Motor Painting

7/28/2019 Motor Painting

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Industrial MotorPaint Facts

GE Industrial Systems
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Industrial Motor Paint Facts:

General

The performance of any paintsystem is a function of the type ofmaterial to be protected and itssurface characteristics, as well as

paint chemistry, film build, andthe environmental exposureexpected for the painted part. Allthese factors must be consideredwhen comparing paint systemsand evaluating results.

Surface TypeBoth the chemistry and surface profile of the

material to be painted will affect its propensity

to corrode. While the characteristics of cast-in

strength of design, heat transfer and precision

machinability make it an ideal material for elec-

tric motor containment, cast iron is also one of

the more challenging surfaces to coat. There islittle in the chemistry of cast iron to prevent it

from rusting, and the typically rough surface

makes building an adequate protective coat dif-

ficult due to natural paint flow away from the

projections. When reviewing paint performance

claims it is important to realize that paint testing

is generally carried out on smooth steel panels.

For equivalent performance on cast iron, the

surface profile must first be filled, and then an

equivalent film built above the projections. This

can be achieved through sophisticated paintchemistry, by expensive multiple coats, or with

filled paints.

Paint Chemistry

A paint system consists of three processes: prop-er cleaning of the machined casting, application

of a suitable primer, and finally the finish coat

itself.

PrimersA primer rich in heavy metals is effective for cor-

rosion resistance, but environmental regulations

now restrict the use of this type of paint. Primers

containing zinc at lower levels than qualifying as

zinc-rich primer are sometimes found on cast-

ings made outside the USA. However a truezinc-rich primer may still be applied to these

under controlled conditions. The casting is first

sandblasted to remove the existing primer coat,

after which new primer is applied in an environ-

mentally approved manner. Since zinc-rich

primers function by creating a galvanic cell with

the metal surface to be protected, they will not

be effective if applied over a previously painted

surface.

Final PaintManufacturers often refer generically to epoxypaint, but there are in fact several grades that

may give entirely different results. For example,

the paint used on GE Standard and Severe Duty

motors is a single part air-dry epoxy ester. The

table below shows a performance comparison of

this epoxy ester against two multi-component

paints. Collectively these are the most common

paints used on industrial motors. Not all may be

available as options on a given motor, depend-

ing on manufacturing location.

Cindy Grimes, GE Industrial Systems, Materials Engineering, 10/17/01


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GE has extensive experience with the single part

epoxyester paint system. This has demonstrated

a consistent ability to perform in a wide range ofenvironments and applications such as paper

mills, steel mills, pumps, and locomotives.

However, this type of paint is not effective in

controlling corrosion in coastal applications,

since the film build of epoxyester paint is inade-

quate to protect the motor from salt corrosion.

For such environments, polyurethane paint pro-

vides both the best corrosion protection and UV

resistance. Because of longer application and

dry times, as well as higher material usage andcost, multi-part catalyzed paint systems are sub-

ject to a price adder if applied at the factory. If

polyurethane paint was not originally specified,

one option is for the customer to apply an addi-

tional coat of two component paint prior to

motor installation.

Epoxy ester Epoxy Polyurethane

# Components 1 2 2 or 3 Cure Mechanism Air Dry Catalyzed Catalyzed

Cure Time 20 min 8-10 hours 8-10 hours

Typical Film Build* 1-2 mils/coat 5-7 mils 5-7 mils

Chemical Resistance Good Excellent Excellent

(HNO3, H2SO4, HCl and NaOH)

Weathering Chalks Chalks Excellent

Impact Resistance Fair *** Excellent Excellent

System Salt Spray **

Bonderite Panels 500 hours +1000 hours +1000 hours Cast Iron 120-350 hours Not Tested Not Tested

IEEE 841 96 hours 96 hours 96 hours

Data reported is based on GE experience* One coat final paint is typical** System implies primer plus topcoat.*** Air-dry epoxy ester paints are fair in impact resistance and will show signs of damage when a chain is dragged across the surface.In some cases, the suppliers will match the primer to the top coat to make it less apparent when the paint chips.


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Baldor

Siemens

GE

USEM

Toshiba

Reliance

Competitive StudiesTo benchmark various paint systems, several

competitive motors were purchased and salt

spray testing performed on their conduit box

covers, motor frames and endshields. Paint per-

formance may vary between parts due to differ-

ent primers used (as indicated by primer color)

and part geometry. Primer type and film thick-

ness can have significant impact on the perform-

ance of the total system. Based on measured

film thickness and performance seen, it appears

that all the motor manufacturers evaluated used

single component air-dry paints (see table on

page 5).


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Conduit Box Covers

Competitor Motor Motor Advertised Salt Top Coat/Primer Conduit Box Salt Spray Failure Type Listed as Spray Performance Film Build* (>2% red rust or blister)

Avg Conduit Box Endshield Frame

Toshiba 324T Severe Duty 96 hours Top Coat + Primer 2.22 120 120 288

Primer 1.09

Toshiba 96 hours Top Coat + Primer 3.17 192

Primer 1.46

Siemens 324T Severe Duty Top Coat + Primer 2.77 168 120 120

Primer 1.55

Siemens 405T Top Coat + Primer 2.98 72

Primer 1.69

Reliance 365T Severe Duty 96 hours Top Coat + Primer 2.38 120 144 144

Primer 1.41

Reliance 445T 96 hours Top Coat + Primer 2.13 48

Primer 1.63

Marathon 324T Severe Duty None Top Coat + Primer 3.68 120

Primer 1.29

USEM 324T Severe Duty 250 hours Top Coat + Primer 3.36 168 144 144

Primer 2.5

Baldor 324T Hostile Duty Top Coat + Primer 2.12 168 120 120

Primer 1.88

GE 405T Severe Duty 96 hours Top Coat + Primer 4.17 336 120** 144

Inside 4.31

Note: Salt spray performed in accordance with ASTM B117. See T99FWL1623 for additional details.* Film build is very difficult to measure on cast iron. Film builds are estimates using an Elcometer magnetic thickness gage.** Unit was not removed until 624 hours for pictures. All other units were removed at the time recorded.

Film ThicknessTwo common failure mechanisms are seen in

painted samples undergoing salt spray tests. The

initial failure mode is caused by inadequate film

build to fill in the profile of the base material.

Subsequently the paint chemistry becomes moreimportant. Film build varied considerably

among the samples tested, as did salt spray per-

formance. However the film thickness that can

be formed in single coats of air-dry primer and

final paint is limited, since excessively heavy

application adversely affects other properties

such as adhesion, appearance and flexibility.

ConclusionField service representatives can help deter-

mine the type of paint suitable for specific

applications. Based on GEs experience and

testing, the paint recommended for coastal

applications where protection against saltcorrosion is important is a catalyzed two

component paint. If a standard single part

air-dry paint is used, motors will begin to

rust after a short period of time, resulting in

unacceptable appearance.


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