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FLEXO Magazine : April 2009
TECHNOLOGIES & TECHNIQUES be calculated from fi rst principles, but instead must be found empirically with tedious attention given to all details of the system studied. There is, however, one very simple and telling indicator of fric- tion and that is heat generation. Ceramic material has little tendency to make such microbonds and therefore exhibits very low frictional properties against metallic surfaces, hence develops less heat. In Table 2, the operating temperature Friction Facts: 1. Kinetic friction is caused by chemical bonding 2. The more chemically similar surfaces are the greater the bonding 3. A telling indicator of friction is heat generation of various doctor blades were measured in a laboratory test. The blades were run against a non-lubricated hardened steel cylinder to deliberately accelerate results to a failure condition. The various ceramic materials all ran far cooler than the steel blade giving clear evidence of far less friction. Microscopically examining the worn blade tips from this ex- periment also reveals very interesting diff erences in the nature of the material wear. In Figure 3a, the ceramic blade tip contact area is completely unaff ected by the harsh conditions, whereas the steel blade tip in Figure 3b exhibits the characteristic plastic deformation and material loss of a typical blade steel. The metal shavings or burs generated in this test—and as seen coming off the blade tip in Figure 3b—are not unlike the tramp metal com- monly found in the ink systems on presses and often attributed to the scoring of printing cylinder surfaces. Remember: Ceramic material exhibits very low frictional property against metallic surfaces, and thus develops less heat. CONCLUSION The need to optimize the practices and materials in the pressroom and to strive for greater productivity is ever increasing. The use of the newly available state-of- the-art doctor blades can be a signifi cant contributor to this goal with their extreme long life and print quality improvement potential. The eff ect of these doctor blades on the cylinder surface is not only safe but actually healthier in many ways than conventional steel blades. With the proper design and specifi cation of the type of ceramic to match to the cylinder material surface, abrasive wear can be avoided, fric- tion signifi cantly reduced and metal slivers in the ink eliminated. ¦ ABOUT THE AUTHOR: Mike Paczkowski is technical direc- tor, Duroblade for BTG Americas. Paczkowski received his Bachelor of Science degree in Chemical Engineering from the University of Minnesota. After a brief two years in the chemical industry, he found his way into the paper industry. In the 30 years since that time, Pacakowski has had a wealth of technical and management experience in paper- making, coating of paper and board, tissue production and printing methods of various substrates. He has been an active member of TAPPI and FTA and has written and presented many papers related to print- ing, paper and board coating, and the manufacture of creped tissue.