The refrigeration system in air conditioners is generally made of non-ferrous metals such as copper and aluminum. In the process of manufacturing, installation and maintenance, the brazing of pipes is of vital importance and should be paid special attention to, as it not only affects the appearance, but more importantly, it determines whether the system can work normally. The copper pipe of air conditioner refers to the copper pipe connecting the indoor unit and the outdoor unit of the air conditioners. Air-conditioning copper pipes are featured with toughness, corrosion resistance, high temperature resistance and high pressure resistance, so it is deeply loved by people.
When the air conditioner is installed, the brazing of the copper pipes directly affects the cooling effect, thus the correct operation steps are very important. Silver brazing rods containing 25%, 15% or 5% silver are generally used for connecting copper tubes. Copper-phosphorus brazing rods are also suitable for this job, as they have good fluidity and no flux is required.
1. Adjust the Flame
Before igniting, open the valves of the oxygen cylinder and the acetylene gas cylinder according to the operating procedures, ensure oxygen pressure meter indicates about 0.2~0.5Mpa, and the acetylene gas pressure meter indicates about 0.05Mpa. Slightly open the oxygen valve of the torch, open the acetylene valve on the brazing torch, and at the same time, quickly ignite from the back of the brazing tip. Do not ignite from the front of the brazing tip to avoid burning your hands. The flame can be adjusted after being ignited. The adjustment of the two valves is to adjust the ratio of oxygen and acetylene gas mixture going into the torch, so as to obtain different flames. The nature of the flame is selected according to the type of metal to be welded and its properties, and it should be selected scientifically, here I will introduce several commonly used flames to you:
(1) Carbonization flame
Carbonization flame can be found when volume ratio of oxygen to acetylene gas is less than 1, and it is slightly hypoxic. It is easy to bring carbon particles into the metal and affect the flow of solder, and black smoke can be found. The temperature of carbonization flame is about 2700 ℃, and it can be used for baking pipelines.
(2) Neutral flame
Its characteristic is that the size of the flame core depends on the composition and flow rate of the combustion gas. The diameter of the nozzle hole of the torch determines the diameter of the flame core, and the flow rate of the mixed gas determines the length of the flame core. The neutral flame is divided into 3 layer, the flame core is pointed and conical, white and bright in color, the inner flame is blue-white, and the outer flame gradually changes from lavender to orange and blue from the inside to the outside. The temperature is about 3000~3500 °C. The volume ratio of oxygen and acetylene gas is 1:1.2. Neutral flames is usually used in the brazing of pipe fittings of refrigeration and air conditioners.
(3) Oxidation flame
Its characteristics are that the flame core is conical, the length is obviously shortened, the outline is not clear, the color is dim, the outer flame is also shortened and blue in color, and there is a sound when the flame burns. The sound depends on the oxygen pressure. The temperature is higher than the neutral flame, suitable for brass pipe fittings brazing.
2. Brazing
(1) When brazing, the weld parts must be preheated. Heat the brazing place of the copper pipe with the flame. When the copper pipe is heated to purple red, remove the flame and put the solder against the brazing joint, so that the solder melts and flows into the weld parts. The temperature after heating can be reflected by the color: dark red means about 600 degrees Celsius; blood red means about 700 degrees Celsius; orange red means about 1000 degrees Celsius.
(2) When brazing, the flame can not directly heat the brazing rods.
(3) For parts that are easily deformed and damaged by heat, corresponding protection measures should be taken. For example, angle valves, evaporators, condensers, etc. should be wrapped with wet gauze before brazing. For solenoid valves, expansion valves, and liquid mirrors, those that can be disassembled, must be disassembled and then brazed.
(4) When brazing, when the copper pipe is annealed after brazing, the annealing temperature should not be lower than 300 degrees Celsius.
(5) After brazing, cool down and clean the oxide and brazing slags in the pipes with dry nitrogen.
3 Repair Brazing
(1) Before repair brazing, wipe off the oxide layer on the surface with gauze. After repair brazing, the oxide skin should be removed. After quenching in water, the copper pipe should be dried without water droplets.
(2) After all brazing is completed, the refrigeration system should be blown out with nitrogen.
Summary of Brazing Steps
1. Prepare for brazing gas, equipment and filler metals;
2. Wear protective equipment;
3. Check the status of brazing equipment and tools;
4. Open the bottle valve, adjust the oxygen reducer to control the outlet pressure to 0.15~0.2MPa, and adjust the acetylene reducer to control the outlet pressure to 0.01~0.02MPa;
5. Open the acetylene regulating valve—ignite—adjust the acetylene regulating valve to get proper flames ;
6. Open the oxygen regulating valve—adjust slowly to get neutral flame;
7. Adjust the flame in the order of neutral flame (small) → more acetylene → plume flame becomes larger → more oxygen → adjust to neutral flame (large);
8. Adjust the flame in the order of neutral flame (large) → lesss oxygen → appear plume flame → less acetylene → wither to neutral flame (small);
9. Make the tip of the flame core 2~4mm away from the weldment, perpendicular to the pipe, and evenly heat the entire length of the weld until it is dark red;
10. Send the solder to heat until the solder melt and fill in the gap perfectly;
11. Remove the flame and keep the weldments from misaligning before the solder is completely solidified;
12. Close the acetylene valve, then close the oxygen valve and turn off the flame;
13. Loosen the pressure reducer and close the bottle valve;
14.Sort out the tools and equipment, and clean the site.