What is brazing fat for: features and types of flux, the use of a neutral and active composition

Soldering people know that it requires solder and flux. Most of them use rosin and liquid formulations as the second component. Not everyone knows what brazing fat is for, which significantly increases the quality and speed of work.

This rather specific composition is rarely used by beginners, but it is used by many professionals. Despite its name, it has nothing to do with animal and vegetable fats.

Description of the composition

Like other fluxes, brazing fat is used to dissolve the oxide film on the metal at the soldering point. It is used in cases where rosin cannot cope with it, for example, when brazing steel. There are two varieties of this soldering flux, which have different compositions and properties:

• Neutral. It is used for soldering electrical and radio components and printed circuit boards.
• Active. It is used for soldering even large and highly oxidized elements made of ferrous and non-ferrous metals.

Neutral soldering fat is made on the basis of rosin and stearin. It easily dissolves oxides and impurities when working with low-temperature solders, for example, when brazing copper. It is not suitable for brazing aluminum and aluminum alloys. This flux provides softness and ease of soldering. It has a dense composition that allows it to adhere to wires and contacts. Unlike other types of flux, the amount of neutral fat can be accurately measured.

This solder composition increases the fluidity of the solder, so that it is evenly distributed over the soldering surface and penetrates well into any crevices. It has good solubility and can be easily washed off with water or organic solvent. Fat works as follows: when heated with a soldering iron, it becomes liquid, then burns out, forming a protective film on the material that prevents oxidation.

The active soldering fat contains petroleum jelly, paraffin, ammonium and zinc chloride. It has better soldering properties than neutral grease. It can be used to solder even hard-to-solder and highly oxidized parts.

But active fat is highly corrosive. It cannot be used for soldering radio and electrical products, as it is very corrosive and can dissolve small parts. After soldering, the surface must be thoroughly rinsed to avoid corrosion. The active composition is washed off as easily as the neutral one.

Advantages and disadvantages

Both types of flux have both advantages and disadvantages. The neutral composition has the following advantages:

• well processes soldered surfaces, which simplifies metal tinning;
• provides high quality soldering;
• easily washed off after the end of the process;
• does not contain active substances that cause corrosion and damage parts;
• does not conduct electricity;
• affordable;
• if stored properly, its shelf life is not limited.

Neutral fat has several disadvantages. These include the following properties:

• it is difficult to solder rusty parts with it;
• after the end of the soldering, a solid residue remains on the surface;
• soldering with it is less comfortable than using other fluxes (flux paste, LTI-120).

The active composition also has many advantages. Its pluses:

• it is better than other fluxes for soldering the surfaces of ferrous and non-ferrous metals.
• even highly oxidized materials can be soldered with it;
• the remainder of the flux is easily removed after the end of the soldering;
• the composition has a low cost and long shelf life.

When working with active fat, precautions must be taken. It has the following features:

• when heated with a soldering iron, the composition emits harmful substances, therefore, the workplace must be equipped with ventilation;
• to prevent corrosion, after the end of soldering, flux residues are removed from the surface;
• active substances of the flux can damage thin wires or electronic elements, therefore it is not suitable for delicate soldering.

Method of using solder fat

Working with this composition is no more difficult than with other fluxes, for example, rosin. Fat is used as follows:

• The required amount is applied to the work surface.
• The soldering iron tip is used to heat the soldering surface. At the same time, the flux melts, removing oxides. After its combustion, a film forms on the metal that protects against oxidation.
• Soldered using solder.
• After the end of the work, the remaining flux is removed with gasoline or other cleaning agents.

Soldering grease is a good tool for removing oxide film from the soldering area. The active composition allows soldering of large and highly oxidized parts, the neutral one is used for soldering radio components and printed circuit boards.

Care must be taken during handling and residual flux must be removed from metal surfaces to prevent corrosion.