JP2009280895A - Hot dip zinc-aluminum-based alloy plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a method for performing hot dip zinc-aluminum alloy plating in the atmosphere and put it into practical use using a furnace which does not generate dross.
SOLUTION: Two furnaces that do not generate dross are used, hot dip galvanization using high-purity zinc is performed in the first furnace, and hot dip zinc-aluminum alloy plating is performed in the next furnace. Based on this plating process, pre-processing and post-processing are added as necessary.

Description

  The present invention belongs to a hot dip galvanizing method.

  Hot-dip galvanizing is used for rusting iron-based materials (steel, cast iron, etc.) to provide corrosion resistance, but hot-dip galvanizing that does not contain toxic substances such as lead and cadmium is required due to the demand for reducing environmentally hazardous substances. High-purity zinc (the highest purity zinc metal and special zinc metal) has come to be used. In addition, hot dip galvanizing with better corrosion resistance is required for longer life and environmental measures, and galvanized aluminum-aluminum alloy plating has come to be used. And even this alloy plating came to use high purity zinc. The reason is that it is not toxic and prevents impurities from segregating between crystal grains and causing intergranular corrosion.

  While molten zinc erodes iron plating furnaces, zinc-aluminum alloys erode the furnaces violently. Therefore, the lifetime of the furnace is short. In addition, the eroded iron reacts with zinc to form dross, increasing the consumption of zinc and floating in the molten metal. This floating dross deteriorates the wettability with iron and increases the viscosity of the molten metal. Therefore, non-plating and plating pools occur, and if it adheres to the plating surface, the corrosion resistance and appearance are deteriorated. As described above, the iron plating furnace has problems of erosion and dross generation.

  When hot dip galvanizing is performed in the air, the flux is treated before plating, and then immersed in hot dip zinc for plating. Although it is desired to perform the same in the case of performing hot dip zinc-aluminum alloy plating in the atmosphere, there is a problem in that the aluminum in the molten metal reacts with the flux, the flux breaks and non-plating occurs frequently. Moreover, since the plating film suppresses the alloy reaction with iron, only a thin film can be obtained and high corrosion resistance cannot be expected.

  Establish a method for hot-dip zinc-aluminum alloy plating in the atmosphere and put it into practical use using a furnace that does not generate dross.

  Using two furnaces that do not generate dross, hot dip galvanization using high-purity zinc is performed in the first furnace, and hot dip zinc-aluminum alloy plating is performed in the next furnace. Based on this plating process, pre-processing and post-processing are added as necessary.

  A practical method for hot dip zinc-aluminum alloy plating has been established.

  Using two ceramic furnaces, hot dip galvanization and hot dip zinc-aluminum plating are performed successively.

  As a pretreatment for hot dip galvanization, a treatment of immersing in a ferric chloride solution is performed. By this treatment, burrs, corners, weld surfaces, high stress portions, and the like are etched, and a substrate with a thin and uniform plating can be obtained. After that, pickling, flux treatment, and hot dip galvanizing. Prior to these treatments, a degreasing or shot blast treatment is performed if necessary.

  After hot dip galvanization, if necessary, it is cooled with water, but usually it is air cooled and hot dip zinc-aluminum alloy plating is performed.

If necessary after plating, the plating pool is removed with a centrifuge or water-cooled.

  The ceramic furnace is made of alumina material, zinc is the purest zinc metal or special zinc metal, and the zinc-aluminum alloy is 5% Al-Zn or 5% Al-1% Mg-Zn. Plating of gas pipes, piping joints, bolts and nuts, etc. was performed by the method described above. As a result, it was confirmed that dross was not generated except for the material to be plated and that good plating was possible.

  The following things were confirmed. The hot dip galvanization is removed and hot dip zinc-aluminum alloy plating is not possible. In the atmosphere, flux treatment is indispensable for hot dip galvanizing. When the material to be plated has burrs, corners, weld surfaces, high stress portions, etc., it is preferable to add a pretreatment soaking in a ferric chloride solution in order to obtain a smooth and uniform plating.

  Since a practical method has been established, it can be used for production upon request.

Claims (4)

  A hot dip galvanizing method characterized by using two ceramic furnaces, hot dip galvanizing in the first furnace, and hot dip galvanizing-aluminum alloy plating in the next furnace.   The plating method according to claim 1, wherein a flux treatment is performed in the pretreatment.   The plating method according to claim 1 or 2, wherein the pre-treatment is pickling after treatment with a ferric chloride solution.   4. The plating method according to claim 1, wherein shot blasting is performed in the pretreatment.