JPH0251977B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is an economical method for manufacturing galvanized steel sections, particularly lightweight steel sections, that have a long corrosion-resistant life in clean air or indoors and have a good appearance. The present invention relates to a hot-dip galvanizing method for manufacturing. [Prior Art] In recent years, with the expansion of the field of use of shaped steel materials, especially lightweight shaped steel materials, there has been a demand for products with superior quality in terms of corrosion resistance, appearance, paintability, etc. In fields where corrosion resistance is important, the use of galvanized steel sections is increasing, but the following types of galvanized steel sections with corrosion resistance have traditionally been used: things are used. (a) Steel sections plated using the general hot-dip galvanizing method (b) Steel sections galvanized using the electrogalvanizing method (c) Galvanized steel sheets [JIS G Products made from galvanized steel sheets such as 3315 etc. Among these galvanized steel sections, those in (a) are "post-plated products", those in (b) are "electroplated products",
Item (c) is called a “pre-plated item”,
There are limits to the thickness of the galvanized film obtained by methods (a) to (c) above due to technical and economic considerations, and the standard amount of zinc coating for general products (one side)
is as follows. Post-plated products: 350 to 600 g/ ^m2 Electroplated products: 30 to 100 Pre-plated products: 30 to 150 [Problem to be solved by the invention] However, the galvanized film cannot be used in normal atmosphere or in a dry room. The annual corrosion weight loss is approximately 10g/
m ² and most of the places where it is used have an annual corrosion loss of about 5 g/m ^2. Therefore, in the case of the above-mentioned post-plated products, the service life is longer than necessary, the corrosion resistance is of excessive quality, and the electrical Plated products and pre-plated products often have unsatisfactory service life in terms of long-term corrosion resistance. In addition, since pre-plated products undergo processing such as cutting and drilling after plating, the processed parts may become corrosion-resistant defects, and post-plated products have poor surface uniformity of the plating layer. There are cases where it is unsuitable as an indoor product for reasons of appearance. Furthermore, the hot-dip galvanized coating applied to the surface of steel sections consists of an iron-zinc alloy layer containing gamma crystals, delta one crystals, and zeta crystals as main components and a zinc layer (eta layer) in contact with the iron base. However, the main cause of the composition of the iron-zinc alloy layer is the diffusion of iron atoms, and the zinc layer is formed by the solidification of bath components that adhere to the zinc bath when the metal is pulled up from the zinc bath. Therefore, in the general hot-dip galvanizing method applied to post-plated products, it is necessary to immerse the zinc bath for a certain period of time (so that the bath temperature and the material temperature become equal), and in addition, the zinc layer is Because the smooth surface is obtained by sagging with
The maximum amount of zinc deposit is ^around 350g/m2, and it is not possible to reduce the amount of zinc deposited below that. On the other hand, in electroplated products, the thickness of the zinc coating increases depending on the electrolysis time, but from the viewpoint of productivity, products exceeding the above range not only significantly increase costs, but also have high internal stress in the coating, making it difficult to hold the substrate. This weakens the adhesion between the coatings and makes peeling more likely. In addition, since all of the above pre-plated products use galvanized iron sheets produced by large-scale continuous steel sheet plating equipment as raw materials, it is difficult to manufacture special products with thick plating layers. There is a risk that the coating may peel off during the molding process. In view of this, for long-term corrosion resistance in normal atmosphere or indoors, the amount of zinc deposited is
A range of 200 to 400 g/m ² is desired, but
It is practically difficult to obtain a galvanized section steel having a zinc coating thickness in this range using the plating methods commonly used at present. In order to obtain a section steel having a zinc adhesion layer in the above range using the hot-dip galvanizing method, it is necessary to enable immersion in a hot-dip zinc bath for as short a time as possible, and also to forcibly remove the excess zinc layer. As a device that is necessary and suitable for this purpose, a continuous plating device for plating the external surface of steel pipes (Japanese Patent Publication No. 53-25809) is proposed.
However, it was considered impossible to use this equipment to plate steel sections with complex cross-sectional shapes. In the hot-dip galvanizing process, a flux solution treatment is performed to remove the residual iron oxide thin film on the surface of the steel material before it is immersed in the molten zinc bath. This reaction generates hydrochloric acid gas, ammonia gas, water vapor, etc., and this gas prevents direct contact between the coating material and molten zinc, preventing the film formation reaction from occurring. For hot-dip galvanizing operations, it is important to maintain a material structure and a position that prevents accumulation on the surface of the coated material during dipping.
is important. Due to the external shape of steel pipes, this type of gas accumulation rarely occurs, but when moving steel sections with complex cross-sectional shapes horizontally in the axial direction, there will always be areas where gas accumulation occurs, making it difficult to maintain good maintenance. It is not possible to apply a coating uniformly and continuously. For this reason, it is conceivable to rotate the shaped steel materials around their axis during the process of transferring them in the zinc bath, but since the cross-sectional shapes of the shaped steel materials are complex and there are various shapes, it is difficult to use as a plating device. is mechanically difficult. As a result of extensive research in view of these problems, the present invention has discovered that good hot-dip galvanizing can be applied to steel sections by fluidizing the hot-dip zinc bath, The object of the present invention is to provide a method for hot-dip galvanizing steel sections using this method. [Means for Solving the Problems] In order to achieve the above object, the method for hot-dip galvanizing steel sections of the present invention is such that molten zinc or zinc-aluminum alloy flows in a constant direction at a flow rate of 2 m/sec or more. As the housing fills and overflows, the steel sections that have undergone pretreatment such as flux treatment are inserted into the housing through holes that are approximately the same size and shape as the cross-sectional shape of the section steel that is drilled in the housing. Plating is performed by introducing the molten zinc or zinc-aluminum alloy in the same direction as the flowing direction and bringing it into contact with the molten zinc or zinc-aluminum alloy. A gas body generated by the reaction with the zinc-aluminum alloy is discharged to the outside by overflow from the housing due to the flow of molten zinc or zinc-aluminum alloy, and a hole is provided in the housing opposite to the introduction hole. Immediately after the shaped steel is drawn out from the outlet hole, which has the same size and shape as the introduction hole, excess molten zinc or zinc-aluminum alloy attached to the surface of the shaped steel is blown off. . [Operation] When a shaped steel material that has undergone flux treatment is passed in the axial direction through a molten zinc bath flowing at a flow rate of 2 m/sec or more in the above housing, a reaction between the flux solution and molten zinc occurs. The gas generated by the molten zinc bath is effectively moved by the molten zinc bath flow and expelled to the outside as bubbles. Therefore, a good continuous galvanized film is produced without causing contact failure between the molten zinc and the surface of the shaped steel material. In addition, the introduction and outlet holes for the shaped steel materials drilled in the housing are formed to have approximately the same size and shape as the cross-sectional shape of the shaped steel materials, so that the molten fluid that fills and flows inside the housing can be removed. It is possible to minimize leakage of zinc or zinc-aluminum alloy from these inlet and outlet holes. Furthermore, since it is a fluidized bath, the thermal conductivity from molten zinc to the steel sections increases compared to a static bath, so the immersion time in the zinc bath is significantly shortened, and the thickness of the iron-zinc alloy layer is reduced. decreases. In addition, since the plating process is performed by moving the shaped steel material in the axial direction, excess zinc deposits can be easily wiped off with compressed air immediately after it is removed from the housing, and the zinc layer (eta As a result, a zinc-plated coating with a very beautiful appearance can be obtained. [Embodiment] An embodiment of the present invention will be explained with reference to the drawings. In Fig. 1, a flux treatment equipment 1, a drying preheating furnace 2, a molten galvanized steel plate, etc. A rolling equipment 3, a water cooling equipment 4, and a roll straightening equipment 5 are installed, and furthermore, the steel sections w are sequentially introduced into these equipment in the axial direction.
A plurality of conveyance rotation rolls 6 are provided for the purpose of leading out. The above-mentioned flux treatment equipment 1 supplies a flux (zinc ammonium chloride) aqueous solution in a treatment liquid tank 7 to a liquid pouring pipe 9 on the treatment liquid tank 7 by a pump 8, and from the pipe 9 to the treatment liquid tank 7. A wiper ring 10 is arranged on the processing liquid tank 7 in front of the processing liquid tank 7 so that the liquid is ejected towards the front. In addition, the drying preheating furnace 2 has an internal temperature of 150 to 250°C.
It is a heating furnace that can maintain a constant temperature of ℃. As shown in Figs. 2 and 3, the hot-dip galvanizing equipment 3 has a structure similar to a normal zinc melting furnace or galvanizing pot, and melts zinc and is a molten galvanizing machine that contains the molten zinc. Zinc bath 11 and this tank 1
It has a housing 12 disposed in the upper part of the interior of the housing 1, and a wiping ring made of iron pipe that is disposed close to the front surface of the housing 12 and has a large number of annular compressed air 13 outlet holes. This housing 12 has a box-shaped molten zinc flow case 16 that is long in the front and back direction and is integrally disposed within an outer wall cover 15 whose lower part is installed in the molten zinc bath 11. A zinc pump 17 transfers the molten zinc from the supply pipe 18 to the branch pipe 1.
The molten zinc is supplied to both the front and rear ends of the bottom surface of the flow case 16 through 9 and 19. Note that the wiping ring is made of shaped steel.
Use one designed in a shape and size that corresponds to the shape and size of the Furthermore, an overflow hole 20 communicating with the bathtub 11 is provided at the upper center of the molten zinc flow case 16, and the front and rear walls of the case 16 and the outer wall cover 15 are located at a height close to the bottom surface of the case 16. Introductory and outlet holes 21, 22, 23, and 24 for the shaped steel materials w are provided on the same axis in the front and rear walls of the case 14, respectively. It is designed to minimize the leakage of molten zinc from the cavity by forming it into a shape that corresponds to the cross-sectional shape of various shaped steel materials. In addition, the zinc leaking from this sky is in the bathtub 11.
Reflux within. The water cooling equipment 4 installed in front of the hot-dip galvanizing equipment 3 is connected to a large number of parallel pipes.
Warmed water at 90°C is sprayed onto the steel sections. Further, the roll straightening equipment 5 employs a roll straightening machine suitable for straightening the bends of the shaped steel materials w. To the equipment having such a configuration, the shaped steel materials w of an appropriate length are supplied onto the conveying rotating rolls 6, and each of the equipment 1 to
5, first, in the flux treatment equipment 1, the steel sections w introduced into the equipment 1 are coated with an aqueous flux solution (zinc ammonium chloride) spouted from the pipe 9 by the pump 8. Then, it passes through a wiping ring 10 that blows out compressed air while removing an excessively attached flux aqueous solution, and is once dried in a drying preheating oven 2. Next, the shaped steel materials w led out from the dry preheating furnace 2 are introduced into the hot-dip galvanizing equipment 3. The composition of the zinc bath filled in the bath 11 of this equipment 3 is the same as that of ordinary hot-dip galvanizing, which is a zinc base metal containing unavoidable impurities with a trace amount (0.01% or less) of aluminum added, or It is a zinc alloy containing less than 10% aluminum. Shaped steel materials w are introduced into the case 16 from the introduction hole 21 formed in the outer wall cover 15 of this equipment 3 through the introduction hole 23 formed in the case 16 of the housing 12. During the passage, the entire surface comes into contact with molten zinc. This molten zinc is pumped from inside the bathtub 11 by a zinc pump 17 to a supply pipe line 18, front and rear branch pipe lines 19, 1
9 flows inside the case 16 from the front and rear directions at a constant flow velocity of 2 m/sec or more, and the shaped steel materials w
The water flows back into the bathtub 11 through an overflow hole 20 formed in the center of the case. At this time, the flux solution applied to the surface of the shaped steel materials W reacts with the molten zinc to generate gases such as hydrochloric acid gas, ammonia gas, and water vapor, but these gases become bubbles as the molten zinc flows. and is discharged to the outside from the overflow hole 20. The steel sections that have been galvanized in this way are
Immediately after exiting the outlet hole 24, the excess molten zinc adhering to the molten zinc is blown off by compressed air which is blown out from a large number of small holes (1 to 3 mm diameter) in the wiping means 14. The pressure of the compressed air used is adjusted to 2 to 5 kg/cm ² . Next, the plated steel sections w are introduced into the water cooling equipment 4, where the molten zinc coating is solidified by spraying heated water, and then passed through the roll straightening equipment 5 to change the shape. It is straightened by rolls and becomes a product. Next, the results of a comparative test of hot-dip galvanized coatings obtained by the above-described hot-dip galvanizing method according to the present invention and the conventional hot-dip galvanizing method will be shown. The conditions for hot-dip galvanizing are as follows. Test material: Rip channel steel (100 x 50 x 20 mm, thickness 2.3 mm, length 5.5 m) Plating pretreatment Degreasing: Sodium orthosilicate + surfactant, liquid temperature 60°C Pickling: 10% hydrochloric acid, liquid Temperature: 20℃, immersion time: 30 minutes Flux treatment: Zinc aluminum chloride 30% aqueous solution, liquid temperature: 60℃ Galvanizing conditions: Zinc ingot used: Distilled zinc ingot: Class 1 distilled zinc ingot, 0.005% aluminum added (1) Molten zinc according to the present invention Plating method Zinc temperature 470℃ Zinc bath flow rate 4m/sec Material transfer speed 0.2m/sec Compressed air pressure for wiping off excess zinc 3Kg/cm ² (2) Ordinary hot-dip galvanizing method Zinc bath temperature 460℃ Zinc bath Immersion time: 60 seconds After inspecting the appearance of the lip groove steel that was hot-dip galvanized under the above conditions, five of each were taken out and the amount of zinc deposited was measured.The results are shown in the table below. Note that the method of the present invention is designated as A, and the conventional method is designated as B.

〔Effect of the invention〕

As described above, according to the method for force-dip galvanizing steel sections of the present invention, galvanizing of 2m/
Since the shaped steel products that have undergone flux treatment are passed in the axial direction through the molten zinc bath flowing at a flow rate of 2 seconds or more, the gas generated by the reaction between the flux solution and the molten zinc is absorbed by the molten zinc. It is effectively moved by the bath stream and can be reliably removed to the outside as bubbles.Therefore, there is no contact failure between the molten zinc and the surface of the section steel, and a good continuous galvanizing film is created. can be generated. Furthermore, since it is a fluidized bath, the thermal conductivity from molten zinc to the steel sections is higher than in a static bath, and the immersion time in the zinc bath can be significantly shortened.
The thickness of the iron-zinc alloy layer can be reduced, and the introduction and outlet holes for the shaped steel materials drilled in the housing can be formed to have approximately the same size and shape as the cross-sectional shape of the shaped steel materials. As a result, it is possible to minimize the leakage of molten zinc or zinc-aluminum alloy flowing inside the housing through the introduction and outlet holes, and prevent excess molten zinc or zinc-aluminum alloy from entering or exiting the grooves of the shaped steel materials. It is possible to efficiently and reliably produce a normal galvanized film by allowing the zinc to pass through the housing without stagnation. In addition, since the plating process is performed by moving the shaped steel material in the axial direction, excess adhering zinc can be easily wiped off with compressed air or the like immediately after it is removed from the housing, and this blowing process By this method, the zinc layer (eta layer) can be reduced and a galvanized coating with a very beautiful appearance can be obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a simplified configuration diagram of the apparatus, FIG. 2 is a vertical side view of the hot-dip galvanizing equipment, and FIG. 3 is a cross-sectional view thereof. 1... Flux processing equipment, 3... Hot-dip galvanizing equipment, 4... Water cooling equipment, 11... Molten zinc bath, 12... Housing, 14... Blowing means,
16... Molten zinc flow case, 17... Pump,
19, 19... Diversion pipe line, 20... Overflow hole.

Claims (1)

[Claims] 1 2m/2m of molten zinc or zinc-aluminum alloy
The cross-sectional shape of the shaped steel material that has undergone pre-treatment such as flux treatment is drilled into the housing, which is filled and overflowing while flowing in a constant direction at a flow rate of more than 1 second. Almost the same size,
Plating is applied by introducing the molten zinc or zinc-aluminum alloy in the same direction as the flow direction of the molten zinc or zinc-aluminum alloy through a hole of the same shape and bringing it into contact with the molten zinc or zinc-aluminum alloy, and the contact coats the surface of the shaped steel material. The gas generated by the reaction between the flux solution and the molten zinc or zinc-aluminum alloy is discharged to the outside by overflow from the housing due to the flow of the molten zinc or zinc-aluminum alloy, and the gas is discharged to the outside by the flow of the molten zinc or zinc-aluminum alloy, and the gas is discharged to the outside by the flow of the molten zinc or zinc-aluminum alloy. Immediately after leading out the shaped steel material from an outlet hole of the same size and shape as the inlet hole that has been drilled, be sure to wipe off any excess molten zinc or zinc-aluminum alloy that has adhered to the surface of the shaped steel material. Features: Hot-dip galvanizing method for shaped steel materials.