MILAN – Since prehistory, man has always sought the most innovative solutions and focused in particular on the study of metals, searching for more resistant alloys, less toxic and more suitable for use. Even ancient Romans knew about the relation between metals ad water and 2000 years ago they used to store at night the water in in copper or brass containers for ionized water to drink, cleaner and smoother thanks to an electrolytic reaction.
Brass, in particular. caught for millennia the attention of builders and inventors for all the benefits it offers in various sectors from mechanical, building, furniture and electrical equipment up to coins and the musical instruments that are named after this alloy.
Brass is in fact an oxidisable alloy formed from copper (Cu) and zinc (Zn), to which other elements can be added to achieve certain properties:
- the manganese and tin increase corrosion resistance;
- the iron increases the breaking load;
- the aluminum increases the resistance to corrosion and abrasion;
- antimony and arsenic inhibit dezincification;
- the nickel improves the mechanical characteristics and corrosion resistance;
- the silicon serves to deoxidize and favors the creation of the β phase.
In the food sector, the brass alloy that is used with more frequency is identified with the BRASS OT 58 – “CW617N” code, and is a standard alloy for hot stamping that associates to the excellent performance of hot-deformability, good workability for removal of chips. It complies with DIN regulations and 4MS group for materials in contact with water intended for human consumption. Can be used in various applications: valves, fittings, accessories for plumbing and heating systems, bolts, handles, clamps and components in general.
1913 is an year that marked a turning point in the field of metallurgy: the Englishman Harry Brearley creates an alloy of iron and carbon with outstanding corrosion resistance, especially in fresh water or in a humid environment: the era of stainless steel begins
The chromium present in the alloy makes stainless able to ‘passivate‘, that is, to become covered with a thin coat (3-5 × 10−7 mm), adherent, invisible oxide, which protect it from the action of external chemical agents. If this film is damaged is reformed from the matrix of the steel.
The stainless steel is then used as a material used for the contact with food, both for its robustness and functionality that for the characteristics of hygiene required in the food industry and processing. The hygiene of a material is in fact characterized by:
- High effectiveness in the removal of bacteria and residues in the cleaning phase for the entire useful life of the tool or of the machinery;
- Difficult bacterial residuality after cleaning actions;
- Resistance to corrosion, ie the inertia of the material to react with the substances with which the same material is in contact. It allows both high resistance to solvents and detergents that prevent the exchange of elements between the material and the food substances, which remain unaltered both from the chemical that the organoleptic and toxicological points of view;
- Absence of any protective coating, which could splintering, cracking and or release substances in food and which needs special chemical products for the cleaning;
- Surface structure compact and free of porosity, which prevents the machinery to absorb substances of various nature, whether they be food or detergents, and then the subsequent release of such substances.
Stainless steel is the metal that is more often used in the food industry and in the espresso machines, both for its characteristics of robustness that of hygiene.
The alloys with a low carbon level are in fact more subject to wear, rust or scale formation. In particular, inside a coffee machine, the metal components are constantly subjected to oxidative stress, which also contributes to an inappropriate hardness level in the entry water:
– Excessively high hardness level: rust formation.
– Excessively low hardness level: first scale formation.
To adjust the water quality, softeners and the reverse osmosis system are the most widespread systems, and they must be properly used.
The R & D department of Nuova Ricambi is working more and more with lead-free materials and, particularly, on stainless steel components.