TREATMENT OF METALLIC STRUCTURES (II).

As we told you in the previous article, in order to keep metallic elements and structures in good condition, a series of protective treatments and paints are applied to extend their useful life, and maintenance work is therefore of vital importance.

But in order to apply any type of protection or paintIn this case, an adequate surface preparation is necessary. We will focus on two methodologies:

• • Mechanical preparation by media manuals, with brushes, scrapers and picks, or mechanical means, with rotating wire brushes, abrasive discs, etc. (residues should be removed with compressed air or gentle brushing.

• • Abrasive blastingThe erosive action of the pressurized particles will remove all types of impurities, scale, rust, as well as layers of old paint.

The surface finish is stipulated according to a series of standards, of which we will highlight the Standard ISO 8501-1:1988(E) Preparation of steel substrate prior to application of paints and related products. Visual evaluation of surface cleanliness.

ISO standards describe 7 degrees of surface preparation:

> The degrees of scratching and brushing manual are identified by the nomenclature St. Louis

• • ISO-St. ISO-St: Manual or mechanical cleaning

• • ISO-St2: Manual or mechanical deep cleaning

• • ISO-St3Very thorough manual or mechanical cleaning

> The degrees of sandblasting are identified with the nomenclature Sa:

• • ISO-Sa: Sandblasting

• • ISO-Sa1: Light blasting

• • ISO-Sa2Deep sandblasting

• • ISO-Sa2 1/2Very deep sandblasting

• • ISO-Sa3: Blasting until the steel is visibly clean

We attach below some images of the works executed some years ago in the RIBA-ROJA HYDROELECTRIC POWER PLANT. We acted in the forced pipe and spiral chamber of one of the turbines proceeding:

• • pressure water washing of metal surfaces

• • subsequent blasting of the same with abrasive material (shot)

• • and the application of the final coating: 2 coats of primer and 2 coats of epoxy paint finish.

Finally, a brief approach to the abrasives. the main factors to be considered for your choice are the particle size and shape, as well as its hardness and its resistance to breakage. The main types abrasives that can be used are:

- Metal abrasives: Pellets, shot, ... Although they are expensive, they are reusable.

- Synthetic Abrasives: With properties similar to metallic ones, they are very hard and have the advantage of not rusting. They are also reusable

- Mineral Abrasives: such as silica sand or slag, which are less expensive, but cannot be reused.

#Applications against corrosion #preparacionssoportes #chorreo #abrasivos #reparacionessestructurales #RevestimientosFraga