We are familiar with and unfamiliar with air conditioners, because we all know that air conditioners are used for cooling in summer and heating in winter, but many people are not clear about the actual structure and components of air conditioners.
For example, the application of air conditioner copper tubes, the more copper tubes are used, the heavier the weight, and the higher the cost, which is what we call "thick" feeling. Moreover, it is particularly important for air conditioner installation and maintenance masters and air conditioner product designers to understand air conditioner copper tubes.
Copper tubes are important raw materials for the processing and manufacturing of refrigeration devices. They have two main uses:
1. Make heat exchangers. It is an important part of the evaporator and condenser of air conditioners.
2. Make connecting pipes and pipe fittings.
The manufacturing of air conditioner copper tubes can currently be divided into two process flows.
●Process 1: Traditional extrusion process: ingot casting-(oblique rolling and piercing) extrusion-rolling-coil pulling-coiling-annealing.
●Process 2: New casting and rolling production process:
Classification of copper tubes
1. Air conditioning copper tubes can be roughly divided into ordinary air conditioning copper tubes and degreased air conditioning copper tubes
Ordinary air conditioning: The thickness is generally 0.5mm for 2-point and 3-point tubes, 0.6mm for 4-point tubes, and 0.7mm for 5-point and 6-point tubes; mainly used for R22, the pressure is controlled at 0.98MPa.
Degreased air conditioning copper tubes: also called "degreased air conditioning copper tubes", 2-point and 3-point tubes are 0.8mm thick, 4-point, 5-point, and 6-point tubes are 1.0mm thick. Mainly used for new refrigerants such as R410, the pressure is controlled at 1.8MPa.
2. Specific classification of air conditioning copper tube materials:
1) Oxygen-free copper: including high-purity oxygen-free copper (TU0, TU1, TU2) and phosphorus deoxidized copper (TUP, TP1, TP2, etc.), characterized by extremely low oxygen content, and a small amount of deoxidizer remains in the deoxidized copper;
2) Oxygen-containing copper: mainly ordinary pure copper (T1, T2, T3, etc.) and tough copper, characterized by high oxygen content;
3) Special copper: arsenic copper, silver copper, tellurium copper, etc., characterized by the addition of different trace alloy elements to achieve the purpose of improving the comprehensive performance of the material.
Pressure resistance and bursting pressure of copper tubes and heat exchangers
1. Working pressure under standard working conditions of commonly used refrigerants
2. Working pressure of copper tubes
Non-destructive testing methods: eddy current testing, water pressure test, air pressure test
Water pressure test calculation formula: P=2st/D-0.8t
P-static pressure of test water Mpat-wall thickness of pipe, mmD-outer diameter of pipe, mms-allowable stress of material, MpaTp2 copper pipe allowable stress is specified as s=41.2Mpa (6000psi)
Several copper pipe test pressures
3. Burst pressure of copper pipe
Calculated and measured values of burst pressure of several air conditioning refrigeration copper pipes
4. Working pressure and burst pressure of heat exchanger
Heat exchanger pressure burst test data
5. Factors affecting heat exchanger pressure
(1) Factors that increase burst pressure: cold hardening of bending and expansion pipes; strengthening of wrapped aluminum fins.
(2) Factors that reduce burst pressure: heat effect of brazing; poor assembly of brazed joints
Common problems of copper tubes during use
1. Copper tube leakage
Copper tube leakage is a fatal defect of air conditioners. Once leaked, all the refrigerant in the air conditioner will leak out, and the air conditioner will lack the "blood" for heat exchange, and therefore fail. The reasons for the leakage of copper tubes are relatively complicated, and the specific reasons are as follows:
① Misuse of defective tubes detected by eddy current flaw detection.
Under normal copper tube production conditions, copper tube eddy current flaw detection not only marks the number of damage points on each copper tube, but also paints the damage points with black marks so that users can identify and pick out this "black tube" during use. In the later installation, some people installed the "black tube" on the product, causing leakage of the air conditioning refrigeration device.
② Processing problems. The main pipe of the air conditioner must go through bending, expansion, flaring, welding and other links in the process of forming the two devices.
In the process of bending, the bent part must be subjected to local force, resulting in local over-stretching, cracking, dark cracks and other problems. Once filled with refrigerant, refrigerant leakage often occurs here.
During the expansion process, the expansion core increases the size of the copper tube by interfering with the inner diameter of the copper tube, so that the outer diameter of the copper tube is fully in contact with the aluminum foil heat sink. During the expansion process, it is very easy for the expansion head to scratch the copper tube, forming a penetration wound and causing leakage of the copper tube; sometimes, due to the large burrs on the inner hole of the aluminum foil, the burrs penetrate the copper tube during the expansion and cause leakage.
③ Leakage caused by poor welding. After the copper tube is inserted into the perforated aluminum foil, the tubes need to be connected, and a small elbow is needed to connect them. In order to make the connection firm, the small elbow and the copper tube are welded together with solder during the production process; the welding method is divided into manual and automatic. During welding, due to the quality of solder, the expansion of the copper tube, and foreign matter on the welding surface, the welding is not solid, forming a virtual weld, causing refrigerant leakage.
2. Cracks in copper tubes
The cracks of copper tubes are mainly concentrated in the expansion and expansion processes of copper tubes. In the production of two devices, the expansion and expansion of copper tubes is a continuous process, which is often completed in one process. There are many reasons for copper tube cracking, and the main reasons are as follows:
① The quality of the copper tube itself. For example, defects on the outer surface, scratches on the inner surface, oxidation on the inner surface, etc., can cause copper tube cracking.
② Human factors. During use, copper tubes are often straightened and cut to size, and chipless cutting is often used for cutting. The surface of the copper tube is relatively soft after heat treatment. When performing chipless cutting, if the cutter is unfavorable or the cutter is too large during cutting, the copper tube will shrink too much or have too many burrs, forming port flash and port hardening, causing cracking during expansion.
