Gentle and smart forming

Date: 15/05/2012

by Markus Lichtl of Haas Group

15 May 2012 – The principle of extrusion can be easily explained: raw materials are put under pressure and forced through restricted openings (dies). It is the dies that give the product its basic shape.

There are two main types of extrusion, hot and cold. The principles of operation are similar in both types: raw materials are fed into the extruder barrel and the rotating screw(s) convey the food along it. As the mass is transported it gets increasingly compressed due to the screw flights becoming smaller.

If the food is heated the process is known as extrusion cooking or hot extrusion. The food is passed to the section of the barrel having the smallest flights, where it is forced through one or more of the dies at the discharge end of the barrel As the food emerges under pressure from the die, it expands to the final shape and cools rapidly as moisture is flashed off as steam.

Cold extrusion does not involve heating the raw material and there is no final expansion after passing through the die.

If another raw material (eg a filling like chocolate or jam for confectionery production) is added, no separate equipment is needed as it is possible to inject fillings during extrusion using special dies –the filling is ‘coextruded’.

Single or twin?

Depending on the method of construction, single or twin-screw extruders are used to build up the required pressure. Inside the twin-screw version, two screws rotate within a figure of eight shaped bore in the barrel. To be effective, these screws have to co-rotate in an intermeshing way. The degree of intermeshing of these screws can be changed to allow the processing of masses that would slip in a single screw. As a result, a wider product range is possible, but twin screw extruders also require a much more complex gearbox which leads to higher purchase costs.

Creative products

Apart from the extrusion temperature and the pressurisation of the mass, it is the die plate technology that enables confectionery manufacturers to create unique products setting them apart from their competitors.

Haas Meincke has implemented a technology called selective laser sintering (SLS). Used in other industries for the production of prototype parts, SLS was adopted to make it suitable for conventional production parts like extruder dies. Compared to standard milling, SLS allows the production of much more complex geometries and more detailed die plates. All in all, it´s the base for truly unique products with countless shapes and small details. Furthermore, using these dies neither affects product quality nor reduces production speed – they bring a series of advantages to the customer.

Extrusion vs dividing

Many producers use both dough extrusion and dough dividing interchangeably. From a technological point of view, extrusion is on a higher level than dividing. The latter is not a continuous process which makes it more difficult to control. Dividing is always linked to depositing which has to be the next step. This means that dough handling is smoother when using extrusion as the dough structure is less destroyed. For the customer, this means higher product quality that is constantly achieved. Dividers are not only said to require more maintenance work, but are also less reliable. Furthermore, extrusion technology is fit for future safety standards: During development, exposed moving parts were reduced to a minimum and compared to dividers, no knives are necessary.

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