Title of Invention

"A PROCESS FOR THE MANUFACTURE OF TRANSLUCENT STRUCTURAL COMPOSITE COMPONENTS"

Abstract

This work basically describes the process of obtaining translucent structural composite components using a novel process. The efficacy of the process yields translucent composites coupled with high structural integrity for the composite systems. The end use applications that can be thought of in this context are aircraft's windows, side windows of automobiles, sub-components of submarines, decorative murals and several structural composite parts calling for extremely high resin-fibre integrity. The process highlights the appropriate positioning of the mould plates, with primary emphasis on the reinforcement layout in such a way as to maximise the resin ingress into the micro structure of the fabric(yarn bundles) due to the combined effects of anti-gravity and capillary action coupled with appropriate positioning of the inlet and outlet ports. Where applicable, best use is made of the optical properties of the reinforcement/resin systems (such as glass- epoxy/polyester) to render translucent characteristics without compromising on the other structural requirement parameters.

Full Text

The present invention relates to a process for the manufacture of translucent structural composite components. The present invention particularly relates to a process for the manufacture of structural composite components using resin ingression technique. The main usage of the invention is in the preparation of composites with improved fibre wetting, fibre-matrix interface, devoid of air pockets, a total homogeneity with either only the matrix or matrix adhered fibre or fibre impregnated resin at any given cross-section of the composite. Another usage is in the preparation of composites with appreciable levels of translucency in such reinforcements/resin systems as glass-resin composites, wherein the optical properties of the two systems are made to match each other. Yet another usage is to occlude the reinforcement form from being clearly visible. Still another usage is to provide products with high strength in the structure coupled with translucent characteristics in selected systems. Among several methods of preparing woven fabric composites, hand lay-up technique, different Resin Transfer moulding techniques reported and autoclave moulding, are being primarily used in their fabrication. Although these processes are widely practised, such composites are obtained with inherent opacity, fibre dis-orientations and lack of a truly desirable fibre-matrix coalescence and integrity. These composites do not really justify the theoretical claims as reinforcement with continuous matrix throughout due to a variety of reasons. All the above processes provide footage to surface wetting without giving importance to the core wetting (micro-structural) of the fabric/yarn partly due to the inherent limitations of the individual techniques. This is more so when specialised requirements need to be thought of such as aircraft's and automobile's windows, sub- components of submarines, decorative murals and such other structural components which calls for some translucent characteristics coupled with high structural integrity. With this background, a patent search was made in the related areas. A new process of preparing composites of structural grade where in they can be rendered translucent as applicable, has been thought of and prepared successfully. The patent search through various databases revealed that no patent is available to the best of our knowledge on the process of the present invention. However the following are reported due to their proximity to the present work Reference may be made to 1. Pat no US 3823794 wherein the claimants have made translucent laminates using glass and ceramics by bonding. The work incorporates an interlayer of optical quality plastics. The drawbacks of the work is that it does not highlight the possibility of composite components. 2. US 5900311 where the inventor claims of preparing fibre-reinforced thermosetting polyesters using vacuum assisted transfer moulding technique. In this processes, the polyester composite is formed by coating the surface of the mould with a gel coat; applying a skin laminate over the partially cured gel coat; applying a fibre reinforcement to the skin laminate; closing the mould and injecting the matrix precursor while the mould is under vacuum. The drawbacks of the work are that it does not mention of the workability at the component level. 3. US 4874450 where the inventors claim of a process for laminating two or more transparent or translucent substrates or one transparent and one opaque substrate together by use of a dye-counter ion complexes. The drawbacks of the work are that it is basically a chemical process and as such does not highlight about the structural applications. US 5397645 where the inventors claim of preparing a fire resistant composition comprising an epoxy resin, a curing agent for the said resin and a boron compound which is not a curing agent for the epoxy resin, the reaction mixture being translucent such that the reaction mixture cures to a translucent reaction product. This work is concentrated on neat resin casting which as such cannot be used in structural components. None of the patents above and other scanned works within our purview reports on the process of the present invention or the product quality obtained. Similarly, a detailed literature scan through various international journals and National Technical Information Services and American Institute for Aeronautics and Astronautics abstracts has revealed that no such process has been carried out. The main objective of the present invention is to provide a process for the manufacture of translucent structural composite components using resin ingression technique. Another objective of the present invention is to occlude the reinforcement from being visible. Yet another objective of the invention is to provide products with high strength coupled with translucency as applicable which would have high end applications In the drawings accompanying this specification: Figure 1 represent the mould internal details for the preparation of flat composite laminates. Figure 2 represents the positioning of the assembled mould plate set-up for resin ingression in the case of flat laminates. Figure 3 represent the assembled set-up for the preparation of a conical component by the above said process with multiple inlets and a single outlet. Accordingly, the present invention provides an improved process for the manufacture of translucent structural composite components characterized in that using resin ingression technique wherein resin system is pressure injected through the resin ingression source against gravity , which comprises preparing a mould having exterior dimension 300 mm x 300 mm and cavity dimension 220 mm x 250 with an outlet at the top end and one or more inlets at the bottom end, placing one or more reinforcement form(s) having dimension 220 mm x 220 mm in the mould in such a manner so as to leave a cavity along the bottom end, attaching the inlet(s) at the bottom end of the said mould to a resin ingression source in such a manner so as to provide a resin column above the top of the outlet in the mould, pouring a resin system as herein described in the ingression source and said ingression source being pressurized by creating vacuum at the mould-set so as to gradual percolating of resin mix into the mould cavity until excess resin comes out the outlet port , followed by switching of the vacuum; curing the de moulded component at room temperature for a period of 24 hours to get desired structural composite. In an embodiment of the present invention the top outlet may be optionally connected to a vacuum source. In another embodiment of the present invention, the resin ingression source may be such as a self weighted resin column, pressure injected resin column. The process of the present invention provides fabrication of composite components by the method of matrix intrusion into the microstructure of the fabric, preparation of composites with perfect interface between the fibre and matrix, preparation of composites devoid of voids, airspace and microvoids, to a major extent, in a manner as to exploit maximally the capillary action of the reinforcement fibres in the fabric structure. Preparation of the composite in a very selective posture) so as to balance the^ effects of gravity and capillary action in order to achieve a perfect packing of even the smallest of the interstices of the yarn and fabric structure in an organised manner, fabrication of composite laminate wherein the matrix material is so verv efficiently packed as a single entity, that prima face on observing the finished product there shall not be available any minute indication whatsoever as to the type and form of reinforcement in the composite. The process of the present invention allows fabrication of the-above without compromising on the other static and dynamic properties already established in the woven fabric composites field, fabrication of the composites avoiding cumbersome manual involvement and layups, fabrication of composites with a plurality of layers off fabric, knits and yet obtaining the translucency where applicable and the same achievable even at higher fibre fractions. In the process of the present invention the translucent structural composite components are obtained due to 1. Maximum exploitation of capillary nature of the fibres/strands of the reinforcement by appropriate positioning ot tne mould plates. 2. Thorough wetting of the fabric/yarn microstructure, fibre bundles, micro-fibres due to unconstrained flow of the resin all over the volume of the laminate. 3. Resin ingression against gravity which enables the resin to pack into every micro- structural detail of the reinforcement until such time as the whole interstitial volume of the reinforcement is completely wetted with the resin system. 4. Least or minimum fibre distortion due to undisturbed resin ingression process in the enclosed cubic space of the mould. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention Example 1 Preparation of flat laminate Reinforcement form : Twill woven glass fabric Fabric weight : 280 Gins per Sq.mtr Resin system : Epoxy (Resin : Hardener = 100 :40) No of fabric layers : 12 Required laminate thickness : 3 mm mould exterior dimension : 300 mm X 300 mm mould cavity dimension : 250 mm X 250 mm Reinforcement Dimension : 220 mm X 220mm Density of glass fabric Density of resin system Inlet port details: 2.54 g/cc : 1.15 g/cc : Single, Self-weighted resin flow assisted by Vacuum from outlet Outlet port details : Single, dual functionality of vacuumising the system as well as excess resin outflow. 12 layers of the reinforcement was positioned in the mould cavity as shown in figure 1. The mould set-up was closed and positioned as in figure 2. The outlet was connected to an external source of vacuum. The resin ingression source was positioned at a point higher than the highest point of the mould plate. Resin system calculations : Area of fabric enclosed in the mould = 0.22 X 0.22 = 0.0484 Sq.mtr Mass of single layer of fabric used in the mould = 0.0484 X 280 = 13.55 gms Total mass of 12 layers of fabric used in mould = 13.55 X 12 = 162.6 gms Total fabric volume in the mould = mass/density = 162.6/2.54 = 64.02 cc Enclosed volume of mould cavity without reinforcement = LXBXH = 25X25 X0.3 = 187.5cc volume of free space in the mould to be filled by resin = 187.5 - 64.02 = 123.48 cc Mass of resin to be filled in the mould = volume X density = 123.48X1.15= 142.0 gms Total mass of resin system required to completely wet the fibres and slight surplus in the inlet and outlet ports will amount to 1.5 times the above calculated value, i.e., total mass of resin system required = 1.5 X 142 = 213 gms (Resin = (100/140) X 213= 152.14 gms; Hardener = (40/140) X 213 = 60.85 gms) The above calculated amounts of resin and hardener are mixed together to form the resin system. The mould set-up is vacuumised and the resin system is poured through the resin ingression source. The. resin system gradually percolates into the mould cavity. The vacuum is switched on until a slight excess of the resin comes out of the outlet port. The vacuum is than switched off and the component de-moulded after 24 hrs of cure at room temperature. Example 2 Preparation of flat laminate Reinforcement form : Uni-directional woven glass fabric Fabric weight : 676 Gms per Sq.mtr Resin system : Polyester (Resin : catalyst: accelerator = 100 : 1.5 : 1.5) No of fabric layers : 4 Required laminate thickness : 2 mm mould exterior dimension : 300 mm X 300 mm mould cavity dimension : 250 mm X 250 mm Reinforcement Dimension : 220 mm X 220mm Density of glass fabric : 2.54 g/cc Density of resin system : 1.2 g/cc Inlet port details : single. Self-weighted resin flow Outlet port details : single, functionality of excess resin outflow. 4 layers of the reinforcement was positioned in the mould cavity as shown in figure 1. The mould set-up was closed and positioned as in figure 2. The resin ingression source was positioned at a point higher than the highest point of the mould plate. Resin system calculations : Area of fabric enclosed in the mould = 0.22 X 0.22 = 0.0484 Sq.mtr Mass of single layer of fabric used in the mould = 0.0484 X 676= 32.72 gms Total mass of 4 layers of fabric used in mould = 32.72 X 4 = 130.88 gms Total fabric volume in the mould = mass/density = 130.88/2.54 = 51.53 cc Enclosed volume of mould cavity without reinforcement = LXBXH-25X25 X0.2 = 125 cc volume of free space in the mould to be filled by resin =125-51.53 = 73.47 cc Mass of resin to be filled in the mould = volume X density = 73.47 X 1.2 = 88.16gms Total mass of resin system required to completely wet the fibres and slight surplus in the inlet and outlet ports will amount to 1.5 times the above calculated value, i.e., total mass of resin system required = 1.5 X 88.16 = 132.25 gms (Resin = (100/103) X 132.25 = 128.4 gms; Catalyst = (1.5/103) X 132.25 = 1.93 gms ; Accelerator = (1.5/103) XI 32.25 =1.93 gms) The above calculated amounts of resin, catalyst and accelerator are mixed together to form the resin system. The resin system is poured through the resin ingression source. The resin system gradually percolates into the mould cavity. The position of the mould setup is not disturbed until a slight excess of the resin comes out of the outlet port. The component is de-moulded after 2 hrs of cure at room temperature. Example 3 Preparation of flat laminate Reinforcement form : Multi-axial woven glass fabric Fabric weight : 695 Gms per Sq.mtr Resin system : Epoxy (Resin : Hardener = 100 :40) No of fabric layers : 4 Required laminate thickness : 2 mm mould exterior dimension : 300 mm X 300 mm mould cavity dimension : 250 mm X 250 mm Reinforcement Dimension : 220 mm X 220mm Density of glass fabric : 2.54 g/cc Density of resin system : 1.15 g/cc Inlet port details : Single, Self-weighted resin flow assisted by Vacuum from outlet Outlet port details : Single, Dual functionality of vacuumising the system as well as excess resin outflow. 4 layers of the reinforcement was positioned in the mould cavity as shown in figure 1. The mould set-up was closed and positioned as in figure 2. The outlet was connected to an external source of vacuum. The resin ingression source was positioned at a point higher than the highest point of the mould plate. Resin system calculations : Area of fabric enclosed in the mould = 0.22 X 0.22 = 0.0484 Sq.mtr Mass of single layer of fabric used in the mould = 0.0484 X 695 = 33.64 gms Total mass of 4 layers of fabric used in mould = 33.64 X 4 = 134.55 gms Total fabric volume in the mould = mass/density = 134.55/2.54 = 52.97 cc Enclosed volume of mould cavity without reinforcement = LXBXH = 25X25 X0.2 = 125 cc volume of free space in the mould to be filled by resin = 125 - 52.97 = 72.03 cc Mass of resin to be filled in the mould = volume X density = 72.03 X 1.15= 82.83 gms Total mass of resin system required to completely wet the fibres and slight surplus in the inlet and outlet ports will amount to 1.5 times the above calculated value, i.e., total mass of resin system required = 1.5 X 82.83 = 124.25 gms (Resin = (100/140) X 124.25 = 88.75 gms; Hardener = (40/140) X 124.25 = 35.50 gms) The above calculated amounts of resin and hardener are mixed together to form the resin system. The mould set-up is vacuumised and the resin system is poured through the resin ingression source. The resin system gradually percolates into the mould cavity. The vacuum is switched on until a slight excess of the resin comes out of the outlet port. The vacuum is than switched off and the component demoulded after 24 hrs of cure at room temperature. Example 4 Preparation of conical shaped composite component Reinforcement form : Knit glass fabric Resin svstem : Epoxy (Resin : Hardener = 100 :40) No of fabric layers : 1 Required Component thickness : 6 mm mould exterior(inner) dimension : Radius = 4.95 cm ; height = 17.98 cm Dimension of core : Radius = 4.35 cm ; height = 17.83 cm Density of glass fabric : 2.54 g/cc Density of resin system : 1.15 g/cc Inlet port details : Four, Pressure-injected resin flow Outlet port details : Single for excess resin outflow. 1 layer of the reinforcement was positioned in the mould cavity. The mould set-up was closed and positioned as in figure 3. The resin ingression source was positioned at a point higher than the highest point of the mould plate. Resin system calculations : Actual mass of knit enclosed in the mould = 63 gms Total fabric volume in the mould = mass/density = 63/2.54 = 24.8 cc Enclosed volume of mould cavity without reinforcement = Exterior mould volume - internal mould volume (1/3 7tr2h) =461-353 = 108 cc volume of free space in the mould to be filled by resin = 108 - 24.8 = 83.2 cc Mass of resin to be filled in the mould = volume X density = 83.2 X 1.15= 95.68 gms Total mass of resin system required to completely wet the fibres and slight surplus in the inlet and outlet ports will amount to 1.5 times the above calculated value, i.e., total mass of resin system required = 1.5 X 95.68 = 143.52 gms (Resin = (100/140) X 143.52 = 102.52 gms: Hardener = (40/140) X 143.52 = 41 gms) The above calculated amounts of resin and hardener are mixed together to form the resin system. The resin system is pressure injected through the resin ingression source. The resin system gradually percolates into the mould cavity. The mould set-up was not disturbed until a slight excess of the resin came out of the outlet port. The component was de-moulded after 24 hrs of cure at room temperature. Based on the examples above, it can be inferred that the process is applicable to a variety of reinforcement forms, resin systems and contoured products. The process is similar in functionality for a variety of thickness' and weight fractions. Change in weight fraction can be easily achieved by either increasing or decreasing the number of fabric layers in any given volumetric space of the mould cavity. Appropriate reinforcement material and suitable resin system combination renders translucent characteristics thus depicting the efficacy of the process. The main advantages of the present invention are 1. Maximum ingression of the resin into the interstitial space of the reinforcements 2. Near perfect optical matching of the reinforcement and matrix, thus rendering the composite laminate as a translucent product. 3. To obtain void free and air-pocket free composites. 4. Resin becoming a truly continuous matrix close to theoretical considerations (as is hitherto being assumed in all the composite analysis and calculations) even in layered opaque composites. 5. Obtaining of maximum fabric resin interfacial bond which is unattainable by the other available advanced techniques, (autoclave, Resin Transfer Moulding, Vacuum assisted Resin Transfer) 6. Finally obtaining composite structures with a unique combination of structural properties and optical translucency. 7. Comparable or often higher impact properties with the added advantages of translucency. 8. Easier preparation of composites with complex contours such as cones, cylinders etc., 9. Elimination of cumbersome manual lay-up operation rendering it a very clean and economical process. We Claim: 1. An improved process for the manufacture of translucent structural composite components characterized in that using resin ingression technique wherein resin system is pressure injected through the resin ingression source against gravity , which comprises preparing a mould having exterior dimension 300 mm x 300 mm and cavity dimension 220 mm x 250 with an outlet at the top end and one or more inlets at the bottom end, placing one or more reinforcement form(s) having dimension 220 mm x 220 mm in the mould in such a manner so as to leave a cavity along the bottom end, attaching the inlet(s) at the bottom end of the said mould to a resin ingression source in such a manner so as to provide a resin column above the top of the outlet in the mould, pouring a resin system as herein described in the ingression source and said ingression source being pressurized by creating vacuum at the mould-set so as to gradual percolating of resin mix into the mould cavity until excess resin comes out the outlet port , followed by switching of the vacuum; curing the de moulded component at room temperature for a period of 24 hours to get desired structural composite. 2. An improved process as claimed in claim 1 wherein the resin ingression source is selected from a self weighted resin column, pressure injected resin column and the resin system used is selected from mixture of epoxy resin and hardener (5:2) , polyester (resin: catalyst: accelerator 100:1.5:1.5). 3. An improved process for the manufacture of translucent structural composite components substantially as herein described with reference to the examples.

Documents:

156-del-2000-abstract.pdf

156-del-2000-claims.pdf

156-del-2000-correspondence-others.pdf

156-del-2000-correspondence-po.pdf

156-del-2000-description (complete).pdf

156-del-2000-drawings.pdf

156-del-2000-form-1.pdf

156-del-2000-form-19.pdf

156-del-2000-form-2.pdf

156-del-2000-form-3.pdf