A central European
tissue machine experiencing
severe blade chatter
after years of trouble-free
running; a UK waste-based
tissue machine challenging
suppliers to increase
doctor blade life beyond 24 hours; complaints of edge breaks on
a virgin fibre crescent former. All of these scenarios can be
part of the daily life of a technical trouble-shooter for a chemical
supplier of yankee coatings. Unfortunately, all too often their
approach has been to make a quick recommendation based on a combination
of their experience and intuition and the product offerings available
in their portfolio. Often this serves the customer well, but what
if it were possible to bring scientific methodology to these situations?
In the first real life example above, the Hercules on-site team
quickly determined that the root cause of the problem was a deteriorating
waste quality that led to higher furnish ash levels, which in
turn hardened the coating film, a well-known factor in propagating
blade chatter. Traditional remedies had failed. What was needed
was a much more doctorable but lower adhesion yankee coating film
that would allow coating levels to be maintained without creating
the chatter-inducing hard build-up.
The on-site team turned to the Hercules Technology Group (R&D)
for assistance, knowing
that they were actively
researching yankee coating films. Hercules, having made a decision
some years previously to review its scientific approach to yankee
coating, had initiated a headline technology p r o j e c t : y
a n k e e fundamentals. Led by a paper physicist, the initial
program objective was to understand creping at a completely fundamental
level. An early result was the construction of a new set of laboratory
instrumentation, including the revolutionary adhesion release
tester (ART) as well as a new crepe simulator. The understanding
of crepe mechanics and sophisticated instrumentation initiated
a new phase of chemistry synthesis.
At the time of the severe blade chatter problems described above,
Hercules technologists were busy investigating the effects of
in-situ plasticisers within the polymer mix that makes up the
yankee coating. Testing on both the ART and the crepe simulator
indicated that this approach would yield the easy doctoring solution
so badly needed in Europe. Technologists in the Hercules ‘fast
track’ group then completed new plasticised analog formulations,
and these were made available to trial.
Early trial results more than justified the effort and expense
that had gone into understanding crepe fundamentals. This approach
eliminated the blade chatter on the first machine, which had concerned
the Hercules on-site team, by restarting the asset following a
regrind with the new Hercules products. This asset has since remained
trouble free. The UK waste-based tissue machine achieved record
doctor blade life and significantly reduced breaks from the first
application of the new products.
In many other cases, the technologies have also largely eliminated
edge problems. Customers
in North America
and Asia have also been enjoying similar success with these latest
products which represent just the first of a series of new product
developments in this field from Hercules, all resulting from the
visionary decision to invest in genuine fundamental research five
years ago. TW
Hercules tissue technologists
The Hercules
tissue technologists are based at the Hercules Research Center,
located in a campus-like setting outside the city of Wilmington,
Delaware, USA, with a small satellite facility in Zwijndrecht,
The Netherlands. Headed by a paper physicist, a dedicated group
of researchers works seamlessly between theoretical modelling,
analytical investigations and synthetic chemistry research.
The newly commissioned instruments, especially the adhesion
release tester (ART), attract the attention of most visitors
to the research centre. The ART is able to measure coating
film adhesion and failure under a variety of temperature, dwell
time, and moisture conditions. Backing up the ART is the crepe
simulator, which is capable of creping at 1500 m/min, measuring
doctoring forces, and investigating micro-crepe formation via
highspeed photography. |
