Frequently Asked Questions

General

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What is metal finishing?

The process of metal finishing changes the surface of an object to improve its appearance and/or durability. Common metal finishes include plating, paint, lacquer, ceramic coatings, and other surface treatments.

The metal finishing industry generally categorizes plating operations as electroplating and electroless plating.

What is electroplating

In electroplating, the object (substrate) being coated is placed in a liquid bath (the electrolyte) that contains ions of the metal selected. When this bath is electrified, the metal ions bind to the object, creating a perfectly adhered coating. We can control the thickness of the deposit by changing the amperage, and the time the object stays in the bath.

Typical metals are zinc, chromium, gold, silver and nickel. Common bulk electroplating methods include rack plating, where the parts are affixed to a fixture, and barrel plating, where numerous smaller parts are tumbled inside a barrel-shaped cage.

What does the RoHS term stand for?

RoHS is a product level compliance based on the European Union’s Directive 2002/95/EC, the Restriction of the Use of certain Hazardous Substances in Electrical and Electronic Equipment (RoHS).

Products compliant with this directive must not exceed the allowable amounts of some restricted materials, such as lead, mercury, cadmium and hexavalent chromium, among others.

What is decorative nickel-chrome plating?

A thin layer of chromium topcoat is applied to nickel-plated components. In this plating application, the thin chromium layer protects the nickel from oxidation and tarnish while providing the bright bluish tint recognized as bright decorative chrome.

What is REACH?

Similar to RoHS, Registration Evaluation Authorization and Restriction of Chemicals (EC) 1907/2006 (REACH) is a product-level regulation that governs the use of substances of very high concern (SVHC). REACH impacts the use of chemicals such as hexavalent chrome.

Electroless Plating

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What is electroless plating?

Electroless plating is an auto-catalytic reaction that is not dependent on an electric current. It deposits an even layer of alloy on the surface of a solid material (substrate), like metal or plastic. During the electroless plating process, we dip the substrate in a bath of the plating solution. In the bath, reducing agents react with the material’s ions to deposit the alloy.

What are the benefits of electroless plating?

Electroless plating eliminates uneven buildup typical of electroplating process that can compromise threads and part tolerances.

What materials can be electroless nickel plated at Eco Finishing?

Eco Finishing can process all steel, aluminum, copper and brass alloys.

Can you replate an electroless nickel-plated part without stripping it?

It can be done, but adherence to the old plating cannot be guaranteed

What makes 'high-phos' electroless nickel different?

Electroless nickel finishes have different levels of phosphorus content. High-phos electroless nickel plating offers increased corrosion resistance because it contains 10-12 percent phosphorus.

What is 'mid-phos' electroless nickel?

Medium-phosphorus electroless nickel, with 7-10% phosphorus content, is considered the standard electroless nickel process which provides a balanced combination of wear resistance, corrosion protection and lubricity at an affordable price.

Anodizing

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What is aluminum anodizing?

During the aluminum anodizing process, we immerse the aluminum in an acid electrolyte bath and pass an electric current through the medium. Rather than a paint or plating alternative, this electrochemical process converts the metal surface so that it has an anodic oxide finish that cannot chip or peel. The finish is highly ordered and porous, making it suitable for secondary processes like coloring and sealing.

What does Conversion Coating mean?

Anodizing is a conversion coating. While paints and plating sit on the surface of the aluminum, anodizing converts the outer layer of aluminum into aluminum oxide, providing a fully integrated coating to its substrate.

What are the benefits of aluminum anodizing?

Aluminum anodizing creates an extremely durable, wear-resistant finish. It is a much harder surface than paint and lasts indefinitely. Other benefits of aluminum anodizing include:

Excellent corrosion protection
Color stability
Ease of maintenance
Good dielectric properties
Provides good adhesion
Fine aesthetics

What is the difference between Type II and Type III anodizing?

The two most commonly specified types of anodizing are: Type II (regular) sulfuric anodizing, and Type III Hardcoat sulfuric anodizing. Type III anodizing is done at a lower temperature than Type II. Both types are very hard, but Type III is much thicker than Type II, making it more resistant to scratching and heavy wear.

What is the difference between coating thickness and build-up in anodizing?

Buildup occurs when the oxide layer adds a dimensional difference to the original aluminum surface. Coating thickness, on the other hand, is the actual thickness of the oxide layer. With anodizing, for example, the dimensional gain is about half the deposit thickness. Zinc results in an absolute dimensional gain equal to the thickness of the deposit.

How to calculate anodizing build-up?

Roughly, it is estimated that 50% of the coating thickness (the oxide layer) in type III hardcoat anodizing corresponds to penetration and 50% to buildup, whereas these values are approximately 67%/33% for type II anodizing, respectively.

What aluminum alloys do you recommend for anodizing?

We can talk to you about the best solution for your anodizing needs. We will take into consideration both the piece we are anodizing and your desired result.

In the anodizing tank, most aluminum alloys build an aluminum oxide. Typically, 5000 or 6000 aluminum series is the easiest, whereas the 2000 series due to copper content is generally the most difficult to anodize.

What aluminum casting alloys do you recommend for anodizing?

Aluminum castings are challenging to anodize because they are often porous. The alloy typically preferred for anodizing castings is 518. C443 is another option, but it does not offer the same corrosion resistance.

What about rack marks in the anodized parts?

Rack marks are proportional to the size of the part going through the anodization process.

We can work together to minimize the appearance of rack marks on your parts. Please indicate in your prints the best location for racking your parts.

What is an alkaline etch?

We use caustic soda (sodium hydroxide) to roughen the surface of a metal to achieve a consistent, matte finish.

I would like to hide scratches. Will anodizing work?

Anodizing is not always effective for hiding scratches. If the scratch is significant enough that you can feel it when you rub it with your fingernail, you will still be able to see it after anodizing.

How do I know what anodize coating thickness I should specify for my product?

Coating thickness depends on the final use for your product and how you want it to look. Typically, we recommend a thicker coat for parts that will used in harsh conditions, like outdoors. If the part will be used primarily inside or away from corrosive materials, we may recommend a thin coat. We will be happy to discuss your needs and make a recommendation.

Zinc Plating

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What is zinc plating?

Metals, like steel, are particularly susceptible to corrosion. Our zinc plating process deposits a thin layer of zinc metal onto another metal surface, or substrate. Once it is coated with zinc, the vulnerable surface is protected from outside elements that would otherwise cause corrosion.

How does a zinc coating prevent corrosion?

In addition to forming a physical barrier, zinc is a sacrificial coating. When the substrate is exposed to an environment that would cause corrosion, the zinc corrodes, rather than the metal substrate.

What are some of the most commons applications of zinc?

Zinc plating is ideal for use with fasteners and metal stampings. It is also useful as an undercoating on surfaces prior to painting.

What are the benefits of zinc plating?

Besides its excellent corrosion protection, some of the zinc advantages are:

Low cost – Zinc is inexpensive compared to other options such as nickel.
Low-stress deposit — Other coatings can damage the substrate by placing additional stress on the part.
Flexibility — There are several types of zinc plating solutions that complement difference plating requirements. Zinc can function in several types of bath chemistries.
Ductility — Zinc easily flexes with the contour of the underlying shape.
Friendly to the environment — Zinc plating is a relatively eco-friendly process. Zinc can be recycled.
Aesthetic appeal — Zinc can give iron or steel components a finished appearance, including allowing for customization. During post-treatment, we can also introduce colors for further customization.

How does a chromate conversion coating work?

Chromate conversion coatings are commonly used on zinc plated parts. The chromate coating is a thin inert layer that acts like a paint, protecting the zinc from white rust and boosting corrosion protection.

What kind of chromate conversion coatings are available at Eco Finishing?

Eco Finishing offers a selection of different chromates conversion coatings. Selection of the appropriate chromate depends on the final use of the parts.

Hexavalent chromates offer increased corrosion protection; however, they are used less frequently due to regulations such as RoHS.

Trivalent conversion coatings are RoHS compliant as they do not contain hexavalent chromium.

Chromate conversion coatings also provide brighter and more uniform appearance or color to the parts. We offer Clear (Tri), Yellow (Hex and Tri), Black (Hex and Tri) and Olive Drab (Hex).

Black Oxide

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What is Black Oxide

Our black oxide finish is a conversion coating. Rather than depositing the finish on the surface of the substrate, like nickel or zinc electroplating, we produce a chemical reaction between the iron on the surface of the ferrous metal and oxidizing salts in the black oxide solution. The result is a substrate with dimensional stability and an attractive matte black appearance.

Eco Finishing offers black oxide on ferrous materials, including stainless steel.

What are the main benefits of Black Oxide?

In addition to an appealing appearance, a black oxide finish (link to Black Oxide page) ensures all equipment components operate smoothly.

A black oxide finish will enhance your products with:

Dimensional stability: It does not significantly change the dimensions of parts
Protection corrosion: When you need increased protection from corrosion, parts with a black oxide finish can be oiled or waxed. It’s a cheaper alternative to other methods of corrosion protection, such as electroplating.
High quality, black appearance: It provides a high-quality, appealing black look when a bright shine is not desired at low production costs.

Phosphate Coatings

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What are phosphate coatings?

Phosphate coating is a conversion coating that chemically reacts with the surface of ferrous substrates to create a layer of crystalline phosphates that provide corrosion resistance and lubricity. We apply our phosphate coatings by immersing parts in a dilute solution of phosphoric acid and phosphate salts.

These are used for corrosion resistance, lubricity, friction properties improvement or as a foundation for subsequent coating or painting.

What kind of phosphate coatings are available at Eco Finishing?

Manganese phosphates (type M) are used for corrosion resistance, anti-galling and lubricity. Typical uses are bearings, bushings, fasteners, and projects that require sliding of parts, such as automotive engines and transmission systems.

Zinc phosphates are used for corrosion protection (phosphate and oil), as a lubricant base layer, and as a paint/coating base. When you need lighter protection for products that are exposed to harsh elements, zinc phosphate is an alternative to manganese phosphate.

Hydrogen Embrittlement

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What is hydrogen embrittlement?

Hydrogen embrittlement is the metal’s loss of ductility and reduction of load-bearing capacity due to the absorption of hydrogen atoms by the metal. Hydrogen embrittlement causes components to crack and fracture at stresses well below the specified tensile strength of the metal.

How is hydrogen embrittlement produced?

Hydrogen can enter and diffuse through steel at room temperature, and this can occur during various manufacturing and assembly operations or operational use – any time that the metal comes into contact with atomic hydrogen. Given enough time, the hydrogen atoms migrate to the metal grain boundaries forming bubbles that reduce ductility and strength.

During the plating processes, hydrogen is present in acid pickling baths used to remove oxide scale from the surface of steel and produced at the surface of the metal being coated.

Are all steels equally susceptible to hydrogen embrittlement?

High-strength steels with a tensile strength greater than about 145 ksi (1000 MPa) are the alloys most vulnerable to hydrogen embrittlement.

What are examples of products susceptible and not susceptible to hydrogen embrittlement?

Susceptible products: Usually, parts with hardness levels 39 Rockwell C and higher are considered susceptible to HE, and HE relief treatment is recommended. Some common examples include:

Grade 9 and higher hex head bolts.
All 12.9 grade screws and bolts.
Hardened tapping screws.
Roll and dowel pins, lock and hardened flat washers.
U and Clip nuts.

Not susceptible: Usually, parts with hardness levels below 39 Rockwell C are not considered susceptible to HE. Some examples include:

Grade 5 and 8 bolts
PC 8.8 and PC 10.9 bolts and screws
ASTM A 325 structural bolts
ASTM A490 structural bolts.
Austenitic stainless steel alloys (304, 316, A2, A4).
Machine screws.
Flat washers when not hardened.
Some nuts and screws

What is hydrogen embrittlement relief?

Hydrogen embrittlement of plated components can be prevented by baking them at temperatures between 375 to 430 °F (190 to 220°C) within a few hours after the plating process. During baking, we can restore strength and ductility by diffusing the hydrogen out of the metal.

Passivation

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What is stainless steel passivation?

Passivation involves removing the free iron from the surface of the metal using a chemical solution of citric acid or nitric acid. It is a non-electrolytic process that helps us make stainless steel more corrosion-resistant. When the surface iron is removed, the other components of the alloy (mainly chromium, often nickel too) are left behind as a surface layer over the underlying steel. These elements react with oxygen to form a non-reactive oxide layer that protects the rest of the steel from corrosion.

Passivation does not remove the heat tint or oxide scale that may be left behind by welding or heat treating. Passivation improves corrosion resistance and leaves a clean finish, but ultimately does not change a part’s appearance or make it visibly brighter.

Why passivate stainless steel?

Stainless steels (SS) are naturally corrosion-resistant, which might suggest that passivation would be unnecessary. The corrosion-resistant properties of SS derive from its chromium content. Under ideal conditions, and in the presence of oxygen, the chromium forms a thin film of inert or “passive” chromium oxide, which covers the surface of the SS, protecting it from corrosion.

However, under normal conditions, any of the following can inhibit the formation of the oxide film which protects stainless steel from corrosion:

Foreign material, especially those found in a manufacturing setting
Sulfides added to the stainless steel for improved machinability
Particles of iron transferred to the stainless-steel surface from cutting tools

Passivation removes these contaminants down to the grain boundary structure of the stainless-steel surface, thus restoring its corrosion resistance properties.

Bright Dip

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What is bright dipping for brass or copper?

During a bright dip, we use a chemical bath to polish brass and copper alloys. The process removes oxides to enhance the brightness of base metals while providing a shiny finish to the original base material color. The bright dip process works well with secondary processes since there is no deposit left behind by bright dipping.

Alkaline Etch

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What is an alkaline etch?

Etching is frequently accomplished in a weak solution of caustic soda (sodium hydroxide). Etching removes metal uniformly and roughens the surface of the metal to give a uniform, matte finish.