In the construction industry, when welding massive metal structures at the joints, serious loads arise, which, if the technology is not followed, carries the risk of collapse of the structure. This is true in the shipping industry and engineering (when installing large-sized machines), in the construction of massive structures. A good joint must be calculated from the outset to avoid possible future deformations. The easiest way to check the correctness of the welded line is to recognize the leg of the seam.
A leg of a weld is a leg of a conditional triangle that fits into the cross section. There is no single number that would become an indicator of a reliable and high-quality seam when determining its leg. The larger the size of the isosceles triangle can be entered instead of the seam, the greater the load it can withstand. Often this characteristic depends on the type of metal and the stress limit that it can withstand. An increase in leg gives the opposite effect - the part is deformed and will not be able to work in the desired mode.
How to determine the size of the leg?
To determine the optimal welded joint, it is necessary to calculate the seam, as well as to determine the leg of the seam during welding. The following factors are taken into account:
- thickness of metal;
- the position of the parts relative to each other;
- type of seam used in connection.
For each product, the leg is selected individually, but here we are only talking about working with heavy loads. For private use of welding, delicate calculations are not necessary, but still professionals take into account the properties of the metal and try to make the seam durable and at the same time not harm the details. A seam leg along the edge is defined if two parts have the same thickness. If it is different, then the leg is determined by a thinner metal. It is important to choose and calculate its size. Indeed, the maximum power that the part can resist depends on this. The leg of the weld is determined by the standardization system GOST 5264-80.
The leg of the seam during welding is equal to the thickness of the sheets with lap joint, but it should not exceed 4 mm. If this parameter is greater, then 40% of the thickness of the metal should be taken and 2 mm added. So you can determine the maximum value of the leg of the seam.
How to choose a leg?
The weld leg is determined when welding reinforcement in the same way as when connecting any other elements of metal structures. The size depends on several parameters, including the position of the workpieces, their length and thickness. Professionals use templates that welders have already worked out before them. The main parameter is the length of the weld, because it affects the strength of the future structure. Material consumption and the likelihood of deformation are the main dangers in a long seam. Much depends on the type of seam with which the parts will connect.
Butt weld
A butt weld implies the following technology - to connect two butt welding elements (i.e., position parts with the ends of surfaces in one or different planes). There are more than 30 types of butt joints , all of them are provided by GOST. In this case, a dependence is made on the thickness of the elements to be welded, equipment and welding technology. If the design will be subjected to voltage of an alternating nature, then this method of connection is the most reliable. You can join and weld various parts. It can be not only sheets of metal, but also pipes, corners, channels. To weld two sheets, they do not even need to be in contact with each other - welding is carried out at a minimum distance of two workpieces.
Lap joint
An overlap joint is a welding method when parts are parallel and their edges overlap each other. Unlike a weld, there are only two types of lap joints. The ends of the products can be welded on two sides or on one. There is also a connection using an additional plate, which is welded to two parts, connecting them at the right angle. Lap weld parts using two types of seams - end and frontal. The welding mode with this connection may be higher, since there is no danger of burn-through of surfaces.
Gusset
Welding of two parts, the edges of which are located at an angle relative to each other, occurs by the method of angular connection. The standard distinguishes up to 10 types of such joints. Sometimes, for the strength and reliability of the weld, a special metal lining is used, which allows better joining of elements and makes structures more reliable. In power structures, this type of connection is rarely seen, therefore, calculations for such joints are not performed. Nevertheless, if this type of welding is necessary, the calculations are carried out by analogy with the T-joint and the seam type must be taken into account.
T-weld
Often there is a need to connect elements that are located in different planes. The best solution in this case is a T-joint, where the end face of one piece adjoins at a right or another angle to the other. Types of such compounds vary within 9 types provided by GOST. T-joints require deep penetration at the junction, the seam is usually made by automatic welding, or the edges are prepared in advance, for example, with an angled seam, which can be done manually, or butt. The type of seam with which the connection was made affects its calculation. Here, the fact is taken into account that the welded place previously processed will be much stronger than the base metal.
Seam quality control
In any of the seams, one should not forget about the leg of the seam during welding, the formula of which is not complicated and consists in determining the thickness of the metal. If it is less than 4 mm, then the leg is taken equal to it, but if it is more, then in the range of 40% - 45% of the thickness with an increase of 2 mm. The formula for calculating the leg: T = S cos 45º, here T is the desired leg, and S is the hypotenuse or width of the weld bead.
It is not difficult to control the connection of the workpieces, while using visual and instrumental methods (using instruments). A tool has been developed that defines the weld leg for welding. How to measure the seam of interest to them? To do this, you need to attach the device to two parts of the workpiece, and direct the middle to the seam, then write down the indicators and perform a simple calculation. Usually the seam is convex, but this is the most unreliable option. Indeed, it is in this form that stress is concentrated.
An ideal option is a concave seam, which is difficult to obtain. Here it is necessary to observe the welding speed, as well as to achieve the correct operation of the welding machine. Experienced craftsmen will be able to make such a seam. But more often it is obtained mechanically, simply cutting off the unnecessary part of the seam.