US 2966173 A
Description (OCR text may contain errors)
Dec. 27, 1960 J. 1. MATHERNE ETAL 2,966,173
IIIPREGNATED FIBROUS "El-[BER Original Filed April 27, 1953 JOSEPH ATTORNEY United States Patent IMPREGNATED FIBROUS MEMBER Joseph L. Matherne, Roane County, Tenn., and Lloyd Ewing and Reid Ewing, Milwaukee County, Wis., assignors to McGraw-Edison Company, a corporation of Delaware Original application Apr. 27, 1953, Ser. No. 351,398,
now Patent No. 2,812,271, dated Nov. 5, 1957. Divided and this application Aug. 21, 1957, Ser. No. 684,385
1 Claim. (Cl. 13878) The present invention relates to an impregnated fibrous member and particularly pertains to a fibrous article having a predetermined proportion of voids throughout its cross-section area wherein the fibers of said fibrous article may be free to expand and contract without deleteriously affecting said surfaces.
This application constitutes a divisional application carved out of our co-pending application Serial No. 351,398, filed April 27,1953, which matured into Patent No. 2,812,271, dated November 5, I957, and entitled impregnation of Absorbent Materials.
In the past there has been serious difliculties encountered with the use of impregnated fibrous conduit. This conduit is used for the protection of underground electrical cables and other devices that must be protected from mold, moisture and other damaging influences. One of the grave problems has been the occurrence of internal blistering and structural breakdown that has been found to be due to swelling and/or shrinking of the fibrous materials from which the base structure is fabricated. In many instances these conduits are imbedded in concrete, which provides a very resistant bond with the external surfaces. If the conduit tends to blister or otherwise deform, the effect will be to block the bore of the tube which Will prevent insertion or withdrawal of cables and the like. In addition, the forces provided by blistering have often caused injury to the electrical insulation of the cables. Blistering reduces the protective area and permits entrance of seepage water with consequent deleterious effects.
In the case of fibrous bases for conduits, waste newsprint and paper pulp, or other cellulose materials, are beaten in paper heaters and the resultant stock screened and then pumped to paper cylinder machines where they are formed into wet felts or paper. The wet paper may be wound about a cylindrical or other shaped tube or mandrel to produce a wet conduit of proper thickness. This conduit is dried in kilns to remove the major por tion of its moisture content. It is to be noted that the wall thickness of the conduits may range from onequarter inch to one-half inch, as compared to an internal diameter range of from 2 to 6" on pipes or conduits that are produced in to 8 foot lengths. It will be obvious that these articles provide a vast amount of wall surface compared to the wall thickness, wherein blistering and other structural deformations may deleteriously afiect their mechanical strength after a relatively short installation period has transpired.
It is an object of this invention to provide as a new article of manufacture an impregnated absorbent article having a predetermined porosity after impregnation to provide void spaces throughout its impregnated surfaces whereby any swelling of its base material subsequent to impregnation will tend to fill these void spaces.
Referring now to the drawing, the single diagrammatic figure, partly in section, denotes a convenient arrangement for impregnating a fibrous conduit or tube in 2,966,173 Patented Dec. 27, 1960 accordance with the present invention. The tubular article 1 is capped or closed at one end with a plug member 2 or similar closure member. The opposite end of the tubular article is enclosed by means of a closure or plug member 3 which communicates with the interior of the tube as well as with an evacuating means (not shown). The plug members are preferably tapered to provide a minimum contact with the tubular article 1 in order to permit optimum access to the Wall surface on subsequent impregnation. The impregnant 4 is maintained in a vessel 5, which may be heated (not shown), if so desired. The impregnating bath may consist of any of the usual impregnating materials, such as heat liquified coal tar pitch, bituminous asphalt, or other known impregnants.
It will be obvious that the most thorough impregnation results from the lowest pressures maintained in the wall thickness and bore of a tubular article. However, it is possible to provide porous impregnated articles under the influence of relatively higher pressures. A convenient way of doing this is to evacuate the tube while it is immersed in the impregnant, drawing the vacuum from the interior of the tube. The impregnation will then take place in the direction from the outside wall surface through the wall surface to the wall interior.
Where it is desired to thoroughly impregnate the tube with a bituminous impregnant, the specific gravity of the finally impregnated article has been found to be 1.28. However, if the absolute pressure in the voids of the wall thickness is kept, for instance, at one atmosphere during impregnation, the specific gravity was found to be 0.98. By maintaining a pressure of one atmosphere inside the tube with a pressure of two atmospheres absolute on the body of impregnant outside the tube, the finally impregnated tube contained about 25% voids. More particularly, by maintaining the differential in pressure between the inside and outside of the tube, small bubbles of air are trapped around the fibers and the impregnant flows around the air bubbles. The bubbles are thus encapsulated by impregnant, and when the impregnant hardens sealed voids are formed.
A porous tube does not have as high a mechanical strength as a thoroughly impregnated one. However, it has the advantage that when subjected to certain atmospheric conditions, the swelling caused by hydration, or shrinkage caused by dehydration will provide fewer strains in the structure, which might cause internal damage to the tube. This is a characteristic greatly desired in the field of underground electrical construction. The underground tube and conduit is usually installed in relatively damp places. The cellulose fibers from which it is made slowly absorbs water and swells. This has been found to happen even under conditions where pipes have been thoroughly impregnated. Strains are often set up which cause the tube to delaminate and fail structurally. When impregnated under controlled evacuating conditions, such as described above, the cellulose fibers may swell, but the swollen fiber has a place into which it may expand. Thus, internal stresses which may be sufficient to cause rupture of the impregnated article are must less likely to occur. The multiplicity of eX- pansion areas prevent a continuous delamination by localized absorption of strains.
It will be obvious from the above description that controlled impregnation may be successfully accomplished under conditions of increased pressure, it so desired. That is, the invention may be practiced by regulating the relative atmospheric pressures exerted on the outer and inner surface of the article to be impregnated. The convenient manner of accomplishing this has been to draw a vacuum on the interior of the tubular member 3 while permitting the body of impregnant to remain at atmospheric pressure.
As a new article of manufacture, a tubular conduit formed of a highly porous mass of fibrous material, said fibers being of a type which swell or shrink under varying conditions of moisture, said fibrous mass being impregnated throughout with a mass of hardened waterproofing material filling and sealing substantially all of the voids between the fibers thereof, of the total volume of said tubular conduit a predetermined substantial proportion thereof being in the form of sealed voids distributed throughout said tubular conduit, each of said sealed voids comprising a void space encapsulated by hardened impregnant, the void spaces in said sealed voids providing spaces into which the fibers of said fibrous mass are free to swell when wetted or shrink 4 from upon drying without deleteriously affecting the wall structure of the conduit.
References Cited in the file of this patent UNITED STATES PATENTS 684,604 Dixon Oct. 15, 1901 1,504,805 Borsodi Aug. 12, 1924 1,678,021 Preble July 24, 19 28 2,012,969 Miller Sept. 3, 1935 2,016,447 Katze-Miller Oct. 8, 1935 2,383,066 McDermott Aug. 21, 1945 2,478,439 Von Liedtke Aug. 9, 1949 2,531,156 Piercy et a1. Nov. 21, 1950 2,730,462 Ewing Jan. 10, 1956 2,806,076 Yamaura et al Sept. 10, 1957