Pitch polishing is a good option for some components that require the highest quality when manufacturing components. It is similar to lapping, which uses loose powder as the grinding agent. However, lapping does not provide the standard of quality that can. In pitch polishing, pitch plates are used instead. 

Read on to learn more about pitch polishing, its advantages and disadvantages, and processes below. 

More About the Pitch Polishing Process

In contrast to the double-sided lapping process, pitch polishing uses a single side, and can be used for many different optical components that require high levels of surface quality. When pitch polishing is used, the surface quality often has a typical Ra of less than 5 Å.

Pitch plates have a semi-fluid surface and resemble the consistency of asphalt. Spiral, concentric, radial, and cross-hatched grooving can be cut by hand or machine into the plates. This allows the polishing slurry to have the ability to reach components, similarly to lapping, abrasive powders and mixed with a base. The outcome of the mixture is the polishing slurry needed for the components. 

In addition to pitch polishing providing better surface quality, it also minimizes surface deformation on the edge roll. Pitch polishing components can range in diameter from 20mm to 600mm. However, depending on the type of machine, other sizes may be possible. 

Cerium Oxide as Polishing Slurry

Cerium oxide (CE02) is commonly used as a polishing slurry, particularly for optical flats. Its long-lasting polishing efficiency makes it a popular choice for some components. Cerium oxide also holds its effectiveness much longer than other polishing slurries. Particle size is typically one to three microns. If you have a brand of CE02 with a higher pH level than others, it can cause oxidation during the polishing process. However, this material is swiftly removed by the polishing pad or the pitching plate itself. 

If you utilize cerium oxide in your polishing machines, using epoxy paints and stainless-steel components can help prevent corrosion. 

Other common polishing abrasives include silicon carbide (SiC) for rough grinding and aluminum oxide  (Al2O3) for fine grinding.  

What Are the Advantages and Disadvantages of Pitch Polishing?

Pitch polishing has several advantages, one of the most obvious being improved surface quality. However, as with any method, there are some disadvantages as well. Some of the advantages of pitch polishing include:

  • Enables best surface quality with surface toughness of ≥ 3 Å
  • Parallelism of ≤ 5 arc seconds
  • Less sub-surface damage
  • Maximum surface flatness tolerances of λ/40
  • Improved flatness and less edge roll-off
  • Wedge angle tolerance of ± 5 arc seconds

Some of the disadvantages of pitch polishing can be:

  • Requires a highly-skilled professional to perform the task
  • Lap must be checked and corrected quite often
  • It is a slower polish than traditional polishing
  • A single-side process is more expensive because of all of the above

For some processes, pitch polishing is a much-preferred choice because of the high level of quality, so the positives outweigh any negatives.

To learn more about pitch polishing or to learn more about what we do, contact IRD Glass today here. It provides links to contact us as well as directions to our facility.