Seamless aluminum tubes
Extruded aluminum pipes are pipes, which are made by hot extrusion. There are also cold-formed pipes (they are also called "cold-drawn pipes"), are first compressed by hot pressing, and then bring them to the predetermined size by cold-drawing through one or more mandrels.
Seamless pipes and "seam"
Extruded aluminum pipes are divided into simple pipes (gunpowder pipes) and seamless pipes.. Term “welded pipes”, which is widely used for a steel pipe, for aluminum pipes do not use. The thing is, that the steel pipe has a pronounced seam weld, and that of the aluminum "seam" pipe this seam implicit, hidden. And not an ordinary welding – owed, gas or electric, and extrusion, i.e. takes place directly in the die under high pressure during extrusion.
For this reason, sometimes clearly "seam" pipe, e.g. coiled tubing length over a kilometer, advertise as seamless pipe, what, of course, can not be.
AND, really, difficult to distinguish visually seamless and "seam" aluminum tubes. However, they have serious differences, and the choice between them depends on, the purposes for which the pipe will be used. In the regulatory and technical literature, such "seam" aluminum pipes are often called structural pipes (structural tubes and pipes).
How to make seamless pipes
Seamless tubes are manufactured mainly by two methods. The first method consists in forcing (extrusion) a hollow aluminum ingot through a die and mandrel of a special press at a high temperature.. In another method, a solid ingot (billet) is first pierced on a press using a special mandrel - the so-called "needle" – and then out of the hollow ingot are already compressed tube also, as in the first method (figure 1).
No matter, which of the two methods is made pipe, it really will not have any weld. it, by the way, making it ideal for anodizing and other ways of decorative surface finish.
Figure 1 – Seamless pipe extrusion principle 
The advantages of seamless pipes
The advantages of seamless pipes are as follows:
- no seams, which is very important for their application under high pressure;
- more uniform appearance anodized surface, especially for thick-walled pipes;
- no welds, which could diverge at a deformation of the pipe, for example, flattening or distribution;
- increased structural strength.
Structural aluminum tubes
"Seaming" manufactured on conventional pipe extrusion presses on special matrices, so-called port-hole or bridge matrices. A solid aluminum ingot (billet) is pushed (extruded) through such a die, which requires significant press forces and high billet temperature (Figure 2)
During such compaction the preform is divided into two or four of aluminum flux, which converge together and then welded together under high pressure in a so-called welding chambers matrix. Traces of these "weld" seams can be seen on the pipes after they have been anodized or etched (Figure 3).
Figure 2 – Porthol pipe extrusion principle 
Figure 3 – Welds in a square tube bag 
Advantages of structural (seam) pipes
The advantages of structural (seam) pipes include:
- the ability to provide tighter tolerances for wall thickness and ovality;
- the ability to apply mnogoochkovye matrix for small diameter pipes, which increases productivity and reduces the cost of the pipes.
The use of seamless aluminum tubes
Applications of seamless aluminum pipes:
- pipes for liquids and gases under high pressure;
- high-strength pipes;
- pipes with high quality appearance of the anodic oxide coating.
Gauge aluminum tubes
Aluminum tubes - seamless and construction - made square, rectangular and round in a wide range of the outer diameter or the circumscribed circle. Durability depends pipes aluminum alloy, and wall thickness dimensions of the tube.