Analysis of paper feeding mechanism of sheetfed offset press
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The function of the paper feeding mechanism is to transport the paper separated from the Feida part smoothly, accurately and unreasonably to the front and side gauges for positioning. The higher the printing speed, the more the paper size or thickness changes, and the higher the work requirements for the paper feeding mechanism. Comprehensive analysis of the current sheetfed offset presses of various brands, the commonly used paper feeding mechanism is mainly two categories: one is the conveyor belt type uniform speed paper feeding mechanism; the other is the vacuum suction belt type speed reducing paper feeding mechanism. Its structural characteristics and work performance have their own merits. This article will compare and analyze these two institutions.
First, the working principle
1. Conveyor belt conveying speed mechanism
On a rectangular paper feeding plate 1 inclined to the positioning member, uniformly wraps 4 to 8 conveying belts 2, and the knurled driving belt shaft 3 drives the belt around the tensioning pulley 4 by friction. With the axle 5, it is turned over the paper feeding plate. The paperboard frame 6 is evenly mounted with a platen 7, a brush wheel 8, a paper stopper 9, a pressure ball 10, and the like, which are all in contact with the wire with a certain pressure, between the wire and the wire. Under the action of friction, it rotates with the movement of the belt, and the paper is conveyed smoothly and evenly to the front gauge 12 until it reaches the front gauge. The paperboard 11 has three paper-thick gaps from the paperboard to prevent paper edges and paper corners from warping.
The conveyor type uniform speed feed device stabilizes the paper on the entire surface, allowing the paper to reach the front gauge flat, and the structure is very simple. However, due to the friction of the paper surface, such as the platen roller, the brush wheel, and the brush, the quality of the paper surface and the existing printing are affected to some extent; the paper has a large impact when it reaches the front gauge. Rebound, and the faster the machine, the more impact and rebound.
2. Vacuum suction belt type speed reduction paper feeding mechanism
Vacuum suction belt type paper feeding method. Two suction belts 2 are symmetrically arranged on the same rectangular paper conveying plate 1, and the transmission is also driven by the driving belt shaft 3 by the frictional force to drive the suction belt around the tensioning pulley 4, and the driven belt shaft 5 through the paper feeding. Turned over the top of the plate. When the paper reaches the paper feeding plate, the suction belt sucks the paper under the action of the vacuum suction chamber 6, and slowly sends the forward gauge until it reaches the front gauge to be stationary.
The driving shaft 1 is provided with an eccentric gear 2, the center of the shaft 1 is B, and the axis of the eccentric gear 2 is fixed on the frame, and the distance between the AB is the eccentric distance "e" of the eccentric gear 2. The eccentric gear 2 meshes with the movable gear 3, and the gear 3 meshes with the gear 4 fixed to the frame. At the same time, the axis C of the gear 3 is connected to the shaft 1 by the rod 5, and the shaft D of the gear 4 is connected by the rod 6. The sprocket 7 is coaxial with the gear 4, and the sprocket 9 is coaxial with the main shaft 10, the belt The shaft 10 is surrounded by a tensioned vacuum suction belt 11.
When the paper feeding mechanism is working, the power of the speed reducing mechanism is input by the driving shaft 1 to drive the eccentric gear 2 to rotate about the axis A, and the movable gear 3 and the eccentric gear 2 are always meshed and rotated by the connecting rod 5, and the movable gear 3 is made through the connecting rod 6. The fixed gear 4 is always meshed and rotated, so that the power is sequentially transmitted to the vacuum suction belt 11 for paper feeding. Due to the eccentricity of the gear 2, the distance AE between the meshing point E of the gear 3 and the axis A is periodically changed. due to:
Line speed at point E = speed of gear 2 n × AE
Therefore, the linear velocity V at the point E changes periodically. Then, the working speeds of the gear 3, the gear 4, the sprocket 7, the chain 8, the sprocket 9, the driving belt shaft 10, and the vacuum suction belt 11 are periodically changed, so that the paper on the paper feeding plate is also in a cycle. The speed of sexual change is transmitted to the front. By design, the paper is conveyed at a high speed in the forward direction on the paper feeding table; when the front gauge is reached, the suction belt is gradually decelerated, and the impact with the front gauge is minimized.
The vacuum suction belt type deceleration paper feeding device can adapt to the small error on the thickness and cutting of the paper; the contact between the paper and the suction belt is stable without slipping; the surface of the paper has no contact and smudging; the paper arrives at the front gauge smoothly and shocks small. However, due to the addition of the air pump, the pneumatic system and the gear-link reduction mechanism, the structure is complicated, the noise is large, and the maintenance is difficult.
Second, the job requirements
1. Conveyor belt feeding mechanism
(1) The thickness of the six tapes needs to be uniform
Paper conveying speed on the paper feeding plate V1=Line moving speed V2=Drive line shaft speed n×(Axis radius R+Line thickness H)
If the thickness H of the tape is not equal, the paper feed speed V is not equal, and the paper is irregularly flickered, causing skew. Therefore, the thickness of the six wire strips should be uniform, especially the seams of the tapes should be sutured after cutting to ensure flatness.
(2) The tension of the six belts must be consistent and moderate
The tension of the six belts and the drive belt shaft determines the frictional force of the belt belt to the belt, which determines the speed of the belt movement, which determines the conveying speed of the paper on the belt. If the six belts are tightly tensioned, the paper tends to be skewed; the belt is stretched too tightly, the tension of the belt is too large, the belt is easy to stretch, and it is easy to age. The tensioning arm is pushed to change the up and down position of the tensioning wheel, and the strap is tightened. Generally, it is preferable to lift the tape from the paper feed deck by about 20 mm. In the long-term use, the belt will inevitably appear to be elongated. Therefore, always check the tightness of the belt and tighten it in time.
(3) The position of the paper roller on the line with the ball and the pressure on the belt should be appropriate
The first row of platen rollers is evenly arranged on the drive belt spool. The paper-pressing point of the lowermost row of paper-pressing rollers is about 3~5mm away from the trailing edge of the paper of the previous specified position. Do not press the trailing tip of the positioning paper to avoid the tipping of the paper when the side gauge is pulled. Or not in place.
In order to prevent the paper on the paper feeding table from arching in the middle, the left and right platen rollers can be slightly opened outward, so that the paper feeding force is slightly deflected outward, thereby ensuring that the paper is flat and smooth. Of course, if the deflection is too large, the paper will be lost and even the paper will be scratched.
The pressure of each platen roller and the tape should be uniform, so that the paper can be smoothly transported forward. The pressure of the left and right platen rollers is uneven, too much weight is transmitted on the back side, and the paper on the light side is slow, causing the paper to be skewed. The pressure of the platen is too high, leaving an indentation on the paper or scratching the original mark on the paper.
(4) The position of the brush, brush wheel and paper ball should be correct.
The brush, the brush wheel and the paper ball are all located at the front of the paperboard, and their function is to prevent the paper from rebounding and fluttering when it reaches the front gauge, so that the paper is positioned accurately. The position of the brush is preferably 5~10mm on the trailing edge of the paper being positioned, so that the rebounded paper is lightly blocked by the bristles. The outer circle of the brush wheel is tangent to the trailing edge of the positioning paper, which prevents the paper from rebounding, and the rotation of the wheel causes the bristles to gently push the trailing edge of the paper to move forward, so that the rebounded paper continues to be delivered to the front gauge. The weight of the paper ball is relatively large. When the thick paper is printed, it is placed in the front half of the paper, and its action and the brush are rotated. When the paper is printed, the brush is moved forward to 25 to 30 mm away from the paper.
The pressure of the brush, brush wheel, paper ball and tape should be properly controlled. The pressure is too small to prevent the paper from rebounding and pushing forward; the pressure is too high, the side gauge can not pull the paper, the paper is skewed, or Pulling is not in place; moreover, it will leave scratches on the surface of the paper, and even make the paper bite wrinkle at the front gauge.
(5) To print paper of different thickness, it is necessary to correct the pressure of the platen roller, etc.
If the paper thicknesses of the two batches of prints are different, the pressure of each of the platen roller, the brush wheel, the brush, the platen ball and the tape should be corrected one by one.
(6) Printing different paper sizes requires moving the position of the platen roller, etc.
If the paper specifications of the two or two batches are different, the position of the last row of the platen roller and the brush wheel, the brush, and the platen ball should be moved to prevent the rebound and flutter of the printed paper when entering the front gauge.
2. Vacuum suction belt feeding mechanism
(1) The tension of the two suction belts should be even and moderate. The friction between the suction belt and the active belt shaft should be able to smoothly transmit the suction belt without slippage.
(2) The vacuum pressure of the suction chamber should be appropriate. It can be adjusted by the suction air pressure regulating valve on the air cylinder. If the vacuum pressure of the suction chamber is too small, the suction belt sucks the paper into the front gauge; if the vacuum pressure of the suction chamber is too large, the surface of the paper is prone to traces of the suction belt, making the image on the back side dirty, or even making The thin paper is broken.
(3) As shown in Fig. 4, in order to avoid the lack of flatness of the thin paper in the conveyance, the paper wrinkles outside the suction belt, and the paper angle is warped. At present, most of the vacuum suction belt The type of speed reduction paper feeding mechanism has added 2~4 conveyor belts on the paper feeding board, and evenly arranged several brush wheel at the trailing point of the positioning paper, and arranged several pressing papers along the trailing edge of 5mm. The main function of the wheel is to control the flatness of the paper on the entire web and prevent the paper from rebounding and fluttering before the arrival of the specified position. Therefore, the pressure between the platen roller, the brush wheel and the wire belt is small, and only a slight tendency to feed the paper forward is required, and the imprint of the paper and its surface is not damaged. If the pressure is too high, not only the paper is operated, but also the smooth feeding of the vacuum suction belt is affected.
(4) The air pump and the suction air path should be cleaned frequently. Regular cleaning can prevent paper powder and paper hair from clogging the air pump and gas path, affecting the effect of suction and paper feeding.
(5) To print paper of different thickness, it is necessary to correct the suction air pressure and the pressure roller.
If the paper thickness of the two batches of prints is different, the suction air pressure valve on the air pump must be adjusted to change the vacuum pressure of the suction chamber so that the suction belt absorbs the paper. At the same time, the pressure of each platen roller, brush wheel and belt should be corrected one by one.
(6) It is necessary to adjust the position of the platen roller, etc. for printing different specifications of paper. If the specifications of the two batches of printing paper are different, the position of the platen roller and the brush wheel should also move accordingly.
Third, the comparison of paper feeding speed and paper feeding effect
1. From the paper feed nozzle to the drive line shaft
Assume that the design speed of the press is 15,000 sheets per hour and the fixed speed is 13,000 sheets per hour. The speed of the paper on the paper stack is 0. When the paper feed nozzle picks up the paper and feeds forward, the paper accelerates. When the paper feed roller reaches the drive belt, the vacuum suction belt type speed reduction paper feed mechanism only requires the paper feed speed. Matching the printing speed of about 8,000 sheets; the conveyor type uniform conveying mechanism requires the paper conveying speed to match the printing speed of about 13,000 sheets. The paper conveying speed is abruptly changed, the acceleration is large, and the stability of paper separation and paper feeding is high.
2. From the active line to the front of the pre-positioning
The paper is conveyed on the paper feed deck under the belt. The conveyor type uniform speed paper feeding mechanism always requires the paper conveying speed to match the printing speed of about 13,000 sheets, which is smooth and non-fluctuating; the paper conveying speed of the vacuum suction belt type speed reducing paper feeding mechanism is gradually accelerated from the corresponding 8000 sheets/hour to the highest. At 18,000 sheets/hour, then gradually slow down to 8000 sheets/hour, then accelerate to 18,000 sheets/hour, then decelerate back to 8000 sheets/hour. Among them, the paper has undergone several large shifts, and the transport stability has been challenged.
3. Arrival time
When the paper reaches the ex-husband, the speed is 0, the position is static, and the side gauge smoothly pulls the paper. For the conveyor type uniform speed feed mechanism, the paper speed is instantaneously reduced from the corresponding 13,000 sheets/hour to zero speed. Due to the strong inertia, on the one hand, the paper bite wrinkles, especially thin paper, the damage is more serious; on the other hand, the paper rebounds, the tip hits the brush, the brush wheel, etc., causing scratches. Although the rebounded paper continues to be delivered to the front gauge under the push of the brush wheel and the paper ball, it is easy to go out of position, resulting in poor positioning accuracy. For the vacuum suction belt type speed reduction paper feeding mechanism, the paper speed is reduced from the corresponding 8000 sheets/hour to zero speed, and the inertia is much smaller. The effect is obvious in preventing the wrinkles of the bite, scratching the tip, and improving the positioning accuracy.
Fourth, auxiliary institutions
1. The air blowing device at the front gauge replaces the cardboard
Platen is installed at the port of the paper feeding iron plate. The pendulum type front gauge is used to integrally mount the platen with the front gauge, and the hem-type front gauge separately mounts the pressure plateboard above the paper feeding table to prevent the bite portion from being warped or arched when the paper reaches the front gauge. The height of the paperboard and the paperboard is approximately three sheets thick. Too high, can not play the role of paper, causing the paper to go over the position; too low, affecting the paper smoothly into the front gauge, causing the paper to go out of place, and may scratch the surface of the paper or the existing footprint. Therefore, the thickness of the printed paper changes, and the height of the paperboard should be adjusted accordingly.
The air blowing device at the front gauge, when the paper is about to reach the front gauge, the air blower blows under the paper bite to form a gas cushion, which holds the paper into the front gauge, and mitigates the impact of the front gauge on the paper. The flow prevents the paper from being over and does not manipulate the surface and footprint of the paper.
This device is currently installed on a variety of offset presses such as Mitsubishi, Komori and Heidelberg.
2. Paper specification preset system
At present, many brands of offset presses have been equipped with a paper specification preset system, and the paper specifications to be printed, such as paper type, thickness, size, etc., are input at the center console, and the various parts of the press will be automatically adjusted, such as: The position of the fly, the amount of inhalation, the amount of air blown, the pressure and position of the platen roller, the brush wheel, and the platen reduce the time and uncertainty of manual adjustment and greatly shorten the preparation time for printing.
3. Paper trend monitor
The offset of the paper entering the pre-defined position not only causes the paper to be misaligned, but also greatly reduces the production efficiency due to multiple shutdowns. Usually, the operator ensures that the paper reaches the pre-defined position accurately by adjusting each control unit in the paper feeding device. Nowadays, many brand offset presses use a paper trend monitor. The operator can check the alignment of the paper at the front gauge through the screen, and easily adjust the paper position by buttons. This eliminates the manual adjustment time and shortens the preparation time and improves the work time. Production efficiency.
4. Suction brush roller device
A suction brush roller was installed above the paper table for the Heidelberg offset press. As the paper is conveyed, the suction brush roller sucks away the paper dust on the surface of the paper, reducing machine downtime and improving print quality.
5. Static elimination device
Electrostatic interference is caused by friction during paper transport, and paper adhesion will affect the smooth separation and transfer of paper. Many sheetfed offset presses have increased the power of static elimination. If the paper feeding plate is not flat and smooth, it is processed into a fish scale shape to reduce the static electricity generated on the paper; or the negative ion ion wind is blown through the presser foot blowing nozzle or the side blowing device to neutralize the positive on the paper. Charge; there is also a static elimination rod as shown in FIG.