Extrusion

Commonly extruded materials include metals, polymers, ceramics, concrete, modelling clay, and foodstuffs.

In 1820 Thomas Burr implemented that process for lead pipe, with a hydraulic press (also invented by Joseph Bramah).

[1] The extrusion process is generally economical when producing between several kilograms (pounds) and many tons, depending on the material being extruded.

[1] Materials that are commonly cold extruded include: lead, tin, aluminium, copper, zirconium, titanium, molybdenum, beryllium, vanadium, niobium, and steel.

Examples of products produced by this process are: collapsible tubes, fire extinguisher cases, shock absorber cylinders and gear blanks.

It was originally intended primarily as a method for production of homogeneous microstructures and particle distributions in metal matrix composite materials.

First, the relative motion in the plane of rotation leads to large shear stresses, hence, plastic deformation in the layer of charge in contact with and near the die.

Because of the deformation heating, friction extrusion does not generally require preheating of the charge by auxiliary means potentially resulting in a more energy efficient process.

Like extrusion, metal is pushed through a die orifice, but the resulting product's cross section can fit through a 1 mm square.

"The small size of the die and ram, along with the stringent accuracy requirement, needs suitable manufacturing processes.

"[8] Additionally, as Fu and Chan pointed out in a 2013 state-of-the-art technology review, several issues must still be resolved before microextrusion and other microforming technologies can be implemented more widely, including deformation load and defects, forming system stability, mechanical properties, and other size-related effects on the crystallite (grain) structure and boundaries.

They vary by four major characteristics:[1] A single or twin screw auger, powered by an electric motor, or a ram, driven by hydraulic pressure (often used for steel and titanium alloys), oil pressure (for aluminium), or in other specialized processes such as rollers inside a perforated drum for the production of many simultaneous streams of material.

During extrusion the metal divides, flows around the legs, then merges, leaving weld lines in the final product.

[14] Accumulator water drives are more expensive and larger than direct-drive oil presses, and they lose about 10% of their pressure over the stroke, but they are much faster, up to 380 mm/s (15 ips).

This diameter, in turn, controls the size of the die required, which ultimately determines if the part will fit in a given press.

[1] The complexity of an extruded profile can be roughly quantified by calculating the shape factor, which is the amount of surface area generated per unit mass of extrusion.

[1] Metals that are commonly extruded include:[17] Magnesium and aluminium alloys usually have a 0.75 μm (30 μin) RMS or better surface finish.

The glass melts and forms a thin film, 20 to 30 mils (0.5 to 0.75 mm), in order to separate it from chamber walls and allow it to act as a lubricant.

A "caterpillar haul-off" (called a "puller" in the US) is used to provide tension on the extrusion line which is essential for overall quality of the extrudate.

The caterpillar haul-off must provide a consistent pull; otherwise, variation in cut lengths or distorted product will result.

This method is effective for large rubber pieces that are long and have a consistent shape, and the dies used in this process are inexpensive.

The main role of extrusion was originally developed for conveying and shaping fluid forms of processed raw materials.

Present day, extrusion cooking technologies and capabilities have developed into sophisticated processing functions including: mixing, conveying, shearing, separation, heating, cooling, shaping, co-extrusion, venting volatiles and moisture, encapsulation, flavor generation and sterilization.

The processed products have low moisture and hence considerably higher shelf life, and provide variety and convenience to consumers.

The dry mix is passed through a pre-conditioner, in which other ingredients may be added, and steam is injected to start the cooking process.

The cooking process takes place within the extruder where the product produces its own friction and heat due to the pressure generated (10–20 bar).

The main independent parameters during extrusion cooking are feed rate, particle size of the raw material, barrel temperature, screw speed and moisture content.

Hot melt extrusion is also utilized in pharmaceutical solid oral dose processing to enable delivery of drugs with poor solubility and bioavailability.

Hot melt extrusion has been shown to molecularly disperse poorly soluble drugs in a polymer carrier increasing dissolution rates and bioavailability.

The resulting fuel briquettes do not include any of the binders, but one natural – the lignin contained in the cells of plant wastes.