FR2689142A1 - Hot dip coating of stainless steel with a tin@ alloy - Google Patents

Abstract

A method of coating a stainless steel substrate with a tin-based alloy coating to form a composite body comprises pickling the substrate to give a surface free from chromium oxide and hot-dip coating the surface with a tin-based alloy to give a coating 7 x 10 power (-3) 2.5mm thick. Also claimed is a composite body formed by the above process. The thickness of the coating is not more than 5mm. The pickling soln. contains one or more acids such as hydrofluoric, sulphuric, nitric, hydrochloric, phosphoric and isobromic acids. Pref. the pickling soln. contains 5-25% HCl and 1-15% HNO3, pref. at 48-60 deg.C.. The surface of the stainless steel is treated with abrasive and/or absorbent prior to pickling. The chromium oxide-free surface is treated with a deoxidising agent such as zinc chloride to remove residual oxides. The surface is also rinsed pref. with oxygen-free water at at least 37 deg.C.. The hot dip coating is carried out in a flux zone and an alloy coating zone. The flux soln. contains 30-60 wt.% ZnCl2 and 5-40 wt.% NH4Cl. The tin-based alloy contains 90-99.9 wt.% Sn and not more than 0.1 wt.% Pb and may contain 0-7.5 wt.% Sb. A protective skin of e.g. palm oil may be provided on the coated substrate. The coated substrate may be treated with a weathering agent such as an asphalt-based or petroleum-based paint to accelerate the weathering and discolouration of the coating.

Description

CORROSION TREATMENT PROCESS, MATERIAL OBTAINED
RAR SAID METHOD AND DEVICE FOR IMPLEMENTING
OF THE PROCESS
The present invention relates to the protection of metal strips against corrosion by the deposition of a surface layer of tin or a tin alloy.

 In a first embodiment of the invention, a tin-lead alloy containing mainly tin and very small amounts of lead is deposited by hot immersion. It is a lead alloy whose lead content is extremely reduced.

 This first example applies mainly to the treatment of steel strips, in particular stainless steel or low carbon steel.

 In a second particularly advantageous embodiment, a surface layer of tin or tin alloy is deposited on a metal strip protected from corrosion by an oxide layer, such as for example a stainless steel strip. Such an oxide layer does not provide sufficient protection of the strip against corrosion, but disturbs the bonding of the tin or the tin alloy on the strip. The preferred embodiment of the invention comprises a step of ablation of the oxide layer prior to the deposition of the protective layer of tin or tin alloy.

The main object of the invention is a method of treatment against corrosion of a metal sheet or strip by hot immersion in a bath of molten metal, characterized in that it comprises the steps consisting in:
a) introducing into a tinning tank a tinning metal containing mainly tin,
b) heating the contents of the tank until the tinning metal melts,
c) immerse the sheet or strip to be treated in the tinning metal.

The invention also relates to a process, characterized in that the treated sheet or strip is made of steel
The invention also relates to a process, characterized in that the sheet or strip treated is made of low carbon steel.

 The invention also relates to a process, characterized in that the treated sheet or lard film is made of stainless steel.

 The invention also relates to a method, characterized in that the tinning metal comprises at least 90% by weight of tin and at most 0.1% by weight of lead.

The invention also relates to a process, characterized in that the tinning metal comprises the following weight percentages
Tin 90 - 99.9%
Lead 0.01 - 0.10%
Bismuth 0.0 - 1.7%
Antimony 0.0 - 7.5%
Zinc 0.00 - 1.5%
Iron 0.00 - 0.1%
Copper 0.00 - 2.7%
The invention also relates to a method, characterized in that the sheet or strip has a thickness of between 1.27 mm and 5.08 mm.

 The invention also relates to a method, characterized in that, during the immersion of the sheet or strip in the tinning metal, it is formed, on at least each of the main faces of the sheet or strip , a protective layer whose thickness is between 0.0762 mm and 1.27 mm.

 The invention also relates to a method, characterized in that it comprises, prior to step c), a step d) of removing iron and chromium oxides on at least the two main faces of the sheet. or of the treated strip.

 A subject of the invention is also a method, characterized in that step d) of removing the oxides comprises a step e) of corrosive pickling, in particular with an acid from the sheet or strip to be treated.

 A subject of the invention is also a method, characterized in that step d) of removing iron and chromium oxides comprises, prior to step e) of corrosive pickling, a step f) of mechanical ablation material of the main faces of the sheet or strip treated by abrasive devices, in particular brushes.

 The invention also relates to a process, characterized in that between step d) of elimination of iron oxide and chromium and step c) of immersion, one proceeds to the isolation of the sheet of the strip treated with respect to molecular oxygen by immersing in a deoxygenated fluid.

 The invention also relates to a process, characterized in that during step e) of corrosive pickling, the treated sheet or strip is immersed in a tank containing a mixture of nitrite acid and hydrochloric acid .

 The invention also relates to a method, characterized in that it comprises, after step e) of corrosive pickling, a rinsing step with a deoxygenated liquid, in particular with deoxygenated water.

 The invention also relates to a process, characterized in that prior to step c) of immersion, it comprises a step g) of chemical activation of the sheet or strip treated.

 The invention also relates to a process, characterized in that step g) is subsequent to a step e) of corrosive pickling, and in that it comprises a step of treatment of the sheet or strip with chloride zinc.

 The subject of the invention is also a method, characterized in that prior to step c) of immersion, it comprises a step h) of immersion of the sheet or strip in a pre-tinning flux.

 The invention also relates to a process, characterized in that the pre-tinning flux comprises zinc chloride and ammonium chloride.

 The invention also relates to a process, characterized in that, after step c) of immersion, it comprises a step i) of rapid cooling of the protective coating to obtain tin grains of desired size .

 The invention also relates to a method, characterized in that in step c), 1 immersion includes a step of passing the sheet or strip between two coating rollers whose spacing determines the thickness of the protective coating.

 The invention also relates to a method, characterized in that it comprises a step of projecting the tinning metal.

 The invention also relates to a process, characterized in that it comprises, after step c) of immersion in the tinning metal, a step j) of coating with a disintegrating agent of the protective coating.

 A subject of the invention is also a weather-resistant covering material in the form of a metal strip, characterized in that it comprises a metal sheet or strip, at least the two main faces of which are tinned with tinning metal. containing at least 90% by weight of tin and at most 0.1% by weight of lead.

The subject of the invention is also a covering material, characterized in that the tinning metal comprises the following weight percentages
Tin 90 - 99.9%
Lead 0.01 - 0.10%
Bismuth 0.0 - 1.7%
Antimony 0.0 - 7.5%
Zinc 0.00 - 1.5%
Iron 0.00 - 0.1%
Copper 0.00 - 2.7%
The invention also relates to a covering material, characterized in that the tinning on the main faces of the sheet or strip has a thickness of between 0.762 mm and 1.27 mm.

 The invention also relates to a roofing material, characterized in that the sheet or strip has a thickness of between 1.27 mm and 5.08 mm.

 The invention also relates to a roofing material, characterized in that the sheet or strip is made of stainless steel.

 The invention also relates to a device for the manufacture of a covering material in the form of weather-resistant strips, characterized in that it comprises an aggressive pickling tank of a sheet or strip and a tank tinning.

 The invention also relates to a device, characterized in that the aggressive pickling tank is filled with acid, in particular with a mixture of hydrochloric acid and nitric acid.

 The invention also relates to a device, characterized in that it comprises a rinsing tank disposed between the aggressive pickling tank and the tinning tank.

 The invention also relates to a device, characterized in that it comprises means for mechanical ablation of the material of the sheet or strip, in particular brushes.

 The invention also relates to a device, characterized in that it comprises means for isolating the sheet or strip from molecular oxygen.

 The invention also relates to a device, characterized in that it comprises a chemical activation tank of the treated strip filled with a chemical activation solution.

 The invention also relates to a device, characterized in that it comprises a flow box, preferably arranged in the tinning tank.

 The invention also relates to a device, characterized in that it comprises, disposed at the outlet of the tinning tank, means for rapidly cooling the sheet or strip treated, in particular means for spraying water cold.

 The invention also relates to a device, characterized in that it comprises coating rollers arranged in the tinning tank.

 The invention also relates to a device, characterized in that it comprises a grader.

 The invention also relates to a device, characterized in that it comprises a device for coating with an agent for disintegrating the tinning metal.

 The invention also relates to a device, characterized in that said device is a continuous manufacturing device, and in that it comprises means for transporting a treated strip passing, in continuous mode, simultaneously to the various stations treatment.

 Description of the first embodiment of the invention.

 The present invention relates to the field of metallic covering materials and more particularly to a leaded coating formulation containing extremely low lead contents and applied by hot immersion on a covering material formed from a metal sheet.

As prior art, mention may be made of the federal specifications US N QQ-T-201F and an article entitled "The making, Shaping and Treating of
Steel ", US Steel Corporation, 1957, pp 655-659, Sci. Tib.

Coll. N TN T30 C16, - 1957. Likewise, US patents N 4,987,716 and 4,934,120 filed by the applicant which describe metal roofing systems, of the type to which the present invention relates.

 For many years, metal roofing systems have been treated in a specific way, a sheet of stainless steel and a sheet of low carbon steel with different thickness gauges, with a leaded coating formed of a metal alloy .

When the leaded steel sheets are assembled to form a roof covering, the adjacent edges of the sheets are folded one above the other and the joint formed is then usually welded, typically a fixed joint, facing the lead coating so as to form a watertight seal. Currently, lead-coated steel sheets are either preformed or formed on the site on roof sections with folded edges, which abut against adjacent edges of the sides which are then pressed or rolled so as to form the joint. Similarly, strip caps, etc. are similarly formed from sheet metal covered with a leaded coating. Besides allowing the welding of the joints, the leaded coating prevents the appearance of rust or oxidation of the sheet metal, which would surely occur over time. .

 The expression leaded coating or coating formed from a leaded alloy is a term used to designate an alloy containing approximately 80 percent lead, the remainder being formed from tin. The lead alloy coating is usually applied to metals using a hot dip process, where the metal is immersed in a bath of the lead coating molten metal. The lead coating largely prevents the formation of ferrous oxide in the metal, thereby preventing corrosion and increasing the life of the metal. The corrosion resistance properties of the lead alloy coating are due to the stability of elemental lead and tin and to lead tin oxide which is formed under exposure to the atmosphere.

 Although leaded metal sheets have excellent corrosion resistance properties and have been used in various applications such as roofing, leaded metal roofing materials have recently been questioned in connection with environmental problems. Leaded metals contain very high percentages of lead and usually contain more than 80 percent by weight of leaded alloy. Although lead in lead alloys is stabilized, there is a problem with the leaching of lead from the lead alloy. As a result, lead materials have limited use in different applications, such as, for example, aquifer cover systems. The problem of possible lead leaching from leaded roofing systems makes normal leaded coating unsuitable and undesirable as a metallic roofing coating for these types of roofing applications.

 Another disadvantage of leaded materials is the soft nature of the leaded coating layer. As will be noted, leaded metal sheets are usually made with different shapes. The machines, which bend the metal sheets, periodically damage the lead coating during the bending process. The lead coating may be damaged by the abrasive action of forming machines.

 Another disadvantage of using normal metals covered with a lead coating is that the newly applied lead coating strongly reflects light. The use of leaded roofing materials on buildings near or located at an airport can produce a certain degree of glare in pilots taking off and landing. Due to the very stable nature of lead-coated alloys, it takes approximately one and a half to two years for leaded metals to begin to oxidize and for the surface of the leaded alloy to tarnish. The object of the invention is to eliminate this drawback of a covering material in the form of normal lead sheet.

 A main feature of the present invention is to provide a low lead leaded coating formulation for use in roofing materials, the coated roofing materials typically having a base of stainless steel or a base of carbon steel with excellent corrosion resistance properties.

 In accordance with the main feature of the invention, there is provided a covering material typically formed from stainless steel or carbon steel covered by a leaded metal alloy containing extremely low weight percentages of lead. The low lead lead coating includes a high weight percentage of tin and a lead content of less than 0.10 percent by weight and preferably less than 0.05 percent by weight, which provides a lead coating which is both corrosion resistant, which prevents oxidation of the roofing material, and is pliable and abrasion resistant so that it can be given the shape of different roofing components, without cracking or the like damage to the lead coating.

 In accordance with another aspect of the invention, bismuth and antimony are added to the leaded low lead coating, which provides a unique combination of bismuth, lead antimony and tin for the formation of '' A protective coating that is highly resistant to corrosion when exposed to the elements, especially in rural environments. Specifically, bismuth and antimony are added to the leaded low lead coating both to stiffen it and to prevent crystallization of the tin. Pure tin is a soft, malleable metal. Due to the physical properties of tin, tin can be abraded and / or deformed if placed in an abrasive environment. Since tin constitutes a large percentage of the low-grade lead coating in lead, many of the physical characteristics and basic states predominate in the properties of the leaded coating. Although tin is a stronger and harder substance than lead, which makes the low lead leaded coating more abrasion resistant than standard leaded alloys, highly abrasive environments can damage the leaded coating. low lead content. The addition of bismuth and antimony consequently improves the hardness and solidity of the leaded coating with low lead content by increasing its resistance to abrasion wear. Bismuth and antimony also combine as is in the lead-free low lead coating to prevent tin crystallization in cold weather. When tin crystallizes, it may not bond properly with roofing materials formed by stainless steel or low carbon carbon steel. As a result, the leaded coating with a low lead content can flake off prematurely and expose the roofing materials to the atmosphere. The addition of bismuth and antimony prevents the crystallization of tin by eliminating possible problems in the bond between the leaded coating with low lead content and the covering materials.

 In accordance with another characteristic of the present invention, a metallic coloring agent is added to the leaded coating with a low lead content in order to attenuate the reflective properties of the leaded coating newly applied to the roofing materials, while also adding additional solidity to the leaded coating so as to better resist abrasion which can damage the leaded coating. Newly applied, the leaded coating with low lead content has a shiny silver surface which is very reflective. In some roofing applications, this highly reflective character is undesirable. By adding metallic copper to the low lead plumb coating, the newly coated roofing material has a dull and less reflective surface. Metallic copper adds a reddish tint to the low lead plumb coating, which greatly reduces the characteristics. of reflection of the light that this coating presents. Copper can also help to give lead plating its corrosion resistance characteristics. When copper oxidizes, the oxide forms a protective layer that protects the roofing materials from the atmosphere. Copper oxide also helps to tarnish the surface of the lead coating.

 In accordance with an additional feature of the present invention, metallic zinc is added to further increase the hardness of the tin-based alloy, while also helping to improve the corrosion resistance of the leaded coating with a low lead content. , since oxidation of zinc produces a coating of zinc oxide which helps protect roofing materials from the elements.

 In accordance with another characteristic of the present invention, the leaded coating with a low lead content has excellent welding characteristics, so that different electrodes can be used, including lead electrodes and lead-free electrodes for soldering together. coated roofing materials.

 A main object of the present invention is to provide a covering material treated with a leaded coating with a low lead content having properties of high resistance to corrosion.

 Another object of the present invention is to provide a covering material treated with a leaded coating with a low lead content containing at least 90% tin and less than 0.10% by weight of lead.

 Another object of the present invention is to indicate a lead coating with a low lead content, as defined above, containing antimony and / or bismuth in order to harden the lead coating with low lead content and prevent the crystallization of tin in the lead coating.

 Another object of the present invention is to provide a covering material covered by a leaded coating with a low lead content containing zinc and / or iron to improve the solidity and hardness of the leaded coating.

 Another object of the present invention is to provide a covering material treated with a leaded coating with a low lead content which comprises metallic copper to tarnish the surface of the leaded coating.

 Another object of the present invention is to provide a leaded coating with a low lead content applied to a basic metal sheet, which coated basic metal sheet can be subsequently cut and shaped with a press so as to form panels of roof, battens, caps and the like, which can later be assembled on site by force mounting, etc. in a roof, without chipping or chip formation of the lead coating during the compression, bending or shearing of the metal sheet.

 Another specific object of the invention is to provide a leaded coating with a low lead content, which can be applied to a roofing base metal and then be preformed in the form of roofing strips, which are then assembled on site either using pressure formed joints or welded joints to obtain watertight joints.

 Another object is to provide a leaded coating with a low lead content, which is suitable for application to roofs and which is adapted to the specifications mentioned above.

 Another object is to provide a leaded coating with a low lead content which exhibits superior corrosion resistance characteristics and makes it possible to apply to the steel sheet a leaded coating which is of a thickness thinner than that required for conventional lead coatings with a high lead content.

 Another object of the invention is to provide a leaded coating with a low lead content, which can be soldered using tin-lead solders or conventional lead-free solders.

 Other characteristics and advantages of the present invention will emerge from the description given below.

 Low lead leaded coating is a corrosion resistant coating, which is applied to roofing materials made of stainless steel or low carbon steel, so as to prevent premature corrosion of roofing materials when exposed to the atmosphere. The leaded coating with a low lead content contains a high percentage by weight of tin and a very low percentage by weight of lead. The leaded coating with low lead content is at the same time very resistant to corrosion, resistant to soldering, bending, weldable and non-polluting.The leaded coating with low lead content can be applied to roofing materials produced both in stainless steel and carbon steel, preferably through the use of conventional hot-dipping techniques, but may be applied by other means, for example by means of an air knife electroplating process , etc. Previously, a protective coating containing high percentages by weight of tin was not used on stainless steel roofing materials. The low lead leaded coating can be applied to both 304 and 316 stainless steel. However, the application of the leaded coating is not limited only to these two types of stainless steel. .Leaded lead-free coating combines with stainless steel to form a durable protective coating that cannot be easily removed. The leaded coating with a low lead content also forms a solid bond with carbon steel, in particular with carbon steel having a low content and an average carbon content. Treating carbon steel surfaces with an organic coating can further strengthen the bond between the lead coating and carbon steel or stainless steel.

 The degree of corrosion resistance provided by the low lead leaded coating is of paramount importance. Carbon steel and stainless steel oxidize when exposed to the atmosphere. For a while oxidized steel, usually referred to as corrosion, begins to weaken and disintegrate the steel. The coating formed by the steel coated with the leaded coating with low lead content acts as a barrier against the atmosphere, which prevents corrosion of the steel. Although the leaded low lead coating will oxidize when exposed to the atmosphere, the rate of oxidation is significantly slower than the oxidation rates of steel. The slower oxidation rates of the coating Leaded lead with low lead content is due in part to the stability of the tin. Covering the steel with the leaded low lead coating increases the life of the roofing material beyond the useful life of the structure of the roofing material on which it is used. The pliability of the low lead leaded coating is also important when used in roofing systems, since the roofing materials are made in different shapes and can be folded back so as to form joints to join the roofing materials together to form a roofing system. A coating of roofing material, which forms a rigid or brittle coating on the roofing material, may crack or prevent the roofing materials from being shaped properly. In addition, a coating of a roofing material, which is brittle or rigid, can hinder or even prevent the correct folding of the roofing material to form the joints necessary for the joining of the roofing materials. Metals such as zinc are known for their very rigid nature. A roofing material covered with zinc, usually designated as galvanized steel, cannot be folded without risk of damaging the protective zinc coating. Besides the fact that the leaded coating with low lead content must be pliable and resistant to corrosion, it must be weldable since the roofing panels are usually joined together by welding. The lead-coated low-lead coating according to the present invention satisfies all of these requirements by the fact that it contains extremely low levels of lead, which provide a metallic coating very resistant to corrosion and having a relatively high bending capacity and can be welded to other materials.

 The low lead leaded coating applied to low carbon steel or stainless steel roofing materials includes a tin content of at least 90% of the alloy. It is believed that such high concentrations of tin have not previously been applied to stainless steel roofing materials. Previous anti-corrosion coatings applied to stainless steel include zinc coatings containing trace amounts of tin, and coatings formed from standard lead alloys containing about 10% to 20% tin. Elemental tin is a relatively soft and stable element, which exhibits unusually high corrosion resistance properties, under a variety of atmospheric conditions. As a result, the leaded coating with a low lead content, which contains at least 90% tin, is very pliable and very resistant to corrosion.

The percentage by weight of lead in the leaded coating with a low lead content is less than about 0.10%.

This amount of lead is significantly lower than in standard leaded alloys, in which the amount of lead in the leaded coating is between 80% and 90%.

 The lead coating also has a high resistance to leaching of lead which may be contained in the lead coating, which expands the uses of roofing materials treated with the low lead lead coating.

 The leaded coating with a low lead content contains a very high percentage by weight of tin. Preferably the tin content greater than 90% can have a value as high as 99.9%. The lead content of the low lead leaded coating can range from 0.001 to 0.10 percent by weight. Preferably, the lead content is less than 0.05 percent by weight and is advantageously equal to about 0.01 percent by weight. In the composition of the lead coating with a low lead content, the composition goes beyond an inversion of the percentages by weight of tin and lead of conventional lead alloy. Previous practice has been to limit the tin content to a quantity low enough to establish a soft bond with the ferrous base material. Conventional formulations limit the percentage by weight of tin to about 20 percent. Formulations with more than 90 percent tin for the lead-free coating with low lead content differ significantly from previous lead-coating formulations. Tin is the bonding agent for lead alloys. Lead does not combine with ferrous metals. The high tin content in the low lead leaded coating according to the present invention substantially increases the uniformity and bond strength between the low lead leaded coating and the covering materials compared to coatings. of leaded alloy standards.The superior bonding characteristics of the leaded coating with low lead content make this coating ideal for use with materials which are formed and shaped after being applied.

 The low lead leaded coating may also contain bismuth and antimony. The bismuth content in the leaded low lead coating is typically between 0 and 1.7 percent by weight of the alloy and preferably is about 0.5 percent by weight. Antimony can also be added to the lead coating, in amounts between 0 and 7.5 percent by weight.

The tin-based alloy preferably comprises bismuth and / or antimony, since these two elements increase the abrasion resistance properties of the lead coating and prevent the tin located in the lead coating from crystallize, which can lead to flaking of tin from stainless steel or low carbon steel roofing materials. Tin begins to crystallize when the temperature begins to drop below 13.2 "C (56 F).

Only small amounts of antimony or bismuth are needed to prevent crystallization of the tin.

Typically, amounts less than 0.5 percent by weight are required to appropriately prevent the crystallization of the tin, which can lead to premature flaking of the lead coating. Antimony and / or bismuth in amounts greater than 0.5% by weight are used to cure the lead coating with a low lead content. Industrial grade tin can be used as the source of tin for the leaded coating with low lead content. It is known that industrial grade tin contains trace amounts of polluting substances, such as cobalt, nickel, silver and sulfur.

 It has been found that these elements do not adversely affect the corrosion resistance properties of the alloy system based on tin with a low lead content as long as the weight percentages of each of these elements are very weak.

 Copper can be added to the lead coating with a low lead content to stiffen it and reduce the reflection coefficient of the lead coating.

The amount of metallic copper in the lead coating can range from 0 to 2.7 percent by weight of the lead coating. The desired color of the lead coating determines the amount of copper used.

 Metallic zinc can also be added to the lead coating to further increase the resistance of the coating to abrasion. Metallic zinc can be added to the lead coating in amounts between 0 and 1.5 percent by weight. The amounts of metallic zinc added depend on the desired hardness of the lead coating. Small amounts of iron can also be added to the lead coating in weight percentages between 0 and 0.1, so as to further increase the hardness and strength of the lead coating.

 It has been found that aluminum and cadmium adversely affect the corrosion resistance properties of the low lead leaded coating.

Preferably, the weight percentages of aluminum and cadmium should be less than 0.05 percent cadmium and 0.001 percent aluminum.

Examples of leaded low lead systems, which have the desired characteristics mentioned above, are as follows
Ingredients of the ABCDEFG alloy
Antimony 0.5 0.75 7.5 2.5 0.75 1.0
Bismuth 1.7 0.5 - - 0.5 0.5 0.5
Copper - - 2.7 2.0
Zinc 0.001 0.5 - 0.5 0.5 -
Lead 0.05 0.05 N <0.05 4 0.05 40.05 40t05 40t05
Iron - 0.1 - - 0.1 0.1 0.1
Tin le le le le le le le
stay rest stay rest stay rest stay rest
The general formulations of the leaded coating with a low lead content include the following percentages by weight: 0.001-0.1% by weight of lead, 0-2.5% antimony, 0-0.5% bismuth, 0-2.7% copper, 0-0.1% iron, 0.5-1.5% zinc and the rest being formed from tin.

 The thickness of the low lead leaded coating can be varied depending on the environment in which the treated roofing system is used. The low leaded lead coating has superior corrosion resistance characteristics in rural environments, which requires a thinner lead coating. The low lead leaded coating also resists corrosion in industrial and marine environments, but may require a slightly greater thickness. A typical thickness of low leaded lead coating on each side of the strip typically ranges from 0.000762 cm (0.0003 inches) to 0.508 cm (0.2 inches). a sheet of roofing steel with the leaded coating with a low lead content according to the present invention, and using such a thickness, the thickness of the leaded coating is based on the expected service life of the building, at which the materials of cover are applied, and on the environment, in which the cover materials are used. The roofing materials covered on each main face with a leaded coating with a low lead content having, for example, a thickness between 0.00254 and 0.00508 cm (0.001 and 0.002 inches) are preferably used in all types of 'environments, reducing the price of roofing materials. Thinner coatings can be applied using an air knife or electroplating process instead of the conventional hot dip process. These ranges of thicknesses for the lead coating with low lead content are applicable to stainless steel and carbon steel cover sheets.

 The low lead leaded coating is designed to be used in all types of roofing applications. Roofing materials having a leaded coating with a low lead content can be used for the formation of joint assemblies by stapling on raised edges and forcibly mounting (mechanical connection, see patent US Pat. No. 4,987,716). In applications of joint formation by assemblies on raised edges, the edges of the covering materials are folded together, then welded so as to form a waterproof joint. The leaded coating with low lead content has excellent welding characteristics in itself. When the leaded coating with low lead content is heated, it has the wetting properties necessary to produce a waterproof seal. As a result, the leaded coating with a low lead content acts both as a corrosion-resistant coating and as a soldering agent for roofing systems with joints formed by assembly on raised edges. Materials covered by the low lead leaded coating can also be welded with typical solders. Typical solders contain about 50% tin and 50% lead. The leaded coating with low lead content has the additional advantage of also being soldered with low lead or lead-free solders. It is also possible to use roofing materials coated with a leaded coating with low lead content, in mechanically linked roof systems, due to the malleability of the lead coating. Mechanically joined systems form watertight seals by joint folding of adjacent edges of roofing material and subsequent application of a compressive force exceeding 6.9.106 Pa (1000 psi). For these high pressures, the leaded coating with a low lead content plastically deforms in the joint and establishes a watertight seal.

 Description of the second embodiment of the invention.

 The present invention also relates to the field of coating a material in the form of a strip or metal strip and more particularly the method of coating a strip of a coating material of stainless steel by depositing tin by hot immersion.

 For many years, cover systems made of a metal having different thicknesses of sheet thickness have been used. Metals such as carbon steel, stainless steel, copper and aluminum are the most common types of metal roofing systems. Carbon steel metal roofing systems are usually treated with a corrosion resistant coating to prevent rapid iron oxidation. One type of corrosion resistant coating for carbon steel is a metallic tin coating. The coating of carbon steel with tin is a well known process, which has been used in many industries, and in particular in the food industry. The coating of carbon steel with tin is normally carried out using a high speed continuous electrolysis process. In an electrolysis process, an electric current is used to reduce alkaline or acidic electrolytes from the tin so as to press the tin onto the carbon steel. The thickness of the tin coating is between 3.8 x 10-4 and 20.7 x 10-4 mm (1.5 x 10-5 to 8.15 x 10-5 inches). The equipment and materials used to electroplate carbon steel are very expensive and relatively complex to use; however, only a thin layer of tin is used so that the cost of using the expensive tin is kept fairly low. A less used method of coating carbon steel is to use a hot dip method, which is not normally used due to very small areas of discontinuity occurring in the coating of tin.

This is why this material is less satisfactory for containers for foodstuffs. In addition, the hot-applied tin forms a thicker coating which is susceptible to chipping.

 Tin is a material very resistant to corrosion. Corrosion-sensitive materials, such as carbon steel, can be coated with tin to obtain products that are very resistant to corrosion and relatively inexpensive, such as tin boxes and tin covering materials. Many metal alloys have been developed which resist corrosion, such as stainless steel. Stainless steel is an alloy of iron and chromium and sometimes includes nickel and molybdenum. The chromium inside the stainless steel alloy is the main component of the alloy which prevents corrosion.

Chromium forms chromium oxide and binds closely to the surface of stainless steel, preventing oxygen from entering the stainless steel to form ferrous oxides that form corrosion. Carbon steel has little chromium, even if it contains it, and therefore iron oxidizes easily with the presence of surrounding oxygen to form ferrous oxides, which is usually known as the phenomenon of corrosion. .

 Although stainless steel corrodes at a significantly slower rate than standard carbon steel, stainless steel eventually corrodes at an even faster rate than coated carbon steel. tin. Previously, the concept of coating stainless steel with a corrosion-resistant material was unknown, since stainless steel is itself a corrosion-resistant material. In addition, attempts to coat stainless steel had had limited success. Specifically, attempts to deposit a coating of tin on stainless steel by hot dipping have not been successful. The tin coating is repeatedly detached from the stainless steel as soon as it has been deposited thereon and / or during preforming and installation. Up to now, the industrial manufacture of steel stainless steel coated with hot dip was unsuccessful.

Currently, the only process, which makes it possible to coat stainless steel with tin with half success, is the electroplating process. Electroplating stainless steel involves the use of very expensive and relatively complex equipment. The deposition of tin by electroplating on stainless steel consists in circulating a strip or strip of stainless steel in a stannous solution. An electric current is introduced into the stannous solution and the tin is reduced and plated on the stainless steel strip. The thickness of the tin plating is limited to not more than 20.7 x 10-4 mm (8.15 x 10-5 inches). The limited thickness of the tin coating provided by electroplating limits the uses and service life of tin plated materials. Although tin is a very corrosion resistant material, it corrodes slowly in aggressive environments such as salt water or acidic environments. Thicker tin coatings in such environments would greatly increase the useful life of materials coated with tin.

 The coating of stainless steel with tin alloys using a hot dip process has been more successful. One of the most common tin alloy coatings for carbon steel and stainless steel is a tin-lead alloy commonly referred to as lead alloy. The composition of the lead alloy generally comprises about 80 percent by weight of lead and about 20 percent by weight of tin. The lead in the lead alloy readily combines both carbon steel and stainless steel to form a coating of tough and durable tin alloy, although the sheet-like metals covered with l lead alloy have excellent corrosion resistance characteristics and have been used in a wide variety of building applications, such as roofing, their implementation has recently posed environmental problems due to the content lead from the leaded alloy. Although the lead in the lead alloy is stabilized, there is a problem, although not disclosed, regarding the leaching of lead from the lead alloy. As a result, the materials covered with the lead alloy have had limited use in various applications, such as aquifer cover systems. Lead alloys are also a softer material than tin, and therefore wear out faster than tin coatings and are not as strong as such coatings. Due to the expensive nature of electroplating applied to stainless steel materials and limitations on the thickness of the stainless steel material, there has been a demand for a method for applying with success of tin to stainless steel materials by hot dipping.

 The present invention relates to a method of manufacturing the water-resistant strip-shaped covering material, consisting of a stainless steel strip or strip having a coating of tin applied by hot dipping. Although tin-coated stainless steel is used primarily for roofing materials, tin-coated stainless steel can be used in a variety of applications that require the use of highly corrosion-resistant materials.

 In accordance with the main feature of the present invention, there is provided a stainless steel strip having a coating of tin formed by hot immersion of the stainless steel in molten tin, which makes it possible to obtain a coating of bound tin, having a desired thickness. A stainless steel strip is treated in a particular way so as to establish a solid and durable bond between the tin applied by hot immersion and the stainless steel strip, this bond opposing flaking of the tin to from stainless steel. The type of stainless steel used is generally 304 or 316 stainless steel. However, other types of stainless steel can be used. The thickness of the stainless steel is generally not more than 0.508 cm (0.2 inches) and typically has a thickness of 0.127 cm (0.05 inches). The pre-treatment of stainless steel includes corrosive pickling and chemical activation of the stainless steel before hot immersion of the latter in molten tin. The corrosive pickling process is designed to remove a very thin surface layer from the stainless steel. Removal of a very thin layer from the surface of the stainless steel is necessary before proper bonding of the tin applied by hot dipping on the stainless steel can be achieved. Stainless steel contains mainly chromium and iron; the chromium on the surface of stainless steel reacts with atmospheric oxygen to form chromium oxide. The chromium oxide film creates an almost impenetrable barrier between the iron inside stainless steel and atmospheric oxygen, which prevents oxygen from combining with iron to form oxides of iron. The chromium oxide film also forms a very close and intense bond with stainless steel and is not easily removed. Although formation of the chromium oxide film is important from the viewpoint of the corrosion resistance properties of stainless steel, the chromium oxide film interferes with the bonding of a thin layer of tin deposited by hot immersion on the surface of stainless steel, which leads to weak bonding of tin and flaking.The corrosive pickling process by removing chromium oxide from the surface of stainless steel allows correct bonding of the molten tin with stainless steel. The corrosive pickling process can also slightly corrode stainless steel by removing a very thin layer on the surface of the stainless steel. Since the corrosion rate is not the same over the entire surface of the stainless steel, microscopic depressions are formed on the surface of the stainless steel which greatly increase the surface area contact with which the hot-deposited tin can adhere to stainless steel. The increased bond surface formed by corrosion further improves the bond between tin and stainless steel. Pickling processes, which are used to treat carbon steel and stainless steel for electroplating of tin do not allow the surface of the stainless steel to be properly and appropriately treated to both remove chromium oxide and partially corrode the surface of the stainless steel so as to form a deposit of tin quality obtained by hot immersion. The corrosive pickling process includes the use of a pickling solution that attacks, removes and / or dissolves chromium oxide from the surface of the stainless steel. The pickling solution contains different acids or combinations of acids such as hydrofluoric acid, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid and / or isobromic acid. Generally, hydrochloric acid is used in combination with nitric acid as a pickling solution to remove chromium oxide from stainless steel. In the pickling solution, a fairly high concentration of the acid is used. In the case of pickling with nitric acid, the pickling solution contains about 5-25% hydrochloric acid and 1-15% nitric acid. The unpredictable success of the combination of hydrochloric acid and nitric acid leads to a rapid superior removal of chromium oxide from stainless steel. The double acid also achieves limited corrosion of the stainless steel, which increases the surface area without causing harmful pitting in the surface of the stainless steel. The temperature of the pickling solution is important to provide an acid very active, which easily removes chromium oxide from the surface of stainless steel. The temperature of the pickling solution is generally greater than 26.7 "C (80" F) and is typically between 49 "C and 60" C (120 to 140 F). The pickling solution must be stirred during the corrosive pickling operation to prevent the pickling solution from stagnating and changing concentration. During the corrosive pickling operation, the concentration of nitric acid and hydrochloric acid varies. In addition, when the acid reacts with stainless steel, the temperature of the pickling solution increases. If the concentration and temperature of the acid are not kept constant, proper removal and pickling of the chromium oxide may not be achieved. Agitation of the pickling solution also disperses pockets of gas which can form on the surface of the stainless steel. These gas pockets prevent the pickling solution from removing chromium oxide from the surface of the stainless steel.

Agitation of the pickling solution can be carried out by placing agitators in the pickling tank and / or by recirculating the pickling solution. Stirring brushes can also be used inside the pickling tank to stir the acid solution and brush the surface of the stainless steel with the acid solution. Brushing the surface of the stainless steel increases and accelerates the removal of chromium oxide from the surface of the stainless steel. The temperature of the pickling solution can be maintained by recirculating the solution in heat exchangers. Typically, a pickling tank which contains the pickling solution is required to treat the stainless steel; however, multiple pickling vessels can be used in series. The pickling tanks have a length of approximately 7.62 meters (25 feet), it being understood that the tank may be shorter or longer.

The processing time of the stainless steel in the pickling solution is an important parameter to remove chromium oxide without damaging the stainless steel by avoiding creating pits or removing stainless steel. Typically, the pickling time lasts less than a minute and typically between 10 and 20 seconds. In a corrosive pickling step in a 7.62 m tank, the stainless steel strip passes through the pickling tanks at speeds generally less than about 45.7 m / min (150 feet / minute) and that is, preferably between 15.24 and 35.05 m / min (50 to 115 feet / minute).

 After being subjected to corrosive pickling, the stainless steel strip is further treated by means of a chemical activation of its surface, which improves the bond between tin and stainless steel.

After the corrosive pickling operation, a very small amount of oxide is present on the surface of the stainless steel. The virgin surface is highly susceptible to forming oxides during the time interval between the time the stainless steel strip leaves the pickling tank and the time it is coated with tin by hot dipping. In addition, some of the remaining chromium oxide may be present on the stainless steel strip after the corrosive pickling.

Chemical activation of stainless steel includes chemical treatment of stainless steel with a deoxidizing agent to remove any residual oxide remaining on the surface of the stainless steel after the corrosive pickling operation. Different deoxidation solutions can be used, such as for example zinc chloride. It has also been found that treating the stainless steel strip with zinc chloride before coating the stainless steel with molten tin provides a protective coating on the stainless steel strip, which prevents oxides from forming. form on the stainless steel strip. Zinc chloride acts as both a deoxidizing agent and a protective coating for the stainless steel strip. The zinc chloride solution is generally kept at room temperature (15,6- 32.3 C (60-90 F)) and stirred to maintain a uniform concentration in the solution.

Small amounts of hydrochloric acid can also be added to the deoxidation solution to further improve the removal of oxides.

 In accordance with another embodiment of the present invention, stainless steel is treated with an abrasive and / or absorbent material before applying a corrosive pickling. Stainless steel strips, which are unwound from stainless steel rolls, usually have foreign debris on their surface. Such debris can consist of dust, oil, glue, etc. Many of these foreign substances do not react or are not easily removed by the pickling solution, which adversely affects the removal of chromium oxide from stainless steel. Treatment of the stainless steel strip with an abrasive and / or absorbent material makes it possible to remove foreign substances from the stainless steel strip. The abrasive material can also initially remove some of the oxides that have formed on the stainless steel, which improves the corrosive pickling process. The abrasive material can be formed by one or more steel brushes disposed in the vicinity of the surface of the stainless steel. The brushes can be fixed or move relative to stainless steel. The brushes rub the surface of the steel to further improve corrosion of the stainless steel during the pickling operation. The roughened surface of stainless steel allows the acid solution to more easily attack this surface.

 In accordance with another aspect of the present invention, the corrosive pickling operation includes maintaining a low oxygen environment before and / or after the steel strip has been subjected to the pickling solution. Maintaining a low oxygen environment for the stainless steel strip is important in order to prevent the formation of oxide on the surface of the stainless steel. The low oxygen environment can take many forms.

The two most common low oxygen environments are the formation of a gas environment containing a low oxygen content around the stainless steel strip, or the immersion of the stainless steel strip in a liquid environment containing a low oxygen content. These two environments act as protective systems against atmospheric oxygen and prevent the formation of iron oxide and chromium. If the stainless steel strip is treated with an abrasive material and / or able to be absorbed when the strip is unrolled, a low oxygen environment is generally maintained around the strip until the latter enters the solution. pickling.

During the abrasion and / or absorption treatment of the stainless steel, some of the oxides are removed from the surface of the stainless steel. The non-oxidized surface is highly likely to oxidize when in contact with oxygen. By creating a low oxygen environment around the stainless steel strip, further oxide formation is prevented. By reducing and maintaining the amounts of oxide on the surface of the stainless steel before it enters the pickling solution, more efficient removal of the oxide and more effective corrosion of the surface are achieved. an environment formed from a low oxygen content gas is used, the gases used to form the environment containing a low oxygen content are typically nitrogen, hydrocarbons, hydrogen, rare gases and / or other gases not containing oxygen. In general, nitrogen gas is used to form the low oxygen content gas environment. Although a low oxygen gas environment is generally formed between the abrasion / absorption process and the pickling process, a low oxygen content liquid environment can be used. A low oxygen environment is also generally formed between the tank containing the pickling solution and the tank rinsing with the pickling solution.

When the stainless steel strip comes out of the pickling solution, most, if not all, of the oxides are removed from the surface of the stainless steel. The low oxide content on the surface of stainless steel makes it easily susceptible to oxide formation. A low oxygen environment is typically provided to prevent the detrimental effects of the formation of oxides at the exit of the stainless steel strip from the pickling solution. A gaseous or liquid environment with low oxygen content can be used to prevent the formation of oxides. Typically, a gaseous, low oxygen, nitrogen-containing environment is used to prevent reformation of chromium oxide and iron oxide on the surface of stainless steel when the latter comes out of pickling solution. In general, an environment with a low oxygen content is also formed before the chemical activation process. A liquid environment with a low oxygen content is typically used at this stage of processing stainless steel. The low oxygen content liquid environment is normally heated water, which is sprayed onto the surfaces of the stainless steel; however, stainless steel can also be immersed in water. The heated water contains very low levels of dissolved oxygen, which means that, by keeping the water at an appropriate temperature, the hot water acts as a screen against the oxygen and preventing the formation of oxide with stainless steel.

The hot water spraying action also removes the remaining pickling solution from the stainless steel before the stainless steel corrodes using the chemical activation process. Generally, the hot water temperature is maintained above 37.8 C (100 F) and typically about 430 C (110 F) or more, so as to exclude dissolved oxygen undesirable. Although not necessary, a low oxygen environment can be formed when the stainless steel strip is subjected to the chemical activation process before it enters the molten tin. Generally, this low oxygen environment is a gas environment.

 In accordance with another aspect of the present invention, the stainless steel strip is rinsed with hot water out of the pickling solution, thereby removing the pickling solution from the stainless steel. Once the stainless steel is removed from the pickling solution, some pickling solution may remain on the stainless steel and continue to attack the latter, leading to the formation of possible pitting in the stainless steel. The pickling solution is removed from the stainless steel strip by passing the strip through a volume of hot water. Typically the water should be above 37.8 "C (100 F) and should be equal to approximately 43 ° C (110 ° F) to remove dissolved oxygen from water, so as to prevent oxidation of the subsequently corroded stainless steel strip. The rinsing solution is generally kept at its desired temperature by recirculation in heat exchangers. Although the rinsing process mainly removes the pickling solution from stainless steel, the rinsing process also removes chromium oxide and other loose oxides the surface of the stainless steel. The rinse solution removes small amounts of oxides due to the slightly acidic nature of the rinse solution. When the rinse solution removes the pickling solution from the leaf rd of stainless steel, it enters the rinsing solution and acidifies the latter. The slightly acidic rinse solution attacks small amounts of oxides on the stainless steel, which further cleans the surface of the stainless steel. Generally, the rinsing solution is stirred to facilitate removal of the pickling solution from the stainless steel and dilute the removed pickling solution in the rinsing solution. The agitators may include movable brushes, which may or may not come into contact with the stainless steel strip. The rinsing solution is generally recirculated and is diluted so as to maintain a low acidity.

 According to another aspect of the present invention, there is provided a tinning tank. The tinning tank generally comprises a flow box, which the stainless steel strip passes through to penetrate the molten tin. The flux box typically contains a flux which has a lower specific gravity than that of molten tin, and therefore the flux floats on the surface of the molten tin. The flux located inside the flux box acts as the final surface treatment element of the stainless steel. The flux removes all residual oxides from the surface of the stainless steel and protects the surface of the stainless steel from oxygen until the stainless steel is coated with tin by immersion at hot. Normally the flux consists of zinc chloride and ammonium chloride. Typically, the flux solution contains about 30-60 percent by weight of zinc chloride and about 5-40 percent by weight of chloride d 'ammonium. However, the concentrations of the two flux agents can be modified accordingly. Once the stainless steel strip has crossed the flux, it enters the molten tin. The temperature of the molten tin is typically between 2960C and 343ex (575-650 F) at the bottom of the tinning tank and can be colder, 37.8C (100 F), at the top of the tinning tank. The tin must be kept above its melting point which is 231.5 "C (449 F) or otherwise, an incorrect coating is obtained. Typically, the tin is kept at a temperature of 310 C (590F) .The tin used to coat stainless steel contains little lead, even if it does contain it. Generally, the lead content is not more than 0.02 percent by weight. tin may contain alloys of bismuth or antimony. Both bismuth and antimony are elements which increase the abrasion resistance properties of the tin coating and prevent the tin from crystallizing during cooling, which could lead to detachment of the tin from the stainless steel.

Tin begins to crystallize when the temperature drops below 13.2 C (56 F). Only a small amount of antimony or bismuth is needed to prevent the tin from crystallizing. Typically, it is necessary to use amounts less than 0.5 percent by weight to adequately prevent the crystallization of the tin, which could lead to premature flaking of the tin coating from the material of the tin. stainless steel strip. Antimony and / or bismuth can be used with weight percentages greater than 0.5 weight percent to cure the tin coating. The hardening effects produced by antimony and bismuth in tin can adversely affect the preforming of tin coated materials for use in different applications. This is why, the quantity of antimony and bismuth added to the tin is a factor intervening in the particular application in which the material covered with tin is used. Bismuth can be present in the range of 0 to 1.7 percent by weight of the tin coating and antimony in the range of 0 to 7.5 percent by weight of the tin coating. Other metal alloys such as zinc, titanium and nickel can be added in small amounts to the tin to increase the rigidity of the tin coating.

The thickness of the tin coating is controlled by the speed at which the stainless steel strip passes through the molten tin, the time interval during which the stainless steel strip is in contact with the molten tin and the distance between the coating rolls.

As the speed of the metal strip passing through the molten tin increases, shear forces inside the molten tin reduce the thickness of the coating formed on the stainless steel layer. The quantity of tin deposited on the stainless steel strip depends on the duration of the immersion in the molten tin. The longer the length of time the stainless steel strip is in contact with the molten tin, the thicker the potential coating of tin.

The speed at which the stainless steel strip passes through the molten tin also affects the alloying of the tin to stainless steel. Too high a strip speed reveals intense shear forces leading to an incorrect and defective alloy of tin and stainless steel. The speed of the stainless steel strip should be kept below 45.72 m / min (150 feet / min) and is typically between 15.24 and 30.05 m / min (50 to 115 feet / min). When the stainless steel strip covered with tin leaves the molten tin, it generally passes between one or more sets of coating rollers, which maintain a uniform thickness of the tin coating. The coating rolls also form a smooth and uniform coating of tin on the strip when the strip passes between these rolls. Typically, palm oil is present on the surface of the molten tin and may partially surround the coating cylinders. Palm oil acts as an agent to facilitate good distribution of the tin and also serves as a coolant for the coating of tin. Palm oil also prevents the top of the molten tin from solidifying and / or oxidizing. The palm oil temperature at the top of the molten tin is normally kept as low as possible by recirculating palm oil in heat exchangers. typically between 238 and 243 "C (460 to 470 F). At higher temperatures, palm oil readily polymerizes, which can lead to the appearance of yellow bands in the tin coating. of tin formed by the hot dipping process has a thickness significantly greater than that provided by an electroplating process. In general, the coating of tin has a thickness which is between 0.00076 cm and 0.127 cm (0.0003 to 0.05 inches); however, thicker coatings can be obtained. Typically, the thickness of the tin coating is maintained between 0.00254 cm and 0.00508 cm (0.001 to 0.002 inches) .

The increase in thicknesses of the tin coating obtained by means of a hot-dipping process greatly increases the service life of the materials coated with tin compared to comparable plated materials coated with a coating. by electroplating.

 In accordance with another aspect of the present invention, metal spraying devices are arranged in the vicinity of the coating rolls to ensure complete coating of the stainless steel with tin. Metal spray devices spray molten tin onto the coating rollers. When the coating rollers rotate so that the stainless steel strip passes between them, molten tin is sprayed onto the rollers and pushed against the stainless steel strip and fills all of the pinholes or surfaces not covered with stainless steel.

Therefore it is not necessary to have two separate tinning stages.

 According to another characteristic of the present invention, there is provided a method of cooling the tin during which the stainless steel strip newly covered with tin is cooled. The tin cooling process generally involves a liquid cooling process. Advantageously, water is used as the cooling fluid; however, other fluids can be used. The tin coating can be cooled at different rates to obtain different grain sizes and densities. Slow cooling of the tin coating leads to larger grains, lower grain densities and a highly reflective surface. Rapid cooling of the tin coating produces small grains, increasing the density of grains and provides a less reflective surface. Small dimensions and fairly high grain densities provide a stronger bond with stainless steel and superior corrosion resistance. The cooling of the tin coating by means of a liquid can be carried out by spraying a cooled liquid onto the deposited tin or immersing the stainless steel strip covered in a container containing the cooled liquid. In a liquid spraying process, water is generally sprayed onto the tin coating. The covered strip is generally guided between the cold water projection systems by an arched guide. The arched guide is designed so that only the edges of the covered strip are in contact with the guide. Reducing the contact between the coated strip and the guides reduces the amount of tin that is inadvertently removed from the coated strip. The arched guide is also designed to allow the water jets to cool the underside of the coated strip. The temperature of the cooling water is generally less than or equal to the ambient temperature. The tin coating can also be cooled by immersing the strip in the cooling water. The water temperature is generally not higher than the ambient temperature. Normally, the cooling water is agitated to increase the cooling rate of the tin. In general, the temperature of the cooling water is maintained at correct values for cooling, by recycling the water in exchangers heat and / or additional water filling. The cooling water is generally not deoxygenated before cooling the tin coating. The oxygen contained in the cooling water oxidizes the tin during rapid cooling, which leads to a slight discoloration of the surface of the tin, which reduces the reflectivity. The reduction in the highly reflective surface of tin-coated stainless steel strips allows the strips to be used in different applications, such as roofing in civil and military airports, which requires non-reflective building materials.

 In accordance with another aspect of the present invention, the coated stainless steel strip passes through a leveling device, whereby the tin coating is uniformly molded over the stainless steel strip. Generally, the leveling device consists of a plurality of rollers. The coated strip passes between the rollers while being placed under tension so as to standardize the coating of tin on the steel strip.

 According to another aspect of the present invention, the deposited stainless steel is sheared after being rolled or leveled. The shearing device normally moves close to and at approximately the same speed as the coated strip so as to allow correct shearing of the strip in motion.

 According to another aspect of the present invention, the material constituted by the coated steel is treated with a disintegrating agent so as to accelerate this weathering treatment and the discoloration of the tin involved. The disintegration material is typically an asphalt-based paint which results in accelerated disintegration of the deposited tin when it is exposed to the atmosphere. The asphalt-based paint greatly reduces the disintegration time of the deposited tin to less than one year. Typically, asphalt paint is a petroleum-based paint, consisting of asphalt, titanium oxide, inert silicates and low clay carbon black or other free carbon. and a suspending agent. Asphalt-based paint is generally applied over a relatively small thickness so as to form a semitransparent or translucent layer on the tin coating.

Generally, the thickness of the asphalt-based paint is between 0.635.10-5 m and 12.7.10-5 m (0.25 to 5 miles) and typically between 2.54.10-5 m and 5.08.10.-5 m (1 to 2 miles). Once the translucent paint has been applied to the tin coated stainless steel, the material is air dried and / or heated using heat lamps.

 The main object of the present invention is to provide a weatherproof stainless steel covering material, covered by a thin layer of tin deposited by hot dipping.

 Another object of the present invention is to carry out a corrosive pickling of a stainless steel strip before hot immersing the stainless steel in tin to form a solid alloy bond between the tin and the stainless steel.

 Another object of the present invention is to carry out a chemical activation of the stainless steel following the corrosive pickling so as to improve the bond between the stainless steel and the tin coating.

 Another object of the present invention is to achieve a reduction in the interaction of oxygen with stainless steel during the pretreatment of stainless steel before coating the stainless steel with tin, by immersion hot.

 Another object of the present invention is to provide a coating of tin containing very small amounts of lead, and preferably not containing lead, and containing antimony and / or bismuth in order to harden and stiffen the coating of tin and preventing crystallization of the tin.

 Another object of the present invention is to provide rapid cooling of the tin deposited by hot immersion to form small grains with high density, which establish a more solid bond, for a coating of decorated tin more resistant to corrosion.

 Another object of the present invention is to carry out an abrasive treatment of the surface of the stainless steel before the corrosive pickling.

 Another object of the present invention is to provide tin projection devices, which project the tin onto coating rolls so as to eliminate surfaces not covered with tin on the stainless steel.

 Another object of the present invention is to carry out an atmospheric type disintegration of the tin coating, obtained by hot immersion, on stainless steel so as to accelerate the tarnishing of the surface of the tin coating.

 Another object of the present invention is to provide a stainless steel strip coated with tin, which allows soldering of the tin solder on the strip, which eliminates the need to use a solder containing lead.

 Another object of the present invention is to produce a coated strip, as defined above, which does not require the application of intentional oxidation to prevent the production of a shiny surface.

Other characteristics and advantages of the present invention will emerge from the description given below taken with reference to the appended drawing, in which
- Figure 1 shows a cross-sectional view of the entire process for treating a stainless steel covered with tin by hot dipping according to the present invention;
- Figure 1A shows a cross-sectional view of another method of cooling tin-coated stainless steel by hot immersion, according to the present invention;
- Figure 2 shows a cross-sectional view of another embodiment, in which metal spraying devices are used during the coating of the stainless steel strip with tin by hot dip;
- Figure 3 is a schematic side elevational view showing a preferred embodiment of the cooling of stainless steel covered with tin by hot immersion, using cold water spraying devices;
- Figure 4 shows a cross-sectional view of another embodiment, in which abrasive treatment devices are used in connection with a low oxygen environment for the pretreatment of the stainless steel strip before the pickling; and
- Figure 5 shows a front view of an arcuate guide.

 Referring now to the drawings, which are intended only to illustrate the preferred embodiments of the present invention, and this without any limiting character, we will first refer to Figure 1 mentioned above, which illustrates the 'the whole process according to the invention of tin deposition by hot immersion on stainless steel sheets. Typically, the stainless steel strip 12 enters the tin coating plant by hot dipping from a large roll 10 of the stainless steel strip. Generally, the stainless steel used is type 304 stainless steel, which contains eighteen percent chromium and about eight percent nickel. The thickness of the stainless steel strip 12 is equal to about 0.0380 cm (0.015 inch) however, the stainless steel strip 12 may be thinner. However, it is understood that the use of thicker strips (for example up to 0.508 cm), in particular steel sheets of usual thickness, does not depart from the scope of the present invention. The stainless steel strip 12 is generally unwound from the stainless steel roll 10 at speeds which are generally less than 45.73 m / min (150 feet / min) and are preferably between 21.34 and 30 48 m / min (70 to 100 feet / min). Guide strips 13 are arranged over the entire extent of the tin coating installation by hot dip so as to correctly guide the stainless steel strip 12 during each treatment operation.

 An abrasive treatment device 14, which is in the form of brush scrapers. The skyscrapers are placed in contact with the stainless steel strip 12 to remove foreign objects from the strip and initially corrode and / or mechanically remove chromium oxide from the surface of the stainless steel strip 12. The abrasive treatment device 14 can be in any form, but is preferably pushed against the stainless steel strip 12 so as to produce the friction necessary between the brushes 16 and the stainless steel strip 12 to have a correct cleaning of this latest. Typically, an abrasive treatment device 14 is provided located on the upper and lower surfaces of the stainless steel strip 12 for obtaining correct treatment of the strip. Typically, an abrasive brush 16 is formed of a metallic material having a hardness greater than that of the stainless steel strip 12 so that the abrasive brush 16 does not wear out quickly and can correctly remove foreign substances and / or carry out a pre-corrosion of the stainless steel strip 12 In general, the abrasive brush 16 rotates in the opposite direction of the movement of the stainless steel strip 12 so as to apply additional abrasion to this strip.

 Once the stainless steel strip 12 has passed through the abrasive treatment device 14, the corrosive pickling process begins. The stainless steel strip 12 enters a low oxygen content gas environment 20. The latter is formed by enveloping the stainless steel strip 12 with gas 22 containing a low oxygen content. Preferably, the gas 22 with a low oxygen content consists essentially of nitrogen gas. The nitrogen gas, which surrounds the strip of stainless steel 12, acts as a barrier against oxygen from the atmosphere and prevents oxygen from reacting with chromium and iron on the strip. stainless steel 12 recently exposed by the abrasive treatment device 14.

 After leaving the low oxygen gas environment 20, the steel strip 12 enters a tank or a pickling tank 30. The pickling tank 30 generally has a length of about 7.62 m ( 25 feet) and a depth sufficient to completely immerse the stainless steel strip 12 in a pickling solution 32. The pickling solution 32 preferably consists of a hydrochloric acid-nitric acid solution. Typically, the concentration of hydrochloric acid-nitric acid in pickling solution 32 contains about 10% hydrochloric acid and 3% nitric acid. Pickling solution 32 is generally kept at a temperature 53-56.5 C (128 to 133 F) so that the pickling solution 32 is maintained in a highly reactive state to appropriately remove chromium oxide from the surface of the stainless steel strip 12.

The pickling solution 32 also performs minor corrosion of the surface of the stainless steel strip 12, which makes it possible to remove a very thin surface layer from the stainless steel strip 12. The pickling tank 30 preferably contains at least one agitator 34. The agitator 34 is intended to agitate the pickling solution 32 so as to maintain a uniform temperature of the solution and to eliminate any gas pocket which may form on the stainless steel strip 12. Agitators 34 are formed generally an abrasive material which both agitates the pickling solution 32 and facilitates the removal of chromium oxide from the stainless steel strip 12. In general, the agitators 34 are made of a material which does not react not with the pickling solution 32. A vent 36 for the pickling solution is preferably placed above the pickling tank 30 to collect and evacuate acid fumes and d other gases escaping from the pickling tank 30. The stainless steel strip 12 immediately enters the environment of low-oxygen gas 20 leaving the pickling tank 30. When the stainless steel strip 12 comes out of the pickling tank 30, it has substantially no chromium oxide and is very sensitive to oxidation by the oxygen contained in the atmosphere. The low oxygen gas environment 20 protects the surface of the stainless steel strip 12 from atmospheric oxygen and prevents the formation of oxides.

 The pickling solution 32 is mainly removed from the stainless steel strip 12 in a rinsing tank 40. The rinsing tank 40 contains a rinsing solution 42 which is preferably water.

The water present in the rinsing tank 40 is deoxygenated under the effect of its heating to a temperature above 37.2 C (100 F) and preferably above 43 C (110 F). Under the effect of the slightly acidic properties of the rinsing solution 42, the latter removes small amounts of oxide which may still exist on the surface of the stainless steel strip 12. The rinsing tank 40 has a length of 6.098 m (20 feet), but can be longer depending on the speed at which the stainless steel strip 12 moves. Typically, the rinse solution 42 is agitated to facilitate removal of the pickling solution 32 from the stainless steel strip 12 and to intensify the removal of small amounts of oxides. When the stainless steel strip 12 leaves the rinsing tank, it enters a liquid environment with a low oxygen content 50. The liquid environment with a low oxygen content 50 consists of at least two projection devices 52, which are located on both sides of the strip. stainless steel 12. The projection devices 52 project a low oxygen content liquid 56 onto the surface of the stainless steel strip 12 to prevent oxygen from reacting with the chromium and / or iron present on the surface of the strip stainless steel 12. The spraying devices 52 also eliminate any additional pickling solution 32 which may remain on the stainless steel strip 12 after it leaves the rinsing tank 40. The low oxygen content liquid 56 is generally hot water having a temperature of about 43 "C (110 F). The low oxygen liquid environment 50 is the last step in the corrosive pickling process of the stainless steel strip 12.

 When it leaves the low oxygen liquid environment 50, the stainless steel strip 12 enters a chemical activation tank 60. The chemical activation tank 60 contains a chemical activation solution 62, which removes in addition, any oxide remaining on the surface of the stainless steel strip 12. Preferably, the chemical activation solution 62 is a zinc chloride solution maintained at a temperature of 26.7-32.2 "C (80 Zinc chloride present in the chemical activation tank 60 not only removes oxides remaining on the stainless steel strip 12, but also acts as a temporary protective coating preventing the formation of oxides on the stainless steel strip 12 before the latter enters the tinning tank 70.

 Before the stainless steel strip 12 is covered by the molten tin 76, it enters a flow box 72 located in the tinning tank 70. The flow box 72 contains a flow 74 having a specific gravity less than that of molten tin 76. The stream 74 preferably consists of a solution of zinc chloride and ammonium chloride. Preferably, stream 74 contains about 50 percent zinc chloride and about 8 percent ammonium chloride. Flow treatment 74 is the last pre-treatment operation of the stainless steel strip 12 for the removal of all the remaining oxides on the surface of the stainless steel strip 12. When it leaves the flow box 72, the stainless steel strip 12 enters the molten tin 76. The molten tin 76 present in the tinning tank 70 is maintained at a temperature above 231 "C (449 F) and is preferably at a temperature equal to about 310 "C (590 F). The tinning tank 70 is preferably subdivided into two chambers by a barrier 80 for palm oil so as to prevent palm oil 78 from spreading over the entire surface of the molten tin 76 in the tank tinning 70. The molten tin 76 has a lead content of less than or equal to about 0.02 percent by weight.

The molten tin 76 preferably contains about 0.5 percent by weight of antimony and / or bismuth so as to prevent crystallization of the coating of tin upon cooling. Molten tin 76 may contain additional amounts of antimony, bismuth or other metals; however, the content of molten tin 76 is advantageously about 99 percent by weight.

Before leaving the tinning tank 70, the stainless steel strip 12 passes between at least one set of coating rollers 82. The coating rolls maintain the desired thickness of the tin coating on the strip d stainless steel 12 and remove excess tin from the latter. The thickness of the tin coating on the stainless steel strip 12 is generally maintained between 0.00076 cm and 0.127 cm (0.003 to 0.005 inches) and is preferably between 0.0254 cm and 0.0508 cm ( 0.01 to 0.02 inch). The palm oil 78 is preferably located near the coating rolls 82. The palm oil floats on the upper part of the molten tin 76 preventing the latter from solidifying and oxidizing and also contributes to distribute the tin correctly on the stainless steel strip 12.

 In another embodiment, Figure 2 shows a metal coating projection device 84, which projects molten tin onto the outer surface of the coating cylinder 82. The molten tin 76, which is projected onto the cylinder coating 82 is pushed against the stainless steel strip 12 when the latter passes in front of the coating cylinder 82 so as to fill all the small surface areas of the stainless steel strip 12, which have not been covered by the tin in the tinning tank 70.

 When the stainless steel strip 12 leaves the tinning tank 70, the tin coating is rapidly cooled by at least one cold water spraying device 92. When the stainless steel strip 12 moves below the cold water spraying device 92 as shown in FIG. 3, it is guided by camel guides 90 as shown in FIG. 5. The camel guide 90 is arranged so that it has two descending edges 192 formed by conical surfaces which are in contact only with the edges of the stainless steel strip 12 so as to reduce the elimination of the tin coating from the stainless steel strip 12. In another form of embodiment as shown in FIG. 1A, the stainless steel strip 12 is rapidly cooled in a cooling tank 94, in which the stainless steel strip 12 is immersed in cooling water 96. The water d Cooling 96 is generally maintained at room temperature and is preferably stirred so as to intensify the rate of cooling of the tin coating. Rapid cooling of the tin coating by means of the cooling tank 94 or the cooling water spraying device 92 is obtained so as to obtain a tin coating having small grains with increased grain density .

Likewise, rapid cooling of the tin coating results in oxidation of the surface of the tin coating, producing a less reflective gray surface.

 After being rapidly cooled, the stainless steel strip 12 passes through a grader 100. This grader 100 preferably contains 17 leveling rollers 102, which produce a uniform and smooth coating of tin on the stainless steel strip 12. When the stainless steel strip 12 leaves the grader 100, it is cut by shears 104 to the desired lengths. When the stainless steel strip 12 has been cut into stainless steel sheets coated with tin 130, these sheets can be covered with a disintegrating pretreatment agent 112. The stainless steel sheets coated with tin 130 are preferably coated by coating devices 114 which apply a disintegrating agent 112. This agent 112 is generally made up of an asphalt-based paint which is applied to a thickness of approximately 2.54 -5.08.10-5 m (1 to 2 miles).

 Preferably, the two surfaces of the tin-coated stainless steel sheets 130 are covered with a disintegration pre-treatment agent 112. In the devices 114 for depositing the disintegration pre-treatment agent, this agent is applied either by the spraying device 116 of this disintegration pretreatment agent, or by rotationally driving the coating devices 114 in the reservoir 110 containing the disintegration pretreatment agent.

The disintegration pretreatment agent 112 can be quickly dried by means of a heat lamp 120 and / or by means of a dryer 122. The stainless steel sheets coated with tin 130 are preformed in the form of roofing materials very resistant to corrosion. Watertight joints can be formed by jointly folding the edges of two sheets. You can also solder the joints together using a tin solder. Solder containing lead does not provide as good a solder as tin solder.

 The present invention has been described with reference to an embodiment and to preferred variants.

It is believed that many changes and modifications to the mode of implementation described herein will become apparent to those skilled in the art upon reading the
Presents detailed description of the invention, which is intended to include all of these changes and modifications.

Claims (39)

 1. A method of treatment against corrosion of a metal sheet or strip by hot immersion in a bath of molten metal, characterized in that it comprises the steps consisting in:  a) introducing a tinning metal (76) containing mainly tin into a tinning tank (70),  b) heating the contents of the tank until the tinning metal (76) melts,  c) immerse in the tinning metal (76) the sheet or strip (12) to be treated.  2. Method according to claim 1, characterized in that the sheet or strip (12) treated is steel.  3. Method according to claim 2, characterized in that the sheet or strip (12) treated is made of low carbon steel.  4. Method according to claim 2, characterized in that the sheet or strip (12) treated is made of stainless steel.  5. Method according to any one of the preceding claims, characterized in that the tinning metal (76) comprises at least 90% by weight of tin and at most 0.1% by weight of lead.  6. Method according to claim 5, characterized in that the tinning metal (76) comprises the following weight percentages  Tin 90 - 99.9%  Lead 0.01 - 0.10%  Bismuth 0.0 - 1.7%  Antimony 0.0 - 7.5%  Zinc 0.00 - 1.5%  Iron 0.00 - 0.1%  Copper 0.00 - 2.7%  7. Method according to any one of the preceding claims, characterized in that the sheet or strip (12) has a thickness between 1.27 mm and 5.08 mm.  8. Method according to any one of the preceding claims, characterized in that, during the immersion of the sheet or strip (12) in the tinning metal (76), it is formed, on at least each of the main faces of the sheet or strip (12), a protective layer whose thickness is between 0.0762 mm and 1.27 mm.  9. Method according to any one of claims 4 to 8, characterized in that it comprises, prior to step c), a step d) of elimination of the iron and chromium oxides on at least the two faces principal of the treated sheet or strip.  10. The method of claim 9, characterized in that step d) of removing oxides comprises a step e) of corrosive pickling, in particular with an acid from the sheet or strip (12) to be treated.  11. Method according to claim 10, characterized in that step d) of elimination of the iron and chromium oxides comprises, prior to step e) of corrosive pickling, a step f) of mechanical removal of material main faces of the sheet or strip (12) treated by abrasive devices (16), in particular brushes.  12. Method according to claim 9, 10 or 11, characterized in that between step d) of elimination of iron oxide and chromium and step c) of immersion, one proceeds to l insulation of the sheet of the treated strip from molecular oxygen (02) by immersing it in a deoxygenated fluid.  13. The method of claim 10, 11 or 12, characterized in that during step e) of corrosive pickling, the sheet or strip treated is immersed in a tank (30) containing a mixture (32) d nitrite and hydrochloric acid.  14. Method according to claim 12 or 13, characterized in that it comprises, after step e) of corrosive pickling, a rinsing step with a deoxygenated liquid, in particular with deoxygenated water.  15. Method according to any one of claims 4 to 14, characterized in that prior to step c) of immersion, it comprises a step g) of chemical activation of the sheet or strip (12) treated .  16. The method of claim 15, characterized in that step g) is subsequent to a step e) of corrosive pickling, and in that it comprises a step of treatment of the sheet or strip (12) with zinc chloride.  17. Method according to any one of claims 4 to 16, characterized in that prior to step c) of immersion it includes a step h) of immersion of the sheet or strip (12) in a flow pre-tinning (74).  18. The method of claim 17, characterized in that the pre-tinning flux (74) comprises zinc chloride and ammonium chloride.  19. Method according to any one of claims 4 to 18, characterized in that, after step c) of immersion, it comprises a step i) of rapid cooling of the protective coating to obtain grains of tin of desired size.  20. Method according to any one of claims 1 to 20, characterized in that in step c), the immersion comprises a step of passing the sheet or strip (12) between two coating rollers ( 82) whose spacing determines the thickness of the protective coating.  21. Method according to any one of the preceding claims, characterized in that it comprises a step of spraying (84) the tinning metal (76).  22. Method according to any one of the preceding claims, characterized in that it comprises, after step c) immersion in the tinning metal (76), a step j) of coating (114) with a disintegrating agent (112) for the protective coating.  23. Weather-resistant cover material in the form of a metal strip, characterized in that it comprises a metal sheet or strip (12) of which at least the two main faces are tinned with tinning metal (76) containing at least 90% by weight of tin and at most 0.1% by weight of lead.  24. Covering material according to claim 23, characterized in that the tinning metal (76) comprises the following percentages by weight  Tin 90 - 99.9%  Lead 0.01 - 0.10%  Bismuth 0.0 - 1.7%  Antimony 0.0 - 7.5%  Zinc 0.00 - 1.5%  Iron 0.00 - 0.1%  Copper 0.00 - 2.7%  25. Covering material according to claim 23 or 24, characterized in that the tinning on the main faces of the sheet or strip (12) has a thickness between 0.762 mm and 1.27 mm.  26. Covering material according to any one of claims 23 to 25, characterized in that the sheet or strip (12) has a thickness between 1.27 mm and 5.08 mm.  27. Covering material according to any one of claims 23 to 26, characterized in that the sheet or strip is made of stainless steel.  28. Device for manufacturing a covering material in the form of weather-resistant strips, characterized in that it comprises a tank (30) for aggressive pickling of a sheet or strip (12) and a tank (70) tinning.  29. Device according to claim 28, characterized in that the aggressive pickling tank (30) is filled with acid, in particular with a mixture of hydrochloric acid and nitric acid.  30. Device according to claim 28 or 29, characterized in that it comprises a rinsing tank (40) disposed between the tank (30) of aggressive pickling and the tank (70) of tinning.  31. Device according to any one of claims 28 to 30, characterized in that it comprises means (16) for mechanical ablation of the material of the sheet or strip (12), in particular brushes.  32. Device according to any one of claims 28 to 31, characterized in that it comprises means (20, 36, 50) for insulating the sheet or strip from molecular oxygen (2)  33. Device according to any one of claims 28 to 32, characterized in that it comprises a tank (60) for chemical activation of the treated strip filled with a chemical activation solution (62).  34. Device according to any one of claims 28 to 33, characterized in that it comprises a flow box (72), preferably disposed in the tinning tank (70).  35. Device according to any one of claims 28 to 34, characterized in that it comprises, disposed at the outlet of the tinning tank (76), means (92) for rapid cooling of the sheet or strip treated, in particular means for spraying cold water.  36. Device according to any one of claims 28 to 35, characterized in that it comprises coating rollers (82) arranged in the tinning tank (70).  37. Device according to any one of claims 28 to 36, characterized in that it comprises a grader (100).  38. Device according to any one of claims 28 to 37, characterized in that it comprises a device (114) for coating with a disintegrating agent (112) of the tinning metal.  39. Device according to any one of claims 28 to 38, characterized in that said device is a continuous manufacturing device, and in that it comprises means (13) for transporting a strip (12) treated passing, in continuous mode, simultaneously to the various treatment stations (16, 20, 30, 40, 50, 60, 70, 92, 100).