Tough nylon cuts manufacturing costs by 40%

Dean Palmer reports on two very different applications for thermoplastics - a housing for an electronic stability control system and a range of ergonomic garden tools

Dean Palmer reports on two very different applications for thermoplastics - a housing for an electronic stability control system and a range of ergonomic garden tools

To meet the main requirements of ruggedness and torsion resistance for the housing of Continental Automotive Systems Division's recently-introduced ESC (Electronic Stability Control) system, the part's developer chose high-impact DuPont Zytel SST (Stiff-Super-Tough) nylon.

"In the past we used aluminium for such housings but to save costs we looked for alternatives," explained Kai Allissat, manager programme planning & control ESC Sensors at Continental's Automotive Systems Division. "Our new design is made of two halves, injection-moulded from heat-stabilised Zytel SST nylon, reinforced with 25 per cent glass fibre. With this material, we were able to cut the housing's manufacturing costs by 40 per cent, compared to metal."

Mounted centrally in a vehicle, the new plastic housing holds the yaw rate sensor, the lateral acceleration sensors and a CPU for internal pre-processing, and a CAN (Controller Area Network) interface, which transmits the collected data to the electronic braking and safety system.

The cluster design and the housing material isolate the sensor module from mechanical shock and vibration and shield it from electromagnetic influences. DuPont Engineering Polymers' Technical Centre at Bad Homburg carried out computer simulations on CAE models, to determine how the parts behave when they are subjected to vibrations at frequencies up to 500Hz at temperatures between -40°C and 85°C.

The precise detection of a vehicle's movements through measurement of the inertia values of yaw rate and lateral acceleration is the basis of modern electronic vehicle stabilisation systems and for roll-over protection, active steering and airbag systems. That is why Continental chose a modular design for the cluster, which allows for incorporation of other sensor functions which may be needed in the future.

Engineering polymers are also playing a vital role in the development of the latest, innovative products for the home.

Lifelong gardener and successful software entrepreneur Bruce Baker has developed an innovative range of hand-held garden tools that are more comfortable to use than anything else on the market, even for users suffering from arthritis or tendonitis.

His company, Radius Garden, based in Michigan, USA, also wanted to produce professional-grade tools with a lifetime guarantee that included a durable soft-grip that adhered to the tool.
The Radius Garden 'NRG' (natural radius grip) tools are uniquely-designed with a curved-bow shaped grip.

Before the company could move from design to production, it needed the appropriate material for the grip and blades, as well as the most efficient and effective manufacturing process.

The blade had to be ultra-lightweight and the handle needed to be high quality, as it was vital to the product design and brand identity. With manufacturing and assembly in China, the firm needed a material with proven global supply reliability and good grip for its unique handle.

Radius Garden chose to work with ExxonMobil Chemical's Santoprene Specialty Products to provide design support, material selection, technical assistance with moulds and to help it identify ISO-qualified companies in China to manufacture the tools.

To manufacture the handle, a soft Santoprene TPE was insert overmoulded onto a polypropylene (PP) base. Santoprene TPE met the design and performance requirements for the combination of materials. The broad portfolio of available grades produced a comfortable grip of suitable hardness and significant ergonomic benefits. The TPE did not peel or fray and, in tests at Radius Garden, the blade did not separate from the handle. The unique bow-shaped handle provided a secure grip regardless of whether it was wet or dry.

The blades were die-cast using an ultra-lightweight aluminium/ magnesium alloy. These were attached to the handle using a mechanical locking device between the PP base and the metal blade.

Santoprene also provided preliminary designs while the manufacturer in China finalised the engineering details. Initially, two-cavity moulds produced the tools. To accommodate increased demand and a boost in production, four-cavity moulds were used.

Radius Garden selected Clariant China to produce a pearlescent lime green masterbatch for the handle. The colour give the garden tools an appealing look that makes them easy to find outdoors or in the tool shed.

The curved-bow shape of the grip enhances the ability to push the tool when working. This, combined with the soft, non-slip grip, provides maximum power and comfort and minimises hand and wrist stress, as it efficiently transfers energy from the muscles directly to the blades.

"The success of our garden tools is due in no small part to the efforts of Santoprene. They were involved in every step of the process," said Bruce Baker of Radius Garden. "We've succeeded in creating a comfortable, ergonomically-sound product to which we proudly affix a lifetime guarantee. We achieved this in the relatively short time of two years."

The first products in the new range became available in the US in early 2006.

Pointers

* By using a super tough nylon reinforced with 25% glass fibre, rather than aluminium for the housing, Continental cut manufacturing costs by some 40%

* The handle on the garden tool was made from Santoprene TPE insert overmoulded onto a polypropylene base, resulting in a low cost, long life, ergonomic design

Author
Tom Shelley

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