When choosing household appliances, consumers Often people pay attention only to the dimensions, the volume of the chambers and the presence of additional functions such as a freshness zone or an ice generator. However, the durability and operating efficiency of the unit directly depend on what the refrigerator is made of and what alloys and polymers the manufacturer used. Understanding the physical and chemical properties of materials helps predict how equipment will behave after 5 or 10 years of operation.
A modern refrigerator is a complex engineering complex, where each element performs a strictly defined function, using the unique properties of specific substances. From the thermal conductivity of the insulation to the corrosion resistance of the outer coating, everything matters. In this article we will analyze in detail the design of the “refrigerating heart” of your home.
Metal casing: steel and its coatings
The basis of any classic refrigerator is its outer casing, which takes on mechanical loads and protects the internal components. It has remained the absolute standard in the industry for several decades. This material is chosen for its high strength, ability to hold shape and relatively low cost in mass production. Sheets of steel with a thickness of 0.5 to 0.8 mm form the outer contour of the device. cold-rolled steel. This material is chosen for its high strength, ability to hold shape and relatively low cost in mass production. Sheets of steel with a thickness of 0.5 to 0.8 mm form the outer contour of the device.
However, pure steel is susceptible to corrosion, so it is never used in its “bare” form. The metal surface undergoes multi-stage processing. First, a layer of zinc is applied (galvanization) for electrochemical protection, and then primer. The finishing layer is most often polyester enamel or powder paint. It is this layer that determines the color and texture: gloss, matte surface or anti-finger texture.
In the premium segment you can find models made from stainless steel. Such refrigerators look aesthetically pleasing and do not require painting, but their cost is much higher. Stainless steel is usually marked AISI 304 or AISI 430, where the first has better corrosion resistance, and the second is more magnetic and cheaper, but prone to rust in aggressive environments.
- 🛡️ Galvanized steel with a polymer coating is the standard for 90% of models on the market.
- ✨ Stainless steel is the lot of expensive models and requires special care products.
- 🎨 Plastic with metal imitation is a budget option, less durable, but lightweight.
⚠️ Attention: When transporting a new refrigerator, protect the body with protective film should be removed only after installation in a permanent place. If you leave it for a long time, the glue can “stick” to the metal, and it will be impossible to remove it without solvents.
Internal chamber: plastic and its varieties
The internal space of the refrigerator is an area in direct contact with food, moisture and temperature changes. It is not advisable to use metal here due to high thermal conductivity and the risk of corrosion, so the main material has become plastic. However, not every polymer is suitable for these purposes. Cheap varieties may crack on impact or release harmful substances.
The most common material for shelves and interior walls is ABS plastic (acrylonitrile butadiene styrene). It has excellent impact resistance, resistance to fats and acids, and maintains elasticity at low temperatures. Most of the white internal chambers of budget and mid-range refrigerators are made from ABS. This material is easily molded, which allows you to create complex reliefs for air ducts.
For surfaces that are more demanding on cleanliness, for example, vegetable boxes or shelves in the freshness zone, polystyrene or its modifications are often used. It is important to note that high-quality food-grade plastic should not have a strong chemical odor. If the new unit smells sharp and unpleasant even after airing, this may indicate the use of recycling (recycled raw materials) of low quality.
In expensive models you can find glass shelves framed by plastic. Glass here is not only a decorative element, but also a hygienic one: it does not absorb odors, is easy to clean and does not scratch as easily as plastic. However, the weight of glass is much higher, which requires strengthening the structure of the shelves.
Thermal insulation: the secret of energy efficiency
The main task of a refrigerator is to keep cold without letting in heat from the outside. A layer of thermal insulation located between the outer metal casing and the inner plastic chamber is responsible for this. For a long time, foam plastic was the standard, but today it has been completely replaced polyurethane foam (PUF). This is foamed plastic that hardens right in the space between the walls.
The technology for filling PUF looks like this: liquid components are mixed and blown into the gap, where they instantly expand and harden, forming a monolithic structure with millions of microscopic cells filled with gas. It is gas (previously freons were used, now more often cyclopentane or isobutane) that provides the main thermal insulation. The smaller the size of the cells and the better the gas is retained inside, the higher energy efficiency the device.
The thickness of the insulation layer can vary from 3 to 6 cm depending on the energy consumption class. Models with class "A++" or "A+++" have a thicker and denser polyurethane foam layer. If you cut such a refrigerator, you will see that polyurethane foam tightly glues metal and plastic, turning the body into a single monolith. This makes repair of the housing almost impossible without loss of thermal insulation properties.
| Insulation material | Thermal conductivity (W/m K) | Environmental friendliness | Application |
|---|---|---|---|
| Polyurethane foam (PPU) | 0,022 - 0,028 | High (inert) | Modern refrigerators |
| Expanded polystyrene | 0,035 - 0,040 | Average | Outdated models |
| Mineral cotton wool | 0,045 | Low (hygroscopic) | Not applicable |
| Vacuum panels (VIP) | 0,004 - 0,008 | High | Premium models (thin walls) |
Why do the walls of the refrigerator sometimes get hot?
In modern models with the No Frost system, the condenser tubes are often mounted directly into the side walls of the case. Therefore, heating of the sidewalls (up to 40-50°C) is not an insulation defect, but the normal operating mode of the heat exchanger.
Cooling system: metals and refrigerants
The heart of the refrigerator is a compressor-condensing unit where the refrigerant circulates. The manufacture of heat exchangers (evaporator and condenser) requires materials with excellent thermal conductivity and corrosion resistance. Historically used copper is an ideal, but expensive material. It is easily soldered and does not rust.
In order to save money, mass market manufacturers switched to aluminum. Aluminum evaporator tubes are lighter and cheaper, but they are less ductile and more susceptible to corrosion when in contact with certain substances. In addition, soldering aluminum requires special fluxes, and in the event of a leak, repairs are often unprofitable - it is easier to replace the entire assembly.
The refrigerant itself is a substance that changes its state of aggregation, taking away heat. Older models used freons (R12), which destroyed the ozone layer. Modern refrigerators work on isobutane (R600a). This is a natural gas that does not harm the environment, is odorless and has excellent refrigeration properties. However, it is explosive in concentration, so the amount of gas supplied is strictly regulated (usually 30-60 grams).
⚠️ Attention: If you hear a hissing or whistling sound when your refrigerator is running, this may be a sign of a refrigerant leak. Since isobutane is heavier than air, it accumulates at the bottom. If you suspect a leak, ensure the room is ventilated and do not use open fire near equipment.
Door seals and fittings
The tightness of the refrigeration chamber is the key to a stable temperature. Door seals are responsible for this. They are made from special rubber based on synthetic rubber. The main feature of this material is frost resistance. Conventional rubber hardens and cracks in the cold, losing elasticity, while the refrigerator seal should remain soft even at -20°C.
Inside the rubber cuff there is often a magnetic cord (ferrite powder in a polymer bond), which ensures a tight fit of the door to the metal body without the use of mechanical latches The quality of the magnet is checked by the force of the clap: the door must close itself, starting from a certain opening angle (usually 30-45 degrees).
Fittings, such as handles and hinges, experience enormous loads. Handles are made of durable plastic with a metal core or solid metal. The hinges are made of steel alloy zinc coated. In modern models, hinges often have a self-closing system and the ability to re-hing the door to the other side.
☑️ Checking the condition of the seal
Electronics and additional materials
A modern refrigerator is a computer with a cooling function. The control board, temperature sensors, fans and displays require the use of specific materials. The wiring is made of copper with PVC insulation, resistant to low temperatures. Temperature sensors (thermistors) are enclosed in sealed housings made of stainless steel or special plastic.
In models with the system No Frost fans are critically important. Their blades are made of plastic, and the motors contain rare earth magnets. The noise level of operation depends on the quality of the bearings and the balancing of the blades. Also, the design uses various types of adhesives and sealants, which must retain their properties over a wide range of temperatures.
Antibacterial coatings deserve special attention. Many manufacturers apply compositions with ions silver or copper to the internal walls and shelves. These metals have the natural property of inhibiting the growth of bacteria. The effectiveness of such coatings decreases over time, but in the first years of operation they really help maintain food freshness.
Environmental friendliness and recycling of materials
The question of what a refrigerator is made of is important not only when purchasing, but also when disposing of it. Household appliances are classified as complex waste that requires special processing. The metal body (steel and aluminum) is recycled almost 100% and returned to the metallurgical cycle. This is one of the most environmentally friendly materials in construction.
Plastic parts (ABS, polystyrene) are also recyclable, but require sorting by type of polymer. The greatest difficulty is presented by polyurethane foam insulation. When burned, it can release toxic substances, so it must be disposed of in special landfills or used as an alternative fuel in the cement industry, subject to strict filtration standards.
The R600a refrigerant discussed above does not harm the ozone layer when released into the atmosphere, but is a greenhouse gas. Therefore, when disposing of an old refrigerator, it is important that the craftsmen select freon using special equipment, and not just cut the tubes.
Is it possible to paint the inside of the refrigerator?
It is strictly not recommended. Conventional paints are not intended for contact with food and low temperatures. They may crack, begin to release toxins, or change the taste of foods. If the inner chamber is damaged, it is better to use a special food-grade sealant to repair the plastic.
Why do interior shelves turn yellow over time?
This is the natural aging process of plastic (ABS) under the influence of ultraviolet radiation and oxidation. Cheap types of plastic turn yellow faster. It is almost impossible to bleach them; chemicals can only accelerate the destruction of the polymer structure.
Is the smell of a new refrigerator harmful?
A faint smell of plastic in the first days is normal. It comes from new polymer materials and lubricants. If the smell is pungent, chemical and does not go away after 2-3 days of airing, this is a sign of poor quality materials or a violation of production technology.
What are the tubes on the back of the refrigerator made of?
The black grille at the back is a condenser. In older models it was made of steel tubes painted with black enamel. Modern ones often use an aluminum tube on which a steel sheet is rolled, or an all-aluminum structure. Aluminum transfers heat better, but is afraid of mechanical damage.
Is it possible to use a refrigerator at temperatures below +10°C?
Most refrigerators are designed to operate in the SN-T climate class (from +10 to +43°C). At temperatures below +10°C, the oil in the compressor thickens, which leads to its breakdown during startup. If the refrigerator is located in an unheated country house, choose models with an extended climate class or use a compressor crankcase heater.