What are the common defects of arc welding and spot welding, and what causes them?

Spot welding is used for relatively large seams.

Arc light, smoke, toxic gas, burning, fire, and electric shock generated during welding operations constitute arc welding.

Six major occupational hazards.

1. Welding arc light.

Strong arc light can cause acute and chronic damage to the eyes, **, etc. Electro-optic ophthalmia is a common occupational disease among arc welders.

The eye is exposed to ultraviolet rays from arc light.

Overexposure can cause keratoconjunctivitis.

In mild cases, there is a foreign body sensation and mild discomfort in the eyes, and in severe cases, there is a burning sensation and severe pain in the eyes, accompanied by photophobia, tearing, face spasms and other symptoms;

2. Welding fumes.

Welding rods, weldments and coatings produce a large amount of harmful fumes under the action of high temperatures, which are one of the main factors polluting the welding environment. The main components of soot are iron, aluminum, manganese, copper, silicon, etc., and the main toxic substance is manganese. Long-term inhalation of metal dust by welders will cause pneumoconiosis.

manganese poisoning and other occupational diseases;

3. Welding gas air will produce nitrogen oxides under the action of arc light.

and other toxic gases. In the absence of good ventilation, the toxic gas content in the air at the welding site is several times or dozens of times higher than the national standard, which is extremely harmful to the human body;

4. The high-temperature arc of welding burns the metal and splashes, which can easily cause people to be burned. When the weld is knocked in order to remove the slag in welding, the slag that is not fully cooled can easily hurt the eyes;

5. Fire. In the process of arc welding, due to the high temperature of the welding arc and the roadblocks of the welding machine and the line, the electric spark and high temperature caused by the aging of the line, overload work or overheating of the cable joint, as well as the splashing of slag, etc., all constitute a dangerous ignition source, when there are flammable and explosive materials nearby.

, will lead to ** disasters and ** accidents;

6. The electric shock operator has many opportunities to contact electricity, such as replacing the welding rod, hand-holding welding tongs, adjusting the current, contacting the workpiece (especially when working in the pipeline and container) and touching the welding cable, etc., if the electrical failure or violation of the operating procedures will likely cause an electric shock accident.

Hope it helps, hope, thank you!

Hello, the hazards of electrode arc welding are: arc radiation, high-frequency magnetic field, splash scalds, burns, electric shock, etc.

Electrode arc welding can also have defects, so what are the common defects of electrode arc welding? Let's learn to tell you the causes of common defects in electrode arc welding! Common defects of electrode arc welding: 1. Undercut and undercut refers to the fact that the groove on the base metal of the electrode edge is not filled with arc melting.

As shown in Figure 1), the main reasons for undercutting are: (1) the welding current is too large; (2) The angle of the electrode is too steep; (3) The arc is too long; Preventive measures: (1) Select the appropriate welding current; (2) When the welding rod swings, it stays at the edge of the groove for a slightly longer time; (3) Do not stretch the arc too long during operation; 2 Porosity refers to the hole in the molten pool where the gas in the molten pool does not have time to escape and stays in the saw seam.

That is, the gas is spherical in the weld, or it may be elongated. There are different types of stomata (Figure 2): a) uniformly distributed; b) dense distribution; c) The main reasons for the formation of stomata in the chain distribution:

1) The surface of the workpiece is unclean (such as rust, grease, water, coating materials, etc.); (2) If the arc is too long, the protective effect will be weakened, so that nitrogen and oxygen in the air will invade; Preventive measures: (1) Clean up the rust and grease of the joint and adjacent skin; (2) Adopt a reasonable way to intervene in the welding condition and process; (3) Dry and store the electrode in a reasonable way; 3. Slag inclusion refers to the defect that the slag in the molten pool is deposited into the weld. (As shown in Figure 3), the production of slag inclusion is not because the welding current is too small; (2) The welding speed is too fast; (3) When multi-layer welding, the designer will use a special way to protect the tissue and material.

The slag is not clean; Measures to prevent ingenious detection: (1) Clean the surface of the previous weld in time when multi-pass welding; (2) Improve the slope of the joint; (3) Choose a reasonable welding technology; 4. Arc pit crack (fire mouth crack) refers to the crack at the end of the weld and the crack formed in the arc pit. Here's why:

The welding rod speed is too fast, the molten metal is too fast, and the curvature shrinks suddenly, especially when using large welding currents, and the shrinkage when the liquid metal solidifies, which leads to the formation of this crack. Precautionary measures: Repeat the arc opening and closing by manual method when closing the curve, and refill the arc 2-3 times.

The unwelded penetration of the sub-substrate is a phenomenon in which the base of the joint is not completely penetrated. (as shown in Figure 4) the reasons for not penetrating: (1) the welding heat input is small; (2) Unreasonable joint design; (3) The slope angle is unreasonable; (4) Improper welding arc control; Precautionary measures:

1) Adopt reasonable welding heat input; (2) Reasonable joint design; (3) Short arc welding is used for alkaline electrodes; How?

There are six kinds of defects in electric welding, namely: 1. Cracks: divided into cold cracks, hot cracks, and reheat cracks.

2. Pore: including nitrogen pores, hydrogen pores, and carbon monoxide pores. 3. Solid inclusions:

Including slag inclusion (electrode hand arc welding, submerged arc welding), tungsten inclusion (tungsten argon arc welding). 4. Unfused and unpenetrated: caused by unreasonable groove structure, too small accompanying gap, short welding pause time and small welding current parameters.

5. Shape defect elimination: including the width of the weld.

First, the fillet weld changes greatly, and the residual height of the weld varies greatly. 6. Other defects: including arc abrasion, welding spatter, etc.

There are many reasons for poor welding.

1. Poor tin eating. The phenomenon is that some parts of the surface of the circuit board are not stained with tin, because the surface is attached to grease, oxidation impurities, etc., which can be dissolved and washed. Improper adjustment of flux use conditions, such as the pressure and height required for foaming.

2. Tin withdrawal. It mostly occurs on tinned lead substrates, which is similar to the situation of poor tin eating; However, when the surface of the soldered circuit is separated from the tin wave, most of the solder that has been adhered to the board is pulled back into the tin pot, so the situation is more serious than the tin eating defect, and re-soldering may not be improved once.

3. Cold welding or solder joints are not smooth. This condition can be classified as a type of uneven solder joint, which occurs when the substrate is separated from the tin wave and the part is moving under the influence of external force.

4. Solder joint cracks. The cause is the coefficient of thermal expansion of the part foot in the substrate through the hole and solder joint.

It can be said that it is not actually a soldering problem, but involves the thermal coordination of the material size in the design of the circuit and parts.

5. Too much tin. Excessive solder joint does not help the flow of current, but has a bad effect on the strength of the solder joint, the reason for the formation is that the contact angle between the substrate and the solder is improper, and changing the angle (3) can make the dissolved tin drop off the line when there is a greater tensile force, and obtain a more moderate solder joint.

To put it simply, the common welding defects of arc welding are: porosity, cracks (cold cracks and hot cracks), non-fusion, non-penetration, slag inclusion, arc pits, undercuts, burn-through, deformation and other defects.

Cold and hot cracks, inclusions, porosity, undercuts, unfused, unwelded.

1. Due to the large heat-affected area of argon arc welding, the workpiece often causes shortcomings such as deformation, high hardness, sand hole, local annealing, cracking, pinhole, wear, scratch, undercut, or insufficient adhesion and internal stress damage after repair. Especially in the process of repairing small defects in precision castings, the surface is prominent. In the field of repairing defects of precision castings, cold welding machines can be used to replace argon arc welding, because the cold welding machine has small heat release, it better overcomes the shortcomings of argon arc welding and makes up for the repair problems of precision castings.

2. Argon arc welding and electrode arc welding compared with the degree of damage to the human body is higher, the current density of argon arc welding is large, the light emitted is relatively strong, the ultraviolet radiation produced by its arc is about 5 30 times that of ordinary electrode arc welding, infrared is about 1 times that of electrode arc welding, and the ozone content produced during welding is higher, therefore, try to choose a place with better air circulation for construction, otherwise it will cause great harm to the body.

3. For metals with low melting point and easy evaporation (such as lead, tin. zinc), welding is more difficult.

Porosity, undercut, lack of penetration, cracks, deformation.

Electrode arc welding is manual arc welding.

Manual arc welding is an arc welding method that uses manual manipulation of welding rods for welding, referred to as manual arc welding.

It is used as two electrodes with electrode and weldment, and the metal to be welded is called weldment or base metal. During welding, the weldment is partially melted due to the high temperature and blowing force of the arc. An oval-shaped pit filled with liquid metal is formed on the welded metal, and this pit is called a molten pool.

As the electrode moves, the weld pool cools and solidifies, forming a weld. The slag shell covered on the surface of the weld is called slag. The distance from the melting end of the electrode to the surface of the weld pool is known as the arc length.

The distance from the surface of the weldment to the bottom of the weld pool is called the penetration depth.

The welding machines of manual arc welding are divided into two categories: AC arc welding machines and DC arc welding machines.

The following is a brief introduction to AC arc welding machine and DC arc welding machine.

AC arc welding machine, also known as arc welding transformer, is a special transformer, which turns the alternating current of network voltage into low-voltage alternating current suitable for arc welding, which is composed of the main transformer and the required adjustment part and indication device. Among the AC arc welding machines, the most widely used moving iron AC welding machine is currently the moving iron type AC welding machine.

DC welding machine: It is used to convert alternating current into direct current through the rectifier converter for welding. It has the advantages of small size and light weight.

Its structure is relatively complex, and maintenance is difficult. However, its performance can completely replace the AC welding machine and is more widely used. Including special materials and special welding rods, etc.

Advantages: The equipment is simple, cheap and easy to maintain. There is no need for complex auxiliary equipment during welding operation, only simple auxiliary tools need to be equipped, which is easy to carry.

Auxiliary gas protection is not required and is highly resistant to wind.

Flexible and adaptable, welding can be carried out wherever the electrode can reach. Electrode arc welding is suitable for welding single or small batches of workpieces, as well as irregular, arbitrary spatial positions and welds that are not easy to achieve mechanized welding.

Disadvantages: 1) Strong dependence. In addition to adjusting the welding power supply, electrode, and welding process parameters, the weld quality of electrode arc welding also depends on the operation skills and experience of the welder.

2) The labor intensity of welders is high and the working conditions are poor. When welding, welders are always subjected to high temperatures and toxic fumes for manual operation and eye observation.

3) Low production efficiency. Compared to automated welding methods, electrode arc welding uses less welding current and requires frequent replacement of the electrode.

Manual arc welding is a special operation, the state stipulates that practitioners must be trained in relevant theoretical and practical knowledge, pass the examination and issue a national general special operation personnel operation certificate, and take up the post with a certificate, because the lack of relevant knowledge of unlicensed operations, the accidents caused by are new.

If the unlicensed operation leads to a disaster or electric shock accident, the responsible person of the relevant unit and the operator will receive corresponding punishments, and some may be investigated for criminal responsibility.