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Solving Installation Problems On Ventilation And Air Conditioning Engineering Ii

  • source:metmac;
  • Time:09/02/2020

TDF/TDC flange interchangeability problem

7.1. Form of expression: the TDF/ TDC duct flange surface is not flat, the round duct flange rotates at any angle and after the rectangular flange is rotated by 180°, it cannot overlap with the flange bolt holes of the same specification; The roundness of the circular flange is poor, and the diagonals of the rectangular flange are not equal; in the circular flange diameter or the inner dimension of the rectangular flange exceeds the "Code for Construction Acceptance" and "Quality Inspection The allowable deviation of the Evaluation Standard.


7.2. Harmfulness: Poor interchangeability of duct flanges will affect the performance of ducts and components on the construction site.

Assemble normally. Smaller flange deviation increases unnecessary modifications during installation,

Punching and other work; large deviations will cause rework and waste manpower and material resources


7.3. Analysis of the causes:

a. The size of the blanking is not accurate, and the angle steel after blanking is not aligned and straightened, causing the method the inner diameter or inner edge size of the blue exceeds the allowable deviation;

b. When the circular duct flange is heated by hand, the surface irregularity caused by the distortion appears the disadvantages of poor peace and roundness;

c. When the circular duct flange adopts mechanical cold simmering, there will be benefits due to the unadjusted simmering TDF/TDC duct bending machine in abnormal state

d. The right angle of the rectangular duct flange mould is not accurate;

e. welding deformation of flange interface;

f. There is displacement when the flange bolt split hole template is split;

g. The displacement of the hole center of the flange punching or drilling.



8. Eccentric duct flange riveting


8.1. Form of expression: the flange and the duct are not perpendicular, and the center of the finished duct is offset; sleeve the air duct behind the flange is bitten and cracked.


8.2. Harmfulness: The level or vertical error of the air duct system after assembly is too large,

Failure to meet the deviation of "Construction Acceptance Regulations" affects its appearance.


8.3. Analysis of the causes:

a. the concentricity of the circular duct is poor;

b. The roundness error of the round duct flange is large; the rectangular duct flange is not square;

c. The inner diameter or inner dimension of the flange is larger than the outer diameter or outer dimension of the after passing the “Code for Construction and Acceptance”, after the flange and the duct are riveted, the wind tube offset to one side

d. The inner diameter or inner dimension of the flange is smaller than the outer diameter or outer dimension of the air pipe.

Lan forcibly put on the duct, causing the duct to crack.


9. The duct is not tight after duct flange riveting

9.1. Form of expression: the riveting is not strict, the surface of the air duct is not flat and the air leakage becomes very

9.2. Harmfulness: After the system is running, due to air leakage and vibration and noise, the air conditioner cold and heat cause undue losses and affect the cleanliness of the air cleaning system degree.

9.3. Analysis of the causes

a. The rivet spacing is large, causing the surface of the air duct to be uneven;

b. The rivet is small in diameter and short in length. It does not fit tightly with the nail hole, which makes the rivet loose.

Lax riveting

c. The amount of flanging of the air pipe on the flange is not enough;

d. The four corners of the duct flanging are cracked or the four corners overlap.




10. The sealing gasket of the air duct pipe and the connection of the air duct pipe do not meet the requirements

10.1 Form of expression: air leakage at the TDF/TDC flange connection of the air duct pipe, and the noise of the air pipe system increases

10.2 Harmfulness: increase the loss of cold and heat in the air duct system, or increase harmfulness

The leakage of gas pollutes the environment.

10.3. Analysis of the causes

a. The material of flange gasket selected for ventilation and air-conditioning system does not meet the requirements of "Construction Acceptance Requirements of the Code;

b. The thickness of the flange gasket is not enough, which affects the elasticity and tightness;

c. The flange gasket protrudes into the duct;

d. The tightness of bolts around the flange is inconsistent.


11. The connection of the flangeless duct is not tight

11.1 Form of expression: the gap between the air duct and the flange of the insert is too large, after the system is running there is a large air leakage phenomenon.

112. Harmfulness: The air leakage of the system is increased due to the improper connection of the air pipe increase the energy consumption of the operation, and even cause the air

It affects the temperature and humidity requirements of air-conditioned rooms and increases environmental noise.

11.3. Analysis of the causes:

a. The shape of the pressed insert flange is irregular;

b. Improper selection of the structure of the insert flange;

c. When the ∪-shaped insert is used for connection, the size of the duct flanging is not accurate;

d. Sealing measures such as applying sealant have not been taken.



12. The stainless steel duct has poor corrosion resistance

12.1 Forms of manifestation: There are scratches, grazing and other defects and welding slag splash on the surface of the air duct the surface of the weld is black, yellow and variegated. Even the air duct has some rust

12.2. Harmfulness: reduce the corrosion resistance of the stainless steel ventilation system and shorten the use life. At the same time, due to local corrosion of the air duct, the tightness of the ventilation system is reduced.

This can cause harmful gases to diffuse into the environment and affect the health of workers.


12.3. Cause analysis

a. Improper cutting and processing methods of duct plates

b. During the operation, the carbon steel is in contact with the stainless steel, causing corrosion on the surface.

Corrosion center, destroy the passivation film of its oxide layer

c. The selected welding process is unreasonable. Argon arc welding and DC arc welding should be used.

However, oxygen-acetylene welding must not be used.