EP0647505B2 - Method and apparatus for the treatment of metallic workpieces, either coated or not - Google Patents

Description

The subject of the present invention is a method for the treatment of coated metal parts or no and, in particular but not exclusively, of elements galvanized scaffolding.

Originally scaffolding systems used were painted and their maintenance was easy. AT each return from the site, a standard shot blasting steel was used to strip the surfaces of the tubes or soiled floors. A repainting returned to material its new appearance.

The generalization of galvanized scaffolding as well as the use on resin sites for sealing building facades that are difficult to remove on the scaffolding elements laid new and delicate problems for cleaning scaffolding elements. So there is a real need for efficient facilities to remove nuisances such as concrete, plaster, paint, resins, etc. on the scaffolding elements without alter the galvanization of these and whose cost remains in relation to the value of the product to be treated

There are other coated parts, for example covered with another type of protection than is necessary to be able to clean under economical conditions acceptable.

Document BR-A-B 201 279 describes a process treatment of coated or uncoated metal parts, including a step of submitting said document, during a predetermined time, at a high speed jet of particles at room temperature, whereby we obtain simultaneously cleaning the room when it shows soiling and the formation of a surface layer adherent of reduced thickness constituted by zinc.

We know several methods to perform cleaning of scaffolding elements: we can cite high pressure cleaners over 1000 bar but they have the disadvantage of requiring recycling very large volumes of water and altering the coating. Associated acid baths were also used to rinsing tanks but the implementation of such installation is delicate and removes the coating. We have proposed to spray carbon dioxide under pressure at low temperature. This process is effective but expensive. We also know shot blasting processes using small plastic balls. This process does not alter the coating but is costly prohibitive.

It is also desirable that the operation of cleaning is accompanied by a reloading operation of the piece of protective material thereof.

An object of the present invention is to provide a process which makes it possible to simultaneously carry out the cleaning the room and reloading of metal parts coated or not, in particular galvanized, for example scaffolding elements, which is a setting simple and inexpensive work while being effective.

To achieve this goal, the treatment process of metal parts coated or not according to the invention includes the features contained in the claim 1.

While being effective, this process is costly of reduced implementation and allows parts to be obtained whose final appearance is perfect thanks to the reloading operation.

Preferably, the metal is zinc and the particles have dimensions less than or equal to 1 mm.

Also preferably, the particles have a speed at least equal to 50 m / s.

• la figure 1 est une vue générale de dessus de l'ensemble de l'installation de nettoyage ;
• la figuré 2 est une vue partielle en élévation montrant le convoyeur supportant des pièces à traiter;
• la figure 3 est une vue partielle en élévation montrant l'enceinte et le convoyeur à vide ;
• la figure 4 est une vue de dessus montrant l'implantation des turbines de grenaillage; et
• la figure 5 est une vue en coupe partielle d'une portion de pièce ayant été soumise au traitement.

Other characteristics and advantages of the present invention will appear better on reading the following description of an embodiment of the invention given by way of non-limiting example. The description refers to the appended figures in which,

• Figure 1 is a general top view of the entire cleaning installation;
• FIG. 2 is a partial elevation view showing the conveyor supporting the parts to be treated;
• Figure 3 is a partial elevational view showing the enclosure and the vacuum conveyor;
• Figure 4 is a top view showing the layout of the blasting turbines; and
• Figure 5 is a partial sectional view of a portion of part having been subjected to treatment.

Before describing in detail the treatment installation, we will explain the principle of the invention with reference to Figure 5. In this figure, there is shown in section the surface of a part P, for example an element of galvanized steel scaffolding. There is an outer layer C ₁ whose zinc content decreases from the periphery towards the inside of the part and the part C ₂ proper of steel. The thickness of the layer C ₁ is conventionally of the order of 70 microns. There is also shown on the external surface of the part a dirt S to be removed.

By subjecting the surface of the part P to a jet of particles of internal dimensions or equal to 1 mm in a material having a hardness at most equal to that of the external layer C ₁ of the part, one obtains surprisingly, in the same operation, successively two results. On the one hand the projected particles eliminate the dirt S which, it should be remembered, is not chemically linked to the milk part of the impact, On the other hand, this jet of particles causes a certain heating of the external surface of the room. Because of this heating, the particles which have dimensions at most equal to 1 mm and whose hardness is at most equal to that of the layer C ₁ of the part, are crushed on the external surface of the part previously cleaned and join by merger. An adherent external reloading layer ₃ is thus formed, the thickness e 'of which is of the order of 7 to 10 microns. By analogy with hot zinc plating, this cold zinc plating process could be qualified given the relatively reduced temperature. Preferably, the projection is carried out in such a way that the rise in temperature of the room is a few tens of degrees Celsius. Preferably, this temperature is at most equal to 60 ° C. At the end of the treatment, a part is thus obtained which is not only clean but which has also been recharged, for example made of zinc. The part must be subjected to the projection of particles for a duration at least equal to 1.5 minutes.

Referring now to Figure 1, we will describe the entire treatment facility. This installation is arranged in a hall. It basically includes a conveyor 10 which allows to move at a controlled speed, for example of the order of 2 meters at the minute of the parts to be treated. The conveyor moves in front of a loading area 12. It crosses a protection and treatment enclosure or tunnel shot blasting 14 and passes in front of an unloading area 16. The boxes 75 and 17 containing the blasting turbines.

Figure 2 shows an exemplary embodiment of the conveyor. The horizontal support rail is shown. 18 and poles suspended by pebbles 22 to the rail and driven for example by a system with chain 24. As best shown in Figure 4, the poles 20 include, for example, nine hooking elements 26 of the parts to be treated 28. The distance between the poles 20 is of course adapted to the length pieces to process. As shown in Figure 3, the enclosure protection 14 or tunnel in which is made shot blasting has a trench on its ground 30 for blasting particles and a conveyor worm gear 32 for recovering these particles. Once dusted, the blasting particles can be recycled.

In Figure 4, there is shown schematically the walls 32 and 34 of the treatment chamber 14 as well as eight electric turbines each equipped an electric motor for making jets of shot blasting particles so that the whole parts 28 crossing the enclosure are subject suitably for the jet of particles. Nozzles turbines are oriented in such a way that the whole suspended parts be subjected to shot blasting. In FIG. 4, only the four turbines 36, 38, 40 and 42 are visible.

According to the invention, the blasting particles are made of zinc or aluminum. In the case of zinc, the particles have dimensions less than or equal to 1 mm. For example, these particles are obtained by cutting a 0.7 mm diameter zinc wire. He can they are also zinc balls whose diameter is between 0.6 and 1 mm. Preferably, each of the eight turbines deliver approximately 140 kn / min of particles of zinc which are emitted with an output speed of around 50 meters per second. Travel speed of the conveyor and therefore the speed of movement rooms in enclosure 14 is around 2 meters per minute in such a way that the exposure time or at least 1.5 minutes.

Tests carried out with this installation show that whatever the nature of the deposits on the parts to be treated, these are effectively removed without resulting in an alteration of the galvanization initial parts. In addition, it has been observed that shot peening carried out under the conditions stated above also allows the simultaneous creation of a layer very thin recharging, for example zinc, if the particles are made in this material. This layer superficial, the thickness of which is around 10 microns, adheres very well to the part by zinc coating "to cold "due to the relatively reduced temperature (at most equal to 60 ° C) resulting from the bombardment of the part by the particles.

We also understand that the installation being automatic, its yield is high.

Finally, the preceding detailed description aims cleaning and reloading of galvanized parts. However, we would not go out of the invention if the parts to be cleaned were coated with a layer of material synthetic, or metallic coating.

Claims (4)

1. A method of cleaning and reloading optionally coated metal parts comprising dirt, the method being characterised in that it comprises a step of subjecting said part at ambient temperature and for a predetermined length of time to a high-speed jet of particles, said particles being completely made of a metal selected from the group comprising zinc and aluminium, said particles are projected in such a manner as to cause the surface of the part to be heated at a temperature less than or equal to 60°C under the effect of the shocks from the particles, thereby causing said particles to melt by being crushed against said part, thereby simultaneously cleaning the part and forming a thin adherent surface layer of the order of 7 to 10 microns constituted by the zinc or the aluminium.
2. A method according to claim 1, characterised in that the metal is zinc and in that said particles are of dimensions less than or equal to 1 mm.
3. A method according to any one of claims 1 and 2, characterised in that the particles have a speed which is greater than 50 m/s.
4. A method according to any one of claims 1 to 3, characterised in that said parts are galvanized.

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