Paper Technology International 2024 - Journal - Page 25
PAPERTECHNOLOGYINTERNATIONAL
Best cleaning practice
PProJeton -forming
fabrics and press felts
Claus Robberts, Founder and CEO, ProJet b.v.
INTRODUCTION:
The Forming Section and Forming Fabrics on Paper Machines
The forming of the paper sheet is the most critical phase in the paper production process. The cleanliness throughout the operating
life of the forming fabrics is critical to maintain paper quality on a high quality. A clean Forming Fabric, with consistently high permeability
and dewatering capabilities, delivers important productivity and performance advantages. Better dewatering in the Forming Section leads
substantial improvement in dryness level when the sheet leaves the Wire Section, into the Press Section. Forming Fabrics loose dewatering
ability when contamination builds up over time. More and more contamination can be found on Forming Fabrics caused by an increasing
use of secondary 昀椀bers, recycling of coated broke, increasing use of sheet 昀椀llers, an increased use of recycled mill water supplies, and
the increased use of process chemicals. Typical contaminants are wet strength resins, retention aids, stickies, scale, de-foamers, calcium
carbonate, clay, starch, and alkaline size.
Controlling contamination on machine clothing on Tissue
machines
Controlling contamination on a tissue machine is critically
important. A customized cleaning program for machine clothing
will keep the tissue machine running ef昀椀ciently and producing high
quality tissue. A Tissue crescent former forming fabric and press felt
are relatively short and run at high-speed making effective cleaning
more challenging. In combination with the industry trend to use
more recycled 昀椀ber, result in unique cleaning requirements for tissue
machines.
Typical contaminants found in tissue clothing are similar
as in paper machines, mentioned afore, plus paper 昀椀nes, Yankee
coatings, and rust, The biggest cleaning challenge for forming
fabrics are stickies and other contaminants that are not watersoluble. These contaminants start to collect in machine’s clothing
yarn crossover points. Once small particles (stickies) attach, they
attract other stickies and they start to conglomerate.
While these conglomerates are growing, they more and
more will affect the drainage path of the fabric, eventually leading
holes in the sheet. Most high-speed tissue machines are using triple
layer forming fabrics which provide the best sheet formation on the
sheet side and longer life for the inner layer of the fabric. Sheet
dewatering occurs when the press felt transfers water from the sheet
to the press through microscopic voids in the felt. Water transfer
cannot occur properly anymore when the channels are blocked with
contaminants or gels. Properly cleaned press fabrics maintain their
voids and provide consistent, dewatering performance throughout
the life and have a positive effect on dewatering ef昀椀ciency, energy
use, sheet pro昀椀le, sheet bulkiness and press felt life.
Conventional cleaning methods for Forming Fabrics and Press
Felts
Cleaning methods can be classi昀椀ed in chemical and
mechanical; while chemical is becoming less common, it still
required for certain conditions. Mechanical (high pressure) is the
most widely used method.
The conventional cleaning method comprises of an
oscillating HP shower on the sheet side and a 昀氀ooded nip shower on
the inside.
Figure 1: Typical “stickies” on a Forming Fabric.
Typical pressure varies between 15-40 bar (230-600 psi) and
typical nozzle size is 0.8-1.0mm (.032”-.040”). This leads, depending
on number of nozzles and sheet width, to a water consumption
between 100.0 – 250.0 ltr/min (25.0 – 100.0 GPM). Typical power
consumption of the HP pump for these showers is 40.0 – 80.0kW
(50.0 – 100.0hp).
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