Analysis of comprehensive troubleshooting of offset press

7.9 Comprehensive troubleshooting

Many faults are related to each other, so comprehensive consideration should be taken when troubleshooting these faults, that is, two or more channels should be linked and analyzed. Here are some common examples to analyze the general method of troubleshooting.

7.9.1 Overprint is not allowed

Inaccurate overprinting means that the positional coordination between graphics and paper is inaccurate. Paper is transmitted through the paper path, and pictures and text are transmitted through the water and ink path. Inaccurate paper path transmission, inaccurate water and ink path transfer, and inaccurate cooperation of the paper path with water and ink path may cause inaccurate overprinting.

From the perspective of the paper path, accurate overprinting means that the position of the paper in each link of the printing process changes without changing the time and conditions. As long as the position changes, it will cause inaccurate overprinting. Line overprinting is generally divided into front and back overprinting, left and right overprinting, and left and right type front and back simultaneous overprinting is not correct (Tucsi skewers therefore analyze the paper path overprinting to find the position of the score sheet (front, back, left, right, front And left and right) the changing factors, and then take corresponding measures to solve them.

1. The paper path causes the body to experience inaccuracy.

(1) Inaccurate positioning of rules. Check the working conditions of the front and measuring rules carefully. When will the paper be positioned before, and when will the paper be positioned according to the rules? Adjust it according to the requirements of the manual. At the same time, we must pay attention to whether the height of the front gauge and the gauge meet the requirements.

(2) Inaccurate paper picking and delivery

â‘ The paper feeding tooth shakes when picking up paper, resulting in unstable handover: adjust the paper feeding tooth's stopper to keep it still on the cardboard, and the transition is the smoothest;

â‘¡Axial tandem motion when handing paper picking paper: adjust the axial lock nut to make it have 0.03mm tandem motion;

â‘¢The bite force of the paper feeding tooth is insufficient, and the paper slides: increase the bite force, especially at high speed, this point should be paid attention to (mainly caused by the inertia of the paper);

â‘£ Inaccurate opening and closing tooth time of paper feeding tooth: readjust the opening and closing tooth time.

(3) Inaccurate coordination between paper-handling and rules

â‘  When the paper delivery teeth have not yet taken the paper, the rules have released the paper: adjust the rules so that there is a common handover time between the paper delivery teeth and the rules;
â‘¡ The rules have not been positioned yet: take the paper and take the paper, adjust as above;

â‘¢When handing the paper out of the paperboard, the ruled part has not been put in the paper: adjust the rule to put the paper in advance;

â‘£The height of the pads of the top-swing paper delivery teeth is not suitable: too low, it is easy to form an impact on the paper and cause the paper to shift; Should carefully check its position on the cardboard. Generally, the height should be: paper thickness + 0.2mm, which is consistent with the height of the front gauge cap and side gauge pressure plate.

(4) The handover between the delivery tooth and the front transfer roller (or impression cylinder) is inaccurate

â‘  The handover time is too short: adjust the position of the corresponding opening and closing tooth cam; â‘¡ the distance between the tooth pads is not suitable: readjust so that the distance is: paper thickness + 0.2mm. But generally this distance should not be adjusted.

(5) The bite force of the impression cylinder's teeth is insufficient, and the paper slides in the impression cylinder

â‘  The pressure of dental tablets is too small: increase the pressure of dental tablets;
â‘¡The friction coefficient of the dental pad is too small: replace the dental pad;
â‘¢ The viscosity of the ink is too large, add ink or viscosity remover to reduce the viscosity of the ink;
â‘£ The surface of the blanket is sticky: replace the blanket;
⑤ Printing pressure is too large: reduce printing pressure.

(6) The rear conveying roller's bite force is insufficient, and the paper slides in the teeth. Since the rear conveying roller on the general machine is involved in the second half of the printing process, it requires the same as the impression roller. The troubleshooting method is the same as above.

(7) The troubleshooting of other rollers with insufficient bite force can be referred to (4) and (5).

(8) If the bite force of the delivery chain is insufficient, the troubleshooting method is the same as (6).

(9) The axial series movement of all the cylinders will cause overprinting to limit the axial series movement of the cylinders. Generally, the double nut mechanism is used. If it is found that the axial series movement exceeds the specified requirements (> 0.03mm), adjust the lock nut, generally it should be fully locked, and then reverse one-third rotation. After adjusting, be sure to tighten the nut. Axial thrust bearing wear will also cause the axial series of the drum, if it is worn, it should be replaced in time. If it is more accurate, it can be tested with a dial indicator.

2. Partial overprint caused by paper path is not allowed. Partial overprinting does not refer to: the local position of the paper slides relatively during the printing process.

(1) When there are only two pre-regulations, when the paper reaches the pre-regulation, the middle part protrudes forward. The softer the paper, the more protruding this situation is. Reduce the speed or increase the number of front rules. So that the paper is accurately positioned at the rules the day before yesterday.

(2) The bite force of the individual grippers on the paper feed teeth is insufficient, so that the first four positions of the paper at this place change to increase the pressure or replace the dental pads.

(3) The amount of paper bite of the delivery tooth is uneven, and there is more on one side and less on the other side. The part with less bite is prone to relatively slip. Adjust the front gauge to make the amount of paper bite even.

(4) The bite force of the individual teeth on the impression cylinder is insufficient to replace the tooth pad or increase the bite force.

(5) The local printing pressure is too large, which causes the resistance of the paper to increase, which causes the paper at this place to be moved to check the blanket and liner to recalibrate the printing pressure.

(6) The unreasonable distribution of graphics and text on the surface of the printing plate is likely to cause relative slippage of paper on large areas. Add ink or reduce printing pressure.

(7) The paper is swelled by water, which causes the second half of the paper to flick and humidify before printing.

3. Joint printing caused by water and ink is not allowed.

(1) The printing plate is loose. Because the printing plate is loose, the position of the print changes during the printing process, so it is impossible to overprint accurately. Adjust the tightening screws to clamp the plate.

(2) The liner under the printing plate is not suitable, making the imprint larger or smaller, resulting in overprinting not to re-check the thickness of the liner, and re-line the liner according to the technical instructions.

(3) The rubber market is loose. Because the rubber cloth is loose, the position of the imprint has changed every time, resulting in inaccurate overprinting.

(4) The amount of water supply is too large, so that the tension of the paper becomes small, and the paper is easily deformed by tension to reduce the amount of water supply.

(5) The amount of ink applied is too large, causing the paper to slide in the gripper to reduce the viscosity of the ink.

4. The overprint caused by the plate-making part is not allowed.

(1) The cross line or corner line is used as the reference line when imposition printing is not allowed, and the cross line average is also used as the reference during imposition. If the position between the graphic and the rule line is inaccurate, it is extremely difficult to overprint accurately when printing, sometimes even impossible. Therefore, the precision of imposition should be maximized.

(2) Inaccurate exposure during printing If this is a one-time job, there is generally no such problem. Two or more sun exposure is prone to such problems. Therefore, try to avoid doing more than two exposures. If you must do this, you should dry the paper first.

(3) Deformation of the plate material when the plate is pulled. Due to the poor resistance of the plate to deformation, it is easy to deform after receiving a large force, and sometimes even a crack. Therefore, it is not appropriate to use too much force when pulling the plate, and you should carefully find the reason when you can't pull it.

(4) Overprinting caused by process layout is not allowed

â‘ Multicolor overprinting is prone to inaccurate overprinting. The more the number of overprinting, the greater the possibility of error. Therefore, the number of overprinting should be reduced as much as possible; In these occasions, spot colors should be used instead of overprinting. In addition, a reasonable process can be used to minimize the number of overprints, and the possibility of errors is also minimized. [next]

7.9.2 Ghosting

Ghosting means that two or more identical marks appear on the printed product, and their positions are close. Therefore, troubleshooting ghosting is to find the factors that cause the misalignment of the imprint.

1. The printing plate is loose. Due to the looseness of the printing plate, the position of the printing plate in the printing process cannot be kept fixed, so the position of the new and old imprints transferred to the printed product twice is different, so ghost images will appear on the printing sheet. Re-tighten the printing plate, and the screws on both sides in the circumferential direction should be in working state, so that the relative position of the plate clamp of the printing plate and the plate cylinder can be kept unchanged; adjust the gap between the plate on the plate clamp to ensure the printing process The relative position of the printing plate and the plate clamp is unchanged; the printing plate is installed under pressure, so that the printing plate can be tightly enclosed on the printing plate cylinder.

2. The blanket is loose. Due to the different position of the blanket when it is in contact with the printing plate (or impression cylinder) twice, there are both old and new marks left on the blanket, and ghosts will inevitably appear when transferring to the printed sheet. The position of the rubber clip on the rubber clip is not correct. Re-install the card to ensure that the rubber cloth and the stopper on the clip are in close contact, and the screw should be tightened in the middle first and then on both sides, so as to prevent the rubber from floating in the middle; The tension of the cloth is too small. Use the newspaper hand to turn the worm gear mechanism to tighten the blanket; the cushion under the blanket is uneven, causing the blanket to loosen in some places and the blanket to tighten in some places. Replace the pad.

3. The paper slides on the impression cylinder. In multi-color printing, when the printed sheet has finished the first color printing and entered the second color printing, because the imprint on the printed sheet is not completely dry, when in contact with the second color rubber market, the first color printing edge is transferred to the second Color blanket. If there is a change in the position of the paper and other parts are in good working condition, the first color print on the subsequent printed sheet should completely overlap the first color print on the second-color blanket, because there is no ghosting; otherwise Will cause ghosting. The pressure of the dental plate on the impression cylinder is too small, which increases the pressure of the dental plate; the dental pad on the impression cylinder is seriously worn, and the dental pad is replaced; the amount of paper in the impression cylinder is too small, adjust the rules, and increase the amount of bite; If the printing pressure is too large, reduce the printing pressure; if the viscosity of the ink is too large, add ink or debonding agent to reduce the viscosity of the ink; when the full version is thick, replace it with a soft liner.

4. The paper is deformed. The uneven surface of the paper and dampness of the paper will cause the old and new marks to not overlap. You can use the machine to press the paper (water, but not ink), so that the paper basically reaches a flat state after the final stamping. And because it has absorbed a certain amount of water itself, the possibility of re-absorption and swelling is much smaller.

5. The cross-talk of the roller. The tandem movement of the plate cylinder, rubber cylinder and other paper transfer cylinders will cause the old and new marks to not overlap, resulting in ghosting. Carefully check the axial eye position device of these rollers, inappropriate re-adjustment, generally the amount of serial motion is controlled within 0.03mm.
6. The layout of the layout is unreasonable. The field change and mesh blocks should be correctly arranged, and generally the axial distribution should be as uniform as possible, so that the viscosity of the ink is evenly distributed along the axial direction, thereby reducing the possibility of paper slippage.

7.9.3 Water and ink bars

The water and ink bars are the water lines or ink lines that appear in the axial direction (or lateral direction) of the printed product. The water line is that the ink is not printed or is printed too little due to the water; the ink line is too much ink due to the large ink. There are many causes of water and ink sticks, and they are also very complicated. The following is a brief analysis of the causes and elimination methods from different perspectives.

1. The pressure of the water stick is too high. Because the pressure of the water roller is too high, the impact generated when contacting the printing plate is also large, so that the amount of water on both sides of the impact position of the water roller is larger than that of other parts around it. After the water roller makes one revolution, the part with large water comes into contact with the printing plate, so that the ability of inking is weakened there, thereby forming a water bar. At this time, the pressure of the water roller should be reduced.

2. The water roller is not round. Because the water roller is not round, some places are high and some places are low. High places will slip when they come into contact with the printing plate, causing water to accumulate and form water bars. The water roller should be replaced.

3. The pressure of the ink roller is too large. The reason analysis is the same as 1, except that the amount of ink impacting both sides increases, thereby forming an ink stick.

4. The ink roller is not round. The analysis is the same as 2.

5. The printing pressure is too high. Because the printing pressure is too high, the impact of the cylinder when switching between the notch and the non-notch is too large, causing the cylinder to vibrate, so the water, ink roller and plate cylinder surface also produce an impact, thereby generating water and ink stick. The solution is to reduce printing pressure.

6. Rolling gear wear or machining accuracy is too low. After the accuracy of the gear is destroyed, unevenness will occur during the rotation of the cylinder, which causes relative slippage between the water, ink roller and printing plate, forming a water and ink company. At this time, the freighter should be replaced or the meshing position of the gear should be changed.

Once the water and ink sticks appear, the consequences are very serious, so it is necessary to find out the reasons in time and eliminate them.

7.9.4 Paper pleating

Paper pleating means that the surface of the paper is not level, so the convex areas are flattened during printing to form pleats. Prints with pleats are generally unacceptable.

1. The paper is not in a flat state at the rules. Because the paper is uneven at the rules, when printing, the uneven parts are flattened to form a grid.

(1) Change the position and direction of the paper pressure roller on the paperboard to make it easier for the paper to be smooth.

(2) Increase the number of front rules so that the paper does not bend forward at the rules.

(3) For the top-swinging paper-feeding tooth, the distance between the tooth trim and the rule weight should be equal to or slightly lower than the distance between the front rule cap and the rule plate.

2. The phenomenon of half teeth appears on the paper teeth. When half teeth appear on the gripper, the paper easily slides inside the gripper, so that the surface of the paper becomes uneven and creases are formed during printing. Try to find a way to make the gripper bit more than two-thirds of the width in the width direction.

3. The hand gripper paper is more uneven, with more sides and less sides. The side with fewer edges is prone to slip during the transfer process, resulting in uneven surface of the paper. Adjust the rules so that the gripping amount of gripper can meet the requirement that the paper does not slide.

4. The printing pressure is too high. The printing pressure is too high, which causes the paper at the individual gripper to slide relatively, resulting in an uneven surface. Reduce the printing pressure or increase the friction of the gripper of the impression cylinder.

5. The ink is too sticky. Because the ink is sticky, the resistance of the paper to forward transmission increases, so that the paper in the individual parts slides backward, and the surface of the paper becomes uneven. Add adjusted ink or debonding agent to reduce the viscosity of ink, and pay attention to the influence of ambient temperature.

6. The paper itself is not flat. The paper becomes uneven due to moisture and other reasons. The shorter the time for unpacking the paper, the better. The environment (temperature and humidity) when unpacking should be consistent with the printing environment. Semi-finished products should be properly kept, preferably covered in plastic. [next]

7.9.5 Uneven ink color

Uneven ink color is uneven distribution of ink on the printed sheet. Causes of uneven ink color: First, the relative contact surface of the ink line is poorly connected; second, the ink fountain is not adjusted properly.

1. The radial runout of the impression cylinder is too large. Because the impression cylinder bounces, the contact condition with the rubber cylinder cannot be kept the same, thus causing uneven ink color. Check with a dial indicator, if its runout exceeds 0.03mm, you should find the reason carefully. The reason why the impression cylinder jumps too much: First, its processing error is large; Second, it is squeezed too much, causing the cylinder to deflect and deform; Third, the bushings on the two side wall panels are worn. According to the specific situation, take corresponding maintenance measures to restore its accuracy.

2. The surface of the impression cylinder is dirty. During the printing process, impurities such as paper powder, sludge, and ink will adhere to the impression cylinder, resulting in uneven distribution of the printing pressure, resulting in uneven ink transfer. In particular, printing high-quality jobs should pay attention to this point.

3. The radial runout of the rubber roller is too large. The cause of failure and the inspection method are the same as the impression cylinder. However, due to the frequent clutch history of the rubber roller, the bushing wear on both sides is relatively more serious; the deformation or non-synchronization of the clutch pressure mechanism on both sides will change the clutch pressure position of the rubber roller.

4. The pad under the blanket is uneven. Because of their inconsistent thicknesses, their printing pressures are inconsistent, and the transfer of ink is uneven. Use a dial indicator to check the thickness of the pad under the blanket. After installation, print the flat screen or fill the plate to further check the unevenness of Baocun. If there is any unevenness, it will be repaired or replaced in time.

5. The plate cylinder jumps radially. The cause of failure and the inspection method are the same as the impression cylinder. However, before checking the runout of the plate cylinder, the parallelism of the cylinder should be corrected first. Using the impression cylinder as a reference, correct the parallelism of the rubber cylinder, and then correct the parallelism of the printing plate cylinder and the rubber cylinder. On some equipment, the plate cylinder also participates in the clutch pressure process, so the faults and troubleshooting methods of this structure are the same as the rubber cylinder.

6. The printing plate and the liner under it are uneven. Because of their inconsistent thickness, the contact between the printing plate and the blanket is uneven. Use a dry ruler to check the thickness of the printing plate and the liner underneath. If it fails, it should be replaced.

7. The graphic on the printing plate is unevenly developed. Some places are deep and some are shallow.

8. The parallelism between the ink path and the printing plate is not good. The degree of parallelism between them determines the quality of the ink transfer performance between them, should hurt "5." Check the parallelism of the ink path.

9. Inking roller is not round. If the inking roller is not round, the effect of transferring ink must be uneven. Use a caliper to check its non-parallelism, and the unqualified ones should be replaced. The same is true for other ink rollers.

10. Poor ink inking. The lower ink volume of the ink fountain should be equal to the required ink volume on the printed sheet, and the adjusted ink volume at this time is the optimal ink volume. If the amount of ink is not adjusted properly, it is very difficult to smooth it by the cross-ink roller and the ink leveling roller, so it is impossible to get the best ink level.

11. Water and ink bars are also one of the factors that cause uneven ink color. Refer to 7.9.3 for the causes and troubleshooting methods of the faults.

7.9.6 Paper tear

Paper tear is when a part of the paper surface is torn. The essential reason of paper flare is mutual interference between moving parts.

1. The side gauge is raised too late. When the delivery paper gripper leaves the paperboard, the regulations have not yet been lifted, causing the paper at the regulations to be torn. Adjust the cam underneath the regulations to make the regulations lift in advance.

2. The front rule fell too late. The front rule hadn't fallen when the paper-handed gripper left the paperboard. If the time of the front gauge is wrong, adjust the front gauge cam to make it fall in advance. If the mutual sales agency does not work, then carefully check the working circuit of the mutual sales agency.

3. The upper swing type delivery system is larger than the distance between the front gauge cap and the cardboard. In this case, the paper will be wavy the day before yesterday, and further increase in the wave shape will cause the paper to break.

4. The hand-over between the paper feed tooth and the front pass paper tube is inappropriate. The reason is similar to the above.

5. The amount of gripping paper of the delivery tooth is too large. As a result, during the handover of the paper, the paper at the mouth cannot complete the handover in the plane, thus tearing the paper. Therefore, as far as possible, the paper should be reduced as much as possible.

6. The unevenness of the teeth during handover is too large. During the hand-over process, the dental pad appears uneven, so that individual parts of the paper appear wavy.

7. The fit between the presser foot and the separation nozzle is inappropriate. Torn the back of the paper.

8. The hand-over between the nozzle and the transfer roller is inappropriate. The handover between them should be performed at a common speed, but due to long-term mechanical wear, their mutual cooperation will change, resulting in paper grabbing.

9. The other components on the paperboard interfere with the performance of the paper, causing the paper to tear. Exclude parts that interfere with each other.

10. The timing of opening and closing the dental mechanism is not accurate. Due to the wrong opening and closing time, the paper could not be delivered in an ideal state. Readjust the opening and closing tooth mechanism.

11. When the paper is moving on the roller. Due to its centrifugal force, the tail of the paper should be thrown outwards, especially on the take-up roller. Therefore, these components that may cause interference should be adjusted carefully.

12. Paper delivery chain is too easy to cause paper tear. Retension the chain.

13. The paper interferes with other parts at the collection site. This will scratch the paper surface.

14. Some open teeth are not flexible, and can also cause paper tearing. Readjust the gripper. [next]

7.9.7 Plate wear

Plate wear is inevitable in the printing process, but if standard operations are taken, the plate wear rate will be greatly reduced. The essential reason for the abrasion of the printing plate is the relative slippage, that is, the frictional force, on the relative contact surface of the contact area between the printing plate and other components. Therefore, reducing plate wear is to reduce friction.

1. Relative slip occurs between the water roller and the printing plate.

(1) The pressure between the water roller and the printing plate is different between the water roller and the water roller, and readjust to make the pressure equal.
(2) The water roller itself is not round and tested with calipers. Should exceed the specified requirements should be replaced.
(3) The water velvet on the water roller is too loose, resulting in folds in individual parts, resulting in plate wear.
(4) There are hard spots on the surface of the water roller, such as ink fixed on it, etc., cleaning the water roller.
(5) Most of the water glue on the surface of the water roller has fallen off. Replace the water glue.

2. There is a relative shift between the inking roller and the printing plate. Refer to "1" for the cause and troubleshooting of the fault.

3. The surface of the printing plate is uneven. The pressure in the protruding place is large, and it is the easiest to be worn. Replace the printing plate and choose a plate with better flatness (surface unevenness? ± 0.02 mm).

4. Uneven pads or loose stools under the printing plate will make the corresponding position on the printing plate wear faster. Replace the gasket.

5. If the plate cylinder is dirty or jumps more than required, it will also cause plate wear. Keep the printing plate clean, and wipe it off in time if it is off; check whether the runout of the printing plate cylinder meets the requirements. If the allowable value is exceeded, the cause should be found in time and eliminated.

6. The plate roll after installing the plate does not match the ideal plate cylinder diameter, so that the tangential speed of the contact surface is not equal, resulting in plate wear. Reselect the lining of the rollers to make their surface linear velocity as consistent as possible.

7. The beating of the rubber cylinder itself causes the plate to wear. Check the wear condition of the bushing on both sides, and if it exceeds the allowable value, it should be corrected in time.
8. The unevenness of the blanket makes the plate wear faster. Replace the blanket.

9. The diameter of the rubber roller Shangbao Village does not match the ideal diameter, which will also cause the plate to wear. The solution is the same as "5".

10. Printing pressure greater than the standard pressure will accelerate the wear of the printing plate. Reduce printing pressure.

11. The high viscosity of the ink will also cause plate wear. Reduce the viscosity of the ink.

12. The stickiness of the blanket will also cause the plate to wear. Replace the blanket.

13. The vibration of the machine causes the plate to wear. Choose appropriate machine speed, use small printing pressure and other measures to reduce machine vibration.
7.9.8 Dot slippage (or imprint deformation)

Dot slip refers to the deformation of the dots on the printed product exceeds the normal requirements. In fact, if any printed product is measured with a ruler, it will be found that it does not match the length of the print on the plate. The cause of dot slippage is similar to the cause of plate wear, and its elimination method is basically the same. However, after the outlet is transferred from the printing plate to the blanket, the transfer from the blanket to the paper is also required. This last step of transfer also has the problem of dot slip. This slippage is related to the contact condition of the impression cylinder and the blanket, and the troubleshooting method can be referred to the above method.

7.9.9 Dirty

Smudge is when the surface of the printed sheet interferes with some parts on the machine during the movement.

1. The pressure between the pickup roller and the pressure roller is too great. Because the pressure between them is too great, the contour of the platen wheel presses on the front of the printed sheet, and the anilox lines or horizontal folds on the receiving roller press on the back of the printed sheet. Because they are driven by friction, there is relative sliding between them and the printed sheet, so that the front or back of the printed sheet is smudged. Reduce the pressure of the pressure roller.

2. There is too much pressure between the grid tape on the cardboard and the pressure roller. Therefore, there may be a slight relative slippage between the pressure roller, paper, paper feeding belt and paper feeding board, so that the front or back of the printed matter will win. Tighten the paper feeding belt to reduce the pressure of the paper pressing roller. In addition, the brushes and other components on the cardboard should be adjusted properly to avoid smearing the front of the printed sheet.

3. The regulation pressure plate was raised too late. Because the filming is too late, when the printed sheet moves forward, there is friction between the printed sheet surface and the rule plate and gauge plate, which makes the printed surface win. Adjust the pull time of the side gauge to make it lift earlier.

4. Give it to the surface of the paper when you want to return. The timing of the pre-regulation is incorrect, readjust. The front gauge cap is too high, reduce the height of the front gauge cap.
5. When passing the paper back, it rubs against the surface of the paper. The paper pressure roller is not installed, which makes the paper curl up too much; the paper supporting mechanism above the delivery tooth is not flexible; the paper is too thick to be bent, so replace the paper.

6. The surface of the front transfer roller and the back transfer paper is dirty.

(1) Anti-rubbing cloth has no effect of anti-rubbing. Anti-rubbing cloth mainly uses the elasticity of its surface to achieve anti-rubbing victory. Once it loses its elasticity, it will not play the role of anti-rubbing. Rub the dirty cloth.

(2) If the anti-rubbing cloth is too tight or too loose, it will not play the role of anti-rubbing and reinstall.

(3) Too much ink and impurities on the surface of the anti-rubbing cloth make it form a slight relative slip with the surface of the printed product, which causes the surface of the printed product to be dirty.

7. The printed sheet moves along the cylinder row of teeth and will also chase its own face to win. Check the bite force in the row of teeth, reduce the viscosity of the ink and reduce the printing pressure.

8. The printed sheet rubs on the surface of the take-up roller. When the printed sheet is on the take-up roller, the thickness of the ink is the largest, so it is also the most easily smeared. Therefore, the printing pressure of the last group should be made as low as possible, so as to reduce the possibility of relative slippage of the printed sheet on the receiving cylinder.

9. The anti-rubbing mechanism does not play the role of preventing dirt. The anti-rubbing mechanism of the paper collecting part generally uses an anti-rubbing cloth belt or an anti-rubbing gas path. The function of the anti-rubbing cloth belt is similar to that of the anti-rubbing cloth, and the causes and troubleshooting methods of the faults are also similar. In theory, it is best to keep the paper suspended in the air at the receiving position, so now more air channels are used to prevent smudging. Blow air under the printed sheet and use the pressure difference to float the paper. If the air path is not working well, it will cause the back to be dirty.

10. Smudge caused by paper leveler. The paper leveler itself is used to straighten the tail of the paper. However, when the paper intake is too large, the back side of the printed sheet will be in close contact with the paper leveler, which will cause the back side to be dirty. Therefore, it is not necessary to use flat paper for reverse printing Device.

11. Surface rubbing caused by the brake roller. The dirty principle is similar to that of a paper device, and the method of troubleshooting is also similar.

12. The paper leveling mechanism causes the surface of the printed sheet to be dirty. When the paper-aligning mechanism neatly prints the sheets, the printed sheets slide on the receiving pile a certain amount, so that the back of the printed matter is dirty. Correctly adjust the position of the paper alignment mechanism to minimize the impact on the printed sheet.

13. Sliding of printed sheets on the stack can also cause smudges on the surface. Therefore, the printed product should be kept still in the receiving pile, and do not turn over by hand.

14. The possibility that other belts cause smudging. Each part of the route that the printed sheet passes in the printing process should be in a normal working state, but some parts are loose or improperly installed and deviate from the normal position, which may cause surface smear. Therefore, when encountering a dirty fault, you should find the cause carefully.

7.9.10 Sticky

That is, the two upper and lower printed sheets are stuck together. The essential reason for the sticky dirt is that the ink is not completely dried. Therefore, how to quickly dry the printed sheets is the fundamental measure to solve the sticky dirt.

1. Use quick-drying ink. Especially in multi-color printing, the quick-drying performance of the ink is particularly important. If the ink drying is found to be too slow, a small amount of desiccant can be added.

2. Use dampening treatment with a pH value close to 7. The lower the pH value, the longer the drying time of the ink, and the concentration of fountain solution should be reduced.

3. Increase the amount of powder sprayed. The larger the amount of powder sprayed, the larger the area between the printed sheets, so that the ink can have a long enough drying time.
4. Ensure the proper temperature. The higher the temperature, the faster the ink oxidizes the conjunctiva.

5. Improve ventilation performance. The better the ventilation, the faster the ink will dry. However, it should be noted that this cannot be done for semi-finished products. In addition, because the ink generates heat when it oxidizes the conjunctiva, ventilation is conducive to heat dissipation.

6. The suction volume of the brake roller should not be too large. There should be a certain amount of air between the printed sheets to prevent the vacuum state of the printed sheets.

7. The printed sheets should not be stacked too high. Too high. Because the paper is too heavy, it may cause the lower paper to stick together.

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