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11-07-2007

Laser-Armored Extruder Screws

Picture: Laser-Armored Extruder Screws

Picture: Laser-Armored Extruder Screws

Extrusion of thermoplastics containing glass fibers or other abrasive fillers results is increased wear along the outer edges of the screw flights. The gaps between the screw flight and barrel wall grow in size, and extruder output drops. This is usually combatted by armoring (hard-surfacing) the screw flights.

In close collaboration with a research institute, 3S GmbH Roitham/Austria is currently developing a new laser-assisted deposition welding technique for screw flights. Starting in mid-2008, it should be possible to use this process to hard-surface screws up to 6 meters in length with diameters ranging from 50 to 500mm.

In the so-called LASEX (Laser Armoured Screws for Extrusion) process, a laser beam is employed instead of an arc or plasma to melt the metal to be deposited. The technique achieves highly accurate surface contours. No extremely high ridges are deposited; edges can be formed precisely. Finish machining is thus simplified dramatically, especially when applying extremely hard filler materials such as tungsten carbide in order to achieve maximum wear resistance.

In addition, the laser permits a much smaller molten pool than other welding techniques, so that the generally undesirable mixing with the base material can be kept to a minimum. This translates into greater hardness and a longer service life for screws hard-surfaced in this way.

Moreover, screws that have been hard-surfaced by means of the LASEX process exhibit a reduced tendency to form cracks. Crack formation is a characteristic of very hard armored surfaces and leads to problems when changing colors in particular. Pigment residues collect in the cracks and continue to "bleed out" over a long period of time, creating streaks.

Dr.-Ing. Harald Sambale
sambale <AT> kunststoffe.de

contact
3S GmbH
Pühretstraße 3
AT 4661 Roitham
Tel: +43 7613 50-04
Fax: +43 7613 50-05

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