One example
of a roll winding defect is illustrated by a “starred” roll. In the image
to the right this defect is illustrated. A roll that becomes starred was produced with low
wound in tension when the roll was started on the winder or soon after the roll
was started. When rolls are produced with low roll density or low wound in
tension followed by rings or bands of higher roll density, or higher wound in
tension, there is a risk of the higher density bands collapsing the lower
density interior of the rolls resulting in the “starring effect.” This type of
defect is more common on older winders that do not have rider rolls to help
provide a uniform, hard, dense start to the roll.
In one
example of a starred roll, as the roll diameter became larger, more weight
(from the roll itself) and the resulting higher wound in tension on the outside
wraps of the roll caused a larger diameter roll being rewound (without a rider
roll) for an envelope converter to have higher density (higher wound in
tension) on the outside wraps of the roll. While the rolls looked good coming
off the winder, pressure from clamp trucks picking up the rolls caused enough
stress to collapse the softer wound (lower density) interior of the roll.
In the winder
of a modern paper machine, crews have tension controls, brakes, and rider roll
pressure to help control the roll density. Uniform roll density translates into
uniform roll hardness. This image illustrates roll hardness, indicated by the
deceleration measurements from the Tapio RQP, from the core to the outside
diameter of the roll. By cutting slabs off the roll and retesting roll hardness
at descending diameters, a graph sometimes known as a plot of “wound-in
tension,” can be created. Understanding roll density and the WIT
characteristics of a roll becomes a powerful diagnostic tool for evaluating
winder performance.
By using a
WIT (Wound-In Tension) analysis with a Tapio RQP, the winder crew was able to
modify tension and braking (even without a rider roll) to deliver rolls with
more uniform hard starts and more uniform roll density. Along with subtle
winder modifications, the clamping pressure on clamp trucks was limited,
eliminating two factors that resulted in starred rolls and eliminating the
defect.
These images are intended to show one of the more advanced
applications for a roll hardness test, or roll quality profiler (Tapio RQP). This example was contributed by Technidyne's Manager-Technical Services, Jon Saatvedt. Please visit the Technidyne website or the
Tapio RQP website for more information.
