Repair of corrosion and wear of offset printing machine drum
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First, the working condition and failure part of the impression cylinder
1. Working condition of the impression cylinder The impression cylinder determines the water before the ink due to the working state, and the water is a chromate solution. The impression cylinder that has been repeatedly printed for many times and in multiple colors will be partially or partially eroded, and is generally lower than the accuracy requirement of the original impression cylinder after being etched. The working pressure of the two impression cylinders is 0.5 to 1 MPa and the total pressure is 50 to 100 MPa. The material of the impression cylinder is ductile iron with a net weight of 300kg. The hardness at the drum is HRC34.
2. Invalid part of the impression cylinder plate cylinder
As shown in the figure, the impression cylinder ∮300 +0.026 × 900, long-term multiple, multi-color repeated printing wear and corrosion of the ink and chromate solution, localized wear and corrosion depth has reached 0.02 ~ 0.50mm, at this time, the concave portion can no longer appear in the printed pattern, and it has been unable to adapt to various printing.
Second, the repair of the impression cylinder
According to the technical conditions of the impression cylinder and the plate cylinder, combined with the specific use environment of the piece, it is decided to use the wire spraying process for repair.
Thermal spraying is one of the surface engineering techniques. It is a special process that uses a heat source to heat the spray material to a molten or semi-molten state and spray it at high speed on the surface of the pretreated workpiece to form a coating.
1. Process foundation,
1 equipment material selection special spraying machine tool; oxygen O 2 ; acetylene gas C 2 H 2 ; QX-1 flame wire air spray gun.
2 Process and requirements, base baking → base roughing → surface pretreatment → preheating → spray bottom layer → spray working layer → finishing
Main chemical composition% Coating hardness HB
Cr C Si Mn P S
12~14 0.36～0.45 ≤0.60 ≤0.60 ≯0.035 ≯0.030 More than 300
Table Spray material martensitic stainless steel (4Cr13)
2. Repair implementation,
1 The surface of the impression cylinder and the plate cylinder is prepared. In order to improve the bonding strength between the coating and the substrate, the surface of the substrate is pretreated, and its function is to enlarge the bonding area between the coating and the substrate, and change the stress distribution to prevent The coating shrinks and falls off, increasing the bonding strength, and the total requirement is to achieve a clean surface. Firstly, the surface is degreased and purified, and the piece is sent to a well type furnace and adjusted to 260-315 ° C, and the oil is baked for 5 hours. After the surface is cooled, the surface is turned to Ra 12.5, and the damaged layer is removed. The fatigue layer, the rust layer, etc.) expose the surface to a new metallic luster to purify and roughen the surface to be sprayed, and to improve the bonding strength between the coating and the surface of the substrate. Then, the part of the brushing agent is not sprayed for protection.
2 Spray coating, pre-heat the workpiece before spraying, preheating temperature is about 100 °C. The underlying material (Mo) is uniformly sprayed on the surface of the preheated roller as a bonding layer, the thickness (100 to 150/μm), and then the working layer (4Cr13) is sprayed. Air pressure (≥0.5MPa), oxygen pressure (≥0.5MPa), acetylene pressure (0.8～1MPa), flame (in neutral flame), jet distance (150～180mm), spray angle and The wire feeding speed is strictly controlled to make the coating evenly and firmly bonded.
3 Finishing after spraying, the method of air cooling is adopted after spraying, that is, after spraying to the specified size, the impression cylinder is continuously rotated on the machine tool to make it slow and prevent the coating from cracking. When it is cooled to normal temperature, it is ground to the dimensions required by the drawings. Grinding uses a medium soft green silicon carbide grinding wheel to grind the surface of the impression cylinder. The grinding wheel speed is 1400r / min, the workpiece moving speed is 1m / min, and the grinding amount is ≤ 0.5mm. After grinding, the working layer of the drum has good bonding performance with the substrate, compact structure, no slag inclusion, no peeling, surface roughness Ra0.8～0.32μm, hardness HRc50 or so, which fully meets the technical requirements.
Surface engineering technology is one of the ten key technologies in the world in the 1980s. Thermal spraying technology is an important part of surface engineering technology. It is an economy that not only restores the size, but also imparts different functions such as wear resistance, corrosion resistance, oxidation resistance, high temperature resistance, heat insulation, electrical conductivity, insulation, sealing, abrasion reduction, radiation, and electron emission. A proven method to meet the needs of a variety of conditions and cutting-edge technology. The oxyacetylene flame wire spraying process solves the problems of surface wear and corrosion of the parts in the printing and packaging industry. It improves the quality of the impression cylinder and the plate cylinder and prolongs the use. life.