4 Receiving part
The receiving part is the last printing unit of the printing press, and its main function is to pile the printed sheets together. However, this stacking is not carried out arbitrarily, and it has strict requirements: ①The surface of the printed sheet is flat; ②The front of the printed sheet is flush; ③The side of the printed sheet is flush; ; ⑤ The printed sheet surface must not have any scratches.
The five points mentioned above are called the free state of the paper at the delivery point. In the printing process, the paper is actually a process from the free state to the controlled state, and then back to the free state.
1. The surface of the printed sheet is smooth. This is one of the most basic requirements for printed products. Puckering on the surface of printed products has a certain impact on the quality of printed products. The uneven surface brings difficulties to the subsequent processing of printed products, so the surface must be flat.
2. The front of the printed sheet is flush. The front opening of the printed sheet is flush, which is convenient for inspection or cutting, and it is also conducive to the stacking of the printed sheet at the receiving pile.
3. The side of the printed sheet is flush. The reason is the same as 2.
4. There is no adhesive force between the upper and lower printed sheets. If the upper and lower printed sheets are stuck together, the graphics on the surface of the printed product will be damaged, and it will cause great trouble to the subsequent process.
5. The printed sheet surface must not have any scratches. If there are scratches on the surface of the printed product, the quality of the printed product is affected, and in severe cases it can only be regarded as scrap.
According to the requirements on the status of the printed sheets, the basic composition of the paper collection part can be analyzed at the paper collection place.
4.1 Surface smoothing of printed sheets (leveler)
The printed sheet reaches the receiving part from the printing unit, and the trailing edge of the printed sheet will be bent and deformed. If no leveling device is added in the middle, the flatness cannot be guaranteed, as shown in Figure 4.1.
(Figure 4.1)
When the printing sheet rotates together with the impression cylinder, it remains stationary with each other (not considering the influence of the speed difference between the rubber cylinder and the impression cylinder). When the impression cylinder delivers the paper to the take-up cylinder, because the take-up cylinder has a certain amount of diameter reduction, that is, after the handover point, the linear speed of its dental pad is lower than the linear speed of the dental pad on the drum surface The speed of the paper suddenly drops. The second half of the printed sheet is not separated from the rubber cylinder in time, but rotates with the rubber cylinder until the printed sheet is in tension again, and the printed sheets begin to separate synchronously. In the process from handover to synchronous separation, a moment when the printed sheet is in a slack state to a sudden tension, a fold is formed near the surface of the blanket. If this fold is not eliminated, it will affect the flatness of the printed sheet. Figure 4.2 shows the entire process of forming folds.
(Figure 4.2)
Therefore, the printing machine of this structure is generally equipped with a sheet leveling device (also called anti-roll device) in the delivery part. The function of the printed sheet leveling device (leveler) is to flatten the second half of the printed sheet. Its working principle is shown in Figure 4.3.
(Figure 4.3)
An air suction device is installed between the two rollers. After the air suction, a pressure difference is formed, and the bending of the printed sheet is corrected by the pressure of the air.
The most thorough way to eliminate printed sheet curling is to eliminate the conditions of its existence, which needs to be solved by design. There are two methods currently used:
â‘ Make the printed sheet completely printed on the impression cylinder and then hand it over to the take-up cylinder. This method generally uses a double-diameter impression cylinder;
â‘¡ Two paper transfer cylinders are added behind the impression cylinder, so that the printed sheets have been completely separated from the rubber cylinder after passing through the two paper transfer cylinders, and there is no process of printing sheets from tension to slack to tension Figure 4.4 shows.
(Figure 4.4)
If the above method is adopted, the leveling device can be removed.
What is a vertical filing cabinet used for ?
In work places, Metal Cupboards and office metal storage drawers are perfect solution for organizing office documents.
Vertical and lateral files are the most common for storing files.
1. Files hanging vertically to be found easily.
2. Files can be kept in alphabetical or numerical order for reference often.
3. For home office storage where space is a problem, 2 to 4 or more drawers filing cabinets are perfect.
4. Two drawer styles are typically used at desks or workstations for every day use.
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