Extrusion is a process used to create objects of a fixed cross-sectional profile, of solid round, square or rectangular shapes, to L shapes and T shapes, tubes and many other different types. Metal is pushed through a die of the desired shape using either a mechanical or hydraulic press, resulting in the finished product. The cavity in which the raw material is pressed is lined with a wear resistant material which can withstand the pressure that is created when the material is pushed through, making extrusion possible without deforming or tearing the metal.
Aluminium extrusion is generally used in the manufacture of windows, doors and balustrades, but is also found in thousands of other items like vehicle parts, truck trays, boats and other marine products and refrigeration, etc to name a few.
Two advantages of this technique over other manufacturing processes are its ability to create very complex cross-sections, plus being able to work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms finished parts with an excellent surface finish. Extrusions often minimise the need for secondary machining. They are not of the same dimensional accuracy or surface finish as machined parts, however, the process produces a wide variety of cross-sections that are hard to produce cost-effectively using other methods.
Extrusion may be continuous (producing indefinitely long material), or semi-continuous (producing many pieces). The minimum thickness of steel is about 3mm, whereas aluminum and magnesium is about 1mm. The extrusion process can be done with the material hot or cold.
Metals that are commonly extruded:
* Aluminium is the most commonly extruded material and can be hot or cold extruded
* Brass is used to extrude corrosion free rods, automobile parts, pipe fittings, engineering parts
* Copper pipe, wire, rods, bars, tubes, and welding electrodes
* Lead and tin pipes, wire, tubes, and cable sheathing
* Magnesium is used in aircraft parts and nuclear industry parts, and is about as extrudable as aluminum
* Zinc rods, bars, tubes, hardware components, fittings and handrails
* Steel rods and tracks -Usually plain carbon steel is extruded, but alloy steel and stainless steel can also be extruded
* Titanium is often used in aircraft components including seat tracks, engine rings, and other structural parts.
Clean Metals for Recycling
The cleaner that a metal is when it’s taken into a scrap metal yard to sell, the better price it will fetch per kilo, as foreign matter is costly to clean off, so this product will always be penalised accordingly in terms of the price. By this we mean no concrete, screws, glass, paper or any other foreign material attached.
All the metal we buy is processed by cleaning any non-metallic off it as required, cutting it into smaller pieces, and then it is put through a baling press to maximise the weights for export to South East Asia, where it will be melted down and manufactured into new products.
The Extrusion Process
The process begins by heating the material (for hot or warm extrusion). It is then loaded into the container for pressing. A dummy block is placed behind it where the ram then presses the material to push it out of the die. Afterward, the extrusion is stretched in order to straighten it. If higher quality properties are required then it may be heat treated or cold worked.
Cold extrusion is done at or near room temperature. Advantages of this over hot extrusion are the lack of oxidation, higher strength due to cold working, closer tolerances, good surface finish, and fast extrusion speeds if the material is subject to heat for a short period.