Title of Invention	"A PROCESS FOR THE PREPARATION OF A FLUX TO REDUCE DROSS AND ASH GENERATION DURING HOT DIP GALVANIZING OF STEEL COMPONENTS AND INCREASE ZINC UTILIZATION FACTOR"
Abstract	The present invention relates to a novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and increase zinc utilization factor and a process for the utilization thereof. The flux claimed in the present process is developed in such a way that it forms a fusible stable composition on articles to be galvanized thus inhibiting the reaction of molten zinc with the steel surface. A controlled reaction of molten zinc with steel helps in reducing the by product generation. The present invention will be useful for the hot dip galvanizing of steel structures, sheets, pipes, nuts and bolts and similar other articles made of mild steel or low alloy steels.

Title of Invention

"A PROCESS FOR THE PREPARATION OF A FLUX TO REDUCE DROSS AND ASH GENERATION DURING HOT DIP GALVANIZING OF STEEL COMPONENTS AND INCREASE ZINC UTILIZATION FACTOR"

Abstract

The present invention relates to a novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and increase zinc utilization factor and a process for the utilization thereof. The flux claimed in the present process is developed in such a way that it forms a fusible stable composition on articles to be galvanized thus inhibiting the reaction of molten zinc with the steel surface. A controlled reaction of molten zinc with steel helps in reducing the by product generation. The present invention will be useful for the hot dip galvanizing of steel structures, sheets, pipes, nuts and bolts and similar other articles made of mild steel or low alloy steels.

Full Text	FIELD OF INVENTION The present invention relates to a novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and increase zinc utilization factor and a process for the utilization thereof. The present invention will be useful for the hot dip galvanizing of steel structures, sheets, pipes, nuts and bolts and similar other articles made of mild steel or low alloy steels. BACKGROUND OF INVENTION Hot dip galvanizing (HDG) of steels is a well known process where a thin layer of zinc coating is deposited on substrate. The HDG is carried out either by batch or continuation operations. The articles to be galvanized are degreased, pickled, rinsed, fluxed (batch galvanizing) or passed through reducing atmosphere at elevated temperature and dipped in molten zinc. During the dipping in molten zinc (normally, the temperature of zinc bath is maintained at 450 ±10°C, the steel reacts with molten zinc to form coating. The steel dissolved into zinc bath combines with zinc atoms to form zinc dross, a zinc compound with molecular formula FeZn13 and referred as zeta phase. The dross contains about 95 to 96% zinc and rest iron. In continuous galvanizing lines where zinc baths contain aluminium, the top dross in addition to the bottom dross is also formed. The bottom dross in both types of galvanizing have identical composition but the top dross is formed by Fe3AI(Zn). In addition to drosses, ash is also formed on the surface of zinc bath. The ash mainly comprises of zinc/iron/chloride/oxygen compounds. In addition to these, shinning are also formed which are mainly zinc oxide and zinc chlorides. The dross, ash and skimming taken together are termed as by product in galvanizing industries. The formation of by products in galvanizing process is inevitable. However, their excess generation adversely affects the economy of the galvanizing industries. Substantial amount of zinc is lost as by-products thus bringing down the utilization factor of zinc. In general, it is reported that about 30 to 35% of total zinc used in galvanizing is wasted as by-products. Most of the available fluxes are based on a mixture of zinc chloride and ammonium chloride with certain additives and claim to provide benefits on different aspects of galvanizing. However, none of them specifically claim the reductions in by product generation and enhanced zinc utilization factors during the process of galvanizing. In addition to this they are not known to provide uniformity in coating, improved inter-metallic layers and corrosion resistance. The formation of inter-metallic layers (IML) during hot dip galvanizing (HDG) of steels is inevitable. Its thickness and nature is controlled by different factors such as the alloying elements present in steel and molten zinc, temperature of the molten zinc bath, and cooling rate of coating and retention time of steel articles in molten zinc bath. In normal galvanizing processes performed at 450 °C, IML comprises of four types of layers. The gamma (┌) layer forms near to the steel substrate followed by delta (δ), zeta (ζ) and eta (η) layers. These layers consist of inter-metallic iron and zinc compounds having well defined crystallographic structures. The gamma layer consists of Fe3Zni0 compound having iron in the range of 21-28%. The layer next to it is delta with7-12% iron. The third layer is zeta (ζ) with iron in the range of 5 -6% and the top layer is eta (η), deposited as iron saturated (0.047%) zinc. The presence of these IML provides good adhesion of HDG with the substrate steel but is associated with greater hardness and brittleness. These result in proneness of coatings to cracking. It is therefore, desirable that the thickness of IML should be as minimum as possible. Out of the above 3 IML, the delta layer possesses the highest hardness and brittleness. This layer is reported to have precracks and under the influence of corrosive environments and tensile loading, the cracks propagate and may cause pre-mature failures of structures. Further, due to the presence of different phases in HDG with varying degree of thermodynamic stabilities, they form very potent galvanic couples in corrosive environments since the corrosion potential of IML in normal environments are always below the potential of hydrogen evolution reactions ( Many techniques have been suggested to minimise the formation of IML during hot dip galvanizing. The most widely studied and practiced is the addition of aluminium in zinc baths. This forms Fe2AI5 (Zn) inhibition layer on steels and is very effective in control of IML. This layer provides an incubation time for attack of molten zinc on steel and slows down the Fe-Zn phase formation. In addition to this, Ni is also added in molten zinc baths, which is mainly used to control Hyper Sandelin effects in reactive steels. The presence of phosphorous in steel is reported to affect only gamma phases where as zeta and delta phases remain unaffected. All the above-described techniques to control IML are feasible only in case of continuous and flux less galvanizing lines. In case of batch galvanizing, there is no escape for use of flux to have good and defect free galvanizing. Most of the fluxes used in batch type galvanizing industries are based on zinc ammonium chloride with different additives. The addition of aluminium in batch galvanizing baths makes the fluxes in effective due to their reaction with aluminium forming volatile aluminium chloride. As a consequence of this, many complications such as appearance of uncoated surfaces, non-uniform coatings etc arise on galvanized products. Similarly, addition of Ni in the bath increases by-products (ash, dross etc.) generation. The most viable and economical option, therefore, left out is to change the flux composition. It is reported that the addition of salts of Ni, Cd, and Sn in flux bath affects the growth of IML and morphology of the coating . These studies suggest that the composition of fluxes affect the kinetics and mechanism of iron - zinc reactions in the galvanizing baths. Literature searches showed that very limited studies have been performed on this aspect. If this approach i.e. modification of IML and coating morphologies by changing the composition of flux is feasible, it will open new areas and tremendous scope for getting better quality coating. The changes in flux characteristics may modify the intermetallic layers and entire characteristics of hot dip galvanized coating. Review of the patent literature provide no such claims where the a specific flux composition reduces by product generation as well as improves the quality of coating. A patent by ABBEY, A. (Dewey & Almy Chemical Co.). July 27, 1943, No. 12240. [Class 82 (ii)] for example, claims a fusible composition of flux for covering molten zinc . However, no information is provided on the impact of this flux on reduction ofby product generation and quality of the coating. Similarly the patent No GB432746 also covers the composition of a flux comprising of ammonium chloride,zinc chloride and one or more surface active reducing agent. It is claimed that the said flux forms a stable froth on the surface of galvanizing bath and reduces the air pollution. The patent No GB203397 also claims the reduction in air pollution. Patent No US4911764 claims a chloride based galvanising flux containing at least zine chloride, ammonium chloride and a rare earth chloride. It is claimed that the said flux forms a stable foam on galvanizing bath and effectively reduces the air pollution. Thus, all the above review of patents clearly demonstrate that non of the published patents claim reduction in by product generation and improved zinc utilization factor. They also do not cover the claims related to the improved quality of the galvanized coating. A flux composition having these mentioned qualities , therefore, is the need of the hour and very much required by the industries. OBJECTS OF THE INVENTION The main object of the present invention is thus to provide a flux composition to reduce dross and ash generation during hot dip galvanizing of steel components. Another object of the present invention is to increase zinc utilization factor during hot dip galvanizing of steel components. Still another object of the present invention is to provide a process for the preparation of a flux to reduce dross and ash generation during hot dip galvanizing of steel components and increase zinc utilization factor to modify the intermetallic layer making the zinc coating more ductile. Yet another object of the present invention is to provide a process to produce galvanized coatings of improved corrosion resistance. Yet another object of the present invention is to provide a process to produce galvanized coatings with improved uniformity on steel components. SUMMARY OF THE INVENTION Accordingly, the present invention provides a novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and to increase zinc utilization factor, wherein the said composition comprises: (a) zinc chloride in the range of 45-75% by weight; (b) ammonium chloride in the range of 25-55% by weight; (c) a surface active agent in the concentration range of 0.1 to 1.0% by weight; (d) a nickel based salt having nickel as cationic group attached with anionic groups selected from the group consisting of halides of nickel, nickel sulphate, nickel acetate, nickel formate, nickel nitrate, nickel stearate and nickel oleate, either in combined or independent form in the concentration range of 0.5 to 12% by weight; (e) optionally along with sodium tetraborate decahydrate in the range of 0.25 to 3.5% by weight and/or non-ionic polyacrylamide in the concentration range of 0.025 to 2.5% by weight. In an embodiment of the invention, the surface active agent is a non ionic agent, preferably alkyl phenol ethoxylate. In another embodiment of the invention, the non-ionic polyacrylamide is preferably in the range of 0.05 to 0.5% by weight. In still another embodiment of the invention, the said composition has the specific gravity in the range of 1.15 to 1.20. In yet another embodiment of the present invention is provided a process for the reduction of dross and ash generation during hot dip galvanizing of steel components and to increase zinc utilization factor, utilizing the said flux composition wherein, the said process comprising the steps of: (i) pretreating the steel sample by pickling it in 10-15% hydrochloric acid solution blended with hexamine inhibitor to remove oxide layers followed by cooling to room temperature; (ii) dipping the cooled sample as obtained in step (i) in 5-10% hydrochloric acid for a period ranging between 5-10 seconds followed by rinsing in running tap water; (iii) dipping the rinsed sample as obtained in step (ii) in the composition as claimed in claim 1 for a period ranging between 20-40 seconds followed by drying while maintaining the temperature in the range of 70 to 80°C; (iv) dipping the dried sample as obtained in step (iii) in galvanizing bath having pure zinc maintained at a temperature in the range of 420-470°C for a period of 20-30 seconds; (v) quenching the sample as obtained in step (iv) in cold water followed by drying. In still another embodiment of the invention, the test sample is preferably taken from steel coupons. DETAILED DESCRIPTION OF THE INVENTION Most of fluxes available are based on a mixture of zinc chloride and ammonium chloride with certain additives and claim to provide benefits on different aspects of galvanizing. However, none of them specifically claim the reductions in by product generation and enhanced zinc utilization factors during the process of galvanizing. In addition to this they are not claimed to provide uniformity in coating, improved inter-metallic layers and corrosion resistance. The flux claimed in the present process is developed in such a way that it forms a fusible stable composition on articles to be galvanized thus inhibiting the reaction of molten zinc with the steel surface. A controlled reaction of molten zinc with steel helps in reducing the by product generations (dross and ash which are respectively a reaction product of zinc and iron and zinc/iron/chloride and oxygen). This controlled reaction also helps in the development of zinc/iron alloy layer at the coating interface with improved microstructure ( fine structure of layers formed in contrast to the coarser structures formed in case of conventional fluxes ) thus resulting in an enhanced resistance to corrosion. The effective surface active agent added in the flux reduces the surface tension of solution of flux and helps in uniform spreading of the flux over entire article to be galvanized. The proportions of ammonium chloride, zinc chloride, surface active agent and film former are such as to give an initial fusing point below that of molten zinc and maintain the fluidity and stability of the molten flux at the galvanizing temperature. In the process of the present invention mild steel coupons in the form of tubes of 10 cm length, 2cm outer dia and 1.8 cm inner dia were pickled in 15% hydrochloric acid solution blended with hexamine inhibitor to remove oxide layers. These samples were cooled to room temperature and weighted to 3rd place of decimal of gram on an electronic balance. The above samples after dipping in 5% hydrochloric acid for 5-10 seconds were rinsed in running tap water and then dipped in flux composition - A,B,C and D separately, and dried in oven maintained at 70-80°C. The samples as prepared above were dipped in galvanizing bath having pure zinc maintained at temperature of 460 °C for 30 seconds, removed from the bath,quenched and dried. The difference of final weight minus initial weight provided the coating weight for the specimens. The following examples are given by way of illustration and therefore should not be construed to limit the scope of this invention. EXAMPLE 1 Preparation of flux compositions: 1. Flux composition A: 70 % of zinc chloride was dissolved in 100ml plain water. To this, 25 % of ammonium chloride was added. Alkyl phenol ethoxylate (0.5%) was added as a surface active agent to the above solution. To the solution prepared 2.5% of Nickel chloride + 2.00 % Nickel acetate was blended to obtain composition A. 2. Flux composition B: 57.50 % of zinc chloride was dissolved in 100ml plain water. To this, 34.50 % of ammonium chloride was added. Alkyl phenol ethoxylate (0.25%) was added as a surface active agent to the above solution. To the solution prepared 1.75% of Nickel chloride + 2.50 % Nickel acetate and 3.5 % sodium tetraborate deca hydrate was blended to obtain composition B. 3. Flux composition C: 50.00 % of zinc chloride was dissolved in 100ml plain water. To this, 40.50 % of ammonium chloride was added. Alkyl phenol ethoxylate (0.15%) was added as a surface active agent to the above solution. To the solution prepared 1.85% of Nickel chloride + 2.50 % Nickel acetate and 4.95 % sodium tetraborate deca hydrate was blended. To this solution, non ionic polyacrylamide (0.05 %) was added to obtain composition C. 4. Flux composition D (reference): This composition was prepared by dissolving 45 % of zinc chloride in 100ml water and then blending of 55 % ammonium chloride. The prepared solution was used as the reference flux for comparison of performance of other fluxes. EXAMPLE 2 The above compositions A-C and the reference composition D were prepared with specific gravity of 1.20 and temperature maintained at 75 °C. Mild steel coupons in the form of tubes of 10 cm length, 2cm outer diameter and 1.8 cm inner diameter were pickled in 15% hydrochloric acid solution blended with 0.25 % of hexamine inhibitor to remove oxide layers. These samples were cooled to room temperature and weighted to 3rd place of decimal of gram on an electronic balance. The above samples after dipping in 5% hydrochloric acid for 5-10 seconds were rinsed in running tap water and then dipped in flux compositions A, B, C and D as stated above at (1) to (4) separately for 30 seconds and dried in oven maintained at 80°C. Said samples were then dipped in galvanizing bath having pure zinc maintained at temperature of 460 °C for 30 seconds, removed from the bath, quenched in cold water ( Temperature of water was 32 °C ) and dried at room temperature. The difference of final weight minus initial weight provided the coating weight for the specimens. EXAMPLE 3 This example illustrates the performance of the flux compositions A-C and reference flux D on coating weight received by the samples during the hot dip galvanizing. Table I shows coating weight deposited on plate samples fluxed in flux compositions A, B & C and reference flux D. (Table Removed) It is seen from the above table that the coating weight is lower in case of the steel articles fluxed in the developed flux compositions vis-a-vis reference flux. In addition to this the surface of galvanized coating was brighter in the case of developed fluxes A-C in comparison to reference flux D. EXAMPLE 4 This example illustrates the performance of the fluxes compositions A-C and reference flux on dissolution rate of the steel in galvanizing bath during the hot dip galvanizing. This was performed by dissolving the galvanized tube samples as mentioned in Table 1, in 5% (w/v) sulphuric acid blended with 0.2% o-toluidine + 0.2 %, sodium arsenide at 30 + 2°C until the reaction completely ceased. They were then removed from the solution, cleaned with soft brush, rinsed in tap water, dried and weighted on an electronic balance. The weight of samples before coating minus the weight taken after their dissolution in acid solution provided the steel dissolved in zinc bath. Table II shows steel dissolved in zinc bath from the samples fluxed in compositions A, B & C and reference flux D. (Table Removed) It is seen from the above table that the dissolution of steel in molten zinc is lower for steel articles fluxed in the developed flux compositions A-C vis-a-vis reference flux composition D and the lowest in flux composition having all the components in the claimed ranges (composition C). This dissolution rate directly influences the dross and ash generations. The efficacy of the flux was established in plant scale trial of the claimed flux as illustrated in the example 5 below. EXAMPLE 5 The flux composition C was used in a galvanizing bath producing tubes of different diameters ranging between 15 mm to 150 mm. The dross and ash generation in the bath were monitored for 4 months. The Data on dross and ash generation in galvanizing bath before and after use of flux are summarized in table III. (Table Removed) It is seen from the above table that the dross and ash generations have started coming down from the first month of use of the developed flux. After 2-3 months of continuous use, the dross and ash generation rate have become constant owing to the stabilization of the flux bath. It is further seen from the table that stabilized data of ash and dross generation rates are considerably lower in comparison to the data generated during the use of Reference flux. EXAMPLE 6 This example gives the Vicker hardness of different intermetallic layers formed during hot dip galvanizing using various compositions of flux. In this example the steel samples to be galvanized were fluxed in compositions 1-3 and reference flux as stated above . After coating the specimens, their cross section were polished and etched in NITAL etching solution to reveal different intermetallic layers namely ζ ( Zeta ) and n, (Eta ). The results are summarized as follows: (Table Removed) __ _ It is evident from the above table that the hardness of different layers of the coating is significantly affected with the developed compositions A-C of the flux in comparison to the reference flux. The most soft and ductile coating is produced when the steel article is galvanized by pre-fluxing in flux composition having all the components in desired concentrations as claimed in this invention. EXAMPLE 7 Effect of temperature of galvanizing bath on performance of fluxes: Table V: Coating weight deposited on samples fluxed in flux compositions A, B &C and reference flux D and dipped in galvianizing bath for 30 seconds, molten zinc bath maintained at different temperatures. (Table Removed) Thus, it is seen from the above table that flux compositions detailed at A-C provide lower coatings and brighter surfaces in comparison to reference flux composition No D, in the range of galvanizing temperatures of 430 to 550 °C. EXAMPLE 8 Effect of dipping time of samples in galvanizing bath on performance of fluxes: Table VI: Coating weight deposited on samples fluxed in flux compositions A,B & C and reference flux D and dipped in galvanizing bath for different time , molten zinc bath maintained at460°C. (Table Removed) Thus, it is seen from the above table that flux compositions detailed at A-C provide lower coatings and brighter surfaces in comparison to reference flux composition No D, in the range of galvanizing time of 20 seconds to 120 seconds. ADVANTAGES OF THE INVENTION • The use of developed flux reduces the generation of dross and ash during hot dip galvanizing, • 2.The produced coating is more resistant to corrosion than the conventional produced coating • The produced coating using developed flux is more ductile than the coating produced by using reference flux. We claim: 1. A novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and to increase zinc utilization factor, wherein the said composition comprises: [a] zinc chloride in the concentration range of 45-75% by weight; [b] ammonium chloride in the concentration range of 25-55% by weight; [c] a surface active agent in the concentration range of 0.1 to 1.0% by weight; [d] a nickel based salt having nickel as cationic group attached with anionic groups selected from the group consisting of halides of nickel, nickel sulphate, nickel acetate, nickel formate, nickel nitrate, nickel stearate and nickel oleate, either in combined or independent form in the concentration range of 0.5 to 12% by weight; [e] optionally along with sodium tetraborate decahydrate in the concentration range of 0.25 to 3.5% by weight and/or non-ionic polyacrylamide in the concentration range of 0.025 to 2.5% by weight. 2. A composition as claimed in claim 1, wherein the surface active agent is a non ionic agent, preferably alkyl phenol ethoxylate. 3. A composition as claimed in claim 1, wherein the non-ionic polyacrylamide is preferably in the range of 0.05 to 0.5% by weight. 4. A composition as claimed in claim 1, wherein the said composition has the specific gravity in the range of 1.15 to 1.20. 5. A process for the reduction of dross and ash generation during hot dip galvanizing of steel components and to increase zinc utilization factor, utilizing the composition as claimed in claim 1, the said process comprising the steps of: (i) pretreating the steel sample by pickling it in 10-15% hydrochloric acid solution blended with hexamine inhibitor to remove oxide layers followed by cooling to room temperature; (ii) dipping the cooled sample as obtained in step (i) in 5-10% hydrochloric acid for a period ranging between 5-10 seconds followed by rinsing in running tap water; (iii) dipping the rinsed sample as obtained in step (ii) in the composition as claimed in claim 1 for a period ranging between 20-40 seconds followed by drying while maintaining the temperature in the range of 70 to 80°C; (iv) dipping the dried sample as obtained in step (iii) in galvanizing bath having pure zinc maintained at a temperature in the range of 420-470°C for a period of 20-30 seconds; (v) quenching the sample as obtained in step (iv) in cold water followed by drying. 6. A novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and a process for the preparation thereof, substantially as herein described with reference to the examples accompanying the specification.

Full Text

FIELD OF INVENTION
The present invention relates to a novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and increase zinc utilization factor and a process for the utilization thereof. The present invention will be useful for the hot dip galvanizing of steel structures, sheets, pipes, nuts and bolts and similar other articles made of mild steel or low alloy steels.
BACKGROUND OF INVENTION
Hot dip galvanizing (HDG) of steels is a well known process where a thin layer of zinc coating is deposited on substrate. The HDG is carried out either by batch or continuation operations. The articles to be galvanized are degreased, pickled, rinsed, fluxed (batch galvanizing) or passed through reducing atmosphere at elevated temperature and dipped in molten zinc. During the dipping in molten zinc (normally, the temperature of zinc bath is maintained at 450 ±10°C, the steel reacts with molten zinc to form coating. The steel dissolved into zinc bath combines with zinc atoms to form zinc dross, a zinc compound with molecular formula FeZn13 and referred as zeta phase. The dross contains about 95 to 96% zinc and rest iron. In continuous galvanizing lines where zinc baths contain aluminium, the top dross in addition to the bottom dross is also formed. The bottom dross in both types of galvanizing have identical composition but the top dross is formed by Fe3AI(Zn).
In addition to drosses, ash is also formed on the surface of zinc bath. The ash mainly comprises of zinc/iron/chloride/oxygen compounds. In addition to these, shinning are also formed which are mainly zinc oxide and zinc chlorides. The dross, ash and skimming taken together are termed as by product in galvanizing industries.
The formation of by products in galvanizing process is inevitable. However, their excess generation adversely affects the economy of the galvanizing industries. Substantial amount of zinc is lost as by-products thus bringing down the utilization factor of zinc. In

general, it is reported that about 30 to 35% of total zinc used in galvanizing is wasted as by-products.
Most of the available fluxes are based on a mixture of zinc chloride and ammonium chloride with certain additives and claim to provide benefits on different aspects of galvanizing. However, none of them specifically claim the reductions in by product generation and enhanced zinc utilization factors during the process of galvanizing. In addition to this they are not known to provide uniformity in coating, improved inter-metallic layers and corrosion resistance.
The formation of inter-metallic layers (IML) during hot dip galvanizing (HDG) of steels is inevitable. Its thickness and nature is controlled by different factors such as the alloying elements present in steel and molten zinc, temperature of the molten zinc bath, and cooling rate of coating and retention time of steel articles in molten zinc bath. In normal galvanizing processes performed at 450 °C, IML comprises of four types of layers. The gamma (┌) layer forms near to the steel substrate followed by delta (δ), zeta (ζ) and eta (η) layers. These layers consist of inter-metallic iron and zinc compounds having well defined crystallographic structures. The gamma layer consists of Fe3Zni0 compound having iron in the range of 21-28%. The layer next to it is delta with7-12% iron. The third layer is zeta (ζ) with iron in the range of 5 -6% and the top layer is eta (η), deposited as iron saturated (0.047%) zinc. The presence of these IML provides good adhesion of HDG with the substrate steel but is associated with greater hardness and brittleness. These result in proneness of coatings to cracking. It is therefore, desirable that the thickness of IML should be as minimum as possible.
Out of the above 3 IML, the delta layer possesses the highest hardness and brittleness. This layer is reported to have precracks and under the influence of corrosive environments and tensile loading, the cracks propagate and may cause pre-mature failures of structures. Further, due to the presence of different phases in HDG with

varying degree of thermodynamic stabilities, they form very potent galvanic couples in corrosive environments since the corrosion potential of IML in normal environments are always below the potential of hydrogen evolution reactions ( Many techniques have been suggested to minimise the formation of IML during hot dip galvanizing. The most widely studied and practiced is the addition of aluminium in zinc baths. This forms Fe2AI5 (Zn) inhibition layer on steels and is very effective in control of IML. This layer provides an incubation time for attack of molten zinc on steel and slows down the Fe-Zn phase formation. In addition to this, Ni is also added in molten zinc baths, which is mainly used to control Hyper Sandelin effects in reactive steels. The presence of phosphorous in steel is reported to affect only gamma phases where as zeta and delta phases remain unaffected.
All the above-described techniques to control IML are feasible only in case of continuous and flux less galvanizing lines. In case of batch galvanizing, there is no escape for use of flux to have good and defect free galvanizing. Most of the fluxes used in batch type galvanizing industries are based on zinc ammonium chloride with different additives.
The addition of aluminium in batch galvanizing baths makes the fluxes in effective due to their reaction with aluminium forming volatile aluminium chloride. As a consequence of this, many complications such as appearance of uncoated surfaces, non-uniform coatings etc arise on galvanized products. Similarly, addition of Ni in the bath increases by-products (ash, dross etc.) generation. The most viable and economical option, therefore, left out is to change the flux composition. It is reported that the addition of salts of Ni, Cd, and Sn in flux bath affects the growth of IML and morphology of the coating . These studies suggest that the composition of fluxes affect the kinetics and

mechanism of iron - zinc reactions in the galvanizing baths. Literature searches showed that very limited studies have been performed on this aspect. If this approach i.e. modification of IML and coating morphologies by changing the composition of flux is feasible, it will open new areas and tremendous scope for getting better quality coating. The changes in flux characteristics may modify the intermetallic layers and entire characteristics of hot dip galvanized coating.
Review of the patent literature provide no such claims where the a specific flux composition reduces by product generation as well as improves the quality of coating. A patent by ABBEY, A. (Dewey & Almy Chemical Co.). July 27, 1943, No. 12240. [Class 82 (ii)] for example, claims a fusible composition of flux for covering molten zinc . However, no information is provided on the impact of this flux on reduction ofby product generation and quality of the coating. Similarly the patent No GB432746 also covers the composition of a flux comprising of ammonium chloride,zinc chloride and one or more surface active reducing agent. It is claimed that the said flux forms a stable froth on the surface of galvanizing bath and reduces the air pollution. The patent No GB203397 also claims the reduction in air pollution. Patent No US4911764 claims a chloride based galvanising flux containing at least zine chloride, ammonium chloride and a rare earth chloride. It is claimed that the said flux forms a stable foam on galvanizing bath and effectively reduces the air pollution.
Thus, all the above review of patents clearly demonstrate that non of the published patents claim reduction in by product generation and improved zinc utilization factor. They also do not cover the claims related to the improved quality of the galvanized coating. A flux composition having these mentioned qualities , therefore, is the need of the hour and very much required by the industries.

OBJECTS OF THE INVENTION
The main object of the present invention is thus to provide a flux composition to reduce
dross and ash generation during hot dip galvanizing of steel components.
Another object of the present invention is to increase zinc utilization factor during hot
dip galvanizing of steel components.
Still another object of the present invention is to provide a process for the preparation
of a flux to reduce dross and ash generation during hot dip galvanizing of steel
components and increase zinc utilization factor to modify the intermetallic layer making
the zinc coating more ductile.
Yet another object of the present invention is to provide a process to produce
galvanized coatings of improved corrosion resistance.
Yet another object of the present invention is to provide a process to produce
galvanized coatings with improved uniformity on steel components.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a novel flux composition to reduce dross and ash generation during hot dip galvanizing of steel components and to increase zinc utilization factor, wherein the said composition comprises:
(a) zinc chloride in the range of 45-75% by weight;
(b) ammonium chloride in the range of 25-55% by weight;
(c) a surface active agent in the concentration range of 0.1 to 1.0% by weight;
(d) a nickel based salt having nickel as cationic group attached with anionic groups selected from the group consisting of halides of nickel, nickel sulphate, nickel acetate, nickel formate, nickel nitrate, nickel stearate and nickel oleate, either in combined or independent form in the concentration range of 0.5 to 12% by weight;
(e) optionally along with sodium tetraborate decahydrate in the range of 0.25 to 3.5% by weight and/or non-ionic polyacrylamide in the concentration range of 0.025 to 2.5% by weight.

In an embodiment of the invention, the surface active agent is a non ionic agent, preferably alkyl phenol ethoxylate.
In another embodiment of the invention, the non-ionic polyacrylamide is preferably in the range of 0.05 to 0.5% by weight.
In still another embodiment of the invention, the said composition has the specific gravity in the range of 1.15 to 1.20.
In yet another embodiment of the present invention is provided a process for the reduction of dross and ash generation during hot dip galvanizing of steel components and to increase zinc utilization factor, utilizing the said flux composition wherein, the said process comprising the steps of:
(i) pretreating the steel sample by pickling it in 10-15% hydrochloric acid solution blended with hexamine inhibitor to remove oxide layers followed by cooling to room temperature; (ii) dipping the cooled sample as obtained in step (i) in 5-10% hydrochloric acid for a period ranging between 5-10 seconds followed by rinsing in running tap water; (iii) dipping the rinsed sample as obtained in step (ii) in the composition as claimed in claim 1 for a period ranging between 20-40 seconds followed by drying while maintaining the temperature in the range of 70 to 80°C; (iv) dipping the dried sample as obtained in step (iii) in galvanizing bath having pure zinc maintained at a temperature in the range of 420-470°C for a period of 20-30 seconds; (v) quenching the sample as obtained in step (iv) in cold water followed by drying. In still another embodiment of the invention, the test sample is preferably taken from steel coupons.

DETAILED DESCRIPTION OF THE INVENTION
Most of fluxes available are based on a mixture of zinc chloride and ammonium chloride with certain additives and claim to provide benefits on different aspects of galvanizing. However, none of them specifically claim the reductions in by product generation and enhanced zinc utilization factors during the process of galvanizing. In addition to this they are not claimed to provide uniformity in coating, improved inter-metallic layers and corrosion resistance.
The flux claimed in the present process is developed in such a way that it forms a fusible stable composition on articles to be galvanized thus inhibiting the reaction of molten zinc with the steel surface. A controlled reaction of molten zinc with steel helps in reducing the by product generations (dross and ash which are respectively a reaction product of zinc and iron and zinc/iron/chloride and oxygen). This controlled reaction also helps in the development of zinc/iron alloy layer at the coating interface with improved microstructure ( fine structure of layers formed in contrast to the coarser structures formed in case of conventional fluxes ) thus resulting in an enhanced resistance to corrosion. The effective surface active agent added in the flux reduces the surface tension of solution of flux and helps in uniform spreading of the flux over entire article to be galvanized. The proportions of ammonium chloride, zinc chloride, surface active agent and film former are such as to give an initial fusing point below that of molten zinc and maintain the fluidity and stability of the molten flux at the galvanizing temperature.
In the process of the present invention mild steel coupons in the form of tubes of 10 cm length, 2cm outer dia and 1.8 cm inner dia were pickled in 15% hydrochloric acid solution blended with hexamine inhibitor to remove oxide layers. These samples were cooled to room temperature and weighted to 3rd place of decimal of gram on an electronic balance. The above samples after dipping in 5% hydrochloric acid for 5-10 seconds were rinsed in running tap water and then dipped in flux composition - A,B,C

and D separately, and dried in oven maintained at 70-80°C. The samples as prepared above were dipped in galvanizing bath having pure zinc maintained at temperature of 460 °C for 30 seconds, removed from the bath,quenched and dried. The difference of final weight minus initial weight provided the coating weight for the specimens.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of this invention.
EXAMPLE 1
Preparation of flux compositions:
1. Flux composition A: 70 % of zinc chloride was dissolved in 100ml plain water. To this, 25 % of ammonium chloride was added. Alkyl phenol ethoxylate (0.5%) was added as a surface active agent to the above solution. To the solution prepared 2.5% of Nickel chloride + 2.00 % Nickel acetate was blended to obtain composition A.
2. Flux composition B: 57.50 % of zinc chloride was dissolved in 100ml plain water. To this, 34.50 % of ammonium chloride was added. Alkyl phenol ethoxylate (0.25%) was added as a surface active agent to the above solution. To the solution prepared 1.75% of Nickel chloride + 2.50 % Nickel acetate and 3.5 % sodium tetraborate deca hydrate was blended to obtain composition B.
3. Flux composition C: 50.00 % of zinc chloride was dissolved in 100ml plain water. To this, 40.50 % of ammonium chloride was added. Alkyl phenol ethoxylate (0.15%) was added as a surface active agent to the above solution. To the solution prepared 1.85% of Nickel chloride + 2.50 % Nickel acetate and 4.95 % sodium tetraborate deca hydrate was blended. To this solution, non ionic polyacrylamide (0.05 %) was added to obtain composition C.
4. Flux composition D (reference): This composition was prepared by dissolving 45 % of zinc chloride in 100ml water and then blending of 55 % ammonium

chloride. The prepared solution was used as the reference flux for comparison of performance of other fluxes.
EXAMPLE 2
The above compositions A-C and the reference composition D were prepared with specific gravity of 1.20 and temperature maintained at 75 °C. Mild steel coupons in the form of tubes of 10 cm length, 2cm outer diameter and 1.8 cm inner diameter were pickled in 15% hydrochloric acid solution blended with 0.25 % of hexamine inhibitor to remove oxide layers. These samples were cooled to room temperature and weighted to 3rd place of decimal of gram on an electronic balance.
The above samples after dipping in 5% hydrochloric acid for 5-10 seconds were rinsed in running tap water and then dipped in flux compositions A, B, C and D as stated above at (1) to (4) separately for 30 seconds and dried in oven maintained at 80°C. Said samples were then dipped in galvanizing bath having pure zinc maintained at temperature of 460 °C for 30 seconds, removed from the bath, quenched in cold water ( Temperature of water was 32 °C ) and dried at room temperature. The difference of final weight minus initial weight provided the coating weight for the specimens.
EXAMPLE 3
This example illustrates the performance of the flux compositions A-C and reference flux D on coating weight received by the samples during the hot dip galvanizing. Table I shows coating weight deposited on plate samples fluxed in flux compositions A, B & C and reference flux D.

(Table Removed)
It is seen from the above table that the coating weight is lower in case of the steel articles fluxed in the developed flux compositions vis-a-vis reference flux. In addition to

this the surface of galvanized coating was brighter in the case of developed fluxes A-C in comparison to reference flux D.
EXAMPLE 4
This example illustrates the performance of the fluxes compositions A-C and reference flux on dissolution rate of the steel in galvanizing bath during the hot dip galvanizing. This was performed by dissolving the galvanized tube samples as mentioned in Table 1, in 5% (w/v) sulphuric acid blended with 0.2% o-toluidine + 0.2 %, sodium arsenide at 30 + 2°C until the reaction completely ceased. They were then removed from the solution, cleaned with soft brush, rinsed in tap water, dried and weighted on an electronic balance. The weight of samples before coating minus the weight taken after their dissolution in acid solution provided the steel dissolved in zinc bath. Table II shows steel dissolved in zinc bath from the samples fluxed in compositions A, B & C and reference flux D.

(Table Removed)
It is seen from the above table that the dissolution of steel in molten zinc is lower for steel articles fluxed in the developed flux compositions A-C vis-a-vis reference flux composition D and the lowest in flux composition having all the components in the claimed ranges (composition C). This dissolution rate directly influences the dross and ash generations. The efficacy of the flux was established in plant scale trial of the claimed flux as illustrated in the example 5 below.

EXAMPLE 5
The flux composition C was used in a galvanizing bath producing tubes of different diameters ranging between 15 mm to 150 mm. The dross and ash generation in the bath were monitored for 4 months. The Data on dross and ash generation in galvanizing bath before and after use of flux are summarized in table III.
(Table Removed)

It is seen from the above table that the dross and ash generations have started coming down from the first month of use of the developed flux. After 2-3 months of continuous use, the dross and ash generation rate have become constant owing to the stabilization of the flux bath. It is further seen from the table that stabilized data of ash and dross generation rates are considerably lower in comparison to the data generated during the use of Reference flux.
EXAMPLE 6
This example gives the Vicker hardness of different intermetallic layers formed during hot dip galvanizing using various compositions of flux. In this example the steel samples to be galvanized were fluxed in compositions 1-3 and reference flux as stated above . After coating the specimens, their cross section were polished and etched in NITAL etching solution to reveal different intermetallic layers namely ζ ( Zeta ) and n, (Eta ). The results are summarized as follows:
(Table Removed)

__ _
It is evident from the above table that the hardness of different layers of the coating is significantly affected with the developed compositions A-C of the flux in comparison to the reference flux. The most soft and ductile coating is produced when the steel article is galvanized by pre-fluxing in flux composition having all the components in desired concentrations as claimed in this invention.
EXAMPLE 7
Effect of temperature of galvanizing bath on performance of fluxes: Table V: Coating weight deposited on samples fluxed in flux compositions A, B &C and reference flux D and dipped in galvianizing bath for 30 seconds, molten zinc bath maintained at different temperatures.

(Table Removed)

Thus, it is seen from the above table that flux compositions detailed at A-C provide lower coatings and brighter surfaces in comparison to reference flux composition No D, in the range of galvanizing temperatures of 430 to 550 °C.
EXAMPLE 8
Effect of dipping time of samples in galvanizing bath on performance of fluxes:

Table VI: Coating weight deposited on samples fluxed in flux compositions A,B & C and reference flux D and dipped in galvanizing bath for different time , molten zinc bath maintained at460°C.
(Table Removed)

Thus, it is seen from the above table that flux compositions detailed at A-C provide lower coatings and brighter surfaces in comparison to reference flux composition No D, in the range of galvanizing time of 20 seconds to 120 seconds.
ADVANTAGES OF THE INVENTION
• The use of developed flux reduces the generation of dross and ash during hot dip galvanizing,
• 2.The produced coating is more resistant to corrosion than the conventional produced coating
• The produced coating using developed flux is more ductile than the coating produced by using reference flux.

We claim:
1. A novel flux composition to reduce dross and ash generation during hot dip galvanizing
of steel components and to increase zinc utilization factor, wherein the said composition comprises:
[a] zinc chloride in the concentration range of 45-75% by weight;
[b] ammonium chloride in the concentration range of 25-55% by weight;
[c] a surface active agent in the concentration range of 0.1 to 1.0% by weight;
[d] a nickel based salt having nickel as cationic group attached with anionic groups selected from the group consisting of halides of nickel, nickel sulphate, nickel acetate, nickel formate, nickel nitrate, nickel stearate and nickel oleate, either in combined or independent form in the concentration range of 0.5 to 12% by weight;
[e] optionally along with sodium tetraborate decahydrate in the concentration range of 0.25 to 3.5% by weight and/or non-ionic polyacrylamide in the concentration range of 0.025 to 2.5% by weight.

2. A composition as claimed in claim 1, wherein the surface active agent is a non ionic agent, preferably alkyl phenol ethoxylate.
3. A composition as claimed in claim 1, wherein the non-ionic polyacrylamide is preferably in the range of 0.05 to 0.5% by weight.
4. A composition as claimed in claim 1, wherein the said composition has the specific gravity in the range of 1.15 to 1.20.
5. A process for the reduction of dross and ash generation during hot dip galvanizing of
steel components and to increase zinc utilization factor, utilizing the composition as
claimed in claim 1, the said process comprising the steps of:
(i) pretreating the steel sample by pickling it in 10-15% hydrochloric acid solution
blended with hexamine inhibitor to remove oxide layers followed by cooling to
room temperature; (ii) dipping the cooled sample as obtained in step (i) in 5-10% hydrochloric acid for a
period ranging between 5-10 seconds followed by rinsing in running tap water; (iii) dipping the rinsed sample as obtained in step (ii) in the composition as claimed in
claim 1 for a period ranging between 20-40 seconds followed by drying while
maintaining the temperature in the range of 70 to 80°C; (iv) dipping the dried sample as obtained in step (iii) in galvanizing bath having pure
zinc maintained at a temperature in the range of 420-470°C for a period of 20-30
seconds; (v) quenching the sample as obtained in step (iv) in cold water followed by drying.
6. A novel flux composition to reduce dross and ash generation during hot dip galvanizing
of steel components and a process for the preparation thereof, substantially as herein
described with reference to the examples accompanying the specification.

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Patent Number

271023

Indian Patent Application Number

181/DEL/2009

PG Journal Number

06/2016

Publication Date

05-Feb-2016

Grant Date

29-Jan-2016

Date of Filing

30-Jan-2009

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	SINGH DEVENDR DEO NARAIN	NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR-831007 JHARKHAND, INDIA

PCT International Classification Number

C23C 2/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA