|Posted by pvac.sales on June 14, 2012 at 10:55 PM|
PVAC (Polyvinyl Acetate) Application in Technology of SMC * BMC
SMC and BMC are thermoset, that means crosslinking materials where the crosslinking is irreversible. This is the base for the unique technical performance of these materials class.
The materials consist of the following components:
In difference to most other polymer materials the shrinkage can be controlled and adjusted very precisely by adding LS or LP additives. For highest precision and optimum surface qualities materials with negative shrinkage (= expansion) are composed.
Manufacturer of SMC
SMC composites are made from chopped multi end rowing strand sandwiched between two layers of film, onto the resin paste (resin, shrink compensation, fillers, additives and curing agent) has already been applied. The prepreg passes through a compaction system that ensures complete strand impregnation and makes a sheet wound into rolls. These are stored for pre maturing before moulding to allow the prepreg to thicken into a mouldable viscosity.
Injection SMC is after pre maturing cut into smaller, coreless coils and packed in styrene tight bags, fitting all UP injection moulding machines stuffer units.
Manufacture of BMC
BMC composites are made from a premix, consisting resin, shrink compensation, additives and curing agent which is compounded in special dissolvers, and the reinforcement, consisting of chopped fibres. The final mix and homogenisation is made in different types of kneeders / mixers. BMC is compacted and packed in styrene tight bags in variable size, fitting all UP injection moulding machines stuffer units.
Molding of SMC/BMC
Moulding is made in heated steel tools at temperatures between 125°C and 170°C. It is very important to take note of the setup instructions of each specific material due to the variety of formulations. All known processes are possible as the material will be tailor made for your specific process and application.
Layers of SMC or preformed pellets of BMC are placed into the heated tool. Through closing the tool the material fills the cavity and polymerizes. After complete cure the parts are released hot.
With compression moulding highest mechanical strengths can be achieved.
Preformed SMC or BMC is placed in the injection valve of the heated tool and is injected into the cavity after closing the tool. The material fills the cavities and polymerizes. After complete cure the parts are released hot.
Transfer moulding is used for multi cavity tools of thick parts with high requirements for strength.
BMC or injection SMC are placed in the stuffer which feeds the injection unit. For these thermosets non return valves are used. The Composit is injected into the closed hot tool, fills the cavities and polymerizes. After complete cure the parts are released hot.
Injection moulding is used for highest precision parts and complex geometries.
Injection Compression Molding
BMC or injection SMC are placed in the stuffer which feeds the injection unit. For these thermosets non return valves are used. The Composit is injected into the semi closed hot tool, fills the cavities and polymerizes. After complete cure the parts are released hot.
Injection compression preserves the fibres and improves the degassing of the cavities. The process is used for parts with high mechanical strengths.