Flagpoles have undergone a number of dramatic changes since people started flying flags. Prior to the industrial revolution, flagpoles were made exclusively from wood. Although a few companies today still practice this craft, most flagpole manufacturers today use more durable materials.
To produce a wooden flagpole, a carpenter would actually cut down a suitable straight tree and would neatly trim and prune the tree until it resembled a shaft-like pole. It was then simply planted into the ground with a flag tied to the top of the tree, thus becoming a flagpole. For a smoother, more refined look, spruce or pine trees were processed and used for flagpoles. These trees would be shaped with knives and then sanded to a smooth finish. Animal fat was then used as a preservative and rubbed over the entirety of the pole for several days to ensure the wood was totally saturated with the fat. In the hands of an expert, these poles could remain functional for over 50 years. These flagpoles were very attractive, but due to their direct installation into the ground, they typically rot at the base. One pole in particular was erected in Glenwood, Arizona in 1911. At over 110 feet tall, this extremely well crafted wooden flagpole lasted until 1964, when it was replaced by a steel pole.
The Steel Era
The turn of the century brought more changes to the flagpole industry. Innovation and fabrication introduced new materials and new processes for producing metals in various forms. As early as 1893, steel tubes and the masts from ships were being used as flagpoles. At the World’s Columbian Exposition held in Chicago in 1893, a steel tube of 75 feet was connected to a ship’s mast of 95 feet. The 164 foot flagpole that was created by attaching these two poles was then sunk into the ground ten feet. The flagpole is still in use today. This use of common items became more prevalent in the early 1900s. One of the initial everyday items to inspire these flagpole manufacturers was steel poles used for trolley wires. These poles were sectional, utilizing swedged ends, male and female ends, to connect the sections of the steel trolley wire poles. As the new steel sectional flagpoles were introduced to the market, the older wooden processed poles became obsolete.
In the years following the stock market crash of 1929, and during the vast expansion of industry during World War II, items like steel shafts for pile driving and cargo booms on large ships became inspiration for an expanding number of flagpole manufacturers. This type of smooth, tapered steel flagpole dominated the industry for over 20 years. Perhaps the most common of these everyday inspirations was the next step in the evolution of the flagpole. The industry producing street light poles made extraordinary advances in extruding aluminum poles. This process has revolutionized the flagpole industry, and comprises the largest portion of today’s flagpole market.
The Aluminum Era
Aluminum has several distinguishing characteristics which allow it to change at the molecular level, and thus create different products for different applications. The aluminum alloy most commonly used for the manufacture of flagpoles is 6063. The flagpoles utilizing this alloy are extruded pipe or tube, and must be produced in accordance with government standard ASTM B241, "Aluminum Alloy Seamless Pipe and Seamless Extruded Tube." Most of these poles are aged, or hardened, by heat treating, to produce a temper rating of T6, the hardest form of this alloy. This temper rating yields an astounding level of minimum stress at 25,000 pounds per square inch, and an allowable design stress for tubes of 18,000 pounds per square inch.
The final step in the manufacture of aluminum flagpoles today is the finish. The majority of these flagpoles are finished with a directional textured mechanical satin, or brushed finish. This finish is accomplished by abrasive polishing and range from a fine to a coarse texture. The most attractive finish option for these poles is anodization.
The Modern Era of Anodized Aluminum
Anodization is a process of actually coating the outside of the aluminum flagpole with an oxide. Typically, the aluminum pole is "bathed" in a solution containing sulfur, chromic, or boric acid. In this bath, the aluminum pole is positively charged by connecting it to the positive terminal of a dc power supply, becoming an anode in the chemical process. An inert electronic conductor, usually a plate or rod of carbon, lead, nickel or steel, is then connected to the negative terminal of a dc power supply, thus becoming the cathode. Upon closing the electric circuit, electrons are withdrawn away from the anode, the aluminum pole, and thereby allow ions on the surface on the aluminum to react with the electrolyzed bath solution to form an oxide layer on the aluminum flagpole. Aluminum cations (an ion in an electrolyzed solution that migrates to the cathode) move away from the aluminum pole to react with the water in the bath at the oxide/electrolyte interface to form an oxide at that surface. At the same time, oxide anions (an ion in an electrolyzed solution that migrates to the anode) move toward the aluminum flagpole to react with the aluminum at the aluminum/oxide interface. New oxide is deposited or created at both interfaces and thus the total oxide thickens. This oxide creates a barrier connected to the aluminum flagpole at the molecular level. This oxide can be altered to produce color changes on the pole; the range of available color is limited to shades of bronze to black.
Flagpoles have undergone changes in style, structure, and composition throughout our history. From the wooden flagpoles of the 1800s, to the brilliant, shiny, clear anodized aluminum flagpoles of today, flagpoles still allow people throughout the world to show their patriotism. As industry continues to innovate and evolve, so will the flagpole.
References
"Anodizing" Electrochemistry Encyclopedia
"Central Campus Flagpole" University of Michigan: Architecture, Engineering and Construction.
Metal Flagpole Manual by The National Association of Architectural Metal Manufacturers.
"Tall wooden pole held flag for 52 years" azcentral.com 2005.
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