Compression

BASIC EQUIPMENT

It is usually recommended a press force of 1000 tons per square meter of moulded part for SMC/BMC/CSMC materials although with “Low Pressure” formulations, less tonnage is required. Press closing speed and parallelism control are very important to obtain the best moulding performance. Air extraction systems to control styrene emissions are recommended.

The moulds, generally made of forged steel, must be either chromated or surface treated to reduce wear, and designed to be electrically, oil or steam heated to 130 – 160ºC. The design and construction of a good mould plays a decisive role in ensuring good moulded part quality. Knowledge about or experience with SMC/BMC/CSMC is required in order to build the mould that best suits the production process. For Class A surface quality it is usually recommended a chrome plated tool with vacuum assistance. To reduce porosity on the part surface, In Mould Coating (IMC) can be applied. This technique involves reducing the moulding pressure during the cure process and injecting a special sealant coating on the appearance side of the part.

Cutting table, weighing machine and fixtures adapted to work with SMC/CSMC rolls, MegaRolls or boxes are necessary. Fixing rig for deflashing operations and cooling rack for moulded parts are sometimes needed. Other secondary operations such as drilling, routing, etc. are easily performed on SMC/BMC/CSMC parts and can also be fully automated.

Depending on moulding volume, almost complete automation of the process can be made.

SMC/CSMC COMPRESSION MOULDING PROCESS

1.- SMC/CSMC Cutting: the cutting operation is usually done manually with a template and a math knife by the press operator, although some high-volume applications are automated.

2.- SMC/CSMC Charge: each part requires specific weight, size and shape of SMC/CSMC cuttings to fill properly the cavity.

3.- SMC/CSMC Placement: SMC/CSMC cuttings are properly distributed and placed on the heated mould surface.

4.- Compression moulding: after charge placement, the mould is then closed and the SMC/CSMC material compressed during a determined cycle time. Cure time depends on the thickness of the part, the temperature inside the mould and the specific formulation used.

5.- De-moulding: after curing, the mould is opened and the part is ejected, normally with the help of ejector pins.

6.- Removal, deflashing, secondary operations and cooling down: some care must be used during part removal to avoid stressing the part. Upon removal of the part from the mould, trimming of the edge flash is necessary. Other secondary operations such as drilling, routing, etc. are easily performed on SMC/CSMC parts and can also be fully automated. Due to special geometries and to avoid problems such as deformation and waving, many SMC/CSMC parts are placed under pressure whilst cooling down.

BMC COMPRESSION MOULDING PROCESS

1.- BMC Charge: each part requires specific weight and shape of BMC to fill properly the cavity.

2.- BMC Placement: the BMC is properly distributed and placed on the heated mould surface.

3.- Compression moulding: after charge placement, the mould is closed and the BMC material compressed during a determined cycle time. Cure time depends on the thickness of the part, the temperature inside the mould and the specific formulation used.

4.- De-moulding: after curing, the mould is opened and the part is ejected, normally with the help of ejector pins.

5.- Removal, deflashing, secondary operations and cooling down: some care must be used during part removal to avoid stressing the part. Upon removal of the part from the mould, trimming of the edge flash is necessary. Other secondary operations such as drilling, routing, etc. are easily performed on BMC parts and can also be fully automated. Due to special geometries and to avoid problems such as deformation and waving, many BMC parts are placed under pressure whilst cooling down.