Optical Quartz Glass Parameters

Surface Features Surface Roughness (Ra)(um) Value Processing Method
Obvious Scratches Ra100, Ra50, Ra25 Rough Grinding & Rough Plane
Tiny Scratches Ra12.5, Ra6.3, Ra3.2 Rough Grinding & Fine Grinding
Invisible Scratches, Extremely Subtle processing ripples Ra1.6, Ra0.8, Ra0.4 Fine Grinding & Abrading
Mirror Surface, Optical Grade Ra0.2, Ra0.1, Ra0.05 Abrading & Optical Polishing

The polishing grade of quartz glass is usually represented by two parameters: Surface Finish (smoothness of the surface–30 / 20, 60 / 40, 80 / 50) and Surface Roughness (RA)

  • The higher value of surface finish, the smoother surface. This is a special representation of the old standard, which is no longer used.

  • The smaller value of surface roughness, the smoother surface. This is the expression method of national standards and international standards currently.

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Surface roughness(Ra) refers to a little smaller distance between machined surfaces and the unevenness of tiny peaks and valleys. The distance between two peaks or valleys is very small (below 1mm), which belongs to micro geometry tolerances. In common, the smaller surface roughness, the smoother the surface.

The surface roughness is generally formed by the processing methods and other factors. For example, the friction between the tool and the part surface in the process of machining or the deformation of the surface when cutting and separating, and the high frequency vibration in the process, etc. Because of the difference between the processing method and the workpiece material, the depth, density, shape and texture of the marks left on the processed surface are different. The surface roughness is closely related to the matching property, wear resistance, fatigue strength, contact stiffness, vibration and noise of mechanical parts. It has an important influence on the using life and reliability of mechanical products. So, “Ra” value is adopted.