Stelter Lambert Frauens Applications of Rotating Magnetic Brush in Powder Coating ICC 2004

• Dr. Eric Stelter • 22 April 2004 • Heidelberg Digital LLC.ppt • page: 1

© Heidelberg Digital L.L.C.

Dr. Eric Stelter, Dr. Pat Lambert, and Mr. Michael Frauens

Heidelberg Digital L.L.C. Rochester, New York USA

Application of

Rotating Magnetic Brush Technology

in New Powder Coating Markets

ICC 2004 22.04.2004



Heidelberg Digital LLC

FixedMagnets

Explanation : What is Rotating Magnetic Brush Technology?

Rotating Magnetic Brush

Magnetic roller with 2 moving parts• Rotating metallic outer shell • Rotating magnetic core

Conventional Magnetic Brush

Magnetic roller with 1 moving part• Rotating metallic outer shell • Stationary magnetic core

RotatingMagnets

S

S

S

N

N

N

N

S

S SN

N

N




Explanation : What is Rotating Magnetic Brush Technology?


Magnetic roller with 2 moving parts• Rotating metallic outer shell • Rotating magnetic core


Magnetic roller with 1 moving part• Rotating metallic outer shell • Stationary magnetic core

RotatingMagnets

S

S

S

N

N

N

N

S

FixedMagnets

S SN

N

N




Characteristics of Rotating Magnetic Brush Technology• Direct deposition of powder to substrate

• Intermediate rollers not required between magnetic brush and substrate of any classification, including magnetic material.

• Non-contact roller (Gap between roller surface and substrate)• Coating thickness adjusted by changing voltage applied to roller• Efficient handling of small particles 9m and larger• Minimal environmental controls required

• Powder particles contained between roller and substrate• Particles not dispersed into air

Performance of Rotating Magnetic Brush Technology• High speed greater than 2,5 m/s • Laydown range with 1 roller: 10 g/m2 to 40 g/m2 (adjustable)• Uniformity better than 10%




• Magnetic carrier particles form a brush on the development roller.

• The powder (-) is attracted to the carrier particles (+)

• The rotation of the outer roller and the magnetic core impart motion to the chains of developer

• Bias voltage applied to metallic shell moves powder to substrate.

Substrate

N SS

++ + +

++

+++

+++ + +

+-- -

- - ---

--- -

- - -- -

--

- ------

---

- - ------

----

---

-----

- - - -

Rotating Magnetic Brush:

Roller with rotating outer metallic shell and rotating

inner magnetic core.




The Powder Coating Process: Experimental Equipment

• Metallic substrate

• Coating apparatus

with magnetic rollers

and drive motors

• Power supplies for

bias voltage to roller

• Motors and motor

speed controllers

• Powder reservoir and

feed mechanism




The Rotating Magnetic Brush

• Modified Imaging/Coating Module

(~ 48cm x 15cm x 15cm)

• Single, non-contact roller

• Deposition onto ferromagnetic

substrate. (Reasons Include:

high field gradient, demagnetize

substrate with rotating core)

• Used in thousands of existing

printing machines.




The Rotating Magnetic Brush: Carrier Particles

• Strontium Ferrite particles

• Permanently magnetized

• Polymer coated

• Can accommodate a wide

range of powder paint

materials.




Magnetic Brush Types


Technology


Technology

Rotating Magnets

"Dynamic/Flipping" Chains Rotating Smooth Shell

S

S

S

N

N

N

"Static/Less Dynamic" Chains Rotating Rough Shell

N

S

Fixed Magnets

S S S N N

N




Initial stage of deposition

Simulation of Deposition

• Magnetic brush moves, creating a

uniform powder coating without streaks.• Carrier particles are large (26 microns)• Powder particles are small (9 microns)

• Particles are deposited in areas of

substrate with electrostatic charge• Particles are colored based on their final

location at the completion of deposition

(final state coloration)

Red particles will end up at the top of the

development zone, blue particles at the bottom




Magnetic Brush and Powder Coating: History

Powder coating from a magnetic brush to an intermediate transfer member and then to a substrate.

(U.S. Pat. 3,306,193)

Powder coating directly from a magnetic brush to a metallic substrate.

(U.S. Pat. 4,041,901)




• Deposition of Paint Particle (Toner

Particle) to Substrate (Photoconductor)

occurs only during 3-body contact

events

• Describes development with a

stationary magnetic core

Equilibrium Theory of Development

(from copier technology)

MQ

V

A

M 0

Schein, "Electrophotography and Development Physics" 1996

Substrate

Paint Particle




• Roller speeds were set

and substrate speed was

varied

• Deposition of particles is

greater with rotating

magnetic brush

• Imaging toner (polymeric

particles) were used in

this test. This toner is

used in Heidelberg Digital

printers.

Comparison of Equilibrium Theory for Conventional

Magnetic Brush with Rotating Magnetic Brush

Comparison of Actual Data to Equilibrium Theory

0

10

20

30

40

0 1 2 3

Web Speed m/s

Po

wd

er A

rea

Den

sity

g

/(sq

m)

High Setpoints Black D1

Equilibrium Theory




Deposition of powder paint

behaves similarly to

deposition of imaging toner.

Modified Powder• particle size for thin films• powder flow aids

Rotating Magnetic Core Development of Modified

Commercially Available Powder

Powder Area Density vs. Web Speed

0102030405060

0 1 2 3Web Speed m/s

Po

wd

er

Are

a D

en

sit

y

g/(

sq

m)

High' Setpoints Gray




• Deposition of powder with

rotating magnetic brush

has exponential behavior

• Extrapolation to high

speeds is straightforward

• Powder area density can

be increased by increasing

bias voltage applied to

magnetic brush.

Rotating Magnetic Core Development vs Web Speed

Powder Area Density vs. Web Speed(Log Plot)

1

10

100

0 1 2 3Web Speed m/s

Po

wd

er

Are

a D

en

sit

y

g/(

sq

m)

High Setpoints Black D1

Lower Setpoints Black D1

Expon. (High Setpoints BlackD1)Expon. (Lower SetpointsBlack D1)




Advantages of this technology for coil coating and other

applications include

• High deposition rates, high process speeds.

• Uniform coatings with controllable coating thickness.

• Wide range of powder particle sizes.

• Manageable hardware tolerances.

• Direct placement of material on ferrous metals. (In many cases no intermediate is necessary.)

• Low chance of arcing to conductive substrates (intrinsically non-conductive)

• Alternative and textured surfaces using projection coating (no contact of brush with substrate, non-metals)




Future Direction – Emphasis on Systems Integration

• Integration into existing coating line.

• Development of control strategy, thickness measurement, powder

feed.

• Testing and certification of powders and related coatings.

• Optimize curing to take advantage of high coating speed.




Acknowledgements

• We would like to acknowledge the assistance of Joseph Guth, Vern Lincoln, and Bret

Johnston of Heidelberg Digital L.L.C. Rochester, New York USA.• Several figures in this presentation were used with permission from L. B. Shein:

Electrophotography and Development Physics, revised 2nd ed. (Electrostatic

Applications, Morgan Hill, CA 1996). • Patents that were shown are from http://www.uspto.gov• The simulation work was done by Ulrich Mutze, Eric Stelter, and Thomas Dera of

Heidelberg Digital with John Zollweg of Cornell University, Ithaca, New York USA.

This research was conducted using resources made available by CTC High

Performance Solutions, a Dell, Intel, Microsoft and Cornell Theory Center (CTC)

alliance that is bringing high-performance computing to the enterprise. CTC also

receives funding from Cornell University, New York State, federal agencies,

foundations, and other corporate partners.

Stelter Lambert Frauens Applications of Rotating Magnetic Brush in Powder Coating ICC 2004

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