Surface Roughness

  • Units: 1 micron (um) = 39.37 micro-inch (u-inch) = 1000 nanometer (nm).
  • Surface roughness is one measure of the texture of a surface. Several other steps are also necessary, like the autocorrelation length (ACL or ß), anisotropy (Str), Surface density, Skewness, Kurtosis, and volumetric measurements. The assessment of texture depends on the resolving power of the probe employed. In an approximate sense, the human eye’s resolution is about 0.3 mm. The resolution of an optical light microscope is ~500 nanometers (nm) spatially and everywhere a micron in the height direction (confocal microscopy provides a smaller height measurement possibility). In a scanning microscope, it is about 10-100 nm, depending on the electron wavelength. For a transmission microscope, it could be less than 1 nm. For an atomic force microscope, it could be 0.2nm.
  • The roughness of a surface asperity height is commonly reported as a Ra number (the absolute arithmetic average roughness of a surface)or reported with an Rq number (root mean squared RMS value of roughness).
  • More advanced reporting procedures include values for waviness, kurtosis, surface skewness, ACL, and Str; however, Ra and Rq adequately capture the height roughness.
  • Units:  The engineering units for both Ra and Rq are either micro-inch or nanometers.
  • 1 microinch= 0.0254 microns =25.4 nanometers
  • Peening or burring improves a metal surface’s material properties. Ion burring with e-ion Plasma is a relatively new process that can be used for curved and complex shapes.
  • Cast surfaces display Ra of about 50-250 u-inch. Sand castings display higher roughness, and plaster shell-type investment castings and die castings show lower roughness values. Squeeze castings also exhibit a higher average roughness.

Participate in no-burr technology with the e-ion or with the use of GoldenBlue® tools.


  • Surface roughness can change the look and feel of products (gloss and luster) and their friction and wear properties. Inadequate roughness can also affect the durability, fatigue, biocompatibility, and reliability of the processed part—Cascade e-ion information request.
  • Several quick machining operations leave behind burrs.
  • Roughness impacts life by impacting wear resistance, erosion resistance, fatigue resistance, creep-fatigues interaction, and other material design parameters.
  • Roughness is called out for metallic, composite, and ceramic parts used in turbomachinery, combustors, engines, cylinders, and other engineering parts.
  • The more commonly reported measurement number for polymeric and other soft surfaces relates to specular reflectivity; the Ra and Rq are generally not called out.
  • High roughness can cause turbulence. A bad casting finish can dramatically alter the energy efficiency in any fluid flow device, e.g., a pump or turbocharger. Roughness can be controlled with e-Ion techniques.
  • For more information regarding surface roughness and surface finishing, see this site, which discusses how coatings fill the voids between sand grains and can also act as refractory, limiting the defects and loss of integrity that can occur with higher melting point alloys. Coatings make casting surfaces harder and smoother.
  • The cascade e-ion is a cost-effective method of altering the texture of a surface, thus changing several engineering properties, including friction and wettability. It prevents slip-stick and improves color and luster.

Role of the Cascade e-Ion Plasma Plume

The Cascade e-ion Plasma is a versatile machine that may be used to impact the surface texture and roughness of metals (Cascade e-Ion source), ceramics (Cascade e-Ion EIZ), or soft plastics (e-Ion LIP). With the e-Ion Plasma machine, one may rapidly “deburr” or create new surfaces, depending on the ions used and other correctly set conditions that change for specific alloy surfaces and temperature. Nanoscale features of texture and porosity that are now known to be essential for surface bioactivity or roughness can now be engineered. Sometimes, trial and error experimentation may be involved regardless of whether it is titanium, steel, cobalt, or PEEK alloy. Contact the manufacturer, MHI.

In its several modes, the e-Ion Plasma™ can deburr, ionic co-deposit to alter surface porosity and be used simultaneously for thermal action in various combinations of use modes to obtain the best surface. Numerous studies are underway for smoothening glasses, semiconductors, and high-hardness materials such as carbides, nitrides, and borides. Selective smoothening or roughening studies with composites and muticompositional alloys are also underway. The initial surface conditioning plays an essential and non-intuitive part in the surface action.


Every competitive “deburring” process has advantages and disadvantages. When comparing processes for a particular action, the comparison should include speed, reliability, tolerance, energy efficiency, chemicals, and other environmental footprint features, including noise for comparison making. Mechanical processing (such as drilling, grinding, stone-tumbling, and polishing) may change or damage materials because of focused stresses, which may lead to residual cracks, residual tensile stresses, and changes in the microstructure, thus reducing the part’s service life. Electropolishing may require chemicals to be stored, replenished, and disposed of. The e-ion, on the other hand, uses only air (or other gas of choice) and electricity as input to the machine. High kinetic and thermal energy ions are used for deburring in the e-Ion Plasma process. It is a noiseless yet controllable process and may be used on a tabletop for almost all configurations because of the small footprint of the cascade e-ion device. The  Cascade e-Ion Plasma™, i.e., the CleanElectricFlame®, can be used continuously with a belt or robot part-handler. MHI provides the user with all the high-temperature holding accessories and a standard part manipulator. See also the welding page.

Additional Benefits with the Cascade e-Ion

Although not all the benefits of new technology like the e-Ion Plasma can be known, several benefits may be anticipated. For example, with the e-Ion Plasma, the rapid “deburring” step can be combined with a rapid surface nitriding and bulk sintering step. The ions do not require a line-of-sight beam, and the product must not be electrically grounded.   This sintering type is called 4DSintering®,  a Trademark of MHI Inc.  Simultaneous ion peening operations can be envisaged. Similarly, welding and weld smoothing may be anticipated as simultaneous operations. For example, the scale from welding and the chromium-depleted layer underneath the weld roughness must be typically removed for improved stainless steel and sea-side corrosion resistance.   Mechanical polishing to match the finish on the parent material is often used, but this must be done carefully so that cracks are not introduced, which can lead to stress-corrosion cracking.   More Online Information.

 Deposition can sometimes further reduce surface roughness. The e-Ion depositor attachment may be used with the same machine.

Example:  Starting from the surface with a Ra = 20-40um, for unsintered powder metallurgy produced alloy part for an alloy that sinters around 1700K, a Ra = 4um surface is easily obtained in minutes to an hour of non-line-of-sight surface e-Ion “deburring” operation.   Multiple parts can be made simultaneously. The production cost saving per part is substantial when comparing 1 hour vs. three days of labor time. The savings from lessened environmental degradation are substantial. The energy savings per year could be thousands of dollars in benefits. Please contact MHI for more precise calculations and to work with you to ensure the best amortization cost for your specific location. Please Contact Us for more information on the best surface finish for metals, ceramics, glass, oxides, garnets, silicon carbide, and many other materials that require nanoscale or microscale smoothening or manipulation.

Mesh sizes


Grit  to  Microns

100,000 1/4
60,000 1/2
14,000 1
13,000 1.5
9,000 2.5
8,000 3
2,800 7
1,800 9
1,400 14
1,200 15
1,050 18
800 25
600 30
500 35
325 45

Cascade e-Ion

Friction Free Tools

High energy and high-velocity e-Ion Plasma™ CleanElectricFlame® can be used for deburring surface operations within seconds or minutes for the biomedical parts (entire surface), casting, forging, or powder-metallurgy fabricated parts.

Curved and non-line-of-sight regions can be treated.

The Scale of Roughness Texture

(Related to the resolving power required of the measurement probe, with light ~ 0.5 microns, with electrons and AFM, theoretically, it is ~ 0.1 nanometer (nm))

Deepest ocean trench: 10.994 Km

Highest mountain: 8.850 Km

Human scale: ~1 m

Human organ scale: ~10 cm

Spoons and forks that fit a human mouth: ~1 cm

Pencil tip: ~1 mm

Grain of salt: ~0.1-1 mm

Human hair or dust mites: ~0.1 mm

Bacterium: ~1-10 micrometer (the typical size of the autocorrelation length features on a smooth surface)

Phages (bacterial virus): ~0.1 micrometers (this is the industrial level of polish in the 21st Century)

Large molecules or virus: ~10-100 nm

Atoms: ~0.1-1 nm (most commonly used materials are comprised of atoms with diameters in the 0.1 nm range)

Water molecule: 0.275 nm

Nucleons: ~10^-6 nm

Electrons: ~10^-7 nm

Planck’s length: ~10^-26 nm (smallest scale believed to exist in space-time)


Other texture properties:  The ACF, the auto-correlation function, measures how similar the texture is at a given distance from the original location. If the ACF rapidly becomes zero along a given direction, the surface becomes “uncorrelated” with the starting measurement location. The Sal (also called ACL or ß) is the Auto-correlation length, a measure of the distance over the surface such that the new location will have a minimal correlation with the original location. For anisotropic surface texture, the direction along the surface of the ACL is the one that has the lowest ACL value. The STR, which ranges from 0-1 for anisotropic to isotropic, is a measure of spatial isotropy.   Spacial isotropy STR~1 is an excellent feature, except in specific directional tools. The word “lay” is also used in the metal machining literature to indicate surface anisotropy, but this is best to have a repeatable hierarchical scale across many length scales. Contact MHI for more information on Shannon and other proofs and how we can recommend technology companies that can do measurements for you.


The value of Hardness depends on the material and processing conditions. The measurement of Hardness also depends on the strain rate sensitivity of the harness. Thus, the hardness measurement does not always represent hardness when used in dynamic conditions. Please contact MHI for high Hardness, low distortion, and tunable coefficient of friction surfaces with the highest Str.

What is the Magnitude of Possible Energy Savings: An astounding ~23% of the world’s total energy consumption (greater than 575 ExaJ/Y) (Exa = 10^18) originates from tribological contacts. About 20% of this total energy (~114 EJ/Y) is used to overcome friction, and ~3% (~17EJ/Y) is used to remanufacture worn parts and spare equipment (Friction 5(3): 263–284, ISSN 2223-7690, 2017). Most friction pairs in use are estimated to be from contacts that are about 50% metallic (bearings, bushings, and rotary components). New technologies are reducing dry friction considerably (Tunable coefficient of friction with surface texturing in materials engineering and biological systems Current Opinion in Chemical Engineering, vol.19, p. 94-106, 2018)

Easy method to deburr steel tool steel and die steel Deburr for pipe threads - Easy

Deburr anything. Beneficial for oil pipelines and pipe threads.

“Deburr” steel parts and create nano-isotropic surfaces in a few seconds. Simultaneously, nitride or oxynitride as required.

On the left is nitrided and deburred. On the right is the surface before the deburring.

Typical Size/Footprint:   A typical ~ 14 kW Cascade e-Ion Plasma™ configuration fits on half a standard desk-top table. Plug and Play type installation.

The expected operating cost is a few cents per part, but please Contact Us for your specific application.

Complex 3D surfaceHuman Pin


Easily nitride Ti-Al-V (Ti64) with the Cascade e-Ion Plasma Plume

The Cascade e-Ion is used for Titanium Alloys (including multilayer graded peening), Co-Cr-Mo type biomedical alloys,

Stainless Steel, High-density plastics, dental alloys, gold alloys, superalloys, Nitinol oxide conditioning, Ni-Ti, Ti-Al, Ni-Al, castings, forgings, and many others where roughness needs to be reduced, or surfaces have to be peened.

Please Contact Us for your specific application.

MHI offers complex part manipulators, from robotic arms to continuous belts

Before and after pictures of Deburr Copper Zinc Nitride after GoldenBlue and deburr

Before e-Ion Ra= 20um » After treatment Ra= 4um surface shown above.

Chart of Grid to Microns