Ventilation Duct

How to Make The Ventilation Duct

How to Make The Ventilation Duct

The ventilation duct is a metal or composite duct used in ventilation and air conditioning engineering of industrial and civil buildings. It is a municipal infrastructure for air circulation and reducing the concentration of harmful gases.

There are many kinds of materials and uses, and the shape is mainly divided into a square ventilation pipe duct and circular ventilation duct. When it comes to metal square ventilation ducts, the most common and commonly used are galvanized sheet ventilation ducts and stainless steel ventilation ducts. Ventilation Duct

Among them, due to its low material cost and low processing difficulty, the application range of galvanized sheet ventilation pipe is much larger than that of stainless steel ventilation pipe. It is also the most common ventilation pipe, which is widely used in smoke exhaust and ventilation facilities of various municipal infrastructure. On the other hand, for the ventilation pipe made of stainless steel, due to the higher tensile strength of stainless steel plate, there will be a greater degree of rebound deformation during processing, resulting in the doubling of processing difficulty. However, due to the specific non-rusting characteristics of stainless steel plate, stainless steel ventilation ducts will be used in places with high requirements, such as kitchen smoke hood, which involves clean and sanitary places.

Although the shape of the ventilation duct looks very simple, its internal structure and processing process are very complex. It is not so easy to make a completely formed ventilation duct. In the beginning, science and technology were not so developed, and industrial technology was still in a relatively backward stage. The ventilation pipes were made by pure manual processing methods, combined with some simple machines for the production of ventilation pipes. The efficiency was very low, and the beauty of the air pipes was not high.

Then, with the development and progress of human society, the gradual improvement of the level of science and technology, the rapid development of creativity in industrial manufacturing, and the invention and popularization of various one-time molding machines, the efficiency of ventilation duct production and manufacture has been greatly improved, time and money have been saved, The finished ventilation duct also has high quality and beautiful appearance. Here, we will briefly discuss the key points and manufacturing process of the ventilation duct, which can be divided into manual ventilation duct process and automatic ventilation duct production process. Ventilation Duct

Ventilation Duct

Key Points of Ventilation Duct Fabrication

  1. The plate shall be provided with a material certificate, and the appearance inspection must be flat, smooth, free of scratch and zinc layer peeling, and meet the design requirements, otherwise, it shall not be used. Ventilation Duct
  2. Before processing, remove the oil stain on the plate, and do one touch, two wipes, and three checks to ensure that the oil stain is completely removed. Ventilation Duct
  3. In the process of processing, in order to prevent the iron sheet from being scratched and worn, damaging the zinc layer, or contaminated with dust, a 3mm thick rubber plate is paved on the flat cement floor, and the blanking is carried out on the rubber plate. Ventilation Duct
  4. When cutting, undercutting, splicing, folding, and transporting sheet materials, the storage rack or four-wheel trolley shall be used to receive and transfer the materials, and shall not touch the ground and drag; Semi-finished products are stacked on the platform with a rubber plate. Ventilation Duct
  5. Key points of flange processing control: the profile must meet the high-quality standard and shall not be rusted, skinned, or pitted; The flatness of the flange welding joint shall not be greater than 0.5mm, the rivets must be galvanized, the rivet spacing shall not be greater than 100mm (screw hole spacing shall not be greater than 12mm), the hole spacing shall be accurate and interchangeable; Welding slag, welding spatter and floating rust shall be completely removed; Apply anti-rust primer with strong adhesion for two times, and there shall be no paint dripping in screw holes and corners. Ventilation Duct
  6. For the combination of semi-finished products of inner pipes, components, and accessories, the dirt at the site shall be removed first. After the combination riveting, the gaps and holes shall be blocked with glue or tin. The flanging width is consistent, greater than 7mm, and the screw hole is not covered; The flatness is less than 1mm. The finished products shall be stored horizontally by category, and attention shall be paid to protect the paint from wear; For the air duct to be reinforced, the stiffener is only allowed to be set on the outer wall. Ventilation Duct
  7. The air duct, components, and accessories shall be manufactured in the form of a single bite, corner bite, joint bite, etc. Ventilation Duct
  8. When making the air duct, the material shall be cut according to the plate to minimize the joints. The specific provisions are as follows: there shall be no joints within 800mm of the bottom edge width of the rectangular air duct, there shall be only one joint within 800mm-1000mm, and there can be two joints within 2400mm. Transverse splicing is prohibited for all the above dimensions, and the ratio of the long side to the short side of the rectangular air duct shall not be greater than 4:1; The butt joint shall be of a single flat type. Pay attention to placing the flat surface of the butt joint on the inner wall of the pipe without reversal during the corner butt joint; The flexible short pipe shall be made of a soft rubber plate or high-quality artificial leather. The inner wall shall be smooth, the longitudinal joint shall be glued smoothly, and there shall be no holes or glue leakage gaps. Ventilation Duct
  9. Cleaning of air duct: the cleaning of the air duct is particularly important. Generally, the galvanized steel plate has not been decreased, and the surface of the steel plate is coated with a large amount of grease. If it is not cleaned, it will be contaminated with dust during transportation, installation, and subsequent operation. During long-term use, it may lead to dust accumulation and flying, resulting in a sudden increase in the dust concentration in the air in front of the filter, This has a very adverse impact on the use of high-efficiency filters. Cleaning is mainly dust removal and degreasing. Clean water or pure water plus neutral cleaning agent shall be used for dust removal, and trichloroethylene or industrial alcohol shall be used for degreasing. Cleaning sequence: clean with clean water or pure water, wash with a neutral cleaning agent, use trichloroethylene or industrial alcohol decreasing water or pure water to wash clean cloth, scrub white silk cloth for inspection (it is qualified if it does not change color). The qualified air duct shall be sealed with plastic film immediately. Ventilation Duct
  10. After the air duct is processed and manufactured, it shall be carefully and comprehensively inspected. After passing the handover inspection and acceptance, it shall be sealed with high-quality flexible plastic film. The sealing part shall be tightly bound with adhesive tape, and then stacked by category. Ventilation Duct
How to Make The Ventilation Duct

Ventilation Duct Processing Instructions

According to the design requirements, to ensure the construction quality and facilitate the on-site supervision and inspection, a small air duct processing workshop needs to be arranged on-site. Before the fabrication of the air duct, the selected galvanized sheet shall be free of rust spots, and the galvanized layer after folding and biting shall be free of peeling; The undercut of processed air duct and pipe fittings shall not crack, and the riveted flange shall not have missing riveting and rivet falling off; The angle steel flange shall be evenly applied with oil, and there shall be no transparent hole at the air outlet mouth installed on the tee, cross, elbow, and round pipe. The flange mouth shall be square, the angle steel shall not collapse or bend, the outer joint of flange flanging shall not have double layers, and the switches of various valves shall be flexible. Ventilation Duct

Construction Technical Measures

In order to ensure the processing quality of the air duct, according to the design requirements and relevant provisions of national construction acceptance specifications, the construction processes are described as follows: Ventilation Duct

1. Manufacturing process flow of air duct:

Draw the processing sketch of air duct, select high-quality galvanized steel plate (with certificate), carry out blanking, shearing, undercut production, folding, forming, riveting flange, flange forming, and inspection.

2. Flange manufacturing process: Ventilation Duct

Straightening, blanking, rivet drilling, welding forming, bolt drilling, and painting of angle steel and angle iron.

3. Thickness table of galvanized steel sheet for ventilation system Ventilation Duct

Length B(mm)Thickness B(mm)
B≤630 mm0.6 mm
630 mm<B≤1000 mm08 mm
1000 mm<B≤2000 mm1.0 mm
2000 mm<B1.2 mm

4. Specification of metal rectangular air duct flange and bolt (mm)

Length of Duct BAngle Steel specificationBolt specification
B≤63025*3M6
630<B≤150030*3M8
1500<B≤250040*4M8
2500<B≤400050*5M10

5. The long side of the rectangular air duct is greater than 630 mm or the side length of the thermal insulation air duct is greater than 800 mm, the section length is greater than 1250 mm or the flat area of one side is greater than 1.2 m. Stiffeners are set along the center of the pipe for reinforcement.

6. Ensure that the tightness of the air duct meets the requirements of design and construction acceptance specifications. According to previous construction experience, our company focuses on the following node problems in Construction: A. undercut joint; B. Gap during connection of air duct interface; C. Loopholes (dead corner holes) during flange riveting and flanging; D. Rivets of flanges and reinforcing bars; E. Abnormal collision, rupture and hole pricking of the air duct. Item e can be avoided in construction as far as possible. Once it happens, we will take the method of solder welding to remedy it. The other four construction items are inevitable. During construction, we will prevent and remedy by adding 1 * 10 rubber strip or KS sealant at the joint.

Draw the decomposition diagram of the ventilation system according to the design drawings and the actual measurement on-site, formulate the processing and manufacturing plan of air duct and parts according to the construction progress, prepare the detailed list and manufacturing list, and submit them to the manufacturing workshop for implementation. The selected air duct supplier is required to supply air ducts for the project with quality and quantity in accordance with the production plan provided. During the production process, professional engineers need to be sent to the production line for process sampling inspection and process control.

How to Make The Ventilation Duct

Processing Technology of Metal Air Duct

  • Cutting of Plates

During cutting, the marking must be rechecked to prevent waste due to blanking. After cutting, the cut of the plate shall be neat, straight, and smooth. The cutting can be carried out by hand tools or plate cutting machines according to the construction conditions.

  • Connection of Sheet Metal

Ventilation pipes and accessories made of the metal sheet can be connected between plates by bite connection, rivet connection, and welding according to the thickness of plates and design requirements.

  • Undercut Connection

In ventilation and air conditioning engineering, bite connection is the most commonly used and simple connection method, which is generally applicable to ordinary steel sheet and galvanized steel sheet with thickness less than 1.2mm, and aluminum sheet with thickness less than 1.5mm; Stainless steel plate with thickness less than 0.8mm.

Bite type: according to the structure of steel plate joint, it is divided into a single bite, double bite, snap bite, combined angle bite, and corner bite; According to the shape of the steel plate joint, it is divided into the flat bite and vertical bite; According to the position of steel plate joint, it is divided into the longitudinal bite and transverse bite

Bite width and allowance: the bite width is determined by the plate thickness of pipe fittings and the performance of bite machinery. Generally speaking, the bite allowance for single flat bite, single vertical bite, and single corner bite is equal to three times the bite width. The reserved amount of joint angle bite is equal to four times the bite width, and the bite shall be left on both sides according to the needs of the bite. Undercut processing: the processing process of plate undercut connection, mainly folding and bite compaction. The quality of the hem shall ensure the tightness and firmness of the undercut joint, and the hem width shall be consistent. Flat or undercut shall be closed and pressed in real-time, and there shall be no phenomenon such as half undercut and tension seam. The undercut processing can be carried out manually or mechanically. The undercut processed manually is prone to such phenomena as loose undercut seam, inconsistent folding degree, half undercut, or open seam, which is time-consuming and can not guarantee the quality. Therefore, our company adopts mechanical processing, which saves money and improves efficiency.

  • Rivet Connection

Riveting between plates is generally used in ventilation and air conditioning projects when the design requirements or the thickness of galvanized steel plate exceeds the processing performance of undercut machinery. Riveting is not only used for the connection between plates, but also the connection between the air duct and flange. Before riveting, the rivet diameter, rivet length, and spacing between rivets shall be selected according to the plate thickness. Rivet diameter d = 2 S (s is plate thickness) but not less than 3 mm; Rivet length L = 2 S + 1.5 D. The spacing between rivets is generally 40-100 mm. When the tightness requirements are high, the spacing should be smaller. The distance from the center of the rivet hole to the plate edge B = (3-4) d. During riveting, the rivet center must be perpendicular to the plate surface, the rivet cap shall compress the plate to make the plate joint close, and the rivets shall be arranged neatly. The plate riveting can be manual riveting and mechanical riveting.

  • Welding

For the connection between plates, in addition, to bite connection and rivet connection, welding shall be adopted when the pipe sealing requirements are high or the plate is thick and cannot be used for bite connection. When making air ducts and components, oxygen-acetylene welding, carbon dioxide gas shielded welding, argon arc welding, electric welding, and contact welding shall be adopted according to the thickness and material of the plate. Tin welding can also be used to weld the bite gap of a general thin steel plate or galvanized steel plate. During welding, the weld surface shall be flat without cracks, burn through, nodulation, etc. Buttweld, fillet weld, lap joint, and lap fillet weld can be adopted according to the thickness, material, and sealing requirements of the plate.

  • Rolling Circle of Plate

The plate can be rolled manually or mechanically.

Manual rounding: for the plate passing through the undercut and folding, the plate edge near the undercut shall be rounded on the steel pipe with a square ruler, and then rolled by hand and then with a square ruler. So that the bite can be buckled with each other, and tighten the bite. The joint shall be rounded again. During rounding, the force of the square ruler shall be uniform and not too large, to avoid obvious traces until the arc of the air duct is uniform. Mechanical rounding: generally, the rounding machine is used. During operation, the plate edge near the bite shall be manually rounded on the steel pipe, and then the plate shall be sent between the upper and lower rollers of the rounding machine. The roller drives the plate to rotate, and the plate will become a circle.

  • Folding of Plate

Folding can be done manually or mechanically.

Manual folding: before folding, the bending curve of the plate shall be drawn first, and then the plate shall be placed on the left workbench to align the bending curve with the channel steel edge. Generally, the long air duct shall be operated by two people, who shall stand at both ends of the plate and press the plate on the workbench with one hand without moving; Press the plate down to a 90 º right angle with one hand, and then trim it with a wooden square until the edges and corners are made to make the plate flat. Mechanical folding: mechanical folding can often be processed by a manual folding machine or pneumatic folding machine.

How to Make The Ventilation Duct

Fabrication of Ventilation System Components

  • Fabrication of Various Fan Port

The common type of air outlet is a rectangular air return outlet with a mesh or strip grid, without a linkage adjustment device. Other types of fan ports are equipped with linkage adjustment devices. The most common 135 fan port in air conditioning engineering has an adjustment range of 135 º, which can be divided into a single layer, double layer, and three layers, which can be selected according to the accuracy requirements. Specific manufacturing quality standards are specified for various forms of diffusers (flat delivery diffusers, disc diffusers, straight plate diffusers, and streamlined diffusers) in the purification project. The following puts forward corresponding provisions on the common characteristics of various fan ports:

The surface of the air outlet shall be flat, and the allowable deviation from the design rain gauge shall not be greater than 2mm. The difference between the two diagonals of the rectangular fan port shall not be greater than 3mm, and the allowable deviation of any two orthogonal diameters of the circular fan port shall not be greater than 2mm.

The rotation adjustment part of the air outlet shall be flexible, the blade shall be straight, and the peripheral frame shall not be rubbed.

for the plug-in plate and movable grate plate fan port, the plug-in plate and grate plate shall be flat, the edge shall be smooth and the pumping shall be flexible. The movable grate-type air outlet shall be fully opened and sealed after assembly.

The blade spacing of the louver air outlet shall be uniform, and the centers of shafts at both ends shall be on the same straight line. The blades of the manual fan port shall be riveted with the frame to adapt to the tightness.

The diffusion ring and regulating ring of the diffuser shall be coaxial, and the axial distance distribution shall be uniform.

The orifice of the orifice plate air outlet shall be free of burrs, and the aperture and hole spacing shall meet the design requirements. The movable parts of the rotary air outlet shall be light and flexible. Pay attention to the size of the parts when processing the fan port. For example, the size of the internal blade and the outer frame shall be correct, and mutual cooperation shall be appropriate, and there shall be no friction between the blade and the outer frame. In addition, the fit size of movable parts such as shaft and shaft sleeve shall be appropriate. Add lubricating oil after assembly to avoid rust. Painting shall preferably be carried out before the installation.

  • Fabrication of Air Valve

Valves commonly used in ventilation and air conditioning engineering include plug valve, butterfly valve, multi-leaf regulating valve, circular flap start valve of centrifugal fan, bypass valve, fire damper, and check valve in the air treatment room, etc. When making various valves for ventilation and air conditioning works, special attention shall be paid to the flexible action of the braking device to avoid the valve jamming and failure to open and close. Due to the high installation position and inconvenient adjustment of the regulating valve on the main air duct of the air conditioning system, the valve often cannot be opened when the air conditioning system is stopped for some time. If it is pulled strongly, the handle plate will be broken. Therefore, the size of the rotating shaft shall be appropriate, and anti-corrosion measures shall be taken during fabrication; The shaft and bearing of the valve are made of copper or copper-tin alloy, which can ensure the flexible adjustment of the valve. The details of valve fabrication are as follows:

The valve shall be firmly manufactured, the adjustment and braking device shall be accurate, flexible, and reliable, and the opening and closing direction of the valve shall be marked.

The blades of the multi-blade valve shall be able to fit, with uniform spacing and consistent overlap. The fire damper shall meet the following requirements; The shell shall be able to prevent deformation and failure in case of fire, and its thickness shall not be less than 2 mm; Rotating parts shall rotate flexibly at any time and shall be made of corrosion-resistant materials.

How to Make The Ventilation Duct

Hand Made Ventilation Duct

In the early years, industrial technology could not keep up. The cost of fully automatic machinery and equipment related to ventilation pipes was high and not popular. Most processing plants used semi-automatic processing methods to produce ventilation pipes. The following is the main process of making ventilation ducts by hand.

  1. Before making the air duct, the material is a whole roll or a whole flat plate. Different lengths of materials are required for different sizes of air ducts, so the marking shall be carried out respectively according to different sizes, shapes, and specifications of air ducts. At the same time, the same section of air ducts shall be carried out completely to prevent wrong marking holes and wrong size and number of blanking.
  2. The plate cutting shall be carried out separately according to different marking stages, and the blanking must be rechecked to avoid errors. Cut with mechanical scissors and manual scissors according to the scribed shape.
  3. During shearing, it is strictly forbidden to stretch your hand into the gap of the mechanical pressing plate, and tools and other items are not allowed to be placed on the upper tool holder. When adjusting the plate, your foot cannot be placed on the pedal machine. When using the fixed vibration shear, hold the steel plate firmly with both hands, and the hand shall not be less than 5cm away from the knife-edge, with uniform and appropriate force.
  4. After blanking and before rolling, chamfering must be carried out with chamfering machine or scissors.
  5. The air duct made of metal sheet steel uses different methods such as bite connection, rivet connection, and welding.
  6. The undercut width and reserved amount are determined according to the plate thickness.
  7. During welding, the weld must be uniform without crack and slag inclusion. During rivet connection, the rivet Center shall be perpendicular to the plate surface first, and the rivet head shall compress the material to make the plate joint tight and arranged neatly and evenly. For riveting between plates, generally, no padding can be added in the middle, and the design shall be followed when specified in the design.
  8. During biting, the distance between the finger and the roller protective shell shall not be less than 50mm, and the hand shall not be placed on the track of the biting machine to stabilize the sheet metal.
  9. For the sheet after undercut, place the drawn square folding line on the square folding machine and the centerline of the lower die. During operation, make the centerline of the upper blade of the machine coincide with the centerline of the lower die and fold it into the required angle.
  10. When folding, they shall cooperate and keep a certain distance from the folding machine to avoid being hurt by the overturned steel plate or accessories.
  11. When making a round air duct, clap both ends of the undercut into a circular arc shape and roll it on the rounding machine. Adjust appropriately according to the diameter and specification of the air duct. The distance between the upper and lower rollers shall not be directly pushed by hand during operation.
  12. The folded or rolled steel plate shall be seamed with a seaming machine or manually. The force shall be uniform during operation and shall not be too heavy. Single and double bite completely, without expansion crack and half bite.
How to Make The Ventilation Duct

Fully Automatic Mechanical Ventilation Duct

The rapid development of industrial technology, while increasing the cost of processing equipment, also greatly improves work efficiency. Some fully automatic air duct production lines, such as the air duct production line 5 machine, are facing the market.

The main processing process is the feeding of plates, the leveling of plates, the reinforcement of large-diameter air duct, the position angle of attack at the folded edge of air duct, the cutting of plates according to size, the biting of forming edge through movable unilateral biting, the forming of bilateral common plate flange, the folding of 7mm right angle edge, L-shape for convenient transportation, and the processing of folded square pipe.

After the full-automatic air duct processing equipment is completed, the air duct can be installed with the simple treatment of some manual or semi-automatic machinery.

Summary of Fabrication of Ventilation Duct

No matter what method is adopted to make the ventilation duct, the ultimate goal is to produce high-quality ventilation duct products. While paying attention to various key points in the production process, we should pay more attention to improving the work efficiency.

2 thoughts on “How to Make The Ventilation Duct

  1. Avatar of Rohit Muhammad Rohit Muhammad says:

    I am currently in the early stage of entrepreneurship. If you can recommend me, please list the equipment I need.

    1. Avatar of Simon Simon says:

      Hello, Rohit.
      In my opinion, if the budget is not enough, the following machines can be purchased. Duct production line 2, TDF flange machine, Pittsburgh lock former machine, manual TDF folding machine. This four machines can be enough for the rectangular air duct making progress.
      More information, you can check our product page.

Leave a Reply

Your email address will not be published. Required fields are marked *