Toll Processing describes an arrangement where the producer or owner of a metallurgical raw material, or of a partly or fully rolled metal product, sends this for further treatment by a third party prior to further in-house processing or sale. He receives back the original material in a different form, and while the third party charges for the work undertaken, it has no ownership rights.
In the steel industry, tolling work usually relates to additional rolling operations or the application of final coatings or special finishes. The term hire rolling is also widely used. In other parts of the metals industry, toll processing is used to transform raw materials into primary metal, and at times it has been particularly prevalent in aluminium (alumina smelted into slab or ingot). The decision whether to process steel in-house or externally can be down to a number of factors, including historical precedent, economics of production, or commercial confidentiality. And for information click and see this link.