GB2208504A - Method and apparatus for filament winding with solvated condensation resins - Google Patents

Description

1 1 2208504 13DV-9056 METHOD AND APPARATUS FOR FILAMENT WINDING WITH

SMATED CONDENSATION RESINS This invention relates to construction of filament wound composite articles such as, for example, composite parts for aircraft gas turbine engines.

Recently it has been found desirable to construct aircraft gas turbine engine components (e.g. ducts, casings, tubes, cowls) from carbon or glass fiber tows, impregnated with high performance resins, using filament winding.

Currently the majority of filament winding is done by combining a resin and fiber at room temperature immediately prior to winding the resinimpregnated tow onto a forming mandrel (wet winding). Typical resins include epoxies mixed with amine or anhydride hardeners, or polyesters mixed with peroxide catalysts and styrene as a reactive diluent. These resin-fiber or composite systems are relatively easy to process, have good translation of constitutent properties into composite properties, and are cost effective for many applications. However, for elevated temperature applications these systems are severely limited when compared to systems with high performance resins-having high glass transition temperatures Tg. One such resin 13DV-9056 is 0 system is designated TGMDA/DDS, a system of a tetrafunctional epoxy (tetraglycidylethermethylinedianiline) and a high temperature curing agent (diaminodiphenylsulfone). The resin is commercially produced by Ciba-Geigy under the trade name Araldite (R7H) MY720.

High performance resins typically will have a room temperature viscosity sufficiently high that they will not wet and penetrate the fiber tow. Thus they have to be heated in order to reduce their viscosity, but then they react too fast to afford a practical pot life. TGMDA/DDS systems must be heated to nearly 1000C to reduce the viscosity to a usable value. But at these temperatures the viscosity builds up rapidly due to the beginning of the curing reaction. In addition, the heat of reaction, combined with the mass of resin being heated, is enough to start a runaway reaction that can produce large amounts of toxic smoke.

A non-TGMDA epoxy resin is disclosed in "Recent Resin Developments for Filament Winding", S. Lehman, 28th National SAXPE Symposium, April, 1983, pages 347-3S8. Lehman used EA9101 resin, a one-component resin produced by the Dexter Corporation (Hysol Division). EA9101 is reported to have properties which equal or exceed those of TGMDA resin. When heated to a temperature of about 83C (180F) the resin had a low enough viscosity (approximately 1.4 Pascal-seconds (Pa-sec)] to enable it to be used for wet winding. However, while EA9101 has a lower reactivity than does conventional.TGMDA/DDS, it still increases in viscosity at its winding temperature at a faster rate than most ambient winding resins.

Two resins are disclosed in "Resins and Impregnation Systems for Higher Temperature Filament Winding Usage", Brown et al, 29th National SAMPE Symposium, April 1984, 13DV-9056 0 pages 1141-1154. These resins were prepared by the Dexter Corporation (Nysol Division). One was a basic EA9101 modified with an epoxide diluent, reduced in reactivity and designated LR100-697. The modification resulted in a low and fairly constant viscosity of 0.3 Pa-sec at a temperature of 66C (1501F). However, the Tg was also reduced from 2130C to 1600C, a serious compromise of the resin properties. The other resin was an acetylene terminated bisphenol resin designated LR100-698. This resin had a very low viscosity (0.2 Pa-sec) at 66C (150IF) and showed very little increase over an eight-hour winding period., In addition, this resin had a remarkably high Tg of 260C (550OF). Unfortunately, these impressive resin properties were not translated into filament winding composite properties. The composites had low mechanical properties and a troubling tendency toward interlaminar failure, a serious compromise of composite integrity.

An alternate approach to the high viscosity problems of high temperature resins is that of preimpregnated, or prepreg, fiber tow. Prepreg tow typically is prepared prior to and separate from the filament winding operation. Indeed it may be prepared by an outside vendor and stored for later use. Prepreg tow is made by first reducing the resin viscosity by means of a suitable solvent to provide a solvated resin. The dry tow is pulled through a room temperature bath of the solvated resin in which the tow is wet and penetrated by the resin. The resin-impregnated tow continues through a drying oven which drives off excess solvent. The dried tow is wound onto spools for later use.

Brown et al, "Resins and Impregnation Systems for High Temperature Service Filament Winding Usage", 29th National SAMPE Symposium, April 1984, pages 1141-1154 also worked with the solvated epoxy resin EA9101. The 13DV-9056 a resin was dissolved in a 75/2S acetone/methanol solvent and used to impregnate Hysol Grafil XAS 6K (6,000 filaments) high strain carbon fiber. The dry carbon fiber spools required a small amount of back tension [less than 1 pound force (lbf)] to reduce tow fuzzing. A 21 epoxide size on the filaments also was helpful in preventing fuzzing. Resin content of the prepreg tow was controlled by the proportions of resin and solvent in the bath. As a result, fresh solvent had to be added during the operation due to excessive solvent evaporation. A drying oven temperature of 830- 990C (1800-2100F) was sufficient to drive off excess solvent and the dried tow was wound onto spools and later used for filament winding of composites.

Prepreg tow overcomes the viscosity problem but others remain. The dry carbon fiber must be completely defect free and without broken filaments, a demanding requirement in spools in which the tow typically is one to three miles long. Prepreg tow must not stick to itself on the spool else the fibers will break during unspooling and cause an interruption in the operation. Additionally, the high-viscosity-resin prepreg tow is difficult to spread during the filament winding operation, resulting in an uneven distribution of fibers through the thickness of the filament wound composite.

Several filament winding techniques with PMRlS resin were reported by K.I. Clayton, "High Temperature Plastic Laminate Evaluation", University of Dayton Research Institute (UDRI) in AFWAL-TR-84-4190, March 198S. PMR15 is a high performance polyimide resin reported in Serafini et al, "Thermally Stable Polyimides from Solutions of Monomeric Reactants", NASA TN D-6611, 1972. The designation PMR15 indicates the type of resin (Polymerization of Monomeric Reactants) and a formulated molecular weight of 1500. Clayton gave descriptions of -1 1 1 k 13DV-9056 5- is 0 filament wound PMR15-carbon fiber cylinders and pressure bottles made by several organizations and mechanically tested by UDRI.

Aerojet and Brunswick used prepreg tape to wind bottles and had considerable trouble in placing and securing the tape. Thiokol used a proprietary process to wet wind both bottles and cylinders. Rohr made thick (30 ply) cylinders by dry winding then impregnating and debulking after each third ply. UDRI made cylinders by wet winding and then debulking after each ply or each second ply. The debulking involved a nylon peel ply, manual wrapping of perforated shrink tape, then exposure to 660C (1500F) vacuum for one hour. The process to make the cylinders was extremely labor intensive and probably required 8-16 hours preparation before molding and post curing. The processing information given in the report indicates that wet winding is better than dry or prepreg winding.

In all of the above cases in the prior art where graphite fiber was impregnated with a PMR resin after wrapping and prior to curing, it was necessary to either debulk or compact after each 1 to 3 wraps to avoid wrinkle formation. Another problem encountered with some of the resins employed, e.g. PMRlS using a dry prepreg, was the difficulty in holding the fibers tightly against the steel mandrel and the flaking off of some of the fiber resin during winding. The wrinkling found in many of the pressure bottles and cylinders was attributed in part to a change in volume in the polyimide resin due to chemical reactions and solvent loss. In considering the additional preparation not encountered with other resins, filament winding with PMR15 would not be very cost effective using the above processes.

The kinetics of the imidization reaction for the PMR polyimide resins are disclosed by Lauver in "Kinetics of 13DV-9056 a Imidization and Crosslinking in PMR Polyimide Resin", Journal of Polymer Science, Polymer Chemistry Edition, Volume 17, 1979, pages 2529-2539. Lauver indicates that the imidization reaction has two distinct stages. Initially, the reaction rate is rapid and then decreases dramatically as the reaction proceeds. It is pointed out that the two stage behavior of the reaction offers a significant advantage of PMR polyimide resin processing in that it allows stepwise staging or partial imidization to be obtained by choice of temperature rather than careful control of exposure time.

Youngs presented a concept of filament winding of thermoplastic prepreg tapes in "Advanced Composite Thermoplastics: A New Structural Material", Society of Plastics Engineers 43rd Annual Technical Conference Proceedings, April 20-May 2, 1985, pages 1181-1183. In contrast to the thermosetting resins, thermoplastics typically have no solvent and they do not undergo a cure reaction. However, they do have very high room temperature viscosities which can be reduced by heat. The suggestion was to place a high intensity heating source (infrared, ultrasonic, hot gas or laser) to heat the pr epreg tape to the resin melt temperature. Although the claim was made that filament winding of thersoplastic prepreg tape was being done using this concept, no photographs, process parameters, material properties or other evidence was presented.

Composites of polyimide resin and carbon fibers are highly effective in reducing the weight and cost of aircraft engines. While the constituent materials command a premium value, the processing needed to change them into a composite is even more expensive. Several cost effective processes are available which are less labor intensive than the traditional prepreg layup and autoclave cure. One such process is filament winding.

z 13DV-9056 0 However, it is difficult to obtain high quality, void-free composites when filament winding with a high-volatile-content polyimide such as PMR15.

The volatiles in PMRlS come from two sources: (1) the methanol which is used as a solvent in resin synthesis and is generated by the monomers as they react; and (2) water which condenses as the solvated resin imidizes. At typical processing temperatures, both water and methanol are in the vapor phase. While the volatiles facilitate flow, they also are trapped in the interior of the composite, causing property-reducing voids and shrinkage cracks. Volatile entrapment is especially troublesome in heatedwall processing. The near-wall resin reacts early in the processing and forms a barrier to the outward diffusion of volatiles. In addition, the considerable mass and associated volume loss causes shrinkage and fiber buckling. A typical filament wound form, which is a body of revolution, only exacerbates these problems.

The solvent content in the resins existing in prepreg tows is below about 30% by weight of the resin. Typically, the solvent levels range from about 8 to 11% solvent by weight of the resin as part of the solvent is removed prior to shipment. Accordingly the present invention is not and need not necessarily be addressed in the prior art.

It is an object of the present invention to achieve the high performance of resin fiber composites using an improved, cost effective method including filament winding.

It is another object of the present invention to provide improved apparatus which prepares impregnated fiber tows for filament winding.

These and other objects and advantages of the present invention will be more fully understood from the 13DV-9056 is 0 following detailed description, drawing and specific examples, all of which are intended to be typical of rather than in any way limiting on the scope of the present invention.

It has now been discovered that the objects of the present invention can be attained with a fiber tow including or impregnated with at least one solvated condensation resin by first subjecting the impregnated tow to at least a two-stage heating process to remove solvent and to partially react the resin, and thereafter subjecting the treated tow to a temperature at least as high as the temperature of the tow in the final stage of -the heating process while winding the tow under a consolidating force.

One form of the apparatus of the present invention includes, in operating sequence, first heating means for heating a fiber tow impregnated with a solvated condensation resin to a first temperature to remove solvent, second heating means for heating the tow to a second temperature higher than the first temperature to at least partially react the resin, third heating means for heating the resin and tow to a third temperature at least as high as the second temperature while filament winding the tow, and tow movement means to move the tow in sequence through the first, second.and third means.

In the accompanying drawings:

Figure 1 is a diagrammatic view of one form of the apparatus of the present invention adapted to practise the method of the invention.

Figure 2 is a diagrammatic, fragmentary view of another form of the apparatus of the present invention.

t 13DV-9056 -g- is 23 0 In carrying out the method of the present invention it has been found that the desired objects are achieved when the tow is impregnated with a solvated resin condensate product, at least a part of the solvent is removed, and the resin is partially but not fully reacted in situ on the fiber tow such as in an evaporator-reactor. Typically such resins will include monomeric condensation resins such as the polyimides or phenolics as well as solvated epoxies, although it is preferred to employ the polyimides or the phenois because of their higher operating temperatures.

Suitable polyimide resins are typified by the FMR type such as PMR15 having a molecular weight of 1SOO, PMR10 having a molecular weight of 1000 and LXRC 160 having a molecular weight of 1600. The solvent employed in these resins is methanol or a mixture of methanol and propanol. These resins must imidize and crosslink (react) in order to be useful composite matrixes. Although crosslinking presents no unusual problems, the reaction, such as imidization, results in condensation of water molecules which can lead to considerable mass and volume loss, voids, trapped volatiles, shrinkage and fiber buckling. The result frequently is a composite with marginal properties or the use of a method that is complicated and expensive, leading to excessive staging, volatile transport and bleeding as well as possible back filling resins into voids and cracks. Suitable phenolic type resins are condensation reaction products of phenol and formaldehyde with an acidic catalyst (which produces a novolac) or an alkaline catalyst (which produces a resol). The solvent content (acetone or methanol) of most resins generally is at least about 301 by weight or more of the resin weight for the resins to stay in 13DV-9056 is solution. Preferably, the solvent content will range between 30 to 50t by weight of the resin. The method of the present invention primarily is useful with solvent contents above about 10 wtA, below which the method generally is not required.

In the method of the present invention, the solvent incorporated in the resin is removed and the resin is reacted as the tows are passed through a series of at least two heat zones, for example, in the evaporator- reactor of the present invention, in a controlled manner. Generally, the weight of the resin is reduced by 30% which effectively removes at least half of the solvent.

The fiber tows employed preferably are carbon fiber tows although glass or aramid fiber tows or the like can also be employed where the structural strength and flexibility provided by the carbon fiber tows are not required.

The resin impregnated fiber tows used in the present invention can be prepared by applying a sufficient quantity of solvated resin to the fiber tow to permit the tow to become impregnated with the resin as is known and practiced in the art. Preferably, the quantity applied is sufficient to impregnate the tow but less than that quantity which could provide sufficient excess resin on the surface of the tow to impede handling.

The resin impregnated fiber tows are passed through a multi-stage evaporator-reactor, for example one with two stages. In the first stage, the low mass, unrestrained tow undergoes a rapid rise in temperature which drives off at least a portion of the solvent. The remaining solvent to be removed is then driven off in the second stage which is maintained at a temperature higher than the temperature of the first stage to enable the resin to react. The resin on the tow partially but a 1 13DV-9056 not completely reacts in the second stage where it undergoes controlled reaction (for example imidization in the case of polyimides) releasing condensation products. Such products are removed from the apparatus, conveniently by a flowing, non-oxidizing gas, for example an inert gas. The solvent and condensation products can be swept from the evap oratorreactor by maintaining a countercurrent flow of such gas through the reactor, in one form of the apparatus of the present invention.

The temperature in the first stage is maintained at a sufficiently high value to drive-off solvent which is not chemically bound to the resin. For a solvent such as methanol, the preferred range is at least 80C and not more than 130C.

In one example using PMR15 resin in the tows, the tows are passed through the first stage at a rate of about 1 to 6 millimeters/second and preferably 2.6 millimeters per second. The length of the first stage is not critical, although it is preferably no more than 400 millimeters long when a residence time of about 1SO seconds is needed to drive off solvent. Preferably the residence time in the first stage does not exceed about 7 minutes and generally is in the range of about 0.6 - 7 minutes. It is possible to vary the stage length depending on the temperature and residence time needed to remove the desired quantity of solvent. In subjecting the fiber tows to heating in the first stage, it has been found that it is possible to raise the temperature of the tow from room temperature to the first stage temperature at a rate which is less than 1C per second to avoid flashing off of the solvent. It has been found that temperatures in excess of about 150C in this example tend to cause flashing off of solvent and accelerate the reaction too rapidly. Such elevated k or is a 13DV-9056 temperatures create problems since it is difficult to control the rate of evaporation of the solvent and the reaction conditions.

The evaporator-reactor of the present invention can be maintained under an inert gas atmosphere using an inexpensive inert gas, typically nitrogen. The gas flow preferably is countercurrent to the direction of the tow feed. The inert gas can be fed from the discharge end of the last stage and pass continuously through all stages in a countercurrent direction. Alternatively, the inert gas can be fed into the apparatus at various intermediate points, preferably in a countercurrent direction. In a preferred arrangement of evaporatorreactor to be described, the temperature maintained in the second stage may range from about 110C to about 2000C. Preferably in the case of PMR15 resin, the temperature range will be below 180C (355F). It has been found that the overall length of the two stages in the heating tube can be varied somewhat depending on the residence time desired in each stage, although preferably the length of the second stage will be no more than 1 metre when a speed of 2Amm/sec is employed and the required residence time is less than about 7 minutes, preferably about 2.5 - 7 minutes.

The heat treated, resin impregnated fiber tows which exit from the second stage of the heating tube are contacted with a heated, consolidating roller maintained at a temperature at least as high as that used in the second stage. Preferably, the temperature range at which the heated consolidating roller is maintained will be 200 to 270C. It has been found that the temperature of the roller must at least as high as the reaction temperature within the last stage of the evaporation-reactor In order to soften the resin and permit a slight flow thereof. The resin impregnated cl 13DV-9056 is 0 fiber tow is contacted by the heated roller as the tow is wound onto the mandrel. The roller is positioned so that it exerts at least a slight force substantially normal to the surface on the resin impregnated fiber tow as it is being wound onto the mandrel, thereby assisting in consolidation of the fiber tow on the mandrel. The consolidated form has a low volatiles content and exhibits little or no shrinking after consolidation.

One form of the improved apparatus for carrying out the method of the present invention includes a staged resin-fiber delivery system, an evaporator-reactor, a winding mandrel, and usually a traversing mechanism. These components are mounted on a framework which can be readily modified and adjusted.

Figure 1 is a diagrammatic view of one form of the apparatus of the present invention. The apparatus shown generally at 10 is provided with a mounting and pay-out device or supply means 6 for the fiber tow 7, such as has been commonly used in the art in winding fiber tows. In flow sequence with the mounting and pay-out device is a tensioning device, typically a pair of rods 11 and 12 preferably made of or coated with a polytetrafluoroethylene-type material such as Teflon. Typically, the first rod 11 of the pair is driven at a speed slower than the tow is being wound and in the reverse direction to movement of the tow to apply a friction drag to the tow. The other rod, 12, with grooves to guide the tow, is free to turn in the same direction and with the same speed as that of the tow. A tensionometer 13 measures tow tension. Mechanical analog or electronic digital readout compatible with a computer control system may be used. In line with the tensioning device is the resin delivery system 14 consisting of a resin reservoir 15 having a resin feed tube 16. Located in proximate relationship to reservoir 1 13DV-9056 is 0 IS and spaced therefrom is a fixed spreader rod 17 over which the tow is pulled causing the tow to spread apart and thus facilitate wetting by the resin. Resin is delivered from reservoir IS. Feed tube 16 is positioned, for example approximately 1-2 vim, above the splayed tow. In line with and following resin reservoir IS is a fiber-gathering roller 18 which not only gathers the tow but also expresses excess resin.

The apparatus of Figure 1 is provided with an evaporator-reactor shown generally at 19 and which follows in sequence the fiber gathering roller 18. Preferably evaporator-reactor 19 is comprised of two resistance, convection type tube furnaces 8A and 8B, respectively first and second heating means, mounted in tandem as shown, with an elongated central conduit or tube 20 generally in line with roll 18 and extending through both the furnaces and adapted to pass the tow therethrough. For example, resistance heating rods 9, shown in fragment in Figure 1, can be included. Conduit 20 has an opening 20a on its first or upstream end and an opening 20b on its second or downstream end. Four thermocou pies 21a, Zlb, 21c and 21d, typically made of chromel-alumel material are located at fifth points along the outside of the tube and within the furnace to assist in monitoring and control of the furnace through a furnace control 22 of a type well known in the art.

In the embodiment of Figure 1, furnace control 22 is connected by conductors, such as 22a and 22b for furnace SA, and 22c and 22d for furnace OB, for control of the heating of the furnaces according to a preselected pattern and responsive to signals from the thermocouples. Such control and sensing canbe accomplished using electrical devices well known and commonly used in the art. The evaporator-reactor is provided with exhaust means 23a and 23b in Figure 1, and Ill 1 13DV-9056 -Is- 0 23 in Figure 2 so that fumes can exit the evaporator-reactor and be collected and condensed, preferably in a controlled manner, for subsequent handling such as for analysis, process monitoring and/or environmental control or safety.

In line with and following evaporator-reactor 19 is a mandrel 24 driven at a preselected rate to draw the tow through the apparatus and a traversing mechanism 25 wherein the traversing motion is supplied, for example by a ball screw, and motion reversal is achieved by limit switches. A weighted, heated tow winding and consolidating means such as consolidator 26, including third heating means, softens the heat-treated resin-impregnated tow and presses it into place on the previously wound surface.

Another form of the evaporator-reactor of the present invention is shown in the fragmentary diagrammatic view of Figure 2, with like numbered elements as described above. In Figure 2, the evaporator-reactor 19 is disposed within an enclosure 30, such as a clear plastic box, with appropriate openings to enable passage of fiber tow 7 therethrough. In Figure 2, exhaust means 23 is disposed in a wall of enclosure 30, being positioned to remove gas from the upstream end of first heating means or furnace 8A.

The following examples demonstrate means of practicing the method of the present invention:

Example I - A 12K carbon fiber tow maintained under a tension of about 7 Newtons (N) (I.S pound force) was spread laterally. A SOt methanol solution of PMRIS polyimide resin was applied to the tow at a rate of about 0.2 al per mm of tow by spraying the resin onto the spread tow from a closed reservoir maintained under a nitrogen gas pressure of 40-100 kilo Pascals (kPa), about 6-IS psi, to saturate the fiber tow. The resin 13DV-9056 is 0 feed tube was positioned about 1-2 am above the spread tow to minimize exposure of resin to air. The sprayed tow was then passed under a Teflon roller to gather and reform the fibers into a tow and express excess free resin from the tow. The resin impregnated, reformed fiber tow was passed through a furnace consisting of a pair of tube furnaces connected in tandem to provide two heat stages. The combined furnaces were approximately 800 am long and an inside diameter of about 25 am. A non- oxidizing or inert gas such as_nitrogen at ambient temperature was introduced into the furnace, for example through a tube 28 in the drawing, about 100 am upstream of the downstream furnace exit, as shown.

The length of the first stage was defined by the distance into the furnace at which the wall temperature first reaches 110C (230F), a temperature high enough to drive off solvent without inducing extensive imidization. The residence tine in the stage is a function of stage length and the speed at which the resin-impregnated tow passes through the furnace. In the present example the tow moved through the furnace at a rate of 2.35mm/sec (about O.S ft/min). The first stage was 300 am long and the residence time was 128 seconds. The second stage, with a maximum temperature of 138C (280F), was 500 am long and had a residence time of 212 seconds.

The tow exiting'the second stage was wound in the form of a 20-mm-wide ring on a 130-am-diameter room temperature circular mandrel. The heat treated resin-impregnated tow was pressed onto the previously wound surface by a weighted sealing iron, represented by consolidator 26 in the drawing, mounted so as to apply a force normal to the mandre.1 surface. The iron was maintained at a temperature of about 2200C (4300F) which softened the now-thermoplastic resin, allowing it to flow, thus facilitating consolidation. S Z 13DV-9056 0 The filament wound ring was molded and post cured at a

temperature of 31SC (600F) and evaluated. The ring had no shrinkage-induced wrinkles and included the following properties: specific gravity 1.4S; resin weight 20; fiber volume 62t and void volume 11t, less than the 12 maximum volume percent desired in the article produced.

Example 2 - The procedure of Example I was repeated except that the heat stages were different. In Example 2, the tow moved through the furnace at a rate of 2.63 am/sec (about O.S ft/min). The first stage was 37S am long and the residence time was 143 seconds. The second stage, with a maximum temperature of 131C (2670F), was 42S mm long and the residence time was 161 seconds.

The filament wound ring resulting from Example 2 was molded and post cured as in Example 1. The ring had no shrinkage-induced wrinkles and included the following properties: specific gravity 1.45; resin weight 33%; fiber volume SS% and void volume 8%.

Example 3 - The procedure of Example 1 was repeated except that the heat stages were different. In Example 3, the tow moved through the furnace at a rate of 2.70 am/sec (about 0.5 ft/min). The first stage was 11S mm long and had a residence time of 42 seconds. The second stage, with a maximum temperature of 147C (29SF), was 68S em long with a residence time of 252 seconds.

The filament wound ring was molded and post cured as in Examples I and 2. The ring had no shrinkage-induced wrinkles and included the following properties: specific gravity l.SO; resin weight 28%; fiber volume 61%; and void volume 7%.

Although the present invention has been described by -reference to specific examples and embodiments, it should be understood that other examples can be used. For example, convection heating was described although 11 13DV-9056 0 other heating means such as infrared, microwave, laser, or the like may be employed. Also, consolidating of the tows on the mandrel can be effected by use of various combinations of heat and pressure applied in the area in which the tow contacts the mandrel as it is being wound.

The present invention permits control of mass and volume losses to be within acceptable limits of resultant shrinkage without the heretofore described disadvantages experienced in the prior art because the impregnated tows are relatively unrestrained and the diffusion paths for the solvent and condensed water ar far shorter than they would be after consolidation.

IQ 0 13DV-9056

Claims (20)

1. In a method for producing a filament wound body from a fiber tow which includes a solvated condensation resin, the steps of: removing at a first temperature at least a portion of solvent in the solvated resin; at least partially but not fully reacting the resin and removing condensation products at a second temperature higher than the first temperature; and then, winding the tow while heating the tow at a third temperature at least at the second temperature.

2. The method of claim 1 in which the removed solvent and condensation products are collected and condensed for subsequent handling.

3. The method of claim I in which removal of the solvent and reaction of the resin, prior to winding, are conducted under a non-oxidizing atmosphere.

4. The method of claim 1 in which: the first temperature is in the range of 800C 1650C, and is a temperature at which the solvent will not flash off; and the second tempera'ture is in the range of 110'C - 200C.

S. The method of claim 4 in which: the first temperature is not in excess of about 1500C; and, the second temperature is not in excess of about 180C.

6. A method for producing a body of revolution comprised of a fiber tow impregnated with at least one solvated condensation resin prior to curing, which comprises the steps of: contacting the fiber tow with at least one solvated condensation resin to impregnate the fiber tow; 1 9 13DV-9056 subjecting the impregnated fiber tow to at least two heating stages under a non-oxidizing atmosphere, the first stage being maintained at a first temperature sufficiently high to drive off at least part of the solvent during the residence time of the tow within the first stage, and the last stage being maintained at a second temperature higher than the first temperature and sufficiently high to at least partially but not fully react the condensation resin during the residence time of the tow within the last stage; subjecting the tow after the last stage to a temperature at least as high as the second temperature; and, winding the tow under a consolidating force while maintaining the tow at least at the second temperature.

7. The method of Claim 6 wherein the first temperature is about 80C to 165C and the second temperature is about 1100C to 2000C.

8. The method of Claim 7 wherein the fiber tow is retained in the first heating stage for about 0.5 - 7 minutes and thereafter is retained in the last heating stage for about 2.5 - 7 minutes.

9. The method of Claim 7 wherein the consolidating force applied to the tow is applied at a temperature of 200 to 270"C.

10. Apparatus for filament winding a fiber tow impregnated with a solvated condensation resin, comprising: an evaporator-reactor including, in operating sequence, (a) first heating means adapted to heat the fiber tow to a first temperature which will remove solvent from the resin, and 11 71 v 13DV-9056 (b) second heating means adapted to heat the tow to a second temperature higher than the first temperature and which will at least partially react the resin; and, third heating means adapted to heat the tow from the evaporator-reactor to a third temperature at least as high as the second temperature while filament winding the tow; and tow movement means to move the tow in operating sequence through said first, second and third heating means.

11. The apparatus of claim 1O.wherein: said first and second heating means comprise consecutive tube furnaces having therethrough a conduit adapted to pass the tow therethrough and having an opening in each of an upstream end and a downstream end, said conduit traversing through said consecutive tube furnaces.

12. The apparatus of claim 10 which includes means to introduce a non-oxidizing gas into said conduit.

13. The apparatus of claim 12 in which the gas is introduced into said conduit in the vicinity of said downstream end and enables flow of the gas toward said upstream end.

14. The apparatus of claim 11 which includes exhaust means connected to said conduit intermediate said upstream and downstream ends.

15. The apparatus of claim 11 which includes exhaust means positioned to remove gas from said upstream end of said first heating means.

16. The apparatus of claim 10 including, in addition, tow winding and consolidating means receiving the tow from said evaporator-reactor and which includes a weighted sealing iron heated by said third heating 35 means.

k 13DV-9056 -22.

17. The apparatus of claim 10 including, in addition, tow winding and consolidating means receiving the tow from said evaporator-reactor and which includes a roller heated by said third heating means.

19. Apparatus for winding resin impregnated fiber tows, comprising, in operating sequence: fiber tow supply means; resin supply means including means'for impregnating the fiber tow; an evaporator-reactor including, in operating sequence, (a) first heating means adapted to heat the fiber tow to a first temperature which will remove solvent from the resin, and (b) second heating means adapted to heat the fiber tow to a second temperature higher than the first temperature and which will at least partially react the resin; and tow winding and consolidating means including third heating means, adapted to heat the tow from said evaporator-reactor to a third temperature at least as high as the second temperature, and to press together the tow during winding; the apparatus including tow movement means to move the tow through the apparatus from said fiber tow supply means to said tow winding and consolidating means.

19. The apparatu of claim 18 wherein: said first and second heating means comprise consecutive tube furnaces having therethrough a conduit adapted to pass the tow therethrough and having an opening in each of an upstream end and a downstream end, said conduit traversing hrough said consecutive tube furnaces.

20. A method of or apparatus for producing a filament wound body, substantially as hereinbefore described with reference to the accompanying drawings.

I'alihshed 1985 at The Paten! Office, Stat e House (3C- '_ H_- Lmdon WC1R 47? Punher emies may be olbtaine:! L-om 77he Patent Offf:ce Sales Branch, St Maiy Cray. Orpingtcn. Ken, BR5 3RD. Printed by Multiplex techmques Rd, St Mary Crky. Kent. Con. 187