Offset Trouble-Troubleshooting Tips

Offset presses, whether they are sheet-fed offset presses or two-color or four-color offset presses, will have different degrees of wear due to various parts after several years of operation, especially with several open cam cams, tooth pads and teeth. Seats, receiving teeth and other parts are easy to wear, the precision decline, so that the printing process, the paper transfer can not be normal. The manifestation of the failure is that the edge of the paper is torn, so that when the second color is overprinted, it cannot be performed normally. The tearing of the paper edge also affects the cleanliness of the paper, and causes the loss of the printed product when it is severe. In the actual work encountered when the paper is torn when the paper should be comprehensive analysis, different treatment, cut points to eliminate faults.

1. Causes and elimination of tearing paper in front of paper

1 The transfer time between the impression roller and the collection tooth is too long. Appropriately shorten the time between two sets of caries transfer.

2 Impression roller teeth are not the same as open and close teeth. Adjust the impression roller teeth to open and close the same.

3 The impression cylinder and take-up tooth row do not intersect at a tangent point or have a large deviation from the tangent point. Adjusted for tangent point handover.

4 The collection of teeth is not the same as the closing teeth. Adjust the makeup teeth to open and close.

5 Take-up teeth The chin mouth is too close to the edge of the impression cylinder, or it hits the edge of the impression cylinder. Adjust the distance between the feed teeth and the edge of the impression roller, which is generally about 1mm.

6 Embossing roller open teeth cam or take-up teeth open teeth cam wear, resulting in open teeth mouth smaller and touch paper. Replace the impression roller or take-up teeth opening cam.

7 Tooth jams Paper jams or other obstacles cause tearing of the flaps during transport. Check the above points.

8 In addition to the misadjustment of the offset press and the improper handling of the paper, the paper itself has a problem with its quality and there is a tendency for it to tear. If the flexibility of the paper is poor, the paper storage time is too long, the sunlight is shining, the paper store environment is dry, and the like causes the paper to turn yellow and brittle. Such paper printing on the machine will also cause the paper opening to tear the paper.

2. Causes and elimination of tearing at the edges of the paper in the normal printing process

In the normal printing process, if there is a phenomenon that the paper is cracked, you should first find out the cause of the problem and carefully check the tearing of the paper. In general, there are three kinds of phenomena in the tearing of the crotch edge. First, the crotch edge of the paper is torn continuously and its position is not changed. Second, instead of tearing each sheet, each sheet of paper is separated by a few sheets of paper that are not torn between them, and are regular. Thirdly, the gaps on the side of the paper are large and small. When it breaks, there is no regularity.

The reasons for the above three types of failures and their exclusion methods are analyzed as follows:

1. During the offset printing process, the edges of the sheet are regularly torn, and the number of sheets in the middle interval is just the number of the delivery rows.

This situation is generally caused by improper adjustment of the receiving tooth row.

Solution: Open the slow speed of the offset printing machine and observe carefully whether the degree of each tooth of the collection tooth row is the same, then adjust it, and then drive and test the paper to see if there is any tearing phenomenon.

2. The edge of the sheet is continuously torn and the position remains unchanged.

If this failure occurs, we must find the reason on the paper-feeding teeth and drum teeth.

First, open the slow car and carefully observe the process of transferring the paper and the big teeth, and see if the time is too slow or the degree of opening of the teeth is not enough to cause tearing.

Solution: Check whether the tooth-bumping of the paper-feeding teeth is worn, such as welding, repair welding or replacing new parts, and make careful adjustments. The requirement is that when the paper-feeding teeth hand the paper to the impression roller, the paper-handling teeth will be delivered. The distance between the roller and the big teeth and the control paper must not be greater than 3mm.

Secondly, because the large tooth base of the roller is screwed into a round hole, the opening degree of the large teeth of the roller is not enough. When the paper is transferred to the roller tooth, the paper edge touches the roller tooth and tears.

Solution: If only one or more tooth bases are damaged by the top silk, repair welding can be done on the machine. If there is more damage at the top, remove the new ones.

Thirdly, the connection between the holder shaft of the drum teeth and the pulley frame is loose, causing the time for the large teeth of the drum teeth to be slow or the opening degree of the teeth to be insufficient to tear the edges of the paper.

Solution: Check whether the pin at the connection is loose or cut off. If it is loose, it can be resold. If it is cut off, it needs to be replaced with a new pin.

Fourth, the distance between the dentition of the paper feed tooth and the side of the impression cylinder is improperly adjusted, and the distance between the dentition and the impression cylinder is too close, which causes the paper escaping pad to erode with the side of the impression cylinder, resulting in tearing of the paper edge. The distance is too far to make the impression cylinder pick up paper. Break the edges of the paper.

Solution: Carefully adjust the distance between the transfer tooth pad and the edge of the embossing roller. Generally the distance between the two is adjusted to 0.5mm. Cardstock should be printed 2 to 3 times the thickness of the paper.

Fifth, the open teeth of the delivery teeth are worn and the time for opening the teeth of the delivery teeth is slowed down, and the tearing of the paper is caused by the small open distance.

Solution: Remove the open bumps by welding or replace new ones.

3. There is no regular paper breakage at the mouth of the paper, and the width of the paper is narrow when it is wide.

This phenomenon is generally caused by misadjustment of the feeder or the former gauge, and should be found on the feeder. (1) Observe whether the tape tension of the feeder is consistent; (2) Check whether the pulley of the feed line can be flexibly rotated by starting the running of the offset press; (3) Check whether the time of arrival of the paper on the offset press is appropriate or not; When the current gauge reaches the receiving position, the distance between the front edge of the paper margin is 8-10mm. If it is not suitable, it needs to be adjusted; 4 carefully check whether the height of the front gauge meets the requirements. The general requirement is that when the current gauge reaches the receiving position, three sheets of paper can be put into the printed paper, and it is advisable to apply slight resistance when pulling.

To sum up, in the case of eliminating the paper breakage, it is necessary to pay attention to the transfer teeth, the roller teeth, and the receiving tooth pads. The transfer between the teeth must be reasonable and must be in accordance with the maneuvering table on the machine instructions. In the request for data to adjust, the level of teeth in a row of teeth must be adjusted to the same level. The closing time of each tooth, and the size of the open tooth, must be the same. The bite force of each tooth was tested with a paper strip to balance its bite force.