The printing quality of carton printing machine is good or bad, people usually understand it as two aspects. On the one hand is the clarity of printing, including consistent color shades, non-blocking patterns, no ghosting, and no bottom leakage. On the other hand, the overprint accuracy of multicolor printing should generally be within ± 1mm, and a good printing machine can reach within ± 0.5mm or even ± 0.3mm. In fact, the printing machine also has a very important printing quality index-the overall positioning of the printing, that is, the color registration of several colors is accurate, but they are inconsistent with the reference edge distance of the cardboard, and the error is large. Because this quality index of the general carton is not strict, it is easy to be ignored by people. If the overall positioning error exceeds 3mm or 5mm, the problem is more serious.

Regardless of the chain feed or automatic feed (backward feed or front edge feed), the reference edge of the overall printing position is perpendicular to the cardboard conveying direction, because the other direction (cardboard conveying direction) is not easy to produce overall positioning (unless The cardboard runs diagonally). This article will analyze the reasons for the overall position of the printing in the automatic paper feed printing press in the back-push mode.

The cardboard conveying of the automatic paper feed printing machine is to push the lowermost sheet of the aligned cardboard forward to the upper and lower conveying rollers, and the forward and downward conveying rollers are forwarded to the printing department. paper. Analyzing the conveying process of cardboard can help us find the reason for the overall printing position.

1. In the process of pushing paper, the transmission chain of pushing paperboard must not have a large accumulation gap.

The automatic paper feeding and printing machine pushes the cardboard into a reciprocating linear motion. Most manufacturers use a crank (slider 1 guide mechanism plus rocker slider mechanism. In order to make the mechanism light and wear less, the slider of the crank slider guide mechanism is a bearing. The gap between the bearing and the two slides is too large The conference caused the uncertainty of the movement of the cardboard, which caused paper feed errors and caused the overall printing to move. So how to ensure that the bearing rolls purely between the two slides of the guide bar, and does not cause a large gap between the bearing and the two sliders? The key is to adopt the double-bearing structure, no matter whether the bearing moves down or up along the slide, it can ensure that the bearing is purely rolling between the two slides without gaps, so that the mechanism is light and wears out, and the gap can be eliminated.

The connection between the guide rod and the rocker and the shaft is easy to loosen due to the alternating load, which is also the reason for the gap to cause the error of the paper pushing. Push other mechanisms in the cardboard transmission chain to drive gears evenly, improve the precision of gear processing (such as grinding and honing), improve the center-to-center accuracy of each pair of gears (such as processing center to process wallboard), and reduce the accumulation of transmission The gap improves the accuracy of pushing cardboard and pushing paper, thereby reducing the overall position of cardboard printing.

2. The moment when the cardboard is pushed to push the cardboard into the upper and lower paper feed rollers, it is actually an instantaneous speed-up process in which the cardboard speed is increased from the linear speed of pushing the cardboard to the linear speed of the upper and lower paper feed rollers.

The instantaneous linear speed of the cardboard must be lower than the linear speed of the upper and lower paper feed rollers (otherwise, the cardboard will be pushed and arched). And how much is smaller, the ratio matching between the speed of the two is very

important. It directly affects whether the cardboard slips at the moment of speeding up, and whether the paper feeding is accurate, thus affecting the overall printing position. And this is precisely not noticed by printing machine manufacturers.

When the speed of the host is constant, the linear speed of the upper and lower paper feed rollers is a fixed value, but the linear speed of the push board is a variable, from zero at the rear limit position to the maximum in the positive direction to zero at the front limit position, from the front limit position The zero then reaches the maximum in the reverse direction and reaches zero at the rear limit position, forming a cycle.

Of course, the factors that affect the overall position of the cardboard printing are such as the curvature of the cardboard, the surface roughness of the cardboard, the moisture content of the cardboard, and whether the gap between the upper and lower paper feed rollers is appropriate, but the factors of the equipment are mainly reflected in the above two aspects.

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