Commonly used duct materials and their selection:
1. Thin steel plate
Thin steel plate is the main material for the production of ventilation pipes and components, and is generally commonly used for ordinary thin steel plates and galvanized steel plates. Specifications are expressed in terms of short side, long side and thickness, and the thickness of the commonly used thin plate is 0.5mm~4mm, and the specification is 900mm×1800mm and 1000mm×2000mm.
Ordinary thin steel plate: Ordinary thin steel plate has 2 kinds of plates and coils, of which the plate specifications are shown in Table 2-5. This type of steel plate belongs to Class B steel, which is a cold and hot rolled steel plate with a steel number of Q235B. It has better processing properties and high mechanical strength, and the price is cheap.
Galvanized steel plate: The thickness of galvanized steel plate is generally 0.5mm ~ 1.5mm, and the length and width size are the same as ordinary thin steel plates. The surface of the galvanized steel sheet has a protective layer to prevent corrosion and generally does not require paint. The requirement for the steel plate is that the surface is smooth and clean, and the thickness of the galvanized layer should not be less than 0.02mm. It is mostly used in moisture-proof duct systems, and the effect is better.
2. Stainless steel plate
Stainless steel plate has high plasticity, toughness and mechanical strength, corrosion resistance, is a stainless alloy steel. Its main element, chromium, has high chemical stability, forming a passivation film on the surface, protecting the steel plate from oxidation, and increasing its corrosion resistance. However, stainless steel is easy to bend during cold working, and when hammered, it will cause internal stress and uneven deformation, so that its toughness is reduced, the strength is increased, and it becomes brittle and hard; Heated to 450 ~ 850 °C, and then slowly cooled, the steel deteriorates, hardens, cracks appear. Stainless steel is commonly used in corrosion-resistant duct systems in the chemical industry because of its smooth surface, non-corrosion and acid resistance.
3. Aluminum plate (aluminum plate has pure aluminum and alloy aluminum).
Alloy aluminum plate mechanical strength is high, corrosion resistance is poor, ventilation engineering aluminum plate is mostly pure aluminum and annealed alloy aluminum plate.
The aluminum plate has beautiful color, small density, good plasticity, strong acid resistance, and good chemical corrosion resistance, but it is easily corroded by hydrochloric acid and alkalis. Because the aluminum plate is soft, there is no spark in the collision, so it is mostly used as a ventilation duct with explosion-proof requirements.
4. Plastic composite steel plate
Paste or spray a layer of plastic film on top of ordinary steel plates, that is, plastic composite steel plates. It is characterized by corrosion resistance, bending, biting, drilling and other processing performance is also good. Its specifications are 450mm× 1800mm, 500mm×2000mm, 1000mm×2000mm, etc. Plastic composite steel plate is commonly used in air cleaning systems and ventilation and air conditioning systems with temperatures in the range of -10 °C to +70 °C.
5. PVC plastic sheet
PVC plastic sheet has good corrosion resistance and generally does not produce chemical reactions with acids, alkalis and salts, but is unstable under the action of concentrated nitric acid, fuming sulfuric acid and aromatic hydrocarbons. This kind of plate has higher strength, better elasticity, poor thermal stability, decreased strength at high temperature, and becomes brittle and crackable at low temperature; At 100 °C ~ 150 ° C, it is in a soft state, and at 190 ° C ~ 200 ° C, a small pressure can make it bond.
The longitudinal and transverse properties of the plate are different, there is residual stress inside, and heating and cooling treatment should be carried out when making ducts and components; The general longitudinal and transverse shrinkage rates are 3% to 4% and 1.5% to 2.0%, respectively. In ventilation and air conditioning engineering, it is mostly used to transport corrosive gas pipes and components containing acids, alkalis, salts, etc., and is also used in clean systems.
6. FRP
FRP is a non-metallic anti-corrosion material made of fiberglass and synthetic resin binders. It is characterized by: high strength, light weight, corrosion resistance.
In practical applications, there are 307, 323, 168 and other polyester resins with good acid and water resistance; Alkali-resistant, water-resistant furan epoxy modified resin, etc.
When there are flame retardant regulations, quantitative flame retardants can be added. In order to increase the strength and stiffness of frp, filler can be added to the synthetic resin. FRP is commonly used as a cooling tower in ventilation and air conditioning engineering, and it is also used as a ventilator, duct and component that transports corrosive gases and a large amount of water vapor.
Duct material thickness selection:
The thickness of the duct material is determined by the size of the long side of the duct (the round duct is the diameter) and the working pressure of the duct. Working pressure:
1. Low voltage system: P≤500Pa;
2. Medium voltage system: 500Pa<P≤500Pa;
3. High pressure system: P>1500Pa;
Example 1, medium and low pressure, galvanized iron duct plate thickness:
| Round duct diameter D or duct long side size b(mm) | Duct thickness(mm) |
| D(b)≤320 | 0.5 |
| 320<D(b)≤630 | 0.6 |
| 630<D(b)≤1000 | 0.75 |
| 1000<D(b)≤2000 | 1.0 |
| 2000<D(b)≤4000 | 1.2 |
Note: The above data is from the “Ventilation and Air Conditioning Engineering Construction Quality Acceptance Specification GB50243-2002” Other materials such as aluminum plate, FRP duct, see the above specification table 4.2.1-1 to 4.2.2-5.
Example 2, glass magnesium duct wall thickness and flange specifications (mm)
| Round duct diameter D or duct long side size b(mm) | Duct thickness(mm) | Flange size (mm) is wide × thick | Flange flatness (mm). |
| D(b)≤300 | 2.5～3.5 | 40×10 | ≤2 |
| 300<D(b)≤500 | 3.5～4.5 | 45×12 | ≤2 |
| 500<D(b)≤1000 | 4.5～5.5 | 45×14 | ≤2 |
| 1000<D(b)≤1500 | 5.5～6.5 | 50×16 | ≤3 |
| 1500<D(b)≤2000 | 6.5～7.5 | 50×18 | ≤3 |
| D(b)>2000 | 7.5～8.5 | 55×20 | ≤3 |
