PU formula for large, high-strength, lightweight products

Among many other products, KraussMaffei’s customer Camoplast Inc. makes plastic hulls and decks for personal watercraft (PWC), more commonly known as jet skis. A leading PWC producer tasked its supplier Camoplast with developing a lighter hull capable of boosting PWC speed and performance, as well as saving manufacturing costs. The challenge was to achieve the weight reduction without loss of strength. Camoplast found the solution by combining KraussMaffei’s LFI process with a new formula for Baydur 814, a polyurethane system from Bayer MaterialScience (BMS). The PWC hull measuring 360 x 90 cm is the first application of this special technology.

Camoplast is ramping up the CLF process for making PWC hulls. Integrated reinforcing ribs boost the strength of this lightweight part.

Traditionally PWC hulls are produced using Sheet Moulding Compound (SMC), i. e., glass fibre-reinforced polyester resin. Camoplast looked at a number of alternative manufacturing methods and materials, finally concluding that the best way of meeting customer specifications was to use a modified LFI process capable of producing a strong, lightweight hull with a very good surface finish, and of reducing manufacturing costs as well.

In the LFI process, the glass fibres are discharged into the mould simultaneously with the PU system in a single process. The PU mixing head, mounted on a robot arm, is equipped with a chopper which cuts fibres to length. The robot moves the mixing head over the open mould during the pour process. The mould is then closed to give the product its final shape. The main challenge in producing the large PWC hull using this process is the PU’s very short curing time.

Camoplast worked with its technology partners KraussMaffei and BMS to develop the CLF (Camoplast Long Fibre) process. KraussMaffei’s main contribution was to modify its LFI process by boosting glass fibre output rate from 180 to 300 g/s in order to deliver a high-strength structural part. Concurrently BMS developed a PU formula that cures in 60 s, much longer than the 10 s taken by conventional formulas. The longer curing time allows the PU/glassfibre mix to flow readily into narrow interstices. This is necessary to produce parts with integrated ribs for extra strength.

Producing the hulls from PU instead of conventional SMC has benefits for the manufacturer and for the end customer. PU’s lower density means that the whole craft is lighter and can accelerate faster. In this application, a hull produced in a CLF weighs 30 % less than the same product produced by the conventional method.

“The hull is the biggest, but also the most vulnerable component of a PWC – it comes into contact with waves that could smash it”, explains Yves Carbonneau, engineering manager at Camoplast. “To achieve the best possible drive characteristics the hull must have an optimised structural and mechanical characteristic, but it must nonetheless be as light as possible. We use a light material with integrated reinforcing ribs. This is how we achieve the necessary strength to withstand even big waves and to provide the safety that PWC drivers want.”

KraussMaffei also contributed its expertise in mould design for the LFI process. Camoplast is now using a nickel mould for the PWC hull. This represents a considerable cost-saving compared with the steel mould required for an SMC process. Using in-mould painting, Camoplast can produce coloured parts with a flawless surface finish directly in the mould. There’s no need for a cost-intensive post-mould painting step. “Camoplast’s innovative CLF process is the most effective method of meeting the exacting criteria that the company sets for the material properties and aesthetics of a PWC hull”, says Craig Snyder, Market Channel Representative at Bayer MaterialScience.