Reaction soldering

Reactive soldering can also be called reactive soldering. It is classified:

1. On the reaction-flux;
2. To contact-reaction.

The soldering principles of these types have much in common, but using one of them achieves the best results in joining parts. Or, the other type of soldering may be impossible.

Reaction-flux soldering

In this type of soldering, the solder is formed by the reaction of flux and metal. Reactive flux soldering allows for joining different metals and their alloys. The soldering process technology:

• The surface of the parts is thoroughly cleaned to ensure optimal interaction with the flux. This also affects the strength of the solder joint;
• A sufficient amount of flux is applied to the surface of the parts to be joined;
• Next, the parts are heated, which melts the flux. It flows into the gap being joined. If the gap is slightly larger, additional solder is added;
• After this, a displacement reaction occurs, sometimes followed by a reduction reaction. A solder is formed between the flux and the base metal;
• Cooling should occur naturally. This will prevent the resulting joint from warping.

Reaction flux soldering has not gained widespread popularity due to its complex technology and the large amount of flux required. Furthermore, this type of soldering has been little studied. Among the many fluxes available, it is important to select the optimal one.

Contact-reaction soldering

This type of soldering relies on the ability of certain metals to form a solid solution or alloy at the point of contact. These metals have a melting point lower than the melting point of the metal being joined. In some cases, if the metals do not have eutectic properties, a galvanic coating or other method is applied to the surface being joined. This coating creates the necessary intermediate layer. The technological process for this type of soldering is similar to flux-reaction soldering, but there are distinctive features:

• No solder or flux is used;
• Pressure is applied during the soldering process. In the first stage of the process, gentle pressure creates good physical contact between the parts. It also forces out excess liquid along with oxide particles. This improves the interatomic bond between the two metals.

When reaction soldering is performed with flux, it is necessary to take into account that they differ:

• By aggressiveness;
• Its state of aggregation;
• By type of solvent.

Common fluxes include:

• boric acid;
• zinc chloride;
• borax;
• potassium fluoride;
• orthophosphoric acid;
• rosin-alcohol flux.

The flux composition is carefully selected for different metals, which determines the quality of the soldering. Particular attention is paid to the flux's reaction with the workpiece, specifically, whether it is chemically active or not. Some metal soldering is performed using fluxes that do not react chemically. Reactive soldering is a relatively fast process for joining metals.