Offset roller surface repair
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The main function of the offset press is to transfer the ink of the graphic part to the surface of the substrate under pressure. This is the core of the whole machine, and all other mechanisms are for the embossing service. This shows the importance of the drum to the printing equipment. However, in actual production, we often roll hard objects into the drum due to poor operation or other accidents, causing the surface of the drum to be crushed. The direct consequence of this situation is that the machine is not usable, so it is necessary to discuss how to repair the surface of the rolled roller. Below we will introduce some solutions to the repair.
Do not disassemble the roller repair
The mechanical mode of the drum is not removed: this method of repairing the surface of the drum is mainly directed to the rolling of the surface of the drum by the rolling of the foreign matter into the drum.
Case 1: Roland two-color sigmoidal dents of 15 cm in length, 2 to 3 mm in width and 0.2 to 0.3 mm in depth were rolled on the surface of the drum after the roller was peeled off.
1. Using a hand drill, 2.5mm drill bit, along the concave line, make a hole of 8~12mm deep on the surface of the drum (the distance between each hole is close, but it cannot penetrate).
2. Use a small chisel to open the hole to make it into the shape of the dovetail groove. The surface is small and the bottom is large.
3. Knock the copper strip slightly larger than the dovetail groove into the groove with a brass rod, and continue to hit the surface to enlarge the bottom of the copper strip in the groove, firmly bite the roller, and then knock the surface flat to make the copper and damage The surface is firmly combined.
4, smooth with a fine shovel, and finally smooth with water sandpaper.
Case 2: The J2108 nut fell into the roller gap, causing the roller surface to roll out a depression having a diameter of about 10 mm and a depth of about 0.5 mm.
1. Select a drill bit of 3 to 6 mm according to the size and shape of the crush, and make a hole of about 15 mm deep on the surface of the roller.
2. Use copper strip of the same diameter, screw in and tighten, and cut at 0.5~1mm from the surface of the drum.
3. with the same beat, flattening, grinding and other processes to smooth the surface of the drum.
The advantage of the mechanical approach is that the cost is lower and the maintenance time is longer after repair. A general factory can handle it as long as it has a fitter, but as long as it is manually operated, the operator's requirements are relatively high, and even then it is difficult to completely recover the situation before the damage.
Non-removable roller argon arc welding method: This method of repairing the surface of the drum, as well as the above, can also deal with the severe surface rolling of a small area of the drum.
Case: In the J2205 printing press, the large eddy support rod of the oscillating tooth fell off, and a long-shaped depression of the deepest 3 mm was rolled on the surface of the drum.
1. Clean the surface of the drum with gasoline and acetone.
2. using a special argon arc welding machine, part of the spot welding, surfacing welding damage.
3. Finally, level the surface and smooth the surface with water sandpaper.
The utility model has the advantages of being able to deal with the serious surface damage of the drum, such as a more serious defect of the surface of the drum caused by the rolling injury, and because the welding temperature of the argon arc welding is relatively low, it is not easy to cause a larger deformation of the surface of the drum, and there is Under the protection of argon, the surface of the drum is not prone to oxidation.
The disadvantage is that it requires more professional welding equipment, as well as more professional welding technology. In addition, since the post-process is still relying on manual grinding, there is still no guarantee of good precision on the surface of the drum.
Filling the roller with glue: This method is more suitable for repairing the surface of the drum due to wear or corrosion. Generally, the depression is not serious, but if it is not treated, it will have a great influence on printing.
Case: Due to the material problem of the roller itself, the J2108B printing machine caused the corrosion of the roller to become thinner at both ends of the roller after several years of use. When printing large-format printed matter, the embossing phenomenon appeared at the edge of the printed product.
1. Clean the surface of the drum first.
2. Use 502 glue mixed iron powder to coat in the depression of the roller. When coating, pay attention to the more accurate the coating range. It is best to scrape along the surface of the drum with a relatively long steel sheet just after coating, as far as possible to ensure that the coating is level with the surface of the drum.
3. When the 502 glue is not dry, wrap it on a flat piece of wood or iron with gauze, and smooth and polish the filling.
One of the advantages of this type of operation is that it is convenient and quick, and the general machine operator can handle it by himself. However, it is generally not maintained for a long time. The main reason is that the surface of the drum is often exposed to various organic solvents and will gradually fall off during use. Therefore, it is generally only suitable for occasions requiring short-term repair.
(If you use a glue to repair the roller, you can also consider epoxy resin, and "two in one" glue)
For the repair of cast iron drums, cast iron repairing agent can also be used. In order to ensure the strong adhesion of the cast iron repairing agent on the surface of the drum, the drum to be repaired should be cleaned with benzene and acetone before use, and then the eye is repaired at the repaired part. For repairs, if the part to be repaired is deep, it is necessary to drill holes in the drum (larger holes can be considered for larger areas), tap the thread on the hole, and then use the repair agent. In the process of completely drying the repairing agent, it is continuously sanded with sandpaper until it is smooth and smooth.
In addition, it is necessary to pay attention to the use of glue to repair the drum. It is best to repair only the surface of the drum due to wear and corrosion. Do not repair the surface of the drum due to the entry of hard objects into the rolling, because such wounds are generally deep and surrounded by depressions. There is usually a bump.
Brush plating thermal spraying technology
Case: Due to the long-term use of four-open paper printing, the machine has a maximum corrosion of 0.15mm due to the corrosion of the ink, and the overprint is not allowed!
Because the circumferential speed of the blanket cylinder and the impression cylinder are the same, the method of reducing the printing pressure to the whole plate is used successively, and the corrosion depth of the four openings is determined based on the four-in-one ink color sample, and the plating is performed and repaired. Below is a more complete process.
1. Pretreatment. First use the saw blade to remove the long-term deposited sludge on the drum, then use the cleaning agent, acetone to initially remove the surface ink, and then further treatment by electrochemical net treatment. Considering that the drum material is cast iron, and due to long-term use, there is dirt such as ink in the molecular gap of the cast iron surface, so the activation solution of No. 2 and No. 3 activation liquid is used twice for the next plating.
2. The whole plate is coated with a roller for the manual disc printing machine. The overall brush plating is to make the coating on the drum as a whole, which reduces the connection of the coating, thereby reducing the problems that may be caused by the combination between the two coatings. Plated to the full version of the field proofing without pits.
3. Repair to the geometric accuracy range. First use the contour tile, red dan powder to find the high point of the roller plating, and then use the oil stone, water sandpaper to grind off the high part, repeat, until the four rollers "circle smooth and synchronous" beating with the magnetic force meter Within 0.05mm, the large surface is slightly beaten within 0.02mm, and the four-color sample is proofed in the full version, and the ink color is even. Because the four-part part is still printed with the grid version, there is no difference between the overprint and the four-opening after the repair. (This example excludes other reasons that cause the press to be overprinted. Other reasons are not discussed in this article)
This kind of process precision is much higher than the above. At present, this technology still needs a professional maintenance department to do it, and the cost is relatively high, but it is more recommended for the printing machine process requirements.
(Xuzhou brush plating thermal spraying company has this technology)
Disassemble the roller to repair the roller surface
Disassembly roller plating repair: This repair is mainly applied to the surface of the drum with small trachoma, and the surface of the drum is uneven due to prolonged wear and corrosion.
Steps:
1 Position the roller first and then remove it.
2 Grind the surface of the drum with a grinder (about 0.1 mm or less per grinding).
3 Plating on the surface of the drum.
4 Repeat step 23 above until the drum surface meets the machining accuracy requirements.
5 Install the roller.
This repair method is a very complete repair method for the surface of the drum. The repair effect can even be compared with the effect of the new drum. Although the process is cumbersome but the effect is very good, the repaired printing machine can print the dot print with very high quality.
In addition, pay attention to the following three problems in the repair process of the drum.
First, the problem of concentricity. Due to the repair of the old parts, the bearing position of the drum sometimes jumps relative to the center hole due to wear, disassembly and assembly, etc., and the grinding machine itself is processed centering on the center of the two center holes, so that it will appear when processed. The two bearing positions are relatively pulsating relative to the body. According to this situation, the method of grinding and grinding the bearing position and the rolling body at the same time after spraying, so that the two bearing positions and the rolling body are "one knife live", thereby achieving "three concentric"!
Second, the problem of taper (ie tip). Due to the requirements of printing, the roller has a high taper requirement. The taper of the drum will appear on the printed matter: that is, the heavy ink is heavy, and the offset of the overprint is a problem! This requires the tip to be adjusted as small as possible during the grinding machine. In addition, there is no elliptical (ie flat) phenomenon!
Third, the problem is biased. The impression cylinder, blanket cylinder and plate cylinder of the offset press are generally not a complete cylinder due to the requirements of use. Some of the gaps are about one-third, so when you directly rotate on the grinding machine, there will be a "great balance deviation" (commonly known as "heavier")! Direct processing of the drum will occur, horizontal ripples, concave belly, ellipse and other issues, affecting accuracy. The weight is made to different rollers to achieve a certain dynamic balance, and then processed on the grinding machine.
Above we introduced several ways to repair the drum. In the actual production, according to different conditions and technical requirements, the repair process of the drum is selected. However, the repair of the roller after the rolling injury can not be the same as before the rolling injury, because once the roller is crushed, including the roller bearing, the gear, the journal, etc., it will be damaged, so it is the most fundamental in actual production. The method is still to strengthen the management, improve the responsibility of the operators, and avoid rolling the roller. Because some damage can be repaired and many injuries can't be reversed.