PP Formed Flange

Product Model	Injection Molded Flat Weld Flange Series
Category	PP Molded Products
Reference Price	Price on request

Hot Customizable for Working Conditions 11 Technical Parameters

Product Overview

The PP Formed Flange is a disc-shaped pipe connection component molded by polypropylene injection molding, with evenly distributed bolt holes on the disc surface. When two flanges are brought together, bolts are inserted and tightened, and a sealing gasket is installed in the middle to achieve a secure connection between pipes and pipes or pipes and equipment. The flange connection exhibits excellent sealing performance and is easy to disassemble, making it the primary connection method in ventilation systems requiring maintenance and sectioning.

Compared to manually welded flanges, injection molded flanges offer higher dimensional accuracy, a smooth disc surface, and precisely positioned bolt holes, ensuring consistent batch quality. When connecting to air ducts, the pipe end is inserted into the flange neck socket and then fixed with a welding rod. The weld is located at the flange neck, leaving the sealing surface unaffected. The product is resistant to acid, alkali, and salt corrosion, does not rust, and is significantly lighter than metal flanges.

The PP Formed Flanges supplied by Xicheng Environmental Protection are compatible with the nominal diameter series of formed air ducts, available in a full range of specifications from smaller to larger diameters, and can also be provided in flame-retardant PP material. The flange sealing surface is flat, and when paired with rubber or PTFE gaskets, evenly tightened bolts can withstand positive and negative pressures in the ventilation system, making it suitable for connections between towers, fans, dampers, and pipes.

Working Principle

The flange connection relies on the pre-tightening force of the bolts to compress the gasket between the two flange sealing surfaces, achieving a seal. After the bolts are tightened, the gasket undergoes elastic deformation to fill the microscopic irregularities of the sealing surface, blocking the path for gas leakage along the joint. The flange distributes the concentrated force of the bolts evenly around the entire circumference, ensuring that the pipe joint maintains tight contact even when subjected to wind pressure and the weight of the pipes.

The corrosion resistance principle of the formed flange lies in its overall polypropylene material, which matches the material of the air ducts and equipment. The inner surface and sealing surface in contact with corrosive gases contain no metal. Although the connecting bolts are typically metal components, they are located outside the flange disc and do not directly contact the medium. Additional plastic bolt caps or corrosion-resistant treatment can be applied to adapt to corrosive environments. The weld and sealing surface work together to ensure the continuity of corrosion and sealing at the connection point.

Structural Composition

The formed flange consists of a flange disc, a neck socket, and bolt holes. The flange disc is a circular ring with a certain thickness, serving as the load-bearing area for bolt tightening and gasket sealing. The neck socket is designed to fit the outer diameter of the air duct and is welded in place after insertion. Bolt holes are evenly distributed around the disc circumference, with their diameter and number increasing with the diameter, ensuring uniform circumferential sealing pressure.

The flange sealing surface is fully flat and machined smoothly. On larger-diameter flanges, reinforcing ribs can be added to the back of the disc surface to enhance rigidity and prevent warping or deformation when bolts are tightened. The neck of the flange, where it is welded to the air duct, has sufficient length to ensure weld strength. Gaskets resistant to acid and alkali, PTFE gaskets, or other corrosion-resistant gaskets are selected based on the medium properties between the two flanges.

Specification and Model Table

The table below provides a structural and compatibility description of the formed flange, with specific dimensions corresponding to the air duct diameter series.

Component	Function	Matching Parts
Flange Disc	Bolt Tightening and Sealing	Bolts and Nuts
Neck Socket	Air Duct Insertion and Welding	PP Welding Rod
Sealing Surface	Sealing with Gasket to Prevent Leakage	Corrosion-Resistant Gasket

Product Features

The PP Formed Flange offers reliable connections and easy assembly, making it a standard connection component for corrosion-resistant ventilation pipes. Its main features are as follows.

Injection molded in one piece, with a smooth disc surface and accurately positioned bolt holes
Reliable flange connection sealing, capable of withstanding wind pressure in the ventilation system
Easy to assemble and disassemble, facilitating equipment maintenance and pipe section cleaning
Overall corrosion resistance to acid, alkali, and salt, without rust, and lightweight
Compatible with formed air duct diameter series, with a full range of specifications for convenient selection
Insertion welding fixation, with welds not affecting the sealing surface
Available in flame-retardant material, meeting indoor fire safety requirements

Material	PP / PPs Polypropylene
Molding Process	Integral injection molding
Connection Type	Flange Bolt Connection
Sealing Surface Form	Flat Panel Display Our flat panel displays are designed for high performance and reliability, meeting the needs of various
Fixed with ductwork	Splice Welding
Corrosion resistance performance	Acid-alkali-resistant
Companion Gaskets	Anti-corrosion gasket
Flame Retardant Options	PPs self-extinguishing
Pressure Rating	Low-voltage ventilation applicable
Matching Port	Multiple size options available
Bolt hole positions	Processed according to standards

Application Industries

Flange connections for inlet and outlet of spray towers and washing towers with air ducts
Corrosion-resistant fan inlet and outlet connections with main ventilation pipelines
Connections of electric and manual dampers at both ends of pipelines
Interfaces for regularly maintained equipment such as activated carbon adsorption boxes
Segmented disassembly and assembly exhaust pipelines in chemical workshops
Connections of acid and alkali exhaust systems in semiconductor and electroplating production lines
Connections of exhaust pipelines of laboratory fume hoods with main pipelines

Typical Process Locations

Formed flanges are installed at pipeline nodes requiring disassembly, maintenance, or equipment connections. Equipment inlet and outlet typically come with flanges. After welding formed flanges to the pipeline ends, they are aligned with equipment flanges, with gaskets added and tightened with bolts. Valves, silencers, and other pipeline components are also connected to the system via flanges for easy replacement later. Flanges are installed at regular intervals along straight pipeline sections for segmented installation and cleaning.

In exhaust treatment systems, flanges are concentrated at the inlet and outlet of towers, inlet and outlet of fans, both ends of dampers, and interfaces of adsorption equipment. During installation, ensure the two flanges are coaxial and parallel, with gaskets centered, and bolts tightened diagonally in stages for even distribution to avoid unbalanced stress causing flange warping and leaks. The quality of flange connections directly determines whether the system leaks under negative pressure. Before installation, verify nominal diameter, sealing surface type, and bolt hole distribution. When welding the spigot end to air ducts, maintain the flange surface perpendicular to the pipeline axis to prevent misalignment. Bolts should be tightened diagonally in two to three stages for even distribution, with gaskets centered and not reused. Protect the sealing surface from scratches during hoisting and handling. If flange leaks are detected during operation, first relieve pressure before evenly retightening or replacing gaskets.

Both types have their specific applications. Formed flanges are produced through injection molding, featuring standardized dimensions, flat faces, and Compliant sealing surfaces, with quick installation. They are ideal for bulk connections of standard-diameter ductwork and equipment, offering lower costs and are widely used in conventional engineering projects. Welded flanges are manufactured by turning sheet metal or splicing and welding, offering high flexibility and can be processed into non-standard dimensions, ultra-large diameters, and special-shaped flanges. However, their production cycle is longer and requires higher welding skills and machining precision. Standard specifications should prioritize formed flanges for stable quality and good interchangeability; welded flanges are used for non-standard, ultra-large diameters, or on-site irregular interfaces. When selecting, verify the diameter, pressure rating, and sealing surface type. It is recommended to standardize flange specifications within the same system to facilitate spare part interchangeability and future maintenance.

Flange leakage is typically caused by gasket aging, bolt loosening, flange face misalignment, or seal surface damage. First, check if the bolts are tightened evenly in a diagonal sequence. Bolts may loosen due to thermal expansion and contraction of pipelines and operational vibration. Re-tightening them according to specifications can eliminate most leaks. If leakage persists, shut down and relieve pressure, then disassemble the flange to inspect if the gasket is damaged, misaligned, or aged. Replace the new gasket and re-center the installation. For warped or deformed flange faces or scratched seal surfaces, the flange needs to be replaced or the seal surface machined. Do not excessively increase bolt torque to force a seal, as this may crack the plastic flange. Establishing records for bolt tightening and gasket replacement during routine maintenance can effectively reduce repetitive leaks.

The material of the gasket should be selected based on the composition of the exhaust gas, temperature, and pressure. For general acid-base ventilation, acid-resistant and alkali-resistant rubber gaskets or EPDM rubber gaskets can be used, which offer good elasticity and low cost. For applications requiring higher temperature and corrosion resistance, PTFE gaskets or PTFE-coated gaskets should be selected. The thickness of the gasket must be uniform, and its dimensions should match the flange sealing surface. During installation, place the gasket centrally and install it in one go without offsetting. Multiple layers of gaskets should not be used to Accumulate thickness . For exhaust gas containing organic solvents, oils, or special media, verify the compatibility of the gasket material to prevent swelling, softening, and failure of the gasket. It is recommended to replace a new gasket each time a flange is disassembled. Reused aged gaskets are a common cause of air leakage. When ordering, ensure the corresponding specification gaskets are matched based on the flange nominal diameter and sealing surface type to avoid incorrect usage on-site.

The flange body is made of plastic material, which is not corrosive, but the connecting bolts are typically metal parts located outside the flange, not directly contacting the internal medium of the pipe. In general acidic or alkaline ventilation environments, the bolts are at the outer edge of the flange, contacting only trace leakage gases, resulting in slower corrosion. In high-concentration corrosive gas environments, during spray wetting, or outdoor rain exposure, stainless steel bolts or galvanized bolts can be selected, or plastic protective caps can be installed on the bolts, or anti-corrosion grease can be applied. During regular maintenance, check the rust and tightness of the bolts. Timely replacement is required for severely rusted bolts to prevent them from breaking inside the holes during disassembly. It is recommended to use bolts of the same material for the same set of flanges and to tighten them evenly to avoid additional corrosion caused by contact between different metals. In coastal or high-humidity, high-corrosion environments, stainless steel bolts are preferred, resulting in lower maintenance requirements in the long term.

Before welding, confirm that the flange and duct diameter are matched, and the socket depth is sufficient. Insert the duct into the flange neck socket to the correct position, ensuring the flange surface is perpendicular to the duct axis and free from tilting. First, spot weld symmetrically at several points around the circumference to secure the position. Check the flange perpendicularity and end face flatness, and only then perform full-welding along the neck circumference. The weld bead should be continuous, full, and free from porosity. During welding, take care not to scorch the flange sealing surface. After welding, remove slag and spatter, and wait for complete cooling before installing the gasket. Flange tilting can cause the two flanges to fail to align parallelly, resulting in excessive local gaps, which is a common cause of flange leaks. For batch welding, use fixtures or templates to ensure flange perpendicularity. After welding, inspect each flange individually with a square or template, and correct any non-compliant pieces promptly.

Large-diameter plastic flanges have limited rigidity. If the bolt tightening force is excessive, the tightening sequence is incorrect, or the pipeline is hung improperly, the flange surface may warp or deform, leading to seal failure. Large-diameter flanges should be selected with reinforced thick flanges, appropriately increasing the number of bolts and flange thickness. During tightening, apply even force in two to three stages following a diagonal sequence; never tighten unilaterally in a single step. The weight of the pipeline and components should be independently supported by hangers; the flange should not bear the shearing force of the pipeline or the weight of the equipment. If necessary, install independent supports near both sides of the flange. After installation, check whether the flange surface is parallel and whether the gaps are uniform. During operation, if warping or air leakage is detected in large-diameter flanges, realignment, additional support, or replacement with a reinforced flange should be performed; avoid indiscriminately increasing the tightening force.

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