NL1020689C2 - Thermally galvanizing of objects, i.e. metal objects, by pretreating object, including blasting with grains to remove at least surface layer from object - Google Patents

Abstract

Objects are thermally galvanized by pretreating the object, including removing surface layer from the object; arranging the pretreated object in a flux bath; arranging the fluxed object in a zinc bath to have the material of the object react with zinc and to apply a zinc containing layer to the object. The pretreating step comprises blasting the object with grains to remove at least the surface layer. Independent claims are also included for: (a) system for thermally galvanizing object, in particular metal objects, comprising an overhead track provided with suspension elements, drive (8) for displacing the suspension elements along the overhead track, shot blaster(s) for hurling streams of grains in the direction of an object, a flux bath (4), and a galvanizing bath (6); and (b) device for shot-blasting object(s) comprising a housing, a displacing device for displacing the objects for shot-blasting in a path through the housing from entrance opening to exit opening, and shot-blasters disposed on both sides along the path in the housing and are oriented differently in relation to the housing.

Description

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METHOD AND DEVICE FOR SINKING OBJECTS

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

A number of techniques are known for protecting steel structures against the effects of corrosion. A known technique is galvanizing, whereby a thin layer of zinc is applied to the object surface. The applied zinc layer offers a cathodic protection to the object, that is to say that when attacked, zinc sacrifices itself and thus protects the underlying metal. Moreover, the corrosion products of zinc will fill in any damage such as scratches and the like, whereby additional protection is obtained.

The zinc can be deposited on the object by electro-chemical means, which is called electrolytic galvanizing. 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 allowing zinc to diffuse into a drum (Sherardizing) or by painting the zinc on the object ( zinc dust paints or cold galvanizing). A further possibility for applying zinc to a metal is hot-dip galvanizing, whereby the object to be treated is immersed in liquid zinc, which is present in a zinc bath at temperatures between 445 degrees and 465 degrees Celsius.

During hot-dip galvanizing, the object to be treated undergoes a pre-treatment in which dirt, oil and fat residues are removed from the object surface. As pretreatment, the article 1 02 0: 2 is then placed in a bath with a dilute hydrochloric acid solution and pickled therein to remove rust and mill scale. The following is a "flux treatment, in which the object to be treated is applied in a flux bath with, for example, zinc-ammonium chloride, in order to later obtain a good adhesion of the zinc to the steel. If the flux is first applied and then dried, one speaks For wet galvanizing, the flux is spread over the zinc bath surface and the steel is pulled through. After being treated, a whole of zinc / iron alloy layers forms on the steel surface. known method, immersed for a few minutes in the zinc bath, where the liquid zinc connects to the steel and over the entire surface thereof, and therefore also on the inside of any hollow structures in the object. a number of alloy layers are formed with metal (Gamma, Delta and 20 Eta layers), while when the object is removed from the zinc bath dt, a layer of pure zinc is formed.

There are a number of drawbacks to the known method device. Firstly, the use of chemical baths, such as hydrochloric acid baths, as a pretreatment of the sample is harmful to the environment. In addition, the supply of hydrochloric acid and the removal of (contaminated) hydrochloric acid entail high costs.

Furthermore, the known method entails a number of labor-intensive and relatively expensive steps, such as arranging the steel in degreasing baths, pickling baths and possible de-zincing baths in the case of renovating galvanized steel in the past. After all, the hydrochloric acid only removes the mill scale from the object and further impurities remain on the object surface. This requires additional processing steps.

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A further drawback of the known method and device is that the use of hydrochloric acid results in brittleness of the treated metal. Subsequently, galvanizing the brittle metal will result in a less smooth surface, which reduces the appearance of the galvanized product.

The object of the invention is to obviate the above drawbacks and to provide an improved method and device for treating objects with a protective material.

According to a first aspect of the invention, a method is provided for thermally galvanizing objects, in particular metal objects, comprising the steps of: - pre-processing an object to be treated, including removing the surface layer from the object; - arranging the pre-processed article in a flux bath for fluxing the article; - applying the fluxed article in a zinc bath for reacting the material of the article with zinc and applying a zinc-containing layer to the article, the pre-processing step comprising granulating the article with grains for removing at least the surface layer. According to this aspect of the invention, the pre-treatment steps of optionally de-zincing, degreasing, treatment with hydrochloric acid, and cleaning with water and the like can be replaced by a single step, namely irradiating the object. Hereby, not only is the roller layer removed from the object, but it is also possible, if desired, to remove more material layers such as the silicon layer from the object. This provides a cleaner surface of the article, which surface requires a smaller amount of zinc for galvanizing. Furthermore, the article thus treated is more suitable for applying a coating to it. In addition, the appearance of I U>: o 4 is an object blasted and galvanized in this way.

It has been found that particles or grains with an average diameter of between 0.25 and 1.6 mm and made of low-carbon steel are particularly suitable for blasting the objects. The grains have a low degree of carbon since at a high degree of carbon an excessively thick layer of zinc deposits on the object and the degree of hard zinc formation increases. Preferably, a mixture of substantially 40% with a grain size of 0.6-1.0 mm and 60% with a grain size of 0.8-1.3 mm is used.

This makes an optimum ratio between toughness, minimum grain consumption and maximum performance possible.

A large chain / spring effect also occurs, which increases the effectiveness of the blasting, and in particular the blasting of parts of the object that are relatively difficult to reach.

It is known to submerge an object to be treated in a bath, then to keep it stationary in the bath for a few minutes and then to remove it from the bath. The next item is next. According to a further preferred embodiment of the invention, the above-mentioned step of arranging the object in at least one of the baths, however, comprises letting the object run through the relevant bath. This means that one object after the other can be transported continuously or substantially continuously through the bath. This not only allows the use of a device according to the aspect of the invention to be mentioned below, but also influences chemical processes that occur during the galvanizing process. The immersion or splashing of the objects in a bath adversely affects the chemical processes occurring. By moving the objects through the bath there is less ash formation and in particular less vapor formation. Moreover, the chance of loss-making formation of hard zinc iron / zinc crystals is smaller.

An object is preferably transported through the bath at a substantially constant speed in order to achieve a uniform and mutually as constant as possible sinking of the object.

According to a second aspect of the invention, a device is provided for hot-dip galvanizing objects, in particular metal objects, comprising a suspension track provided with suspension elements on which one or more objects to be treated can be suspended, and drive means for moving along the suspension track of the suspension elements, wherein at least along the suspension track are arranged: jet throwing means for throwing one or more grain rays in the direction of an object moving along it for removing at least the surface layer of the object; a flux bath for fluxing the object moving through the bath; and a galvanizing bath for thermally galvanizing the object moving through the bath. Irradiating the objects instead of degreasing, treating with hydrochloric acid and cleaning with water provides the previously described advantages. Moreover, the overhead conveyor belt along which the objects are continuously transported during the galvanizing process makes it possible to automate the galvanizing process entirely or at least to a large extent. This makes better control of the different process steps possible, while up to 80% fewer personnel are required.

According to a preferred embodiment of the invention, the jet throwing means comprise a number of throwing beams, which are arranged to irradiate the object to be treated at a number of predetermined beam angles. In a preferred embodiment, eight throwing nozzles are positioned and directed in such a way that all parts of the objects to be processed can be reached.

According to a further preferred embodiment, the jet throwing means are arranged in an enclosure 5 (for example a blasting cabin) whose dimensions of the entrance and exit openings are adjustable depending on the shape and dimensions of the objects moving through the enclosure. This ensures that the amount of granules released during the irradiation is limited. This benefits the treatment. After all, granules that are outside the enclosure can end up in the flux baths or zinc baths and thus adversely affect the flux or galvanizing process.

According to a preferred embodiment of the hanging track, it is designed with at least one drop and at least one rise for carrying the objects downwardly into a bath and upwardly from the bath, respectively. With a relatively simple construction, a substantially constant treatment of the objects in the flux bath and / or the zinc bath is hereby possible.

According to a further preferred embodiment of the invention, the device comprises detection means for detecting an object hanging from one of the suspension elements, as well as control means for controlling the drive means of the hanging track and at least the jet throwing means for interrupting the with a predetermined time delay drive of the suspension element and the jet throwing means. When, for example, it is detected with one or more detection eyes that the supplied suspension elements no longer contain objects to be treated, the control means can determine, on the basis of the previously known conveying speed of the suspension elements, when the irradiation process must be terminated. Moreover, it can be determined when the last item has been fully processed. At that time, the drive of the hanging track is also terminated.

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According to a further aspect of the invention, a suspension element is provided, preferably the aforementioned suspension element, which is made of such an alloy that substantially no zinc is absorbed or adheres to the surface of the element. Once a suspension element has been guided past the zinc bath, zinc could otherwise remain on the surface of the suspension element. During the processing of a subsequent object, this can lead to explosions, in particular when this object is irradiated, which can pose a danger to man and machine.

An explosion can occur in the system if zinc residues mix with steel grains of a different composition (metals).

Further advantages, features and details of the present invention will be elucidated on the basis of the following description of a preferred embodiment thereof. Reference is made in the description to the accompanying figures, in which: Figure 1 shows a schematic top view of a preferred embodiment of the invention;

Figures 2a and 2b are schematic side views of the preferred embodiment of Figure 1; and

Figure 3 shows a schematic perspective view of a preferred embodiment of a blasting cabin according to the invention.

Figures 1 and 2 show the preferred embodiment of a galvanizing device 1 according to the invention. The objects V, 30 to be galvanized, such as for example steel profiles, are supplied and coupled to a transport system at a starting position. The transport system is a hanging track system and in the embodiment shown comprises a chain box rail 2 along which with the aid of rollers 21 (Fig. 2a) a number of (for example approximately 100) suspension elements 22 can be displaced with an intermediate distance of approximately 60 cm. Such a chain box rail system is per se of a conventional type and will not be detailed herein. . λ '' (· 8 are discussed. Other transport systems are also conceivable.

The suspension elements 22 are advanced by a drive 8 which is connected to an electric drive motor 9. The transport system 2 is provided with two tensioning elements 10 and 11 in order to bring the system permanently under a certain voltage.

Once the objects V to be treated are attached to the suspension elements 22 at the starting point B (arrow Ρχ), for example by hooking the objects to them, the suspension elements are conveyed in the direction of arrow P2.

First, the untreated object V undergoes a blasting treatment in a blasting cabin 3.

Objects are irradiated in the blasting cabin by means of a number of blasting throwers arranged at a preset angle. Not only the irradiation angle at which the objects are irradiated, but also the grain diameter and the material of the grains is important here. It has been found that when using steel grains or other-shaped steel particles with a grain thickness of between 0.25 mm and 1.6 mm and preferably in a ratio of 40% particles with a grain size of 0.6-1.0 mm and 60% particles with a grain size of 0.8-1.3 mm an optimum removal of the surface layer of the article can be achieved. A good chemical composition of the granules is, for example, 0.14-0.18% C, 0.65-0.85% Si and 0.35-0.55% Mn. A choice can be made here to remove only the roller layer present on the object. In that case, the term surface layer only covers the roller layer of the object in question. However, if desired, more layers can be removed from the article in addition to the roller layer. For example, it is possible to remove unwanted unevennesses from the object, so that it acquires a smoother and more attractive appearance.

Z- '· · 4 9

By irradiating the object in the above-mentioned manner, it is so clean that it can be directly "fluxed" without additional processing. The term "fluxes" refers to the placement of an article in a flux bath filled, for example, with zinc ammonium chloride. The flux agent should be low in smoke, i.e. a relatively small concentration of ammonium chloride, preferably around 10% NH 4 Cl (and about 90% ZnCl 2), is used. The zinc ammonium chloride forms a thin layer on the object which in the following galvanizing process promotes the connection of zinc with the material of the object. Figure 2a shows that the fluxing takes place by moving the object, hanging from a suspension element 22, through a flux bath 4.

In another preferred embodiment, not shown in the figures, immediately after the steel blasting and therefore before fluxing, the first is cleaned by blowing it off with air and / or subsequently spraying it clean with water to which chemical additives may or may not have been added. Chemical additives are added to promote the draining of the water containing the residual dust, mainly consisting of steel blasting dust.

The spraying is effected by arranging a number of spray showers along the conveyor track which remove the last iron residues as a result of the blasting treatment. The mixture of water (with or without additives) and iron residues is then collected and de-ironed by using a magnetic filter. The water can then be used again for cleaning. Due to such a recovery, no iron residues end up in the area. Moreover, no iron residues end up in the flux bath and / or zinc bath (to be discussed later), so that these baths need to be refreshed less often. These are further environmentally friendly aspects of the present invention.

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After the flux layer has been dried on the article, for example by guiding the article along a drying unit 5, the article is guided through a zinc bath 6 (Figure 2a), which is filled with zinc of a temperature 5 of approximately 453 ° C . It has been found that at this temperature and at a transport speed through the zinc bath in the order of magnitude of 50-250 cm per minute and preferably 80 cm per minute, an optimum chemical bond of the liquid zinc with the material of the article 10 is achieved. is being brought.

The zinc layer thus formed has a complicated structure. In addition to a pure zinc layer on the surface, a number of alloy layers with zinc and iron in different proportions are formed between the zinc and the material of the article. The combined layer thickness of these layers varies between 50 and 150 micrometers.

When the galvanized objects run out, compressed air is directed in the direction of the objects. This can for instance take place by providing a perforated construction next to the conveyor track and blowing air through the perforations with great force. Any zinc droplets present on the object are thereby blown off the object. This is important if the tolerances in the dimensions of the object play a role, for example in order to control the fit of the object. The blown away zinc droplets are collected and returned to the zinc bath so that excess zinc is retained and therefore less zinc is lost during galvanizing. After having undergone the galvanizing treatment, the articles cool down by heat exchange with the environment such as the outside air or heat exchange in an (optional) cooling system. In the embodiment shown, the cooling system comprises a cooling bath 7 along which the objects can be carried.

The objects are cooled from approximately 453 ° C to approximately 85 ° C. If one or more heat exchangers are used, a temperature of approximately 80 ° C can be achieved

* 11 can be reached. In the embodiment shown in Figure 2, cooling is accomplished in a cooling bath. Separately or in combination with this cooling bath, a brightening bath can be provided, in which brightening agent is applied over the surface of the galvanized object in order to give the object surface a glossy appearance. A combined coolant / brightener is preferably Karizol 2508 from Dipl. Ing. Herwig GmbH. Such a brightener has good cooling properties, while at the same time avoiding so-called white rust to promote a beautiful, shiny product. After being cooled and optionally provided with brightener, the object in question is transported until it has reached the end point E15. Once there, the object can be removed from the relevant suspension element 22 and discharged (P3). Since the temperature of the objects is approximately 85 ° C or less, employees can package the treated objects directly and without hindrance.

Figures 2a and 2b show a side view of a part of the device. In the embodiment shown, the blasting and fluxing take place directly one after the other, in contrast to the embodiment of Figure 1. This is, however, not relevant for the description of the invention. As shown in Fig. 2a, the objects V are irradiated with a number of ejection elements or ejectors 24 which are positioned such that all angles and holes of the objects can be irradiated. Therefore, blasting takes place not only on the outside, but also on the inside of an internal structure of the object, insofar as this internal structure is at least accessible from the outside.

In figures 1 and 2 it can be seen that the rail system 21 of the transport system 2 has rises and falls at a number of places. At the starting point (B), where the objects are attached to the collecting system, the height of the rail 21 above 1 ü 2; 1 4 12, the floor is approximately 2.3 meters. At the height of a rising part 26 of the rail 20, the height increases from 2.3 meters to about 3 meters, so that the irradiation of the objects takes place at that height. After this, a further rise will occur in part 27 from 3 meters to approximately 5.3 meters. Having arrived at the flux vessel 4, a drop first occurs (part 28) so that the objects end up in the flux bath 4 uniformly. A horizontal displacement occurs at part 29, while again at part 10 an increase takes place to lift the objects uniformly from the flux bath 4. After being dried in the dryer 5, a fall, a horizontal displacement and a rise occur at parts 31, 32 and 33, respectively, so that the respective object 15 is pulled uniformly through the galvanizing bath 6. In parts similarly, parts 33, 34 and 35 of the rail 20 cause a fall, a horizontal displacement and an increase of the object in order to cool the object and optionally provide it with brightener.

Finally, a decrease from approximately 5.3 meters to 3.0 meters occurs at part 36, so that the objects can easily be removed from the relevant suspension element 22 at the end point (arrow P3).

Figure 3 shows a preferred embodiment of the blasting cabin. The blasting cabin is made up of an enclosure 38, which is provided with an entrance opening 39 and an exit opening 40. Via the entrance opening the objects V can be brought in and through the exit opening the objects are again carried out. . To ensure that as few grains as possible get out of the enclosure, the shape of the entrance and exit openings can be adjusted to the shape of the objects to be treated at that time. For bulky objects, the entrance and exit openings are enlarged to, for example, a width w of 60 cm, while for smaller objects the opening can be reduced to, for example, a width w of approximately 20 cm.

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The lead time of the system, i.e. the time between attachment of an object to be treated to a suspension element and removal of treated object from the suspension element, in the embodiment shown is approximately 1.5 hours, while the capacity is variable between approximately 3000 and 3750 kg per hour.

In the embodiment shown, a number of detection eyes 41 are provided which detect the presence or absence of an object V on a suspension element 22. Depending on whether or not an object is detected, a central control of the device (not shown) can control the transport of the suspension elements 22 and / or the operation of the blasting cabin 3. It is also possible to control the other elements of the system, i.e. the flux bath 4, the drying unit 5, the galvanizing bath 6 and the cooling unit 7, depending on the detection result. This makes a (fully automatic sinking of the objects possible).

In a further preferred embodiment the radiating capacity and / or the running speed can be controlled. Depending on the degree of rust formation on the objects to be treated, the blasting capacity (the amount of grains per unit of time, the blasting angles, the force with which the grains touch the objects etc.), must be varied depending on the speed of the conveyor system. . This can be done, for example, by using a frequency control mechanism.

Moreover, it must be possible for the suspension elements to be able to change position fully automatically during the movement along the conveying system in such a way that the quality of the zinc layer is promoted and the speed of the run-through speed is high.

Depending on the process that an object undergoes at a given position and moment in the conveyor system, the position of the suspension hooks is adjusted.

The position of the suspension hooks (length approximately 60 cm) is adjusted by providing automatic pivot points at the correct positions in the conveying system which cause a suspension hook to change position during transport along it.

In another preferred embodiment of the present invention, not shown in the figures, a conveyor track of a different type is used. In this conveyor track, after a substantially horizontal movement along the conveyor track 10, the objects to be galvanized are moved substantially vertically down into the flux bath, the galvanizing bath or the cooling bath. After a given time, the object is again moved upwards substantially vertically, whereafter the substantially horizontal movement of the object is continued. This embodiment has the advantage that the height required for the conveyor track is smaller than is the case in the aforementioned conveyor track. Furthermore, the use of a conveyor track according to the present embodiment means that the various baths need to be executed for a shorter period of time, since no horizontal displacement of the object in the relevant bath need be taken into account. The capacity of the system can therefore increase to around 5500 kg of processed material per hour.

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

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Claims (26)

5 Method for hot-dip galvanizing objects, in particular metal objects, comprising the steps of: - pre-processing an object to be treated, including removing the surface layer from the object; - arranging the pre-processed article in a flux bath for fluxing the article; - arranging the fluxed article in a zinc bath for reacting the material of the article with zinc and applying a layer containing zinc to the article, wherein the pre-processing step comprises the granular irradiation of the article for removing at least the surface layer. The method according to claim 1, wherein the average diameter of the grains is between 0.25 and 1.6 mm. 3. Method according to claim 1 or 2, wherein approximately 40% of the grains have an average grain size of 0.6-1.0 mm and 60% of the grains have an average grain size of 0.8-1.3 mm. 4. Method according to claim 1, 2 or 3, wherein the granules are made of steel of a low carbon content, preferably less than 0.18% by weight. 5. Method as claimed in claim 1, wherein between the blasting step and the fluxing step the object is blown clean with air, and / or sprayed clean with liquid. A method according to claim 5, wherein the liquid is water, to which preferably chemical additives are added to promote the dripping of the liquid from the object. 7. Method as claimed in any of the foregoing claims, wherein after the step of galvanizing air is guided along the object for blowing off zinc drops on the object. A method according to claim 7, comprising recycling the blown zinc drops into the zinc bath. A method according to any one of claims 1-8, wherein the step of arranging the object in at least one of the baths comprises letting the respective bath pass through. 10. Method as claimed in claim 9, comprising substantially continuous transport of the object through the bath. A method according to claim 9 or 10, comprising transporting the object through the bath at substantially constant speed. Method according to claim 11, wherein the transport speed through the zinc bath is in the order of magnitude of 50 to 250 cm, preferably 80 cm, per minute. 13. A method according to any one of the preceding claims, comprising drying the fluxed object. A method according to any one of the preceding claims, comprising cooling the article coated with a zinc layer. A method according to any one of the preceding claims, comprising subjecting the zinc-coated article to a gloss treatment. 16. Device for hot-dip galvanizing objects, in particular metal objects, comprising a suspension track provided with suspension elements on which one or more objects to be treated can be suspended, and drive means for moving the suspension elements along the suspension track, wherein along the hanging track are arranged at least: - jet throwing means for throwing one or more grain rays in the direction of an object moving along it for removing at least the surface layer of the object; - a flux bath for fluxing the object moving through the bath; - a galvanizing bath for the hot-dip galvanizing of the object moving through the bath. Device as claimed in claim 16, wherein the jet throwing means comprise a number of throwing nozzles which are arranged to irradiate the object to be treated at a number of predetermined irradiation angles. Device as claimed in claim 17, wherein the jet throwing means are arranged in an enclosure whose dimensions of the entrance and exit openings are adjustable depending on the shape and dimensions of the objects moving through the enclosure. Device as claimed in claim 16, 17 or 18, wherein the hanging track is designed with at least one drop and at least one rise for carrying the objects downwards in a bath and upwards out of the bath, respectively. 20. Device as claimed in any of the claims 16-19, comprising detection means for detecting an object hanging from one of the suspension elements, as well as control means for controlling the drive means of the suspension track and at least the jet throwing means for interrupting with a predetermined time delay of the drive of the suspension element and the jet throwing means. 21. Device as claimed in any of the claims 16-20, comprising means for drying the objects, means for cooling the objects and / or means for shining the objects Device as claimed in any of the claims 16-21, wherein cleaning means are provided between the blasting means and the flux bath 4 for blowing the object clean with air and / or removing material residues from the object with liquid. 23. Device as claimed in claim 22, comprising collecting means for collecting the mixture of material residues and air and / or liquid, means for separating the material residues, and means for returning the air and / or the liquid to the cleaning means. Device as claimed in any of the foregoing claims, wherein means are arranged at a position beyond the galvanizing bath for guiding air along the object for blowing off zinc drops on the object. 25. Suspension element for suspending an object in a device according to any one of the preceding claims, wherein the suspension element is manufactured from such an alloy that substantially no zinc is received or adheres to the surface of the element 20. 26. Device as claimed in any of the claims 16-25, which is suitable for carrying out the method according to any of claims 1-15. 1'οπο '0} «