Porous filament wound pipe and method for making same
United States Patent 91 Medney POROUS FILAMENT WOUND PIPE AND METHOD FOR MAKING SAME [76] lnventor: Jonas Medney, 3504 Woodward St.,  
 Oceanside. N.Y. l 1572 22 Filed: Jan. 5, 1973 21 Appl. No.: 321,205  
 [52] US. Cl. 156/155; 156/168; 156/173;  
  156/195; 210/497.1; 138/144 [51] Int. Cl B32b 5/06 [58] Field of Search 156/168, 180, 276, 279.  
 Primary Examiner-Charles E. Van Horn Assistant Examiner-David A. Simmons Attorney, Agent, or FirmLeonard H. King WlND RESIN BONDABLE FILAMENTARY MATERIAL ABOUT MANDREL [4 1 Apr. 22, 1975 [57] ABSTRACT An improved resin bonded, wound filament pipe is disclosed having a wall with a precisely determined and accurately controlled porosity. The method for forming the pipe includes building up the wall thereof with a combination of a resin bonded fibers and a removable matrix material. After the filamentary mate rial and the matrix material are applied to a mandrel, such as by helical winding techniques or circumferential longitudinal winding techniques and after the resin is cured, the matrix material is removed such as by the application of heat, a solvent, the application of a vacuum etc. depending upon different considerations, for example the type of material used for the matrix. By closely controlling the volume of the matrix material applied as well as the removal thereof, the porosity of the resulting tube wall is precisely determined.  
 8 Claims, 5 Drawing Figures APPLY REMOVABLE MATRIX TO MANDREL c VARY BAND WIDTH VARY BAND WIDTH OF FILAMENT CURE OF MATRIX WHILE WINDING RESIN WHl| wmome d. L REMOVE MATRIX MATERIAL PIITENTEUAFRZZIBYS ABOUT MANDREL WIND RESIN BONDABLE FILAMENTARY MATERIAL VARY BAND WIDTH OF FlLAMENT WHILE WINDING APPLY REMOVABLE MATRIX TO MANDREL VARY BAND WIDTH CURE 0F MATRIX RESIN wnu WINDING REMOVE MATRIX MATERIAL POROUS FILAMENT WOUND PIPE AND METHOD FOR MAKING SAME BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to resin bonded, wound pipes and the like and more particularly to a pipe having a wall of predetermined porosity as well as a method for making the filament pipe.  
 2. Description of the Prior Art 1 In the construction of water wells or waste wells, a pipe having a porous wall is normally used. The porous wall of the pipe may be thought of as a screen which permits the water to flow through the wall and which keeps the sand and granular material out of the&#39;well formation. In some instances the well must be developed in whatever soil is available. Where this occurs there is no control over the grain size of the soil that is in the well opening adjacent to the well casing and the wall of the pipe or screen. Thus, it is necessary to use a very fine mesh screen for example having openings in the order of 0.006 inch. Even where such a small size screen is used grain material that is smaller than the mesh will pass therethrough and damage both the flow of the well and the equipment in the well. such as the pump. Naturally the smaller the openings in the screen the more expensive the screens are to produce.  
  One presently used method for winding the screen described above is to use a wire of trapezoidal cross section for forming openings that are smaller on the outside diameter of the pipe and larger on the inside diameter of the pipe. The purpose of this type of con struction is to trap the larger sand particles on the outside diameter of the pipe so that the sand particles cannot get into the openings and thereby clog the screen.  
  A wire wound screen such as is commonly used in the prior art is extremely expensive to produce and costs approximately $65.00 per foot in stainless steel for a 6 inch screen. In order to avoid this excessive cost it is a common practice to cut slots, such as by sawing or shearing in the wall of the pipe. However, the wall of the pipe is thereby weakened by the quantity of material that is taken out of the pipe. When glass fibers are used in the pipe the slotting technique has an additional detrimental effect in that individual strands ofthe pipe that are wound continuously are thereby cut so that even in those areas where material is not removed the pipe is weakened because the cuts have been provided adjacent the solid areas and failure may occur under load. It should be noted that slot cutting ofthe pipe cuts down on the crush and tensile strength of the pipe. In addition, whatever material is removed at the slots is thereby wasted.  
  Another method that is used in well production is to dig a hole larger than the outside diameter of the pipe. Usually an annular dimension of at least three inches is provided around the screen and, after the holes are drilled and the screen and casing are set, gravel is packed in the annular opening in order to insure that fine material is trapped in the gravel. Normally the gravel pack consists of granules that are large enough not to enter the openings in the screen.  
  A drawback to the gravel packing technique is that the gravel must frequently be shipped over large distances and escessive costs are incurred in packing the gravel into the wells. It should be noted that unless the gravel packing of the well is done absolutely perfectly there is always the possibility of collapsing the well due to the weight of the gravel.  
  A specific example of the prior art in this field is disclosed in US. Pat. No. 3,601,159 granted on Aug. 24, 1971 to M. Marks et al. The issued patent discloses a porous tube, the wall of which is defined by the combination of a porous paper strip and a layer of resinimpregnated glass fibers. The paper strip may be on the outside or the inside diameter of the pipe. In both embodiments the glass fiber rovings are furnished with just enough resin to hold the glass together without filling the interstices between rovings so that the resulting structure will be sufficiently permeable to allow for the flow of the product water therethrough. The permeability of the glass fiber structure about the paper is greater than that of the paper. Thus, the permeability will progressively increase away from the paper with the glass fiber structure having the greatest permeability, the paper having an intermediate permeability and a thin layer of a reverse-osmosis membrane having a small and selective permeability allowing only for purified water and the like to pass therethrough. It will be appreciated from a reading of the issued patent that the end product consists of a multi-layer, multicomposition wall.  
 SUMMARY OF THE INVENTION In its broadest aspect the present invention provides a pipe having a porous, monolithic wall. Layers of resin bonded glass fibers are wound, for example, in a helical pattern on a mandrel together with a matrix material that is removable by any convenient means such as the application of heat, a solvent or a vacuum. The matrix material may be formed of polyvinyl alcohol or the like. After the resin is cured appropriate means such as the application of heat or a solvent are used, depending upon the composition of the matrix material for the removal of the matrix material. The resulting structure is a pipe having a wall whose porosity is determined by the volume of the matrix material that is initially applied and which is subsequently removed.  
  The matrix material may either be in granular form or may be a plurality of filaments or a slit film. All of the foregoing materials may be included in the mixture of filamentary winding material as the pipe is made. The matrix material keeps its form and shape while the resin gels but may subsequently be removed by heating to a high temperature or by washing out with water or some other appropriate solvent solution or by the application of suction at the appropriate time.  
  Some examples of granular materials that could be included in the manufacture of the pipe comprising the present invention and which can subsequently be removed from the pipe wall in order to form voids are salt, wax beads, polyvinyl alcohol granules, carboxymethyl cellulose or other soluble cellulose materials. In a similar manner thread, twine, strips of polyvinyl alcohol, carboxymethyl cellulose, wax etc. could be used for winding and could be subsequently removed from the finished product either be melting or dissolving the material out.  
  Combinations of the foregoing material may be used in order to form a tube or pipe with a known void content and path so that the porosity may be accurately controlled with respect to both the size of the opening and the degree of porostiy.  
  In an alternative embodiment of the present invention the bandwidth of the filamentary material and the matrix material may be varied as the winding head passes over the mandrel. A wider mesh may be provided on the inside diameter of the pipe with a finer mesh on the outside diameter of the pipe so as to selectively filter out different size particles. In combination with the variation in the bandwidth. different bandwidths of matrix strips may be used in order to vary and control the size of the openings in a radial direction with respect to the longitudinal axis of the pipe.  
  Accordingly, it is an object of the present invention to provide an improved, porous walled pipe.  
  It is another object of the present invention to provide an improved method for forming the porous walled pipe described hereinabove.  
  A particular object of the present invention is to pro vide a method for forming a porous walled pipe wherein a matrix material is applied to the mandrel in addition to the filamentary material and the matrix material is subsequently removed after the resin used to bond the filamentary material has cured.  
  These and other objects, features and advantages of the present invention will, in part, be pointed out with particularity and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawing, which forms and intregal part thereof.  
 BRIEF DESCRIPTION OF THE DRAWING In the various figures of the drawing like reference characters designate like parts. In the drawing:  
  FIG. 1 is a schematic diagram illustrating several steps comprising the method of the present invention;  
  FIG. 2 is a perspective view schematically illustrating one embodiment of the method of operation of the present invention;  
  FIG. 3 and FIG. 4 are fragmentary, schematic sectional side and end views, respectively, illustrating the formation of a porous tube in accordance with the method of the present invention; and  
  FIG. 5 is another schematic view illustrating an alternative mode of the method comprising the present invention.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1 there is shown a schematic diagram illustrating the several steps comprising the method of this invention. As shown therein by step a filamentary material such as glass fibers or the like is wound about a mandrel. In accordance with conventional techniques which need not be described in detail the filamentary material may be preimpregnated with a suitable resin or the resin may be applied after the filamentary material is wound about the mandrel. Either concurrently with the winding of the filamentary material or, alternatively thereto as shown by step b, a removable matrix such as fibers of polyvinyl alcohol or the like are also wound about the mandrel. In its broadest aspect, step b also encompasses the application of soluble granules such as described hereinabove. After the winding operation is completed the resin is cured (step c) by any suitable means well known in the art. After the resin is cured and, depending upon the matrix material used, means are provided for removing the matrix material as shown by step d. The means for re moving the matrix material may be the application of an elevated temperature, the application of a suitable solvent and/or the application of a vacuum. As will be pointed out more fully hereinafter, and as schematically illustrated by step al and bl, the bandwidth of the filamentary material and the matrix material may, as an alternative feature, be altered by changing the winding angle during the winding process so as to provide variable size openings in the wall of the pipe, for example, openings that increase from the outside diameter to the inside diameter of the pipe.  
  Referring to FIG. 2 there is shown a mandrel 10 that is adapted to be rotated about the longitudinal axis thereof by conventional drive means such as a motor, a gear train etc., (not shown). A source 12 of filamentary material is arranged to apply bundles of filaments 14 to the mandrel 10 through a feed eye 16. Apparatus well known in the filament winding art may be used for this purpose. Typically, a bundle of glass fibers of about 0.0035 inch diameter may be used. There is also shown in FIG. 2 a source 18 for the removable matrix material which, in this embodiment, is in the form of a plurality of filaments 20 that are fed, for purposes of illustration, through a second feed eye 22. Any one of the matrix materials hereinbefore described may be used. The filaments 14 may be passed through a resin bath 24 or the filaments 14 may be of the preimpregnated type which is also well known in the art. A resin material such as epoxy has been found to be satisfactory with a complete cure being achieved at 400F for l /2 hours.  
  FIGS. 3 and 4 schematically illustrate a porous tube 30 that may be formed by the method of the present invention. The tube 30 includes a wall that is comprised of fiber bundles 12 defining a plurality of layers 34 of filamentary material 14. The layers 34 are also intially comprised of the removable filamentary matrix material 20. When the filamentary matrix material 20 is removed, such as by any of the methods described hereinabove, there will be a plurality of intersecting voids through the wall 32. The voids are shown schematically in FIG. 3 and in FIG. 4 and are designated by the reference character 20a.  
  Instead of using a filamentary material as the removable matrix, a removable granular material 36 may be applied from a suitable source 38 as shown in FIG. 5. After the resin is cured the granular matrix material 36 may then be removed by any of the means previously described so as to result in a porous walled tube.  
  There has been disclosed heretofore the best embodiment of the invention presently contemplated. However, it is to be understood that various changes and modifications may be made by those skilled in the art without departing from the spirit of the invention.  
  What I claim as new&#39;and desire to secure by Letters Patent is:  
  l. A method for forming a well pipe having a porous wall that permits passage of a liquid therethrough, said method comprising the steps of:  
 a. winding a plurality of layers of resin bondable filamentary material onto a mandrel;  
 a applying resin to the filamentary material;  
 b. changing the winding angle during the application of the filamentary material;  
 c. winding a predetermined quantity of a subsequently removable matrix material with the filamentary material whereby the porosity of the well pipe is determined by the volume of the applied matrix material;  
 d. changing the winding angle of the matrix material during the application thereof;  
 e. curing the resin; and  
 f. removing the matrix material whereby a well pipe having a wall with a predetermined porosity is obtained.  
  2. The method in accordance with claim 1 wherein said matrix material is thermoplastic and said removing step includes the step of applying sufficient heat to melt the matrix material 3. The method in accordance with claim 1 wherein said matrix material is soluble and said removing step includes the step of applying a solvent to dissolvesaid matrix material. I  
  4. The method in accordance with claim 1 wherein said steps of winding the filamentary material and the matrix are carried out concurrently.  
  5. The method in accordance with claim 1 wherein said filamentary material is preimpregnated with resin.  
  6. The method in accordance with claim I wherein there is further included the step of applying a resin to the filamentary material during the winding thereof.  
  7. The method in accordance with claim 1 wherein a resin is applied to the filamentary material after the winding thereof.  
  8. The method in accordance with claim 1 wherein there is further included the step of varying the winding angle during the winding of the filamentary material whereby voids are formed through the wall in the resulting pipe, the winding angle being varied so that the voids are larger on the inside diameter of the pipe than on the outside diameter thereof.