After several decades of development, domestic R&D production of offset presses has been completed from open to closed, from low speed to high speed, and from single to multiple units. Regardless of the intrinsic quality, function, or appearance of the machine, there has been considerable progress. In particular, the development speed of the multi-color machine has been faster. Compared with foreign brands, the distance between technology and quality is rapidly shrinking. However, we still have to clearly see that there is still a considerable gap between the design and manufacture of domestic offset presses and foreign brands, and how we can quickly catch up with the development pace of offset press manufacturing industry in the world’s advanced countries in a short period of time, narrowing or even eliminating this gap. Make domestic offset printing out of Asia. To face the world, the difficulties faced by printers are still very difficult. Through analysis and comparison, it is not difficult to see that the fundamental guarantee for the improvement of the quality of the offset printing press lies in the need to firmly grasp the five degrees of precision, strength, stiffness, hardness, roughness, as long as the five degrees to the extreme. Offset presses really catch up with the world's developed countries, and it will not be too long to truly become a big producer and powerhouse of offset presses.
First, accuracy
Offset press is a very precise type of printing industry equipment, and the precision index is the first element of the offset press. In order to achieve accurate reproduction of graphic and graphic texts on thin paper such as flaps, two indicators must be grasped. One is that the thickness of the ink layer is uniform, and the other is that the position and size of the dots are relatively constant. The thickness of the ink layer is uneven and the ink color of the print is uneven. Different shades of light; machine accuracy can not meet certain requirements, the printing dot size changes and the network position changes, and ultimately also showed uneven ink, shades of different shades, overprinting can not reproduce the original color, graphic and visual effects are discoloration, loss of beauty , and become a waste of printing defective. The total thickness of the ink layer is generally less than 2 microns, and the allowable range of the ink layer thickness is smaller. The conventional detection method is to use a density meter to judge the amount of ink applied by detecting the intensity of reflected light, and similarly the size and position of the dots will also be changed. The densitometer was used to measure the intensity of the light reflected by the printed product and the density was calculated. It can be seen that the ink color will change when the machine accuracy is slightly unsatisfactory.
Paper is a very weak graphic carrier. It is necessary to separate the paper from the stack of paper and send it to the rules department every second. Before and after left and right positioning, re-delivery into the printing unit, print finishing code output. Multi-color printing machine needs to transfer more than ten times for each paper. The error register between each color image must be controlled within 0.03-0.05 mm. Otherwise, there will be ghosting, discoloration, and other defective printing defects due to the displacement of the imprint. Paper conveying system parts. The length of the transmission chain, the accuracy of the position of each part, the control of the movement speed and stroke, the coordination between the movements of the body, and the frequency of the cadence are all inseparable from parts processing and assembly accuracy.
In order to achieve the ideal color effect, the printing machine generally uses alcohol dampening instead of moist version. Because the surface tension of alcohol is far less than the surface tension of the water, the thickness of the dampening water film is much thinner than the thickness of the ordinary water-moistened water film. The ultra-thin water film's alcohol dampening mode requires a high degree of precision for the machine's swivel, when the dampening roller beats. More than 0.008 mm, the water film has been destroyed, it will appear dirty on the printing plate. Bars and other printing failures will result in scrapped prints.
Offset printing presses inevitably need to change the parts movement speed and direction of movement, which will produce some shock and vibration. If the ink roller reversal, the gripper arms open and close. Roller clutch, delivery arm back and forth, etc., these subtle impact vibration will cause the print dot size changes or dot blots displacement. The vibrations caused by these unavoidable actions can only be eliminated or weakened by the machine without gap movement. For example, the clearance between the tooth profile of the main transmission gears should be reduced, the error of the gear tooth circumference must be reduced, and the tooth profile contact surface must be Big, so the gear movement accuracy. The smoothness of the transmission is guaranteed to effectively eliminate the impact of external vibration sources on the gear transmission accuracy. Similarly, the conjugate cam must have almost no clearance between the pair of rollers and the cam profile. For some shaft-type components, the axial radial clearance, coaxiality, and roundness of the hole and shaft must meet the accuracy requirements. Precise instrument level standards, such as bearing rotation accuracy grade must reach P4 level or above. Ultra-precision machining must be used to meet design requirements.
Second, strength
Offset printing speed is getting faster and faster. Domestic offset printing presses currently print at speeds of around 10,000 sheets per hour, while foreign printers of the same specifications print at speeds not under 10,000 sheets, and the speed of calibration is mostly 1.5 times per hour. Ten thousand sheets. Some brands have even reached 18,000 sheets per hour. The printing speed is a challenge for an offset press to increase by 1 thousand impressions per hour. Increasing the speed of printing is not only a severe test of the accuracy of the machine, but also a severe test of the strength of machine components. The condition of high-speed components will rapidly deteriorate, and the damage caused by the additional load caused by the change of acceleration when the speed is changed to the impact of the machine will be very serious. Many mechanical parts will not stand out from the standstill or low-speed conditions, almost from the strength. There is no damage. When the speed is increased, the inertia force, vibration frequency, impact force, etc. are increased exponentially or even more than ten times. The original part safety margin can not guarantee the normal use of the parts at all. After the speed is increased, the parts are damaged. Significant increase in frequency, resulting in increased maintenance downtime, such as the North's 08 machine, 05 machine water roller motor shaft head only φ30 mm. And use ordinary carbon steel manufacturing, quenching and tempering. The motor power is only 80W. No damage was found during normal use. However, when the part was borrowed from other models, the speed was slightly increased and the damage occurred frequently. Comparing with foreign machines such as Mitsubishi of Japan and Heidelberg, Germany, the diameter of the head of the open-width water roller motor is up to φ40mm, which is an increase of nearly 30%. With high-quality alloy steel, the motor power reaches 400W, and the allowable torque differs by a factor of five. There are also some other brand machines that use motors larger than Mitsubishi and Heidelberg machines, up to 1200W. Similar to the adjustment of the motor, paper stack lift motor, ink roller roller bearings and other power may be used to double the torque increase. Therefore, the strength of these parts must be sufficiently guaranteed at high speed.
Third, the stiffness
Strength is the ability of the part to resist damage, stiffness is the ability of the part to resist deformation under the action of external forces. Offset press is a high-precision printing industry equipment. Under the normal working load, its deformation must be small. Because of the additional load generated by acceleration, the offset press is no longer a light load type device, especially a high-speed offset press. The stiffness of the machine is more noteworthy. Although some machines and equipment have a large workload, the premise of normal operation is that parts do not break. When designing such parts, the parts need only be checked for necessary strength, as long as no damage occurs, and the offset press not only has a large load, but also The important thing is that the premise of normal operation is that the deformation of the parts must be within the allowable range. The scope of this permission is very small. The focus of his design calculation is not only the strength but also the stiffness. We know that meeting the stiffness requirements of parts is much more difficult than meeting the strength requirements, because the parts may be destroyed after the deformation exceeds the limit, and the allowable variation of the critical parts of the offset press is only a few micrometers, otherwise the machine cannot print, so in order to ensure offset printing The machine parts have sufficient rigidity, and the statically indeterminate mechanism must be used in a large amount in the design, and a large number of over-positioning structures are used. This is a major feature of the printing press that distinguishes it from other machines. The so-called over-static is the total number of support reactions more than the total number of equations within the theoretical mechanics, the so-called over-positioning. It is the number of parts constraints more than the degree of freedom. In this case, the parts must be able to move according to a predetermined movement law, and the constraints cannot interfere with each other. The prerequisite is to improve the manufacturing precision. Otherwise, the additional internal stress of the parts will increase the resistance of the mechanism, consume power, and accelerate the damage to the parts. Even parts can't move, such as the XYZ three-dimensional joint of the frame, the multi-supported shaft support of the shaft, the large flange long bearing sleeve, the gear hub coupling with the conical face contact at the same time, etc. These over-positioning structures abound, they form High-precision, high-strength, high-stiffness organic combination.
Fourth, hardness
Compared with foreign equipment, the disadvantages of home-made machines are not only the stability of the operation, but also the low precision retention, and the low precision retention is a consideration of the stability of the machine over a long period of time. For example, the precision of the machine must be the same as the factory at the time of 2 years, 5 years or more. Although it is related to the manufacturing precision of parts, the more crucial reason is the selection of parts materials and the determination of the heat treatment process methods and the internal metallographic structure of the metal materials. It is related to the load size of the parts during operation and the internal stress distribution of the materials. . After a long time of work. The surface of the part is worn out, resulting in dimensional accuracy, and loss of geometrical accuracy of the position of the shape. Whether the parts wear or not is a deep knowledge, unlike the processing of parts is the external quality, more intuitive, is guaranteed by the machine tool precision and tooling of metal cutting processing equipment, easier to control, testing also Intuitive and precise, the technical requirements of the design output can also be determined through computer demonstrations, simulations, and even experiments. The wear resistance of parts is mainly determined by the internal organization of the metal material, and the material is not as hard as possible. . The data of some indicators depends on a large number of tests and can only be determined after a long period of actual use. Process operations are also relatively difficult and inspections are relatively difficult. More abstract. Because it is not intuitive, it is often ignored. Innovation. Combining the roads of production, study, and research is an effective way to break this technological fortress. Reducing the contact stress of delicate parts and designing the bearing capacity of vulnerable parts is an effective shortcut.
Fifth, roughness
As a kind of precision machine, the offset press has high precision in dimension and accuracy of the parts. To maintain this precision for a long time, the surface quality of the parts must be guaranteed. Rough surface of the parts, large resistance to movement, easy to generate heat, power consumption, more serious is easy to wear, the accuracy of maintaining the decline, the main key parts of the offset press with the size of the parts precision, shape accuracy are μm class, a machine Because of the rough surface, entering the rapid wear period ahead of schedule means that the accuracy of the offset press has been lost, and its moving parts will be in a state of micro out of control, and the dots will expand, resulting in water bars, ink bars, ghosting, discoloration, and misregistration. , while the noise increases. Violent equipment accidents such as vibration, leaking oil, loose fasteners, parts falling off, and broken parts will also occur.
Accuracy, strength, stiffness, hardness, and roughness are the fundamental guarantees for the quality assurance of printing machinery and are the soul of the design and manufacture of printing machines. They are interrelated, interact, and influence each other. Only the five degrees are firmly grasped, and the stability of offset presses is stable. And reliability can only be guaranteed. The quality of offset press can reach a new level.
First, accuracy
Offset press is a very precise type of printing industry equipment, and the precision index is the first element of the offset press. In order to achieve accurate reproduction of graphic and graphic texts on thin paper such as flaps, two indicators must be grasped. One is that the thickness of the ink layer is uniform, and the other is that the position and size of the dots are relatively constant. The thickness of the ink layer is uneven and the ink color of the print is uneven. Different shades of light; machine accuracy can not meet certain requirements, the printing dot size changes and the network position changes, and ultimately also showed uneven ink, shades of different shades, overprinting can not reproduce the original color, graphic and visual effects are discoloration, loss of beauty , and become a waste of printing defective. The total thickness of the ink layer is generally less than 2 microns, and the allowable range of the ink layer thickness is smaller. The conventional detection method is to use a density meter to judge the amount of ink applied by detecting the intensity of reflected light, and similarly the size and position of the dots will also be changed. The densitometer was used to measure the intensity of the light reflected by the printed product and the density was calculated. It can be seen that the ink color will change when the machine accuracy is slightly unsatisfactory.
Paper is a very weak graphic carrier. It is necessary to separate the paper from the stack of paper and send it to the rules department every second. Before and after left and right positioning, re-delivery into the printing unit, print finishing code output. Multi-color printing machine needs to transfer more than ten times for each paper. The error register between each color image must be controlled within 0.03-0.05 mm. Otherwise, there will be ghosting, discoloration, and other defective printing defects due to the displacement of the imprint. Paper conveying system parts. The length of the transmission chain, the accuracy of the position of each part, the control of the movement speed and stroke, the coordination between the movements of the body, and the frequency of the cadence are all inseparable from parts processing and assembly accuracy.
In order to achieve the ideal color effect, the printing machine generally uses alcohol dampening instead of moist version. Because the surface tension of alcohol is far less than the surface tension of the water, the thickness of the dampening water film is much thinner than the thickness of the ordinary water-moistened water film. The ultra-thin water film's alcohol dampening mode requires a high degree of precision for the machine's swivel, when the dampening roller beats. More than 0.008 mm, the water film has been destroyed, it will appear dirty on the printing plate. Bars and other printing failures will result in scrapped prints.
Offset printing presses inevitably need to change the parts movement speed and direction of movement, which will produce some shock and vibration. If the ink roller reversal, the gripper arms open and close. Roller clutch, delivery arm back and forth, etc., these subtle impact vibration will cause the print dot size changes or dot blots displacement. The vibrations caused by these unavoidable actions can only be eliminated or weakened by the machine without gap movement. For example, the clearance between the tooth profile of the main transmission gears should be reduced, the error of the gear tooth circumference must be reduced, and the tooth profile contact surface must be Big, so the gear movement accuracy. The smoothness of the transmission is guaranteed to effectively eliminate the impact of external vibration sources on the gear transmission accuracy. Similarly, the conjugate cam must have almost no clearance between the pair of rollers and the cam profile. For some shaft-type components, the axial radial clearance, coaxiality, and roundness of the hole and shaft must meet the accuracy requirements. Precise instrument level standards, such as bearing rotation accuracy grade must reach P4 level or above. Ultra-precision machining must be used to meet design requirements.
Second, strength
Offset printing speed is getting faster and faster. Domestic offset printing presses currently print at speeds of around 10,000 sheets per hour, while foreign printers of the same specifications print at speeds not under 10,000 sheets, and the speed of calibration is mostly 1.5 times per hour. Ten thousand sheets. Some brands have even reached 18,000 sheets per hour. The printing speed is a challenge for an offset press to increase by 1 thousand impressions per hour. Increasing the speed of printing is not only a severe test of the accuracy of the machine, but also a severe test of the strength of machine components. The condition of high-speed components will rapidly deteriorate, and the damage caused by the additional load caused by the change of acceleration when the speed is changed to the impact of the machine will be very serious. Many mechanical parts will not stand out from the standstill or low-speed conditions, almost from the strength. There is no damage. When the speed is increased, the inertia force, vibration frequency, impact force, etc. are increased exponentially or even more than ten times. The original part safety margin can not guarantee the normal use of the parts at all. After the speed is increased, the parts are damaged. Significant increase in frequency, resulting in increased maintenance downtime, such as the North's 08 machine, 05 machine water roller motor shaft head only φ30 mm. And use ordinary carbon steel manufacturing, quenching and tempering. The motor power is only 80W. No damage was found during normal use. However, when the part was borrowed from other models, the speed was slightly increased and the damage occurred frequently. Comparing with foreign machines such as Mitsubishi of Japan and Heidelberg, Germany, the diameter of the head of the open-width water roller motor is up to φ40mm, which is an increase of nearly 30%. With high-quality alloy steel, the motor power reaches 400W, and the allowable torque differs by a factor of five. There are also some other brand machines that use motors larger than Mitsubishi and Heidelberg machines, up to 1200W. Similar to the adjustment of the motor, paper stack lift motor, ink roller roller bearings and other power may be used to double the torque increase. Therefore, the strength of these parts must be sufficiently guaranteed at high speed.
Third, the stiffness
Strength is the ability of the part to resist damage, stiffness is the ability of the part to resist deformation under the action of external forces. Offset press is a high-precision printing industry equipment. Under the normal working load, its deformation must be small. Because of the additional load generated by acceleration, the offset press is no longer a light load type device, especially a high-speed offset press. The stiffness of the machine is more noteworthy. Although some machines and equipment have a large workload, the premise of normal operation is that parts do not break. When designing such parts, the parts need only be checked for necessary strength, as long as no damage occurs, and the offset press not only has a large load, but also The important thing is that the premise of normal operation is that the deformation of the parts must be within the allowable range. The scope of this permission is very small. The focus of his design calculation is not only the strength but also the stiffness. We know that meeting the stiffness requirements of parts is much more difficult than meeting the strength requirements, because the parts may be destroyed after the deformation exceeds the limit, and the allowable variation of the critical parts of the offset press is only a few micrometers, otherwise the machine cannot print, so in order to ensure offset printing The machine parts have sufficient rigidity, and the statically indeterminate mechanism must be used in a large amount in the design, and a large number of over-positioning structures are used. This is a major feature of the printing press that distinguishes it from other machines. The so-called over-static is the total number of support reactions more than the total number of equations within the theoretical mechanics, the so-called over-positioning. It is the number of parts constraints more than the degree of freedom. In this case, the parts must be able to move according to a predetermined movement law, and the constraints cannot interfere with each other. The prerequisite is to improve the manufacturing precision. Otherwise, the additional internal stress of the parts will increase the resistance of the mechanism, consume power, and accelerate the damage to the parts. Even parts can't move, such as the XYZ three-dimensional joint of the frame, the multi-supported shaft support of the shaft, the large flange long bearing sleeve, the gear hub coupling with the conical face contact at the same time, etc. These over-positioning structures abound, they form High-precision, high-strength, high-stiffness organic combination.
Fourth, hardness
Compared with foreign equipment, the disadvantages of home-made machines are not only the stability of the operation, but also the low precision retention, and the low precision retention is a consideration of the stability of the machine over a long period of time. For example, the precision of the machine must be the same as the factory at the time of 2 years, 5 years or more. Although it is related to the manufacturing precision of parts, the more crucial reason is the selection of parts materials and the determination of the heat treatment process methods and the internal metallographic structure of the metal materials. It is related to the load size of the parts during operation and the internal stress distribution of the materials. . After a long time of work. The surface of the part is worn out, resulting in dimensional accuracy, and loss of geometrical accuracy of the position of the shape. Whether the parts wear or not is a deep knowledge, unlike the processing of parts is the external quality, more intuitive, is guaranteed by the machine tool precision and tooling of metal cutting processing equipment, easier to control, testing also Intuitive and precise, the technical requirements of the design output can also be determined through computer demonstrations, simulations, and even experiments. The wear resistance of parts is mainly determined by the internal organization of the metal material, and the material is not as hard as possible. . The data of some indicators depends on a large number of tests and can only be determined after a long period of actual use. Process operations are also relatively difficult and inspections are relatively difficult. More abstract. Because it is not intuitive, it is often ignored. Innovation. Combining the roads of production, study, and research is an effective way to break this technological fortress. Reducing the contact stress of delicate parts and designing the bearing capacity of vulnerable parts is an effective shortcut.
Fifth, roughness
As a kind of precision machine, the offset press has high precision in dimension and accuracy of the parts. To maintain this precision for a long time, the surface quality of the parts must be guaranteed. Rough surface of the parts, large resistance to movement, easy to generate heat, power consumption, more serious is easy to wear, the accuracy of maintaining the decline, the main key parts of the offset press with the size of the parts precision, shape accuracy are μm class, a machine Because of the rough surface, entering the rapid wear period ahead of schedule means that the accuracy of the offset press has been lost, and its moving parts will be in a state of micro out of control, and the dots will expand, resulting in water bars, ink bars, ghosting, discoloration, and misregistration. , while the noise increases. Violent equipment accidents such as vibration, leaking oil, loose fasteners, parts falling off, and broken parts will also occur.
Accuracy, strength, stiffness, hardness, and roughness are the fundamental guarantees for the quality assurance of printing machinery and are the soul of the design and manufacture of printing machines. They are interrelated, interact, and influence each other. Only the five degrees are firmly grasped, and the stability of offset presses is stable. And reliability can only be guaranteed. The quality of offset press can reach a new level.
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