Features

High installation location: Elevated ducts are generally installed at the top of buildings, above ceilings, or on steel structures at high elevations to provide ventilation or air conditioning coverage for specific areas.

Efficient use of space: It can deliver air to the required areas without occupying floor space. This is particularly important for places with limited space, such as industrial plants, large warehouses, and gymnasiums, as it can effectively utilize vertical space and improve space utilization.

Long air delivery distance: Due to the high installation position, the air duct can utilize natural air flow and pressure differences to deliver air over long distances, thereby achieving large-area ventilation or air conditioning coverage.

Aesthetically pleasing: Elevated ductwork is typically installed at a height where it is not easily visible to people, thereby minimizing its impact on the appearance of the building and keeping the interior neat and attractive.

High construction difficulty: Installation at high altitudes requires specialized high-altitude work equipment and technical personnel. Safety issues must be addressed during construction, which also increases the difficulty and cost of construction.

Maintenance inconvenience: Due to its elevated position, maintenance personnel need to use professional climbing equipment to perform repairs, maintenance, and other tasks, which increases the difficulty and cost of maintenance and places higher demands on the skills and safety awareness of maintenance personnel.

application scenarios

Industrial plants: Used to remove exhaust gases, dust, and heat generated during production, provide fresh air, improve the working environment, protect workers’ health and safety, and also help protect equipment and improve production efficiency.

Large warehouses: such as automated multi-level warehouses, which can control the temperature and humidity of different areas within the warehouse to ensure proper storage conditions for goods and prevent them from becoming damp, moldy, or spoiled.

Commercial buildings: such as shopping malls, supermarkets, shopping centers, etc., used to regulate indoor air temperature, humidity, and air quality, providing customers and employees with a comfortable shopping and working environment.

Sports venues: Able to meet the ventilation and air conditioning needs of large numbers of spectators and athletes in sports venues, ensuring fresh air and comfortable temperatures inside the venue, thereby enhancing the spectator experience and the competitive performance of athletes.

Transportation hubs: such as train stations and airports, can effectively regulate the air environment in areas such as lobbies, waiting rooms, and waiting areas, providing passengers with a comfortable waiting space.

Installation points

Construction plan formulation: Based on the specific conditions of the construction site, including building structure, duct installation location, height, quantity, specifications, and models, formulate a detailed construction plan, clarify construction objectives and construction sequence.

Safety measures: Set up safety warning signs at the construction site, cordon off the construction area, and prevent non-construction personnel from entering. Set up a suitable aerial work platform, ensure that the platform legs are evenly distributed, install guardrails and anti-slip boards, and set up safety nets below the work platform.

Duct inspection and hoisting: Inspect the ducts before construction to ensure that they are free of damage, deformation, and other issues. Set hoisting points based on the length and weight of the ducts, generally at both ends and in the middle, and use special lifting lugs to secure them firmly. During hoisting, a designated person should be in charge to ensure that the ducts are lifted vertically and do not hit nearby obstacles.

Duct connection and sealing: Align the duct ends and ensure that the interface is flat and straight. Use sealing tape, sealant, or flanges to seal the duct system and prevent air leakage. For duct bends and diameter changes, use special elbow components and diameter change pipes, and pay attention to the sealing of the interface.

Installation Quality Inspection: After installation is complete, inspect the installation quality of the ductwork section by section, including whether the ductwork is straight, whether the connections are secure, and whether there are any air leaks. Use professional testing instruments to conduct airtightness tests, airflow and air velocity tests, etc., on the ductwork system to ensure that it meets design requirements.

1. Classification of air ducts by material and specification characteristics

Different types of ductwork vary in terms of material, specifications, and applicable scenarios:

Galvanized steel sheet ductwork
Thickness: Determined based on duct dimensions, commonly ranging from 0.5mm to 2.0mm (e.g., for rectangular ducts with a long side ≤320mm, thickness is 0.5mm; for long sides between 1600mm and 2000mm, thickness is 1.2mm).

Size range:
Rectangular ducts: Long sides typically range from 120mm to 2000mm, with corresponding short sides from 60mm to 1250mm (e.g., 320×200mm, 800×400mm, etc.). Larger
sizes require customization.

Round ducts: Diameter generally ranges from 100mm to 1600mm (e.g., φ150mm, φ800mm, etc.), with extra-large diameters requiring welding.

Fiberglass ductwork

Dimensions: Rectangular ducts can be up to 3000 mm long, circular ducts can be up to 2000 mm in diameter, with wall thicknesses ranging from 5 mm to 10 mm. These ducts are corrosion resistant but relatively heavy, making them suitable for use in humid environments.

Stainless steel ductwork

Dimensions: Similar to galvanized steel ductwork, but thicker (generally 0.8 mm to 3.0 mm), suitable for clean rooms, food processing plants, and other locations requiring corrosion resistance.

2. Duct Dimension Notation Rules

Rectangular ducts: denoted as “long side × short side” (unit: mm), e.g., “500×320mm” indicates a long side of 500mm and a short side of 320mm.

Round ducts: Denoted as “diameter φ + numerical value,” e.g., “φ300 mm” indicates a diameter of 300 mm.

Dimension tolerances: National standards permit ±1 mm to ±3 mm (depending on size) to ensure connection sealing integrity.

3.Selection Criteria for Duct Specifications

Air flow Requirements: The cross-sectional area of the duct is related to the air velocity. The calculation formula is: Airflow (Q) = Cross-sectional Area (A) × Air Velocity (v) × 3600 (Unit: m³/h)

Air velocity must be reasonable (e.g., main duct air velocity in HVAC systems: 8–12 m/s; branch ducts: 3–6 m/s). Excessively high air velocity can cause excessive noise and resistance, while excessively low air velocity may result in overly large duct dimensions.

System Pressure: High-pressure systems (>1500 Pa) require thicker panels and reinforcement measures; duct dimensions should not be too large. Low-pressure systems (≤500 Pa) can use thinner panels.

Installation Space: Constrained by building ceiling height, beams, etc., duct dimensions must be balanced with spatial layout (e.g., rectangular ducts are preferred in narrow spaces to save height).

4.Notes

Duct specifications must comply with the “Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering” (GB 50243) to ensure strength and airtightness.

Non-standard ducts (e.g., elliptical) must be custom-made, with specifications calculated based on equivalent cross-sectional area.

Large-sized ducts (long side > 2000 mm) must be equipped with reinforcing ribs to prevent deformation.

Selecting appropriate duct specifications can ensure system performance while reducing costs and installation complexity.

PP square ducts have a modular design, a design concept that greatly simplifies the installation process. Each module is like an independent component, and at the construction site, the installer can quickly put the modules together like building blocks. This approach not only reduces the time and workload of on-site processing, but also reduces the probability of errors in the installation process.

PP square ducts offer a variety of choices in terms of connection methods. Heat fusion connection is one of the commonly used methods, through the special heat fusion machine to heat the air duct port, so that it melts and quickly butt and apply pressure, after cooling, the joint can be tightly combined to form a solid whole. The advantage of this connection method is that the strength of the connection is high, almost equal to the strength of the pipe body, and can effectively prevent leakage. In some places that require very high sealing, such as laboratories, pharmaceutical workshops, etc., PP square ducts with heat fusion connection can meet the needs very well.

Flange connection is also one of the common connection methods. First, the flange is welded to the duct port to ensure that the flange is horizontal and there is no gap, and then a bolt is placed in the middle of the flange to tighten the two flanges and align the ports, and finally a sealing gasket is used to seal the gap to ensure that there is no air leakage in the connection. This type of connection is relatively simple to operate, easy to disassemble and repair, and is suitable for some ventilation systems that require frequent maintenance and adjustment.

In the installation process, the sealing treatment is crucial. Regardless of the type of connection, it is important to ensure that the sealing material is used correctly. Commonly used sealing materials include rubber gaskets and sealants. When selecting the sealing material, it should be determined according to the environment in which the duct is used and the medium to be conveyed. When conveying corrosive gases, chemical-resistant sealing materials should be selected to ensure the durability of the sealing effect.

In addition, the installer needs to pay attention to the installation position and direction of the duct to ensure that it meets the design requirements. Plastic shims with a thickness of 3-5mm should be inserted between the duct and the bracket to minimize friction and vibration. The distance between the brackets is generally 1.5 – 3m, for the side length or diameter greater than 1250mm duct, lifting shall not exceed 2 sections; side length or diameter less than 1250mm duct, combined lifting shall not exceed 3 sections. When handling the duct, it should be carried gently and put down gently to avoid falling and touching to prevent cracks. When lifting vertically, control ropes should be tied to prevent the air duct from swinging and collision and rupture.

(ii) Maintenance

The routine maintenance of PP square duct is relatively simple, mainly including cleaning and inspection. Because of its smooth surface, dust and dirt are not easy to adhere to, so cleaning is very convenient. Regularly wipe the surface of the duct with a damp cloth to keep it clean. For the inside of the duct, you can use professional cleaning tools, such as duct cleaning brushes, vacuum cleaners, etc., to remove accumulated dust and debris to ensure smooth ventilation. In some dusty industrial places, quarterly internal cleaning can meet the requirements.

The inspection work is mainly to see whether the connection parts of the air duct are loose, whether there is any leakage phenomenon, and whether there is any damage to the air duct body. Regular inspections can detect potential problems in time and avoid malfunctions. It is generally recommended to conduct a comprehensive inspection every six months. When checking the connection parts, pay attention to see whether the bolts are tight, and whether the sealing gasket is aging or damaged. If problems are found, they should be repaired or replaced in time. For damage to the duct body, small cracks can be repaired with special repair materials, while larger damage requires replacement of the damaged section.

The stability of PP material makes PP square ducts have low maintenance cost. Compared to metal ducts, it does not require corrosion protection and there is no need to worry about rust. Under normal use, PP square ducts are only 30% – 50% less expensive to maintain than metal ducts. And, because of its long service life and low replacement frequency, long-term maintenance costs are further reduced. In commercial buildings, the use of PP square duct ventilation systems can save tens of thousands of dollars in annual maintenance costs.

The maintenance cycle varies according to different use environments and places. In commercial and public places, such as shopping malls, office buildings, etc., it is recommended to carry out a comprehensive maintenance once a year; in industrial places, due to the harsher environment, the maintenance can be carried out once every half a year; the ventilation system of the residential houses is used less frequently and the environment is relatively good, so it is enough to carry out a maintenance once every 2 – 3 years. Of course, if the ventilation system appears obvious odor, air volume decreases or energy consumption increases and other abnormalities, it should be promptly inspected and maintained.

In the chemical and electroplating industries, the production process often produces various gases with strong corrosive properties, such as sulfuric acid, hydrochloric acid, sodium hydroxide, etc. PP ducts can easily cope with these “acid and alkali attacks” by virtue of their excellent chemical resistance. In the sulfuric acid plant, PP ducts are used to transport high concentration of sulfuric acid vapor, and after a long time of use, the inner wall of the ducts is still smooth as before, without the slightest trace of corrosion. While the traditional metal duct, in the same environment, may be just a few months will appear serious corrosion, resulting in pipe leakage, not only affect the production, but also may bring potential safety hazards. According to relevant data, in the chemical industry, the use of PP duct equipment maintenance frequency than the use of metal duct equipment reduced by more than 50%, greatly improving production efficiency.

(ii) Sealing: “zero air leakage” guarantee

PP ducts are connected by heat fusion connection, flange connection and many other advanced connection methods. These connection methods can ensure that the ducts are tightly bonded to each other and realize “zero leakage” of air. In hospital operating rooms, good sealing is crucial. If there is leakage in the ventilation system, it will not only affect the air quality in the room, but may also lead to an increased risk of surgical infections. the excellent sealing of PP ducts can effectively prevent the leakage of harmful gases, providing a safe and clean environment for patients and healthcare workers. In industrial production, for some processes that require high gas purity, such as electronic chip manufacturing, the sealing of PP air ducts can ensure that the production environment is not interfered by external impurities, ensuring the stability of product quality.

(iii) Low noise: quiet ventilation system

PP material has good damping properties, which is the key to its noise reduction. As air flows through the duct, the PP material absorbs and attenuates sound waves, thus reducing the transmission of noise. Compared with metal ducts, PP ducts are significantly quieter in operation. According to professional tests, under the same conditions of air speed and air volume, the operation noise of metal ducts can be over 60 dB, while the noise of PP ducts can be controlled at about 40 dB, which is about 30% lower. In hospital wards, school classrooms and other noise-sensitive places, PP ducts can provide a quiet and comfortable environment, which is conducive to the recovery of patients and students’ learning.

(iv) Thermal insulation: energy saving and comfort

PP ducts can be equipped with specialized insulation, which effectively reduces heat loss. This feature is especially important in HVAC systems. In winter, PP square ducts with insulation can better retain heat in the room and reduce the energy consumption of heating equipment; in summer, it can prevent cold air from escaping and reduce the power consumption of air conditioning. Comparisons of real-world examples show that buildings with insulated PP ducts use 15% – 20% less energy for their HVAC systems than buildings with ordinary ducts. This not only saves energy costs for users, but also helps to reduce carbon emissions and realize green environmental protection.

(v) Long life: durable

PP material ages slowly, mainly due to its stable molecular structure and good chemical stability. Under normal operating conditions, PP ducts have a practical service life of 30 – 50 years. In some large industrial plants, PP ducts have been in continuous use for more than 30 years and are still performing well and do not need to be replaced. From a long-term cost perspective, although the initial investment in PP ducts may be slightly higher than some common ducts, the overall cost is lower due to their long service life and low maintenance costs. For example, while metal ducts require regular anti-corrosion treatment and repairs during use, PP ducts require little or no such additional costs, greatly reducing the operating costs of the enterprise.

Wind speed plays a key role in the determination of duct size, and there is a clear inverse relationship between it and the duct size. According to the formula for duct sizing (duct size = air volume / air velocity / 3600), the larger the air velocity, the smaller the calculated cross-sectional area of the duct for a fixed air volume of 20,000 m³/h; conversely, the smaller the air velocity, the larger the cross-sectional area of the duct.
The choice of different air velocities can affect the ventilation system in many ways. In terms of noise, a higher wind speed will lead to greater noise when the fan is running, and at the same time, the air flows at high speed in the duct, and when it passes through elbows, valves and other components, it is easy to generate airflow noise. For example, in some places with extremely high noise requirements, such as recording studios, libraries, etc., if a higher wind speed is used, the noise problem will seriously affect their normal use. Analyzing from the perspective of energy consumption, the higher the wind speed, the greater the resistance of the wind flowing in the duct, and in order to overcome these resistances, the fan needs to consume more electricity, thus increasing the operating cost of the system. In large commercial buildings, the ventilation system runs all day long, and if the wind speed is unreasonable leading to high energy consumption, it will generate a considerable amount of money in the long run. In addition, the wind speed will also affect the uniformity of ventilation, too high wind speed may lead to uneven distribution of air in the room, localized areas of under-ventilation or over-ventilation .

(二) Impact of system pressure

System pressure is another important factor that governs duct sizing. In a ventilation system, pressure is divided into static and dynamic pressure, with static pressure used to overcome the resistance of the duct and dynamic pressure related to the flow rate of the air . When the system pressure is high, it means that the duct needs to withstand a greater pressure load, which requires the duct to have enough strength and sealing to prevent the duct from rupturing or leaking .
In general, ducts in high-pressure systems require thicker, stronger materials. For example, in industrial ventilation, some air ducts conveying high-temperature and high-pressure gases may be made of steel plates of greater thickness and more stringent in terms of the connection parts of the air ducts and reinforcement measures . For low-pressure systems, the strength requirements of air ducts are relatively low, and thinner materials can be used, so as to meet the operational requirements of the system and reduce costs. If air ducts that do not meet the pressure requirements are used in high-pressure systems, it may lead to deformation and rupture of air ducts, which not only affects the ventilation effect, but also may cause safety accidents.

(三) Impact of usage scenarios and demand

Different scenarios and needs have different requirements for the size of the 20000 air volume ducts. In industrial plants, due to the large space and relatively low sensitivity to noise, in order to save cost and space, a higher air velocity is usually used, and the corresponding duct size can be smaller. For example, in some large-scale machinery processing plants, the air velocity of the main duct of the ventilation system may reach 10m/s or even higher, so that the cross-sectional area of the duct can be designed to be relatively small under the circumstance of meeting the 20,000 air volume.
Commercial buildings such as shopping malls and supermarkets are densely populated and have high requirements for indoor air quality and comfort, and also need to consider the impact of noise on the shopping experience of customers. Therefore, the air velocity of the ventilation system in such places is generally controlled in a moderate range, such as 6 – 8m/s, and the size of the air ducts will be designed according to the specific layout and air volume distribution. Moreover, commercial buildings usually have decorative structures such as suspended ceilings, and the installation of air ducts needs to be coordinated with the building structure, which also affects the selection of air duct sizes.
Residential ventilation systems are relatively small, but the requirements for noise are more stringent, because noise can directly affect the quality of life of residents. In residential houses, even if the airflow reaches 20,000 (which is relatively rare, and generally the airflow of residential houses is small, but assuming special circumstances), a lower air velocity, such as 4 – 6m/s, will be used to ensure a quiet living environment . In this case, in order to meet the demand for airflow, the size of the ducts may be relatively large, but the space of the house is limited, which requires full consideration of the layout and installation location of the ducts in the design, to minimize the occupation of indoor space.

1.Metal ducts: common metal ducts include galvanized steel ducts, stainless steel ducts and aluminum ducts. Galvanized steel duct price is relatively low, has good mechanical strength and fire performance, the most widely used, in general industrial and civil building ventilation system can see its figure. Stainless steel ducts have excellent corrosion resistance and are suitable for chemical, food and other industries with high requirements for hygiene and corrosion resistance, such as the ventilation ducts of food processing plants, stainless steel ducts are often used to ensure the purity of the air and the durability of the ducts. Aluminum plate duct is lightweight and not easy to produce sparks when collision, so it will be used in places with explosion-proof requirements, such as coal mine underground ventilation system.

2.Composite duct: Composite duct is made of a variety of materials composite, generally including thermal insulation materials and surface materials. For example, phenolic composite duct, it is phenolic foam as the core material, the surface covered with aluminum foil and other materials, with lightweight, good thermal insulation performance, sound insulation effect, etc., commonly used in the air conditioning and ventilation system with high requirements for thermal insulation and sound insulation, such as hotels, office buildings, central air conditioning ducts. There is also glass-magnesium composite air duct, which has excellent fireproof performance and high strength, and is used more in some buildings with strict fire safety requirements, such as shopping malls, hospitals and other places.

3.Polymer duct: Polymer duct is made of polymer material, such as polyvinyl chloride (PVC) duct, PVC duct has the characteristics of strong corrosion resistance, low price, easy installation, etc., which is widely used in some industrial places with corrosive gas emission, such as the ventilation system of electroplating workshop. However, PVC ducts have poor high temperature resistance and relatively narrow temperature range.

How to size ducts for 20000 air volume.

1.Assumed air velocity method
The assumed wind speed method is a common and relatively simple calculation method for determining the duct size required for 20,000 airflow. The core formula is: duct size (cross-sectional area) = air volume / air velocity / 3600. The principle of this formula is based on the relationship between flow rate, velocity and time. The unit of air volume is usually cubic meters per hour (m³/h), which indicates the volume of air passing through the duct in a unit of time; the unit of wind speed is meters per second (m/s), which describes the speed of air flowing through the duct; and 3600 is the conversion factor for converting hours to seconds, which gives the cross-sectional area of the duct in square meters (m²).
When applying this, it is first necessary to make reasonable assumptions about the wind speed. The choice of wind speed is not arbitrary, but to consider a variety of factors. For example, in the civil building ventilation system, if the noise control requirements are high, the wind speed should not be too large, generally the main duct wind speed can be controlled at 4 – 7m / s; in industrial plants and other relatively low noise requirements of the place, in order to reduce the size of the duct, reduce costs, the main duct wind speed can be increased appropriately, such as 6 – 12m / s . Suppose we have to determine the duct size for 20000m³/h airflow in an industrial project with general noise requirement, assuming the air velocity is 8m/s. According to the formula, the cross-sectional area of the duct = 20000÷8÷3600 ≈ 0.694m².
If a circular duct is used, we can further calculate the duct diameter according to the formula of the area of a circle S = πr² (where S is the area and r is the radius). From 0.694 = 3.14×r², we can get r² = 0.694÷3.14 ≈ 0.221, r ≈ 0.47m, then the diameter d = 2r ≈ 0.94m. If you choose rectangular duct, you also need to determine the ratio of length and width according to the actual installation space and design requirements, assuming that the ratio of length and width of 2:1, set the width of x meters, then the length of 2x meters, 2x × x = 0.694, that is, 2x ² = 0.694, can be obtained x ² = 0.347, x ≈ 0.59m, then the length of 2x ≈ 1.18m, that is, the size of the rectangular air duct can be 1180mm × 590mm.

2. Introduction to other calculation methods
In addition to the assumption of wind speed method, there are also a variety of methods to calculate the size of the duct, such as specific resistance method, area method, flow coefficient method. Specific resistance method is to calculate the friction resistance per unit length of the duct (specific resistance), combined with the total resistance of the duct and the air volume to determine the size of the duct, this method of calculation is relatively complex, you need to consider more resistance factors, such as the roughness of the duct, air viscosity, and so on. Area method is based on the known cross-sectional area of the duct and wind speed to calculate the air volume, and the assumption of wind speed method of calculation of the opposite idea, in the known air inference duct size, you need to determine the appropriate size through a number of trial calculations. Flow coefficient method is based on the flow coefficient of the inlet or outlet of the duct, combined with the wind speed and cross-sectional area to calculate the air volume, the method needs to know the flow coefficient of the duct in advance, and the flow coefficient is usually provided by the manufacturer or determined by experiments.
However, in practical engineering applications, the assumed air velocity method is most commonly used because it is relatively simple and intuitive to calculate, and can meet the accuracy requirements of most projects. In this discussion on 20000 air volume duct sizing, we also focus on the assumed air velocity method as an example to analyze and calculate, so that we can understand and grasp the basic method of duct sizing more clearly.

In the ventilation system of all kinds of buildings, the suitability of air volume and duct size is crucial, which is directly related to the ventilation effect, energy consumption and the stability of the operation of the whole system. Imagine a large shopping mall or factory, if the ventilation system duct size is unreasonable, either can not meet the indoor ventilation needs, resulting in dirty air, stuffy, affecting people’s comfort and work efficiency; or will cause energy waste, increase operating costs. Today, we focus on a specific problem: when the air volume is 20000, how big should the air duct be? This seemingly simple question involves a series of complex calculations and consideration of various factors. Let’s dig deeper and solve the mystery for you.

二.Duct Basics

(1) Role of air ducts

Duct, as a key component of the ventilation system, undertakes the important mission of conveying and distributing air . In the ventilation system, it is like the trachea in the human body’s respiratory system, which is the channel for air circulation. Fresh air is introduced into the room through the air ducts to provide people with sufficient oxygen and maintain a comfortable indoor environment; at the same time, indoor dirty air, harmful gases, and excess heat and moisture, etc., also rely on the air ducts to be discharged outdoors to ensure indoor air quality and hygiene. For example, in the operating room of a hospital, the air duct continuously sends in purified sterile air and discharges the exhaust air that may carry germs to create a safe air environment for the smooth operation; in the factory workshop, the air duct can timely discharge the dust, smoke and other harmful pollutants produced during the production process to protect the health of the workers.

（2）Classification of air ducts（Classified by cross-section shape）

• Round Duct: Round duct has superior aerodynamic performance, air flows in it with minimum resistance, which makes the round duct can effectively reduce the energy consumption of the fan under the same air volume, and the operation cost is lower. At the same time, it has good sealing performance, which can reduce air leakage and ensure the efficient operation of the ventilation system. Circular air ducts are widely used in places with high ventilation requirements and where space permits, such as the central air conditioning ventilation system of large shopping malls. However, the production process of round air duct is relatively complicated and occupies a large space height, so the installation may be restricted in some buildings with limited space.

• Rectangular Duct: The biggest advantage of rectangular duct is that it can better adapt to the building structure and combine closely with the walls and ceilings of the building, which makes it easy to install and layout. In most office buildings, residential and other places, due to the characteristics of the space layout, rectangular duct is more common. It is relatively simple to fabricate, and the fittings are easy to make and connect. However, the air resistance of rectangular duct is relatively large, in the case of conveying the same amount of air, it requires a more powerful fan, and the energy consumption will increase accordingly, and its air leakage rate is relatively high.

• Flat round duct: Flat round duct combines part of the characteristics of round duct and rectangular duct, it reduces the height size of round duct to some extent, and less resistance than rectangular duct. In some of the space height has some limitations, but also on the ventilation resistance requirements of the occasion, such as some of the lower level underground parking lot ventilation system, flat round air duct can play its advantage. However, the production difficulty of flat round duct is between round and rectangular duct, the application scope is relatively narrow.

Polypropylene is a high-density, side-chain-free, high-crystalline linear polymer with excellent comprehensive properties. Common products: basins, barrels, furniture, films, woven bags, bottle caps, car bumpers, etc.

pp plastic, chemical name: polypropylene, English name: Polypropylene (abbreviated as pp) specific gravity: 0.9-0.91 g/cm3, molding shrinkage: 1.0-2.5%, molding temperature: 160-220 °CPP is a crystalline polymer, and the comprehensive performance of PP is better than that of PE material. PP products are lightweight, tough and chemically resistant. The disadvantages of PP: low dimensional accuracy, insufficient rigidity, poor weather resistance, it has the phenomenon of post-shrinkage, and after demoulding, it is easy to age, become brittle and easy to deform. In engineering projects, the commonly used air duct is made of PP material.

In the PP material inside the high-purity propylene as the main material, including a small amount of ethylene copolymer, after drying, mixing, extrusion, granulation, screening and homogenization into polypropylene particles, this particle is cylindrical particles, the particles are very smooth, without any mechanical impurities, it has good mechanical properties and heat resistance, in the temperature range of minus 30 degrees Celsius to 140 degrees Celsius is not toxic.

Mechanical properties PP has high crystallinity and regular structure, so it has excellent mechanical properties. However, at room temperature and low temperature, the impact strength is poor due to the high regularity of its molecular structure. The most outstanding performance of PP is its resistance to flexural fatigue.

Chemical stability PP has good chemical stability, in addition to being eroded by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable to various other chemical reagents; However, low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can soften and swell polypropylene, and its chemical stability is improved with the increase of crystallinity, so PP is suitable for making various chemical pipes and fittings, and the anti-corrosion effect is good.

Electrical properties PP has excellent high-frequency insulation properties, and since it hardly absorbs water, the insulation properties are not affected by humidity. It has a high dielectric coefficient, and with the increase of temperature, it can be used to make heated electrical insulation products. It also has a high breakdown voltage, making it suitable for use as an electrical accessory, etc. It has good voltage resistance and arc resistance, but has a high degree of electrostatic electricity. Due to the presence of the side methyl group in PP, tertiary carbon atoms alternately appear on the molecular chain, and the tertiary carbon atoms are very easy to oxidize when in contact with copper ions, resulting in poor oxidation resistance and radiation resistance of polypropylene. Therefore, copper inhibitors must be added in applications that come into contact with copper.

The performance can be changed through additives: PP can change its performance by adding various fillers, plasticizers, antistatic agents, etc., so that it has the characteristics of flame retardant, antistatic, antibacterial, and reinforcing. For example, adding glass fiber can enhance the rigidity and strength of PP, adding carbon black can make PP have anti-ultraviolet and antistatic properties, adding antioxidants can extend the service life of PP, etc.

Physicochemical properties

1. Odorless, tasteless and non-toxic. It is one of the lightest resins commonly used;

2. Excellent mechanical properties, including tensile strength, compressive strength and hardness, outstanding rigidity and bending fatigue resistance, the movable hinge made of PP can withstand more than 7 × 10 to the power of 7 folds and bends without breaking, and the impact strength is poor at low temperatures. The tensile strength of PP is generally 21-39 MPa; The flexural strength is 42-56 MPa, the compressive strength is 39-56 MPa, the elongation at break is 200%~400%, the notched impact strength is 2.2-5 kJ/m2, and the low-temperature notched impact strength is 1-2 kJ/m2. Rockwell hardness R95~105;

3. Good heat resistance, continuous use temperature up to 110-120°C;

4. Good chemical stability, except for strong oxidants, it does not interact with most chemicals; The solvent cannot dissolve PP at room temperature, only some halogenated compounds, aromatic hydrocarbons and high boiling point aliphatic hydrocarbons can make it swell, and the water resistance is particularly good;

5. Excellent electrical properties, good resistance to high-frequency electrical insulation, and good electrical insulation in humid environments;

6. Since there are many tertiary carbon atoms with methyl groups on the backbone of PP, the hydrogen on the tertiary carbon atoms is susceptible to oxygen attack, so the weathering resistance of PP is poor, and antioxidants or ultraviolet absorbers must be added

7. Mice were gavaged 1~5 times at a dose of 8g/kg, and no obvious poisoning symptoms were caused. The decomposition products of polypropylene heated to 210~220 °C were inhaled 30 times for 2 hours each time, and the symptoms of ocular mucosa and upper respiratory tract irritation appeared. As with polyethylene, it is forbidden to use its recycled products for food.

Polypropylene modification

In view of the poor impact resistance, poor weather resistance, poor surface decoration of polypropylene at low temperatures, and the gap between the functionality and actual needs in electricity, magnetism, light, heat, combustion, etc., the polypropylene has been modified, which has become the most active and fruitful field in the current plastic processing development.

• PP chemical modification

Through copolymerization modification, cross-linking modification, grafting modification, adding nucleating agent, etc., the polypropylene polymer components and macromolecular structure or crystal configuration are changed to improve its mechanical properties, heat resistance, aging resistance and other properties, improve its comprehensive properties, and expand its application fields.

(1) Copolymerization modification

Copolymerization modification is the modification of propylene monomer synthesis stage by using catalysts such as metallocene. When the monomer is polymerized, the added olefin monomer is copolymerized with it, and the random copolymer, block copolymer and alternating copolymer are polymerized, and the mechanical properties, transparency and processing fluidity of homopolymer PP are improved. The complexes formed by metallocene catalysts are used as a single active center in a transition state with a certain restriction of irregular shape, so as to achieve precise control of the relative molecular weight and its distribution, comonomer content, distribution on the backbone and the crystal structure of the polymer.

(2) Grafting modification

The PP (polypropylene) resin molecule has a non-polar crystalline linear structure, low surface activity, and no polarity. Poor surface printability; Poor coating and adhesion; Difficult to blend with polar polymers; Disadvantage that it is difficult to be compatible with polar reinforcing fibers and fillers. Graft modification is to introduce polar groups to its macromolecular chain to improve the blendability, compatibility and adhesion of PP, and to overcome the shortcomings of difficult blending, incompatibility and bonding. When the active free radical encounters the unsaturated carboxylic acid monomer, it promotes the unstable bond of the unsaturated carboxylic acid monomer to open and react with the PP active free radical to form the free radical, which is then terminated by the molecular chain transfer reaction. The common grafting modification methods of PP are: melting method, solution method, solid phase method, suspension method, etc. The hydrogen atoms in the grafted modified PP molecular chain are replaced and show strong polarity, and these polar groups enhance the compatibility of PP, and the heat resistance and mechanical properties are greatly improved.

PP flame retardant pipe and PVC pipe are both common pipe materials, and they each have unique advantages and application scenarios. PP flame retardant pipe is widely used in specific occasions due to its flame retardant performance and good durability, while PVC pipe is used in many fields due to its excellent corrosion resistance and low cost. When these two materials are connected, although they are connected in different ways (PP flame retardant pipes are usually connected by hot melt, while PVC pipes are connected by adhesive), they can be used together in practical use, especially in occasions where flame retardant properties are required, such as the protection of electrical circuits.

• Connection of PP flame retardant pipe: Since the PP flame retardant pipe adopts the hot melt connection method, this connection method ensures the firmness and tightness of the pipe connection, so as to ensure the safety and durability of the pipeline system. The hot melt connection melts the pipe end by heating it, and then quickly connects the two sections of pipe, which when cooled to form a strong connection.
• Connection of PVC pipes :PVC pipes are usually connected by adhesive, which is suitable for the connection of PVC pipes and fittings, which can provide a certain degree of tightness and durability. Adhesive connections require the use of specialized glue to apply glue to the ends of pipes and fittings, and then butt them to cure them under a certain pressure and time, thus forming a strong connection. Although PP flame retardant pipes and PVC pipes are connected differently, they can be used together in practical engineering applications, especially in occasions where flame retardant properties are required, such as the protection of electrical wiring. In addition, if you need to make a connection between PP flame retardant pipe and PVC pipe, you can consider using a special PP adhesive PVC plastic glue, which can effectively solve the bonding problem between these two materials, provide strong adhesion and firmness, and can maintain its performance and quality for a long time in different temperature environments

PP flame retardant air duct and PPH air duct

With its excellent corrosion resistance and mechanical properties, PPH pipes are widely used in chemical industry, environmental protection and other fields. Both materials can be joined by hot melt welding, including hot plate welding, hot air welding, and hot melt butt welding, which allows them to be flexibly combined in practical applications.

• The properties of PP flame retardant pipe make it ideal for fireproof occasions. It has good flame retardant properties, which can effectively stop the spread of flames and protect the safety of people and property.

• PPH pipes are known for their excellent corrosion resistance, wear resistance and high temperature resistance, and are suitable for chemical, electronics, pharmaceutical factories and other fields. The β modification of PPH tubing gives it a uniform and delicate Beta crystal structure, which improves its chemical resistance and mechanical strength.

Since both can be joined by the method of hot melt welding, this means that in engineering projects, PP flame retardant pipes and PPH pipes can be combined according to specific needs, and they can be joined together by welding technology to form a complete system. This combination not only increases the safety and reliability of the system, but also expands the range of applications for materials that meet the special needs of different engineering fields. In summary, PP flame retardant pipes and PPH pipes can be used together to achieve a seamless connection through hot melt welding technology, providing more options and possibilities for various engineering applications