Today - Polyurethane Association of India

PU
Today
Technical Article
foaming station, thus requiring an
almost automatic adjustment of the
jig’s walls, to be performed quickly.
The foaming concept had to be rethought,
as well as the design of the
required tool.
The same approach had to be followed
for the chemical side, for the very good
reason that a major change in foaming
technology would not be adopted by
the appliance manufacturers if the
obtained savings were not more than
substantial in terms of foam’s lambda
value, demolding time and molded
density. Here, too, a major amount
of R&D work was demanded to the
chemical specialists.
The V.A.I. Project
Cannon approached this project
– named V.A.I. (Vacuum Assisted
Injection) – using the human, financial
and technical resources available
in their two Divisions involved in
refrigerators manufacturing: Cannon
Afros for the metering and mixing
equipment, and Cannon Crios for the
cabinet’s polymerization and handling
solutions. A team of specialists
identified a number of technical
problems, and soon started to suggest
various hypothetically viable solutions,
to be ground tested in Cannon R&D
laboratories. The development work
took several months.
After a number of unsuccessful
attempts with available formulations
modified on purpose, a new,
dedicated chemistry was developed
by Dow. Cannon in the meantime
designed the first industrial solution
for the production jig.
The V.A.I. Jig construction
The new jig has the same functionality
and movements of a standard jig but
28 p o l y u r e t h a n e s t o d a y
its lateral sides, the upper plate
which holds the plug and the top and
bottom walls are fitted with special
seals that, when the jig is locked,
provide an airtight cavity (Picture 6).
The vacuum is applied through the
upper plate. The main difference
Picture 6 – The Cannon V.A.I. foaming jig
with a standard polymerization jig
is the use of a sliding plate, called
pallet, where the back wall of the
fridge rests. This pallet is sliding in
and out from the jig for the cabinet’s
loading and unloading operations.
It is not recirculated around the
plant and thus can be permanently
connected to a hot water circuit for a
very efficient thermostatization.
The V.A.I. module:
Productivity/investment
optimization
An industrial foaming plant based
on V.A.I. jig is typically composed of
eight jigs placed side-by-side, each of
them served by one loading and one
unloading conveyor (Picture 7). The
two automatic devices travel above
these conveyors: the loader picks the
empty, warm cabinet coming from
Picture 7 – A typical foaming plant with
eight Cannon V.A.I. foaming jigs
the pre-heating oven (on the far right
of the plant) and carries it towards
the jig that has produced the latest
cured cabinet. The unloader picks it
from the pallet where it is carried,
and moves to the left of the plant to
the discharge area. In the meantime
the loader moves right over the pallet
and unloads on it the empty cabinet,
which immediately is brought in
the waiting jig. The cycle starts, as
described before. Productivity of
this configuration can be up to two
cabinets per minute.
V.A.I. – Main Advantages
Several innovative features provide a
number of interesting advantages:
l Faster demolding time, up to 50%
less than with conventional foams
l The system is suitable for difficult
cabinet geometries: even the
combined use of VIP (Vacuum
Insulated Panels) is possible, since
the foam filling operation is much
easier than with a slow, conventional
formulation.
l k-factor values of the foamed
refrigerators are very low, due to the
finer cell structure and the very even
distribution of densities across the
entire cabinet.
The Rotojig Development
In order to reduce the service time
to get full advantage of this new
fast curing formulation, Cannon
developed a new solution for the
d e c e m b e r 2 0 1 1