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High-Efficiency Round-Bending Technology of Upper and Lower Chord Steel Pipes of Arched Trusses

High-efficiency round roll bending technology for steel pipe

The project involves a semi-circular steel pipe arch truss structure for a bulk cargo shed (Figure 1). The truss weighs 8.9 tons and is supported by concrete columns with a height of 3.800 m. The columns are spaced at 7.5 m intervals, and the shed has a total area of 16,576.96㎡. The truss is constructed using longitudinally welded steel pipes, with Q345BΦ194×6 and Φ194×7 pipes for the upper and lower chords, and Q235BΦ89×4.5 pipes for the web members. The spacing between the upper and lower chords is 1.6 m. The upper chord has a radius of 24.05 m and an arc length of 72.5 m, while the lower chord has a radius of 22.45 m and an arc length of 67.5 m. The stability of the spatial structure is ensured through the use of tie rods, vertical supports, and horizontal supports. The top elevation at the mid-span of the truss is 28.147 m.

High-efficiency round-bending technology of upper and lower chord steel pipes of arched trusses
Figure 1: High-efficiency round-bending technology of upper and lower chord steel pipes of arched trusses

Overview of Pipe Bending Solutions

There are various methods for pipe bending, and the proposed approach is to use a highly mechanized three-roll pipe bending machine. However, after conducting market research, it was found that the loading height of the bending machine is as high as 1.2 m, which is not conducive to the loading and unloading of steel pipes and may not be suitable for on-site conditions. To address this issue, the loading height needs to be reduced. The bending machine available in the market is designed to meet the requirements of different users, with comprehensive functionality and high automation, but it also comes with higher maintenance costs. Considering that the project requires a limited range of bending specifications in large quantities and does not require excessive functionality, it is more cost-effective to build a custom-made machine that can better meet the project’s needs. The bending process of a three-roll bending machine typically involves feeding the pipe into the machine, applying pressure and bending, and repeating this process until the desired bend radius is achieved. However, this process results in straight sections at both ends of the bent pipe, which cannot be directly used. Additionally, each pipe needs to undergo repeated rolling and bending to gradually check if the desired bend radius has been achieved, which is time-consuming and labor-intensive. To improve bending efficiency and achieve zero loss, a continuous bending process needs to be established, where the initial adjustment of pressure is made and subsequent pipes are connected using connectors to form a continuous pipe bending process without the need for frequent adjustments of the intermediate roll pressure.

Bending Machine Design

  • Three-roll rolling method is adopted, with two powered rolls and one pressure roll.
  • The reducer is mounted vertically, with the power unit positioned above and the rolling wheels below to reduce the loading height and facilitate loading and unloading of materials.
  • The design aims for simplicity, with a direct connection between the reducer and rolling wheels.
  • Considering the continuous forming process and the need for efficiency improvement, the feeding speed is reduced to a moderate level. A low-power, high reduction ratio power unit is selected. The chosen reducer is TBY 5527-1003-3KW/4P, which is paired with a speed control motor to further adjust the speed, control the output torque, and ensure successful trial production. It also meets the requirements for bending profiles and steel pipes with an I25 and Φ250 or smaller dimensions.
  • The height of the rolling wheel support is suitable, taking into account the side bending height of I25.
  • Since frequent adjustment of the pressure roll is not required in the continuous forming process, an existing idle screw jack can be used to further reduce costs.
  • Non-powered roller tracks are installed on both sides of the bending machine to facilitate loading and unloading.
  • The machine frame is made of -30 steel plate and I25 splicing welding to ensure the rigidity of the machine.
  • The rolling wheels are replaceable to accommodate various cross-sectional profiles for bending.

Continuous Bending Process

Profile bending machine for bending steel pipes

A simplified continuous bending process is designed using pipe connectors. The slight curvature discrepancy at the joints of the pipes makes the actual operation more convenient. By adjusting the intermediate roll pressure for the first pipe and consecutively bending subsequent pipes, the bending efficiency is greatly improved, resulting in zero loss.

Bending Form

Correction As the chord members are designed as longitudinally welded pipes, material deviations and welding stress can affect the bending process. Therefore, monitoring, inspection, and correction are necessary.

  • Strengthening the control of the procurement process to ensure that the purchased steel pipes meet the national standards regarding dimensions, weight, and other deviations.
  • Creating a reference mold for monitoring and making necessary adjustments during the bending process.
  • Inspecting and correcting each bent pipe on the inspection frame.
  • Employing thermal correction for areas with curvature deviations.


High-efficiency round-bending technology of upper and lower chord steel pipes of arched trusses

By building a custom-made profile bending machine and implementing a continuous bending process using connectors, the bending technique has been improved. The one-time adjustment and continuous bending process have significantly increased operational efficiency, ensured bending quality (Figure 3), and achieved zero loss, resulting in positive social and economic benefits.