18 Profiles of Temperature and State of Cure Developed Within Rubber in Injection Molding Systems Downloaded by UNIV OF CALIFORNIA SAN DIEGO on November 18, 2014 | http://pubs.acs.org Publication Date: January 8, 1985 | doi: 10.1021/bk-1985-0270.ch018
A. SADR, R. GRANGER, and J. M. VERGNAUD Laboratory of Materials and Chemical Engineering, University of Saint-Etienne, U.E.R. of Sciences 23, Dr. Paul Michelon, 42023 Saint-Etienne Cédex, France
To reduce the time of cure cycle in processes of rubber injection molding, higher temperatures for vulcanization as well as for storage bulb are being used. Our purpose in this work was to determine the profiles of temperature gradients and state of cure developed through rubber sheets by using the kinetics of the cure reaction, the thermal properties of rubber and a convenient model. The kinetics of the overall cure reaction could be described by a single first-order reaction with a single activation energy, although vulcanization is a complex series of reaction. The calculation was solved applying an explicit method with finite differences, by taking into account the heat of the cure reaction and the heat transfer by conduction through the rubber and the mold-rubber interface. The effect of the values of the temperature of the mold and storage bulb on the profiles of temperature and state of cure developed within rubber was studied by considering rubber sheets of different thicknesses. Up to now the rubber industry has shown great interest i n the development of processes f o r faster vulcanization. Accordingly, higher temperature (1-2) for the mold and also the storage bulb are being used to reduce the time cycle of cure i n i n j e c t i o n molding processes f o r rubber. However, we believe that the best method of reducing the cure cycle without detriment to quality i s to ensure that the process i s properly carried out and stopped at the right time (3-4). Obviously, a s u f f i c i e n t knowledge on the time-temperature r e l a t i o n at any point within the rubber mass i s required to a t t a i n this purpose. Some early works (5-7) haw shown that the temperature gradients developed i n the rubber mass during vulcanization could be predicted by using the data of the cure k i n e t i c s and heat transfer. The extent of cure reaction could be determined by the balance of internal heat generation from the cure reaction, conduction through the rubber mass and the mold rubber interfaces. 0097-6156/ 85/0270-0279$06.00/0 © 1985 American Chemical Society
In Reaction Injection Molding; Kresta, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
280
REACTION INJECTION M O L D I N G The
purpose
of
this
work
t u r e s of mold and s t o r a g e molding process
of
rubber.
different
thicknesses
enthalpy.
The
method w i t h consists heat
a
could
for
The
series
be d e s c r i b e d by
activation
energy, as
show
that
important
study
was
sheets
the
values
parameters
for in
(6). of
Although
reactions
a first-order
shown
previously
tempera injection
performed by u s i n g a n d two
values
for
s o l v e d by a p p l y i n g an e x p l i c i t
differences
complex
to
are
rubber
p r o b l e m was
finite
of
is
bulb
rubber
(8),
the
two the
cure
numerical
vulcanization overall
reaction with
a
cure
single
(6).
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on November 18, 2014 | http://pubs.acs.org Publication Date: January 8, 1985 | doi: 10.1021/bk-1985-0270.ch018
THEORETICAL Mathematical
Treatment.
rubber
of
of
sheet
transient
The
thickness
heat
unidirectional was
t
heat
expressed by
flow
the
through
general
the
equation
conduction
3T dt
9x
\pC
3x /
PC
conduction heat by
taking
into
account
the
dt
reaction
heat
internal
heat
generation
from
and boundary c o n d i t i o n s
were
as
:
the
cure
reaction. Initial t
= 0
t
>
t
0 ^ x ^ £
0
>
x < 0
0
Ο
I
χ
