The large volume, new materials, and high space make the installed air duct easy to deform and crack, resulting in incomplete air duct connections and air leakage, which ultimately affects the air conditioning effect!
Through the quality control of the production and installation of large-volume air-conditioning ducts, the following aspects are summarized:
I. Entry materials
The design of air-conditioning ducts requires a flexural strength greater than 1.8 MPa, a thickness of 2.6 mm for heat-insulated ducts, and a thickness of 1.8 mm for non-insulated ducts.
In order to ensure that the materials used in the construction process are of good quality and excellent performance, the brand chosen when ordering must be confirmed by the supervisor and the owner, and have to make sure that the performance and reputation of the brand are high.
The incoming materials must be strictly and carefully inspected in accordance with the material purchase inspection procedures to ensure that the materials used are of acceptable quality and reliable performance.
Line the sheet before cutting it.
The basic lines are: right angle line, perpendicular bisector, parallel lines, angular bisector, straight bisector, circle bisector and etc.
The unfolding method should adopt parallel line method, radiation method and triangle line method.
According to the different geometric shapes and specifications of the design drawings and large-scale drawings, the lines are unrolled separately.
The cutting of the sheet must be checked for cutting, so as to avoid mistakes, cut with a hand-held cutter according to the shape of the scribe.
When cutting, do not reach into the gap of the mechanical platen.
The upper knife holder is not allowed to place tools and other items.
When adjusting the sheet, feet cannot be placed on the pedal.
When using a fixed vibration shear, hold the steel plate with both hands, and keep the hands from the knife edge not less than 5cm.
Remember to use the shear with even force.
The cutting line is straight, and the error of the diagonal length of the duct board should be less than 0.5mm.
The depth of the step line is 18-21mm, and the cutting line must be at an angle of 90 ° with the board surface, creating conditions for the splicing of the duct angle to 90 °.
The straight pipe section of the rectangular duct must be accurate, and the corner line should be straight.
The four end lines of each port of each section of air duct (including tees, elbows, etc.) should be on the same vertical plane as the center line of the pipe.
Number the cut boards so that they can be numbered during assembly.
Ⅲ. Duct Assembly
According to the design requirements, in order to ensure the construction quality and facilitate the site supervision and inspection by the owner, the project department arranges a small duct processing workshop on the site.
1. Preparation of special glue
The special glue for assembling the air duct has the characteristics of high bonding strength, no burning, no fear of water, convenient construction, and good adhesion to the air duct material.
The special glue is composed of powder and liquid. The weight ratio of powder and liquid is 10: 9. The glue should not be too dry or too thin, it is better to have a slight fluidity. Use an electric mixer to mix.
2. Assembly process (straight pipe)
2.1 First use a knife to cut off the step-shaped thermal insulation layer of the side panel, cut it cleanly to ensure that the position of the step is flat.
2.2 Apply special glue to the side panel steps. The glue should be applied evenly and fully. It is better to squeeze a small amount of residual slurry when the upper and lower plates are brought together.
2.3 First: Place the bottom panel of the air duct on the group stand.
Second: Insert the left and right panels on the edge of the bottom panel and offset 100mm from the length of the upper and lower panels, and then insert the upper panel between the left and right panels.
Third: Bundle the freshly assembled air ducts firmly with a strapping band. The spacing between the strapping bands is generally about 600mm. Four corners should be protected by angle steel. The angle steel is coated with mold release oil in advance. The mold release oil is composed of 1 kg of saponified oil, 5 kg of water, and a small amount of diesel oil. In order to solve the changes caused by the wet expansion and dry shrinkage of the air duct, when the continuous length of the straight section is greater than 15m, an expansion joint should be set.
2.4 The inner angle of the 4 bundled air ducts is 90 ° and positionit. Prevent the deformation of the air duct and affect the splicing quality of the air duct, and remove the excess glue extruded and fill the gap.
2.5 Remove the strapping and remove the residual pulp from the splicing seam depending on the solidified state of the slurry.When solidified too hard, the residual slurry is difficult to remove. When the curing strength is not enough, the air pipe will shake to affect the splicing strength. Grasp its initial setting strength to remove the strapping in a timely manner, and remove residual pulp, and strictly control the air pipe shaking. Generally, the ambient temperature is 10 ° -20 ° for 24 hours, the ambient temperature is above 0 ° for 48 hours, and is below 0 ° for 72 hours.
Because the construction is in winter and the period is tight, natural cooling based on ambient temperature will affect the construction period. We adopt the method of centralized stacking and heating to promote coagulation. Gather the air ducts to be spliced in a room and close all the doors and windows of the room. Set up two electric heaters in the room and turn them on 24 hours a day and night to increase indoor temperature. Through the above measures, the temperature was raised from -2 ° C to 11 ° C, and the solidification time of the air duct was changed from 72 hours to 24 hours, which greatly shortened the solidification cycle and created conditions for ensuring the construction period.
Attachment production of the same cross section
Cut the duct plate according to the drawing size, and cut 45 diversion angles along the wind direction.
When the elbows and three heads are folded in half, the internal extrusion method is used instead of the external opening method. That is, when a sheet is to be folded in half, a V-shaped seam is cut on the inside of the sheet. Remove the middle foam and apply the appropriate proportion of glue, then make the sheet folded in half (in the case of half folding, the glue is best squeezed out a little). The side panel is cut into a step shape, and special glue is applied to the step position, and then fixed by binding. Clean up the remaining glue, fill the gaps, and solidify in a flat place.
Ⅳ. Duct Hoisting
Setting of duct hangers and supports
In order to ensure the stability of large-volume air ducts, the distance between booms should not exceed 2.0m. The beam is made of 50×50×5mm angle steel, the hanger is made of Ф10 round steel, and the expansion bolts are fixed to the load bearing structure.
Strengthening measures for large-volume air ducts
Large-volume air ducts have been strengthened during the production and installation process.
When the long side of air duct is greater than or equal to 800mm and less than 1250mm, the measure of reinforcing strips will be implemented. That is, 25×40mm reinforcing strips are affixed to the four corners of the inside of the air ducts, the length is the same as the air ducts, and the glue should be applied dense and seamless. When the long side of the air pipe is greater than 1250mm, a reinforcing rib is adopted. That is, a support column is connected between the upper and lower plates of the air ducts. The support column uses a Ф10 screw and is fixed to the upper and lower plates of the air duct with nuts. A 80×80×5mm silicon-magnesium plate is used as a gasket on the inside and outside of the upper and lower plates, and a plastic insulation cover is applied externally. The distance of the ribs is not more than 1.5m.
The air ducts should not be hoisted until it has fully solidified.
The hoisted ducts can be connected to a certain length on the ground and then hoisted in place.
The length should not be more than 10m, and it is easy to cause fracture if it is too long. It can be hoisted by using chain block or pulley. The hoisting steps are as follows:
- First, according to the specific conditions of the site, select two reliable hoisting points on the beam-columns, and then hang the chain block or pulley.
Use a hemp rope to tie the air duct firmly, usually two ties are tied at 1/4 from both ends. The rope must not be directly tied to the wind duct, and a cushion of soft material should be provided where the hemp rope contacts the corner of the duct to prevent the duct from being deformed by the rope.
When hoisting, it is strictly forbidden for persons to be under the hoisted air duct and forbidden to stand on the air duct. When the air duct is 200 – 300mm above the ground, stop hoisting, and carefully check the stress point of the chain block or pulley and the rope that binds the air duct, check whether the buckle is secure and the center of gravity of the air duct is correct. If there’s no problem, continue hoisting. For those longer ducts, the hoisting speed should be carried out synchronously to prevent deformation of the duct due to excessive pressure on the middle duct.
When the air duct is hoisted to the height of the scaffold, the overhanging part of the scaffold should be wrapped to prevent the air duct from being punctured during hoisting, resulting in damage to the protective layer, heat insulation layer and even air leakage.
After the air duct is placed on the support and hanger, connect all the trays and booms, and confirm that the air duct is stable before unlocking the rope.
The hoisted air ducts should be spliced in time. Be careful not to shake the ducts too much during splicing. When working on the air duct, it is not allowed to step on the air duct directly with feet. Two wooden boards of about 1000 × 200mm shall be used to pad the feet (to increase the stress area) and advance alternately to ensure safety.
After the splicing is completed, the remaining glue should be cleaned in time when the glue is solidified, check for gaps, and fill the glue in time. When the glue is completely solidified, the duct will be inspected with the supervision unit, and after approval, the aluminum foil tape will be affixed.
Attention should be paid to finished product protection after construction. Put the “Please pay attention to finished product protection” label in a conspicuous place, and send workers to inspect and maintain it regularly.