The Big Three
METAL FINISHING
What is Metal Finishing?
Metal finishing is commonly the last process of metalworking, in which a broad range of surface improvements are achieved as a final step in completing the manufacturing cycle. The type of finish or treatment applied is dependent on a parts form, fit, and function; taking into account the parts final application, necessary performance attributes, dimensional and visual requirements and service life expectations. Metal finishing processes are commonly relied upon to satisfy one or more of the following value-added benefits:
Durability and Wear Resistance
Environmental Protection
Lubricity (Reduced Friction)
Paint Adhesion
Decorative/aesthetic appeal
Abrasion Resistance
Chemical/Corrosion Resistance
Electrical Resistance
Dimensional Tolerance Control
Contaminant Removal
Nottam Faber’s Metal Finishing Processes Include:
Anodize | Chemfilm | Passivation | Electropolish
Nital/Temper Etch | Stress Relief | Hydrogen Embrittlement Baking
Anodize
What is anodizing?
Anodizing in an electrochemical process that converts the metal surface into a durable, corrosion resistant anodic oxide finish. Anodizing is accomplished by immersing the material into an acidic electrolyte bath and passing electric current through the medium. A cathode is mounted inside the anodizing tank and the test piece acts as the anode. During the process, oxygen ions are released from the electrolytic bath to combine with the atoms at the surface of the part being anodized, creating anodize buildup.
The oxide layer is not applied to the surface as seen with painting or plating operations, but instead the oxide is fully integrated into the materials substrate. This full integration results in a surface finish that doesn’t experience chipping or peeling as seen with other surface coating applications.
What materials can be anodized?
Aluminum is ideally suited for anodizing, although other nonferrous metals such as magnesium, zinc, manganese and titanium may also be anodized.
What are the benefits of anodizing?
The most widely known benefits of anodizing are increased durability and resistance to corrosion. Anodizing also offers additional functional and aesthetic enhancements, making it a surface finishing process preferred by a range of industries.
The anodize process enhances the adhesion of subsequent coatings, i.e., dry film lubricant, powder coating, primer, masking. The process also improves dielectric properties of the material, with the anodize acting as an insulator. Additionally, anodized surfaces can be color dyed and sealed to match aesthetic or drawing requirements.
What specifications and industry standards does Nottam comply with?
We perform anodizing in accordance with industry standard MIL-A-8625. For verification of compliance to other standards, or specifications, please contact a member of our team at hello@nottam.com.
What types of anodizing are performed?
Below is a brief description of the three different types of anodize we provide along with their identification per MIL-A-8625.
-
A chromic acid solution produces a very thin non-reactive oxide layer. Commonly used in A&D applications where environmental and mechanical stresses induce heat into components.
Class 1: Non-dyed, natural finish, including dichromate seal
Class 2: Color dyed as specified by customer
Thickness Range (Class 1 & 2): .00002” - .0001”
-
A sulfuric acid bath suitable to all aluminum alloys and product forms, producing surface buildup which exceeds that of Type I. Type II is the most common method of anodizing, and is applied to a wide range of industries because of the excellent corrosion protection and overall durability it provides.
Class 1: Non-dyed, natural finish
Thickness Range: .0002” - .0004”
Class 2: Color dyed as specified by customer
Thickness Range: .0004” - .0006”
-
A sulfuric bath creates an extremely hard, abrasion-resistant oxide layer. Typically applied to sliding parts, i.e., actuators, cams, and other surfaces that experience extreme wear. The process also enhances dielectric properties with the coating acting as an electrical insulator.
Class 1: Non-dyed, natural finish
Class 2: Color dyed as specified by customer
Thickness Range (Class 1 & 2): .002” +/- 20%
Chromate Conversion Coating (Chemfilm)
What is chemfilm?
Also known by trade names Alodine or Irridite, chemfilm or chromate conversion is an electroless chemical process where the metal undergoes a chemical reaction at the surface. Unlike plating, which adds a new layer to a metal surface, chromate conversion coatings transform the existing metal surface into a protective layer while maintaining the original part dimensions. Chemfilm is commonly applied by processing through a series of open tanks, however application methods also include brushing or spraying.
What materials can undergo chemfilm processing?
Aluminum is the most common material to be processed, however copper, magnesium, cadmium and tin also benefit from the protection of chromate conversion coatings.
What are the benefits of chemfilm?
The primary benefit of chemfilm is corrosion protection, but as seen with anodized surfaces some less obvious benefits also present themselves. The process creates a base finish that provides better adhesion for organic coatings, therefore it is commonly applied as a pre-treatment to masking and coating operations. Chemfilm is also an effective solution in offering thermal conductivity and maintaining electrical conductivity.
What specifications and industry standards do you comply with?
Nottam Faber complies with the requirements of MIL-DTL-5541, the most commonly used specification for chromating aluminum. For verification of compliance to other standards, and specifications, please reach out to our team at hello@nottam.com.
What types of chemfilm does Nottam Faber offer?
As identified per MIL-DTL-5541, the following chemfilm types and classes are offered by Nottam Faber.
• Type I Composition containing hexavalent chromium.
• Type II RoHS compliant composition containing non-hexavalent chromium.
• Class IA Intended to provide corrosion prevention of aluminum and its alloys, while also improving adhesion properties. Commonly applied as a pretreatment to masking and coating operations.
• Class III Intended for use as a corrosion preventative film for electrical applications where low resistance is required.
Passivation
What is passivation?
Passivation is defined as the final treatment process used to remove free iron from the surface of corrosion resistant steel. A nitric acid bath creates a passive oxide layer which is less likely to chemically react with air, resulting in improved corrosion protection. Parts which undergo passivation processing will experience no dimensional change.
Corrosion resistance testing is required following the passivation process. The verification methods performed at Nottam Faber are shown in the drop-down list below.
-
Parts are subjected to 95% relative humidity at 100-115⁰F for 24 hours.
-
Parts are swabbed with copper sulfate, sulfuric acid and water for a minimum of 6 minutes.
-
Potassium ferricyanide solution and water is swabbed onto parts. Parts shall show no evidence of discoloration due to the presence of iron.
-
Parts are exposed to a saltwater atmosphere in accordance with ASTM-B-117. A successful verification results in no evidence of rust
What materials can undergo passivation processing?
Passivation is performed on stainless steel categorized under the 200, 300, and 400 designations as well as precipitation hardened stainless steel.
What are the benefits of passivation?
As a surface finishing treatment applied to newly machined parts, the benefits of passivation include the formation of a protective barrier to rust and corrosion, removal of contaminants and metallic inclusions, as well as extended service-life.
What specifications and industry standards do you comply with?
SAE-AMS-2700 (formerly AMS-QQ-P-35) governs the passivation processes performed at Nottam Faber. Please reference the drop-down list below to identify the four types of passivation we offer per method 1 of SAE-AMS-2700. For a review of compliance with other specifications please contact a member of our team at hello@nottam.com.
-
Low temp. nitric acid solution w/sodium dichromate
-
Medium temp. nitric acid solution w/ sodium dichromate
-
High temp. nitric acid solution w/ sodium dichromate
-
Medium temp. high concentration nitric acid solution for free machining steels
Electropolishing
What is electropolishing?
An electrochemical process that removes the outermost layer of metal to create a uniform surface and diminish the appearance of scratches, burrs and unwanted sharp edges.
Electropolishing reduces surface roughness by up to 50%, creating a high-luster, ultra-clean and blemish-free surface. The process can be thought of as reverse electroplating. Instead of adding a thin coating, electropolishing utilizes electric current to dissolve a thin layer of metal from the parts surface into an electrolyte solution.
What materials can be electropolished?
Nearly any metallic surface may be electropolished, but the most common metals processed are 300 & 400 series stainless steel. Forged, wrought, and welded surfaces experience a higher degree of success than cast surfaces, with the rough and porous surface of castings limiting the control of removal. Materials which contain high percentages of carbon, sulfur or silicon also experience adverse effects during electropolishing (and should be processed utilizing a different form of metal finishing.)
What are the benefits of electropolishing?
Electropolishing is a preferred surface fishing method for a wide range of industries, including medical and dental, food processing, aerospace and automotive. The benefits of the process for A&D and automotive applications are the reduction of friction and improved corrosion resistance of the components. Commercial manufacturers prefer the process because it enhances the visual appearance and longevity of their finished products. The medical, dental, and food processing industries utilize electropolishing to keep their tools sterile, functioning and looking like new.
Electropolishing material removal rates can be controlled at intervals of +/- .0001”
What specifications and industry standards do you comply with?
Electropolishing is performed in accordance with ASTM-B-912, of which also addresses the procedures for post-processing and performance testing, i.e., salt spray, humidity or copper sulfate testing.
What is nital etch?
Nital (Temper) etch is a chemical process which unveils the microstructure of carbon steels to visually evaluate the effects of manufacturing processes such as grinding, machining, and heat treating. Following nital etch, all parts should be magnetic particle inspected to ensure product integrity and serviceability. Depending on the hardness of the material, a post-etch hydrogen embrittlement bake may be required.
Nitel/Temper Etch
What standard does Nottam Faber comply with?
The process is performed in accordance with industry standard ASTM-B-912.
Stress Relief & Hydrogen Embrittlement Baking
Stress Relief
Stress relieving is carried out on metal products in order to minimize residual stresses in a materials microstructure, thereby reducing the risk of distortion and material failure during further manufacturing and service life. Stress relief may be required preceding and/or following some of our metal finishing operations depending on the materials hardness and chemical composition.
Hydrogen Embrittlement Relief
Some of our chemical processes introduce hydrogen into the materials substrate, leading to embrittlement and the potential loss of ductility and load bearing capacity. However, the lasting effects hydrogen has on the substrate can be eliminated by employing a post-process hydrogen embrittlement relief bake.
Hydrogen embrittlement relief is performed in an industrial oven at a specified temperature which “bakes” the hydrogen out of the part. This method of embrittlement relief is preferred in the aerospace industry and must typically be performed within 2 hours of introducing hydrogen into the substrate.