Repairing the refrigerant circulation system in a refrigerator is an operation that requires not only theoretical knowledge, but also the correct selection of materials. Circuit tightness is a critical parameter on which the performance of the entire unit depends. An error in choosing a connecting material can lead to freon leakage, moisture entering the system and, as a result, to expensive repeated repairs.
The question how to solder refrigerator tubesdoes not have one universal answer, as it depends on the type of metal (copper, steel, aluminum) and the specific unit refrigeration unit. Modern refrigerators, such as Indesit or Atlant, often use combined compounds, which requires a special approach to the choice of melting temperature and chemical activity of consumables.
In this article we will analyze in detail the physical and chemical properties of various types of solders, consider the need to use fluxes and determine the optimal temperature conditions for creating a reliable seam.
Physics of the process and requirements for the connection
Soldering is the process of obtaining a permanent connection of metals by introducing molten metal between them, called solder. Unlike welding, where the base metal melts, during soldering melting temperature of solder the melting temperature of the parts being connected is always lower. This is a key point that allows you to work with thin-walled refrigerator tubes without disturbing their geometry.
Refrigeration equipment is characterized by high operating pressures and vibration loads. Therefore, the connection must have not only tightness, but also a certain mechanical strength. Copper tubes used in condensers and evaporators have different degrees of purity and structure, which affects the wettability of the solder.
The quality of the seam directly depends on the cleanliness of the surface. The oxide film formed when copper is heated prevents the solder from spreading. This is why the use of the correct auxiliary materials, such as fluxes or a reduction burner flame, is a must. Without removing the oxides, the solder will simply roll into a ball without penetrating into the gap between the tubes.
⚠️ Attention: The use of lead-containing solders for repairing food refrigerators is unacceptable due to the toxicity of lead, although such compounds are technically possible. For household appliances, only lead-free compounds are used.
Classification of solders for refrigeration systems
All solders are divided into two main groups: soft and hard. The boundary between them is conventionally considered to be a melting point of 450 degrees Celsius. The choice of group depends on which circuit of the refrigerator is being repaired and what loads the connection will experience.
Soft solders (melting point up to 450°C) are usually alloys of tin with copper, silver or antimony. They are most common in household repairs of evaporators (evaporators) inside freezers, where pressures are lower and vibrations are minimal. A typical example is alloys of the series SnCuAg (tin-copper-silver), which provide good adhesion to copper.
Hard solders (melting point above 450°C) are most often copper-phosphorus or silver alloys. They are used for soldering capacitors, discharge tubes and compressor joints. Copper-phosphorus solders (for example, BCuP) have a unique property: phosphorus in their composition acts as a reducing agent, allowing copper to be soldered without flux (but only copper with copper!).
- 🔹 Tin-copper solders (SnCu): Ideal for low-temperature soldering inside the cabinet, do not require high heating, but are afraid of high pressures.
- 🔹 Silver solders (Ag): Contain from 5% to 40% silver, have high fluidity and strength, suitable for critical components.
- 🔹 Copper-phosphorus (CuP): Specialized material for joining copper pipes, provide high weld strength, but are brittle at low temperatures.
Hard solders: copper-phosphorus and silver alloys
For connecting highways refrigerator, where the refrigerant pressure can reach 15-20 atmospheres (especially in systems with R600a or R134a), hard solders are most preferred. Copper-phosphorus alloys (for example, PhosphorusCu or BCuP-2) are the de facto standard for copper-copper connections. Phosphorus lowers the melting point of copper and increases the fluidity of the melt.
The main advantage of such solders is the absence of the need for flux when soldering pure copper. Phosphorus binds oxygen, preventing the formation of an oxide film. However, if you are soldering copper to steel (for example, a compressor fitting), the use of flux becomes mandatory, since phosphorus does not protect the steel from oxidation as effectively.
Silver solders (with a silver content of 15%, 30% or 40%) have even higher strength and ductility. They better withstand vibrations transmitted from a running compressor. The cost of such materials is higher, but for the repair of expensive inverter refrigerators (brands Liebherr, Siemens) this is a justified investment.
| Type of solder | Melting point (°C) | Tensile strength | Application |
|---|---|---|---|
| Copper-phosphorus (2%) | 650 - 750 | Average | Copper-Copper (capacitors) |
| Silver (15% Ag) | 640 - 720 | High | Copper-Steel, critical components |
| Silver (40% Ag) | 600 - 680 | Very high | Vibration loads, complex alloys |
| Tin-copper | 220 - 240 | Low | Internal elements of the evaporator |
Soft solders and their scope
Soft solders are used in those areas of the refrigeration system where temperatures and pressures are relatively low. The basis of such alloys is tin. Pure tin is prone to “tin plague” at low temperatures (crystalline change in structure), so copper, silver or antimony are always added to modern solders.
The most popular lead-free solder for refrigeration equipment is an alloy Sn97Cu3 (97% tin, 3% copper) or Sn95Ag5. They melt at a temperature of about 230°C, which makes it possible to work with thin aluminum or copper evaporator tubes, the risk of burning through which when using hard solders is very high.
It is important to understand that soft solders require mandatory use. active flux. Without chemically cleaning the surface, tin will not spread onto copper. In addition, after soldering, flux residues must be carefully removed, as they can cause corrosion of the metal over time.
⚠️ Attention: Never use soft tin solders to solder the discharge tube of a compressor or condenser. The pressure and temperature in these nodes will exceed the tensile strength of the soft seam, which will lead to explosive depressurization.
The role of fluxes and the gas environment during soldering
Flux is a chemical substance designed to remove oxides from the surface of the metal and preventing their re-formation when heated. For soft solders, paste-like fluxes based on rosin or acids are used. For hard solders (torch soldering), powder fluxes or borax are often used.
However, in professional refrigerator repairs, the “gold standard” is soldering in a medium nitrogen. The supply of nitrogen into the internal cavity of the tubes during soldering displaces oxygen, completely eliminating the formation of an oxide film (scale) inside the pipe. Scale entering the system can clog the capillary tube or filter drier, which will require re-disassembly of the system.
If soldering is performed without nitrogen (which is acceptable for simple repairs), it is necessary to use the smallest possible flame and quickly introduce solder. For copper-phosphorus solders, flux is not needed, but to connect copper to steel (for example, a compressor tube), the use of flux (for example, Borax or specialized pastes) is strictly necessary.
Why does scale form inside?
When copper is heated to a reddish color, it actively reacts with oxygen of the air. Copper oxide (CuO) forms and appears as a black deposit inside the tube. This coating is fragile and can break off, creating an abrasive suspension in the system.
Tools and safety precautions
For high-quality soldering of refrigeration tubes, a conventional soldering iron is not enough. A high temperature open flame source is required. The optimal solution is oxygen-propane or oxygen-acetylene a burner. Propane-butane mixtures produce a less hot flame, but for working with soft solders and thin copper they are often sufficient.
The soldering process requires strict adherence to the sequence of actions. First, the tubes are cleaned (mechanically or chemically), then the connection is assembled (pipe to pipe with a gap of 0.1-0.2 mm). Heating is carried out evenly around the perimeter. The solder is inserted end-to-end: it must melt from the heat of the metal, and not from the flame of the burner.
☑️ Algorithm for safe soldering
Safety is priority number one. Freon, heating up in the burner flame, disintegrates to form phosgene a chemical warfare agent. Therefore, before any soldering, the system must be completely evacuated or purged.
FAQ: Frequently asked questions
Is it possible to solder aluminum tubes with conventional solder?
Aluminum is extremely difficult to solder using conventional methods due to instantaneous formation of an oxide film. This requires special high-temperature zinc-based solders (for example Castolin 192) and active fluxes. In domestic conditions, it is safer to use mechanical connections (crimp couplings) or replace the section with copper.
Which solder is better: with or without silver?
Solders containing silver (Ag) have better fluidity, strength and ductility. They are less susceptible to cracking due to vibrations. If the budget allows, choosing silver solder (at least 15% Ag) is always justified for the durability of the repair.
Do you need to strip the tubes before soldering?
Yes, definitely. Copper should shine. Use fine sandpaper or special cleaning brushes. Grease stains also need to be removed with a solvent, otherwise the flux will not work and the solder will not adhere.
What is the danger of flux getting inside the tube?
Acidic flux residues will cause corrosion of the metal from the inside, which will lead to the formation of fistulas and leakage of freon in a few months. In addition, corrosion products can clog the capillary. Therefore, the flux is applied minimally, and after soldering, it is advisable to wipe the joint with a damp cloth (after cooling).