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Two-stage granulation of engineering thermoplastics |
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| WEIMA is presenting at PLAST’06
(14-18.2.2006, Milan) a further development of a two-stage processing plant with
features that include both a primary as well as a secondary granulator (photo).
The plant is used for economic granulation of engineering thermoplastics such as
ABS, PA, PBT, PC, POM, PPA, LCP etc., especially also of glass fibre reinforced
grades, in the form of heavy start-up waste lumps or large volume surplus
production material with large dimensions. |
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With two-stage granulation,
the material to be granulated is pre-granulated in a robust WLK type single
shaft primary granulator to particle size of approx. 40 mm and then granulated
further to final particle size of approx. 3-10 mm by a NZ type downline
secondary granulator, specially designed for secondary granulation of
pre-granulated material.
More efficient production process with two-stages – lower noise level
Grinding mills require continuous, well dosed feeding for trouble-free
granulation and this is often difficult to guarantee manually. Should overdosing
occur, it often leads to an uneven granulation process, taking place in waves
and accompanied by a high level of noise, as a result of which there may be
accumulation of material or thermal degradation of the material being granulated,
due to friction. Furthermore, higher sensitivity to disturbing materials will be
observed, as well as generally higher blade wear, involving frequent changing of
blades.
In contrast to this, two-stage granulation enables discontinuous feeding of the
primary granulator, whereby the hopper serves as a buffer zone. The entire
production process is significantly optimised by this way of material feeding,
as the operating staff does not have to constantly operate the granulator, but
can be employed for other tasks.
The pre-granulated granulate is now well fed to the NZ type secondary granulator,
that is controlled by a stop-and-go switch. The arrangement of the two
granulating units can be made here by a choice of one above or after the other.
The secondary granulator works on the cutting mill principle and has been
designed specially for pre-granulated granulate. It has much smaller dimensions
compared with the conventional type of such granulators, whereby less overall
drive power is needed. Quiet running at a rotation speed of approx. 450 min?1
without disturbance takes place, due to the even feeding. The noise level
arising when such a granulator is used for secondary grinding of pre-granulated
material is also much lower compared with single-stage processing at the same
rotation speed (n = 450-500min-1).
The plant is characterised in particular by optimised blade life, also when
granulating reinforced plastics, filaments, etc. This is possible on account of
the use of tempered metals for the blades, as well as their shape.
Number of characters (with spaces): 2,900
Caption: Two-stage granulation plant with a WLK single shaft granulator and NZ
type secondary granulation equipment, arranged one after the other
(Photo: WEIMA Maschinenbau GmbH, Ilsfeld)
PLAST’06, 14-18.2.2006, Milan, Hall 15, Stand C43 |
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| © WEIMA Maschinenbau GmbH · September 2008 |
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