Welding is an ideal process for joining two metallic surfaces. By creating high-temperature at contact points, the fusion of material is achieved. This helps in a molecular-level joining of materials resulting in a strong weld. There are various types of welding processes that cater to different applications. These types differ from each other based on working principles.
One such type is the thermite welding process. Thermite welding works on the principle of welding two materials using a controlled chemical reaction. This chemical reaction produces high temperatures at the intended spot to fuse the material. To understand this welding technique in detail, we have explained every aspect of thermite welding in this article.
The Working Principle Of Thermite Welding
Thermite welding is based on the exothermic reaction. This process involves the production of immense heat. This helps in creating favorable temperatures for the fusion of two similar metals. This welding technique uses thermite, which is a combination of metallic oxides and powders. The mixture of aluminum and iron oxide is the most common combination used for thermite welding.
This welding technique was discovered due to the imitation of other welding techniques. Other welding techniques are suitable for a thinner surface. When the thickness of the material to be welded increases, the density of that material hinders the heat transfer process. Thermite welding offers a continuous heat supply and creates special alloys for joining such thick materials.
Thermite Welding Equipments
The thermite welding setup is a little different from the conventional welding setup. Since electricity is not used in this welding technique, the overall number of equipment is less. The equipment and materials are explained below:
1. Thermite Mixture
It is the most important material for this welding process. The thermite mixture has a specified percentage of aluminum powder and metal oxide. Aluminum is mainly used due to its attraction toward Oxygen. This helps in reaching higher temperatures to melt metal oxides.
2. Crucible
The crucible is a container made up of refractory materials. These refractory materials are resistant to high temperatures and allow the burning of thermite powder. The crucible holds the molten mixture before pouring it into the mold.
3. Mold
To guide the molten mixture onto the welding spot, a proper guideway is necessary. A mold is created around the parts to be welded with arrangements for unrestricted flow of the mixture. The mold is strengthened by using sand with a certain moisture content.
4. Runner
A runner is a small channel created in the mold which guides the molten mixture. It is fully responsible for the proper flow of mixture in the cavity between the workpieces.
All these pieces of equipment and material are set for the welding process. Now that we have a better understanding of the equipment and material, studying the welding process will be easy.
Steps Of Thermite Welding
Thermite welding is done in different stages since it involves high working temperatures. Steps must be followed properly to get a strong and clean welded joint of the metals. These steps are explained below:
1. Preparation Stage
This stage includes the preparation of metal surfaces for welding. Impurities on the surface create cracking of the joint and make it weaker. Proper cleaning of the surface is required to keep any impurities away. The surface to be wedded is then aligned properly to its intended position to avoid misalignment after welding. Preheating of the surface is done to remove any moisture from the material. This also helps in reducing the cracking of the surface by allowing faster dissipation of hydrogen gas.
2. Mold Fixation Stage
Creating a proper mold is an important stage of thermite welding. The mold helps in guiding the molten mixture in the cavity between the surfaces. The mold is provided with a runner to guide the mixture properly. A riser and gating system is also provided for letting the hot fumes away from the mold and helping in releasing trapped air.
If a wax pattern is used inside the mold, an opening is provided at the bottom for the safe draining of the molten wax. A thermite crucible is then connected to the mouth of this mold. The crucible holds the molten mixture before pouring it into the mold.
3. Welding Stage
In this stage, the thermite powder is prepared. By keeping the base metal of the surface in mind, the metal oxide and aluminum powder content can be decided. This powder is then placed into the thermite crucible. After ensuring preheating of the surface, this thermite mixture is ignited. The molten mixture is discharged into the mold and eventually reaches the cavity between two surfaces. Fusion of the metals starts due to the high temperature of more than 2,000 degrees Celsius. After the welding process, proper cooling of the welded joint is allowed.
4. Finishing And Inspection
After the welded joint is completely cooled down, surface grinding is done. This process is done to remove the rough edges on the surface and smoothen it. This also helps in making any surface crack visible. After grinding and surface fishing, a proper inspection of the weld is done. The surface is checked for any type of crack or air pockets. An inspection ensures the welded surface is free from any irregularities and the welded joint is then approved for safety.
Pros And Cons Of Thermite Welding
So far we have learned about thermit welding and its detailed process. Being a type of welding, this technique does have some advantages and disadvantages over other wedding types. These points are addressed below:
Pros
- Joining of dissimilar metals is possible due to the thermite mixture properties
- It is ideal for welding a workpiece with high thickness
- The welding process is less complex than other welding types
- It does not require electricity and can be used where a power supply is not available
- The process is less expensive and uses a minimal amount of equipment
Cons
- It is not suitable and economical to use thermite welding for thin workpiece
- Uncontrolled exposure to the high temperature leads to distortion of the metal’s grain structure which may further weaken the welded joint
- The overall welding rate is slow due to high preparation and cooling time
Application Of Thermite Welding
Having discussed the advantages of thermite welding, it is used for various industrial applications. These applications are based on various factors like the thickness of the material, overall cost, availability of electricity, etc. Some popular applications are mentioned below:
- Thermite welding is used in railway line constructions. To join two rail sections, thermite welding provides the needed strength and fusion of the rail material. The joint can sustain heavy loads of the locomotive and their loaded coaches
- It is used in welding thick sections of ship hulls. The welded joints use an aluminum powder mixture which creates a protective coating against rust. This property helps in keeping the joints away from corrosion when the ship is sailing in corrosive water of the sea
- Heavy gears of industrial machines like power presses are repaired with termite welding. The joints resist the continuous vibration of the power press and do not creep easily
Safety In Thermite Welding Process
The welding process involves high temperatures at the welding spot. Release of fumes and gas is expected from welding. Using electricity makes it important to use proper safety measures to keep users from getting electrocuted. Thermite welding is a comparatively safer technique yet the safety depends on the user. Only skilled professionals are preferred for this welding technique.
Igniting a thermite mixture creates a continuous chemical reaction leading to temperatures above 2,000 degrees Celsius. Maintaining the aluminum powder and metal oxide percentage in the thermite mixture helps in controlled burning. The thermite mixture is also checked for impurities which leads to unrefined molten material. Keeping a proper distance from the welding spot helps avoid any burning injuries.
Conclusion
Thermite welding has been proving a boon for joining thick workpieces. The welded joint creed using this technique has good strength making it ideal for heavy applications. With continuous development in thermite mixture materials, this technique is getting more popular and economical. With this article, we tried to provide all the necessary details related to thermite welding. The step-by-step process of thermite welding helps in getting a better idea about the working of this welding technique.
