US2075700A - Structural element - Google Patents

Description

March 30, 1937. E. BURKE STRUCTURAL ELEMENT Filed Jan. 3, 1934 Patented Mar. 30, 1937 UNITED STATES STRUCTURAL ELEMENT Edmund Burke,

of Maine Portland, Maine, assigner to Brown Company, Berlin,

N. H., a corporation Application January 3, 1934, Serial No. 705,058

2 Claims.

This invention relates to a structural element designed more particularly for use as a brace, stay, or cross arm'on the poles or masts of electric power transmission systems.

lt has heretofore been the custom to tie the transmission wires to insulators carried by cross arms on the poles or masts and to stay each cross arm on either side by an iron bar aflixed at one end near the extremity of the cross arm and at the other end to the pole or mast. The trouble with such stays is that they are electro-conductors and that when an overload occurs on the line from lightning or other causes, the flashover is apt to travel down such stays and blow the lag screw out of the pole, perhaps setting the pole on fire, splitting it, or rendering it a source of danger and possible electrocution to any one touching it while it is in wet condition. The use of wood instead of iron as the material for the stays has been attempted, but with little satisfaction, not only because wood rots and is attacked by worms and woodpeckers, but also because it is a poor dielectric material when it is in Wet condition.

The objective of the present invention, genera-ily stated, is the manufacture from inexpensive materials of construction of a structural element which is without the faults of the iron or wood elements heretofore used in the respects that it remains substantially dielectric under all climatic conditions and does not deteriorate with age and service.

The structural element of the present invention is cylindrical and comprises a fiber-walled tube impregnated with a suitable water-repellent, J

dielectric material, and a solid core of inexpensive structural material tted snugly within the tube and reinforcing the tube wall substantially completely throughout. The solid core of structural material is ccnned within the tube by suitable closures or caps fixed over the ends of the tube, the tube thereby serving the function of a waterproof and dielectric armor about the core, which latter may be an inexpensive struc tural material like wood, hydraulic cement, etc., of comparatively poor dielectric qualities in a wet condition, but of good structural characteristics. When the core is a wooden or other one preformed for insertion within the tube, it may be coated with a suitable binder, preferably a waterrepellent one, such as pitch, which closes its superficial pores and interstices as well as bonds it against displacement to the internal wall of the tube. If desired, a wooden or similar preformed core may be impregnated as far as possible with pitch or similar waterproofing material serving to improve its waterproof and dielectric qualities so that should the tube become locally or otherwise fractured, the core itself will afford an improved structural element; but such an expedient is unessential for the purposes of my invention. In the case of an hydraulic cement or similar plastic core which may be formed in situ in the tube, it is unnecessary to provide an extraneous binder, such as pitch, since upon setting of they cement or similar plastic, tenacious bonding of the core with the internal wall of the tube is had.

The fiber-walled tube used in the structural element of the present invention is preferably of substantial thickness and rigidity so as to lend adequate electro-insulating and water-repelling protection to the core.` While it may be made in various ways, as by molding wet pulp to tubular form, drying the tube, and impregnating it with the desired waterproof and dielectric material, or by extruding a mixture of libers and fusible, dielectric and waterproof material under heat through a suitable die, nevertheless, I prefer to use a fiber-walled tube which has been made by convoluting wet plies or webs of interfelted fibers, as delivered by a cylinder or similar paper-making machine, to the desired wall thickness, drying the resulting tube, and impregnating it with molten pitch or other suitable dielectric and waterproof material. A tube made in this latter way is characterized by great wall toughness and strength, inasmuch as the bersexist as integrated, superposcd plies of interfelted fibers, owing to the tendency of the wet webs or convolutions entering into the tube wall to become bonded together into a substantially homogeneous structure.

With the foregoing and other features and objects in view, I shall now describe my invention in further detail with particular reference to the accompanying drawing, wherein- Figure 1 shows in perspective the end portion of a structural element embodying my invention.

Figure 2 isa section onthe line 2-2 of Figure 1.

Figure 3 is a ure 2.

Figure 4 shows in perspective the end portions of a pair of other modified forms designed to be tied together in end-to-end relationship.

Figure 5 is a section through such forms after they have been tied together.

Figure 6 shows the use of such tied-together forms as an electro-insulator for a tie cable.

section on the line 3-3 of Fig- Cil As shown in Figure 2, the structural element comprises a wooden core I tted accurately inside a ber-walled tube 2 of substantial thickness, the core extending throughout the length of the tube and making a close or snug fit with the internal wall of the tube whereat it may be bonded to the tube by pitch or similar dielectric and waterproof material. As already indicated, the tube wall is impregnated throughout with suitable waterproof and dielectric material, preferably pitch, which not only renders the tube a waterproof and dielectric protector for the core, but greatly enhances the toughness and strength of the tube wall.

The wooden core I may, as best shown in Figure 2, terminate somewhat short of the end of the tube 2 and the empty space or pocket at the end of the core lled with blown asphalt 'i0 or other suitable waterproofing material that prevents access of moisture to the core. The fastening part for such a structural element may take the form of a single piece of flat iron bar that comprises a vertical leg portion 50 projecting downwardly over the external wall of the tube, a horizontal or bridge portion 5l that extends across the end face of the structural element, and a vertical leg portion projecting upwardly beyond the end of the tube at 52 whence it is folded back onto itself and continues downwardly in single thickness 53 over the external wall of the tube. Suitable rivets or other fasteners 5i! may be passed through the portions 5D and 53, the wall of the tube, and the core. tion 52 may be apertured to permit the insertion of suitable fasteners therethrough.

The ends of the structural elements shown in Figures 4 and 5 are also sealed with blown asphalt 'IU or the like, but they are equipped with pieces adapting them for ready end-to-end union. Thus, the lower element is shown equipped with a fastening piece in the form of an H, the lower legs 55 of the piece overlapping the end portion of the element and being fastened thereto, as by rivets 56, and the upper legs 5'! of the piece being of double thickness and offset outwardly from the lower ones. The upper element is shown equipped with a complementa] fastening piece 55 in the form of a U which is fastened thereto as by rivets 69, and whose legs overlap the end portion of the element and can be iitted nicely in between the legs 5l' with the ends of the two elements next to each other. When such a t is made, apertures 59 in the legs 5l may be brought in line with an opening G0 extending through the fastening piece 58 and its structural element so as to permit a bolt 6i to be inserted clear through the alined openings and a nut 62 to be threaded tightly on the end portion of the bolt and hold the two structural elements iirmly together. Such tied-together elements may advantageously serve as an electro-insulator in a wire tie cable such as is frequently used to stay the poles or masts oi electric power transi 'ssion systems. Thus, as shown in Figure 6, two structural elements 63 and 64 are so united at their inner end portions, whereas the outer end portion of each element is tied to a wire cable 55, the cable being threaded through the aperture of the outwardly projecting portion 52 of a fastening part, such as shown in Figure l, to form a loop 66 bound by a pair of clamps B1.

When a wooden core is used as the reinforcing structural material within the tube, it is preferable that the wood chosen be of a toughness and resiliency typified by such wood as ash. Inasmuch as the pitch which I prefer to use as the waterproof and dielectric impregnant for the fiber-walled tube is subject to some deterioration when exposed to sunlight, heat, and other atmospheric influences, it is preferable that the outer walls of the tube be coated with blown asphalt of high melting point, which, as is well known, is characterized by its tough and rubbery nature and great durability under prolonged exposure to the atmosphere.

It might be mentioned that wood, so long as it is unaected by exposure and age, is a good material for cross arms and braces. While the tubular armoring which I use as a vital part of the structural element of my invention may not per se possess the desired strength, nevertheless, it adds to the strength of the core and possesses, by reason of its high percentage of pitch or equivalent impregnant, dielectric qualities and a permanence or age-resistance impossible of attainment through the impregnation of wood. Indeed, the fiber-walled tubes which employ as the armoring or protecting element can be impregnated with pitch or equivalent impregnants much more uniformly and to a much greater pitch to ber ratio than is possible in the case of wood.

I claimr- 1. A cylindrical structural element of an electroinsulating character and adapted for use in electric power transmission systems, comprising a fiber-walled tube impregnated with a waterrepellent dielectric material, a solid core of dielectric material adversely affected by moisture, within said tube but terminating short of the ends of said tube, and water-repellent dielectric material substantially completely filling the cylindrical pockets at the ends of said core and preventing access of moisture to said core, said element being equipped with metallic fastening parts at its ends.

2. A cylindrical structural element of an electro-insulating character and adapted for use in electric power transmission systems, comprising a liber-walled tube of substantial thickness and rigidity wherein the bers exist as integrated superposed plies of interfelted fibers and are protected by water-repellent dielectric material, a solid core of wood tted snugly within said tube but terminating short of the ends of said tube, and water-repellent dielectric material substantially completely illing the cylindrical pockets EDMUND BURKE.

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