Introduction to Thermite Reactions and Rail Welding
Thermite reactions, discovered by Hans Goldschmid, involve the reaction of metal oxides with aluminum powder to produce pure liquid metal. This process has been widely employed in various applications, including railroads, where it is used to weld rails together, eliminating gaps and reducing wear and vibrations.
History and Challenges of Rail Welding
Initially, railroad managers were skeptical of welding rails together due to the potential for catastrophic consequences, such as buckling and derailments. However, with the invention of thermite, a process for welding with liquid metal, tram rails were the first to be discussed for removal due to their smaller size and lesser forces involved.
The Process of Rail Welding
Rail welding involves creating a gap between two rails, which is then filled with liquid thermite steel. To achieve a seamless connection, the rails must be aligned and angled upward to compensate for the contraction of the steel as it cools, ensuring a balanced pulling force and zero tension at the desired temperature. The process involves several steps, including:
- Aligning the rails, ensuring they are both vertically and horizontally level, with a specific gap of 2.4 to 3.6 units.
- Adjusting the clamping system to hold the mold shoes and preheating torch in place.
- Attaching the molds to the clamps, lining them up, and aligning them to create a watertight seal.
- Pouring steel into the mold, with emphasis on proper preparation, including aligning the rails and using sand with a high clay content to hold everything in place and prevent leaks.
Properties of Thermite Steel
Rapid cooling of liquid steel causes it to become hard but brittle, forming a structure known as martensite, which can break easily. The solidification of thermite steel occurs from the sides to the center, creating microscopic pores and a darker line. The boundary of the thermite steel isn’t sharp due to the liquid steel melting some of the rail, forming a strong bond.
Testing the Strength of Welded Rail
To test the strength of welded rail, sections are welded and then subjected to bending tests until failure, analyzing chemistry, hardness, and bending force. The tests show that the welded rail can withstand significant force, with catastrophic failure occurring at over 150 tons, and the crack propagating from the bottom upwards.
Mechanical Stress and Thermal Expansion
Mechanical stress can change the length of a rail, and the relationship between stress and strain is linear with elastic deformation. The rail will return to its original length when the stress is removed. There are two ways to change the length: thermal and mechanical, and one can be used to compensate for the other. Sleepers and ballast are used to pin down the rail and lock it in place, allowing the rail to expand sideways when the temperature increases.
Conclusion and Future Developments
Railways don’t need expansion joints due to mechanical stress counteracting thermal expansion and contraction, allowing trains to run faster with fewer bumps. A future episode will discuss working with thermite under different conditions, and the use of thermite in rail welding continues to be an important application of this technology.
Grammatical Structures
- Passive voice: “Thermite reactions, discovered by Hans Goldschmid, involve the reaction of metal oxides with aluminum powder to produce pure liquid metal.”
- Conditional sentences: “If the rails are not aligned properly, the weld may not be strong enough to withstand the forces involved.”
- Relative clauses: “The process of rail welding, which involves creating a gap between two rails, is a complex and challenging task.”
- Causal relationships: “The rapid cooling of liquid steel causes it to become hard but brittle, forming a structure known as martensite.”
- Comparative forms: “The welded rail can withstand significant force, with catastrophic failure occurring at over 150 tons, which is more than the force required to break a non-welded rail.”
Key Vocabulary
| Term | Definition | Example Usage |
|---|---|---|
| Thermite Reaction | A chemical reaction involving the combination of metal oxides with aluminum powder to produce pure liquid metal. | Thermite reactions are used in rail welding to produce a strong and durable bond between two rails. |
| Rail Welding | A process of joining two rails together using thermite steel to eliminate gaps and reduce wear and vibrations. | Rail welding is a crucial process in maintaining railway tracks and ensuring safe and smooth train operations. |
| Martensite | A type of steel structure that forms when liquid steel cools rapidly, becoming hard but brittle. | The rapid cooling of thermite steel can result in the formation of martensite, which can be prone to cracking and breaking. |
| Thermal Expansion | The tendency of materials to expand or contract when subjected to temperature changes. | Railway tracks are designed to accommodate thermal expansion, allowing them to expand and contract with temperature changes without compromising their structural integrity. |
| Mechanical Stress | The force or pressure exerted on a material, causing it to deform or change shape. | Mechanical stress can cause railway tracks to deform or become misaligned, leading to safety hazards and maintenance issues. |
| Thermite Steel | A type of steel produced through thermite reactions, characterized by its high strength and durability. | Thermite steel is used in rail welding due to its ability to form a strong and lasting bond between two rails. |
| Expansion Joints | Gaps or joints in railway tracks designed to accommodate thermal expansion and contraction. | The use of thermite steel in rail welding eliminates the need for expansion joints, allowing for a more continuous and smooth railway track. |
| Sleepers and Ballast | Components of railway tracks that provide support and stability to the rails. | Sleepers and ballast work together to pin down the rail and allow it to expand sideways when the temperature increases, reducing the risk of buckling and derailments. |
| Bending Tests | A type of test used to evaluate the strength and durability of welded rails. | Bending tests are used to determine the maximum force that a welded rail can withstand before failing, providing valuable insights into its structural integrity. |
| Catastrophic Failure | A sudden and complete failure of a material or structure, often resulting in significant damage or loss. | Catastrophic failure of a welded rail can occur when it is subjected to excessive force or stress, highlighting the importance of proper testing and maintenance. |
Watch The Video
Vocabulary Quiz
1. What is the primary purpose of using thermite reactions in rail welding?
A) To reduce the cost of rail maintenance
B) To increase the speed of trains
C) To produce pure liquid metal for welding rails together
D) To replace traditional welding methods
2. What is the result of rapid cooling of liquid steel in thermite steel?
A) It becomes soft and flexible
B) It becomes hard but brittle, forming a structure known as martensite
C) It becomes resistant to corrosion
D) It becomes heavier than the original metal
3. What is the function of sleepers and ballast in rail welding?
A) To absorb mechanical stress
B) To pin down the rail and lock it in place, allowing the rail to expand sideways when the temperature increases
C) To reduce thermal expansion
D) To increase the strength of the weld
4. What type of sentence is “If the rails are not aligned properly, the weld may not be strong enough to withstand the forces involved” an example of?
A) Passive voice
B) Conditional sentence
C) Relative clause
D) Causal relationship
5. What is the benefit of using thermite welding in railways, in terms of expansion joints?
A) It requires more expansion joints to accommodate thermal expansion
B) It eliminates the need for expansion joints due to mechanical stress counteracting thermal expansion and contraction
C) It has no effect on the need for expansion joints
D) It increases the number of expansion joints required
Answer Key:
1. C
2. B
3. B
4. B
5. B
Grammar Focus
Grammar Focus: Causal Relationships
Grammar Quiz:
Choose the correct answer for each question:
1. The use of thermite in rail welding ____________________ the need for expansion joints.
- A) eliminates because of mechanical stress
- B) reduces due to thermal expansion
- C) eliminates as a result of mechanical stress counteracting thermal expansion
- D) increases since the rails are more prone to buckling
2. The alignment of the rails ____________________ a strong and durable weld.
- A) hinders the formation of
- B) has no effect on the quality of
- C) is essential for creating
- D) reduces the importance of
3. The pouring of steel into the mold ____________________ the creation of a seamless connection between the rails.
- A) prevents the formation of
- B) has no impact on the quality of
- C) is crucial for achieving
- D) reduces the need for
4. The rapid cooling of liquid steel ____________________ the formation of a hard but brittle structure.
- A) slows down the process of
- B) has no effect on the formation of
- C) causes the formation of
- D) prevents the creation of
5. The use of sleepers and ballast ____________________ the rail to expand sideways when the temperature increases.
- A) prevents the rail from
- B) allows the rail to
- C) has no impact on the rail’s ability to
- D) reduces the need for the rail to
Answer Key:
1. C) eliminates as a result of mechanical stress counteracting thermal expansion
2. C) is essential for creating
3. C) is crucial for achieving
4. C) causes the formation of
5. B) allows the rail to
