Surface Finishing Processe

sBy Hassan Habib

Table of Contents

1.2.3.4.4.A4.B4.C4.D4.E4.F

What is surface finishing?

What is Electroplating?

Anodizing

Zinc Plating

Phosphating

Why we use electroplating?

Types of electroplating?

Alodining

Cadmium Plating

Passivation

What is surface finishing?

Surface Finishing is a set of processes that we use to achieve desired mechanical properties on

different products

1Purpose

What is surface finishing?

• Mechanical properties are desired in products as per the intended use e.g toothpaste, non-stick utensils, impeller blade

• One of the most widely used process of achieving desired qualities is electroplating

• Electroplating is the most widely used process, used in variations to achieve desired properties

1Purpose

Why we use electroplating?

Electroplating is used to deposit a foreign material on mechanical parts to protect them from corrosion, wear and tear and to increase

visual aesthetics in some cases

2Purpose

What is electroplating? 3Process

Anode• Metal to be plated

Cathode

• Part to be plated

Sulphate solution of the same metal

Electroplated Part

Types of surface finishing processes

Following types of surface finishing processes are being used world wide:

• Anodizing (MIL-A-8625F, MIL-STD-171E, ASTM B-766-86)• Alodining (MIL-STD-5541C, MIL-DTL-16232G)• Zinc Plating (ASTM-B-117, B-633)• Cadmium Plating (DEF-DTD-904)• Phosphation (DOD-P-16232 F)• Passivation (QQ-P-35B)

4Types

4.A Anodizin

g

Anodizing

Formation of a chemical conversion coating on metal surface by anodic oxidation is called anodizing. This process is carried out on

aluminum and aluminum alloys or titanium alloys

4A

Purpose

Anodizing 4A

Process

Jigging Degreasing

Cleaning

Anodizing Dyeing Sealing Anodize

d Part

According to MIL-STD-8625 E:

Type I – Chromic acid anodizing, conventional coatings produced from chromic acid bath

Type IB – Chromic acid anodizing, low voltage process, 22 ± 2V

Type IC – Non-chromic acid anodizing, for use as a non-chromate alternative for Type I and IB coatings

Type II – Sulfuric acid anodizing, conventional coatings produced from sulfuric acid bath

Type IIB – Thin sulfuric acid anodizing, for use as a non-chromate alternative for Type I and IB coatings

Type III – Hard Anodic Coatings

Class 1 – Non-dyed

Class 2 – Dyed

4A

AnodizingTypes and Classes

• Bath Concentration = 10% H2SO4

• Current Density = 10-15 A/ft2

• Time = Depending upon

requirement

• Temperature = 18oC-22oC

4A

AnodizingProcess Specifications

4A

AnodizingProcess Tests

Test Type Applicable

Specimen Preparation

Requirement Test method

Coating Weight

I, IB, IC, II, IIB, III Specimen Panels:(min width 3 in, min thickness 0.032 in)

3.7.1.13.7.2.1.1

- ASTM B 244- Weigh

- Metallographic Microscope

Coating Thickness

III Specimen Panels:(min length 3 in, min width 3 in, min thickness 0.032 in)

3.7.2.1 - Weigh after stripping of coating

Corrosion Resistance

I, IB, IC, II, IIB Specimen Panels:(min length 10 in, min width 3 in, min thickness 0.032 in)

3.7.1.2 - Salt Spray test for 336 hrs

Light Fastness

I, IB, IC, II, IIB for Class 2 only

Specimen Panels:(min length 10 in, min width 3 in, min thickness 0.032 in)

3.7.1.3 - Ultraviolet Radiation exposure for 200 hrs

Abrasion Resistance

III Specimen Panels:(min length 4 in, min width 3 in, min thickness 0.063 in)

3.7.2.2 - CS 1000 g wheels at 70 rev/min for 10,000

cycles.

4A

AnodizingAdvantages

• Highly Durable• Inexpensive to produce and maintain• Won’t chip, flake, peel or chalk• Maintains metallic appearance of aluminum• Environmental Friendly

- No heavy metals- By products aid municipal waste water treatment facilities to

separate solids and neutralize pH• Fire Protection

- Anodic oxide layers give a minor increase in the fire protection of aluminum constructions. The melting point of the oxide surface

increases from approximately 650oC to approximately 2000oC

4.B Alodining

Alodining

Alodining is the chemical application of a protective chromate conversion coating

on alumiunum

4B

Purpose

Alodining 4B

Process

Alkaline

Cleaning

RinsingDeoxidation Rinsing

Chromate

CoatingRinsing Alodined

Part

According to MIL-STD-5541 C:

Class 1A – For minimum protection against corrosion resistance. Good quality for the surfaces to be painted or not

Class 3 – For protection against corrosion where lower electrical resistance is required.

4B

AlodiningClasses

4B

AlodiningProcess Tests

Test ClassApplicable

Specimen Preparation Test method

Corrosion Resistance

1A, 3 Specimen Panels:(min length 10 in, min width 3 in,

min thickness 0.02 in)

- Salt Spray test for 168 hrs

Adhesion wet tape

1A, 3 Specimen Panels:(min length 10 in, min width 3 in,

min thickness 0.02 in)

- Adhesion Wet Tape Test

Electrical resistance

testing

3 Specimen Panels:(min length 4 in, min width 3 in,

min thickness 0.063 in)

- At 200 psi nominal electrode pressure class 3 must not have resistance

greater then 5000 microhms

4B

AlodiningAdvantages

• Adds no measurable weight• Does not alter the dimensions of parts (does not make holes

smaller)• Requires essentially no cleanup after application. Encourages

treatment of all small parts as they are fabricated and installed• Requires no electricity or skill to apply

4.C Zinc

Plating

Zinc Plating

Zinc Plating is an electroplating process performed by using Zinc Sulphate solution. It

is a low cost process making it feasible for smaller parts

4C

Purpose

Zinc Plating 4C

Process

CleaningSoak & Electro

CleaningRinsing Plating Rinsing Bright

Dip

Chromate Coating

and Rinsing

Zinc Plated Part

Zinc Plating 4C

Types and Classes

According to ASTM B-633:

Classification Number Service ConditionThickness

Fe/Zn 25 SC 4 (Very Severe) 25Fe/Zn 12 SC 3 (Severe) 12Fe/Zn 8 SC 2 (Moderate)

8Fe/Zn 5 SC 1 (Mild) 5

Type I – Zinc, as platedType II – Zinc, w/colored chromate CoatingType III – Zinc, w/colorless chromate CoatingType IV – Zinc, w/phosphate conversion Coating

Zinc Plating 4C

Process Tests

Test Specimen Preparation Test method

Coating Thickness

Specimen Panels:(min length 100 mm, min

width 25 mm, min thickness 1 mm)

- B487, B499

Adhesion Specimen Panels:(min length 150 mm, min

width 100 mm, min thickness 1 mm)

- B571

Corrosion Resistance

Specimen Panels:(min length 254 mm, min width 76.2, min thickness

0.02 in)

- Salt Spray Test

Hydrogen Embrittlement relief

test

Defined By Purchaser - Sustained Load of 75% of UTS

Zinc Plating 4C

Advantages

• Chromate protected zinc offers higher corrosion resistance• The process is cheap• Electrolytic zinc coatings are used to protect and improve the

appearance of ferrous metals, (i.e iron and steel) as a corrosion barrier, and then as a sacrificial coating

4.D Cadmium Plating

Cadmium Plating

Cadmium Plating is an electroplating process performed by using Cadmium cyanide solution

4D

Purpose

Cadmium Plating 4D

Process

Degreasing

CleaningSoak

ElectroRidoline

Pickling Rinsing

Cd Plating Proces

sRinsing

Cd Plated Part

Cadmium Plating 4D

Types and Classes

According to QQ-P-416 F:

TypesI – As platedII – Supplementary Chromate CoatingIII – Supplementary Phosphate Coating

Classes1 – 0.005 in minimum thickness2 – 0.003 in minimum thickness3 – 0.002 in minimum thickness

Cadmium Plating 4D

Process Tests

Classes

Minimum Thickness

For external surface that can be touched by a ball 0.79 in in

diameter

For external surface that can not be touched by a ball 0.79 in in diameter

Inch Micrometer

Inch Micrometer

1 0.0050 18 0.00030 82 0.0030 8 0.00020 53 0.0020 5 0.00015 4

Cadmium Plating 4D

Advantages

• Cadmium Plating is the preferred method of protecting close-tolerance steel parts against corrosion

• It is particularly useful for reducing or avoiding bi-metallic corrosion and is suitable for soldering

• Cadmium plating is liable to rapid attack by vapors emanating from certain woods, varnishes, plastics and other organic materials, particularly in poorly ventilated or humid conditions

• This plating is mostly used on carbon steel and low alloy steel parts for protection against corrosion

4.E Passivation

Passivation

Passivation is a post plating process and is normally applied to cadmium and zinc plated

parts and to zinc based alloy die-casted parts. Passivation process on plated surfaces

reduces corrosion.

4E

Purpose

Passivation 4E

Process

Clean/Degrease Rinse

Immersion Rinse Immers

ion Dry Passivated Part

Passivation 4E

Types and Classes

According to QQ-P-35 C:

TypesI – Nitric Acid + Sodium Dichromate solution 70-90oFII – Nitric Acid + Sodium Dichromate solution 120-130oFIII – Nitric Acid + Sodium Dichromate solution 145-155oFIV – For steels containing large amounts of sulfur or selenium (0.15%)V – Part Anodic at 3-5 V for high carbon martensitic (440) steelsVI – Concentrated Nitric Acid solution 70-90oFVII – Concentrated Nitric Acid solution 120-140oFVIII – Concentrated Nitric Acid solution 120-130oF

Passivation 4E

Process Tests

Test Test Specimen Test method

Water Immersion Test

The specimen shall consists of samples of parts that are submitted or

selected for acceptance inspection.

- MIL-STD-753B- Parts shall be cleaned with

acetone- Parts then must be immersed in

distilled water for 1 hour and allowed to dry for 24 hrs

- No stains or rust must be visible

High Humidity Test

The specimen shall consists of samples of parts that are submitted or

selected for acceptance inspection.

- MIL-STD-753B- Parts shall be cleaned with

acetone- Parts shall be subjected to 100% humidity at 100oF for 24

hours- No stains or rust must be visible

Salt Spray Test The specimen shall consists of samples of parts that are submitted or

selected for acceptance inspection.

- Salt Spray Test for 2 hrs- ASTM B117

Copper Sulfate Test

The specimen shall consists of samples of parts that are submitted or

selected for acceptance inspection.

- MIL-STD-753B- Parts shall be cleaned with

acetone- Parts then must be swabbed

with copper sulfate solution for 6 minutes

- Parts must not show copper deposits

Passivation 4E

Advantages

• Passivation process on plated surfaces reduces corrosion white rusting of cadmium and zinc under humid conditions

• It helps to reduce the attack on both metals by certain vapors and organic substances

• It improves the performances of subsequently applied parts• It can remove sulfides exposed on the surface of free-machining

stainless alloys• It can remove surface contamination, such as particles of iron-

containing shop dirt and iron particles from cutting tools that can form rust or act as initiation sites for corrosion

4.F Phosphatio

n

Phosphation

Phosphation is a treatment process carried out on iron and steel to provide

coatings for the protection of items against corrosion/rust or wear

4F

Purpose

Phosphation 4F

Types and Classes

According to DOD-P-16232 F:

I – Type M (Manganese Phosphate Base)Class 1 : Supplementary Preservative Treatment or CoatingClass 2 : Supplementary Treatment with lubricating oil as per MIL-L-3150Class 3 : No Supplementary TreatmentClass 4 : Chemically converted with no supplementary treatment

II – Type Z (Zinc Phosphate Base)Class 1 : Supplementary Preservative Treatment or CoatingClass 2 : Supplementary Treatment with lubricating oil as per MIL-L-3150Class 3 : No Supplementary TreatmentClass 4 : Chemically converted with no supplementary treatment

Phosphation 4F

Process Tests

Test TypeApplicable Specimen Preparation Requirement Test method

Coating Weight M & Z

Specimen Panels:(10to 100 sq. cm with AQL

1.8 % defective)3.6

- Weight Balance(Coating weight shall

be 16 gm /m2 & 11 gm / m2 for M & Z type

coatings respectively)

Coating thickness

M 0.005 to 0.010 mm6.6 - Coating thickness

gaugeZ 0.005 to 0.015 mm

Corrosion Resistance

M & Z Specimen Panels:(10 TO 100 Sq cm)

3.6, 4.7.5 - Salt spray test for 72 hours

Surface Finish 6.5 - Surface tester

(0.8 mm)

Adhesion Resistance 6.5 - Grit size 320 or grade

1000 glass beads

Phosphation 4F

Process Tests

Coating Type Material

HardnessHRC

(Minimum)Heat Treatment Stage of

operation

Z Alloy SteelCarbon Steel

3939

98 to 107 degree for 8 hours or room

temperature for 120 hours

For both coatings Heat Treatment is

carried out after coating but before any stressing

operation M

Alloy SteelCarbon Steel

3939

Alloy SteelCarbon Steel

3939

163 ± 14 degree for 4 hours or room temperature for

120 hours

Stress relief shall be given to all parts having minimum hardness value of 39 HRC (Rockwell c)

Phosphation 4F

Process Tests

Coating System E24xposure Time Minimum

Type Class Salt Spray (Hours)

Springfield Immersion

Tests(Minutes)

M

1 1-1/2

10

2 1-1/23 1-1/24 24

Z1 22 23 24 24

Accelerated corrosion resistance requirements are as under:

Phosphation 4F

Advantages

• Phosphation provides drastic protection of items against corrosion and wear & tear

• It helps to reduce the attack on both metals by certain vapors and organic substances

• It can remove surface contaminations, particles of iron-containing shop dirt and iron particles from cutting tools that can form rust or act as initiation sites for corrosion

• It also gives anti-war properties to sliding surfaces during continuous running periods

M Bilal Khan

Umer Farooq

Saqlain

Acknowledgements

References

• MIL-A-8625 F• MIL-STD-171E• ASTM B-766-86• MIL-C-5541C• MIL-DTL-16232G• DEF-DTD-904• L-10205B• QQ-P-35 C• ASTM B-633• DOD-P-16232F• Photos Taken from Flickr’s shares for commercial purpose. Special

Thanks to the people who shared.