Centrifugally cast pole and method
Herein disclosed is a centrifugally cast pole having a substantially uniform wall thickness along the long axis of the pole. During centrifugal casting, molten metal is poured inside a rotating, tapered mold. As chilled liquid is poured over the outside of the rotating mold, the metal forms, or paints, to the contour of the mold interior creating a metal pole. By precisely controlling casting gyrations such as the spin, travel, pitch, and yaw of the rotating mold and the calibration and physical mechanisms of the casting machine, hollow, tapered, tubular metal poles are produced with previously unknown uniformity of wall thickness. The controlling principles, designs, and mechanisms of this centrifugal casting method enable wall uniformity to extremely high tolerances. By extension, the ability to precisely control the metal volume painted inside the mold allows, as a design choice, wall thickness variation in any embodiment if so desired.
1. Field of the Invention
This invention relates generally to hollow structural members and more specifically to hollow utility poles having tapered external dimensions and substantially uniform wall thickness.
2. Description of the Prior Art
The geometric shape of tapered poles in high stress, high lateral-force environments typically encountered in the utility industry inherently provides the greatest cross-sectional strength at or near the base of the pole where reactive forces tend to combine and converge.
Problems associated with the use of wooden poles within the utility industry are numerous and well documented. These problems include ground line decay, the tendency of wooden poles to bend or arc under high lateral forces (thereby requiring the use of guying cables, anchors and other auxiliary hardware), deterioration caused by birds and other animals, vibration damage to attached hardware and fixtures, shortages of suitable trees for producing large poles, and high breakage rate due to natural and manmade forces. Additionally, wooden poles as a general rule must be replaced after approximately 20-30 years of service. Of particular note, replacement and disposal of wooden poles is a mounting, exorbitant liability for companies, especially when these poles cannot be incinerated due to regulatory mandates. Further, some utility companies have resorted to wrapping their wooden poles in wire mesh to prevent damage to the poles by birds and other animals.
Other companies have resorted to using hollow concrete poles, particularly with regard to high voltage electric transmission systems, in order to overcome some of the difficulties associated with wooden poles. Concrete utility poles, however, are expensive to produce, are very heavy and require special heavy-duty equipment to load, transport, unload and install. Further, due to strength requirements, concrete poles are usually solid at the top, where the pole has its smallest diameter. Moreover, field modifications of concrete poles are generally very time consuming, cumbersome and thus very costly.
Steel utility poles are currently available in the market. Steel poles are typically produced by cutting thin and malleable steel plates and forming the plates, using metal brakes and other hot and/or cold metal shaping methods, into two multi-sided halves which are then welded together. Such poles are quite expensive to produce and, as a consequence of the thin walls necessary to form them, result in poles having relatively large base diameters in order to achieve the necessary strength to be used in high stress, high lateral-force situations such as those subject to utility poles. Further, wall thickness can be varied only sectionally, if at all.
Aluminum alloy utility poles are also available. However, these poles are generally appropriate for low stress, single-use application, such as highway lighting. Further, aluminum poles are not currently formed by centrifugal casting methods and are typically produced by hot or cold metal-shaping methods. Moreover, aluminum poles do not have the necessary qualities or strength to be used in high lateral-force environments, such as those to which utility poles are subjected.
Ductile iron has characteristics which are ideal for use in the utility pole environment. For example, ductile iron has a superior strength/weight ratio, is machineable, resilient (as opposed to brittle), has favorable damping properties, is rust proof and is cheaper than aluminum and concrete. Therefore, if centrifugally cast into geometric shapes necessary for utility pole applications, ductile iron would provide a virtually maintenance free, extremely long life (many 100+ year old ductile iron water mains are still in use), low cost utility pole which effectively overcomes the problems and difficulties associated with other utility poles as discussed hereinabove.
Centrifugal casting offers additional benefits over alternative production techniques such as metal forming. For instance, centrifugal casting produces a seamless pole, which ensures overall strength in high stress, high lateral-force environments. Furthermore, centrifugal casting allows a large volume of poles to be produced inexpensively through a mechanized process involving little human labor. Since long, seamless sections can be cast in a single pass, subsequent joining procedures during manufacture or field installation are reduced or eliminated. Also, centrifugal casting produces a much more precise pole than that created through metal forming, and is capable of producing poles within tolerances of 0.001 mm. In summary, centrifugal casting produces stronger, less labor-intensive poles that are more easily mass produced for a wider variety of applications.
Prior to the present invention, centrifugal casting of tapered metal utility poles (including ductile iron) has been limited by the casting technology. Single-speed casting methods (such as that disclosed in Applicant's prior U.S. Pat. No. 5,784,851) prevented the metal infusion from dispersing properly such that the amount painted on the inside of the mold as it spins and travels can be deposited end-to-end uniformly to high tolerances (0.001 mm.). This has meant that centrifugal casting of tapered poles was only slightly more versatile than metal rolling, though there are other advantages mentioned hereinabove. The present invention overcomes this limitation by introducing a variable-speed, variable-infusion casting method, whereby the metal-painting is precisely controlled by increasing or decreasing the metal pouring rate and the spin speed of the mold. Depending upon the desired specifications, poles can be formed with walls that are thick at bottom and thin at top, that vary in thickness at specified points, or that are substantially uniform in wall thickness along the long axis of the pole.
Further, the present invention allows production of poles that fulfill specific application requirements. For example, while some applications require variable thicknesses (thin at the top, thick at the ground line to resist line loads and corrosion), other applications may require uniform thickness for maximized structural support. The present invention also fulfills applications that require extreme or variable heights, in that the poles may be cast with slip-jointed pole sections, whereby the tapered section of one pole can be secured into the butt end of another pole to reach specified effective pole lengths. Additionally, special applications may require further enhancement of the pole during or post-casting including, but not limited to, wind-resistant texturing, mount flanges, hardware and fixture access holes or panels, and top-end caps.
SUMMARY OF THE INVENTIONIn view of the foregoing, the present invention relates to a centrifugally cast hollow pole having a wall thickness which is substantially uniform along the long axis of the pole.
In one embodiment, a conically tubular pole having tapered external dimensions and a substantially uniform wall thickness along the long axis of the pole is produced via centrifugal casting, whereby molten metal is poured inside a rotating, tapered mold. As chilled liquid is poured over the outside of the rotating mold, the metal forms, or paints, to the contour of the mold interior creating a metal pole. By precisely controlling casting gyrations such as the spin, travel, pitch, and yaw of the rotating mold and the calibration and physical mechanisms of the casting machine, hollow, tapered, tubular metal poles are produced with previously unknown uniformity of wall thickness. The controlling principles, designs, and mechanisms of this centrifugal casting method enable wall uniformity to extremely high tolerances. By extension, the ability to precisely control the metal volume painted inside the mold allows, as a design choice, wall thickness variation in any embodiment if so desired.
It is an object of the present invention to provide a hollow, tapered pole which is easy and economical to produce having a wall thickness that is substantially uniform along the length of the pole. The ability of this new method to produce uniform wall thicknesses is especially important in applications where lateral forces can cause disastrous utility pole failure, such as by hurricane-force winds.
Another important advantage of the present invention is the centrifugal casting of poles utilizing any molten materials such as ductile iron, steel, aluminum, or castable composite material, thereby rendering the pole virtually maintenance free and impervious to ground line decay, fungus, humidity, animal damage and other causes of deterioration.
A further advantage of the present invention is that a pole centrifugally cast of ductile iron would be comparatively lightweight, would have the physical strength of mild steel with the long life expectancy of gray cast iron, would be virtually unbreakable in ordinary service and would be 100% salvageable.
Yet another advantage of the present invention is that a pole centrifugally cast of ductile iron would offer the greatest possible margin of safety against service failure due to ground movement and beam stresses and would provide increased resistance to breakage caused by handling, shipping and installation.
An important advantage of the present invention is that molds can be produced by welding, flanging or threading shorter sections together into a single molding tube.
The invention is particularly advantageous in that a pole centrifugally cast can be direct buried or may be flanged for attachment to poured or preformed foundations.
A further advantage of the present invention is that the hollow design of a centrifugally cast pole allows for internal wiring of fixtures and other attachments to said pole.
An important improvement to the present invention is the provision of a texturing process during casting that augments the strength of the pole. A mold with a textured interior wall surface may be utilized, thereby producing a final product with a pimpled exterior surface. The resulting pimpled pole benefits through improved wind resistance in whatever embodiment and field of use.
To enhance extreme height/extreme stress applications, the pole may also be cast in such a way that the wall thickness near the butt of the pole is sufficient to accommodate the formation, during the casting operation, of a slip joint having internal cross-sectional dimensions sufficient to allow the pole to slidably receive the top portion of another centrifugally cast pole whereby providing for virtually unlimited pole extensions.
Additionally, an end cap can be designed for field installation to protect all internal hardware.
The present invention also addresses the post-cast annealing process in a new way. This new method begins during casting, whereby mold-induced flanging of the large-diameter end of the tapered pole becomes, in effect, a control-point for hearing the pole through the annealing process. The flange is simply a larger based circle, or ring, cast at the pole's large-diameter end. Once the pole is removed from the mold, this flanged ring is engaged by a control rail such that the pole can be run through a straight annealing furnace. As the rail engages the running ring, the tapered pole is prevented from inadvertently sliding or rolling from the conveyance as the pusher chains engage and move the pole through the furnace. This ring also allows the pole to be placed inside of a straight pipe which rolls through the annealing furnace.
Lastly, it is noteworthy that the present invention is not limited to use in the utility pole field. Rather, the present invention may be advantageous wherever a structural pole member is needed. For instance, the present invention could be used as a tapered support piling. The tapered shape of the piling would impart the necessary load capacity while minimizing the piling's embedment in the bearing stratum. The tapered shape would also require less concrete volume to fill than a traditional cylindrical piling. Further, the piling could be pimpled on its surface to enhance the load bearing capacity of the piling. Finally, ductile iron would be an ideal choice for pilings because of its compressive strength and corrosion resistance.
The foregoing and other objects, features, and advantages of the present invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Also shown in
While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various alterations in form, detail and construction may be made therein without departing from the spirit and scope of the invention.
Claims
1. A centrifugally cast, hollow pole comprising:
- an elongated, hollow, conically tapered pole member which is formed by centrifugal casting so as to have a substantially uniform wall thickness throughout the long axis of said pole member, said pole member comprising a plurality of asymmetric pimples extending away therefrom, that is formed by centrifugal casting.
2. The apparatus of claim 1, said pole member having a variable outside cross-sectional dimension that varies perpendicularly to said pole member's long axis.
3. The apparatus of claim 1, said pole member having a first end and a second end, said first end having an end cap.
4. The apparatus of claim 1, said pole member having a first end and a second end, said second end being flanged.
5. The apparatus of claim 1, said pole member having a first end and a second end, said first end having a slip joint with an internal cross-sectional dimension sufficient to allow said first end of said pole member to slidably receive the second end of another said pole member.
6. The apparatus of claim 1, wherein the apparatus is manufactured from a castable material.
7. The apparatus of claim 6, said castable material is selected from the group comprised of ductile iron, cast iron, steel or aluminum.
8. The apparatus of claim 1, said pole member including a panel to allow access to the hollow interior of said pole member.
9. A centrifugally cast, hollow pole comprising:
- an elongated, hollow, conically tapered pole member which is formed by centrifugal casting so as to have a substantially uniform wall thickness throughout the long axis of said pole member, said pole member comprising an outer surface comprising a plurality of pimples extending away therefrom, said plurality of pimples are formed during the centrifugal casting of said member.
10. A centrifugally cast, hollow pole comprising:
- an elongated, hollow pole member having a tapered outer diameter with a first end and a second end, the first end having a smaller outer diameter than the second end, wherein the hollow pole member is formed by centrifugal casting such that it has a substantially uniform wall thickness from a first location adjacent the first end to a second location adjacent the second end, and wherein a wall thickness at the second end is larger than the wall thickness between the first and second locations, the hollow pole member further comprising a running ring that extends outward from the second end, and a plurality of asymmetric pimples extending away from an outer surface of the pole member.
11. The apparatus of claim 10, further comprising a slip joint located along a portion of an inner diameter of the second end, the slip joint being configured to slidably receive the first end of another said pole member.
12. The apparatus of claim 10, wherein the pole member is formed from a castable metallic material.
13. The apparatus of claim 12, wherein said castable metallic material is selected from the group consisting of ductile iron, cast iron, steel and/or aluminum.
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Type: Grant
Filed: May 7, 2014
Date of Patent: Jan 13, 2015
Inventor: Tom W. Waugh (Birmingham, AL)
Primary Examiner: Mark Wendell
Application Number: 14/272,076
International Classification: E04C 3/00 (20060101);