analysis of forming geometrical macrostructure in walls of extrusion

analysis of forming geometrical macrostructure in walls of extrusion

Kompozyty 11: 3 (2011) 273-277
Tomasz Klepka1*, Jacek Nabiałek2
1 Politechnika
Lubelska, Katedra Procesów Polimerowych, ul. Nadbystrzycka 36, 20-610 Lublin
Częstochowska, Instytut Przetwórstwa Polimerów i Zarządzania Produkcją, al. Armii Krajowej 19c, 42-200 Częstochowa
* Corresponding author. E-mail: [email protected]
2 Politechnika
Otrzymano (Received) 25.03.2011
ANALYSIS OF FORMING GEOMETRICAL MACROSTRUCTURE IN WALLS
OF EXTRUSION PRODUCTS MANUFACTURED FROM POLYPROPYLENE
COMPOSITE FILLED WITH CaCO3
Extrusion products in the form of polymeric ducts are mainly manufactured in the process of single-screw extrusion, coextrusion and extrusion with the expansion of an extrudate wall under negative pressure in movable segments. Different
methods of forming the extrusion product allow one to obtain products with solid, cellular or corrugated walls. In addition, in
all the mentioned extrusion processes, it is possible to apply extra technological treatments enhancing a given quality which
might be significant in terms of the function to be fulfilled by the product or conditions of its use. Products obtained in this
manner from the material display special, extra properties enabling their application in the latest technological solutions.
At the moment, the greatest technical progress has been observed in optical communications technologies and it is in this sector that duct-shaped extrusion products have been applied most widely. They are laid in special concrete conduit installations
and subsequently, innerducts of smaller dimensions or directly teletechnical, power or optotelecommunication cables are installed inside them. Considering all this, it is required that the structures of modern extrusion products have good mechanical
properties. Less resistance to motion during the introduction of cables into the interior part of the extrusion product can be
obtained through the manufacture of its internal wall with a proper geometrical macrostructure in the form of special slide
ribs. Until present, extrusion products in the form of such ducts have been manufactured from high density polyethylene
(PE-HD), however, due to the need to obtain enhanced circumferential rigidity, other alternative polymeric materials, copolymers as well as calcium carbonate (CaCO3) or talc (Mg3(OH)2Si4O10) filled composites have been pursued. The article presents the patterns of changes in the rheological properties of propylene composites with different CaCO3 content during their
flow through the channel gap in the extrusion die. Numerical analysis was conducted with the use of the finite element method
(FEM) in the area between the core forming the slide ribs and a cylinder-shaped external wall. The material within the core
area flows through a specific number of macro depths whose shape corresponds to the shape of the slide ribs which are manufactured in the inner surface of the extrusion product. The ratio of rib height to wall thickness was 1:8. The rheological sevenparameter Cross-WLF model was used to analyze changes in the shear rate and viscosity of the material in a given section of
the extrusion die. The results for the filled polypropylene composite (PP + CaCO3) were compared to the results obtained for
a PE-HD without additives or fillers in the same processing conditions.
Keywords: composite of polypropylene with CaCO3, geometrical macrostructure, rheological properties, computer simulation
ANALIZA KSZTAŁTOWANIA MAKROSTRUKTURY GEOMETRYCZNEJ ŚCIANKI WYTŁOCZYNY
WYTWORZONEJ Z KOMPOZYTU POLIPROPYLENU NAPEŁNIONEGO CaCO3
Wytłoczyny będące w efekcie kanałami z tworzywa polimerowego wytwarza się głównie w procesie wytłaczania ślimakowego, współwytłaczania oraz wytłaczania z podciśnieniowym rozciąganiem ścianki kanału w ruchomych segmentach.
Różne metody kształtowania wytłoczyny pozwalają na otrzymywanie wytworów o ściance litej, porowatej lub strukturalnej.
Ponadto do wszystkich wymienionych procesów można stosować dodatkowe zabiegi technologiczne, poprawiające wybraną
cechę, ważną na przykład z uwagi na funkcje, jakie ma spełniać wytwór, lub warunki, w jakich będzie eksploatowany. Otrzymane w ten sposób produkty z tworzywa wykazują specjalne, dodatkowe właściwości, które pozwalają na stosowanie ich
w nowoczesnych rozwiązaniach technicznych. Obecnie największy postęp techniczny można zaobserwować w technikach optotelekomunikacyjnych i właśnie tam wytłoczyny kanałowe z tworzyw znalazły największe zastosowanie. Układa się je
w specjalnych betonowych instalacjach, a do nich wciąga się rurociągi o mniejszych wymiarach lub bezpośrednio kable teletechniczne, energetyczne lub optotelekomunikacyjne. Wszystko to powoduje, że nowoczesne konstrukcje wytłoczyn muszą
mieć dobre właściwości mechaniczne. Uzyskanie mniejszych oporów ruchu przy zaciąganiu do wnętrza wytłoczyny kabli
otrzymuje się, wykonując wewnętrzną jej ściankę z odpowiednią makrostrukturą geometryczną, w postaci żeber ślizgowych.
Dotychczas wytłoczyny w postaci kanałów tego typu były wytwarzane z polietylenu dużej gęstości (PE-HD), jednak z uwagi na
potrzebę uzyskania większej sztywności obwodowej poszukuje się również innych alternatywnych tworzyw polimerowych,
kopolimerów, a także kompozytów napełnionych kredą (CaCO3) lub talkiem (Mg3(OH)2Si4O10). W artykule przedstawiono
przebieg zmian właściwości reologicznych kompozytu polipropylenu z różną zawartością CaCO3, podczas przepływu przez
szczelinę w głowicy wytłaczarskiej. Analizę numeryczną prowadzono metodą MES, w obszarze pomiędzy rdzeniem kształtującym żebra ślizgowe a walcową ścinką zewnętrzną. Przepływ tworzywa w obszarze rdzenia przebiegał przy określonej liczbie
wgłębień, odpowiadających kształtom żeber ślizgowych wytwarzanej wytłoczyny. Stosunek wysokości żebra w odniesieniu do
grubości ścianki wynosił 1:8. Obliczenia prowadzono przy wykorzystaniu siedmioparametrowego modelu reologicznego
274
T. Klepka, J. Nabiałek
Cross-WLF, analizując rozkład zmian wartości szybkości ścinania oraz lepkości tworzywa na interesującym odcinku głowicy.
Wyniki otrzymane dla kompozytu (PP + CaCO3) porównano z wynikami uzyskanymi dla PE-HD bez dodatków i napełniaczy
w tych samych warunkach przetwórstwa.
Słowa kluczowe: kompozyt polipropylenu z CaCO3, makrostruktura geometryczna, właściwości reologiczne, symulacja komputerowa
INTRODUCTION
As a result of polymeric material processing, it is
possible to obtain products with precisely specified
qualities, properties and top-layer structure [1, 2]. Depending on the function and conditions of use, various
types of axisymmetric products in the form of ducts
such as innerducts, pipes, tubes, profiles with a surface
of different geometrical macrostructure (Fig. 1a) play
a significant role in the technology [3].
the manufacturing of modern duct structures from various types of materials; copolymers and composites.
These ducts and conduits may consist of a number of
layers of different materials bound by adhesion during
polymer processing or of material filled with a high
content of calcium carbonate (CaCO3) or talc
(Mg3(OH)2Si4O10).
a)
PROCESSING
b)
Fig. 1. Examples of polymer ducts: a) consisting of several layers, b)
with group of innerducts with smaller dimensions
Rys. 1. Przykłady kanałów z tworzywa: a) składających się z kilku
warstw, b) z grupą kanałów o mniejszych wymiarach
Those elements are connected into special duct-line
systems and used for the construction of different kinds
of power conduits, telecommunication or water supply,
heat or gas distribution. New structures made of this
kind of duct-shaped products manufactured from materials characterized by additional features such as e.g.
enhanced mechanical or tribological properties on
a demanded surface or a given area (Fig. 1b). The obtained enhanced mechanical properties in the major
duct enable the placement of a relevant system of specialized conduits of inferior resistance, such as: power,
telecommunication engineering or optical communications innerducts in its interior [4, 5]. This ensures their
long-term mechanical protection from being crushed or
resistance to the impact of the environment.
It is possible to receive specific mechanical properties and enhanced resistance to external factors during
Kompozyty 11: 3 (2011) All rights reserved
Considering the design requirements and specific
nature of processing in the extrusion line, this process
should run in specific conditions [1, 2]. Depending on
the given type and content of filler used in the material,
the conditions and processing shall be different, which
ultimately also affect the product properties [6, 7].
What is more, the required geometrical macrostructure
of the internal wall of the extrusion product in the form
of slide ribs, results in additional complications in the
manufacturing process. Due to the fact that literature
provides no data useful for tool design or any guidelines
regarding the dimensions of slide ribs, products of this
type should be analyzed via computer simulation. In the
case of manufacturing ducts made of polymeric material with ring-shaped cross sections, as a result of melt
flow, they acquire a shape determined by the geometrical macrostructure of the surface of the shaping core.
Thus formed, the slide ribs obtain dimensions which are
determined by the shape and dimensions of the core
macro depths, adjusted by shrinkage and the Barrus
coefficient [6, 8].
SIMULATION INVESTIGATION
In order to predict the properties of the extrusion
product, simulation investigation was conducted on the
laminar flow of the polymeric material in the section
between the core and the external cylindrical surface of
the channel gap. The extrusion product was 40 mm in
diameter; the number of formed slide ribs was 120 and
their height 2 mm. The finite element method was used
in the investigation. The computational model (Fig. 2)
was built out of tetrahedral finite elements, with a side
length of 1 mm.
The following conditions of extrusion were used:
plastic plasticized temperature T1 = 220°C, temperature
of the extrusion die T2 = 190°C and volumetric flow
rate equal γ = 45 cm3/s. The study was conducted with
Analysis of forming geometrical macrostructure in walls of extrusion products manufactured from polypropylene composite filled with CaCO3
modeled flows of the following materials: high density
polyethylene PE-HD (GeForce 7740 Hostalen F - Targor Company), polypropylene composite filled with
20% CaCO3 (GPP20CF57HBGY) and polypropylene
composites filled with 35% CaCO3 (GPP35CS7678)
Ferro Company.
275
a)
Fig. 2. Appearance and selected fragments of FEM model used in the
research
Rys. 2. Wygląd oraz wybrane fragmenty modelu MES zastosowanego
w badaniach
b)
In calculating the rheological model, a sevenparameter Cross-WLF (Cross, Wiliiams, Landel, Ferry)
was used [8-11]. The mathematical model describes the
rheological relation to equation (1) while the model
coefficients for the analyzed materials are shown
in Table 1. Viscosity plots have been presented in Figure 3.
η=
η0
 •
η γ
1 +  0•
 τ





(1−n )
(
(
)
)
 − A1 T − T ∗ 
η 0 = D1 exp
∗ 
 A2 + T − T 
and
(1)
c)
where:
T * = D 2 + D3 ⋅ p
A2 = A2~ + D 3 ⋅ p
•
with: η - viscosity, γ - shear rate, η o - zero viscosity,
T - temperature, p - pressure, n,τ *, D1, D2, D3, A1, A2 coefficients.
TABLE 1. Characteristics of test materials rheological model
coefficients
TABELA 1. Współczynniki modelu reologicznego badanych
tworzyw
Model coefficients
n
-
PEHD
PP + 20%
CaCO3
PP + 35%
CaCO3
0.5285
0.2974
0.3255
τ
[Pa]
8585.8
30397
22082
D1
[Pa·s]
5.72e+017
7.35e+014
1.86e+014
D2
[K]
153.15
263.15
263.15
D3
[K/Pa]
0
0
0
A1
-
35.27
33.986
31.161
A2~
[K]
51.6
51.6
51.6
Fig. 3. Viscosity plots: a) PEHD, b) PP + 20% CaCO3, c) PP + 35%
CaCO3
Rys. 3. Krzywe płynięcia: a) PEHD, b) PP + 20% CaCO3, c) PP + 35%
CaCO3
ANALYSIS OF SIMULATION INVESTIGATION
RESULTS
On the basis of the conducted calculations and finite
element analysis (FEM), a set of data was obtained
allowing us to present graphically the examined changes in the rheological properties during the melt flow
through the channel gap. The curves determined in
accordance with the Cross-WLF model enabled us to
prepare the shear rate and viscosity distribution of the
Kompozyty 11: 3 (2011) All rights reserved
276
T. Klepka, J. Nabiałek
analyzed materials. Sample results have been presented
in Figures 4 and 5.
a)
Shear rate
b)
c)
Fig. 4. Shear rate distribution during extruded plastics flow: a) PE-HD,
b) PP + 20% CaCO3, c) PP + 35% CaCO3
Rys. 4. Rozkład szybkości ścinania podczas przepływu wytłaczanego
tworzywa: a) PE-HD, b) PP + 20% CaCO3, c) PP + 35% CaCO3
a)
Viscosity
b)
CONCLUSIONS
On the basis of the duct analysis of forming geometrical macrostructure in the walls of extrusion products
manufactured from a polypropylene composite filled
with CaCO3, it can be concluded that in the examined
conditions, changes in shear rates for all the examined
materials along the channel gap are of a similar nature.
It is a consequence of processing all the examined materials under exactly the same conditions. Interesting
results have been obtained while comparing the changes
in the viscosity of the materials at different temperatures. For high density polyethylene, considerably differentiated viscosities in the area of the slide ribs in
relation to the main wall have been recorded. This state
of affairs will consequently lead to differentiation of the
macrostructure in both of the mentioned areas. This
phenomenon may be eliminated by changing the geometrical shape of the slide ribs, which the authors of the
paper shall attempt to prove in subsequent research. In
the case of polypropylene composites with the calcium
carbonate content, the changes in viscosity are much
less rapid. Therefore, it might be expected that filled
polypropylene lends itself better to the manufacture of
goods of this type. It should be noted however, that
extrusion products will have different properties at the
tops of the slide ribs than those in the main wall (Figs. 4
and 5). Differences in the forecast properties of the
extrusion products are clearly visible in plastics selected
for product manufacture, whereas the filler content of
20 and 35% in filled propylene is less significant for the
examined scope of changes.
With regard to the required complex geometrical
macrostructure, a number of simulations should be
conducted in order to determine the most efficient dimensions of slide ribs. This especially refers to the rib
shape, their number, dimensions (ratio of height to
thickness of the supporting wall) of the extrusion product with regard to the type of material and higher filler
content. Advances have taken place in simulation software, which offers increasingly wider possibilities of
predicting phenomena occurring during the processing
of polymeric materials and composites, and therefore
they can be used with success in this type of analyses.
Acknowledgements
An article written under the Ministry of Science and
Higher Education research project no. N N 508 486138.
REFERENCES
c)
Fig. 5. Viscosity distribution during extruded plastics flow: a) PEHD,
b) PP + 20% CaCO3, c) PP + 35% CaCO3
Rys. 5. Rozkład lepkości podczas przepływu wytłaczanego tworzywa:
a) PEHD, b) PP + 20% CaCO3, c) PP + 35% CaCO3
Kompozyty 11: 3 (2011) All rights reserved
[1] Sikora R., Tworzywa wielkocząsteczkowe - Rodzaje, właściwości i struktura, Wydawnictwo Uczelniane Politechniki
Lubelskiej, Lublin 1991.
[2] Rauwendall C., Polimer Extrusion, Carl Hansen Verlag,
Munich 1986.
[3] Sikora R., Klepka T., Przegląd konstrukcji rur optotelekomunikacyjnych z tworzyw, Projektowanie, stosowanie
i eksploatacja elementów maszyn i urządzeń. Politechnika
Częstochowska, Częstochowa 1996.
Analysis of forming geometrical macrostructure in walls of extrusion products manufactured from polypropylene composite filled with CaCO3
[4] Klepka T., Konstrukcje osiowo-symetrycznych wytworów o kształtach złożonych, Polimery 2008, 53, 5, 390-395.
[5] Kargin V.R., Gorshkov Yu S., Vol’nykh Yu A., Method of
fabricating multichannel pipes with longitudinal and helical
ribbing, International Journal of Mechanical Science 2000,
42, 2, p. 693-703.
[6] Jiang Z.Y., Tieu A.K., Lu C., Thermo-mechanical analysis
of ribbed strip rolling by a three-dimensional rigid–viscoplastic FEM. Jouranal of Materials Processing Technology
2002, 130, 20, 189-194.
[7] Lee K., Mackley M.R., The significance of slip in matching
polyethylene processing data with numerical simulation,
Journal of Non-Newtonian Fluid Mechanics 2000, 94, 2-3,
159-177.
277
[8] Ilinca F., Hetu J.-F., Derdouri A., 3D Modeling of Nonisothermal filling, SPE Technical Journals, Polymer Engineering and Science 2002, 42 4, 760-769.
[9] Nabialek J., Kwiatkowski D., Investigations of the plastics
flow during the injection moulding process selected results,
14-th International Scientific Conference AMME’2006,
Gliwice 2006, 225-228.
[10] Koszkul J., Nabiałek J., The influence of viscosity model on
the results of injection molding process simulation, 9-th
International Scientific Conference AMME’2000, GliwiceSopot-Gdańsk 2000, 311-314.
[11] Koszkul J., Nabiałek J., Viscosity models in simulation of
the filling stage of the injection molding process, Journal of
Materials Processing Technology 2004, 157-158, 183-187.
Kompozyty 11: 3 (2011) All rights reserved