Manufacturing plastic parts from clear material is a common request for manifolds and machined components. Clear parts allow a user to monitor the internal activity of a process. Many amorphous materials in their raw state are clear. However, after machining they become translucent to opaque depending on tool wear and cutting efficiency. To return the machined part to clear, a secondary polishing operation is often required. Specifying the proper clarity to match the application can be a challenge. Controlled Fluidics has defined 4 levels of clarity to aid the design effort.
Grade 1 – As machined: This finish is the standard machined plastic finish. Surface roughness is better than 32 microinch (.8 microns). Surfaces range from translucent to opaque depending on the feature geometry and cutting conditions. This is appropriate for non-visual applications.
Grade 2 - See through finish: This finish allows for activities like visual fluid flow and bubble detection. It is the most common request and meets a broad range of design requirements. Processes such as vapor polishing are appropriate for this clarity. Polishing the entire part is typical. Parts can vary in haze and clarity. Tool marks are present and do not affect functionality. Some scratches. This is the most cost-efficient method with limited quantitative measurements for quality.
Grade 3 - Optical window finish: This finish is appropriate for imaging thru the manifold or plastic part for detection sensors. To the
unaided eye, a Grade 3 finish looks similar to window glass. Tool marks are not readily apparent. Few scratches. To achieve this clarity, specifying a surface finish of less than 2 microinch Ra (.05 micron) is appropriate. This clarity is specified in a localized area beneath the optical sensor and not used for entire parts.
Grade 4 - Optical finish: This finish is a true optical finish specified in both surface finish and surface form. Surface finish for optics is measured with a white light interferometer and specified in angstroms. Surface form represents waviness of the surface and its adherence to the ideal profile. Form is also measured with an interferometer and specified in fringes. This level of clarity is appropriate for lenses and doesn’t find use in manifold applications.