The most common rubber manufacturing processes are extrusion, compression molding, injection molding and calendaring.
Rubber extrusion is the perfect choice to manufacture articles like seals, tubes, rods, and cable insulation or sheaths.
High throughput required by modern extrusion manufacturer is achieved with perfect balance of cure speed and flow properties.
Injection molding is ideal molding technique when large-volume serial manufacturing is required. Injection molding affords high quality part with high efficiency and short cycle times thanks to preheating of the compound during the plastification and flow throughout channels to the mold cavities.
Mixing compounds for injection molding requires a precise control of viscosity and reactivity. Cure speed is balanced to guarantee mold filling and minimize curing time. This is even more true today, with modern molds designed to maximize number of parts per shot and minimize wastes due to flashes and sprues.
Nowadays, automotive, aerospace and oil & gas industries do not tolerate any failure due to leakage of fuels, oils and fluids distribution circuits. This is possible only through high re-producibility of mixing and high consistency of properties of cured parts affording durable sealing properties.
Careful and continuous selection of raw materials allows for obtaining compounds with enhanced thermal and chemical stability that these markets pursuit.
Precise dosage and accurate choice of process-aids, accelerants, stabilizers, reduce mold fouling and minimize mold maintenance and blooming on parts.
Compression molding is still a popular manufacturing method of rubber goods due to easiness and versatility.
Although compression molding affords the least control of tolerance, any part with any size is virtually possible as long as clamp force is sufficient. Compounds often need to be preformed before being molded to decrease waste and increase dimension stability.
Compounds for compression molding need viscosity and plasticity suitable to little shear process and fast cure speed to minimize cycles.
By compression molding, the highest hardness parts are affordable, enabling the use of the most reinforcing fillers.
When compression molding is used to make big parts, precise control of lubricants and releasing agents are needed to avoid part ruptures when clamp force is released.
Transfer moulding is an evolution of compression moulding with enhanced precision. Rubber is placed in a reservoir pot on the mould and then distributed into several cavities through channels.
Compounds for transfer moulding combine low viscosity necessary to fill mould cavities and reduce clamp pressure with high cure speed. Indeed, transfer moulding is still little shear process and curing occurs only by thermal exchange of material with mould plates.
Calendering is an important industrial process where a rubber compound is formed to a continuous sheet or coated on a fabric. This is accomplished by forcing rubber compounds trough different roll gaps.
Calendering is essential process for the manufacturing of tyres, conveyor belts, sheets and hoses.
Compounds for calendering require extremely control over viscosity and green strength of compound to guarantee thickness stability. Proper selection of polymer architecture is thus fundamental for smooth processing. Dimensional stability of calendered compounds is also influenced and desired to avoid distortions upon storage.
Precise control over curing is also requested, especially when multi-layered structures are formed by overlapping of different calendered materials, to avoid again distortions.
Adhesion to fabrics is obtained by addition of proper ingredients such as primers or resins and by use of selected non-interfering process aids.
High surface quality is often requested in industrial process using calendered rubber compounds like offset printing. Extreme control over process mixing and appropriate selection of raw material purity is crucial.
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