By M.J. Stevens, J.A. Covas
ISBN-10: 9401042470
ISBN-13: 9789401042475
ISBN-10: 940110557X
ISBN-13: 9789401105576
This publication is meant to fill a spot among the theoretical reports and the sensible adventure of the processor within the extrusion of thermoplastic polymers. the previous have supplied a foundation for numerical layout of extruders and their parts, yet typically supply scant cognizance to the sensible functionality, in particular to the clash among creation expense and product caliber. In perform extruders are usually bought to accomplish a number tasks; however, the operator can have to take advantage of a desktop designed for an additional objective and never unavoidably appropriate for the polymer, technique or product in hand. The operator's adventure permits him to make sturdy product in unpromising situations, yet a great number of variables and interactions frequently supply it appears contradictory effects. The desire is this publication will supply a logical historical past, in response to either idea and adventure, for you to support the commercial processor to acquire the easiest functionality from his gear, to acknowledge its boundaries, and to stand new issues of self belief. arithmetic is used merely to the level that it clarifies results which can't simply be expressed in phrases; ifit is omitted, no less than a qualitative realizing should still stay. The approximate concept won't fulfill the purist, yet this turns out to the authors less significant than a transparent illustration of the actual mechanisms on which a lot of the polymer processing relies. M. J. STEVENS J. A.
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Additional resources for Extruder Principles and Operation
Sample text
E. 8% increase in pressure gradient. 1 gives for wall shear rates: . 'Yw2 R1 . 41) Then for equal flow rate Q, dP2 dL = dPI . (RI)4(RI)3n-3 dL R2 R2 = dPI . 3, dP2 dL = 1 102 dPI . e. 2% increase in pressure gradient. 3, respectively. For two capillaries of equal length in parallel, as in a multistrand die, the pressure drop and pressure gradient across each is the same. e. 6% reduction in flow rate. 75%. This is important with, for example, a common haul-off from a multistrand die. 1 gives: 1 R2 TJw2 2 .
This does not usually apply to piggy-back machines where the screw preplasticizing unit is separate from the injection ram, though a non-return valve and intermittent rotation are still usual. In modern machines under computer control, the screw speed and/or the back pressure against which the screw acts may be programmed to vary during the filling cycle. The first requirement is that the screw should refill the cylinder with the necessary volume of molten polymer within the cooling and 'dead' times of the particular moulding and machine, so that plasticization does not extend the overall cycle time.
3, dP2 dL = 1 102 dPI . e. 2% increase in pressure gradient. 3, respectively. For two capillaries of equal length in parallel, as in a multistrand die, the pressure drop and pressure gradient across each is the same. e. 6% reduction in flow rate. 75%. This is important with, for example, a common haul-off from a multistrand die. 1 gives: 1 R2 TJw2 2 . dP dL /w2 = - - - . - . - R2 . TJwl =/wl - - . 7): Therefore TJw2 = ~W2 = /wl or . /wl R2 RI (~W2) I-n /wl . e. 9% reduction in mean velocity - greater than in the Newtonian case.
Extruder Principles and Operation by M.J. Stevens, J.A. Covas
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