VDI 3400 Surface Finish & SPI Surface Finish Standards
VDI Surface Finish – is a scale often used by German machine manufacturers and quite widely used in Spark and Wire Erosion (Verein Deutscher Ingenieure, the Society of German Engineers)
RA is calculated by an algorithm that measures the average length between the peaks and valleys and the deviation from the mean line on the entire surface within the sampling length. Ra averages all peaks and valleys of the roughness profile and then neutralizes the few outlying points so that the extreme points have no significant impact on the final results.
RT is calculated by measuring the vertical distance from the highest peak to the lowest valley within five sampling lengths, then averaging these distances. Rz averages only the five highest peaks and the five deepest valleys—therefore, extremes have a much greater influence on the final value.”
SPI Surface Finish Standards
The SPI is that Society of the Plastics Industry sets standard for plastics industry in the United States that identifies the cosmetic quality of plastics, NEWAY uses the SPI standard to define finish of plastic injection molded parts.
There are twelve grades of finishes specified by the SPI in four categories that range from A1 12 to D3 . The card comes with notes of DIAMOND, Grift paper, STONE , DRY BLAST GLASS BEAD and OXIDE for each SPI-SPE number.