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PROCESSING EQUIPMENT 97
irregularity. Such a condition may be caused by (a) the film not being positively driven by the sprocket on any rack, (b) any roller on either the faulty rack or the one preceding it having seized up on the top or bottom shafts or (c) the rack immediately preceding the faulty one not being well seated in its bearings and, therefore, not being driven by the main chain.
If any of the lower rollers in any rack fall to the bottom of their guide channels (indicated by the thin guide rod, mentioned previously, falling below the level of its neighbours) this will indicate that the film has broken in this rack. In these circumstances everything depends on the operator who should keep perfectly calm and not attempt to mend the film immediately. By far the safest plan, at least until he becomes familiar with this type of machinery, is to stop the machine thereby preventing any more film from entering the tanks and quickly to insert the handturning gear and lifting all those racks between the break and the supply end of the machine away from the driving chain. These moves will salvage the film between the break and the take-up roll. Since breakages are extremely rare, and will only occur when either bad splicing or faulty maintenance has been permitted, this course of action is easier than attempting to re-join the film while the machine is running.
The Drying Cabinet Temperature
In this particular machine a thermometer is provided in the drying cabinet and the operator is required to keep a close watch on this instrument, both to ensure that the temperature does not rise too high and also to become familiar with the temperature ranges to be expected from the various combinations of heating which are available. The normal working temperature in the cabinet is found to be approximately 180°F.
The Appearance of Drying Film
If, after thoroughly soaking a length of 35-mm film, it is suspended from one end it will show a marked tendency to curl in a tubular fashion. This curling will be such that the side which is coated with emulsion will become convex and the uncoated side will become concave. Such a condition is known in the trade as a 'negative curl'. If the same length of film is then suspended in a drying cabinet and left until completely dry it will pass through the following phases. Firstly, it will gradually flatten out so that the tubular effect is completely eliminated. Then, as the drying