Hong Kong Builder
57
THE WORLD'S LARGEST
BRIDGE.
Preservation of the Pillars.
One of the finest harbours in the world is enclosed within the San Francisco Bay. On the shores of this bay are situated two cities of approximately 500,000 inhabitants each. The traffic between these cities had to pass over ferries and inasmuch as the number of vehicles was steadily increasing, a large bridge across the bay was finally projected. In the designing of this bridge one of the difficulties to be overcome was in the depth of the bay, another in the enormous and continuous flow of tide water past the caissons and piers of the bridge.
In order to insure the permanency of the concrete pillars on which this bridge was to rest, an engineering board composed of experts from all over the United States specified the use of Inertol on the outside as well as on the chambers inside the piers. Before the construction was started the State of California tested dozens of products for the protection of the concrete because under the specifications, "Inertol or other approved protective coatings" were to be used. It is a unique tribute to the quality of Inertol that it was used exclusively under such competitive conditions.
BUILDING QUALITY INTO OTIS PRODUCTS.
An important phase of metal car manufacture- one in which Otis has established and maintained its leadership-is rust-proofing. This involves the special treatment of all ferrous materials entering into the production of our cars and car fixtures prior to the application of the various final coatings of lacquer.
The method used at the Harrison Works is called Bonderizing, which is a chemical conversion of metallic surfaces to a non-metallic phosphate coating, consisting of millions of microscopic crystals, insoluble in water. In addition to rust-proofing, Bonderizing actually "keys" the lacquer coatings to the metal surfaces, and is an important element in the even, flake-proof panels that typify a finished Otis car. This process superseded the old "priming" method of spraying metal surfaces with a neutralized oil base material, which required 24 hours to dry. The Bonderizing operation is completed in 10 minutes, and the more effectively rust-proofed and primed surfaces are immediately ready for the lacquer applications.
Bonderizing is a further development of the Parker Rust-Proofing Process (Parkerizing), which was adopted for Otis car manufacture in 1929. This was considerably in advance of its acceptance by the automotive industry, which has since included it as standard almost universally.
The adherent coating which Bonderizing provides is a solution of obtained by immersing the metal in "Bonderite" and water, heated to a temperature of 212° F. This stabilizes the final finishes to the ultimate limits of the lacquer, as the base metal is protected from corrosion under the lacquer film. Rust will form sooner or later if the film becomes scratched or abraded, but the Bonderizing process confines the rusting to the damaged area only. Lacking this, the rust would eventually extend over the entire surface.
Many tests have been made on lacquer finishes to determine their durability with and without the protec- tion of Bonderizing. One of the most severe tests is obtained by continuously subjecting lacquered panels to a 20% salt spray solution. In other tests, panels have been immersed in water in order to determine the porosity of the film, and have resulted in an accurate reading of the ability of the lacquer finish to protect the base metal.
The illustration shows the bridge finished November 1936, connecting San Francisco in the foreground with Oakland. All the piers are safeguarded against the ravages of time inside and out. The bridge has two decks, the lower one for street cars, electric and freight trains, while the upper road has six lanes for automobile traffic. Each of the large piers has three chambers on the inside, with openings to control high water pressures from the outside at times of incoming tide. The bridge is built sufficiently high above the highest water level to permit the largest steamships to pass under it. The construction costs amounted to nearly U.S.$80,000,000.00. and moisture.
As far as it has been possible to determine, Otis is the only manufacturer of metal lift cars employing the Bonderizing method of rust-proofing. Its effective- ness is indicated by the fact that since its use there bas never been a failure of an Otis lacquer finish on metal, in either the most exposed conditions of installa- tion or in actual service, under all extremes of heat