Deep water flotation devices
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to composite materials useful as buoyancy devices and more particularly relates to syntactic foam materials assembled to form deep water, submergible buoyance devices. 
     2. Brief Description of the Prior Art 
     Buoyancy devices have been assembled of syntactic foam compositions prior to the present invention; see for example the descriptions given in the U.S. Pat. Nos. 3,622,437 and 3,729,756. In general, such devices comprise a syntactic polymeric resin foam matrix incorporating a large volume of hollow spheres, designated as &#34;macrospheres&#34; to distinguish them from the smaller hollow spheres designated &#34;microspheres&#34; which constitute a component of the syntactic foam composition. The macrospheres generally have diameters of from 0.5 to 6 inches and are generally made of thermoplastic, synthetic, polymeric resins reinforced with filler materials such as mica and chopped fibers of glass. The prior art macrospheres employed generally have densities of from 7.5 to 12.5 lbs/cubic foot. When encapsulated in a conventional syntactic foam matrix, the implosion pressure limit of these macrospheres is approximately doubled, allowing for the buoyancy devices made of the macrosphere/foam compositions to be usefully employed at substantial depths in the open sea, i.e. at depths up to about 4,500 feet. At deeper sites there is a likelihood of macrosphere implosion due to the higher hydrostatic pressures associated with those depths. 
     We have now found that implosion resistant macrospheres for use in buoyancy devices at sea depths in excess of 4,500 feet and up to at least about 12,000 feet may be fabricated from syntactic foams, preferably made-up from synthetic thermosetting polymeric resins. 
     SUMMARY OF THE INVENTION 
     The invention comprises a macrosphere for use in a buoyancy device, which comprises; a hollow, closed sphere having a diameter of from about 0.5 to about 10 inches, a wall thickness of from about 0.010 to about 0.500 inches, a density of from about 6 to about 32 lbs/cubic foot, said sphere being fabricated from a hardened syntactic foam of a synthetic, polymeric resin. 
     The invention also comprises buoyancy materials and devices which include the macrospheres of the invention as a component thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a section of conduit encased in a buoyancy device made up from a syntactic foam/macrosphere composition. 
     FIG. 2 is a view along lines 2--2 of FIG. 1. 
     FIG. 3 is an enlarged fragmentary view of a portion of the syntactic foam shown in FIG. 2. 
     FIG. 4 is a further enlarged, fragmentary view of the syntactic foam 18 in FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     Referring to FIG. 1 of the accompanying drawings, there is seen a side elevational view of a section of conduit 10 encased within a jacket formed of a plurality of syntactic foam formed modules 12 held in place by bands 14. The modules 12 as shown in FIG. 2, a view along lines 2--2 of FIG. 1 comprise 90° sections. They could be of varied arc length, for example, up to 180°. The jacket made up of the four modules 12 is a buoyancy device for adding buoyancy to the attached conduit 10 in deep sea environments. The FIG. 3 is an enlarged, fragmentary view of the buoyancy material of which the modules 12 are formed. Thus, a syntactic foam 18 of a synthetic, polymeric resin serves as a matrix to bind together and encapsulate hollow, closed macrospheres 16 which are uniformly dispersed throughout the matrix foam 18. FIG. 4 is a greatly enlarged fragmentary view of the syntactic foam 18, showing that it is made up of a hardened, synthetic polymeric resin 20 loaded or filled with a plurality of microspheres 24, i.e.; a syntactic foam. Methods of manufacturing syntactic foams are well known; see for example U.S. Pat. Nos. 3,353,981; 3,230,184; and 3,622,437. In general, syntactic foams are hardened or cured synthetic, polymeric resins filled or loaded with hollow, closed microspheres, as defined by the ASTM Committee on Syntactic Foam. The microspheres act as fillers, but advantageously also reduce the overall density of the foam. The resin may be, for example, a polyester, phenolic or like resin. The microsphere filler materials are also well known and may be fabricated from glass, ceramic, polymeric resins and like materials; see U.S. Pat. Nos. 2,797,201 and 3,133,821. Preferred microsphere components of the syntactic foam matrices employed in the present invention are represented by the commercially available &#34;Glass Bubbles&#34; (3M Corporation, St. Paul, Minn.). Generally such microspheres have diameters of 5 to 500 microns. 
     The proportion of microspheres or other fillers may constitute from 50 to 75 percent by volume of the resin foam composition, i.e. the syntactic foam. 
     Methods of forming buoyancy articles and devices by encapsulating macrospheres in the matrix of a syntactic foam are well known to those skilled in the art and need not be described in detail herein; see for example the methods described in U.S. Pat. Nos. 3,729,756; 3,622,437; 3,996,654; and 4,021,589. In the present invention, the macrospheres encapsulated are of a specific and novel construction. They are employed to reduce the overall weight of the buoyancy device, without a sacrifice of strength, particularly resistance to implosion under deep water submergence conditions (hydrostatic pressure). Preferably, low density macrospheres are desired to give maximum bouyancy to the buoyancy device of which the macrosphere becomes a component. Advantageously the density of the macrospheres of the invention lie within the range of from about 0.15 to about 0.45 gms/cubic centimeter; preferably 0.22 to 0.33 gms/cc. 
     A wide range of synthetic, polymeric resins may be used to prepare the resin component of the syntactic foams employed in the fabrication of the macrospheres of the invention. Representative of such resins are polyurethanes, polyesters, polyepoxides and like resins. Co-polymer resins such as styreneacrylonitrile and the like may also be used. The polyester resins such as those described in the U.S. Pat. No. 4,104,357 are advantageous. Preferred for fabricating the macrospheres of the invention are thermoseting resins, which appear to enhance the compressive strength of the macrosphere product over thermoplastic resins. Particularly advantageous in this respect are the thermosetting polyvinyl ester resins of the general formula: ##STR1## wherein n is an integer of such value that the resin has an average molecular weight starting from 485 and up. Such resins are commercially available and are represented for example by Corrolite 31-345 (Reichhold Chemical Inc., White Plains, N.Y. 
     The syntactic foams employed in the fabrication of the macrospheres of the invention may contain the same fillers described above for the foam matrix, i.e. microspheres of glass, ceramic or polymeric resin materials. In their preparation, a curable syntactic foam forming composition is made by admixture of a curable resin with from 20 to 80 percent by volume of fillers. The resin component is then cured, generally with a curing agent to obtain the syntactic foam. Preferably, the resin is a polyepoxide and the curing agent an organic amine. 
     Polyamine agents for curing polyepoxides are well known as is the method of their preparation. Representative of such agents are those of the formula: ##STR2## wherein R represents hydrocarbylene and n is an integer of from 1-5. 
     The term &#34;hydrocarbylene&#34; as used herein means the divalent moiety obtained upon removal of a hydrogen atom from a hydrocarbyl radical as previously defined. 
     Representative of polyamine curing agents of the formula given above are ethylene diamine, diethylene triamine, diethyleneaminopropylamine, m-phenylenediamine, p-phenylenediamine, methylenedianiline, triethylene tetramine, tetraethylene pentamine and the like. 
     Additional ingredients may be added to the foam forming compositions as is conventional in the art. Representative of such additional ingredients are inert solvents for the epoxide reactant, inert fillers and reinforcing materials such as textile fibers and the like, impact resistance modifiers such as vinyl terminated butadiene/acrylonitrile copolymers, bonding or coupling agents such as silanes to improve the bond between glass microspheres and the resin matrix, flame retardants such as potassium and antimony salts, catalysts and promotors for curing the resins and the like. 
     The macrospheres of the invention may be manufactured from the above-described syntactic foam-forming compositions by conventional and known molding techniques. One technique would comprise the injection molding of two halves or hemispheres from the syntactic foam-forming composition and sealing the halves together to complete the macrospheres. An advantageous molding technique is to rotary mold the entire sphere so as to obtain a seamless, one-piece macrosphere in the form of a complete sphere. In general, the macrospheres are fabricated with a wall thickness of from about 22 to about 52 mm. 
     The following examples describe the manner and process of making and using the invention and set forth the best mode contemplated by the inventors for carrying out the invention but are not to be considered as limiting the scope of the invention. All parts are by weight unless otherwise specified. All specified test results, where given, were according to the following procedures. 
     Compressive strength and compressive modulus tests were performed according to the ASTM procedure D-695. 
     Flexural strength tests were performed by using the formula: ##EQU1##  where D=diameter, P=Load and L=Span. Rapid Loading Burst Strength tests were carried out by Isostatic Press, rate of hydrostatic pressurization between 500-1200 pounds per square inch per second, preferably between 600-900 psi/sec. Long term Hydrostatic Creep Performance was determined by continuous hydrostatic exposure at design pressure required. 
     Sympathetic Implosion tests were conducted by casting three spheres in syntactic foam, one sphere underdesigned for short-term testing at design test pressure. 
     EXAMPLE 1 
     An appropriate vessel was charged with 100 parts of a polyester resin (Polylite 31-001; Reichhold Chemicals, Inc., supra). To the charge there was added with stirring 15 parts of 3M Glass Bubbles (B38/4000) having a density of 0.38 gms/cc, and 0.375 parts of a silane coupling agent (Z-6030, Petrarch Chemical Co.). To the resulting mixture there was added with mixing 1 part of 60% methyl ethyl ketone peroxide, 1 part of 6% cobalt naphthenate and 1.5 parts of dimethylaniline. The resulting mixture was injected into a rotary molding apparatus to mold spheres with a diameter of 2.47 inches and an average wall thickness of 0.090-0.200 inch range. Representative spheres so molded were then subjected to physical testing. The test results are set forth in the following table. 
     EXAMPLE 2 
     The procedure of Example 1, supra., was repeated except that the proportion of glass bubbles as used therein was reduced to 7.5 parts. The test results are given in the following table. 
     
                       TABLE I                                                     
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Rapid Loading Burst Strength Results                                      
(Sphere weight in grams, yielding                                         
designated burst pressures)                                               
Burst Pressure Composition                                                
PSI            Example 1 Example 2                                        
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1500                         24.9                                         
1600           22.8   23.3                                                
1700                                                                      
1800                                                                      
1850                         25.9                                         
1900                                                                      
2000                                                                      
2100                                                                      
2200                                                                      
2300                                                                      
2400                                                                      
2500           26.2   28.1   27.4                                         
2550                                                                      
2600           28.0          28.5                                         
2700                                                                      
2800           29.6   27.7   29.4                                         
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Long Term Hydrostatic Creep Performance                                   
           Pressure    Time                                               
Formulation                                                               
           psi         (Days)  % Survivors                                
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Example 1   750        5        80                                        
Example 2   750        5       100                                        
Example 1  1100        5       100                                        
Example 2  1100        5       100                                        
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         ______________________________________                                    
Mechanical Properties of Sphere Material Compositions                     
               Example 1                                                  
                       Example 2                                          
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Uniaxial         18200     20100                                          
Compressive Strength                                                      
psi                                                                       
Uniaxial         5.26      5.53                                           
Compressive Modulus                                                       
psi (× 10.sup.5) -Flexural Strength                                 
                  4900      5600                                          
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Sympathetic Implosion Test Results                                        
          Design      Sphere                                              
Composition                                                               
          Pressure, psi                                                   
                      Weights, g.                                         
                                 Results                                  
______________________________________                                    
Example 1  750        23.3       no implosion                             
                      25.2       propagation                              
                      27.9                                                
Example 2  750        25.0       no implosion                             
                      26.1       propagation                              
                      28.1                                                
Example 1  1100*      29.2       no implosion                             
                      30.6       propagation                              
                      31.3                                                
Example 2 1100        29.1       no implosion                             
                      31.2       propagation                              
                      31.3                                                
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     EXAMPLE 3 
     A riser (buoyancy) module was prepared, encapsulating macrospheres prepared in accordance with the procedure of Example 1, supra., in a syntactic polyepoxide foam matrix. The module, identified by the serial number 5212-1 was then subjected to hydrostatic testing as follows: 
     
         ______________________________________                                    
Test    Buoyancy loss of module as manufactured, over                     
performed:                                                                
        a period of 210 hours at 3340 psig.                               
        Buoyancy loss of the module was monitored                         
        continuously throughout the duration of the                       
        test.                                                             
Procedure:                                                                
        The riser module was &#34;suspended in the test                       
        chamber by three stainless steel springs each                     
        having a spring constant of 5 lbs. per inch&#34;.                     
        A Bourn&#39;s Model 108 0-5000 OHM, Linear                            
        Displacement Transducer with a maximum travel                     
        of four inches was used to continuously                           
        measure the extention of the spring as the                        
        module absorbed water. The resulting output                       
        signal from the transducer was monitored on a                     
        Hewlett package model No. 3465B digital                           
        multimeter. A Heise 0-5000 psig pressure                          
        gage and a CEC pressure transducer model No.                      
        402 with digital readout were used to monitor                     
        test chamber.                                                     
        The pressure chamber used was a 90-inch                           
        I.D., 4000 psig test chamber. Hydrostatic                         
        pressure test was performed using fresh water                     
        at ambient temperature.                                           
210 Hour                                                                  
        Test chamber pressure was increased to                            
Hydrostatic                                                               
        approximately 50 psig and maintained at this                      
Test:   level for 8 hours. The test chamber pressure                      
        was then increased to 3340 psig in 100 psig                       
        increments every 15 minutes and maintained at                     
        this level for approximately 210 hours. At                        
        3340 psig, the module showed 1.39 percent                         
        loss of original calculated buoyancy or a                         
        total of 9.17 pounds loss. Upon completion                        
        of the 210 hour hold period, module 5212-1                        
        showed a total of 2.36 percent buoyancy loss                      
        (15.57) lbs. The module was left in the test                      
        chamber at 0 psig from 2015 hours, through                        
        0800 hours, four days later before being                          
        removed. Upon removal of the module from the                      
        test chamber, the steel ballast was removed                       
        and the module weight in air was recorded.                        
        There was no major damage to the module                           
        observed and the total weight gain of the                         
        module was 4.25 pounds.                                           
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     SUMMARY OF DATA 
     
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TEST DATA                                                                 
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Wt. in air before test                                                    
                      865.75 lbs.                                         
Total steel ballast   771.5 lbs.                                          
Negative buoyancy (measured)                                              
                      -13.0 lbs.                                          
Initial buoyancy (calculated)                                             
                      661.29 lbs.                                         
Spring rate           5 lbs./inch                                         
Displacement rate     .012 lbs./OHM                                       
Wt. in air after test 870 lbs                                             
Wt. gain              4.25 lbs                                            
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     The results of the hydrostatic testing indicate that the module identified as 5212-1 met or exceeded the test requirements identified. The percentage weight gain 0.49% after 210 hours was within acceptable levels.