Exothermic Welding Powder

What is exothermic welding powder and what are the safety requirements for its storage and transportation?

Basic concept of exothermic welding powder
Exothermic welding powder is a high-energy reaction material used for connecting metal conductors and is an indispensable key material in exothermic welding technology. It is mainly composed of a mixture of metal powder and oxidant in a certain proportion, and the common ratio is aluminum powder and copper oxide. The reaction is triggered by an ignition device, and the exothermic welding powder quickly undergoes an aluminothermic reaction to produce high-temperature molten metal, thereby achieving a fusion connection between conductors.
The heat released by this chemical reaction can reach more than 2500℃, which is enough to melt copper or steel and complete the flow and cooling of liquid metal in the mold cavity. After the welded joint is formed, it has good electrical conductivity and mechanical firmness, and is widely used in grounding grids, lightning protection systems, cable connections, railway signal systems and other scenarios.

Main components and reaction principles of exothermic welding powder
The core reaction of exothermic welding powder is "aluminothermic reaction", and its reaction principle can be briefly expressed as:
3CuO + 2Al → 3Cu + Al₂O₃ + heat
During the reaction, copper oxide is reduced by aluminum to form copper and aluminum oxide, while releasing a large amount of heat. This high temperature can not only melt the metal part of the solder powder, but also partially melt the contact surface of the connected conductor, thereby achieving molten bonding.
Depending on the purpose of use, exothermic solder powder can be divided into copper-based solder powder, steel-based solder powder and dissimilar metal connection solder powder and other formulas. The amount and ratio of solder powder required for different conductor materials, conductor diameters, and mold structures will also vary.

Packaging form and use of exothermic solder powder
Exothermic solder powder is usually supplied in the form of quantitative packaging, and each package is a single-use dose. Common packaging includes aluminum foil bags, plastic sealed bags, metal cans, etc. Some are also equipped with ignition powder for auxiliary ignition. Each package of solder powder does not need additional mixing before use, and can be directly poured into the mold.
In order to achieve safe and rapid ignition, the matching ignition devices include match-type igniters, electronic igniters, flamethrowers, etc. Operators should be familiar with the packaging structure and ignition method of solder powder before use to avoid misoperation or ignition failure.

Storage environment requirements for exothermic solder powder
Since exothermic solder powder contains metal powder and oxidizing components, its storage conditions must be strictly controlled to avoid material failure or danger. The main requirements are as follows:
* Moisture-proof sealing: Exothermic solder powder is sensitive to humidity. If it absorbs moisture, it will cause difficulty in ignition, incomplete reaction or explosion. All packages should be sealed intact, and unopened unused solder powder must be resealed for storage.
* Dry and ventilated: The storage place should be kept dry and ventilated to avoid high humidity environment. It is recommended that the relative humidity is less than 60% to avoid solder powder agglomeration.
* Temperature control: Solder powder should be stored at room temperature, avoid being close to heat sources or direct sunlight, and avoid premature reaction or deterioration of materials due to high temperature.
* Isolation storage: It should not be stored mixed with acids, strong oxidants, strong reducing agents, combustibles, fire sources, etc. to avoid chemical reactions or fire hazards.
* Stable stacking: It should be stacked on a solid, horizontal, waterproof platform to avoid external force squeezing or falling from a height.

Transportation safety requirements for exothermic welding powder
When transporting exothermic welding powder, relevant transportation regulations for dangerous goods or sensitive materials should be followed to ensure the safety of personnel and goods. The main precautions include:
* Classification and identification: Although most exothermic welding powders are not included in the official dangerous goods catalog, they should still be marked as special materials that need to be handled with caution in international transportation or sensitive areas.
* Pressure-resistant and shock-resistant packaging: The outer packaging must have good shock resistance and sealing properties to prevent rupture, powder leakage or moisture absorption during transportation.
* Transportation tool requirements: Closed transportation tools should be used, and mixed transportation with flammable, corrosive, and moisture-releasing goods should be avoided. Severe vibrations should be avoided during long-distance transportation.
* Fire and explosion prevention measures: Fireworks should be prohibited during transportation, and drivers and escorts should understand basic emergency handling knowledge.
* Labels and documents: The transportation package should be clearly marked with the product name, weight, precautions, batch number, etc. At the same time, it should be equipped with a certificate of conformity and product instructions for inspection.

Expiration date and failure identification of exothermic welding powder
If welding powder is exposed to air or moisture during long-term storage, it may slowly oxidize or absorb moisture, thus affecting the reaction efficiency. Usually, manufacturers set the shelf life to 12 to 24 months, depending on the packaging and environment.
Ways to determine whether welding powder is expired include:
*Packaging bulging, air leakage, and damage
*Powder color darkening, agglomeration, and dampness
*Incomplete reaction after ignition and unstable sparks
*The joint metal fails to melt completely and welding fails
If the above situation occurs, it is recommended to stop using it immediately and properly dispose of the expired welding powder. Do not dump it at will.

Safety protection recommendations for using exothermic welding powder
When using welding powder for exothermic welding, it is recommended to wear the following protective equipment:
*High temperature resistant gloves to prevent high temperature burns
*Protective mask or goggles to prevent sparks from flying
*Heat-resistant long-sleeved clothing to protect arms and body
*Keep the construction site away from flammable materials and personnel concentration areas
During welding, avoid operating in confined spaces, maintain air circulation, and avoid smoke accumulation. Operators should receive basic training to ensure they are familiar with the usage procedures.