The choice of flux for soldering is very important, the durability of the product depends on it.Soldering today is widely used in various industrial fields, it is used to obtain a permanent connection between solid materials. However, in order for the work to be done properly, you need to have the necessary set of tools and equipment, as well as consumables.

Among such materials - flux. And today we will tell you that it is and what this item represents.


  • 1 What is flux and its key features
  • 2 Features of fusible fluxes for soldering
  • 3 Description of refractory fluxes for soldering
  • 4 Classification of alternative types of solder
  • 5 How to collect flux for soldering do it yourself

What is flux and its key features

So, flux is such an alloy of metals, having a low-melting structure, which is used for soldering two different materials. This alloy can be made with your own hands, if you know the peculiarities of the combination of two different materials during their heat treatment.

The combination of two materials using flux comes out, provided that one or another temperature is maintained at the level of the seam. Depending on what material is taken,

temperature varies from 50 to 500 degrees. The melting temperature of the solder must be much higher than the melting temperature of the material that you process.

Such a thing as a flux for soldering has several varieties, it must be chosen depending on such factors:

  • metal;
  • soldering temperature.
  • temperature of the flux itself;
  • work surface parameters;
  • material strength;
  • its corrosion resistance.

There are two groups of fluxes:

  • solid, which have a high temperature threshold;
  • soft, such flux have a low melting point.

Depending on your needs, you can choose low-melting or refractory fluxes.Refractory solder has a melting point of 500 degrees or moreIt creates a fairly strong type of compound. But its disadvantage is that sometimes high temperatures can cause overheating of the key part of the structure and disable it.

And the melting temperature of low-melting solders ranges from 50 to 400 degrees. This type of flux includes the following components:

  • lead;
  • tin;
  • other impurities.

Such fluxes are mainly used for soldering items of radio engineering during their installation.

Fluxes for smelting various types of steel, copper and cast iron are sold in specialized stores.There are also superfusible solders, which are used for soldering and connecting transistors. The melting temperature of these fluxes can reach 150 degrees maximum.

To solder thin surfaces, you should use soft fluxes, and for soldering wires with a large diameter, you need to take solid solder, which has a high temperature threshold.

The required flux characteristics are:

  • the ability to conduct heat and current normally;
  • structural strength;
  • stretching ability;
  • corrosion resistance;
  • temperature differences in the melting of solder and base materials.

In the form of solder used materials such as:

  • twigs;
  • tapes;
  • wire coils;
  • colophony tubes;
  • other flux.

The most common form is a tin rod, the diameter of which is 1-5 meters.

There are also multichannel types of fluxes, which have several sources of solder inflow to create stronger connections. They can be sold in hanks or flasks, have a spiral shape and be contained in reels. For single use it is best to take a small piece of wire the size of a match.

For soldering the electrical circuit it is necessary to use pipe fluxes that contain colophonies. This is a resin that plays the role of solder. This filler material is perfectly capable of combining such types of metals as:

  • copper;
  • silver;
  • brass.

Features of fusible fluxes for soldering

Fluxes for soldering soft type can melt at temperatures up to 400 degrees. With their help, the seam becomes durable, soft and elastic.

Fusible fluxes are divided into the following categories:

  • with a minimum amount of tin;Anti-corrosion fluxes are needed for soldering products that are exposed to moisture.
  • lead-tin;
  • special;
  • ultrafusible.

The best option for solder is tin, but in its pure form it is practically not used, because this material is too expensive in itself. Most often, tin-lead solders are used, which provide strong joints.

The marking of such a flux contains the percentage of tin contained in it. Also, these solders contain antimony in small quantities and can be used for non-critical types of compounds that are not subject to stress or vibration.

Lead-free flux with low tin content is used for soldering contacts on small electrical circuits at temperatures up to 300 degrees.

At temperatures from 60 to 145 degrees ultrafusible fluxes able to become liquid and be used for manual soldering of delicate parts. The connection is not too strong.

And special solders are needed when you need to get compatibility characteristics with the main type of material. To do this, take compositions that are not amenable to soldering, including:

  • aluminum;
  • nickel;
  • low carbon steel;
  • cast iron.

So, for soldering aluminum parts, you need to make solder, which is almost entirely composed of tin, and for better diffusion, you need to add in a small amount of zinc, borax and cadmium.

Description of refractory fluxes for soldering

Refractory fluxes are also represented by a wide range.Solid solder is used to join joints that are subjected to different loads, shocks, vibrations and temperature drops. These fluxes can melt at temperatures of 400 degrees..

Solid solders are divided into the following categories:

  • copper-zinc alloys;
  • phosphor copper alloys;
  • silver flux;
  • pure copper.

It is worth noting that copper-zinc alloys are not used too often, because the strength of the seam is not too high, and their cost is unreasonably high.

Such a solder can be replaced with brass, or a bronze-zinc alloy.

Copper-based alloy with phosphorus can be used when brazing parts made of copper, bronze and brass, which are not heavily stressed, it is also used instead of the more expensive silver solder.

Solid fluxes can not be used when soldering iron and low carbon steel, because when heated iron with copper or phosphorus, brittle elements are formed, which then destroy the seam.

The best solder for iron is silver, but very expensive. However, using it materials are connected fairly well. Silver solder is used for soldering wires, complex silver-based boards.

Classification of alternative types of solder

Flux for aluminum soldering will help to connect fragments of aluminum wires and other products from this material.There are also other alternative types of solder:

  • flux with enhanced anti-corrosion properties based on acids, phosphorus and solvent. After soldering, there is no need to apply additional cleaning agents;
  • liquid type fluxes based on petrolatum, gold, salicylic acid and ethyl alcohol. They are used for soldering electrical wires or radiators, and the seams come out neat and clean;
  • air-bonded rosin. This flux is neutral and is used for high-precision electrical devices, such as relays, switches, cell phone circuits. Rosin should be used on pre-tinned and refined metals, and in order to clean diamond contacts with high quality, you can take laser;
  • auger mixed with rosin. This mixture is used for soldering copper water pipes, it is highly active and does not need to be stripped of materials. Borax is able to melt at a temperature of about 70 degrees and does not emit harmful substances;
  • homemade activated fluxused for soldering connections that are often subject to shocks and other stresses. To prepare it, you need to mix aniline rosin, anhydride, diatilamine and salicylic acid;
  • rosin-based flux with alcohol. Refers to the active, but at the time of high temperature indicators not only the oxide is removed, but also the metal itself. In addition, after soldering, you must carefully clean the board.

You can not leave the remains of the flux, they not only have an unattractive appearance, but also harmful. In electrical circuits, they can cause a short circuit, if not clean the surface on time.

To solder the tubes with colophony, you need to do the following:

  • clean the surfaces being joined from oxidation and dirt thoroughly;
  • the part in the weld must be heated to a value that exceeds the temperature of flux melting;
  • we make the soldering.

This method should not be practiced for large surfaces with good thermal conductivity, because to heat the metal sufficiently, the power of the soldering iron will be small.

How to collect flux for soldering do it yourself

When soldering traditionally used ascorbic acid, rosin or a special flux for aluminum.For the purpose of soldering radio wires you can use solders in the form of thin rods having a diameter of 2 mm, which are easily made with your own hands.

To make them, you will need a vessel at the bottom of which a hole is made, and then you will need to pour tin-lead solder into it in molten form. The vessel should be placed above the tin sheet or above the metal plate. After the rods harden, they can be cut into pieces of the required length.

This mixture can still be poured into forms:

  • tin gutters;
  • duralumin tanks;
  • plaster.

This is all done in the following way:

  • weigh the required amount of lead and tin;
  • melt the metal in a metal crucible above the gas burner, mixing it with a steel rod;
  • remove the thin film from the molten surface with a steel plate;
  • pour the alloy into forms.

Regardless of what type of flux you use, wipe the finished soldering with a cloth previously moistened with acetone or rectified. The seam is cleaned with a stiff brush, which you need to dip into the solvent before.

In the market can be purchased liquid and gel washless fluxeswhich have such advantages:

  • the absence of components that provoke oxidation and corrosion;
  • this type of flux does not conduct current;
  • no need to clean after soldering.

Liquid flux of this type should be applied with a cotton swab or brush. You can also make devices for its application on the basis of a conventional syringe and silicone hose, which will be filled with liquid flux.

Today in the shops you can buy a wide list of different fluxes.Soldering is one of the best methods for joining metals. It provides high level of strength, tightness, the process itself is simple and does not take much time compared to welding.

However, the ration of harm is due to the fact that during it harmful gases are emitted, therefore, one should not forget about protective gloves, glasses and apron on the basis of dense fabric.

In addition, the risk of poisoning can be significantly reduced through the use of mixtures from good manufacturers.