 |
|
 |
| |
 |
Organic liner for thermoset composite tank |
| H943 |
Organic liner for thermoset composite tank
|
|
| Patent Drawings: | |
| Inventor: |
Garvey |
| Date Issued: |
August 6, 1991 |
| Application: |
07/449,175 |
| Filed: |
December 13, 1989 |
| Inventors: |
Garvey; Raymond E. (Knoxville, TN)
|
| Assignee: |
The United States of America as represented by the United States (Washington, DC) |
| Primary Examiner: |
Wallace; Linda J. |
| Assistant Examiner: |
|
| Attorney Or Agent: |
Lovingood; Katherine P.Hamel; Stephen D.Moser; William R. |
| U.S. Class: |
220/560.04; 220/901 |
| Field Of Search: |
220/901; 220/5A; 220/457; 220/456; 220/453 |
| International Class: |
|
| U.S Patent Documents: |
2788306; 2927867; 3257265; 3383004; 3406857; 3738527; 3795573; 3814275; 4117947; 4366917; 4378403; 4452375; 4785955 |
| Foreign Patent Documents: |
|
| Other References: |
|
|
| Abstract: |
A cryogenic tank that is made leak-proof under cryogenic conditions by successive layers of epoxy lining the interior of the tank. |
| Claim: |
I claim:
1. A cryogenic tank comprising:
a tank configuration of suitable material to withstand cryogenic conditions;
the interior of said tank configuration lined with consecutive layers of organic coatings, said layers comprising;
a first layer of minimum thickness, from about 0.0001 to 0.001 in. thick, to establish a continuous coating for bonding;
a layer subsequent to said first bonding layer of suitable thickness, from about 0.0001 to 0.001 in. thick, to establish bonding reliability;
a layer subsequent to said bonding reliability layer of suitable thickness, from about 0.001 to 0.010 in. thick, to insure molecular impermeability;
a layer subsequent to said molecular impermeability layer of suitable thickness, from about from 0.001 to 0.010 in. thick, to guarantee integrity at cryogenic temperatures;
a layer subsequent to said integrity layer of suitable thickness, from about 0.0001 to 0.001 in. thick, to insure a smooth defect-free surface.
2. The cryogenic tank of claim 1 wherein said organic coatings comprise epoxy resins.
3. The cryogenic tank of claim 2 wherein said first bonding layer comprises the epoxy mixture of Table 1 and Table 3, as follows:
said bonding reliability layer comprises the epoxy mixture of Table 1 and Table 3, said molecular impermeability layer comprises the epoxy mixture of Table 5 and Table 7, as follows:
said integrity layer comprises the epoxy mixture of Table 5 and Table 7, and said smooth defect-free layer comprises the epoxy mixture of Table 1 and Table 3. |
| Description: |
This invention relates toa coating for sealing surfaces having complex geometry, particularly to a coating of epoxy layers that forms a surface impermeable in harsh cryogenic and chemically corrosive environments.
BACKGROUND OF THE INVENTION
Previously, scientists have followed two approaches in the development of cryotanks that were impervious to deterioration caused by the contained material and environmental factors. One is a metal lined tank with the metal usually in the form ofa foil. The other is an organically coated tank where the coating is a film. Both the foil and the film are theoretically impermeable; however, the bond to the substrate and the integrity of the final surface have proven to be unsatisfactory in bothapplications.
Cryotanks are generally fabricated from composites of either graphite fiber reinforced fiberglass or a glass reinforced polymer matrix. These tanks have been lined with either the metal foils or organic films. Metal coatings have also beenutilized but the coating process, usually some form of deposition, has resulted in a porous surface that does not satisfactorily bond to the substrate.
In the case of metal foils, application is suitable for cone, cylinder or flat surface geometry; however the surfaces that need to be covered are not limited to these configurations making foils an unsuitable approach. With organic coatings, aswith foils, the adhesion between the liner and the tank has not been satisfactory when exposed to cryotank temperatures. Therefore, there is a need to develop a containment tank that is impermeable to liquids and gases in harsh cryogenic and chemicallycorrosive environments.
SUMMARY OF THE INVENTION
In view of the above needs, it is an object of this invention to provide a cryotank that is impermeable to molecular intrusion at fluctuating temperatures.
It is another object of this invention to provide a molecularly impermeable coating that can adhere to a surface and maintain integrity at cryogenic temperatures.
It is another object of this invention to provide a molecularly impermeable coating that can adhere to a surface of irregular configuration.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned bypractice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the article of manufacture of this invention may comprise a tank configuration of suitable materialto withstand cryogenic conditions. The interior of the tank is lined with consecutive layers of organic coatings. The first layer is of minimum thickness to establish a continuous coating for bonding; the next layer is of suitable thickness toestablish bonding reliability; the next layer is of suitable thickness to insure molecular impermeability; the next layer is of suitable thickness to guarantee integrity at cryogenic temperatures; the final layer is of suitable thickness to insure asmooth defect-free surface. In the preferred embodiment the coating is an epoxy. The first layer is from about 0.0001 to 0.001 in. thick; the second layer is also about 0.0001 to 0.001 in. thick. The third layer is about 0.001 to 0.010 in. thick andso is the forth layer. The final layer is from about 0.0001 to 0.001 in. thick.
The invention is an improvement over past line cryotanks since the integrity of the lining has a longer life under cryogenic conditions than prior art methods.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention relates generally to a leak-proof seal for structural composites in extremely harsh cryogenic and chemically corrosive environments. Such seals have particular applicability for sealing surfaces having complex geometry as may beencountered on hypervelocity transport vehicles.
The method of the invention comprises the application, successively, of layers of epoxy resin formulations. First, two very thin layers, from about 0.0001 to 0.001 in. thick, are applied. This is followed by two thicker layers, about 0.001 to0.010 in. thick. A final layer, from about 0.0001 to 0.001 in. thick, is added for a smooth defect-free surface.
EXAMPLE
In the preferred embodiment, the thin and thick epoxy resin formulations are each comprised of an A-component and a B-component. The application of each layer is followed by a curing step. A thin A-component composition is shown is Table 1,with thin A-component properties given in Table 2. The ingredients and solvents of thin B-component are shown in Table 3. Thin B-component properties are given in Table 4.
TABLE 1 ______________________________________ THIN A-COMPONENT COMPOSITION Percent by Wt Ingredient (.+-.0.010%) ______________________________________ Epon 1002 or 1002F.sup.1 54.9 Dye, Oil Red PD15344.sup.2 0.20 Isopropyl Alcohol (ASTMD770) 1.30 Xylene (ASTM D846) 2.80 Methyl Isobutyl Ketone (ASTM D1153) 5.60 Cyclohexanone, Tech. Grade 2.60 Methyl Ethyl Ketone (ASTM D740) 8.20 Normal Butyl Alcohol (ASTM D304) 2.60 1-Methoxy-2-Propanol Remainder ______________________________________ .sup.1 Shell Chemical Co., Polymer Division #1 Shell Plaza, Houston, Texa 77002 .sup.2 Eaton Chemical Division, Western Eaton Solvents & Chemical Co., 13395 Huron Dr., Romulus, Michigan, 48174
TABLE 2 ______________________________________ THIN A-COMPONENT PROPERTIES Property Requirement Method ______________________________________ Color Red Visual Specific gravity at 25.degree. C. 1.03-1.05 ASTM D1963 Resin Wt/Epoxide Equiv- 600-730 Dry 5-10 ml sample at alent (gm/eq) 65.degree. C.; D1652; crst. vio. indicator Viscosity Seconds 25-40 ASTM D3794 Zahn-Cup No. 3 Solids, percent 54-56 ASTM D1944 Clarity Clear ASTM D2090 ______________________________________
TABLE 3 ______________________________________ THIN B-COMPONENT COMPOSITION ______________________________________ Ingredient Percent by Wt (.+-.0.05%) ______________________________________ Diethylenetriamine 1.43 AEW = 34.4 to 37.0 g/eq Sp Grav = 0.945-0.955 Amido-Amine 3.53 Celanese, #1 Riverfront Plaza (Epi-Cure 855) Louisville, KY 40202 Epoxy Resin Solution 3.25 Shell, #1 Shell Plaza (Epon 1001 CX 75) Houston, TX 77002 Solvent Mixture Remainder (See Below) ______________________________________ Solvent Weight percent (.+-.0.8%) ______________________________________ Toluene (ASTM D362) 5.24 1-Methoxy-2-Propanol 51.38 Isobutyl Alcohol 23.75 (ASTM D1719) Methyl Ethyl Ketone 7.85 (ASTM D740) MethylIsobutyl Ketone 10.16 (ASTM D1153) Xylene (ASTM D846) 1.62 ______________________________________
TABLE 4 ______________________________________ THIN B-COMPONENT PROPERTIES Property Requirement Method ______________________________________ Amine equivalent weight 1360-1608 N cmpds in gm (gm/eq) providing one titratable N. equiv. Specific gravity 0.883-0.907 ASTM D1963 Non-volatiles, wt % 6.00-6.60 ASTM D1644 Appearance yellow to amber Visual clear liquid ______________________________________
To prepare the thin B-component composition, the amido-amine and diethylenetriamine are mixed at room temperature until homogeneous. The epoxy resin solution (EPON 1001CX 75) is preheated to 75.degree. C..+-.5.degree., then gradually added tothe amido amine diethylenetriamine mixture. Constant stirring is provided during the addition to provide for a complete reaction, while the temperature is maintained at 52.degree. C..+-.3.degree.. Mixing is discontinued when the brown solution becomesclear, after which the reaction mixture is allowed to cool to 37.degree. C..+-.3.degree.. The solvent mixture (Table 4) is added slowly with constant stirring until the solution is homogeneous and meets non-volatile requirements.
To prepare the thin coating, 45 volume % (.+-.0.5%) quantities of A-component and B-component compositions are combined and thoroughly mixed. Methyl isobutyl ketone is gently stirred into a mixture of A-component and B-component to reach the100% volume. The thin coating is then filtered through a Resco fine filter and allowed to stand for 45 minutes before using.
After degreasing the surface to be coated with one of several conventional degreasing solvents such as Freon TA or acetone, the thin coating is applied to the interior of a cryotank made of fiberglass reinforced with graphite fiber or of apolymer matrix reinforced with glass fiber. Application can be made with a dry lint-free and oil-free cloth or with a Teflon applicator such as a paddle, scraper or roller. The thin layers are allowed to dry for 30 minutes after which they are cured at230.degree. F..+-.5.degree. for 2 hours. The combined components must be used within 8 hours of mixing and should be stored, if necessary, in a closed container at room temperature.
A thick A-component is shown in Table 5 with thick A-component properties given in Table 6. The ingredient and solvents of thick B-component are shown in Table 7. Thick B-component properties are given in Table 8.
TABLE 5 ______________________________________ THICK A-COMPONENT COMPOSITION Ingredient Percent by Weight ______________________________________ Dye, Oil Red, PD15344.sup.1 0.1 .+-. 0.01 Liquid Epoxy Resin Remainder Shell Epon 828.sup.2 ______________________________________ .sup.1 Eaton Chemical Division, Western Eaton Solvents & Chemical Co., 13395 Huron Dr., Romulus, Michigan, 48174 .sup.2 Shell Chemical Co., Polymer Division #1 Shell Plaza, Houston, Texa 77002
TABLE 6 ______________________________________ THIN A-COMPONENT PROPERTIES Property Requirements Method ______________________________________ Weight per Epoxide Equivalent 180-196 ASTM D1652 Refractive Index 1.5660-1.5760 ASTM D1218 Color Red Visual Specific Gravity at 25.degree. C. 1.15-1.18 ASTM D1963 Water, wt % 0.25 max. ASTM E203 Viscosity at 25.degree. C., CPS 10,000-15,000 ASTM D2393 Workmanship Free of visible Visual bubbles and contaminants ______________________________________
TABLE 7 ______________________________________ THICK B-COMPONENT COMPOSITION Ingredient Percent by Weight ______________________________________ P-Nonylphenol.sup.1 45 .+-. 0.5 Versamid 125.sup.2 45 .+-. 0.5 Mix well, then add 1-(2-Aminoethyl)piperazine.sup.3 (Remainder) ______________________________________ .sup.1 Eastman P7956 or equal, CAS Reg. No. 10440-5, Jan. 1979 .sup.2 Magnolia Plastics, Inc., Chamblee, CA; or Henkel Corp., Resin Div. 4620 W 77th St., Minneapolis,MN 55435 .sup.3 Eastman 10643 or equal, CAS Reg. No. 14031-8
TABLE 8 ______________________________________ THICK B-COMPONENT PROPERTIES Property Requirement Method ______________________________________ Amine equivalent 190-210 N. compounds in gm providing weight, gm/eq one titratable N.sub.2equivalent Refractive Index 1.5095-1.5195 ASTM D1218 ______________________________________
The thick A+B composition comprises a 50:50 mixture (.+-.1%) of the two solutions. The combined mixture has a maximum work life of 12 minutes at 75.degree. F..+-.10.degree. and must, therefore, be quickly applied using a dry lint-free andoil-free cloth or with a Teflon applicator such as a paddle, scraper or roller. The applied thick layers are cured at 150.degree. F. for about 90 minutes, or at 165.degree. F. for 60 minutes, or at 205.degree. F. for at least 45 minutes. It is notrecommended that the article be subjected to a temperature of more than 215.degree. F. until curing is completed.
* * * * * |
|
|
|
 |
|
 |
|
| |
Randomly Featured Patents |
|
