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METAL IMPREGNATION
GUIDE TO TREATMENT
Impregnation is the process that is used to eliminate defects connected to the porosity of components obtained by fusion, pressure die casting and by sintering.
It is well known that micro-pores occurs contextually with the withdrawal of the material during the processes of fusion and pressure die casting in the passage of the metal from the liquid state to the solid state because of the release of gases previously absorbed.
In spite of various attempts made by scientific research in recent years to improve the productive processes in foundries, this natural phenomenon still continues to exist and consequently creates problems of hold against liquids and gases in components.
Technological progress and the need to contrast the weight and costs of treating the detailed elements of motors, pumps, compressors, valves, etc., have gradually imposed the use of jets in light alloys, indicated for creating very complex forms and with very thin walls. At the same time the solution to the problem of hold against liquids and gases has been identified in the modern techniques of vacuum impregnation.
Many companies have, therefore, adopted systematic impregnation of all components obtained by fusion to optimise their production cycles, (eliminating waste), reducing costs and qualifying their product.
  Impregnating after mechanical treatment and before testing for hold. This is the optimal solution.

As in the area of foundries, the sintering industries have also widened their horizons thanks to the modern techniques of impregnation. The intrinsic micro-porosity of sintered elements that until a few years ago prevented their use in all those cases that required hold against liquids and gases is no longer a limit today. In the same way, electroplated coverings can now also be made perfectly for these components. Mechanical treatments after impregnation can now be carried out at a more rapid speed and with a notable increase in the duration of the tools.


TIPES OF POROSITY

There are several types of porosity:

• Porosity visible to the naked eye that are difficult sealed with the impregnation. These are in many cases also indicates a structural defect of the piece.
• Porosity of some tens of microns, usually called "micro porosity" hardly visible to the naked eye and perfectly sealed with the impregnation

The porosity may take different types, grouped into three basic categories: closed, blind and passers-by porosity.

The closed porosity, not enter the resin and therefore not treatable by impregnation, does not produce loss of fluids and gas. Also, no contraindications to subsequent treatments galvanic and painting. It can be done emerge on surface after machining of the piece making it one porosity blind. For this reason, it is always a good idea to run the impregnation after machining.

The blind porosity part from the surface to take shape among the most disparate. This porosity presents no problem from the viewpoint of sealing component to liquids and gases but clearly affect the ultimate outcome after the surface treatments. It represents a receptacle for air, water, for fluids treatment, for oil by cutting, etc..
In the piece painting, in paint baking is high risk of creating bubbles in the coating (blistering). This occurs because the expansion of and/or evaporation of water contained, derived from preliminary treatments fosfo-degreasing. In galvanic treatments, fill liquid baths that subsequently emerge after processing attack and corrode the basic metal coating. In case of oxidation such as anodic this phenomenon is known as "white spotting" (pitting). Again, since a machining can turn a blind porosity in a porosity passing is a good idea to impregnate after running machining.

The passing porosity involves the largest amount of damage. In addition to presenting the same issues of porosity blind in surface treatment, unused components as generate losses and escape of liquids and gases once in operation. This can include components for hydro-guide, steering boxes, tested the engine, oil pumps and advance, to exchange boxes, to collectors, the carburettors, the carter, components for brakes, alloy wheels, gas valves and compressed air. For all these components is essential maintenance that ensures with modern techniques impregnation.



METALLOGRAPHIC
SECTIONS
Porosity of a fusion before the impregnation process.
Porosity after the impregnation process. The resin in clearly recognisable in the pores and assume a blue colour under ultraviolet rays.

THE PRINCIPLE
OF IMPREGNATION

The modern technology of impregnation with thermal-hardening, catalysed acrylic resins, by now welcomed by all the major automobile companies, allows the almost complete recovery of pieces that would otherwise be discarded because of blind and passing micro-pores.

The pieces are subjected to a vacuum until reaching a pressure up to 5 mbar.
The air and possible humidity are evacuated from the pores.
The pieces are subjected to a vacuum until reaching a pressure up to 5 mbar. The air and possible humidity are evacuated from the pores. Once the vacuum has been reached, the pieces are immersed in the liquid resin. The vacuum is at first still maintained for a few minutes and then released.
The atmospheric pressure presses on the resin making it penetrate the micro-pores.
The surface of the pieces is adequately washed with water.

The polymerisation of the withheld resin is obtained by heating the metal with hot water at 90C. After polymerisation, blind and passing micro-pores are completely sealed and the product, after cooling, can be immediately used.


TREATED METALS
Cast iron
Aluminium and its alloys
Stainless steel
Copper and its alloys
Plastic materials
Magnesium and its alloys
Metal Components fused in lost wax
Sintered
Porous Coverings
Electricity Bobbins
 
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MAION s.r.l. - 35010 Limena (PD) - IT - Via XXIV Maggio 6 - Tel. 049 8842661 - Fax 049 8847449 - info@impregnazione.com
C.S. 10200 euro i.v. - CF/P.IVA/Registro Iimprese n 01127730297 - R.E.A. PD310114