Sustainable plastics manufacturing with solar rotational moulding systems

LightManufacturing is a company innovating in sustainable plastic moulding with its Solar Rotational Moulding (SRM) process.  Unlike traditional methods that heat moulds with fossil fuels, SRM uses a system of mirrors (heliostats) to concentrate sunlight. This process significantly reduces the environmental impact of plastic production.  

Editor Rebekah Jordan spoke to LightManufacturing's CEO Karl von Kries to learn more about the company's SRM systems that can achieve even heat distribution through a combination of mould rotation and controlled heating during sunlight hours. The interview also delves into the technology's high level of automation, which allows for precise temperature control and consistent part quality.

Q. Could you explain more how the rotational moulding process works with solar energy?

Our Solar Rotational Moulding (SRM) systems reflect heat from the sun onto a rotational mould to eliminate the need for fossil fuels.

Arrays of sun-tracking mirrors called heliostats concentrate thousands of watts of heat onto the mould, heating it quickly without the emissions and cost of natural gas. Depending on local market conditions product cost 15-30% less to make with SRM than traditional equipment.

Q. What types of plastic materials are currently compatible with your solar rotomoulding system?

Any thermoplastic used in traditional rotomoulding can be used in SRM - most common resins are polyethylene and polypropylene, but PVC, Nylon, and Polycarbonate are also rotomolded.

A brief video of how LightManufacturing's SRM systems work:

Q. With concentrated sunlight, how do you ensure even heat distribution across the rotating mould to avoid hot spots or uneven melting of the plastic?

Rotation in two axes (typically at one to five revolutions per minute) does an excellent job of averaging out small variations in heat intensity, and of course steel or aluminium moulds convey heat laterally across the mould surface to even out temperatures. But most importantly, our patented control systems actively speed up and slow down the mould as each face passes through the solar heat beam to achieve target temperatures - to the extent that we can heat certain mould faces more (producing thicker plastic in that area) or heat other faces less (forming a thinner part in that area). This per-face thickness control is difficult to achieve in traditional moulding, yet we can do it ‘programatically’. An example of how this is useful:  we can mould water tanks with extra thick bottoms for durability, but thin upper walls to save plastic.

Q. What is the current capacity of your "factory in a box" system in terms of production volume per day or week? Is the system easily scalable for larger production needs?

Production volume varies greatly with product size, wall thickness, can multiple tools be mounted at once, etc. Cycle times are similar to traditional gas fired moulding (that is to say, heating times are similar - cooling times tend to be faster because we radiatively target the tool, not the surrounding machinery and thus there is less mass to cool).  

Our CONEX containerised systems are transported like any other shipping container (crane/truck/forklift etc) and don’t require infrastructure - e.g. a building with a poured concrete floor, utilities, etc. They are placed directly on the ground, and our heliostats deploy on weighted ‘pods’ which require no digging. This factory in a box approach is highly scalable, and even re-deployable if market conditions change. No sunk costs! 

Due to low CapEx (@ 10% of a traditional factory/machine) it is cost effective to run multiple systems in parallel during sunlight hours, then if needed do secondary operations on a second shift.

Q. How automated is the overall process? What control systems are in place to manage sunlight concentration, mould rotation, and temperature regulation?

This is a key point: our system are ~highly~ automated in a way not possible with traditional systems. Recall that traditional moulding systems have the mould in a 300C+ oven, deadly to servo motors, complex electronics, many sensors etc. It’s a harsh environment. As a result most traditional moulding systems temporarily monitor plastic temperatures using a sensor package in a chilled box, then use a ‘best guess’ for how long to cook the part.

In contrast, we radiatively heat the mould using the solar beam and largely avoid heating anything else in the chamber. Thus, we can use servo and stepper motors in the chamber, put active temperature monitoring systems permanently in the chamber, and generally use a wide range of sensors and electronics not available in traditional machines.  We can monitor mould surface and internal mould air temperatures, mould position, beam intensity, and much more. 

Our machines adapt cycle times to varying solar conditions and always produce a well-cured part - likewise the machines automatically begin cooling with fans, cool the parts to an ideal de-moulding temperature then ‘beep’ and stop, waiting for the operator to remove the finished product.

Q. While you mention zero carbon emissions and fuel costs, can you elaborate on the initial setup cost of the "factory in a box" system compared to traditional moulding methods?

As mentioned above, we estimate CapEx for SRM is @ 10% of traditional moulding systems including building / infrastructure costs. This is important, but quickly dwarfed by the reduction in product cost.  Also important is our ability to supply customers and markets from nearby locations; because deploying SRM does not require infrastructure but just ‘raw land’ we deploy near-to-the-need and greatly reduce transportation costs and associated emissions. LightManufacturing currently does not offer SRM systems for sale, but rather provides moulding-as-a-service for partner brands. 

In some markets like Hawaii LM sell product B2C (direct to customer); there we sell water tanks at prices 30-40% less than our traditional rotomoulding competitors.