Soft brazing and strong brazing

Brazing is divided into two principal categories based on the fusion point of the filler metal used in the process: soft brazing and strong brazing.

As we know, brazing is used to join two pieces with the same material or different ones without having their fusion, for this reason, there are many alloys available to guarantee the best results in several applications.

Soft brazing

At what temperature brazing does turn soft?

Brazing is intended as soft when the filler material has a fusion point lower than 450° C.

Soft Brazing features

The most known soft brazing is the tin one and it is often used in the electronic field. Initially for this kind of brazing were used tin-lead alloys but they came out to much harmful due to the lead toxicity and its fumes emit during brazing.

In 2003 it has been releasing the new RoHS regulations (Restriction of Hazardous Substances Directive), and the lead alloys are been replaced with tin-copper and tin-silver ones,  forcing some restrictions about the utilization of specific dangerous matters. Today they are used several materials to compose soft brazing alloys and they all have a low fusion point such as copper, silver, but also antimony, bismuth, and others that are added to the tin in order to reach better performance during the soldering.

Soft brazing has some mechanical seal limits and it is generally used where it is not required a high level of mechanical seal and a low fusion point.

It is important to notice that if the operating temperature of the final product is high, soft brazing cannot be used.

making of soft brazing

Strong brazing

What is strong brazing?

Strong Brazing is a kind of welding that involves the use of filler materials with a fusion point upper than 450° C.

Strong brazing features

In strong brazing, they are used several kinds of alloys based on the materials to join or on the kinds of applications. The most used alloys are those based on silver, copper, and zinc with fusion points between about 600 and 900° C, and they are used for the welding of steels, copper alloys, and for many more material kinds.

The alloys based on silver have a fusion pint between about 500 and 600° C and they are mainly used in the refrigeration field, cooling, and automotive fields.

When it comes to using an alloy for the aluminum soldering characterized by lower temperatures, they are used alloys based on zin and aluminum that have a fusion point between 380 and 470° C.

A typical sample of the utilization of this kind of alloys is in the conditioning field, where the tubes thicknesses do not permit the utilization of alloys based on aluminum.

With this kind of alloy, it is also possible to make brazing copper-aluminum, radiators, or old brazed joints repairing.

Other kinds of alloys for strong brazing are: copper-phosphorus alloys, brass and copper alloys, and alloys based on silver.

Every operator, or brazing expert, has to well know the condition of the application he is facing, such as the operating temperature and the joint solicitations, in order to choose the most efficient and fitted filler material and soldering process.

esecuzione brasatura forte

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