TPT September 2012

Article

the tube to protect the inner surface against oxidation in the annealed area. After a short soaking zone, the red-hot tube is rapidly cooled below the oxidation threshold by special cooling elements in three stages. This cooling process also takes place with the exclusion of oxygen. Residual cooling of the tube to room temperature takes place in a water spray chamber. Induction tube hardening and tempering with EloMat TM multi-zone technology Innovative solutions from SMS Elotherm offer higher flexibility than conventional furnace systems for induction hardening and tempering of long products, especially with small batch sizes. In just a few minutes, tube hardening and tempering lines can be ramped up or down and reconfigured for the next material batch. In situations where materials of different sizes and batches with different steel grades need to be hardened and tempered at different temperatures on a daily basis, output capacity can sometimes be increased by more than half compared to hardening and tempering in a conventional furnace. In induction tube hardening and tempering systems, thermal energy is induced directly in the material to achieve maximum throughput for the entire range of tube products. This avoids lost time due to conductive heating, which requires longer process times. A significant feature of modern tube hardening and tempering systems is the high homogeneity of the tempered structure, with uniform Rockwell hardness (variation ±1 HRC or better) measured over the entire tube length.

Tube end heating prior to a sizing press

Due to the very short heating times achieved with induction heating, surface decarburisation does not occur and scale formation is minimal compared to furnace hardening. The negative effect of tempering brittleness with various material grades that are preferably used for hardening and tempering does not occur with induction technology. Precise process management with high reproducibility in conjunction with specific material handling during transport, induction heating with controllable multi-zone technology, effective quenching and a special cooling bed allow a high degree of tube straightness to be achieved after hardening and tempering. The straightness corresponds to that of the input material and usually does not exceed 2mm/m; sometimes it is even better. SMS Elotherm offers to customers complete quench & temper system solutions with comprehensive process expertise. Induction tube heating Induction heating processes have been the key technology for round tubes and tubular sections for decades. Cost-effective heating solutions for coating, bending and cutting have delivered an optimal performance in practice. Tube end heating before sizing or compression moulding in several steps is also a precise and cost-effective induction process. In cooperation with a renowned German customer, SMS Elotherm has developed a modern tube end joining technology and has already delivered the first production systems. Unlike conventional friction welding of round tubes, this new induction pressure welding method also allows pressure-welded joints to be made with oval or square tubes. The new process avoids irritating material bulging at the joint as commonly seen with friction welding.

Layout of a typical induction equipment for heat treating of tubes (Quench & Temper)

SMS Elotherm GmbH – Germany Email: g.ommer@sms-elotherm.com Email: d.schibisch@sms-elotherm.com

Seamless, thick walled tubes after the quench & temper process

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September 2012