KR101036868B1 - Method for hot dip aluminum coating for the improvement of thermal resistance - Google Patents

Abstract

PURPOSE: A method for plating melted aluminum for improving heat resistance is provided to facilitate aluminum removal work, extend service life, and guarantee reusability. CONSTITUTION: A method for plating melted aluminum for improving heat resistance comprises following steps. The surface of a base material is degreased(S11). The surface of the degreased base material is cleaned by water(S12). The surface of the base material is cleaned by acid and water for the activation of the base material(S13, S14). The melted aluminum is plated on the surface of the base material(S20). The plated base material is post-processed(S40).

Description

Hot dip aluminum coating for the improvement of thermal 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 After immersing the water-soluble fluxed base material in the alloy plating solution to suppress excessive growth of the alloy layer formed during pure aluminum plating, an aluminum-silicon plating layer having an appropriate thickness is formed on the alloy layer. The base material is immersed in a salt bath to allow the plating layer to penetrate deeply into the surface of the base material.The compact precision of bolts and nuts, etc., is achieved under conditions that ensure dimensional accuracy that is difficult to achieve in conventional galvanizing or aluminum plating. Melting to give heat resistance to the surface of parts or products It relates to an aluminum plating method.

Generally, as a method of imparting heat resistance to a product manufactured in a specific shape using a material such as carbon steel, a method of plating a surface of a carbon steel product or coating a heat resistant resin is known. Until now, it is widely applied in Korea to provide heat resistance by galvanizing the surface of carbon steel products using hot dip galvanizing.

However, the existing galvanized products are not only applicable to steel-related machinery and automobile internal combustion engines that require high levels of heat resistance due to the limitations of zinc metal, but also the service life of zinc-plated products as heat-resistant applications is not reliable. As a substitute, expensive stainless steel products, Teflon coated products, high heat resistant polyamide films or bioplastic coated products are mainly used.

However, the above heat-resistant products are also difficult to ensure sufficient service life when used in steel-related machinery or automobile internal combustion engines, and the price of the product itself is not enough, so it is not a smooth solution in terms of providing economic and practical heat-resistant materials. have.

Therefore, many studies have been conducted to secure heat resistance using aluminum alloys in place of existing galvanized products or heat resistant materials, and among these, a molten aluminum plating method for forming an alloy layer of aluminum and iron replaces expensive heat resistant materials. It is spreading as an alternative.

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 ( It is known that the present invention has been filed and registered in the patent application No. 36451 (No. 10-0436597) by the present applicant in 2002 to improve the corrosion resistance and heat resistance of the plated products.

However, the hot-dip aluminum plating method pre- filed by the applicant also similarly provides a high level of heat resistance that can be sufficiently applied to parts such as steel-related mechanical equipment, automobile internal combustion engine, nuclear power generation equipment or chemical equipment exposed to poor high temperature conditions. There was a rather lacking side, and the base material to be plated is mainly limited to medium and large structures, and it was difficult to apply to precision parts such as bolts and nuts.

The reason why the base material to be plated was mainly limited to medium and large structures was because the melting point of aluminum was high at about 660 ° C., so that the base material was immersed in the plating solution and immediately melted upon lifting the base material out of the plating solution. Since aluminum hardens, it is difficult to maintain the dimensional accuracy of the parts by uniformly coating thickness across the surface of the base material during plating of precision parts such as bolts and nuts.

In particular, surplus aluminum is easily attached to small and narrow parts such as threads of bolts and nuts. In order to remove this and increase the dimensional accuracy, it is necessary to post-process the plated products by hand one by one. Due to excessive time, manpower, and difficult manual labor, mass production of plated products is impossible, and therefore, it is difficult to apply heat-resistant 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 has been made to solve the conventional problems as described above and to provide a more excellent heat-resistant plating surface by supplementing the heat resistance required in the high temperature environment, which is a problem of the prior application, melting for improving heat resistance according to the present invention In the aluminum plating method, after the pretreatment process of the base material including degreasing and pickling, the fine oxide film and scale formed on the base material before plating are suppressed by water soluble flux treatment, and then the molten flux-added aluminum- After immersing the water-soluble flux-treated base material in the silicon alloy plating solution to suppress excessive growth of the alloy layer formed during pure aluminum plating, an aluminum-silicon plating layer having an appropriate thickness is formed on the alloy layer. The base material is immersed in the salt bath in order to make the plating layer deep into the surface of the base material. By going through the salt bath step to infiltrate, it is possible to give heat-resistant characteristics to the surface of small precision parts such as bolts and nuts or products under conditions that ensure dimensional accuracy that is difficult to achieve in conventional galvanizing or aluminum plating. At the same time, the first technical problem is that the wear resistance imparted by pure aluminum plating can also be improved with this.

In addition, the present invention is to ensure the dimensional accuracy of the base material first through the process of allowing the aluminum plating layer to deeply penetrate deep into the base material surface in the dye bath step, and then the polishing step for the plating surface as a post-treatment step As it is additionally processed, heat-resistant aluminum plating of precision parts such as bolts and nuts is performed under conditions that ensure better dimensional accuracy, and removal of excess aluminum attached to narrow and narrow parts such as threads is also required. It is very easy and easy to perform, and thus it can be optimally applied to parts such as steel machinery equipment, automobile internal combustion engine, nuclear power plant or chemical equipment exposed to harsh high temperature conditions. Compared to heat resistant material, the price The second technical task is to enable manufacture of various types of heat-resistant plated products which are very inexpensive and have sufficient lifespan and reusability.

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 performing a flux treatment on the surface of the rough base material, a plating process for plating molten aluminum on the surface of the base material, and a 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. Is performed on the basis of

The plating process is 10 to 30% by weight based on 100% by weight of the water-soluble flux mixed with 35 to 50% by weight of potassium chloride, 5 to 10% by weight of cryolite, 40 to 60% by weight of ammonium fluoride or aluminum fluoride The water-soluble flux treatment step of immersing the base material in the flux solvent added and dissolved in the furnace, and maintained for 1 to 10 minutes under the temperature condition of 40 ~ 90 ℃, and 3 to 15% by weight of silicon based on 100% by weight of aluminum and Dissolving to form a melt plating solution at 600 to 750 ° C, alternatively 25 to 35% by weight sodium chloride, 15 to 25% by weight potassium chloride, 20 to 30% by weight cryolite, ammonium fluoride or ammonium fluoride or aluminum fluoride A molten flux mixed with 20 to 30% by weight of a fluoride is added at 5 to 10% by weight based on 100% by weight of the molten plating solution, and the substrate is immersed in the plating solution for 1 to 20 minutes. The surface of the ash is subjected to a melt flux treatment and plating step of performing aluminum-silicon plating.

After the plating process as described above, the salt-bath step is performed before the post-treatment process as an additional step of immersing the plated base material in a salt bath so that the aluminum-silicon plating layer diffuses into the surface of the base material. The salt bath step is a process of immersing the plated base material in a salt bath of 650 ~ 700 ℃ 5 to 20 minutes, the salt bath, 40 to 60% by weight of potassium chloride and 40 to 60% by weight of sodium chloride The eggplant is formed by melting chloride, and after the salt bathing step, the base material is subjected to an air cooling step of cooling the base material in air under normal temperature conditions, and after the chemical cleaning step and the washing step as the post-treatment process, The polishing step, the washing and the sorting step of the plated surface are additionally performed, and the polishing step is an alternative method of vibratory polishing or sandblasting. It is characterized.

According to the present invention as described above, it is possible to impart excellent heat resistance to the base material of a level difficult to achieve by the existing zinc plating method or aluminum plating method, and at the same time, the wear resistance imparted by aluminum plating is also improved with it. In addition, heat-resistant plating of precision parts such as bolts and nuts is also performed under conditions that ensure high dimensional accuracy, and removal of excess aluminum attached to threads is also very easy and easy. have.

As a result, it has the effect of providing various kinds of heat-resistant plating products that can be optimally applied to parts such as steel-related machinery equipment, automobile internal combustion engine, nuclear power plant, chemical equipment, etc. exposed to poor high temperature conditions. Compared to expensive stainless steel materials or heat resistant materials, the price is very inexpensive and sufficient lifespan and reusability are ensured to provide more economical and practical heat resistant plating products.

1 is a process block diagram showing a molten aluminum plating method for improving heat 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), after the salt bath step (S31) as an additional step (S30) for immersing the plated base material in the salt bath, and then chemical cleaning step (S41) for the plating surface thereafter. And after the post-processing step (S40) comprising a washing step (S42) is carried out, when the plating operation for precision parts such as bolts and nuts is made, polishing step (S43) of the plating surface in the post-processing step (S40) And washing and sorting step (S44) is further performed.

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 heat-resistant aluminum plating to small and precision parts such as bolts and nuts as well as medium and large structures.

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 600 ° 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.

After the plating step (S20) from the water soluble flux treatment step (S21) to the melt flux treatment and the plating step (S22) as described above, as a step corresponding to another essential part of the present invention, the plated base material A salt bath step S31 of immersing in a salt bath is performed in an additional step S30.

The salt bath step (S31) is made through a process of immersing the plated base material in a salt bath of 650 ~ 700 ℃ for 5 to 20 minutes, the salt bath can be formulated using a variety of chloride It is most preferable to melt the chloride having a component ratio of 40 to 60% by weight of potassium chloride (KCl) and 40 to 60% by weight of sodium chloride (NaCl).

The dye bath step (S31) as described above is to diffuse the aluminum alloy layer plated on the surface of the base material and the aluminum-silicon coating layer formed thereon so that the plating layer is deeply diffused into the surface of the base material, the adhesion between the base material and the aluminum alloy layer and It serves to further strengthen the adhesion between the aluminum alloy layer and the aluminum-silicon coating layer.

In addition, by passing through the dye bath step (S31) in the small precision parts, such as bolts and nuts, the excess aluminum, which is formed in a narrow narrow part such as a screw thread, is induced to spread out evenly along the surface of the plating, the dimensions of the base material It can also contribute to improving the precision.

Therefore, when the temperature of the salt bath is less than 650 ° C., the diffusion function and the diffusion speed of the plating layer are lowered, so that it is difficult to obtain the required level of heat resistance and dimensional accuracy, and the plating time is delayed in the salt bath step (S31). When the productivity of the product is lowered and the temperature of the salt bath exceeds 700 ° C., the composition and management of the salt bath becomes difficult, as well as the cooling of the base metal in the subsequent air cooling step (S32) takes much time.

In addition, the treatment time in the salt bath can be adjusted according to the size of the base material, but about 5 minutes for small parts such as bolts and nuts, and about 10 minutes for medium parts such as steel pipes and frames. In this case, the processing time of about 20 minutes is required. In the processing time of less than 5 minutes, it is difficult to expect the diffusion effect of the plating layer, and the processing time of more than 20 minutes is a factor of lowering the productivity.

The reason for the optimal embodiment of the potassium chloride and sodium chloride for the composition of the salt bath is to form a salt bath with the components contained in the flux used in the plating process (S20) to double the diffusion and adhesion of the plating layer, potassium chloride and sodium chloride It is most preferred to use a mixture of 1: 1, but in the range of 40 to 60% by weight in consideration of the error in the mixing and use process.

As described above, when the plating process (S20) including the water-soluble flux treatment step (S21) and the melt flux treatment and plating step (S22) is performed, an aluminum alloy layer is first coated on the surface of the base material, and again thereon. A mechanism in which the aluminum-silicon plating layer is coated is implemented, and this mechanism provides a snowy structure (dense globular structure) by the reaction between metals.

In addition, in the process of passing through the dye bath step (S31), as the aluminum alloy layer and the aluminum-silicon coating layer formed on the surface of the base material is diffused based on the snow-like structure, deeply diffused into the surface of the base material, And the adhesion between the aluminum alloy layer and the aluminum alloy layer and the aluminum-silicon coating layer are further strengthened, so that the plating layer does not peel off even from a strong impact from the outside, and the plated product is made by the high adhesion double aluminum coating layer. It has excellent heat resistance.

As a result, it is possible to impart excellent heat resistance to the surface of the base material while securing dimensional accuracy that is difficult to be achieved by the existing zinc plating method or aluminum plating method, and at the same time improve the wear resistance imparted by aluminum plating. Since it can be made, it is possible to manufacture heat-resistant plating products that can be optimally applied to parts such as steel-related mechanical equipment, automobile internal combustion engine, nuclear power plant, chemical equipment, etc. exposed to poor high temperature conditions.

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

After the plating process (S20) and the salt bath step (S31) corresponding to the main part of the present invention as described above, the base material is removed from the salt bath and subjected to an air cooling step (S32) for cooling the base material in air under normal temperature conditions. This is to prevent the gap or crack of the plating layer which occurs during rapid cooling of the base material by slow cooling the base material as much as possible.

After the additional step (S30) consisting of the plating step (S20) and the salt bath step (S31) and the air cooling step (S32) as described above, the post-treatment step (S40) of the plated base material is subjected to, after The treatment step S40 includes a chemical cleaning step S41 and a water washing step S42 for the plating surface of the base material as in the conventional plating method.

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 performed as a post-treatment step (S40), is an important step in terms of improving the quality of the plated product, unlike the pretreatment step (S10), and thus, the concentration of the chemical solution stored in the chemical cleaning tank is increased. It should be checked from time to time so that the chemical solution in the chemical cleaning tank is always maintained 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 primarily completed.

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, the post-treatment to further improve the dimensional accuracy by further processing the surface of the plated base material After the chemical cleaning step (S41) and the water washing step (S42) as the step (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.

As described above, when the polishing step S43 as the post-treatment step S40 is included in the process step of the present invention, heat-resistant plating of small precision parts such as bolts and nuts is performed under conditions to further secure dimensional accuracy. On the other hand, it is also very easy and easy to remove a small amount of excess aluminum attached to narrow and narrow parts such as threads.

As a result, it is possible to produce a large amount of heat-resistant aluminum plating products on small precision parts such as bolts and nuts, thereby reducing the cost of the plating products as well as the scope of application of aluminum plating products. In addition, it can contribute to securing external competitiveness by providing wider dimensional accuracy and excellent heat resistance, and can provide heat-resistant plating products with almost the same quality as expensive stainless steel products or special heat-resistant materials. will be.

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 under a temperature condition of 720 ° C. At this time, a plating solution in which 5% by weight of silicon was added and dissolved based on 100% by weight of molten aluminum was used. The plated carbon steel pipe was immersed for about 15 minutes in a salt bath in which potassium chloride (KCl) and sodium chloride (NaCl) were mixed and melted at a temperature of 650 ° C., which was removed from the salt bath and air cooled. Subsequently, it was immersed in a 10% aqueous solution of nitric acid (HNO ₃ ) for about 5 minutes, followed by washing with water and drying to prepare a heat-resistant carbon steel pipe product coated with aluminum.

[Example 2]

A carbon steel frame 1m 50cm long and 5mm thick was sequentially immersed in a degreasing bath, a washing tank, a pickling tank and a washing tank, and then pretreated.The surface was pretreated, followed by 35% potassium chloride (KCl), 5% cryolite, and ammonium fluoride ( NH ₄ F) 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 composed of a component ratio of 60% was dissolved at a concentration of 10% by weight, and 25% sodium chloride (NaCl) and potassium chloride ( Melt flux consisting of 25% of KCl), 25% of Cryolite and 25% of Ammonium Fluoride (NH ₄ F) was added to the flux in the plating solution added at 7% by weight based on 100% by weight of molten aluminum-silicon. The treated carbon steel pipe was plated by immersion for about 4 minutes under a temperature condition of 710 ° C. At this time, a plating solution in which 4% by weight of silicon was added and dissolved was used based on 100% by weight of molten aluminum. The plated carbon steel frame was immersed in a salt bath in which potassium chloride (KCl) and sodium chloride (NaCl) were mixed and melted at a temperature of 680 ° C. for about 10 minutes. After immersing in a 10% aqueous solution of nitric acid (HNO ₃ ) for about 5 minutes, washing with water and drying, sandblasting the surface of the carbon steel frame, and finally washing and drying the heat-resistant carbon steel frame product coated with aluminum Was prepared.

Example 3

Structural bolts and nuts having a diameter or inner diameter of 2 cm in the fastening part are sequentially immersed in the degreasing bath, the washing tank, the pickling tank and the washing tank, and the surface is pretreated. 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 carbon steel pipe flux-treated in the plating solution added at 10% by weight was immersed for about 2 minutes under a temperature condition of 730 ° C, where 6% by weight of the molten aluminum was used. A plating solution in which silicon was added and dissolved was used. The plated bolts and nuts were immersed for about 5 minutes in a salt bath in which potassium chloride (KCl) and sodium chloride (NaCl) were mixed and melted at a temperature of 680 ° C., which were removed from the salt bath and air cooled. Subsequently, it was immersed in a 10% aqueous solution of nitric acid (HNO ₃ ) for about 5 minutes, washed with water, and dried. Then, the bolts and nuts were put into a vibratory polishing machine to perform polishing on the surface. Through the aluminum plated heat-resistant bolts and nuts were manufactured.

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 heat-resistant plating product without any part plated or pin-hole generated throughout the plating surface.

In particular, in the case of small precision parts such as bolts and nuts, excellent heat-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 the plating was completed. It showed that the level of dimensional accuracy without problems, it was found that the molten aluminum plating method according to the present invention can be sufficiently applied to the production of heat-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: salt bath stage S32: air cooling stage
S40: Post-treatment process S41: Chemical cleaning step
S42: washing step S43: polishing step
S44: washing and sorting stage

Claims (4)

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), the dye bath step (S31) is performed as an additional step (S30) to immerse the plated base material in the salt bath so that the aluminum plating layer penetrates into the surface of the base material. Hot-dip aluminum plating method for improving heat resistance characterized in that it is. The method of claim 1, wherein the dye bath step (S31), the immersed in a salt bath of 650 ~ 700 ℃ the base material is subjected to a process of maintaining for 5 to 20 minutes,
After the dye bath step (S31), the air-cooled step (S32) for cooling the base material in the air at room temperature conditions is further performed before the post-treatment step (S40), the molten aluminum plating method for improving heat resistance . The molten aluminum of claim 2, wherein the salt bath is formed by melting a chloride having a component ratio of 40 to 60 wt% of potassium chloride (KCl) and 40 to 60 wt% of sodium chloride (NaCl). Plating method. According to any one of claims 1 to 3, after the chemical cleaning step (S41) and the water washing step (S42) as the post-treatment step (S40), polishing step (S43) and water washing and Screening step (S44) is further performed,
The polishing step (S43) is a molten aluminum plating method for improving heat resistance, characterized in that the alternative method is applied from the vibration polishing or sand blasting (Sand blasting) method.

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