Cold rolling process, also known as cold pilgering or tube rocking, this process reduces the tube sizes across three dimensions: outside diameter, internal diameter and wall thickness. The cold rolled or cold-pilgered steel tube is a product with small dimensional variations and high-level surface qualities. Owning to the stress pattern, the cold rolling process is also an option in manufacturing non-ductile steel tube and pipe.

The cold rolling process is that the hot-rolled steel tubes are forged and elongated over a stationary, tapered mandrel by two rolls with ring dies of a corresponding pas design which reciprocate back and forth over the stock. This rolling action is imparted by a rack and pinion arrangement in which the pinions are rigidly connected to the pilger rolls, so causing them to rotate as the rolling stand traverses to and from. The rolling stand motion, and thus the longitudinal travel and rotation of the rolls, is powered by a crank drive.

The pass design of the two rolls consists of a circular recess, corresponding to the cross section of the steel tube, which tapers over a certain portion of the roll circumference to provide an ideal, continuous transition to the finished tube diameter. Consequently, as the rolls move forward and backward, the steel tube is formed in the desired manner. An essential aspect of the process lies in the fact that elongation of the steel tube to produce the finished tube is performed by simultaneous reduction of the diameter and the wall thickness. This is aided by the shape of the mandrel which tapers from the steel tube inside diameter to the finished tube inside diameter. Following a forward and backward rolling cycle, the rolls release the blank which is then advanced by a certain, infinitely variable feed value. The corresponding material volume is then elongated with the subsequent forward and backward rolling cycle executed by the stand.

As the steel tube is advanced, it is also rotated by a certain angle to achieve a perfectly circular cross section as the material is forged to the finished tube dimensions.

The pass length determines the length of steel tube which is rolled with each forward stroke of the stand. The portion of the roll containing the pass may take the form of either a half-round die or a ring die. The half-round die with its approx. semi-cylindrical design and short pass (arc length up to 180°) is a characteristic feature of short-stroke mills. Nowadays, however, it is the long-stroke mills which dominate, and these with their ring dies offer longer working passes (arc length up to 300°) while operating at the same high rotational speeds. As a result, they attain higher levels of productivity, more favorable deformation results, improved surface quality and more dimensional precision in the finished steel tube.