Three Different Air Duct Fabrication Techniques: Requirements for Process, Quality Control, and Product Protection

Galvanized steel sheet

Duct fabrication

Process requirements

1. should be used nibble connection or riveted, shall not be welded.
2. duct plate splicing nibble seam should be staggered, there shall be no cross-type splicing seam.
3. bite seam tight, consistent width, folded corners straight, evenly rounded and parallel at both ends.
4. No obvious distortion and warping of the duct, the surface should be flat, concave and convex not more than 8mm.
5. the allowable deviation of duct outer diameter or outer edge length is negative deviation, when the duct length is less than or equal to 630mm, -1mm; when greater than 630mm, -2mm.
6. the allowable deviation of the flatness of the pipe mouth is 1mm, the difference between the length of the two diagonals of the rectangular duct should not be greater than 2mm.
7. rectangular duct side length greater than 630mm, insulation duct side length greater than 800mm, pipe section length greater than 1250mm or low pressure duct single side flat area greater than 1.2 square meters, medium and high pressure duct greater than 1.0 square meters, should take reinforcement measures.

Quality control points

1. duct and flange riveting before the first technical quality review, pipe section left 10mm flange amount.
2. in connecting the flange riveting, must make the rivet centerline perpendicular to the plate, so that the rivet head to press the plate, so that the plate seam tightly.
3. riveting flange should use the hydraulic riveting machine mechanical riveting, riveting to be firm, rivets can not appear to fall off and leak riveting phenomenon.
4. Duct and flange connection flanging width of not less than 6mm, flanging uniform and flat, close to the flange, flanging shall not cover the screw holes, the corners must be shovel flat, no openings.
5. Shearing machine, nibbling machine and other equipment should be adjusted according to the thickness of the plate before use, in order to ensure the processing accuracy of the duct.

Finished product protection measures

1. Duct processing equipment should be covered with flexible materials and should not affect the operation of the equipment.
2. into the workshop should be replaced with cloth shoes, prohibit stepping on galvanized steel.
3. Use rubber hammer with hydraulic seaming machine when closing and knocking the edges of the duct, and do not use metal hammer.
4. The processes of air duct undercutting, seaming and flange assembly must be operated on flexible carpet, and direct contact between galvanized layer of air duct and ground is strictly prohibited.
5. Duct semi-finished and finished products must be neatly placed on square wood, each layer not exceeding 1.2m, and multi-layer stacking is strictly prohibited to cause deformation of ducts.
6. the finished ducts should be covered with plastic film when stacked for a long time to avoid accumulation of dust.
7. galvanized steel should be placed on a spacious and dry moisture-insulated wooden mat frame, yardage according to the system numbering, neat, reasonable, easy to ship. Handling and loading should be done gently to prevent damage to the finished product.

Cold-rolled steel sheet

Air duct fabrication

Process requirements

1. The outer diameter or outer edge length of the duct shall prevail, welding.
2. the weld seam of the welded duct should be flat, there should be no cracks, convex tumor, penetrating slag, porosity and other defects, etc., the deformation of the plate after welding should be corrected, and the weld slag and spatter removed cleanly.
3. the surface of the duct should be flat, concave and convex not more than 8 mm.
4. the allowable deviation of the outer diameter or outer edge length of the duct is negative deviation, -1mm when the large edge length of the duct is less than or equal to 630mm, and -2mm when it is greater than 630mm.
5. the allowable deviation of the flatness of the pipe mouth is 1mm, and the difference between the length of the two diagonals of the rectangular duct should not be greater than 2mm.
6. rectangular duct side length greater than 630mm, insulation duct side length greater than 800mm, pipe section length greater than 1250mm or low pressure duct single side flat area greater than 1.2 square meters, medium and high pressure duct greater than 1.0 square meters, should take reinforcement measures.
7. not insulation of ordinary thin steel duct inside and outside the surface of each coated with red Dan rustproof paint two times, the outer surface of the surface paint two times, the smoke exhaust duct, after coating red Dan rustproof primer, inside and outside the surface of the heat-resistant paint two times. The color of the top coat is black if there is no special requirement for the decoration profession; the ducts of insulation should be coated with anti-rust primer twice on the inner and outer surfaces before insulation.

Quality control points

1. Duct welds are strictly prohibited to have defects such as burn-through, leakage and cracks, longitudinal welds must be staggered, no cross-type splicing seams.
2. When the duct and the flange are connected by welding, the end surface of the duct shall not be higher than the flange interface plane; when the fixed connection is made by spot welding, the welding joints shall be well integrated and the spacing shall not be greater than 100mm.
3. The flange and the duct should be tightly fitted, and there should be no penetrating gaps or holes.
4. When anti-corrosion treatment of ducts, the next anti-corrosion treatment should be carried out only after each paint has dried.
5. The welding of unlicensed personnel on duty is strictly prohibited.

Finished product protection measures

1. the duct semi-finished products, finished products must be neatly placed on the square wood, each layer does not exceed 1.2m, multi-layer stacking is strictly prohibited to cause deformation of the duct.
2. not mixed with other materials, equipment, etc., and rain, snow measures.
3. the finished duct should be covered with plastic film when stacked for a long time, to keep the surface of the steel plate clean and avoid accumulation of dust.
4. the yard should be numbered according to the system, neat, reasonable, easy to ship.
5. handling should be handled gently to prevent damage to the finished product.

Duct flange production

Process requirements

1. duct flange processing using the mold method, the same type of flange using a mold to ensure the interchangeability of the flange and size accuracy.
2. after straightening the material should be chamfered, punching, and then placed on the corresponding mold clamping fixed, welding.
3. The allowable deviation of the flange flatness is 1mm, and the difference between the two diagonals of the rectangular flange should not be greater than 2mm.
4. the four corners of the flange must have screw holes, medium and low pressure system duct flange bolts and rivet holes of the hole distance should not be greater than 150mm; high pressure system shall not be greater than 100mm.
5. the flange should be straightened after forming, and the welding slag cleaned up after the welding parts brush rustproof paint two, silver powder paint a.

Quality control points

1. the flange angle material should pay attention to make the flange after welding the inner diameter can not be less than the outer diameter of the duct.
2. The welding seam of the duct flange should be well fused and full, without false welding and holes.
3. the same batch processing of the same specification flange screw hole arrangement should be consistent and interchangeable.
4. duct flange anti-corrosion treatment, should be in the last paint dry before the next anti-corrosion treatment.
5. strictly prohibit unlicensed personnel on duty welding.

Finished product protection measures

1. duct flange semi-finished products, finished products must be neatly placed on the square wood, and should be classified according to the specifications of the model yard.
2. not mixed with other materials, equipment, etc., and rain, snow measures.
3. finished air duct flange should be covered with plastic film when stacked for a long time to keep the surface clean and avoid accumulation of dust.
4. handling should be lightly handled, shall not damage the galvanized layer of the flange, such as scratches should be made up paint integrity.

Duct installation

Process requirements

1. Before installing the air duct, the drawings should be checked with the construction site to check whether the installation can be carried out according to the designed elevation and location.
2. Use infrared positioning to ensure the spacing and straightness of the duct, and find out the installation position of the boom according to the center line of the duct, and carry out the installation of the support hanger.
3. After the size and angle of each part of the duct system is confirmed to be accurate, the grouping and installation will begin. The connection of the duct should be straight, not distorted, and the nuts of the connecting flange should be on the same side.
4. The gasket between the duct and the duct flange should be 3mm thick and above heat-resistant rubber sheet, the gasket should not be protruding into the duct, nor should it protrude from the flange, and the gasket should not contain asbestos and other harmful ingredients, and should be resistant to oil, moisture and acid and alkali corrosion.
5. When installing the duct, the level of the centerline of the duct must be maintained, and the level should be measured with a level after installing a section of the duct; when the length of the duct exceeds 20m, anti-sway brackets must be set, and not less than one pair for each system.
6. in the duct through the need to close the fire, explosion-proof wall or floor, should be set up pre-buried pipe or protective casing, the thickness of its steel plate 2mm. between the duct and protective casing, the application of non-combustible and non-hazardous to human beings flexible material blocking.
7. all kinds of duct components and operating mechanism installation, first check the valve shape and operating mechanism is intact, check the flexibility of the action, to confirm that all aspects of the valve is normal before installing the installation direction, location should be correct, there should be at least 350mm of net space on the side of the valve operating mechanism for operation, maintenance; fire damper on both sides of the fire partition wall, the distance from the surface of the wall should not be greater than 200mm.
8. the support and hanger of the fire protection smoke exhaust duct must be set separately, and the branch duct, duct type muffler, muffler elbow and fire protection valve must be set separately as support and hanger.
9. After the installation of ducts, tightness inspection shall be conducted according to the system pressure level.

Quality control points

1. No debris or other ducts are allowed to cross inside the duct, and do a good job of cleaning and protection.
2. the lower edge of the support hanger and the outer edge of the contact network charged body (including the bearing cable, under the feeder, etc.) safety distance must be maintained greater than 230mm, and should be implemented in strict accordance with the requirements of the limit.
3. the connecting bolt should be galvanized bolt, and at the same time must be equipped with the corresponding flat pad, spring pad and nut.
4. The working temperature of the duct flange gasket shall be not less than 70℃; for the smoke exhaust duct flange gasket, the working temperature requirement shall be not less than 250℃.
5. the allowable deviation of the duct installation level should not be more than 3mm per meter, and the total deviation should not be more than 20mm; the allowable deviation of the vertical installation verticality should not be more than 2mm per meter, and the total deviation should not be more than 20mm.
6. No interface shall be set at the duct through the wall or floor, and when the duct is installed along the wall or floor, the distance from the wall and floor shall be more than 150mm.
7. the installation of the electric actuator of the dampers must be reliable and fixed, and is strictly prohibited to be placed on the duct.
8. the manual airtight valve installation, the direction of the arrow marked on the valve must be consistent with the direction of the impacted wave.
9. the configuration of the site duct interface, shall not reduce its effective cross-section.
10. air conditioning duct support hanger should be set up non-combustible adiabatic pad to prevent the generation of cold bridges, adiabatic pad should be anchored in the cross-arms when the hanger is made
11. the detection of the system air duct, it is appropriate to use the method of segmentation detection, summary analysis. On the basis of strict installation quality management, the detection of the system air duct is based on the main duct and trunk duct. When using the light leakage method to detect the tightness of the system, low-pressure system ducts to every 10m joints, light leakage point is not more than 2, and 100m joints on average not more than 16 for qualified; medium-pressure system ducts every 10m joints, light leakage point is not more than 1, and 100m joints on average not more than 8 for qualified.

Finished product protection measures

1. duct handling should be lightly handled, not dragged on the ground, and avoid bumping, falling and tripping; not to damage the flange galvanized layer, such as scratches should be replenished paint integrity.
2. Duct lifting process, the two ends of the unconnected must be sealed with plastic film, duct on the air outlet before installation should also be sealed with plastic film, transparent tape to prevent dust from entering.
3. for crossing the equipment management room duct, through the wall part within 500mm from the wall must be well protected with plastic film to prevent the civil construction unit ash material pollution duct.
4. the installation of the duct is strictly prohibited above the stacking of debris or stand on the construction.