MXPA99003744A - Sustainable stainless steel sheet used in the cuber sector and especially in the vinic cuber sector - Google Patents

Abstract

Austenitic stainless steel sheet used in the sector of the cubería and especially in the sector of the wine cellar, being laminated in cold the sheet and presenting a state of surface whose rugosidad measured by AFM in zones of 100 um by 100 um is defined by a Ra between 0.05 um and 0.15

Description

Austenitic stainless steel sheet used in the sector of the cubería and especially in the sector of the viticulture DESCRIPTION OF THE INVENTION: The present invention concerns a steel usable in the sector of the cubería and especially in the sector of the wine cellar. Stainless steel is a material frequently used in the sector of the wine cellar. During the elaboration of the wines, a cold stabilization operation is carried out whose purpose is to precipitate the tartaric acid in the form of potassium hydrogen tartrate (THK), contained in the wine, and to avoid the sediments of background in the bottles. The layers of tartar formed during the alcoholic and malolactic fermentations and the elaboration of the wines can be adherent and difficult to eliminate by means of classic cleaning operations carried out at the end of a wine campaign. Currently, the automation of viticultural techniques has implied a reduction, in the number, of the personnel responsible for the maintenance of the vats. For this reason, wine growers look for vats that have easily cleanable surfaces and a limitation of the consumption of water and effluents when cleaning the vats. Steel plates used in the wine sector are known, which have a surface condition of the type referred to as "2R finish", considered as susceptible to limiting the incrustation. The surface quality of these sheets, of the type of bright annealing, without surface defects, is considered as preponderant to reduce these mechanisms. REF. : 30152 However, the steel sheets presenting the surface condition just described, pose the problem of maintaining the gloss quality of the sheets during the manufacture of the tank by a boilermaker, and the cleaning of the vats by the viticulturist, because of the very strong reverberation of the electric lighting lamps (torches), used when cleaning these vats. To date, it has always been considered that the stainless steel surfaces, which have the smallest possible average roughness values, allowed to limit the incrustation of the surfaces in the wine sector, from which the use of metal sheets is inferred. steel with a brilliant state of 2R finish. The purpose of the invention is to produce sheets comprising a surface state that provides certain characteristics with respect to precipitation, for example tartaric in the case of wine, this surface condition limiting the adherence of certain compounds of wine, in particular the THK, improving at the same time the cleanliness. The object of the invention is an austenitic stainless steel sheet which can be used in the sector of the container and especially in the sector of the wine cellar, the sheet being cold rolled and having a surface condition whose roughness, measured by AFM in areas of 100 μm per 100 μm, is defined by a Ra between 0.05 μm and 0.15 μm. The other features of the invention are: the grain boundaries have a depth between 0.1 μm and 0.5 μm and preferably about 0.4 μm and a width between 0.5 μm and 1.8 μm μm and preferably about 1.5 μm, - the grains of the metal, on the surface, have an average diameter between 5 μm and 20 μm, - the average amplitude of the surface of the grains, measured by AFM, is between 5 nm and 30 nm and preferably is approximately 10 nm. The invention also relates to a process for the production of an austenitic stainless steel plate, which can be used in the sector of the container, and especially in the sector of the wine cellar, characterized in that in an austenitic steel plate having a surface of type 2B a cold rolling is carried out in such a way that the grains are flattened by pushing them towards the grain boundaries, in such a way that said grain boundaries are closed, the surface of the steel sheet presenting a narrow and shallow grain boundary joints and very flattened grains without superficial surface corrosion. According to another characteristic of the process, the flattened shape of the grains is obtained by means of a final cold rolling, such as a rolling of the "skin pass" type (surface hardening pass) with a degree of reduction of less than 5%, preferably lower than 4% The following description and the appended figures, all having been given as a non-limiting example, will make the invention well understood.

Figures 1a and 1b respectively have a surface profile and a histogram that materialize the surface state of a laminated steel plate of the classic type 2B. Figures 2a and 2b respectively have a surface profile and a histogram that materialize the surface state of a sheet of rolled steel according to the invention. The mechanisms of incrustation of the surfaces have been demonstrated in a comparative manner, and the cleaning tests have allowed to differentiate, in terms of quality, the states of the surfaces of industrial stainless steel sheets with respect to the surface state of a sheet according to the invention. The use of steel has spread widely in the food industry sector. Its evolution for more than sixty years is explained by the fact that it responds perfectly to the expected requirements for materials that come into contact with food and can be summarized in three points: - chemical, bacteriological and organoleptic neutrality against the product food, - ability to clean and guarantee hygiene in relation to other materials, - inalterability, resistance to corrosion and aging of the food product. By virtue of its mechanical and physical characteristics, the austenitic stainless steel responds perfectly to the expectations of the boilermakers: - absence of fragility and perfect resistance to shocks, - insensitivity to temperature and pressure variations, - high mechanical characteristics that allow a lightening of the facilities, - a very good soldabílídad and a very good ductility, which ensure easy conformations. The topography of a surface of a sheet steel can be characterized at three different levels: The level of order 1, which materializes, for example, the grooves due to rolling or also the corrugations of the sheet. The size of the rolling flutes is greater than or equal to approximately 100 μm. The level of order 2, which presents a steel surface at the level of the grains of the metal with an order of magnitude of 10 to 20 μm. The level of order 3, which takes into account the defects in the surface of a grain that corresponds to the microgeometry of the surface. Level 3 is visible only by means of the AFM (atomic force microscope), which has a very high sensitivity in relation to the other techniques commonly used in the field of surface characterization. In areas of 100 μm x 100 μm, an analysis at an order 3 level of the so-called normalized surfaces, classified as 2B, shows subgrains that constitute a grain where the sub-joints have a depth of 0.1 μm and a width of 0.15 μm. Small depressions with a width of approximately 0.3 μm and a depth of approximately 80 nm are also observed. The grain boundaries have a depth of 0.5 μm and a width of 5 μm. The presence of holes whose diameter can reach several meters is also observed. The roughness measured on such a surface and represented by the Ra index is approximately 0.5 μm, determined by interferometry and AFM in areas of 100 μm x 100 μm. From the point of view of the mechanisms of incrustation, it is revealed that the yeasts present in the wine adhere in the first place to the steel surfaces and serve as germs of nucleation for the crystals of the tartar. It has been shown that the adhesion of yeasts to the surface of a stainless steel depends both on the physical-chemical properties of the surface, quantifiable by measurements of the contact angles, but also of the topography of the quantifiable surface by roughness measurements. In addition, because of the presence of the grain boundaries on the surfaces, for example of type 2B, the yeasts adhere preferentially to the grain boundaries at the surfaces and adhere preferably in the form of heaps on the surfaces. surfaces of type 2R, of bright annealing. Because of the basic character of the surface of the yeasts, the tartaric acid present in the wine has a great affinity for the yeasts and preferentially precipitates on said yeasts. The macromolecules present in wine have an inhibiting effect on tartaric precipitation. It has been observed that this effect is visible especially for polyphenols and polysaccharides, macromolecules of wine. Depending on the composition of the wine, which varies from year to year, and depending on the amount of polyphenols adsorbed, the growth of a crystal can be greatly inhibited or not. In the case of a white wine, where the polyphenols are in much smaller amounts, the THK crystals can grow on the surface.

In a comparative example, incrustation tests have been carried out with two red wines whose compositions are presented in table 1.

Table 1 Composition Wine 1995 Wine 1997 Ph 3,6 3.7 Tartaric acid (g / 1) 5,9 2,6 Polysaccharides (mg / l) 342,4 457 AGPs 120,5 301 Mps 70,6 69 RG-II 137 67 RG-I 13.5 14 Polyphenols (g / 1) 1, 42 1, 23 The wine of 1995 is more loaded with tartaric acid than that of 1997. On the contrary, the latter has a higher content of polysaccharides. The sediments obtained after having gone through cold, measured in mg / cm2, in different types of surface qualities, have been analyzed by physical-chemical techniques and have been presented in table 2.

Table 2 1995 Wine 1997 Wine 2B 2R 2B 2R Yeast (%) 24 65 20 22 THK (%) 69 9 76 77 Polyphenols (%) 1, 6 27 1, 9 1, 8 Polysaccharides (%) 0.9 - 0.7 0.6 It is evident that the composition of the sediment varies depending on the composition of the wine and the surface condition of the plate of the tank. The stainless steel sheet according to the invention, usable in the sector of the cubería and especially in the sector of the viticultural cube, is a austenitic steel cold rolled and that presents a state of surface characterized because the grains of the metal have an average diameter between 5 μm and 20 μm, being 10 nm the average amplitude of the grains measured by AFM. The grain boundaries have a depth between 0.1 μm and 0.5 μm and a width between 0.5 μm and 1.8 μm. The roughness, measured by the Ra index in areas of 100 μm x 100 μm by means of the AFM method, is between 0.05 μm and 0.15 μm. According to the invention, the surface state is obtained by means of a cold rolling which allows to flatten the grains of a type 2B surface by pushing them towards the grain boundaries. For this reason, the grain boundaries are closed. In this new structure, it has been observed that the grain boundaries can no longer trap microorganisms. The sheet of stainless steel, for example of the type AISI 304 or 316L, has been made from a package or flat, and then has undergone a hot rolling, annealing, shot blasting and pickling, a cold rolling and a final annealing, followed by a chemical etching and a lamination with a small degree of final reduction, called "skin pass", according to the process of the invention. After classical processing of this steel sheet, grain boundaries are obtained together. On the contrary, thanks to an optimization of the manufacturing conditions according to the invention, the metal is pushed towards the grain boundaries thanks to the final cold rolling with a small degree of reduction, less than 5% and preferably less than 4%, which deforms the joints limits of the metal grains. In this case, the grain boundaries have a specific size and shape, a flattened shape that allows the elimination of microorganisms that usually adhere to stainless steel surfaces. Figures 1a and 1b, which respectively have a surface profile and a hystogram materializing the surface state of a steel plate of the classic type 2B, have to be compared with figures 2a and 2b, which respectively have a surface profile and a histogram which materializes the surface state of a steel sheet according to the invention. In embedding tests, the sample plates are placed on a plate exchanger through which a cooling liquid circulates. The temperature of the samples is between 4 and 5 ° C. The samples constitute the cold site of the wall of the tank and therefore the sedimentation of THK takes place on the sample. After the stabilization of the wine, determined thanks to the decrease in conductivity, the sample is removed and dried in air before consolidation.

In the area of surface cleaning, it has been shown that the cleanliness was a function of the topography of the surface, the yeasts or tartar being able to settle preferentially on the surfaces of the grains of the steel sheet or in the zones with defects such as the grain boundaries, or also in areas with defects in a specific way with a grain limit gasket imposed. According to the invention, the surface of the steel sheet has the characteristic of having a narrow and shallow grain boundary seal and a very flattened grain without microroughness.

Imposed shape is defined as the shape of the grains with an average dimension reduced to an equivalent circle, comprised between 5 μm and 20 μm, and having a grain surface having a micro-roughness comprised between 10 nm and 100 nm, the limit board of the grains. The crushed shape of the grains is obtained by a final cold rolling of the "skin pass" type with a degree of deformation comprised between 0.4% and 2%. Cleanliness is measured by the loss of mass before and after cleaning. The cleaning is carried out in a cell with laminar flow in which the water pressure is controlled, for example at 0.1 bar, the cleaning time, and the temperature chosen between 20 ° C and 50 ° C. Tables 3 and 4 show the mass losses after cleaning of sheet metal samples for two types of wines and for the steel sheet according to the invention and two steel plates of the bright annealing type 2R and of the type 2B. Table 3: Clearance% A Acceerroo according to the invention Finish 2R Finish 2B Red wine Cold water 84 91 80 Hot water 98 99 98 In all cases, traces of colored material of the order of 1% remain on the sheet, which must be removed by washing with soda.

Table 4: Clearance% A Acceerroo s according to the invention Finish 2R Finish 2B White wine Cold water 44 90 45 Hot water 91 97 88 The steel according to the invention has, in terms of quality, intermediate characteristics between those of a bright annealing type steel and a type 2B steel. After the formation of the THK sediments on the surfaces, it is necessary to clean with cold water and then with hot water. The quantities of cold water and hot water that are useful for cleaning sheet metal samples have been measured. The passage of cold water to hot water is carried out when visually the sediment does not already come off the surface. The consumption of water for cleaning surfaces, after contact with wine, is presented in tables 5 and 6.

Table 5: Consumption (m3 / m2) Steel according to the invention Finish 2R Finish 2B Red wine Cold water 2,2 2,6 3,0 Hot water 1, 8 2,0 2,7 Table 6: Consumption (m3 / m2) Steel according to the invention Finishing 2R Finishing 2B White wine Cold water 2,8 2,4 2,9 Hot water 1, 4 1, 7 1, 6 In the example of table 6, the white wine taken as a reference is very rich in polysaccharides, which generates very adherent stools. In the case of red wines, after cleaning with cold water and hot water, in all cases there are traces of coloring materials that are very visible to the naked eye. These coloring materials are red initially but blacken by oxidation with air. It is necessary to clean the surfaces with soda in order to ensure the cleaning of the surfaces of the tanks. The consumption of soda is given in table 7.

Table 7: Surfaces Steel according to the invention Finishing 2R Finishing 2B Consumption (l / m2) 220 410 320 With the steel sheet according to the invention, which comprises the surface condition which has been proposed, the treatment of the effluents is considerably limited. The whiteness and brightness of the surface of the steel sheet have been measured before and after use and cleaning in order to verify the aesthetic appearance and the conservation of the surface condition. Indeed, colorants may remain on the surface after cleaning. Table 8 indicates the brightness and whiteness that have been obtained before and after cleaning.

Table 8: Surfaces Steel according to Finishing 2R Finishing 2B the invention Before After Before After Before After Brightness 18.7 11, 4 43.7 28 6.2 4.2 Whiteness 74 66 75 61 73 73 On a surface with bright annealing of the prior art sheet, after contact with red wine and cleaning, the brightness and whiteness of the surface have been greatly modified. These variations are minor on the surface of the steel sheet according to the invention.

In the course of making the wines, the acetic bacteria adhering to the surface of the tub steel are the origin of the acescence.

These oxidize the alcohol to form acetic acid, of which a part is esterified to form ethyl acetate, this compound having a penetrating smell and a burning flavor for the wine-maker, noticeable even with a small concentration, which is therefore a loss of quality Of the wine. Measurements have been made of the adhesion of the acetic bacteria "Acetobacter aceti" on the surface of the steel sheet according to the invention and on a steel plate of the type of bright annealing 2R and of the type 2B taken as reference. After 8 days of contact of the plates with a white wine, at room temperature, a light microbial veil has formed on the surface. The surfaces rinsed with cold water and then dried have been metallized and analyzed in a scanning electron microscope. Adherent bacteria have been counted as shown in table 9, with adhesion expressed as the number of adherent cells per mm2.

Table 9: Surfaces Steel according to the invention Finishing 2R Finishing 2R Cells / mm2 1,985 4,327 2,204 The observation shows that the microorganisms adhere in piles on the surfaces of the sheet steel with reference bright annealing, the microgeometry of this surface allows the formation of the piles. Adherent microorganisms regroup thanks to lateral forces that interact between microorganisms. On the surface of the steel sheet according to the invention, the microorganisms adhere preferably to the level of the limit gaskets of the steel grains, which act as a trap for microorganisms. Furthermore, the microgeometry of the surface of the steel sheet according to the invention allows the release of these microorganisms and therefore improves the hygiene of the surfaces. The steel sheet according to the invention can also be used in dairy since the establishment of a biofilm on the steel surfaces is effected by the adhesion of microorganisms on the surfaces which in turn initiate the enmugrecimenti and the crunch in a milk medium . The steel sheet can also be used in the pharmaceutical industry or in a hospital environment, where the hygiene of the surfaces remains a major problem.

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.

Claims (6)

CR. ^ CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1 . Steel sheet can be used in the section of the cube and espaaaliraite in the sector of the wine cellar, cacacl z ria because the sheet is cold rolled and presenting a surface condition whose rugosity measured by AFM in areas of 100 μm per 100 μm, is defined by a Ra between 0.05 μm and 0.15 μm. Veneer according to claim 1, characterized in that the grain boundaries have a depth between 0.1 μm and 0.5 μm and preferably about 0.4 μm, and a width between 0.5 μm and 1.5 μm and preferably approximately 1.5 μm. Sheet metal according to claim 1, characterized in that the grains of the metal have, on the surface, an average diameter comprised between 5 μm and 20 μm. Four . Sheet metal according to claim 1, characterized in that the average amplitude of the surface of the grains, measured by AFM, is between 5 nm and 30 nm and is preferably approximately 10 nm. Process for producing the sheet according to claims 1 to 4, characterized in that in a stainless steel sheet having a surface of type 2B a cold rolling is carried out in such a way that the grains are flattened by pushing them towards the boundary joints of the sheet. the grains in such a way that said grain boundaries are closed, with the surface of the steel sheet presenting tight grain boundaries and shallow and very flattened grains without microroughness on the surface. Method according to claim 5, characterized in that the flattened shape of the grains is obtained by a final cold rolling such as a lamination of the "skin pass" type with a degree of reduction of less than 5%, preferably less than 4% .