IL217477A - Resin infusion apparatus and method - Google Patents

Description

RESIN INFUSION APPARATUS AND METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of resin infusion, more particularly but not exclusively, the present invention is related to the field of systems and methods for manufacturing of reinforced composite structures, wherein a liquid resin is infused through a reinforcement positioned in a mold and cured or hardened to form the composite structure. 2. Description of Related Art Fiber reinforced composite materials are an important class of engineering materials that offer outstanding mechanical properties and unique design flexibility. Such materials are lightweight, corrosion resistant, impact resistant, and exhibit excellent fatigue strength. Composite materials are used in a wide variety of applications including automotive parts, aviation, marine vessels, offshore structures, containers piping, sporting goods and etc. Liquid resin molding, which includes resin transfer molding, reaction injection molding, and resin vacuum infusion, is one of the most attractive manufacturing solutions for producing high quality, affordable, and environmentally friendly composite materials .

Liquid resin molding requires the incorporation of a resin or other flowable elastic material into a reinforcing fiber. Reinforcing fiber generally takes the form of one or more layers of woven or felted fiber reinforcement, typically comprised of carbon, graphite, or fiberglass. The resin infusion or impregnation process is usually done by either a wet or dry fiber lay-up technique. In the wet fiber lay-up process, the resin "wetted" fiber reinforcement consists of a prepreg which already contains a resin and is laid up on a mold and cured. In the dry lay-up process, the fiber reinforcement is laid up dry on a mold or form which serves as a mold. The form may be incorporated as part and parcel of the finish product. Thereafter, the fiber is sprayed, brushed, impregnated, infused, or otherwise coated or "wetted" with the resin. The 2 217477/2 resin is then cured to form the fiber reinforced plastic structure. During the curing stage of either process, the structure can be placed in a vacuum to assist the curing process. To this end, vacuum bag techniques have been used to provide such vacuum assistance. In a vacuum technique, a flexible impervious sheet, liner, or bag is used to cover a single mold which contains the dry or wet (resin impregnated) fiber lay-up. In the wet fiber process, the edges of the flexible sheet are clamped against the mold to form an envelope and seal the resin impregnated fiber lay-up to the mold and out of the atmosphere. A vacuum is then applied to consolidate the preform during the cure of the resin. In the dry fiber lay-up, catalyzed liquid plastic or resin is generally introduced into the envelope or bag interior to wet the dry fiber, usually using a vacuum to help push the resin into the bag and wet out the dry fiber. Vacuum is applied to the bag interior via a vacuum line to collapse flexible sheet against the fiber and the surface of the mold, while the plastic wetted fiber is processed, compacted and cured to form the fiber reinforced structure. The vacuum bag used in this process is critical because it provides not only a vacuum seal but also a distribution mechanism for moving the liquid resin over the preform. These flexible bags are difficult to work with and although some are considered to be reusable, are typically inadequate for large volume manufacturing production. Also, flexible bags do not perform adequately when used by themselves for processing complex three dimensional shapes. It has been found that flexible bags do not conform entirely to the reinforced structure around corners and other high radius curves. "Bridging" is a term used to describe this condition. When the flexible bag bridges across corners, a gap or void is created between the bag and the reinforced structure, thereby preventing a continuous, uniform distribution of resin.

Molding technology of fiber reinforced resin composite material is disclosed in patent No. C 102009480 to Jinming. This technology comprises the following processing steps: adding a rigid sealed cap outside of the vacuum bag of a mold-closed die combined by a single-surface rigid pre-molding mold and an elastic vacuum bag; cutting the whole die into two sealed cavities; laying a reinforced fiber pre-molding body which is completely or partially dipped with resins in the pre-molding cavity in advance; removing gas in the pressurizing cavity; vacuumizing the pre-molding cavity; and when the pre-molding cavity reaches the vacuum degree of below 0.07 atm, pouring gas into the pressurizing cavity while keeping on vacuumizing the pre-molding cavity to cause the vacuum bag to compact the reinforced fiber pre-molding body laid in advance.

An improved resin infusion process is disclosed in US patent No.7862322 to Okoli. In the process disclosed by Okoli, only a single mold is used and the resin is drawn from an outer source, via an inlet conduit, into a cavity formed between two flexible diaphragms. The mold is then pressed into the lower diaphragm, thus driving the resin to take the form of the mold.

Although the resin infusion method described by Okoli produces reinforced composite structures, it is disadvantageous in that large amount of excess resin waste is produced. In particular, since the resin cannot be removed from the resin supply lines before the resin cures or hardens in the mold, the resin supply lines including the resin left within them must be destroyed or disposed of as hazardous waste. Moreover, curing or hardening of the chemically catalyzed resin in the mold may occur prematurely, resulting in lack of repeatability from one finished structure to the next. As a result, the process disclosed by Okoli requires set-ups, handling and clearing by a skilled worker during each and every mold. This process is time consuming and expensive.

Therefore, there exists a need in the art for a resin infusion method and apparatus that overcomes the aforementioned problems and disadvantages.

It would be advantageous to have a flexible infusion method which does not require an external resin reservoir.

It would be advantageous to have a flexible infusion method which evenly spreads resin without causing air pockets or Bridging.

It would be advantageous to have a flexible infusion method which allows control over the amount of the resin which is inserted into the mold and to enable extraction of excess resin from the mold if necessary.

It would be advantageous to have a flexible infusion method which allows control of the pressure applied over the reinforcements both from inside the mold as well as from outside of the mold.

It would be advantageous to have a flexible infusion method for complex shapes which can be used repeatedly, applied quickly, is reliable in holding stable vacuum and provides uni form resin distribution.

Other advantages will become apparent as the description proceeds. 4 217477/2 SUMMARY OF THE INVENTION The present invention comprises a method of resin infusion, wherein the resin is applied over a large portion of the reinforcement, rather than onto a specific point via a conduit as in the prior art methods. Applying the resin over a large portion of the reinforcement facilitates uniform distribution of the resin and diminishes the number of the air pockets.

The method of resin infusion of the present invention comprises the steps of providing a mold having a mold cavity, placing a reinforcement inside the mold cavity, pouring a liquid resin into said mold cavity, placing an elastic cover inside the mold cavity, creating a vacuum between said mold cavity and said elastic cover, wherein said vacuum causes the elastic cover to be pressed against the walls of said mold cavity, thus causing the resin to be driven up the walls of the mold cavity and impregnating said reinforcement.

The present invention also comprises an apparatus for resin infusion, the apparatus comprises a mold having a vacuum port adapted to be connected, via a conduit, to an external vacuum source, said mold also contains a cavity with inlet-outlet port. The apparatus for resin infusion also comprises an elastic cover having a seal, the elastic cover is adapted to be placed inside said cavity and to create a sealed space between said elastic cover and the cavity, and wherein said sealed space contains said vacuum port.

The apparatus for resin infusion may additionally comprise a lid having a seal and a conduit, wherein said conduit is adapted to be connected to an external high pressure source, and wherein said lid is also adapted to seal the mold and to create a sealed space between the elastic cover and the lid.

The apparatus for resin infusion may additionally comprise a pressure sensor, positioned inside the mold, and a controller connected to said sensor, wherein said controller is adapted to regulate the pressure and vacuum level of the resin infusion apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. l A is a perspective view of a prior art resin infusion apparatus.

FIG. IB is a flowchart of a prior art resin infusion method.

FIG.2 is an exploded view of an embodiment of the resin infusion apparatus of the present invention.

FIG.3 is a perspective view of an embodiment of the resin infusion apparatus of the present invention, FIG.4 is a perspective view of another embodiment of the resin infusion apparatus of the present invention.

FIG.5 is a flowchart of an exemplary resin infusion method of the present invention.

DETAILED DESCRI PTION Referring to Figs. 2-4. an apparatus 20, in accordance with an embodiment of the present invention, is illustrated for making a reinforced composite structure. The apparatus 20 is illustrated as comprising a mold 27 having a mold cavity 26. corresponding to the shape of the finished end product, in which a reinforcement 24 is placed. An elastic cover 200 (which is used as a vacuum bag), corresponding to the shape of the cavity 26, is placed in the mold cavity 26 and is pressed to the walls of the mold cavity 26 by a vacuum pressure created between the mold cavity 26 and the elastic cover 200. The vacuum pressure between the mold cavity 26 and the elastic cover 200 is created by connecting an external vacuum source to the vacuum conduit 21 , which is connected with the other end to the vacuum port 28 of the mold 27, and removing the air from the sealed space between the mold cavity 26 and the elastic cover 200, wherein the sealing is achieved by use of the seal 201 which is located on 6 217477/2 the upper part of the elastic cover 200. The seal 201 encloses the mold cavity 26 and the vacuum port 28, when the elastic cover 200 is placed in the mold cavity 26.

The elastic cover 200 could be made from an appropriate elastic material such as silicone rubber.

The mold cavity 26 has an inlet-outlet port 29 which is used for the removal of an excess resin from the mold cavity 26. Alternatively, additional resin may be added to the mold cavity 26, via port 29, by using a conduit 22.

The apparatus 20 may also comprise a lid 33 having a seal 32. The lid 33 is attach'ed to the upper part of the mold 27, as shown in Fig. 4. The lid 33 is used for creating an extra pressure on the elastic cover 200 by connecting a lid conduit 31 to an external high pressure source.

The apparatus 20 may also comprise a pressure sensor 23 positioned in the mold cavity 26. The sensor 23 measures the pressure exerted by the elastic cover 200 onto the mold cavity 26 and the resin 25. The sensor 23 is connected to a programmable controller which automatically regulates the pressure and the vacuum level supplied to the apparatus 20 according to a predefined criteria.

The present invention also comprises a method for making a reinforced composite structure. In order to create a reinforced composite structure, a mold 27 having a cavity 26 of the shape of the desired product is selected. A reinforcement 24 of the desired shape is placed inside the cavity 26. The liquid resin 25 is applied or poured into the cavity 26, on the reinforcement 24 or beneath it, and the elastic cover 200 is inserted into the mold cavity 26 and pressed against cavity walls and against the liquid resin 25 by a vacuum pressure created between said elastic cover 200 and the mold cavity 26, thus driving the resin 25 up the walls of the cavity 26 and therefore coercing the resin 25 to take the form of the cavity 26, while infusing or impregnating the reinforcement 24 (see Fig.3). Additional pressure for pressing the elastic cover 200 against the walls of the mold cavity 26 could be provided by sealing the mold 27 with the lid 33 and connecting the conduit 31 to an external high pressure source. The excess resin, if any, is removed from the mold cavity 26 via the conduit 22. Alternatively, additional resin, i f needed, could be added to the cavity 26 via the conduit 22.

An exemplary method 50 for making a reinforced composite structure by the vacuum infusion method of the present invention is shown in Fig.5. The first step 51 of the method 50 is setting up a mold, i.e. providing a mold of the desired shape with a reinforcement already placed inside. The second step 52 is applying a resin into the mold. The third step 53 is covering the mold and the resin by an elastic cover. In the fourth step 54, the vacuum is activated. In the last, fifth step 55, excess resin is removed via a conduit.

Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims (1)

1/6 Fie. 1A (Prior Art) 2/6 Set-u p resin reservoir Fig. IB (Prior Art) 3/6 Fig. 2 4/6 Fig. 3 Fig.4 6/6 Fig. 5