FROM THE NEW POSSIBILITIES ON OFFER FROM BIOPOLYMERS AND ROTOMOULDING COMES A MORE ENVIRONMENTALLY-FRIENDLY FORM OF MOBILITY
The rotomoulding technology has taken on a leading role within the world of design thanks to its design, feasibility and financial potential. One limitation, however, when both developing solutions and using it in other application areas, is still linked to the materials that can be used with this manufacturing technique. With the arrival of the new Bio TP Seal from Total new possibilities have appeared on the horizon, as an interesting meeting organised by Persico at its production plant back in June showed. In particular, the use of this biopolymer together with the rotational method and the Leonardo systems available from Persico could provide a number of new answers for the mobility industry which is always on the look-out for vehicles that are more environmentally-friendly, therefore, more lightweight, with lower consumption levels, less pollutant and easier to dispose of at the end of their lifespan.
Two for the environment
One of the most promising solutions within sustainable mobility circles would seem to be that of electric vehicles. Much work is needed, however, when it comes to the weight of the batteries, where the aim is to make the frames lighter, so as to be able to keep costs down and improve the autonomy of the cars. In response to this problem, Total, which being a petrochemical company is well aware of the need to reduce the dependency on fossil-based fuels, has come up with Bio TP Seal, a modified polyethylene, created using metallocenic catalysts,which includes considerable percentages of PLA (polylactic acid of vegetable origin). Far from being a commercial stunt on the wave of today’s ecological trend, this biopolymer aims to provide a sound alternative to conventional polymers. In fact, besides being more environmentally-friendly, it also has innovative mechanical performances, so much so in fact that Total experimented with it when making the chassis for an electric city car by replacing the conventional metal parts with components made out of rotomoulded Bio TP Seal. The outcome was a chassis that was 3 times lighter than the one made out of metal and can be made in just one moulding cycle, so reducing the number of parts that need assembling. Last but not least, being 100% recyclable, the new biopolymer from Total helps manufacturing companies to comply with the ever-increasing number of regulations when it comes to recycling products at the end of their lifespan. Total carried out quite a lot of specific research so as to be able to adapt Bio TP Seal to suit the car-component rotational moulding process. Every aspect was designed on the basis of the dimensional characteristics of the parts that are made. At present there is one type that has been created that consists of a foamed layer sandwiched between two outer skins that can be painted, but others structures could also be developed upon request.
The high flexibility of the foam nucleus, besides being a positive response to mechanical stress, also enables designers to come up with original shapes, which could also include asymmetrical parts, all made in the same production cycle, thanks to the thermal control that the rotomoulding process allows for. As with traditional rotomoulding processes, it is possible to colour components en mass, so doing away with the need for any further surface treatments. Collaboration with the Rotomoulding Division at Persico meant that it was possible to optimise the results and, in particular, improve the aspects linked to the design, the robustness and the surface finish of the components. For example, when developing the roof for the concept car, the partnership between Total and Persico resulted in a part that was not only eye-catching, thanks to better shiny effect than the one you get with other plastic machining technologies, but also had structural and functional properties that are effectively combined. To improve the aesthetic results of the moulded parts, the Leonardo machines from Persico make it possible to control the temperature of the mould and inside the component, as well as pressurise and depressurise the cavity of the rotational mould. In particular, the Research & development section showed how, by using the vacuum process, it is possible to prevent any bubbles forming on the inside and outside of the parts, when dealing with different kinds of polyethylene and different wall thicknesses. What’s more, the Leonardo machines are fully automatic, therefore, they are more beneficial in terms of the reliability and reliability of the results when it comes to the quality, the interaction of the materials, the evenness of the thicknesses and so on.
Ecology at work
The VSV (Viability Service Vehicle) was developed by Noremat from an all-round eco-compatibility point of view. First off, the basic structure was designed to be fitted with one, two or three pieces of operational equipment (used for mowing, pruning, collecting off-cuts, grinding up branches, gritting, etc.). This equipment was designed to reduce consumption levels and, those used for cutting the grass, were designed to improve the job by focusing on ‘green’ energy production. What’s more, the components were chosen to reduce the consumption of fuel and aid recyclability. Compared to the initial project, which included a chassis made out of non-recyclable polyester, the vehicle was developed in such a way so as to integrate various functions into the parts, so reducing the actual number of them and, as a result, also the assembling requirements. The aim was also to use materials that could be recycled at the end of their lifespan, whilst ensuring not only the need to keep the weight down, so as to be able to reduce consumption levels, but also the glossy finish that was first thought of. In collaboration with Total, the Evok ecodesign studio for the materials and Persico for developing all the parts of the bodywork, the tanks and access to the cabin, numerous components that were previously intended to be made using thermoforming were then redesigned in light of rotomoulding. In particular, thanks to this transformation in the top of the cabin it was possible to integrate 7 parts into just one componentwhich was moulded using the rotational technique, the side wings of the cabin had 3 parts reduced into one, additional functions were added to the front bumpers, the fuel tank was developed as a one-off component integrating the access to the cabin, the radiator cover and the engine hood were achieved in one part using just one mould and the rear part of the cabin roof was made as a single component which is a combination of the two parts made by thermoforming. The water tank was made using rotational moulding and the cover for the hydraulic devices (consisting of two parts in the thermoforming version) is currently at the development stage. The wheel covers and the mudguards with housing for the headlamps, however, are still made using thermoforming. This redesign and the synergy between the partners who, in their own different ways were involved in developing the VSV, made it possible to keep the overall costs down compared to the initial design with the possibility of a financial return that should increase over time.
Leonardo: ELECTRIFYING MOULDING
The new, fully electric Leonardo machine was launched onto the market recently which has even more advanced thermal performance levels. The innovative heating system is based on a number of resistors that are applied directly to the surface of the mould which, besides allowing for better temperature control, also means that it is possible to do away with the heating/cooling diathermal oil, so making maintenance much easier (it’s no longer necessary to change the oil every two years) and makes the production process environmentally sustainable. Its use enabled the R&D centre at Persico to achieve interesting results when rotomoulding is applied to materials that are usually not used with this technique because they cause problems during the moulding phase. Polyamide is moulded using two tanks that make it possible to evenly blend the raw materials, additives and catalysts and then reduce them to their liquid state before transferring them into a pre-chamber. Here, once that have been heated up to the polymerisation temperature, they are added to the mould layer-by-layer: in fact, the material solidifies thanks to the chemical reaction and not as a result of it cooling down, therefore, it is fundamental to accurately control and monitor the temperature of the mould. In the case of transparent polycarbonate, one of the most crucial aspects of the moulding process regards the formation of air bubbles on the inner and outer surfaces of the parts, which are caused by both the hygroscopicity of the material and the moulding process itself. To overcome this problem the material is usually processed at a much higher temperature, for the time it takes for the bubbles to be reabsorbed, with a waste of time and money that is not indifferent. The tests carried out by Persico showed how using the electric Leonardo machine, which makes it possible to control, accurately and directly, the temperature of the m
ould and inside the component as well as increase or reduce the pressure in the mould, leads to a rapid elimination of the air bubbles. What’s more, particular surfac
e treatments and design/constructive modifications made to the mould resulted in a considerable improvement in the quality of the moulded parts: besides a lack of bubbles and, therefore, an improvement in both the look and the mechanical properties, the distribution of the material also proves to be better with greater transparency, free from any marks caused by oxidisation.