galvanising process

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TABLE 1

Corrosivity of atmospheres and corrosion rate of zinc.

Corrosivitycategory

EnvironmentsCorrosion rate of zinc

(µm/year)

C1 Interior: Dry 0,1

C2Interior: Ocasional condensation.

0,1 to 0,7Exterior: Rural, inside the country.

C3

Interior: High humidity, air slightlypolluted.

0,7 to 2Exterior: Urban, inside the countrycoastal or low salinity.

C4

Interior: Pools, chemical plants, etc.

2 to 4Exterior: Industrial on the outside ofcountry or coastal city.

C5Exterior: Industrial wet or coastal highsalinity.

4 to 8

All our products have a galvanised finish, which is applied to improve steelcorrosion resistance (and also that of iron alloys) by means of a thin surfacecoating. This type of solution is very effective also in highly corrosiveenvironments (See Table 1).

El Unprotected steel has an average useful life of only two years before itsfunctionality or structural integrity are affected. However, galvanised coatingsapplied at galvanising plants last at least ten years without the need for anymaintenance, even in the worst atmospheric conditions.

The basic standard specifying the requirements to be met by galvanisedcoatings applied at hot-dip galvanising plants is the Spanish and internationalStandard UNE EN ISO 1461:2009, "Hot-dip galvanised coatings on productsfinished in iron and steel".

The galvanising process consists of applying a zinc coating to the iron or steelparts and products by immersing them in a zinc bath smelted at 450ºC.

During their immersion in molten zinc, a diffusion reaction occurs between thezinc and the steel, which results in the formation of different layers of zinc-iron

alloys.

When the materials are removed from the zinc bath, these alloy layers arecovered by an outer layer of pure metal, which, as a whole, give the steel anexcellent level of resistance to corrosion.

The galvanising reaction is only produced if the material surfaces arechemically clean, which is why the latter must previously undergo a surfacepreparation process.

Therefore, the stages we go through at our plant to achieve a correct surfacefinish are the following:

1- Hanging the parts

2- Degreasing

3-Stripping

4- Fluxing

5- Galvanising

6- Unhanging the parts

7- Finishing touches

Our galvanising vat measures 12.5 m long x 2.5 m deep x 1.5 m wide,measurements that permit us to galvanise materials of different lengths andwith hardly any limitations.

After galvanising the parts, we subject them to an inspection process to checktheir final appearance as well as the thickness of the coating obtained, to

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TABLE 2

Minimum thickness of the coating on saples without centrifugation.UNE EN ISO 1461:2009.

Workpiece thickness(mm)

Local minimum thicknesscoating (µm)

Minimum average coatingthickness (µm)

Steel ≥ 6mm. 70 85

Steel ≥ 3mm. up to <6 mm.

55 70

Steel ≥ 1,5mm. up to< 3mm.

45 55

Steel< 1,5 mm. 35 45

Castings ≥ 6mm. 70 80

Steel< 6mm. 60 70

Our galvanising vat measures 12.5 m long x 2.5 m deep x 1.5 m wide,measurements that permit us to galvanise materials of different lengths andwith hardly any limitations.

After galvanising the parts, we subject them to an inspection process to checktheir final appearance as well as the thickness of the coating obtained, toensure they comply with Standard UNE EN ISO 1461:2009.

(See Table 2).

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INDUSTRIAS JOVIR, S.L. http://www.jovir.com/en/galvanizacion.html

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