Thermite Welding Portion
a) Definition and Applications
Thermite welding flux is a specialized material used in thermite welding. It utilizes the intense exothermic reaction between aluminum and oxygen at high temperatures to generate extreme heat, melting metal into molten steel and enabling the welding of metallic materials such as rails. Thermite welding portion is widely applied in:
● Continuous welded rail (CWR) joint welding for railways.
● Seamless welding of crane rails in subways, urban tram lines, and industrial production lines.
b) Key Components and Characteristics
The primary components of thermite welding flux include:
● Iron oxide powder (main reactant)
● Aluminum powder (fuel for the exothermic reaction)
● Alloy additives (e.g., ferrosteel, ferromanganese, ferrovanadium) to enhance weld properties.
During the reaction, these components produce molten steel and slag at temperatures exceeding 2,500°C. Key advantages of thermit welding flux:
● Portability: Minimal equipment required.
● High efficiency: Rapid welding process.
● Ease of operation: Suitable for field applications, including rail repair and splicing.
c) Safety and Handling Guidelines
● Composition control: Precise ratios of components must be maintained to ensure weld integrity.
● Storage: Keep in a dry, ventilated environment to prevent moisture absorption and contamination.
● Operational safety:
Wear heat-resistant gloves, goggles, and protective clothing.
Follow strict ignition protocols to avoid accidental combustion.
Sand Mould
a) Definition and Applications
The sand mould is a refractory mold used to secure and support rails during the thermite welding process. In thermite welding, pre-mixed thermite flux is ignited in a crucible, producing molten steel that is then poured into the preheated sand mold. The high-temperature molten metal fuses the rail ends within the mould, forming a welded joint upon cooling.
b) Structure and Materials
● Composition: Typically made of heat-resistant materials such as quartz sand or graphite, ensuring dimensional stability under extreme temperatures (up to 2,500°C).
● Design: Customized for rail profiles (e.g., UIC60, AREMA) to guarantee joint integrity and mechanical strength.
c) Key Considerations
● Preheating: Mandatory to eliminate moisture and enhance thermal shock resistance.
● Fabrication & Installation: Must adhere to welding specifications (e.g., alignment tolerances ≤0.5mm) to prevent defects.
● Process Monitoring: Real-time observation of mould condition (e.g., cracks, deformation) to adjust welding parameters (e.g., pour rate, preheat temperature).
One-shot Crucible
Definition & Function
The one-shot crucible is a high-temperature vessel fabricated from compressed and sintered quartz sand, designed for thermite welding of continuous welded rails (CWR). It serves dual purposes:
a)Reaction Chamber: Hosts the exothermic thermite reaction.
b)Self-Pouring System: Automatically releases molten steel into the sand mould post-reaction via an integrated tapping mechanism.
Key Features
● Robust Construction:
Quartz sand body: Withstands extreme temperatures (>2,500°C).
Outer iron casing: Provides moisture-proofing and impact resistance during transport/handling.
● Universal Compatibility: Adaptable to all standard rail profiles (e.g., UIC54/60, AREMA 115RE, DIN536 etc.).
Applications
Widely used for seamless welding in:
● Transport Infrastructure: Railway CWR joints, metro/tram tracks.
● Heavy Industries:
Steel mills (crane rails)
Ports & shipyards (gantry rail splices)
Power plants/refineries (process rail alignment).
Operational Note
● Single-use design: Ensures consistent reaction efficiency and eliminates cross-contamination risks.
● Storage: Maintain in original packaging until use to preserve dryness.
Luting Sand
Definition & Composition
Luting sand, also known as Luting paste, is a refractory sealing material formulated from a precisely blended mixture of quartz sand and bentonite. It is an essential consumable in thermite welding systems.
Primary Function
● Gap sealing: Fills cavities between the sand mold and rail surfaces to prevent molten steel leakage (>2,500°C).
● Pressure containment: Maintains metallostatic pressure during solidification for defect-free joints.
Technical Specifications
● Thermal stability: Withstands direct contact with molten metal without cracking (tested per ISO 17653).
● Workability: Exhibits optimal plasticity for manual application while resisting premature drying.
Operational Protocol
a)Pre-application:
Verify moisture content (typically 3-5% by weight).
Pre-pack sealing channels in sand mold.
b)Post-weld: Remove residual material to facilitate non-destructive testing (NDT).
Industry Applications
Mandatory for:
● High-speed rail CWR joints (EN 14730 Class C/D welds).
● Heavy-haul mining track repairs (ASTM A759 compliance).
Safety Note
Contains crystalline silica – Use of NIOSH approved respirators is recommended during handling.
