MXPA99008366A - Slurry preform system - Google Patents

Abstract

An efficient, low cost method and apparatus for controlling fiber deposition in a fiber reinforced preform (12) is provided. In the method, a main screen (26) is placed in a tank (36) filled with liquid (44). The main screen (26) has a major surface (30), upright side walls (28) and a plurality of openings (32) formed therein. Reinforcing fibers (42) are added to the liquid (44) to create a slurry (45). The main screen (26) is raised through the slurry (45) to a level beneath the top ofthe slurry (45), thereby causing the reinforcing fibers (42) to be deposited on the main screen (26). A retainer screen (34) is inserted into the slurry (45) so that the reinforcing fibers (42) are sandwiched between the main screen (26) and the retainer screen (34). Both the main screen (26) and retainer screen (34) are raised out of the tank (36) effectively forming a preform (12) with minimal deformation. An alternative embodiment includes a bubbler zone control device (86) for mixing the slurry (45). The tank (36) is divided into separate areas or zones (88) whereby the supply of fluid (44) to each bubbler zone (88) is controlled. The bubbler zone controller (86) may be used to initiate or diminish a vortex in the slurry (45) as the screen (26) is being raised out of the tank (36). Another embodiment includes a fiber dispenser system (103) for adding fibers (42) to the slurry (45).

Description

AGUADA PASTE PREFORMATION SYSTEM BACKGROUND OF THE INVENTION The present invention relates generally to producing fiber-reinforced plastic preforms and, more particularly, to a method and apparatus for controlling fiber deposition in a fiber-reinforced preformed composite. Pieces or pieces composed of fiber reinforced plastic (PRF) are well known and used in a wide variety of applications. A piece of PRF generally comprises a plastic form in which carbon, glass fibers, or other reinforcing fibers are dispersed to provide strength to the component, a method of making a piece of PRF is known as resin transfer molding (MTR). ). In MTR, the fibrous material in a mold is injected with the resin that is cured to form the piece. Examples of these techniques are disclosed in commonly assigned US patents Nos. 4,740,346 Resin Feeding Perimeter Composite Structures; 4,849,147 - Manufacturing Method of a Molded Structure Having Integral Formed Supplemental Members: and 4,863,771 - Hollow Fiber Reinforced Structure and Method of Manufacturing thereof, each of which is specifically incorporated herein by reference. In MTR, the fibrous material is frequently formed in a preliminary configuration before being placed in the mold. The formed sections generally form the contour of the adjacent mold surfaces and are known as preforms. The preforms have been constructed using several different manufacturing approaches. One approach is to direct the staple fibers, by a stream of air, onto a screen. One problem with this technique is that it is difficult to obtain the desired orientation of the fiber. Another method uses mats of fibrous material to make the preforms. This method, however, produces undesirable amounts of waste material and requires labor intensive, resulting in inefficiencies in production costs. Another technique is revealed, for example, known as the wet slurry process, in Keown et al. ("The Wet Process of Aguada Paste Brings Precision to Reinforced Plastic"). Keown reveals a watery paste containing staple fibers attracted by a vacuum to a camera covered by a screen. As a result, the fibers are deposited on the screen. This method, however, is associated with certain disadvantages. For example, it is difficult to consistently obtain the desired strength and orientation of the fibers using this equipment.

In addition, the pumps and other equipment needed to create the vacuum and attract the slurry through the screen can be excessively complex and difficult to maintain. In addition, the process is relatively slow. An improved wet slurry process is disclosed in commonly assigned US Patent No. 5,039,465 - Method and Apparatus for the Formation of Fiber Reinforced Plastic Preforms using Water Paste, which is also incorporated herein by reference. The process disclosed therein teaches the creation of a preformed composite by lifting a screen in a tank containing a slurry of fibers resulting in the fibers being deposited on the screen. While this method is promising, it also has some disadvantages. For example, the structural integrity of the preforms can be compromised at the moment of removing the liquid screen. As the screen moves down the surface of the slurry, the pressure of the slurry forces the fibers onto the screen and holds them in place. However, when the screen reaches the surface plane of the slurry when removing the preformed compound from the tank, the fiber and liquid mixture surrounding the screen tends to flow into the internal cavity of the preformed composite. When introducing the slurry into the preform, the vertical side walls of the preform can fall apart, thus creating the need for costly repair or complete loss of the preform. Another challenge in the construction of reinforced fiber preforms is to keep the thickness of the wall uniform throughout the preform. By dragging the screen through the watery paste, more liquid is forced through the larger surface of the screen which is perpendicular to the direction of drag of the vertical side walls which are parallel to the direction of movement of the screen. Because the amount of fiber deposited on the screen is proportional to the amount of liquid forced through the screen, preforms constructed in this way can contain sections of non-uniform thickness. Another challenge exists with respect to creating preforms in a production environment. Currently, the chopped fiber must be weighed and added to the watery paste at the start of each cycle. The weighing operation is expensive and time consuming. In addition, obtaining a uniform dispersion of the fibers within the water is not an easy job. Because of the surface tension created on the surface of the water, the fibers of least weight are above (on the surface) of the water until a sufficient amount is piled up and they sink. Sometimes everything that has been piled up sinks to the bottom of the tank before dispersing.

SUMMARY OF THE INVENTION According to the present invention, an efficient and low-cost apparatus and method for controlling fiber deposition in a fiber reinforced preform is presented. In one mode, a main screen is placed in a tank filled with liquid. The main screen has a larger surface, vertical side walls and a variety of openings formed in it. Reinforcing fibers are added to the liquid to create a watery paste. The main screen is lifted through the slurry to a level below the surface of the slurry, thereby causing the reinforcing fibers to deposit on the main screen. A retainer screen is inserted into the waxy paste in such a way that the reinforcing fibers are tight between the main screen and the retainer screen. The main screen and retainer screen are raised together outside the tank effectively forming a fiber-reinforced preform with minimal deformation. In another embodiment, the apparatus includes a choke screen positioned adjacent to the main screen to reduce the flow of liquid through this portion of the main screen as it is drawn through the slurry. To optimize the thickness of the walls of the preform, the choke screen may have openings formed therein which are off-center in location or are different in size from the openings in the main screen. In another embodiment, a work cell is provided which includes a rotating plate placed between the tank of the slurry and an oven for an efficient mass production of the preforms. In another embodiment, the apparatus includes an aerator control apparatus and separate bubble zones. The uniformity of the slurry can be increased to the maximum using certain control sequences of the aerator depending on the geometry of the preform. In yet another embodiment, the apparatus includes a fiber dispersion system for controlling the addition of different types of fibers to the slurry. The dispersion controller regulates the addition of several fibers to a spray of water directed to the tank. The addition of the fibers is calculated in sequence to correspond with the lifting of the main screen through the tank. By adding different types of fibers to the watery paste during the ascent run of the main screen, a composite preform can be constructed whose cross section comprises different levels of materials.

BRIEF DESCRIPTION OF THE DRAWINGS The various advantages of the present invention will become apparent to a person skilled in the art after reading the following specification and referring to the drawings in which: Figure 1 is a perspective view of a work cell for creating fiber reinforced preforms of a gouache paste constructed in accordance with the teachings of the present invention. Figure 2 is an enlarged side view of the tank station together with the pallet transfer mechanism positioned directly above the tank and also moved outside the frame of the portico shown in phantom; Figure 2A is a top view of the tank showing the bubble zone controller; Figure 3 is an enlarged top view of the tank station with the paddle transfer mechanism positioned above the tank; Figure 4 is a side view of a portion of the pallet transfer mechanism with the inner pins of the cart extended; Figure 5 is a view of a portion of the tank station showing an outer peg of the cart and a tank peg hooked with a transferable head; Figure 6 is a partial sectional view of the partially removed work cell to illustrate the order of operations; Figure 7 is a partial sectional view of the work cell showing the palette rotated below the pallet transfer mechanism; Figure 8 is a partial sectional view of the work cell showing the transfer mechanism extending down to engage the pallet; Figure 9 is a sectional partial view of the work cell showing the inner and outer pins of the cart in an extended position; Figure 10 is a sectional partial view of the work cell showing the cart assembly and the raised pallet of the plane of the turntable; Figure 11 is a sectional partial view of the tank station showing the transfer mechanism of the paddle moved above the tank station; Figure 12 is a sectional partial view of the tank station showing the paddle below to engage the plate washer; Figure 13 is a partial sectional view of the tank station showing the outer peg of the removed cart and the extended tank peg, thereby connecting the vane to the plate washer; Figure 14 is a partial sectional view of the tank station showing the ball screws displaced downward to place the main screen at the bottom of the tank; Figure 15 is a partial sectional view of the tank station showing the ball screws displaced upwards, dragging the screen through the watery paste while the cart is lowering the retainer screen to submerge in the slurry; Figure 16 is a sectional partial view showing the tank pegs removed and the outer pegs of the cart extended and the guide bar of the retainer screen seated in the installation or assembly blocks; Figure 17 is a sectional partial view showing the retraction of the cart assembly and the pallet; Figure 18 is a sectional partial view showing the retainer screen, the main screen, and the auxiliary screen; Figure 19 is a side view showing the fiber dispersion system with the first fiber battery entering the slurry; and Figure 20 is a side view showing the fiber dispersion system with the second fiber bank entering the slurry.

DESCRIPTION OF THE PREFERRED EMBODIMENT A.- Summary With reference to Figure 1, a work cell 10 is shown to create a preform reinforced with fiber 12 of a slurry. The work cell 10 comprises four stations including a tank station 14, a rotating plate 16, an oven 18 and a cooling station (not shown). The turntable is placed inside a work cell 10 such that the parallel rails 20 of the tank station 14 extend above the turntable 16 thereby providing support from above for a vane transfer mechanism 22. An oven 18 is positioned adjacent to the turntable 16 to effect easy and efficient transfer of a vane 24 between the turntable 16 and the oven 18. In general, the process of creating the fiber reinforced preform begins with loading the vane 24 on the turntable 16, as shown in Figures 1 and 6. Mounted on the pallet 24 is the main screen 26, configured in accordance with the shape of the component that will ultimately be formed, having lateral vertical walls 28, larger surface 30, and a variety of 32 openings in it. The retainer screen 34 is formed to conform at least to the vertical side walls 28 of the main screen 26 as shown in Figure 6. As shown in Figures 2 and 6-11, the vane transfer mechanism 22 is used to lift the blade 24 of the turntable 16 to a position above the tank 36, and lower the blade 24 into the tank 36. Referring to Figures 11-14, the blade 24 is disconnected from the blade transfer mechanism 22 and subsequently connected to the plate washer 38. The plate washer 38 can be lifted and lowered in the tank 36 by the rotation of the screws 40. The reinforcing fibers 42 and the liquid 44 are added to the tank 36 to create a watery paste 45. The watery paste 45 is mixed using a mechanical apparatus or by means of an aerator as set forth in commonly assigned Patent No. 5,039,465, which is hereby incorporated by reference. As shown in Figure 2A, one embodiment of the present invention includes a bubble zone controller 86 for regulating the fluid supply, preferably air, sent to the variety of bubble zones 88. Tank 36 is divided into minus two, but preferably four, bubble zones 88, indicated by A, B, C, and D. The air source 90 is connected to a variety of supply lines 92 positioned upstream of the aerator valves 94, 96, 98 and 100. In a part of the typical sequence of operation, the bubble zone controller 86 commands the aerator valve 94 to open to allow air to enter the bubble zone A. The air supplied to the bubble zone A escapes through a variety of openings 102 and thus mixes the watery paste 45 in zone A. In normal operation mode, air pulsations are sent to the bubble areas 88 in a certain sequence to ensure smooth movement. order of the watery paste 45. For example, air is sent to zone A and zone C for 3 seconds while zones B and D are closed. Then zones B and D are activated for 3 seconds while zones A and C are closed. This cycle is repeated until the preform 12 is removed from the slurry 45. Without the use of the bubble zone controller in its normal mode of operation, a vortex is formed in the slurry 45 when the main screen is lifted through the tank 36. Depending on the geometry of the preform 12, a vortex can be detrimental to the structural integrity of the preform 12 because the turbulent movement of the slurry 45 washes the reinforcing fibers 42 from the vertical side walls 28. On the other hand, in instances where the preform 12 has the vertical side walls 28 small or nonexistent, a vortex can help to wash the reinforcing fibers 42 from the plate washer 38 and towards the main screen 26. In these cases, a vortex can be initiated with air pulsations in bubble areas from zone A to zone D in sequence of alphabetical order. Referring now to Figures 15-17, the paddle 24 including the main screen is initially lowered to almost the bottom of the tank 36. The paddle 24 is then drawn upwardly through the tank 36, thus forcing the liquid 44 pass through the variety of openings 32 and the reinforcing fibers 42 are deposited in the main screen 26. Before the main screen 26 breaks the plane of the surface of the watery paste 45, the retainer screen is inserted - in the slurry 45 in such a manner that the reinforcing fibers are pressed between the main screen 26 and the retainer screen 34. The retainer screen 34 is positioned to protect the preform 12 from damage due to the gust movement of the slurry 45 on the vertical walls side 28 when the main screen 26 of the slurry 45 is lifted. As soon as the retainer screen 34 is correctly positioned, the main screen 26 and the screen are lifted together retainer 34 of the watery paste 45 by means of the vane transfer mechanism 22. As shown in Figures 1 and 2, the vane transfer mechanism moves the vane 24 from the top of the tank 36 to a position above the turntable 16. The vane 24 is lowered again on the turntable 16 on the way to the furnace 18. The turntable 16 is rotated 180 ° on an axis 46 to bring the vane 24 in close proximity to the furnace 18. Any indicated transfer mechanism can be used. for unloading the vane 24 of the turntable 16 and into the oven 18. The vane 24 including the main screen 26, the retainer screen 34 and the preform 12 are heated in the oven 18 to evaporate so much liquid 44 trapped between the reinforcing fibers 42 as possible. The hot vane 24 is transferred to a cooling station, not shown, where air is forced through the main screen 26, the retainer screen 34 and the preform 12 to cool the vane 24 and evaporate any remaining liquid 44. The retainer screen 34 is removed to give access to the preform 12 which is then removed as a contiguous component. As shown in Figure 18, an alternative embodiment of the invention includes an auxiliary screen 82 positioned below at least a portion of the main screen 26. The auxiliary screen 82 acts as a choke effectively reducing the amount of liquid 44 that is forced to through the variety of openings 32 in the main screen 26. The choke serves to deflect the flow of liquid 44 in such a way that the amount of liquid passing through the larger surface 30 is approximately equal to that which is passing through. of the vertical side walls 28. Because the amount of reinforcing fibers deposited on the main screen 26 is proportional to the allowed amount of liquid 44 that passes through the variety of openings 32, equal flow rates of the liquid 44 through of different portions of the main screen 26 will produce a preform 12 of a substantially uniform wall thickness. The auxiliary screen 82 also has a variety of openings 84 that can be formed, scaled or positioned distinctly in the variety of openings 32 in the main display provided the auxiliary display 82 restricts the flow of the liquid 44 through the main screen 26. An example of the auxiliary screen 82 constructed in accordance with the present invention utilizes the variety of openings 84 in the auxiliary screen 82 positioned in misalignment relative to the variety of openings 32 in the main display 26. This misalignment is useful to provide a tortuous path. for the liquid 44, thereby throttling the flow of the liquid 44 through the main screen 26. Another embodiment of the invention, shown in Figures 19 and 20, includes a fiber dispersion system 103 having a dispersion controller 104, a first fiber threader 105, a first trimmer 107 and first spray nozzles 109, to introduce the fibers to the slurry 45. Based on the geometry and type of fiber used, the controller Dispersion 104 regulates the amount of the first group of fibers 106 to be added to the slurry 45. The dispersion controller 104 acts together with the spray nozzles 109 and the mechanism used to lift the main screen 26 such that the fibers 106 are covered with water sprayed from the first spray nozzles 109 while being added to the tank 36, while the screen The main 26 is immersed deep within the slurry 45. While the main screen 26 is lifted through the slurry 45, the first group of fibers 106 forms the first layer of the preform 12. As shown in Figure 20, it is shown in FIG. continues to drag the main screen 26 through the slurry 45 while the dispersion controller stops supplying water to the spray nozzles 109 and stops the advance of the first fiber threader 105 to a first trimmer 107. If the preform to be created is homogeneous including only the first fibers 106, the main screen 26 continues to be lifted and removed from the tank in the manner described above. However, if more than one type of fiber is to be included in the final component, the dispersion controller 104 initiates the second spray nozzles 110 and regulates the second trimmer 114 to cut the second fiber thread 112. The dispersion controller 104 indicates also to the second trimmer 114 to introduce a specific amount of the second group of fibers 108 into the slurry 45. While the second group of fibers 108 leaves the second trimmer 114, the fibers are entrained in the spray of the nozzles 110 and carried by the time of the stream directly into the slurry 45. The addition of fibers with different properties of physical characteristics such as fiber length, fiber diameter, chemical composition, tensile strength and conductivity produces from this Thus, a stratified preform 12 can be manufactured to the order of the final application. For example, components that require only an aesthetically pleasing exterior surface, such as an oil collector or housing cover, can be constructed using a cosmetic-pleasing material on only this surface while the other layers of the structure are made of a less expensive material. In the same way, the impact resistance of the component can be optimized by incorporating into the preform 12 fiber layers with different tensile strengths. If high flexural strength and low cost are required, a multilayer composite with at least 3 layers can be designed to meet these needs in an economically feasible manner. Specifically, the outer layers would be constructed of high strength fibers while the lower tension layers would consist of fibers in lower strength and lower cost. Another example showing that this invention has many uses includes a component with a high conductivity layer of electricity between layers of matter of lower electrical conductivity. This objective can be achieved by using a group of fibers of high electrical conductivity or by adding particles with high electrical conductivity to a supply reservoir of fibers 110. B.- Details of the Apparatus and Method To further assist the reader, the preferred apparatus and method are here described in more detail. With reference to Figures 1 and 6, the pallet includes the main screen 26 having vertical side walls 28, a larger surface 30, and a variety of openings 32 therein, positioned in an opening 48 of a mask 50. The inner portion of the mask 50 defining the opening 48 is provided with an off-center surface 52 allowing the extended edge 54 of the main screen 26 to be matched with a flat surface 56 of the mask 50. Guiding bars 58 are connected to the retainer screen 34. Mounting blocks the retainer screen 60 are secured to the mask 50 and are designed in such a manner to position the retainer screen 34 relative to the main screen 26 when the guide bars 58 engage the mounting blocks of the retainer screen 60. To facilitate the movement of the vane 24 of the turntable 16 to the tank 36, transfer heads 62 are also mounted stationary in the mask 50. As shown in Figure 5, each transferal head 62 contains an upper opening 64 and a lower opening 66. As shown in Figures 1, 3 and 5, the upper openings 64 they are oriented to cooperate with the outer pegs of the cart 68 mounted to a cart 70. When the outer pegs of the cart 68 have engaged the upper openings 64, the vane 24 can be lifted using the cart 70 in conjunction with a hydraulic ram 72. The hydraulic ram 72 is able to raise and lower the cart 70 relative to the turntable 16 and the tank 36. The cart 70 and the hydraulic ram 72 can be moved from a position above the turntable 16 to a position above the tank 36 and back using parallel rails 20 of the tank station 14. With reference to Figures 1 and 7-9, the turntable 16 rotates about the axis 46 of such so that the main screen 26 is placed below the cart 70. The cart 70 is lowered in position when extending the hydraulic ram 72. The outer pins of the cart 68 extend to engage the upper openings 64 of the transfer heads 62. Figure 4 shows the inner pegs of the cart 74 extended below the guide bars 58 to support the weight of the retainer screen 34. As shown in Figures 1, 2 and 10-12, the cart 70 and the pallet 24 are now interconnected sufficiently to lift the vane 24 of the turntable 16. The cart 70 together with the vane 24 are moved along the parallel rails 20 placed in position above the tank 36. The hydraulic ram 72 is activated again to lower the cart 70. The plate washer 38 is connected in four places with the individual ball screws 40 which in turn are mounted to frame of the gantry 76. The position of the plate washer 38 inside the tank 36 is controlled using the ball screws 40. As shown in Figures 5 and 12, the cart 70 is lowered until the mask 50 clutches the off-center surface 77 of the plate washer 38. When the mask settles, the surface 56 is substantially in the same plane with the upper flat surface 78 of plate washer 38. As shown in Figures 13 and 14, the outer pegs of cart 68 are removed, thereby disengaging main screen 26 of cart 70. The pegs of the tank 80, stationary mounted to the plate washer 38, are extended to engage the lower openings 66 of the transfer head 62. The main screen 36 is lowered by activating the ball screws 40. While lowering the main screen 26 in the tank 36 , the hydraulic ram keeps the trolley 70 stationary. The retainer screen 34 is maintained partially above the water slurry 45 with the inner pins of the trolley 74. As shown in Figures 15-17, the preform 12 is created by dragging the main screen 26 through the slurry 45 at a rate that causes the liquid to pass through the openings in the main screen 26, thereby depositing the reinforcing fibers 42 on the surface of the main screen 26. When the main screen 26 is being lifted, the hydraulic ram 72 is activated in a downward movement to introduce the retainer screen 34 into the slurry 45. "The ball screws 40 continue to raise the main screen 26 until the mounting blocks 60 engage the guide rods 58. At this time, the pegs of the tank 80 are removed, thus disconnecting the plate washer from the cart 70. The outer pegs of the cart 68 extend to engage again the upper openings 64 of the transfer heads 62. The hydraulic ram 72 is activated to lift the cart 70 together with the main screen 26 and to retainer 34. The cart 70 is moved via the parallel rails 20 to its original position above the turntable 16. Referring again to Figure 1, the cart 70 goes down by way of the hydraulic ram 72 on the turntable 16. The inner and outer pins of the cart, 74 and 68, respectively, are removed by effectively disconnecting the cart from the screens 26 and 34. The cart is lifted by means of of the hydraulic ram 72. The turntable rotates 180 ° about the axis 46 for "facilitating the discharge from the vane 24 of the turntable 16 and into the oven 18 or any other indicated drying apparatus." The vane 24 is transferred to a cooling station, not shown., where a fan is used to direct air to through the preform 12 and the screens 26 and 34. When the screens 26 and 34 have cooled, the retainer screen is lifted and the preform 12 can be removed. The preform 12 is now ready for more conventional processes such as the MTR to form The final component The prior discussion discloses and describes exemplary embodiments of the present invention A person skilled in the art will readily realize from such discussion, and by the accompanying drawings and claims, that various changes, modifications and variations may be made therein. without departing from the spirit and scope of the invention as defined in the following claims.

Claims (3)

1. REINVIDICATIONS 1. A method to form a fiber reinforced structure characterized in that it comprises: placing a main screen having a selected form of preform in a tank filled with a liquid, the main screen having a larger surface, vertical side walls and a variety of openings formed in it; add reinforcing fibers to the liquid_ to create a watery paste; lifting the main screen through the slurry at a level below the surface of the slurry causing the reinforcing fibers to be deposited on the main screen thus creating a preform; introducing a retainer screen into the watery paste above the main screen in such a manner that at least a portion of the preform is placed between. the main screen and the retainer screen; and simultaneously lifting together the main screen and the retainer screen out of the tank with at least a portion of the preform held therebetween where deformation of the preform is minimized when the main screen is lifted from the tank.
2. 2. The method of claim 1 characterized in that it also comprises the step of placing a choke screen adjacent to the main screen, the choke screen having openings formed therein which are different in size from the openings in the main screen.
3. 3. The method of claim 1 characterized in that it also comprises the step of placing a choke screen adjacent to the main screen, the choke screen having openings formed therein which are off-center from the openings in the main screen thus limiting the flow of liquid. 4. - The method of claim 1 characterized in that the main screen has a greater contoured surface. 5. The method of claim 1 characterized in that the step of introducing a retainer screen is carried out with a retainer screen generally complementary in shape to at least a portion of the vertical side walls of the main screen. 6. The method of claim 1 characterized in that the step of introducing a retainer screen is carried out with a retainer screen generally complementary in shape to at least a portion of the larger surface of the main screen. 1 . - A method for forming a fiber reinforced structure characterized in that it comprises: placing a main screen in a tank filled with a liquid, the main screen having a larger surface, vertical side walls and a variety of openings formed therein; placing a choke screen adjacent to the larger surface of the main screen, the choke screen having a variety of openings formed therein; add reinforcing fibers to the liquid to create a watery paste; and lift the main screen and the choke screen through the watery paste causing the liquid to flow through the openings in the main screen where the flow of the liquid through the main screen is limited by the 'choke' screen thus creating a preform having a uniform thickness. 8. An apparatus for forming fiber reinforced preforms characterized in that it comprises: a tank having an upper portion and a lower portion, the tank containing a slurry of liquid and reinforcing fibers; a main screen having a larger surface, vertical side walls and a variety of openings formed in it, the main screen being arranged inside the tank; a mechanism to move the main screen through the tank and causing the liquid to flow through the main screen thus depositing the fibers in the main screen; a retainer screen formed to generally complement the lateral vertical walls of the main screen, the retainer screen being positioned to tighten the reinforcing fibers between the main screen and the retainer screen before the main screen is lifted above the upper level of the dough watery; and the mechanism then to simultaneously raise the main screen and the retainer screen of the watery slurry where the retainer screen serves to minimize deformation of the preform. 9. The apparatus of claim 8, characterized in that it also comprises a choke screen for selectively restricting the flow of the liquid, the choke screen having a variety of openings formed therein. 10. The apparatus of claim 8, characterized in that it also comprises a "choke" screen placed adjacent to the main screen to selectively restrict the flow of the liquid, the choke screen having a variety of openings • formed therein which are off-center from the openings in the main screen 11. The apparatus in claim 8 characterized in that the larger surface is contoured 12. The apparatus of claim 8 characterized in that the retainer screen is generally complementary in shape to at least a portion of the walls lateral verticals of the main screen 13. The apparatus of claim 8, characterized in that the retaining screen is generally complementary in shape to at least a portion of the larger surface of the main screen 14.- An apparatus for forming reinforced structures with fiber characterized in that it comprises: a tank having _ one for upper and lower portions, the tank containing a slurry of liquid and reinforcing fibers; a main screen having a larger surface, vertical side walls and a variety of openings formed in it, the main screen being placed inside the tank; a choke screen positioned adjacent to the main screen to selectively restrict the flow of the liquid, the choke screen having a variety of openings formed therein; and a mechanism to cause the liquid to flow through the main screen, thus depositing the fibers on the main screen. 15. A work cell for forming fiber-reinforced preforms characterized in that it comprises: a tank station having an upper portion and a lower portion, the lower portion having a tank containing a slurry of liquid and reinforcing fibers; a transfer mechanism placed inside the upper portion of the tank station to move a main screen throughout the tank and tank station; a furnace to remove the liquid from the preform, and a rotating plate placed between the tank and the furnace, the turntable having a rotation axis to facilitate the transfer of the preform and the main screen of the tank station to the furnace. 16. The work cell of claim 15, characterized in that it also comprises a choke screen placed adjacent to the main screen to selectively restrict the flow of the liquid, the choke screen having a variety of openings formed therein. 17. The work cell of claim 15, characterized in that it also comprises a retainer screen formed in such a way that it complements generally at least a portion of the main screen, the retainer screen being placed to tighten the reinforcing fibers between the main screen and the retainer screen 18. The work cell of claim 17, characterized in that said transfer mechanism includes a trolley having a pair of slideable clutch pins for disengagably coupling the main screen to the trolley and a second set of sliding clutch pins for uncoupling the screen. Retainer to the cart. 19. The work cell of claim 15, characterized in that it also comprises a cooling station to rapidly remove heat from the preform and from the main screen. 20.- The cell of work of claim 15 characterized in that the transfer mechanism includes at least one hydraulic ram to selectively raise and lower the main screen within the tank station. 21. The work cell of claim 15, characterized in that it also comprises a fiber dispersion controller for sequentially adding different types of fiber to the slurry. 22. An apparatus for mixing a watery paste characterized in that it comprises: a tank containing the slurry of liquid and reinforcing fibers; a bubble zone controller, the controller being able to direct a flow of liquid to each of the bubble zones. 23. The apparatus of claim 22, characterized in that the zone controller is capable of sequencing pressures of fluid of pressures and variable durations to zones of specified bubbles where a vortex can be initiated or diminished in the slurry. 24. A method for forming a fiber-reinforced structure characterized in that it comprises: placing a main screen having a selected form of preform in a tank filled with a liquid, the main screen having a variety of openings formed therein; add the first group of fibers to the liquid to create a watery paste; lift the main screen through the watery paste causing the first group of fibers to be deposited on the main screen thus creating the first layer; add at least a second group of fibers to the slurry while raising the main screen causing the second group of fibers to be deposited in the first layer thus creating a preform, the preform having at least the first and second layers of fibers. 25. The method of claim 23, characterized in that the first layer has a property of physical characteristic, the property of the physical characteristic being different from a property of the physical characteristic of the second layer. 26. The method of claim 24, characterized in that the property of the physical characteristic is the resistance to tension of the first and second group of fibers. 27. The method of claim 24, characterized in that the property of the physical characteristic is the conductivity of the first and second group of fibers. 28. The method of claim 25 characterized in that the property of the physical characteristic is along the first and second group of fibers. 29. The method of claim 25, characterized in that the property of the physical characteristic is the finishing of the surface of the first and second layers. 30. An apparatus for forming fiber-reinforced preforms characterized in that it comprises: a tank containing a liquid; a screen placed inside the tank, the screen having a variety of openings formed in it; a fiber dispersion controller for sequentially adding a first and second group of fibers to the liquid, thereby creating a watery paste; A mechanism to move the screen around the tank and causing the liquid to flow through the screen thus depositing the fibers on the screen. 31. - A method for forming a fiber reinforced structure characterized in that it comprises: placing a main screen having a selected form of preform in a tank filled with a liquid, the main screen having a variety of openings formed therein; add a specific amount of fibers to a spray of liquid directed into the tank to create a watery paste; Lift the screen through the watery paste causing the fibers to be deposited on the main screen thus creating a preform. 32. The method of claim 31, characterized in that it also comprises the step of introducing the threading of fiber in a cutting mechanism, thus creating a deposit of fibers before the step of adding the fiber to the liquid spray. EXTRACT OF THE INVENTION An efficient and low cost method and apparatus for controlling fiber deposition in a fiber reinforced preform is provided. In the method, a main screen (26) is placed in a tank (36) filled with liquid (44). The main screen (26) has a larger surface (38), lateral vertical walls with openings (32) formed therein. Reinforcing fibers (42) are added to the liquid (44) to create a watery paste (45). The main screen (26) is lifted through the slurry (45) to a level below the surface of the slurry (45), thereby causing the reinforcing fibers (42) to be deposited on the main screen (26). ). A retainer screen (34) is introduced into the slurry (45) so that the reinforcing fibers (42) are pressed between the main screen (26) and the retainer screen (34). The main screen (26) and the retainer screen (34) are raised together outside the tank (36) effectively forming a preform (12) with minimal deformation. An alternative embodiment includes a bubble zone control apparatus (86) for mixing the slurry (45). The tank (36) is divided into separate areas or zones (88) by means of which "the fluid supply (44) is controlled to each bubble zone (88)." The bubble zone controller (86) can be used to starting or decreasing a vortex in the slurry (45) when the screen (26) is lifted out of the tank (36) Another embodiment includes a fiber dispersion system (103) for adding fibers (42) to the slurry ( Four. Five).