Mechanical polishing is used to remove large amounts of surface metal stock to impart a surface texture and roughness of the surface for either cosmetic or practical (technical) reasons.
Smooth surfaces are often required in vessels and hoppers or other product contact surfaces to help reduce the likelihood of "snagging" of product which will lead to "bug traps" etc.
These surfaces which are rendered smooth mechanically are much easier to wipe down by hand or indeed when using a CIP system to help the liquid and debris run-off the surface.
Once upon a time surface values were often expressed in grit values; 80, 120, 240 320 etc. It is more common today to have these values expressed in specific easy to define values in microns; 0.8, 0.6, 0.5 etc Ra µm (roughness average µm). The old system of grit values was too subjective and could result in a variety of wide swinging surface measurements when read. There is no mistaking a defined value such as <0.8 Ra µm.
Warning: even this secure system of specifying fixed values which appear tangible is not without its controversy.
Q) What number of measurements shall be taken on the surface of the job?
A) There is no guidance on the issue but SRL would suggest perhaps an average of 10 reading on a job under 3m² and say, 2 readings per m² on larger surfaces. Of course this can be negotiated between the client and supplier.
Q) What if one of the surface measurements is above the specified Ra µm value?
A) Again there is no guidance however one could work on an average reading so one value out of ten reading should still give a mean of less than the maximum value.
Q) On uni-directional grained surfaces which way do I take the Ra um reading; transverse or parallel to the direction of the grain?
A) Careful! if the reading is taken transverse to the grain then this is a severe and strict test, since this measurement will be higher than if taken parallel to the grain (in the direction of the grain). This issue has to be agreed before the job starts.
Note: in vessel and hopper work it is prudent to ask the mechanical polishing company to polish the surface so the grain is flowing (pointing) in the same direction as the product flow. This will aid CIP cleaning and minimise the amount of product trapping in the grain.
So in this instance the Ra µm could be taken in the same direction.
SRL have a team of dedicated mechanical polishers with a vast amount of experience in terms of time served skills and diversification of work done.
SRL's team have conducted work across all market sectors from; Pharmaceutical, food, Architectural but to name a few.
Surface finished from simple grinding off welds to sanding surfaces to building-up specific surface finished with exacting Ra µm values for specific application right through to mirror finishes.
All SRL's mechanical polishing members are CONFINED SPACE TRAINED with SAFETY PASSPORTS.
SRL do offer mechanical polishing services either in-house here at our 60,000sq/ft undercover metal finishing facility in Hyde Manchester or alternatively we can send a team of mechanical polishing engineers to you're site anywhere in the world.
A full documentation pack will be submitted prior to the start of any site work which will include;
- Method Statement
- Risk Assessment
- Insurance certificate
- Confined space training certificate if applicable
- Safety Passport
- Certificate of Conformity with Ra µm readings present - signed