Cooling and exhaust system

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Developing section

Basic Engineering

Adjustments and maintenance

COOLING AND EXHAUST SYSTEM.Excessive amounts of heat or ammonia vapors should NOT reach the room in which the machine is located because of the installed exhaust and cooling system. The system consists of twin blowers, driven by a motor that exhausts fumes and hot air from the machine enclosure through a vent to the outside atmosphere. Therefore, a partial vacuum is created within the machine covers, thereby causing air to flow into the machine rather than the counterflow that would otherwise exist. A blower time switch operates the blower motor independently of the rest of the machine thereby ensuring the removal of vapors and hot air after the mercury-vapor lamp is turned off. The switch may be adjusted to operate for any given length of time up to 30 minutes.

MACHINE OPERATION. A short warm-up period is required before material can be fed into the machine. Always follow the manufacturers instructions during machine operation. When starting the machine, make sure that the developer drain tube is inserted in the residue bottle (fig. 3-64). Then, fill the storage tank with ammonia. If bubbles are encountered in the feed system because of increased temperature or high altitude, dilute the ammonia with cold water. Usually, a one-eighth to one-fourth dilution is sufficient.

After the ammonia storage tank has been filled, turn on the main switch, and adjust the ammonia feed to 50 to 60 drops per minute. At high speeds (30 ft per minute and above), the rate of drops per minute can be increased. On virtually all modern, large-size diazo machines, ammonia feed is automatically increased and decreased to correspond with variation of machine speed.

CAUTION

During machine operation, the ammonia feed regulator should NEVER be turned completely off. If the machine is left running and no moisture is entering the developer section, the evaporation tray and heater rods are likely to be warped because of excessive heat.

After a short warm-up period, the machine is ready for operation. The machine should be run for approximately 20 min or until the operating temperature is between 180F and 210F. Time and temperature may vary; therefore, always follow the manufacturers instructions. Feed the material into the machine with the original on top, adjusting the speed of the machine so that a clear print is obtained.

Printing speed is dependent on the trans-lucency of the original, the density of the opaque image, and type of sensitized material used.

Running the machine at speeds that are too fast will result in a background on the print. Running the machine too slowly will cause the image to be weak or missing from the print altogether. The only positive method for obtaining the correct speed for your machine is by running a test because each machines light intensity changes with age.

When stopping the machine, turn the ammonia flow off, then feed a sheet of porous wrapping paper, 16 in. wide, into the machine. Stop the machine with the paper in position around the printing cylinder and between the sealing sleeve and the perforated tank. This will prevent the sleeve from sticking to the perforated tank top and will also protect the belts from the heat of the cylinder while it is cooling.