EP0647505B1 - 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 or uncoated metal parts and, in particular but not exclusively, of galvanized scaffolding elements.

Originally the scaffolding element systems used were painted and their maintenance was easy. At each return from the site, a conventional steel shot blasting allowed to strip the surfaces of the tubes or soiled floors. A repainting made the equipment sound new appearance.

The generalization of galvanized scaffolding as well as the use of facade waterproofing resin on construction sites buildings that are difficult to remove on the scaffolding elements have posed new and delicate problems for cleaning the scaffolding elements. There is therefore a real need for facilities effective in removing nuisances such as concrete, plaster, paint, resins, etc. on the scaffolding elements without affecting their galvanization and the cost of which remains in proportion with the value of the product to be treated.

There are other coated parts, for example covered with a other type of protection which it is necessary to be able to clean in the acceptable economic conditions.

Document BR-A-8 201 279 describes a process for treating coated or uncoated metal parts, comprising a step of subjecting said part, for a predetermined time, to a high speed jet of particles at room temperature, whereby one obtains simultaneously cleaning the part when it has dirt and the formation of an adherent surface layer of reduced thickness consisting of zinc.

We know several methods to perform cleaning scaffolding elements: we can mention high pressure cleaners more than 1000 bars but they have the disadvantage of requiring the recycling of very large volumes of water and altering the coating. Acid baths have also been used in combination with rinsing tanks but the implementation of such installations is delicate and removes the coating. It has been proposed to spray carbon dioxide under pressure at low temperature. This process is effective but expensive. We know also shot blasting processes using small balls of plastics. This process does not alter the coating but is prohibitive cost.

It is also desirable that the cleaning operation is accompanied by a reloading operation of the material part to protect it.

An object of the present invention is to provide a method which allows simultaneous cleaning of the piece if dirty or dirty parts of the piece and reloading of coated or uncoated metal parts, in particular galvanized, by example of scaffolding elements, which is of simple implementation and inexpensive while being effective.

To achieve this goal, the parts processing process metallic coated or not according to the invention comprises the features contained in claim 1.

While being effective, this method is costly to implement reduces and allows to obtain parts whose final appearance is perfect thanks during the reloading operation.

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

Preferably also, 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 figure 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;
• Figure 2 is a partial elevational view showing the conveyor supporting 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 dimensions less than 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 soiling S which, it should be remembered, is not chemically linked to the part due to the impact. On the other hand, this jet of particles causes a certain heating of the external surface of the part. 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. This constitutes an adherent outer layer C ₃ of recharging whose thickness e '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 whole of the treatment facility. This installation is arranged in a lobby. It essentially comprises a conveyor 10 which allows 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 an area of loading 12. It crosses a protective and processing enclosure or blasting tunnel 14 and passes in front of an unloading area 16. Also shown are the boxes 15 and 17 containing the blasting turbines.

Figure 2 shows an embodiment of the conveyor. We have depicted the horizontal support rail 18 and hanging poles by rollers 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 treat 28. The distance between the poles 20 is of course adapted to the length of the parts to be treated. As shown in Figure 3, the enclosure of protection 14 or tunnel in which the blasting is carried out comprises on its soil a trench 30 for recovering blasting particles and a worm conveyor 32 for recovering these particles. A once dusted, the blasting particles can be recycled.

In FIG. 4, the walls 32 and 34 of the treatment chamber 14 as well as eight electric turbines each equipped with an electric motor for making jets of shot blasting particles so that all of the pieces 28 passing through the enclosure is suitably subjected to the jet of particles. The turbine nozzles are oriented in such a way that all the suspended parts are subjected to shot blasting. On the Figure 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. It could be also zinc balls whose diameter is between 0.6 and 1 mm. Preferably, each of the eight turbines delivers around 140 kg / min of zinc particles which are emitted with an exit speed of the order of 50 meters per second. The speed of movement of the conveyor and therefore the speed of movement of the parts in the enclosure 14 is of the order of 2 meters per minute so that the duration exposure is 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 actually removed without resulting in alteration of the initial galvanization of parts. In addition, it was observed that the shot blasting carried out under the conditions set out above allows in addition to the simultaneous production of a very thin layer of reloading, for example zinc, if the particles are produced in this material. This surface layer, the thickness of which is of the order of 10 microns, adheres very well to the part by "cold" galvanization in due to the relatively reduced temperature (maximum equal to 60 ° C) resulting from the bombardment of the part by particles.

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

Finally, the preceding detailed description relates to the 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 synthetic material, or metallic coating.

Likewise, the process is specially well suited for carrying out cleaning the parts and reloading them in a single operation. he It goes without saying, however, that the invention would not be departed from if the process was applied to initially clean parts in order to recharge them a layer of reduced thickness of zinc or aluminum.

Claims (4)

1. A method of treating optionally coated metal parts, 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 aluminum, 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 simultaneously cleaning the parts, if dirty, and forming a thin adherent surface layer of the order of 7 to 10 microns constituted by the zinc or the aluminum.
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 claim 1 or 2, characterised in that the particles have a speed that is greater than 50 m/s.
4. A method according to any one of claims 1 to 3, characterised in that said parts are galvanised.

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