International photographer (Jan-Dec 1935)

Twenty-eight The INTERNATIONAL PHOTOGRAPHER May, 1935 The Manufacture of Illuminating Carbons By W. C: KALI! Upper Left — Crushing and Milling Equipment. Upper Center — Pugs of lampblack ready for removal from the Calcining Furnace. Upper Right — Carbon Mixing Room. Lower Left — View within the Lampblack Furnace Building. Lower Right — Hydraulic Extrusian Press for forming the Plastic Mix. Center — Photographic effect from Studio Carbon compared with that from Sunshine. JjT is a striking paradox, yet none the less a fact, that the most brilliant light man has ever produced comes from one of the blackest of materials — lamp black. When Sir Humphrey Davey in 1800 produced the first electric arc between two pieces of carbon he little realized that his discovery provided a means of obtaining the highest temperuiure and the most brilliant light ever produced by artificial means, nor did he realize that his discovery would be such an important element in the growth of the industry so large as the motion picture industry of today. The carbon arc has been of great service to the motion picture industry from the standpoint of photography. It was the first artifcial source of illumination used when the production of pictures was taken into the studio. Today it is essential to the production of the highly popular color films and is extensively used for black and white photography. In the motion picture theatre, the carbon arc stands supreme. No other source of light possesses the concentrated brilliancy demanded for projection by the large screens and long throws of present-day movie palaces — a brilliancy millions of times that of the light reflected from the screen. Without carbon arc motion pictures would still be confined to small auditoriums, probably seating no more than a few hundred patrons. The production of electrodes capable of withstanding the terrific electronic bombardment of the electric arc and temperatures in excess of 6600° Fahrenheit reguires the most careful selection and preparation of raw materials, the utmost care and precision in the processes of production, and constant research to keep the product abreast of new developments in the art of motion picture production and projection. No material other than carbon is able to endure the destructive forces of the arc. In a thoroughly modern plant at Fostoria, Ohio, devoted exclusively to the manufacture of carbon products, National photographic and projector carbons are manufactured under strict technical control. Accuracy and precision mark every step of production. The basic raw materials used are the purest commercial forms of carbons, such as lamp black, and the bonding agents, tar and pitch. Although these materials are as black as night, great care is constantly exercised to establish and maintain their purity. The tar and pitch are refined and distilled in one unit of this plant to insure their purity and to obtain the required degree of viscosity and bonding properties. The lamp black is produced by burning oil or other suitable hydro-carbons in special forces under restricted draft. A view within the lamp black building is shown in Figure 1. The conditions under which the fuel is burned leave unconsumed a large portion of the carbon and this settles out in the form of soot or lamp black in large settling chambers adjacent to the burners. The lamp black as originally deposited, however, is not ready for use in the making of carbons since it contains a high percentage of volatile material. It is accordingly mixed with tar into a plastic dough, formed into brick-like pugs and baked at a sufficiently high temperature to drive off all volatile elements and leave a solid block of pure carbon. In Figure 2 the calcined pugs of lamp black may be seen ready for removal from the furnaces in which they have been baked. Before the carbons are formed, the solid material of which they are composed must be reduced to a fine flour. Figure 3 shows the crushing and milling equipment in which the calcined pugs of lamp black are pulverized and separated into lamp black flour of suitable fineness. Each lot is thoroughly blended with portions of preceding lots in order to maintain the maximum degree of uniformity. The powdered ingredients of the carbon are then mixed in exact proportions with the bonding agent, pitch, in the mixers shown in Figure 4. The resulting mix is plastic and when heated can be formed under pressure into "green" carbon rods of the required diameter. Large hydraulic extrusion presses, Figure 5, are used to form the carbons. Under a pressure of several tons per square inch, the plastic carbon mix is squirted through an accurately ground die on to cooling boards as shown in the illustration. For carbons that are to have a central core of modified composition, the pure carbon shell is extruded in the form of a thick walled tube. After cooling, these green carbons become substantially rigid but, in reality, are still in plastic form. Before they can be used they must be baked at high temperature to drive off the volatile elements of the pitch and leave a homogeneous structure of pure carbon in which the originally powdered elements are firmly bound together by the coke residue from the pitch. Naturally this baking process results in some shrinkage and the die through which the carbons are extruded must be made somewhat larger than the diameter required in the finished carbon. When the carbons come from the furnace they are cleaned, cut to the required length and inspected for straightness and Please mention The International Photographer when corresponding with advertisers.