Overall position of the carton printing

The printing quality of carton printers is generally understood as two aspects. On the one hand is the clarity of printing, including the consistent color depth, pattern no adhesion, no ghosting, no bottom leakage. On the other hand, the overprint accuracy of multicolor printing should generally be within ±1mm, and a good printing press can be within ±0.5mm or even ±0.3mm. In fact, the printing press also has a very important printing quality indicator - the overall printing position, that is, several colors of color registration is accurate, but they are inconsistent with the paperboard reference edge spacing, the error is larger. Due to the lax requirement of the general quality of the carton box, it is easily overlooked. If the overall walking error exceeds 3mm or 5mm, the problem is more serious.
Regardless of the chain feed or automatic feed (post feed or leading feed), the reference edge of the overall print position is perpendicular to the paper board transport direction, and the whole direction (paper feed direction) is less likely to generate an overall pass (unless The cardboard runs obliquely). This article will analyze the reason why the post-push paper automatic printing press prints the overall position.
The paper feeding of the automatic paper feeding printing machine is carried out by pushing the paper board to push the bottom sheet of the paper board forward to the upper and lower conveying rollers, and conveyed by the upper and lower conveying rollers forward to the printing department. paper. Analyzing the transport process of the cardboard can help us find the reason for the overall walk.
First of all, in the paper pushing process, the drive chain of the push paper board must not have a large accumulation gap. The automatic paper feed printing machine pushes the paperboard in a reciprocating linear motion. Most manufacturers use a crank (slider) guide rod mechanism plus a rocker slider mechanism. In order to make the mechanism light and wear small, the slider of the crank slider guide mechanism is a bearing. Because the gap between the bearing and the two slides is too large, the uncertainty of the movement of the push-pull board may be caused, thereby causing a paper feed error and causing the print to take an overall position. Therefore, it is crucial to ensure that the bearing performs pure rolling between the two slide plates of the guide bar without making the bearing and the two sliders have large gaps. With the double bearing structure, whether the bearing moves down or moves up along the slide plate, the pure rolling without clearance between the two slide plates can be ensured, so that the mechanism can not only be lightly worn but also can eliminate the gap.
The connection between the guide rod and the rocker and the shaft is easy to be loose due to the alternating load, and it is also the reason that the clearance is caused to push the paperboard to push paper. All the other mechanisms in the push plate drive chain are gear transmissions to improve the processing accuracy of the gears (such as grinding teeth and dents), and to improve the center-to-center accuracy of each pair of gears (such as using a machining center to process wallboards), reducing the accumulation of transmissions. Clearance improves the accuracy of push paper pushing, thus reducing the overall walking position of cardboard printing.
Second, the moment when the cardboard is pushed into the upper and lower feed rollers is actually an instantaneous speed-up process in which the speed of the paperboard is increased from the linear speed of the push-cardboard to the linear speed of the upper and lower feed rollers. This instantaneous paperboard line speed must be less than the upper and lower feed roller line speeds (otherwise, the board would be bowed). The smaller the number, the ratio of the two speeds and the matching relationship is very important. Directly affect the speed of the cardboard to slip, whether the paper is accurate, thus affecting the overall position of the printing. This is exactly what the press manufacturer can't notice.
When the speed of the main machine is constant, the linear speed of the upper and lower feed rollers is a fixed value, while the linear speed of the pusher board is a variable, from the zero of the rear limit position to the maximum of the front limit position to the zero of the front limit position. Zero to the reverse maximum to the rear zero position, forming a loop.
The figure on the right is a schematic diagram of the crank mechanism of the push-pull board (slider), and the linear velocity formula of the push-pull board can be deduced by the analytical method.
V=nπcos(α-α2)cosα2cosα11
In the picture: c1 is the rear limit point of the guide rod end c2 is the front limit point of the guide rod end s is the stroke of the guide rod end (ie, the stroke of the push paperboard)
Where: V is the linear velocity of the rod end of the guide (ie, the linear velocity of the paperboard)
n is the rotation speed of the crank OB, which is a known quantity. Expression 1 shows that V is a variable and varies depending on the position of the C point (a2 is different). Through calculations, different speeds of the pushboard in different positions can be determined. According to the proportional relationship between the linear speed of the paperboard and the linear speed of the paper feed roller, after determining the linear speed of the paperboard pushing the paperboard into the upper and lower paper feed rollers, the best position of the paperboard at this time can be determined.
Of course, the factors affecting the overall position of cardboard printing include the curvature of the paperboard, the surface roughness of the paperboard, the moisture content of the paperboard, and whether the gap between the upper and lower paper feed rollers is appropriate, but the factors of the equipment mainly manifest in the above two aspects.