An Overview of the Rotary Pierce Process
Rotary piercing is an effective process that is widely used among metal manufacturing companies. The metal manufacturers use rotary piercing to create very high quality seamless metal tubing that other industries can use them for machining parts and other uses. The resulting tube does not have micro-cracks in it as most other tubing gains through simpler forging processes, so this tubing can be used to transfer very low-molecular-weight fluids through it without leaking. There are two methods of performing rotary piercing: The Mannesmann Process and The Stiefel Process.
In the simplest form of the process, Mannesmann Rotary Piercing consists of two convex-shaped rollers that are placed at a slightly smaller distance apart from each other than the diameter of the resulting tube. The rollers are tapered, meaning they are not horizontally parallel, however they are a few degrees twisted from each other’s axes to help provide rotation. They rotate in the same direction, while the shaft rotates in the opposite direction. A shaft of very hot metal (in many cases, titanium) is then pushed between the two rotating rollers. Once the shaft reaches the convex-shaped section of the rollers, it then becomes compressed and fissures begin to form on the outer surface of the shaft. These fissures are formed in a circumferential pattern due to the tapered orientation of the rollers, and normally would cause the structural integrity of the tubing to become greatly decreased.
At the same rate, a mandrel (hollowing dowel) greets the shaft of hot metal at the exiting half of the convex section of the rollers. The mandrel itself must be the same diameter as the inside of the tubing, because it serves to hollow out a previously solid shaft. The mandrel begins hollowing out the shaft, but also serves to apply inner pressure to fuse the fissures that were formed by the rollers. This strengthens the tubing and also makes it very solid and dense, having very few stress points and also not allowing materials of low molecular weight to seep out through any parts of the tube.
Once the entire shaft has been pushed through the rollers and mandrel, it is then cooled to room temperature. To reduce the amount of fissures that form at this stage of manufacturing, at first the metal is allowed to cool several hundred degrees Fahrenheit in the air, and is then dropped in water to cool the remaining amount of heat until room temperature. Remaining changes and adjustments are made without heating the tube up to thousands of degrees again.
The other form of Rotary Piercing, which is called the Stiefel Process, is very similar in fashion to Mannesmann Rotary Piercing. The process is the same, although conical disks are used in place of a convex surface. This allows the manufacturer to make larger-diameter tubing. Many titanium manufacturers use these two methods to create high quality pipes for industrial scenarios, and even offer these pipes in different grades and alloys of titanium as well.
