How to Polish Polycarbonate: Methods and Steps

There are multiple techniques for polishing polycarbonate out there. From sanding and vapor polishing to buffing and flame polishing.

We’ll explore the fundamentals of each technique, its advantages and disadvantages.

1. Sanding

Sanding is a common surface finish-technique to remove scratches and make the surface smooth. It is one of the widely-used techniques for polishing polycarbonate.

In this process, an abrasive material is used to remove imperfections and create a smooth surface. The process starts with coarse grit sandpaper (200), followed by progressively finer grits (800 or more) to achieve the desired finish.

Sanding can be wet or dry. The dry sanding can heat the surface and make it gum. So, for the best results, wet sanding is recommended, as it helps to reduce heat buildup and prevent surface damage.

How Polycarbonate Sanding is Done? Stepwise Procedure

The results of the sanding operation depend on the skill of the worker and the technique followed to complete the process. Here’s one tested technique to attain the best finish:

• Step 1: Gather multiple grades of sandpaper (e.g., 200, 400, and 600 grit), water, wiping cloth, gloves, apron, and goggles.
• Step 2: Prepare the polycarbonate workpiece by slightly wetting it, but avoid excessive water usage.
• Step 3: Sand the surface progressively. Start with the lowest grit sandpaper, rub in circles to remove prominent scratches, and focus on accuracy while avoiding rushing the process.
• Step 4: Mist the surface with water to prevent debris buildup and keep the sandpaper lubricated.
• Step 5: Keep sanding until the surface is clean and smooth.
• Step 6: Progress from coarser to finer grit sandpapers for a smoother finish, and change the sanding technique from heavy pressure to lighter pressure as you proceed.

Advantages of Sanding Polycarbonate

• Inexpensive and straightforward method.
• Suitable for small or large surfaces.
• Can remove deep scratches and surface imperfections.

Disadvantages of Sanding Polycarbonate

• Labor-intensive and time-consuming.
• Can cause surface damage if not done correctly.
• Requires expertise for achieving a consistent finish.
• Doesn’t produce a very smooth and clear finish

2. Vapor Polishing

Vapor polishing is a chemical process that uses solvent vapors to dissolve the surface of the polycarbonate, resulting in a smooth, glossy finish.

The part is exposed to the vapor for a short period, causing the surface to melt and even out. The common solvents used in vapor polishing for polycarbonate is WELDON-4 (methyl acetate, methylene chloride, and methyl methacrylate monomer).

Moreover, as vapor polishing produces a fine and glossy finish, it is widely used in applications where high transparency is required, for instance, in optical lenses.

Vapor Polishing Polycarbonate: A Step-Wise Procedure

• Gather all required items. You will need a chemical solvent (e.g., Weld-ON 4), heating equipment (e.g., kettle), respirator or mask, and gloves.
• Prepare the polycarbonate surface for polishing by cleaning it.
• Heat the chemical solvent in a kettle until boiling point.
• Gradually apply the heated solvent vapor onto the polycarbonate surface.
• Observe the surface becoming clearer, smoother, and glossier as the vapor melts the polycarbonate.

Advantages of Vapor Polishing Polycarbonate

• Produces a high-gloss, mirror-like finish.
• Faster than manual sanding and buffing.
  Does not introduce new scratches or surface imperfections.

Disadvantages of Vapor Polishing Polycarbonate

• Requires specialized equipment and handling.
• Solvent fumes are toxic; the process needs to be done in a highly-controlled environment.
• Expensive compared to other polishing techniques.

3. Buffing

Buffing is a mechanical polishing technique that uses abrasive compounds and a rotating buffing wheel to create a smooth, glossy surface. This process is usually used in conjunction with sanding, to achieve a high-gloss finish of the polycarbonate sheet.

Like sanding, buffing also involves the use of polishing compounds with varying levels of abrasiveness, starting with a coarser compound and finishing with a finer one for a mirror-like finish.

How Buffing of PolyCarbonate is Done? 

Step 1: For the buffing operation, you” ll need these tools:

• Buffer
• Loose abrasive
• Protective clothing (e.g., gloves, goggles)
• Fine grit sandpaper

Step 2: Before initiating, sand the polycarbonate workpiece surface to remove deep scratches.

Step 3: Apply loose abrasive to the buffing machine, then buff the polycarbonate sheet, avoid holding the workpiece in one place, as this may damage the mop.

Step 4: Maintain a firm grip on the buffer. Before switching the machine on, hold it firmly to ensure your safety and carry out the buffing process effectively.

Advantages of Buffing PolyCarbonate

• Can produce a high-gloss finish.
• Removes fine scratches and imperfections.
• Creates an even, smooth finish.
• Cheaper and inexpensive.

Disadvantages of Buffing PolyCarbonate

• Messy process.
• Cannot repair deeply affected polycarbonate pieces.
• Can introduce new scratches if not done correctly.

4. Chemical Polishing

Chemical polishing involves immersing the polycarbonate part in a chemical solution that dissolves the surface, smoothing out any imperfections.

This method is effective for complex geometries and hard-to-reach areas. The solution typically contains a mixture of acids, solvents, and other chemicals that selectively dissolve the material’s surface. The common chemical polish usually used is methylene chloride.

How Chemical Polishing of Polycarbonate is Done?

• For the process, you will need a chemical polish (mainly methylene chloride), sandpaper, and protective clothing.
• Prepare the workpiece by sanding its surface to remove any apparent scratches. Then, wipe it clean using a wet cloth to remove debris.
• Apply the chemical polish and allow time for passivation to occur. It will smoothen the surface and polish it while dissolving the upper layer of the polycarbonate material.
• After the chemical polish has cured, run the surface under water to prevent cracking due to post-polishing stress.

Advantages of Chemical Polishing

• Can achieve a high-gloss finish.
• Suitable for complex geometries.
• Very less labor intensive.

Disadvantages of Chemical Polishing

• Requires specialized equipment and handling.
• Expensive compared to other processes.
• Highly-toxic chemicals are used during the process.
• May destroy the piece if not done correctly.