EQUIPMENT FOR GENERAL USE:
1. Resin mixers
2. Impregnation equipment
3. Vacuum equipment
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.
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
e. RollersBarcol hardness tester.