Metal Finishing Fundamentals

Which Metal Finishing Option Is Best for You?

What Is Metal Finishing?

Metal finishing is the process of changing the surface of an object, for improving its appearance and/or durability. Many types of metal finishing exist. Electroplating, electroless plating, anodizing, HVOF, vapor deposition, nitriding, and more are all processes used to enhance the surface characteristics of objects large or small. Applications range from industrial, commercial, military to residential use. At U.S. Chrome we focus on the production of a thin surface coating of the metal upon another by electrodeposition or autocatalytic reaction. That object could be any type of metal itself, like steel, aluminum, titanium, or it could be nonmetallic.

Why Metal Finishing?

There are many reasons to use metal finishing. Increasing an object’s strength and durability, improved wear and/or corrosion resistance, reduced sliding forces (friction), improved release properties, changes to optical properties, and altering the appearance are several that come to mind.

How’s It Done?

There are many processes and technologies employed to perform metal finishing. Two of the more fundamental techniques are electroplating (electrodeposition) and electroless (autocatalytic) plating. Below is a breakdown of each of these types, layer by layer.

Electroplating

In electroplating the object being coated is placed in a liquid bath (also called the electrolyte) that contains ions of the metal selected. When this bath is electrified, the metal ions bond to the object, creating a perfectly adhered coating. Thickness of the deposit can be manipulated via changes to the amperage being applied and the length of time the object stays in the bath. The coating is deposited on the surface areas of the object (negatively charged Cathode) that are directly exposed to a positively charged inert Anode. This method can build heavy deposits for repair and salvage work. Typical metals are Chromium, Cobalt, and Nickel.

Electroless plating

Much like electroplating, this process also involves a liquid bath with metal ions, but the transfer of metal requires no electricity. The metal ions and bath constituents react on a catalytic surface (the object) causing the deposit of metal to occur. This is called an autocatalytic reaction. This method of plating has a much slower deposition rate than electroplating and only thin deposits of up to 50 micrometers thick is typical. It is not used as a buildup coating. Typical metals plated in this manner are Nickel and Copper.

Chrome Electroplating

There are a variety of types of chrome plating that exist to suit the end products intended use. The two major sub-categories are Decorative and Hard chrome.

Decorative chrome plating

Decorative chrome has a shiny appearance and is designed for aesthetics. The chromium is usually applied over bright nickel or copper plating with a very thin thickness range of only 0.05 to 0.5 micrometers. Pleasing to the eye, decorative chrome offers good corrosion and durability suited for automotive, hand tools and the like. Decorative chrome is not offered by U.S. Chrome Corporation.

Hard chrome plating

Commonly referred to as industrial chrome or engineered chrome, hard chrome plating is used to reduce friction, improve durability and wear resistance, enhance corrosion resistance and aid release properties. The standard thickness for non-salvage applications can range from 20 to 40 micrometers and up to 100 micrometers for extreme wear resistance. Chromium is a buildup coating and can be deposited to much greater thicknesses. It is often used to restore worn or mis machined parts to their original dimensions and can be viewed as a sustainable technology. With the increase in plating thickness comes amplified surface defects and non-uniform deposition rates that are influenced by a parts geometry. The thicker deposits require post plating surface operations such as grinding or lapping to bring parts back into tolerance.

Which Metal Should Be My Base?

As with plating, the various types of metals have different attributes and ranges in properties, making each most suitable for their intended use. There are two general types of base metals; ferrous and non-ferrous.

Ferrous metals like alloy steel, carbon steel (structure steel), and cast iron, are widely used for their tensile strength and durability. The high carbon content of Ferrous metals makes them vulnerable to rust when exposed to moisture.  

Non-ferrous metals include aluminum, copper and copper alloys, nickel and nickel alloys, zinc and titanium, as well as precious metals. Their main advantage over ferrous materials is their pliability. They also have no iron content, giving them a higher resistance to rust and corrosion.

Aluminum is best for lightweight needs, like aerospace, while titanium offers lightweight strength and ability to withstand extreme temperatures. excellent heat resistance.

Electro-plating and electroless plating can be applied to most ferrous and non-ferrous metals including; aluminum, most stainless steels, Inconel and titanium.  No matter the type of base metal chosen, the metal finishing requirement of the object will largely depend on the industry, application and intended use. Metal finishing is found in most industries today including; agriculture, aerospace, automotive, energy production, food processing, machine tool and die, marine, medical, military, mining, Oil & Gas, and many others.

Aluminum

Lightweight aluminum is popular for medical, aerospace, and engine components, but the low surface wear characteristics and propensity to gall also means it requires a coating to make it work properly. In addition, aluminum quickly oxidizes making it difficult to coat with traditional electroplating techniques.

U.S. Chrome’s proprietary processes removes the oxide film and adds an intermediate, preparatory layer to the surface allowing the metal plating to bond and deliver an even, durable coating to boost a components longevity.

Titanium

Like aluminum, titanium has an ever present, tenacious oxide film which makes it difficult to electroplate. Titanium is also a metal that easily galls making for a poor wear surface making it a good candidate for metal finishing.

U.S. Chrome’s method removes the oxidized layer and applies chromium directly to the titanium, reducing any adhesion problems from multiple deposits. Plating titanium with chromium greatly improves the objects wear resistance, making this metal a perfect match for industrial, aerospace, and oil and gas components.

Which metal coating process is right for me?

Hard Chrome Plating

Ideal for OEM and salvage components that repeatedly grind, rub, or brush against one another, electroplating with hard chrome adds extra sliding, abrasion resistance, corrosion and heat protection. The chromium metal provides an extremely hard surface, 67 to 70 HRC, that in most instances exceeds the hardness of the base metal adding greatly to a parts durability. Consistently the most popular process for industries such as agriculture, aerospace, machine tool and die, motion and control, energy and more. This classic finish is also one of the toughest, most economical, and most reliable available. Typical thickness is 0.001” to 0.010” thick.

Flash chrome plating

A very thin layer of chrome is applied to objects needing only light wear and corrosion protection. Flash chrome plating reduces the coefficient of friction, improves release properties and provides moderate wear resistance, while maintaining tight tolerances in applications where post plating processes, such as grinding, are not practical. Typical thickness is 0.0002” to 0.001” thick

Thin Dense Chrome

Ideal when you need the thinnest, most precise, and most dense, crack-free layer that chrome has to offer. This material lengthens wear life and offers improved corrosion protection. Thin dense chrome is ideal for aerospace and medical components and eliminates the post plate operations such as grinding. Typical thickness is 0.00005” to 0.00015” thick

Crack-free Chrome

Slightly softer and thinner than standard hard chrome, our crack-free chromium offers protection against corrosive elements and greater wear resistance. It is very popular in the production of commercial hydraulics, rifle barrels, and other parts subject to regular wear or exposure to corrosive gases. Typical thickness is 0.0001” to 0.0005” thick

Electroless Nickel

While most metal plating involves applying a direct electrical current to the object, in electroless nickel (EN) plating, the object reacts to the plating bath chemistry, creating a uniform and smooth, layer with very little surface porosity. The even deposition makes it an ideal choice for complex, non-line of sight, geometries and often eliminates grinding after plating. EN is applied to improve the corrosion and wear resistance of an object. Electroless nickel metal is a softer metal than chrome and can range from 40 to 60 HRC depending on the phosphorous content. Many times, a layer of hard chrome is applied over the nickel layer maximizing the objects ability to resist corrosion and wear.

This versatile and dependable plating is trusted for plastic and glass molds, bearings,complex gears, medical parts, oil and gas pieces, and aircraft components.  The nickel layer can be made harder by a post plate heat treatment, however, this a reduces the coatings effectiveness to resist corrosion. Typical thickness is 0.0002” to 0.002” thick

Alternative and Green Coatings

NiCom

A composite coating that mixes nickel with a hard particulate, NiCom protects against corrosion and wear on all metals, including aluminum and titanium. It also has the added value of providing good oil retention which is well suited for internal combustion engines of all varieties, including drones, snowmobiles, motorcycles, marine, automotive, high performance racing, or any other cylinder/piston mechanism where sliding wear resistance and lubricity are important.
2 links to learn more - About NiCom and www.usNiCom.com 

TriCom

Another composite coating, TriCom, is a proven alternative for electroless nickel, nickel chrome, electrolytic nickel, and hard chrome processes. The TriCom family of eco-friendly, composite coatings are available in various formulations designed to provide low frictional properties, wear resistance, and superior corrosion resistance. The coating is applied using an electrodeposition process like chrome but with much greater efficiency. The result is a fully-dense, barrier coating that can be heat treated to increase the hardness and wear ability. Hardened particles can also be incorporated in the coating matrix to further enhance the coatings wear resistance properties. The coating hardness can range from 52 to 64 HRC.

Ideal for both OEM and salvage, these highly versatile coatings have been fielded successfully in applications that include aerospace actuator housings, agricultural planters, nuclear piston seals, helicopter rotor dampeners, truck suspension components, rotary engine components, oil and gas exploration housings, military actuators, marine shafts and more.
Learn more about TriCom

Call or Request a Quote Today: 

http://www.uschrome.com/locations

https://www.usctechnologies.com 

 

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