuou~ strands ~ -of lengthwise fiber reinforce~ent material, preferably in SUBSTITUTE SHEET ~
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substantially parallel array, and a continuous ~asing around the core.
This invention also relates to a process for preparing an elongated structural element comprising:
(1) preparing a hollow tubular solid casing being an integral part of the structural element;
(2) filling the interior of the casing with a polymer material in liquid form; and distributing throughout said polymer material a plurality of elongated continuous strands of fiber reinforcement material substantially parallel to each other and extending lengthwise of the casing; and (3) allowing the polymer material to solidify with the strands of fiber reinforcement material embedded therein.
The process and element may include a tubular shape employing an external casing and an internal casing with the space therebetween being filled with the polymer material and fiber reinforcement materials. The element may also be shaped before solidification, or thereafter by reheating, into a helical coil or spring, or other shape like an I-beam or an H beam or any irregular shape. Sometimes this requires the displacement and~or removal of some of the plastic mater~
ial.
BRIE~ DESCRIPTION OF THE DRAWINGS
The invention as to its organization and method of operation, together with further objects and advantages thereo, is best understood by reference to the following description taken in connection with the accompanying drawings in which:
FIG. 1 is a side elevational view of one embodiment of the structural element of this invention;
FIG. 2 is an end elevational view of the structural element shown in FIG. l;
FIG. 3 is an end elevational view of a second embodi- ~ ;
ment of the structural element of this invention;
FIG. 4 is a~ end elevational view of a third embodim~nt of the structural element o~ this in~ention;

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W092/16347 ~ ,3 Pcr/us9l/01636 FIG. 5 is an end elevational view of a fourth embodi-ment of the structural element of this invention;
FIG. 6 is an illustration of one type of article, e.y., a coil spring, that can be made from the structural element of this invention;
~ IG. 7 is an illustration of one embodimenk of the process of this invention;
FIG. 8 is an illustration of a second ~imbodiment of the process of this invention;
FIG. 9 is an illustration of a third embodiment of the process of this invention;
FIG. 10 is an illustration of the structural element of this invention with end caps attached;
PIG. 11 is an end elevational view of a hollow struc-tural element of this invention;
FIG. 12 is an illustration of a fourth embodiment of this invention;
FIG. 13 is an illustration of a fifth embodiment of this invention; and ~-FIG. 14 is an illustration of a process for c~anging a stxuctural element having a round cross section to one ;~
having a non-round cross section.
DETAILED DESCRIPTION OF THE INVENTION
, . , This invention relates to articles of manufacture which are shown in FIGS. 1-6, 10, and 11 of the attached drawings, and to processes for preparing such articles which are shown in FIGS. 7-9, and 12-14. ~
In FIGS. 1-6, 10 and 11 there are depicted several ~``
types of structural elements according to this invention. In FIGS. 1-2 there is shown a cylindrical rod element having three components; namely, an external casing 11, an internal `-binder 12, and strands 13 of fiber reinforcement material.
These are all joined together into a slngle~unitary structure which has an indefinite length and a substantially similar cross section at any place along that length. ~;
External casing 11 is a flexible, semiflexible, or rigid pipe or tubing having whatever properties are important ~ ;
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for the eventual use of the structural element. If corrosion resistance, abrasion resistance, or weather resistance is important, casing 11 must provide that property; and so on for other property requirements~ Generall~, casing 11 should be a flexible or semiflexible thermoplastic material which is compatible with binder 12 and does not react chem- ;
ically therewith. In other embodiments casing 11 may be a metallic tube, an animal or human vein, intestine, or the like. Preferably there is no bond between the two, although in certain embodiments binder 12 and casing 11 may be bonded to each other. Typical materials for casing 11 include poly-olefins, poly~inyls, polyesters, polyacetals, polyacrylics, polyamides, polyfluorocarbons, polycarbonates, and other plastics of similar properties, aluminum, human or animal tissue, and the like.
The internal space in casing 11 is filled with binder 12 and fiber reinforcement 13. ~inder 12 must be capable of tightly adhering to strands 13. Preferably, binder 12 should be available in liquid form for ease in manufacturing tAe structural element of this invention, and capable of being transformed into solid form at ambient conditions for use as binder 12 in the structural element in ordinary use. Binder 12 may be a thermoplastic or a thermosetting material each of which exists in both liquid and solid forms. The thermoplastic material~ normally change from liquid to solid and from solid ~ -to liquid by temperature changes. Thermosetting materials normally involve two or more starting components which are mixed together to produce a liquid which is hardened by chemical reaction between the component and cannot later be liquefied. Typical thermoplastic~ include polyolefins, poly- l -esters, polyvinyls, polyacetals, polyacrylics, polyamides, polyfluorocarbons, polycarbonates, and the like. Typical ~hermosetting binders in~lude phenol~formaldehyde resins, melamlne resins, epoxy resins, urea-formaldehyde resins, polyesters, and the like.
The fi~er reinforcement material 13 is a plurali~y of -strands of fiber or fLlament that are distributed throughout 1 ` -SlJB~TITUTE SH~E~ , ~

W092/~6~7 2 ~ 8 ,3 PCT/US91/01636 .~ , the binder and are in substantially parallel arrangement running lengthwise of the structural element. The strands may be in a linear arrangement or in a sinuous or helical arrangement preferably mutually parallel to each other, although there may be embodiments where strands 13 are in any desired nonparallel arrangement. Ideally, the strands 13 would be separated from each other and equally distributed throughout all of the binder 12. From a practical point o~
view this may not be achieved, but preferably, the strands are extended lengthwise throughout the structural element and distributed as evenly as possible in the binder. Each strand 13 may be a single filament or a plurality of filaments twisted together, or may be a single fiber or a plurality of fibers twisted into a thread; or may be any other combination of fibers, filaments, threads, yarns or the like that are relatively small in diameter and relatively long and contin- ~
uous in length. Tubular filaments, threads, yarns and the ;
like are also useful as strands 13. The word "strand" herein is meant to be generic and to include all of the above con-figurations. The material of the strands may be organic or inorganic. The organic strands include materials such as cotton, wool, bagassee, hemp, polyamide, polyacrylonitrile, polyester~ rayon and the like. Inorganic strands include ;
materials such as glass, steel, copper, aluminum, titanium, graphite, and the like.
In order to assure good adhesion between the binder 12 ~ ;
and the strands 13, certain promoters or agents may be em-ployed to enhance the bonds between binder 12 and strands 13.
In FIGS. 3-5 there are shown other structural elements -of other cross sectional shapes, e.g., square (FIG. 3), ohlong (FIG. 4), and triangular ~FIG. 5), which may be solid as show~
or tubular with an internal open space, as shown in FIG. 11. ~
Any of these shapes may be prepared in ~inite lengths and~end- ~ ' capped, as shown in FIG. 10, if it is desirable to protect the open ends fxom the surrounding medium in which the s~ructural element is used. Still other shapes are within the scope of this invention since any geometric design like an H-beam, an - - ~
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The structural element Df this invention can be sawed, drilled, tapped, twisted, bent, and otherwise used to form useful articles of manufacture. For example, the element may be coiled into a helix to form a coil spring as shown in FIG.
6. If the structural element is made with a thermoplastic binder 12, a preformed straight length of element may be heated, and formed into another shape, e.g., coiled to form the spring of FIG. 6, and cooled to solidify the binder 12, and thereby produce a stable shape. Alternatively, the element may employ a thermoplastic molten binder 12 in casing and the element may be coiled into a spring or formed into another shape before the binder 12 is allowed to sol-idify. If the binder 12 is a thermosetting material, it must b~ formed into the final desired shape, e.g., coiled into the spring of FIG. 6, before binder 12 has had time to set to a solid. There are a multitude of applications for the struc-tural element of this invention including ropes, rpds, struc-tural beams for chemical processing equipment, articles used under sea water, strands or bones used in human surgical pro-cedures, and the like.
In the process of this invention as shown in FIGS 7-9 and 12-14 a plug 17 is moved through the internal hollow of casing 11 with binder 12 and fiber reinforcement strands 13 filling the hollow behind the plug 17 as it moves along. In the process depicted in FIG. 7, a length of casing 11 is fitted with a feed funnel 16 into which is fed a continuous length of a plurality of strands 13 and at the same time is ~ed liquid or molten binder 12 from a supply reservoir 15.
Plug 17 is slidable within casing 11 and has an eye 18 to which the hank of strands 13 is attached. A pull cable 19 is attached to the front;of plug 17 to pull plug 17 through casing`ll by windup drum 20. As plug 17 is moved downward toward drum 20, binder 12 fills-the interior hollow of casing 11 and~the individual strands in thè hank disperse themseives 6 throughout the entire cross section of the interior hollow of casing 11 to eventually approach the distribution shown in ,. ~
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YIGS. 2-S. It can be appreciated that casing 11 and plug 17 may take any shape, such as those in FIGS, 2-5. Furthermore, hollow shapes as shown in FIG. 11 may be made b~ making plug 17 into an annular object and sliding between an inn~r casing 29 and an outer casing 11 (see FXG. 11). If pre~erred, inner ; casing 29 may be supported by an internal mandrel (not shown) to support inner casing against collapse until binder 12-hardens.
In FIG. 8 the same general arrangement as that of FIG.
7 is shown except that instead of a windup drum 20 and a cable 19 to move plug 17 there is a vacuum pump 21 to produce a lower pressure in the space 25 ahead of plug 17 causing plug 17 to move toward vacuum pump 21.
-- In FIG. 9 there also is the same general arrangement .~.. ~ .
of casing 11, plug 17 and strands 13, attached to eye 18. In this instance the force to move plug 17 through casing 11 is provided by the pressure on binder 12. Inlet pipe 22 feeds liquid binder 12 to pump 23 which pumps binder into pressure ;p vessel 27 which has an outlet into casing 11. Roll 14 of `~
fiber reinfor~ement strands 13 is mounted inside vessel 27 in a pressurized space 26 designed to offset the pressure on binder 12 emitted from pump 23. Binder 13 is supplied to ;~
space 24 under pressure and this bears against plug 17 causing it to move to the right and fill up casing 11. ;~
In all of the embodiments of FIGS. 7, 8, and 9 the -strandsi will be substantially linear and parallel to each other and to the longitudinal axis of casing 11 if plu~ 17 is -simply pulled through casing 11. If plug 11 is rotated about its axis of travel as it is pulled through casing 11, strands 13 can be made into a sinuous or helical orientation while the individual strands 13 remain generally parallel with each other. ~;
It is contemplated that in certain corrosive conditions there may be a need to completely insulate binder 12 and ~-strands 13 from the surrounding corrosive medium. In such instances there may ~e end caps 28 sealed onto any cut ends of ~
the structural element so as to leave only the material of the ~;
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casing e~posed as shown in FIG. 10. End cap 28 can be heat sealed or otherwise attached to casing 11 so as to be leak proof and therefore completely corrosion-resistant.
It is an important feature of this invention to pro-vide elements in which the fiber reinforcing component is a continuous strand and not a plurality of chopped fi~ers. The continuous strands emplo~ed in this invention provide a greatly improved modulus of elasticity as compared to that of the strand containing short lengths of reinforcing ~ibers or filaments. It is for this reason that an excellent coil spring can ~e made from the structural element of this inven-tion, while such a coil spring from the prior art would not be operableO
FIGS. 12-14 show alternate embodiments of the process of making the structural elements of ~IGS. 2-5 and 11. In FIG. 12 there is illustrated a procedure to make hollow tubular structural elements as shown in FIG. 11. Outer casing 11 is attached to funnel 16 by clamp 30. Inner casing 2~ with a plug at its lower or forward end is introduced into funnel 16 along with plug 33 into which the forward ends of fiber strands 13 have been embedded by previously molding plug 33 with strands 13 embedded therein. Plug 33, lnner casing 29, and plug 34 are moved downwardly in the direction of arrow 35 while outer casing 11 and funnel 16 remain stationary and filled with liquid binder 12. As inner casing 29, plug 34, plug 33 and strands 13 move downwardly the annular space between casing~ 11 and 29 fills with binder 12 and fiber strands 13 are dispersed throughout. Plug 34 is needed to prevent binder 12 from leaking into the interior hollow of internal casing 29. Plug 34 may be independent of plug 33 or attached thereto in different embodiments of this process. ~;-Centering guides 31 and 32 keep inner casing 29 centered in casing ll as casing 29 advances. Guides 31 and 32 are spider -legs. Guide 31 is attached to funnel 16 with its distal ends rubbing against inner casing 29 as it moves forward. Guides 32 are attached to casing 29 or its plug 34 with its distal ends rubbing against outer casing 11 as inner casing 29 moves ;
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forward. Preferably, guides 31 and 32 are spring biased to bear against casings 29 and 11, respectively. Furthermore, guides 31 preferably are pivotable so as to be no obstacle to the initial entrance of plug 33 into and through funnel 16 to the top of outer casing 11. When the desired length of 7 tubular structural element 11 has been made, the process can be repeated by starting again with a new length of outer casing 11.
In FIG. 13 there is shown an alternative to the process of FIG. 9 for making the structural element by 1uid pressure causing the movement of the plug to which fiber strands 13 are attached. A plurality of fiber strands 13 are introduced over a feed roller 37 in header box 38 and downward through funnel 16 into outer casing 11 which is temporarily attached to ;
funnel 16 by clamp 20. The forward ends of strands 13 are embedded in plug 36. Casing 11 rests on a base plate 39 which will serve as a stop to plug 36 which moves downward in the process. Binder 12 is kept in container 40 which is con-nected by passageway 43 to funnel feeder 16 permitting the level of binder 12 to be the same in funnel 16 and in container ~-~
40. Air pressure is maintained in tank 44 which is connected by lines 45, 46 and 47 to both of header box 38 and binder con~
tainer 40 to equalize the pressure on both surfaces of liquid ;
binder 12. The pressure is transmitted to plug 36 causing it to move forward in casing 11 until it reaches base plate 39.
Lid 41 is provided for adding binder 12 to container 40, and lid 42 is provided for replacing a supply of strands 13 over roller 37 in head box 38.
In FIG. 14 there is shown a procedure for transforming an element of circular cross section, as in FIG. 2, to an ele~
ment of noncircular cross section, as in FIGS. 3-5, when outer casing 11 is flexible and capable of being bent and formed -~into different shapes. The problem in such modifications is ;~that~the cross sectional area and-circumference of the begin- ~`
ning element, e.g., circular, may not be the same as those of the final element, e.g., a rectangle. The limiting factor normally is that the circumference or perimeter of the ~, ~ . ~
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? 10 ~ ~ 8 ~ PCT/US91/01636_ beginning element and final element must be the same i~ the outer casing 11 is to remain smosth, continuous, and un-wrinkled. Generally this is accomplished by ~ixing the perimeter dimensions of the desired final element and ad-justing the process of making the beginning element to ~it those dimensions. It is basic geometry that for any given cross sectional area, a circle will have the smallest perim-eter length of any shape that encloses that area. Accord-ingly, as an example, if the final element is to be a rec-tangular beam having dimensions of one inch by two inches, a perimeter length of six inches and a cross sectional area o~
two square inches; a circle of the same perimeter length o~ -six inches will have a diameter of 1.91 inches and a cross sectional area of 2.865 square inches. Therefore, an element of circular cross section (2.865 square inches) must be squeezed to a cross sectional area of 2.0 square inches to be reshaped into a rectangular cross section of one inch by two inches. Referring to FIG. 14, the above means that a circular cross section element 50 with a cross sectional area of 2.865 square inches and with binder 12 in a liquid form is squeezed by rollers 49 turning in the direction of arrows 52 as the '~
element moves past an internal solid of about 0.865 square inch cross section to reduce the cross sectional area to 2.0 square inches.
Rollers 49 with or without the assistance of other '' forming devices can then shape element 5I into a rectangular cross section of one inch by two inches before binder 12 sol-idifies. It may be seen that this procedure may be applied to the end of the procedures of FIGS. 7-9 and 13 or before '~
binder 12 solidifies, or alternatively, a rigid element may '-be heated to liquefy binder 12 (if it is thermoplastic) and '~ ' then subjected to the reshaping procedure of FIG. 14. While the beginning'element may have anv shapej it preferably'is circular'because it-is easier to make'and it-automatically pxovides a better dispersion of strands 13 than any other' shape. ' - :'- ' v ~ v ~ v v ~ y v~
-` :- P(~T/US 91/01636 As seen hereinabove, the binder 12 may be thermo-plastic in certain embodiments and thernos~tting in other embodiments. In any event the binder needs to be a plastic or polymer material which is capable of tightly adhering to strands 13 and not reacting chemically with casing 11.
While the invention has been described with respect to certain specific embodiments, it will be appreciated that , many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention.
I~ is intended, therefore, by the appended claims to cover all such modifications and changes as fall within the txue spirit and scope of the invention.
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Claims

1. A process for preparing a non-extruded elongated struc-tural element characterized by the steps of:
(A) preparing a hollow external solid walled casing of a tubular material being an integral part of the structural element;
(B) filling the interior of the external casing with a polymer binder material in liquid form and simultaneously distributing generally uniformly throughout the polymer binder material a plurality of individual elongated contin-uous strands of fiber reinforcement material extending sub-stantially parallel and lengthwise of the external casing;
and (C) solidifying the polymer binder material with the strands of fiber reinforcement material embedded therein.

2. The process of Claim 1 further characterized by the steps of:
(D) preparing a hollow internal solid walled casing of a tubular material being an integral part of the structural element;
(E) positioning the internal casing generally concen-trically within the external casing to provide a space there-between; and said step (B) fills the space between said ex-ternal and internal casings and the reinforcement material extends lengthwise of both of the casings thereby forming a hollow elongated structural element.

3. The process of Claim 1 wherein said step (B) includes the step of:
(D) moving a plug through the length of the external casing to cause the polymer binder material and the fiber re-inforcement material to be fed into the casing behind the moving plug.

4. The process of Claim 3 further characterized by the step of (E) connecting a hank of the fiber reinforcement material to the plug so that the fiber reinforcement material is pulled behind the plug as it moves through the casing.

5. The process of Claim 3 further characterized by the step of:
(E) pressurizing the polymer binder material inside the casing behind the plug for moving the plug through the casing.

6. The process of Claim 3 further characterized by the step of:
(E) moving the plug by mechanical means.

7. The process of Claim 3 further characterized by the step of:
(E) moving the plug by the influence of unequal pressures on the plug resulting from maintaining a vacuum in the external casing.

8. The process of Claim 1 wherein step (C) is accomplished while main-taining the external casing containing the polymer material and the fiber reinforcement in the shape of a helical coil.

9. The process of Claim 1 further characterized by the steps of:
(D) reheating the solidified structural element;
(E) forming it into a desired shape; and (F) allowing the polymer binder material to resolidify with the element in the desired shape.

10. The process of Claim l wherein step (B) includes the steps of:
(D) moving a plug through the length of the external casing while admitting into the casing behind the plug the polymer binder material, the plug having embedded therein one end of each of the fiber reinforce-ment strands with the other end of each strand free to trail behind the plug as it moves.

11. The process of Claim 1 which is characterized by the following addi-tional step accomplished after step (B) and before step (C);
(D) passing the filled casing while the polymer binder material is liquid through a shape forming means to cause the element to assume a noncircular cross sectional shape.

12. The process of Claim 1 which is characterized by the steps of:
(D) treating the solidified element to reliquefy the polymer binder material;
(E) reshaping the element while the polymer binder material is liquid to produce a noncircular shape; and (F) resolidifying the polymer binder material while maintaining the element in the noncircular shape.

13. A non-extruded rigid structural element comprising an elongated solid member, said member having a solid rigid core of solidified polymer material, a plurality of elongated substantially continuous and individual strands of fiber reinforcement material extending lengthwise of and em-bedded in and substantially uniformly throughout and filling said core, and a continuous elongated solid walled casing around said core of polymer material.

14. The element of Claim 13 wherein said strands axe disposed within said core substantially parallel to each other.

15. The element of Claim 13 wherein said polymer material is a thermo-plastic material.

16. The element of Claim 15 wherein said element after solidification of said core is adapted to be reheated and formed into another shape and thereafter solidified to such other shape.

17. The element of Claim 13 wherein said solid core has an elongated hollow extending generally centrally thereof and generally parallel to said elongated casing.

18. The element of Claim 17 further comprising an elongated internal casing extending substantially throughout said elongated hollow with said core being contained between said casings.

19. The element of Claim 13 wherein said casing is selected from the group consisting of a corrosion resistant material human tissue, animal tissue, a metal and a thermoplastic material.

20. The element of Claim 13 wherein said fiber reinforcement material is selected from the group consisting of fiberglass, carbon, graphite, bagasse, cotton, hemp, rayon, polyester, nylon, polyacrylonitrile, steel, copper, aluminum, titanium, and magnesium.