Perpetuum harvest the benefits of low-pressure moulding

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Perpetuum Ltd is now using low-pressure, low-temperature overmoulding with Macromelt to protect components used on its vibration energy harvesting systems against the harsh operating environments in which they are deployed. The Macromelt process has replaced traditional potting techniques, which the Southampton-based company found prohibitively laborious.

Perpetuum harvest the benefits of low-pressure mouldingEvery so often, an idea comes along that tears down barriers and enables approaches that change the world forever. Perpetuum energy harvesters convert mechanical energy (vibration) to electrical energy via an oscillating mass (magnet) which traverses across a fixed coil to create a varying amount of magnetic flux, inducing a voltage in accordance with Faraday’s law.

Central to the operation of these innovative, maintenance-free systems is the coil assembly housing the oscillating magnet. This is the energy harvester’s means of obtaining power from vibration. The induced voltage is conditioned via a small PCB to provide the necessary DC voltage output.

The company’s NPI Manager, Terry Maynard explains: “Both the coil and PCB need to exhibit mechanical strength and insulation resistance, hence the requirement for encapsulation.”

Operating in environments such as oil rig platforms, Perpetuum’s energy harvesters can be exposed to temperatures ranging from -40degC to +85degC, while for certain rail applications, acceleration force can be anywhere up to 300g.

Mr Maynard says: “We were using potting originally but it was a messy, two-part process, and very labour-intensive. We then investigated traditional injection moulding but found we were limited by the associated temperatures and pressures, which would be too high for our PCB. As we continued our search for a reliable and economic process, we came across Macromelt moulding from Engineering Solution.”

Engineering Solution, through its partnership with Henkel, provides manufacturers across several industry sectors with a low-pressure moulding service. In a class between casting and injection moulding, Macromelt moulding is non-aggressive, highly cost effective and fast. Because it uses low pressures of typically 2–20bar, lower-cost mould tools can be employed. And of course the technology is well suited for encapsulating and enclosing delicate components and assemblies, providing protection from vibration fatigue and atmosphere/liquids that could promote corrosion or conductive paths.

Faced with producing an overmould for Perpetuum’s coil and PCB, measuring 48mm diameter and 25mm tall, Engineering Solution created a one-part, single-hit mould tool capable of encapsulating the parts in a cycle time of around 60s.

Test phase for mould tool

Via its contract overmoulding service, Engineering Solution liaises with customer designers to understand and advise on parameters such as temperature range, dimensions and substrates to seal. Designs are then translated into a mould tool. First-off impressions go through the customer’s test phase before Engineering Solution begins manufacturing to an agreed schedule.

According to Mr Maynard, Perpetuum is now producing its second-generation vibration energy harvesting systems and the reliability of the Macromelt process is already assured, as confirmed by recently completed accelerated life tests. All Perpetuum systems comply with ATEX and IECEX stipulations.

He concludes: “We are the only company in the world with a production solution for vibration energy harvesting and volumes are now ramping up as word spreads. As a result, we are currently in discussions with Engineering Solution about the production of a multi-impression mould tool that would make our requirements even more economic.”

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