Applications Overview
Focus on Improved Composite Applications
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SMC is one of the commonest closed compression molding techniques. VINNAPAS® from WACKER is an effective low-profile additive.
Sheet Molding Compound (SMC)
SMC resin mats are produced from a high-viscosity fiber/resin compound. When the fiber/resin compound is processed in a closed mold under heat and pressure (approx. 70 bar), its viscosity decreases. That allows the resin containing the isotropically distributed reinforcing fibers to flow in the mold. The thermoset then cures within the closed mold.
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BMC and SMC processes have more or less the same characteristics. But because BMCs contain shorter glass fibers, they flow more easily into extremely
Bulk Molding Compound (BMC)
BMC is a doughy mass that can be produced from any conventional thermoset matrix systems and is also processed by reaction injection molding. The BMC part can be produced as soon as the BMC compound has been mixed. The main difference from SMC is the fiber content and length.
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RTM: used in the transportation, wind power and construction sectors. It is particularly suitable for producing complex three-dimensional shapes.
Resin Transfer Molding (RTM)
RTM (resin transfer molding) involves the injection of a low-viscosity thermoset into the closed mold under moderate pressure (usually 3.5 – 7 bar) via one or more injection ports. The injected resin fills all the voids in the mold, impregnating and wetting out the entire surface of the reinforcing material.
The reinforcement can comprise a variety of fiber types and forms, such as fiber tows, mats or woven structures. A vacuum is sometimes applied to enhance resin flow and reduce void formation. The part is typically heat cured.
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Pultrusion: used for consumer articles and in the electrical and construction sectors.
Pultrusion
In the pultrusion of thermosets, the reinforcing fibers are impregnated by passing them through a resin bath. The resin-impregnated fiber strand is then brought to the near net shape at a number of preform stations and shaped and cured in a heated mold.
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Hand lay-up is by far the most widely used process and is used in a wide range of industries.
Hand Lay-Up:
Following application of the liquid release agent (PVA, liquid wax or PTFE/silicone spray), a gel coat is applied. This high-resin coat usually contains pigments and fillers; it will form the decorative exterior surface of the finished part. The gel coat is followed by a layer of resin and then of reinforcing agent. Resin is forced through the reinforcing material by rolling, thus removing air and completely impregnating the reinforcement.
HDK® performs the function of optimally adjusting the viscosity of these resin-based formulations (gel coat and laminating resins) to the hand lay-up application process.
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Spray-Up
Chopped glass fibers and resins are supplied to an open mold. This involves feeding the rovings into a chopper and then blowing them into a precured resin. The advantage is the high speed at which the material can be applied. After application, the material is usually consolidated with a hand roller in the same way as with hand lay-up.
Thanks to HDK® from WACKER, rheological characteristics can be controlled optimally.
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