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The welding process of manual arc welding, the precautions of manual arc welding

The welding process of manual arc welding, the precautions of manual arc welding

  • Categories:Industry News
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  • Time of issue:2021-07-29 17:02
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The welding process of manual arc welding, the precautions of manual arc welding

(Summary description)

Manual arc welding is a manual welding method that uses the heat generated by the arc to melt the metal to be welded. Because it requires simple equipment and flexible operation, it can easily weld the welds formed by different positions and different joints in space. Therefore, it is still widely used at present.

Manual arc welding is shown in the figure:



Before welding, connect the welded workpiece and the welding tongs to the two poles of the electric welding machine and clamp the welding rod with the welding tongs. During welding, the welding rod and the workpiece are in instantaneous contact, forming a short circuit, and then they are separated by a certain distance (about 2-4mm), and the arc is ignited.

The workpiece under the arc immediately melts to form a semi-oval molten pool. After the electrode coating is melted, part of it becomes a gas that surrounds the arc to isolate it from the air, thereby protecting the liquid metal from oxygen and nitrogen; part of it becomes molten slag, or sprayed into the molten pool alone, or melted with the core The molten droplets of liquid metal are sprayed to the molten pool together.

In the arc and the molten pool, the liquid metal, slag and arc gas will undergo certain physical and chemical changes with each other, such as the dissolution of the gas into the liquid metal and the oxidation-reduction reaction. The gas and slag in the molten pool float up due to its light weight. When the arc is removed, the temperature drops and the metal and slag will solidify one after another. In this way, two pieces of metal are joined by melting and crystallizing weld metal. Because the shrinkage of the slag is different from that of the metal, it will slip on the slag shell and the metal boundary, and the slag shell may fall off automatically, or fall off after being knocked, and the metal weld seam with fish scales can be exposed.

The main equipment of manual arc welding is electric welding machine. Electric welding machine is a power source that generates welding arc, and there are two kinds of AC and DC. At present, there are many kinds of electric welding machines produced in China, which can be divided into AC electric welding machines and DC electric welding machines according to their structure.

There are two different connection methods for DC welding machines. When the electrode is connected to the negative electrode and the workpiece is connected to the positive electrode, it is the positive connection method; the opposite is the reverse connection method. Generally, when welding with alkaline low-hydrogen electrode (such as J507), in order to make the arc burn stably, it is stipulated to use the DC reverse connection method; when using the acid electrode (such as J422) to weld thick steel plates, the forward connection method is used, because the anode part The temperature is higher than the cathode part, and the forward connection method can get a larger penetration depth; when welding thin steel plates and non-ferrous metals, the reverse connection method is used. When welding with alternating current, since the polarity changes alternately, there is no need to choose the polarity connection.

The welding material for manual welding is an electric welding rod, which consists of a steel core and a coating on the outside of the steel core.



Steel core

The role of the steel core (welding core) is mainly to conduct electricity and form a deposited metal with a certain composition at the end of the electrode. The welding core can be made of various steels. The composition of the welding core directly affects the composition and performance of the deposited metal. Therefore, the welding core is required to minimize the content of harmful elements. In addition to limiting S and P, some welding rods have required the welding core to control As, Sb, Sn and other elements.

Medicated skin

Electrode coating can also be called paint. The main purpose of coating it on the core is to facilitate the welding operation and to ensure that the deposited metal has a certain composition and performance. Electrode coatings can be mixed with hundreds of raw material powders such as oxides, carbonates, silicates, organics, fluorides, ferroalloys, and chemical products in a certain formula ratio. Various raw materials can be divided into the following categories according to their role in the electrode coating:

1. Stabilizer makes the electrode easy to start the arc and can keep the arc burning stably during the welding process. Any substance that is easy to ionize can stabilize the arc. Generally, compounds of alkali metals and alkaline earth metals, such as potassium carbonate, sodium carbonate, marble, etc., are used.

2. Slag-forming agent can form molten slag with certain physical and chemical properties during welding, covering the surface of the molten metal, protecting the welding pool and improving the shape of the weld.

3. Deoxidizer through the metallurgical

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2021-07-29 17:02
  • Views:
Information

1

Manual arc welding is a manual welding method that uses the heat generated by the arc to melt the metal to be welded. Because it requires simple equipment and flexible operation, it can easily weld the welds formed by different positions and different joints in space. Therefore, it is still widely used at present.

Manual arc welding is shown in the figure:

1

Before welding, connect the welded workpiece and the welding tongs to the two poles of the electric welding machine and clamp the welding rod with the welding tongs. During welding, the welding rod and the workpiece are in instantaneous contact, forming a short circuit, and then they are separated by a certain distance (about 2-4mm), and the arc is ignited.

The workpiece under the arc immediately melts to form a semi-oval molten pool. After the electrode coating is melted, part of it becomes a gas that surrounds the arc to isolate it from the air, thereby protecting the liquid metal from oxygen and nitrogen; part of it becomes molten slag, or sprayed into the molten pool alone, or melted with the core The molten droplets of liquid metal are sprayed to the molten pool together.

In the arc and the molten pool, the liquid metal, slag and arc gas will undergo certain physical and chemical changes with each other, such as the dissolution of the gas into the liquid metal and the oxidation-reduction reaction. The gas and slag in the molten pool float up due to its light weight. When the arc is removed, the temperature drops and the metal and slag will solidify one after another. In this way, two pieces of metal are joined by melting and crystallizing weld metal. Because the shrinkage of the slag is different from that of the metal, it will slip on the slag shell and the metal boundary, and the slag shell may fall off automatically, or fall off after being knocked, and the metal weld seam with fish scales can be exposed.

The main equipment of manual arc welding is electric welding machine. Electric welding machine is a power source that generates welding arc, and there are two kinds of AC and DC. At present, there are many kinds of electric welding machines produced in China, which can be divided into AC electric welding machines and DC electric welding machines according to their structure.

There are two different connection methods for DC welding machines. When the electrode is connected to the negative electrode and the workpiece is connected to the positive electrode, it is the positive connection method; the opposite is the reverse connection method. Generally, when welding with alkaline low-hydrogen electrode (such as J507), in order to make the arc burn stably, it is stipulated to use the DC reverse connection method; when using the acid electrode (such as J422) to weld thick steel plates, the forward connection method is used, because the anode part The temperature is higher than the cathode part, and the forward connection method can get a larger penetration depth; when welding thin steel plates and non-ferrous metals, the reverse connection method is used. When welding with alternating current, since the polarity changes alternately, there is no need to choose the polarity connection.

The welding material for manual welding is an electric welding rod, which consists of a steel core and a coating on the outside of the steel core.

1

Steel core

The role of the steel core (welding core) is mainly to conduct electricity and form a deposited metal with a certain composition at the end of the electrode. The welding core can be made of various steels. The composition of the welding core directly affects the composition and performance of the deposited metal. Therefore, the welding core is required to minimize the content of harmful elements. In addition to limiting S and P, some welding rods have required the welding core to control As, Sb, Sn and other elements.

Medicated skin

Electrode coating can also be called paint. The main purpose of coating it on the core is to facilitate the welding operation and to ensure that the deposited metal has a certain composition and performance. Electrode coatings can be mixed with hundreds of raw material powders such as oxides, carbonates, silicates, organics, fluorides, ferroalloys, and chemical products in a certain formula ratio. Various raw materials can be divided into the following categories according to their role in the electrode coating:

1. Stabilizer makes the electrode easy to start the arc and can keep the arc burning stably during the welding process. Any substance that is easy to ionize can stabilize the arc. Generally, compounds of alkali metals and alkaline earth metals, such as potassium carbonate, sodium carbonate, marble, etc., are used.

2. Slag-forming agent can form molten slag with certain physical and chemical properties during welding, covering the surface of the molten metal, protecting the welding pool and improving the shape of the weld.

3. Deoxidizer through the metallurgical chemical reaction in the welding process to reduce the oxygen content in the weld metal and improve the mechanical properties of the weld. The main deoxidizers are ferromanganese, ferrosilicon, and ferro-titanium.

4. Gas generating agent can separate and liberate gas under the action of arc high temperature to protect the arc and molten pool and prevent the intrusion of oxygen and nitrogen in the surrounding air.

5. Alloying agent It is used to compensate for the burning of alloy elements and the transition of alloy elements to the weld during the welding process to ensure that the weld metal obtains the necessary chemical composition and performance.

6. Plasticizing lubricants to increase the plasticity, slippage and fluidity of the coating powder in the welding rod pressure coating process, so as to improve the pressure coating quality of the welding rod and reduce the eccentricity.

7. Adhesive agent Make the coating powder have a certain viscosity during the compression coating process, can be firmly bonded with the welding core, and make the electrode coating have a certain strength after drying.

Safe operation of manual arc welding

1. The manual arc operation guarantee must undergo safety technical training. After passing the examination and obtaining the operation certificate, it can work independently.

2. Before welding and cutting in the no-fire zone, the fire approval system must be implemented, and the fire permit must be issued by the relevant department before the operation can be performed.

3. The power switch must be turned off when carrying the welding machine, repairing the welding machine, replacing the fuse, and changing the polarity.

4. The installation and maintenance of the welding machine or the replacement of the fuse should be carried out by an electrician, and the welder shall not do it without authorization.

5. There shall be no flammable and explosive materials within 10m of the welding site.

6. No part of the welder's hand or body can touch the conductor. When operating in damp locations, rubber insulation pads should be laid on the ground.

7. Before work, check whether the insulation layer of the equipment and tools is damaged and whether the grounding is good.

8. Personal protective equipment must be worn in accordance with regulations when working.

9. When pushing or pulling the power switch knife, wear insulated gloves, stand on the side, push the switch with your left hand, and move fast to prevent the arc spark from burning your face.

10. Guardians and ventilation devices should be installed in the welding of containers and cabins. The running light voltage used is 12V.

11. Before ascending operations, check whether the ground below the operating point meets the safety requirements. Whether the scaffolding and bridge board are firm. Standard fire safety belts should be worn for climbing operations, and care should be taken to prevent heavy objects and tools from falling and hurting people.

12. Pay attention to explosion-proof and fire-proof during welding.

13. After the work is over, check the site carefully and leave after confirming the safety.

Precautions for manual arc welding

(1) Should master general electrical knowledge, follow the general safety regulations of welders, and be familiar with fire-fighting techniques, electric shock first aid and artificial respiration methods.

(2) Before work, check whether the welding machine's power cord, lead-out line and each connection point are in good condition: the line should be overhead or a protective cover should be installed when the line crosses the carriageway; the secondary circuit and the shell of the welder must be well grounded; the clamp insulation of the welding rod must be good.

(3) Open-air electric welding is not allowed on rainy days. When working in damp areas, stand on a place covered with insulating materials and wear insulating shoes.

(4) The work of connecting or disconnecting the mobile electric welding machine from the power network, as well as grounding, etc. should be carried out by an electrician.

(5) When working, turn on the power switch first, then turn on the welding machine; when stopping, first turn off the welding machine before pulling off the power switch.

(6) To move the position of the electric welding machine, stop and cut off the power first; if there is a sudden power failure during welding, the electric welding machine should be turned off immediately.

(7) When welding in crowded places, a fence should be installed to block the arc. When there is no obstruction, the surrounding personnel should be reminded not to look directly at the arc light.

(8) Wear gloves when changing welding rods, and do not lean against iron plates or other conductive objects. Wear protective glasses when knocking on the slag.

(9) When welding non-ferrous metal parts, ventilation and detoxification should be strengthened, and filter gas masks should be used when necessary.

(10) Turn off the welding machine after the work is completed, and then cut off the power supply.

Source: welding technology, electronic fever

Note: All pictures in the article are reprinted on the Internet, and infringement will be deleted!

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