The air duct is a prefabricated structure used in forced or natural ventilation. They are necessary to maintain a good indoor climate and air purity. For the system to function properly, it must be sealed. The welded connection of air ducts is considered the most durable and reliable, but there are other ways of installation.
Duct classification
System design influences the choice of connection method. Also, the docking method depends on the operating conditions, the parameters of the removal of polluted air.
Round and rectangular
Round and rectangular structures are distinguished by their geometric shape. The advantage of the first option is that there is no risk of vortex flows. The noise level is lower here. This type of duct is more often used in industrial premises.
For residential buildings, a rectangular design is better. Thanks to its high flow capacity, it provides good ventilation. It is easier to hide such a system under the finishing material. Due to its tight fit to the wall, the product does not take up a lot of usable space.
In rare cases, elements of a triangular cross-section are used to form an air conditioning system. They matter for the interior.
Rigid and flexible
Rigid air ducts have different shapes: round, square, rectangular. For the manufacture of the structure, aluminum, stainless steel, and polymer materials are used. Flexible options are only round in shape. They are made from aluminum, textile, PVC. To give additional rigidity to the product, wire is used. An efficient system combines both types of ductwork.
Air ducts are located inside the wall or outside it. The first option is a ventilation shaft in a capital structure. It is used in residential areas. An external duct is more suitable for industrial or technical areas where design is not always important.
Welding methods
The craftsmen do not often have to connect the air ducts to each other by welding, since the process is expensive. This method is used if special requirements are imposed on the tightness of the structure. The welding process can be manual or mechanized.
Manual
Electric arc welding is used if the material thickness is more than 1.5 mm. Gas equipment is necessary if the metal is 0.8 mm thick. The second method is rarely used.
Mechanized
The mechanized welding method can be semi-automatic or automatic. It is used in businesses.
Connection types
The connection of ventilation pipes to each other is carried out by a welded or flanged method. In addition, the elements can be fixed with a bandage, nipple or sleeve.
Welded
It is possible to connect fragments of the air duct by welding if they are metal, while the thickness of their walls exceeds 1.5 cm. This method is most often used in industrial premises in which harmful gases accumulate.In this case, the seams should be as tight as possible. For galvanized materials, highly professional welding is required to avoid corrosion in the seam area.
Nipple
A nipple is a part of a pipe with a raised rib in the middle. It is inserted into the main structure. The same rib is used for fixation. Another section of the duct is put on the product. The joint is sealed with metallized tape.
The nipple connection is made using a sleeve. Its diameter is larger than the main pipe. The coupling can combine 2 structural fragments. The rib in this case is on the inner surface of the element. This method is used to connect round ducts.
Flanged
According to GOST, pipes can be connected using the flange method. For fastening parts, spot or solid welding is used. The flanges are fixed between themselves with nuts and bolts, as well as rivets. To ensure reliable sealing of the weld, it must be painted over. A sealing gasket is placed between the steel elements. Although efficient, flanged duct connections are labor intensive and expensive.
Bandage
The bandage method of joining the structure is in demand at chemical industry enterprises. It provides high reliability of the joint, but the manufacturing process itself is expensive, therefore it is unpopular for domestic use. The bandage is attached over the connecting seam. Before this, the ends require flanging. The bandage space is filled with a chemically inert sealant. This method is used to connect plastic ducts to each other.
Equipment and materials used
To create a nipple connection of ducts or a welded joint, the following tools and materials are required:
- stainless steel;
- tape measure, marker;
- hammer, pliers;
- vice;
- tools for cutting metal;
- sealant and a gun for its application;
- welding machine;
- fragments of a pipe of the corresponding diameter.
The construction assembly technology must be observed to the smallest detail. If you combine parts of the duct without sealing, the functionality of the system is impaired. The connection of the structure to the hood is carried out taking into account the diameter of all parts. Before the installation of the air duct, its drawing is made.
Advantages and disadvantages of a welded connection of air ducts
The welded joint is one-piece and does not require additional fixing elements. It has the following advantages:
- the ability to manufacture large-sized structures;
- reduction in weight compared to cast elements;
- high strength and reliability of the joint;
- relatively low labor intensity in domestic conditions.
Residual stress often occurs in the welded joint. In this case, the technical properties of the metal change, which eventually loses its strength. If welding is used ineptly, the seams may be defective. After using the device, the joints must be checked visually and with the help of tools. Local heating of the metal in the heat-affected area can change the mechanical properties of the material.
Scope of application
You need to connect air ducts to the hood in any room. Welded joints are used in systems for removing fumes, moving air saturated with moisture or acid fumes. They are necessary in structures with high pressure inside or hot air masses circulating.
This type of connection is used in basements, attic floors. It is suitable for residential and technical premises. This type of installation of air ducts is fireproof, durable and sealed.
The welded connection of the duct allows for good ventilation. However, the work must be carried out strictly according to the instructions.
