Unison develops tube-bending cell for Rathgibson

Unison has developed a novel bending cell for tube and pipe manufacturer Rathgibson to serve the growing demand for U-shaped heat exchanger components.

A version of Unison's servomotor-based tube-bending machine uses a roll-forming tool to create custom-radius tubular parts under software control, eliminating much of the expensive tooling and set-up time conventionally required for this application.

The automatic bending cell is directly linked to the tube-manufacturing process at Rathgibson's Janesville, Wisconsin, facility.

At the start of the cell is a saw and in-feed conveyor.

Once a U-shape part is programmed by the operator or selected from a database of existing designs, the control program computes the length of tube required and issues a command to the saw.

The cut tube length is fed into the cell's conveyor system, and then accurately positioned for bending with the aid of laser reflection sensors.

Unison's tube-bending machine incorporates a special roll-forming tool.

Under software control, roll-form tools are accurately positioned to create the desired 'U' shape, with the correct bend radius and leg lengths.

As the bending machine can produce 'U'-shape parts with leg lengths of 15m or more, a swinging cantilever structure is fitted on the output section to support tubing as it progresses through the forming process.

Once the 'U' shape is formed, the cantilever gantry swings away, and the conveyor then lifts and tilts the tubing to free it from the machine and slide it laterally onto a second conveyor, which takes it onto the final annealing stage.

This sideways offloading action is said to cut cycle time significantly as it eliminates the need to drive the remaining 15m and more of tubing through the machine.

The novel action of the tube-bending cell allows Rathgibson to make the majority of parts for any heat exchanger using a single software-controlled tool, and in a single rapid stage of less than 10 minutes including annealing.

The innermost elements of the heat exchanger bundle, which have very tight radii, are bent on the Unison machine with the aid of conventional tube-bending dies.

The bending cell has allowed Rathgibson to offer a complete range of tubing for heat exchanger applications in the power generation industry and processing sectors such as chemical, petrochemical and food.

Rathgibson's choice of Unison's novel bending cell has resulted in considerable cost savings over a conventional tube bending machine, according to Unison.

It also provided a simple software set-up process that allows parts to be created easily by entering a few simple parameters, or repeated on demand by recalling an existing design from a database.

The software-based configuration also means that Rathgibson avoids the operational complexities associated with traditional batch-processing production techniques - where die-based bending machines are used to produce progressive batches of heat exchanger parts of different sizes.

As a complete 'U'-shape part can be sawn to length, bent and annealed in less than 10 minutes and both the tube mill and bending cell operators are located right next to each other, Rathgibson has complete control over the entire processing chain.

This avoids any issues that might result from using tubing with different material characteristics and ensuring that these large and difficult-to-handle components are fabricated right first time.

Rathgibson's 'U'-bend tubing cell is able to supply custom-bent heat exchanger elements using a large variety of tubing materials including all major stainless steel grades, numerous types of duplex stainless steel, super austenitic steel, and ferritic or super ferritic steel.

As the heat exchanger elements come direct from the tube mill, Rathgibson is able to supply detailed quality and traceability information as required.

The company's low-oxidation, acid-free annealing process also complies with the ASTM/ASME 688 and 803 Feedwater Heater specifications used in this application sector.

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