The present invention relates to a method and device for treating objects, in particular metal objects .

A number of techniques are known for the protection of steel constructions from the effect of corrosion. One known technique is galvanizing, wherein a thin layer of zinc is applied to the object surface. The applied zinc layer provides the object with a cathodic protection, i.e. in the case of corrosion zinc is relinquished and thus protects the underlying metal. The corrosion products of zinc will moreover fill up possible damage such as scratches and the like, whereby an additional protection is obtained.

The zinc can be deposited by electrochemical means onto the object, this being known as electrolytic galvanization. In addition, the zinc can be applied to the metal object by spraying zinc onto the surface of the object using spray guns (zinc-spraying), by having zinc diffuse in a drum (sherardizing) or by painting the zinc onto the object (referred to as zinc dust painting or cold-galvanizing) . A further option for applying zinc to a metal is thermal galvanizing, wherein the object for treating is immersed in liquid zinc located in a zinc bath at temperatures between 445°C and 465°C. In thermal galvanizing the object for treating undergoes a pretreatment in which dirt, oil and fat residues are removed from the object surface. As pretreatment the object is then placed in a bath with a diluted hydrochloric acid solution and pickled therein so as to remove rust and mill scale. There then follows a "flux" treatment in which the object for treating is

arranged in a flux bath with for instance zinc ammonium chloride so as to later obtain a good adhesion of the zinc to the steel. If the flux is first applied and then dried, this is known as dry galvanizing. In wet galvanizing the flux is spread over the zinc bath surface and the steel is pulled therethrough. After the treatment there is formed on the steel surface an entity of zinc/iron alloy layers. After said pretreatment the object is immersed, in accordance with the known method, for some minutes in the zinc bath where the liquid zinc bonds to the steel, this over the entire surface thereof and therefore also on the inside of possible hollow structures in the object. During the immersion a number of (gamma, delta and eta layer) alloy layers are formed through reaction of zinc with metal, while a layer of pure zinc is formed when the object is taken out of the zinc bath.

A number of drawbacks are associated with the known methods . Firstly, the use of chemical baths such as hydrochloric acid baths as pretreatment of the steel has an environmental impact. In addition, the supply of hydrochloric acid and the discharge of (contaminated) hydrochloric acid entails high costs.

The known method further involves a number of labour-intensive and relatively costly steps, such as the arranging of the steel in degreasing baths, pickling baths and possible dezincification baths in the case of reconditioning of steel once galvanized in the past. The hydrochloric acid after all only removes the mill scale from the object and further impurities remain present on the object surface. Additional processing steps are hereby necessary.

A further drawback of the known method and device is that use of hydrochloric acid results in brittleness of the treated metal. Subsequent galvanizing of the

brittle metal will therefore produce a less smooth surface, which adversely affects the appearance of the galvanized product.

A further drawback of the known methods is that the objects acquire a zinc-coloured appearance after the zinc treatment, which is in many cases undesirable. When the treated objects are for instance disposed in a space, it may be desirable for the objects to be given a different colour. Methods are per se known for colouring galvanized objects, for instance using wet chemical processes. According to a known method, so-called "green chromating", the galvanized objects are for instance treated with a mixture of chromic acid, phosphoric acid and sulphuric acid, with the result that the thus treated objects acquire a green appearance. This known method does however have a great environmental impact, and for this reason alone is increasingly being judged unsuitable. With the known method it is moreover only possible to obtain a green appearance.

It is an object of the present invention to provide a method and system in which the above stated drawbacks are obviated and in which the objects can be treated rapidly and efficiently in environmentally-friendly manner.

According to a first aspect of the invention, there is provided a method for treating objects, in particular metal objects, the method comprising the steps of: a) arranging the objects in a transport system; b) transporting the objects along shot-blasting units and blasting the objects with grains for the purpose of removing at least one surface layer provided on objects; c) transporting the shot-blasted objects in a flux bath and fluxing at least the outer side of the objects;

d) transporting the fluxed object in a zinc bath and applying a zinc layer to the outer side of the objects by having the outer side of the object react with the zinc from the zinc bath; e) transporting the galvanized objects along a colouring unit and having the colouring unit apply to the zinc layer a dye and/or pigment-containing solution of predetermined colour; f) drying the galvanized and coloured objects. According to this aspect of the invention the pretreatment steps of possible dezincification, degreasing, the treatment with hydrochloric acid and cleaning with water and the like can therefore be replaced by a single step, i.e. shot-blasting of the object. Not only is the mill scale here removed from the object, but it is also possible, as required, to remove multiple material layers, such as the silicon layer, from the object. This produces a cleaner surface of the object, which surface requires a smaller quantity of zinc for the purpose of galvanization. The surface of an object shot-blasted and galvanized in this manner is smoother than would be possible in the prior art.

This smoother surface of the object further makes it easier to give the objects the desired colour or colours. The method of colouring the objects is herein such that the colouring step can be carried out rapidly and efficiently and with a greatly reduced environmental impact .

The colouring unit preferably comprises a colouring bath containing said solution, and step e of the method comprises of arranging the objects in said colouring bath, holding the objects in the colouring bath for a predetermined time, and removing the objects from the colouring bath. By arranging the objects in the colouring bath for a predetermined time using the

conveyor and immersing the objects in the colouring bath, the objects can be provided in efficient manner with the correct colour.

When use is for instance made of a conveyor which displaces the objects at a predetermined speed and the objects are pulled through the colouring bath at this speed, the objects can be immersed in the colouring bath for a sufficient period of time. At a relatively high speed, and therefore a relatively short time period, the objects acquire a light colour, while at a low speed and therefore a long time period the objects acquire a deeper colour. It has been found that good results can be achieved with a duration of stay of the objects in the colouring bath of between 1 minute and 30 minutes and preferably between 2 and 10 minutes, and more preferably between 3 and 5 minutes.

The temperature of the solution can have a value between 15 ^° and 100° Celsius. When water is used as solvent however, operation preferably takes place at a temperature between 60° and 80° Celsius. In this temperature range sufficient dye can be taken up in a short time.

As already stated above, objects to be thermally galvanized are guided through a zinc bath with a high temperature (temperature of the zinc of at least 400° Celsius) . This has the result that the galvanized objects have a relatively high temperature when they reach the colouring unit. In such a situation it is recommended to opt for a lower temperature of the colour solution, preferably in the range between 15 ^° and 40 ^° Celsius. The objects can hereby be cooled and coloured simultaneously, which reduces the running time of the treatment process.

As an alternative to, or in addition to the use of a colouring bath, the objects can also be coloured by

embodying the colouring unit with one or more spray units, so that the objects are coloured in step d by spraying said solution onto the objects which are transported therealong. When use is furthermore made of a solution of a volatile solvent such as ethanol, methylethylketone, cyclohexanone, methoxy propanol etc. and the required dye and/or the required pigment, the thus treated objects will dry very quickly (in practice within a few seconds) . According to another aspect of the present invention, there is provided a system for treating objects, in particular metal objects, comprising:

- a conveyor for transporting objects for treating at an adjustable speed; - one or more shot-blasters disposed along the conveyor for hurling one or more streams of grains in the direction of objects displacing therealong for the purpose of removing at least the surface layer from the objects; - a flux bath disposed along the conveyor for fluxing the objects displacing through the bath;

- a galvanizing bath disposed along the conveyor for thermally galvanizing the objects displacing through the bath; - a colouring unit disposed along the conveyor for applying a dye and/or pigment-containing solution of predetermined colour to the zinc layer of the objects displacing therealong.

In a preferred embodiment of the invention the colouring unit comprises a colouring bath containing said solution, and the conveyor is adapted to arrange the objects in said colouring bath, hold the objects in the colouring bath for a predetermined time and remove the objects from the colouring bath. The colouring bath

is preferably provided with heating means for bringing the colour solution to the correct temperature.

In another preferred embodiment the colouring unit comprises one or more spray units disposed along the conveyor which can spray said colour solution in the direction of the objects.

Further advantages, features and details of the present invention will be elucidated on the basis of the following description of a preferred embodiment thereof. In the description reference is made to the annexed figures, in which:

Figure 1 shows a schematic top view of a preferred embodiment of the invention; and

Figures 2a and 2b show schematic side views of the preferred embodiment of figure 1.

Figures 1 and 2 show the preferred embodiment of a galvanizing device 1 according to the invention. The objects for galvanizing V, such as for instance steel sections, are supplied and coupled at a starting position to a transport system. The transport system is an overhead track system and in the shown embodiment comprises a chain box rail 2 along which, using rollers 21 (figure 2a) , a number of (for instance about 100) suspension elements 22 can be displaced at an intermediate distance of about 60 cm. Such a chain box rail system is of a conventional type per se and will not be discussed here in detail. Other transport systems can also be envisaged.

The suspension elements 22 are advanced by a drive 8 connected to an electrical drive motor 9. Transport system 2 is provided with two tensioning elements 10 and 11 in order to place the system permanently under a determined tension. Once the objects for treating V have been fastened to suspension elements 22 at starting point B (arrow P ₁ ) , for instance by hooking the objects

thereto, the suspension elements are transported in the direction of arrow P ₂ .

The untreated object V first undergoes a shot- blasting treatment in a blasting cabinet 3. Objects are shot-blasted in the blasting cabinet by means of a number of shot-blasters disposed at a preset angle, so that the surface layer is removed. It is possible here to opt for the removal of only the mill scale present on the object. In that case the term surface layer is understood to mean only the mill scale of the object in question. If desirable however, more layers can be removed from the object in addition to the mill scale. It is possible for instance to remove undesired unevenness from the object so that it acquires a smoother and more attractive appearance.

By shot-blasting the object in the above stated manner it is clean to the extent that it can be "fluxed" immediately without additional operations. The term "flux" relates to the introduction or immersion of an object into a flux bath which is for instance filled with zinc ammonium chloride. Figure 2a shows that fluxing takes place by displacing the object, hanging from a suspension element 22, through a flux bath 4. Once the flux layer on the object has dried, for instance by guiding the object along a drying unit 5, the object is guided through a zinc bath 6 (figure 2a) which is filled with zinc at a temperature of roughly 453° C. It has been found that at this temperature and at a transporting speed through the zinc bath in the order of magnitude of 50-250 cm per minute, and preferably 80 cm per minute, there is brought about an optimal chemical bonding of the liquid zinc to the material of the object.

After undergoing the galvanizing treatment, the objects cool through heat exchange with the environment

such as outside air or heat exchange in colouring bath 7 to be described hereinbelow. In bath 7 there is arranged a mixture of solvent, such as for instance water or ethanol, and one or more dyes. In addition to dyes, or instead thereof, the mixture can contain pigment of correct colour. Tests have shown that dyes on the basis of azo, disazo, phthalocyanine and carbonyl compounds are particularly suitable for colouring the galvanized objects. As stated above, the objects can also be coloured by arranging spray heads (not shown) on either side of the transport path with which the objects transported therealong can be sprayed with the colour solution referred to herein. Although the objects in this embodiment are not liquid-cooled, the present embodiment has the advantage that rapid colour changes are possible. Furthermore, the drying time of the thus treated objects is generally shorter. This of course results in the total running time being shortened. Finally, the spray units are in some cases easier to fit into a conveyor.

In the embodiment with colouring bath 7 (figure 2) the objects are cooled from the above stated, relatively high temperature (about 450° C) to about 85° C or less as a result of immersion in the zinc bath. After cooling, the relevant object is transported until it reaches end point E. Having arrived here, the object can be removed from the relevant suspension element 22 and discharged (P ₃ ) . Since the temperature of the objects amounts to less than 80° C, employees can package the treated objects immediately and without problem.

Figures 2a and 2b show a side view of a part of the device. In the shown embodiment the shot-blasting and fluxing take place one immediately after the other, in contrast to the embodiment of figure 1.

The running time of the system, i.e. the period of time between fastening of an object for treating to a suspension element and the removal of a treated object from the suspension element, amounts in the shown 5 embodiment to about 1 to 1.5 hours, while the capacity is variable between about 3000 and 5000 kg per hour.

A number of experiments have been carried out in order to determine the parameters which influence the colouring process. Table 1 shows the results of a number

10 of these colouring experiments. Table 1 shows the results of a colouring process according to the invention (experiments 1-11) and of two per se known colouring processes, wherein use is made in the colouring of chemicals having an impact on the

15 environment.

Table 1: Overview of the results of the colouring of galvanized objects.

In experiments 1 and 2 no pretreatment has taken place before the galvanized objects were coloured. In experiments 3-11 a pretreatment has taken place. A

pretreatment can consist of a wet chemical process wherein the galvanized objects are treated with a wet chemical solution in order to form an oxide layer on the zinc surface of the objects. The pretreatment can also consist of applying an organic coating layer to the galvanized surface of the object for the purpose of taking up the colour solution therein. In some cases heating in an oven has taken place to a temperature of about 250 ^° Celsius in order to simulate a cooling immediately after the thermal galvanization.

The pretreatment designated ^λλ PVP dip" relates to immersion of the galvanized object for 1 minute in a solution of 1 g/1 polyvinylpyrrolidone at room temperature. This has the result that a very thin coating is provided on the zinc surface, which coating ensures a more uniform adhesion of the dye to the surface of the object. This pretreatment has the advantage that the materials used do not impact the environment, or hardly so, so that the total process of galvanizing and colouring remains environmentally- friendly.

The pretreatment designated with "Alodine 4830" (zirconation) relates to immersion of the galvanized object for 10 s (experiment 7) and for 30 s (experiments 8 and 10) in a solution of 1 g/1 fluorozirconic acid (H2ZrF6) in water, with a pH of 2 (with HNO3) and at room temperature (supplier: Henkel) .

The pretreatment designated with "chromating" or "chrome-plating" relates to a method wherein an object was immersed for 2 minutes in a mixture of 200 g/1

sodium dichromate and 10 g/1 sulphuric acid (H2SO4 (96%)) at a pH of 1 and room temperature.

The galvanized objects can also be pretreated by being oxidized with hydrogen peroxide. The wet chemical processes of Alodine 4830, hydrogen peroxide and chrome-plating are all used to arrange an oxide to take up the dye so that a more durable colour is obtained. The oxide layer also provides protection against corrosion of the zinc. The optionally pretreated objects are then immersed for the time indicated in the table in a bath having a different content in each case:

Process A indicates that the object is immersed in 0.5 g/1 Duasyn Yellow 3GF-SF in water at a pH of 6 and 60° Celsius (Disazo compound (Na2C27H22N6 S2O9) Colour index Direct Yellow 132, supplier: Clariant Benelux BV) .

Process B indicates that the object is immersed in 5 g/1 Savinyl Blue GLS in ethanol (Phthalocyanine (C32H16N8M) solvent-based 44, supplier: Clariant Benelux BV) ;

Process C indicates that the object is immersed in 30 g/1 Chromic acid (CrO3) ; 10 ml/1 phosphoric acid (H3PO4 (85%)), 15 ml/1 sulphuric acid (H2SO4 (96%)) at a pH of 1 and room temperature.

The experiments show that the concentration of the dyes influences the colouring of the object. At a concentration of 0.1 - 0.5 g/1 a relatively light colour is observed, at a concentration of 5 - 10 g/1 a relatively dark colour is observed. The duration for

which the objects are immersed has a similar influence on the colouring of the object.

The present invention is not limited to the above described preferred embodiments thereof; the rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.