Rebar welding

Rebar welding

Welding a rebar allows you to quickly make a strong frame of any size. However, the use of this technique is not always acceptable. The solution depends on the material of the rods and the load acting on them.

What is rebar?

Concrete has high compressive strength, but performs poorly in tension. In order to avoid cracking under these loads, steel bars with a circular cross-section – reinforcement – are embedded in it. Their additional function is to strengthen the concrete in compression.

Armature varieties:

1. Smooth rods made of hot-rolled quiescent, semi-quiescent or boiling St3 steel.
2. Rebars of this and the following classes have a periodic profile – protrusions which provide a firm grip on concrete. The bars with diameter less than 40 mm are made from steel (calm and semi-calm).
3. This variety is an improved version and is marked by applying an indelible white paint on the ends. Unlike the first, it can be joined by electric welding; the rods have increased strength due to cold drawing. This is one of the most common types of reinforcement. It is used in critical structures, including prestressed ones.

Two types of reinforcement are distinguished in reinforced concrete products:

Longitudinal. Is the main one, holds the calculated load.
Transverse. Serves to connect the belts of the longitudinal reinforcement into a 3-dimensional framework. Provides a bond between the compressed concrete and the stretched bars, absorbs the forces of thermal expansion.

Features of rebar welding

The round shape of the rods led to the emergence of a special method – tubular. It is used in butt welding, when the ends of the elements are adjacent to each other.

Basic requirements

At the point of welding, the metal should not lose its strength and ductility. Some steels is forbidden to join by this method, as the material in the area of the weld becomes brittle. Frames of such rods are assembled with binding wire or spring steel clamps.

Before welding, dirt and dust are removed from the reinforcement. For small amounts of work, it is cleaned to a metallic shine, which has a positive effect on the quality of the weld. This is not done on large construction sites, as such preparation entails a significant increase in the cost of the process and stretches it out in time. The thickness of the electrode and the welding current are chosen so as to avoid burning through the rod.

Fittings welding methods

Use manual arc welding, automatic and semi-automatic. There are several ways of positioning the rods in relation to each other.

Overlapping

This method is used in areas that are not subject to heavy loads.

Butt joint

This type of connection is used for rods of 20-100 mm in diameter. Welding is carried out by the bathing method. The disadvantage is the high consumption of electrodes. To fill a bath between bars with 28 mm thickness, 3 4-mm consumables are needed. If they melt in series, the master is required to know how to change them quickly. It is easier to clamp all 3 electrodes in a special comb and weld them simultaneously.

Spot contact

Such welding is used in automated production. Its advantage is high productivity. Its disadvantages: high power consumption; The need for special large-sized equipment (can be used only in the conditions of an industrial enterprise).

Cross-shaped

Welding is carried out strictly horizontally or vertically. This ensures firm contact of the fittings and prevents the molten metal from spilling out. The electrode is held at an angle of 30-45° to the plane of the bars.

Reinforcement welding technology

As an example, it is useful to consider the connection by the bath method. Proceed as follows:

  1. The rods are trimmed with a guillotine or a bolt cutter to the desired length. You can use a welding machine, but it is a more expensive way.
  2. Dirt and dust are removed and the ends are ground to a metallic luster at a length of 3-4 cm. Then they are washed and degreased.
  3. Install the valve in the designed position. The maximum permissible deviation from the alignment is 5% of the rod thickness. The size of the gap between the ends depends on the voltage: 1.5D (diameter of the electrode), if 220 V; and 2D, if 380 V.
  4. Fasten in the connection area the pads or the bracket, preventing the metal from flowing out. Steel parts have to be left, which leads to more expensive work. Removable ceramic or graphite pads are used many times. They are fixed with a wire or wire clamp.
  5. If metal pads are used, they are screwed to the armature.
  6. Clean one of the ends with a consumable and melt it, making oscillatory movements between the bars of the reinforcement. The burnt electrode is quickly replaced by a new one, and so on until the bath is full.
  7. Wait for the weld to cool and check its quality.

Checking the strength of the finished construction

The quality of the joints is checked:

  • Visually. Examine the connection for cracks, through-burns, undercuts, non-cutting, pores and craters.
  • Gamma-ray inspection. A method for detecting internal defects (blind holes, pores, microcracks, non-metallic inclusions).
  • By tapping with a hammer or by dropping the frame on the floor from a height of 1-1.5 m (strength test).
Staircase welding and fabrication

Staircase fabrication process

Metal is an excellent material, we can assemble a variety of structures, with high reliability and durability. From metal we can easily make not only small lightweight stairs, but also solid construction of any complexity.

Stairs fabrication assembled according to instructions, will benefit all the architectural features of the house, will fit perfectly into any interior, both inside and outside the house. The main advantage of the metal staircase is that it can easily be assembled on their own, without using specific materials or tools. Staircase welding will not take much time, but it will please you for many years.

Staircase fabrication, is important to make sure that the thickness of metal is not less than 3 mm, and its surface should be grooved. Safe staircase, should have a special anti-slip coating. It can be a mat of rubber, overlay made of crumb rubber or abrasive adhesive tape. Such coatings will protect from injury and serve as a decoration of the external staircase.

The staircase fabrication and welding is a big part of the work, however not the most important. Do not underestimate the role of finishing. It will provide ready-made structure reliable protection against metal corrosion and give the staircase great look.

At this stage, the final processing of all welds, protruding parts, sharp corners and roughness. To this end, it is necessary to use a grinder with an emery wheel, which will help to thoroughly grind everything. Grinding work will be performed once the staircase is assembled, on a metal surface.

Also, you have to choose the suitable roughness, to give your metal stairs a fine surface, there are two ways of doing it: by grinding or by air-blast finishing. For this process, metal stairs are held in compression steel cage, in which you attach you assembling mat. This process will require a high skill level of fabrication and metal working, and it will allow you to obtain a satisfactory finish on your staircase.

A staircase fabrication should begin with the manufacture of the frame. To do this, you need to take the channels, whose length should be calculated in advance at the preparatory stage, and put them on the rib. Next, using an electric arc welder, weld the corners, which will be the basis for installing the steps.

On top of them are mounted steel steps, made of smooth metal with slots. You can also use any other material that is provided by your design project. It is important that all the steps are strictly parallel to the floor, so pay attention to right angles.

Railing and railings

Railing and railings are made by welding square metal pipes, and after they should be attached to the right place using all the same welding.

At the final stage of the staircase is installed in the already prepared for this opening, and then securely fastened with anchor bolts.

Stairs fabrication final stage

At the final stage it remains only to deal directly with the decoration of the staircase. For example, you can use artistic forging for the railing, bright color of paint or a rare type of wood for making steps – please use your imagination. The main thing to remember is that the internal staircase should blend in with the interior of the room in which it is located, and the outdoor staircase should not stand out from the overall architecture of the house.

Stairs is very important part of a house. They are required for the entrance to the house, to the first floor, attic or attic. For the most part, people choose a metal staircase. Because of the advantages of metal, its strength, durability, the ability to give any shape.

Welding in construction industry

Welding in construction industry

One of the main technological processes in the construction industry is the connection of parts and elements by welding. Welding is used in the manufacture and installation of metal and reinforced concrete structures, process pipelines and equipment of various grades of steel, non-ferrous metals and alloys, other materials.

Productivity to ensure the necessary quality of welding, efficiency of construction and installation work and reliability of buildings and structures are determined in no small measure, the technical level and qualifications of specialists.

This is all the more important in terms of using for structures of difficult to weld effective steels and alloys, the use of new welding materials and increasingly sophisticated welding equipment, the application of new and progressive technological processes, increasing demands on the quality of building products created.

The content of the lecture notes corresponds to the curriculum of the section “Welding in construction” of the discipline “Metals and welding in construction”. The material is somewhat broader, which allows using it when working on the course and diploma projects.

About welding

The problem of firm connection of solid materials has been of great importance since ancient times. The processes of joining parts made of metal, wood, stone, ceramics, bricks, plastics, etc., as well as separating and crushing them complement each other and form the basis for the processing of solid materials. Without these processes it is impossible to imagine industry and construction nowadays.

There are two large groups of compound solids

  1. Mechanical methods of joining
  2. Methods of connection by molecular and atomic forces of adhesion

The first group includes various types of bolted connections, rivet and wedge connections, tight fit, etc.; the second group includes welding, brazing, gluing, cementing, etc.

The second group listed methods of connection of solid bodies differ in their features, and has its own areas of application, complementing each other, and allow you to perform a variety of production tasks.

The methods of the first group allow to obtain detachable joints, i.e. giving the possibility to separate the parts without destroying them. Connections of the second group are mostly inseparable.

One of the main methods of the second group is welding, which allows to join almost all metals and their alloys, glass, plastics, ceramics, etc. Welding methods are constantly improving, the scope of their application is expanding. This is required by the rapid development of technology, the use of new materials, the creation of new original designs.

Welding History

Welding History

What is welding?

Welding is a technique of joining metallic parts through high temperatures, adding fillers to make a pool, and cooling them to allow their fusion. Materials used to generate heat sources include gas, electricity, laser beams, friction, and ultra-recently robotic-welding.

Friction stir-welding, laser-welding, and ultrasonic-welding are some of the processes commonly used in joining aluminum. Welding of Aircraft-grade aluminium is not possible by using traditional-welding methods to its oxide layer, thus requiring alternating current.

The sight of welding-rods emitting sparks and holding pieces of metal together excites a curious mind to wander back to medieval times. How did the ancient people manage to pull off such a feat without electrode rods?

The History of Welding

The history of welding is traced to the Bronze age that occurred 2000 years ago. During the time, gold circular boxes were made from pressure welded lap joints.

Then in approximately 1000 B.C. came the Iron age. Many tools believed to have been made during this time are traced to the Egyptians and inhabitants of the eastern Mediterranean area, who were thought to have learned to weld iron pieces together.

The development of the art of blacksmithing in the middle ages led to the production of many iron items through hammering. Typical-welding as it is today was invented in the 19th century.
Chronological Advances in Welding’s/cutting Techniques

1800

Humphrey Davy is credited with arc production by the use of a battery to create two electrodes. Edmund Davy was instrumental in the discovery of acetylene in 1836. Mid 19th century witnessed the invention of the generator, which popularised arc lighting.
The late 1800s led to the development of gas-welding and cutting. As a result, arc-welding with the carbon arc and metal arc was developed, and what came to be known as resistance-welding became a practical joining process.

1880

Augusta De Meritens used the heat of an arc for joining lead plates for storage batteries in 1881. His student Nikolai N. Bernados made progress in welding’s cast iron and lead. The periods between the 1890s and early 1900s were the years of carbon arc-welding.

1890

C.L. Coffin of Detroit became the pioneer in using a metal electrode for arc welding-processes which involved the deposit of filler metal in the joint to create a weld. On the other side, N.G. Slavianoff was busy with the same idea of transferring metal across an arc, but instead, to cast metal in a mold.

1900

Strohmrnger brought into the picture a clay or lime-coated metal electrode. Oscar Knellberg brought in a coated electrode between 1907 to 1924. Stick electrodes were made by dipping bare iron wire in mixtures of carbonates and later drying the coating.

At the same time, resistance-welding continued to be developed, and processes like spot-welding, seam-welding, projection-welding, and flash butt-welding became commonplace, with Elihu Thomson being credited their originator tag.

The invention of thermite-welding in 1903 by Goldschmidt was accelerated by the need to weld railroad rails. Gas-welding and cutting were advanced by the emergence of a torch that was used with acetylene during this period.

With First World War came the demand for armaments, and many companies began to manufacture electrodes and welding-machines to meet the demand.

1920

Automatic-welding came about and utilized electrode wires and arc voltage to control the feed. Thanks to P.O. Nobel who introduced it to be used in building women motifs shafts and crane wheels. The automotive industry adopted its use in the production of rear axles housings.

During the 1920s, various electrodes were developed, fuelling debates on heavily coated rods versus light coated rods.

1930

The arrival of stud-welding to attach wood decking and metal popularized what later became helpful in the shipbuilding and construction industries. Then came the automatic submerged arc-welding process, which was used in shipyards and ordinance factories.

1940

The Gas metal arc-welding (GMAW)was developed in 1948 and replaced Gas Tungsten. Here the tungsten electrodes were replaced by electrodes wires using constant voltage power sources. The process was initially meant to deal with non-ferrous metals, and users tried to introduce this on steel, but the cost of gas impeded its use.

1950

Russian scientists K.V. Lyubavskii and N.M. Novozhilov came ump using consumable electrodes subjected through the use of carbon dioxide. Consumable electrodes were immediately adopted because they utilized equipment that was initially applied to gas metal arc-welding. The introduction of smaller diameter electrode wires allowed welding on thin materials and gained more popularity.
Plasma arc-welding came in 1957.

1960

The early 1960s witnessed the use of inert gas that economizes oxygen through spray-type arc transfer. The electron beam-welding-process, which uses a focused beam of electrons, was introduced in 1957.

The US automotive industry and aircraft engine industries are heavy users of electron beam-welding. Due to the high strength-to-weight ratio of aluminium, it is popular in the aviation industry. One of the ways of attaching aluminum to aircraft is through welding’s.

The electro-molding process was introduced in 1959 for the fabrication of welded diesel engine blocks. The electro gas was introduced in 1961.

Laser-welding developed by Bell Telephone Laboratories leads the newest processes used for cutting metals and aluminum in the automotive industry. Manual metal arc-welding has become popular in cast iron welding’s.

Recent Welding Developments

Welding-techniques have continued to be invented, with the latest being the use of AI robotics to perform strenuous tasks such as cast iron-welding on vehicles or fixing hard surfaces. Furthermore, robotics reduces human injuries through lifting and welding’s; this releases people to work in other productive areas.