US2440965A - Improved tank for hydrocarbon fuels - Google Patents

Description

J. A. MERRHLL ETAL 2,440,365

mrnovnn mm FOR umaocamaou FUELS Filed Mare}: 19, 1943 Jbmas/i' WEI-r/Y/ major/77,5 dab/1.

Patented May 4, 1948 IMPROVED TANK FOR HYDBOCARBON FUELS James A. Merrill, Akron,

Cnyahoga Falls, Ohio, Corporation, Wilmington, ml, a corporation of Delaware and Lorin B. Sebrell,

assisnors to Wins'ioot Application March 19. 1943. Serial No. 479,756

1 Claim. (01. 154-435) This invention relates to improvements in vessels intended to contain liquids and, more particularly, to tanks or containers for hydrocarbon fuels exposed to conditions under which the tanks may be punctured, as, for example, in military airplanes.

In the construction of fuel and oil tanks for airplanes, a difilcult problem is presented by the necessity for providing a self-sealing liner which will automatically close a bullet hole before any great quantity of gasoline or oil has escaped. Heavy structures and thick walls are excluded by the requirement that weight and volume, for a given quantity of liquid to be carried, must be kept at a minimum.

This problem has been solved with respect to airplane fuels of an aliphatic character, such as into the plane wing. Also, the material must IOU-octane gasoline, by providing in a tank liner a layer of unvulcanized rubber or gum which readily seals after the passage of a bullet and which is surrounded and protected by a layer of stronger material, such as fabric or cyclized rubber. Such a gum layer is further protected on the inner side by a layer or coating of hydrocarbon-resistant synthetic rubber, such as Buna- N or butadiene-acrylonitrile rubber.

The advent of aromatic fuels has, however, presented a problem in that synthetic rubber alone is not sufiiciently resistant to aromatic fuels to be satisfactory. Such fuels may contain benzene, toluene, xylene, cymene, and other aromatic constituents and, while these improve the octane rating of the fuel to such an extent that available horsepower from a given engine is increased and take-offs may be accomplished at greatly increased speeds, fuel tanks containing them and constructed according to practices found satisfactory withfuels of aliphatic nature swell to a considerable extent and thus gain weight. This gain in weight increases the dead weight of the plane and softens the tank lining so that it is more susceptible to destruction by projectiles. A material suitable for such use as a barrier to the difiusion of contained liquids, such as hydrocarbon liquids containing aromatic constituents, must possess suflicient elasticity that the layer or coating of the material will stretch without breaking when the cell or container expands due to internal pressure caused by the passage of a projectile. The material must also be flexible so that the barrier will not crack when thecell is collapsed and squeezed together for installation. For example, cells for aircraft must often be squeezed through a comparatively small manhole or other opening for insertion maintain its flexibility at temperatures well below zero, as in high-flying airplanes, so that the material does not shatter under such conditions upon impact of a projectile. And finally,

the material mustefliciently resist diflusion of the contents of the cell, a dimcult matter where fuels containing aromatic constituents are involved.

It has now been found that a layer or coating of the material known as nylon efiectively resists the action of aromatic fuels when placed on the inner surface of.a tank lining next to the fuel contents. As a result, no gasoline penetrates to the interior layers of the liner and thus no swelling and softening of the bullet-sealing composition takes place.

The materials of which nylon is representative fulfill the above specifications for a barrier to the liquid contents of a vessel in all respects, and no other materials are. at present, known which fulfill them to the same extent. Thus metal foil has been employed since it is not soluble in gasoline and the like, but these foils have no elasticity and, therefore, break when the ves= sel expands under internal pressure, nor do they have sumcient flexibility to prevent cracking when flexible fuel cells are collapsed and squeezed together for insertion into narrow spaces. Likewise, cellulose sheets do'not possess the required elasticity and flexibility, nor are they reliable at low temperatures. Nylon-type materials afiord the only compositions which have met with practical success in this field.

Nylon may be described as a high-molecular straight chain polyamide resulting from the condensation of a diamine and a dibasic acid. These materials are described at length in United States Patents No. 2,130,523 and 2,130,948. They are there described as synthetic linear polyamides resulting from the interaction of a polybasic acid and a diamine. More particularly, the substances which may be used for the purposes of the pres- -ent invention as a barrier to aromatic fuels are the synthetic linear polyamides prepared from dibasic carboxylic acids and their amide-forming derivatives combined with an organic diamine whose amino nitrogens carry at least one hydrogen atom and are attached to carbon atoms which are, in turn, attached to other atoms by single bonds only, the reactants being selected so that the sum of their radical lengths exceeds eight.

By radical length is meant the number of toms 1 the chain of the radical, each molecule of diamine and each molecule of carboxylic acid contributing this much to the unit length of the polyamide. Thus the unit length of the polyamide is made up of the sum of the radical lengths of the amine and oil the polybasic acid. this structural unit having at least nine chain atoms. In the case of a polyamide derived from glutaric acid and ethylene diamine the structural unit is The unit length, i. e., the radical length of the polyamide structural unit is therefore nine, the

number of atoms in the chain of each contribut-- ing radical, diamine and dibasic acid, being added together to give the unit length. The hydrocarbon-resisting material will be made up of a number of these structural units, each having a chain length of at least nine, in recurring fashion. Such a recurring structural unit may be represented by the formula in which X and X are hydrogen or monovalent organic radicals, preferably hydrocarbon, whose atoms adjacent to nitrogen are carbon atoms joined in turn to other atoms only by single bonds; R is a divalent organic radical, preferably hydrocarbon, whose atoms adjacent to nitrogen are carbon atoms joined in turn to other atoms only by single bonds; and R is a divalent acyl radical. In order that the unit length shall exceed eight, the ingredients should be so selected that the sum of the radical lengths of -N(X)-R'--N(X')- and R exceeds eight.

Suitable materials may be made by heating the selected diamine and dibasic acid, preferably in equimolecular amounts, although an ex cess of one or the other reactant may be present, in a closed vessel at a temperature above the melting point of the polyamide. In general, a final temperature above 180 C., which may be as high as 270 to 290 (3., will be required, the reaction being brought up to this temperature from a starting temperature above 120 C., and customarily in the neighborhood of 160 to 180 C. The vessel may be opened or evacuated in the later stages of the reaction. Inert diluents, such as benzene, may be present and basic substances may also be added, such as caustic alkalies or carbonates. A satisfactory material may be prepared by the reaction of adipic acid and hexamethylene diamine; others are the polymides derived from hexamethylene diamine and glutaric acid, propylene diamine and sebacic acid,

' pentamethylene diamine and dodecamethylene dlcarboxylic acid, and pentamethylene diamine and ethyl sebacate.

The aromatic gasoline barrier may be applied to the fuel tank liner by pressure and heat, or a coating may be applied by painting or spraying. Sufficient adhesion between the polyamide and the natural rubber and synthetic rubber layers in contact therewith can be obtained without the use of an added adhesive, if great care is exercised, although for practical purposes adhesives are employed. For example, adherence of the polyamide to Buna-N (butadiene-acrylonitrile rubber) may be secured by the use of a cement of Buna-N in toluene, while adherence of the nylon to the natural rubber sealing layer is brought about by the use of a chlorinated rubber cement, toluene being the solvent. It will also be understood that the nylon or other p yamide may contain other ingredients such as plasticizers customarily incorporated in the commercial product, e. g. polyglycerol.

A preferred form of the invention is illustrated in the accompanying drawing which presents an enlarged section oi a fuel tank liner broken away to show the various layers going to make up the liner.

As indicated therein, the liner may be made up of an outside layer of cord fabric properly frictioned with oil-resistant synthetic rubber to resist the action of sprayed or spilt gasoline. which is cross-plied with a second layer of such fabric irictioned with natural rubber. Next to this are two layers of partially vulcanized or un vulcanized rubber with or without reclaimed rubber mixed therewith, and separated by a sheet of rayon cord fabric. On the face of the gum layer nearest the fuel is spread a coating of nylon or other synthetic linear polyamide of the above description, and this in turn is succeeded by a thin layer of oil-resistant rubber, such as Buna-N. This thin layer of oil-resistant rubber contacts the gasoline but, while not sufiicient in itself to completely exclude the aromatic fuel i rom the self-sealing layers of partially vulcanized or unvulcanized rubber, does not take up suflicient fuel for this to be of any consequence. The layer does, however, protect the nylon from damage during installation and from attrition by the sloshing of fuel in the tank. Thus it is possible airplanes. It can, of course, be modified in various particulars, as by substitution of other selfsealing materials for the soft rubber and rubber and reclaimed mixtures described, by the addition of more layers of any of thekinds described or by the omission of one or more of certain of these layers. construction of, other types of containers for liquids, particularly hydrocarbon liquids, such as crash-proof tanks, storage tanks and bladdertype containers. In these, there may be no need for bullet-sealing means, but a flexible bladder which is resistant to diflusion of the liquid either does away with the necessity for a metal tank and its concomitant weight, or makes it possible to store liquids in a metal vessel which need not be liquid-tight. Thus, a flexible cell of the abovedescribed construction may be inserted in a steel or aluminum tank or may be placed in an airplane bulkhead without regard to the tightness of the supporting structure. In smaller sizes, even the metal shell may be eliminated, the liquid container consisting merely of a. bladder of rubber, synthetic rubber or other flexible material having an inner surface of the above-described material to resist diflusion of the liquid, such as aromatic gasoline. In general, then, the present invention comprises a combination of a layer or coating of synthetic linear polyamide of the type described herein with a layer of material capable of self-sealing when penetrated by a projectile, such as a bullet.

While there has beendescribed above a preferred embodiment of the invention, it will be apparent to those skilled in the art that various The invention is also useful in the teriorly of the self-sealing layer resistive to pene- 10 tration of aromatic hydrocarbon fuels and comprising a linear condensation polyamid and a layer of oil-resistant synthetic rubber only partially resistant to aromatic hydrocarbon fuels located interiorly or and protecting said insulat- 15 ing layer against physicalI dinage.

6 summons mm The following references are of record in the file or this patent:

UNITED STATES PATENTS Number Name Date Damseletal. Oct. 24, 1933 Carothers no. 16, 1937 Caz-others Sept. 20, 1988 Carothers Oct. 8, 1940 Carothera Aug. 12, 1941 Gray et a]. June 8, 194'!

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