Which surface qualities expressed as Ra values are customary for hygienic applications in milk powder production?
In milk powder production, high requirements apply to the surface roughness of product-contact components, since smooth and defect-free surfaces facilitate cleaning, reduce product build-up and lower the risk of microbial contamination. The decisive parameter is above all the arithmetic mean roughness Ra, supplemented by further hygiene-relevant criteria.
Usual Ra values
Ra ≤ 0.8 µm: this is the common standard for product-contact stainless steel surfaces in food and dairy processing. The value is widely used as a hygienic guide value and is supported by EHEDG and the 3-A Sanitary Standards, among others.
Ra 0.4 to 0.6 µm: in particularly critical areas a finer surface is frequently specified, for example with sensitive products, in areas with a high tendency to build-up or where particularly good cleanability is required.
Ra ≤ 0.4 µm: this is a demanding range for particularly sensitive applications. Such surfaces are usually achieved by fine polishing or electropolishing.
What matters besides Ra
The Ra value alone is not sufficient. A topography with few pores and grooves, clean weld seams, no burrs or gaps and a hygienic design with good drainability and access for CIP/SIP are equally decisive.
Practice in milk powder plants
For most product-contact components, Ra ≤ 0.8 µm is regarded as the established minimum standard. In critical process zones, for example with strongly hygroscopic powders or in sensitive products such as infant formula, Ra ≤ 0.6 µm or even finer values are frequently required.
How amixon® solves surface finish and material selection for hygienic powder processes
Surfaces: ground, low in adhesion, cleanable
At amixon®, the mixing chamber and mixing tool are welded free of crevices and ground smooth, without scratches, pores or undercuts in which product residues could adhere or biofilms could form. The surface quality is defined according to the application – from industrially ground to highly polished versions for GMP-critical processes such as pharmaceuticals or infant formula. Since every amixon® apparatus is a one-off to the URS, the required Ra value is defined and documented project by project. The surface roughness can be selected project-specifically, typically with Ra values of 0.8 µm, 0.6 µm, 0.4 µm or 0.2 µm; beyond that, amixon® can lap to a mirror finish and electropolish. On request, amixon® can also supply the product-contact parts mirror-polished; electropolishing is requested more frequently, however. Both are possible.
Smooth, homogeneous surfaces reduce build-up directly – together with the microfine addition of liquids, the mixing chamber remains free of deposits even during moistening processes.
A range of materials for every product chemistry
As a welding specialist with European, Japanese, Korean and American qualifications, amixon® processes, depending on the application, mild steel S355J2+N, Hardox, austenitic stainless steels 1.4301, 1.4541, 1.4571, 1.4404, 1.4539 and 1.4529, duplex stainless steels 1.4462, 1.4162 and 1.4363 as well as Alloy 59 (2.4605), Hastelloy-C22 and nickel for highly corrosive media. For abrasive materials, hardened tools and ceramic plasma coatings are available as wear protection.
Constructional complement
Surface quality only takes effect together with freedom from dead space: the mixing tool supported only at the top, dead-space-free discharge fittings and Clever-Cut® inspection doors with the OmgaSeal® seal. Residual discharge of 99.997 % and better with free-flowing materials minimises the quantity of residues that has to be cleaned at all. On request, the mixers meet the EHEDG guidelines, the FDA hygiene guidelines and the 3-A Sanitary Standards.
Manufacture in Paderborn as the quality foundation
amixon® develops and manufactures exclusively at the Paderborn works with the greatest depth of manufacture and uses components from Germany exclusively. As a certified welding company with European, Japanese, Korean and American qualifications, amixon® designs every apparatus as a one-off on the basis of the operator's URS. Quality control remains entirely in-house without gaps, and every specification is verifiable down to component level. This manufacturing autonomy also secures long-term supply: every component can still be re-manufactured reproducibly decades later.
Qualifiable and documented
For regulated environments, amixon® supplies the plant in qualifiable form: every apparatus is a one-off in accordance with the URS from its own manufacture with quality control that has no gaps; amixon® assists on request with DQ, IQ and OQ, and documentation and execution follow, on request, EU GMP and FDA 21 CFR Part 11. On request, the mixers meet the relevant standards – EHEDG, the FDA hygiene guidelines, the 3-A Sanitary Standards, USDA, GMP, ATEX and ASME – and are integrated into the operator's validation concept from the URS through to commissioning.
Verification in the amixon® pilot plant
Whether the specific formulation delivers the expected results is verified by amixon® in advance at the pilot plant with 35 test units under real conditions. Trials with the original product are carried out, evaluated and documented jointly – as a robust basis for decision-making before the investment.