"Offset bars" (hereinafter abbreviated) is a relatively common quality problem in offset printing. When encountering the fault of the product in actual production, they all feel intractable and difficult to solve. This is because the production of the bar is often caused by a variety of factors, and the cause is more complicated. Therefore, for many years, many technicians and operators have been constantly researching and exploring how to quickly and accurately determine and find out the reasons for the emergence of bars, and quickly eliminate them. This article combines his many years of experience in corporate work practice, a cursory analysis of the causes of the emergence of the point on the sheetfed offset press, and at the same time, he discusses various points of identification, search, and determination of the origin of the bar, and discusses with peers.
First, the definition and classification of bars 1. The definition of bars:
The so-called "means" refers to the occurrence of irregular changes in the thickness of the dot or ink film during printing, and the streak of different shades of ink formed parallel to the axis of the drum. It is due to the influence of certain factors, so there is a slight slip between the rollers, between the platen roller and the plate cylinder, and between the plate cylinder and the paper. During the ink transfer process, this tiny Slip changes the ink film thickness or dot shape and size, resulting in a stripe ink change.
2. The classification of bars:
(1) According to the appearance characteristics, the bars can be divided into two types: ink sticks and water bars.
The ink bar: The irregular expansion of the outlets, the deformations are elongated, and the ink is increased, forming a noticeable deep streak on the layout (also called ink sticks).
The water bar: irregularly shrinking outlets, ink dodge, constitute a significant shallow streak (also known as white bars).
(2) According to the causes, the bars can be divided into four types: roller bars, gear bars, vibrating bars and other bars.
Roller bars: Due to the unreasonable design of the uniform ink part, the accuracy of the rubber roller is not enough and the adjustment is not proper, causing slight slippage between the rubber roller and the printing plate or disturbing the normal ink transfer, which causes the printing density to change and produce rubber roller bars.
Gear Lever: Each roller of the offset printing press and the driving gears of the even ink and wet parts have various errors such as tooth shape, inter-tooth and tooth surface smoothness. Shaking occurs in the meshing process, which can not guarantee smooth operation and produce gear bars.
Vibrating lever: Due to the offset printing machine, there is a roller gap, the impact of the opening and closing of the gripper, the reciprocating motion and the impact vibration caused by the inertia of the cam linkage mechanism, and the transmission components with the gap and many other unbalanced factors. The transfer site generates relative slip due to chatter, creating a vibrating bar.
Others: Since the offset printing process is a complex and complex process that combines mechanical action with physical and chemical reactions. The bars, inks, printing plates, blankets, liners, papers, etc. that are involved in the printing process are classified as other bars if a certain factor is processed or improperly selected. Due to space limitations, this article does not analyze such bars.
Second, the cause of the cause of the analysis of the production process of the bar, there are sudden, but also gradually revealed. As far as the offset press itself is concerned, there are many reasons for causing it. This article will be summarized as three aspects of improper operation adjustment, mechanical problems and design issues for analysis.
1. Improper operation adjustment (1) Incorrect adjustment of ink roller pressure. Ink roller and layout pressure is too large. When the ink roller contacts the plate roller, the ink roller impacts the edge of the plate, the ink roller will vibrate on the plate, and the line speed will change instantaneously. The ink film is disturbed (as shown in Fig. 1(a)). The ink film at point A is disturbed and transferred to A' on the plate to form an ink bar, which may appear again at A" (A'A" arc length is the circumference of the inking roller).
Also in FIG. 1(b), the ink film at B may also be disturbed and transferred to the printing plates B', B" to form a bar (B'B" arc length equal to the circumference of the ink roller).
Although in order to avoid the occurrence of ink bars in the nip due to the vibration of the rubber roller, the plate cylinder is advanced by about 70mm in the design, but since a string of ink rollers is pressed against the two ink rollers, when the second ink roller jumps up, In addition, the tandem roller is topped up, and when the ink dripping roller falls, the pulsating roller also affects the first ink roller. At this time, the first ink roller is already inside the graphic, so it is generated. As shown in Fig. 1(c), a sheet-fed offset press generally has four inking rollers and two lower ink rollers (as shown in Fig. 1(d)), thus forming more than one tap-off bar. In addition, because the 3, 4 ink rollers not only play an ink role on the printing plate, but also play a role in collecting ink. The existence of the above phenomenon is the easiest cause of the lever, so it should be precisely adjusted.
Ink roller with string ink roller pressure is too large. Since the ink roller is rotated by the friction of the plate cylinder and the ink roller, the pressure between the ink roller and the ink roller is too large, so that the ink roller depends on the ink roller too much, and the friction on both sides of the ink roller is not equal. There may be frictional slippage on the surface of the printing plate, which produces a bar.
In the same way, when the pressure between the water roller and the plate roller and the water roller is too heavy, it will affect the uniform transfer of the water film and cause white bars.
(2) Roller lining excessive. As the pressure on the upper or lower pressure is too small, increase the drum lining, so that the drum lining over, increase the roller in the rolling of the micro-speed difference and trace friction. From the microscopic point of view, the linear speed of the drum is not absolutely equal due to the influence of various factors. It is only a relative balance, and a certain degree of micro speed difference is always present. Overfilling the blanket results in excessive friction under the effect of the blanket, and there is intermittent wear and imprinting of the plate layout, resulting in a clubbing.
(3) The blanket and impression cylinders are under too much pressure. The offset press is printed by three rollers and the working face of the roller has a certain pressing force. When the drum runs to neutral, the load will change (as shown in Figure 2): When point B contacts out of neutral, an impact occurs at point A. Because there are tiny gaps in the roller bearing and the elastic deformation of the roller and bearing, the roller will produce slight displacement and cause vibration. The pressure between the blanket roller and the impression roller is too large, it will aggravate the vibration, and it will not roll. In the case of pillow presses, this kind of vibration is not eliminated and produces a bar.
(4) The blanket is loose. When the blanket is too loose, due to the rolling action, the blanket slides back and forth on the surface of the drum. This relative movement produces one or more bars.
(5) The layout is too watery. In the printing process of the offset printing press, too much water on the plate will affect the uniform transfer of the ink film, making the printing density too low and aggravating the appearance of the bar. Therefore, for offset printing, under the premise of ensuring that the layout is not dirty, the amount of water supply should be controlled within the smallest possible range, and the amount of water supply and ink supply should be in a relatively stable state. A well-controlled ink balance is an important part of improving print quality.
2. Mechanical problems (1) The roller gear is worn and the precision is reduced.
The accuracy of offset roller gears is very high, and it is almost close to the aircraft's aviation gear. In order to make the center distance can be adjusted in a small amount (to accommodate a certain range, printing different thickness of paper), to minimize the increase of the backlash To ensure smooth operation, most offset presses use involute gears and toothed pressure angles of 14.5° to 15°. In general, due to the slight periodic speed change between the gears caused by the gear transmission, it is not sufficient to display the bars. However, when the gear tooth surface is excessively worn or the individual tooth is damaged, and there is foreign matter in the tooth groove, the gear cannot roll at a uniform speed according to the meshing line. Shaking occurs during operation, which can cause the roller speeds to be mutually inconsistent, resulting in relative slippage between the transfer surfaces. Cyclic gears. Gears are characterized by the spacing between the bars T = π Ms (Ms is the face of the gear module), the shape of the board is covered by the entire layout, if it is a few teeth or foreign objects in the tooth groove, then produce a few correspondence The position of the tap.
(2) The bushing sleeve wears badly or the skewer gear wears excessively. The sleeve clearance is enlarged, and the vibration generated by the gear mesh is transmitted to the ink string roller, which affects the normal transmission of the ink film and causes the emergence of the lever. Due to wear of the shaft head mating surface or debris, the three ink fountain rollers are installed with different concentricity, which causes the pulsation of the ink string to affect the transfer of the ink film and generate a lever.
(3) Roller bearing wear. Roller bearing wear causes various bars, depending on the bearing position. When the load is not normal, poor lubrication or debris immersed into the bearing wear caused by improper bearing clearance, the drum load changes, resulting in vibration caused by the lever.
(4) Ink roller bouncing and end play. Ink roller outer aging, uneven, mandrel bending, shaft seat lock wear and other factors will cause ink roller beat, resulting in the emergence of bars. Abrasion of the ink roller shaft seat and excessive error in the length of the bearing step produce end play. The ink roller will generate excessive axial movement under the action of the ink roller, affecting the transfer of the ink film and causing the lever.
(5) Vibration and impact of the drive system load. The structure of the sheet-fed offset press is complex, and there are quite a lot of impact and vibration parts. For example, the clutch of the drum, the roll gap into the roll, various types of reciprocating paper-feeding mechanisms and cam-driven mechanisms, and paper-handling mechanisms for opening and closing the paper, The ink roller is oscillating and the water transfer roller is oscillating. Due to the vibration and impact of these mechanisms, the uniform rolling between the drums will be destroyed, resulting in instantaneous speed changes and relative slip between the drums to form a bar. Especially when the main motor belt is loosened, these shocks and vibrations worsen the operation of the offset press. There are defects in design and manufacturing, and there are also factors that regulate improper use.
(6) Excessive wear of transmission components. Various types of parts of the transmission system such as transmission belt wear and slip, wear and deformation of various key links, wear and slip of couplings, wear of cams, gears, and bearing parts. Excessive wear of these parts affects offset press to varying degrees. The balance of operation and the possibility and severity of the emergence of bars.
3. Design issues The appearance of the offset press depends not only on the structure of the core part of the drum and its bearings, but also on whether the print cylinder rests on the pillow, but also on the structure and rigidity of the machine wall plate, frame, and chassis, as well as the water supply, There are many factors such as the structure and reliability of the inking components. This article only briefly describes the defects of the occipital and the underlying infusion system.
(1) Pillow and No Pillow There are two kinds of printing methods for sheet-fed offset presses: one is the printing method of contact with the drum shoulders, namely the printing method of the pillow. The use of an offset press that does not contact the shoulder iron may cause vibration of the drum during high speed operation due to the impact of the idler and reciprocating motion of the drum and the presence of the intermittent motion mechanism, the bearing clearance of the drum, and the backlash of the gear. Easy to produce bars. For offset presses with pillows, the shoulder iron diameter is equal to the pitch circle of the gears. The roller gears are always in precise meshing operation. The center distance of each printing roller is fixed, the tooth gap is not enlarged, and the drum shoulders are iron. The contact pressure is greater than the printing pressure of the drum, so during the operation of the drum, the impact of bearing clearance, work surface and neutral shift will not affect the printing quality. The vibrations caused by the rollers are eliminated, especially in the case of bearing and roller gear wear. Therefore, it can be said that the offset printing machine can effectively prevent the emergence of the lever and ensure the quality of printed products.
(2) The defects of the lower ink system, two-color satellite-type five-roller arrangement, and BB-type four-roller arrangement, offset presses, and the structure of the upper ink system and the lower ink system are different. Figure (3) shows the arrangement of the J2205 two-color offset press.
The first color ink roller is directly above the plate cylinder, while the second color four ink rollers, two directly below the plate cylinder, the other two in the lower position of the plate cylinder. The ink roller of the first color group, the second color group and the pressure of the printing plate surface are obtained by the pressure of the two compression springs, and the compression springs used in the two color groups are the same. Due to the influence of the gravity of the ink roller, the pressure of the two color groups on the layout pressure varies greatly when the compression spring pressure is the same. Therefore, if the second color group is debugged using the same tuning method as the first color group, it is very easy to cause malfunctions, and there are network dots, ink film unevenness and white bars. Therefore, the pressure adjustment of the second color group should be larger than that of the first group, or the pressure spring can be replaced with a spring with a larger elastic force. In addition, the entire structure of the second color group of the J2205 offset press is not a single unit with the main roller unit, and it is a removable type. Therefore, the vibration of the second color group is large, and it is easy to cause the appearance of a lever.
Third, the search and exclusion points
First, the definition and classification of bars 1. The definition of bars:
The so-called "means" refers to the occurrence of irregular changes in the thickness of the dot or ink film during printing, and the streak of different shades of ink formed parallel to the axis of the drum. It is due to the influence of certain factors, so there is a slight slip between the rollers, between the platen roller and the plate cylinder, and between the plate cylinder and the paper. During the ink transfer process, this tiny Slip changes the ink film thickness or dot shape and size, resulting in a stripe ink change.
2. The classification of bars:
(1) According to the appearance characteristics, the bars can be divided into two types: ink sticks and water bars.
The ink bar: The irregular expansion of the outlets, the deformations are elongated, and the ink is increased, forming a noticeable deep streak on the layout (also called ink sticks).
The water bar: irregularly shrinking outlets, ink dodge, constitute a significant shallow streak (also known as white bars).
(2) According to the causes, the bars can be divided into four types: roller bars, gear bars, vibrating bars and other bars.
Roller bars: Due to the unreasonable design of the uniform ink part, the accuracy of the rubber roller is not enough and the adjustment is not proper, causing slight slippage between the rubber roller and the printing plate or disturbing the normal ink transfer, which causes the printing density to change and produce rubber roller bars.
Gear Lever: Each roller of the offset printing press and the driving gears of the even ink and wet parts have various errors such as tooth shape, inter-tooth and tooth surface smoothness. Shaking occurs in the meshing process, which can not guarantee smooth operation and produce gear bars.
Vibrating lever: Due to the offset printing machine, there is a roller gap, the impact of the opening and closing of the gripper, the reciprocating motion and the impact vibration caused by the inertia of the cam linkage mechanism, and the transmission components with the gap and many other unbalanced factors. The transfer site generates relative slip due to chatter, creating a vibrating bar.
Others: Since the offset printing process is a complex and complex process that combines mechanical action with physical and chemical reactions. The bars, inks, printing plates, blankets, liners, papers, etc. that are involved in the printing process are classified as other bars if a certain factor is processed or improperly selected. Due to space limitations, this article does not analyze such bars.
Second, the cause of the cause of the analysis of the production process of the bar, there are sudden, but also gradually revealed. As far as the offset press itself is concerned, there are many reasons for causing it. This article will be summarized as three aspects of improper operation adjustment, mechanical problems and design issues for analysis.
1. Improper operation adjustment (1) Incorrect adjustment of ink roller pressure. Ink roller and layout pressure is too large. When the ink roller contacts the plate roller, the ink roller impacts the edge of the plate, the ink roller will vibrate on the plate, and the line speed will change instantaneously. The ink film is disturbed (as shown in Fig. 1(a)). The ink film at point A is disturbed and transferred to A' on the plate to form an ink bar, which may appear again at A" (A'A" arc length is the circumference of the inking roller).
Also in FIG. 1(b), the ink film at B may also be disturbed and transferred to the printing plates B', B" to form a bar (B'B" arc length equal to the circumference of the ink roller).
Although in order to avoid the occurrence of ink bars in the nip due to the vibration of the rubber roller, the plate cylinder is advanced by about 70mm in the design, but since a string of ink rollers is pressed against the two ink rollers, when the second ink roller jumps up, In addition, the tandem roller is topped up, and when the ink dripping roller falls, the pulsating roller also affects the first ink roller. At this time, the first ink roller is already inside the graphic, so it is generated. As shown in Fig. 1(c), a sheet-fed offset press generally has four inking rollers and two lower ink rollers (as shown in Fig. 1(d)), thus forming more than one tap-off bar. In addition, because the 3, 4 ink rollers not only play an ink role on the printing plate, but also play a role in collecting ink. The existence of the above phenomenon is the easiest cause of the lever, so it should be precisely adjusted.
Ink roller with string ink roller pressure is too large. Since the ink roller is rotated by the friction of the plate cylinder and the ink roller, the pressure between the ink roller and the ink roller is too large, so that the ink roller depends on the ink roller too much, and the friction on both sides of the ink roller is not equal. There may be frictional slippage on the surface of the printing plate, which produces a bar.
In the same way, when the pressure between the water roller and the plate roller and the water roller is too heavy, it will affect the uniform transfer of the water film and cause white bars.
(2) Roller lining excessive. As the pressure on the upper or lower pressure is too small, increase the drum lining, so that the drum lining over, increase the roller in the rolling of the micro-speed difference and trace friction. From the microscopic point of view, the linear speed of the drum is not absolutely equal due to the influence of various factors. It is only a relative balance, and a certain degree of micro speed difference is always present. Overfilling the blanket results in excessive friction under the effect of the blanket, and there is intermittent wear and imprinting of the plate layout, resulting in a clubbing.
(3) The blanket and impression cylinders are under too much pressure. The offset press is printed by three rollers and the working face of the roller has a certain pressing force. When the drum runs to neutral, the load will change (as shown in Figure 2): When point B contacts out of neutral, an impact occurs at point A. Because there are tiny gaps in the roller bearing and the elastic deformation of the roller and bearing, the roller will produce slight displacement and cause vibration. The pressure between the blanket roller and the impression roller is too large, it will aggravate the vibration, and it will not roll. In the case of pillow presses, this kind of vibration is not eliminated and produces a bar.
(4) The blanket is loose. When the blanket is too loose, due to the rolling action, the blanket slides back and forth on the surface of the drum. This relative movement produces one or more bars.
(5) The layout is too watery. In the printing process of the offset printing press, too much water on the plate will affect the uniform transfer of the ink film, making the printing density too low and aggravating the appearance of the bar. Therefore, for offset printing, under the premise of ensuring that the layout is not dirty, the amount of water supply should be controlled within the smallest possible range, and the amount of water supply and ink supply should be in a relatively stable state. A well-controlled ink balance is an important part of improving print quality.
2. Mechanical problems (1) The roller gear is worn and the precision is reduced.
The accuracy of offset roller gears is very high, and it is almost close to the aircraft's aviation gear. In order to make the center distance can be adjusted in a small amount (to accommodate a certain range, printing different thickness of paper), to minimize the increase of the backlash To ensure smooth operation, most offset presses use involute gears and toothed pressure angles of 14.5° to 15°. In general, due to the slight periodic speed change between the gears caused by the gear transmission, it is not sufficient to display the bars. However, when the gear tooth surface is excessively worn or the individual tooth is damaged, and there is foreign matter in the tooth groove, the gear cannot roll at a uniform speed according to the meshing line. Shaking occurs during operation, which can cause the roller speeds to be mutually inconsistent, resulting in relative slippage between the transfer surfaces. Cyclic gears. Gears are characterized by the spacing between the bars T = π Ms (Ms is the face of the gear module), the shape of the board is covered by the entire layout, if it is a few teeth or foreign objects in the tooth groove, then produce a few correspondence The position of the tap.
(2) The bushing sleeve wears badly or the skewer gear wears excessively. The sleeve clearance is enlarged, and the vibration generated by the gear mesh is transmitted to the ink string roller, which affects the normal transmission of the ink film and causes the emergence of the lever. Due to wear of the shaft head mating surface or debris, the three ink fountain rollers are installed with different concentricity, which causes the pulsation of the ink string to affect the transfer of the ink film and generate a lever.
(3) Roller bearing wear. Roller bearing wear causes various bars, depending on the bearing position. When the load is not normal, poor lubrication or debris immersed into the bearing wear caused by improper bearing clearance, the drum load changes, resulting in vibration caused by the lever.
(4) Ink roller bouncing and end play. Ink roller outer aging, uneven, mandrel bending, shaft seat lock wear and other factors will cause ink roller beat, resulting in the emergence of bars. Abrasion of the ink roller shaft seat and excessive error in the length of the bearing step produce end play. The ink roller will generate excessive axial movement under the action of the ink roller, affecting the transfer of the ink film and causing the lever.
(5) Vibration and impact of the drive system load. The structure of the sheet-fed offset press is complex, and there are quite a lot of impact and vibration parts. For example, the clutch of the drum, the roll gap into the roll, various types of reciprocating paper-feeding mechanisms and cam-driven mechanisms, and paper-handling mechanisms for opening and closing the paper, The ink roller is oscillating and the water transfer roller is oscillating. Due to the vibration and impact of these mechanisms, the uniform rolling between the drums will be destroyed, resulting in instantaneous speed changes and relative slip between the drums to form a bar. Especially when the main motor belt is loosened, these shocks and vibrations worsen the operation of the offset press. There are defects in design and manufacturing, and there are also factors that regulate improper use.
(6) Excessive wear of transmission components. Various types of parts of the transmission system such as transmission belt wear and slip, wear and deformation of various key links, wear and slip of couplings, wear of cams, gears, and bearing parts. Excessive wear of these parts affects offset press to varying degrees. The balance of operation and the possibility and severity of the emergence of bars.
3. Design issues The appearance of the offset press depends not only on the structure of the core part of the drum and its bearings, but also on whether the print cylinder rests on the pillow, but also on the structure and rigidity of the machine wall plate, frame, and chassis, as well as the water supply, There are many factors such as the structure and reliability of the inking components. This article only briefly describes the defects of the occipital and the underlying infusion system.
(1) Pillow and No Pillow There are two kinds of printing methods for sheet-fed offset presses: one is the printing method of contact with the drum shoulders, namely the printing method of the pillow. The use of an offset press that does not contact the shoulder iron may cause vibration of the drum during high speed operation due to the impact of the idler and reciprocating motion of the drum and the presence of the intermittent motion mechanism, the bearing clearance of the drum, and the backlash of the gear. Easy to produce bars. For offset presses with pillows, the shoulder iron diameter is equal to the pitch circle of the gears. The roller gears are always in precise meshing operation. The center distance of each printing roller is fixed, the tooth gap is not enlarged, and the drum shoulders are iron. The contact pressure is greater than the printing pressure of the drum, so during the operation of the drum, the impact of bearing clearance, work surface and neutral shift will not affect the printing quality. The vibrations caused by the rollers are eliminated, especially in the case of bearing and roller gear wear. Therefore, it can be said that the offset printing machine can effectively prevent the emergence of the lever and ensure the quality of printed products.
(2) The defects of the lower ink system, two-color satellite-type five-roller arrangement, and BB-type four-roller arrangement, offset presses, and the structure of the upper ink system and the lower ink system are different. Figure (3) shows the arrangement of the J2205 two-color offset press.
The first color ink roller is directly above the plate cylinder, while the second color four ink rollers, two directly below the plate cylinder, the other two in the lower position of the plate cylinder. The ink roller of the first color group, the second color group and the pressure of the printing plate surface are obtained by the pressure of the two compression springs, and the compression springs used in the two color groups are the same. Due to the influence of the gravity of the ink roller, the pressure of the two color groups on the layout pressure varies greatly when the compression spring pressure is the same. Therefore, if the second color group is debugged using the same tuning method as the first color group, it is very easy to cause malfunctions, and there are network dots, ink film unevenness and white bars. Therefore, the pressure adjustment of the second color group should be larger than that of the first group, or the pressure spring can be replaced with a spring with a larger elastic force. In addition, the entire structure of the second color group of the J2205 offset press is not a single unit with the main roller unit, and it is a removable type. Therefore, the vibration of the second color group is large, and it is easy to cause the appearance of a lever.
Third, the search and exclusion points
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