Simple calculation of drum pressure
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I have been in contact with many offset printers. When the printing pressure is changed when the thickness of the printing paper is changed, the lining on the blanket cylinder is simply removed, and the lining of the stencil is added to the plate cylinder as if it is simple. Sometimes it can also work, but these can only work if the paper has a small range of variation (in fact, the pressure of the plate cylinder and the water roller and the ink roller has increased, which will affect the durability of the printed version. The impact of the short version of the lively will not be felt). If the thickness of the paper varies greatly, it is not correct to simply reduce the lining.
In fact, any offset press has a theoretical pressure. We need to make a variety of adjustments based on this theoretical pressure (adjust the gap, change the lining) to achieve the ideal printing pressure to meet the printing requirements. This paper will introduce the theoretical pressure calculation by taking the basic parameters of a certain model as an example. The formula, the rough calculation formula of thick paper, the accurate calculation formula of thick paper and a set of test data, so that the friends can flexibly use in practice:
Example:
The technical parameters of a model are as follows:
Clearance:
Between the plate cylinder and the blanket cylinder 3.70 mm
Between the blanket cylinder and the impression cylinder 3.05 mm
Lining:
Plate cylinder (including plate, liner) 0.65 mm
Rubber roller (including rubber, lining, backing paper) 3.25 mm
With these technical parameters, we can use a simple formula to calculate the theoretical pressure:
The formula for calculating the theoretical pressure:
The lining of the lining - gap = pressure
Calculation:
First calculate the pressure between the impression cylinder and the blanket cylinder
Substitute data: 3.25-3.05=0.20(mm)
Secondly calculate the pressure between the plate cylinder and the blanket cylinder
Substitute data: 3.25+0.65-3.70=0.20(mm)
The three rollers have a pressure of 0.20 mm with each other without printing. However, in normal printing, a normal printing paper (standard printing paper) should be added with a thickness of 0.10 mm between the impression cylinder and the blanket cylinder, and the printing pressure between the impression cylinder and the blanket cylinder is 0.30. Mm.
Conclusion: The printing pressure of this model should be kept within the above calculation range, that is, 0.20mm between the plate cylinder and the blanket cylinder, and 0.30mm between the blanket cylinder and the impression cylinder.
If the thickness of the paper we print is less than 0.10mm, we can do without any adjustment and subtraction. When printing thin paper, the printing pressure should be smaller, so we can guarantee the printing pressure of the thin paper without adjustment, because our minimum pressure can be guaranteed at 0.20mm.
If the thickness of the paper we print is greater than 0.10mm and less than 0.20mm, we can adjust it according to the following formula:
Thickness of thick paper (only adjust the gap, not lining) calculation formula:
X=3.05+paper thickness-0.10
Where: X is the gap between the blanket cylinder and the impression cylinder that needs to be adjusted when printing thick paper
If the thickness of the paper we print is greater than 0.20mm, we can adjust it according to the following formula:
The accuracy of the thick paper (both adjustment of the gap, but also reduce the lining) calculation formula:
X=3.05+paper thickness—0.10—B
B=(paper thickness—0.10)/10
Where: X The gap between the blanket cylinder and the impression cylinder that needs to be adjusted when printing thick paper.
B The amount of paper from the blanket cylinder
The test basis for the amount of paper taken:
We have organized the trainees to conduct experiments. After adjusting the gap between the blanket cylinder and the impression cylinder, the gap between the plate cylinder and the blanket cylinder is measured and recorded:
Data 1
The gap between the blanket cylinder and the impression cylinder: 3.05mm - 3.45mm +0.40mm
The gap between the plate cylinder and the blanket cylinder: 3.70mm - 3.66mm - 0.04mm
Data 2
The gap between the blanket cylinder and the impression cylinder: 3.05mm - 3.25mm +0.20mm
The gap between the plate cylinder and the blanket cylinder: 3.70mm - 3.68mm - 0.02mm
Test Conclusions:
The enlarged gap between the blanket cylinder and the impression cylinder and the reduced gap between the plate cylinder and the blanket cylinder are exactly 10:1, which is the source of the amount of paper B.
The third calculation formula can only meet the offset printing machine without the roller, and the offset printing machine does not need to perform the gap between the printing cylinder and the blanket cylinder after adjusting the gap between the blanket cylinder and the impression cylinder. Adjusting, the offset printing machine can calculate and adjust with the second formula when the thickness of the printing paper is greater than 0.10mm.