US3861995A - Liquid impermeable plastic case - Google Patents

Abstract

A liquid impermeable plastic case for use especially in containing transformers and other electric equipment designed to be immersed in insulating oil and buried in the ground comprises an inner lamina providing an oil barrier, an intermediate lamina providing structural strength, and an exterior lamina providing a water barrier. The inner lamina comprises a set resin gel; the intermediate lamina, set resin reinforced with fiberglass strands; and the exterior lamina, set resin admixed with thin glass plates oriented flatwise in a multiplicity of layers.

Description

United States Patent [191 Kellogg, Jr.

[451 Jan. 21, 1975 [54] LIQUID IMPERMEABLE PLASTIC CASE [75] Inventor: Charles W. Kellogg, Jr.,

Battleground, Wash.

[73] Assignee: No-Korrod, Inc., Kirkland, Wash.

[22] Filed: Feb. 9, 1973 [21] Appl. No.: 331,213

[52] US. Cl 161/162, 161/168, 161/195, 161/198,161/208,161/234,161/D1G.4, 174/17 R, 174/17 LF, 174/37, 336/90 [51] Int. Cl 1332b 5/16 [58] Field of Search 161/162, 168, 195, 208; 174/17 R, 17 LP, 37; 336/90 [56] References Cited UNITED STATES PATENTS 2,977,264 3/1961 Shapero et al. 161/162 3,026,228 3/1962 Robinson et al 161/195 3,080,272 3/1963 Jackson l6l/l68 3,133,825 5/1964 Rubens l6l/l95 3,158,528 11/1964 Brown 161/208 3,225,131 12/1965 Conklin et al. 161/162 3,416,990 12/1968 Robinson 161/162 3,730,808 5/1973 Fekete et al. 161/195 Primary ExaminerGeorge F. Lesmes Assistant Examiner-William R. Dixon, Jr. Attorney, Agent, or FirmEugene D. Farley [57] ABSTRACT A liquid impermeable plastic case for use especially in containing transformers and other electric equipment designed to be immersed in insulating oil and buried in the ground comprises an inner lamina providing an oil barrier, an intermediate lamina providing structural strength, and an exterior lamina providing a water barrier. The inner lamina comprises a set resin gel; the intermediate lamina, set resin reinforced with fiberglass strands; and the exterior lamina, set resin admixed with thin glass plates oriented flatwise in a multiplicity of layers,

12 Claims, 2 Drawing Figures LIQUID IMPERMEABLE PLASTIC CASE This invention relates to liquid impermeable plastic cases. It is described herein with specific reference to weatherproof electric transformer cases designed to be immersed in electric insulating oil and buried in the ground, although no limitation thereby is intended since the cases are applicable with equal facility to housing electric switches and other items of equipment, as well as to the underground or above ground storage of various solids and liquids.

For aesthetic reasons, it has been the trend in present day building development to locate the electric lines underground, thereby hiding them from view and eliminating the necessity of erecting unsightly poles for their support. The practice of burying the electric lines underground makes mandatory, or at least desirable, the practice of also burying underground the transformers associated with the lines. This presents serious problems.

In an underground environment the transformer case is exposed to the action of a variety of chemical agents from the soil and ground water. It also is exposed to the action of micro-organisms causing mold and rot.

In addition, a number of chemical agents from human activities may come in contact with the case. Such agents include petroleum products, surfactants, alkalies and phosphates from cleaning agents, sulfite compounds from pulp mills, organic acids such as lactic acid or acetic acid resulting from biological activities, chlorine derived from bleaching operations, and ammonia from the decomposition of nitrogenous matter.

' Still further, if the case is to be sufficiently versatile to be used in pole mount situations, it must be resistant to the effects of sunlight, wide temperature variations, and atmospheric constituents.

Thus, in summary, to be suitable for the intended use, an electric transformer case must be resistant to atmospheric chemical agents, underground chemical agents, degrading micro-organisms, extreme temperature changes, and, above all, to moisture. In addition, it must be electrically non-conducting, strong enough to support great weights and impermeable to the insulating oil with which transformer cases customarily are filled.

Because of their strength, availability, ease of manufacture and chemical inertness, the various fiberglassrcinforced synthetic resins at first sight would seem per se well suited for application in the manufacture of electric transformer cases intended for subterranean use. However, such is not the case, since the fiberglass strands used to reinforce the plastic furnish a multiplicity of tiny tubes or capillaries which physically conduct ground water and moisture into the interior of the case.

It accordingly is the general purpose of the present invention to provide a fiberglass-reinforced plastic case for use particularly in housing electric transformers and lilce equipment, which is strong, resistant to corrosion, electrically non-conducting, and adaptable either for burial in the ground or for mounting above ground, at the option of the user.

Other important objects of the present invention are the provision of a fiberglass-reinforced plastic case which is resistant to oil, water, chemicals, rot, severe temperature changes, and sunlight.

Still a further important object of the present invention is the provision of a fiberglass-reinforced plastic case of reasonable cost and having a service life of twenty years or more, even when buried in the ground.

Broadly considered, the weatherproof case possessing properties which achieve the foregoing and other objects of this invention comprises a sealed, laminar shell comprising three laminae.

An inner lamina of set resin provides an oil and mold barrier. An intermediate lamina of set resin reinforced with fiberglass strands and bonded to the inner lamina provides the necessary structural strength. An outer lamina of set resin admixed with thin glass flakes and bonded to the intermediate lamina provides a barrier particularly to moisture, but also to various chemical and atmospheric agents.

In the exterior lamina, the glass flakes are arranged flatwise in a multiplicity of layers. This overcomes the above noted tendency of fiberglass strands when used as reinforcement to lead moisture through the plastic.

Considering the foregoing in greater detail and with particular reference to the drawings, wherein:

' FIG. 1 is a perspective view of the hereindescribed weatherproof case, and

FIG. 2 is an enlarged, fragmentary sectional view taken along line 2-2 of FIG. I.

The weatherproof case of my invention basically comprises a body indicated generally at 10 and a top indicated generally at 12. The top is provided with various electric fittings 14 of conventional construction designed and arranged to accommodate a particular piece of electric equipment housed within the case, e.g. an electric transformer indicated schematically at 16.

In use, the transformer is suitably mounted within the case, the electrical connections attached, and lid 12 applied and sealed in place by the application of plastic sealant in known manner. This provides an assembly ready for transport to the site of installation.

The case, body and lid have a similar construction which achieves the purposes of the invention and which is illustrated in FIG. 2. Both comprise a laminar shell built up on an appropriately contoured mold. The laminae are applied to the mold with a spray gun, one at a time, permitting time for setting and bonding between each spray gun application.

In formulating the plastic compositions to be sprayed on the mold in compositing the final case, use preferably is made of a class of settable resins having properties particularly well suited for the intended purpose. These are the polyester resins, in particular the thermosetting polyester resins made by condensing polybasic organic acids or acid anhydrides with polyhydric alcohols or glycols. In the manufacture of the resins, after the condensation reaction is complete, styrene or other crosslinking monomer is added to liquefy the polyester. The styrene then reacts with the polyester under curing conditions and becomes an integral part of the cured resin.

A particularly suitable resin is the thermosetting resinous condensation product of approximately equimolar amounts of isophthalic acid, propylene glycol and maleic anhydride dissolved in approximately 30-60% by weight of styrene monomer and catalyzed with about 1% by weight of methyl ethyl ketone peroxide. This resin is available commercially and is termed herein isophthalic polyester resin".

Another suitable polyester resin is the resinous condensation product of a glycol comprising neopentyl glycol, a mixture of maleic anhydride and chlorendic acid.

and a polymerizable cross linking monomer for polyester resins.

Still another suitable polyester resin comprises the thermosetting resinous condensation products of propoxylated bisphenol A, fumaric acid, and a polymerizable cross linking monomer for polyester resins, such as styrene monomer.

Yet another suitable polyester resin for the purposes of the invention comprises that prepared by the condensation of a glycol comprising a mixture of propoxylated bisphenol A and hydrogenated bisphenol A, an acid component comprising maleic anhydride, and a polymerizable cross linking monomer such as styrene monomer.

However, resinous products other than polyester resins may be employed in compositing the hereindescribed waterproofcase provided they have properties suited for the intended purpose. Such another resin is a furfuryl alcohol-formaldehyde resin prepared by the reaction of furfuryl alcohol and formaldehyde in the presence of an acid catalyst.

in all cases, the resins before use may be admixed with suitable quantities of thixotropic agents, inhibitors, promoters, catalysts and pigments as required to condition the resin and impart to it the desired properties.

As noted above, the inner lamina 18 of the case serves the primary functions of retaining the transformer oil and providing mold and rot resistance. The spray composition used for making it comprises uncured resin, an inert dry earth filler (clay), colloidal silicate (silica), and a fade-resistant pigment. in this formulation the dry earth filler and colloidal silicate are added to extend the resin and give body to the plastic.

A typical formulation for the inner lamina is the following:

Per Cent B Weight The intermediate lamina 20 applied in compositing the hereindescribed case has the above noted primary function of providing structural strength to support the heavy loads which the case is designed to contain.

To this end the plastic resin mix includes from 10-50%, preferably from 20-40% by weight, of the cured intermediate lamina, of fiberglass strands 22. The strands preferably have a length of from /2to 1% inch, although they may be continuous if desiredlf cut to length, they are prepared by chopping commercial grade 60 end glass roving to the indicated length. Preferably, the glass strands are of the class having a silanechrome sizing on their surfaces. This provides a bonding medium for bonding the strands to the resin matrix.

The preferred resin for use in the formulation of the spray mix for the intermediate lamina again comprises a polyester resin. The uncured resin is mixed with the selected amount of reinforcing fiberglass and sprayed onto the inner lamina to the desired thickness. A preferred working thickness comprises 0.250 inch. This should be applied in two layers of 0.125 inches each,

with time being allowed between applications to dissipate the heat of setting and avoid the formation of heat spots" i.e. areas of resin degradation caused by excessive heating. 5 Optionally, but preferably, a sealing layer 24 next is applied to the intermediate lamina. The purpose of this layer is to seal all pinholes on the surface. A preferred resin again is uncured polyester resin, but in the form of a gel. It is applied in sufficient amount to provide a sealing layer having a thickness of from 0.015 to 0.030 inches.

The outer layer 26 has for its primary function sealing the case against transmission of water and water vapor. However, it also protects against chemical and atmospheric agents, increases thermal shock resistance, and imparts abrasion resistance.

The raw materials for the outer layer spray mix comprise uncured resin, preferably isophthalic polyester resin, and admixed therewith from -50% by weight, preferably from -40% by weight of the cured exterior lamina, of thin glass flakes 28. Glass flakes suitable for the intended purpose comprise C-Glass flakes hammermilled through a screen to a particle size of minus one thirty-seconds inch. The maximum dimension of the flakes thus is one thirty-seconds inch. Their thicknesses range from 0.00l to 0.005 inch.

Also employed as constituents of the spray coating composition for the outer lamina are a pigment and a proportion of a mineral wax.

The pigment is used in amount sufficient to impart a desired color, for example yellow. it also serves as a light reflectant, a supplemental filler, and a color coding material.

The wax is employed in amount sufficient to form a thin wax layer on the exterior surface while the resin is setting. This layer excludes air and insures curing of the resins to a hard, set condition.

A typical spray gun formulation for the outer lamina is as follows:

Per Cent By Weight When the above formulation is mixed, the glass flakes are arranged in random orientation. However, once the mixture has been sprayed on the substrate, the flakes orient themselves flatwise in substantially the plane of the lamina. This is accomplished through the action of the forces of adhesion and cohesion.

The net effect is to provide an outer lamina comprising a multiplicity of tiny glass flakes arranged in as many as two hundred layers, overlapping each other, and embedded in the set resin. It is these layers of glass flakes which are responsible for the impervious character of the outer layer of the case to water and water vapor.

To test the properties of a case manufactured in the manner described above, a transformer case having a height of about 40 inches, a maximum diameter of about 36 inches, and an average wall thickness of 0.18

inch first was subjected to a moisture vapor transfer test.

To this end the case was evacuated to 2.8 mm of mercury and heated in a wet-stream chamber for 5 days. The pressure at the end of 5 days had increased to 5.] mm of mercury, equivalent to 0.03 atmospheres. Assuming that the increase in pressure was entirely due to passage of moisture through the walls of the case, this is equivalent to 0.34 grams of water in 5 days or but 0.07 grams per day.

It is to be noted that these conditions are most severe and far exceed the environmental conditions to be encountered in actual field application.

Next the case was subjected to tests indicating its resistance to attack by various chemicals and environ ments.

In these test A inch X 4 /2 inch pieces ofthe case were soaked in each of several test chemicals at elevated temperatures for 200 hours. The test solutions and their pH values are as follows:

Tcst Chemical pH Water Solutions of (7: by weight):

Sodium Carbonate (l'/1) l 1.5

Trisodium Phosphate (571 and Ammonium Dihydrogen Phosphate (5'71) Acetic Acid (50%) Lactic Acid (50% Surfactant Sodium Sulfite (l07t) Calcium Hypochlorite (10%) Ammonium Hydroxide by weight of the intermediate lamina of fiberglass strands, and c. an exterior lamina providing a water barrier bonded to the intermediate lamina and comprising 5 a thermoset resin admixed with from 10-50% by weight of the exterior lamina of thin glass flakes oriented substantially flat-wise with respect to the surface of the case in a multiplicity of layers. 2. The case of claim I wherein the resin comprises a 10 polyester resin. I

3. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of propylene glycol. maleic anhydride and isophthalic acid, and cross linking monomer.

4. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of neopentyl glycol, maleic anhydride, chlorendic acid, and cross linking monomer.

5. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of propoxylated bisphenol A, fumaric acid, and cross linking monomer.

6. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of a glycol comprising a mixture of propoxylated bisphenol A and hydrogenated bisphenol A, an acid comprising maleic anhydride, and a cross linking monomer comprising styrene.

7. The case of claim 2 wherein the polyester resin comprises the acid-catalyzed resinous condensation product of furfuryl alcohol and formaldehyde.

8. The case of claim 1 wherein the fiberglass strands have a length of from /2 inch to 1% inch.

9. The case of claim 1 wherein the glass flakes have a maximum dimension of about one thirty-seconds inch.

10. The case of claim 1 including a thin mineral wax seal coat substantially covering the outer surface of the case.

11. The case of claim 1 including a sealing lamina between the intermediate lamina and the exterior lamina bonded to the same and comprising a resin gel in set a are continuous.

Claims (12)

1. A LIQUID IMPERMEABLE PLASTIC CASE COMPRISING : A. AN INNER LAMINA PROVIDING AN OIL BARRIER AND COMPRISING A THERMOSET RESIN GEL, B. AN INTERMEDIATE LAMINA OF SUBSTANTIAL STRUCTURAL STRENGTH BONDED TO THE INNER LAMINA AND COMPRISING A THERMOSET RESIN REINFORCED WITH FROM 10-50% BY WEIGHT OF THE INTERMEDIATE LAMINA OF FIBERGLASS STRANDS, AND C. AN EXTERIOR LAMINA PROVIDING A WATER BARRIER BONDED TO THE INTERMEDIATE LAMINA AND COMPRISING A THERMOSET RESIN ADMIXED WITH FROM 10-50% BY WEIGHT OF THE EXTERIOR LAMINA OF THIN GLASS FLAKES ORIENTED SUBSTANTIALLY FLAT-WISE WITH RESPECT TO THE SURFACE OF THE CASE IN A MULTIPLICITY OF LAYERS.

2. The case of claim 1 wherein the resin comprises a polyester resin.

3. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of propylene glycol, maleic anhydride and isophthalic acid, and cross linking monomer.

4. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of neopentyl glycol, maleic anhydride, chlorendic acid, and cross linking monomer.

5. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of propoxylated bisphenol A, fumaric acid, and cross linking monomer.

6. The case of claim 2 wherein the polyester resin comprises the resinous condensation product of a glycol comprising a mixture of propoxylated bisphenol A and hydrogenated bisphenol A, an acid comprising maleic anhydride, and a cross linking monomer comprising styrene.

7. The case of claim 2 wherein the polyester resin comprises the acid-catalyzed resinous condensation product of furfuryl alcohol and formaldehyde.

8. The case of claim 1 wherein the fiberglass strands have a length of from inch to 1 1/2 inch.

9. The case of claim 1 wherein the glass flakes have a maximum dimension of about one thirty-seconds inch.

10. The case of claim 1 including a thin mineral wax seal coat substantially covering the outer surface of the case.

11. The case of claim 1 including a sealing lamina between the intermediate lamina and the exterior lamina bonded to the same and comprising a resin gel in set condition.

12. The case of claim 1 wherein the fiberglass strands are continuous.

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