Thermal and surface treatments
The company Anzolin Fernando & Con-Press S.p.A. is equipped with specific machines for surface sandblasting. It also has some strong relationships with some external qualified suppliers to carry out numerous treatments on brass items, such as: sandblasting, brass sandblasting, annealing, pickling and nickel-plating.
The following treatments are also available for aluminium: sandblasting, tumbling, varnishing, impregnation, passivation and cataphoresis.
The company can also provide further special treatments upon request.
All the thermal and surface treatments described comply with the 2002/95/EC (RoHS) directive.
THERMAL AND SURFACE TREATMENTS
Sandblasting: This is a mechanical treatment with which the superficial part of a material is eroded by means of an abrasive action provoked by a sand and air blast. It is mainly used to clean the surface of metal products. At the end of this operation the material under the layer removed is completely uncovered and its roughness depends on the size of the grit used and on the pressure of the blast, however, it is very accentuated compared to the typical values of the mechanical processing.
Therefore, sandblasting is one of the most widespread treatments to prepare an element to the following varnishing operation or to improve the look of the product.
- Sandblasting with thick steel grit: it is the roughest of the three types considered. It is mainly used where the superficial look is not an important factor for the customer.
- Sandblasting with fine steel grit: it is a good quality sandblasting. It provides a good look and a good definition of the writings on the item.
- Brass sandblasting: the best sandblasting of the three types considered. It provides a great quality level to the surfaces treated and it grants outstanding levels of definition to the writings or symbols on the product considered.
Annealing: The metal alloy annealing is a thermal treatment based on which an item is heated up at a lower temperature than the melting point. The item is then placed in a furnace for a certain period of time, where it slowly cools down. This treatment must achieve one of more of these goals:
- Chemical balance: reduction of the minor segregation.
- Structural balance: transformation of the meta-stable phases.
- Mechanical balance: reduction of the internal residual tensions, including the strain-hardening.
Annealing alters the microstructure of the material and changes its characteristics, including its flexibility and strength. The material becomes softer and more homogeneous, according to the customer’s guidelines. The typical result is the removal of the defects from the crystalline structure.
Pickling: This operation is carried out to eliminate any surfactants, corrosion inhibitors or other chemical substances by means of acid solutions, as well as any scale and rust residues from the hot laminated steel products. Pickling is a compulsory operation to be carried out in brass products since annealing causes the oxidation of the surface, which is removed by soaking the item in sulphuric acid (10% water solute), washing and brushing it.
Passivation: This chemical treatment is carried out to protect the metal surface from corrosion. It occurs after pickling and it serves the purpose of spurring the spontaneous formation of an inhibiting and protective film. This is a very important phenomenon in the atmospheric corrosion of metal structure, based on which an “active” metal (i.e. a metal that tends to become spontaneously oxidized) forms a layer made up of a sealing oxidized compound that isolates the metal beneath from the reagent, thus preventing the continuation of the oxidation reaction.
Certain metals passivate spontaneously, since they form some “compact” oxides, such as aluminium. Some others, instead, passivate exclusively under certain environmental conditions.
Cataphoresis: The cataphoresis varnishing is a surface varnishing treatment carried out to make iron, steel and other alloy elements (current conductors) particularly resistant to corrosion.
An epoxy or an acrylic resin is evenly deposited on the surface of the element, thus granting a long lasting extraordinary protection against chemical agents and other types of attacks and fostering a better adhesion of the finishing varnishes.
The acrylic resin is different compared to the epoxy resin since it can directly stay in touch with the weathering agents preserving its technical characteristics. This treatment provides a further protection against rust.
Impregnation: This surface treatment is carried out to seal the micro-pores of the casting process by means of special resins that seal the micro-pores of the metal forged elements.
Since it can permanently seal the pores and cut the repairing or recovery costs due to the well-known problems that pores can create, including loss in pressure, double skin, damages to the surface finishing, this surface treatment has become a cutting edge system during the design and construction phases.
Tumbling: This mechanical operation is mainly used to mechanically remove the substrate residues, mainly burrs, produced during processing, including forging and casting. It is particularly suitable to provide a final finish to many small elements.
The items to be treated are placed in a barrel (tumbling barrel), where they rotate and hit each other. A specifically moulded abrasive material is then inserted to speed the operation up. This operation can be also carried out by soaking the elements in a liquid to prevent any chemical attack. The rotation speed of the barrel affects the speed of processing.
This processing provokes general size variations on the element surfaces between 2 and 20 μm.
Varnishing: Powder varnishing enables to coat the metal surfaces with an organic film to create some decorations and/or to protect the surface from aggressive agents.
The elements treated are coated with a varnishing powder containing a synthetic resin, which adheres onto the surface thanks to an electrostatic effect. Then they are placed in a furnace, where thanks to the temperature, varnish melts down and then polymerizes, thus creating an adherent layer.
Just like the other types of varnishing operations, the result in terms of adherence, duration and corrosion resistance is strongly influenced by the surface pre-varnishing treatment.
Nickel-plating: This surface treatment serves the purpose of modifying the superficial characteristics of the processed materials (strength, resistance to external agents, etc.). Electrolytic nickel-plating can be carried out exclusively on metal materials due to the nature of its processing. These materials are soaked in specific baths and coated by means of a electric current passage, which transports atoms from the bars of pure material to the material to be coated.
Chemical nickel-plating boasts a better performance than the electrolytic one and it is recommended for certain items used in the medical and in the food industry.