Exothermite Welding 铝热焊

Exothermite welding is a liquid state welding process in which the metal to metal joint created by melting of base material or applying filler material in liquid form. This welding is further classified into chemical welding process because the heat required for melting the base material or filler material is achieved by exothermic chemical reaction. The word “thermite” is used for mixture of aluminum metal and iron oxide in ratio of 1:3. This process was discovered by Goldschmidt in 1898. This welding is mostly used to welding railroads and electric connectors.
放热焊接是一种液态焊接工艺,在此工艺中,金属与金属之间的连接是由基体材料熔化或填充材料以液态形式应用而产生的。由于熔炼基材或填充材料所需的热量是通过放热化学反应获得的,所以这种焊接进一步被划分为化学焊接工艺。“热剂”一词是指铝、金属和氧化铁按1:3的比例混合使用。这个过程是由Goldschmidt在1898年发现的。这种焊接主要用于焊接铁路和电气连接器。

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1 Principle 原理

As we discussed thermite welding is a liquid state chemical welding process, in which joint formation takes place in molten state. Practically, it is combination of welding and casting process in which, the molten iron poured at the welding plates and allow solidifying to make a permanent strong joint. The molten state of iron creates without application of external heat or conventional furnace so this is taken as a welding process. In this type of welding, a mixture of aluminum and iron oxide is used in ratio 1:3 by weight. This mixture chemically reacts as follow.
正如我们所讨论的,铝热焊是一种液态化学焊接工艺,其中接头形成在熔融状态下进行。实际上,它是焊接和铸造工艺的结合,其中,铁水浇注在焊接板上并且允许凝固以形成永久的牢固连接。铁的熔融状态在不施加外部热量或传统炉的情况下产生,因此将其作为焊接工艺。在这种类型的焊接中,铝和氧化铁的混合物以1:3的重量比使用。该混合物如下化学反应。

8 Al + 3 Fe3O4 –> 9 Fe + 4 Al2O3 + Heat

This reaction gives aluminum oxide and iron and also liberate a huge amount of heat which coverts this mixture into molten state. Because the molten iron have higher density compare to aluminium oxide so it remains bottom of the crucible. There is an opening at bottom of the crucible from where, this molten iron poured at the required plates where we want to create joint. This is basic principle of thermite welding.
该反应产生氧化铝和铁,并释放出大量的热量,将该混合物转化为熔融状态。因为与氧化铝相比,铁水具有更高的密度,因此它保持在坩埚的底部。在坩埚底部有一个开口,从那里,这个熔化的铁浇注在我们想要创建接头的所需板上。 这是铝热焊的基本原理。

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2 Equipment 设备

2.1 Refectory Crucible 坩埚

The thermite mixture of iron oxide and aluminum reacts in a refectory crucible. This crucible is made by graphite or other suitable refectory materials, which can handle temperature around 3000 degree centigrade. There is a gate at bottom of the crucible for exit of molten metal. The slag form by aluminum oxide floats over molten metal due to density difference which is removed from there.
氧化铁和铝的铝热剂混合物在坩埚中反应。该坩埚由石墨或其他合适的食品材料制成,可处理约3000摄氏度的温度。 坩埚底部有一个浇口,用于排出熔融金属。由于从那里除去的密度差异,由氧化铝形成的熔渣漂浮在熔融金属上。

2.2 Thermite Mixture 铝热混合物

A mixture of aluminum and iron oxide in proper ratio known as thermite mixture. The ratio of aluminum to iron oxide is about 1:3 by weight. In the copper thermite welding copper oxide with aluminum mixture is used.
铝和氧化铁的混合物,以适当的比例称为铝热剂混合物。铝与氧化铁的重量比约为1:3。在铜铝热处理中,使用具有铝混合物的氧化铜。

2.3 Mold 模具

In the thermite welding mold is created by either graphite or sand. Graphite molds are permanent mold which is used to make various similar joints. Sand mold are used where the joint design is different every time. For making sand mold, wax pattern is used. This mold made around the part that needs to be welded. It receives the molten metal. The mold contains runner, riser, gating system, heat opening etc. same as used in casting.
在铝热焊模具中,石墨或砂子都可以形成铝热焊模具。石墨模具是一种永久性模具,用于制造各种类似的接头。砂型用于每次接缝设计不同的地方。砂型采用蜡模制作。这个模具是围绕需要焊接的零件制作的。它接收熔化的金属。模具包括浇道、冒口、浇注系统、热口等,与铸造用相同。

2.4 Wax Pattern 蜡模

Wax pattern is used to make sand mold around the welding work pieces. The sand is rammed around the wax pattern to make sand mold. After proper ramming action, the mold is heated which removes the wax pattern by melting of it.
蜡模是用来在焊接工件周围制作砂型的。砂子在蜡模周围捣成砂型。在适当的捣打动作后,模具被加热,通过熔化去除蜡模。

2.5 Moulding Flask 砂箱

The sand mold creates into the moulding flask. The wax pattern which is created around the weld cavity, is placed at the middle of the flask. The molding sand rammed into the flask to make sand mold.
砂模形成模塑瓶。在焊接腔周围产生的蜡模放置在烧瓶的中间。将型砂夯入烧瓶中以制成砂型。

2.6 Mold handle clamp 模柄夹

This is a clamp which is used to fix moulding flask around the welding plates.
这是一个夹具,用于固定成型烧瓶周围的焊接板。

2.7 Ignite powder 点燃粉末

To ignite the thermite mixture, preheating of this mixture is essential, which is done by ignite powder. It is highly inflammable powder which can achieve the maximum temperature of 1300 degree centigrade which is essential to start thermite reaction.
为了点燃铝热剂混合物,必须预热该混合物,这通过点燃粉末来完成。 它是一种高度易燃的粉末,可以达到1300摄氏度的最高温度,这是开始铝热反应的必要条件。

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3 Working 工作

Now we know basic principle and essential parts of thermite welding. Thermite welding is similar like a casting process in which the molten state of metal is created by the chemical reaction. Its working can be summarized as follow.
现在我们知道了铝热焊的基本原理和基本部件。铝热焊接类似于铸造工艺,其中通过化学反应产生金属的熔融状态。其工作可归纳如下。

  • First both the work pieces which are needed to be weld, are cleaned.
    首先清洁需要焊接的工件
  • Now a wax pattern is created around the weld cavity.
    现在在焊接腔周围形成蜡模
  • A moulding flask is fixed around the joint with the help of mold handle clamp. This wax - pattern is situated at the middle of the flask.
    借助于模具手柄夹具将成型瓶固定在接头周围。这种蜡模式位于烧瓶的中间
  • Now the molding sand rammed around the wax pattern to create mold in which the molten metal will pour. This mold involves all necessary parts like runner, riser, pouring basin, gating system, opening for wax pattern etc. same as involves in casting.
    现在成型的沙子在蜡模周围打滚,形成一个模子,熔化的金属会在里面倾倒。该模具涉及浇道、冒口、浇注盆、浇注系统、蜡模开口等所有必要的零件,与铸件相同
  • Now this mold is heated to remove wax pattern. The wax is melted and run off from the wax pattern outlet prepared at bottom of the sand mold.
    现在加热该模具以除去蜡模。蜡熔化并从砂模底部制备的蜡模出口流出
  • Now the thermite mixture is taken into the refectory crucible. The ignite powder is placed over the mixture. This mixture is ignited by a magnesium ribbon.
    现在将铝热剂混合物放入坩埚中。将点燃粉末置于混合物上。该混合物用镁带点燃
  • This will start the thermite reaction which liberates a huge amount of heat. This reaction form molten state of iron which flows from crucible to sand mould.
    这将开始铝热反应,释放出大量的热量。该反应形成铁的熔融状态,从坩埚流到砂模
  • This molten metal fills the weld cavity and fuses the parent metal to make a permanent joint. This will allow to cool down. After proper cooling, flask is removed from the joint.
    这种熔化的金属充满了焊接腔,熔化了母材,形成了一个永久的接头。这样可以冷却下来。适当冷却后,从接头上取下烧瓶
  • After removing the flask, machining is done to remove the welding burr or other extra metal.
    拆下烧瓶后,进行机械加工以去除焊接毛刺或其他额外金属。

4 Application 应用

  • It is mostly used to weld railroad at the site.
    它主要用于现场焊接铁路
  • It was used to weld thick plate before introduce electroslag welding.
    在引进电渣焊前,用于厚板的焊接
  • They are used to repair heavy castings.
    它们用于修复重型铸件
  • It is used to weld cable connectors of copper.
    它用于焊接铜的电缆连接器
  • It is used to make structure joints in large ships etc.
    它用于制造大型船舶等的结构接头
  • It is used to joint pipe, thick plate etc. where power supply is not available.
    用于不供电的管道、厚板等的连接

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5 Advantages and Disadvantages 优点与缺点

5.1 Advantages 优点

  • It is simple and easy process.
    工艺较为简单
  • Low setup cost.
    安装成本低
  • Metal joining rate is high.
    金属连接率高
  • Thermite welding can be done at site where casting is impossible.
    铝热焊接可在无法浇铸的现场进行
  • This can be used where power supply is not available.
    可在没有电源的地方使用

5.2 Disadvantages 缺点

  • It is used for limited metals like iron and copper.
    仅限于有限的金属,如铁和铜
  • It is uneconomical for welding light parts.
    焊接轻型部件是不经济的
  • Highly depends on environmental condition like moisture contain, work piece alignment etc.
    高度依赖于环境条件,如含水率,工件对齐等