Final Report Summary - ROTOFLEX (Innovative rotomoulding development to improve cycle times and process efficiency whilst facilitating greater flexibility in product design and integrity ...)
The ROTOFLEX project, which has run over three years from January 2009 to December 2011, aims to make innovative rotomoulding developments in order to improve cycle times and process efficiency, whilst facilitating greater flexibility in product design and integrity for the small and medium enterprises (SMEs) - rotomoulding sector.
Rotational moulding, or rotomoulding, is a process that is especially suited to the manufacture of medium-sized and large hollow plastic items such as: tanks, materials handling products, industrial components and a range of leisure products.
The sector has seen significant growth over the last 30 years or so, which is attributed to the development of a range of new applications that harness the inherent design flexibility of the method, and utilise some innovative process developments across a range of new and mature markets across Europe and beyond.
In order to maintain the market momentum that has recently built up, it is essential that process developments continue apace, opening up new and more demanding applications for rotomoulding, considering both new materials and more challenging part geometries and property requirements.
As an almost zero shear process, the current range of materials with suitable flow, or rheological, characteristics to successfully produce rotomoulded parts is very limited, with over 95 % of parts produced using various forms of polyethylene (PE). However, for a growing range of new rotomoulding applications, PE on its own cannot fulfil the performance requirements.
One possible strategy is to use alternative polymers (like foaming PE, polypropylene, polyamide (nylon), ethylene vinyl alcohol copolymer (EVOH)) in combination with PE, as a multi-layer structure. In principle, this combines the best characteristics of the individual components, in a synergistic manner.
Taking these factors into consideration, the main objective of the ROTOFLEX project was to produce a retro-fittable automated filling system that, ideally, did not require the mould to be removed from the oven during multi-shot moulding.
Funding from the European Union's (EU) Seventh Framework Programme (FP7) under grant agreement No.217727 enabled the four SME associations and four SME partners in the project to access the research and development skills of several prestigious research companies and universities to aid with the development.
In parallel to, and as part of, developing the automated filling system, the project aimed to:
- aid the production of improved multilayer or composite parts;
- give greater control for enhanced product tolerances;
- expand the rotomoulding processing window, allowing greatly accelerated consolidation of resins and use of engineering resins;
- decrease the processing cycle time by as much as 30 % by feeding whilst heating;
- develop design guidelines to accommodate the new feed system and optimise processing performance;
- apply the developments outlined to achieve target end-user specifications.
Project context and objectives:
The main objectives of the ROTOFLEX project were to advance the competitiveness of the European SME rotational-moulding sector through:
- development of an automatic feed system that can be retrofitted to standard rotomoulding machines that will confer reductions in cycle time, and give associated energy savings,
- quantification of the rotomoulding process through the use of simulation software, leading to improved process understanding, control, and product quality,
- development of processes using the automatic feed system to make advanced composite products,
- development of processes using the automatic feed system to make advanced multilayer products.
Rotational moulding is the process of choice for the manufacture of large hollow, seamless products, such as automotive components (10 % of the rotomoulding market), tanks (27 %), containers (15 %), toys (20 %) and kayaks (5 %), usually in various grades of polyethylene.
It is a very competitive alternative to blow moulding, thermoforming, and injection moulding, using simple and relatively inexpensive moulds, and offers designers the opportunity to achieve the economic production of low-stress articles, with uniform wall thickness and in complex shapes (undercuts and intricate contours are difficult with competing technologies).
The principle of rotational moulding of plastics comprises introducing a known amount of plastic in powder, granular, or viscous-liquid form into a shell-like mould. The mould is then rotated whilst heating and cooling so that the plastic coats the inside of the mould evenly, replicating its shape.
The European rotational moulding sector has an estimated annual turnover approaching EUR 3 billion. Europe is one of the world leaders in the field, second only to the United States of America, with around 450 processors, mainly SMEs, spread across the continent, holding circa 28 % of the global market.
Despite continued growth in the global rotational moulding market, the European Union (EU) rotational moulding sector is being affected by globalisation and increased competition from low-wage economies that has led to substantial relocation of many manufacturing plants to other regions.
This is especially true for rotational moulding, because it is currently a labour-intensive and a relatively slow moulding process. Therefore, continual innovation and the expansion of rotational moulding into new areas and applications is necessary in order to maintain the EU rotational moulding community at the forefront of this rapidly increasing market.
Due to the relatively small nature of SME rotational moulding companies (approximately 90 % of which are SMEs), they can only achieve this through access to cutting-edge technologies within Europes leading research institutions, and through collaboration with their counterparts across Europe and with their industrial associations. The ROTOFLEX project achieved this with a supply chain approach where machinery manufacturers, mould makers, instrumentation suppliers, moulders, and designers, were able to collaborate. ROTOFLEX was able to deliver the pan-European effort needed to deliver a step change in the sophistication of rotomoulding, leading to greatly more efficient processing and value-added products that cannot be produced with existing technology.
As recognised by the Lisbon Objective, the transition of industry towards knowledge-based technologies and services is a fundamental priority for the continued sustainability and high levels of competitiveness.
The European plastics processing industry accounts for more than 37 000 companies, spanning the whole of the EU, processing 39 million tonnes of plastic per year. The industry employs more than one and a half million people and generates yearly sales exceeding EUR 160 billion. SMEs represent a significant portion of the plastics industry, employing over one million people (70 % of the total) in more than thirty-six thousand companies (98 % of the total). Rotational moulding is the fastest growing sector of the plastic processing industry with an average annual growth of over 20 %, largely due to important technical advances including new types of machines, moulds, and materials becoming available. The SME core members of the ROTOFLEX consortium were drawn from the national and transnational industrial associations that represent the plastics, machine manufacture, polymer processing, and rotational moulding sectors and they are representative of the SMEs from these associations. European SME industries are coming under sustained pressure from abroad, due to increased customer demands, lower cost manufacturing in China (despite transport costs), technological advancements in the US, and energy costs.
Rotomoulding is a relatively undeveloped technology in comparison with injection moulding and blow moulding. The ROTOFLEX project identified and addressed the large scope for step-change advancement in the automation of the process with the moderate investment.
There are fundamental technological problems faced that have been overcome via ROTOFLEX, allowing rotational moulding to advance into a cost-effective alternative to blow moulding, thermoforming, and injection moulding, and drive the international competitiveness of EU SMEs into value-added markets such as aerospace, furniture, and automotive:
1) The cycle times are long (20 - 30 minutes). The polymer is subjected to high temperatures leading to degradation; few materials can survive without degradation, greatly limiting the use of engineering plastics that can be used to make added-value products.
2) The rotational moulds, of large surface area, are heated and cooled for every moulding produced. Heating is facilitated by hot air, which is highly inefficient; consequently, rotomoulding is one of the highest energy consuming plastic processing technologies at 5.8 kW kg-1 hr-1.
3) Shrinkage and warpage of parts are not well understood or controllable and tight tolerances cannot, therefore, be guaranteed. This limits high added-value applications in automotive and aerospace.
4) It is difficult to mould composite parts by this process, as fibres tend to segregate to the inside of the mould. Mouldings can be made by building up layers of material, but this currently involves the use of 'drop boxes' bolted to the mould to deliver a second charge of material which are costly and take up space. The number of individual layers is, therefore, limited.
5) It is usually an atmospheric-pressure moulding process and so it is limited to powder resins that will readily fuse at low pressure and unsuitable for those, such as engineering resins, with unsuitable rheological properties.
The ROTOFLEX project has addressed these specific needs through the following:
1. Development of an integrated, automated, continuous-feed system for polymer, additives, (and theoretically coolants) direct to the rotating mould at any point in the cycle. It can be fitted to any standard rotomoulding equipment. This will allow the production of:
- improved multilayer parts, with more layers, and greater control for enhanced product tolerances and performance,
- fibre-reinforced composites,
- without interrupting the moulding cycle.
2. Decreasing the processing cycle time, since feeding and heating occur simultaneously. Reduced thermal stress to the polymer will allow the use of engineering plastics for value-added applications and improved dimensional stability. The EU rotational moulding sector uses 1.8 TWh of energy each year; therefore, reducing energy consumption by 30 %, through improving cycle times, will result in a saving of 0.34 TWh of electrical energy, and hence save EUR 30 million in production costs. The Kyoto protocol aims to cut CO2 emissions by 50 % by 2050. It is estimated that across the EU 750 kilotonnes of CO2 are emitted each year due to rotational moulding. Reduced energy usage due to ROTOFLEX will reduce CO2 emissions by 150 kilotonnes per annum.
3. Knowledge-based rotational mould and machine design criteria / guidelines to accommodate the new configurable feed system, and optimise processing performance; reinforcing the supply chain. Use of rotational moulding simulation software (RotoSim) to quantify variables for control of shrinkage, residual stress and warpage.
4. Applying the new automatic feed system, mould and machine design, and knowledge-based processing to enable the use of engineering materials, and the development of new multilayer, fibre-reinforced and wood-polymer composite (WPC) products, achieving target end-user specifications
Designers will be able to use ROTOFLEX's best practice guide in designing new, innovative products for rotational moulding. Potential new markets or products for rotational moulding include high-quality furniture and furnishings, medical components, and fuel tanks with high barrier performance to meet the new standards required by CARB and the EPA for marine and motor vehicle fuel tanks.
In addition to the rotational moulding community, ROTOFLEX will benefit other industrial sectors:
- Machine manufacturers will integrate their existing designs with the new configurable feed system and benefit from improved process control and efficiency.
- Other plastic processing technologies, most notably blow moulding (injection / extrusion), will benefit from a greater insight into micro-structural development and the relationship between process parameters and issues of warpage, shrinkage and residual stress, and their consequences.
Project results:
As part of the initial work undertaken within the project, a patent and literature review was carried out, along with a state of the art survey, in order to discover any barriers to market entry and to identify any potentially competitive technologies being developed. A free polymer bulletin service was set up providing the latest literature updates to registered parties throughout the project, helping to ensure that the work was focussed and targeted at the right areas.
In addition, a range of target products was defined. These were chosen to showcase the achievements possible with the ROTOFLEX system and include products not normally produced by rotational moulding.
A clear specification for each of the target products in terms of performance has been drawn up and used to select the materials required for each application.
The experimental work has been at all stages focussed on delivering the specifications of the target products, providing clear evidence of the technical benefits conferred by the system and the complimentary knowledge developed and documented for future reference.
A range of ideas for an automated feed system were developed, refined, and led to the production of an initial prototype feed system, which has been installed on a small industrial scale machine and used to produce parts. Refinements have been made throughout the project, culminating in a working, automated prototype device, which has been built, tested and run under industrial conditions.
Extensive trials have been carried out on process optimisation and validation. This work involved modifications to the ROTOFLEX material delivery system in order to maximise its efficiency and to ensure the accurate delivery of the automated lance safely into the mould. In addition there were also modifications to the lance system to prevent it trapping the self sealing silicone valve upon withdrawal from the mould. A lot of effort was also focused on designing, testing and optimising a system on the mould which could connect effectively with the material delivery lance and prevent powder loss during rotation in the moulding. This involved the design of a range of different valve / vent systems in order to deliver and keep powder in the mould during rotation.
As mentioned in the previous paragraph, the prototype includes a feed pipe system (lance) with a special feed system and self-sealing valves to stop material leakage during rotation, which was developed to substitute conventional side feeding from dump boxes attached to the mould by feeding either through the oven roof or from the sides.
Complimentary work has also been undertaken to characterise the flow characteristics of media to be fed using the system, allowing the delivery mechanism to be optimised.
The new feed system has helped determine optimum process parameters for conventional and engineering thermoplastic rotomoulding, complex and multi-layer skin-foam-skin and engineering polymer structures as well as fibre-reinforced composites with multiple alternating layers of polymer and fibre. Rotomoulded parts with up to seven layers have been produced, in a variety of different material combinations.
All of the results from this work have formed the basis of the ROTOFLEX best practice guide, which is a resource for the industry as the ROTOFLEX system is adopted and used to develop new and more challenging applications / parts for rotomoulding.
Two other important areas have also been addressed by the technical investigations:
A study of dimensional stability and moulding properties to characterise the effects of process variables on the morphology evolution in mouldings has led to the development of property relationships, and a report documenting the processing-structure-properties-product performance relationships of ROTOFLEX mouldings.
This work takes understanding to a new level, beyond the current state of the art, and again, will prove an invaluable reference resource for the exploitation of the ROTOFLEX system post-project. Currently, shrinkage and warpage of rotomoulded parts is not well understood and/or controllable and tight tolerances cannot be guaranteed. This has until this point constrained the production of high added value products for special applications in automotive and aerospace sectors.
With the increasing automation of the rotomoulding process comes also an increasing need to understand and control warpage, and shrinkage as products become increasingly more complex and require highly organised manufacturing methods.
In addition to progressing the state of the art in this area, this work has provided experimental characterisation data from a rotomoulding system, which has been utilised in a comparison with FEA generated data using the same parameters and conditions.
The process simulation and analysis was used to provide a quantitative analysis of the processes occurring in the rotomoulding operation as the system is deployed. Although the simulation work was unsuccessful in creating a suitable model of the rotomoulding process, it still aided the development of a fundamental understanding of the process in order to guide the optimisation of the ROTOFLEX feed system and to determine the optimum processing parameters.
In parallel to the main technical programme, an environmental, technical and economic evaluation of the ROTOFLEX system and of the rotomoulding process using the system has been carried out, considering factors such as energy consumption, lifetime and recyclability. This has ensured that the developed system is beneficial not just technically, but also provides a demonstrable return on investment within a reasonable period of time, and has no negative environmental effects.
A life cycle analysis from gate to gate was carried out to quantify and evaluate environmental impacts of the manufacturing phase of two-layer 70 L-fuel tank, employing the automatic feeding developed within the ROTOFLEX project in comparison to the conventional manual fed method. The rotomoulding production using the ROTOFLEX process has been demonstrated to give the benefit to environment in comparison to the manual fed production. The main finding are: energy required in the manufacturing phase of two-layer 70 L-fuel tank using the ROTOFLEX feeder is approximately 75 % of energy used in the conventional process with manual feeding process, and the production employing the ROTOFLEX feeder will benefit to the environment by reducing the greenhouse gases as indicated by carbon dioxide equivalent release by 22 %.
A desk-based economic evaluation has been carried out on two different types of rotomoulded product: a two-layer fuel tank (70 L capacity) and a four-layer tank (6000 L capacity). The cost from the ROTOFLEX process is compared to the conventional manual feed process. The reduction in labour cost and heating cost were found in the ROTOFLEX process. The major cost benefits from using ROTOFLEX are due to an increase in production rate and a decrease product unit cost. The payback time on the ROTOFLEX system was excellent (less than two years) for both product scenarios examined. The cost benefit of the ROTOFLEX system will need to be considered on a case-by-case basis, because the changes in production rate will vary, depending on the precise stage times required for cooking, cooling and mould servicing.
Technical evaluation of the ROTOFLEX automatic feeding system has been conducted and the results are as follows:
- The ROTOFLEX system has been designed be retrofitted to conventional rotomoulding machines. Limited structural modifications will be needed to be made to the machine.
- The ROTOFLEX system has been proved to be perfectly used in the industrial production.
- An improved quality and wall distribution of the layers of a multilayer tank can be expected, as well as an optimise d cycle time using the ROTOFLEX system.
- The ROTOFLEX system eliminates safety risk to operators associated with manual feeding.
Best practice guide of the ROTOFLEX process has been produced in accordance with the best industrial and environmental practices. The system mounts on the roof / or side of the oven and must have the facility to be interlocked with the existing rotomoulding machine control system. The equipment allows for the automatic gravity / venturi assisted filling of tooling with free flowing polymer resins where the tooling has been suitably configured for use with the system. There are some requirements for rotomoulding machine modifications such as excess movement/slack removed from plate and arm, installation of Autopark system, and minimum clearance above / side of oven (2710 mm), and tool modifications such as minimum diameter hole of 100 mm and clearance depth within mould of 100 mm. The operation procedure of the ROTOFLEX feeder is included.
Potential impact:
The technology developed within the ROTOFLEX project has the potential to provide a step change to the sophistication, control and productivity of the EU rotomoulding sector. It will allow rotomoulders to advance production to engineering resins, such as PA6,6, Acetal, and PBT, produce composite products, such as carbon fibre-reinforced PBT and glass reinforced PE, to employed sustainable resins, such as PLA and PHA, use natural fibres, and produced multilayer mouldings.
The European rotational moulding sector has an estimated turnover approaching EUR 3 billion annually and Europe is one of the world leaders, second only to the United States of America, with around 450 processors employing an estimated 68 000 people within SMEs spread across Europe. Europe currently holds a dominant position representing around 28 % of the global market and rotational moulding is now the fastest growing sector of the plastic processing industry, with annual European plastic consumption in 2005 around 315 000 tonnes. Other industrial communities, which serve, and the continuing prosperity of which depends upon, rotational moulding, will also benefit from the achievements in the project, such as the mould makers, material suppliers, machine manufacturers and a growing number of end-user industries. ROTOFLEX will, therefore, have a very positive impact on the 450 SMEs associated with the rotomoulding sector.
The competitiveness of the core group of SMEs will markedly increase as a result of:
- a considerable increase in output for rotational moulders resulting from lower cycle times;
- a reduction in production costs;
- price per part reduced;
- greater profit, lower energy consumption,
- higher quality products and lower waste due to less thermal degradation and control on dimensional stability leading to new market opportunities through,
- new materials and material combinations (engineering materials with improved properties),
- new high performance composite materials (multilayer, fibre reinforced and WPC),
- machine manufacturers will see increases in demand (and sales) for the 'universal' feed attachment
The EU rotomoulding industry is expected to experience an average growth in annual turnover on completion of the project, benefiting from greater processing flexibility, new high-performance composite products and capture of new markets made possible by the innovations outlined herein.
The development of a new feed system allowing materials to be added at any point during the moulding cycle will overcome the technological barriers that exist in the production of high-performance composite products. Furthermore, the quantitative and qualitative analysis of material behaviour during and after the moulding cycle will significantly strengthen the knowledge base and competitiveness throughout the rotational moulding supply chain, contributing to the continued sustainability of the industry sector and the generation of new economic wealth.
Key industry sectors that will benefit include the following:
- Rotational moulding:
The project results present an opportunity for rotational moulders to improve the efficiency of their processes, cycle times and improve product quality. Furthermore, the new innovative techniques will offer greater flexibility in product design, providing greater scope for materials selection, fibre reinforcement, and multilayer systems to meet increasing customer demands. New markets, notably in the automotive and aerospace sectors, will readily welcome greater control on product integrity.
- Machine manufacturers / toolmakers:
Innovative techniques allowing the automatic feeding of material into the mould during the rotomoulding process are a breakthrough for the industry and present machine manufacturers and toolmakers with the opportunity to benefit from increasing demand for such systems
- Materials suppliers / end-users:
New markets will be created for rotationally-moulded products, taking advantage of stress-free mouldings and high-quality products produced using the ROTOFLEX innovations. Rotational moulding will become increasingly competitive with other plastic processing technologies and provide end-users with greater design freedom for products that cannot be manufactured by other techniques. Multilayer and fibre-reinforced systems will be competitive with injection-moulded and blow-moulded products, resulting in increasing demand, notably from the automotive sector for fuel tanks.
The outcome from the project will, therefore, have a very positive and substantial impact for the SME community as a whole, especially those involved in rotational moulding.
Implementation and evolution of EU policies
- CO2 emission reductions:
The EU has committed itself to the Kyoto protocol (2002/358/EC), aiming to cut CO2 emissions from their 1999 levels by 50 % by 2050. One of the easiest ways to achieve this (without affecting gross domestic product) is through greater energy efficiency. CO2 emissions will be reduced during the rotational moulding process
- Polymer processing:
The annual EU energy consumption due to the main plastic processing technologies (injection moulding, extrusion and blow moulding) is estimated to be of the order of 74 TWh, relating to approximately 30 000 000 tonnes per annum of CO2 emissions. Therefore for every 1 % reduction in energy usage for this process, annual EU CO2 emissions will be reduced by approximately 300 000 tonnes
- Rotational moulding:
The annual EU energy consumption due to rotational moulding is estimated to be of the order of 1.8 TWh, relating to approximately 750 000 tonnes per annum of CO2 emissions. Therefore, a 30 % improvement in energy efficiency as a result of the new feed system will reduce annual EU CO2 emissions by approximately 150 000 tonnes. 73 % of energy is used in heating the auxiliary equipment in conventional oven heated tooling. This waste will be significantly reduced.
- Recycling:
The ROTOFLEX system can be used to incorporate hidden recyclate layers in rotomouldings for reduced and waste disposal, in-line with the landfill directive (1999/31/EC)
- Reduced VOC emissions from vehicles:
The production of advanced multilayer mouldings with barrier layers will reduce the VOC emissions from vehicles such as motorcycles, cars, strimmers and off-road vehicles, in line with the solvent emissions directive (1999/13/EC). Specifically, the development of a three-layer motorcycle tank in ROTOFLEX will cut the VOC transmission rate of conventional crosslinked PE from 8 mg m-2 per day to less than 1 mg m-2 per day.
- Framework seven policy objectives:
This project develops a new production process, contributes towards sustainable development, and grows the EU knowledge base
The project has also contributed to the following EU social objectives:
- Quality of life:
ROTOFLEX will lead to greater development of rotomoulding as a mainstream polymer processing technology for moulding of more complex structured products. A greater range of plastic materials can be accommodated within the rotational moulding process and this will open up new markets areas. This will lead to the development of manufacturing companies and improvement of machinery.
- Health and safety and working conditions:
The less labour-intensive automated feed system will lead to easier manual handling. Greater cooperation between material suppliers, machine manufacturers and rotational moulders will lead to innovative products and processes, which will make rotational moulding more competitive with other processes.
- Employment and levels of skills:
New innovations (e.g. rotomoulding manufacture) will ensure continuing growth within this sector within the EU and increase the competitiveness against low-wage economies. Technological advancements in high-technology economies will have a resultant positive effect on European employment.
- Environment:
Widespread adoption of the ROTOFLEX technology will lead to substantial environmental benefits in terms of CO2 emission reduction during the rotational moulding process and increased recycling.
The know-how and the intellectual property developed during the course of the project is owned by the SME association participants and will be exploited for the benefit of their members, through an agreement with the ROTOFLEX exploitation group, which is made up of two of the SMEs involved in the ROTOFLEX project, and an additional external investor.
The results of the ROTOFLEX project constitute a breakthrough for European rotomoulders, machine manufacturers, toolmakers, rotational moulders, and product designers and will establish this technology as a major technology of EU source. A specific dissemination plan for the ROTOFLEX project included several actions:
- a web site for information flow between partners and general dissemination,
- industrial-scale dissemination through the active work of all of the partners, through their close relationship with their own country's industries and trade associations,
- international fairs such as ARM International, European ARM and SPE events were be used to present the technology,
- non-commercial scientific dissemination by the research and technology development (RTD) performers through:
i. RTD networks and industrial associations at national and EU levels;
ii. trade and technical journals with industrial focus;
iii. papers delivered to specialist conferences when the opportunities arise;
iv. seminars and specialised forums to polymer processors.
The ROTOFLEX website address is http//:www.rotoflex-eu.org
Rotational moulding, or rotomoulding, is a process that is especially suited to the manufacture of medium-sized and large hollow plastic items such as: tanks, materials handling products, industrial components and a range of leisure products.
The sector has seen significant growth over the last 30 years or so, which is attributed to the development of a range of new applications that harness the inherent design flexibility of the method, and utilise some innovative process developments across a range of new and mature markets across Europe and beyond.
In order to maintain the market momentum that has recently built up, it is essential that process developments continue apace, opening up new and more demanding applications for rotomoulding, considering both new materials and more challenging part geometries and property requirements.
As an almost zero shear process, the current range of materials with suitable flow, or rheological, characteristics to successfully produce rotomoulded parts is very limited, with over 95 % of parts produced using various forms of polyethylene (PE). However, for a growing range of new rotomoulding applications, PE on its own cannot fulfil the performance requirements.
One possible strategy is to use alternative polymers (like foaming PE, polypropylene, polyamide (nylon), ethylene vinyl alcohol copolymer (EVOH)) in combination with PE, as a multi-layer structure. In principle, this combines the best characteristics of the individual components, in a synergistic manner.
Taking these factors into consideration, the main objective of the ROTOFLEX project was to produce a retro-fittable automated filling system that, ideally, did not require the mould to be removed from the oven during multi-shot moulding.
Funding from the European Union's (EU) Seventh Framework Programme (FP7) under grant agreement No.217727 enabled the four SME associations and four SME partners in the project to access the research and development skills of several prestigious research companies and universities to aid with the development.
In parallel to, and as part of, developing the automated filling system, the project aimed to:
- aid the production of improved multilayer or composite parts;
- give greater control for enhanced product tolerances;
- expand the rotomoulding processing window, allowing greatly accelerated consolidation of resins and use of engineering resins;
- decrease the processing cycle time by as much as 30 % by feeding whilst heating;
- develop design guidelines to accommodate the new feed system and optimise processing performance;
- apply the developments outlined to achieve target end-user specifications.
Project context and objectives:
The main objectives of the ROTOFLEX project were to advance the competitiveness of the European SME rotational-moulding sector through:
- development of an automatic feed system that can be retrofitted to standard rotomoulding machines that will confer reductions in cycle time, and give associated energy savings,
- quantification of the rotomoulding process through the use of simulation software, leading to improved process understanding, control, and product quality,
- development of processes using the automatic feed system to make advanced composite products,
- development of processes using the automatic feed system to make advanced multilayer products.
Rotational moulding is the process of choice for the manufacture of large hollow, seamless products, such as automotive components (10 % of the rotomoulding market), tanks (27 %), containers (15 %), toys (20 %) and kayaks (5 %), usually in various grades of polyethylene.
It is a very competitive alternative to blow moulding, thermoforming, and injection moulding, using simple and relatively inexpensive moulds, and offers designers the opportunity to achieve the economic production of low-stress articles, with uniform wall thickness and in complex shapes (undercuts and intricate contours are difficult with competing technologies).
The principle of rotational moulding of plastics comprises introducing a known amount of plastic in powder, granular, or viscous-liquid form into a shell-like mould. The mould is then rotated whilst heating and cooling so that the plastic coats the inside of the mould evenly, replicating its shape.
The European rotational moulding sector has an estimated annual turnover approaching EUR 3 billion. Europe is one of the world leaders in the field, second only to the United States of America, with around 450 processors, mainly SMEs, spread across the continent, holding circa 28 % of the global market.
Despite continued growth in the global rotational moulding market, the European Union (EU) rotational moulding sector is being affected by globalisation and increased competition from low-wage economies that has led to substantial relocation of many manufacturing plants to other regions.
This is especially true for rotational moulding, because it is currently a labour-intensive and a relatively slow moulding process. Therefore, continual innovation and the expansion of rotational moulding into new areas and applications is necessary in order to maintain the EU rotational moulding community at the forefront of this rapidly increasing market.
Due to the relatively small nature of SME rotational moulding companies (approximately 90 % of which are SMEs), they can only achieve this through access to cutting-edge technologies within Europes leading research institutions, and through collaboration with their counterparts across Europe and with their industrial associations. The ROTOFLEX project achieved this with a supply chain approach where machinery manufacturers, mould makers, instrumentation suppliers, moulders, and designers, were able to collaborate. ROTOFLEX was able to deliver the pan-European effort needed to deliver a step change in the sophistication of rotomoulding, leading to greatly more efficient processing and value-added products that cannot be produced with existing technology.
As recognised by the Lisbon Objective, the transition of industry towards knowledge-based technologies and services is a fundamental priority for the continued sustainability and high levels of competitiveness.
The European plastics processing industry accounts for more than 37 000 companies, spanning the whole of the EU, processing 39 million tonnes of plastic per year. The industry employs more than one and a half million people and generates yearly sales exceeding EUR 160 billion. SMEs represent a significant portion of the plastics industry, employing over one million people (70 % of the total) in more than thirty-six thousand companies (98 % of the total). Rotational moulding is the fastest growing sector of the plastic processing industry with an average annual growth of over 20 %, largely due to important technical advances including new types of machines, moulds, and materials becoming available. The SME core members of the ROTOFLEX consortium were drawn from the national and transnational industrial associations that represent the plastics, machine manufacture, polymer processing, and rotational moulding sectors and they are representative of the SMEs from these associations. European SME industries are coming under sustained pressure from abroad, due to increased customer demands, lower cost manufacturing in China (despite transport costs), technological advancements in the US, and energy costs.
Rotomoulding is a relatively undeveloped technology in comparison with injection moulding and blow moulding. The ROTOFLEX project identified and addressed the large scope for step-change advancement in the automation of the process with the moderate investment.
There are fundamental technological problems faced that have been overcome via ROTOFLEX, allowing rotational moulding to advance into a cost-effective alternative to blow moulding, thermoforming, and injection moulding, and drive the international competitiveness of EU SMEs into value-added markets such as aerospace, furniture, and automotive:
1) The cycle times are long (20 - 30 minutes). The polymer is subjected to high temperatures leading to degradation; few materials can survive without degradation, greatly limiting the use of engineering plastics that can be used to make added-value products.
2) The rotational moulds, of large surface area, are heated and cooled for every moulding produced. Heating is facilitated by hot air, which is highly inefficient; consequently, rotomoulding is one of the highest energy consuming plastic processing technologies at 5.8 kW kg-1 hr-1.
3) Shrinkage and warpage of parts are not well understood or controllable and tight tolerances cannot, therefore, be guaranteed. This limits high added-value applications in automotive and aerospace.
4) It is difficult to mould composite parts by this process, as fibres tend to segregate to the inside of the mould. Mouldings can be made by building up layers of material, but this currently involves the use of 'drop boxes' bolted to the mould to deliver a second charge of material which are costly and take up space. The number of individual layers is, therefore, limited.
5) It is usually an atmospheric-pressure moulding process and so it is limited to powder resins that will readily fuse at low pressure and unsuitable for those, such as engineering resins, with unsuitable rheological properties.
The ROTOFLEX project has addressed these specific needs through the following:
1. Development of an integrated, automated, continuous-feed system for polymer, additives, (and theoretically coolants) direct to the rotating mould at any point in the cycle. It can be fitted to any standard rotomoulding equipment. This will allow the production of:
- improved multilayer parts, with more layers, and greater control for enhanced product tolerances and performance,
- fibre-reinforced composites,
- without interrupting the moulding cycle.
2. Decreasing the processing cycle time, since feeding and heating occur simultaneously. Reduced thermal stress to the polymer will allow the use of engineering plastics for value-added applications and improved dimensional stability. The EU rotational moulding sector uses 1.8 TWh of energy each year; therefore, reducing energy consumption by 30 %, through improving cycle times, will result in a saving of 0.34 TWh of electrical energy, and hence save EUR 30 million in production costs. The Kyoto protocol aims to cut CO2 emissions by 50 % by 2050. It is estimated that across the EU 750 kilotonnes of CO2 are emitted each year due to rotational moulding. Reduced energy usage due to ROTOFLEX will reduce CO2 emissions by 150 kilotonnes per annum.
3. Knowledge-based rotational mould and machine design criteria / guidelines to accommodate the new configurable feed system, and optimise processing performance; reinforcing the supply chain. Use of rotational moulding simulation software (RotoSim) to quantify variables for control of shrinkage, residual stress and warpage.
4. Applying the new automatic feed system, mould and machine design, and knowledge-based processing to enable the use of engineering materials, and the development of new multilayer, fibre-reinforced and wood-polymer composite (WPC) products, achieving target end-user specifications
Designers will be able to use ROTOFLEX's best practice guide in designing new, innovative products for rotational moulding. Potential new markets or products for rotational moulding include high-quality furniture and furnishings, medical components, and fuel tanks with high barrier performance to meet the new standards required by CARB and the EPA for marine and motor vehicle fuel tanks.
In addition to the rotational moulding community, ROTOFLEX will benefit other industrial sectors:
- Machine manufacturers will integrate their existing designs with the new configurable feed system and benefit from improved process control and efficiency.
- Other plastic processing technologies, most notably blow moulding (injection / extrusion), will benefit from a greater insight into micro-structural development and the relationship between process parameters and issues of warpage, shrinkage and residual stress, and their consequences.
Project results:
As part of the initial work undertaken within the project, a patent and literature review was carried out, along with a state of the art survey, in order to discover any barriers to market entry and to identify any potentially competitive technologies being developed. A free polymer bulletin service was set up providing the latest literature updates to registered parties throughout the project, helping to ensure that the work was focussed and targeted at the right areas.
In addition, a range of target products was defined. These were chosen to showcase the achievements possible with the ROTOFLEX system and include products not normally produced by rotational moulding.
A clear specification for each of the target products in terms of performance has been drawn up and used to select the materials required for each application.
The experimental work has been at all stages focussed on delivering the specifications of the target products, providing clear evidence of the technical benefits conferred by the system and the complimentary knowledge developed and documented for future reference.
A range of ideas for an automated feed system were developed, refined, and led to the production of an initial prototype feed system, which has been installed on a small industrial scale machine and used to produce parts. Refinements have been made throughout the project, culminating in a working, automated prototype device, which has been built, tested and run under industrial conditions.
Extensive trials have been carried out on process optimisation and validation. This work involved modifications to the ROTOFLEX material delivery system in order to maximise its efficiency and to ensure the accurate delivery of the automated lance safely into the mould. In addition there were also modifications to the lance system to prevent it trapping the self sealing silicone valve upon withdrawal from the mould. A lot of effort was also focused on designing, testing and optimising a system on the mould which could connect effectively with the material delivery lance and prevent powder loss during rotation in the moulding. This involved the design of a range of different valve / vent systems in order to deliver and keep powder in the mould during rotation.
As mentioned in the previous paragraph, the prototype includes a feed pipe system (lance) with a special feed system and self-sealing valves to stop material leakage during rotation, which was developed to substitute conventional side feeding from dump boxes attached to the mould by feeding either through the oven roof or from the sides.
Complimentary work has also been undertaken to characterise the flow characteristics of media to be fed using the system, allowing the delivery mechanism to be optimised.
The new feed system has helped determine optimum process parameters for conventional and engineering thermoplastic rotomoulding, complex and multi-layer skin-foam-skin and engineering polymer structures as well as fibre-reinforced composites with multiple alternating layers of polymer and fibre. Rotomoulded parts with up to seven layers have been produced, in a variety of different material combinations.
All of the results from this work have formed the basis of the ROTOFLEX best practice guide, which is a resource for the industry as the ROTOFLEX system is adopted and used to develop new and more challenging applications / parts for rotomoulding.
Two other important areas have also been addressed by the technical investigations:
A study of dimensional stability and moulding properties to characterise the effects of process variables on the morphology evolution in mouldings has led to the development of property relationships, and a report documenting the processing-structure-properties-product performance relationships of ROTOFLEX mouldings.
This work takes understanding to a new level, beyond the current state of the art, and again, will prove an invaluable reference resource for the exploitation of the ROTOFLEX system post-project. Currently, shrinkage and warpage of rotomoulded parts is not well understood and/or controllable and tight tolerances cannot be guaranteed. This has until this point constrained the production of high added value products for special applications in automotive and aerospace sectors.
With the increasing automation of the rotomoulding process comes also an increasing need to understand and control warpage, and shrinkage as products become increasingly more complex and require highly organised manufacturing methods.
In addition to progressing the state of the art in this area, this work has provided experimental characterisation data from a rotomoulding system, which has been utilised in a comparison with FEA generated data using the same parameters and conditions.
The process simulation and analysis was used to provide a quantitative analysis of the processes occurring in the rotomoulding operation as the system is deployed. Although the simulation work was unsuccessful in creating a suitable model of the rotomoulding process, it still aided the development of a fundamental understanding of the process in order to guide the optimisation of the ROTOFLEX feed system and to determine the optimum processing parameters.
In parallel to the main technical programme, an environmental, technical and economic evaluation of the ROTOFLEX system and of the rotomoulding process using the system has been carried out, considering factors such as energy consumption, lifetime and recyclability. This has ensured that the developed system is beneficial not just technically, but also provides a demonstrable return on investment within a reasonable period of time, and has no negative environmental effects.
A life cycle analysis from gate to gate was carried out to quantify and evaluate environmental impacts of the manufacturing phase of two-layer 70 L-fuel tank, employing the automatic feeding developed within the ROTOFLEX project in comparison to the conventional manual fed method. The rotomoulding production using the ROTOFLEX process has been demonstrated to give the benefit to environment in comparison to the manual fed production. The main finding are: energy required in the manufacturing phase of two-layer 70 L-fuel tank using the ROTOFLEX feeder is approximately 75 % of energy used in the conventional process with manual feeding process, and the production employing the ROTOFLEX feeder will benefit to the environment by reducing the greenhouse gases as indicated by carbon dioxide equivalent release by 22 %.
A desk-based economic evaluation has been carried out on two different types of rotomoulded product: a two-layer fuel tank (70 L capacity) and a four-layer tank (6000 L capacity). The cost from the ROTOFLEX process is compared to the conventional manual feed process. The reduction in labour cost and heating cost were found in the ROTOFLEX process. The major cost benefits from using ROTOFLEX are due to an increase in production rate and a decrease product unit cost. The payback time on the ROTOFLEX system was excellent (less than two years) for both product scenarios examined. The cost benefit of the ROTOFLEX system will need to be considered on a case-by-case basis, because the changes in production rate will vary, depending on the precise stage times required for cooking, cooling and mould servicing.
Technical evaluation of the ROTOFLEX automatic feeding system has been conducted and the results are as follows:
- The ROTOFLEX system has been designed be retrofitted to conventional rotomoulding machines. Limited structural modifications will be needed to be made to the machine.
- The ROTOFLEX system has been proved to be perfectly used in the industrial production.
- An improved quality and wall distribution of the layers of a multilayer tank can be expected, as well as an optimise d cycle time using the ROTOFLEX system.
- The ROTOFLEX system eliminates safety risk to operators associated with manual feeding.
Best practice guide of the ROTOFLEX process has been produced in accordance with the best industrial and environmental practices. The system mounts on the roof / or side of the oven and must have the facility to be interlocked with the existing rotomoulding machine control system. The equipment allows for the automatic gravity / venturi assisted filling of tooling with free flowing polymer resins where the tooling has been suitably configured for use with the system. There are some requirements for rotomoulding machine modifications such as excess movement/slack removed from plate and arm, installation of Autopark system, and minimum clearance above / side of oven (2710 mm), and tool modifications such as minimum diameter hole of 100 mm and clearance depth within mould of 100 mm. The operation procedure of the ROTOFLEX feeder is included.
Potential impact:
The technology developed within the ROTOFLEX project has the potential to provide a step change to the sophistication, control and productivity of the EU rotomoulding sector. It will allow rotomoulders to advance production to engineering resins, such as PA6,6, Acetal, and PBT, produce composite products, such as carbon fibre-reinforced PBT and glass reinforced PE, to employed sustainable resins, such as PLA and PHA, use natural fibres, and produced multilayer mouldings.
The European rotational moulding sector has an estimated turnover approaching EUR 3 billion annually and Europe is one of the world leaders, second only to the United States of America, with around 450 processors employing an estimated 68 000 people within SMEs spread across Europe. Europe currently holds a dominant position representing around 28 % of the global market and rotational moulding is now the fastest growing sector of the plastic processing industry, with annual European plastic consumption in 2005 around 315 000 tonnes. Other industrial communities, which serve, and the continuing prosperity of which depends upon, rotational moulding, will also benefit from the achievements in the project, such as the mould makers, material suppliers, machine manufacturers and a growing number of end-user industries. ROTOFLEX will, therefore, have a very positive impact on the 450 SMEs associated with the rotomoulding sector.
The competitiveness of the core group of SMEs will markedly increase as a result of:
- a considerable increase in output for rotational moulders resulting from lower cycle times;
- a reduction in production costs;
- price per part reduced;
- greater profit, lower energy consumption,
- higher quality products and lower waste due to less thermal degradation and control on dimensional stability leading to new market opportunities through,
- new materials and material combinations (engineering materials with improved properties),
- new high performance composite materials (multilayer, fibre reinforced and WPC),
- machine manufacturers will see increases in demand (and sales) for the 'universal' feed attachment
The EU rotomoulding industry is expected to experience an average growth in annual turnover on completion of the project, benefiting from greater processing flexibility, new high-performance composite products and capture of new markets made possible by the innovations outlined herein.
The development of a new feed system allowing materials to be added at any point during the moulding cycle will overcome the technological barriers that exist in the production of high-performance composite products. Furthermore, the quantitative and qualitative analysis of material behaviour during and after the moulding cycle will significantly strengthen the knowledge base and competitiveness throughout the rotational moulding supply chain, contributing to the continued sustainability of the industry sector and the generation of new economic wealth.
Key industry sectors that will benefit include the following:
- Rotational moulding:
The project results present an opportunity for rotational moulders to improve the efficiency of their processes, cycle times and improve product quality. Furthermore, the new innovative techniques will offer greater flexibility in product design, providing greater scope for materials selection, fibre reinforcement, and multilayer systems to meet increasing customer demands. New markets, notably in the automotive and aerospace sectors, will readily welcome greater control on product integrity.
- Machine manufacturers / toolmakers:
Innovative techniques allowing the automatic feeding of material into the mould during the rotomoulding process are a breakthrough for the industry and present machine manufacturers and toolmakers with the opportunity to benefit from increasing demand for such systems
- Materials suppliers / end-users:
New markets will be created for rotationally-moulded products, taking advantage of stress-free mouldings and high-quality products produced using the ROTOFLEX innovations. Rotational moulding will become increasingly competitive with other plastic processing technologies and provide end-users with greater design freedom for products that cannot be manufactured by other techniques. Multilayer and fibre-reinforced systems will be competitive with injection-moulded and blow-moulded products, resulting in increasing demand, notably from the automotive sector for fuel tanks.
The outcome from the project will, therefore, have a very positive and substantial impact for the SME community as a whole, especially those involved in rotational moulding.
Implementation and evolution of EU policies
- CO2 emission reductions:
The EU has committed itself to the Kyoto protocol (2002/358/EC), aiming to cut CO2 emissions from their 1999 levels by 50 % by 2050. One of the easiest ways to achieve this (without affecting gross domestic product) is through greater energy efficiency. CO2 emissions will be reduced during the rotational moulding process
- Polymer processing:
The annual EU energy consumption due to the main plastic processing technologies (injection moulding, extrusion and blow moulding) is estimated to be of the order of 74 TWh, relating to approximately 30 000 000 tonnes per annum of CO2 emissions. Therefore for every 1 % reduction in energy usage for this process, annual EU CO2 emissions will be reduced by approximately 300 000 tonnes
- Rotational moulding:
The annual EU energy consumption due to rotational moulding is estimated to be of the order of 1.8 TWh, relating to approximately 750 000 tonnes per annum of CO2 emissions. Therefore, a 30 % improvement in energy efficiency as a result of the new feed system will reduce annual EU CO2 emissions by approximately 150 000 tonnes. 73 % of energy is used in heating the auxiliary equipment in conventional oven heated tooling. This waste will be significantly reduced.
- Recycling:
The ROTOFLEX system can be used to incorporate hidden recyclate layers in rotomouldings for reduced and waste disposal, in-line with the landfill directive (1999/31/EC)
- Reduced VOC emissions from vehicles:
The production of advanced multilayer mouldings with barrier layers will reduce the VOC emissions from vehicles such as motorcycles, cars, strimmers and off-road vehicles, in line with the solvent emissions directive (1999/13/EC). Specifically, the development of a three-layer motorcycle tank in ROTOFLEX will cut the VOC transmission rate of conventional crosslinked PE from 8 mg m-2 per day to less than 1 mg m-2 per day.
- Framework seven policy objectives:
This project develops a new production process, contributes towards sustainable development, and grows the EU knowledge base
The project has also contributed to the following EU social objectives:
- Quality of life:
ROTOFLEX will lead to greater development of rotomoulding as a mainstream polymer processing technology for moulding of more complex structured products. A greater range of plastic materials can be accommodated within the rotational moulding process and this will open up new markets areas. This will lead to the development of manufacturing companies and improvement of machinery.
- Health and safety and working conditions:
The less labour-intensive automated feed system will lead to easier manual handling. Greater cooperation between material suppliers, machine manufacturers and rotational moulders will lead to innovative products and processes, which will make rotational moulding more competitive with other processes.
- Employment and levels of skills:
New innovations (e.g. rotomoulding manufacture) will ensure continuing growth within this sector within the EU and increase the competitiveness against low-wage economies. Technological advancements in high-technology economies will have a resultant positive effect on European employment.
- Environment:
Widespread adoption of the ROTOFLEX technology will lead to substantial environmental benefits in terms of CO2 emission reduction during the rotational moulding process and increased recycling.
The know-how and the intellectual property developed during the course of the project is owned by the SME association participants and will be exploited for the benefit of their members, through an agreement with the ROTOFLEX exploitation group, which is made up of two of the SMEs involved in the ROTOFLEX project, and an additional external investor.
The results of the ROTOFLEX project constitute a breakthrough for European rotomoulders, machine manufacturers, toolmakers, rotational moulders, and product designers and will establish this technology as a major technology of EU source. A specific dissemination plan for the ROTOFLEX project included several actions:
- a web site for information flow between partners and general dissemination,
- industrial-scale dissemination through the active work of all of the partners, through their close relationship with their own country's industries and trade associations,
- international fairs such as ARM International, European ARM and SPE events were be used to present the technology,
- non-commercial scientific dissemination by the research and technology development (RTD) performers through:
i. RTD networks and industrial associations at national and EU levels;
ii. trade and technical journals with industrial focus;
iii. papers delivered to specialist conferences when the opportunities arise;
iv. seminars and specialised forums to polymer processors.
The ROTOFLEX website address is http//:www.rotoflex-eu.org