In the process of welding, various compounds are obtained . Welds can connect not only metals, but also other dissimilar materials. Elements docked in an integral unit are a connection that can be delimited into several sections.
Weld Zone
The connection obtained during the welding process is divided into the following zones:
- The place of fusion is the boundary between the base metal and the metal of the resulting weld. In this zone there are grains that differ in structure from the state of the base metal. This is due to partial melting during the welding process.
- The area of thermal influence is the zone of the base metal, which has not been melted, although its structure was changed during the heating of the metal.
- Welding seam - the area that was formed during crystallization during the cooling of the metal.
Types of welding joints
Depending on the location of the joined products relative to each other, the connections are divided into the following types:
- Butt Docking of structural elements is carried out in one plane with the ends to each other. Depending on the various thicknesses of the parts to be joined, the ends can be displaced vertically relative to each other.
- Gusset. In this case, the combination of the ends is made at an angle. The welding process is carried out at the adjacent edges of the parts.
- Lap joint. Parts for welding are located in parallel with partial overlap.
- End connection. The elements to be welded are aligned parallel to each other and joined at the ends.
- T-joint. In this case, the end face of one part is adjacent to the side of the other at an angle.
Welding joints also characterize the types of welds, which can be qualified according to some criteria.
Weld rates
There are several parameters by which you can characterize all the welds obtained:
- width is the size between the boundaries of the seam, which are drawn by the visible fusion lines;
- the root of the seam is its reverse side, which is located at the maximum distance from the front part;
- convexity - is determined in the most convex part of the seam and is indicated by the distance from the plane of the base metal to the border of the largest protrusion;
- concavity - this indicator is relevant if it occurs in a weld, because, in fact, it is a defect; this parameter is determined in the place where the seam has the greatest deflection - the concavity size is measured from it to the plane of the base metal;
- the leg is welded - it takes place only in the corner and tee joints; this indicator is measured by the smallest distance from the side surface of one welded part to the boundary line of the seam on the surface of the second.
Types of seams according to the method of execution
- One-sided welding seams. They are performed with full penetration of metal along the entire length.
- Bilateral execution. According to the technology, after performing one-sided welding, the seam root is removed, and only after that welding is performed on the other side.
- Single-layer seams. They are performed by single-pass welding with one weld bead.
- Multilayer seams. Their use is advisable with a large thickness of the metal, that is, when welding in one pass is not possible by technology. The seam layer will consist of several rollers (passes). This will limit the spread of the heat-affected area and get a durable and high-quality weld.
Types of welds in spatial position and length
Distinguish such welding positions:
- lower, when the welded seam is in the lower horizontal plane, that is, at an angle of 0º relative to the ground;
- horizontal, the direction of welding is horizontal, and the part can be at an angle from 0º to 60º;
- vertical, in this position the surface to be welded is in the plane from 60º to 120º, and welding is carried out in the vertical direction;
- ceiling, when work is carried out at an angle of 120-180º, that is, welds are located above the master;
- "in the boat", this position applies only to corner or tee joints, the part is set at an angle, and welding is carried out "in the corner."
Breakdown by length:
- continuous, so almost all seams are performed, but there are exceptions;
- interrupted seams, they occur only in corner joints; double-sided seams of this type can be performed both staggered and chain.
Edge cutting
This design feature is applied when the thickness of the metal used for welding is larger than 7 mm. Edging is the removal of metal from the edges in a specific shape. This process is performed with single-pass welding of butt welds. This is necessary in order to get the right welding seam. As for thick material, cutting is necessary in order to initially melt the root pass and then with the following fusible rollers, evenly filling the cavity, boil the metal over the entire thickness.
Edging of edges can be performed if the thickness of the metal is not less than 3 mm. Because its lower value will lead to burnouts. Cutting is characterized by such design parameters: clearance - R; angle of cutting edges - α; dullness - p. The location of these parameters is shown in the drawing of the weld.
Edge cutting increases the amount of consumables. Therefore, they try to minimize this value in every way. It is divided into several types of design:
- V-shaped;
- X-shaped;
- Y-shaped;
- U-shaped;
- crevice.
Edging Features
For small thicknesses of the welded material from 3 to 25 mm, a single-sided V-shaped groove is usually used. Beveling can be performed on both ends or on one of them. It is advisable to weld metal with a thickness of 12-60 mm with two-sided X-shaped cutting. The angle α when cutting in X, V form is 60º, if the bevel is performed on only one edge, then the value of α will be 50º. For a thickness of 20-60 mm, the most economical will be the consumption of deposited metal in a U-shaped cutting. The bevel can also be made one at a time or at both ends. The blunting will be 1-2 mm, and the clearance will be 2 mm. For a large thickness of metal (over 60 mm), the most effective way will be crevice cutting of edges. For a welded joint, this procedure is very important, it affects several seam factors:
- connection health;
- strength and quality of the weld;
- profitability.
Standards and GOST
- Manual arc welding. Welds and joints according to GOST 5264-80 include types, structural dimensions for welding, coated with electrodes in all spatial positions. This does not include steel pipelines only.
- Welding steel pipelines. GOST 16037-80 - defines the main types, cutting edges, structural dimensions with a mechanized method of welding.
- Welding of pipelines made of copper and copper-nickel alloys. GOST 16038-80.
- Arc welding of aluminum. Welds GOST 14806-80 - shape, dimensions, preparation of edges for manual and mechanized welding of aluminum and its alloys, the process is carried out in a protective environment.
- Under the flux. GOST 8713-79 - welding seams and joints are performed by automatic or mechanized welding on weight, on a flux pad. It extends to a metal thickness of 1.5 to 160 mm.
- Inert gas welding of aluminum. GOST 27580-88 - the standard for manual, semi-automatic and automatic welding. It is performed by a non-consumable inert gas electrode with filler material and extends to an aluminum thickness of 0.8 to 60 mm.
Weld designation
According to regulatory documents, the presence of welds is shown on the assembly drawings or in a general view. Welds are shown in solid lines if they are visible. And if on the contrary - then by dashed segments. Leads with one-sided arrows are retracted from these lines. The symbol for the welds is carried out on the shelf from the leader. The inscription is made over the shelf if the seam is on the front side. Otherwise, the designation will be under the shelf. This includes information about the seam in the following sequence:
- Auxiliary signs. At the intersection of a leader with a shelf, there may be an icon:
○ - closed seam;
┐ - welding of the seam is carried out during installation.
- Designation of welds, their structural elements and GOST connections.
- The name of the seam according to the standard.
- Welding method according to regulatory standards.
- The leg is indicated, this item applies only to corner joints.
- Intermittent seam, if any. The step and location of the weld segments is indicated here.
- Additional icons of auxiliary value. Let's consider them as a separate item.
Auxiliary notation
These signs are also applied on top of the shelf if the weld in the drawing is visible, and below it when invisible:
- removal of reinforcement of the seam;
- surface treatment, which will ensure a smooth transition to the base metal, eliminating the influx and unevenness;
- the seam is made on an open line; this mark applies only to welds visible in the drawing;
- purity of surface treatment of the weld
To simplify, if all welds of the structure are made in accordance with one GOST, have the same edge cutting and structural dimensions, the designation and welding standard are indicated in the technical requirements. The design may not be all, but a large number of identical seams. Then they are divided into groups and assigned them serial numbers in each group separately. On one seam indicate the full designation. On the rest they put only serial numbers. The number of groups and the number of seams in each of them should be indicated in the normative documentation.