PP Flame Retardant Processed Elbow

Product Model	PPs plate-welded rectangular elbow
Category	PP Machined Products
Reference Price	Price on request

Hot Customizable for Working Conditions 11 Technical Parameters

Product Overview

The PP fire-retardant fabricated square elbow is a plate-welded fitting used to change the direction of rectangular ventilation ducts. It is made from PP fire-retardant plates, cut according to the elbow layout, bent, and welded together. The ends of the square elbow are square flanges, which connect to the rectangular ducts. Based on the direction of turn, they are classified as horizontal elbows or vertical elbows, with common angles being 90 degrees, but other angles such as 45 degrees can also be processed.

Elbows are areas where local resistance is concentrated in exhaust ducts. When airflow changes direction at an elbow, it generates eddies and pressure loss. Fabricated square elbows can be equipped with internal flow guide vanes to smoothly direct airflow, significantly reducing local resistance and noise, which is particularly important for large-capacity rectangular ducts. The PP material is acid and alkali-resistant, self-extinguishing, and matches the material of the square ducts, ensuring uniform corrosion and fire protection performance of the entire system after welding.

Xicheng Environmental can customize fire-retardant fabricated square elbows based on the cross-sectional dimensions of the rectangular ducts, the turning angle, and installation space. The curvature radius of the elbow, flange type, and number of flow guide vanes can be designed according to requirements. They are compatible with square ducts, square tees, and square-to-round transitions, making them suitable for turning sections of rectangular ducts in laboratories, electroplating workshops, and factory mezzanines.

Working Principle

The function of the square elbow is to change the direction of airflow. After entering the elbow, the airflow turns 90 degrees or other angles along an arched or angled channel and exits. During the turning process, the outer wall guides the airflow, while the inner wall forms a low-speed eddy zone. Elbows with flow guide vanes use multiple arched vanes to divide the duct into several parallel flow paths, allowing the airflow to turn in layers, reducing eddy zones and secondary flow, thereby lowering the local resistance coefficient, reducing fan energy consumption, and minimizing elbow noise.

The corrosion and fire-retardant properties of the square elbow are guaranteed by the PP plates and matching welds. Corrosive exhaust gases exert stronger scouring force on the outer wall during turning. The PP material does not react with acids or alkalis, so the outer wall and flow guide vanes remain corrosion-resistant even under continuous airflow scouring. The fire-retardant components ensure self-extinguishing when exposed to fire, and the indoor rectangular duct system does not propagate flames when passing through ceilings or floors, just like straight ducts. Welds run continuously along the plate joints, preventing air leakage at turning points.

Structural Composition

The square elbow consists of two side wall plates, inner and outer curved plates (or folded plates), end square flanges, and optional flow guide vanes, all welded together. The side wall plates are cut according to the elbow angle and curvature, and the inner and outer side plates are bent or joined to form the turning channel. Longitudinal seams at the corners and circumferential seams are continuously welded. The two end flanges are matched with the flanges of the rectangular ducts, with bolt holes aligned.

Flow guide vanes are arched PP plates fixed at equal intervals between the side walls. Large-capacity elbows are equipped with multiple vanes, while small-capacity elbows may not have them. The outer wall of the elbow is reinforced with ribs based on negative pressure and size, with additional triangular reinforcements near the flanges. Horizontal and vertical elbows have the same structure, differing only in the plane where the airflow turns after installation.

Specification and Model Table

The table below shows the classification and configuration of square elbows, with cross-sectional dimensions matching rectangular ducts.

Classification	Turning Direction	Configuration
Horizontal Elbow	Horizontal Plane Turning	Optional Flow Guide Vanes
Vertical Elbow	Vertical Turning	Optional Flow Guide Vanes
Angle	90 Degrees / 45 Degrees	Custom Made

Product Features

The PP fire-retardant fabricated square elbow offers smooth turning and flexible dimensions, making it a matching turning component for rectangular corrosion-resistant ducts. Key features include:

PP plates bent and welded, acid and alkali-resistant with self-extinguishing properties
Available in horizontal and vertical angles, custom-made on-site
Internal flow guide vanes reduce turning resistance and noise
End square flanges for easy connection to rectangular ducts
Matching welds with square ducts ensure uniform system corrosion and fire protection performance
Outer wall ribs maintain cross-sectional stability under negative pressure
Compatible with square tees and square-to-round transitions for complete network connections

Material	PPs Flame Retardant Boards
Processing Technology	Panel splicing
Section Shape	Rectangle
Elbow Angle	90 degree / 45 degree customizable
Steering Form	Horizontal bending / Vertical bending
Guide Vane Our guide vanes are designed for optimal fluid flow management in industrial	Optional Configuration
Connection Method	Square Flange
Flame Retardancy	Self-extinguishing
Corrosion resistance performance	Acid and Alkali Resistant Salt
Strengthening Method	Back Reinforcement Rib for Elbow
Plate Thickness	Select by cross-section

Application Industries

Rectangular duct elbows for laboratory fume hood exhaust
Horizontal turning of wall-mounted rectangular ducts in electroplating workshops
Up-and-down bending of wide flat ducts in factory ceilings
Square duct elbows for exhaust in semiconductor factory interlayers
Elbows for connecting vertical shafts to horizontal square ducts
Corrosion-resistant ducts requiring small-radius turns in confined spaces
Rectangular ducts with flow guides for high airflow turning sections

Typical Installation Locations

Square elbows are installed at nodes where rectangular ducts change direction, commonly found at pipe corner turns along walls, intersections between vertical and horizontal pipes, and bending points to avoid beams, columns, and equipment. Horizontal elbows are used for horizontal turns, while vertical elbows are used for vertical bends. The flanges at both ends of the elbow connect to the square duct. Elbows near fan inlets/outlets and high-flow sections are preferably equipped with flow guide vanes.

During installation, ensure the elbow orientation aligns with airflow direction. Flange gaskets must be sealed, and bolts tightened evenly. The elbows and connected fittings are supported by hangers; flanges should not bear the weight of the pipes or flow guide vanes. Small-radius elbows have high resistance, so where space permits, larger radius elbows or those with flow guide vanes should be prioritized to reduce system resistance and operating noise.

Before installing square elbows, verify cross-sectional dimensions, turning angles, and horizontal/vertical orientation. For elbows with flow guide vanes, note the airflow direction markings. Flanges must be centered and tightened before securing the hangers. The back of the elbow and flow guide vanes are prone to wear and dust accumulation. Hangers should be positioned near the elbow's center of gravity. During operation, inspect flow guide vane fastenings and wall dust accumulation. In negative pressure systems, promptly reinforce and weld leaks if suction collapse or air leakage is detected.

When airflow changes direction at a bend, the velocity distribution is uneven between the outer and inner sides. The inner side is prone to forming eddies and flow separation, resulting in significant local resistance and noise, which is more pronounced at high airflow and high velocity. Flow guide vanes divide the air duct into several smoothly curved branch ducts, guiding the airflow to turn uniformly, which can significantly reduce the bend resistance coefficient. They also reduce wear and vibration on the outer side of the bend, showing notable effectiveness in large-section, high-velocity rectangular ducts. For small-section, low-velocity bends, the inherent resistance is limited, and flow guide vanes can be omitted to reduce costs and machining difficulty. Whether to install flow guide vanes and the number of vanes should be determined through resistance calculations based on velocity, cross-sectional dimensions, and deflection angle. For bends with flow guide vanes, the airflow direction must be noted—the flow curve should align with the direction of turn; installation in the opposite direction will be counterproductive. The ends of the flow guide vanes must be securely welded to the wall panels to prevent loosening during operation, which could generate noise.

The distinguishing basis is the plane where the airflow changes direction after installation. Horizontal elbows cause the duct to turn left or right within a horizontal plane, with the side plates of the elbows placed horizontally; vertical elbows cause the duct to bend up or down, with the duct turning within a vertical plane. Although their processing structures are similar, their installation directions and side plate stress differ, making them not easily interchangeable. When ordering, it is essential to specify on the drawing whether it is a horizontal or vertical elbow, left or right turn, upward or downward bend, as well as the elbow angle to avoid directional errors that could lead to on-site installation issues. For ducts installed against walls or beams, the relationship between the elbows and the wall or beam bottom must also be noted. Elbows with flow guides also require the indication of the turning plane. Before installation, verify the elbow direction against the drawing and on-site layout to ensure the curvature center and airflow direction align before positioning, which can prevent the need for a full rework.

With a large radius of curvature, the airflow transition is smooth, resulting in low resistance and noise, but the elbow occupies more space and consumes more materials. With a small radius of curvature, the installation is compact and material-saving, but the airflow transition is abrupt, leading to increased resistance and noise. When space permits, using a larger radius of curvature is beneficial for energy saving and reducing fan load. When space is limited, small-radius elbows can be used, and the resistance can be compensated by adding guide vanes. In engineering practice, the radius of curvature is typically selected as a certain multiple of the duct side length to balance installation space and system resistance, avoiding an exclusive pursuit of either large or small radii. For high-speed, high-capacity duct sections and elbows near the fan, the radius of curvature should be prioritized. Low-speed branch ducts can be appropriately reduced. During selection, the layout space, air velocity, and noise reduction requirements should be comprehensively considered, and resistance calculations may be necessary for critical elbows when required.

Cannot be directly connected, as the rectangular and circular cross-section shapes are different, and the flanges are also different, making it impossible to achieve a sealed connection. Rectangular elbows can only be connected to rectangular ducts or square fittings via square flanges, while round elbows are connected to round ducts. When converting between rectangular and circular pipes in the system, a square-to-round transition fitting should be installed between them, and then the elbows and pipe sections corresponding to the respective cross-sections should be connected. Attention should also be paid to smooth transition of the cross-section at the conversion point to avoid sudden expansion or contraction, which increases resistance and noise. When ordering, select elbows and transition components based on the actual cross-section of each section. For nodes with frequent use of both square and round sections, the manufacturer can provide integrated processing of transition-shaped elbows with built-in transitions. Using soft connections or variable-diameter hard connections for square-round cross-sections on-site will cause flow deviation and air leakage, and should not be used.

When dusty or liquid-containing airflow changes direction, particles and droplets are easily thrown to the outer side of the elbow due to inertia and adhere to it. Liquid and mud may also accumulate at the bottom of the horizontal elbow. When handling dusty, sticky, or liquid-containing gases, inspection ports or drain ports can be installed on the outer wall and bottom of the elbow to facilitate regular cleaning. The design of the internal pipe velocity should not be too low to maintain a certain self-cleaning ability and reduce particle sedimentation. The plastic inner wall is smooth, with lower adhesion for debris compared to metal, but regular inspection should still be conducted during maintenance to check for fouling and wear on the elbow. Accumulated dust and liquid should be cleaned promptly, and it is necessary to verify whether the drain port is unobstructed and whether the elbow orientation is reasonable. Elbows near dust sources and mist segments can have their outer walls thickened or be made of wear-resistant materials to extend service life.

For custom elbows, the following parameters are required: rectangular duct cross-sectional dimensions (length x width), elbow angle, turning direction (horizontal left/right turn or vertical up/down flip), flange type and dimensions, whether to include flow-directing vanes and the number of vanes, sheet thickness and flame retardancy requirements, as well as on-site installation space and curvature radius limitations. Providing pipeline layout drawings or on-site measured dimensions allows the manufacturer to proceed with cutting, reducing on-site modifications and ensuring first-time installation. For elbows attached to walls, beams, or avoiding equipment, note the clearances to building structures and the curvature center positions. For flanged elbows, specify whether the two ends of the flanges conform to the standards of adjacent fittings. Complete parameters and clear directions are essential to ensure the elbow curvature, flow-directing vanes, and interface dimensions match the site, avoiding rework upon arrival due to directional or dimensional discrepancies.

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