Ems-Grivory goes further with fibres

Polyamide LFT materials are being made to work even harder with new glass rovings and impregnated tape technology.

Polyamide producer Ems-Grivory, based in Switzerland, has an established position in long-fibre reinforced thermoplastics (LFT) for injection moulding. Its materials – by combining light weight with strength values similar to metals – have been successful in targeting metal automotive applications.

Glass fibres with a length of up to 10mm form a fibre skeleton inside the component, says the company, and this improves thermo-mechanical properties without affecting the polyamide-specific features such as resistance to chemicals or surface quality. One application using a high glass fibre loading is the rear seatback for an Audi A8 model which is made of Grilon TSGL-50/4 reinforced with 50% long glass fibres.

“This material offers enormously high stiffness values, even at high temperatures, and ensures high toughness at break which is an advantage above all for passengers in the case of a possible impact to the side of the car. High notched impact strength and extremely low tendency to warp round off the material profile,” says Ems-Grivory.

The company is building on its LFT expertise with two developments, one focused on the glass fibre and the other taking a new approach to strengthening.

Newly developed glass fibre rovings have enabled Ems-Grivory to develop an injection moulding material, Grivory GVL-6H HP, which for the first time exceeds the value of 300 MPa for tensile stress at break (as measured in ISO 527 tensile tests).

The company says: “The new rovings have a different kind of geometry and therefore, a different length-to-thickness ratio – both in 10 mm granules [and] in the injection moulded finished component. In this way, even better surface quality is possible allowing a combination of excellent surface quality and extraordinary mechanical properties to be achieved.”

In the second project, the company has developed Ems Tape Technology, which places pre-impregnated continuous fibre tapes within the mould to eliminate weak points in the component. “With their help, for example, a component’s weld line strength can be increased massively,” it says.

The tape technology, which is delivered on spools, was developed in cooperation with the HSR Advanced Technical College at Rapperswil, Switzerland. Tests carried out on demonstration parts show that areas around weld lines have up to twice as high strength values when a single tape is applied, according to Ems-Grivory

It said that as well as improving bending strength, other properties such as creep, long-term, alternating or pulsating fatigue strength were also improved.

At K 2013, Ems-Grivory showed applications for its polyamide LFT materials in the sports and leisure sector.

The Spectre touring ski boot made by the Italian company La Sportiva weighs 1.395 kg, which makes it the lightest four-buckle ski boot. Key components are in the boot’s heel shell, where a long carbon fibre-reinforced PA 12 and a tough Grilamid PA 12 confer very high levels of stiffness and high notch impact strength, said Ems-Grivory.

The long fibre reinforcement means the notch impact toughness is more than twice as high, tensile E-modulus is 60% higher and strength 70% higher than for short fibre reinforced PA 12 grades. The materials can be welded together using two-component injection moulding.

A neck support from off-road sports equipment company Alpinestars is made of Grilamid LCL-3H, a long carbon fibre reinforced PA 12. The Bionic Neck Support, which received the ISPO Award for sports goods in 2013, is 38% lighter than its predecessor model. The material’s density is 1.15 g/cm3, but its energy absorption is more than five times higher than that of standard compounds.

Alpinestars also uses Grilamid LCL-3H in its Fluid Tech Carbon Knee Brace.

The brace, which consists of two half-shells, protects the kneecap even when falling on sharp stones. The brace is design-ed with toothed linkage between the two half-shells, which enables an anatomically correct rolling movement of the knee joint.

The mechanical loads on this toothed linkage can be exceptionally high, say Ems-Grivory. But the high tensile E-modulus and high strength of Grilamid LCL-3H means the toothed linkage can withstand this stress.

Courtesy: European Plastic News