Electrolytic Polishing: The Ultimate Guide

If you want to learn more about electrolytic polishing read this guide.

It has all the vital information you are looking for about electrolytic polishing – from techniques, features, and history, to applications.

Everything about electrolytic polishing is right here.

 

What Is Electrolytic Polishing?

Electrolytic polishing is a finishing polishing that involves the removal of material on metal surfaces using chemicals and electrical current.

This process reduces the roughness of metallic surfaces and improves the surface finish.

It is sometimes called anodic polishing, electrochemical polishing, or electropolishing.

 

 

Benefits Of Electrochemical Polishing

Decorative Appearance
Decorative Appearance

Electrolytic polishing may result in a shiny and bright surface. This surface is often reflective and very pleasing aesthetically. Besides, it is uniform.

Microscopic Smoothness
Microscopic Smoothness

Electropolishing removes valleys and peaks on metal surfaces. It also improves the surface roughness to up to 50%.

Elimination Of Oxide Scale
Elimination Of Oxide Scale

The process removes the discoloration marks caused by oxide scales and heat tint.

 

Ultra-clean Surface Finish
Ultra-clean Surface Finish

The surfaces created by electropolishing are effortless to sterilize.

 

Deburring
Deburring

It removes small pieces that can break and slag on the surface material.

History Electrochemical Polishing

The earliest record of electropolishing was cited in 1907. Buetel observed the satin-like gold surface finish when placed in an acidic bath. In 1910, a German chemist discovered cyanide brightening silver, gold, and other metals. For about a decade, no improvement was made.

In the 1920s, sulfuric acid and phosphorous acid were more effective. The present electrolytic polishing resembles the 1929 Jacquet Pierre’s discovery. In the discovery, fine wires of copper anodes were electrolyzed in phosphoric and perchloric acids solution for polishing in organic solvents.

History Electrochemical Polishing
Passivation Vs Anodic Polishing

Passivation Vs Anodic Polishing

Passivation uses chemical solutions such as citric and nitric acid, while anodic polishing uses electric current.  Passivation removes free ions and contaminants and creates an inert layer of oxide. On the other hand, anodic polishing removes all contaminants and leaves the surface clean from all free and foreign material.

Additionally, anodic polishing is preferred for aesthetic products due to the smoother and polished surface finish. Passivation does not change the surface appearance and is not very effective in removing surface oxide contaminants.

Hand Polishing Vs Electrolytic Polishing

Hand polishing is referred to as mechanical polishing. It uses belts and wheels in the removal of layers of material on metallic parts. The process is dependent on the workpiece condition and the finished product requirement. It is also labor-intensive and challenging to maintain consistency.

Electrolytic polishing removes contaminants using electric current and chemical solutions. Moreover, electropolishing is also more advantageous compared to hand polishing. It enhances corrosion resistance, deburrs edges, removes oxide scales and heat tints, improves the product aesthetics, and has an ultraclean surface finish.

Hand Polishing Vs Electrolytic Polishing
Electroplating Vs. Electropolishing.

Electroplating Vs. Electropolishing.

The two processes are electrochemical processes that involve the use of chemicals and electrical current on metal to finish their surfaces. They, however, electroplating and electrolytic polishing work in ways that are opposite to another.

Electropolishing removes contaminants and levels the surface to make the surface smoother and more uniform. On the other hand, electroplating dissolves metal ions on the material’s surface to form a new protective metal layer.

Anodic Polishing Quality Standards

There are different standards that the electropolishing process must adhere to. These standards help ensure the electropolished products and the process taken during electropolishing.

These standards include;

  • ISO 15730:2000 – it is involved in electropolishing metallic and inorganic coatings.
  • SEMI F19 –states the specification of standards for semiconductor applications.
  • SEMI F17 ­– involves the specifications for high purity electropolishing of quality stainless steel tubes.
  • ASTM E1558 – metallographic specimens follow the guidelines of this standard
  • ASTM B 912 – specifications for passivation of metals using electrolytic polishing.
  • ASME BPE – bioprocessing equipment must conform to this standard.
Anodic Polishing Quality Standards

Step-by-step Electropolishing Process

Step-by-step Electropolishing Process
Step-by-step Electropolishing Process

The process occurs in three phases.

  • Surface preparation
  • Electropolishing
  • Post dip

Surface Preparation

In this step, some contaminants such as grease and oil are removed. These contaminants interfere with the uniformity when applying an electric current.

After cleaning, you should be careful not to be in contact with your hands or equipment. The common cause of rejection is improper cleaning. Surface preparation can be done in the following steps;

i. Vapor degreasing and alkaline soak cleaner

ii. Rinsing

iii. Acid pickling or descaling –is used to remove surface discoloration.

iv. Rinsing

Electropolishing

The polishing process occurs here to smooth, brighten, and deburr metal.

i. Electropolish – the process takes 10 to 20 seconds

ii. Boiling off – also called spray rinse or dead rinse.

The used electrolytic solution is captured in a tank.

Post Dip

This step is also called the post-treatment phase. Normally, the residual electrolyte and the by-products of the chemical reaction are removed. Again here, the metal is dried to avoid staining.

Besides, the chemical reaction by-products are removed to ensure surface consistency and product sterility. Finally, the step removes white spots that may appear on metals after drying.

Increasing Efficiency Of Electropolishing Process

Increasing Efficiency Of Electropolishing Process
Increasing Efficiency Of Electropolishing Process

i. Proper maintenance of electropolishing solution – the electrolyte must be tested and maintained regularly.

ii. Monitor the level of dissolved metals in the solution and add an appropriate fresh solution.

iii. Perform the process in a well-controlled environment to ensure good surface quality and operational safety.

iv. Maintain the correct, current density at the anode.

v. Agitate the solution to disperse dissolved metals and remove oxygen and hydrogen from the terminals.

vi. Maintain the material/ workpiece composition and surface cleanliness to improve the quality of electropolishing.

Applications Of Electrolytic Polishing

Marine
Marine

It improves the corrosion resistance of the material and the surface finish. These factors are beneficial to the marine industry. Again, it can be used in boat components such as anchors, ladders, davits, and anchor guides

Paper And Pulp
Paper And Pulp

Electropolishing help produce smooth surfaces that reduce the potential building up of fiber and stringers.

Pharmaceutical
Pharmaceutical

Electropolishing helps in the cleaning of pharmaceutical parts and systems to maintain the consistency needed in the manufacture of pharmaceutical products. The parts include; pipes, tanks, and 300 series steel contact surfaces.

Oil And Gas
Oil And Gas

Heat-treatment, machining, grinding, lifting, and welding sometimes contaminates material surfaces and temper the material’s corrosive properties. Alloys used in oil and gas are exotic and corrosion-resistant. Electropolishing is used to remove contaminants and improve corrosion-resistant properties.

Biotech Industry
Biotech Industry

Biotech equipment requires microscopically featureless surfaces. The electropolished surfaces are less reactive, easily sanitized, and free from contaminant particles. Also, electropolishing reduces the formation of bacterial films and the product’s adhesion.

Nuclear
Nuclear

Electropolishing is used in preparing stainless steel used in the nuclear industry. Improved corrosion resistance assures the material’s performance in service. Electropolishing is helpful in reducing the buildup of radioactive contaminants and easing the decontamination of surfaces.

Polymer Production
Polymer Production

Polymers are produced by components that have smooth and corrosion-resistant surfaces. Smooth surfaces reduce potential stringers and product buildup. Also, buildups lower the rate of product transfer and system efficiency. Here, electropolishing reduces the rate of product buildup significantly.

Semiconductor Industry
Semiconductor Industry

Semiconductor applications are corrosive and need high purity use electropolishing as a standard. It can be used in stringent guidelines for quality systems and packaging services.

Solar Industry
Solar Industry

The high purity and corrosion resistant standards required in a semiconductor is also needed in the solar industry. Electropolishing produces high luster surfaces used in reactors used to produce polysilicon.

Petrochemical Industry
Petrochemical Industry

Components used in this industry are required to be corrosion resistant. The surfaces of the components reduce product adhesion. Some of the components and parts include; surge hoppers, pipeline components, pressure vessels, tubing and pipes, and large tankers.

Anodic Polishing Metals

Electropolishing Stainless Steel
Electropolishing Stainless Steel

It is a reverse plating process that applies electrical current and chemical electrolyte bath to eliminate surface deformities.The process helps in;

  • Improving the corrosion resistance
  • Making it easier to clean the material
  • Repairing the surface of materials.
Electrolytic Polishing Nickel Alloys
Electrolytic Polishing Nickel Alloys

It removes oxides and other embedded impurities on the surface. Thereby, improving the corrosion resistance of nickel alloys.

Electrolytic Polishing Carbon Steel.
Electrolytic Polishing Carbon Steel.

It is a process where the surface is polished to improve surface finish, reduce product adhesion and improve cleanability. Carbon steel polished components include valves, reactor piping, exchangers, product transfer piping, and mixers.

Electrolytic Polishing Aluminum
Electrolytic Polishing Aluminum

It is an anodic process of removing metal surfaces in phosphoric and sulfuric acid electrolytes. Thereby, reducing surface roughness and giving the metal a high gloss appearance.

Electrolytic Polishing Titanium
Electrolytic Polishing Titanium

This electrochemical process removes controlled amounts of surface material on the part of the out layer. It eliminates imperfections, contaminants, sharp edges, and pits that might lead to corrosion.

Electropolishing

People Also Ask:

What Is Flash Electropolishing?

Flash electropolishing is a technique of eliminating oxide scales from heat-treated metal surfaces. It is the only way of removing oxide scales on the stainless-steel surface that is not labor-intensive. Additionally, it is advantageous for achieving consistent results.

How Does Electropolishing Work?

The workpiece is the anode connected to the positive DC power rectifier terminal. The negative terminal is connected to the cathode. Electric current passing through anode and cathode through the electrolyte oxidizes the ions on the metal surface and dissolves them.

Which Chemical Do You Use In Electrolytic Polishing?

Electropolishing uses different chemicals in its process. The most common chemicals include acidic electrolytes such as phosphorous acid and sulfuric acid. Their nature of high acidity makes them perfect for removing contaminants easily and quickly.

Which Acid Do You Use In Electropolishing?

The acids used in electrolytic polishing are many. Here, the most commonly used are sulfuric acid and phosphorous acid due to their highly acidic nature. They can remove metal surfaces quickly and efficiently.

What Quantity Of Material Does Electropolishing Remove?

The quantity of material removed during electropolishing is dependent on the time taken and the amp-minute. Besides, the variables must be controlled to achieve consistency and a reliable surface finish. With precise monitoring, you can remove 0.0001″ on the metal surface.

Can Electrolytic Polishing Burrs?

Electrolytic polishing can be used in deburring of metal surfaces. It removes small pieces that can break and slag on the surface material.

What Is Electrolytic Plasma Polishing?

It is an electropolishing process that uses thermal and electrochemical processes to attain superb surface gloss. The surface finish degree is difficult to obtain through other standard polishing processes.

What Are The Disadvantages Of Electrolytic Polishing?
  • It is limited to the removal of scratches and material.
  • It isn’t easy to establish correct conditions
  • Difficult to control temperatures
  • Limited to the area of polish
  • Some electrolytes are hazardous.
  • Only conductive elements can be used.
  • Pitting can occur
Does Electrolytic Polishing Improve Surface Finish?

Yes, electrolytic polishing improves the surface finish to about 50%

It improves surface roughness, and removes scratches and contaminant.

More Resources:

Electropolishing Process Considerations

Electropolishing

Any Questions About Electrolytic Polishing?
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