Adjustment principle of printing pressure and analysis of common problems (2)
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Above we discussed how to determine a suitable printing pressure and how to adjust the printing pressure. The purpose is nothing more than to ensure that the printing pressure is within a reasonable range during printing. In actual production, whether the printing pressure is large or small, it will cause such problems.
If the printing pressure is too small, the ink will not be transferred normally, and the printed matter will be empty, and the printing defects will be caused. We are accustomed to think that the printing pressure is large, then the amount of ink transfer will be larger, but the printing pressure and the amount of ink transfer in production are not proportional. When the printing pressure is larger than a certain range, the amount of ink transfer can not only become larger as the printing pressure increases, but will become smaller, and at the same time, the printing pressure is too large, causing the print dot to increase or even spread. Excessive printing pressure can also damage the mechanical structure of the printing press. The more direct performance is the wear on the printing plate and the damage to the surface of the printing plate. It can be seen from the above that the printing pressure is too small and too large to be necessary in printing, and it is necessary to accurately ensure a reasonable printing pressure.
Other common problems caused by printing pressure (the pressure expressions mentioned below are all blanket compression), the following discussion will mainly be based on mechanical compression.
Ink bar
cause:
(1) The ink stick that is seriously generated by the wear of the drum gear.
1. Adjust the center distance too large;
2. The roller gear is severely worn, and the gear side clearance is more than 1.0 mm. When the drum is pressed, the gear vibrates, causing frictional sliding on the surface of the contacted roller, which eventually causes the mesh to deform during the transfer process.
Solution:
1. Replace the new gear;
2. Properly reduce the center distance of the roller, and tighten the gears so that the backlash is less than 0.1 mm;
3. Use soft lining. The compression between the plate cylinder and the blanket cylinder is not more than 0.1 to 0.15 mm; the pressure between the blanket cylinder and the impression cylinder is not more than 0.15 to 0.2 mm plus the thickness of one sheet of paper.
(2) The ink rod which is seriously generated by the wear of the roller bearing gear. When the shaft head and the sleeve are severely worn, the jaws are immediately released after being pressed, causing sliding friction to generate a deep ink stick. Solution: 1 Replace the new bushing; 2 If the old-fashioned low-speed offset press can tighten the strap on the plate head.
(3) The pressure between the plate cylinder and the blanket cylinder is too large. The ink stick feature is the ink bar in the fixed area. The pressure between the printing plate and the blanket cylinder is too large, and the blanket generates a large frictional sliding under the action of the pressing, thereby causing the dot to be deformed to form a ink stick. It is identified whether the pressure between the two rollers is too large, and the obvious feature is that a "beep" sound occurs when the pressure is pressed, and generally the surface of the printing plate is bright after printing to 5,000 sheets.
Solution: Plates and blankets should be data-based. The thickness of the plate liner should be within ±0.03 mm of the standard. The thickness of the liner in the blanket should be such that the pressure is as high as possible.
2. Vertical ghosting
cause:
(1) The drum is not properly pressed. The ghost feature is a few vertical ghosts that appear when you start printing. This is because the roller can not be combined once, and when it needs several times to complete, the pressure of each pressure is different, and the compression deformation of the blanket is also different, so that the dots on the printing plate are transferred to the blanket each time. The blots do not coincide and produce ghosting. The reason for this is that the roller clutch mechanism is worn or loose, or the pressure between the rollers is too large.
Solution: Check the roller clutch mechanism, tighten the screws, and replace them if they are worn out. If it is a pneumatically combined model, pay attention to whether there is air leakage in the air circuit or whether there is any problem with the compressor air pressure. When the pressure between the rolls is too large, the pressure of the rolls should be appropriately reduced.
(2) The blanket is too loose. The ghost feature is a full or partial vertical ghost. There are two situations in which the blanket is too loose: first, the entire blanket is stretched too loose, so that the blanket cannot be reset in time after being pressed, resulting in a large area of ghosting. Second, the blanket is cut or skewed or clamped. Not allowed, causing the local stretch too loose and causing local ghosting.
(3) The pressure between the rollers is too large. The ghost feature is a large area of vertical ghosting. The pressure between the rollers is too large, especially when the combined pressure of the blanket cylinder and the impression cylinder is too large, the displacement of the blanket is large, and after the transfer is not completely reset, a large-area longitudinal ghost is generated.
Solution: When generating large-area longitudinal ghosts, check that the pressure between the rollers is too large. If it is too large, the pressure between the plate cylinder and the blanket cylinder should be adjusted to 0.1 to 0.15 mm, and the pressure between the blanket cylinder and the impression cylinder should be adjusted to 0.2 to 0.25 mm.
3. Paste, flower version
Cause: The pressure between the rollers is too large, sometimes the pressure between the impression cylinder and the blanket cylinder is insufficient, and the pressure between the plate cylinder and the blanket cylinder is just right. The operator then pads the blanket to cause the plate cylinder. The pressure between the blanket cylinders is too large and the friction is increased.
Solution: When the above drawbacks occur, check if the roller pressure is too large.
1 Recalculate and check whether the roller gap of the roller is normal (the old-fashioned domestic model should be re-measured by the pressure between the rollers)
2 Measure whether the thickness of the blanket or the printing plate is appropriate (±0.03mm);
3 Check if the blanket has partial unevenness.
4. Unilateral outlets are empty
Cause: The influence of the roller pressure. The center distance between the two ends of the drum or the pressure at both ends of the drum should be kept equal, but some of the center of the machine will go away from the side, causing the pressure on one side to be light, resulting in a unilateral dot not being full.
Solution: Before checking the pressure regulation, the factors such as the flower plate, the unilateral water, and the light pressure on one side of the ink should be excluded.
First, the pressure of the drum is measured on both sides of the drum by the method of pressing the lead wire. If the pressure on both ends of the drum is more than 0.05 mm than the other side, it is confirmed that the pressure is reduced. Remove the plate and blanket, then measure the naked roller and correct the center distance.
5. Blanket adhesive paper
(1) The timing of the transfer of the roller paper and the delivery paper is incorrect. Paper from the oscillating paper to the paper, to the roller paper to complete the printing process, to the delivery of the dent, there must be a certain transfer time between them, to ensure accurate overprinting and paper continuity, if the roller 叼The transfer time between the paper and the delivery is too short, which will cause the paper to lose control in an instant, causing the paper to stick to the blanket. The paper-bonded blankets caused by this cause occur mostly in the second group of two-color printing presses and the last group of multi-color printing presses. In some cases, this may occur in each color group of a multi-color printing press. .
(2) The pressure between the blanket cylinder and the impression cylinder is too large. In the printing process, too much pressure will cause the paper to stick to the blanket. Even if the force of the roller gripper and the pick-up bite (or the transfer roller) is increased, this phenomenon occurs from time to time, especially in the printing ink layer. Thicker, paper-smooth paper is more common, because the friction caused by excessive pressure plus the adhesion of the surface is greater than the force of the gripper. The paper is very strong on the surface of the blanket, and it will be difficult to lift it by hand.
Solution: Adjust the biting time and adjust the printing pressure.
6. The roller can not be pressed
cause:
(1) The low speed clutch slips. The low speed machine roller can not be pressed, and the common is the clutch (mechanical) crescent bump slip.
Solution: (mechanical) remove the clutch, cut a few diamond-shaped lattices on the plane of the crescent block, or do the repair welding height treatment in the bumps.
(2) The roller is loosened by the pressure of the mountain. One of the reasons why the high-speed machine can not be pressed is that the pressure "backing" screw is loose. The "backing" screw is mounted on the drive wall plate. When loosened, the roller will be over-pressured. At this time, the clutch on the operating surface passively supports the tooth and returns to the head. When the pressure is again pressed, the electromagnet will actively support the upper teeth, and the active support teeth cannot be meshed with the passive support teeth, causing the roller to not press. If this phenomenon is not discovered early, the electromagnet coil will soon be burned. Sometimes the operator judges the error and thinks that the electromagnet has failed. As a result, the replaced electromagnet coil is burned in succession, causing loss.
Solution: When the roller is not pressed, remove the protective cover and jog the machine to check if the electromagnet is working. If it has burned out, replace it with a new one. At the same time, check whether the roller clutch pressure is too heavy. When the pressure is excessive, the active tooth can't be engaged with the passive tooth. At this time, the driving face cover should be disassembled, and the roller should be tightened in the moment of the needle. When tightening, you can screw 1~2 turns more, so that the active support teeth can enter the support part of the passive support with a margin of 0.1 mm, and then the "backing" screw can be locked.
7. Clutch shaft buffer
(1)During the printing process, the clutching and pressing working mechanism is the clutching movement of the eccentric bushing, which is operated by the roller clutching and pressing mechanism. However, due to the wear and improper adjustment of the machine parts, the buffering action of the clutch shaft occurs after the drum is pressed. Its roots are mainly on the roller clutch mechanism, which occurs mostly after adjusting the pressure or replacing the padding. Its characteristic is that the first circle after the pressure is combined, the clutch shaft, the swing rod and the connecting rod are not in line, and it is only after a few weeks of operation.
Solution: Firstly, carefully adjust and measure the roller gap according to the machine manual. Strictly press the data pad to avoid the buffering phenomenon of the clutch shaft when the pressure is increased.
(2) The wear of the pawl or the supporting tooth makes the clutch mechanism lose its self-locking ability. When the pawl or the supporting tooth wears, the clutching amount is insufficient, so that the clutch shaft, the swing rod and the connecting rod are not in line, and the self-locking ability is lost. Buffering phenomenon.
Solution: After the pressure is pressed, the center of the clutch shaft is pulled through the axis of the pendulum rod to the axis of the connecting rod. When observing three points is not a line, when there is a gap between the pressure and the backing, it is possible to try to add a plug between the pawl and the supporting tooth, when it is three points into a line, or slightly more than some. The wear data is measured and then solved by repairing the pawl or supporting the teeth.
(3) Loss of control of clutch sleeve wear As the shaft diameter of the drum and the wear of the bushing cause sway, the appearance of the "ink stick" causes the clutch mechanism to lose its proper precision control, causing the clutch shaft to act.
Solution: Promptly set or replace for remediation.
8. Adjust the roller center distance should pay attention to the problem
Attention must be paid during the adjustment process:
(1) The liner of the plate cylinder and the blanket cylinder (including plates, erasers, linings, linings, etc.) must be removed, and the roller gap, the bolster clearance and the gear clearance are measured under pressure.
(2) A roller (plate cylinder or impression cylinder) without an eccentric bearing must be selected as the reference. This roller must be calibrated horizontally at a vertical angle to the wall panel.
(3) When turning the eccentric bearing of the blanket cylinder to the embossing position, it must be noted that the positions of the eccentric bearings at both ends should be in the same direction. This avoids the intermediate phase error of the axis of the blanket cylinder against the axis of the reference cylinder.
(4) For the offset-free offset press, the gear meshing clearance must be adjusted within the specified range. Beware of the “top tooth” of the tooth root. For the offset press that measures the roller, adjust the gap between the two ends to the standard value and roll simultaneously. The pillow must be kept clean and round. Then select the two ends and the middle three points on the surface of the roller to check whether the roller gap is the same, and ensure the parallelism of the roller.
appendix:
Machine model Heidelberg RVK3B Mitsubishi Beiren PZ4880—01 Beiren J2108
Speedmaster DIAMOND 3D-4
102-4 Roland
Transmission gear
indexing circle
diameter 270 mm 300 mm 310mm 275mm 300mm
Plate cylinder diameter 269 mm 299 mm 309.54mm 274mm 299mm
Blanket cylinder diameter 263.6 mm 293.5 mm 304.1mm 268.5mm 293.5mm
Embossing cylinder
diameter 270mm 300mm 620.4mm 275mm 300mm
Plate roller shoulder
iron diameter 270mm 300mm 309.88mm 274.8mm 299.8mm
Blanket roller shoulder
iron diameter 270mm 300mm 310mm 275mm 300mm
Embossing roller
shoulder iron diameter 269.3mm 299.5mm 620mm 274.5mm 299.5mm
Standard roller gap 0.1mm 0.1mm 0.2mm 0.2mm
of plate cylinder and (allowing range 0.05~0.30mm)
blanket cylinder
Blanket gap between 0.35mm 0.25mm 0.05mm 0.25mm 0.2mm
blanket cylinder and +substrate thickness
impression cylinder
Plate and pad total
thickness 0.6 mm 0.7 mm 0.4mm 0.7mm 0.7mm
The total thickness 3.20 mm 3.25 mm 2.95mm 3.25mm 3.35mm
of the blanket and pad