Extrusion
Rodrigo Santos Andrade, 15044874, Faculty of Science and Engineering, Materials Processing, M4!4"
Introduction
Extrusion is a common process used to produce shaped materials with use of raw sources such as polymers, composites, etc. Usually products like pipes, sheets, wires, plastic bags come from extrusion process which depends of parameters that will define the mechanical properties of the final product such as velocity, cooling time, rate, etc. An extruder consists of three main sections (igure !"# eed, $ompression and %etering, that allow the material to flow into a desired shape through a die. In the feed section the polymer is introduced through a hopper into the first section of the screw, whereas the raw polymer is going to fulfil the spaces on the screw lead, which is small sections between each flight. ollowing the feed, the polymer then is melting down in the compression &one by consecutives frictions and electric source to the final section, the metering &one. 'he final section is responsible for homogeni&ing the final polymer and direct the flow to a die which will shape the desired material.
Figure 1: Extruder sections.
'he extruder screw is designed to develop the pressure reuired to pump the molten polymer through the die, which also acts on the screw. )ince the thrust bearing mechanism supports the drive mechanism into which *ts the shank of the screw, the thrust+bearing mechanism resists the axial thrust exerted by the molten polymer on the screw. ressures of up to - psi can be developed in many extruder operations. )ome polymers contain unreacted volatile monomer, moisture, and entrapped gases, which might emit during the extrusion process and potentially contribute to poor product uality. )ome extruders are provided with vents to remove these volatiles from the melt before it reaches the die. 'he vent is a hole in the barrel about screw diameter si&e, and located about three+fourths of the distance from the feed throat to the front of the barrel. In some cases, a vacuum is attached to the vent to facilitate gas removal. 'he screw for a vented extruder, referred to as a two+stage screw, has a special design. 'he screw section under the vent has a deep channel. 'he section of screw before the
vent can be considered a normal screw with feed, transition, and metering sections. 'he section following the vent consists of a short transition &one and a metering section. 'he channels of the metering section after the vent are deeper than those of the metering section before the vent. 'his, coupled with the relatively higher channel depth under the vent, means that the channel is partially *lled at and beyond the vent section and aids gas removal.
%aterial and %ethods An Extruder /avis+)tandard 0$-1 (%E)A" was used in this experiment which consists four electrical heaters around the barrel and three around the die. olypropylene was used following the !+2A3 directories for in4ection processing. All the mechanic aspects are shown in 'able !. Table 1: %achine specifications. D= barrel diameter
0.0254 [m]
Ꝋ = helix angle
!5.51 678
P= pitch
.-19 6m8
= length !" metering #!ne
.- 6m8
h= channel depth
.- 6m8
$= material% &i%c!%it'
! 6a.s8
( !" PP = p!l'pr!p'lene den%it'
: 6kg;m<38
)p = pre%%ure di""erence bet*een the "r!nt and rear !" the metering #!ne
eual !;3 of ressure
e= "light +and *idth
.3!51 6m8
c= "light land clearance
.1 6m8
Ꝋ = helix angle
.3! 6rad8
A tutor explained all the settings and the machine functionality, furthermore presenting tests and concepts about the process. All the data was collected for further discussions on the sub4ect.
=b4ective 'he aim of this experiment is to provide understanding about Extruders, the concepts, parameters and directories in the extrusion process.
>esult and /iscussions
ive machine settings were used in the experiment, changing between the velocity, pressure and ?aul off time as shown in 'able -. Table 2: %achine )ettings.
Scre# S$eed %RPM& 1 / " 4 5
"0 "" " " "
Pressure %'ar& 0.1 / /. /. /.
(aul )* %++in& 1 1 1 1./ 1.4
#eig-t 1+ %g& /7.!5 "0.7/ ""." /.8 /"
'he information was collected through 'able - and then calculations were made to obtain the screw velocity and the mean velocity as shown in 'able 3 and 9. Table ,# )ettings analyses in )I measurement.
Scre# S$eed %RPS&
$ %Pa&
2olu+e %+3"& $er +
ti+e 1+ %s&
Pressure %Pa&
0.5
10000
""""."
".1E05
0.0
0.55
/00000
.7
".4E05
0.0
0.
/0000
8.7
".7E05
0.0
0.
/0000
8.7
".0E05
50.0
0.
/0000
8.7
/.E05
4/.!
Table 4: )crew velocities.
Mean elocity %+s& 0.00!0 0.0100 0.010! 0.010! 0.010!
%+s& 0.0181 0.01!! 0.0/17 0.0/17 0.0/17
1 / " 4 5
@ith the velocity, the dragging time, leakage, and pressure were calculated using the Euation !., as shown in the 'able 1. Table 5# /ragging time, eakage and pressure.
6 6 6 6 6
drag drag drag drag drag
1 / " 4 5
9.2E-07
1.0E-06
1.1E-06
1.1E-06
1.1E-06
6 6 6 6 6
lea lea lea lea lea
1 / " 4 5
1.1E-08
2.2E-07
2.9E-07
2.9E-07
2.9E-07
6 6 6 6 6
$res $res $res $res $res
1 / " 4 5
8.2E-09
1.6E-07
2.1E-07
2.1E-07
2.1E-07
'hen the actual and theoretical flow were calculated and discussed as shown in 'able B.
'able B# )crew flow.
)etting ! 3 9 1
'heoretical low :.!E+5 :.:E+5 !.!E+B !.!E+B !.!E+B
Actual flow 1.-E+5 1.5E+5 B.-E+5 1.:E+5 B.E+5
Error 99C 93C 9-C 91C 91C
'he extrusion velocity has significant role on the thickness of the final product, as shown in 'able 3 and 9, different velocities were evaluated and more thickness were presented in materials which higher velocity. urthermore, pressure and rotational area were increased. $onseuently providing more cooling time and wider products. 'he thickness response is duo basically to faster cooling throughout the contact with the water, therefore giving the material dense alignments with good mechanical properties in the opposite side of the chain alignment and good elastic stress through the alignment.
ressure, cooling time, ?aul off, and velocity can be change to provide several settings to a wide range of polymer products. 'herefore, pipes need to have specific settings for a desire mechanic properties, the thickness can be promoted by a series of changes among these three variables, pressure for more contact area, velocity for thickness and cooling time for shape and mechanical resistance.
As can be seen in 'able B and 1, the theoretical flow is different than the actual flow due to disturbances, process called backflow, leakage and dragging time. 0ackflow happens along the extrusion process which an amount of raw material come back to screw due to exaggerated pressure, as same as leakage that occurs with loss of mass throughout the system. ?owever, this variables present small amount and cannot be seen directly during the process, but impact considerably in the final flowrate.
$onclusion 'he experiment showed the aspects and functionality of the extrusion process giving understand of its concepts, parameters, properties that need to be taken in consideration and its applications in the materials processing. /uring extrusion process it is important to know the polymer characteristics and behaviour. Also, variables such velocity, pressure and cooling have a strong significance in the properties in the final product.
