Apply High Pressure - Get ESTRIM Results!
The Automotive sector is looking with great interest at the industrialisation of the injection process involving the use of Epoxy resins and Carbon or other continuous fibers, provided that this allows for typical part-to-part cycle time of 3 minutes or less. Until now this fast production has not been possible, for a number of reasons linked with the involved chemistry and with the manipulation of the fiber's substrates. Thanks to ESTRIM – a fast-demoulding, high-pressure injection technology for Epoxy resins recently launched by Cannon – lightweight, thin-walled composite mouldings of complex shape and medium-large dimensions can now be produced at very reduced cycle times. An interview with Antonio Cossolo, Cannon Group's Corporate Director for Product Development, details the various aspects of this innovative application.
Cannon News: Epoxy-based composites produced with high pressure injection: what can you tell us about the innovative aspects introduced by Cannon for this technology?
Antonio Cossolo: The innovation introduced by Cannon consists in providing the right mix of technologies able to achieve Automotive industry's production cycles for mass production of large composite parts:
properly formulated family of liquid Epoxy components in a closed mould: this decreases demoulding times from up to 30 minutes to 2 – 3 minutes, maintaining optimum mechanical properties and surface aspect characteristics.
• High-pressure technology for metering, mixing and injecting a
• Self-cleaning mixing heads eliminate the use of flushing or cleaning solvents, achieving significant economic savings and environmental advantages. In addition, they can be permanently fixed on the tools, speeding up the production and eliminating leakage problems from the injection point.
• High-pressure injection, in combination with closed-loop
controlled metering systems, guarantees optimum repeatability of the dispensed weight from shot to shot. This provides high standardisation of the moulded parts and avoids unnecessary overfilling of the mould, with all relevant advantages (material savings, no leaks, cleaner working environment, no emissions of vapours from the moulds, much lower scrap rate, etc.)
• Dedicated preformers provide repetitive and fast production of inserts to be manually or automatically positioned in the moulds prior to the injection, avoiding long manual preparation of the production tools and increasing the profitability of presses and dispensing equipment.
Dedicated high pressure metering equipment for Epoxy resins is available in Cannon Afros R&D lab for moulding trials.
Cannon FPL Functional Scheme
CN: What does this mean in terms of advantages for the end user? AC: A production rate up to ten times faster than that provided by RTM speaks for itself:
• Presses and moulds generate ten times more parts per unit of time (shift, day, month…) potentially with the same manpower.
• Production lines can be automated, making use of 40+ years of industrialisation experiences matured by other plastics processing technologies. Production costs and scrap parts are significantly reduced.
• Multiple heads can be connected to a single dispensing machine to serve several moulds in a row, reducing the required equipment's investment per point of injection and optimising the performances of formulation and dosing machine.
Automotive, transportation and aerospace industries can think in new terms the production of structural or decorative lightweight composite parts, since their production rates can be brought nearer to their assembly lines' timings and logistic needs.
CN: What is the “state of the art” for Epoxy-based Composites? AC: Traditional manufacturing methods used until now for the production of composite parts in moulds – such as the Resin Transfer Moulding (RTM), whose typical field of application is the automotive industry – are characterised by long part-to-part cycles (20 to 30 minutes), deriving mostly from two basic obstacles:
• the long preparation phase of the moulds prior to the introduction of the liquid formulations, which require manual positioning of several layers of different reinforcing mats or tissues of glass or carbon fiber.
• the long polymerisation time, deriving from the intrinsically slow reactivity of the formulations, required to allow for a smooth and complete filling of the cavity with a liquid which is progressively growing its viscosity in the time immediately following the start of the injection in mould.
The lack of faster manufacturing methods has – so far – slowed the development of a wider number of lightweight structural or decorative parts which could be used by mass-production industries unable to cope with long processes still relying on heavy manual operations. The fast manufacturing cycles demanded by the automotive industry require demoulding times which are up to ten times shorter than those provided by the currently most used process.
CN: What kind of solution were you able to develop, then? AC: The Cannon Group and Huntsman Advanced Materials have
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CN: You say “High pressure”: how does this work? AC: The high pressure technology is based on positive displacement pumps able to reach pressures (measured at the head's injectors) above 200 bars: this provides the desired solutions for this problem. The chemical components are warmed in storage tanks up to the required temperature and are kept, separately, in continuous recirculation through the circuit of the dosing machine – up to the inner part of the mixing head – to ensure that their viscosity remains constant through the complete process. By increasing the temperature the viscosity drops. The mixing is obtained by pulverising – with appropriate injectors or “jets” – the reactive components in a cylindrical mixing chamber, whose diameter can be as small as 4-5 mm. The mixing chamber – when not in use – is tightly sealed by a precisely-machined piston which avoids that the components get mixed at the wrong time. The computerised control determines the precise amount of liquid materials required by each different mould and calculates a precise injection time in function of the pump's actual output. When the machine's control sends an injection command the piston sealing the mixing chamber is operated hydraulically, the mixing chamber is opened and the liquid components are conveyed through pressure- inducing pulverising nozzles: the chemicals meet and mix thoroughly in the small cylindrical cavity, converting their kinetic energy into turbulence. The blended liquid is forced through an “L”-shaped circuit within the head: this non-linear path provides a good conversion of turbulent forces into laminar flows – an ideal dispensing situation for those applications where any inclusion of air into a liquid formulation must be avoided. This laminar flow of liquid leaves the head through an injection nozzle that fits a hole drilled in the mould. All the blended material is therefore quickly transferred into the cavity, without waste: at the end of the injection the control panel sends a signal to the hydraulic pack, which quickly closes the mixing head and brings it to the rest position. This quick action perfectly cleans out the cylindrical wall of the mixing chamber, removing any residual liquid. These heads, therefore, do not require any flushing with solvents or detergents. There are neither moving parts to be washed at the end of each injection, nor static mixers or plastic pipes to be disposed of. The injection is a clean operation, and the heads can be fixed on the moulds and left there for a long time: they can be dismounted periodically for routine maintenance or for cleaning the pressure-inducing injectors. The positive pressure applied to the liquids by the high-pressure dosing pumps is kept constant throughout the whole injection process: this pressure allows for fast and complete filling of the mould, even where the mass of reinforcement provides a high resistance to the flow of liquid. Pressure within the mould's cavity is continuously monitored using a pressure transducer fitted in the mould's wall opposite to the injection hole. A pressure curve can be plotted and analysed to determine the best output and filling time values to be adapted to each different type of mould.
CN: “Dedicated preformers” seem to be a winning plus, for Cannon: can you tell us something more on these special machines AC: Cannon Tecnos – the Cannon Group's Unit dedicated to the development of dedicated solutions for the Automotive sector – have designed and supplied dedicated preformers for composites for more than three decades. Glass, Carbon, Aramidic and natural fibres of every type and consistency have been successfully handled and precisely dispensed in large or small moulds in dozens of different applications. The availability of these dedicated tools – in addition to a complete range of mould carriers, presses, manipulators and other specially-designed equipment – is a significant plus in the search for a complete industrial solution
joined forces to develop an alternative process, designing production equipment and chemical formulations able to overcome the two basic problems described above. The experience grown by Cannon and Huntsman in another field of the plastics industry – the Polyurethanes, in which both Companies are recognised leaders – taught that fast demoulding is primarily depending on a very fast injection time. This is a direct function of three fundamental parameters of the process:
• the viscosity of the liquid formulation (which derives directly from the employed chemistry and from the temperature)
• the wettability of the reinforcing material (which depends upon the geometry of its deposition within the mould, and from intrinsic characteristics of the mat or the fabric)
• the pressure exerted on the mould's inner surfaces by the liquid, which progressively encounters resistance to its flow (due to the progressive rise of viscosity and to the presence of a solid mass of reinforcing material in each part of the mould cavity)
It is of paramount importance, therefore, to fill the mould before than the viscosity of the liquid formulation reaches an unmanageable value. Employed successfully for more than three decades in other reacting processes – such as Polyurethanes, DCPD and Nylon RIM – the high-pressure metering and mixing technology has allowed the industry to reach production rates and mechanical properties once unheard of. The same approach has been used for Epoxy.
aimed at the automated high-yield manufacture of injected composites based on Epoxy formulations. One of these preformers has been specified and purchased in 2001 by BMW for their Landshut's Innovation and Technology Centre (LITZ), within the frame of a major development project aimed at the production of a complete “composite” car. A fruitful joint cooperation with the prestigious client allowed Cannon to supply a state-of-the-art preformer: this sophisticated machine is now carrying the whole production of preforms for the composite parts manufactured in-house by BMW for their M3 and M6 models. See the annex article to get more details on this innovative project.
CN: For the success of this project a smart chemistry must have been used: what did you do in this case? AC: The availability of high-pressure equipment for very fast injections of Epoxy opened a world of opportunities to Huntsman Advanced Materials: they were able to select – from a wide range of Araldite ® resins and Aradur ® hardeners and catalysts – the right combination, providing high reactivity but also the right viscosity at the injection temperature and viscosity build-up characteristics in order to cope with the performances demanded by this new process.
CN: How did you proceed with the development of the process? AC: Several sets of trials were organised during 2009 and 2010 at Cannon Afros R&D Lab near Milano, Italy, using high pressure metering and mixing equipment specifically modified to cope with Huntsman's Epoxy chemical behaviour and viscosities. Hardener and resin required very different processing temperatures, and chemical compatibility suggested us the use of plunger-dosing piston for the hardener side rather than the use of the conventional high-pressure pump used for the resin. Moulding series were run using progressively higher quantities of formulation, until a proper filling rate was identified and repeated with regular results using various types of reinforcing materials. Successful production of test plates was achieved with demoulding times as low as 2 minutes, with resin processed at or near 90°C and mixing ratio Resin/Hardener of 5:1. The resulting test plates were submitted to characterisation in Huntsman Advanced Materials TS&D Labs in Basel, Suisse, and provided the following results.
Fiber Glass
Glass Carbon
fiber vol fraction (%)
40 52 48
resin output (g/s)
36 24 24
injection time (s)
15 17 17
cure time (min)
4 2 3
Max
pressure (bars)
44
> 50 44
resin temp (°C)
70 90 90
mould temp (°C)
87 90 90
perform weight (g)
663 773 541
plate weight (g)
1031 1162 878
ILSS (Mpa)
42,1 42,9 59,5
Tg by DMA Onset (°C)
79 73 79
Tg by DMA Peak (°C)
99 98
102
Flexural Modulus (Mpa)
17560 23271 44147
Flexural Strenght (Mpa)
Tensile Modulus (Mpa)
Tensile Modulus (Mpa)
413 434 771 51616 710
These data confirm the success of the project. Mechanical characterisation of the specimen confirms that structural Epoxy- based composites can be obtained by ESTRIM technology – used in combination with properly designed dosing machines, mould carriers, preformers and ancillary equipment – with a production rate up to ten times faster than that provided by RTM technology.
CN:To summarise, then what are the benefits of this new ESTRIM process? AC: The advantages over a conventional technology are evident:
• Presses and moulds generate ten times more parts per unit of time, potentially with the same manpower.
• Production lines can be automated, making use of 40+ years of industrialisation experiences matured by other plastics processing technologies.
• Production costs and scrap parts are significantly reduced. • Multiple heads can be connected to a single dispensing machine to serve several moulds in a row, reducing the required equipment's investment per point of injection and optimising the performances of formulation and dosing machine.
CN: Where do you think that this process will be applied in the near future? AC: Automotive, transportation and aerospace industries can think in new terms the production of structural or decorative lightweight composite parts, since their production rates can be brought nearer to their assembly lines' timings and logistic needs. The Cannon Group can supply, as a One-Stop-Shop supplier carrying the whole responsibility of the line, all the equipment required by this technology:
• High-pressure closed-loop controlled metering and injecting machine, and self-cleaning mixing heads.
• Dedicated preformers for repetitive and fast production of inserts
• Dedicated moulding clamps and moulds, in various lay-out configurations
• Water-jet trimming equipment for the finished preforms • Storage tanks and distribution circuit for chemical components
• All the ancillary equipment required by the process
Any local Cannon Office will gladly discuss with the interested Companies their specific manufacturing requirements, in order to tailor for them the most appropriate “ESTRIM solution” – just give us a call!
Fast demoulding and perfect surface aspect is obtained using well-tuned Epoxy formulations processed with high pressure technology.
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