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Offset-Press Operations

Ch. 21 from the Offset Lithography Technology Book
by

Laura Roberts

on 13 June 2013

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Transcript of Offset-Press Operations

Offset-Press
Operations

The Preliminary Inspection
The Starting Procedure
Printing and Cleaning and Maintenance
Safe Operation
To complete a preliminary inspection, examine the press to make sure all safety devices and operating components are in place.

Set all controls in the off position.

Remove any loose articles from the press.

Install any rollers and fountains that might have been removed earlier.

Wipe away any lint or paper dust from the feeder and register board.

Turn the handwheel on the press two or three revolutions by hand. Check to see that nothing interferes with the operations of the press.

If all is clear, turn on the power and set the speed selector at a slow speed. Check to see that all parts are functioning properly.

Pressure checks must be made before the pressrun. The proper sequence of checks is given in the operator manual.
Safe duplicator and press operations means the duplicator
or press is always operated in a sensible manner.

Personal safety, as well as mechanical general shop conditions, should be considered.
Learning Objectives
When you have completed this presentation and the assigned activities related to this chapter, you will be able to do the following:

Prepare the feeder unit and register board of an offset duplicator, in preparation for running a job.

Set up the printing, inking, dampening, and delivery units of an offset duplicator.

Successfully complete jobs on an offset duplicator and a small offset press.

Clean and secure an offset duplicator and a small offset press at the end of a job or the working day.

Operate an offset duplicator or a small press while following safe work procedures.
Safe Work Procedures
The following material provides an understanding of the sequence of operations involved in setting up and running a job on a duplicator.

Press instructors are the experts in this area, and there is no substitute for their qualified
professional guidance, especially
regarding procedures and
safety precautions.

Instruction manuals should be
available for the particular
duplicators and presses in the lab.
Check Job Ticket
Look at the job ticket to determine the specs for the job you are running.

These specs should include:

Type of job.

Quantity.

The correct paper stock, plus makeready.

The correct ink and color.

Special instructions.
Press Lubrication
Correct press lubrication reduces wear on all moving parts and lengthens press life.

Study the manufacturer's lubrication chart to locate the oil hole, grease fitting, and point of lubrication.

These locations on the press should be marked with red paint for easy identification.Always begin your lubrication at a certain point on the press and work your way back to the same point.

Lubricate the feeder and delivery drive chains once a week.

Use gear grease compound on all gears.
Paper and Ink
Verify the paper supplied for the job. Make sure the grade, size, and quantity
are correct.

Make sure the press sheet's grain direction is appropriate for the job.

Typically grain direction runs parallel to the direction of travel through the press.

Obtain the required ink for the job. A job might require a Pantone-numbered ink or a special color that must be mixed.
A standard procedure for starting the press should always be followed. The following is the general sequence of steps in setting up and running a job on an offset duplicator.
Preparing the Inking Unit
The ink rollers should be cleaned of all lint and dust before filling the ink fountain. Check the rollers carefully for lint or dust.

Fill the ink fountain by applying small amount of ink with an ink knife against the fountain roller. Before removing ink from the can with an ink knife, skim any hardened crust from the top.

The fountain is equipped with a number of adjusting keys, or screws. Turning these keys inward (clockwise) decreases the flow of ink, and turning the keys outward (counterclockwise) increases the flow of ink.

Establish an even flow or pickup line between
the ductor roller and the fountain roller
across the width of the fountain.

If the revolving ink rollers sound similar to
"eggs being fried," there is too much ink
on the rollers. Turn the press off and remove
some ink from the rollers. Restart the press
and recheck the ink.
Preparing the Dampening Unit
The dampener fountain and fountain roller should be clean and free of dirt. Fill the fountain bottle with the proper mixture of fountain solution.

Bring it over the side of the press, but not over the ink rollers, and insert it into the holder.
Attaching the Plate
Always be sure the plate cylinder is clean before attaching a plate.

Turn the handwheel until the lead plate clamp is in position.

Attach the lead (gripper) edge of the plate to the plate clamp.

Hold the tail of the plate square, tight and down near the feedboard, to prevent the plate from becoming detached.

Holding the tail end of the plate with
your right hand, turn the handwheel
clockwise until the tail end is in position
for attaching the plate.

Tighten the plate clamp by turning
the plate-clamp tightening dial
counter-clockwise.
Preparing the Feeder Unit
Setting the Register Board
To manually set up the register board, hand feed a sheet of paper onto the feedboard.

Feed the paper manually until it hits the paper stop bar and the
left jogger moves to touch the paper and push it into the leaf spring.
Setting the Delivery Unit
Set the delivery tray, jogger, and stacker for the sheet width and length required.
Before putting your paper in you should set the double sheet detector. Tear a strip of paper and make a short fold. Then turn the main switch and feed on. Put the short fold strip under the double sheet detector making sure that it doesn't drop until two sheets are inserted.
Fan and job the sheets of paper to separate any that might be sticking together. Place the paper in the center of the feed table using the scale as a guide for centering. Move the paper stack forward so it touches the separator blocks.

Bring the paper stack to the red line on the separator block. Make sure both side guides and the back guide are touching the paper.
Feeding Test Sheets
Once the press has been prepared as described, several test sheets should be run through the press to determine if any adjustments are required.

With the press set up according to the previous directions, feed several test sheets as follows:
Using a cotton pad, moisten the plate with etching solution.
Start the duplicator say 'clear' and turn main power on.
Lower the dampener from roller to the plate cylinder (control lever to 1 position).
Allow to run for 4-8 revolutions.
Lower the ink form rollers to the
plate cylinder (control lever to
2 position) and turn ink rachet
to the first position. Allow to run
for 4-8 revolutions.
Turn the feed on, which will
start the vacuum and
blower motor.
Set the duplicator on impression.
Run a sheet of paper through
the duplicator.
Take the duplicator off impression.
Check the position of the image
on the sheet.
Make all necessary adjustments to achieve the position.
Checking Test Sheets
Inspect the test sheets carefully.

The image on the paper should be clear, well inked, and free from background tone.

If the plate tends to pick up in ink the nonimage areas, this indicates an excessive amount of ink or insufficient amount of dampening solution.

If toning occurs, it could be that there needs to be more moisture on the plate or reduce the amount of ink.
Handling the Delivery
Observing the run on a duplicator involves more than maintaining specific settings and adjustments.

The press operator must also be concerned with maintaining the appearance and quality of the job produced on the duplicator.

These aspects include that the feeder is
functioning properly, the sheet is
registering, the color is consistent
with customer specs, and the printed
sheets are being delivered and jogged
in a satisfactory manner.
The ink train of offset duplicators must be washed at the end of the day or pressrun or when a color change is required.

During the washup, students might want to keep ink off of themselves by wearing an apron and gloves.

To wash the duplicator, follow these steps:
Remove the fountain-solution bottle.
Remove the fountain solution from the fountain with a sponge
or syringe.
Use an ink knife to remove and discard the ink from the ink fountain.
Remove the ink fountain from the duplicator.
Clean the ink-fountain roller with blanket and roller wash.
Attach a cleanup mat to the plate cylinder and start the duplicator.
Squirt a small amount of blanket and roller wash over the ink oscillating roller, allowing it to work into the ink system. Do not add too much. Continue to add small amounts of wash until rollers appear clean.
After all ink is removed, use a snowtek towel and wipe the blanket and rollers with wash to remove all lint and ink residue.
Clean the floor around the duplicator of all ink, solvents, and loose papers.
Set the night latch.
Clean all tools and put them back in their places.
Cleaning the Press
Remove coats and sweaters.
Roll shirt sleeves above elbows.
Remove neckties and tie back long hair.
Remove all jewelery.
Use hand tools appropriately.
Oiling the duplicator or press should only be done when the press is stopped.
Never reach into the duplicator or press while it is running!
Never operate press unless all of its guards are in place!
Always turn the power off before cleaning.
Don't use solvents near an open flame.
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