How to weld air conditioning copper pipe
The refrigeration piping system in refrigeration and air conditioning generally uses non-ferrous metal materials such as copper pipe and aluminum pipe. In the process of manufacturing, installation and maintenance, pipeline welding is a key link. It not only affects the beauty, but also affects whether the system can work normally, which must be paid great attention to.
What is a air conditioning copper pipe?
Air conditioning copper pipe refers to the connecting copper pipe connecting the indoor unit and outdoor unit of the air conditioner. Air conditioning copper pipe has the characteristics of hard texture, not easy to corrosion, high temperature and high pressure resistance, so it is deeply loved by people. Air conditioning copper pipe can be divided into ordinary air conditioning copper pipe and degreasing air conditioning copper pipe. Of course, according to the use of air conditioning copper pipe, it can also be divided into R22 air conditioning copper pipe, R410A central air conditioning copper pipe, capillary copper pipe, special-shaped copper pipe, etc.
Silver welding is generally used for copper pipe and copper pipe welding, and the silver content of silver electrode is 25%, 15% or 5%; Copper phosphorus series electrodes can also be used. They all have good fluidity and do not need flux.
Different copper pipe welding methods have different welding tools
Copper pipe welding tools should be very many. Copper pipe welding tool is a necessary tool to realize copper pipe welding. Without copper pipe welding tools, copper pipe welding cannot be carried out. This shows the importance of copper pipe welding tools. Copper pipe welding is a local rapid heating and cooling process. Copper pipe welding is a kind of maintenance. As we all know, there are many copper pipe welding methods, including gas welding, electrode arc welding and tungsten argon arc welding. Different copper pipe welding methods have different welding tools. So what are the characteristics of these copper pipe welding tools? What about their structure? Now come with me to understand the relevant knowledge of copper pipe welding.
Welding method of copper pipe
- 1. Copper pipe gas welding method: copper pipe gas welding refers to the fusion welding method that uses the heat generated by the combustion of combustible gas in oxygen to heat the base metal and use solder to achieve connection.
- 2. Copper pipe electrode arc welding method: refers to the arc welding method of welding with manual electrode. Arc welding is a fusion welding method using arc as heat source.
- 3. TIG welding method of copper pipe: TIG welding is a method of heating and melting the base metal (at the same time, the welding wire is also melted) with the help of the arc generated between the tungsten electrode and the weldment.
Methods and characteristics of copper pipe welding
1. Characteristics of copper pipe gas welding method:
(1) Advantages of copper pipe gas welding method:
- It has good adaptability to the welding of cast iron and some non-ferrous metals;
- When welding is needed in places with insufficient power supply, gas welding can play a greater role.
(2) Disadvantages of copper pipe gas welding method:
- Low production efficiency;
- After welding, the workpiece deformation and heat affected zone are large;
- Difficult to automate.
2. Welding method characteristics of copper pipe electrode arc welding:
- (1) The welding method of copper pipe electrode arc welding has the advantages of good flexibility, convenient operation, low requirements for pre welding assembly and wide range of weldable materials;
- (2) Disadvantages of copper pipe electrode arc welding: low productivity; Strong human factors.
3. Characteristics of TIG welding method for copper pipe:
- (1) Argon has excellent protective effect and can effectively isolate the surrounding air; It neither reacts with metal nor dissolves in metal, which makes the metallurgical reaction in the welding process simple and easy to control. Therefore, it provides good conditions for obtaining high-quality welds.
- (2) Tungsten arc is very stable and can burn stably even under very small current (< 10a), especially suitable for welding thin plate materials.
- (3) The heat source and filler wire can be controlled separately, so the heat input is easy to adjust. Therefore, this welding method can carry out all-round welding. It is also an ideal method to realize single-sided welding and double-sided forming.
- (4) Since the filler wire does not pass through the current, there is no splash and the weld formation is beautiful.
- (5) AC argon arc welding can automatically remove the oxide film on the surface of weldments during welding. Therefore, it can successfully weld some non-ferrous metals with strong chemical activity, such as aluminum, magnesium and alloys.
- (6) Tungsten electrode has poor current carrying capacity. Excessive current will cause melting and evaporation of tungsten electrode, and its particles may enter the molten pool and cause tungsten inclusion. Therefore, the deposition speed is small, the melting depth is shallow and the productivity is low.
- (7) Argon is expensive, the deposition rate is low, and the argon arc welding machine is complex. Compared with other welding methods (such as electrode arc welding, submerged arc welding and gas shielded welding), the production cost is higher.
- (8) The argon arc is greatly affected by the air flow and is not easy to work outdoors.
Requirements for copper pipe welding tools
- (1) The volume of the oxygen cylinder is 40L, the working pressure is 15MPa, the appearance is sky blue, and the black paint is “oxygen”. Prevent oil contamination during storage and use; It must be placed stably and reliably, and shall not be mixed with other cylinders; Do not expose to the sun, fire and knock to prevent explosion. When using oxygen, do not use up all the oxygen in the bottle, and leave at least 100 – 200KPa to blow away dust and avoid mixing other gases when refilling oxygen.
- (2) The volume of acetylene cylinder is 40L and the working pressure is 1.5MPa. The appearance is white and the red paint is “acetylene” and “do not get close to fire”. A porous filler filled with acetone is installed in the bottle body, which can store acetylene stably and safely in the bottle. When using acetylene cylinders, in addition to complying with the use requirements of oxygen cylinders, it should also be noted that the temperature of the cylinder body should not exceed 30 – 40 ℃; During handling, loading, unloading, storage and use, it shall be upright and stable. It is strictly prohibited to lay on the ground and use it directly. Once the lying acetylene cylinder is to be used, it must stand upright first, then stand still for 20min, and then connect the acetylene pressure reducer before use; Can not be subjected to violent vibration, etc.
- (3) A regulator that reduces high-pressure gas to low-pressure gas. For gases with different properties, special pressure reducers meeting their respective requirements must be selected. Generally, the working pressure required for gas welding is generally relatively low. For example, the oxygen pressure is generally 0.2 – 0.4MPa, and the maximum acetylene pressure does not exceed 0.15Mpa. Therefore, the gas pressure output from the gas cylinder must be reduced before use. The function of the pressure reducer is to reduce the gas pressure and stabilize the gas pressure transmitted to the welding torch, so as to ensure the stable combustion of the flame. The pressure reducer shall be firmly installed on the special gas cylinder. The special pressure reducer for various gases shall not be replaced or replaced.
- (4) During the normal gas welding of the tempering fuse, the flame burns outside the welding nozzle of the welding torch, but when the gas supply is insufficient, the welding nozzle is blocked, the welding nozzle is too hot or the welding nozzle is too close to the weldment, the flame will burn back along the acetylene pipeline. This phenomenon of reverse combustion when the flame enters the nozzle is called tempering. If tempering spreads to acetylene cylinder, explosion accident may be caused. The function of tempering safety device is to intercept tempering gas and ensure the safety of acetylene cylinder.
- (5) Welding torch the function of welding torch is to evenly mix acetylene and oxygen in a certain proportion, spray it from the welding nozzle, ignite and burn, and produce gas flame. Welding torches of various models are equipped with 3 – 5 welding nozzles of different sizes for use when welding Weldments of different thicknesses.
Technology of copper pipe welding
Welding of similar materials
- Phosphor copper solder or phosphor copper solder with low silver content, such as 2% or 5% silver based solder, can be selected for brazing between copper and copper. This kind of solder is cheap and has good molten liquid. It adopts caulking and wetting process and does not need flux.
- For the welding of steel and steel, brass bar solder and appropriate flux can be selected. During welding, the solder shall be heated to a certain temperature and inserted into the flux to make the flux adhere to the solder after melting. However, the residual flux near the weld junction must be brushed clean after welding to prevent corrosion.
Welding of different materials
- Silver copper solder and appropriate flux can be used for the welding of copper and steel or copper and aluminum. After welding, the residual flux near the weld junction must be brushed with hot water or steam to prevent corrosion. When using the flux, it is best to dilute it into a paste with alcohol and apply it on the surface of the welded junction. During welding, the alcohol evaporates rapidly to form a smooth film, which is not easy to lose. At the same time, it can avoid the risk of water immersion in the refrigeration piping system.
- Phosphorus copper solder or brass strip solder can be used for the welding of copper and iron, but corresponding flux, such as borax, boric acid or mixed flux of boric acid, shall also be used. 3. Welding operation is different for the size of welding gun and flame temperature required for welding different materials and pipe diameters. The size of flame during welding can be controlled and adjusted by two needle valves. The flame adjustment can be divided into carbonization flame, neutral flame and oxidation flame according to the volume ratio of oxygen and acetylene.
Types and characteristics of flame
(1) Carbonization flame
The utility model is characterized in that the volume ratio of oxygen to acetylene gas is less than 1, which is slightly anoxic. It is easy to bring carbon particles into the metal and affect the solder flow, emitting black smoke, and the temperature is about 2700. It can be used for baking pipes, etc.
(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 torch nozzle hole determines the diameter of the flame core, while the flow rate of the mixed gas determines the length of the flame core. The flame of the neutral flame is divided into three layers. The flame core is sharp conical, white and bright, the inner flame is blue white, and the outer flame gradually changes from lavender to orange and blue from inside to outside, The temperature is about 3000 – 3500 ℃, and the volume ratio of oxygen to acetylene is 1:1.2. Neutral flame is often used for the welding of pipe fittings of refrigeration and air conditioning.
(3) Oxidation flame
The utility model is characterized in that the flame core is conical, the length is obviously shortened, the outline is not clear, the color is dim, and the external flame is also shortened. The flame is blue, and the flame combustion is accompanied by sound. The sound depends on the oxygen pressure, and the temperature of the oxidation flame is higher than that of the neutral flame. It is suitable for the welding of brass pipe fittings. The nature of the flame is selected according to the type and nature of the metal to be welded, and attention should be paid to the scientific selection and use.
Flame adjustment
Before ignition, open the valves of oxygen cylinder and acetylene cylinder respectively according to the operating procedures, so that the indication of low-pressure oxygen meter is about 0.2 – 0.5MPa, and the indication of acetylene gas meter is about 0.05Mpa. Then slightly open the oxygen valve of the welding gun. Then slightly open the acetylene valve on the welding gun, and colleagues quickly ignite from behind the welding nozzle. Do not ignite on the front of the welding nozzle to avoid burning your hands. It can be adjusted after ignition. The adjustment of the two valves is to adjust the proportion of oxygen and acetylene immersed in the mixed gas of the welding gun, so as to obtain different flames.
Brazing of copper and copper
Phosphor copper solder or phosphor copper solder with low silver content can be selected, such as 2% or 5% silver based solder. This kind of solder is cheap and has good solution. It adopts caulking and wetting process and does not need flux. Welding steps: strictly follow the steps during welding, otherwise the welding quality will be affected.
Welding method of red copper
The methods of welding red copper (commonly known as industrial pure copper) include gas welding, manual carbon arc welding, manual electric arc welding and manual argon arc welding. Automatic welding can also be used for large structures.
- 1. Gas welding of red copper butt joints are most commonly used for welding red copper, and lap joints and T-joints shall be used as little as possible. Two kinds of welding wires can be used for gas welding. One is the welding wire containing deoxidizing elements, such as wires 201 and 202; The other is the cutting strip of general copper wire and base metal, using gas agent 301 as flux. Neutral flame shall be used for gas welding of red copper.
- 2. For manual arc welding of red copper, red copper welding rod copper 107 is used for manual arc welding, and the welding core is red copper (T2, T3). Before welding, the edge of the welding joint shall be cleaned. When the thickness of the weldment is greater than 4mm, it must be preheated before welding, and the preheating temperature is generally about 400 – 500 ℃. Copper 107 electrode shall be used for welding, and DC reverse connection shall be adopted for power supply. Short arc shall be used during welding, and the welding rod shall not swing laterally. The welding rod makes reciprocating linear motion, which can improve the weld formation. The step-by-step back welding method shall be adopted for long welds. The welding speed should be as fast as possible. During multi-layer welding, the slag between layers must be completely removed. Welding shall be carried out in a well ventilated place to prevent copper poisoning. After welding, flat hammer shall be used to knock the weld to eliminate stress and improve weld quality.
- 3. Manual argon arc welding of red copper during manual argon arc welding of red copper, the welding wires used include wire 201 (special red copper welding wire) and wire 202, as well as red copper wire, such as T2. Before welding, the oxide film, oil and other dirt on the welding edge of the workpiece and the surface of the welding wire must be cleaned to avoid defects such as pores and slag inclusion. The cleaning methods include mechanical cleaning method and chemical cleaning method. When the thickness of butt joint plate is less than 3mm, no groove shall be made; When the plate thickness is 3 – 10mm, V-groove shall be opened, and the groove angle is 60 – 70 º.
When the plate thickness is greater than 10mm, open an x-groove with a groove angle of 60 – 70 º; In order to avoid incomplete penetration, blunt edges are generally not left. According to the plate thickness and groove size, the assembly clearance of butt joint shall be selected within the range of 0.5 – 1.5mm. Manual argon arc welding of red copper usually adopts DC positive connection, that is, tungsten electrode is connected to negative electrode. In order to eliminate air holes and ensure reliable fusion and penetration of weld root, it is necessary to improve the welding speed, reduce argon consumption and preheat the weldment. When the plate thickness is less than 3mm, the preheating temperature is 150 – 300 ℃; When the plate thickness is greater than 3mm, the preheating temperature is 350 – 500 ℃. The preheating temperature should not be too high, otherwise the mechanical properties of the welded joint will be reduced. There are also carbon arc welding of red copper. The electrodes used in carbon arc welding include carbon electrode and graphite electrode. The welding wire used for carbon arc welding of red copper is the same as that used for gas welding. The base metal can also be cut, and the flux for gas welding of red copper can be used, such as gas flux 301. For thinner copper wires, soldering is economical and practical. During welding, the impurities on the surface must be completely removed.
Common methods of copper aluminum welding
Copper aluminum welding methods conventional civil or equipment production has the following welding methods:
Method 1: ALCU-Q303 copper aluminum welding rod solves copper aluminum welding. Description: a copper aluminum welding wire with self brazing fluoride agent is favored by the operator because it does not need to use any welding powder and flux. When the temperature of the base metal reaches 400 ℃, use the end of the flame to burn the welding wire slightly, The molten welding wire will flow in water under the action of powder. Because of its very good fluidity, it is widely used in the refrigeration industry, such as the socket connection of copper and aluminum tubes and the socket connection of aluminum tubes and aluminum tubes. In addition, the overlapping and corner connection of copper aluminum conductor bars in the transformer industry are also widely used. How to make the connected conductor bars work under the environment of high voltage and high current, the compactness of the welding layer is particularly important.
Method 2: Welding53 solid solder solves the welding of all white metals, but aluminum alloy is widely used, especially including the welding of aluminum alloy and various cast aluminum, including copper aluminum welding, aluminum and iron welding, and heterogeneous welding between aluminum and stainless steel. Note: because WE53 is a solid welding wire, WE53 low-temperature aluminum welding wire has two operation modes.
- 1) Welding without welding powder: there is no need to use any welding powder and flux in the welding process. It is mainly used to solve the welding of aluminum alloy. It is very suitable for the welding of products with special requirements for deformation. When the temperature of the base metal reaches 400 ℃, wipe the welding joint with we53 like a rubber brush for forming. Where it is welded, it is the formed weld. In the auto repair industry, repair welding of water tank and intercooler root, repair welding of air conditioning pipe, repair welding of pipeline with poor angle of refrigerator, repair welding of thickness junction, etc.
- 2) Welding method with welding powder: this method is we53 welding wire combined with we53-f welding powder. At this time, it is functionally equivalent to a universal electrode (copper aluminum welding rod, aluminum iron welding rod, aluminum stainless steel welding rod) to solve some aluminum parts with high strength and high sealing requirements. Copper aluminum welding, aluminum iron welding, aluminum and stainless steel welding method 3: M51 + m51-f low temperature copper aluminum welding rod, Solve low-temperature copper aluminum welding at 179 ℃. Note: it belongs to low-temperature brazing copper aluminum welding. This kind of welding is most suitable for extremely thin or even exaggerated thin cases. However, field experience has proved that the welded products must have a welding angle. If the welding angle is not good, the welding effect will be discounted, Because the principle of this copper aluminum welding wire is completely formed by the heat conduction of the base metal and the molten welding wire. If the angle is not easy to burn the welding wire and flux, it will lead to welding failure. It is mainly used for irregular welding, preferably forming at one time, and the welding of copper aluminum enamelled wire, which is especially used for leads on electronic products and motor products.
Precautions for copper pipe welding
Welding shall be carried out in strict accordance with the steps, otherwise the welding quality will be affected.
The surface of the pipe fitting to be welded shall be clean or flared. The flared mouth shall be smooth, round, without burr and crack, with uniform thickness. The copper pipe joint to be welded shall be polished with sandpaper, and finally wiped with a dry cloth. Otherwise, the solder flow and welding quality will be affected.
Insert the copper pipes to be welded overlapping each other (pay attention to the size) and align the center of the circle.
During welding, the weldment must be preheated. Heat the copper pipe welding place with flame. When the copper pipe is heated to purplish red, remove the flame and lean the solder against the welded junction to melt the solder and flow into the welded copper parts. The temperature after heating can reflect the temperature through color.
Editor’s summary: pay attention to flame during copper pipe welding. Welding flame includes carbonization flame, neutral flame and oxidation flame. The nature of the flame is determined according to the type and nature of the metal to be welded. We should pay attention to scientific and reasonable selection and use. Neutral flame is generally used for pipe welding of refrigeration and air conditioning.
For different materials and different pipe diameters, the size of welding gun and flame temperature are different. The size of flame during welding can be controlled and adjusted by two needle valves. The flame can be divided into carbonization flame, neutral flame and oxidation flame according to the volume ratio of oxygen and acetylene.
Detailed process of copper pipe welding
Strictly follow the steps during welding, otherwise the welding quality will be affected.
Preparation and piping
- 1. Check whether the quantity in oxygen cylinder and acetylene cylinder is sufficient.
- 2. Check the drawing requirements to ensure that all parts are complete and functional.
- 3. Ensure that the optical path of the pipeline is horizontal and vertical, and pay attention to the directionality of each valve.
- 4. According to the size and pipe diameter required by the drawing, measure the corresponding length with a tape measure and write the position with a wire number pen.
- 5. The thicker copper pipe shall be fixed and then removed with a cutter to ensure that the cutting opening is flush and not deformed.
- 6. File the rough edge of the cutting edge with a file and wipe it clean with a rag. Material flow and welding quality.
- 7. Except for the welding of red copper and red copper, all pipe fittings shall be cleaned with gauze or stainless steel wire brush before welding to expose the bright metal surface（ The inner surface shall be cleaned, and the metal chips and sand particles shall be cleaned)
- 8. Insert the copper pipes to be welded overlapping each other (pay attention to the size) and align the center of the circle.
- 9. See the table for the insertion depth and clearance between copper pipe joint and copper pipe（ Insertion depth (approximately equal to pipe diameter)
Protect
- 1. During welding, the welded pipe shall be filled with low-speed nitrogen to prevent oxidation.
- 2. Acetylene gas shall pass through the oxidation free welding generator to prevent oxidation on the outer surface of the welded object.
Welding
- 1. During welding, the weldment must be preheated. Heat the copper pipe welding place with flame. When the copper pipe is heated to purplish red, remove the flame and lean the solder against the welding junction to melt the solder and flow into the welded copper parts. The temperature after heating can reflect the temperature through color. Dark red: about 600 ℃; Crimson: about 700 ℃; Orange: about 1000 degrees Celsius.
- 2. During welding, the gas welding flame shall not directly heat the welding rod.
- 3. Corresponding protective measures shall be taken for parts that are easy to deform and damage under high temperature conditions. For example, the angle valve, evaporator and condenser shall be welded after the interface is wrapped with wet gauze. For solenoid valve, expansion valve, liquid mirror and four-way valve, those that can be disassembled must be disassembled and welded. The above measures shall be taken for those that cannot be disassembled
- 4. During welding, when the copper pipe is annealed after welding, the annealing temperature shall not be lower than 300 ℃.
- 5. After welding, cool and clean the oxide and welding slag in the pipe with dry nitrogen.
Repair welding
- 1. Repair welding shall be carried out where leakage is found during the pressure test. During the repair welding, the nitrogen of the system pressure test shall be discharged, and the pressure test shall be carried out again after welding.
- 2. Before repair welding, wipe the oxide layer on the surface with gauze. After repair welding, the oxide scale shall be removed. After quenching in water, the copper pipe shall be dried without water droplets.
- 3. After all welding, purge the system with nitrogen.
Summary of welding steps
- 1. Prepare gas, equipment and materials for welding;
- 2. Wear protective equipment;
- 3. Check the status of welding equipment and tools;
- 4. Open the cylinder valve, adjust the control outlet pressure of oxygen pressure reducer to 0.15 – 0.2MPa, and adjust the control outlet pressure of 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 wither the joint to make the flame neutral;
- 7. Adjust the flame in the order of neutral flame (small) → adding acetylene → increasing plume flame → adding oxygen → adjusting to neutral flame (large);
- 8. Wither the flame in the order of neutral flame (large) → reduce oxygen → appear plume flame → reduce acetylene → wither into neutral flame (small);
- 9. Make the tip of the flame core 2 – 4mm away from the weldment and perpendicular to the pipe, and evenly heat the whole length of the weld to dumb red;
- 10. Apply flux. When the flux becomes a transparent liquid and evenly infiltrates the weld, send the solder coated with flux to heat until the solder is fully melted and fully fills the weld;
- 11. Remove the flame and keep the weldments from dislocation before the solder is completely solidified;
- 12. Close the acetylene valve, and then close the oxygen gas valve to shut down;
- 13. Loosen the pressure reducer and close the bottle valve;
- 14. Sort out tools and equipment and clean the site.
Anti oxidation and anti-corrosion treatment after welding
After the copper pipe is welded, if the necessary anti-oxidation and anti-corrosion treatment is not carried out, the welded joint will be oxidized and corroded quickly, affecting the overall beauty of the equipment. How can we quickly and economically carry out anti-oxidation and anti-corrosion treatment?
Red copper anti-corrosion paint is used for spraying. The copper paint has good guidance, provides good anti-oxidation protection for the copper metal surface, and can prevent oxidation and corrosion. This process is a copper spray paint prepared with thin copper powder with copper purity of 99.9%, which has good guidance.
Comparison of application effects:
Product usage:
Step 1: wipe the product with a towel to remove stains, grease or scale.
Step 2: shake the can body several times before use.
Step 3: use copper anti-corrosion paint for product spraying, and the spraying distance is recommended to be about 25cm.
Step 4: spraying is completed.
The simplest can be welded with solder. If you consider pressure resistance or strength, you can use brazing, that is, buy a set of copper pipe welding tools. The conventional welding methods of copper can be summarized as brazing and fusion welding. Brazing is divided into soft brazing, hard brazing, and fusion welding is divided into TIG and MIG welding. Soldering is generally used to weld copper at low temperature. Soldering iron is used to weld thin materials, such as copper wire and copper foil. It is represented by low temperature 179 viodin 51 welding wire and WEwelding51-f flux welding. Brazing is generally carried out by flame welding, such as burning liquefied gas alone, or using oxygen and acetylene as heat source to match the welding wire, total phosphorus copper welding wire or brass and silver welding wire, such as the welding wire of viodin 202a. Fusion welding is generally argon arc welding or double pulse gas shielded welding machine. If argon arc welding is used, argon arc welding wire specially used for red copper shall be used. This can understand the welding application of weiodin copper alloy. If double pulse gas shielded welding is used, copper alloy coil wire welding shall be used, such as weiodin 204m gas shielded welding wire welding and high-purity argon protection.
Analysis of common welding defects
1. Weld bead
Features: solder flows out of the brazing joint and forms accumulation.
Causes:
- 1. Welding thermal efficiency is too high;
- 2. Excessive or improper application of solder;
- 3. When welding, the weld is not in the same horizontal plane.
Precautions:
- 1. Swing the welding gun back and forth during heating to prevent local overheating;
- 2. The added solder shall slide along the weld from the back of the heating position;
- 3. The weldment is positioned stably.
2. Undercut
Features: the weld edge is burned into a rotten shape by flame, but it is not completely burned through, and the pipe wall itself is burned.
Causes:
- 1. Too high welding thermal efficiency
- 2. Wrong heating mode.
Precautions:
- 1. Neutral flame welding is adopted.
- 2. The torch swings back and forth to avoid centralized heating.
3. Overburning or dissolution.
Features: the oxide on the joint surface will fall off naturally after welding. After the joint is cleaned, there are black pits embedded on the joint surface.
Causes:
- 1. Too high welding thermal efficiency (too high temperature);
- 2. Too long welding time, etc.
- 3. Use oxide flame welding.
- 4. Repeat welding (repair welding).
Precautions:
- 1. Adjustable neutral flame welding;
- 2. Do not repeat welding.
4. Trachoma
Features: there are impurities in the weld, resulting in deep holes on the weld surface.
Causes:
1. The filler metal or base metal itself has oil stain, impurity or oxide film.
2. Too high weld temperature causes phosphorus volatilization in solder.
3. Heating speed is too fast.
Precautions:
- 1. Ensure the cleanliness of solder and base metal;
- 2. The welding efficiency is appropriate, so that the gas dissolved in the high-temperature molten pool can be effectively discharged during weld solidification.
5. Stomata
Features: the heating time is insufficient, and the gas in the liquid seam metal fails to overflow completely, forming holes on the surface or inside.
Causes:
- 1. The fiber or base metal itself has oil stain or oxidation;
- 2. If the welding speed is too fast, the gas in the welding is effectively discharged;
- 3. The flame is a reducing flame, producing reducing hydrogen pores.
Precautions:
- 1. Ensure the cleanliness of base metal fiber;
- 2. Choose neutral flame welding with moderate speed.
6. Burn through
Features: the weldment is burned and pierced near the seam.
Causes:
- 1. Unskilled operation without swinging the welding gun;
- 2. Improper flame adjustment and uneven temperature control.
Precautions:
- 1. Swing the welding gun back and forth during welding to prevent overheating;
- 2. Select neutral flame grounding.
7. Crack
Features: Cracks in brazed joints include base metal cracks and brazed joint cracks. The mechanical properties of base metal and brazed joint decrease, and cracks occur under the action of residual stress.
Causes:
1. When the phosphorus content of solder is too high, the toughness of the material decreases;
2. The cold shrinkage of copper is obvious, and the residual thermal stress causes cracks.
Precautions:
1. Use electrodes with better grounding performance;
2. Tempering treatment to eliminate residual stress.
8. Welding leakage
Features: the weld is incomplete, some positions are not fully fused into a whole weld, and there is a leakage channel in the weld.
Causes:
- 1. The heat input of flame brazing welding is too small;
- 2. The temperature is not uniform when solder is applied;
- 3. There are oxide scale, oil stain and other impurities on the weld surface.
Precautions:
- 1. Uniform heating;
- 2. Heat the workpiece with flame and add it when the workpiece is dark red.
9. Preventive measures
During welding:
- 1. During brazing heating, the welding gun swings back and forth at the parts to be heated, and fixed-point heating is not allowed;
- 2. When adding solder, solder must be added from the back of the flame heating direction;
- 3. During welding, the gun nozzle shall not be too close to the workpiece, otherwise it is easy to temper;
- 4. When brazing red copper, generally preheat the inserted pipe to make the pipe fit closely, and then heat the external piping intensively.
After welding:
The ratio of thermal expansion and cold contraction between matched workpieces is different. Internal stress is generated between matched workpieces during welding. Tempering is required to eliminate the internal stress between welded workpieces after welding.
Operation method of tempering:
After the workpiece is welded, when the temperature drops to 200 ℃ – 300 ℃, tempering treatment shall be carried out within 30mm of the welding edge. During tempering, the external flame shall be quickly swept through the joint and the welding gun shall be swept back and forth. Fixed point heating is not allowed. Each workpiece shall last for about (3-5) seconds.
Source: China Copper Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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