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1945 Theatre Catalog, 4th Edition, Page 320 (296)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 320
Page 320

1945 Theatre Catalog, 4th Edition, Page 320

Reflector Manufacture

The design of an elliptical reflector as used in motion-picture projection, requires a staff of skilled technicians to compute the exacting physical and optical requirements necessary to pick up the light from the positive arc crater and focus the light at the film aperture. Gauges are developed to these predetermined computations and the actual glass forming molds are accurately ground to ' match these master gauges.

Actual production of the reflector begins in carefully selecting the flat glass which is then cut into round discs. This flat blank is carefully edged and rough ground. The circular disc of flat glass is then placed over the concave forming mold, after which the mold is placed in the bending furnace where it is rotated while the glass is heated to the softening point where it is sucked down by vacuum to make perfect contact with the optically ground and polished surface of the mold. After the forming operation is completed, the mold is removed from the furnace and the glass blank dumped from the mold.

The formed glass is then transferred to the annealing lier wherein it is cooled slowly and uniformly to assure freedom from strain. During this cooling process, the reflector blank travels on a conveyor belt until it emerges at the other end of the oven at room temperature. The curved reflector blank is rough trimmed, following which the center hole is cut out with a diamond tool.

REFLECTOR-MAKING STARTS with the preparation of the actual forming molds. Gauges developed to predetermined computations are accurately ground to match the master gauges shown here. All pictures of reflector manufacture are used through the courtesy of Harry H. Strong and the Strong Electric Corporation, with the textual material compiled from that company's recent brochure on reflectors and from other authorized sources.

A finished grinding operation follows, in which the reflector is edged to exact size and concentric, then the front edge is ground Hat to assure accurate optical placement. To facilitate handling during polishing operations, the reflector blank is secured or blocked within a metal shell by means of melted pitch. This shell

THE ROUGH SHAPED BLANK is molded under heat from a flat sheet of glass. In the bending furnace, seen in the background, the mold is rotated while the glass is heated to the bending point and, through suction, sucked down into the mold to make perfect contact with the optically ground surfaces of the mold. From this point, the formed blank is annealed, rough trimmed, the center hole cut out, finished ground, polished. It's now ready for silvering.

containing the reflector is transferred to a power polishing machine where both surfaces are polished, with periodic inspection, until the required optical surface is attained. Hand finishing and inspection follow.

In the next operation, the optical blank is chemically, cleaned. Further inspection follows in anticipation of etching into the glass the trademark and serial number of that particular reflector.

All of these operations are quite mechanical and merely determine the final design and appearance of the mirror. To prepare the glass for the actual silvering operation, it is thoroughly washed with a paste of rouge and washing powder to eliminate last traces of dirt and grease that may have accumulated in handling. The glass then is rinsed with copious quantities of water to insure a surface most receptive to silvering.

The silver coating generally is prepared by reducing an ammoniacal solution of silver nitrate with any one of several reducing agents. A common production technique is to arrange the glaSS on a perfectly level table in such a manner that the solutions can be poured over the surface and allowed to stand for a period of time suflicient to completely deposit the silver. A more rapid and efficient method is where the solutions are sprayed on the glass with specially designed spray guns.

For projection reflectors, the silver is deposited by a continuous flow of the silvering solution on the back of the mirror, so as to form a uniform and brilliant reflecting surface.

The solutions of both the reducing agent and the silver salt are prepared with particular care to insure their stability over the period that they are stored.

After the silver deposit has been formed on the glass, all traces of the remaining soluble salts, which later might react with the silver finish, are removed by a battery of rinse sprays.

1945 Theatre Catalog, 4th Edition, Page 320