Classification of welds and joints

The effectiveness and quality of work depends on the availability of the necessary tools, material and skills. Success in any business, whatever direction it may be, is also significantly influenced by the knowledge of the theory. Welding works are 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 a classification of welded seams exists and how to choose the best option for the coupling of various metal products.

What is a welding seam?

During welding, three metal sections are involved in the process: among themselves, with the aid of the third, which protrudes the electrode, two pieces of iron are fastened together. In the place where the metallic parts join together, a thermal process takes place, forming a seam. Thus, the seam is a part of the metal structure obtained as a result of the action of the fused and solidified iron.

Welding can be joined by any metals. They have their own structural features, according to which a certain type of fastening is selected. The classification of welded seams is made depending on the type of adhesion, material and other parameters. Each connection has its own instructions and its order of execution.

Dimensions

There is a classification of welds along the length. Depending on the size, 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.
• Medium. The length of the seam is from 30 cm to 1 m. These seams are welded from the middle to the edges. For them, the back-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 sites will be larger.

Types of welded joints

The classification of welded joints is also carried out according to the type of fastening. There are four types of connections:

• Butt joint;
• T-wave;
• Lapped;
• Angular.

The most common form

During the butt clutch, the thickness of the product is taken into account. This saves a significant amount of material.

Butt grip is considered the most popular. This is due to the fact that this welding process is the fastest and most economical.

T-wave welding. Features and Recommendations

For this type of adhesion is typical T-shaped connection of metal products. As in the joint coupling, special attention is paid to the thickness of the metal, depending on which the seams are one-sided and two-sided.

Applying this type of adhesion, it is necessary to adhere to the following recommendations:

• Carrying out T-weld welding with two products having different thicknesses, it is necessary to hold the welding torch in relation to the product at an angle of 60 degrees.
• Welding works can be facilitated by placing the structure "in the boat". This position of the processed product will exclude undercuts, missed undercooked areas, which for this type of adhesion are considered to be the most common defects.
• If one pass of the welding torch proves to be ineffective, since defective parts can remain, they should be cooked by oscillating the welding electrodes.
• In the T-joint, you can limit yourself to one-sided welding. To do this, use the welding equipment Oineo Tronic Pulse, which allows you to carry out RW-cooking.

Lap welding

The principle of this type of connection is the two-side 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 welded joint is considered to be long and not economical, since more materials are required for 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, angular welding is characterized by the presence or absence of bevelled edges. If necessary, this type of connection is made from the inside of the product.

Weld Forms

The classification of welded seams according to the shape of the outer surface defines three types:

• Flat. Effective under dynamic and alternating stress, since these joints (as well as the concave ones) lack the stress concentration, which can cause sharp changes and destroy the welding clutch.
• Concave. Acceptable is the concavity of the seam, not exceeding 0.3 cm. Otherwise, the concavity of the weld is considered excessive and is regarded as a defect. Measures the level of concavity in the area where there is the greatest deflection.
• Convex seams. There are as a result of accumulation of a large amount of frozen metal and are considered uneconomical. But at the same time, a welded joint giving a convex seam is more effective at static loading than a joint with a flat or concave weld. The convexity index is the distance from the surface of the main metal to the point of the largest projection. The standard is convexity, not exceeding 0.2 cm for bottom welding and not more than 0.3 cm for welding performed in other positions.

Classification of welded joints by position in space

According to the placement criteria in space, there are four types of seams, each with its own characteristics and recommendations for welding:

• Lower seams. In the technical aspect, they are considered to be the simplest. Welding of the lower seams is made on a flat surface in a position from the bottom. This process is characterized by high efficiency and quality. This is due to more comfortable conditions for the welder. The molten metal with its weight is directed to a welded bath in a horizontal position. It is easy to follow the cooking of the lower seams. The work is done quickly.
• Horizontal seams. Weld a little harder. The problem is that the melted metal under the influence of its weight flows into the lower edges. This may result in the appearance of undercuts in the area of the upper edge.
• Vertical seams. They are the result of joints of metal products placed in a vertical plane.
• Ceiling joints. This welding is considered the most difficult and responsible. Characterized by minimal comfort. In the process of welding, it is difficult to separate slags and gases. With this case not everyone will cope, a lot of experience is needed, since it is not easy to keep slag falling on the face during work. It is important to observe the quality and strength of the connection.

How are welds and joints marked?

The classification and designation of welded joints 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 joints is designated, according to the normative document, by means of special lines, which can be solid or dashed. The visible weld seams are indicated as continuous, the dashed lines are invisible.

Symbols of the seam are placed on the shelf from the leader (in case the seam is located on the front part). Or, on the contrary, under the shelf, if the seam is placed on the reverse side. With the help of icons, the classification of welded seams, their intermittence, placement of welding segments is indicated.

Next to the main icons are additional. They contain auxiliary information:

• On the removal of reinforcement of the weld;
• On the surface treatment for a smooth transition to the base metal and to prevent sags and unevennesses;
• About the line along which the seam is made (whether it is closed).

For identical designs and products of the same GOST standard signs and technical requirements are provided. If the construction has the same seams, then it is better to give the serial numbers and break them into groups, which also assign numbers for convenience. All information about the number of groups and seams should be indicated in the normative document.

Seam position

The classification of welds is based on the position of the seam. They are:

• One-sided. Formed as a result of welding sheets, the thickness of which does not exceed 0.4 cm.
• Two-sided. Occur when double-sided welding of metal sheets with a thickness of 0.8 cm. It is recommended to leave 2 mm clearances for each connection, ensuring the quality of the clutch.

Possible flaws

Defects during welding can occur due to excessively high current and voltage on the arc. This can also be the result of incorrect manipulation of the electrodes. Classification of defects in welds at their location:

• Internal. To identify them, a technique is used that consists in monitoring: not destroying the construction, destroying in whole or in part.
• 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:

• Unforgiven. It is manifested in the local absence of fusions between the elements being joined. The defect leads to an increase in stress concentration and a decrease in the joint cross-section. The design with such a flaw is characterized by reduced strength and reliability. The reason for the failure can be both insufficient current strength and welding in a fast mode.
• Undercutting. A defect consists in a local decrease in the thickness of the base metal. This problem is observed near the boundaries of welded joints.
• Burning. The flaw has the appearance of a cavity in the weld seam. It occurs because of the leakage of molten metal from the weld pool. Burnout is an impermissible defect, it needs to be urgently corrected.
• Unprevented crater or indentation. Occurs because of arc breaks during approach to the end of the seam.
• The influx. The defect is manifested in the flowing of the weld metal onto the base metal without melting them.

The causes of the defects can be very different, but they are equally capable of reducing the adhesion strength, operational reliability, accuracy and spoil the appearance of the product.