Offset printing press role and adjustment (2)

2.7.3 Adjustment of Printing Pressure

There are two factors that affect the size of the printing pressure that have been analyzed above. Under normal circumstances, the lining material is constant (ie, E is constant). Changing the printing pressure will only change the compression of the lining (this is why the gap between the drum shoulders always represents the printing pressure. size). There are two ways to change the compression of the lining: one is to keep the lining unchanged and to change the size of the center distance; the other is to keep the center distance constant and change the thickness of the lining. Changing the center distance can be performed by a dedicated pressure regulating mechanism. The thickness of the lining is changed. It is only troublesome to open the lining. From the point of view of the gear transmission, the gears are preferably meshed in the position of the indexing circle, and the center-to-center distance will change, which will affect the smoothness of the transmission. So the ideal situation is not to move the center distance, change the thickness of the lining to adjust the printing pressure. However, since printing paper often changes, its thickness difference is generally very small, as long as the center distance is adjusted slightly. This change is also permitted by the involute gear, but its adjustment is limited. If you print thick paper, you cannot just adjust the center distance. You need to combine the thickness of the liner. In summary, it is impossible to move the center distance, but it is best not to move. If the printing pressure is insufficient, it can be compensated by changing the thickness of the pad. The size of the printing pressure can be calculated by calculation, as shown in Figure 2.11.

The compression of the lining represents the printing pressure, ie, L=R1+R2-A; A increases, ie, the center distance increases, L decreases; A decreases, ie, the center distance decreases, and L increases.

R2, R1 increase, that is, increase the thickness of the lining, L increases; R2, R1 decreases, that is, the thickness of the lining decreases, L decreases. Change the thickness of the lining, usually by adding or subtracting paper.

The above is to find L through the values ​​of R1, R2, and A. Similarly, R1, R2, and A can also be obtained through L, that is:
R1=L+A-R2; R2=L+A-R1; A=R1+R2-L.

What is often used in the actual process is not the specific values ​​of R1, R2 and A, but the thickness of the paper (Tz), the thickness of the rubber pad (Tbc), the thickness of the rubber (Tb), the thickness of the printing plate (Tp ), the thickness of the printing plate liner (Tpc), let Ri, Rp, Rb denote the diameter of each drum body, Aib, Abp denote the center distance between the impression cylinder and the blanket drum respectively, the center of the plate cylinder and the blanket drum The distance Lbi indicates the amount of compression between the blanket cylinder and the impression cylinder, and Lpi indicates the amount of compression between the plate cylinder and the blanket cylinder. Thus, there are:
Lpb=Rp+Tpc+Tp+Rb+Tbc+Tb-Abp
=Tpc+Tbc+Tb-Abp+Rp+Rb
Lbi=Rb+Tbc+Tb+Ri+Tz-Abi
=Tbc+Tb+Tz-Abi+Rb+Ri

1. Under normal circumstances.

1 For devices that do not use shoulder irons:
Lpb=Tpc+Tp+Tbc+Tb-Abp+C11 C11=Rp+Rb
Lbi=Tb+Tbc+Tz-Abi+C21 C21=Rb+Ri (1-1)

Factors affecting Lpb include: Tpc, Tp, Tbc, Tb, and Abp; factors affecting Lbi are: Tbc, Tb, Tz, and Abi.

2 For shoulder iron equipment (between printing plate and blanket cylinder, between rubber blanket and impression cylinder):
Lpb=Tpc+Tp+Tbc+Tb+D11 D11=Rp+Rb-Abp
Lbi=Tbc+Tb+Tz-Abi+D21 D21=Rb+Ri (2-1)

Factors that affect Lpb are: Tpc, Tp, Tbc, and Tb; factors that affect Lbi are: Tbc, Tb, Tz, and Abi.

2. Assume that the blanket thickness (Tb) and plate thickness (Tp) are both constant.

1 For devices that do not use shoulder irons:
Lpb=Tpc+Tbc-Abp+C12
C12=C11+Tp+Tb
Lbi=Tbc+Tz-Abi+C22
C22=C21+Tb (1-2)

The factors affecting Lpb are: Tpc, Tbc, Abp; factors influencing Lbi are: Tbc, Tz, Abi.

2 Equipment for shoulder irons are:
Lpb=Tpc+Tbc+D12 D12=D11+Tp+TbL
Lbi=Tbc+Tz-Abi+D22 D2=D21+Tb (2-2)

Factors that affect Lpb are: Tpc, Tbc; Factors that affect Lbi are: Tbc, Tz, Abi.

3. If the gear is completely in standard engagement, other conditions are the same as 2.

1 For devices that do not use shoulder irons:
Lpb=Tpc+Tbc+C13 C13=C12-Abp
Lbi=Tbc+Tz+C23 C23=C22-Abi (1-3)

Factors that affect Lpb are: Tpc, Tbc; Factors that affect Lbi are: Tbc, Tz.

2 Equipment for shoulder irons are:
Lpb=Tpc+Tbc+D13 D13=D12
Lbi=Tbc+Tz+D23 D23=D22-Abi (2-3)

Factors that affect Lpb are: Tpc, Tbc; Factors that affect Lbi are: Tbc, Tz.

4. Assume that the liner of the rubber and the liner of the plate cylinder are unchanged, and other conditions are the same as 2.

1 For devices that do not use shoulder irons:
Lpb=C14-Abp C14=C12+Tpc+Tbc
Lbi=C24+Tz-Abi C24=C22+Tbc (1-4)

Factors affecting Lpb are: Abp; factors affecting Lbi are: Tz, Abi.

2 Equipment for shoulder irons are:
Lpb=D14 D14=D12+Tpc+Tbc
Lbi=D24+Tz-Abi D24=D22+Tbc (2-4)

The factors affecting Lbi are: Tz, Abi; Lpb is a fixed value.

Of the four situations mentioned above, the factor of influence in 1 is the most complete, but the actual adjustable factors are not always so much. This situation can only be used when overhauling or debugging the machine. The factor that influences pressure in 3 is to exclude the influence of the center distance. Even if the relative relationship of the gears always remains the same, this is very favorable for the smooth operation of the machine, but this situation is also difficult to achieve in the actual process. Relatively speaking, the two most commonly used formulas are two and four formulas.