A Review Of Powder Coating Technologies And Application ... · 0 Excellent electrical insulating properties 0 Cured films have good release properties, allowing for easy cleaning

A REVIEW OF POWDER COATING

TECHNOLOGIES AND

APPLl CAT10 N METHODS

Copyright @ Ron Joseph & Associates, Inc. Ail rights reserved. January 1991. No part of this Publication may be reproduced or distributed in any form or by any means. or stored in a data bass or a retrieval system. without the prior permission of Ron Joseph &Associates. Inc.

POWDER COATING PARTICLE

contains all of the ingredients

Resin Fillers Pigments Additives

Particle size = 20-150 um

$141

Source: Tho1

Session 3-1 40 8 Page #8

GI

FLUIDIZED BED

Permeable Plate I Low Pressure Air

ELECTROSTATIC APPLICATIOPN

OF POWDER COATING

POWDER COATINGS

Advantages

Environmental Considerations:

Powders have almost zero VOC emissions. Volatile emissions are 0.5-5% by weight, but these are not necessarily ozone precursors.

Hazardous waste disposal costs may be minimal.

Excess or waste powder can often be melted into solid blocks and disposed of t o a solid waste site.

No water disposal problems as would occur when liquid coatings are applied in water-wash spray booths.

Disadvantages

Session 3-1 40 Page # I

POWDER COATINGS

Advantages

Physical Considerations:

Excellent physical performance properties; hardness, abrasion resistance, flexibility, elongation, resistance UV light, etc. (Depending on resin system).

Excellent salt spray (corrosion) resistance, particularly when applied over properly prepared surfaces.

Many powders have excellent machinability, and coated parts can be post formed.

Disadvantages

Session 3-1 40 Page #2

65

POWDER COATINGS

Advantages

Application Considerations:

Ideal for f la t parts or ones with relatively simple configurations.

Relatively clean process particularly if spray booths operate under negative pressure.

Powder can be applied to hot or cold parts.

Ideal for robotic or reciprocating application.

Requires considerably less skill than for application of liquid coatings.

Skilled operators not required to apply the coatings.

Often applies excellent film to otherwise inaccessible areas.

Coats all sharp edges and cut ends and often provides a relatively heavy coating in these areas.

Disadvantages

For most decorative resin systems, requires temperature of 325"F-450°F (1 63" - 204°C) for curing. Some functional resins require temperatures in excess of 500°F. Amarentlv. some epoxies a i e available at 250°F (1 21 "C).

Does require skilled operator to set up guns for each run, and check for quality before parts enter oven.

Often requires manual "touch- up" by an operator who stands a t the end of an automated booth.

Can be more difficult to repair after coating has cured, compared with liquid coatings.

Must be applied to well-cleaned and treated metal surfaces (however, not cleaner than for equivalent liquid coatings).


6s

POWDER COATINGS

Advantages

Application Conditions (Cont:)

Can provide heavy film build in one application. Film thickness can be controlled by adjusting application parameters.

Ideal for coating of parts where minimal masking is required.

In some cases, masking is not required as uncured powder can be brushed or vacuumed off critical surfaces before the coated part enters the curing oven.

To a large extent clean up of the spray booth can be carried out using compressed air. Solvents may only be required during the final stage of cleaning.

Parts are ready for packing and shipping soon after leaving the curing oven.

Disadvantages

Difficult t o adequately coat "Faraday Cages", unless alternative techniques can be used.

With electrostatic equipment, not easy to achieve high film thicknesses (greater than 5 mils), unless part is preheated prior t o coating application. (In most cases you will not need to achieve 5 mils).

In fluidized bed applications cannot easily control film thickness due t o differing heat contents of metal assembly (i.e.light gauge metal fixed t o casting)

Requires clean oven in which dust and other contaminants will not blow onto the coated parts while they are curing.


67

POWDER COATINGS

Advantages

Cost Considerations:

Applied as a single-coat system: - primer and topcoat in one. Therefore, eliminates one operation.

Very high transfer efficiencies greater 95 percent achievable if powder "overspray" is collected and recycled.

Economical for long runs of a few colors.

Lower labor cost since less skilled labor is required to apply the coatings.

Environmental cost are dramatically reduced. (Air, water and waste)

Disadvantages

Generally, capital equipment outlay is greater than for conventional coatings. ($5,000 - $100,000). Small or portable systems are available which are less expensive.lNofe: The costs for converting to powder can be comparable with that for liquid coatings. However; if you intend to go to an automated system, the costs can be higher.)

High-energy usage due to high temperature ovens.


POWDER COATINGS

~

Advantages Disadvantages

Other Considerations:

Available in several resin formulations: acrylic, polyurethane, epoxy, polyester, epoxy/polyester hybrids, TGIC, nylon, etc.

Military agencies are starting to accept powder coatings as replacements for liquids.

Obtainable in a wide range of colors, gloss levels and textures, depending on resin system.

Not suited t o every application: such as:

on thermoplastic or heat sensitive plastics, wood upholstery, rubber tubing, etc.

on parts that cannot tolerate warpage for short runs of multiple colors

where thin films (less than I mil) are required


POWDER COATINGS

Advantages

Other Considerations (Cont):

For short runs of multiple colors it is often more economical to apply the coatings in non- reclaimable, dry filter batch booths.

Disadvantages

for certain metal alloys which may loose critical metallurgical properties when cured a t elevated temperatures for long period

for porous castings in which air blisters will mar the final coated finish

Usually not suited to large parts which cannot enter a high temperature oven. (Note: Some low temperature epoxies which cure at approximately 250°F are available)

Custom colors may not be easily available in quantities of less than 1,000 Ibs. (Some vendors do specialize in small batches).


7 0

FARADAY CAGES

POWDER COATINGS

(Continued)

ELECTROSTATIC APPLICATION

ADVANTAGES DISADVANTAGES

Powder can be applied to hot or cold parts

Adaptable to robotic or reciprocating application

High percentage recovery of unused powder (up to 95% possible)

Requires less skill than application of liquid coatings

Difficult to adequately coat "Faraday Cages." These are areas such as corners, cages, holes, etc. in which there is a reduced electric field to attract the coating.

Not easy to achieve high film thicknesses (greater than 5 mils), unless part is preheated

FLUIDIZED BED APPLICATION

Cannot easily control film thicknesses due to differing heat contents of metal assembly (i.e., light gauge metal next to casting) Applies excellent film to otherwise inac-

cessible areas

Coats all sharp edges Must preheat metal part sometimes to greater than 4OO0F before applying powder

Can provide heavy film build in one application May require special fixturing to ensure total

coverage Relatively inexpensive equipment

Session 3-140 Page #3 72

FLUIDIZED BED

Porous Plate -*

Low Pressure Air b

7.1

PROPERTIES OF SPECIFIC RESIN POWDER COATINGS(')

POLYETHYLENE POWDERS

0 Thermoplastic properties

0 Excellent chemical resistance and toughness

0 Excellent electrical insulating properties

0 Cured films have good release properties, allowing for easy cleaning

0 Used for coating laboratory instruments and equipment

POLYPROPYLENE POWDERS


0 Excellent chemical-resistant properties

NYLON POWDERS


0 Tough finishes, abrasion, wear, and impact-resistant

0 Low coefficient of friction and good lubricity

0 Used on mechanical components of machinery where sliding, rotation, etc. takes place, e.g., spline shafts, shift forks, etc.

POLYVINYL CHLORIDE POWDERS


0 Good chemical resistance

0 Good exterior durability

(I) Source: "User's Guide to Powder Coating," AFP/SME Powder Coating Div. E. Miller, Editor, Published AFP/SME, Michigan 1985.

Session 3-1 40 Page #4 7Ll

PROPERTIES OF SPECIFIC RESIN POWDER COATINGS(')

(Continued)

THERMOPLASTIC POLYESTER POWDERS


0 Excellent decorative coatings for exterior exposure, e.g., patio metal furniture

EPOXY POWDERS, DECORATIVE (Thin-Film)

0 Thermosetting properties

0 Very popular decorative thin-film coating for indoor applications such as toys,

0 Should not be used for outdoor applications because of its poor resistance to

shelving, power tools, kitchen furniture, etc.

sunlight

FUNCTIONAL, CORROSION-RESISTANT, EPOXY POWDERS (Thick-Film)

0 Excellent for internal and external surfaces of pipes and pipelines, rebars, valves,

0 Some coatings can tolerate elevated temperatures up to 25OoF

0 Some coatings can be used in aggressive chemical gaseous environments such as

0 Application by several technologies, including blow coating, powder lance, electros-

0 Some coatings can cure in very short times, such as 10 seconds at 45OoF

0 Excellent electrical insulation properties, and can be used on automotive alternators,

fittings, joints

hydrogen sulphide, carbon dioxide, methane

tatic, fluidized bed, hot spray

electric motors, switch gear, etc.

EPOXY POLYESTER HYBRIDS

0 Thermosetting properties

0 Properties similar to epoxy coatings, but generally have poorer chemical resistance

0 Excellent electrostatic spray properties, with improved penetration into corners and

0 Used for a wide variety of indoor applications, such as: transformer covers, oil

(') Source: "User's Guide to Powder Coating," AFP/SME Powder Coating Div. E. Miller, Editor, Published AFP/SME, Michigan 1985.

and better weatherability. Also better resistance to overbake yellowing.

recesses

filters, air conditioning housings, and power tools.


PROPERTIES OF SPECIFIC RESIN POWDER COATINGS(') (ConUnued)

POLYESTER POWDERS (Thermoset)

(a) Urethane Polyesters

0 Outstanding thin-film appearance and toughness

0 Excellent exterior durability of thin-film

0 Similar properties to liquid polyurethanes

0 Applications include: lighting fixtures, steel and aluminum automotive wheels, garden tractors, playground equipment

(b) Polyester TGlC powders

0 Excellent mechanical properties at high film thickness

0 Good edge coverage

0 Applications include: outdoor furniture, air conditioning units, steel and aluminum automotive wheels, and aluminum extrusions

ACRYLIC POWDERS

0 Excellent exterior durability

0 Excellent resistance to alkalis

0 Thin-film coating

0 Typical applications include: refrigerator cabinets and doors, washing machine parts, range side panels, and garden tractors

(1) Source: "User's Guide to Powder Coating," AFP/SME Powder Coating Div. E. Miller, Editor, Published AFP/SME, Michigan 1985.

Session 3-140 Page #6 7G

POWDER COATING END USES

Automobile parts.

Appliances (dishwashers, washing machines, refrigerators, etc.)

Metal office furniture

Lawn mowers and snowblowers

Metal patio furniture

Tools

Bicycles

Fire extinguishers

Metal shelving

Bathroom faucets

Microwave ovens

Coil springs

Motor mounts

Shock absorbers

Oil filters

Disk drive housings

Automobile wheel rims

Tubular exercise equipment


POWDER COATINGS OW

Advantayes of Powder Coating Blanks'

Blanks are flat pieces of metal which have been precut and punched but not yet post formed, welded or assembled.

Disadvantapes

0

0 0

0 0

0

0 0

0

0

Line speeds can be fiom 15 to 16 fpm. Faster cure times possible If curing can quickly bring steel blanks to temperature while conventional convector heating can maintain temperature. Smaller plant space requirements Reduced costs of surface preparation Dried in Place conversion coatings can be used Faster response to color changes Less waste disposal Higher transfer efficiencies possible

0

0

0

Powder coating must be able to have the flexibility required for

Welding during assembly may not be feasible. Assembly may need to comprise the use of nivets, mechanical fastemers, structural adhesives, etc.

post forming

'Peter Gribble, "Coat it now, Form it Later," Products Finishing, February 1994, p.56

(3-1403)

POWDER COATINGS APPLIED BY TURBOELECTRIC CHARGING

The electrostatic charge is generated by using compressed air to force the powder against the inside of the gun barrel.

Friction charges the power before it leaves the gun.

Apparently, the external electrostatic field is eliminated. This reduces or eliminates the Faraday Cage effect.

MANUFACTURERS OF ELECTROSTATIC SPRAY EQUIPMENT

Ransberg-Gema, Indianapolis, Indiana

Volstatic, Inc., Florence, Kentucky

Nordson Corporation, North American Division, Amherst, Ohio

DeVilbiss Company, Toledo, Ohio

POWDER COATING VENDORS

Glidden Industrial Coatings, Cleveland, Ohio

Ferro Corporation, Coatings Division, Cleveland, Ohio

Morton Chemical Division, Morton Thiokol, Inc. Reading, PA.

H. B. Fuller Company, Vadnais Heights, Minnesota

Thermoclad Company, Erie, PA

O’Brien Corporation, Fuller OBrien Powder, Coatings Division, Houston, Texas

Pratt & Lambert, Inc. Cheektowaga, New York

Atochem, Glen Rock, New Jersey

Farboil, Baltimore, Md.

Session 3-1 40 Page #8 7Q

A Review Of Powder Coating Technologies And Application ... · 0 Excellent electrical insulating properties 0 Cured films have good release properties, allowing for easy cleaning

Documents