Cold-finishing of tubes

Cold-finished tubes are fabricated to very strict size tolerances and have excellent surface properties. Rohrwerk Maxhütte employs two processes of cold forming to produce these tubes– cold pilger rolling and cold drawing. Before the cold forming process, the tubes undergo an appropriate heat treatment (including carburization if requested). Following this, the tube blanks are pretreated in a fully-automatic
hydrochloric-acid pickling facility to which a phosphate-treatment is attached. After cold forming, the finished tubes undergo a heat treatment, if requested, are then straightened in dressing and straightening lines, undergo nondestructive testing, are packaged by specific order, and released for shipping.

Cold pilgering

Cold pilgering involves rolling out the tube blanks over a fixed mandrel between two rollers arranged in a roll stand which are calibrated such that the sizing cross-section is reduced gradually over a predefined segment of the rolling circumference down to the diameter of the finished tube. During this rolling process, the tube blanks are reduced in outer diameter and wall thickness as required by the forward and backwards movement of the roll stand within the cold pilger rolling machine. At Rohrwerk Maxhütte, the tube blanks are rolled out in three cold pilgering systems to final dimensions ranging from 20.75 mm up to 120 mm in outer diameter.

Cold drawing

The tube blanks are swaged in preparation for the cold-drawing process, then a mandrel is inserted into the swaged tube. The gripper of the mandrel grips the swaged end of the tube and draws this with a maximum drawing force of 50 to through the drawing die. The drawing die determines the outer diameter of the finished tube, while the inner diameter is determined by the mandrel selected.

Heat treatment

Depending on requirements, the hotfinished and cold-finished tubes undergo a heat treatment. With our continuous furnaces, we are able to meet customer requirements in terms of microstructure, mechanical/technical properties, and surface quality.

The following annealing qualities are offered: