MXPA96003344A - Galvanized process for preparing steel to be used as super coating - Google Patents

Abstract

The present invention is directed to a process for treating galvanized steel to prepare it for the application of a top coating. The process of the invention treats the surface of the zinc layer to "roughened" the surface without impurities being embedded in the zinc. The invention comprises a method for preparing the galvanized steel for the top coating, the galvanized steel thus prepared and the galvanized steel when it is finally coated.

Description

GALVANIZED PROCESS FOR PREPARING STEEL TO BE USED AS TOP COATING BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION The corrosion resistance can be imparted to steel parts, such as beams, joists, fencing materials, reinforcing bars, etc., by galvanizing, that is, coating the steel with zinc or a zinc alloy. A conventional process for galvanizing steel is the process by immersion in a hot bath. The hot dip process usually requires a pretreatment step to remove the rust and rust layer or mold before the steel is coated with zinc or zinc alloy. This pretreatment step improves the adhesion of the zinc coating to the steel strip or sheet. Typically, the oxide layer or the mold or rust is removed by immersion in a hydrochloric acid solution often followed by rinsing in water. The parts are then immersed in an aqueous flow solution containing ammonium chloride and zinc and, in some cases, sodium and / or potassium fluoride, cerium chloride or nickel. In the galvanizing step, the steel is submerged REF: 22932 in a bath of molten zinc. After leaving the bath, the zinc coating is substantially uniform. Many commercial galvanized steel applications require that an additional topcoat or topcoat be applied over the zinc coating. These top coatings are both for their aesthetic appearance, that is, they provide a color choice, as well as to provide a maintenance free, durable topcoat. The top or top coatings must be specially formulated to ensure good compatibility, adhesion and uniformity of appearance when applied to the zinc coating.

Even where manufacturers are aware of this fact and use the appropriate coatings, the coatings will quickly begin to peel and break. Many manufacturers simply spray the top coating on the zinc coating with little or no surface preparation. Without surface preparation, appropriate, and dependent on the environment, surface detachment and oxidation will begin rapidly.

Other manufacturers pretreat the zinc coating, typically by sandblasting, before application of the final coating. This serves to "roughen" the surface. The rough or rough surface has an increased surface area to improve the bonding of the coating to the zinc. It has been found that with the processes of the prior art to prepare the zinc surface for the final or finishing coating, typically by sandblasting, the silica particles (impurities) become embedded or tucked into the layer of zinc. Subsequently these zinc particles are oxidized and the oxidation reaction results in corrosion, i.e., breaking and separation of the surface. That is, the processes of the prior art generally treat the zinc surface with materials that remain immersed in the zinc layer. These materials are impurities in the zinc coating and form oxidation sites which are the basis for the subsequent corrosion of the top coating. The present invention is directed to a process for treating galvanized steel to prepare it for the application of a top coating. The process of the invention treats the surface of the zinc layer to "roughen or roughen" the surface without impurities being embedded in the zinc. The invention comprises a method for preparing the galvanized steel for the top coating, the galvanized steel thus prepared and the galvanized steel when it is finally coated. The scope of the invention comprises a method for preparing galvanized steel materials for the application of a top coating. As understood in the art, for galvanized steel there are typically four layers in the zinc coating. A first layer (e) eta interconnecting with the steel surface, a layer (?) Zeta, a layer (?) Delta and then finally a layer (y) range. In the process of the invention, the zinc surface of the galvanized steel material has at least one outer layer and one layer? adjacent to the layer? . The invention in one aspect comprises treating the zinc coating with zinc granules to remove the layer and the zinc surface while the coating becomes rough. to provide a grain-like, rough surface. The coating is treated in such a way that there is at least 15-40% more surface area available after the treatment than before. The roughness value (quadratic mean value) is typically in the range of 1.5 to 4.0 μm. In addition, the zinc treatment step and the application of the top coating are effected while the zinc coating is still malleable, typically within twelve hours after the completion of the galvanizing step. Finally, the process ensures that there are no impurities in the treated zinc coating. As used herein, "impurities" comprises particles introduced into or formed in the zinc coating during the treatment step whose particles could later form oxidation sites.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of the process steps forming the body of the invention. Figures 2a, 2b and 2c illustrate the formation of a final or finished surface of the invention; and Figure 3 is an illustration of a surface treated, coated, after roughening the surface, DESCRIPTION OF THE PREFERRED MODALITY The present invention broadly includes a galvanized coating process and, in particular, an architectural finish which provides more than twenty years of protection against more than 10% of the surface rust in an environment such as fences or ornamental fences. outside and banister. In a preferred embodiment, the steel could contain carbon lower than 0.25%, phosphorus lower than 0.5% and manganese lower than 1.35%. The pretreatment comprises steel elements and assemblies that have been submerged using a process with a dry galvanizing tub and a bath of molten zinc containing nickel and other alloys of the state of the art designed to apply the particular steel composition and to ensure the Remaining dilation or homogenous metallurgical germination and greater resistance to corrosion in the galvanizing process by immersion in hot bath. Within twelve hours of galvanizing, the coating surface is treated to impart a surface similar to rock crystal or similar to the grain of substantial uniformity to the surface. A material that can be sprayed, metallurgically compatible, specifically pellets or zinc granules, are used to remove the outer layer and to form the surface similar to the rock crystal in the layer. This ensures that in the preparation of the surface impurities are not incorporated in the layer which could later form a place for galvanic action (mold or oxidation). Referring to Figure 1, the steel material 10 is pretreated and galvanized in accordance with prior art techniques. While the zinc coating is malleable, the steel material is then passed through a sandblasting machine 12 with shot where the balls or zinc granules influence the zinc surface to remove the layer and and to corrugate the layer ? . A suitable machine for this step is a Wheelabrator sandblasting machine (Shot Blasting Wheel) (Model WCRC-4). Subsequently, while the treated zinc coating is still malleable, it passes through a coating zone 14 where a top coat is applied. Typical liquid coatings suitable for the purpose of the invention comprise epoxy polyamide antioxide paints and aliphatic polyurethane topcoats or finishes. The coatings may also comprise powder coatings. Collectively, these coatings are well known in the art and do not need to be described in detail. Rather than the fact that the treated steel material passes through the coating zone while the zinc coating is malleable, the step of coating, per se, is well known in the prior art. That is, the color of the coating, its composition and thickness are determined by specification. The following illustrative and non-limiting examples exemplify the process of the invention. The steel material, that is, an I-shaped beam of 20.32 c (8 inches) galvanized as shown in Figure 1. Layers? Y ? of the zinc coating are approximately 0.0102-0.0152 cm (4-6 miles, inch) and the outer layer is approximately 0.0051 cm (2 miles, in) an external surface 16, substantially smooth, see Figure 2a . The steel element travels continuously through the shot blasting machine 12 at a speed of 0.6096 cm / min (2 feet / min). The pure zinc granules hit the zinc surface to remove the Jf layer and treat the layer? 18, see Figure 2b. The granules typically collide with the surface at a speed of 4267.2-5791.2 m / min (14,000- 19,000 ft / min) and a variation of approximately 13,608 kg / min / ampere / wheel £ 30 lbs / min / ampere / wheel). The profile of roughness or roughness of this treated surface is approximately 1.5-4 xm. Subsequently, and while the zinc coating is still malleable, an upper coating is applied to the treated surface, see Figure 2c. A plan view of a treated coated surface is shown in Figure 3. It is well understood that depending on the composition of the steel, the specific galvanizing process used, that the apparatus and method for treating the zinc surface will vary. This could also be consistent with the top coating expected to be applied. Where the sandblasting machine is used, the size of the granules can vary between 0.030 to 0.060 microgranules, the speed of the granules can vary between 4267.2 to 5791.2 meters / min (14,000 to 19,000 feet / min) and the Displacement speed of the galvanized steel material passing through the treatment zone can be varied. It is possible that other metallurgically compatible particles could be used, which could remain in situ in the treated coating but would not form oxidation sites. The above description has been limited to a specific embodiment of the invention. It will be evident, however, that variations and modifications can be made to the invention, with the obtaining of some or all of the advantages of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications that are included in the true spirit and scope of the invention.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property

Claims (7)

1. A process for treating galvanized steel to prepare it for the application of an upper coating, the galvanized steel has a zinc coating, which is characterized in that it comprises: contacting the zinc surface with metallurgically compatible particles to rough the surface and increase its surface. area of the surface to join with an upper coating, the particles chemically inert to oxidation.

2. The method according to claim 1, characterized in that the treated surface has a roughness or roughness value of between about 1.5 to 4.0 tm.

3. The method according to claim 1, characterized in that the zinc surface comprises an outer layer and an internal layer? and which comprises: contacting the zinc surface and removing the layer? .

4. A galvanized steel material that has a zinc coating, the zinc coating is characterized in that the zinc coating has a layer? treated external that has a roughness value of 1.5 to 4.0 / a.

5. The steel material according to claim 4, characterized in that the layer? treated has the appearance of a grain-like structure.

6. A galvanized, coated steel material, which comprises: galvanized steel having a zinc coating, the coating is characterized in that the zinc coating has a coating of? external treated that has a roughness value of 1.5 to 4.0 a; and an upper coating adhered to the treated layer.

7. The steel material according to claim 6, characterized in that the coating is selected from the group consisting of paints anti-rust or epoxy polyamide primers, aliphatic polyurethane top coatings and powders.