C-bar™ Q boosts cylinder
quality, screen efficiency
By Jim Pinkham, Marketing and Business Development Specialist,
and May Fursey, Application Manager - Screening and Cleaning,
Voith Paper
Over the past decade, the high-performance tandem of MultiFoil
rotor and C-bar screen cylinder has boosted efficiency, shaved
power consumption, improved product quality, and strengthened
stickies removal for hundreds of paper mill screening systems.
Now the latest innovation in screen cylinder technology from Voith,
the C-bar Q, is advancing these benefits at tissue mills worldwide.
The MultiFoil rotor, with its swept-back foil design, generates
pressure and suction pulses to lift a fibre mat from the cylinder
surface, keeping it clean. The hallmarks of the C-bar cylinder
have always been its sturdy, non-welded design and the high-precision
workmanship that enables extremely accurate slot width sizing.
Voith engineers leverage this combination to optimize the bar
width, slot width, and profile for the specific needs of each
installation. The width of their vertically arranged bars is a
key distinguishing factor among the various products of the C-bar
series. The narrower the bar width, the more open screening area
the cylinder affords. The new C-bar Q takes this tradition of
precise apertures and tailored profile design to lessen its profile
width, providing a 20% larger open screen area, through narrower
bars, than the former standard cylinder.
The C-bar Q features a low profile angle and is capable of lower
slot velocity, across all stages and various furnish types, than
its predecessors. The results include increased efficiency, concomitantly
increased quality, and uncompromised fibre yield.
Increased efficiency specifically addresses an ongoing concern
of tissue-makers, namely, the efficient removal of stickies. Stickies
removal occurs more readily with lower slot velocities. Trend
analysis data indicate that the C-bar Q attains higher production
capacity without significantly altering its ability to efficiently
remove stickies.
Tissue mill deployment of the C-bar Q highlights this higher
production capacity and shows just how significant the C-bar Q
gain in open screen area can be: The potential increase in production
varies directly with the increase in open area. In other words,
the C-bar Q can provide as much as a 20% capacity increase over
the standard C-bar S cylinder.
While greater production capability, and the corresponding prospect
of needing to install or maintain less machinery, is appealing
in its own right, energy consumption is an increasingly important
factor in the equation. Recent installations of the C-bar Q have
documented the ability to increase throughput without necessarily
increasing total power consumption. In fact, in some cases, the
combination of the cylinder and MultiFoil rotor has significantly
reduced energy demand.
The important gains of the C-bar Q are cemented by the longevity
of its construction. This cylinder is made of a corrosion- and
wear-resistant stainless steel that is specially formulated for
Voith. We call this material NDura™. The cost is comparable to
high-quality stainless steel, and the ability of the material
to withstand acidic assault is comparable as well. The telling
factor, however, is that NDura has double the strength properties
of 316L stainless steel.
BTG's holistic approach to yankee dryer creping
Given today's quality requirements and high machine speeds,
tissue manufacturing has never been more demanding. Perhaps the
most challenging unit operations within the tissue making process
is at the point of yankee dryer creping. Here overall productivity
and the final sheet quality are impacted by a multitude of variables
including doctor blade design, coating chemistry, water & fibre
chemistry and wet-end additives, to name but a few. Furthermore,
all of these variables can have interdependencies. If approached
individually, specific variables can be suboptimized and the over-all
result still unacceptable.
Therefore, it is important to fully understand these inter-dependencies
and establish a systematic approach to process control and optimization.
To take the example of sheet breaks: various process conditions
are impacting the runnability of the machine, such as edge build-up,
sheet bypassing and holes in the paper. One very important factor
is sheet strength, another is the creping blade, its geometry
and material, any wear or damage to it. Blade holder settings
also greatly influence sheet breaks, and so do the coating and
release chemicals used, as well as temperature and sheet moisture.
Due to the uniqueness of every process and machine configuration
a comprehensive approach is necessary.
BTG is now offering a holistic and integrated approach to help
tissue makers optimize and control creping.
Its first step is an in-depth survey of a producer's current
installation, carried out by BTG specialists. This aims to find
the optimal solutions to challenges by integrating BTG technologies
and application knowhow which include:
- State-of-the-art, ceramic and cermet creping doctors that
provide superior
creping properties
and process stability thanks to their long lifetimes and durability.
- Self-profiling creping doctor blade holders
- Wet-end chemistry control instrumentation and fibre & fines
properties analysis
- Vibration monitoring
- A wide range of process and application knowhow and recommendations
on yankee coating
chemicals, yankee
surface technology, etc.
Ultimately, the aim is to deliver process reliability, lower
total cost of operation, and enhance tissue quality and uniformity.
