Pilgering is a metal-working process for reducing the dimensions of a metal tube. The two key components of a pilgering press (or mill) are a conical mandrel, which fits inside the tube, and ring dies which roll over the outside of the tube. This process reduces the diameter of the tube to the size of the mandrel and, at the same time, reduces the wall thickness of the tube from the action of the dies rolling over the outside of the tube along the mandrel.
Video on Pilgering mill die design(did it as AutoCAD project)
The name comes from the German word for pilgrim, “Pilger”.
Pilgrims used to approach a shrine slowly and then go backwards, without turning round, still facing the shrine. The same back and forth motion is used in the pilgering process.
It is used for cold-rolled tubes, which are the strongest type of tubing, used where high tensile tubing is needed, such as in the construction of high pressure water tube boilers. Of particular interest is composite tubing, where a corrosion resistant stainless steel alloy is cold rolled over a load carrying carbon steel alloy using the pilgering process.
This is used in the construction of corrosive atmosphere furnaces and heat exchanges, such as black liquor recovery boilers, waste heat boilers, syn gas coolers etc. The corrosion-resistant material is bonded to the load-carrying material by the cold rolling pilger process.