I. The difference between brass and copper
Brass
Brass is a yellow-colored alloy made up of copper and zinc. Ordinary brass is composed of only these two elements, while special brass is composed of more than two elements, such as lead, tin, manganese, nickel, iron, and silicon.
Brass with a copper content of 62% to 68% has a melting point ranging from 934 to 967 degrees. It is known for its strong wear resistance and good mechanical properties, making it suitable for use in manufacturing pressure equipment.
Special brass is also known for its high strength, hardness and resistance to chemical corrosion. This makes it a popular choice for producing seamless tubes, which can be used in applications such as heat exchangers, condensers, low-temperature pipelines and subsea transport pipelines.
In addition to tubes, brass can also be used to manufacture sheets, bars, castings and other products. With its strong plasticity and high copper content, brass is an ideal material for manufacturing pressure equipment.
Red copper
Red copper is a type of copper that gets its name from its reddish-purple color. It is also known as industrial pure copper and is composed exclusively of copper.
Red copper has a melting point of 1083°C and does not undergo isomeric transformation. Its relative density is 8.9, five times greater than that of magnesium. It is also about 15% heavier than regular steel.
When an oxide film forms on its surface, red copper takes on a reddish-purple hue, which is why it is called red copper. This copper also contains a certain amount of oxygen and is sometimes called oxygen-containing copper.
II. Brass welding method
Methods for welding brass include gas welding, carbon arc welding, manual arc welding, and argon arc welding.
1. Gas welding of brass
Gas welding is the most commonly used method for welding brass due to the low temperature of the gas welding flame, which reduces the evaporation of zinc in brass compared to electric welding methods.
Commonly used welding wires for gas welding brass are 221 wire, 222 wire, and 224 wire. These wires contain elements such as silicon, tin, and iron, which help prevent and reduce evaporation and loss of zinc burning during the welding process, guaranteeing the quality of the weld and preventing the formation of pores.
Two types of flux are commonly used in gas brass welding: solid powder and gas flux. The gaseous flux is composed of methyl borate and methanol, such as gaseous agent 301. This flux helps to improve the quality of the weld and prevent contamination.
2. Manual arc welding of brass
In addition to copper 227 and copper 237, homemade electrodes can also be used for brass welding. During brass arc welding, it is recommended to use a DC power source with the positive electrode connected to the workpiece and the negative electrode connected to the electrode.
Before welding, it is important to thoroughly clean the surface of the part. The groove angle must be between 60 and 70 degrees to ensure proper weld formation.
To improve the quality of the weld, the part must be preheated to a temperature between 150 and 250°C. During welding, it is recommended to use a short arc and a linear movement without transverse or back and forth oscillations. The welding speed must be high for best results.
It is important to note that brass weldments that come into contact with corrosive media such as seawater and ammonia must be annealed after welding to relieve any welding stress.
3. Manual argon arc welding of brass
Standard brass welding wires such as 221 wire, 222 wire and 224 wire can be used for manual brass argon arc welding. Alternatively, filler materials with the same composition as the base metal can be used.
Both DC positive connection and AC welding can be used for this process. When using AC welding, zinc evaporation is less compared to DC positive connection.
In most cases, preheating is not necessary before welding. However, if there is a significant difference in plate thickness, preheating may be necessary.
It is recommended to weld as quickly as possible to obtain the best results. After welding, the weldment must be heated to a temperature between 300 to 400°C for annealing to relieve any welding stress and prevent cracking during use.
4. Carbon and brass arc welding
For carbon brass arc welding, 221 wire, 222 wire and 224 wire can be selected based on the base metal composition. Alternatively, self-made brass welding wire can also be used.
Gas flux 301 can be used as flux during welding.
The use of short arc welding is recommended to minimize evaporation and loss of zinc through burning.
III. Red copper welding method
Red copper, also known as industrial pure copper, can be welded using various methods such as gas welding, manual carbon arc welding, manual electric arc welding, manual argon arc welding, and automatic welding for larger structures.
1. Gas welding of red copper
Butt joints are the preferred method for soldering red copper, with lap joints and T-joints only being used when necessary. There are two welding wire options in gas welding: welding wires that contain deoxidizing elements, such as 201 and 202 wires, or a combination of general copper wire and base metal, using 301 gas agent as flux. A neutral flame should be used when gas welding red copper.
2. Red copper manual arc welding
In manual arc welding, 107 red copper welding rod is used with a red copper welding core (T2, T3). Before welding, it is important to clean the edges of the welding joint.
If the thickness of the part is greater than 4mm, preheating is necessary, with a temperature of approximately 400 to 500°C. The 107 copper electrode should be used for welding, and a DC reverse connection power supply should be adopted.
During welding, a short arc must be used and the welding rod must not move sideways. A reciprocating linear movement of the welding rod can improve weld formation. For long welds, the step-by-step reverse welding method should be used. The welding speed should be as fast as possible.
When welding multiple layers, it is important to remove any slag between the layers. Welding must be carried out in a well-ventilated area to avoid copper poisoning. After welding, the weld should be flattened with a hammer to relieve stress and improve the quality of the weld.
Related Reading: How to Choose the Right Welding Rod?
3. Manual argon arc welding of red copper
In manual red copper argon arc welding, welding wires such as 201 wire (special red copper welding wire), 202 wire and T2 red copper wire can be used. Before welding, it is important to clean the welding edges of the workpiece and the surface of the welding wire from any oxide film, oil or other contaminants to avoid defects such as pores and slag inclusions. This can be done through mechanical or chemical cleaning methods.
The size of the groove made in the part depends on its thickness. If the thickness is less than 3 mm, no groove is required. For thicknesses of 3 to 10 mm, a V-groove must be opened at an angle of 60 to 70 degrees. If the thickness is more than 10 mm, an X-shaped groove with an angle of 60 to 70 degrees must be made. It is generally recommended to avoid blunt edges to avoid incomplete penetration. The gap for butt joints should be between 0.5 and 1.5 mm, depending on the board thickness and groove size.
DC positive connection is generally used for manual argon arc welding of red copper, with the tungsten electrode connected to the positive electrode. To avoid pores and ensure reliable fusion and penetration of the weld root, it is necessary to increase the welding speed, reduce argon consumption and preheat the part. The preheating temperature must be between 150 and 300°C for parts less than 3 mm thick, and between 350 and 500°C for parts thicker than 3 mm. The preheating temperature should not be too high, as this may reduce the mechanical properties of the welded joint.
4. Red copper carbon arc welding
Carbon arc welding can also be used for red copper. Carbon electrodes and graphite electrodes can be used as welding electrodes, and the welding wire used is the same as that used in gas welding. The base metal can also be cut and the 301 gas stream can be used as flux.
4. Examples of copper alloy welding
Example 1. Manual tungsten inert gas (TIG) welding of copper piping
During the installation of the equipment, a company needed to weld six copper tubes (model T2) with dimensions of Φ180mm×10mm. For this task, manual welding with tungsten inert gas has been employed with great success. The welding process steps were as follows:
1. Pre-Welding Preparation
1.1 The welding equipment used was a WSE-350 AC/DC TIG welding machine with positive DC polarity. The welding material chosen was copper wire (201 wire), with a diameter of 3mm. The purity of argon gas was ≥99.96%.
1.2 The chamfers were aligned without leaving spaces between them.
1.3 The welding area of the copper tube and copper wire was kept free of oil, oxidation layers, moisture and other contaminants and exhibited metallic luster.
1.4 Welding parameters: A Φ3mm cerium tungsten electrode was used along with a Φ14mm nozzle. The welding current was adjusted between 160~180A and the argon gas flow was 15L/min.
1.5 Preheating: Due to the high thermal conductivity and coefficient of thermal expansion of copper, as well as its brittleness when heated, the bevel of the copper tube and the 60 mm area on each side were preheated before welding. This preheating was carried out using an oxy-acetylene flame, reaching a temperature of approximately 500°C. Temperature was measured with a point contact thermometer.
1.6 Two areas of the tube were spot welded (dividing the circumference of the tube into three equal parts, two of which were spot welded and one was the starting point of the weld). The spot welds had a required length ≥10mm and a suitable weld height of 3mm.
2. Welding procedure
The welding process was carried out in two layers: a root pass and a cover pass. All welding was done in the rotational welding position, specifically between 10 and 11:30 on a clock face, with a random upward rotation during welding.
2.1 Root walk: The root walk was carried out using a left hand welding technique. During welding, measures were taken to prevent the formation of gas pockets, slag inclusions, welding spatter and incomplete penetration. The angle between the welding wire and the tube surface was kept as small as possible to improve the effectiveness of argon shielding, as shown in Figure 7.
Ensure smooth movement of the welding gun and proper control of the weld pool temperature. It should be neither too high nor too low for the welding process to proceed smoothly. It is crucial to closely monitor the flow of molten copper into the weld pool and control the melting and penetration time.
When the molten metal in the weld pool begins to sink slightly, this indicates penetration (with good basic root formation).
Adopt an “interrupted” wire feeding method for inserting the filler wire, that is, the copper welding wire advances and recedes alternately. The wire should advance “quickly” and retreat “cleanly,” maintaining this state while welding uniformly forward. If the welding speed is slightly slow or penetration is uneven, incomplete penetration or burning may occur, resulting in weld nodules. The arc formation method, joint and operation are the same as the argon arc welding method mentioned above.
2.2 Cover layer welding: The welding gun swings left and right, and the welding wire is fed with the movement of the welding gun. When the arc moves to both sides of the groove, pause briefly and add welding wire to fill the groove and rise 1.5~2mm above the pipe surface. The welding gun and welding wire must cooperate properly and swing evenly to control the consistency of the weld pool shape and produce an excellent quality weld inside and out.
3. Precautions:
1) During welding, “tungsten touching” (that is, the tungsten electrode comes into contact with the welding wire or the weld pool) is strictly prohibited. If “tungsten ringing” occurs during welding, a large amount of metal dust and vapors will enter the weld pool, resulting in numerous pores or honeycomb-shaped cracks in the weld. If “tungsten ringing” occurs, stop welding, grind it, and replace the tungsten electrode or resharpen the tungsten tip until the metal is free of copper tarnish.
2) Ensure firm contact of the overlapping lines and avoid scratching the pipe surface.
3) After the solder has cooled a little, rotate the tube and clamp it tightly.
4) Control the interlayer temperature. If welding fusion becomes difficult, this indicates a low temperature. Reheat above 500°C before soldering again to avoid incomplete fusion or poor fusion defects.
5) Ensure good fusion, slightly faster welding speed and adequate wire feeding. Pay attention to the simultaneous fusion of the base metal and welding wire to fuse into one to avoid incomplete fusion or poor fusion defects.
6) When extinguishing the welding arc, the welding gun should not be lifted immediately. Continue to use the post-flow shielding gas function to protect the weld pool and prevent pore formation.
4. Post-welding treatment:
After inspection, if there are no defects such as pores, cracks or slag inclusions, reheat the welding area of the welded pipe joint to 600 ~ 700 ℃, and then quench it with tap water to increase the plasticity of the area of welding.
Example 2: Oxy-acetylene welding of a thin sheet of purple copper with δ=2mm
The waterstop in the blast furnace cooling pool is composed of thin sheets of purple copper with δ = 2 mm welded together. Soldering is challenging due to copper's excellent thermal conductivity.
Either the temperature is insufficient to form a weld pool, resulting in unmolten or poorly fused metal in the weld, or the temperature is too high, causing a large area of the welding zone to melt, resulting in welding defects such as burning or pieces of solder. Soldering thin sheets of purple copper is a very “complicated” problem.
The problem can be effectively solved using the “brass brazing” welding method. The preparations before welding and the welding operation process are as follows:
1) Decontaminate 60 mm on each side of the weld seam and use a wire brush to buff it to reveal the metallic shine.
2) The workpieces are paired without groove, and the pairing gap should be less than 1mm.
3) Use Ф3mm silicon brass welding wire (224 wire) with 301 welding flux.
4) Level the area to be welded (the pad is made of flat steel sheet, which must be thicker to avoid thermal deformations).
5) Preheat. Two welders use medium welding torches and neutral flames to heat the welding area simultaneously, reaching a temperature of 500~600℃. One person welds and the other continues to heat the welding place to ensure the stable progress of the welding process.
6) The preheating welder uses a neutral flame and the welding welder uses a slightly oxidizing flame.
7) Spot welding and formal welding should be carried out continuously, with a spot welding distance of 60 ~ 80 mm. The spot welding point should be smaller.
8) Pay close attention to the temperature changes in the welding area during heating and welding to prevent it from being too high or too low. Generally, judge visually by the dark red (550 ~ 600 ℃).
9) The movement of the welding nozzle must be constant and advance at a uniform speed. The flame core (white point) must be 5~8mm above the weld pool. The contour of the flame must always cover the melting pool to avoid contact with air. Make sure the brass liquid spreads naturally and smoothly on both sides of the weld and penetrates the gap.
10) To make the crystal structure of the welded joint denser and improve its strength and toughness, tap the weld with a small hammer after welding.
11) Carry out a tightness test after welding.
