Weld joint seams: characteristics and properties
The strength of the weld is determined by severalfactors. The first important indicator is the mode of welding two metal structures between themselves. The second factor is the right consumable. The third parameter determining the strength of the joint of the metal structure is the exact dimensions of the weld joints.
What is a catheter
This name comes from the fact that ifto consider the welding seam in a section, then, with its ideal performance, it will look like an isosceles triangle. In this case, the leg will be the distance that lies between the end of the seam of one part and the plane of the other part. In its essence, the weld joint will be the leg of this isosceles triangle, hence the name.
So, what is the cathette, it is now clear. It is important to understand that the strength of the connection will strongly depend on the value of the angular connection. However, it is important not to be mistaken. The fact that the weld joint is responsible for its strength does not mean that the thicker it is, the stronger the connection will be. In this case, it must be understood that too many welded elements will degrade the performance of the connection. In addition, too much consumption of electrodes, gas, flux and additives will greatly increase the cost of such work.
For the reasons that were described above, very muchit is important to consider the geometry of the joint. The main parameter when joining two metal structures is that the weld joint should have large longitudinal section parameters.
For example, when welding twometal elements having different thicknesses, the size of the joint of the seam should be determined by the part that has a smaller thickness. Most often, the dimensions of the weld joint are determined and measured according to pre-prepared templates. Today, welders use the most versatile tool for measuring the leg. Such devices are called "catheter welder".
This tool has the form of two thin plates,the ends of which are in the form of a recess designed to define various parameters of the leg. The expert in turn applies various catheters to the seam. Among them, there is necessarily one that will accurately repeat the geometry of the weld joint.
Shape of seam
After conducting welding works, only two types of seam are formed.
The first type is a conventional welding seam, whichlooks like a roller with a convex surface. However, it is important to note that this type of seam, according to experts, is not optimal. There are two reasons for this statement. Firstly, the stress on the structure will increase greatly within such a seam, and secondly, the consumption of materials to create such a seam greatly increases.
The second type of suture is considered ideal. It looks like a roller with a concave surface, but to achieve this performance when welding two designs is very, very difficult. In order to achieve this type of seam, it is important to correctly adjust the parameters of the welding machine, and also maintain the same electrode discharge rate. In order to fulfill both conditions, you need a specialist who has a lot of experience in such works. It is worth adding that this type of welding seam is not used in the assembly of metal structures.
Dimensions of the angle joint
If we talk about the dimensions of the angle of the weldedseam, then, as mentioned above, the decisive factor will be the thickness of the parts being welded. For example, if there are parts with a thickness of 4-5 mm, then the size of the leg will be 4 mm. If the thickness increases, then the cathete will also grow.
A very important factor that affects concavityor the convexity of a welded roller is what the electrode was used for. This refers to the chemical composition of the consumable element. Suppose, if you use an electrode that will become thick and viscous when used, the result is a convex surface of the roller. If, during melting of the roller, the metal is liquid and spreading, its surface will be concave.
Speed and mode of welding
In order to get the optimum weld joint and to ensure a strong connection during the work, several points must be considered.
- The main parameters of the selected operating modewill be the current strength, as well as the voltage. Specialists in this field know that if the current is increased and a stable voltage is created, the weld will be deeper and will have a smaller thickness. If you keep a stable current while working, but change the voltage, the resulting connection will be less deep, but its thickness will increase. From this follows the logical conclusion that the thickness of the weld joint will also vary.
- The second factor is speed. If this parameter is not exceeded by more than 50 m / h, the depth of the joint welding will increase, and the thickness will decrease.
- If you do the opposite, that is, increasespeed, then not only the depth of welding will decrease, but also the thickness of the joint's seam. Also, the characteristics of the metal formed inside the gap between the blanks will be reduced. This is due to the fact that the rapid heating of the bath is insignificant.
How to determine the weld seam
It should be said that this is not verydifficult. The basis for this statement is that in the section this seam is an isosceles triangle, and calculating the leg of such a figure is a fairly simple operation. In order to perform calculations, we can use the usual trigonometric formula: T = S cos 45º.
T is the size of the weld joint, and S is the width of the resulting bead, or the hypotenuse of the triangle.
In order to determine the seam cut, it is important to knowthe thickness of the seam itself. This operation is quite simple, plus to this in that case cos 45º will be equal to 0.7. After this, you can substitute all the available values in the formula and get the value of the leg with high accuracy. Calculation of the weld joint by this formula is one of the simplest operations.
Types of seams
To date, there are two main types of welded seams. Here it is important to understand that the seam and the welding joint are different things.
- Welded butt seams. This type is used when joining parts butt-end, that is, ends. Most often in practice, this type of joint is used in the assembly of pipelines, as well as in the production of sheet metal structures. The use of this type of seam is considered the most economical, and also the least expensive in terms of energy.
- There are also corner seams. In fact, here it is necessary to distinguish three types - angular, T-wave, lapping. Cutting edges of materials in this case can be either one-sided or two-sided. It depends on the thickness of the metal. The angle of cutting is in the range of 20 to 60 degrees. However, here it is important to understand that the more the angle is chosen, the more you will need to spend consumables, and the quality will also decrease.
Weld Seam Configuration
Welds also differ in their configuration. There are several types: longitudinal rectilinear and curvilinear, annular.
If longitudinal seams are to be welded,it is very important to carefully prepare the surface of the metal, especially if the work will take place with a large length of the seam. When creating this type of seam, it is important that the surface is not wavy, and all the barbs of the edges need to be cleaned. Also important is the removal of moisture, rust, dirt or any other undesirable elements from the work surface before welding.
If there will be a ring welding, then hereit is very important to adjust the operating mode of the welding machine. If the diameter of the product is small, then in order to achieve a quality welding seam, it is important to reduce the current.
You can add that the obtained seams may not beonly concave or convex, but also flat. Flat and concave types are best suited for those structures that are operated under dynamic loads. The reason for this was that this type of seam lacks a tangible transition from the joint itself to the metal.
GOST of weld seams
GOST 5264-80 is a document thatestablishes the main types, structural elements, as well as the dimensions of all welded joints. However, it is important to note that this paper does not cover the types of seams used to connect the pipeline.
One of the points of this GOST says thatwhen carrying out welding operations of the butt type and different thickness of the parts, they can be connected in the same way as the parts with the same thickness, if their difference does not exceed certain parameters.
Also, this document describes what is alloweddisplacement of the welded edges before welding with respect to each other. Also, there are set numerical displacement parameters, which are resolved at a certain thickness of the workpiece.
To this document there is an application in whichall the minimum dimensions of the weld joints are prescribed. It should be added that the convexity, like the concavity of the seam, can be no more than 30% of the value of its leg.