Removal of process induced hardened layer via chemical polishing

1. Metalmorphic layer formation due to the existence of forieng elements
2. Amorphous layer created due to the lattice structure change
3. Surface stress affected layer due to the remaining stress on a component
4. Surface deformation due to machining, grinding, mechanical polishing, and tumbling
The hardened layer caused by abovementioned four major causes can be removed using chemical polishing.

Supplement of ions in the defective outer layer due to machining

Every element in stainless steel is located according to their own valence bond potential, forming a suitable metalic lattice structure.  After machining, polishing, grinding process, the elements located on the outermost layer are removed and defected, and these defects comply with the nearby enviroments and look for various chemical medium or dust to compensate for its lacking state.  Various media is in contact with the chosen objects and and some of the corrosive media are easily penetrated and absorbed to the surface of the machined part.  As a result, the cleanliness and the corrosion resistance of the surface is compromised, and certain technical requirements are not satisfied.
Chemical polishing and electropolishing and passivation supplements hydroxyl and hydrogen groups.
Different manufacturers have different proprietary recipes to achieve various effects.  We are using proprietary chemical polishing and passivation solutions imported from Japan.

Comparison of Effective Area among typical tubing

Polishing Methods Surface roughness Geometric surface area effctive surface area surface area ratio
Typical 2B plate 0.20~0.50 16 34 2.1
Typical sanitized tube 0.20~0.30 16 21 1.3
Typical Typical shiny polished tube 0.10~0.03 16 21 1.3
2B Chemically polished plated tube 0.05~0.20 16 16 1.0
After an ordinary stainless steel tube goes through a series of machining processes, the inner and outer wall surfaces will alter their characteristics, with the indicators such as roughness, burrs, hardened layer, etc., which may cause sticking and adsorption of small particles, slowing the flow rate of the medium, clogging the tube, bacterial colony growth and many other phenomena.  These electropolishing (EP) or chemical polishing (CP) process must be used to meet the demanding requirements of high-tech equipment manufacturing technology.
Foreign milk can be stored for 14 days of milk can be stored for 4 days. In fact our milk shelf life should be far more than four days, and it is because a lot of unwanted substances are added in the milk due to the use of low quality tubes in the factory. 

Cr/Fe Content Change on the Surface Layer

XPS Test Results: Surface Ce/Fe ratio change before and after CP processing
Each stainless steel, for example SUS304 / 316 / 316L raw materials, the Cr / Fe composition ratio is about 0.4.  Since the Fe element molecules are more active, they are more prone to cause a chemical reaction with external substance and corrode stainless steel; the chemical properties of Cr or Cr network element are more stable than the Fe compounds and are more resistant to corrosive solutions, so the surface elements Cr / Fe ratio is changed after chemical polishing .  Its value reaches 1.0 or higher, and the higher content of Cr element in the surface layer, the corrosion resistance characteristic becomes better. 
Cr/Fe composition ratio of SEMI stanards compliant stainless steel ratio
Before Chemical Polishing After Chemical Polishing High Purity standards Ultra high pirity standards
≦0.4(0.8) ≧3.0(4.0) ≧1.0(2.0) ≧3.0(4.0)

Surface Roughness Change

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                                    Alteration on a machined suface after chemical polishing 100X magnification
                                    Alteration on a machined suface after chemical polishing 100X magnification
                       After mechanical polishing (MP),20kv*3500(RJLee)   
                 After chemical polishing(CP),20kv*3500(RJLee)

Air pockets created by mechanical polishing


Defective trenches and residual impurities in precision rolled stainless steel pipes

ditches removed

Change of corrosion resistance characteristics after chemical polishing

Corrosivity data of a SUS316L-2B stainless steel plate after chemical polishing