KR101045389B1 - Hot dip aluminum plating method to improve corrosion resistance - Google Patents

Abstract

PURPOSE: A molten aluminum coating method for the improvement of corrosion resistance which applies anticorrosion property and secures dimension precision is provided to improve the thermal resistance, weather resistance and anti-abrasion proper by aluminum plating. CONSTITUTION: A molten aluminum coating method for the improvement of corrosion resistance comprises the next step. A preprocessing process(S10) comprises grease removing and washing steps(S11,S12) for a surface of a base material and pickling and washing steps(S13,S14) for activating the surface of the base material. Molten aluminum is plated on the surface of the base material(S20) after an aqueous flux processing for the base material surface, in which the preprocessing process is performed. A post-processing process(S40) comprises a chemistry cleaning step(S41) and washing step(S42) for the base material in which a plating process is performed.

Description

Hot dip aluminum coating for the improvement of corrosion resistance

The present invention, after the pretreatment process of the base material including degreasing and pickling, to suppress the fine oxide film and the scale (Scale) formed on the base material before plating through a water-soluble flux treatment, the aluminum-silicon to which the molten flux is added Existing aluminum plating is performed by immersing the water-soluble flux-treated base material in the alloy plating solution to suppress excessive growth of the alloy layer formed during pure aluminum plating, thereby forming an aluminum-silicon plating layer having an appropriate thickness on the alloy layer. However, the present invention relates to a molten aluminum plating method capable of imparting corrosion resistance to the surface of small precision parts such as bolts and nuts or products under conditions that ensure a level of dimensional accuracy that is difficult to achieve in zinc plating.

In general, as a method of imparting corrosion resistance to a product manufactured in a specific shape using a material such as carbon steel, plating or paint coating on the surface of the carbon steel product is known. Until now, the use of hot dip galvanizing to impart corrosion resistance to zinc on the surface of carbon steel products has been widely applied in Korea.

However, the existing galvanized products are not only applicable to salty areas or offshore structures requiring high corrosion resistance due to the limitations of zinc metal, but also the service life of the galvanized products is not reliable. As a substitute, stainless steel products, rubber coated products, or Teflon coated products are mainly used.

However, the above corrosion resistance products are also difficult to ensure sufficient service life when used in salt areas or offshore structures, and the price of the product itself is not easy, and thus it is not a smooth solution in terms of providing economic and practical corrosion resistance materials. For this reason, the molten aluminum plating method utilizing the corrosion resistance which aluminum metal has has spread.

In the molten aluminum plating method as described above, the surface of the base material is formed to be suitable for plating through pretreatment consisting of degreasing, pickling, and washing with water, and then the base material is placed into a plating bath in which pure aluminum having a purity of 99.7% or more is stored in a molten state. After immersing and plating aluminum on the surface of the base material, a process of manufacturing a plated product is performed through post-treatment on the plated surface of the base material.

However, according to the general molten aluminum plating method as described above, the oxidation of aluminum frequently occurs in the high temperature bath due to the plating temperature of about 700 ℃, even if the surface of the base material to be plated is thoroughly pretreated Some of the plating is not, or a pin-hole (Pin-hole) is generated in the plated layer is a factor that adversely affects the quality of the plated product, such as adhesion between the base material and the plated layer is reduced.

In order to solve the problems of the conventional molten aluminum plating method as described above, by plating aluminum on the surface of the base material by the double flux treatment of the water-soluble flux and the molten flux, the unplating rate and the pinhole generation rate of the base material surface are almost zero ( In order to improve the corrosion resistance of a plated product by making it zero), it was known by the applicant of the patent application No. 36451 in 2002 and registered a patent (registration number: 10-0436597).

According to the molten aluminum plating method previously filed by the present applicant as described above, it provides a level of corrosion resistance that can be applied to parts such as offshore plants or ships that are easy to be exposed to seawater and parts such as power pipes or steel towers used in harsh corrosive environments. Although it can be, the base material to be plated is mainly limited to medium and large structures, there was a disadvantage that it is difficult to apply to small precision parts and products such as bolts and nuts.

The reason why the base material to be plated was mainly limited to medium and large structures is because the melting point of aluminum is about 700 ° C., so that the base material is immersed in the plating solution and then melted immediately after lifting the base material to the outside of the plating solution. While the aluminum hardens and the excessive diffusion of the alloy layer forms a plating layer of excessive thickness over the surface of the base material, there is no method of uniformly and uniformly adjusting the plating, so that the plating of small precision parts such as bolts and nuts is performed. This is because it was difficult to maintain the dimensional accuracy required for the system.

In particular, in order to remove dimensional aluminum by removing excess aluminum formed in small and narrow parts such as bolts and nuts, it is necessary to post-process the plated products by hand one by one. Due to time, manpower, and difficult manual work, mass production of plated products has become impossible, which makes it difficult to apply molten aluminum plating to precision parts such as bolts and nuts.

On the other hand, some products are produced in which aluminum powder is buried on the surface of precision parts such as bolts and nuts and then baked in an oven. However, since aluminum powder material is imported from abroad and its price is also high, it is not popularized. Although it is partly used as a substitute for stainless steel, it is a method of dissolving aluminum powder on the surface of the product, so that the coating film is easily peeled off and discarded in an unusable state during the assembly and disassembly of the product. It was to have.

The present invention is to provide a molten aluminum plating method that can solve the conventional problems as described above and supplement the problems of the prior application to impart excellent corrosion resistance to the surface of the base material even for products requiring more detailed dimensional accuracy. After the pretreatment of the base material including degreasing and pickling, the water-soluble flux treatment is used to suppress the fine oxide film and scale formed on the base material before plating, and then into the aluminum-silicon alloy plating solution to which the molten flux is added. In order to suppress the excessive growth of the alloy layer formed during pure aluminum plating by immersing the water-soluble flux-treated base material, the aluminum-silicon plating layer of the appropriate thickness is formed on the alloy layer, so that the existing aluminum plating or zinc plating Secures dimensional accuracy that is difficult to achieve Under these conditions, the surface of small precision parts such as bolts and nuts or the like can be imparted with corrosion resistance, and at the same time, the heat resistance, abrasion resistance and weather resistance imparted by aluminum plating can be improved. It is a technical problem.

In addition, the present invention further performs a centrifugal separation step as an additional step between the plating step and the post-treatment step for the plating surface, and includes the polishing step for the plating surface in the post-treatment step, Corrosion-resistant aluminum plating for precision parts such as nuts and nuts is performed under conditions that ensure higher dimensional accuracy, while removing excess aluminum attached to narrow and narrow parts such as threads is also very easy and easy to perform. As a result, it can be optimally applied to parts such as offshore plants, ship parts, and power pipes and steel towers used in harsh corrosive environments, as well as expensive stainless steel or corrosion resistant materials. Its price is very low and its service life is long enough. And that to manufacture a wide variety of corrosion-resistant products coated with soluble guarantee a technical problem of the second.

The present invention as a means for solving the above technical problem, a pretreatment step including a degreasing step and the washing step of the surface of the base material to be plated, and a pickling step and washing step for activating the surface of the base material, and the pretreatment step After the flux treatment on the surface of the rough base material, the plating process for plating the molten aluminum on the surface of the base material, and the molten aluminum plating method comprising a post-treatment process including a chemical cleaning step and a washing step of the base material subjected to the plating process. In the plating process, the water-soluble flux mixed with potassium chloride 35-50% by weight, cryolite 5-10% by weight, ammonium fluoride or aluminum fluoride 40-60% by weight based on 100% by weight of water 10-30 A water-soluble flux treatment stage in which a base material is immersed in a flux solvent added and dissolved in weight% and maintained for 1 to 10 minutes under a temperature condition of 40 to 90 ° C. .; 3 to 15% by weight of silicon is added and dissolved based on 100% by weight of aluminum to form a melt plating solution at 600 to 750 ° C, while 25 to 35% by weight of sodium chloride, 15 to 25% by weight of potassium chloride, and 20 to 30 of cryolite. In a state in which a molten flux mixed with 20% to 30% by weight of an optional fluoride among wt%, ammonium fluoride or ammonium fluoride or aluminum fluoride is added at 5 to 10% by weight based on 100% by weight of the molten plating solution. The melt flux treatment and plating step of immersing the base material in the molten plating solution to which the molten flux is added to perform aluminum-silicon plating on the surface of the base material for 1 to 20 minutes;

In addition, when corrosion-resistant plating of precision parts such as bolts and nuts is performed, between the plating process and the post-treatment process, bolts and nuts, etc., as the plated base material, are put into a centrifuge and narrow as threads. The centrifugation step is performed as an additional step of removing excess aluminum attached to the narrow part, and the centrifugation step may be performed at atmospheric temperature under normal temperature conditions, but the centrifugal bath for securing better dimensional accuracy. While heating the internal temperature of about 500 ~ 650 ℃, characterized in that performed for 1 to 5 minutes under the condition of maintaining the rotational speed of the centrifuge in the range of 500 ~ 2000rpm, after the centrifugation step, the base material It is characterized in that the air-cooling step of cooling in air under room temperature conditions is further performed before the post-treatment step, After the chemical cleaning step and the washing step as a process, the polishing step and the washing and sorting step of the plating surface is further performed, the polishing step is characterized in that the alternative method of vibration polishing or sandblasting method is applied. .

According to the present invention as described above, while providing the corrosion resistance to the surface of the base material while ensuring the dimensional accuracy of the level difficult to achieve by the existing zinc plating method or aluminum plating method and the heat resistance imparted by aluminum plating , Abrasion resistance and weather resistance are also improved, and corrosion-resistant plating of precision parts such as bolts and nuts is also performed under conditions that ensure high dimensional accuracy, and also removes excess aluminum attached to threads. It is very easy and easy to perform.

As a result, it has the effect of providing various kinds of corrosion-resistant plating products that can be optimally applied to parts such as offshore plants, ship parts, and power pipes and steel towers, which are exposed to seawater, and in harsh corrosive environments. Compared to expensive stainless steel materials or corrosion resistant materials, the price is very inexpensive and sufficient lifespan and reusability are guaranteed to provide more economical and practical corrosion resistant plating products.

1 is a process block diagram showing a molten aluminum plating method for improving corrosion resistance according to the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the molten aluminum plating method according to the present invention, as shown in the process block diagram of Figure 1, pretreatment of the surface of the base material consisting of a degreasing step (S11) and washing step (S12) and pickling step (S13) and washing step (S14) After the step (S10), the water-soluble flux treatment step (S21) and the melt flux treatment and plating step (S22) consisting of a plating step (S22) is subjected to.

On the other hand, after the plating step (S20), a post-treatment step (S40) including a chemical cleaning step (S41) and a water washing step (S42) for the plating surface is in progress, to a precision component such as a bolt or nut When the plating operation is performed, the additional step S30 including the centrifugal separation step S31 is performed between the plating step S20 and the post-treatment step S40, while the polishing step S43 is performed. ) And washing and sorting steps (S44) are included in the post-treatment process (S40).

First, as a pretreatment step (S10) for forming a surface of a metal material (mainly a carbon steel material) to be suitable for plating, a degreasing step (S11) and washing step (S12) and pickling step (S13) and washing step Each process step consisting of (S14) is a matter that is widely applied to various other plating methods such as electroplating, chemical plating, and deposition plating as well as various hot-dip plating including the aluminum plating of the present invention. Let's do it.

The degreasing step (S11), by immersing the metal material to be a base material in a degreasing tank in which an alkali solvent or an organic solvent is stored, cutting oil or press oil attached to the surface of the base material due to various machining, gamma agent according to the drawing process, polishing processing Corresponds to the process step of removing various foreign matters such as abrasive oil or metal powder according to.

Alkali solvent used in the degreasing step (S11), as used in most plating methods, sodium carbonate (Na ₂ CO ₃ ), sodium phosphate (Na ₃ PO ₄ ), sodium silicate (= sodium metasilicate; Na ₂ SiO ₃ ) Select one species or species and dissolve it in water, and use sodium hydroxide (NaOH) in some cases in order to improve the cleaning effect by increasing alkalinity.

However, it is most preferable to remove the foreign matter adhering to the surface of the base material as much as possible by appropriately selecting and applying the type of alkali solvent, its pH and use temperature according to the material and size of the base material to be plated. As the organic solvent, chlorine-based solvents such as trichloroethylene (C ₂ HCl ₂ ) and methylchloroform (CHCl ₂ ) are generally used.

After the degreasing step (S11) as described above, by immersing the degreasing base material in a washing tank in which water at room temperature is stored, the washing step (S12) to remove the alkali solvent and residual foreign matter adhering to the surface of the base material do.

The washing tank used in the washing step (S12) is preferably formed of a structure in which water at room temperature is continuously supplied from one side to the inside of the washing tank, and the other side may be naturally discharged treatment water inside the washing tank. In order to remove the alkali solvent adhering to the surface of the base material more effectively, in some cases, two or more washing tanks may be installed, and the washing step of one amount may be divided into several times.

After going through the degreasing step (S11) and washing step (S12) as described above, the pickling step (S13) to immerse the base material into the interior of the pickling tank in which the aqueous solution of acid (酸) is stored. ) Neutralizes a small amount of alkali solvent remaining on the surface of the base material, removes scale and oxide film formed on the surface of the base material, and gives the surface of the base material an etching effect by acid corrosion. It becomes an activation step of the base material surface for improving the adhesiveness of a plating layer.

The aqueous solution of the acid used in the pickling step (S13) may also be an aqueous solution of various acids such as hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ) or nitric acid (HNO ₃ ) or a mixed acid solution thereof depending on the material of the base material. For example, the most commonly used carbon steel material may be an aqueous solution having a concentration of hydrochloric acid (HCl) of about 10 to 20%, since the pickling treatment contributes to the plating rate of the surface of the base material. It is preferable that the aqueous solution of the acid selected according to the material of the base material is always maintained at a constant concentration inside the pickling bath.

After the pickling step (S13) as described above, the plating process by passing through the washing step (S14) to remove the pickling solution attached to the surface of the base material by immersing the pickled base material in a washing tank of water at room temperature ( S20) the previous pretreatment process (S10) is completed, the same technical matters as the washing step (S12) performed after the degreasing step (S11) in the case of the washing step (S14) performed after the pickling step (S13). Apply.

In addition, in the process block diagram of FIG. 1, the pretreatment step S10 is illustrated as being performed once, but if necessary, the pretreatment step S10 may be repeatedly performed two or more times. As described in the earlier application, the pretreatment step (S10) may be reduced to three steps of degreasing step, pickling step and washing step.

After the pre-treatment step (S10) as described above, the plating step (S20) corresponding to the main part of the present invention is performed, the plating step (S20) is a water-soluble flux treatment step for the base material (S21) and the base material The melt flux treatment and the plating step (S22) of performing the melt flux treatment and the aluminum-silicon plating operation on the surface of the base material are sequentially performed.

The water soluble flux treatment step (S21), by immersing the base material after the pre-treatment step (S10) in a flux treatment tank in which the water-soluble flux is dissolved, an oxide film or scale (Scale) is formed on the surface of the base material before the aluminum hot dip plating It is a step for forming a chemical coating or the like on the surface of the base material while suppressing the coating, while smoothly spreading the aluminum component during plating to form a good plating layer.

Water-soluble flux used in the water-soluble flux treatment step (S21), 35 to 50% by weight of potassium chloride (KCl), 5 to 10% by weight of cryolite (Cryolite), ammonium fluoride (NH ₄ F) or aluminum fluoride (AlF ₃ ) Consists of a component ratio of the alternative fluoride 40 to 60% by weight.

The flux solvent was prepared by adding and dissolving the water-soluble flux having the above component ratio at 10 to 30% by weight based on 100% by weight of water, and then storing the flux solvent thus prepared in a flux treatment tank to prepare the flux solvent. In the state of maintaining the temperature in the range 40 ~ 90 ℃, proceeds to the process of immersing the base material through the pretreatment step (S10) in the flux solvent for about 1 to 10 minutes.

Each component used in the water soluble flux and the mixing ratio thereof, the surface of the base material together with the melt flux is added to the plating bath in the melt flux treatment and plating step (S22) to proceed to the process step after the water soluble flux treatment step (S21) It is to limit the optimal component ratio that can form a chemical film by a water-soluble flux to a certain thickness over the entire surface of the base material so that the unplating ratio of aluminum to about (zero).

On the other hand, when the water-soluble flux is solventized with water at a concentration of less than 10% by weight, the thickness of the chemical film formed on the surface of the base material becomes relatively thin, as well as a long time for the drying of the chemical film flux-treated It is not suitable to apply the base material immediately to the next process step, and even if the water-soluble flux is solvented with water at a concentration exceeding 30% by weight, the thickness of the chemical coating layer does not rise above a certain range, so that it exceeds 30% by weight. The concentration range becomes uneconomical.

In addition, if the temperature of the flux solvent is maintained at 40 ° C. or lower, excessive time is required for 10 minutes or more to form the chemical coating layer on the surface of the base material. If the flux solvent is maintained at a temperature of 90 ° C. or higher, the surface of the base material is Although it is possible to shorten the time for forming the chemical coating layer in about 1 minute, evaporation of water from the flux solvent is promoted, making it difficult to maintain the concentration of the flux solvent at an appropriate level.

On the other hand, when the temperature of the flux solvent is set in the range of 40 ~ 65 ℃ a short drying step for the complete drying of the chemical coating layer between the water-soluble flux treatment step (S21) and the melt flux treatment and plating step (S22) Preferably, when the temperature of the flux solvent is set in the range of 65 to 90 ° C., a separate drying step is not necessary because the base material is removed from the flux solvent and the chemical coating layer is dried.

After the water-soluble flux treatment step (S21) as described above, by immersing the flux-treated base material into the aluminum-silicon plating solution to which the molten flux is added, to form an aluminum alloy layer (Fe-Al alloy) on the surface of the base material The melt flux treatment and the plating step (S22) are performed so that the aluminum-silicon plating layer is formed thereon.

The melt flux treatment and plating step (S22), while forming a molten plating solution by adding 3 to 15% by weight of silicon based on 100% by weight of aluminum and heating and dissolving it at a temperature of 600 ~ 750 ℃, The molten flux is sprinkled on the surface of the molten plating solution prepared as described above, and the water-soluble flux-treated base material is immersed in the molten plating solution for about 1 to 20 minutes and then taken out.

The reason for adding silicon to the molten aluminum in the melt flux treatment and plating step as described above is that by suppressing excessive diffusion of the alloy layer formed when the silicon component is plated, plating of uniform thickness is performed along the surface of the base material. This is because it is possible to apply corrosion-resistant aluminum plating not only to medium and large structures but also to small precision parts such as bolts and nuts.

Therefore, when less than 3% by weight of silicon is added based on 100% by weight of molten aluminum, the function of suppressing excessive diffusion of the aluminum alloy layer is not properly expressed, and 15% by weight of silicon is based on 100% by weight of molten aluminum. If it is added in excess of%, it is not preferable because the high melting point of the silicon is difficult to manage the plating bath.

In addition, a method of forming a molten aluminum plating bath containing silicon can be applied in various ways, but most representative example, after the first melting of the aluminum alloy ingot containing 25% silicon, purity 99.9% Ingot of pure aluminum is added in a ratio by weight to form a bath of 3 to 15% by weight of silicon, and then the mixture is sufficiently stirred until the temperature of the bath is increased to 600 to 750 ° C in accordance with the silicon content. It is.

On the other hand, the melt flux used in the melt flux treatment and plating step (S22), sodium chloride (NaCl) 25 to 35% by weight, potassium chloride (KCl) 15 to 25% by weight, cryolite (Cryolite) 20 to 30% by weight, fluorine It is composed of 20-30% by weight of a fluoride selected from ammonium hydride (NH ₄ HF ₂ ), ammonium fluoride (NH ₄ F) or aluminum fluoride (AlF ₃ ), and the powder particles of the molten flux are evenly distributed. In the mixed state, it is sprinkled and melted on the surface of the molten plating solution before immersion of the base material.

More specifically, the molten flux is added to the surface of the plating solution based on 100 wt% of the molten plating solution composed of aluminum-silicon alloy, and the molten flux is added to the surface of the plating solution. The flux layer is formed in a floating state on the top.

The components of the molten flux and the mixing ratio thereof form a flux layer having a predetermined thickness over the entire upper surface of the molten plating solution, thereby blocking contact between the molten aluminum-silicon component and external air to prevent various impurities or aluminum oxides (Al ₂ O ₃ ) to effectively prevent the occurrence of water, and by the water-soluble flux treatment to interact with the chemical coating layer coated on the surface of the base material to achieve an almost zero plating rate of aluminum on the surface of the base material Range.

In addition, according to the components of the molten flux and the mixing ratio thereof, when the base material is immersed in the plating bath by securing the excellent fluidity of the flux layer, the formation of aluminum oxide due to the resistance to the base material and contact with external air is generated. When the base material is removed from the plating bath, the amount of flux attached to the surface of the base material can be minimized.

Therefore, when the molten flux is added below 5 wt% based on 100 wt% of the molten aluminum-silicon plating solution, the thickness of the flux layer formed on the upper portion of the molten plating solution becomes relatively thin. In the process of immersing or taking out the plating bath, there is a high possibility of contact between the molten plating solution and the external air.

On the other hand, when the amount of the molten flux exceeds 10% by weight based on 100% by weight of the molten aluminum-silicon plating solution, contact with external air and heat dissipation from the molten plating liquid can be effectively blocked. However, the amount of molten flux attached to the plated surface of the base material is slightly increased, which adversely affects the plating process.

After setting the state of the plating bath so that the flux layer is formed on the upper surface of the molten aluminum-silicon plating solution using the molten flux as described above, and then immersed the water-soluble flux-treated base material into the plating bath 1 ~ When plating is performed on the surface of the base material for 20 minutes, it is possible to form a very good aluminum alloy layer and aluminum-silicon plating layer over the surface of the base material.

In other words, while the flux layer provided by the molten flux suppresses the generation of various impurities and aluminum oxide (Al ₂ O ₃ ), trace impurities and aluminum oxide are almost all formed by the water-soluble flux component coated on the surface of the base material. By dissolving and removing, the aluminum component is very easily fused to the surface of the base material.

As a result, it is possible to form a very good aluminum alloy layer in the state that there is no unplated surface or pin hole on the surface of the base material, and the flux layer present on the upper surface of the molten plating solution to the outside By blocking heat dissipation, it is also possible to prevent heat loss from the plating bath to the outside, thereby saving fuel and energy.

The time required to perform the plating operation on the surface of the base material in the melt flux treatment and plating step (S22) is somewhat different depending on the temperature set in the plating bath, that is, the temperature of the molten plating solution and the thickness and shape of the base material. When the temperature range of the molten aluminum-silicon plating solution is within the range of 600 to 750 ° C, it is about 15 minutes to plate a 20-30 mm thick steel plate under the temperature of 680 ° C, and about 4 minutes under the temperature of 750 ° C. It takes plating time.

Therefore, as the size of the base material to be plated is large and the shape thereof becomes complicated, the plating time becomes longer at the same temperature condition, but in the case of the present invention, the aluminum alloy on the surface of the base material in the melt flux treatment and plating step (S22). Since the layer is formed first, then another aluminum-silicon coating layer is formed on the alloy layer. In view of the overall plating thickness, the plating time in this step (S22) is preferably not to exceed 20 minutes. .

In addition, when the size is small and precise parts such as bolts and nuts become the base material, this step (S22) so that the plating of a certain thickness over the surface of the base material including a narrow and narrow portion, such as a thread It is preferable to set the plating time in 1) to about 1 minute to 10 minutes, and in the plating time of less than 1 minute, it becomes difficult to form the aluminum alloy layer and aluminum-silicon plating layer of a required level.

When the plating process (S20) from the water-soluble flux treatment step (S21) to the melt flux treatment and the plating step (S22) as described above, the aluminum-silicon layer is again coated on the aluminum alloy layer is implemented. Since such a mechanism provides a tongue-like structure (dense spherical structure) by the reaction between metals, the plating layer does not peel off even from a strong impact from the outside, and has a very excellent corrosion resistance by the double aluminum coating layer.

Therefore, it is possible to impart sufficient corrosion resistance to the surface of the base material while securing excellent dimensional accuracy that is difficult to achieve by the existing zinc plating method or aluminum plating method, and at the same time, the heat resistance and weather resistance provided by aluminum plating and aluminum Abrasion resistance developed by the alloy layer can also be improved along with it, so that it can be optimally applied to parts such as offshore plants, ship parts, and power pipes and steel towers that are exposed to seawater. The product can be manufactured.

In addition, the price is much lower than that of expensive stainless steel or corrosion-resistant materials, which were previously used to replace galvanized products, and coated products using aluminum powder, which depended on imports. By ensuring this, it is possible to provide a more economical and practical corrosion-resistant plating product.

After the plating step (S20) corresponding to the main part of the present invention as described above, the after-treatment step (S40) of the plated base material is subjected to, and the post-treatment step (S40) is the same as the conventional plating method The chemical cleaning step (S41) and the washing step (S42) for the plating surface of the.

The chemical cleaning step (S41) is by immersing the plated base material in a 5 to 15% aqueous solution of nitric acid (HNO ₃ ) for about 3 to 10 minutes, without any additional machining of the residual flux powder that may remain attached to the plating surface It is an easy and complete removal process in a very short time, and it is a process step that smoothes and smoothes the plating surface of the base material by using acid corrosion.

In addition, as described in the contents previously filed by the applicant, instead of the aqueous solution of nitric acid, 2-10% aqueous solution of hydrofluoric acid (HF), 5-10% nitric acid (HNO ₃ ) and hydrofluoric acid (HF) ) 0.5 ~ 5% mixed acid solution, nitric acid (HNO ₃ ) 5 ~ 10%, sulfuric acid (H ₂ SO ₄ ) 1 ~ 3% and glacial acetic acid (CH ₃ COOH) 0.5 ~ 2% and chromic anhydride (CrO ₇ ) 1 ~ A mixed solution of 3% mixed acid, 5-10% nitric acid (HNO ₃ ), 2-5% hydrofluoric acid (HF) and 2-3% chromic anhydride (CrO ₇ ) may be applied in this step (S41). It is to be revealed.

When preparing an aqueous solution having a concentration below the defined concentration for each acid type listed above, not only the surface treatment effect of the plated surface by the acid is reduced, but also takes an excessive treatment time of 10 minutes or more, and when the aqueous solution is prepared above the limited concentration, Although the time required for the surface treatment can be shortened to about 3 minutes, the corrosion of the plated layer proceeds somewhat deeply, making it difficult to maintain the plated layer of the required thickness.

As described above, the chemical cleaning step (S41), which is carried out as the post-treatment process (S40), is an important step in terms of improving the quality of the plated product, unlike the pretreatment process (S10), and thus, the concentration of the solution stored in the chemical cleaning tank is often changed. Check to ensure that the solution inside the chemical cleaning bath is always at a constant concentration range.

After the chemical cleaning step (S41) as described above, the rinsed plated product is immersed in a washing tank with water stored at room temperature to go through a washing step (S42) for washing the surface of the water, and thus washing step (S42) When the plated product is finally dried, the molten aluminum plating method according to the present invention is completed, and the process steps in the order described up to now are applied to a base material having a relatively simple shape and a medium or large size. Most preferred.

On the other hand, when the base material applied to the molten aluminum plating process according to the present invention is a small precision parts such as bolts and nuts, it is necessary to further improve the dimensional accuracy of the plated base material, the plating process ( It is preferable to go through the centrifugation step S31 as the additional step S30 between S20) and the post-treatment step S40.

In the centrifugal separation step (S31), a small precision component such as a bolt or a nut is put into a centrifuge as a plated base material, and then the centrifuge is rotated at high speed, such as a screw thread by using a centrifugal force generated in the rotation process. This step is to remove excess aluminum attached to narrow and narrow parts.

Representative examples of the centrifugal separator that can be used in the step (S31), including a drive having a cylindrical basket that can put a plated base material by a predetermined amount as a bath, the tub rotating at high speed, The basket-type centrifuge is provided with a metal net for separating and discharging excess aluminum inside the bathtub, or the discharge passage of excess aluminum is formed in the bathtub itself.

However, as long as the plated base material can prevent the surface damage of small precision parts such as bolts and nuts while removing excess aluminum components from the surface of the base material, any type of centrifuge may be used. It is advantageous to perform the centrifugation operation before the surplus aluminum is completely solidified by immediately introducing the base material having undergone the (S20) into the centrifuge.

Most preferably, the internal temperature of the centrifugal bath is set to 500 to 500 in a state where the centrifuge is set to allow heating of the centrifugal bath by placing an electric heater or a high frequency induction heater at the outer periphery of the centrifugal bath. The rotational speed of the centrifugation bath at 650 ° C. is in the range of 500 to 2000 rpm, and the separation of excess aluminum is performed for about 1 to 5 minutes.

The reason why the internal temperature of the centrifugal bath is 500 to 650 ° C. as described above is to soften the excess aluminum adhered to the surface of the base material so that aluminum parts other than the plating layer can be more easily separated. Under the temperature condition of the removal efficiency of the excess aluminum is lowered, under the temperature condition exceeding 650 ℃ there is a risk that the normal coating layer is softened and the coating layer is damaged during the centrifugation process.

In addition, as the number of revolutions of the centrifugal bath increases, the removal efficiency of excess aluminum is improved. However, since the centrifugation is performed under the condition that the internal temperature of the centrifugal bath is increased, the number of revolutions over 2000 rpm is uneconomical. In addition, there is a risk that the plating layer is damaged by the compression between the base metals put into the bath, the removal efficiency of excess aluminum is lowered at a rotation speed of less than 500rpm.

In addition, the treatment time for the removal of excess aluminum is adjusted by the treatment temperature and the rotation speed set in the centrifugal bath, at a temperature of 550 ° C. and the rotation speed of 500 rpm, based on a conventional bolt and nut. It takes about 4 to 5 minutes of processing time, and about 1 minute of processing time at a temperature of 650 ℃ and a rotation speed of 2000rpm.

When the centrifugation step (S31) is performed in the same manner as above, the excess aluminum attached to the narrow and narrow space of the precision part can be removed more quickly and accurately to further improve the dimensional accuracy of the corresponding base material. In consideration of requirements such as size and dosage of the base material, the number of revolutions of the bath (rpm) and the treatment temperature and time of the base material may be within the above range, may be somewhat out of the range, and may be centrifuged under ambient temperature conditions. Note that it is also possible to perform the separation step (S31).

After passing through the centrifugation step (S31) as described above, the base material is taken out of the centrifugal separation bath and subjected to an air-cooling step (S32) for cooling the base material in air under normal temperature conditions, which quenches the base material by cooling the base material as slowly as possible. It is to prevent any gaps or cracks in the plating layer that occur during the process.

In addition to the additional step (S30) including the centrifugation step (S31) and the air cooling step (S32) as described above, by further processing the surface of the plated base material to further improve the dimensional accuracy, the post-treatment process ( After the chemical cleaning step S41 and the washing step S42 as S40, it is preferable to go through the polishing step S43 of the plating surface.

As a typical surface treatment method that can be applied to the polishing step (S43), there may be mentioned vibration polishing or sand blasting (Sand blasting), the vibration polishing method is a fine particle ceramic ball, polish and water with a base material It is a method of treating the plating surface of the base material by introducing into the inside of the tank by vibrating or rotating the treatment tank, and sandblasting is a method of treating the plating surface of the base material by spraying fine sand particles onto the surface of the base material.

The vibration polishing or sand blasting method as described above is a well-known technique widely used in the surface treatment technology, and the apparatus capable of performing the corresponding work is also very diverse, so a detailed description thereof will be omitted. The particle size of the sand may be selected according to the dimensional accuracy of the base material which requires surface treatment, and the polishing step S43 may be applied even when the base material is a medium or large structure rather than a small precision part.

As described above, the polishing step S43 further provides a function of adjusting the dimensional accuracy of the base material and further provides a function of improving the strength of the plated layer by providing a work hardening on the surface of the plated material. Preferably, after the polishing step (S43), the surface of the plated product is finally washed with water, and then subjected to washing and sorting step (S44) for separating the plated product by type and screening out defective products. All process steps of the invention are completed.

When the centrifugation step (S31) as an additional step (S30) and the polishing step (S43) as a post-treatment step (S40) as described above are included in the process of the present invention, corrosion resistance to small precision parts such as bolts and nuts Plating can also be carried out under conditions that ensure very high dimensional accuracy, while removal of excess aluminum attached to narrow and narrow parts, such as threads, can also be performed very easily and easily.

As a result, it is possible to produce a large amount of products subjected to corrosion-resistant aluminum plating on small precision parts such as bolts and nuts, thereby reducing the cost of the plated product and of course applying a range of aluminum plating products. Further wider and more conducive to securing external competitiveness, while having high dimensional accuracy and excellent corrosion resistance, it is possible to provide corrosion-resistant plating products having almost the same quality as expensive stainless steel products.

Example 1

Carbon steel pipes 50cm in diameter and 20mm thick were sequentially immersed in degreasing baths, rinsing tanks, pickling tanks and rinsing tanks, and the surface was pretreated, followed by 40% potassium chloride (KCl), 10% cryolite, and ammonium fluoride (NH). ₄ F) The carbon steel pipe was immersed in a flux solvent in which a water-soluble flux composed of 50% of component ratio was dissolved at a concentration of 15% by weight under a temperature condition of 80 ° C. for about 2 minutes, 25% sodium chloride (NaCl) and potassium chloride (KCl). ) 15%, Cryolite 30%, Ammonium fluoride (NH ₄ HF ₂ ) Melt flux consisting of a component ratio of 30% was added to the plating solution added at 10% by weight based on 100% by weight of molten aluminum-silicone. The flux-treated carbon steel pipe was plated by immersion for about 5 minutes at a temperature of 700 ° C., and a plating solution in which 5 wt% of silicon was added and dissolved based on 100 wt% of molten aluminum was used. The plated carbon steel pipe was immersed in a 10% aqueous solution of nitric acid (HNO ₃ ) for about 5 minutes, then taken out and washed with water to prepare an aluminum-silicon plated corrosion-resistant carbon steel pipe product.

[Example 2]

Carbon steel frame for iron tower of length 1m 50cm, thickness 5mm was immersed in degreasing tank, washing tank, pickling tank and washing tank in order to pretreat the surface, and then pretreated with 35% potassium chloride (KCl), 5% cryolite, and fluorination The carbon steel frame was immersed for about 3 minutes under a temperature condition of 70 ° C. in a flux solvent in which a water-soluble flux having a component ratio of 60% of ammonium (NH ₄ F) was dissolved at a concentration of 10% by weight, 25% of sodium chloride (NaCl), Plating solution containing 7% by weight based on 100% by weight of molten aluminum-silicon melted flux consisting of 25% potassium chloride (KCl), 25% cryolite and 25% ammonium fluoride (NH ₄ F) The carbon steel frame fluxed therein was plated by immersion for about 4 minutes at a temperature of 700 ° C. At this time, a plating solution containing 4% by weight of silicon was added and dissolved based on 100% by weight of molten aluminum. Used. The plated carbon steel frame was immersed in a 10% aqueous solution of nitric acid (HNO ₃ ) for about 5 minutes, taken out, washed with water, dried, and sandblasted on the surface of the carbon steel frame, followed by final washing and drying. An aluminum-silicon plated corrosion resistant carbon steel frame product was prepared.

Example 3

Structural bolts and nuts with a diameter or inner diameter of 2 cm in the fastening part are sequentially immersed in the degreasing tank, the washing tank, the pickling tank and the washing tank, and the surface is pretreated, followed by 40% potassium chloride (KCl), 6% cryolite, and fluorine. Aluminum bolts (AlF ₃ ) were immersed for about 8 minutes in a flux solvent in which a water-soluble flux composed of a component ratio of 54% was dissolved at a concentration of 20% by weight under a temperature condition of 50 ° C., and a drying time of about 1 minute. Melt flux consisting of 25% sodium chloride (NaCl), 25% potassium chloride (KCl), 20% Cryolite and 30% aluminum fluoride (AlF ₃ ) is based on 100% by weight of molten aluminum-silicone. The bolts and nuts which were flux-treated in the plating solution added at 10% by weight were immersed for about 2 minutes under a temperature condition of 720 ° C., and were plated by 6% by weight based on 100% by weight of molten aluminum. The plating liquid solution in which silicone was added and dissolved was used. Put the plated bolts and nuts into the centrifuge bath, remove the excess aluminum for 2 minutes with the internal temperature of the bath at 650 ℃ and the rotation speed of the bath at 1000rpm, and then remove the bolts and nuts from the bath. After removing, it was sufficiently cooled in the air. The cooled bolts and nuts were immersed in a 10% aqueous solution of nitric acid (HNO ₃ ) for about 5 minutes, removed, washed with water, and dried. After the polishing was performed, and after the final washing and drying to produce aluminum plated corrosion-resistant bolts and nuts products.

The aluminum plated product manufactured by the process steps of the present invention including each of the embodiments described above, the base material layer (Fe), the alloy layer (FeAl ₃ ~ Fe ₂ Al ₃ ), the aluminum-silicon coating layer ( Al-Si) was formed sequentially, while each layer had a very strong adhesion based on the on-snow structure, and there were some differences depending on the material of the base material, but most alloy layers were about 0.03 to 0.05mm, aluminum coating layer. It is made of 0.03 ~ 0.1mm, and is made of a very good corrosion-resistant plated product with no unplated parts or pin-holes generated throughout the plating surface.

In particular, even in the case of small precision parts such as bolts and nuts, excellent corrosion-resistant plating products were manufactured in the same manner as above. In the case of bolts and nuts, the bolts and nuts were fastened immediately after plating was completed. It showed that the level of dimensional accuracy without problems, it can be seen that the molten aluminum plating method according to the present invention is sufficiently applicable to the production of corrosion-resistant bolts and nuts.

S10: pretreatment process S11: degreasing step
S12, S14: washing stage S13: pickling stage
S20: Plating Process S21: Water Soluble Flux Treatment Step
S22: melt flux treatment and plating step S30: additional process
S31: centrifugation step S32: air cooling step
S40: Post-treatment process S41: Chemical cleaning step
S42: washing step S43: polishing step
S44: washing and sorting stage

Claims (5)

delete delete delete A pretreatment step (S10) including a degreasing step (S11) and a washing step (S12) of the base material surface to be plated, and a pickling step (S13) and a washing step (S14) for activation of the base material surface, and the pretreatment step After performing the water-soluble flux treatment on the surface of the base material (S10) and plating the molten aluminum on the surface of the base material (S20), and the chemical cleaning step (S41) and water washing of the base material after the plating process (S20) In the molten aluminum plating method comprising a post-treatment step (S40) including a step (S42),
The plating step (S20),
100 wt% of water-soluble flux mixed with 35-50 wt% potassium chloride (KCl), 5-10 wt% Cryolite, 40-60 wt% ammonium fluoride (NH ₄ F) or aluminum fluoride (AlF ₃ ) Water-soluble flux treatment step (S21) to immerse the base material in the flux solvent added and dissolved at 10 to 30% by weight based on%, and maintained for 1 to 10 minutes under a temperature condition of 40 ~ 90 ℃,
After passing through the water-soluble flux treatment step (S21), by adding and dissolving 3 to 15% by weight of silicon based on 100% by weight of aluminum to form a melt plating solution of 600 ~ 750 ℃, sodium chloride (NaCl) 25 ~ 35 wt%, 15-25 wt% potassium chloride (KCl), 20-30 wt% Cryolite, ammonium fluoride fluoride (NH ₄ HF ₂ ) or ammonium fluoride (NH ₄ F) or aluminum fluoride (AlF ₃ Immersing the base material in the molten plating solution to which the molten flux is added, while the molten flux mixed with the alternative fluoride 20 to 30 wt% is added at 5 to 10 wt% based on 100 wt% of the molten plating solution. 1 to 20 minutes through the melt flux treatment and plating step (S22) to perform the aluminum-silicon plating on the surface of the base material,
Between the plating step (S20) and the post-treatment step (S40), by adding a plated base material to the centrifuge to remove the excess aluminum attached to the base material (S30), the centrifugation step (S31) is Performed,
In the centrifugation step (S31), the plated base material is put into a centrifugal bath, and then the internal temperature of the centrifugal bath is 500 to 650 ° C., and the number of revolutions of the centrifugal bath is 500 to 2000 rpm. Under conditions of maintaining for 1 to 5 minutes,
After the centrifugation step (S31), the air cooling step (S32) for cooling the base material in the air under room temperature conditions is further performed before the post-treatment step (S40),
The base metal is a molten aluminum plating method for improving the corrosion resistance, characterized in that the small precision parts comprising a carbon steel bolt and nut. The method of claim 4, wherein after the chemical cleaning step (S41) and the washing step (S42) as the post-treatment step (S40), the polishing step (S43) and the washing and sorting step (S44) of the plating surface is further added. Is performed,
The polishing step (S43) is a molten aluminum plating method for improving the corrosion resistance, characterized in that the alternative method is applied from the vibration polishing or sand blasting (Sand blasting) method.

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