Tips for welding copper and aluminum tubes in high and low temperature alternating heat and humidity test chamber
[Introduction] The refrigeration system of the high-low temperature and damp heat test chamber is generally made of non-ferrous metal materials such as copper and aluminum. During the manufacturing, installation and maintenance process, the welding of the pipeline is a key link, which not only affects the appearance but also the influence. The issue of whether the system can work properly must be highly valued.
The high and low temperature damp heat test chamber copper pipe refers to the copper pipe connected to the cold heat unit. The copper tube has the characteristics of hard texture, non-corrosion, high temperature resistance and high pressure resistance, so it is very popular among people. Copper pipes can be divided into two types: ordinary copper pipes and degreased copper pipes. Of course, it can also be divided into copper tubes, capillary copper tubes, and shaped copper tubes according to the use of copper tubes.
When installing high-low temperature damp heat test chambers, special copper pipes are used to connect the refrigeration units. The welding of high-low temperature damp heat test chambers to copper pipes is directly a factor affecting the cooling effect. The correct operation steps are very important.
The copper tube and the copper tube are generally welded by silver, and the silver electrode has a silver content of 25%, 15% or 5%; a copper-phosphorus series electrode can also be used. They all have good fluidity and do not require flux.
Selection of solder
Copper pipes are important raw materials for refrigeration equipment, and are mainly used to make heat exchangers and connecting pipes and fittings. Most of the pipe fittings are made of copper (purple) pipes. Commonly used solder types are copper-phosphorus solder, silver-copper solder, copper-zinc solder, and the like. In the welding, according to the characteristics of the pipe material, the solder is selected correctly and skillfully operated to ensure the quality of the welding.
1. Welding of similar materials
Copper and copper brazing can be selected from phosphor bronze solder or low-phosphorus phosphor bronze solder, such as 2% or 5% silver-based solder. This solder is cheaper and has a good solution, using caulking and wetting processes, and does not require flux.
2. Welding of different types of materials
Copper and steel or copper and aluminum may be soldered with silver-copper solder and appropriate flux. After soldering, the residual flux near the solder joint must be cleaned with hot water or steam to prevent corrosion. When using flux, ZUI is diluted with alcohol to form a paste, which is applied to the surface of the solder joint. When the solder is evaporated, the alcohol rapidly evaporates to form a smooth film which is not easily lost, and the danger of water immersing in the refrigeration system can be avoided.
Copper and iron soldering: Phosphorus copper solder or brass strip solder may be used, but a corresponding flux, such as a mixed flux of borax, boric acid or boric acid, is also required.
Welding operation
For the welding of different materials, the size of the welding gun and the temperature of the flame required for different pipe diameters are different. The size of the flame during welding can be controlled by two needle valves. The adjustment of the flame is based on oxygen and acetylene gas. The volume ratio can be divided into three types: carbonized flame, neutral flame and oxidized flame.
1, the type and characteristics of the flame
(1) Charring flame: It is characterized by a volume ratio of oxygen to acetylene gas of less than 1, slightly oxygen deficient, easy to bring carbon particles into the metal and affect the flow of solder, black smoke, the temperature is about 2700, can be used for pipelines Bake and so on.
(2) Neutral flame: It is characterized in that the size of the flame core depends on the composition, consumption 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 mixture determines the flame core. The length of the neutral flame is divided into three layers. The flame core has a pointed cone. The color is white and bright. The inner flame is blue-white. The outer flame gradually changes from lavender to orange and blue. The temperature is about Between 3000 and 3500 °C, the ratio of the volume of oxygen to acetylene gas is 1:1.2. The tube welding of refrigeration and air conditioning uses a neutral flame.
(3) Oxidation flame: It is characterized in that the flame core is conical, the length is obviously shortened, the outline is not clear, the color is dim, the outer flame is shortened, the flame is blue, the flame is accompanied by a sound, and the sound size depends on the size of the sound. At oxygen pressure, the temperature of the oxidizing flame is higher than that of the neutral flame, which is suitable for the welding of brass fittings. The nature of the flame is chosen according to the type of metal being welded and its nature, and should be carefully selected for scientific use.
2, the adjustment of the flame:
Before ignition, first open the valves of the oxygen cylinder and the acetylene cylinder according to the operating procedures, so that the low-pressure oxygen meter is indicated at 0.2~0.5Mpa, and the acetylene gas in the eye is indicated at 0.05Mpa. Then slightly open the oxygen valve of the torch. Then slightly open the acetylene gas valve on the welding torch, colleague, quickly ignite from the back of the welding tip. Do not ignite on the front side of the tip to avoid burning fire. It can be adjusted after ignition. The adjustment of the two valves is to adjust the ratio of oxygen and acetylene gas immersed in the welding torch mixture to obtain different flames.
3, welding steps
(1) Preparation and piping:
1. Check that the amount in the oxygen and acetylene bottles is sufficient.
2. Check the drawing requirements to ensure that all components are complete and functional.
3. Ensure that the optical path of the pipeline is horizontal and vertical, pay attention to the directivity of each valve.
4. Depending on the dimensions and pipe diameter required by the drawing, use a tape measure to measure the length and use the line number pen several times.
5. After the thick copper pipe is to be fixed, remove it with a cutter, and make sure that the cutting edge is flush and not deformed.
6. Use a hoe to flatten the edges of the cut and wipe it clean with a rag.
7. The surface of the pipe to be welded is cleaned or flared. The flared bell mouth should be smooth, round, burr-free and crack-free. The thickness of the bell mouth should be evenly polished. Use sandpaper to clean the copper pipe joint to be welded. Finally, wipe it with a dry cloth. Otherwise, it will affect the solder flow and the quality of the weld.
8. Except for the welding of copper and copper, all the pipe fittings are cleaned with gauze or stainless steel wire brush before welding to expose the bright metal surface. (The inner surface should be cleaned, the metal shavings and sand should be removed)
9. Insert the copper tubes to be welded on each other (note the size) and align them with the center.
(2) Protection:
1. When welding, the nitrogen gas should be passed through the welded pipe to prevent oxidation.
2. Acetylene gas should pass through the non-oxidation welding generator to prevent oxidation of the outer surface of the welded object.
(3) Welding:
1. When welding, the weldment must be preheated. The flame is baked at the hot copper tube. When the copper tube is heated to purple, the flame is removed and the solder is placed at the weld to melt the solder and flow into the welded copper. The temperature after heating can be reflected by the color. The temperature is high and low, dark red: about 600 degrees Celsius; deep red: about 700 degrees Celsius; orange: about 1000 degrees Celsius.
2. When welding, the gas welding flame shall not directly heat the electrode.
3. For parts that are easily deformed under high temperature conditions, damaged parts should be protected accordingly. For example, angle valves, evaporators, condensers, etc. should be welded with wet gauze and then welded. For solenoid valves, expansion valves, liquid mirrors, and four-way valves, they must be disassembled and then welded. Take the above measures.
4. When welding, when the copper tube is annealed after welding, the annealing temperature is not lower than 300 degrees Celsius.
5. After the welding is completed, cool and clean the oxide and slag in the tube with dry nitrogen.
(4) Repair welding:
1. In the process of pressure test, it is found that the weld has leakage repair. When repairing the weld, the nitrogen pressure tested by the system should be released, and the pressure should be re-tested after welding.
2. Clean the surface of the oxide layer on the front waist and clean it with gauze. After repair welding, the scale should be removed. After quenching in water, the copper tube should be dried and no water droplets should exist.
3. After all soldering, purge the system with nitrogen.
Summary of welding steps
1. Prepare welding gas, equipment and materials;
2, wear protective equipment;
3. Check the status of welding equipment and tools;
4. Open the bottle valve, adjust the outlet pressure of the oxygen pressure reducer to 0.15~0.2MPa, and adjust the outlet pressure of the acetylene pressure reducer to 0.01~0.02MPa;
5. Open the acetylene regulating valve - ignition - adjust the acetylene regulating valve to make the flame length moderate;
6, open the oxygen regulating valve - slowly withering the flame into a neutral flame;
7. Adjust the flame in the order of neutral flame (small) → add acetylene → feather-like flame becomes large → add oxygen → adjust to neutral flame (large);
8. According to the neutral flame (large) → reduce oxygen → appear plume flame → reduce acetylene → wither as a neutral flame (small) in the order of flame;
9. Make the tip of the flame core 2~4mm away from the weldment, perpendicular to the pipe, and uniformly heat the entire length of the weld to the magenta;
10. Applying a flux, when the flux becomes a transparent liquid and uniformly wets the weld, the solder coated with the flux is heated until the solder is sufficiently melted and satisfactorily filled with the weld;
11. Remove the flame and keep the weldments not misaligned before the solder is completely solidified;
12, close the acetylene valve, and then turn off the oxygen valve to extinguish;
13. Adjust the pressure reducer and close the bottle valve;
14, finishing tools, equipment, sweeping the scene.
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