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Most biopharmaceutical processes have strict requirements for the surface finish of wetted components. Proper surface finish reduces the chances of bacterial contamination due to adhesion and helps aid the cleaning process between runs. This article explores some common questions that come up regarding the surface finish of Hamilton products.

What surface finish comes on Hamilton products?

The standard surface finish of wetted components on the majority of Hamilton products with metallic components is Ra < 0.4µm (N5). A general conversion chart is provided below.

micrometer (µm)
microinch (µin.)
Roughness Grade Number

Where can I find the surface finish information for my product?

Surface finish information can be found on any of the documents listed below:

An example of how the surface finish is listed for each product is shown below.

What Hamilton products have surface finish information?

Any product with wetted metallic components including the following:

  • Dissolved Oxygen Sensors (Optical and Polarographic)
  • Dissolved Oxygen Caps (Optical and Polarographic)
  • Conductivity Sensors (2-pole and 4-pole)
  • Cell Density Sensors
  • Flowcells
  • Housings
  • G1-1/4 Sockets and Plugs

Why aren't materials such as glass (pH sensors) or o-rings listed with surface finish values?

Metallic components are normally machined and polished to a specific surface finish. The machining process leaves microscopic grooves in the metal. A precision test instrument called a profilometer uses a stylus which moves across the metal surface to determine its overall roughness. Profilometer tests have been used to establish most of the world's surface finish standards therefore metal materials have documented values.

Profilometer tests and surface finish standards do not work well for glass and elastomers since they are not machined. Glass is formed during its liquid state and has an extremely smooth surface finish. Elastomer materials used in o-rings and seals are too soft for normal testing standards.

The image below shows a close-up of a prototype machined sensor cap. The surface finish can be seen in this picture.

What is electropolishing? Are Hamilton products electropolished?

Electropolishing is an electrochemical process that changes the surface finish by reducing the surface roughness to level micro-peaks and valleys on the metallic surface. If a Hamilton product comes electropolished, this will be denoted on the Material Specification Sheet.