OPEN-WORK KNITTED TEXTILE RESIN INFUSION MEDIUM AND REINFORCING COMPOSITE LAMINA

FIELD OF THE INVENTION The present invention relates to a resin infusion medium and reinforcing composite lamina consisting of open-work knit textile articles produced on a warp knitting machine. BACKGROUND OF THE INVENTION Fiber reinforced resin composite structures are used in various industries, including the manufacture of parts and finished goods in automotive, recreation vehicle, trucking, aerospace, marine, rail, appliance, athletic equipment, container, construction, anti-corrosion, electrical and medical industries. There are several generally known technical approaches to the forming of fiber reinforced laminate composites. Closed molding has existed for many years but is gaining wider adoption as manufacturers seek to reliably produce high-volume, high quality parts, yet simultaneously reduce emissions of hazardous air pollutants. In closed mold processing, fiber and/or other reinforcement(s), collectively referred to as the "pre-form," are cut to fit and then placed in the two-part mold. A method of enclosing and compressing the pre-form against the mold is then employed. The resin is then typically introduced into the pre-form via ports through the enclosure. Upon curing of the resin, the mold enclosure member is first removed, followed by the finished part. Of the available closed mold processes, vacuum infusion is perhaps the easiest to use and provides engineers with an arsenal of design options to attain many benefits over other processing methods (e.g. lamination, also known as open molding) including: improved performance-to-weight, higher fiber volume ratios and efficient structural designs; reduced cost through fewer parts and production steps, efficiency of material and labor use, and simplification and standardization manufacturing methods; improved structural properties and longevity, reduced fatigue properties in structural laminate, smoother ply drop transitions and processes that increase reliability of fiber placement, orientation, and laminate composition. There are two basic vacuum infusion techniques, surface infusion and interlaminar infusion. In surface infusion, before applying the flexible bag or membrane a disposable barrier layer, commonly referred to as a peel ply, is placed on top of the laminae pre-form. A disposable infusion medium with rigid open structures that do not buckle under vacuum and/or perforated injection tubing is then placed on top of the peel ply to aid in the delivery

and distribution of the liquid resin down through the laminae stack. In the case of a reusable vacuum bag or membrane the distribution channels may be incorporated into the bag. Vacuum pressure is then applied to draw resin through feed-lines into the mold and through the fiber pre-form. This technique is commonly referred to as surface vacuum infusion processing since the resin is introduced at the top surface of the laminae assembly. Examples are described in Seemann et. al. U.S. patents 4,902,215, 5,052,906 and 5,601,852. The greatest drawback of surface infusion is the high waste and non-profit stream costs due to the disposal of peel plies and surface infusion medium. Other drawbacks include steep implementation learning curves and increased complexity with increases in part size. Further drawbacks will be recognized by those fluent in the art. In interlaminar infusion the infusion medium is integrated with other laminae in the ply stacking sequence of the laminae pre-form. There are numerous advantages to interlaminar infusion processing over surface infusion processing other than waste and cost reduction. Surface infusion is a one-sided process in which the resin flows from the top down through the laminae stack. Interlaminar infusion medium can be sandwiched and/or placed on either face to promote infusion on all sides of the dry laminae, greatly speeding infusion. Further, since the composite becomes the infusion pathway, placement of vacuum and resin feed lines is greatly simplified. Those fluent in the art will recognize the maintenance of medium porosity under vacuum induced compression as prerequisite to flow efficacy. SUMMARY OF THE INVENTION A new type of resin infusion medium and reinforcing composite lamina textile has been invented, and is the primary subject of the present invention. The textile comprises a warp knit open work structure preferably produced in an approximately polygonal form, of which at least some of the edges of the polygons are defined by knops such as to give prominence to the design to provide for fluidic channels, with three dimensional fluid flow with preferential flow in the weft direction. The knops are knitted to be sufficiently non- compressible in order to resist collapse of the fluid channels during compression of the composite preform under vacuum induced process pressure. The present invention relates generally to a resin infusion medium textile for closed molded resin infusion molding for the production of fiber reinforced resin plastic (composite) structures. More specifically this invention relates to a new type of resin infusion medium and reinforcing composite lamina constituted by a warp knit open work textile; wherein the open

mesh, foraminous textile structure has a dominant apertured construction wherein the fiber or yam components occupy substantially less volume than the apertured voids of the textile material; and wherein the apertured construction is defined by polygons of which at least some of the edges are defined by knops such as to give a third dimensional prominence of periodically raised or ribbed members to the design to provide for bilateral (e.g. warp and weft) fluidic channels, the knops being knitted to be sufficiently non-compressible in order to resist collapse of the fluid channels during compression of the composite preform under vacuum induced process pressure; and wherein an appropriate ratio of holes are located in the fabric as selected for the desired axial fluid flow (i.e. perpendicular to the warp/weft plane of the textile) by and within the skill of the practitioner of this invention. The resulting fiber reinforced plastics may form part of or all of the composite laminate. In these respects, the use of the inventive open work textile interlaminar infusion medium and reinforcing composite lamina to aid in the transfer, delivery and distribution of resin according to the present invention substantially departs from the conventional concepts and designs of the prior art. In so doing, the invention provides a technique and use of a material that increases the resin distribution rate and uniformity throughout the laminae pre- form. Additionally, the capability to custom design the interlaminar medium according to the teachings herein provides a vast spectrum of options with which one skilled in the art can enhance process performance and the physical properties of the composite. Thus, in seeking to improve over the foregoing disadvantages inherent in the known types of resin infusion techniques now present in the prior art, the present invention provides a new technique for resin infusion through the novel use of an new open work textile interlaminar resin infusion medium and reinforcing composite lamina in the preform lay up. Accordingly, a general purpose and objective of the present invention is to employ an open work textile, discussed above, for the resin infusion medium and reinforcing composite lamina, while retaining the other advantages of the resin infusion techniques, as mentioned above. Further, since the open work textile of the invention can be sandwiched either in the middle and/or placed on either or both sides of the laminate schedule, it can be utilized either as an interlaminar infusion medium, or alternatively as the last or top ply of the laminate stack, thus serving as a surface infusion medium. The invention may be applied to the production of composite parts and/or finished goods for use in the automotive, recreation vehicle, trucking, aerospace, marine, rail,

99 appliance, athletic equipment, container, construction, anti-corrosion, electrical and medical

100 industries, among others.

101 This invention features an open-work textile for use as a resin infusion medium,

102 comprising an open-work fabric defining resin flow channels in both dimensions in the warp-

103 weft plane of the fabric and also in a third dimension through the thickness of the fabric; and

104 a plurality of spaced projecting knops integrally formed in the fabric that create a preferential

105 resin flow in the weft direction of the fabric. At least some of the knops are preferably

106 elongated, and these may be elongated in the weft direction. At least some of the knops may

107 be arranged in rows along the weft direction, and the knops comprising the rows in the weft

108 direction are preferably spaced from one another. The spacing may be essentially regular.

109 The knops in adjacent rows are preferably offset from one another in the warp direction. The

110 spacing between the knops in the rows in the weft direction may be approximately the same

111 as the length of the knops in the weft direction.

112 The knops may be regularly spaced in at least one dimension, and may be regularly

113 spaced in both the warp and weft directions. The knops may be arranged in rows along the

114 weft direction. The knops in adjacent rows may be offset from one another in the warp

115 direction. At least some of the knops may be formed by knitting together at least two yarns

116 of different decitex values. One yarn may have a decitex value which is at least about five

117 times that of another yarn comprising the knop. At least portions of some of the knops may

118 be formed by knitting together three yarns, two of which are of substantially greater decitex

119 values than the third yarn. In a specific embodiment, one yarn may be about 140 decitex and

120 two other yarns may be about 1100 decitex, and the three yarns may be of non-texturized

121 polyester.

122 The open-work textile may be warp knit. The textile may comprise open stitched and

123 inlaid yarns with relatively low decitex values, and two knop stitched yarns with substantially

124 greater decitex values. The textile may be heat set after knitting. The textile may have a

125 finished weight of about 380 grams per square meter. The textile may define at least about

126 70 % void volume. The textile may define a plurality of relatively open resin flow paths in

127 the weft direction, and a plurality of less open flow paths in the warp direction. The weft

128 direction flow paths may comprise adjacent weft-direction courses without knops in the

129 courses. The warp direction flow paths may comprise adjacent warp-direction wales having

130 knops spaced along and within the wales. The knops may be elongated in the weft direction.

131 The open-work textile may further comprise a fibrous lamina layer on at least one face of the

132 textile. The knops may define edges of generally polygonal shapes formed by knop knit high

133 decitex fibers. The polygonal shapes may be generally hexagonal. The generally hexagonal

134 shapes may be essentially space filling in a honeycomb pattern.

135 To further illustrate the invention in certain useful but non-limiting embodiments,

136 reference is made to the accompanying drawings.

137 BRIEF DESCRIPTION OF THE DRAWINGS

138 Other objects, features and advantages will occur to those skilled in the art from the

139 following description of the preferred embodiments and the accompanying drawings in

140 which:

141 Fig. Ia is a cross sectional view, and Fig. Ib a partial exploded top view, of a typical

142 vacuum infusion mold assembly comprised of a rigid mold and a flexible bag or membrane

143 disposed thereon, but with an open-work textile resin infusion medium of the invention and

144 reinforcing composite lamina placed in the laminate, or ply stacking sequence;

145 Figure 2 shows Figure 1 a with vacuum applied, and thus with the fabric laminae

146 compressed in the mold;

147 Figures 3 diagrammatically illustrates in plan view the general construction of a

148 preferred embodiment of an open-work textile of the invention;

149 Figure 4 diagrammatically illustrates a cross section of the open work textile shown in Figure

150 3, along with cover fibrous laminae;

151 Figures 5 a-f diagrammatically show the lapping motions of the preferred embodiment

152 of the inventive open-work warp knit fabric; and

153 Figures 6a-f diagrammatically show the lapping motions of an alternative

154 embodiment of the inventive open-work warp knit fabric.

155 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE

156 INVENTION

157 In the drawings, Figure Ia is a cross sectional view of a typical vacuum infusion mold

158 assembly comprised of one rigid mold 1 having a shaped mold surface or face 2 and one

159 flexible bag or membrane 3, but with an open-work textile resin infusion medium of the

160 invention employed, and reinforcing composite lamina placed in the laminate, or ply stacking

161 sequence. The vacuum bag 3 is placed over the open mold, and is associated with the

162 perforated resin infusion tubing 4 (shown in cross sectional and top plan views). The laminate

163 layup is composed of fibrous lamina 5, an open-work textile layer 6 (also shown in top plan

164 view), and a vacuum tubing inlet 7, and with a sealant tape 8.

165 Dry fiber reinforcement is laid into a mold 1 of the desired shape. In this example, the

166 open-work textile 6 is placed between two layers of fiber reinforcement or lamina 5 to make

167 up the laminae. A flexible sheet of plastic 3 is placed over the mold and laminate. The edges

168 of the sheet are sealed against the mold, in this example with sealant tape 8 to form a sealed

169 envelope surrounding the laminate. Vacuum pressure is then drawn through one or more

170 strategically located ports 7 in the mold or plastic cover to collapse the flexible sheet against

171 the reinforcement. The vacuum serves to shape the fibers to the mold, provide consolidation

172 of the fibers via atmospheric pressure, and to remove any entrapped air, as shown in Figure 2.

173 Resin is then introduced into the envelope via perforated feed-lines, in this example spiral

174 wrap 4 is used, and the vacuum serves to draw the resin through the fiber pre-form via the

175 paths afforded by the open-work textile. Vacuum pressure is maintained until the laminate is

176 fully saturated with resin and subsequently cures.

177 Figure 2 illustrates the configuration of the device of Figure 1 with the vacuum

178 applied and resultant compression of the layup.

179 Figure 3 diagrammatically shows in top plan view the general construction of a

180 suitable fabric for use as the open-work textile resin infusion medium and reinforcing

181 composite lamina 6. The fabric depicted in Figure 3 is a bilateral fabric. As used herein, the

182 term "bilateral" is construed to mean a fabric that defines fluid flow paths in both the

183 longitudinal (i.e., "warp" or "machine") direction and the transverse (i.e., "weft" or "cross-

184 machine") direction of the fabric.

185 Thus, the fabric illustrated in Figure 3 is bilateral in that it the open-work apertured

186 voids 9 of the structure are defined in form by a plurality of generally polygonal forms of

187 which at least some of the edges are defined by knops 10 that give a third dimensional

188 prominence of periodically raised or ribbed members to the design, the remaining edges 12 of

189 the polygonal forms being comprised of fiber strands 11 therebetween. The fibers

190 comprising the knops 10 can include fibers formed from various materials such as natural

191 materials (e.g. cotton, flax, etc.), polymeric materials (e.g. polyesters, polyamides, etc.),

192 inorganic materials (e.g. glass fibers, carbon fibers, etc.), and combinations thereof.

193 The plurality of knops are spaced apart by a distances, d _x and d _y , where distance d _x is

194 dependant upon the gauge of machine on which the fabric is knitted, the size of the yarns

195 making up the fabric, and the knit structure and where d _y is dependant upon the selected

196 course count.

197 The appropriate ratio of holes are located in the fabric as selected for the desired axial

198 fluidic flow (i.e. perpendicular to the warp/weft plane) by and within the skill of the

199 practitioner of this invention. The resulting fiber reinforced plastics may form part of or all of 200 the composite laminate.

201 Upen work textile 6 defines resin flow channels in both dimensions in the warp-weft

202 plane of the fabric, and also in a third dimension through the thickness of the fabric. A

203 plurality of spaced projecting knops 10 integrally formed in fabric 6 create a preferential resin

204 flow in the weft direction of the fabric. In the embodiment shown in Figure 3, for example,

205 knops 10 are arranged in rows along the weft direction, for example adjacent rows 23 and 25.

206 In this embodiment, each individual knop 10 is elongated in the weft direction, although such

207 is not a limitation of the invention. The knops 10 that define each such row are spaced from

208 one another. In this embodiment, the spacing between knops in a row is approximately the

209 same as the length of the knops, to define regularly spaced knops. Because fiber strands 11

210 that interconnect the knops in the generally polygonal (hexagonal) fashion as shown in the

211 drawing are defined in this case by two spaced parallel fibers rather than a knop, these sides

212 11 of the polygons are more open than are knops 10. Further, the central area 9 of these

213 generally polygonal shapes is even more open, as is apparent from Figure 5f. The result is

214 that a relatively unrestricted flow path in the weft direction between adjacent rows 23 and 25

215 of knops 10 is defined in textile 6.

216 Knops 10 defining adjacent rows 23 and 25 are offset from one another in the warp

217 direction. The result of this is that the rows in the warp direction such as three adjacent rows

218 27, 21 and 29 define therebetween flow paths that are not as open as the flow paths in the

219 weft direction. The flow in the warp direction is constrained to be more circuitous because

220 each path in the warp direction is effectively blocked at spaced intervals by the spaced series

221 of knops 10. This causes the preferential flow in the weft direction, while allowing flow in

222 both the weft and warp directions.

223 Figure 4 is a cross section of the fabric of Figure 3 but in which fabric 6 is applied as

224 in Figures 1 and 2, and where fibrous lamina 5 are present on both sides of open-work textile

225 6, under vacuum. In use the ribbed textile surface 6 is arranged in face-to-face contact with

226 the adjacent lamina of the preform, 5. In one preferred embodiment of this invention the

227 open work textile is constructed such that open paths are maintained within said open-work

228 textile in both the weft and warp directions by knops 10 when subjected to vacuum

229 compression thereby permitting the resin to flow freely throughout said laminae. This quality

230 can be imparted to the fabric 6 through the selected construction technique, construction

231 architecture, construction material, stabilizing coatings or sizings, or a combination thereof as

232 described herein.

233 It will also be appreciate that a desired laminate stack may have more than one ply of

234 the open-work textile, placed within or on an outer surface of the stack with a plurality of

235 conventional textiles plies suitably arranged on either side thereof.

236 For instance, for the one or more lamina other than the open-work textile, there may

237 be used unidirectional fabrics of various construction, woven or knit fabrics, multiaxial

238 fabrics of stitched construction, or braided fabrics, Fiber types used therein may also be of

239 various compositions, including organic, such as, polyester, aramid (i.e.. Kevlar, or Nomex),

240 etc., or carbon fibers, or inorganic, such as glass or ceramic.

241 Figures 5a-f are warp knit guide bar-lapping diagrams with point paper notations (the

242 needle heads being represented as dots) of the preferred embodiment of the inventive

243 knopped open work textile 6, as explained further below.

244 Figures 6a-f are warp knit guide bar-lapping diagrams with point paper notations (the

245 needle heads being represented as dots) of another example of a suitable knopped open work

246 textile 6, as explained further below. 247

247 Non-limiting examples of the invention

248 Example 1:

249 The following is an example of the practiced invention utilizing a warp knit open-

250 work knop textile architecture, an example of which is shown diagrammatically in Figure 3

251 (6).

252 As indicated above, one form of the open-work textile 6 may be a warp knit fabric

253 wherein the open mesh has a dominant apertured construction defined in form by polygons of

254 which at least some of the edges are defined by knops such as to give a third dimensional

255 prominence of periodically raised or ribbed members.

256 The plurality of knops are spaced apart by a distances, d _x and d _y (see Figure 3), where

257 distance d _x is dependant upon the gauge of machine on which the fabric is knitted, the size of

258 the yarns making up the fabric, and the knit structure and where d _y is dependant upon the

259 selected course count. These spacings are thus design choices.

260 In use the knopped open-work textile surface 6 is arranged in face-to-face contact

261 with the adjacent lamina of the preform, 5. The knops are knitted to be sufficiently non- 262 compressible in order to resist collapse of the fluid channels defined within the textile during

263 compression of the composite preform under vacuum induced pressure. In this manner rapid

264 transport of the resin is affected during resin infusion.

265 Further to the example, Figures 5a-f are warp knit guide bar-lapping diagrams with

266 point paper notations (the needle heads being represented as dots) of a said suitable open-

267 work textile 6. The lapping motion of a suitable ground mesh is shown in Figure 5a and

268 Figure 5b where Figure 5a Guide Bar 1 is shown to undergo a 0-4/4-0 repeat motion in order

269 to create an open chain stitch defined by yarn 13 as link in by weft yarn 14 which undergo a

270 0-0/16-16 repeat motion in order to create an inlay over 4 needles as shown in Figure 5b

271 Guide Bar 2. Typically Barl is fully threaded (full set) at typically one end per guide

272 although it is envisaged that Bar 1 may be partially threaded. Typically Bar 2 is half set (one

273 in-one out) at typically one end per guide but may be fully threaded or otherwise partially

274 threaded. Typically the yarn for 13 and 14 is about 140 decitex non-texturized, preferably

275 high tenacity polyester, but could be any one of the contemplated yarns or combinations

276 thereof. Likewise, yarn 13 and 14 need not be the same.

277 The lapping motion for a suitable knop stitch is shown in Figure 5c and 5d. Figure 5c

278 Bar 3 is shown to work according to the following weave: 4-4/4-0/4-0/4-4/12-16/12-16 and is

279 threaded at two ends per guide, one in, one out, one in, five out repeat. Figure 5d Bar 4 is

280 shown to working according to the follow weave: 4-4/12-16/12-16/4-4/4-0/4-0 and is

281 threaded at two ends per guide, four out then one in, one out, one in, five out, repeat. In order

282 to render the knops 10 resistive to compressive deformation, and thereby resist collapse of the

283 warp and weft fluidic flow paths, a relatively inextensible yarn 15 and 16 is chosen and the

284 stitches making up respective knops 10 are knitted sufficiently tightly. Typically the knop

285 yarn 15 and 16 is about 1100 decitex non-texturized, preferably high tenacity polyester, but

286 could be any one of the contemplated yarns or combinations thereof. Likewise, yarn 15 and

287 16 need not be the same.

288 The timing of the lapping motion of Bar 3 and Bar 4 is shown in Figure 5e. The

289 interlacing of the knop laps of Bar 4 with Bar 3, as shown, serves to increase the knop

290 prominence and is the preferred embodiment of the inventive textile.

291 Figure 5 f shows the lapping motion Bars 1 through 4. The resulting textile is

292 preferably heat set after knitting in order to remove lubricants, conditioners, etc from the

293 yarn. The heating is preferably performed on tenters disposed lengthwise such as to affix the

294 machine state weft dimension during the setting process. Articles thus obtained show

295 excellent stability whereas the starting knitted fabric is in itself somewhat deformable. The

296 textile may also be finished with a form of resin coating, such as an acrylic, that acts to

297 further stabilize the open-work architecture from deformation during application and

298 processing.

299 Further to the example Table 1 below details the knitting specification and resulting

300 textile per the example presented in Figures 5a-f. 301

3Oi

302 Table 1

03 O4

304 Example 2:

305 The warp knit guide bar-lapping diagrams of another non-limiting example of an

306 open-work textile 6 of the present invention are shown in Figures 6a-f.

307 The lapping motion of the ground mesh is shown in Figure 6a and Figure 6b where

308 Figure 6a Guide Bar 1 is shown to undergo a 0-4/4-0 repeat motion in order to create an open

309 chain stitch defined by yarn 13 as link in by weft yarn 14 which undergo a 0-0/16-16 repeat

310 motion in order to create an inlay over 4 needles as shown in Figure 6b Guide Bar 2. The

311 lapping motion for a suitable knop stitch is shown in Figure 6c and 6d. Figure 6c Bar 3 is

312 shown to work according to the following weave: 4-4/4-0/4-0/4-4/8-12/8-12 and is threaded

313 at two ends per guide, two in, six out repeat. Figure 6d Bar 4 is shown working according to

314 the follow weave: 4-4/8-12/8-12/4-4/4-0/4-0 and is threaded at two ends per guide, four out

315 then two in, six out, repeat.

316 The timing of the lapping motion of Bar 3 and Bar 4 is shown in Figure 6e.

317 Figure 6f shows the lapping motion Bars 1 through 4. The resulting textile is preferably heat

318 set after knitting in order to remove lubricants, conditioners, etc from the yarn.

319 Further to the example Table 2 below details the knitting specification and resulting

320 textile per the example presented in Figures 6a-f. 321

Table 2

The manner of usage and operation of the present invention, and variations and equivalents thereof, will be apparent to those skilled in the art from the above description, and it will be recognized that a wide variety of specific practices may be employed.

With respect to the above description and example, it is also to be recognized that the optimum dimensional relationships for the parts of the invention, may include variations in size, materials, shape, form, function and manner of operation, assembly and use.

Obviously, the invention is not limited to the examples given hereinabove and on the contrary covers any variants thereof which remain with its scope or its spirit.

For example, although in the described example the knitted fabric is obtained on a one-needle bar Raschel machine, it could also be possible to produce tubular knitted fabrics

333 on a two needle bar Raschel machines, the resulting article being either used in its tubular

334 shape, or optionally cut along a generating line, to double the width of the finished article.

335 Also, the articles according to the invention could also be produced on any other warp

336 knit machines such as warp looms or crocheting machines.

337 It is further possible, by combining different stitches, to obtain open-work with

338 interstices shaped differently one from the other, alternating for example diamond and

339 hexagonal shapes.

340 Therefore, the foregoing specific working embodiments are considered as illustrative

341 only of the principles of the invention. Further, since numerous modifications and changes

342 thereto may be made by those skilled in the art, without departing from the spirit of this

343 invention, which is limited only by the scope of the following claims.

344 What is claimed is: