US 3668740 A
A high strength non-corrodible strap of composite materials for support or securement of articles and a method of making the strap. The strap is reinforced with filaments, such as glass fibers, looped into a continuous band having two sides merged in the middle to form an elongated body portion between end connecting loops. The matrix material, such as polyester resin, surrounds and protects the filaments from abrasion and corrosion while the filaments impart high strength to the strap. Loop-shaped thimbles can be fabricated into the loops to provide bearing surfaces at the connections. The strap with associated guides is particularly useful as a hold down strap to anchor underground storage tanks.
Description (OCR text may contain errors)
United States Patent [151 3,668,740 Pearson 1 June 13, 1972  HIGH STRENGTH STRAP AND 2,803,576 8/1957 Donaldson METHOD OF MAKING IT i liii t i ii 161/59 arzocc  Inventor: Lee E. Pearson, Granville, Ohio 73 Assi e Owens-Cornin Fibe as Co ation Exawnm-Donald Grim e g r8] Attomey-Staelin & Overman and Charles F. Schroeder  Filed: Nov. 27, 1970 r 21 Appl. No.: 93,190  ABSTRACT A high strength non-corrodible strap of composite materials for support or securement of articles and a method of making 'i the strap. The strap is reinforced with filaments, such as glass 58] i 248/36l 24/16 h AL fibers, looped into a continuous band having two sides merged 3 4 265 5, 161/59 in the middle to form an elongated body portion between end connecting loops. The matrix material, such as polyester resin,
surrounds and protects the filaments from abrasion and corro-  References Cited sion while the filaments'impart high strength to the strap. UNITED STATES PATENTS Loop-shaped thimbles can be fabricated into the loops to-provide bearing surfaces at the connections. The strap with asl apple "24/351353 sedated guides is particularly f l as a hold down strap to 7 g anchor under ound stora e tanks. 2,259,917 10/1941 Wiggins a a]... ....24/l6 PB gr 2,680,272 6/1954 Radtke ..24/l 6 PB 18 Claims, 6 Drawing-figures FATENTEDJUH 13 I972 sum 1 or 2 INVENTOR A; 5. f/4F50/V WYQM PATENTEUJun 13 I972 SHEET 2 BF 2 I N VE N TOR [5 P54 250 .JTTORXEYS HIGH STRENGTH STRAP AND METHOD OF MAKING IT This invention relates to a new and useful longitudinal tensile structural member which has particular advantages over existing tensile structural members such as straps, guy lines, slings, bands, braces, ropes and cables in its corrosion resistance, high strength, low weight, flexibility, ease of fabrication and other advantages which will become apparent from the description. This invention has particularly useful application in solving a problem encountered with underground storage tanks used for storing gasoline and other fluids. The problem arises where the underground tanks are installed in areas having a high water table and the tanks are partially or totally submerged in ground water. In such situations, the surrounding water exerts a buoyant force on the tank and if the tank is empty or has light-weight contents, it will float. The result can be injurious to the installation by causing, in addition to other harmful effects, the tank to erupt through the surface and come out of the ground. To prevent the tank from floating, it is necessary to anchor it by an effective anchor such as is accomplished by wrapping hold-down straps over the positioned tank and securing each end of the straps to a secure object such as a concrete deadman.
The anchoring straps used in the past for this purpose have been made from steel, a material which has the disadvantage of being corrodible. Because of anticipated loss of metal from corrosion and resulting loss of strength, the steel straps must be overdesigned. Overdesigning results in more weight, less flexibility and additional cost. Other metals with greater corrosion resistance can be used in place of steel, but cost of such metals is usually such as to make their use for such purposes economically impractical.
Another disadvantage of steel straps is the inconvenience of attaching connector means to the ends of the strap. integrally fabricating the connector means with the strap body would be difficult and expensive and the only satisfactory method of attaching the connector means after. the strap has been fabricated is welding. Other attaching methods, unless sophisticated and costly, reduce the effective strength of the strap. All of the attaching methods, including welding, require substantial additional labor or the expense of a sophisticated attachment.
Underground storage tanks, today, are often made of reinforced plastic and have spaced reinforcing ribs. Since the ribs of such tanks are circumferentially disposed and are designed to withstand constricting forces, they ofier an excellent base for mounting the hold-down straps. A feature of this invention lies in the adaptability of the strap to incorporation of positioning guides or other members for location or'securement of the strap on such ribs. i
In light of the foregoing, it is an object of this invention to provide a new and improved strap member of reinforced resinous material which is flexibly adaptable to many securement or lifting purposes and particularly to anchoring of underground storage tanks.
. Another object of this invention is to provide a strap having greater corrosion resistance than metal straps frequently used for similar purposes.
A still further object of this invention is to provide a strap structurally assembled in a manner permitting integral incorporation of connector means.
These and other objects are achieved in the present invention by making the strap from hardenable matrix-forming material, such as resin, reinforced with continuous filaments of high tensile strength material such as glass. The filaments extend continuously and longitudinally from end to end of the strap by bending at the ends of the strap and returning through the strap. The hardenable matrix-forming material surrounds and embraces the filaments to give integrity to the body and to protect the filaments. This form of construction achieves cooperation between both materials to obtain a composite which has the advantages of each material without many of the disadvantages of either material. Thus, reinforcing material can be selected for desired properties such as high tensile strength, elasticity and dimensional stability while undesired properties, such as corrodibility or abradability, are eliminated from the product by the protective matrix and need not be a limiting factor in selecting the reinforcing material. The matrix-fon-ning material can be selected for properties such as abrasion resistance, chemical resistance, non-corrodibility and flexibility, while strap tensile strength requirement does not limit the selection.
Glass filaments are especially desirable for use as the strap reinforcing material because of their high tensile strength, flexibility, light weight and adaptability to producing a high strength-to-weight ratio construction. Abrasion resistance and chemical resistance are provided by the protective matrix of, preferably, hardenable resin, while glass fibers enhance the composite because of their relatively low modulus of elasticity and their resistance to stretching. Low stretchability enables the strap to stably hold an object more securely and prevents deflection or movement in the object. Structural members of glass filaments and resin matrix also have the feature of being electrically non-conductive. This feature is of particular advantage when the structural member is used to support, hold or guy an object which conducts electricity or when electrolytic effects are found to be objectionable.
While a preferred embodiment of this invention is a simple longitudinal strap with connector means at both ends and with the preferential function of holding down an underground storage tank, it will be obvious to one skilled in the art that the invention encompasses other types of structural members. Such members include slings for lifting objects, guys or braces to lend rigidity or support to a structure, bands to give circumferential reinforcement to a container such as a tank or barrel, and substitutes for ropes or cables. These types of structural members employ various forms of connector means to attach them to the objects that they support. A widely used connector means is a thimble which is usually attached to a member by looping the member around the thimble and securing the member against itself by welding or clamping. Another widely used connector means is an integral clamp and eyelet which is clamped to the plain unlooped end of the member. The eyelet or thimble is attached to the object to be supported by a hook or bolting arrangement such as a clevis. If the member is to be used as a sling, the .thimble on at least one end must be large enough to allow the other end of the member to be passed through it to form a noose. The structural member of the present invention can perform its function by being secured through the same forms of connector means as used with existing structural members that perform thesame function. However, a particular advantage in the form of construction of this invention is the ease of integrally fabricating connector means into the body of the member. The connector means can be integrated into the body by looping the continuous reinforcing filaments about them. This process is simple and inexpensive and results in a structural member having equal strength at its connections as in its body.
A preferred form of incorporating connector means into the strap is by providing the means in an aperture in the body of the strap. The aperture is formed by looping the reinforcing filaments at the end of the body. While an aperture alone is an adequate connector means for many applications, the use of thimbles incorporated integrally therein adds structural advantages by distributing forces and protecting the matrix from highly concentrated stresses. Such thimbles can be inserted before or after curing the matrix of the strap; but if inserted before curing, they make an excellent template for forming the apertures by looping the reinforcing filaments about them. Although integral incorporation of connector means into both ends of the strap results in a desirable strap member for most applications and is the preferred form of this invention, it will be obvious to one skilled in the art that the strap can also be constructed with connector means in only one end.
Other objects, advantages and features of this invention will become apparent when the following description is taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates a strap of the present invention;
FIG. 2 illustrates a strap of the present invention with integral strap guides and thimbles;
FIG. 3 illustrates straps of the present invention with integral strap guides and thimbles being used to hold down an underground storage tank;
. FIG. 4 illustrates somewhat schematically the apparatus and the process of the first phase of production of the strap of the present invention;
FIG. 5 illustrates the assembly of strap elements preparatory to the final phase in the production of the strap, with a section cut out to show the alignment and arrangement of the reinforcing filaments therein; and 1 FIG. 6 illustrates the strap placed in the mold used in the final phase in the production of the strap.
Referringto FIG. 1, there is illustrated a finished strap having a longitudinal central portion 101 with a configuration which has a basically rectangular cross-section and end portions 104 consisting of loops having one-half the thickness and the same width as the central portion and being integral with the central portion.
FIG. 2. illustrates a preferred strap for holding down underground storage tanks having circumferential reinforcing ribs. The strap has strap guides 4 extending through the central portion of the strap body at spaced locations perpendicularly to the longitudinal and thickness axes of the body. Their function is to position and secure the strap to the ribs. The strap illustrated in this figure also has a thimble 2 being encompassed by each loop.
FIG. '3 illustrates a fiber glass reinforced underground storage tank 5 being held down by straps as shown in FIG. 2. The central portions 1 of the straps lay on the peripheral surface of the ribs 6 and are held in position by the strap guides 4. The straps are anchored by extending the cables or cable shackles 7 through the thimbles 2 and securing the cables to anchor points 8. The number of straps required to hold a tank down depends upon the size of the tank and the strength of the straps. For example, it has been found that a storage tank having a capacity of 10,000 gallons can be suitably secured in place with four straps each having a tensile strength of 20,000 pounds.
Referring to FIG. 4, FIG. 5, and FIG. 6, there is shown a preferred method of manufacture. As shown in FIG. 4, a bundle of glass filament rovings 9 is pulled from a source such as a creel (not shown) through a resin pot 40 where the filaments are impregnated with resin. The resin pot comprises: a vessel 11, for holding a reservoir of liquid resin 12; a cylinder 13, which serves as the resin applicator; a guide bar 10, which serves to confine the advancing filaments in the desired path; and, an adjustable eye 14, which serves the same function as the guide bar 10 in addition to its function of removing excess resin from the filaments.
To be more specific, the applicator cylinder 13.is rotatably mounted at a location in the vessel 11 which partially submerges the cylinder in the liquid resin 12 and with the rotation axis of the cylinder perpendicular to the filament path. The guide bar 10 is centrally mounted on the entrance side of the pot. The adjustable eye 14 is centrally mounted on the exit side of the pot. The guide bar 10 and adjustable eye 14 are vertically positioned in such a manner that each is below a line which passes through the other and is tangent to the surface of the applicator cylinder 13.
To describe the impregnation process more specifically, the filaments pass through the pot 40 by advancing under bar 10, over the applicator cylinder 13, and through the adjustable eye 14. In the pot 11 is a reservoir 12 of hardenable resin in the uncured stage. The filaments, advancing arcuately over the rotatable cylinder 13, cause rotation of the cylinder by frictional transfer of linear force. A coating of resin adheres to the rotating applicator cylinder and is brought into contact with the advancing filaments. The filaments, coated with excess resin, advance through the adjustable eye 14 which restricts the flow of the conveyed resin and wipes the excess from the filaments.
The coated filaments 15, having the desired ratio of resin to glass, advance from the resin pot to the winding apparatus 16. The winding apparatus consists of four adjustable arms 17, each with a finger l8 perpendicularly mounted on the end of the arm. The arms are mounted on a rotatable shaft 20 which is driven by a conventional power source (not shown). Thimbles 2, to be employed as connector means on the strap, are slipped over two oppositely positioned fingers 18. The rotation of the shaft 20 revolves the winding apparatus 16, thus winding and pulling the resin-impregnated filaments 15 into loops to form a continuous band 21 encompassing the thimbles 2. 1
Referring back to the glass filament rovings 9, a predetermined number of roving ends are advanced together to form a layer of the desired amount of glass. Although the filaments may have any of a wide range of diameters, glass filaments with a diameter of approximately 0.0005] inches, designated in the industry as K filaments, have been found to work well in this application. The filaments are coated with a size which functions as a coupling agent to enhancethe adhesion of the filaments to the resin and also as a lubricant on the pre-impregnated filaments to prevent them from abrading against each other. The size is desirably compatible with the matrix resin. For example, if the matrix consists of a polyester resin, a size which has performed successfully for this purpose is gamma-methacryloxy-propylthimethoxy-silane, commercially available from Union Carbide as Union Carbide A-l74. The number of filaments which are advanced together in the process can be varied depending upon the desired width and depth of each layer of reinforcing in the wound band 21. By way of example, a strap successfully constructed in accordance with the principle of the present invention was made using K filaments wound into a band having a width of 1% inches with approximately 3,400 filaments, yielding 450 yards per pound of glass in each bundle ofglass filament roving. However, the number of filaments used in each bundle may be increased or decreased and still provide a satisfactory strap. For example, 6,800 filaments (225 yd./lb.) and 2,550 filaments (675 yd./lb.) have also provided satisfactory results.
Referring back to the reservoir of resin 12, the preferred resin is a flexible polyester such as isophthalic polyester. This type of resin is especially adaptable for underground applications because of its high moisture resistance. Other types of hardenable resins such as bisphenol or epoxy could be used. And they might be preferred for certain applications. When isophthalic polyester is used, it is combined with an accelerator such as cobalt naphthenate and a catalyst such as methylethyl ketone peroxide.
The percentage of glass in the composite of the resin impregnated filaments 15 can be varied between 55 percent and percent by weight of the composite and still obtain good results. With lower percentages of glass the strength per composite unit area is reduced, but in using too high a percentage of glass, the disadvantage of incomplete resin impregnation of the glass can result. It has been found that a composite which consists of approximately 65 percent glass gives excellent results.
Referring back to the thimble 2, a preferred embodiment is that formed by bending a piece of steel channel of the desired width into a loop with the edges of the flanges forming the outside periphery of the loop. The function of the thimble is to resist abrasion and to distribute the load on the strap and thus avoid highly concentrated stresses on the matrix. Any material or shape which accomplishes this goal can be substituted for the formed steel channel.
Referring back to the continuous or endless band 21 wound from the resin-impregnated filaments 15, the number of required revolutions is determined by the desired strength of the finished strap. Straps constructed according to this invention have been measured as havinga tensile strength of approximately 50,000 pounds per square inch. A strap 1% inches wide and having a 54 inch thickness can be wound with twenty revolutions of a bundle of glass filaments to provide a tensile strength of 20,000 pounds.
The length of the finished strap is determined by the distance between the winding fingers 18, which, in turn, is determined by the length of the adjustable arms 17. The length of the finished strap is equal to approximately twice the distance between two adjacent winding fingers or approximately 2.8 times the length of one arm 17. The maximum length of the strap is limited only by practical considerations involved in the length of the winder arms.
After the desired number of revolutions are made, the winding apparatus is stopped and the advancing resin-impregnated filaments 15, are severed from the wound continuous band 21. The loose end is then pressed into the uncured resin of the wound continuous band 21 where it is integrated into the matrix. The wound continuous band 21 and the thimbles 2 are removed from the winding apparatus by sliding them off of the winder fingers 18. If necessary, an adjustable arm 17 can be retracted to give slack in the band to facilitate its removal. The band and thimbles are then assembled with strap guides 4, as shown in FIG. 5.
Referring to FIG. 5, the strap guides 4 are placed at desired locations between the two sides of the band 21 of wound filaments and uncured resin. The assembly is then placed in the mold table 24, shown in FIG. 6, and the two sides of the band are merged together by applying slight pressure along the central portion 1 to form a strap with integral thimbles and strap guides. The formed strap is left in the mold until the resin cures into a hard matrix.
The purpose of the strap guides 4 is to hold the position of the strap on the reinforcing ribs of the underground reinforced plastic storage tanks and therefore the required configuration is such that they securely fit on the ribs. The strap guides can be made of any suitable material of sufficient strength and rigidity, although a corrosion resistant material such as plastic reinforced with glass fibers is preferred.
Referring back to the mold 24, there is illustrated a table having grooves 26 to retain the central portions of the strap 1. At each end of the table is a slot 25 to retain the thimbles 2. At spaced locations and traversing perpendicularly to the grooves 26 are short grooves 27 to retain the strap guides 4. The mold illustrated has three berths but the number can vary from one to as many desired.
Referring to the finished strap in FIG. 1, there is shown the I junctions 103 of the loops 104 and the central body portion of the strap. Tension is transferred from the connector means to the central portion of the strap through the converging legs of the loop. Since the forces in the loop legs are directed somewhat away from each other, there is a tendency to delaminate the central portion of the strap. The larger the angle formed by the loop legs, the greater the delaminating forces. Resisting these forces is the matrix strength of the resin. To avoid delamination, the junction must be spaced a sufficient distance from the widest part of the loop to reduce the angle formed by the loop legs to one that will not tend to encourage injurious delaminating forces. However, the problem caused by failure to form the junction a sufiicient distance from the widest part of the loop is not usually critical, because delarnination, if it occurs, will displace the junction away from the loop and continue only until the junction has been moved far enough to reduce the delaminated forces to the matrix strength.
While the structural member of this invention is readily produced by the preferred method described, it will be obvious to one skilled in the art that the strap can be produced by winding the resin-impregnated filaments in a helical manner and thus producing a band which is capable of being made wider than the advancing filament bundle or layer 15. The strap can also be produced by winding the filaments into the desired loop shape and then impregnating the assembled elements with resin to form the matrix of the strap construction. The impregnating resin can be applied by such methods as spraying, dipping, or injecting into a mold. In addition to these methods of producing a wound filament strap, a strap or other structural member can be produced with reinforcing filaments extending basically longitudinally and continuously from one end of the member to the other, but not looping. The resinous matrix can be applied either by advancing the bundle of filaments through a pot of resin or impregnating after the filaments have been placed into the desired configuration. It is to be noted that this invention is not limited to the use of filaments in the form of rovings, but also contemplates the use of strands, yarns, or woven filaments.
While glass filaments and polyester resin are the preferred constituents for this invention, it will also be obvious to one skilled in the art that other materials can be readily substituted. The reinforcing material can be of any high tensile strength filaments of materials such as carbon, nylon, rayon, and metals. The matrix of the strap can be made from any abuse-resistant material such as epoxy resins, vinyl, and rubber, as long as it is compatible with the reinforcing filaments. The matrix material can be selected to give particular desired effects. For example, a soft, resilient material such as rubber could be used to form a matrix with the ability to firmly grip the object to be secured by the strap through the frictional advantages gained by compressing the matrix against the object. The advantages of such a strap would be useful in securing an object, such as a tank, against rotation when subjected to motion such as occurs aboard a ship. Other possible desired effects, such as extensibility can be had by using the construction form of this invention with elastomeric matrix materials and reinforcing material having a high coefficient of expansion or extensibility created by twisting the filaments.
Although the present invention has been illustrated and described in connection with specific embodiments thereof, it is to'be understood that variations and modifications may be made which are within the spirit and scope of the appended claims.
1. A longitudinal high strength securing member comprising a body portion reinforced by a bundle of continuous filaments extending the length of said body portion and reversed in the end region and extending back through the body portion again, said filaments being open in the reversal region and forming a loop of said filaments in said end region integral with said body portion, and a matrix of hardened resin dis tributed as a unitary mass throughout said body portion and surrounding said filaments.
2. A longitudinal high strength securing member comprising a longitudinal body portion, a bundle of continuous filaments extending through said body portion and being reversed in at least one end region to extend the bundle at least twice through said body portion, said filaments being looped in the reversal region to provide a loop in said end region integral with said body portion, and a matrix of hardened resin distributed as a unitary mass throughout said body portion and integral loop and embracing said filaments.
3. A longitudinal high strength securing member comprising a longitudinal body and an integral loop at least at one end whereby a connection may be made to said strap, said body and loop being reinforced by a plurality of strands of filaments in the form of a roving extending in longitudinal paths through the length of said body and through the loop and returning through the body, and the matrix of said strap being a hardened resin distributed as a unitary mass throughout said body and loop and embracing said filaments.
4. A longitudinal high strength composite member for securement or support of articles comprising a bundle of continuous glass reinforcing filaments extending longitudinally through said member substantially from end to end with the direction of said continuous bundle being reversed at the end regions and extending back through the body of said member, a loop in an end region formed by spreading said filaments in the end region of said member, and a hardened resinous matrix distributed throughout the bundle of filaments and embracing said glass filaments in both said body and said end regions of said member.
5. The member as defined in claim 4 wherein said resinous matrix is isophthalic polyester resin.
6. The member as defined in claim wherein the percentage of glass of the filaments in the composite member is between 55 percent and 80 percent by weight.
7. The member as defined in claim 4 including a loopshaped thimble about which said connector loop extends in snug fit relation.
8. The member as defined in claim 7 wherein said thimble is metal. I
9. A non-corrosive strap for anchoring reinforced plastic storage tanks comprising a bundle of continuous glass reinforcing filaments in the form of loops, said bundle of loops being aligned with one side of the loops in close adjacent relation to the opposite side to form a longitudinal strap body, a connection loop formed by said glass reinforcing filaments at least in one end region of said bundle of filaments, a hardened resinous matrix embracing the full length of said bundle of filaments forming said strap body and filaments forming said connector loop, and at least one strap guide suitable for guiding said strap in its circumferential extension about said tank, said strap guide being securely held by said matrix in its position transverse to said strap.
10. The strap as defined in claim 9 wherein said strap guide comprises glass fiber reinforced plastic.
11. The strap as defined in claim 9 wherein said strap guide extends between said adjacent opposite sides of said loop.
12. The method of constructing a longitudinal high strength tensile member comprising coating high strength reinforcing filaments with hardenable matrix material, forming a continuous band of loops of the coated filaments, merging two opposite sides of the band to form a single longitudinal body portion of the member between two continuous bends of filaments in the end region of the member and hardening said matrix material to provide a hardened matrix for the member.
13. The method of constructing a longitudinal high strength tensile member comprising winding a bundle of reinforcing filaments into a continuous band, coating said filaments with uncured resin, merging two opposite sides of said band to form a body portion of the member and curing said resin to form a hardened matrix throughout said body portion.
14. The method of constructing a strap comprising coating a bundle of reinforcing filaments with uncured resin, winding said bundle of filaments as a continuous band about a support with the two end regions of the strap filaments spaced from each other on said support, removing said continuous band 8. from said support, extending the endless band between said two end regions, merging the two sides of the band into a single body portion in the region between said two end regions, and curing said resin to hardness.
15. The method of constructing a strap comprising coating continuous glass reinforcing filaments with uncured hardenable resin, winding said filaments into a continuous band forming a body portion of the'strap by holding together in bundled relation the filament portions between the end regions while maintaining a loop at each end, and curing said resin into a hardened matrix.
16. The method of constructing a high tensile strength strap comprising coating continuous glass reinforcing filaments with uncured hardenable resin, winding said filaments into a continuous band about two-spaced loop-shaped connector thimbles, merging the resin coating of both sides of said continuous band to form a longitudinal strap having a loop which encompasses a thimble at each end of said strap, and curing said resin to form a hardened matrix.
17. The method of constructing'a strap comprising advancing a plurality of continuous glass filaments through a source of hardenable matrix-forming material, coating said filaments with said matrix-forming material, removing excess matrixforming material from said filaments, winding said filaments into an endless band about two spaced loop-shaped connector thimbles, pressing opposite sides of said endless band together into contact to form a longitudinal single body portion and to establish a snug fit engagement of the coated continuous glass filaments about said connector thimbles in the end re ions'pf the strap, and curing said matrix-forming material to t e point of hardness.
18. The method of constructing a strap for anchoring reinforced plastic storage tanks having circumferential reinforcing ribs comprising coating continuous glass reinforcing filaments with uncured hardenable resin, winding said filaments into a continuous band, placing a strap guide suitable for guiding said strap on said circumferential reinforcing ribs of said tank transversely between the sides of said continuous band, merging the resin coating of both sides of said continuous band while maintaining separation of the sides at each end of said band to form a strap with a loop at each end and a strap guide extending transversely through the strap and embraced by said resin, and curing said resin to the point of hardness.