FIBER-REINFORCED THERMOPLASTIC COMPOSITE CROS S PULL TAPE LAYING
BACKGROUND OF THE INVENTION
This invention relates to the production of articles from fiber-reinforced materials, and, more particularly, to the production of hollow pipes from fiber- reinforced thermoplastic resins.
Plastic-resin pipe is used in a wide variety of applications. In some such applications, the plastic-resin pipe has sufficient strength. In other applications, the plastic-resin material cannot meet the strength or modulus requirements, and it is necessary to reinforce the plastic of the pipe with fibers such as carbon or glass fibers.
One such application requiring the use of fiber-reinforced plastic pipe is protective downhole pipe liner used in oil production. The interior surface of the steel drill pipe used in the drilling and pumping operations is susceptible to accelerated corrosion in the aggressive downhole environment. The interior of the steel drill pipe may be protected from the corrosive environment by a fiber- reinforced plastic pipe liner. The pipe liner must retain its strength at the moderately elevated temperatures experienced at great depths below the earth's surface. Such plastic liner pipe is now made by filament winding glass or carbon fiber tows, which are impregnated with a thermosetting liquid resin system, onto a mandrel at various angles of inclination to the long axis of the mandrel. The wrapped composite material is cured to impart strength at the required service temperature. With this processing, it is not possible to position fibers extending parallel to the long axis of the mandrel, resulting in limited strength in that direction. The products made by this approach have less than the desired strength at elevated temperature, and also may be subject to impact damage, brittle fracture, and fatigue failure. The fabrication operation is labor intensive and results in relatively expensive reinforced plastic pipe.
The high cost of manufacturing hollow structures of fiber-reinforced plastic-resin materials and the resulting less-than-optimal properties have inhibited their use -in a number of applications where they are suited, and increased their price in the others. There is a need for an approach for producing such hollow structures which achieves technically satisfactory results and also is economical. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a method and an apparatus for producing a continuous length of hollow pipe made from fiber-reinforced thermoplastic resin, as well as pipe made by the approach. The thermoplastic resin may be of any operable type, such as low-temperature polypropylene or high-temperature polyetherefher-ketone, because the production machinery is suitable for use over the wide range of temperatures required to work with such resins. The pipe is made in a continuous long length and cut to the required shorter lengths, rather than made in discrete lengths as with the filament winding approach or where a bladder compaction technique is used. Consequently, the pipe made by this approach is cost competitive with existing manufacturing processes. The pipe may be made in a wide range of sizes and cross-sectional shapes. The pipe is made with strengthening fibers extending both parallel to the axis of the pipe and wound spirally around the pipe, providing excellent static and fatigue mechanical properties. The pipe is resistant to a wide variety of corrosive agents.
The present invention thus provides a method for producing a fiber- reinforced thermoplastic resin hollow pipe from a base fiber/matrix material comprising fibers embedded in a thermoplastic resin. The method includes depositing the base fiber/matrix material onto an elongated mandrel parallel to a direction of elongation of the mandrel, moving the deposited base fiber/matrix material parallel to the direction of elongation of the mandrel, and consolidating the base fiber/matrix material onto the mandrel using a combination of heat and radially inwardly directed pressure. The base fiber/matrix material preferably includes unidirectional fibers, which are deposited so as to lie parallel to a longitudinal axis of the mandrel and thence to the pipe. The method further
includes providing an overwrap fiber/matrix material comprising fibers embedded in a thermoplastic resin, thereafter overwrapping the overwrap fiber/matrix material" .over the consolidated base fiber/matrix material, and thereafter consolidating the overwrap fiber/matrix material onto the base fiber/matrix material using a combination of heat and radially inwardly directed pressure.
The overwrap fiber/matrix material may be the same as or different than the base fiber/matrix material. The overwrap fiber/matrix material is applied by spirally wrapping with the fibers lying at an angle to the longitudinal axis of the mandrel. Desirably, the overwrap fiber/matrix material is applied in balanced pairs of layers, with one layer of the pair wrapped in one (e.g., clockwise) direction around the pipe, and the other layer of the pair wrapped in the opposite (e.g., counter-clockwise) direction around the pipe.
The present invention also provides apparatus operable for the continuous production of the pipe. The machinery includes a heated, elongated mandrel having a diameter of about a desired inner diameter of the hollow pipe, and a pipe support and drive operable to move the hollow pipe material parallel to the direction of elongation of the mandrel. A laydown head is oriented to deposit a base fiber/matrix material parallel to the mandrel and overlying the mandrel, at a first station. The laydown head includes a heated consolidation die having an inner diameter of about the same diameter as a desired outer diameter of a consolidated layer of the base fiber/matrix material. The production apparatus also includes at least one overwrap fiber/matrix material winding head oriented to deposit an overwrap fiber/matrix material at an angle to the mandrel and overlying the mandrel, at a second station, and a consolidation head overlying the mandrel at a third station. There are preferably at least two of the overwrap fiber/matrix winding heads, provided in pairs that wrap layers in opposite directions around the consolidated base fiber/matrix material. Each of the fiber winding heads preferably has multiple material sources, to increase the permissible winding speed. The base fiber/matrix material and the overwrap fiber/matrix material each utilize long, substantially continuous fibers embedded in a thermoplastic resin material. The fiber/matrix material is preferably provided in a pre-embedded form with the fibers embedded in a pliable precursor of the final matrix material.
Examples of commercially available forms of such a material are prepreg tapes and pre-impregnated tows. The matrix may be any thermoplastic resin material, even those which are operable at elevated temperatures. In the past, it has been difficult to use thermoplastic resins having high-temperature capability in pipes because the available bladder materials are not suitable for high-temperature consolidation and curing procedures. The present apparatus does not utilize non- metallic materials in contact with the heated composite material, and therefore allows the use of high-temperature materials in the fabrication of the pipe.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a pipe according to the invention, with one end shown in cross section;
Figure 2 is a schematic depiction of a longitudinally exploded view of the pipe of Figure 1, showing the various layers;
Figure 3 is a block diagram for a preferred method for making the pipe; Figure 4 is a side elevational view of a preferred apparatus for producing pipe;
Figure 5 is an enlarged detail of a portion of Figure 4, illustrating the deposition and consolidation of the base layer;
Figure 6 is a schematic sectional view of the mandrel and base layer, taken along line 6-6 of Figure 5 but with the consolidation die absent for clarity of illustration;
Figure 7 is a schematic elevational view of one of the winding heads, taken along line 7-7 of Figure 4; and
Figure 8 is a schematic view of the pipe-moving mechanism.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 depicts a hollow pipe 20 made by the approach of the invention. The illustrated pipe 20 is cylindrical with a circular cross section, the preferred form. However, the pipe may be irregularly curved (e.g., elliptical) or prismatic (e.g., square, hexagonal) in cross section. The shape of the pipe is determined by the shape of the mandrel to be discussed subsequently, which can have any operable shape as required.
The pipe 20 is formed of multiple overlying layers of a fiber/matrix composite material, as also shown in the longitudinally exploded view of the pipe 20 in Figure 2. A base layer 22 is adjacent to an inner wall 24 of the hollow pipe 20. One or more overwrap layers 26 overlie the base layer 22. In the embodiment of Figures 1-2, there are four overwrap layers 26a, 26b, 26c, and 26d. There could be greater or lesser numbers of such overwrap layers. Preferably, the overwrap layers are provided in pairs, so that the number of overwrap layers 26 is even (as distinct from "odd").
The base layer 22 and the overwrap layers 26 are both made of the type of fiber/matrix composite material to be discussed subsequently in greater detail. Preferably, the composite material is made with unidirectional fibers. In such a unidirectional fiber composite material, the fibers are all arranged to be generally parallel to each other, as distinct from a woven or nonwoven cloth wherein the fibers are at a variety of angles. The unidirectional fiber material has excellent mechanical properties and is relatively inexpensive. However, non-unidirectional fiber material may be used as required in the layers 22 and 26.
The fibers in the various layers 22 and 26 are preferably unidirectional within each layer, but they are not of the same orientations in all of the various layers, as shown in Figure 2, which for clarity of illustration depicts the layers separately as though they could be removed from contact with each other. In the base layer 22, the fibers 22' are preferably all oriented so as to be substantially parallel to a longitudinal axis 28 of the pipe 20. In the overwrap layers 26, the fibers 26' are oriented at angles to the longitudinal axis 28, as shown. Preferably, the fiber angles are matched in a pairwise but complementary fashion. For example, the fibers 26a' in overwrap layer 26a are oriented at an angle +A to the
longitudinal axis 28, and the fibers 26b' in overwrap layer 26b are oriented at an angle -A; the fibers 26c' in overwrap layer 26c are oriented at an angle +B to the longitudinal axis 28, and the fibers 26d' in overwrap layer 26d are oriented at an angle -B. Angles A and B are preferably the same value, such as, for example, 45 degrees, but they may be different values. The use of matched but complementary orientations in pairs of layers (e.g., 26a and 26b; 26c and 26d) ensures symmetry in the structure to achieve the best strength properties for general purpose applications. However, the preferred fabrication apparatus provides flexibility in the selection of the wrap angles A and B, for special purpose applications. Figure 3 depicts the preferred approach for practicing the present invention. A fabrication apparatus 60 is provided, numeral 40. The preferred form of the fabrication apparatus 60 is illustrated in Figures 4-8. The apparatus 60 includes an elongated mandrel 62 whose exterior shape defines the shape and size of the inner wall 24. The mandrel 62 is preferably circular, but may instead be prismatic or curved, in cross section. The mandrel 62 is supported on supports 64 to hold it in a stationary position. The mandrel is heated by any operable approach, preferably electrical resistance heaters inside the mandrel.
As shown in Figure 4, a laydown head 66 is positioned at a first position, termed a "first station" in the art, along the length of the apparatus 60. The laydown head 66, illustrated in greater detail in Figure 5, includes a consolidation die 68 having a central opening surrounding the mandrel 62. The consolidation die 68 is heated by any operable approach, but preferably by electrical resistance heaters inside the consolidation die. Adjacent to the consolidation die 68 is at least one, and preferably several, sources 72 of the base fiber/matrix composite material 70. The sources are preferably spools with the pliable base fiber/matrix composite material 70 wrapped thereon, and from which the base fiber/matrix composite material is continuously pulled during production operations.
The base fiber/matrix composite material 70 is pulled into the bite of the consolidation die 68 and thence guided to overlie the mandrel 62, as the pipe under fabrication is pulled parallel to the direction of elongation of the mandrel by a mechanism to be discussed subsequently. Optionally but preferably, a heater 73 heats the base fiber/matrix composite material as it is guided into the bite of the consolidation die 68. When the base fiber/matrix composite material 70 is laid
down onto the surface of the mandrel 62 in this manner, there initially are spaces and voids between the adjacent regions of the material. The opening of the consolidation die 68 is therefore sized so that it compresses the laid-down material 70 radially inwardly with the simultaneous application of heat, to compress the material and at least partially remove the spaces and voids that would otherwise be present. This consolidation need not be, and typically is not, a complete consolidation, inasmuch as there is further consolidation at a later station of the apparatus 60.
To achieve a uniform arrangement of the base fiber/matrix composite material 70 around the periphery of the mandrel 62, and thence around the circumference of the finished pipe 20, there are preferably multiple sources 72 of the base composite material. In this case, there are six sources of the base composite material, and accordingly six separate feeds of the base composite material into the bite of the consolidation die 68, as seen in the view of Figure 6. The apparatus 60 includes at least one overwrap fiber/matrix material winding head 74, at a second station along the length of the apparatus, to wrap the layers 26 of the overwrap fiber/matrix composite material around the previously deposited and consolidated base fiber/matrix composite material 70. In Figure 4, there are four such overwrap fiber/matrix material winding heads 74a, 74b, 74c, and 74d, respectively corresponding to the four overwrap layers 26a, 26b, 26c, and 26d. Each of the overwrap fiber/matrix material winding heads 74 includes a source 76 of the overwrap fiber/matrix material 78, and a guide 80. The guide 80 directs the material 78 from the source 76 onto the mandrel to overlie the previously deposited and consolidated base layer 22. The mandrel is heated and the material 78 is under tension, so that there is some consolidation during the winding operation.
The wrapping may be accomplished with a single such source 76. More preferably, multiple sources 76 are provided, as illustrated in Figure 7. The use of multiple sources 76 speeds the winding operation, and also makes the wrapped layers more uniform because the winding tension in the material 78 is distributed uniformly around the periphery of the mandrel 62 so that the mandrel inside the pipe does not bend longitudinally with resulting deformation of the pipe during fabrication. Thus, each individual layer 26 may include multiple plies (i.e.,
sublayers) of the overwrap fiber/matrix material 78, but the plies within a layer all have the fibers similarly oriented. The sources 76 are mounted to a frame that rotates about the mandrel 62 in a winding direction 82, which in Figure 7 is illustrated as counter-clockwise. The winding heads 74 are operated in a paired fashion to correspond to the pairing of the layers 26. That is, one of winding heads 74a and 74b rotates in the clockwise direction about the mandrel, and the other rotates in the counterclockwise direction about the mandrel. This opposite rotational pairing results in the +A and -A orientations of the fibers in the respective layers 26a and 26b. Other pairs of winding heads, such as heads 74c and 74d, operate in a similar fashion and may be rotated to achieve the same +A and -A orientations or different +B and -B orientations.
Even though the material is heated and consolidated during lay-down and the first and second stations, the as-wound layers of overwrap fiber/matrix material and the underlying layer of base fiber/matrix material have spaces and voids therein. A consolidation head 84 is positioned at a third station along the length of the apparatus 60. The consolidation head 84 is heated, preferably by electrical heaters inside the consolidation head. The consolidation head 84 compresses the as-wound layers of the overwrap fiber/matrix material radially inwardly, preferably while simultaneously heating them. The consolidation head 84 is illustrated as a pair of counter-rotating consolidation rollers 86 having circumferential ly grooved outer peripheries of a size and shape such that the wrapped material is compressed inwardly to remove the spaces and voids and achieve complete consolidation of both the base composite material and the overwrap composite material. Alternatively or additionally, the consolidation head 84 may comprise a heated die 87 similar to the consolidation die 68. The pipe 20 is drawn through the heated die 87 to precisely define the outside size and diameter of the pipe, and also to produce a smooth outer surface.
A pipe drive 88 is provided to move the pipe under fabrication longitudinally parallel to the longitudinal axis 28. In a preferred form, illustrated in Figure 8, there are two grips 90. The grips 90 operate in a coordinated fashion to grasp and move the pipe 20 parallel to the longitudinal direction 28, using a "hand-over-hand" movement. The pipe 20 moved in this fashion slips over the
mandrel 62, which is stationary and supported interiorly of the pipe at the location of the laydown head 66 and die 68, and at intermediate positions as necessary.
Returning to Figure 3, the fabrication apparatus 60 is used to produce the pipe 20 in the following manner. The base fiber/matrix composite material 70 is provided, numeral 44. The base fiber/matrix composite material is preferably a unidirectional composite material with the fibers all oriented substantially parallel to each other. Suitable starting material is available commercially as tapes, fibers consolidated into a thermoplastic matrix, or a pre-impregnated tow. The fibers are preferably graphite or carbon, but other fiber materials such as glass and kevlar may be used.
The matrix is an organic thermoplastic resin such as nylon, polyetherether- ketone (PEEK), or polypropylene. A thermoplastic resin, which becomes deformable at elevated temperature before melting and flowing, is distinct from a thermosetting resin which sets when exposed to elevated temperature. The heated base fiber/matrix composite material that forms the base layer
22 of the pipe 20 is fed into the consolidation die 68 to adhere to the pipe being fabricated, and thence is drawn parallel to the longitudinal axis 28 by the movement of the pipe 20 produced by the pipe drive 88. The base fiber/matrix composite material is thence deposited onto the mandrel in the laydown head, numeral 46, and immediately at least partially consolidated by the consolidation die 68, numeral 48.
The overwrap fiber/matrix composite material is provided, numeral 50. The overwrap fiber/matrix composite material is like the base fiber/matrix composite material, in that it is formed of unidirectional fibers in a thermoplastic matrix. The fibers and thermoplastic matrix used in the two composite materials may be the same or different. Different overwrap fiber/matrix composite materials may be used in the different pairs of overwrap layers 26. That is, the layers 26a and 26b may be made of one type of overwrap fiber/matrix composite material, and the layers 26c and 26d may be made of another type. It is preferred, however that the base fiber/matrix composite material and all of the layers of overwrap fiber/matrix composite material be made of the same materials, to avoid chemical and thermal-expansion incompatibilities between the layers.
The overwrap layers 26 are wound onto the mandrel, numeral 52, with the
cured and at least partially consolidated base fiber/matrix material already in place, by the winding heads 74. The overwrap layers are thereafter consolidated by the consolidation head 84, numeral 54.
This apparatus and approach produces a continuous composite pipe 20, which is cut to desired lengths by a saw (not shown). The pipe is produced continuously at a rate of about 1 -3 feet per minute.
Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.