Volume 05 - Surface Engineering Part 9 potx

Equipment for Powder Coating Electrostatic spray system for application of powder coatings... Times required for interfaces of two steel parts of equal area but different mass to reach

Parts that can be efficiently coated by dip painting If considerably larger, parts like these could be painted more efficiently by the flow coating process (a) Blower wheel (b) Wire fan guard

Equipment for Dip Painting

Table 6 Equipment requirements for dip painting two steel production parts

Procedure or equipment Angle bracket (a) Spring hanger (b)

Production requirements

Equipment requirements

Assembly for which flow coating is an efficient painting method

Equipment for Flow Coating

Part A

Equipment for Roller Coating

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Equipment for Curtain Coating

Examples of curtain coating equipment (a) Pressure head curtain coater (b) Double head machine gives fast color changes, applies two component coatings (c) Gravity flow coater with synchronized conveyors

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Electrocoating finishing system

Cathodic electrodeposition coating system (1) Load area (2) Conveyor (3) Pretreatment (4) Deionized water rinse (5) Electrodeposition tank (6) Recirculated permeate rinse (7) Fresh permeate rinse (8) Deionized water rinse (9) Dryoff (10) Curing oven (11) Deionized quench for cooling (12) Offload area (13) Source for direct current (14) To anodes in paint bath (15) To work on conveyor (16) Particle filter (17) Cooler (18) Ultrafilter (19) Paint solids return (20) Permeate (21) Controlled flow to waste (22) Permeate storage (23) Recirculated permeate (24) Overflow permeate (25) Source of deionized water (26) Deionized water storage

Advantages

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Equipment for Powder Coating

Electrostatic spray system for application of powder coatings

The electrostatic disk

In a cloud chamber,

In the Gourdine tunnel,

μ μ

Fluidized bed system for application of powder coatings

Electrostatic fluidized bed for application of powder coatings

Direct-fired batch ovens

Convection ovens for curing of paint coatings (a) Direct fired (b) Indirect fired

Indirect-fired batch ovens

Continuous ovens

Convection continuous ovens,

Indirect-fired continuous convection oven for curing of paint coatings (a) Exhaust system (b) Burner

and recirculating fan

Radiant continuous ovens

Times required for interfaces of two steel parts of equal area but different mass to reach baking temperature of 150 °C (300 °F)

Table 7 Causes and corrections of paint film defects associated with baking

Soft film

Pinholing or blistering

• Racks:

• Oven:

• Heat input:

• Exhaust air:

• Air recirculation rate inside oven:

• Space for oven and controls:

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• Dollies:

• Oven:

• Heat input:

• Exhaust air:

• Air recirculation rate inside oven:

• Space for oven and controls:

• Paint Testing Manual, Physical and Chemical Examination of Paint, Varnishes, Lacquers, and Color

Table 8 Selected test methods for paint and painted surfaces

method 141

Wet or liquid tests

Dry film performance tests

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•

The efflux cup method

The torsional method

With the bubble viscometer,

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Colorimeters

Spectrophotometers,

Spectrophotometric curves of gray, red, and blue flat paints

Photoelectric glossmeters

Dial micrometers

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Eddy current thickness gages

Magnetic thickness gages

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The penetration method

The microscopic method

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The Gravelometer

Gravelometer Used to measure impact resistance of paint films

Table 9 Common causes of paint film defects

application methods

ft gal spreading

Table 10 Theoretical spreading rate for coatings

13 μm (0.5 mil) 25 μm (1.0 mil) 38 μm (1.5 mils) 51 μm (2.0 mils) 64 μm (2.5 mils) 76 μm (3.0 mils) Volume

Table 12 Characteristics of the resins for coating structural steel

Chemical and weather resistance Resin Curing method Solvents

Acid Alkali Solvent Water Weather

Remarks

Table 13 Steel Structures Painting Council (SSPC) designations of surface preparation methods for painted coatings

Equipment and materials

Remarks

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Table 14 Paint compatibility

Vinyl Chlorinated rubber

Styrene- butadiene/

styrene- acrylate

Acrylic Polyvinyl

acetate

Epoxy Coal

tar epoxy

Polyester Urethane

Solvent thinned

Lacquer

Water thinned (latex)

Chemically reactive

Table 15 Classification of coatings according to methods of cure

Method of curing Generic type Comments

• Lamb's wool (pelt):

Pitted and weathered metal

Nap length Roller

Table 17 Minimum surface preparation requirements for steel with commonly used coatings

Coating Minimum surface preparation

Table 18 Estimated life of paint systems in years

Average dry film thickness

Climatic conditions Immersion service Splashes and spills Paint

system

Cleaning SSPC designation

m

mils Mild Moderate Severe Fresh

water

Salt water

Petroleum products

Acid Alkaline Halogens

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Robert M Piccirilli and John Burgman, PPG Industries

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Organic Chemistry of Film Formers,

T T

T T

T T

T T

R

T

J Coatings Technol.,

T T

T T

T

T

T

Silsesquioxane used by Stephenson (Ref 30) to improve resistance to environmental etching

Dimethylolpropionic acid, used to make polyurethane water-dispersible

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Technical Publications Committee of the Porcelain Enamel Institute, Inc

Table 1 Melted oxide compositions of frits for groundcoat enamels for sheet steel

Acid- resistant enamel

Water- resistant enamel

Table 2 Melted oxide compositions of frits for cover coat enamels for sheet steel

Clear enamel

Table 3 Melted oxide compositions of frits for enamels for cast iron

Zirconium- opacified (a)

Titania- opacified (a)

Titania- opacified (b)

Table 4 Melted oxide compositons of frits for enamels for aluminum

Barium enamel

Table 5 Fineness of various types of porcelain enamels for sheet steel, cast iron, and aluminum

Type of enamel Milled fineness,

% on 200-mesh screen (a)

Sheet steel

Cast iron

Aluminum

Table 6 Typical end uses and required service criteria

Product Service criteria

Wet process and dry powder, electrostatic

Dry process

Table 7 Mill additions for wet-process enamel frits for sheet steel and cast iron

Additional material Amount

added, %

Effect of addition

R

R

Comparison of sag resistance of selected enameling steels A, low-carbon enameling steels; B, decarburized steels; C, interstitial-free steels

Comparison of yield strength of four enameling steels after firing at 870 °C (1600 °F) A, low-carbon

enameling steels (drawing quality); B, low-carbon enameling steels; C, interstitial-free steels; D, decarburized

Table 8 Maximum dimensions accommodated by enameling facilities

Maximum dimensions of workpiece

Length Width Height

enameling facility

Table 9 Suggested sizes of steel sheet for adequate flatness, rigidity, and sag resistance

Sheet width Maximum total area

Flange forming (a) Flanges can be formed from blanks with notched corners, but they must be welded

in the corner for strength, shape retention, and chip resistance (b) Flanges can be formed with drawn shapes Here, no welding is required

Radius of curvature, two-coat enameling process A minimum radius of 4.8 mm ( in.) must be maintained at flanges, corners, and embossments to minimize assembly and field damage to parts coated by the two-coat enameling process

Radius of curvature, one-coat enameling process A minimum radius of 3.2 mm ( in.) must be maintained at flanges, corners, and embossments to minimize assembly and field damage to parts coated by the one-coat enameling process

Embossed panels Panels may be embossed to increase strength of the part and to provide design relief for flat areas Embossing also stretches the metal, thus reducing "oil canning." In embossing, an outside radius

of 9.5 mm ( in.) and an inside radius of 4.8 mm ( in.) should be maintained for optimum enamelability and service life

Preparation of Steel for Porcelain Enameling

Temperature Stage Solution

composition

Cycle time, min

"Clean only" metal preparation, immersion process

Temperature Stage Solution

composition

Cycle time, seconds

"Clean only" metal preparation, spray process

Temperature Cycle time,

min

No Solution Composition

Ground-coat enameling, acid-etch/nickel-deposition process (dip or spray application)

Table 10 Acid-etch and nickel-deposition solutions for preparing decarburized steels for direct-on cover coating

Operating temperature Cycle time, min Solution (a) Composition of solution

Acid solutions (b)

Nickel deposition solution (g)

Preparation of Cast Iron and Aluminum for Porcelain Enameling

Composition of solution Operating

temperature

No Type

Cycle time, min

Process for preparing heat-treatable aluminum alloys for porcelain enameling

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Schematic of equipment for manual wet spray application

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• Direct-on ground-coat application over parts prepared by the "clean only" method:

• Cover-coat application only:

• Two-coat/one-fire application:

μ μ

Table 11 Cycles for firing ground-coated and cover-coated sheet steel parts in a continuous furnace

Operating temperature (a)

Type of part Gage of

steel

Firing time, min (b)

Coating and firing installation using a U-type continuous furnace Personnel stations: A, loader and stoner; B, spray operator; C, brusher; D, loader; E, unloader and inspector

Temperature and time data for an intermittent furnace Difference in temperature between two sheet steel parts during a 10 min firing cycle at 825 °C (1520 °F) in a 4.9 m (16 ft) intermittent furnace with radiant-tube heating Indicating thermocouple was 710 mm (28 in.) below the top of the conveyor and 580 mm (22.75 in.) above the differential thermocouple Both thermocouples were attached to the parts

Table 12 Cycles for firing porcelain enamel on aluminum

Firing temperature

part

Section thickness, 0.025 mm (001 in.)

Firing time, min

°C °F

μ μ

μ

μ μ

μ μ

Table 13 Applications in which porcelain enamels are used for resistance to corrosive environments

Corrosive environment

Temperature Application

Table 14 Service-temperature limits for porcelain enamels

acid-resistant cover-coat porcelain enamel and low-carbon steel

Table 15 Effect if porcelain enamels on torsion resistance of metal angles

Increase of stress, % (a) Material

Ground coat

One coat Two coats

Table 16 ASTM test methods for porcelain enamels (under jurisdiction of ASTM Porcelain Enamel Subcommittee B.08.12)

Designation Title

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Revised by Woodrow W Carpenter, The Ceramic Coating Company

frit.

Table 1 Compositions of unmelted frit batches for high-temperature service silicate-based coatings

Parts by weight for specific frits (a) Constituent

UI-32 UI-285 UI-346 UI-418 NBS-11 NBS-331 NBS-332

Table 2 Compositions of melted silicate frits for high-temperature service ceramic coatings

Percentage for specific frits (a) Constituent

UI-32 UI-285 UI-346 UI-418 NBS-11 NBS-331 NBS-332

Table 3 Compositions of slips for high-temperature service silicate-based ceramic coatings

Parts by weight for specific coatings (a) Constituent

22

53

UI-32- 1

UI-285- 2

4

UI-346- 1

4

UI-418- 19H

418

417 A- 520

Table 4 Melting points of principal oxides used in ceramic coatings

Melting point Oxide

Table 5 Physical properties of alumina and zirconia flame sprayed from rod

compressive strength

Thermal expansion (a)

Thermal conductivity (b) Coating

g/cm 3 lb/in 3

Porosity, % Color

MPa ksi μm/m·K μin./in.· °F W/m·K Btu·in./ft 2 ·h·°F

Table 6 Melting points of carbides

Melting point Carbide

Table 7 Silicide coatings for protection of refractory metals against oxidation

Oxidation protection (a) Application Constituents of as-applied coating

Suitable substrate metal

°C °F

Life, h Method

Table 8 Characteristics of phosphate-bonded ceramic coatings

Density Maximum service

temperature Type of phosphate Constituents

kg/m 3 lb/ft 3 °C °F

Table 9 Cermet electrodeposited coatings for high-temperature oxidation protection

Service temperature Thickness Constituents

of coating

as applied

Suitable substrate metal

Service life, min

Table 10 Descaling of stainless steels and heat-resisting alloys before ceramic coating

Immersion time, min Alloy

Solution 1 Sodium hydroxide (a)

Solution 2 Sodium hydride (b)

Solution 3 Nitric-hydrofluoric acid (c)

Solution 4 Nitric acid (d)

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Recirculating dip tank for the application of ceramic coatings

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Alumina Zirconia

Cycle time, min Process

Alumina Zirconia

Metal nozzle coated with alumina and zirconia

Operational principle of a gravity-feed powder spray gun

Rod spray installation

Operational principle of rod gun

Comparison of spray particle velocity from rod and powder guns : Velocimeter; •: streak camera, fast particle; : high-speed motion pictures

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Variation in thickness of hand-sprayed alumina and zirconia coatings on steel test coupons Coatings flame sprayed from rod (a) Alumina on steel, 20 tests (b) Zirconia on steel, 30 tests

μ

Use of an inert filler during application of pack cementation coating to the internal surfaces of a nozzle

Table 11 Cycles for application of silicide and other oxidation-resistant ceramic coatings by pack cementation

Processing cycle

Temperature (a) Substrate metal

Time, h (b)

μ μ

μ

Designs of retorts used in the pack cementation process

Fluidized-Bed Cementation Process

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Fluidized-bed cementation process

Effects of (a) time and (b) temperature on the thickness of a silicide coating applied by the bed process to Mo-0.5Ti alloy

fluidized-μ

Vapor-Streaming Cementation

μ μ

μ

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Sectioning and testing of ceramic coatings (a) Sectioning of 3 mm ( in.) thick coating on a cylinder for preparation of specimens for determination of tensile strength, transverse bending, and other properties by standard test methods (b) Testing the bond strength of coatings applied by plasma-arc or combustion flame spraying (c) Testing bond strength of coatings applied by detonation gun process

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Table 12 Hardness of three ceramic coatings deposited by three processes

Hardness of coating, HV Coating material

Flame sprayed

Plasma sprayed

Detonation gun sprayed

Revised by Milton F Stevenson, Jr., Anoplate Corporation

• Increase corrosion resistance:

• Improve decorative appearance:

• Increase paint adhesion:

• Improve adhesive bonding:

• Improve lubricity:

• Provide unique, decorative colors:

• Provide electrical insulation:

• Permit subsequent plating:

• Detection of surface flaws:

• Permit application of photographic and lithographic emulsions:

Table 1 Conventional anodizing processes

density

Film thickness

Bath Amount,

wt%

°C °F

Duration, min

Voltage, V

A/dm 2 A/ft 2 μm mils

Appearance properties

Other properties

Sulfuric acid bath

Alumilite

Temperature Current

density

Film thickness

Bath Amount,

wt%

°C °F

Duration, min

Voltage, V

A/dm 2 A/ft 2 μm mils

Appearance properties

Other properties

Oxydal

Anodal and anoxal

Bengough-Stuart (original process)

Commercial chromic acid process

Eloxal GX

Temperature Current

density

Film thickness

Bath Amount,

wt%

°C °F

Duration, min

Voltage, V

A/dm 2 A/ft 2 μm mils

Appearance properties

Other properties

Oxal

Ematal

Table 2 Typical products for which anodizing is used in final finishing

Size Product

Alloy Finishing

before anodizing

Anodizing process

Post-treatment Service

requirements

or environments