镀锌概论

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1、镀锌(Galvanizing)之字源

(1)以热浸方式将锌镀在钢品表面以便防蚀之方法吾人称为'镀锌(Galvanizing)'，或称为'热浸镀锌(Hot-dip Galvanizing)'。'Galvanizing'一字起源于意大利科学家Luigi Galvani(公元1737－1798年)之姓氏。Galvani于1791年发现以两只脚分别用铁与铜制成之夹子，夹住一块已死去的青蛙腿时，青蛙腿会抽动。Galvani误认为系青蛙腿本身存有电流使之抽动。
(2)过了几年，另一位意大利科学家，Alessando Volta(1745-1827)解释青蛙腿系一导体，并指出Galvani发现了另一个新的可产生电(流)的方法，即以不同的金属相接或直放于酸液槽内，则其中一金属会得一正电压，而另一个得一负电压(即电位差)。如再以一条电线连接两金属则可发现电线有电流通过。Galvani与Volta系人类首次发现可产生稳定电流之科学家。从此很多科学家投入研究，而成为一门新的领域称为'电化学(Electrochemistry)'。如电池与电解均利用此原理制成。
(3)吾人为纪念Volta之发现而将电压称为'Voltage'，其单位则称伏特(Volt)。另将不同金属之间因电位差(电化学)产生电的流动现象称为'Galvanic Action'用以纪念Luigi Galvani。将锌热浸镀在钢品表面而防钢品腐蚀之方法，即利用锌与铁(不同金属)之电位差，锌之电子流向铁而保护铁之方法称为Galvanizing，并专用为镀锌称呼。
2、镀锌方式之演进
(1)板片镀锌
1786年在英国发明以氯化铵(NH4C1)作为助镀剂(Flux)镀锌之方法。
1800年在德国将上述之方法工业化，此后镀锌制程主要在欧洲发展。
1837年，切板之镀锌技术取得英国之专利。
1846年在镀锌槽出口侧装设一对辊轮以控制镀锌量之方法开发成功。但此后约一百年间镀锌制程并无多大改善。
2、连续镀锌
a.Sendzimir制程

1931年波兰人Tardenz Sendzimir发现一套足以改变镀锌工业之制程，其方法为：冷轧后之钢带先在氧化气氛中预热，以去除在板面上之轧延残油，但也会在板面上形成一层薄氧化铁。钢带再进入氢—氮之还原气氛中高温将氧化铁还原，而使钢带表面达到适合镀锌之状况。接着钢带必须冷却控制以便在出炉时之温度适合镀锌。1936年美国Armco钢铁公司Butler工场成功地工业化故称为Armco—Sendzimir法，并于1938年取得美国专利。此制程亦称为氧化性直燃式炉(Oxidizing Direct—Fired Furnace)。Sendzimir法之另一优点在于不用助镀剂(Flux)故可在镀槽中加入铝(Al)以抑制硬脆之锌铁合金层(Zn-Fe Alloy Layer)过度形成，可提高锌之附着性与成形性。但因须在高温下将钢带表面氧化层还原，故无法生产全硬板。

1. The word source of galvanizing

(1) The method of hot dip galvanizing is called galvanizing or hot dip galvanizing. The word 'galvanizing' originated from the surname of the Italian scientist Luigi Galvani (1737-1798). Galvani discovered in 1791 that when a dead frog's leg was clamped with a clamp made of iron and copper, the frog's leg would twitch. Galvani mistakenly believed that the frog's leg had an electric current that made it twitch.

(2) A few years later, another Italian scientist, alessando Volta (1745-1827), explained that the frog leg was a conductor, and pointed out that Galvani had discovered another new method of generating electricity (current), that is, when different metals were connected or placed directly in an acid bath, one metal would get a positive voltage and the other a negative voltage (i.e. potential difference). If the two metals are connected by a wire, the current flowing through the wire can be found. Galvani and Volta are the first scientists who have discovered that a stable current can be generated. Since then, many scientists have devoted themselves to research and become a new field called 'electrochemistry'. If the battery and electrolysis are made by this principle.

(3) In memory of the discovery of Volta, we call voltage 'voltage', and its unit is called volt. In addition, the flow of electricity between different metals due to potential difference (Electrochemistry) is called 'galvanic action' to commemorate Luigi Galvani. Galvanizing is a method to protect iron from corrosion by hot dip galvanizing on the surface of steel products, i.e. by using the potential difference between zinc and iron (different metals), and the electron flow of zinc to iron, the method is called galvanizing, which is specially called galvanizing.

2. Evolution of galvanizing methods

(1) Sheet galvanizing

In 1786, the method of zinc plating with ammonium chloride (NH4C1) as flux was invented in England.

This method was industrialized in Germany in 1800, and since then the zinc plating process has been mainly developed in Europe.

In 1837, the zinc plating technology of cutting plate was patented in England.

In 1846, the method of installing a pair of rollers at the exit side of the galvanizing bath to control the amount of zinc plating was successfully developed. However, the galvanizing process did not improve much in the next 100 years.

2. Continuous galvanizing

a. Sendzimir process

In 1931, tardenz Sendzimir, a polish, discovered a set of methods to change the process of galvanizing industry. The method is: the cold rolled steel strip is preheated in the oxidizing atmosphere to remove the rolling residual oil on the plate surface, but a thin layer of iron oxide will also be formed on the plate surface. The steel strip enters the reduction atmosphere of hydrogen and nitrogen to reduce iron oxide at high temperature to make the surface of steel strip suitable for zinc plating. The steel strip must then be cooled so that the temperature at discharge is suitable for galvanizing. In 1936, the Butler workshop of Armco iron and steel company was successfully industrialized, so it was called Armco Sendzimir method, and obtained the American patent in 1938. This process is also known as oxidizing direct fired furnace. Another advantage of Sendzimir method is that without flux, Al can be added into the bath to inhibit the excessive formation of hard and brittle Zn Fe alloy layer, which can improve the adhesion and formability of zinc. However, due to the reduction of oxide layer on the surface of steel strip at high temperature, it is impossible to produce full hard board.