Design & Manufacturing

Approaches to Improve

Dewatering in Machine Fabrics

David W. Rosen & Chad Hume*

George W. Woodruff School of Mechanical Engineering

Georgia Institute of Technology

Atlanta, GA 30332-0405

david.rosen@me.gatech.edu 404-894-9668

*visit Poster Session

Dewatering Proposal • Press Fabric designs

Goal: design features, such as holes and

grooves, in inner layer of multi-layer fabric to:

– facilitate dewatering

– prevent rewetting (water flow from roller side

to web side)

• Inner layer manufacturing

Goal: develop 2D and 3D ink-jet printing

testbeds to fabricate designed inner layers

using high viscosity fluids such as thermoplastic

polyurethane (TPU).

Outline

• Press Fabric Designs

• Press Fabric Flow Modeling

– 2D

– 3D

• Ink-Jet Printing

– High viscosity droplet generator

– Droplet impingement results

• Conclusions

Paper Machine Overview

Increasing Dry Solids

1%

20% 50% 95%

𝑑. 𝑠. = 𝑚𝑓𝑖𝑏𝑒𝑟

𝑚𝑓𝑖𝑏𝑒𝑟 + 𝑚𝑤𝑎𝑡𝑒𝑟

Pressing Overview: Basic Physics

• Water movement occurs only with pressure differential

• Pressure must be higher in the sheet than felt

• If hydraulic pressure exists, saturation must exist at

least locally

– There must be a continuum of fluid

• To move fluid:

– Voids must exist in the felt, or

– Voids must exist beyond the felt, or

– Water must flow in MD or CD, or

– Sheet explodes (Crushing)

Press Fabric Design

• Focus on barrier layer

• Design of holes, grooves, features

– circular, elliptical, square, rectangular; conical holes

– grooves in MD, CD

– narrow region at top, bottom, both of layer

• FEA to simulate deformations of layer through

nip.

• Computational Fluid Dynamics to simulate

dewatering and rewetting performance of

features.

Recent trends and directions

• Non-woven bases – Research observed better pressure uniformity,

higher solids, less marking, and less rewet

• Inclusion of polymer membranes and layers

• New manufacturing techniques – Additive manufacturing can build optimized geometry

for polymer layer

Albany AperTech Voith Evolution Voith Revelotion

Outline

• Press Fabric Designs

• Press Fabric Flow Modeling

– 2D

– 3D

• Ink-Jet Printing

– High viscosity droplet generator

– Droplet impingement results

• Conclusions

Research Objective

• Investigate fluid flows in press fabrics to

design novel fabric layers with improved

dewatering.

• Study the effects of hole size, shapes,

patterns, and material behavior on press

fabric performance.

Press Fabric Flow Modeling

• Fluent CFD is used to model steady state

flow through different geometries

• Realizable k-ε turbulence model

Flow Modeling: 2D and 3D

• 2D Simulations

• 3D Simulations

Data Available

• Stream Lines

• Velocity/Pressure

• Pressure Drop

– This is related to flow resistance

2D Base Layer Designs

• 8 designs were studied, forward and reverse

flow Design Variations

Dimensions

Edge

Internal Shape

Rectangle #1 Rectangle #2 Rectangle #3

Rounded #1 Rounded #2 Undercut

Cone #1 Cone #2

Edge Rounding Results

14

Rectangle #1

Rounded #1

Rounded #2

Rounding edge lowers

pressure drop

Edge Undercut Results

Rectangle #1

Undercut

Undercut increases

pressure drop in reverse

direction

2D Conclusions

• Based on the results the following observations are made

– Rounding paper side edge lowers pressure drop

– Reducing membrane thickness lowers pressure drop

– Undercut increases reverse flow pressure drop

– Cone showed negligible difference between forward and reverse flow

• Rounded cylinder with undercut could be best option

3D Base Layer Designs

• Various designs are studied including woven,

nonwoven circular, conical, rounded, undercut

3D Results

• Base Weave

Cone Results – Forward Flow

Cone Reverse Flow

Tesla Hole Concept

• Can we design a hole that has lower forward

resistance and much higher reverse flow

compared with base weave?

Tesla Reverse Flow

3D Results

3D Cone Results

Summary

• 1st order approximation for how hole

design affects flow

• Various designs tested and one proposed

which improves through flow and resists

backflow

• Phase 2:

– How can we manufacture these membranes?

– Inkjet Printing!

Outline

• Press Fabric Designs

• Press Fabric Flow Modeling

– 2D

– 3D

• Ink-Jet Printing

– High viscosity droplet generator

– Droplet impingement results

• Closure

Ink-Jet Printing – 3D Printing • High resolution

• Fast

• Scalable – just add more nozzles

• Multiple materials

• $15-20B industry and

growing

3D Systems SolidScape

Objet

• Print high viscosity (>100cP) and complex fluids (non-Newtonian, suspensions/colloids)

• Ultrasonic droplet generation technology

• New approach to printing. Excite material at resonant frequency in nozzle + acoustic focusing in nozzle causes ejection of droplet.

• Easily scaled for printing repeated patterns.

• Collaborators: Levent Degertekin and Andrei Fedorov (NSF)

28

Ink-Jet Printing

4 mm droplets

• Print high viscosity (>100cP) and complex fluids (non-Newtonian, suspensions/colloids)

• Ultrasonic droplet generation technology

• New approach to printing. Excite material at resonant frequency in nozzle + acoustic focusing in nozzle causes ejection of droplet.

• Easily scaled for printing repeated patterns.

• Collaborators: Levent Degertekin and Andrei Fedorov (NSF)

29

Ink-Jet Printing

4 mm droplets

Ink-Jet Printing

• Develop our high viscosity print-head into

a 3D printing testbed.

• At present, we have:

– print-head, actuation strategies for fluids to

3000 cP, experimental ejection testbed

• Need:

– 2D, 3D stages for 2D, 3D structure printing

– material delivery system

– droplet visualization equipment

Ink-Jet Printing Research • Assemble 2D testbed: XY stages, droplet visualization.

• Experiment with several fluids, various ejection methods:

frequency, power, duty cycle, pulse shape.

• Experiment with deposition patterns: droplet spacing,

timing. Determine resolution, accurcy. Ensure

dependable printing.

• Assemble 3D testbed: XYZ stages, material delivery

system.

• Experiment with layering strategies.

• Determine printable aspect ratios, Z-direction resolution,

accuracy of 3D features.

• Demonstrate the capability of printing inner layer sheets

with designed holes.

Generation

Background

3D Solver

Summary

Deposition

3D Numerical Solver Wenchao Zhou, Ph.D. graduate

32

Droplet distance = 0.6*Droplet Diameter

Regime I: We = 100; Oh = 0.04; High impact velocity and low viscosity

Closure

• 1st order approximation for how hole

design affects flow.

• Rounded entrance, conical shape,

undercut at exit.

• Tesla design is promising. Investigating

variants.

• Ink-Jet printing proposed as manufacturing

process with high viscosity materials.