Reinforcement is a structure consisting of metal bars of various shapes and sizes. Its main task is to redistribute the compressive and tensile stresses inside the construction object. Accordingly, increased requirements are imposed on the rigidity of such a design. The rigidity index, in turn, is determined by the quality of the reinforcement joint by welding . Currently, several welding methods are used. We will consider the features of some of them in the article.
Welding fittings: GOST 14098–91
The most common types of compounds are:
- semi-automatic electroslag;
- bath-suture;
- manual electric arc;
- contact;
- the bathroom.
GOST defines the design, geometric parameters, types of joints obtained by electric arc and resistance welding of reinforcement .
The provisions of the standard apply to rods with a cross section of not more than 30 but not less than 4 mm, as well as metal wire with a cross section of more than mm.
Connection types
GOST defines three types of them:
Overlap welding is performed on 2 reliefs and seams (manual electric arc method). T-joint is performed in inventory form (using one electrode in the bath), submerged (in this case, filler wire is not used), mechanized, manually, by contact (by continuous reflow of the product with resistance).
Butt welding of reinforcement is carried out in various ways. The most common are:
- In combined bearing and forming parts of twin rods with one rod.
- Mechanized method using electric arc and wire (powder additive).
- In inventory form.
- Manual arc method and multilayer seams.
Bathroom Welding Fittings
This method is usually used to connect:
- Reinforcing products of large diameter (2-10 cm).
- Joints of rods arranged in several rows in reinforced concrete structures.
- The joints of flanges made of steel strips with a large cross section.
This method of welding reinforcement is ideally suited for the foundation and other large reinforced concrete products, complex frames in the construction of different buildings. It ensures the preservation of the strength of parameters and structural rigidity along the entire length. Such welding of reinforcement allows you to create a single power frame.
The connection can be performed both horizontally and vertically. Bathroom welding of column fittings and other vertical products can, therefore, be carried out without moving them and bringing them into a horizontal position.
Another advantage is that standard fixtures are used to make the connection, as in electric arc welding.
Important point
A key condition for obtaining high-quality joints in bathroom welding of reinforcement is a clear combination of bars. It is necessary to ensure that the axis of the rods do not move more than half their section relative to each other.
To comply with this condition, conductors of various types are used. In them, the geometric parameters and the location of the rods during welding of the reinforcement remain unchanged.
The essence of the method
Before direct welding, a steel mold is attached (welded) to the rods. In it form a bath with molten material. An electric arc is used for this. The ends of the bars melt under high temperature. This results in a single bath of seam material.
Before welding the reinforcement, the ends and surfaces of the rods are cleaned. They remove scale, corrosion, and dirt from them. To do this, use a stiff brush with steel bristles.
After cleaning, the rods are placed coaxially. Between the ends there should be a gap. Its size is less than 1.5 diameters of the rods.
When welding the reinforcement of columns , a stamped sheet form acts as a forming element. It is attached to the bottom by welding without the use of additives. The joint is melted over the entire cross-sectional area by performing oscillatory gradual movements of the electrode. Regarding the axes of the rods, such movements are perpendicular.
Surplus excess is removed using a scoop. Then the end of the upper rod is attached to the end of the lower, after which the metal is directed into the mold.
Slag is discharged from the mold through a special hole that is burned with an electrode. After the connection of the rods is completed, it is brewed.
Bathroom Welding Options
In practice, three methods are used:
- Semi-automatic (in ceramic form).
- Single, three-phase electric arc using a steel bracket (manual version).
- Automatic bath-slag (in copper form).
The most economical option is considered in which the pads are not used when connecting the rods. The fact is that for their manufacture it is necessary to spend a certain time and metal. In the absence of overlays, in addition, a compact connection is provided.
Nuances
Welding in the bath is carried out at currents with high rates. It can be 450 amperes if 5-6 mm electrodes are used.
If the products are connected at low temperatures, a current of approximately 10% higher than the standard is used. Professionals recommend the use of UONI-13/55 rods.
When using three-phase welding, a gap of 1.5-2 cm larger than the diameter of the electrode should be left. The mismatch index of the axes of the reinforcing rods should not be more than 5% of the cross-sectional area of the electrodes. Specialists recommend giving the "back deflection" to the bars, if they are long.
Elimination of slagging
Quite often, the ends of the rods when sloping a welded joint are slagged. This is due to rapid heat dissipation. As a result, the reliability of the connection is significantly reduced. You can reduce the likelihood of slagging:
- Heated ends before welding.
- Using metal molds made of heat-conducting materials. As a rule, copper elements are used.
Staple
It is used to secure the joint at the bottom. A low-carbon steel sheet clamp or bar is used.
Girth allows you to hold liquid metal and prevents it from flowing. To increase the efficiency of fixation along the edges of the bracket, limiters are mounted that prevent the slag from spreading along the rod.
Do not use overhead elements made of copper, brass, bronze alloys. As a rule, they are made of pure copper. Such braces serve for quite some time.
Contact method
It is considered one of the most common welding methods. The contact point of the products is melted by heating to a temperature of deformation and compression. This is accomplished by passing current through the circuit, the links of which are also the rods themselves. The current appears in a closed circuit, and the greatest resistance is concentrated on the contact area of the rods. At the same time, heat is released, which ensures maximum heating of this area.
You can reduce the welding time by increasing the current strength to 10, and in some cases up to 20 thousand amperes. In this case, the melting of the metal occurs almost instantly. Accordingly, the passage of current through the circuit is significantly reduced.
Contact connection of products can be carried out by butt or point method. The first is used when the end parts are butt. Spot welding of reinforcement is applied when the rods overlap each other. They are connected at several points simultaneously.
Equipment
A professional apparatus is used to connect the rods in a contact way . Welding of reinforcement should be carried out at a certain current strength and level of compression of the contact area, for a given time.
All equipment is conditionally divided into mobile and stationary. The simplest device you can assemble yourself. It should include 2 functional nodes. The first is the power supply, the second is the electrode holders of the remote type.
Butt joint
Its technology is based on the use of heat at the ends of products. Heating occurs due to the passage through these areas of electric current. It is fed after closing the circuit by connecting the ends. Provides heating with high resistance.
After completion of the transmission and disconnection of current, a “precipitate” of the heated section is produced. To quickly heat the metal in the connection area and prevent heat loss, a high current load mode is used.
Butt welding is used to connect smooth rods with a diameter of at least 14 mm. To connect fittings manufactured in a hot way and having a profile, this method is used if the diameter of the rods is not less than 32 mm.
Features of the work
Butt welding technology is divided into two types:
- Continuous way.
- Intermittent method.
Priority is given to the second type. Before starting work, the end of the reinforcement is cleaned of slag formations, paint residues, and rust. For this, a chisel, a hammer and a metal brush are used. The cleanliness of the ends is essential for the quality of welding.
Point connection
It is mainly used in the creation of reinforcing cages reinforcing nets from bars with a small cross section.
You can also use spot welding at home, for example, when repairing household appliances.
There are two ways to connect. In the first case, the metal at the joint site is brought to a molten state and to the formation of a molten core. In the second - the metal just heats up.
If a large current flows at the intersection of the point-contacting rods, high heat transfer will occur in this area. This is due to the fact that the resistance of the reinforcing bars is higher than that of copper conductors included in the secondary circuit of the apparatus for welding.
The process should be carried out at high rates of current. Due to this, not only productivity is improved, but also the quality of the connection. For this, powerful expensive equipment is used. At home, you can use the compact device, which was made independently.
The key node of the device for spot welding is a transformer. Due to it, a large current is generated. A transformer of the standard type OSM-1 can be used in the apparatus. However, it needs to be slightly modernized to obtain a secondary winding of greater power.
Point connection process
The work is carried out in stages:
- The rods are stacked in a certain position and placed between the electrodes of the apparatus. They are pressed tightly in the area of the future connection.
- Current is supplied to the contact area; the metal is heated to the plastic state required for deformation. Due to the pressing, a sealing belt is formed, which prevents the spreading of the metal.
- The current pulse must be strong and short-term. This will ensure the formation of strong point contact of the rods after the cessation of supply.
Lap joint
It involves the fixation of the rods, partially superimposed on each other. When using this method, the rods form one line with the mutual overlapping of their length in the docking areas.
The lap joint is used to distribute the longitudinal compressive / tensile load on the surface of the rod. When performing work, you must follow some rules:
- Overlap is allowed in areas with minimal stress on the structure.
- Rods of different diameters should be distributed evenly. However, it is better to use the same rods.
- Lap welding is used to connect the rods with a cross section not exceeding 20 mm.
- The mutual overlapping of the bars should be more than 50 cm.
Lap welding of industrial products under increased load is recommended to be performed using manual arc welding. It is carried out with one or two seams from the flanks. In order for the joint to turn out to be of high quality, the seam length must exceed the diameter of the rods by at least 10 times.
Manual arc welding is performed, as a rule, in the horizontal position of the rods. For work, conventional equipment is used, which includes a transformer, gas burner, or devices with neutral gas.