Compression Mold

NOCENTE has extensive technical expertise in compression molds used for producing parts from composite materials, rubber, or silicone.

Unlike injection molds where the plastic is injected into a cavity under pressure, in compression molds, the material is placed in the cavity before being compressed under pressure.

Main Elements of a Compression Mold:

Mold Plates:
Compression molds are typically composed of two mold plates, upper and lower, which close together to form the cavity where the material will be compressed and shaped.

Mold Cavity:
The mold cavity is precisely machined to define the geometry of the part to be manufactured. It is designed to allow uniform material filling and withstand the mechanical stresses generated during the compression process.

Heating/Cooling System:
Compression molds are equipped with heating and cooling systems to control the mold’s temperature during the compression process. This ensures optimal thermal conditions for the material’s curing or vulcanization.

4. Application of Pressure and Heat:

• Pressure: High pressure is applied by the hydraulic or mechanical press to compact the material. Typical pressures vary based on the material and part size, usually between 5 and 50 MPa.
• Heating: Heating elements integrated into the mold plates increase the material temperature. Typical temperatures range from 150°C to 200°C for thermosetting resins.
• Curing: The combination of heat and pressure initiates the thermosetting material's chemical crosslinking, transforming it from a plastic to a rigid state.

5. Pressure and Heat Maintenance:

• Curing Cycle: Pressure and heat are maintained for a set time to ensure complete material curing. The cycle time depends on the part thickness and material type, usually from a few minutes to over an hour.
• Parameter Control: Control systems continuously monitor and adjust temperature and pressure parameters to ensure the final product's quality.

6. Cooling and Mold Opening:

• Cooling: After curing, the mold is cooled to a safe temperature to solidify and stabilize the part. This can be achieved through internal or external cooling circuits.
• Opening: The press releases pressure, and the mold halves are separated to allow part ejection.

7. Part Ejection:

• Ejectors: Pins or ejection plates are activated to push the finished part out of the mold cavity. Ejectors must be designed to avoid damaging the still hot and fragile part.
• Inspection: The part is inspected for defects such as burrs, bubbles, or inclusions, and corrective actions are taken if necessary.

Hot Compression Molding: This variant involves preheating the material before placing it in the mold, reducing cycle time and improving material flow.

Vacuum-Assisted Compression Molding: This method uses vacuum to compact the material in the mold cavity, reducing air bubbles and part defects.

• High Mechanical Strength: Compression molded parts typically exhibit high mechanical strength, characterized by properties such as tensile strength, compressive strength, and flexural strength. This attribute is due to the uniform distribution of fibers or fillers within the polymer matrix, resulting in a reinforced and robust structure.
• Dimensional Precision: The compression process offers high dimensional precision, allowing tight tolerances on part dimensions. This is crucial in many applications where precise fit is necessary for the assembled parts' proper functioning.
• High-Quality Surface Finish: Compression molds produce parts with a smooth and uniform surface finish. This quality is achieved through carefully machined mold cavities and controlled pressure and temperature conditions during compression.
• Environmental Resistance: Materials used in the compression process can be formulated to offer exceptional resistance to high temperatures, aggressive chemicals, humidity, and other harsh environmental conditions. This makes compression-molded parts suitable for a wide range of industrial and specialized applications.
• Reinforcement Integration: Compression molded parts can be reinforced by incorporating fillers or reinforcements such as glass, carbon, or aramid fibers. These reinforcing materials enhance the parts' strength and rigidity, making them ideal for applications requiring high structural performance.