The production process of air conditioning and refrigeration copper pipes and common problems The air conditioner is mainly composed of a compressor, a radiator, and an automatic control system. The copper tube in the radiator is called the "blood vessel" of the air conditioner in the industry. The quality of the "blood vessel" will directly determine the quality of the air conditioner. Let's combine production practice , Talk about the problems that often occur in the use of air conditioning and refrigeration copper pipes.
Copper pipe is an important raw material for refrigeration devices. It has two main uses:
①Making heat exchangers. Such as commonly used evaporators and condensers, commonly known as "two devices"
②Make connecting pipes and fittings. No matter what kind of use it is, it is a channel for refrigerant, and its role is very important.
On the one hand, copper pipe manufacturers are required to provide high-quality copper pipes, and on the other hand, air-conditioning and refrigeration enterprises are required to use copper pipes properly.
Introduction to the production of copper pipes for one and two appliances
1.1 Process flow
The manufacture of copper pipes can be divided into two processes at present.
●Process 1: Traditional extrusion process: ingot casting-(cross-rolling piercing) extrusion-rolling-coil drawing-coiling-annealing.
Process 2: New casting and rolling production process:
Process flow chart of new cast-rolling production
Comparison of two production processes
1.2 Several states of external supply of copper tubes
Copper coil: currently mainly used for two main pipes, connecting pipes, pipe fittings, etc. Features: Convenient transportation, users are not restricted by length during use.
mosquito coil: mainly used in the maintenance market. Features: Easy to use.
Straight pipe: Mainly used for central air conditioning and connecting pipes. Features: Inconvenient transportation and length limitation in use.
Second, the problems that often occur in the use of copper pipes
2.1 Copper pipe leakage
The leakage of copper pipes is a fatal flaw of air conditioners. Once leaked, the refrigerant of the air conditioner will all overflow, and the air conditioner will fail due to lack of heat transfer medium. The reasons for the leakage of copper pipes are more complicated, and the reasons for the frequent leakage are explained below.
●Manufacturing reasons
①Eddy current flaw detection missed. GB stipulates that copper pipes must be 100% eddy current flaw detection, and stipulates the diameter of artificial flaws (through holes) on the sample tube used for checking flaw detectors to ensure the sensitivity of eddy current flaw detection and prevent over-standard flaws from being missed.
This requirement can be fully guaranteed in a regular large copper pipe factory, because the flaw detection is on-line inspection. This on-line eddy current flaw detection ensures that all lengths of the pipe are tested by eddy current, which is 100% flaw detection.
Some copper pipe factories are not like that, either without eddy current testing, or using low-standard eddy current flaw detectors. In this way, copper pipes have excessive defects, missed inspections or undetected, causing air conditioners to leak when users use them.
②The defect is detected by eddy current flaw detection, but the surface of the copper pipe is not marked or the marking is inaccurate and unclear. In the production process of copper pipes, the defects detected by eddy current flaw detection are required to be covered with ink marks on the defects that exceed the standard, so that the user can remove the defective copper pipes during use.
However, due to the insufficient adhesion of the ink selected by the manufacturer during the production process, improper adjustment of the inkjet spray gun, incomplete drying, and high temperature fading of the ink composition, users cannot detect eddy current flaw detection during use. If the defect is picked out, once the defective copper pipe is used on the air conditioner, it will inevitably cause leakage.
● Reasons for user use
Users use copper pipes to make two devices. The process flow: cut-elbow-pipe expansion-cleaning-welding-pressure test.
①Defective tube detected by eddy current flaw detection. Under normal production conditions of copper pipes, eddy current testing of copper pipes not only marks the number of damaged points on each coil, but also paints the damaged points with black marks so that users can identify and pick out this "black pipe" during use.
Air-conditioning and refrigeration enterprises must make it clear to the operators, especially the newly hired workers, in order to prevent such injured pipes from being installed on the air-conditioning refrigeration equipment.
We have found this problem many times when we went deep into customer service. Some workers asked us what happened to the black on the tube, while others were dissecting substandard products. It was precisely because the "black tube" was installed on the product to cause air conditioning. The refrigeration unit leaks.
②The problem of processing. In the process of forming the two devices, the air-conditioning main pipe has to go through the bending, expanding, expanding, welding and other links.
In the process of bending the pipe, the bending part has to undergo local stress, causing local over-extension, forming cracks, dark cracks and other problems. Once filled with refrigerant, refrigerant leakage often occurs here.
Internal test leak
Outside leak
After the copper tube passes through the fins, the tube must be raised in the tube expander. The tube expander is divided into two types: vertical and horizontal. The vertical tube expander mainly expands two devices with relatively small lengths, and the efficiency is relatively high; horizontal expansion The pipe machine mainly expands the two devices with longer length, and the efficiency is relatively low.
In the process of tube expansion, because the core expansion is to increase the size of the copper tube by interference with the inner diameter of the copper tube, the outer diameter of the copper tube is fully in contact with the aluminum foil heat sink. In the process of expanding the tube, it is very easy for the copper tube to be scratched by the expanding head, forming a penetrating injury and causing the copper tube to leak; sometimes the burr penetrates the copper tube when the tube is expanded because the burr in the inner hole of the aluminum foil is too large.
③Leakage caused by poor welding. After the copper tube is penetrated into the aluminum foil with holes, the tube and the tube must be connected, and a small elbow connection is needed. In order to connect firmly, in the production process, the small elbow and the copper tube are welded together with solder;
Welding methods are divided into manual and automatic. Due to the quality of the solder, the flaring of the copper tube, and the presence of foreign objects on the welding surface, the welding is not solid, forming a false welding, and causing refrigerant leakage.
2.2 Copper pipe cracking
The cracking of copper pipe is mainly concentrated in the process of expanding and expanding the copper pipe. The cracking situation is shown in the figure below. In the production of the two devices, the expansion and expansion of the copper tube is a continuous process, which is often completed in one process.
There are many reasons for copper pipe cracking, the main reasons are as follows:
①The quality of the copper pipe itself. The quality of copper pipe itself can be divided into external surface defects, internal surface scratches, internal surface oxidation and so on.
During the cold working deformation of the tube expansion and flaring, the surface of the copper tube is stretched under tensile stress. When there are deep scars on the outer surface of the copper tube, the outer surface of the copper tube cannot withstand the surface tensile stress, resulting in a phenomenon of breaking. The outer surface of the copper pipe was cracked.
The mechanism of cracking caused by scratches on the inner surface of a copper pipe is similar to that caused by scratches on the outer surface. When the inner surface of the copper pipe is oxidized, the friction on the inner surface of the copper oxide pipe is not equal to the friction on the inner surface of the copper pipe without oxide when the pipe is expanded, resulting in inconsistent lengths of the lower piers of the copper pipes of the same length. The copper pipe with a small amount has a long extension, which causes the flaring to be too large and cracks.
② Reasons for user use. In the use of copper pipes, coil pipes are often straightened and cut to length. Chipless cutting is often used for cutting.
The surface of the copper tube is relatively soft after heat treatment. When cutting without chips, when the cutting knife is unfavorable or the cutting knife is too large during cutting, it will cause the copper tube to shrink too much or too much burrs, forming port flash, port hardening, and causing flaring. Cracked.
A heat exchanger is composed of many “U"-shaped tubes. The length of each “U"-shaped tube and the length of the two ends of each “U"-shaped tube must have a very high consistency. When bending a “U"-shaped tube The difference between the length of each "U" tube and the length of the two ends of each "U" tube is too large (more than 2 mm) due to equipment or adjustments, so there will be excessive port The protruding length of the long copper pipe is too long, causing the flaring to be too large and cracking.
2.3 Wrinkles and breaks in elbows
Wrinkles and fractures of copper pipe bends occur in the process of making "U"-shaped pipes, and copper pipes are often scrapped in this process. See the table below for the causes of wrinkling and fracture of the bent pipe.
Left: Wrinkles on the outside Right: Wrinkles on the inside
Left: Wrinkles on the outside Right: Wrinkles on the inside
Three, the problem in the elbow
poor welding
In the process of copper pipe welding, if the operation is improper, it is easy to cause defects such as false welding, melting and melting through, overburning and burning through. Welding is a quality problem that often occurs in the welding process of two devices. The main reasons are:
●The flaring is small, and the brazing material is not easy to enter, resulting in weak welding;
The heating is uneven during welding, causing part of the brazing solder to not be completely heated and melted;
There are oil, oxides, residual carbon and other substances on the surface of the copper pipe at the weld;
●The quality of the solder itself.
caused the solder to fail to fill the full length of the socket joint or fail to completely weld the full length of the socket joint, causing leakage. Leakage caused by erosion and dissolution.
In short, there are many failure factors that cause copper pipes to appear, such as internal and external surface oxidation. Therefore, during use, process control must be strengthened and process requirements must be mastered.
