A Simplified Model for the Melting of Polymer Pellets under Compression in a Twin-Screw Extruder
Plastic energy dissipation (PED) is an important mechanism involving the melting of polymer in a twin-screw extruder. In the present study, the melting behavior of polymer pellets under compression is studied by a simplified model with the finite element method, based on the fact that mechanical energy from the deformation of a single pellet is converted into heat energy. The model shows that the heating of the pellet is not uniform. Under compression, the contact area of the pellet yields first, and the deformation in the pellet depends on the compression ratio and properties of the pellet. The simulated results show that the temperature in the volume around the line passing through the contacting point and the center of the pellet is higher than the temperature further from the contact area.
Theoretical and Experimental Investigations of the Melting of Pellets in Co-Rotating Twin-Screw Extruders
Abstract Knowledge of the plasticizing behavior in tightly intermeshing, co-rotating twin-screw extruders is of crucial importance for assessing the compounding process. Experiments were conducted on a laboratory extruder in order to establish the parameters that influence the melting process. Solidified samples of material were taken from the screw and microtome cuts produced from the plasticizing section. These were then assessed on the basis of image analysis. This visualization of the solid and molten phases which are present simultaneously together with the distribution of the two phases made it possible to quantify the reduction that occurs in the amount of solid material over the length of the screw configuration employed. A model is additionally presented for the calculation of the melting lengths and the melting profiles. This works on the basis of individual particles which are uniformly dispersed in the polymer melt. Allowance is made for the temperature increase in the solid material conveying section. A comparison of calculated and experimentally determined melting lengths revealed a satisfactory level of agreement.
STUDIES ON TERRESTRIAL CONTAMINANTS OF METEORITES
During t h e l a s t ha l f d e c a d e a n unpara l le led upsu rge h a s t aken p l ace in t h e s tudy of meteor i tes , e s p e c i a l l y t h e ca rbonaceous chondr i tes . S c i e n t i s t s from all ove r t h e world, employing t h e newes t a n d most s e n s i t i v e an a1 y t i c a l t ec hni q u e s , i n v e s t i g a t e t h e ch e m i c a l composition of t h e o rgan ic mate t ia l found in t h e s e meteor i tes . In t h i s way they a r e trying to de te rmine t h e phys ica l c o n s t a n t s of t h e meteor i tes and e s t a b l i s h , on t h e b a s i s of minera logica l and petrolog ica l s t u d i e s , t h e cha rac t e r i s t i c s of t h e environmental condi t ions f r o m which t h e s e s t o n e s or ig ina ted and to desc r ibe and ident i fy cer ta in mic ros t ruc tu res which abound in s o m e of t h e s e ca rbonaceous chondr i tes . A l l of t h e s e research i n t e r e s t s a r e d i rec ted towards o n e pa r t i cu la r problem, t h e def in i te so lu t ion of which may indeed have revolutionary e f f e c t s o n ou r c o n c e p t s of t he universe. T h e ques t ion is whether or not t h e s e meteor i tes conta in t r a c e s of ex t ra t e r r e s t r i a l l i fe , t hus proving tha t some kind of biota eve r e x i s t e d o ther t han on t h e ear th , o r if a l l of t h o s e f ea tu res tha t t end to subs t a n t i a t e t h e prev ious ly mentioned h y p o t h e s i s a r e only t h e r e s u l t of contaminat ion by te r res t r ia l matter. T h e impor tance of t h i s problem w a s emphas ized by Berna l (1961: 130) in t h e following way: “ T h e v i t a l ques t ion cou ld be s e t t l e d o n c e and for a l l if s p e c i f i c molecu le s s u c h a s porphyrins o r nuc leo t ides were found. A counter ind ica t ion a t t he moment is t h e extremely low phosphorous conten t of t h e meteorite.” S ince tha t s t a t emen t w a s made, porphyrins (Hodgson & Baker, 1964) a n d poss i b l y nuc leo t ides (Nagy et al., 1963a) have been ident i f ied f r o m t h e Orgueil meteor i te , but s t i l l t he q u e s t i o n of t h e e x i s t e n c e of extrat e r r e s t r i a l life is far from be ing proven. I t is clear from the a b o v e tha t o n e of t h e b a s i c problems tha t o n e faces in t h e s tudy of meteor i tes is tha t of contamination. In order t o e s t a b l i s h unques t ionably t h e e x i s t e n c e o r p a s t e x i s t e n c e of ex t ra te r res t r ia l l i f e through t h e s t u d i e s of meteor i tes , two primary q u e s t i o n s h a v e to b e dea l t with s imul taneous ly . O n e h a s to d e c i d e