Fundamental of Manufacturing Processes CH.14

Calendering

- Rubber stock is passed through a series of gaps of decreasing size by a stand of rotating rolls - Rubber sheet thickness is slightly greater than final roll gap due to die swell

Molding Processes for Rubber

1. Compression molding (most important because of its use in tire manufacture) 2. Transfer molding 3.Injection molding - Curing (vulcanizing) is accomplished in the mold in all three molding processes

Shaping and Related Processes for Rubber Products

1. Extrusion 2. Calendering 3. Coating 4. Molding and casting

Roller Die Process

Combination of extrusion and calendering that results in better quality product than either extrusion or calendering alone

polymer matrix composite (PMC)

a composite material consisting of a polymer imbedded with a reinforcing phase such as fibers or powders

Filament winding

continuous filaments are dipped in liquid resin and wrapped around a rotating mandrel, producing a rigid, hollow, cylindrical shape

Pultrusion

similar to extrusion only adapted to include continuous fiber reinforcement

Miscellaneous for short-fiber PMCs

- Centrifugal casting - Continuous laminating

Closed-mold processes for continuous-fiber PMCs

- Compression molding - Resin transfer molding

Closed-mold processes for short-fiber PMCs

- Compression molding - Transfer molding - Injection molding

Fiber‑reinforced polymers (FRPs)

- FRP composites can be designed with very high strength‑to‑weight and modulus‑to‑weight ratios - These features make them attractive in aircraft, cars, trucks, boats, and sports equipment

Open-mold processes for continuous-fiber PMCs

- Hand lay-up - Automated lay-up

Processes for short-fiber PMCs

- Open-mold processes - Closed-mold processes - Miscellaneous

Processes for continuous-fiber PMCs

- Open-mold processes Closed-mold processes - Filament winding - Pultrusion - Miscellaneous

FRP shaping processes

- Processes for continuous-fiber PMCs - Processes for short-fiber PMCs

Extrusion

- Screw extruders are generally used - The L/D ratio of the extruder barrel is less than for thermoplastics - Typical L/D range = 10 to 15 - Reduces risk of premature cross‑linking - Die swell occurs in rubber extrudates - The highly plastic polymer exhibits "memory" - The rubber has not yet been vulcanized

Open-mold processes for short-fiber PMCs

- Spray-up

Vulcanization

- Treatment that accomplishes cross‑linking of elastomer molecules - Makes the rubber stiffer and stronger but retain extensibility

Miscellaneous for continuous-fiber PMCs

- Tube rolling

Common fiber materials:

- glass - carbon - Kevlar

Coating (Impregnating Fabrics with Rubber)

Important industrial process for producing tires, conveyor belts, inflatable rafts, and waterproof cloth