Thermally conductive composites revolt undersea

Konduit thermally conductive composites from US-based LNP Engineering Plastics have made possible an innovative new thermoplastic encapsulated electric motor for an undersea remotely operated vehicle (ROV).

The Quest ROV from Alstom GEC of Davis, CA must withstand pressures of 10,000 psi at depths up to 20,000 feet below sea level. Konduit composites provide the necessary strength while also radiating heat away from the electric motor, preventing overheating and potential burnout.

Part of the stator, the thermoplastic encased electric motors-10 per ROV-replace hydraulic thrusters.

According to Griffith Neal, Founder, Encap Technologies of San Francisco, an engineering consultancy contracted by Alstom to help develop the ROV’s submersible motor, ‘The motor has to withstand approximately five tons of pressure – picture a tractor trailer sitting on end on a postage stamp.

The only way for an electric motor to work in this type of undersea environment is to encapsulate it in a very strong plastic that has a very high thermal conductivity. Until LNP invented Konduit composites, no one could do this-I believe it was physically impossible.’

Thermal conductivity of the motor’s encasements is essential to prevent heat build-up and potential burnout of the electric motor. ‘The problem with conventional plastics is that they don’t transfer the heat generated in the windings,’ says Neal. ‘In 7,500 watt motors like these, the wire will actually melt if the packaging material does not dissipate the heat.’ Encap’s solution, Konduit composites, provide 10 to 50 times more thermal conductivity than typical unfilled and reinforced thermoplastics, radiating heat out and away from the motor.

Another key benefit of using Konduit is its low coefficient of linear thermal expansion (CLTE). ‘Konduit is the only material that I am aware of that matches the CLTE performance of metals over the moulding temperature range,’ says Neal. ‘For us to successfully eliminate plastic micro-fissures caused by differential contraction on cooling, LNP tailored a resin with a specific CLTE performance.’

Another benefit of matching the CLTEs is the elimination of cracking from thermal shock that can hinder plastic application development in larger parts.

The Quest ROV also features three other thermoplastic compounds from LNP Engineering Plastics. High strength Verton long fibre composites are used in the nozzle flanges that protect the motor, bearings and impeller; Lubricomp lubricated composites are used in hydrodynamic bearings due to their wear properties and good dimensional stability; and Thermocomp reinforced composites are used in the bearing flanges because they deliver the necessary high stiffness, dimensional stability and mouldability.

‘The actual development of the thruster design was accomplished quite quickly,’ says Neal. ‘We were fortunate to work with an excellent toolmaker (Industrial Molds of Rockford, Illinois). To ensure encapsulation of the 42-pound stator, we developed a retracting pin system capable of pulling 16 pins, 2 inches in less than a third of a second. I think there are about 5 companies in the world who could have built the stator tool.’

At $5,000 per stator, zero defect moulding is a must. The moulder, Pyramid Plastics of Rockford, IL, employed Dart Vision advanced mould control from RJG Inc. of Traverse City, Michigan and cavity pressure measurement to augment the traditional moulding machine controls.

LNP Engineering Plastics are at:00 1 (610) 363-4782 or jlucas@lnp.com.

LNP Engineering Plastics: www.lnp.com

Encap Technologies: www.encaptech.com