The Heidelberg four-color offset press was in operation when an issue with the automatic suction system was observed. The paper transfer suction was unstable, leading to frequent failures. Due to the urgent production schedule at the time, there was no immediate disassembly for inspection and maintenance. After some time of continued use, the gas distribution valve failed, and the suction nozzles could no longer function properly.
To address the problem on-site, the first step was to remove the check valve. Upon inspection, a 30mm section of the valve body (with a diameter of 42mm, made of cast copper) had severe surface damage, appearing as if it had been "burned" due to grinding. The worn area showed clear groove marks. At this point, either replacing the entire body or repairing the damaged surface to ensure proper mating with the sleeve was necessary. However, since spare parts were not available, a repair by welding was decided upon.
Using soldering instead of brazing was chosen because it avoids deformation during the heating process, is easier to handle, and requires less technical skill. Although the hardness after soldering would not match that of copper, it was acceptable for emergency repairs. For better results, rosin flux was used instead of solder paste, as it provided a more effective bonding effect.
A 150W electric iron was used to heat the area until the solder reached its melting point. The solder was applied until the layer was slightly higher than the original cylindrical size. Once cooled, the valve body was mounted on a lathe, and the soldered area was sanded down to restore its normal dimensions. As for the valve sleeve, it was also mounted on the lathe and polished using 0# abrasive cloth to smooth out the damaged areas.
This repair was completed quickly and reinstalled into the machine. The performance was back to normal, meeting all operational requirements. This method proved to be effective and practical under emergency conditions.
In addition to the welding repair, adhesive repair could also be considered for similar wear issues. Adhesive coating technology offers advantages such as ease of application, wide adaptability, strong adhesion between the coating and the base material, fast repair speed, good quality, and low cost. The adhesives typically come in two components (A and B), which are mixed in a specific ratio before being evenly applied to the cleaned surface (using acetone for cleaning). After curing, the repaired part can return to its original size.
The cured adhesive has a hardness close to that of copper, making it suitable for various applications. Brands like Belzona from the U.S. and domestic options such as TS111 are reliable choices, offering high-quality performance. These adhesives can be a great alternative for similar repair tasks.
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