“Not New Problems:

Roll dynamics caused vibration problems are not new. A decade ago, their detection was difficult. Dynamics caused symptoms were over- shadowed by imbalance and misalignment symptoms. This is no longer true. During the past decade, considerable improvements have been made in balancing and alignment methodology. As a result, the frequency with which undesirable vibration symptoms attributable mostly to imbalance and or misalignment occur have been greatly diminished Now, problems here-to-fore not easily isolated are being detected. These, in large part, include interaction problems. Four prominent interaction problems include: multiples, barring, roundness and wandering alignment. The elimination of these problems is difficult. On existing machines, it may be very expensive. Corrective actions might include buying new rolls, improving roundness quality, and developing new tolerance standards.

"Multiples:

Machines, like some people, have preexisting potential health problems. Multiples are one of those preexisting conditions. They are the only adverse machine conditions that are not an imperfection caused problem. They are a generic problem. 

They are designed into the machine. The multiples syndrome exists when the circumference ratios between two rolls, in nip or in a cluster, are a whole number or a whole number and a simple fraction. Examples of some undesirable multiples are 1 to 1, 2 to 3, 3 to 4, and 4 to 5 (Figure 1). Multiples only come into play, when one of the involved components has or develops a significant sized imperfection. The roll with the significant sized imperfection will gradually imprint an imperfection on the other roll. This will occur because the same areas mate, over and over, ultra frequently. There are also complications. Except for a 1 to 1 multiples situation, a single imperfection on one roll will mate in more than one location on the other roll (Figure 1). As an example, a 4 to 5 multiple condition implies that the smaller roll circumference is 4 units and the larger roll circumference is 5 units (Figure 1). As a result, a specific area on the larger roll will mate, over and over, with four specific areas on the smaller roll. This will occur every five rotations of the smaller roll and four rotations of the larger roll (Figure 1). These mating areas would be 90 degrees apart (25% of roll surface). Five equally spaced defects on the smaller roll would mate 25 different specific locations on the larger roll, every 5 smaller roll cycles. These matings would be spaced at 14.4 degrees apart (4% of the roll surface).”