Chemistry Reference
In-Depth Information
mation state characterized by the criterion (4.44), is reached in solid-phase
extrusion process.
At plastic or ductile deformation mechanism the value
d
c
can be deter-
mined as follows [15]:
2
.
(14.9)
d
=
c
3
y
(
-
y
)
At the criterion (4.44) fulfillment
d
c
=
d
f
= 2.87 and at l
>
3 and y = 0.78
according to the criterion (14.9). This corresponds well to the ductile defor-
mation achievement condition at y > 0.65 [15].
And at last, let us estimate the value of limiting extrusion draw ratio l
lim
,
which can be reached in solid-phase extrusion process, on the basis of con-
sidered above model. The extrusion draw ratio l there changed at expense of
different diameter dies usage and calculated according to the formula [18]:
2
b
d
l
=
,
(14.10)
2
d
d
where
d
b
,
d
d
are billet and calibrating die section diameters, respectively.
In its turn, the value y can be written as follows [11]:
d
-
d
b
d
y
=
.
(14.11)
d
b
Assuming the limiting value
d
c
= 3, from the Eq. (14.9) y = 0.79 and
from the Eq. (4.12)
d
b
= 4.76
d
d
can be obtained. Let us obtain the limiting
value l
lim
= 22.7 according to the Eq. (14.10). This value is close to limit-
ing values of l for considered extrusion mode, cited in Ref. [19], if a billets
preparation special methods are not applied.
Hence, the stated above results shown, that sharp structure change in sol-
id-phase extrusion process of polymerization-filled compositions UHMPE-
Al and UHMPE-bauxite is due to deformation mechanism change from brit-
tle to ductile one. In its turn, the indicated mechanism change is induced to
dissipative structures type spontaneous change at achievement of criterion,
when shape change cannot be compensated by volume change. The usage
of deformable solid body synergetics and fractal analysis methods allows to
estimate limiting draw ratio in solid-phase extrusion process [11].
The reduction of elasticity modulus
E
of oriented (extruded) amorphous
polymers in comparison with initial polymer is there main feature [20].
