Tube rolling in heat exchangers: Best practices and key considerations
The expanding of tubes is an essential process step in the manufacture of heat exchangers, steam turbines, condensers, air coolers and boilers. Manufacturers must consider factors such as safety, speed, cost, required operator skills, repeatability and overall quality when selecting tube rolling machines and tools.
Importance of tube rolling
As a large number of tubes usually have to be rolled into a heat exchanger, condenser or boiler, it is crucial to use proven processes and high-quality tube rolling technology and tools for tube rolling. In this way, frequent and costly tool changes and damage to the tube to be rolled can be avoided.
The tube rolling process
During tube rolling, the tube is rolled using a tube expander so that the Tube inner diameter is enlarged. The tube wall is reduced by the expansion and pressed against the inside of the bore of the tube sheet. The percentage increase in the inner diameter of the tube from the point at which the tube comes into contact with the bore is called adhesive expansion. There are generally two types of rolling: Contact rolling and sealing rolling.
Contact rollings generally have an adhesive expansion of between 3% and 5%. Contact rolling is sufficient if the tube is only to be applied after orbital welding to prevent crevice corrosion. The rolling itself does not fulfill a sealing function.
Sealing rolls usually have an expansion of adhesion of between 15% and 20%. Sealing rolls have a sealing function and are generally used as the sole tube tube sheet connection. An exception to this is, for example, titaniumtubes, which must be roll-sealed before welding. It is important that the tubes are not over-rolled, i.e. the tubes are not widened so much that the molecules of the pipe material lose their cohesion. The pipe material then begins to flake, which can lead to leaks in the tube tube sheet connection.
Optimal equipment for tube rolling
The optimum equipment for expanding from tubes, in particular the equipment to be used tube expanderalways depends on the tube to be rolled and the conditions. In principle, however, at least one drive machine and one tube expander is always required. While there are tube expander are available in a wide range of sizes and designs, tube rolling machines are only available in pneumatic and electric versions.
Electric tube rolling systems
Electric tube rolling systems are characterized in particular by their wide range of applications, ease of operation and durability. They consist of the following elements:
Electronic tube expanding controller: Controls the drive machine and ensures compliance with the set adhesive expansion at expanding by precisely preselecting the cut-off torque.
Electric drive machine: Provides the rotary movement of the tool. High-quality Technodata-drive machines are characterized by their suitability for almost all rolling tasks and are optionally available with 42V protective voltage.
telescopic shaft: Provides the connection between drive machine and tube expander and enables maximum ergonomics and work safety thanks to the pull-out function and ball guide.
Assembly trolley: Transforms the electronic rolling-in unit into a "mobile rolling-in unit". Cardanic suspension and swivel-mounted boom ensure maximum ergonomics and flexibility.
The mechanical-hydraulic rolling-in system is a special type of electronic tube rolling-in system. This rolling-in technology, which is used in particular for the expanding of tubes made of high-quality materials such as titanium, consists of the drive machine and a hydraulic cylinder, which controls the feed of the tube expander is controlled. In addition, special 5-rollertube expander The rollers are arranged in parallel and also have a guide sleeve. This prevents damage to the inside of the tube and allows the operator to precisely control the rolling process.
Pneumatic rolling machines
Pneumatic rolling machines are characterized by their simple setup and quick operational readiness, as they only require an upstream maintenance unit in addition to the pneumatic drive machine . The disadvantage, however, is the limited range of application compared to the electronic rolling-in machine and the lack of a rolling-in controller for simple and precise control of the rolling-in process.
Best practices for tube rolling
Use high-quality tube rolling technology that enables high-quality and reproducible rolling results, is easy to operate and ensures ergonomic and safe working.
Only use tools tube expander with long tool life to minimize frequent tool changes and thus delays in the work process.
Use sufficient lubrication to reduce tool wear and prevent pipe damage.
Check the pipe hardness to avoid cracks and ensure the correct wall reduction.
Ensure that the tube ends is clean and aligned to achieve optimum results.
By following these best practices and understanding the material-specific requirements for wall reduction, manufacturers can ensure high-quality pipe joints and reduce the risk of leaks and the need for repairs.