Tech Talk - Clipper Controls

1 tech (415) 808-AHOYPage 1 of 2 Surface FinishesBackgroundThe finish quality of a machined surface is very important in industries that require sanitarysurfaces such as Food, Biotech, Pharmaceutical, and Semiconductor manufacturing. Thereare a number of ways to define the Surface Finish, and thisTech Talk attempts to give asimple overview of the common terms. Surface finish measurement procedures, generalterminology, definitions of most parameters and filtering information can be found in AmericanStandard ASME - 2002, Surface Texture, and in International Standards, ISO 4287 andISO termsRa The most common surface roughness parameter is Ra, or Arithmetic AverageRoughness. It basically reflects the average height of roughness componentirregularities from a mean line. Ra provides a simple value for accept/rejectdecisions. It is a default parameter on a drawing if not otherwise specified, and isavailable even in the least sophisticated measuring instruments.

2 Ra is not a gooddiscriminator for different types of surfaces as it is incapable of differentiatingbetween spiky and scratched surfaces having the same Maximum Peak heightRv Maximum Valley depthRy maximum Peak-to-Valley Roughness heightRz Mean Roughness Depth. It is the average distance between the highest peak andthe deepest valley in five sampling lengths, or cutoffs. Rz is more sensitive then Rato the changes in surface finish because maximum profile heights, and not theaverages, are being Number of abrasive grains per given areaEP Electro polishPolished FinishThe high end of the sanitary finishes is an electro-polished ID which yields a 10 or 15 -inchRa maximum roughness. These electro-polished products are generally used in very highpurity Finish Industrial32 Ra Sanitary20 & 15 Ra Pharmaceutical20 RaEP Pharmaceutical15 RaEP Ultra-Pure ApplicationsTech (415)

3 808-AHOYPage 2 of 2 Surface Finishes Cross-Reference ChartCommonNameGrit#USAF inish#RaMicroinchEP RangeRa MicroinchRaMicronRmaxMicroinchRmaxMicron Appx RMSM icronISO#ASTM StdRa MicroinchJapaneseStd200050 7875 1968 50N10 Mill Plate60125050 492 Sheet80240-6070 #4 120 4 40-603A Sanitary150430-3542 max15-2042-4745 maxANSI # 126 Finish180420-3030 max15-203425 maxBuff #100 Biotech Finish200-220420-2525 17 max N56-1532078-1212 13-14 Buff # #300 Mirror Finish 400 84-8 Super MirrorFinish50083-8<4 Super MirrorFinish500 # INFORMATION IS SUPPLIED AS IS WITHOUT A GUARANTEE OF ANY KIND. Clipper Controls Inc. does not guarantee that the data is suitable for your particular application, nor do weassume any responsibility.

4 Clipper Controls Inc. 2006