Polishing | Types | Metal Polishing

What is Polishing?

Polishing is the process of creating smooth and shiny surfaces by rubbing them with a polishing wheel or using a chemical treatment, leaving a clean surface with a significant specular reflection. The polishing process is to remove scratches, pits, marks, and other defects on the metal surface. In some cases, such as metal, glass, black and transparent stone, this process reduces diffuse reflection to its lowest value. Polishing wheels are made of leather, canvas, felt or wool which gives extra-fine shininess depending on the wheels.

Polishing and buffing are two different terms used in the surface finishing process. It is a more aggressive process as compared to the buffing process. A most polished surface is done by a polishing process not by buffing.

Why is polishing required?

When any unpolished surface or workpiece is handled or magnified, mountains and valleys are found on the surface. It is because of its rough finish.

After the polishing on the surface, the hilly surfaces are worn down entirely. This polishing has been done by using a coarse wheel first and a fine wheel at last.

The accuracy, size, and shape of the finished surface are not so important in this process. But, in some cases, by sung of machine polishing, 0.025 mm of tolerance can achieve.

The polishing process enhances the aesthetics of any workpiece or object by removing contamination and uneven finishing of the workpiece. It is also in use to create reflective and corrosion-free objects.

What is Metal Polishing?

Metal polishing is the process of removing oxidation, preventing metal from corrosion and contamination, and making metal surface shiny to enhance its appearance.

Metal polishing is the process of removing oxidation, preventing metal from corrosion and contamination, and making metal surface shiny to enhance its appearance.

The polishing of metal is usually carried out in several types of abrasion processes. The type of abrasion depends upon the condition of the workpiece or object and the environment.

If a workpiece has an unfinished or uneven surface, then the polishing process gives several stages. During the first stage, rough abrasive material removes uneven or imperfection on the surface from the workpiece. After that, fine abrasive material removes tiny imperfections on the surface.

In some cases, wax, kerosene, and other lubricants using with the polishing wheel to obtain a good surface finish.

To obtain mirror finishing, polishing compounds using after the rubbing of the polishing wheel with a high-speed machine. Other than that, some typical polishing machines give a great surface finish.

Polishing Compound

Polishing compounds are the mixture of the abrasives used to give a shiny effect and to reduce minor scratches from the car body.

After the rubbing process, a polishing compound applies to the car body to pop out the shininess of the car body paint. Periodically it requires using this compound to maintain the shininess.

But for long-lasting shininess to the paint of car body parts, only polishing compound is not sufficient.

Benefits

• It gives a fine appearance.
• One-step process.
• Gives extra shine to the paint.
• Durable finish.

Metal and Abrasives

In the cases of smooth materials such as brass or aluminum, copper-plated grits using first to remove uneven imperfection in the surface, and after that to obtain shiny surface airflow mop is used.

Non-ferrous alloys, alloy steel, and carbon have high tensile strength. During the polishing of these materials, abrasive materials of white and grey aluminum oxides are used.

Cemented carbide and grey iron are brittle and hard, whereas aluminum, copper, and brass are low tensile strength metals. For polishing of these materials, abrasives of the grey silicon carbide are used.

Polishing wheels are available in the market in various materials such as plastic, wood, leather, rubber(impregnated), paper, canvas, etc.

To treat the flat and flat edge surfaces wooden wheels are suitable because emery or other abrasive materials are glued on the wooden wheel surface.

Whereas for hard surfaces cemented clothes wheels are suitable, and glued cloths wheels are for soft surfaces.

For hard surfaces, a disc of strawboard papers, and for soft surfaces disc of felt paper is suitable.

Types of polishing

There are three types of polishing usually carried out.

• Chemical-Mechanical Polishing
• Flame Polishing
• Vapor Polishing
• Electropolishing

Chemical-Mechanical Polishing

Chemical-mechanical polishing is the process of creating a smooth and shiny surface finish using chemical and mechanical forces. This process is also called planarization. 

As the name implies, chemical means using abrasive and chemical slurry with mechanical means polishing pad with retaining ring (E Clip). In this process, the retaining ring diameter is kept larger than the wafer diameter.

Wafer and pad are pressed against each other with a dynamic polishing head and positioned by the retaining ring of plastic. Non-concentric rotation of the dynamic polishing head with slurry removes the irregularities from the surface and makes it plane. 

CMP tool brings the entire surface within the depth of field.

Flame Polishing

Flame polishing is one of the polishing processes used to polish the material, such as glass or thermoplastic, by applying heat or flame. It is also called as fire polishing process.

When heat applies to the surface of the object, the upper layer gradually melts, and great surface finishing occurs due to surface tension. But it requires the high-skilled worker to obtain a good surface finish.

This method is for components made of acrylic plastic material that has a flat surface. The use of an Oxyhydrogen torch is typical in the flame polishing process.

Vapor Polishing

Vapor Polishing is the process of polishing plastic objects which enhances the surface finish and clarity of objects. Chemical vapor is applied on a plastic object, due to the flow of vapor on a plastic surface, finishing of the surface occurs.

Polycarbonate, acrylic, and ABS objects using in the vapor polishing process. As we know, 3D printed objects are made by adding layer by layer which causes imperfect and uneven surface finish. Such cases can be polished by the vapor polishing process.

Electropolishing

Electropolishing is the electrochemical process in which uneven surfaces are removed by anodic dissolution utilizing adjusting current and temperature.

The electropolishing process is the reverse of the electroplating process.

In this process, the workpiece is dipped in the electrolyte and considered an anode that is connected to the positive terminal. And negative terminal is connected to the parent material and serves as the cathode.

When current passes through the anode, materials oxidize from the surface of the workpiece and dissolve in the electrolyte to the cathode. 

The electropolishing process used to obtain a good surface finish and deburr the object. This process caused corrosive-resistant and progeny-resistant objects to have a glossy surface finish.

Applications of polishing

1. Polishing is used in car body parts, kitchen appliances, metal decorative objects, and more to enhance the appearance and look. 
2. In dairies, to protect appliances and pipes from bacterial contamination and corrosion.

Advantages                    

1. This process enhances the object’s aesthetics by providing a good look and a better surface finish.
2. The polishing process gives a shiner and glossy look to objects.
3. The mechanical strength of the polished workpiece is comparatively higher than the non-polished object. Because of stress –concentration is minimum on the shiny object.
4. Polished objects are mainly corrosion resistant.
5. Scratched, pits, and imperfections on the surface are nil in the polished object.
6. High durability.

Disadvantages

1. The polishing process is costly as compared to others
2. Requirement of abrasive particles and machines.
3. Time-consuming process