Nuts and bolts with coatings of cinc

Exists a wide variety of coatings metallic that can use to protect the components of small steel, as they are the elements of subjection. If we speak of the use of the cinc, there is at least three different forms to employ it with characteristics very shoot regarding coating and performance.

These three systems are:

1. Galvanizing in hot by centrifugation
2. Metallic Coating with dust of cinc (or sherardización)
3. Cincado electrolytic

The term centrifuges galvanizing uses to describe the process of galvanizing in hot of threaded components and other small pieces. The process is very similar to the usual galvanizing of sections of big steel. However, in this case the small components plant in containers drilled, allowing the processed of elements until 8 mm of diameter. After the immersion in the bathroom of galvanizing, the container centrifuga to high speed so that the fast twist delete any excedente of cinc for like this ensure a clean profile.

When the articles submerge in the bathroom of galvanizing form a series of layers of alloy cinc-ironinging joined metalúrgicamente to the surface of the steel. These alloys are harder that the sweet steel and usually are covered by an external layer comparatively soft of cinc that remains after the operation of twist. This structure is only and is what gives him to the coating galvanised his optimum resistance: the direct hits are cushioned by the external layer of cinc, whereas the layers of hard alloy are the managers to bear the abrasion.

The norm JOINS IN ISO 1461 contemplates coatings galvanised that they obtain on these small pieces, with or without threaded parts, specifying minimum values for his half thickness that are comprised between 25 and 55 micrometers (μm) as it was the thickness of the basic material. The pieces of this type have to manufacture with suitable steel for galvanizing and his form has to be also appropriate for the characteristics of the process. Like this, for example, they are not adapted for this procedure the pieces in shape of capsules or tubular elbows and, in general, all those that have blind orifices or concave zones in which it can remain retained the cinc.

The norm JOINS-IN ISO 10684 specifies with elder detail the characteristics of the coatings galvanised on the fasteners and establishes rules for the galvanizing and the mechanised to sobremedida of the threaded parts. The most common practice is to galvanise the screws with his already mechanised threads to his dimensions and normal tolerances. The threads of the nuts, however, are used to mechanise once galvanised the nuts, with a sobremedida sufficient to compensate the increase of the diameter of the thread of the screw because of the coating galvanised. The threads of the nuts cover with fat or neutral oil like temporary protection until his attachment. Once mounted in his corresponding screws, the threads of the nuts remain protected by contact with the coating of the screws. A proof of this protection is that the unions with screws and nuts galvanised in hot can slacken easily after a lot of years of attachment.

Nuts of ironinging with coatings of cinc.

With this procedure obtain deposits of cinc on small pieces by means of treatment of the same with dust of cinc in drums giratorios, to inferior temperatures to the one of fusion of the cinc. The articles have to be chemically clean and dry. Any remaining water can cause problems when it mixes with dust of cinc. The pieces with the clean surface of oxides and impurities, together with 90% of dust of cinc and 10% of dust of oxide of cinc (to avoid the sintering) load in a drum that heats to 440°C. In some cases adds fine sand to help to obtain a uniform distribution. The dust has to be very fine. Dusts thicker require more time to form the revestimiento wished. The need to ensure a uniform temperature inside the barrels imposes a limitation of size in the process, that uses generally for small pieces and quite complex.

Is a process of electrolytic deposition in bathrooms (JOINS IN ISO 2081 or 10152), similar to the cromado or cobreado. The layer of cinc is much finer (5-20 micras), by what is used to realizar later a process of pasivado (treatment that increases the protection). Even so, the length is a lot lower and in principle except that resort to pasivados expensive, only is adapted for interiors. Like advantages, the pieces are softer and uniform increasing his aesthetic value, and can pasivar, lacar or paint.