Compression Moulding
(SMC and BMC)

Compression moulding is a method of moulding in which the moulding material, generally preheated, is first placed in an open, heated mould cavity. The mould is closed with a top force or plug member, pressure is applied to force the material into contact with all mould areas, while heat and pressure are maintained until the moulding material has cured. The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms. Compression moulding is a high-volume, high-pressure method suitable for moulding complex, high-strength Advanced Basalt Fiber reinforcements. Advanced composite thermoplastics can also be compression moulded with unidirectional tapes, woven fabrics, randomly oriented fiber mat or chopped strand. The advantage of compression moulding is its ability to mould large, fairly intricate parts. Also, it is one of the lowest cost moulding methods compared with other methods such as transfer moulding and injection moulding; moreover it wastes relatively little material, giving it an advantage when working with expensive compounds. However, compression moulding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. Fewer knit lines are produced and a smaller amount of fiber-length degradation is noticeable when compared to injection moulding. Compression-moulding is also suitable for ultra-large basic shape production in sizes beyond the capacity of extrusion techniques. Materials that are typically manufactured through compression moulding include: Polyester fiber resin systems (SMC/BMC).

SMC and BMC are thermoset, that's means cross-linking materials where the cross-linking is irreversible. This is the base for the unique technical performance of these materials class.

The materials consist of the following components:

  • Resin
  • Shrink compensation
  • Fillers
  • Reinforcement
  • Additives
  • Curing system

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.

Sheet Moulding Compound (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 mould-able viscosity.

Sheet Moulding Compound (SMC) Application Process
Layers
Basalt Fiber Tech SMC Application Process©2015 - Designed by Lucas Sant'Anna
  • 1Basfiber® Rovings are placed in position to be chopped. The selected Tex of the roving and the length of the chopped strand depend on the proprieties that the final product require.
  • 2 Chopping Machine cut the fiber strands to receive the resin, raw Basfiber® Chopped Strands can be used. The chopped strand falls over a film where it receives a resin layer.
  • 3 The Resin Paste chamber injects the resin paste (resin, shrink compensation, fillers, additives and curing agent) to the strands and film.
  • 4 A Top Film Layer is applied to the bottom film layer which already impregnated with the resin and chopped fibers compound.
  • 5 The Moulding phase is when the composite already impregnated and heated gets the form of the desired material applying pressure and curing the material with a low temperature application.
  • 6 The Compaction system applies pressure in the resin and fiber compound, sandwiching it between the film layers, distributing the compound equally.
  • 7 The final Product is a roll of a pre impregnated sheet created from a chopped fibers and resin compound ready to be applied or stored.

Bulk Moulding Compound (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 fibers. The final mix and homogenization is made in different types of kneaders / mixers. BMC is compacted and packed in styrene tight bags in variable size, fitting all UP injection moulding machines stuffer units.

Bulk Moulding Compound (BMC) Application Process
Layers
Basalt Fiber Tech BMC Application Process©2015 - Designed by Lucas Sant'Anna
  • 1Basfiber® Chopped Strands is placed with resin, shrink compensation, fillers, additives and curing agent.The final mix and homogenization is made in different types of kneaders / mixers.
  • 2The Compound is placed in the stuffer which feeds the injection unit. For these thermosets non return valves are used. The Composite is injected into the closed hot tool, fills the cavities and polymerizes. After complete cure the parts are released hot.

Moulding is made in heated steel tools at temperatures between 125°C and 170°C. It is very important to take note of the set-up 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.

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Compression Moulding:

Compression Moulding:

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.

Compression Moulding:

Transfer moulding:

A 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.

Compression Moulding:

Injection moulding:

BMC or injection SMC are placed in the stuffer which feeds the injection unit. For these thermoset non return valves are used. The Composite 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.

Compression Moulding:

Injection Compression Moulding:

BMC or injection SMC are placed in the stuffer which feeds the injection unit. For these thermoset non return valves are used. The Composite 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.