Commonly Used Air Duct Materials, Specifications And Connection Methods

Ventilation and air conditioning engineering ducts and accessories used materials, generally can be divided into two kinds of metal materials and non-metallic materials. Metal materials are mainly ordinary thin steel plate (commonly known as black iron), galvanized thin steel plate and steel and other ferrous materials. When there are special requirements (such as anti-corrosion and fire protection requirements), materials such as aluminium and stainless steel plates are available. Non-metallic materials include rigid polyvinyl chloride sheets (rigid plastic sheet PVC), glass steel sheets, etc. ( More details to click picture below )

1-Metal-based sheet

1-Metal-based sheet

(1) Plain thin steel sheets

Ordinary thin steel sheets are made of soft carbon steel by hot rolling or cold rolling. The surface of hot rolled steel plate is blue glowing iron oxide film, hard and brittle in nature, easy to fracture when processing; cold rolled steel plate surface is flat and smooth without light, softer in nature, most suitable for air conditioning projects. Cold rolled steel sheets are generally Q195, Q215 and Q235, divided into plates and coils, with a common thickness of 0.5~2mm, the specifications of plates are 750mm X1800mm, 900mm X 1800mm and 1000mm X 2000mm, etc.

(2) Galvanised thin steel sheets (“white iron”)

Galvanised thin steel sheets are made of ordinary thin steel sheets with a galvanised surface, commonly known as “white iron”. The common thickness is 0.5~1.5mm, and its size is the same as that of ordinary thin steel. Galvanised steel coils are commonly used in the introduction of projects and are very convenient for the production of air ducts.

As the surface zinc layer acts as an anticorrosive, it is generally not oiled to prevent corrosion and is therefore commonly used as ducts and fittings for ventilation systems and air conditioning systems in humid environments that are not subject to acid mist. All grades of galvanised steel are required to have a smooth and clean surface, with a crystalline pattern characteristic of the hot-dip galvanised layer, and a galvanised layer thickness of not less than 0.02mm.

(3) Plastic laminated steel sheets

Plastic composite steel plate is sprayed on the surface of Q215, Q235 steel plate with a layer of soft or semi-soft PVC plastic film with a thickness of 0.2~0.4mm. Its main technical properties are as below:

①Corrosion resistance and water resistance can be resistant to acid, oil and alcohol erosion, good water resistance. However, the resistance to organic solvents is poor.
②Insulation and abrasion resistance are good.

③peel strength and deep punching performance of plastic film and steel plate peel strength ≥ 0.2MPa.

④Processing performance with general carbon steel plate has the cutting, bending flushing, drilling, riveting, nibbling and folding and other processing performance. Processing temperature of 20~40°C is the best.

⑤Using temperature can be used under 10~60°C for a long time, short-term temperature resistance of 120°C.

Due to the above mentioned properties, plastic composite steel sheets are often used in air conditioning systems with high requirements for dust protection and corrosion resistant ventilation systems at temperatures of -10 to 70°C.

(4) Stainless steel plate

① With high plasticity, toughness, mechanical strength and corrosion resistance, it is a stainless steel commonly used in chemical corrosion resistant duct systems.

②The main element of stainless steel is chromium, which has a high chemical stability. A passivation film is formed on its surface to protect the steel sheet from oxidation and improve its corrosion resistance.

③Stainless steel is easy to bend in cold working, hammering will cause internal stress and uneven deformation, thus reducing the toughness of the stainless steel plate, improving its strength and making it brittle and hard.

④When stainless steel is heated to 450℃~850℃, the steel will be metamorphosed, hardened and cracked after slow cooling. Stainless steel tubes have a long service life, good corrosion resistance and high internal smoothness of the tube wall, which results in low fluid resistance, a clear shape and a permanent brightness like new, and are widely used in the production of ventilation pipes.

(5) Aluminium and aluminium alloy sheets

The use of aluminium sheets for the production of air ducts is generally based on pure aluminium sheets.
①Pure aluminium sheet has good electrical and thermal conductivity and has a high stability in many media. Pure aluminium is available in both late fire and cold work hardened versions. Late fire has better plasticity and lower strength, while cold work-hardened has higher strength. Aluminium sheets have the advantages of beautiful colour, low density, good plasticity and acid resistance, but are easily corroded by hydrochloric acid and alkali and have good chemical corrosion properties.

②Aluminium alloy panels: In order to change the performance of aluminium, one or several other elements (such as copper, magnesium, etc.) are added to aluminium to make aluminium alloy plate, whose strength is substantially increased than aluminium plate but the chemical corrosion resistance is not as good as aluminium plate. Aluminium alloy sheet has high mechanical strength and poor corrosion resistance. Most of the aluminium sheets used in ventilation projects are pure aluminium sheets and annealed aluminium alloy sheets. As the aluminium sheet is soft, there is no spark in the collision, so it is mainly used as a ventilation duct with explosion-proof requirements.
2. Non-metallic sheet

(1) Rigid polyvinyl chloride plastic sheet (rigid PVC plastic sheet)

Hard PVC is made by pressing (or die-casting) PVC resin with stabilisers, plasticisers, fillers, colourants and lubricants. It has a smooth surface, is resistant to acids and alkalis (it is unstable to strong oxidising agents such as concentrated nitric acid, fuming sulphuric acid, aromatic hydrocarbons and chlorinated hydrocarbons), has good physical and mechanical properties and is easily moulded for secondary processing. The surface of the rigid PVC sheet should be flat, free of scars, and should not contain air bubbles of uniform thickness, without the phenomenon of leaving the layer.

(2) Glass fibre reinforced plastic (FRP Sheet)

FRP sheet is a lightweight, high-strength composite material made of glass fibre products (such as glass cloth) as reinforcing material and resin as binder, through a certain moulding process. It has the advantages of good corrosion resistance, fire resistance and simple forming process. Due to its light weight, high strength, excellent heat resistance and corrosion resistance, good electrical insulation and easy processing and forming, FRP is commonly used in textile, printing and dyeing, chemical and other industries to exclude corrosive gases in ventilation systems.

3. Auxiliary materials

(1) Bedding material

The auxiliary materials commonly used in ventilation and air conditioning are gaskets, fasteners and other materials. Gasket material is mainly used between the air ducts, air ducts and equipment between the connection to ensure the sealing of the interface. Flange gaskets should be non-dusty, not easy to age and have a certain strength and elasticity of the material, the thickness of 5 to 8 mm gaskets are rubber sheet, asbestos rubber sheet, asbestos rope, soft PVC sheet, etc.

(2) Fasteners

Fasteners are bolts, nuts, rivets, washers, etc.

(3) Other materials

Some auxiliary consumable materials are also commonly used in ventilation and air conditioning works, such as oxygen, acetylene, gas, welding rods, saw blades, cement, wood blocks, etc.

To sum up:

The above is a detailed introduction to the common materials used for ventilation ducts in HVAC engineering systems and what to pay attention to when installing air conditioning ventilation ducts, hopefully it will help you to answer your questions. If you want to know more about it, you can continue to pay attention to our official website.