(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected)
In printing, due to improper adjustment of the machine, insufficient processing and use of raw materials and other reasons, many failures often occur. The occurrence of a fault phenomenon is sometimes caused by many different reasons; sometimes the same cause may cause different faults. Therefore, this causes the complexity of the failure. To solve the fault well, we must find out the source of the fault. To correctly find or estimate the root cause of the fault, the operator must not only have a certain work experience, but also have a certain theoretical knowledge, and combine theory with specific practice, so that the problem can be quickly and correctly has been solved.
Any failure, if the source of the failure is not clear, the purposeless adjustment and correction will not only make the real failure unresolved, but will also cause other normal parts to fail, which further complicates the problem. Therefore, we should pay special attention to this when correcting malfunctions, and strive to avoid such bad working habits.
There are many printing faults caused by paper feeding. In order to make it easier for the operator to analyze, judge and eliminate the faults, and master the skills of paper feeding operation, the common faults are introduced as follows:
One, two or more sheets
1. The suction power of the paper separation nozzle is too large, and the following sheets of paper are simultaneously sucked up. This failure is caused by the following situations:
(I) The inspiratory volume is adjusted too much;
(2) The rubber band is too large;
(3) The separation nozzle is too close to the paper surface;
(4) The paper is too thin.
Solution: â‘ reduce the air volume; â‘¡ replace the small rubber ring, or cut the rubber ring small, and the rubber ring on the paper suction nozzle can be removed when the paper is thin; â‘¢ adjust the length of the paper pressure foot to increase the paper stack The distance from the paper separation nozzle, or adjust the eccentricity above the paper separation nozzle rod to increase the distance from the paper stacking surface; â‘£ Press the paper blocking brush down.
2. The separation nozzle is too close to the edge of the paper, or even beyond the edge of the paper, or the paper stacking is uneven, and the paper cutting size is inconsistent, which causes multiple sheets of paper to be sucked up by the separation nozzle at the same time.
Solution: The former increases the distance between the separation nozzle and the edge of the paper by adjusting the front and rear positions of the separator, and the latter should restack the paper. For unevenly cut paper, try to make the trailing edge tidy when stacking; if the size difference is large and affects the accurate positioning, the paper should be changed or printed separately.
3. The height of the paper stack exceeds the allowable height of the paper stack. The height of the general paper stack should be about 5mm lower than that of the paper stack. Due to reasons such as paper curling or improper adjustment of the stack height, the stack height of the stack exceeds the allowable range, and double or multiple sheets of paper will be brought into the paper feeding table.
Solution: â‘ When the paper is upturned, the paper can be knocked back; â‘¡The double sheets caused by the stack of paper being too high can be inserted into the wooden wedge for control. Offset presses such as J2203 and J2108 can also be solved by reducing the height of the separator.
4. The trailing tip of the paper is raised upwards. When the air flow from the loose paper nozzle touches the edge of the paper, the upturned edge of the paper has an arc. When the arc meets this arc, it is divided into two parts. A part of the airflow turns downwards, and the paper cannot be separated, making the paper blocking brush useless. At the same time, the upturned paper edge is generally elastic. When the paper presser presses the paper, it shrinks, and when it is lifted, it lifts up again, causing double sheets, multiple sheets, and even paper to enter the paper feed one after another. station.
Solution: â‘ Remove the paper and carry out reverse knocking treatment; â‘¡ Adjust the angle of the bottom surface of the separation nozzle to keep it parallel to the paper stacking surface.
5. Too little paper pressure foot or paper brush to reach the edge of the paper. If there is too little paper pressure on the paper presser foot, the paper stack will automatically rise and become unstable, making it unable to hold down the paper below; the paper blocking brush is too high or the paper edge is too little, and the effect of brushing and brushing the paper below is lost.
Solution: If the separation nozzle is on the edge of the paper, the whole separator should be moved forward; if the edge of the separation nozzle is about 5mm away from the edge of the paper, you need to adjust the paper pressure foot or the paper blocking brush to Standard working position (as mentioned above).
6. The paper is not loose and sticky.
(1) Adhesion of white paper cutting incision.
(2) When printing semi-finished products, the previous color is full-plate solid or multi-color overlap. Due to the excessive thickness of the ink layer, the paper will stick up and down; water stains and ink stains are also prone to stick up and down.
Solution: â‘ Before printing, the white paper should be slightly twisted, skimmed, shaken, and collided. â‘¡The semi-finished product is stuck due to the excessive thickness of the ink layer, and a small stack and a small stack should be shaken when loading the paper. â‘¢ Due to the small number of semi-finished products, the ink of the previous color is not dry and the adhesion occurs in the next color printing. When twisting the paper, it should be twisted several times repeatedly to allow enough air to enter between the paper and promote the ink to dry. The paper stack on the machine should be piled a little less, so as to avoid the adhesion of the paper below due to heavy pressure.
7. The paper has static electricity. When the surfaces of two objects rub against each other, the electrons on the surface of one object will be transferred to the surface of the other object. When these two objects in contact are separated, because many electrons cannot return to the atoms they were originally in, this creates an inequality in charge. The paper is an insulator and has poor conductivity, especially in dry air, it is difficult to replenish the lost electrons. When the charge is stabilized in the formed area, static electricity is generated. Electrostatically charged paper can tightly attract another piece of paper or other objects in contact with it, causing difficulties in conveying paper during printing, causing problems such as skew, double sheets, multiple sheets, and uneven paper collection. When the static electricity is large, it will even stand still on the surface of the paper conveying table, making the production unable to proceed normally.
The solution is a workshop with constant humidity and constant temperature control, and the relative humidity between the workshop and the drying room should be properly increased to keep the paper with a certain moisture content.
For workshops without constant humidity and constant temperature devices, some water can be sprinkled on the floor of the workshop. This treatment method has a certain effect on reducing the static electricity of paper, but improper treatment will cause the relative humidity of the workshop to be too high, causing the paper to expand and contract, resulting in the disadvantages of wrinkling and overprinting, so it needs to be used with caution.
2. Vacancy
1. The distance between the paper stack and the paper separation nozzle is too large. The distance between the bottom surface and the paper stack surface when the paper separation nozzle is at the lowest position is about 6-8 mm for thin paper and 2-3 mm for thick paper. When the distance between the paper separation nozzle and the paper stacking surface is too large, if the vacuum degree of the air pump is not enough, it is easy to produce empty sheets.
Solution: â‘ shorten the length of the paper pressure foot rod, so that the distance between the paper separation nozzle and the paper stack surface is reduced; â‘¡ adjust the eccentricity above the paper separation nozzle rod, and reduce the height of the paper separation nozzle.
2. The paper trailing edge curls downwards. Because the paper trailing edge curls downward, the airflow blown by the loose paper blower cannot easily enter the paper gap and cannot be separated from the paper. At the same time, when the paper-separating nozzle comes down to suck the paper, the paper surface rolls down, and the air leakage phenomenon of the nozzle is easy to occur, and the paper cannot be sucked up.
Solution: â‘ Adjust the adjusting screw on the separation cylinder to change the angle of the bottom surface of the separation nozzle to keep it parallel to the paper surface; â‘¡Move the paper down and knock on the paper.
3. The distance between the paper suction nozzle and the paper stacking surface is too large.
Solution: Adjust the height of the paper suction nozzle. When the paper suction nozzle is at the lowest position, the distance between the bottom surface and the paper stacking surface: SZ201 type paper conveying device is about 1.5mm; SZ206 type paper feeding device is about 5mm. The height of the paper suction nozzle can be adjusted individually or as a whole. (As mentioned above)
4. The paper blocking brush is too low or too far into the paper stack. The application of the paper blocking brush should be closely coordinated with the loose paper blowing nozzle. When the air volume of the loose paper blowing nozzle is normal, it can blow the edge of the paper and raise it by about 5mm. This is also the distance that the paper blocking brush should leave the stack . When the paper separating nozzle comes down to suck the paper, it just touches the paper surface being blown up, or 1-2 mm higher than the paper surface. The paper blocking brush is pressed too low, so that the paper cannot be blown up, which increases the distance between the paper separation nozzle and the paper surface, resulting in empty sheets; sometimes the paper blocking brush extends too much, although the paper separation nozzle can It sucks the paper but also bounces off the brush, causing empty sheets.
Solution: If the paper-blocking brush is moderately elastic, adjust its height and the distance into the stack to the data described above.
5. Blockage of the gas path Most of the blockage of the gas path occurs in the suction system. The clogging comes from paper wool and dust, and most of them are blocked within a section of the suction nozzle pipe and the control piston. Because the piston has oil dirt, paper wool and dust are attracted by the oil dirt, and it accumulates more and more, and finally the suction air path is blocked, resulting in insufficient suction and empty.
Solution: Clean the gas path and control piston regularly, and the machine printing rough paper should be cleaned once a week.
6. Insufficient suction. Due to the accumulation of ink on the suction nozzle and the rubber ring or the wear and tear of the rubber ring, air leakage during paper suction causes insufficient suction and also causes empty sheets. The paper nozzle is particularly serious.
Solution: Strengthen the inspection and do the cleaning work, especially if the previous color is printed on the ground, you should pay special attention to the next color.
3. Paper skew
1. Paper skew caused by the separator:
(1) Two suction nozzles or two paper nozzles have different suction power, especially the working positions of the two paper nozzles are inconsistent;
(2) The working positions of the paper blocking brushes on both sides are inconsistent;
(3) The paper is not loose and partially stuck;
(4) The paper has static electricity;
(5) The working positions of the two loose paper blow nozzles are inconsistent;
(6) A suction nozzle is blocked or leaking.
For the solution, please refer to the solutions for the double-sheet and blank sheet failures mentioned above.
2. The pressure of the pick-up wheel is inconsistent or the time of pressing is different, or the rotation of the roller is not flexible.
Solution: â‘ Adjust the pressure and pressing time of the two paper receiving wheels as described above; â‘¡ Scrub the roller with kerosene to make it rotate flexibly.
3. The tension of the belt is inconsistent. The tension and thickness of the belt are inconsistent, and the tension wheel is tightened, etc., which causes the belt speed to be inconsistent, causing the paper to be skewed.
Solution: â‘ The thickness of the four lines on the paperboard should be uniform, and the degree of tightness should be adjusted; â‘¡ If the tension wheel does not rotate, it can be scrubbed with kerosene and then lubricated with engine oil.
4. The weight of the pressure roller on the belt is inconsistent. If the position of the pressure roller is inaccurate or the rotation is not correct, the pressure of the pressure roller will be inconsistent.
Solution: â‘ Keep the paper pressing roller on the belt running smoothly, and often wipe the paper wool, dust and other dirt on the cardboard. â‘¡ The position of the paper pressing roller should be symmetrical on both sides, and the weight is appropriate.
5. The paper on the paperboard is broken, the paper safety bar and the billiard rack fall, etc. In general, the paperboard of the printing machine is lined with paper strips to prevent the corners of the paper from hitting the seam at the front and rear ends of the paperboard. When the leading edge of the paper touches the broken part of the pad paper, it will cause the paper to be skewed. The paper feed safety bar and the drop of the billiard rack also cause this kind of failure.
Solutions: â‘ Frequently check or replace the paper pads on the paper table; â‘¡ Eliminate the falling phenomenon of the paper safety bar and billiard ball rack.
6. The lifting track of the separation nozzle is worn. The separation of the paper by the paper separation nozzle depends on the up and down movement of the paper separation nozzle rod in the track and the cooperation of the air volume. In order to ensure the smooth separation of paper, the separation nozzle rod must be moved regularly under the control of the track. Therefore, if it is used for a long time, the track will have different degrees of wear. Long-term non-cleaning and no lubricating oil are the main reasons for rail wear. After abrasion, the nozzle rod will sway when it moves along the track, causing the separated paper to be skewed.
Solution: â‘ Normally lubricate the nozzle rod and the track regularly with lubricating oil and take preventive measures; â‘¡ Mount the track that has been severely worn in time to restore it to its original state.
7. The positioning of the cam of the delivery nozzle is inaccurate. The motions of the paper feeding nozzles of the currently used low-speed machine and J2201 two-color machine are controlled by two cams respectively. If the actions of the two cams are inconsistent, there will be a twisting phenomenon of the paper delivery nozzle, causing the paper to be skewed.
Solution: When the return nozzle of the delivery nozzle is in place and is at the lowest point, you can loosen the fixing screw and adjust the two cams to be consistent.
8. The paper pressure lever of the paper separation nozzle is too low. The paper pressing lever of the paper separation nozzle is adjusted too low or naturally loosened; sometimes the unevenness of the thickness of the printed paper on both sides or parts, the accumulation of ink on the semi-finished products, etc., and the unevenness of the paper stack appears. The trailing edge of the sheet of paper will be pressed by the pressing lever of the falling separation nozzle, which will cause resistance to the forward paper feeding, and the phenomenon of slow paper feeding and skew.
Solution: â‘ The uneven paper pile can be leveled with a wooden wedge or paper pad; â‘¡The paper lever of the paper separation nozzle should not be adjusted too low, (the adjustment position is as described above) to avoid falling Squeeze the paper stack.
4. Overprinting is not allowed
In the process of paper feeding, in addition to paper skew, which will cause overprinting of printed materials, the following reasons may also cause overprinting:
1. The paper feeding device feeds paper too fast or too long, but it is out of sync with the previous rules, which causes the paper to "walk over" or "underrun".
Solution: adjust the speed of the paper feeding device, the operation method is as described above.
2. The pressure of the pick-up roller is too light, which causes the paper to "run insufficiently".
Solution: Adjust the pressure of the roller to make it light, uniform and appropriate.
3. The paper conveyor belt is too loose to cause slippage, or the belt tensioner and fixed pulley lack oil and the rotation is not flexible, causing "inadequate walking".
Solution: â‘ Tighten the belt; â‘¡ Remove and wash the tension pulley and fixed pulley, and add oil to make it fully lubricated.
4. The position of the paper pressure roller on the paper feeding table is incorrect. The pressure is too light or too heavy, causing "inadequate walking" or "over heading".
Solution: â‘ Position the pinch roller accurately to make it accurately connected with each other; â‘¡ Twist or loosen the pressure spring to increase (or decrease) the pressure.
5. The paper is too thin and too soft, and the stress on the edge of the paper is insufficient, causing the edge of the paper to curl, causing the paper to "walk over" or "pull over".
Solution: Knock the paper bite edge and the specified position on the side to strengthen the paper edge stress.
6. The distance between the paper and the side gauge is too far or too close, which may cause "under-pulling" or "pulling too far."
Solution: Keep the distance of pulling paper 5-8mm.
Fifth, the stains caused by the pick-up wheel and the brush wheel are dirty
The main reason is that the former color has not yet dried out, and the latter color is then printed. The dirt caused by the pick-up wheel is easier to find because it has both the front and back sides; and the dirt caused by the brush wheel is on the back, so it is not easy to be found. Modern high-speed offset printing machines are overlapping paper feeds. When the teeth hold the paper, the paper advances nearly twice as fast as it advances on the paper table. There is high-speed friction between the two papers. Under the pressure of the brush wheel, the back of the paper is more frictional, causing the ink on the lower sheet to rub on the back of the upper sheet.
Solution: When the pick-up wheel is dirty, you can move the feed wheel to the blank spaces on both sides. In addition, the back inspection should be strengthened, and the brush wheel can be lightened. If it is a double-sided printing, the amount of dry oil should be increased appropriately to ensure that the blot is dry and prevent smudging.
Six, uneven paper
Uneven paper feeding means that the conveyed paper itself is uneven. Printing often affects normal paper feed and overprinting due to uneven paper. The causes and solutions of uneven paper feeding are as follows:
I. The moisture content of the paper is uneven. When this phenomenon occurs, it will cause the paper to curl, tight edges and other deformations, it will cause uneven feeding and affect overprinting.
Solution: adjust the humidity of the paper before printing to match the temperature and humidity of the printing workshop, and also reduce the sensitivity of the paper to moisture. In addition, it is necessary to strictly control the moisture of the printing surface during printing.
2. Partial ink layer accumulation is too thick.
Solution: You can use the paper pressure lever and paper pressure steel sheet to gently press the paper during feeding. In addition, do not increase the amount of ink arbitrarily during printing. For the ink with a large amount of ink, the final printing should be arranged.
3. Unevenness when printing thin paper or three-sheet paper. When printing thin paper or three-fold paper under 60g / m2, because the paper thin or three-fold paper is a narrow strip, it is not easy to control when feeding paper, and it is prone to uneven feeding.
Solution: â‘ When printing the above paper, firstly control the air volume. The loose paper nozzle is suitable for blowing up 5-8 sheets of paper on the surface of the stack; â‘¡ It can be solved by adjusting the angle of the paper pressing roller on the paper pressing frame, namely The angle of the front pinch roller is larger, and it has an outer "eight" shape. When the paper with the middle protrusion is forwarded, the convex hull is gradually flattened by the axial force generated by the outer "eight" pinch roller. . Practice has proved that this method has certain effect to solve the uneven feeding of thin paper or three-fold paper.
Seven, paper wrinkle arch (also known as "bow wrinkle", "fold", etc.)
1. The paper pressing foot is too blown. Because the paper pressing foot is blown too much, the paper bulges in the middle. If the bulging phenomenon cannot be eliminated during the paper feeding process, it will cause paper wrinkles. Especially for thinner paper, the bulging phenomenon is more difficult to eliminate.
Solution:
â‘ Reduce the blowing air volume of the paper pressing foot;
â‘¡When printing thin paper, the suction power of the suction nozzle should be appropriately reduced and the pressure of the paper pressing wheels, balls and brushes on the paper conveying table should also be reduced;
â‘¢ Properly lower the position of the paper feed safety bar and the front paper pressure piece.
2. Improper position of the paper pressing ball, paper pressing wheel or brush wheel or excessive pressure.
Solution:
â‘ Adjust the position of the paper ball and wheel.
â‘¡ Adjust the pressure of each paper ball and wheel.
â‘¢ When printing thin paper, the platen roller can be lifted properly.
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