Selecting flux for soldering material. How and with what to replace missing flux.

Soldering galvanized iron requires a specific approach to the process. Flux is required for this. This substance is both a solvent and an oxidizing agent. Additionally, this substance allows the metal to be wetted with iron, so you can get a high-quality seam. Most often, rosin or hydrochloric acid is used as a flux for working with galvanized parts or products at home. In some cases, it is possible to use boric acid or zinc chloride.

Soldering galvanized iron at home: tips from professionals

Soldering galvanized sheets - Metalworker's Guide

Both in production and at home, people are faced with the need to solder parts made of tin, which has its own characteristics and preparation.

In fact, tin is cold-rolled sheet steel, which is subsequently subjected to heat treatment and galvanic coating in the form of tin, zinc, chromium and other materials.

Tin (white and tinned) is used in the production of cans for cold drinks or metal containers of any size. In this way, lightening of the packaging body is achieved. Therefore, correct soldering of this metal is important.

Welding galvanized steel: technology

Welding galvanized steel is a process based on introducing a low heat content into the product (steel), which leads to further melting of the filler material used. Steel welding is used today in many types of construction work for fastening various structures, sheets, frames and other things.

Scheme of the steel galvanizing process.

Modern requirements for the protection of metals from corrosion during and after work are increasingly reduced to the use of materials already coated with a protective layer.

When is galvanized metal suitable for soldering?

To correctly solve the question of how to solder galvanized steel, it is necessary to consider some of the properties of zinc. This metal begins to melt at a temperature of +460 o C. And at a temperature of +960 o C it begins to evaporate. Above these temperature values, pores, cracks and solder joint defects begin to form in the material. Therefore, the procedure can be carried out only with lower rates. An alternative is to use filler wire. In industrial conditions, the procedure in this case is carried out in a protective gas environment. Wire containing copper with silicon, bronze and aluminum is more often used.

These materials provide the following advantages:

the welding seam is protected from corrosion;
Spattering during soldering is minimal;
the coating fades slightly;
the procedure requires low heat levels;
processing the formed seam is simple;
Natural cathodic protection is formed in the weld area.

Solder for household work, its composition and properties

Solders are usually classified into hard and soft. For soldering galvanized steel at home, only the second group is used. If you use hard solders, it is not only impossible to achieve a high-quality weld, but there is also a risk of warping of the galvanized iron products themselves. Filler materials must have a low melting point, the point should be lower than that of the base material. Most often, POS-30 solder is used at home; it is a tin-based substance. It is better to use zinc chloride as a flux. If the surfaces have been tinned in advance, then rosin can be used. POS 30 is characterized by the following properties:

optimal fluidity, materials penetrate into all spaces, filling even small voids;
relatively low melting point;
POS 30 are produced in various standard sizes, which allows you to select the optimal modification for specific work;
a high degree of wettability facilitates the process and guarantees higher quality results;
materials can be used for tinning workpieces;
POS 30 has good conductivity and low resistance, which allows it to be used for soldering small parts;
After hardening, the materials rigidly fix the parts together.

The connections are smooth and tight. The seams are balls on top of the base material.

If the elements to be soldered are large, then before soldering they need to be tinned - cover the surfaces with a thin layer of solder. The same action is necessary when soldering cylindrical products that fit into each other. If these are pipes, then solder is applied to an element with a larger diameter from the inside, and for a part with a smaller diameter - from the outside.

POS 30 consists of 30% tin and 70% lead. The material has the following technical parameters:

the material begins to melt at +180 o C;
complete melting of POS 30 occurs at a temperature of +256 o C;
density – 10.1 kg/m3;
alloy elongation in relative terms – 58%;
crystallization interval – 73 o C;
tensile strength – 32 mPa.

Soldering parts from different types of sheet metal: features and technology

Both in production and at home, people are faced with the need to solder parts made of tin, which has its own characteristics and preparation.

In fact, tin is cold-rolled sheet steel, which is subsequently subjected to heat treatment and galvanic coating in the form of tin, zinc, chromium and other materials.

Materials for soldering metal

The classic version of soldering sheet metal requires solder containing tin and other chemical elements, flux, and a soldering iron with an awl.

According to the recommendations, solder of the POS 40, POS 30 and POSS 4-6 brands should be used. This is due to the chemical properties of the materials during the tin soldering process. Each solder may contain several elements, including tin, antimony, arsenic, copper and bismuth.

These solders differ from others in shear resistance due to the impurity content. For example, POS 40 contains 40% tin, 2% antimony, 0.05 - 0.1% of the remaining elements. It also increases the tensile strength of the seam after soldering. When tin decreases in the composition, antimony is increased.

But it also happens that soldering requires the presence of a component such as lead (POS 90). In the case of galvanized material, the situation is different.

Soldering iron requires the presence of flux. Essentially, it is a solvent and a chemical oxidizing agent. During soldering, thanks to this element, oxidation does not occur. It also ensures that the metal is wetted with iron for better weld quality. Popular fluxes for metal are hydrochloric acid and rosin. The latter is actively used in the radio engineering industry. Zinc chloride and boric acid are sometimes used.

It will not be possible to select the most suitable flux for soldering parts made of tin, since each of them gives a positive result. If it is necessary to dissolve thick fatty substances, ammonium chloride is used. Often, mixtures of the above components are made for this procedure.

An important role in the process of soldering with tin is played by the tool used, which is usually a soldering iron. According to recommendations, its power should be more than 40 W. It is advisable to use an electric soldering iron. In this case, soldering will be convenient, and the resulting seams will be strong and reliable.

It should be noted right away that you should not leave the tool in a heated state unnecessarily in order to avoid a fire, as well as deterioration of the properties of the handle.

Soldering stations are used in industry, the cost of which is several times higher than classical equipment, but the products have various attachments, as well as additional elements (stand, temperature sensor, etc.).

Soldering process of metal parts

Soldering involves several stages, during which a high-quality seam is ensured. To solder metal you need:

surface cleaning;
degreasing;
applying flux;
preparing a soldering iron;
tinning the place of the future seam;
soldering of tin plate elements;
cleaning the surface with a gasoline mixture;
control of the resulting seam.

Cleaning of surfaces is ensured by the following tools:

The gap between the parts must be 0.3 mm for capillary forces to occur. This situation allows the metal to fill the edges of the gap and provide a quality seam. Sometimes parts cannot be cleaned mechanically and etching is used, but in the case of tinplate this is a rare option. If there are grease stains on the surface, it is necessary to use a soda solution (10%). At home, degreasing is done using acetone, gasoline or alcohol-gasoline mixture. Their properties ensure excellent cleaning.

The next stage of soldering tin metal is the application of flux. As a rule, this is done with a brush or rag. The flux is stored in ordinary containers at room temperature. Soldering involves abundant wetting of the seam area with this component.

In the process of preparing the soldering iron, it is necessary to ensure that the surface is clean so that in the future the solder can spread freely along the working plane. To do this, use coarse sandpaper or a regular file to sharpen the tip of the tool.

Then it is plugged into the network and warms up. Periodically, the tip is moistened with ammonia tincture to avoid unnecessary contamination. By the way, it is with this mixture that the heating level of the instrument is checked.

When the soldering iron is well heated, the ammonia on the surface begins to hiss and becomes covered with a greenish-blue tint.

Next, tinning is carried out. It should be noted that when soldering tin parts such as cans, this step is skipped, since it is included in the manufacturing technology. It provides increased density and strength of the seam. An important aspect is that the process is performed with the same material that is used during soldering. Thus, if metal soldering is carried out by POS 30, then tinning is also carried out with this solder.

The process of soldering metal products itself involves securing the elements for the convenience of creating a seam. One piece of tin is placed on top of another, or a small gap is formed between them. You can hold the edges using an awl or other similar tool. Using the heated tip of a soldering iron, take a little POS 30 (POS 40) solder and turn it to the side to spread this material over the entire surface (if the surface is not completely filled, it means the tool has not been properly cleaned).

The tip with solder is brought to the iron products and passed along the intended seam with smooth movements. Consolidation plays an important role in this case, since in the event of a potential shift, the process will have to be repeated again. Thus, the required amount of solder is applied to the surface, forming a high-quality seam. The soldering iron should be pressed with the entire edge, and not with its individual end. During this process, the elements of the sheet metal are also heated, due to which the seam is well attached to the surface.

After soldering is completed, the resulting metal layer should be treated with a gasoline mixture or alcohol to reduce the heat concentration and clean it from solder and acid residues. This helps prevent rust from occurring in the future.

Equipment for work at home

Before wondering how to solder galvanized iron at home, you need to prepare the necessary equipment. The main tool is a regular soldering iron with an awl-shaped tip. But other devices will also be useful. A soldering iron requires a special holder or stand that will hold the tool in a heated state. To accurately connect small parts, you will need tripods with optical lenses. To remove smoke from the room - smoke absorbers. Tin pumps will be needed to remove excess tin. There are various switches, thermal pastes, control modules and adapters. This equipment will not only allow you to perform the soldering process, but will also provide the highest quality results.

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Differences between metal soldering and welding

There are two main methods of joining two metals: welding and soldering. In the first case, the elements are held together by melting the edge of the metal. This can be either heating or bonding using pressure. In the case of soldering, the workpieces are fastened together using filler material - solder.

In some cases, soldering is a more gentle and economical way of joining workpieces. Soldering also has a number of advantages:

Both parts do not heat up to the melting point. In this way, it is possible to preserve their physical and chemical properties.
The workpieces do not require thorough cleaning and processing, as is required when welding.
Soldering equipment costs much less than welding machines.
Possibility of manufacturing complex units and structures.
The strength of the resulting joint. The parts do not bend or deform after soldering.

Let's take a closer look at the methods of soldering different metals.

Flux for soldering microcircuits

In many industries and production, flux is used for soldering microcircuits, which serves as an integral attribute of the permanent connection of solid materials with each other.

In order to ensure a high-quality connection, you will need special kits, working tools, as well as consumables in the form of solder and liquid flux for soldering microcircuits. According to generally accepted rules, the material should have an excellent low melting point nature as well as low specific gravity.

Soldering of non-ferrous metals

Products made of non-ferrous metals require precise fitting. That is why they are often soldered rather than boiled. Let's study certain types of non-ferrous metals and their bonding using soldering.

Always secure both workpieces using a vice, clamps or other fasteners. Especially if you are working with large parts. Vibrations or shifts during soldering can warp the seam and the solder can drip. This will make the joint brittle and, over time, cracks or fistulas may form on it.

Soldering copper

Copper is a fairly common metal in everyday life. Water pipes, electrical cables, electronic components - they are all partially or completely made of copper.

There are mainly two methods for soldering copper:

High temperature (working temperature about 600 ˚С);
Low temperature (working temperature up to 450 ˚C).

In this article, we are considering soldering at home, so we will take low-temperature technology.

To solder copper you will need:

Solder. It is mainly made from alloys of tin (95-97%) with copper, antimony, bismuth, silver, and selenium. Silver-containing solders have the best properties. Three-component types, which include tin, copper and silver, are also widely used. The use of tin-lead solders in production is limited due to the harmfulness of lead. At home, you should also protect your lungs from lead fumes. Use an active hood.
Flux for soldering copper (activated, acidic, non-acidic, anti-corrosion).
Gas-burner.

Large industries and factories often use solder paste. Most often it contains: flux, small particles of solder and special additives.

Let's look at the step-by-step technology for soldering two copper elements:

Flux is applied to both parts. They cover the joint and the area where solder will be applied.
Solder is placed at the joint. This can be tin wire or a special paste.
The resulting compound is heated using a gas burner. Solder is distributed over the joint, as well as partially over the area near the solder.
The resulting workpiece is left to cool. At this moment, you cannot twist or bend the resulting part. The joint must be completely cool before the solder can fully harden.
Remaining flux is removed using an abrasive brush.

Do not point an open flame directly at the solder. It should melt and fill the seam due to heating of the edges of the parts.

Soldering aluminum

Aluminum is a rather capricious material. Many experts believe that it is simply impossible to fasten two aluminum blanks at home, since the place of fastening must be heated to a temperature of about 600 ° C, and this risks burning out the aluminum sheet itself.

But this statement is not entirely true. You can solder two aluminum elements if you use a special flux and solder. Let's take a closer look at all the components that will be needed to work with aluminum:

Solder. The best solders for working with aluminum are those containing: silicon, aluminum, copper, silver and zinc. These include domestic solder “34A” or its foreign analogue “Aluminium-13”.
Flux. It is better if it contains ammonium fluoroborate with the addition of triethonalamine. Some people use regular borax.
Soldering iron with a power of at least 100 W.

Solders with a high zinc content have better anti-corrosion properties.

Flux for soldering metal parts: what it is, its purpose and types

In many industries and in everyday life, soldering is used to connect metal parts and repair any equipment. In order for the work to be of high quality, you need special tools and consumables in the form of solder and flux. And while everything is relatively clear with tools and solder, few people know about flux. Therefore, before the soldering process, you need to understand what flux is and why is it needed?

Fluxes - definition, purpose

Fluxes are chemical active substances with the help of which soldered surfaces are cleaned of grease and oxide films. Surface tension on parts treated with flux is reduced, resulting in improved solder flow. In addition, this chemical can protect joints from environmental influences.

Without flux treatment, solder may not adhere to the surface of the workpiece. Therefore, the material should be selected carefully, guided by the following requirements:

The flux must have a melting point lower than that of the solder.
It should not react chemically with the solder. That is, when these two materials melt, two immiscible layers should form.
In the gaseous state, the material should allow the solder to flow.
In a liquid state, it should spread well, wetting the products being connected and flowing between them.
The material must destroy and remove non-metallic films formed on them from surfaces.
It must be minimally active or chemically inert with respect to soldered alloys and metals.

What types of fluxes are there for soldering?

Most often, soldering material is prepared from 10 grams of ammonium chloride and 30 grams of zinc chloride , dissolving them in 60 milliliters of water.

"Soldering acid" or "soldering fluid" is also used. They can be prepared from preserved hydrochloric acid and zinc metal:

pour the acid into a porcelain or glass container and add zinc in portions;
as a result of dissolving zinc in acid, oxygen should begin to be released and zinc chloride should form;
after the release of oxygen slows down, the container should be placed in warm water;
at the end of the reaction, the liquid is drained and only undissolved zinc remains, to which ammonia must be added (2 grams of ammonium per 3 grams of metallic zinc).

The liquid can not be drained, but evaporated to dryness. Then, immediately before soldering, the resulting mixture is dissolved in water (1:2).

However, fluxes prepared in this way are not suitable for all metals. According to the degree of effectiveness, they are divided into three groups:

Due to their weak activity, protective or non-corrosive materials They are mainly used for joining copper, its alloys and cadmium-, tin- or silver-plated steel products. In this case, solders should only be low-melting. Protective fluxes include rosin and its various solutions, petroleum jelly, stearin, wax, and wood resins.
Slightly corrosive substances They are more active compared to non-corrosive ones.
Most often these are mineral oils, animal fats, organic acids (oxalic, benzene, stearic, oleic, citric, lactic, etc.) dissolved in alcohol, water or organic acid derivatives.
In order to weaken the corrosive effect of such substances, rosin or other substances that do not cause corrosion are added to them. Slightly corrosive substances are used when soldering only with low-melting solders, since they easily decompose, burn and evaporate.
Corrosive soldering fluxes consist of metal fluorides and chlorides and inorganic acids. They are capable of destroying any resistant films of non-ferrous and ferrous metals, therefore they are effective when soldering by any method. Corrosive materials are used in the form of aqueous solutions in paste and solid states.

Materials for soldering aluminum

It is difficult to connect aluminum products by soldering under normal conditions, since an oxide film forms instantly on its surface. Therefore, it should be poured with molten rosin immediately after stripping .

To solder aluminum, you need a powerful soldering iron, as well as special solder and flux.

In most cases, connections of aluminum parts are made with tin-lead and multicomponent solders, which include bismuth, cadmium, zinc and other materials. They can also be applied to aluminum alloys. Such solders contribute to durable and excellent joining of aluminum products.

For soldering aluminum, concentrated orthophosphoric acid or “binary” flux is most often chosen. The no-clean material must be applied to the part in a thin layer until the surface turns white.

You can also use an active no-clean flux, after which no cleaning of surfaces is required. It can be used to solder copper and stainless steel .

How to clean stainless steel

In most cases, phosphoric acid is used for stainless steel. This substance of inorganic origin of medium strength is hygroscopic colorless crystals. When brought to 213C, it turns into pyrophosphoric acid.

As a rule, flux in the form of an 85% aqueous solution of phosphoric acid is used for stainless steel. However, other solvents, such as ethanol, can also be used.

The acid is applied to the surface of the steel in a thin layer, thereby cleaning it from dirt and rust and forming a film protective against corrosion.

Flux for brass

This material requires a special flux. However, you can also use a universal one, which is suitable for soldering galvanized iron, aluminum, copper, corrosion-resistant alloys, and bronze.

The flux special for brass must be shaken . With its help, a strong connection will be obtained and an anti-corrosion coating will be formed.

Silver processing material

For soldering silver, it is recommended to choose a specialized flux. This material will neutralize the soldering area and prevent the appearance of an oxide film. Before using it, the surface of silver products must be slightly heated using a gas burner.

The operating temperature range of flux for silver is 520-820C. Thanks to it, an excellent strong connection of silver parts is achieved.

Flux for ferrous metals

For soldering ferrous metals, zinc chloride is used, which is an active flux. In addition, you can choose materials of low or medium activity, for example, ammonium chloride. A similar flux is also used for enameled metal baths .

Active flux can be in the form of a solution, powder or paste. The most popular solder paste. A worthy alternative to it is a solder tube, which contains a flux filler.

Fluxes for processing microcircuits

Previously, only rosin, which is an active flux, was used for soldering circuit boards and other various parts. However, it is not recommended to use an alcohol rosin solution for repairing microcircuits, as it has several significant disadvantages:

At high temperatures, rosin removes not only metal oxide, but also the metal itself.
Cleaning the soldering after using rosin becomes a big problem. Its remains are washed off only with solvents or alcohol. It is impossible to leave excess flux on the board, since various short circuits caused by contamination are possible.

But there is a way out for radio amateurs. Modern materials markets offer a large selection of different fluxes, which ensure high quality soldering, do not destroy the soldering iron tip, and are easily washed off with water. Such materials are most often sold in convenient-for-use packaging - syringes.

Soldering of ferrous metals

The quality of fastening of steel products depends on several factors:

steel grades;
porosity of workpieces;
level of cleanliness of the joining seam.

Tin or brass alloys are chosen as solder. They are used depending on the task at hand. An easier way is to use tin. It is easier to work with, however, the final seam will not have a high level of strength.

Brass-based solders are much stronger, but you will need special equipment to work with them.

Tips for proper and strong soldering of metals

When working with steel or other metals, you must adhere to basic safety rules and also know some of the nuances of soldering.

How to heat and cool metal

An important step before starting work is preparing the workpieces. And here you need to know for sure which alloy you will solder or check it yourself:

See how a metal workpiece reacts to heating with a soldering iron or torch. How quickly an oxide film forms on the surface. It’s better to know this in advance and for sure, otherwise subsequent work will be done in a hurry.
It is best to warm up the prepared and secured parts gradually. Make sure that no overheated spots appear on the metal. The soldering area must be heated evenly over the entire area.
Do not heat only the butt seam; also work on the area near the joint. Most often, you need to warm up 0.5 - 2 cm, depending on the purpose of soldering and the dimensions of the elements being connected.
Use only soldering irons or torches that produce solder at operating melting temperature.
Do not cool the finished seam with cold water or other liquids. Let the metal “rest” and cool evenly for several minutes in the open air.
Remove soldered workpieces from a vice or clamps only after the solder has completely cooled.

Which metals are most strongly soldered to each other?

Unlike welding, in soldering the main indicator of the quality of the finished product is not the grade of steel or metal, but the choice of solder, as well as the technology for forming the solder seam itself. So the question here is rather about which metal, which solder sticks best to which metal. Of course, the closer in composition and density the solder and metal are, the better the adhesion will be. In the end, it all comes down to choosing the right solder for each individual case.

You also need to ensure that when connecting two metals, no electric couples are formed. Otherwise, the connection will rust and collapse from the slightest moisture. So a compatibility table for connecting non-ferrous metals with each other would be appropriate here.

The letter “A” in the compatibility table means “limitedly permissible in atmospheric conditions.”

Here are some more simple tips :

Choose solders that are more refractory.
Carefully clean the joints of fastened parts. Apply sandpaper not only to the seam itself, but also 0.5 - 2 cm near the joint on the metal surface.
Tin and overlap seal. Thus, you increase the total area of fastening two or more parts.

Safety precautions when soldering steel at home

Often, neglect of basic rules for working with electrical or flammable appliances leads to loss of health or damage to property.

I strongly recommend following safety precautions when soldering:

Keep the soldering iron on a metal pad or a special holder that takes the heated tip of the tool away from the plane of the table.
Turn off the soldering iron from the mains immediately after finishing work.
Check the quality of the connection of the gas cylinder to the burner itself. Avoid gas leaks.
Work in a well-ventilated area.
Do not leave the burner on if you have already finished working.
Remove any flammable substances from the work area.
Do not touch the heated seam with your bare hands. You may get burned.
Do not touch the solder with your fingers to check the strength of the seam.

By following these measures, you can avoid injuries and also keep your property intact. Solder with pleasure and knowledge!

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Soldering iron with tin solder

The soldering process is the chemical joining of two metals using solder. Moreover, the crystal structure of the metal does not change. That is, the connected parts remain with their technical characteristics.

The connection itself is quite reliable, but much will depend on the type of solder and soldering technology. In addition, it should be noted that not all metals can be joined by this process. Basic metals, especially steel (iron), can be soldered together.

Three technologies

There are three technologies for soldering iron with tin:

soldering iron To do this, you will have to use soft solders with a high lead content;
blowtorch. This will require hard solders with a high tin content;
electrical soldering of iron.

The first method is used if the iron will not be subjected to heavy loads during operation. The second is tinning of iron with tin, when tin solder is applied to the surface of a metal product and rubbed over its entire plane in a thin layer.

This technology requires soldering flux. The third option is used on a production scale, for which special equipment is used.

Soldering sheet metal

Soldering tin (thin sheet iron) is a common process in the manufacture of metal containers. But often, even at home, it is necessary to fasten sheets of iron together, assembling sealed structures. Therefore, before soldering one sheet to another, you need to prepare everything you need.

For the process of soldering iron with tin, you will need solder with a small concentration of tin, for example, POS-40, flux, a soldering iron and an awl.

In the process of soldering iron, flux acts as a solvent and an oxidizing agent at the same time. That is, the metal is immediately wetted and protected from oxidative processes. Rosin and hydrochloric acid or zinc chloride and boric acid are used as fluxes.

As for the soldering iron, for high-quality tin soldering it is better to choose an electric tool with a power of more than 40 W. The old soldering tool, which is heated by the flame of a fire, is practically not used today, even at home.

Sequencing

Here are the main stages of this process:

cleaning of joined sheets;
applying flux;
heating up the soldering iron and tinning;
soldering with tin;
cleaning the joint with gasoline.

Cleaning is carried out mechanically with sandpaper. If the contamination is large, you will have to treat it with a solvent. If it is not possible to clean it using this method, then etching is carried out with sulfuric acid.

Two pieces of sheet iron are brought to each other at a distance of 0.3 mm. Their edges are treated with paste-like flux using a brush. The soldering iron tip is cleaned with sandpaper, and the tool itself is plugged into the electrical network through an outlet. To check whether it has heated up well, you need to place its tip in the ammonia mixture, which should boil.