CRE WHEELS
Wheels for continuous rotary extrusion
A special method of metal extrusion is the continuous rotary extrusion process, also known as the “CRE” process. This continuous process utilises friction generated heat to plasticise the feedstock. It is mainly used for small and medium-sized profiles of aluminium and copper or its alloys.
The process starts with feeding wire rod into the groove of the wheel, which is supported by a solid pressure shoe. The wire rod usually has a diameter between 8 mm and 25 mm. The friction between the groove and the feeding wire rod produces a high temperature and simultaneously a high forming pressure. In the die chamber, an abutment protrudes into the groove of the wheel diverting the plasticised feedstock into the die chamber then leaving the die as a final shaped product. The process can also be carried out with metal powder fed into a suitably sized wheel groove.
The principal item of the plant is the wheel which is highly stressed due to high operational pressures and temperatures. In addition to the high dimensional accuracy of the wheel, the correct selection of the most suitable material and optimum hardness range is essential to achieve a good hot creep strength and to maximise life.
Rolls for cold pilger mills
In the cold pilger process, thick walled seamless tubes (hollow blooms) are finished to the required final size. The roll stand consists of two rolls that turn in reverse to the rolling direction. The roll profi le steadily reduces, in a taper, to the finished tube diameter. The tube is rolled over an internally located conical mandrel. It is essential that during the rolling of the hollow bloom down to the finished tube, a stretching of the diameter as well as a reduction of the wall thickness occurs. The process repeats itself cyclically until the entire tube has been finish formed. Depending of the type of mill, reduction is carried out using either a roll die jaw or a ring roll. Due to its higher production output and more favourable deformation ratios, long stroke pilger mills, utilising ring rolls, are mainly used today.
S+C manufactures ring rolls, to customers’ drawings and tables, for a wide range of sizes. In addition to the required high accuracy and quality of finish in the working zone, the selection of the optimum combination of material and hardening process are crucial for the product quality and the life of the rolls. Depending on the application, a selection of case hardening, through hardening and flame hardening tool steels are available.
