How much is the packaging offset? (239-243)

239 how to calculate the maximum compression at print?

λ plate cylinder / blanket cylinder = (plate cylinder lining thickness + plate cylinder diameter reduction) + (rubber cylinder lining thickness + blanket cylinder diameter reduction) - plate cylinder and blanket cylinder roll gap

For roll printing machines, the roll gap between the plate cylinder and the blanket cylinder is always equal to 0; the roll gap of the roll printing machine can be read out or directly measured by the scale value of the pressure regulator.

λ blanket cylinder / impression cylinder = (radiator lining thickness + blanket diameter reduction) + paper thickness + reduction of the impression cylinder - blanket cylinder and impression cylinder roll gap

Among them, the gap between the blanket cylinder and the impression cylinder can be read out or directly measured by the scale value of the regulator.

240. How to measure the roll gap?

Under normal circumstances, the roll gap can be read by the scale value of the pressure regulator on the machine. For example, when the scale value of the pressure regulator of the domestic type J2108 off-color monochrome offset press is 0, the roll gap is 0.2 mm. However, during the long-term use of the printing press, the actual value and scale value of the roll gap will be deviated, requiring measurement and inspection. The measurement method is as follows.

1 Thickness Gauge Measurement

Thickness gauge is also called feeler gauge. It is composed of several metal sheets of different thicknesses. One of them is selected to be inserted between two rollers and the feel of looseness is considered as the thickness of the bearing. Because this measurement method is based on subjective feelings of people, the error is large.

2 rolling pressure fuse measuring method

Put a small amount of ink or glue on the fuse wire between the pillows, take it out after pressing and pressing, and measure the thickness with a micrometer, which is the value of the roll gap.

241. What methods are commonly used in production to measure the lining thickness?

The thickness of the liner is usually measured using a micrometer or a cylinder meter.

242. What do you need to pay attention to when measuring the lining thickness with a micrometer?

The contact surface of the one-micrometer fixed anvil and the measuring rod should be kept clean. When they are close together, the scale value should be zero.

2 When measuring the workpiece, the ratchet protection knob at the end of the micrometer can hold a fixed measuring force. Usually, blankets, paper, or other underlays will deform due to changes in measurement force, causing measurement errors. Therefore, the correct measurement method is to place the object to be measured between the fixed anvil and the measuring rod, and turn the ratchet wheel protection knob to slowly move the measuring rod. When the measuring rod can no longer be moved, this value is the correct thickness value.

3 When measuring blankets and other cushions, several points should be measured and averaged. In addition, when measuring the thickness of the lining, all linings must be superimposed and measured to reduce the cumulative error caused by the addition of fractional measurements.

243. Why does the thickness of the lining measured with a micrometer not equal to the thickness of the lining on the drum?

Because the micrometer can only measure the thickness in the free state before the lining does not cover the roller, the stretch deformation occurs after the blanket is tight, the adhesive layer becomes thinner, and the thickness of the lining decreases. Therefore, the thickness of the lining measured with the micrometer in the free state is greater than the actual thickness after the tensing. In addition, there is a large plastic deformation at the initial stage of use of the new liner, which will gradually reduce the thickness of the blanket.
Therefore, to accurately measure the tight lining thickness, a caliper should be used.

Source "Printing Technology - Packaging Printing"