US3412891A - Fluid-handling wall structure - Google Patents

Description

NOV. 26, 1968 BASTONE ET AL 3,412,891

FLUID-HANDLING WALL STRUCTURE Filed Aug. 6, 1964 8 Sheets-Sheet 1 INVENTORS AND/FEW L. 5/75T0A/E, Jusm/ H. 505mm &

BY FRED E. KL/MPL F1 .29

Nov. 26, 1968 BASTONE ET AL 3,412,891

FLUID-HANDLING WALL STRUCTURE Filed Aug. 1964 8 Sheets -Sheet 2 vii Egg.

dus-n/v A. Bee-Km & BY F250 E. AL lMPL 4 TTOIP/VEKS Nov. 26, 1968 A; BASTONE ET AL FLUID-HANDLING WALLSTRUCTURE 8 Sheets-Sheet 5 Filed Aug. 6, 19

& mm; ms z s NA P V 2W M m/Bm w EN 7 R/ LPA 0 T D Mg AJF Y B m 6 9 1 FL NOV. 26, 1968 T N ET AL 3,412,891

FLUID-HANDLING WALL STRUCTURE 8 Sheets-Sheet Filed Aug. 6, 1964 INVENTORS 5545 70/1/15,

ANDREW L.

dusr/A/ A? 05mm & BY F /MPL V M TTOP/VEVS Nov. 26, 1968 BA TONE ET AL 3,412,891

FLUID-HANDLING WALL STRUCTURE Filed Aug. 6, 1964 8 Sheets-Sheet 5 Hil IIHII 242 ii 4 0 r EigiQ INVENTORS ANDREW A. 545T0A/5, Juan/v A. 50am? &

BY FRED .5. K1. IMPL 4 TTOIZMEYS NOV. 26, 1968 BASTONE ET AL 3,412,891

FLUID-HANDLING WALL STRUCTURE Filed Aug. 6, 1964 8 Sheets-Sheet 6 AND/25w L. 545mm", Jus T/lV IF. Baa/(5? &

B FRED A". KL/MPL w ATTQPMK;

2 2 INVENTORS Nov. 26, 1968 A. BASTONE ET Al 3,412,891

FLUID-HANDLING WALL STRUCTURE Filed Aug. 6, 1964 8 Sheets-Sheet 7 INVENTORS ANDREW L. Basrow,

Arramvs rs NOV. 26, 1968 BASTONE ET AL 3,412,891

FLUID-HANDLING WALL STRUCTURE Filed Aug. 6, 1964 8 Sheets-Sheet 8 INVENTORS ANDREW L. Basra/v5,

firm/mews United States Patent "ice 3,412,891 FLUID-HANDLING WALL STRUCTURE Andrew L. Bastone, Granville, and Justin R. Boeker,

Newark, Ohio, and Fred E. Klimpl, West Orange, N.J., assignors to Owens-Corning Fiberglas Corporation, a corporation of Delaware Filed Aug. 6, 1964, Ser. No. 387,945 11 Claims. (Cl. 220-83) ABSTRACT OF THE DISCLOSURE A fluid-handling wall structure, as for use in an underground storage tank for gasoline, comprising a resin rich inner surface; a predominately resinous body layer including chopped and randomly oriented, admixed reinforcement strand lengths; and importantly containing, during production, layers of woven stabilizing scrim material to keep the resin rich body stable until such time as it sets by polymerization; and as an overlay to such stabilized resin rich body, a plurality of strands of filament wound material forming an outer high strength shell; and including rib structures overlaid with parallel filament windings. Also, the invention relates to apparatus and method of producing the fluid-handling wall structure described.

This invention relates to fluid-handling wall structures, storage vessels, and conduits made therefrom, and to apparatus and methods of production.

The problem Corrosion by underground fluids, such as soil acids, as well as the liquid stored within a tank, has. been a severe problem of black iron tanks heretofore used for the underground storage of liquids such as gasoline.

Black iron tanks are coated with an asphalt paint which is of low abrasion resistance. Further, it is of relatively low durability in most environmental media. Naturally, when placed underground in the presence of soil water on the outside, and the corrosive agents in the liquid stored within, destruction by corrosion is an imminent ending for such structures. First, as the tank is shipped from its point of manufacture to the site of use, and as the tank is placed in the ground at the site of use, the exterior protective coating will be abraded; this starts the corrosion process.

Therefore, a substantial advance to the art would be provided by underground storage tanks and associated fluid-handling vessels having the following characteristics:

Long'life as characterized by a high degree of corrosion resistance to ambient elements; and

Radial crush resistance of a high level of magnitude.

It is also obvious that apparatus for producing such fluid-handling components and methods for their production would also contribute substantially to the art.

However, in order to make tanks and analogous fluidhandling vessels of a glass composite, the poor stiffness factor of the composite must be surmounted. Glass filaments are of such high strength that when embedded in a matrix material such as a hardened resin, the section is so thin as to be flexible and lacks necessary stiffness to resist radial collapse forces. Internal bursting forces are rather easily surmounted by the strength factor. However, the radial collapse force as in an earth buried tank does present a challenge. Therefore, skillful application of the tensile strength of glass is necessary in order to provide appropriate stiffness. It is from the foregoing that the present invention was born.

The problem with glass is to provide wall stiffness with low glass content. Thus, the composite structure must not contain an unnecessarily high glass content for 3,412,891 Patented Nov. 26, 1968 stiffness, because the cost of glass will prevent economic competition. Also, in the case of underground storage tanks encountering high earth loadings, stiffness alone is not enough. Therefore, rib structures are provided by this invention.

It is, accordingly, an important object to provide a rigid, fluid-handling wall structure made of fiber-reinforced plastics, characterized by high corrosion resistance, high burst and crush resistance, and light weight.

A further object is to provide an underground storage tank made of fiber-reinforced plastic and characterized by high radial collapse resistance with relatively low glass content.

A further object is to provide an underground storage tank made by a process comprising filament-winding as a part thereof, and holding a mobile resin system in place during the filament-winding operation.

A further object is to provide a method of producing a stiff but low-glass content wall structure in a single step by holding the liquid resin in place while compacting with a filament-wound overwrap.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

FIGURE 1 is a side elevational view, partly in section, of a convex tank end made in accordance with this invention;

FIGURE 2 is a side elevational view of one form of the tank of invention, made with the tank end of FIG- URE 1.

FIGURE 3 is a side elevational view of a concave and cap of invention, and further schematically illustrat ing a pressure-resistant tank made therefrom;

FIGURE 4 is an enlarged, sectional view illustrating an end cap construction;

FIGURE 5 is an elevational view of a wall increment made in accordance with the present invention;

FIGURE 6 is an enlarged, fragmentary, sectional view of the side wall increment of FIGURE 5, showing the profile of the rib for radial crush resistance;

FIGURE 7 is an enlarged, fragmentary, perspective, sectional view about double actual size, as taken between the strengthening ribs, along line 7-7 in FIGURE 5;

FIGURE 8 is a fragmentary, sectional, perspective view about actual size of the wall structure at the rib, as taken along theline 88 of FIGURE 5;

FIGURE 9 is a transverse sectional view of a separately formed loop-type rib, for application to :a smooth frusto-conical wall of the type shown in FIGURE 2, to produce a structure of the type shown in FIGURE 5;

FIGURE 10 is a fragmentary, sectional view showing the rib of FIGURE 9 used to produce a structure similar to the structure of FIGURE 5 (however, note that there vis a difference: compare with FIGURE 6, where the bottom of the rib 'has no bridging wall :as in FIG- URE 10);

FIGURE 11 is a fragmentary, sectional, perspective view similar to FIGURE 10, but wherein criss-cross helican windings are laid on top of the ribs to bury the peripheral windings of the ribs beneath the surface for unusual strength;

FIGURE 12 is a fragmentary, sectional, perspective view showing a rib filled with a low-density, form-developing material, as applied after part of the resin-rich layer is developed on the forming mandrel, and the remaining materials then laid on over the form-developing material;

FIGURE 13 is a fragmentary, elevational view of a fluid-handling wall structure of invention embodying a continuous, spirally formed rib for radial crush resistance;

FIGURE 14 is an elevational view of a completed tank segment of invention, comprising a ribbed tank wall increment and a joined convex end cap;

FIGURE 15 is an enlarged, fragmentary, elevational vie-w, partly sectioned to show the wall structure of FIGURE 14, this view being particularly presented to show the welded joint between the end cap and the endless wall; FIGURE 15 is above twice actual size;

FIGURE 16 is a fragmentary, sectional view, approximately actual size, showing the structure of a weld for joining two tank halves of the nature of FIGURE 14, to produce a finished tank as shown in FIGURE 17;

FIGURE 17 is an elevational view of an end product tank for underground gasoline storage;

FIGURE 18 is a sectional view illustrating end cap formation;

FIGURE 19 is a sectional view illustrating the rotatable winding mandrel used to produce endless wall increments of invention;

FIGURE 20 is a fragmentary, side elevational view, showing the dead center used to hold :an end cap in place on the winding mandrel;

FIGURE 21 is an axial sectional view of FIGURE 20 after application of tank wall forming components;

FIGURE 22 is an end elevational view, partly in section, showing apparatus associated with the mandrel for applying-the tank wall-forming components;

FIGURE 23 is an end elevational view of the diametrioally opposite side of the mandrel from FIGURE 22, showing the filament winding apparatus;

FIGURE 24 schematically illustrates the helical development of the filament-wound overlay;

FIGURE 25 is an enlarged, fragmentary, elevational view showing filament overlay at the ribs;

FIGURE 26 is :a fragmentary, elevational view illustrating filament overlap onto the end cap to anchor the end cap to the endless "wail increment;

FIGURE 27 is a transverse sectional view of one :form of rib component;

FIGURE 28 is a side elevational view of the form of rib component shown in FIGURE 27;

FIGURE 29 is an elevational view of a completed rib made from the component of FIGURES 27 and 28;

FIGURE 30 is a schematic illustration of the manufacturing process inherent in the invention, as regards the production of components and shipment in nested form, for field assembly.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways.

1. THE TANK COMPONENTS Briefly, it can be stated that the ultimate unit of construction in accordance with the present invention is onehalf of a tank, called a construction segment, comprising an end cap increment and a frusto-conical wall section, called a wall increment, these two units being joined together. It will be understood that, due to the tapered nature of the tank wall, these units can nest one within the other for transportation purposes.

The convex cap Referring to FIG. 1, anend cap 50 is shown that can be used to produce storage tanks for liquids.Cap 50 has an outer convex surface 52 and an innerconvex surface 54. The tank wall, as designated bydotted outline 55, and to which theend cap 50 is joined to produce a tank half segment, has a slight taper, illustrated betweenlines 56 and 58.

In order to fit on the end of the mandrel and mate to wall 55, theperipheral wall portion 60 of end cap 52 has the same taper, as along the bracketed area 62.

A general tank profile made, using the end cap and a wall designated in FIGURE 1, is shown in schematic outline in FIGURE 2. Here, theend cap 50 has been joined to thetank wall increment 55 along theweld area 64. A tank half or constructional segment is the result. In FIGURE 2, twosuch segments 65 have been joined by acentral weld 63 to produce a complete tank.

The concave end As shown in FIGURE 3, this type of end cap is designated 86. Theouter surface 88 is concave and theinner surface 90 is convex. The lip is tapered the same aswall 55.

Cap 86 is designed to resist internal pressures in a vessel.

The manner in which a pressure vessel is fabricated is illustrated schematically in FIGURE 3, utilizing aconvex cap 86 at the end of a frusto-conical wall increment 55. Two of these are joined at the center to form a tank.

It is to be noted that the structure of the end caps is a relatively simple lay-up. This is illustrated in FIGURE 4, and is essentially a matrix of chopped strand and resin. Theinner surface 90 is resin-rich 92 for corrosion resistance. Next, there is anoptional surface mat 94, followed by the substantial thickness of chopped strand andresin matrix 96. On top of thelayer 96 is alayer 98 of surfacing mat. This is optional where thematrix 96 is sufficiently glass-rich to provide a protective coating of resin on the surface.

As a usual thing, the chopped strand and resin structure will meet the design standards for most vessels. However, as for example with theconcave caps 86 just described, higher burst resistance may be in order. This may be provided by an outer shell of roving orglass cloth 97.

The frusto-conical wall increment This is shown in FIGURE 5 of the drawings and is designated by the numeral 102. This is a preferred form of the invention for resisting external crushing forces, as an earth overburden for a buried tank. The structure is essentially an open-ended, frusto-conical, endless wall form. However, in addition to the simple taper previously mentioned bynumeral 55 above, thewall 102 includes a plurality of axially spacedrib structures 104. These extend peripherally of thewall segment 102 and act in the nature of barrel hoops to resist inward crushing forces. This structure will also resist outward bursting pressure, as for storing compressed materials.

The profile of theribs 104 is shown in greater detail in FIGURE 6. Thus, there arevalley sections 106 between each of theribs 104. Eachrib 104 comprises anupper plateau region 108. These have slopingsides 110. In this particular embodiment, the sides slope at about a 45 angle and extend between theplateau regions 108 and thevalley regions 106.

The valley structure This is shown in FIGURE 7. A resin-rich surface 92 is indicated on the inside. This is pure resin and is held in place by anoptional surface mat 94 that is laid directly on the mandrel at the time of formation. The purpose of the resin-rich layer is to provide corrosion resistance against the fluid being stored.

In the center of the structure is a rather heavy layer that is resin-rich in character. This is designated 112 because ditferent in structure from the pure choppedstrand resin layer 96 of the end cap of FIGURE 4.

As is meant to be conveyed by FIGURE 7, the choppedstrand segments 114 extend in random array. All are in a generally planar configuration, but are crisscrossed relative to one another. Thus, they provide strength in all directions in the body oflayer 112.

An important feature of the present invention resides in the attainment of a wall structure that is stiff yet of low glass content. It will be appreciated by those skilled in the art that this is an easy goal to attain where enough glass cloth or filament-wound materials are used to provide thickness, and thus stiffness or rigidity. However, when so operating, the amount of glass used is wastefully high because the strength of only a portion of it is needed for necessary strength. The task therefore is to achieve stitf ness by a less expensive medium.

It might be stated at this point that it is known to first gel a chopped strand layer before covering with a filament-wound material. However, this is an expensive procedure because the resin subsequently applied with the filament-wound material must also be polymerized to provide a finished structure, e.g., a two-step process.

Also, an inherent weakness asserts itself relative to this dual layer constructional technique. It cannot be stated with certainty that formation of two layers causes them to weld into an effective monolithic structure. There is always the parting line where first one resin was hardened and then another resin was placed thereon and subsequently polymerized.

In accordance with the present invention, a novel feature is provided by polymerizing both the resin-rich layer 112 and the subsequently applied, filament-wound layer in one step, thereby providing a truly monolithic, composite body. This is made possible by a mechanical stabilizer.

For purposes of exemplary discussion, and as actually used in manufacture ofa tank shown in FIGURE 17, cotton scrim was dispersed within the resin-rich layer as a stabilizer. However, within the extended scope of invention, glass strand scrim, glass surfacing mat, Mylar-modified polyester fibers and the like, formed into an openmesh type of scrim, can be used.

The purpose of this material is to stabilize theresinrich section 112 against fluid flow during formation. In order to do this effectively, thescrim 116 is not just placed over the entire layer of resin and chopped strand. Instead,

it is preferably applied in layers, on top of each incre-' ment layer of chopped strand and resin as applied to the forming mandrel. Thus, a thin layer of chopped strand and resin and an overlayer of scrim are present in a repetitive pattern.

By so operating, the entire mass remains coherent and resists flow during formation, to produce a product that retains its high resin content for stiffness with low glass content for adequate strength, yet economy of manufacture.

Next on top of the choppedstrand resin matrix 112 there appears a filament-wound layer 118. This is made of a plurality of criss-cross, spirally oriented plies of continuous strand. These are laid directly over the choppedstrand resin matrix 112. It will be evident that during application of such a filament-wound layer 118 the soft and fluid resin-rich matrix 112 will be displaced unless it is stabilized as indicated by thescrim interlayers 116.

Thus, a point of novelty becomes evident in the present invention by a stabilized, resin-rich, choppedstrand layer 112. This gives high bulk and stiffness, with nevertheless appreciable strength by virtue of the glass content. The overwrapped filament-wound layer 118 provides tremendous shell strength. Thus, a low-cost and COmpetitivelypriced wall is achieved even though a relatively high cost item in the form of glass is utilized. Further, this wall is superior in corrosion resistance, light weight, and economy of shipping.

As pointed out above, in order for fiber-renforced plastic tanks to compete with the economically entrenched and traditionally used iron tanks, skillful use must be made of the extremely high tensile strength of glass fibers, or the modulus factor thereof. In fact, the modulus is so favorable that a wall of sufficient strength has substantially no bulk and is, therefore, flexible. Accordingly, the

challenge has been met in the present invention in a single step operation.

From the foregoing, it is vigorously submitted that the structure disclosed above as made by stabilizing a resinrich layer to produce stiffness in a glass-containing body provides a substantial advance to the art. Further, novelty is evidenced by the fact that in being made in a single step, a monolithic structure is produced that inherently contains features of strength that could not be obtained in a two-step operation as mentioned above. Therefore, invention is evident from thestabilizer 116 to provide this unique structure in a single step.

Further, the tank of invention is a flexible system, depending on its strength to transfer the earth overburden load to the surrounding earth, when used for underground storage. In simple terms, a strong, flexible material is used to advantage by its ability to deflect and transfer the load to the surrounding earth.

Returning now for a moment to the bottom portion of FIGURE 7, note aglass flake layer 120. This is optionally added in order to make certain that a fluid barrier is produced by the total wall composite.

The outer resin-rich surface For purposes of external corrosion resistance, the layer of filament-wound roving 118 acts as a surfacing mat to produce a resin-rich surface 92 on the outside of the finished article.

A number of materials can be used to load or extend the glass-resin matrix 112. These include silicates in powdered form, calcium carbonate, glass flakes, titanium dioxide, mica platelets, and others. In some instances, even fine sand or powdered silica can be used.

The rib structure By reference to FIGURE 8, observe the rib structure 164. Thisstructure 104 contains all of the components of thevalley structure 106 and, accordingly, the reason why FIGURE 8 has not been magnified to the degree of FIGURE 7. However, an additional component of therib structure 104 over thevalley structure 106 is atop theplateau area 108. This comprises alayer 123 of truly peripherally wound,continuous glass strand 124. These are embedded in resin and act as a surfacing mat to hold the resin-rich surface 92 in place as previously described.

Thisperipheral layer 123 produces the action of a barrel hoop that is tremendously efiicient in resisting external crushing forces as encountered in the underground gasoline storage situation, as where a water-logged earth fill surrounds a buried tank. Tremendous crushing forces are present, and these are particularly severe when the tank is empty and the inside of the tank wall is not supported by an incompressible body of liquid.

At this point, it should be mentioned that this crush resistance also manifests itself by resisting oil canning. In order to hold a tank underground in high water table conditions, straps must be used to anchor the tank in the ground. These are placed around the ends of the tank and fastened to concrete piers to prevent the tank from bursting out of the ground under such conditions.

It will be evident that when a high water table bears against a so-anchored tank, and when the tank is empty, it will collapse between the straps, unless stressed to stand the forces. Thus, it will be evident that the rib structure comprises an important feature of the invention.

The prior discussion has related to integrally formed ribs. However, other ramifications are possible, Thus, in FIGURE 9, there is shown a separately formed and appliedrib structure 132. This is applied as in FIGURE 10, to a smooth, tapered wall structure of the nature of that shown in FIGURE 2. A bond is effected by application of cement at thepoint 134.

It is to be understood that theloop ribs 132 will be of graded sizes to fit at spaced points along the length of thetank wall increment 55.

The extension shown in FIGURE 11 This also includes the use of the separately formedrib 132 of FIGURE 9. The final structure is made by applying therib 132 directly to the mandrel. Then, the wall is laid up over this rib so that the two become integrally fused together.

Presurning that theribs 132 are of the same structure as in FIGURE 9, they will be understood to have a top layer or overlay of peripherally woundcontinuous strands 132 for radial strength. By operating in accordance with FIGURE 11, these now become buried well within the wall mass, rather than being only beneath the top, resin-rich layer 122, as shown in FIGURE 8. This may be understood to give a unique modulus structure capable of withstanding certain types of forces not readily absorbed by the structure of FIGURES 8 or 10.

The further extension FIGURE 12 Here the rib is either a separately formed item or an in situ-formed item. In the separately formed aspect, it is made from a material of relatively high density, but analogous to a sponge. Thus, high density blown fiberboard or foamed polyurethane would be illustrative of typical materials. These may be pre-formed, as in the case of the high density glass fiberboard. However, as regards the foamed polyurethane, this can be laid on part of the chopped strand layer, as indicated by thereference numeral 138 of FIGURE 12.

From the foregoing, it will be evident that the rib mem ber 140 or substance thereof is buried within the chopped strand layer, designated by thereference numeral 112.

As in prior formations, thescrim stabilizer 116 is used to prevent fluid flow when the filament-wound layer 118 and the truly peripherally appliedlayer 123 are applied.

In this embodiment, added stiffness is also supplied by the buried rib of a material having substantial body, but low density.

In this embodiment, the polyurethane rib may be formed by foaming onto the partially completed, chopped strand matrix during formation, as well as being preformed and applied as described above.

Other rib forms, as of a hollow, box-like cross section can also be used, like the polyurethane.

The spiral rib This is shown in FIGURE 13 and is analogous to the embodiments previously described. The distinction is evident by the fact that therib 142 is continuous. Also, the rib is a spiral instead of a truly peripherally extending hoop.

The construction is the same as that of FIGURES 8, 10, 11 or 12. Thus, the filament-wound overlay 118 covers the chopped strand-resin matrix; and, on theplateau regions 108, are theperipheral windings 123 that are oriented in the direction of the rib.

The assembled cap and wall, forming a tank constructional segment A tank or fluid handling segment of construction is illustrated in FIGURE 14. This comprises acap end 50, per FIGURE 1, and aribbed wall increment 102 from FIGURE 5. These parts are integrally joined together by method and apparatus that will be discussed later. The joint is indicated at 64. The filament-wound layer is inindicated by thereference numeral 118, and the peripherally oriented, hoop-forming layer, by the numeral 123.

As shown in FIGURE 15, theinternal surface 92 is resin-rich for corrosion resistance. Above this, and optionally holding it in place, is a layer ofsurface mat 94. Above thesurface mat 94 is asubstantiaal body 112 of resin-rich chopped strand with thescrim interlayers 116 for stabilization. Next follows the criss-crosswound filament layer 118, and on theplateau areas 108, the peripherally woundlayer 123, with a resin-richouter surface 92.

Theline 142 is the place where theend cap 50 of resin-rich chopped strand joins to and is overlapped by the resin-rich choppedstrand stratum 112 of thebody increment 102.

The bracketedarea 144 indicates an overlap of the criss-cross filament-wound material 118 from thefrustoconical side wall 102. During production, this layer is lapped over, as indicated by thebracket 144, in order to provide support and holding power for theend cap 50. It is believed that the bond between thebody 112 and the end cap develops substantial strength in its own right. However, since the end cap is a preformed and substantially fully cured element prior to joining with thewall segment 102, a join line of less than true monolithic nature is evident, as compared to the remainder of the truly monolithic structure. Since a true monolithic structure is the ultimate goal, theoverlap area 144 is provided.

Within the extended scope of invention, theend cap 50 can be formed integrally while forming thewall segment 102. Although this produces some complexities of manufacture and increases the expense of the forming mandrel, as distinguished from the separately formed and applied end cap method of operation, it is nevertheless possible.

Optionally, aweld 146 can be applied by application of strip glass cloth and resin as a post-forming operation, for further strength if desired. This has not been found necessary in underground gasoline storage operations, however, because there are no great stress factors at this area in those situations. The forces involved are essentially the crushing forces of back fill earth. The ribs in thewall segment 102 fully withstand these forces. The convex curvature of theend cap 50 inherently withstands such forces also.

In the internally pressurized vessel illustrated in FIG- URE 3, thesupplemental weld 146 may be desirable to withstand excessively high bursting forces.

The assembled" rank using two halves and the center joint This is shown in detail in FIGURE 16.Strips 148 of glass cloth are successively laid down and liberally coated with an air cure, catalyzed resin. Not that each layer of cloth is olfset relative to the layer beneath. This spreads the weld over a substantial area on each side of theabutment line 150 between the twohalves 102. Thus, thespread 152 of the weld area distributes the loading on each side of theabutment line 150; and also thickens the weld sufficiently to produce an absolutely fluid-proof seal.

A completed tank is shown in side elevational view in FIGURE 17. This includes two half segments as made at a central manufacturing point and shipped in spacesaving nested form to a local distribution or use point. Acenter weld 152, FIGURE 16, is suitably made either at the local distribution point or at the actual point of use. Note that the crush-resistant ribs 104 are spaced axially along the tank. Note also that the two ribs at the center are spaced relatively close together so that the free edges of thetank segments 102 are rigidified and remain oriented in a true circle for effecting thefield joint 152.

Typical dimensions for a field-tested tank of the configuration shown in FIGURE 21 are as follows:

Capacity: 6000 gallons.

Wall thickness: about one-fourth inch, including 34 filament-wound layer.

Wall taper: about 1.5 to permit mold release. This is not to be considered limiting on the invention. This figure is close to the minimum, however, that is necessary for release of the tank wall from the forming mandrel.

Length: each 'wall segment is about 9 feet long, tapering from 7'9 diameter to about 7' diameter. The end caps 50 added about 16" of axial length. Therefore, in round numbers, the tank is about 8' in diameter, by about 20' long.

Rib spacing: the ribs as shown in FIGURE 17 are spaced on about 22" centers. This puts the two center members about 16" apart.

Advantageous features of the tank of FIGURE 17 for the underground storage of gasoline are as follows:

Suflicient strength in theperipheral ribs 102 to resist crushing forces of an earth overlay;

A naturally built-insump 154, for accumulation of moisture, and also providing a loading point at the center of the tank;

A naturalhigh point 156 for venting the tank, i.e., for the collection of gases within the tank above the contained liquid so that the gases can be expelled during the filling of the tank; and

Asuction point 158 that is away from the sump and loading point.

The tank end or cap apparatus and method As shown in FIGURE 18, amandrel 210 of steel, aluminum, or other suitable material is utilized. This has an external contour equivalent to the contour of thecap 50 shown in FIGURE 1. Other contours can be used for purposes of producing flat and concave structures.

To themandrel 210, there is first applied a release agent by means of agun 212 or, manually, by wiping with a cloth saturated with the material. The release agent is suitably a wax or the like to aid in removing the cured part from the polished surface of themandrel 210.

To thecoated mandrel 210, there is next applied, by suitable means, a matrix of liquid resin and chopped strand reinforcement material. One exemplary means for effecting this application comprises agun 214 that chops strand and propels it by blowing toward the exterior surface of themandrel 210. Simultaneously, as the chopped strand is flying through the air, agun 216 produces a surrounding mist of resin, also directed toward the external surface of themandrel 210. By so operating, a matrix is built-up into a layer 218 over the surface of the mandrel.

An infrared lamp orheat source 220 is used for curing the wet lay-up.

Removal of the part from themandrel 210 is suitably effected by lifting off. In some instances, an assist from a jet of air introduced, as by a built-inconduit 222, may be helpful.

The method steps that follow from the prior description include the following:

Coating a forming mandrel with a suitable release agent;

Applying chopped strand and resin and other components as necessary to proper thickness to develop an appropriate wet lay-up;

Curing the lay-up to a hard, solid condition; and

Stripping the cap from the mandrel.

This produces a cup-like piece that will nest, in the nature of paper cup lids. Such parts are shown in FIG- URES 1 and 3.

THE SIDE WALL APPARATUS AND METHOD The mandrel for the side wall and its rotation As shown in FIGURE 19, the mandrel is designated 224. This is a hollow, open-ended, frusto-conical shell. The frusto-conical taper provides part release from the mandrel. Themandrel 224 is supported for rotation on asubstantial base member 226 carryingbearings 228 at the top.

Arotatable shaft 230 is supported within thebearings 228, and extends into the interior of theshell structure 224 to support it in a cantilevered manner. This leaves the left end of themandrel 224 exposed for application of the end cap, as will be discussed relative to FIGURE 21.

Spiders 232 radiate outwardly from theshaft 230 and are fastened at their outer ends to the interior of themandrel 224.

Rotation ofmandrel 224 is provided by a lowspeed motor mechanism 229. This suitably carries apulley 229a on the output shaft. Apulley 231 is aligned onshaft 230. A driving connection is provided by a belt 22%.

The apparatus for holding the end cap to the side wall mandrel Referring to FIGURE 20, it will be noted that anend cap 50 is held in position at the end of themandrel 224 by means of a dead-center mechanism 234. This includes abase 236. To thefloor 238, there is suitably secured anangle iron 240. A clamp 242, or equivalent, is applied to hold the parts in operable relationship.

The dead-center per se comprises ashaft 244 having arubber pad 246 at the right-hand end thereof. This serves as a contact member with thecap 50. Theshaft 244 is journaled in bearing blocks 248. Also, in addition to being rotatable, theshaft 244 is axially movable, in order that bias or pressure may be imposed by way of therubber pad 246 in thearrow 250 direction.

To provide the 250 biasing force, acollar 252 is fitted uponshaft 244. Acompression spring 254 is applied uponshaft 244, between thecollar 252 and the left-hand pillow block 248.

The apparatus and manner of forming the side wall layup to produce a wall increment 162 of either the ribbed or smooth configuration is schematically illustrated in FIG- URE 21. As there shown, a layer ofmaterial 256 has been applied over the outer surface of themandrel 224. This is of a thickness the same as that of theend cap 50 and includes the components as shown in FIGURE 7:

At this time, thefilament overlay 118, as shown in FIGURE 7, has not yet been applied. The manner in which this is done will be described later.

The production equipment associated with the mandrel for developing the stabilizing lay-up This is shown in FIGURE 22. Along one side of themandrel 224 there is provided anelevated trackway system 258 that includes aframe structure 260 upon which two spacedtracks 262 are mounted in aligned relationship.

A carriage 264 is movable alongtracks 262 byrollers 266 that are conformed to the tracks. Carriage 264 is used to carry a roving chopper, resin guns, and stabilizer application media. The carriage 264 is moved back and forth along themandrel 224 is an ordered manner to apply the total chopped strand layer as a plurality of laminae, in order that a scrim stabilizer may be dispersed throughout the thickness of the layer.

For this purpose, agear motor 268 is supported beneath thetracks 262, and has anoutput shaft 270 that carries asprocket 272. Achain 274 laps thesprocket 272 and also laps anupper sprocket 273. At the far end of theframe 260 are similar sprockets to supportchain 274.

Carriage 264 is provided with anangle iron 276. This receives ashear pin 278 that passes through thechain 274 and into a hole in theangle iron 276. In event of malfunction in either the carriage mechanism 264 or elsewhere, the shear pin disconnects the carriage from thedrive chain 274. Also, since the traverse of thecarriage 274 is quite slow, resetting of the mechanism is usually effected by removing theshear pin 278 and pushing the carriage back to starting position by hand.

Thegear motor 268 is programmed by acontrol box 280 that establishes the speed of traverse and number of passes of the carriage 264.Limit switches 282 are placed at each end of the trackway for reversing purposes.

The components on carriage 264 A strand chopper 284 is supported at the top of carriage 264. This has a downwardly extending tubular con- I 1 duit 286 that gravitationally carries and guides the chopped strands to ablower conduit 300.

Strand 288 is fed to the chopper 284 fromsuitable spools 290.

A motor-drivenfan 292 has the outlet blended into theconduit 286 at the 90curve point 294. In this construction, the exhaust stream from thefan 292 moving in the arrow direction 296 boosts and picks up the fallingstrand lengths 298. The air stream then shoots thestrand lengths 298 from theoutlet tube 300 with sufficient velocity to carry them into contacting engagement with the outer surface of themandrel 224.

Also mounted on carriage 264 are threelower resin guns 302 and oneupper gun 304.

This combination ofelements 284, 300, 302 and 304 builds the matrix on the surface of the mandrel in an incremental layer as the carriage 264 is traversed axially along the length of the mandrel on thetracks 262. The total layer is ultimately built up in a number of passes, as indicated by thereference numeral 256 of FIGURE 21.

The scrim.application A bracket 306 extends upwardly from carriage 264. Ashaft 308 is rotatably journaled at the upper end of thebracket 306. Aroll 310 of cotton scrim (open mesh cloth) is mounted on theshaft 308 and is paid out onto the chopped strand as it is increment-applied to the surface of themandrel 224.

Abrake pad 312 is mounted at the end of aleaf spring 314 and bears againstshaft 308 to impose a slight drag thereon. The brake pad is effective to place just enough tension on thescrim roll 310 to hold the chopped strand and resin in place against fluid movement. This action can be called mechanical stabilization.

It should be noted at this point that glass cloth, glass scrim, cotton cheesecloth, a scrim made of Mylar-moditied polyester fibers, and other materials can be utilized by application in the manner of thecotton scrim 310.

As an option, agun 316 can be positioned next to theoutlet tube 300 to apply a filler, such as a silicaceous material. This would be effective to extend the resin as applied by theguns 304 and 302. Placement of thegun 316 at the point of application of the chopped strand provides appropriate admixture with the resin and complete wetting of the filler by the resin.

The curing radiants Heat for curing the wet lay-up is generated by an infrared source, designated 318. However, these are not utilized in accordance with the preferred operation of the present invention until after the filament-wound layers are completely applied. Accordingly, a discussion of the manner in which these are used will be deferred until the next topic has been developed, namely, the filamentwound programming system as shown in FIGURE 23.

The filament-winding apparatus, FIGURE 23 This includes atrack system 320 extending along the opposite side of themandrel 224 from the strand and scrim-applying apparatus discussed relative to FIGURE 22. Theparallel tracks 322 are fastened to the top of aframe 324, which holds the tracks up at an appropriate height.

Acarriage 326, provided withwheels 328, travels back and forth along thetracks 322.

Achain 330 is mounted for movement along one side of thetrack system 320 and is lapped oversprockets 332 rotatably mounted at each end of theframe 324. A shear pin type connection is provided between thecarriage 326 and thechain 330 at thearrow point 334. This is effective to disengage the apparatus in the event of malfunction.

Traverse of thecarriage 326 is effected by agear motor 336 that is suitably programmed from acontrol box 338. Thegear motor 336 is connected into thechain 330 system by means of asprocket 340 carried on the output shaft.

It will be understood that as thecarriage 326 is moved back and forth the full length of themandrel 224, continuous strands saturated with liquid resin are applied in a criss-cross laid layer.

The wetting of the strand is effected using aflat container 342. Thecontainer 342 is mounted on top of thecarriage 326 and thecontinuous rovings 344 are fed through a body of liquid resin retained at an appropriate level withincontainer 342. By suitable mechanism to be described, therovings 344 are permitted to pickup appropriate amounts of resin for the filament-wound overlay.

Therovings 344 are fed frompackages 346 that are mounted a substantial distance from thetraversing mechanism 348 so that they have sufiicient length for alignment for proper passage through thedip tank 342. Additionally, thepackages 346 are spaced a sufficient distance away from thetraversing mechanism 348 to allow traverse of the combined number of rovings from one end to the other of the approximately 10long mandrel 224.

Aguide roll 350 is mounted on a rotatable shaft that is journaled on abracket 352, extending outwardly from thecarriage 326. Additionally, agathering ring 354 is positioned ahead of theguide roll 350 to group theseveral rovings 344 into aligned relationship as they pass over theroll 350. Thegathering ring 354 is also supported by thebracket 352 that is extended to the left for such purpose.

The combination of thegathering ring 354 and theguide roll 350 is effective to orient therovings 344 for proper angle of entry into the bath of liquid resin contained within thetank 342.

Adip roller 356 is mounted withintank 342 and therovings 344 pass beneath this structure to be submerged within the body of liquid resin. Aligned squeegee rollers or bars 358 are also supported withintank 342. As the wetted rovings pass into the nip between theelements 358, the resin picked up from the bath is reduced to a selected amount. For this purpose, it is to be understood that theelements 358 can be adjusted relatively to one another to close or open the nip therebetween.

The traverse of thecontinuous rovings 344 As themandrel 224 is turned, thecarriage 326 is moved back and forth along thetracks 322. This is effective to lay the gathered rovings into the fresh or still wet, but stabilized, chopped strand layer previously applied as illustrated in FIGURE 22.

It will be evident that due to the traverse of the wettedrovings 360 along the surface of themandrel 224, the orientation of the rovings applied in overlay manner to the previously laid-up, resin-rich chopped strand layer is both axial and peripheral. This imparts strength in both axial and peripheral directions to the tank. Additionally, the criss-cross lay of therovings 360 produces a high-strength shell structure.

Additionally, the traverse is adjusted to la therovings 360 carefully along the sloping sides of theribs 104, as shown in FIGURE 25. Considerable care is exercised in getting this orientation quite exact in order to provide a smooth contour over the ribs.

Control at this point is provided by having a properly dry glass-to-resin ratio, or by spraying on catalyst at these points or applying polymerizing radiation to ge the underlay resin ascontinuous strands 344 are applied thereover. I 5

Previously, it was mentioned that the filament windings are both axially and radially oriented on the surface of the structure. This is schematically shown in FIGURE 24. In the extended scope of invention, the orientation can be utilized to control strength in any direction desired for a particular application. Thus, by orienting the filamentwound portion of the structure in an axial direction, axial strength is obtained. In the application as a storage tank, axial strength is not so necessary as radial strength because the bursting forces are inward in that direction. The earth overlay or back fill supports the tank end and the load it carries as regards axial stresses. However, in other applications, orientation as desired can be provided for appropriate strength.

Because of the need for radial strength, the barrel hoop structure discussed above, and as illustrated in FIGURE 26, is emphasized. Actually, these are supplemented by the axial traverse of therovings 360 to provide a combination of strength factors both axial and radial. These are just about balanced when a 45 helix is utilized.

The end cap overlay As illustrated in FIGURE 26, there is at least a hypothetical joint 142 between the end cap and the subsequently applied chopped strand matrix when the previously formedend cap 50 is laid up against the fresh resin in thelayer 256 of FIGURE 21. Although subsequent curing of the resin of thelayer 256 should theoretically produce a monolithic-composite structure, added strength at the joint 142 is provided in accordance with the present invention.

It will be understood that the wettedrovings 360 are traversed beyond the joint 142. These are saturated with resin and build a grasping or a holding shell over the free edge of theend cap 50. The configuration of the overlay is also shown in detail in FIGURE 15. There, the bracketedportion 144 indicates the degree to which the layer of filament-wound rovings 118 extends beyond the joint 142.

The ultimate result in this structure is, in efiect, a monolithic composite when all of the resin applied fresh at this time is cured into solidified condition with that of the previously formed end cap. Substantially unitary or monolithic structure is produced due to the strength now inherent at the joint by the overlapping condition of the continuous strands, as indicated by thebracket 144.

In those instances where it is elected to produce the end cap with a glass cloth overlay, as optionally shown in FIGURE 4, the glass cloth being designated 98, the overlapped roving will bond to it. This will in effect form an outer, high strength glass shell that is continuous over the entire tank surface.

The peripheral winds It was previously mentioned that theplateau areas 108 of theribs 104 were overlaid at the last portion of the cycle with a layer of peripheral wraps. This is designated 123 in FIGURE 25. The peripherally wound strands are there shown in exaggerated view and individually designated 124. Note the manner in which they cross over the previously-appliedtraverse rovings 360.

These peripheral winds are laid up by the equipment of FIGURE 23. To effect this, thecarriage 326 is very slowly traversed, with themandrel 224 turning, along each of theplateau regions 108 of theribs 104.

Compacting the resin-rich chopped strand layer Referring to FIGURE 23, it is pointed out that therovings 360 for the peripherally wound and appliedlayer 123 of FIGURE are not in a condition that can actually be called tension. The condition is perhaps more aptly described as being oriented. Thus, the continuous filaments are placed on the chopped strand layer with a methodical lay that is applied with just enough drag by thesqueegee elements 358 intank 342 to lay it on over the resin-rich layer. The effect is to compact or bodyup the resin-rich layer 256. This expels entrained gases and also renders the chopped strand layer coherent or truly monolithic in structure.

Point of novelty It is at this precise point that the uniqueness of the scrim interlayer or stabilizer, designated 310 in FIGURE 22, becomes so clearly apparent.

The resin-rich layer 256 is mobile, but for the scrim stabilizer. Therefore, by the present invention, a stabilized, unified, or monofied layer is developed in a wet stagenot heretofore presented by the art. Further, this is all unexpectedly accomplished in a single layup step, because, as previously mentioned, there has been no activating energy applied to gel the mobile resin in the least. Economics of operation greatly favor this type of procedure, and further, as discussed above, it is believed that a truly monolithic structure of unique strength characteristics is developed that has not heretofore bee-n obtainable.

The final cure This is now the point where the Wet lay-up is cured into a hard, solid, or se monolithic composite.

Therefore, theradiants 318, indicated at the top of both FIGURES 22 and 23, are now turned on and their energy directed toward themandrel 224, which continues to rotate. In an actual tank half of 3000 gallons capacity, having a quarter-inch thick lay-up wall of 8' diameter, about two to three rows of radiants were utilized about 18 inches .above the surface of the mandrel, and these developed about 5000 watts of radiating power. The mandrel was rotated at about 6 rpm. With this set of conditions, the quarter-inch thick resin was gelled through in about one hour, and total cure time was in the range of two to three hours. Actually, theexternal radiants 318 direct their rays through the wet lay-up and these are then reflected back from the surface of the mandrel. All portions of the resin are therefore activated effectively bv the exterior type of energy application.

The monolithic result In view of the foregoing, the final unitary polymerized body is of monolithic character that has oneness but yet inheres the unique structural strength and stress resistance characteristics of a composite structure wherein perhaps the most far-reaching importance in the performance and use of composites are the effects produced by the combination and/or interaction of the constituents thereof.

Here, a truly composite body has been produced, including the following materials:

The resin matrix;

Chopped strand randomly oriented in a resin-rich or resin-filled zone to provide strength in all directions;

Scrim stabilizer, holding the mobile body together;

Surfacing mats holding a pure resin surface for high corrosion resistance;

Optional flake layer for absolute fluid-imperviousness (this can be put on by theguns 316 in FIGURE 22); and

Continuous strand overlays producing a tough outer shell.

Further, a composite structure is inherent in the fact that an end cap of thetype 50, FIGURE 1, with or without a glass overlay, is combined -with a tank body structure having acontinuous shell overlay 360. Thecontinuous shell overlay 360 is oriented to grasp or hold the end cap to the body along theoverlap area 144, FIGURE 41.

The effects of the combination of materials in the monolithic type composite structure produced by the invention may be summarized as follows:

SUMMATION OF THE INDIVIDUAL PROPERTIES OF THE CONSTITUENT MATERIALS This happens when the contribution of each constituent is independently acting relative to the other components. Such factors appear at least in part here.

Complementing Each constituent complements the others by contributing separate and distinct properties. Thus, the tank wall has radial crush resistance, by the hoop structures contained therein. The end cap is of convex construction and, therefore, has strength inherent in its con-figuration.

Supplementing This results when a given property or action of one constituent is not independent of the property or action of another constituent. The resulting component properties are often higher than those of the constituent parts. This has taken place in the structures of this invention. There is radial burst resistance and radial crush resistance by the ribs; there is axial strength by the orientation along the axis of the structure as indicated in FIGURE 24; there is end thrust resistance by the shape and construction of the end caps; and, further, there is corrosion resistance, light weight and utility, as enumerated hereinbefore.

The method In view of the foregoing, it becomes clearly apparent that a method inheres from the present invention. Broadly, the method steps are as follows:

(1) Forming an end cap separately;

(2) Positioning the end cap in space, as on the end of a tapered mandrel, and holding as by the use of a dead center;

(3) Orienting to the free edge of the end cap a resinrich bodying layer of the nature of the end cap, i.e., resin-rich chopped strand for stiffness;

(4) Stabilizing the mobile, resin-rich layer by means such as interposed strips, either continuous or incremental, of scrim;

(5) overlaying the total understructure, comprising end cap and body layer, with one or more properly oriented layers of spirally wound-on, continuous strands and orienting these axially and/or radially for strength in the directions necessary for particular applications;

(6) Compacting the body structure produced by step 5 by means of the filament windings;

(7) Developing a crush-resistant rib structure or step configuration as desired, simultaneously with the performance of steps 3-6; and

(8) Developing inner and outer resin-rich surfaces for appropriate corrosion resistance.

The various embodiments by which the rib structures can be developed have been purposely omitted from the foregoing description in order to keep it as uncomplicated as possible. At this point, however, the various rib ramifications will be developed.

THE RIB FORMATION The molded-in rib This has been shown in FIGURES 5, 6, 8, 11, 12, 13, 14, 15 and 17. In the preferred equipment embodiment for producing the molded-in rib, a smooth tapered mandrel has been employed for ease of part release. This is shown in FIGURE 21. When using this type of mandrel, ribs of high density glass fiberboard, containing cured phenolic resin for the bonding medium, are suitably utilized. As shown in FIGURES 27 and 28, these are cut to an external profile to which the ultimate rib is to conform. Here, the taperedsides 110 are of about 45 inclination. The ribs shown were cut from fiat stock and saw 364 were formed transversely on the inside surface to permit the flat units to bend and conform to the outer surface of the forming mandrel. Other equivalent materials can be used, such as performed polyurethane foam ribs. and the like, and thus the invention is not limited to the high density glass fiber material.

Application of the structures shown in FIGURES 27 and 28 to the mandrel is effected in the manner shown 16 in FIGURE 29. Butt joints 366 are formed at all except the removal position 368. The ends then are scarfed, as at 370, for inward removal, indicated byarrow 374.

These units may be made in preformed circular configuration and slipped over the end of the mandrel, and positioned at spaced points therealong. Also, the segments, as illustrated in FIGURES 27 and 28, may be applied individually at certain points along the mandrel to build up the ribs. Note the internally appliedfastening elements 372 in FIGURE 29, such as a large screw, to hold the scarfed ends 370 together. By drawing this inwardly, along thearrow line 374, the ribs can be removed and collapsed inwardly and separated from the cured tank half.

In a production operation, a release agent or release film, such as cellophane or Mylar, is first applied to each rib area of the mandrel, and the rib is then built over it. Over the rib there is then applied a fluid barrier, such as 1 mil. Mylar film. The reason for encasing the rib is that it is of spongelike nature; and thus, the liquid resin subsequently applied must be kept from saturating this piece so that it can be removed and not become a part of the laminate. This procedure is distinguishable from the method of operation discussed above relative to FIGURE 12, wherein the porous rib was actually embedded in the side wall.

By encasing the ribs, however, they are isolated from the resin and thus can be stripped out and reused a number of times. This improves economy of operation and there is no real necessity for the strength the rib form material might contribute to the ultimate structure.

The above covers the formation of separate ribs in accordance with an actual production operation and worked very saitsfactorily.

However, an extension of the invention suggests itself at this point. Thus, a spiral wrap of rib form material can be applied to the forming mandrel. This will develop the continuous spiral rib shown in FIGURE 13.

' As regards either one of the previous embodiments, i.e, separate rings or the spiral unit, these also could be individual rubber sleeves or boots, or a long, inflatable tube that would be spirally laid on the surface of the mandrel and the resin then applied. In short, a rib form as a separate attachment is to be encompassed within the scope of invention. In this method of operation, the tinished molded tank and the rib form are both removed from the mandrel; then the rib is removed from the interior of the tank half shell. Reuse of the rib is therefore feasible.

The prior discussion has related to peripherally disposed strengthening ribs. In the extended scope of invention, axially oriented ribs can be used, by application of the principles set forth. These may even be used in combination with the peripheral ribs described. Further, the rib plateau areas can be overlaid with glass cloth, as well as filament-wound materials.

Glass fibers or equivalent are usable as the reinforcement media.

Polyester resin systems have been employed in actual production according to the invention. However, extensions to epoxy systems, and acrylic systems are contemplated where the higher resin cost is justified. Actually the principles of the invention would be applicable with analogous materials where a transition from a liquid or mobile stage to a hardened stage is apparent.

As regards the center weld for producing a tank from two increment halves, it is to be understood that the major orientation of the strands will be along the tank axis, across the joint. By so operating, the center weld has sufficient strength to transmit stresses across the joint and flex enough to allow the entire tank to deflect a small amount under load.

A note relative to control of the mobility of the resin: during the development of the resin-rich layer 256, in

17 FIGURE 22, the right degree of wetness is to be considered an added factor and a further mechanical means of stabilization.

As a note of interest, a truncated cone form as used in this invention would be very difficult to render in steel, and expensive. A definite advantage as regards economy of shipment is therefore inherent in the invention that is substantially impossible in steel.

Stabilizing the resin-rich layer In the extended scope of invention, the stabilizing agent could be a thixotropic agent, added to the resin. However, in order to clearly distinguish from the art, the use of heat to body or gel the resin and thus hold it in place is not to be included within the scope of the invention. This two-step operation is previously dedicated to the art.

The distinct novelty here is in the manufacture of the fluid handling wall of invention in one curing step and thereby producing a monolithic but yet composite wall structure. In the production of similar wall structures by curing the underlayer to render it immobile, so that the filament windings can be put over without resin run-out, a different structure is believed to be formed. This is because of the parting line that is inherent between the two layers.

The broader method of the half-tank concept This method is schematically illustrated in FIGURE 30 of the drawings.

Step 1.Numeral I in the block diagram illustrates the manufacture of a tank wall increment. These could be tank halves.

Step 2.Numeral II represents the production of a tank end cap.

Step 3.Numeral III represents the nesting of 15 to 20 tank wall shells and a number of tank end caps on a railroad flatcar for shipment to one of a strategically located number of subassembly or distribution points of a commercial marketing pattern.

Step 4.Numeral IV represents the completion of a number of different structural forms using the components shipped by the method step III. Thus, IV-a represents a storage tank such as discussed relative to FIG- URE 2 ofthe drawings. IV-b represents a simple storage shed structure. If this structure were inverted, and the top simply laid on and held there by gravity or suitable strap means, it would be representative of a grain storage bin. IVc represents a high-pressure resistant tank of the type discussed relative to FIGURE 3 of the drawings, or, with convex ends, an underground storage tank as in FIGURE 17.

IVd of FIGURE 30 contemplates the shipment of wall increments only in nested form, with two types of nested end caps. These are put on later by field assembly.

IVe depicts a pipeline; or if disposed vertically, a stand pipe or silo. In case of a pipeline, the wall increments would be made in relatively small diameter, and would be field-joined by a weld, as shown in FIGURE 16. This open-end increment would form an ideal conduit system because of its corrosion resistance, both for the materials being pumped and for the environmental corrosive materials contained within the surrounding soil. Due to the light weight of these materials and their abrasion resistance, they could be joined up to substantial lengths on the surface and dropped into the ditch and covered. Rapid pipeline construction would be evident from this type of operation because the resin-rich layer is there for corrosion resistance. Accordingly, the com plicated and expensive field wrapping and tar coating as now used to protect underground steel pipelines and the rather laborious welding procedures involved would be alleviated.

Summation Steps I through IV are meant to illustrate the following broader method of fluid vessel manufacture:

Manufacturing wall and cap increments;

Shipping such components in nested form for economy of transportation, to a subassembly-distribution point or actual use site, for final fabrication by field joints to provide a wide variety of tanks, fluid conduits, shelters and others, by appropriate selection and combination of the components.

We claim:

1. In a composite, fluid-handling wall structure,

a thin layer of synthetic resin forming one surface, and means holding said thin layer against checking and crazing by corrosive elements placed in contact therewith,

a body layer containing chopped strand reinforcement and resin, the latter in a predominant amount,

stabilizing layers of fabric interspersed within the thickness of said chopped strand-resin layer and oriented in planar relation therewith,

a criss-cross layer of continuous strand, filament Windings adjacent to said stabilized chopped strand-resin layer,

said filament-Wound layer holding a thin coating of resin on the other surface of said composite body,

and said resin throughout said body being cured to a hard, solid state.

2. The invention of claim 1, including a layer of impervious flakes positioned within said body layer, and said flakes being positioned in overlapping relationship and separated from one another by thin layers of resin, thereby providing a barrier against the passage of fluid materials.

3. The invention of claim 2 wherein said flakes are made of glass.

4. In a monolithic-composite fluid-handling wall structure,

a body of hardened synthetic resin containing admixed and randomly oriented reinforcement strand lengths, the resin being present in a predominant amount,

and strata of woven fibrous mechanical stabilizing material interspersed within the thickness of said body of hardened synthetic resin and randomly oriented reinforcement strand lengths.

5. In a monolithic-composite, fluid-handling wall structure,

a body of hardened matrix material containing admixed and randomly oriented reinforcement strand lengths, the matrix material being present in a predominant amount,

strata of woven fibrous mechanical stabilizing web media interspersed through the thickness of said body of hardened matrix material and randomly oriented reinforcement strand lengths,

a criss-cross layer of continuous reinforcement strands forming a covering shell over said matrix-containing layer,

and a layer of parallel oriented strands disposed in adjacent, substantially contacting relation to said crisscross layer.

6. In a composite fluid-handling wall structure,

an endless wall of frusto-conical configuration and having an axis,

at least one peripherally extending rib member on said endless Wall, being defined by,

a first plateau area along a first level relative to said frusto-conical profile,

a second plateau area along a second level relative to said frusto-conical profile,

one of said plateau areas being spaced further from strata of mechanical stabilizing media interspersed within the thickness of said body of matrix material,

a cris s-cross layer of continuous strand filament windings forming a covering over said stabilized body,

and a layer of parallel strands disposed in adjacent substantially contacting relation to said criss-cross layer on the larger diameter plateau area, and embedded in said matrix material.

7. In a composite fluid-handling wall structure,

an endless wall of frusto-conical configuration and having an axis,

at least one peripherally oriented rib member on said endless wall being defined by,

a first plateau area along a first level relative to said frusto-conical profile,

a second plateau area along a second level relative to said frusto-conical profile,

one of said plateau areas being spaced further from said axis than the other,

an intermediate wall extending between said first and second plateau areas,

said endless wall comprising a body of hardened matrix material containing reinforcement, the matrix material being present in predominant amount,

mechanical stabilizing media interspersed within the thickness of said body of matrix material,

a first shell of continuous strand material over said stabilizer-containing body,

a second shell of continuous strand material disposed in adjacent, substantially contacting relation to said first shell on the larger diameter plateau area,

and both said first and second shells being embedded in said matrix material.

8. In a composite, fluid-handling structure having an endless side wall with cap ends closing the side wall,

the improvement wherein,

the side wall comprises opposed frusto-conical increments, having their axes coaligned, and the larger ends abutted and joined together,

each increment being made of a main stratum, for stillness, of synthetic resin and chopped strand rein forcement, and additionally comprising separate strata of fiber scrim stabilizer displaced throughout the thickness of said main stratum,

said frusto-conical increments including peripherally extending ribs displaced further from said axes than the remainder of said increment walls, and said ribs spaced along said axes,

a first shell overlay of continuous strand entirely covering said wall increments including said ribs,

said first shell at least partially overlapping said ends to hold them to said wall increments,

a second shell overlay of peripherally oriented continuous strand disposed on said ribs, and in adjacent substantially contacting relation to said first shell,

and both of said shells being embedded in said synthetic resin.

9. In a composite, fluid-handling structure comprising an endless side wall, with an axis, and with a cap end closing the side wall,

the improvement wherein,

the side wall is of frusto-conical profile configuration,

and has at least one peripherally oriented rib member disposed thereon, and defined by a valley area along a level relative to said frusto-conical profile,

a rib plateau area along a level relative to said frustoconical profile,

said rib plateau areas being spaced further from the axis of the endless side wall than the other,

an intermediate wall extending between said valley and plateau areas,

the endless wall comprising a body of hardened matrix material containing reinforcement, the matrix material being present in predominant amount, and additionally comprising separate strata of mechanical stabilizing media, displaced substantially through the thickness of the wall,

the end cap comprising a body of hardened matrix material containing reinforcement,

a first shell of continuous strand material over the endless wall and at least part of the cap end,

a second shell of continuous strand material disposed in adjacent, substantially contacting relation to said first shell substantially on the rib member,

and both said first and second shells being embedded in said matrix material.

10. In a monolithic-composite fluid-handling wall structure,

a body of hardened matrix material containing admixed and randomly oriented lengths of reinforcement strand material, the matrix material being present in predominant amount,

and strata of woven fibrous stabilizing material interspersed within the thickness of said body of matrix material and randomly oriented reinforcement strand lengths.

11. In a composite fluid-handling wall structure,

an endless wall of frusto-conical configuration having an axis,

at least one axially extending rib member on said endless wall, being joined by,

a first plateau area along a first level relative to said frusto-conical profile,

a second plateau area along a second level relative to said frusto-conical profile,

one of said plateau areas being spaced further from said axis than the other,

interconnecting wall means extending between said first and second plateau areas,

said endless wall comprising a body of hardened matrix material containing reinforcing media,

mechanical stabilizing media interspersed within the thickness of said matrix material,

a criss-cross layer of continuous strand filament windings forming a covering over said stabilized body, .and a layer of parallel strands disposed in adjacent,

substantially contacting relationship to said crisscross layer on the larger diameter plateau area, and

embedded in said matrix material.

References Cited UNITED STATES PATENTS 650,949 6/1900 Phillips 22072 XR 2,522,527 9/ 1950 Manning 161 2,546,230 3/1951 Modigliani.

2,614,058 10/ 1952 Francis.

2,718,583 9/ 1955 Noland.

2,764,545 9/ 1956 Primich 2205 X 2,843,153 7/1958 Young.

3,134,704 5/1964 Modigliani.

3,239,400 3/ 1966 Anselm 156-171 THERON E. CONDON, Primary Examiner.

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