Prevention of corrosion in offset printing machines Offset printing machines – just as all other technical products – are susceptible to corrosion. In offset machines corrosions damage mainly arises as a consequence of careless use of the necessary dampening solutions. What is corrosion? Corrosion is the chemical or electrochemical attack of gases or liquids on metals or other materials (plastics, glass, ceramics) in the course of which the function characteristics deteriorate. Corrosion reaches a critical stage if the operation of a machine is impeded. Colourations of metal surfaces without any detrimental effect on operations are not considered to be corrosion. How can corrosion damage be avoided? The printing machinery manufacturers guarantee an optimum selection of materials. However, a close cooperation with the suppliers of printing materials as e.g. printing inks, printing plates, printing chemicals and printing paper is necessary, too. The pressman who works with and processes these materials at the printing machine must know how to use and apply the materials properly. At the same time, the pressman is expected to operate, maintain and service the machine according to the operating instructions.  An offset machine can only work smoothly if: For maintenance and service of the machine, as e.g. protecting and cleaning the cylindrical surfaces, only the recommended cleaners are used. These materials are used only on the recommendations of supplier Liquids are not left on machine parts longer than necessary Hints for maintenance, cleaning and service from the manufacturer are strictly adhered to. A few examples: The materials used in offset printing Printing ink Dampening solution Printing plate Gumming (protection) Paper Cleansing agents have a reciprocal effect on each other, which may result in unexpected chemical reactions. Printing ink in interaction with the dampening solution may lead to chemical reactions resulting in corrosion. Above all chloride, bromide, sulphate and nitrate in high concentrations in printing inks may cause damages. It is recommended to use only printing inks of experienced printing ink manufacturers since these manufacturers make routine chemical analysis. Only dampening solutions with a PH – value between 4.3 and 9 should be used. In the respect, the pressman must always see to it that additives to dampening solutions are dosed according to the instructions of the supplier. Constant checking of the dampening solution in the machine is imperative. In plate making, printing plates with coats of gum Arabic should be free of gum residues on the reverse side, since the PH – value of coating materials is often high. In interaction with dampening solutions, the printing plate may be under- washed, the result is an excess concentration. When gumming is made in the machine, gum material with an inadmissible PH – value must not reach the machine parts. This is especially true for the use of printing plate activators, which must not get in touch with machine parts. Paper as a print material must not lead to corrosion either. As a rule the paper does not contain any corrosion stimulating substances above the allowed maximum values. Inspection or analyses of the paper respectively are comparatively costly. Cleaning and washing material containing aggressive substances that stimulate corrosion must not be used. Some printing cylinders are sealed with a ceramic coat. If inappropriate detergents are used, the sealing may imperceptibly be solved out of the ceramic coat. As a result, the ceramic coat will peel off, corrosion begins. On principle, the printing plate should be taken off the cylinder after printing. The cylinder surfaces must be carefully cleaned and finished with a protection against corrosion. Felt pads for cylinder bearer lubrication must be maintained at regular intervals. Summary Please keep to the recommendations of the machine manufacturer. Operate, clean and maintain the machine according to these recommendations. Handle the machine just as you handle your car. Your car, too, will not run without regular service. In case of damage, inform your machine supplier or engineer immediately. Do not go on printing until the process breaks down. And, take your time with maintenance and service – only then will you be able to operate the machine profitably.