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1953-54 Theatre Catalog, 11th Edition, Page 284 (248)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 284
Page 284

1953-54 Theatre Catalog, 11th Edition, Page 284

Continuous Arc Lamp Operation

Description of a Method of Recarboning Without Interruption of Lamp Operation

BRIEF: Brighter lamps hare a greater consumption of carbons . . . Recarboning has to be done frequently . . . When the interruptions of light resulting from recarboning are undesirable . . . continuous feeding becomes necessary.

This article describes a method of operating a very bright carbon arc with positive carbons aml joined by a magazine mechanism . . . The negative carbons can also be fed and joined by the same process . . . or replaced by a negative disk which rotates slowly . . . These methods have been applied by the author inu the construction of arc lamps that operate for sereral hours without interruption.


Two years ago we decided to develop a carbon arc lamp that would be brighter and more powerful than any are lamp existing on the market. In a carbon arc lamp the source of light is the tip of the positive carbon: to increase its brightness, the density of the current in the carbon must be increased, that is, the ratio of the current (Amperes) to the area of the section of the positive carbon.

When, in a given carbon, the current is increased, the density of current is raised and the brightness becomes greater. But, if the density becomes too great, the arc becomes noisy and unsteady, the positive carbon sputters and the lamp becomes unsuitable for projection.

We were able to make a steady arc lamp, with a current of 200 amperes in an 11 millimeter diameter positive carbon: then, the density of current was 2.1 amperes per square mm and the brightness greater than 1600 candles per square millimeter.

A very bright arc lamp has a very high positive carbon consumption. Theatre operators are familiar with this dilemma: they are asked to increase the brightness of the projection in order to satisfy the requirements of 3-D and extra-wide. screen projection; and they find that this increases the consumption of carbons to such an extent that the operation between two urecarbonings" becomes too short.

In Figure 1 we show how the consumption of the positive carbon increases with the current in the very bright arc lamp, Model ll.l. This lamp has watercoolcd positive contacts, 11 mm. diameter positive carbons.

At 200 amperes the consumption is 45 inches per hour. A standard length of 22 inches is consumed in less than a


President, Genarco. Inc.

half-hour. The necessity of recarboning every half-hour means that this arc lamp would scarcely be suitable for operation in a projection lamp, a spotlight, or a searchlight. Therefore, we had to find method that would assure a continw 0143 Supply of carbons to the arc without interruption for recarboning.

Joined Corbons for

Continuous Feeding

Several methods to achieve this end have been imagined since the invention of the arc. They all apply the same principle: a positive carbon uA" partially consumed is joined with a new carbon ifBll, either with cement, or with glue, or by a metallic sleeve. The ends of the carbons are properly shaped to assure the best possible adherence between the surfaces of the joined carbons.

Some of these methods have been used for years and they have given satisfactory results to operators who use them mostly to save the stubs of carbons that would be too short for the lamp mechanism.

But an arc lamp with a high density of current is very sensitive to the introduction of cement, glue or metallic sleeves in the arc. These foreign matters create a perturbance of the flames and an unsteadiness which result in unacceptable brightness variations of the lamp. Therefore, it was necessary to join the carbons without introducing foreign matter but solely through a characteristic shaping of the carbons themselves.

Fig. 1-1:: a high intensity carbon arc lamp with

water-cooled positive jaws, the consumption of

the positive carbon measured in inches per hour increases steeply with the current.



\50 \75 200 AMPERES

Mechanical Requirements

of the Join!

The joint has to be tight enough to prevent the carbons from coming apart after they have been joined. This means that the carbons cannot be drawn apart easily when pulled in opposite directions, as shown on Figure 2a, and also that one of the carbons cannot rotate and slip into the other when one is submitted to a twisting force while the other is held firmly in place (Fig. 2b).

In the arc lamp the positive carbon ifA" is held by the upper and lower positive contacts. The contacts cool the carbon and carry the current to the carbon tip; they offer a resistance to the rotation of carbon tiA." This resisting torque can be measured and adjusted by setting the pressure of the upper contact on carbon ttA." Carbon "Bf is rotated by a rotating mechanism (not shown on figure). If the joint between the carbons is not tight, there is slippage of carbon itB" into carbon "A" which will not rotate. This will prevent the smooth operation of the lamp.

We have developed a method of joining the carbons that has been successfully applied on thousands of joined carbons. The principle is extremely simple: the ends of the carbons to be joined are machined in the shape of a male and female taper and the ends are pressed into each other.

The machining of the carbons is a delicate operation. The carbons are hard, brittle and unhomogeneous. They are made up of a shell (outside surface) and a core. The shell is a homogeneouslooking matter that is made of fine carbon. The core is powdery and contains rare metals compound.

The machining must be done in the shell region and it requires a lot of care and experience.

When the carbons are machined into their final shape, they can be joined either by pressure or by percussion. Once joined, they should not be forced apart because successive joining and separating operations change the physical dimene sions of the ends and the nature of the surfaces which become slippery. When two carbons are joined, the tightness of the joint can be measured; the torque

Fig. 2-Ioined carbons must resist traction (A) and torque (B) illustrated in simplified sketch.


1953-54 Theatre Catalog, 11th Edition, Page 284