Efficiency and quality of work depends on the availability of the necessary tools, material and skills. Knowledge of theory also significantly affects success in any business, no matter what direction it is. Welding is considered to be one of the most common.
This type of activity requires material, equipment, work experience, as well as theoretical knowledge. Having mastered the necessary information, a person gets an idea of what a seam is, what classification of welds exists and how to choose the best option for coupling various metal products.
What is a weld?
During welding, three metal sections are involved in the process: two pieces are fastened together with the help of the third, which acts as an electrodegland. At the junction of metal parts with each other, a thermal process occurs, forming a seam. Thus, a seam is a part of a metal structure obtained as a result of the action of fused and solidified iron.
You can connect any metals by welding. They have their own structural features, according to which a certain type of fastening is selected. Classification of welds is made depending on the type of adhesion, material and other parameters. Each connection has its own instructions and its own order of execution.
Sizes
There is a classification of welds by length. Depending on the size, the welding seams are:
- Short. The size does not exceed 30 cm. Such a seam appears as a result of welding performed in one direction from the very beginning to the end.
- Average. Seam length - from 30 cm to 1 meter. These seams are welded from the middle to the edges. For them, the reverse-step method is ideal. Its essence lies in the fact that the entire seam is divided into several sections, which are alternately processed by welding. Each of these segments has a length of 10 to 30 cm.
- Long (over one meter). They are welded in the same way as the middle seams, with the only difference being that the number of sections here will be greater.
Types of welded joints
Classification of welds is also carried out according to the type of fastening. There are four types of connections:
- butt;
- T-shaped;
- overlapping;
- angular.
The most common type
During butt bonding, the thickness of the product is taken into account. This saves a lot of material.
Butt clutch is considered the most popular. This is due to the fact that this welding process is the fastest and most economical.
T-welding. Features and Recommendations
This type of clutch is characterized by a T-shaped connection of metal products. As in butt bonding, special attention is paid to the thickness of the metal, depending on which the seams are single-sided and double-sided.
When applying this type of clutch, you must adhere to the following recommendations:
- When performing T-welding when joining two products with different thicknesses, it is necessary to hold the welding torch in relation to the thicker product at an angle of 60 degrees.
- Welding work can be facilitated by placing the structure "in the boat". This position of the workpiece will eliminate undercuts, missed undercooked areas, which are considered the most common defects for this type of adhesion.
- If one pass of the welding torch is ineffective, since defective areas may remain, they should be welded by vibrating the welding electrodes.
- In a T-joint, one-sided welding can also be limited. To do this, you need to use weldingequipment Oineo Tronic Pulse, which allows RW-brewing.
lap welding
The principle of this type of connection is double-sided welding of products, the thickness of which is not more than 1 cm. This welding is used in cases where it is necessary to prevent moisture from entering the gap between the steel sheets. As a result of this work, two seams are formed. This type of weld is considered time consuming and is not economical as it requires more materials to work.
Angular grip
This type of welding is used to connect metal products in a position perpendicular to each other. Depending on the thickness of the sheets, fillet welding is characterized by the presence or absence of beveled edges. If necessary, this type of connection is made from the inside of the product.
Shapes of welds
Classification of welds according to the shape of the outer surface defines three types:
- Flat. Effective under dynamic and alternating loads, since these seams (like concave ones) do not have a concentration of stress that can cause sharp drops and destroy the welding bond.
- Concave. The concavity of the weld, not exceeding 0.3 cm, is considered acceptable. Otherwise, the concavity of the weld is considered excessive and is regarded as a defect. The level of concavity is measured in the area where there is the greatestdeflection.
- Raised seams. They arise as a result of the accumulation of a large amount of solidified metal and are considered uneconomical. But at the same time, a convex weld is more effective under static load than a flat or concave weld. The convexity index is the distance from the surface of the base metal to the point of greatest protrusion. Bulges not exceeding 0.2 cm for bottom welding and not exceeding 0.3 cm for welding made in other positions are considered standard.
Classification of welds by position in space
According to the criterion of placement in space, there are four types of seams, each of which has its own characteristics and recommendations for welding:
- Lower seams. In a technical aspect, they are considered the simplest. Welding of the lower seams is carried out on a flat surface in the position from below. This process is characterized by high efficiency and quality. This is due to more comfortable conditions for the welder. The molten metal is directed by its weight into a welded pool located in a horizontal position. It is easy to follow the cooking of the bottom seams. Job done quickly.
- Horizontal seams. Welding is a little more difficult. The problem is that the melted metal, under the influence of its weight, flows to the lower edges. This may result in undercuts at the top edge.
- Vertical seams. They are the result of joining metal products placed in a vertical plane.
- Ceiling seams. This welding is consideredthe most difficult and responsible. It is characterized by minimal comfort. During the welding process, the release of slags and gases becomes more difficult. Not everyone can cope with this business, a lot of experience is needed, since it is not easy to keep slag falling on your face during work. It is important to observe the quality and strength of the connection.
How are welds and joints identified?
Classification and designation of welds is made using special icons, lines and callouts. They are placed on the assembly drawing and on the structure itself. The classification of welded joints and seams is indicated, according to the regulatory document, using special lines that can be solid or dashed. Continuous indicates visible welds, dashed indicates invisible.
Seam symbols are placed on the shelf from the callout (if the seam is located on the front part). Or, conversely, under the shelf, if the seam is placed on the reverse side. The icons indicate the classification of welds, their discontinuity, the placement of segments for welding.
Additional icons are located next to the main icons. They contain supporting information:
- about removing the weld reinforcement;
- on surface treatment for a smooth transition to the base metal and to prevent sagging and unevenness;
- about the line along which the seam is made (is it closed).
For identical designs and products of the same GOST, standard symbols and technical requirements are provided. If the structure has the same seams, then theyit is better to give serial numbers and break them into groups, which are also assigned numbers for convenience. All information about the number of groups and seams must be indicated in the regulatory document.
Seam position
Classification of welds is based on the position of the weld. They are:
- Single-sided. Formed as a result of welding sheets, the thickness of which does not exceed 0.4 cm.
- Double-sided. Occurs during double-sided welding of metal sheets with a thickness of 0.8 cm. For each connection, it is recommended to leave 2 mm gaps to ensure adhesion.
Possible flaws
Defects during welding can occur due to excessive current and arc voltages. It can also be the result of improper manipulation of the electrodes. Classification of weld defects by their location:
- Domestic. To identify them, a technique is used that consists in control: not destroying the structure, destroying completely or partially.
- Outdoor. They are easily identified by external examination.
Due to violation of the welding regime caused by lack of necessary experience, insufficient preparatory work, incorrect measurements, defects are divided into:
- Lack of fusion. It manifests itself in the local absence of fusions between the connected elements. The defect leads to an increase in stress concentration and a decrease in the cross section of the weld. A design with such a flaw is characterized by reduced strength and reliability. Cause of lack of fusionthere can be both insufficient current strength and welding in fast mode.
- Undercut. The defect consists in a local decrease in the thickness of the base metal. This problem occurs near the edges of welds.
- Burn. The flaw looks like a cavity in the weld. It occurs due to the leakage of molten metal from the weld pool. A burn is an unacceptable defect and needs to be fixed urgently.
- An unsealed crater or depression. Occurs due to arc breaks during the approach to the end of the seam.
- Influx. The defect manifests itself in the flowing of the weld metal onto the base metal without their fusion.
Defects can come from a variety of causes, but they can all reduce adhesion, serviceability, accuracy and appearance.
