EQUIPMENT
FOR GENERAL USE:
1.
Resin
mixers
2.
Impregnation
equipment
3.
Vacuum
equipment
4.
Presses
5.
Miscellaneous
equipment
1.
Resin
mixers:
Resin
mixing equipment runs the entire range from the bent rod in the hand drill
motor to the continuous vacuum deaerated, proportional pump, in-line mixer.
The
type of mixing equipment depend on the type of mixing manufacturing operation
e.g. short runs of resin mix employs propeller type mixers. Some other typical
mixers are lightening portable drum mixer, converted bakery dough breakers and
other types of rotary and planetary paddle mixers.
For
high production moulding and encapsulation, a metered, shot dispensing mixing
equipment is used to
a.
Eliminate
pot life problems
b.
Provide
shot weight control
c.
Allow
multi-station dispensing from a single system
d.
Improve
house-keeping.
For
continuous laminator or extruder, an in-line, proportional metering pump system
is used to
a.
Get
higher running speeds with hotter catalytic system
b.
Provide
steady controllable flow
c.
Provide
uniform mixture
For
boat and other large area of hand lay up or spray up components, a pressure
pot, spray mixing unit is used because of their compatibility with the rest of
the processing equipment and the ability to deposit a relatively large volume
of resin mix over extensive surfaces rapidly.
Regardless
of the system used, they must be accompanied by the mix and/or the base resin
if high quality end product is to be attained.
2.
Impregnation
equipment:
Different
equipment used for impregnation have basically the same operating principle but
they vary widely in the specific details. The four common preimpregnated form
of reinforcement are fabrics, rovings, mats and chopped fibers.
Impregnation
of sheet material (fabrics, woven roving and SMC material) produce usually a
B-staged material or SMC. While the impregnation of BMC material (roving as
continuous fibers or as chopped fibers) may or may not result in B-staged
stock.
The
impregnation equipment basically consist of
a.
Unwind
stations for PE support films (top and bottom)
b.
An
unwind station for reinforcement
c.
Impregnating
area where the resin is applied
d.
A
compacting area
e.
Oven
curing tunnel or tower for B-staging
f.
Rewind
station where the laminate is wound.
However
for production of chopped fiber SMC, the sheet is formed at the machine and the
impregnation is somewhat more complicated.
Application
and control of resin:
It
varies widely from station immersion and squeeze rolls to doctor blade
techniques and many forms of roll coating. Complex control and read out system
must be used in the B-staging area because proper temperature zoning and
control is extremely critical to achieve quality and reproducibility. Many
types of heating, depending on local economics, are used like gas, electricity,
steam etc.
Impregnation
of continuous fiber roving:
Here
the fibers are simply run through a resin bath, then through squeeze rolls or a
compaction die and then the fibers are directly applied to the part.
Preparation
of premix BMC:
It
consists of mechanically mixing chopped fibers, resin, catalysts, fillers, and
other additives by various methods. One method employs a water jacketed chamber
and spiral or sigma mixing blades and is used for batch preparation. Such a
system contains automatic weighing and feed of the material. Continuous mixing
and extruding equipment is also used. Where a rotating screw similar to the
conventional extruder is used except that the L/D ration is less to minimize
the glass fiber degradation. Automatic feed and metering mechanism assures a
steady, proper flow of ingredients to the mixer. The product can be a putty
like rope which then can be simply cut to length for moulding, thus eliminating
the weighing operation.
Other
continuous system for premix include:
a.
Chopping
of the impregnated roving and then pelletizing, then running resin and
reinforcement through meshing gears.
b.
Chopping
the roving and impregnating the fibers on a belt.
3.
Vacuum
equipment:
To
choose the type of vacuum pump for a reinforced plastic plant, the specific
operation must be determined e.g. In plants for vacuum bag lamination, small
individual pumps are preffered than a central system because the pump can move
with the job. While in a plant where primary de-aeration or vacuum impregnation
is used, a central system with large receiver is desirable. In any case,
precautions should be taken to insure adequate trap capacity between every job
and the pump otherwise the system will not function for long time. Even with
the best trap and filter system, some of the resin reach the pump in vapour
form. The floating eccentric vane type of cylindrical pump can tolerate this
type of service better.
4.
Presses:
Specialized
presses for the reinforced plastic differ from most other types of press in
that they have relatively low ram forces compared to their platen area. However
the premix moulders are looking for increased tonnage and faster closure speeds
and the military job shops, moulding ablative components for rocketry use
extremely high moulding pressures on outside components.
5.
Miscellaneous
equipment:
Depending
on the particular process being used, all or only part of the following
equipment can be used:
a.
Various
capacity scales for weighing the ingredients
b.
Several
types of fiber cutters
c.
Spray
equipment
d.
Polishers
e.
Rollers
Barcol hardness tester.
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