Offset part of the offset press (3)

6. Inking roller. The ink roller has the following four functions:

(1) Supplying ink to the plate cylinder This is one of the most basic functions of the ink roller. During printing, the ink on the plate is continuously transferred to the paper. If there is no ink supply afterwards, the printing cannot be performed normally. In fact, how much ink is lacked on the plate cylinder and how much ink should be added to the ink roller, so it can also be said that the ink roller has played a role in making up for the loss of the ink on the plate.

(2) Make up for the unevenness of the surface of the printing plate and the surface of the screed roller The unevenness exists in both the screed roller and the plate surface. If the ink roller cannot be in close contact with the two, the ink does not transfer well. The unevenness of the surface of the rubber roller must be used to make up for its unevenness.

(3) Absorbing and absorbing the ink roller When the ink roller is operated, it receives force from both the ink roller and the plate. The force of the printing plate is constantly changing. In addition to the forces generated by the surface non-uniformity, the impact is greatest when each gap and non-notch position is exchanged. The pulsation and runout of the ink stringer will cause the ink roller to vibrate. These forces continuously transmit energy to the ink roller, and the ink roller continuously absorbs and releases, thereby absorbing vibration.

(4) Safety function When a foreign object enters between the ink roller and the plate, the deformation caused by the foreign object becomes a deformation of the surface of the ink roller, and the other surfaces are not damaged, thus playing a safety role.

Ink roller is generally more than two, the current popularity is four, then each role is the same? Practice can not be the same. If the diameter is the same, as shown in Fig. 3.7, the ink sticks appear in the same place in the circumferential direction of the printing plate when the four ink sticks are inked. If each ink has the same amount of ink, that is, 25 percent of each ink, it cannot compensate each other because the ink on the surface must be uniform from the plate point of view. Therefore, printing on the plate should be able to play a role in ink and even ink, the actual process is also true. The ink supply of each ink roller can be obtained by the separation rule of the ink. The separation law of ink is more complicated, but it is transmitted in the same way in the way of “half of meeting”. According to this rule and the layout of the ink path, the amount of ink applied to the ink roller can be determined.

As shown in Figure 3.8, it can be seen from the calculation that the amount of each ink is different. The first and second roots were 42%, and the third and fourth roots were 80%.

It can be seen that the first two rollers mainly play the role of ink, they provide 84% of the ink demand on the plate, they are called the main ink roller. The amount of ink on the two rollers is relatively small, mainly to play a role in evenly distributing ink, and more precisely, to make up more and less. This is because after the first two rollers are inked, the ink layer is not completely consistent. Some places are less than 84%, some are more than 84%, and individual places are even greater than 100%.

Less than 84% of the need to add ink to reach 100%, more than 84% less than 100% of the place also need to add ink to reach 100%, but less to supplement. More than 100% of the place can not be refilled with ink, and the extra ink should be taken back. For finer points, the third inking roller has the role of assisting ink supply (playing the role of filling), and the fourth roller plays a role in stopping ink, even ink, and collecting ink. This is even more prominent in the modern and popular ink road. The amount of ink applied to the first and second rollers was 44%, the amount of ink applied to the third roller was 9%, and the amount of ink applied to the fourth roller was 3%.

7. Adjustment of the ink roller. The adjustment of the ink roller is very important because it is directly related to the transfer of the ink and cannot be remedied in the event of an error. So how to adjust the ink roller? If you put a round roll on a plane, as shown in Figure 3.9.

Obviously, regardless of the angle at which the roller is placed at any angle with the plane, the contact state with the plane is the same in the plane, and it can be said that it is insensitive to changes in the position.

If the plane below is changed to a cylinder, as shown in Fig. 3.10, the sensitivity of the roller is higher than the plane energy when the position of the roller changes. However, if the position is not too far, the sensitivity is still low. .

If the large cylinder is changed to a small cylinder, as shown in Figure 3.11, when the position of the roller is changed, its sensitivity to the position is significantly increased, and some places are out of contact.

The above analysis results are applied to the ink fountain roller, ink roller and plate cylinder, as shown in Figure 3.12. It can be seen that the sensitivity of the change in position between the ink form roller and the tandem roller is high, and the sensitivity to positional changes between the ink form roller and the plate cylinder is low.

In terms of installation requirements, the axis of the plate cylinder and the axis of the tandem roller are still parallel lines. If the contact relationship between the inking roller and the serigraph roller is adjusted, the contact relationship between the inking roller and the plate cylinder can be guaranteed, and vice versa. However, due to sensitivity reasons, the axis of the ink roller may not be completely parallel to the axis of the plate cylinder, and therefore it cannot be parallel to the axis of the ink roller.

Therefore, when adjusting the pressure, the pressure between the ink roller and the ink roller must be adjusted (the ink undercarriage is raised), and then the pressure between the ink roller and the plate cylinder (the undercarriage landing gear is lowered) is designed. It is exactly this requirement.

Adjusting the pressure between the ink roller and the ink roller uses an eccentric mechanism. At present, almost all machines use the worm gear mechanism to drive the cam (the ink roller is installed on the eccentric). The eccentric must be at the same time to ensure that the axis of the ink roller and the axis of the ink roller are parallel to each other and can be checked with a (0.20 mm thick) plug.

An eccentric or other similar mechanism is used to adjust the pressure between the ink form roller and the plate cylinder. The pressure exerted by the ink roller on the printing plate depends on the spring and its own ability, and the spring also acts as a buffer to absorb vibration. The pressure between the ink roller and the ink roller should not affect each other, but this condition must be established on the premise that the three axes are completely parallel. If the pressure between the ink form roller and the plate cylinder is not the same, the pressure between it and the tandem roller is affected.

The question of how much pressure is appropriate between the ink roller and the printing plate is different. However, ideally, it is best to have line contact, but this is practically impossible because the imprint must be smooth and smooth. If this cannot be done, the prints appear to be false, so there must be some printing pressure. Need to print pressure must have the existence of contact surface, usually require ink line width of about 4-5mm.

The movement of the ink roller is driven by the friction between the ink roller and the plate cylinder. If it is not suitable, it may cause slippage on the surface of the printing plate, thereby expanding or sliding the dots.

The landing roller mechanism of the ink roller controls the clutch between the ink roller and the plate cylinder. The requirement is: When leaving, all the distances between the rollers and the plate cylinder are the same; after closing, all the rollers should also be the same as the distance between the plate cylinders. The position change caused by the ink roller pressure regulation is small compared with the clutch amount.

Some equipment uses a clutch mechanism, when it is found that the amount of clutch is not suitable, can be adjusted through the screw on the landing gear, and some equipment is through strict calculation to ensure the same amount of clutch, but the processing and installation requirements Very high. The ink-and-wash mechanism must be stable and reliable. The time for this cooperation should be sufficient, and the time must be separated to ensure the normal operation of the machine.