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The RIM-process — A highly developed technology
The RIM-Process - A Highly Developed Technology K 8 o h u l t e , BayerAG, PUApplications Technology 5090, Leverkusen, Federal Repubfic of Germany
Abstract To produce high.quality polyurethane.reaction injection moulding (PUR.RIM) of the sort used in automotive exterior applications, the essential requirements are high.performance machinery and equipment plus a thorough understanding of aU the processing parameters. Successful production of blemish free articles at fast cycles, ready for painting and requiring no post. treatment is only possible if the interconnected chemical and technical processing sequences all function in perfect harmony. Working towards this goal, several teams of chemists, processing engineers and manufacturers have been co.operating on intensive programmes of research and developmen~ and today it can justifiably be claimed that the RIM process is remarkably mature for such a young technology. A determined effort is now required to incorporate the latest findings into the design of new machinery and to modify existing machinery accordingly. In this paper, a detailed discussion is presented of the two most important processing parameters (temperature and pressure) and the various factors which depend on them, and the need for accurate control of these parameters during the manufacturing process is stressed Details are also given of a production line complete with tooling designed specifically for the process. Together with an appropriate system of measuring, monitoring and recording the processing parameters, this is an essential prerequisite for cost- efficient production~
Introduction Three successful, key areas of development have made an essential contribution towards further rationalising the RIM process: • the chemical development of easy-release, IMR systems (In Mould Release) means that it is now possible to largely dispense with the external application of release agent to the mould prior to each injection cycle. • mastering the "on-the-spot" chemistry no longer presents any problems. The three states of aggregation that have to be processed - liquid (starting components), solid (eg, milled glass fibre) and gaseous (eg air or nitrogen) can be reliably controlled during the process. • significant knowledge has been acquired in the field of mould engineering in terms of a suitably-tailored mould lay-out and design for PUR. This paper looks into the basic improvements and findings.
Multiple-head Metering The metering system that is generally employed in the production of foamed parts has proved to be a weak point in the process engineering. The arrangement whereby several mixing heads and moulds are fed from a single metering unit via distributor stations does not always permit a suitably-configured pipeline system for the process or the constant temperature and pressure that this would ensure. A sensible compromise between the "one-to-one unit" in exclusive use in the USA (one
MATERIALS & DESIGN Vol. 9 No. 6 N O V E M B E R / D E C E M B E R 1988
metering unit to one mixing head) and the multiple-head metering system used in the past (where one metering unit feeds ten or more mixing heads) would be to have a symmetrical distribution system incorporating a maxim u m of two mixing heads. These are the only conditions that will allow an optimum pipeline configuration. Such a configuration requires: • the shortest possible link between the machine tank, the positive displacement piston metering unit and the mixing head • optimum pipeline cross-sections: Pipe dimensions should be kept as small as possible so that flow rates of approximately ~> 0.5 m / s can be achieved, thereby avoiding any settling out of the glass fibre-filled polyol. There should not, however, be an excessive loss of pressure in the pipeline system between the metering unit and the mixing head in order to ensure that most of the energy introduced, and the operating pressure of 150 to 250 bar, can be used for the impingement injection mixing process.
Temperature Control The temperature control of the starting materials is very important in reaction injection moulding. The two basic components are pre-heated to approximately 25°C in the tank farm. The polyol c o m p o n e n t is conveyed from the tank farm to the glass fibre mixing station. Whilst the glass fibre is being mixed in, the polyol is heated to the
325
i Z Fig i
Schematic diagram of a RIM unit with multiplehead metering (showing only the polyol section): (a) machine tank, (b) positive displacement piston metering unit, and (c) clamping unit with mould and mixing head
subsequent processing temperature of approximately 45°C. As the two chief c o m p o n e n t s are conveyed into the buffer and machine tanks (preferably in quantities of less than 10% of the effective tank capacity at a time) they are maintained at a constant temperature, and the heat of dissipation that has been introduced through highpressure circulation is removed by a closed-circuit cooling system. The physical correlation between temperature and viscosity m a k e s it essential to keep the temperature constant to < +1.5cC in order to achieve a constant pressure profile during the process. Pressure
Control
When one considers the pressure that the starting c o m p o n e n t s and, later, the reaction mix are subjected to, then the vital importance of this process parameter b e c o m e s evident. The starting pressure in the machine tank of 3-10 bar,
Fig2
Schematic diagram of a RIM plant with two positive displacement piston metering units, each supplying two mixing heads (showing only the polyol section): (a) machine tank, (b) positive displacement piston metering uniL and (c) clamping unit with mould and mixing head
which is also the pressure at which the polyol c o m p o n e n t receives its 20 to 70% gas loading, is increased to as high as 20 bar when the positive displacement pistons are filled, in order to make full use of the effective volume of the metering stroke. In the high-pressure circulation phase, which lasts s o m e 3-5 s, the c o m p o n e n t s are c o m p r e s s e d to between 150 and 250 bar. With highly reactive RIM systems, the injection process takes between 1 and 1.5 s. When the reaction mix flows into the mould it first of all relaxes to atmospheric pressure. This can then immediately rise to a level of 30 bar by the end of the injection phase, close to the gate, as a function of the flow resistance in the mould, the viscosity of the reaction mix and the output. Once injection is complete, high-pressure circulation of the c o m p o n e n t s is continued for a further 0.5 s or so, whilst the chemical reaction is taking place in the mould itself and a pressure profile develops up to the point of demoulding. The switchover from circulation to
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The constituent units of a RIM plant (showing only the polyol section): (a) storage tank, (b) glass fibre preparation station, (c) buffer tank, (d) machine tank with gas loading uni~ (e) positive displacement piston metering uniL (i) clamping unit with mould and mixing head
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A typical operating pressure profile for polyol and polyisocyanate.
MATERIALS & DESIGN Vol. 9 No. 6 NOVEMBER/DECEMBER 1988
include a standardised gate design (such as a dam gate) and an optimally configured venting system in conjunction with a precision-machined parting surface, which can be achieved with a gap of < 40/z today for contoured parts. The design of the venting system at the end of the flow path is particularly important on account of the internal
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A typical cavity pressure profile (recorded near to and away from the gate).
injection should be completed in < 10 ms. The resultant pressure peaks should not exceed 20 to 30 bar. Maximum shot reproducibility can only be obtained if rapidswitching mixing head systems are used - a requirement that is particularly important for operation with internal holding pressure.
Internal Holding Pressure The mould cavity is filled to 95-97% capacity with liquid reaction mix. The gas-loaded reaction mix relaxes once injection is completed and exerts an internal holding pressure for the full duration of the reaction. The maximum reaction pressures are between 10 and 15 bar. This produces blemish-free surfaces without sink marks. The pressure profiles in the mould, recorded close to and away from the gate, display a virtually identical course, ensuring a uniform density gradient over the whole of the moulding.
F~g6 Dam gate with an upstream flow restricton (a) mixing head, (b) interchangeable gate insert, (c) restrictor bar gate with flow restrictor, and (d) moulding. ¢2
b
Clamping Unit The cavity pressure profiles established give an indication of the clamping forces that are required. The pressure peak when the reaction mix enters the mould can be as high as 30 bar, whilst the pressure prevailing during the reaction generally lies between 10 and 15 bar. This then gives locking forces of > 2000 kN for large-area mouldings with a projected area of 1 m 2. By using easyrelease IMR systems, which largely obviate the need for release agent to be sprayed in the mould prior to each shot, it will be possible in some cases in the future to dispense with the open-book technology with its high outlay on design (ie tilting clamping plates to allow easier reach inside the mould). In addition, the level of automation has been considerably increased through the installation of parts-removal robots.
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Mould Design Considerable importance must also be attached to a suitably-tailored mould design for PUR. All the mould engineering details must be discussed in depth right at the design stage, with customers, processors and process engineers working closely together, and these must be adapted to the requirements of PUR. These requirements
MATERIALS 8, DESIGN Vol. 9 No. 6 N O V E M B E R / D E C E M B E R 1988
Fig7
Design of the venting region with an overflow chamber: (a) parting plane, (b) recess, (c) flash chamber, (d) moulded part, (e) venting and overflow slot, and (f) load removal slot.
327
holding pressure required. Flash chambers must be carefully connected to the moulded part and provision made for load removal whilst the mould is being run in. /
Fig8
reached an advanced stage of development. The pressure sensors, in particular, are subject to extreme fluctuations in load. Sensors working on the strain gauge principle will satisfy the requirements. Apart from the continuous monitoring of the injection pressure, it is also possible for individual pressure curves to be presented on a monitor with the aid of diagnostic units. The operator then sees what is currently happening at the workstation in question. Diagnostic units of this type are also required for setting up, ie, when changing moulds, in order to ensure that the circulation and injection pressure can be rapidly and reliably adjusted to the new values, which are a function of
Filling pattern for a car bodyside moulding compiled with the CADMOULD-Mephisto program.
I],,,L,'I ..........: I 7,5
45
Comparative observations of partial shots and filling pattern calculations have shown that the advance calculation method for the flow front, which has long been used in the field of thermoplastics, is also suitable for application with RIM. It is also possible to determine the optimum position of the gate in advance. It is, however, r e c o m m e n d e d that the recesses for the gate units be made somewhat larger than necessary (eg, twice the length of the gate) so that corrections can still be made at the running-in stage. The amount of time-intensive and costly alterations required to the mould during the running-in stage can be reduced at all events by using the flow front calculations. Tests in which a dye is injected illustrate the striking effect of a design that is not correctly tailored to PUR. With this method, a dye is briefly injected into the polyol section (eg, for 0.1 s) prior to entry into the mixing head. This not only shows up how the reaction mix settles into layers with time but also reveals the flow engineering problems that are created by sudden, extreme changes in wall thickness. Further design details that require careful consideration include: • the layout of grille sections with vertical shear edges and mating cams • a favourable layout for openings in flow engineering terms in order to ensure that the flow fronts meet up preferentially in a V-shaped configuration • gradual transitions to different wall thicknesses • the layout of wall thickness at the end of the moulded part, plus many more
Monitoring of Process Parameters Modern positive displacement piston metering units, with a linear amplifier drive and servo valve or proportional valve controls, satisfy the stringent requirements for accurate metering and maintenance of the requisite stoichiometric ratio. In addition, rapid-switching mixing head systems ensure a high shot reproducibility of < + 1% of the particular moulding weight. As already mentioned, precise monitoring of the temperature and pressure during the process is very important. These two key process parameters should be recorded in the highpressure section just prior to entry into the mixing head. Any deviation from the set target values can be displaye~l directly, thereby providing the operator with information on the cause of the malfunction and the means of rectifying it. The pressure and temperature sensors have
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temperature, operating pressure and gas loading of the polyol as a function of production time. lain lq 0 Jilt , ,
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Fig I 0 Time breakdown for a 60 sec cycle. the output. Since the process parameters of pressure, temperature, shot weight and gas loading are monitored for each injection cycle on each mould, it is also possible to record the current values and draw up production analyses at the end of a shift, for instance. If the temperature, pressure and gas loading are plotted as a function of the number of articles produced, then this will provide information as to the accuracy of process control on one hand, and will also indicate malfunctions and other down-time on the other. This ensures a transparent and reliable production sequence and means that selective measures may then be taken to correct any irregularities in the process. Cycle times Since the introduction of easy-release IMR systems, the cycle time for RIM mouldings has been reduced considerably. The prerequisite for this has been rapid, precisely-
MATERIALS & DESIGN Vol. 9 No. 6 NOVEMBER/DECEMBER 1988
operating RIM machines and clamping units with a rapid opening and clamping movement, which make it possible to dispense with the time-consuming tilting clamping plates in some cases, as already mentioned above. If the movements required for the mould, such as on core pullers and mechanical ejectors, are performed in a coordinated sequence, then cycle times of 60 sec are no longer impossible in large-scale production. The improved process dynamics becomes clear when the cycle is broken down into individual steps. Conclusion Making due allowance for all the findings and advances described, and also employing the latest in technology, the investment required for RIM machinery and equipment will inevitably be higher than it was a number of years ago. There is, however, no doubt but that the intensive development work undertaken has brought the process to maturity and given it a high level of economic efficiency. Being able to produce mouldings that are ready for painting and require no finishing in a 60 sec cycle makes the RIM process capable of standing up to competition from rival processing methods on all counts.
Acknowledgement This article was presented at the Polyurethanes World
Congress 198 7 and is reproduced by kind permission of the author, the US Society of the Plastics Industry and Fachoerband Schaumkunststoffe e V Federal Republic of Germany. General References Knipp, U Herstellung yon Grossteilen aus Polyurethan.Schaumstoffen Speyer, Zechner u H(ithig Verlag (1974). Piechota, H and H Rhhr lntegralschaurnstoffe. MLinchen, Carl Hanser Verlag (1975). Becker, W Reaction Injection Moulding, New York: van Nostrand Comp (1979). Boden, H, K Schulte and H Wirtz. "Verfahrenstechnik der P(_IRHerstellung", in Polyurethane, KunststoffHanclbuch, Bd 7 Munchen, Wein: Carl Hanser Verlag (1983). Mfiller, H, B K6per, U/V~ier and L Pierkes. "Neues zur Formteilfertigung aus Polyurethanen", 12 Kunststofftechnisches Kolloquium Aachen (1984). M611er, H "RIM-Technologie Beitrag zur Verbesserung und Sicherung der Fertigung technisch hochwertiger Formteile", Dissertation an der RW-rH, Aachen (1985). Begemann, M, U Maier and L Plerkes. "RIM-verbesse~e Maschinentechnik und gezielte Werkzeugauslegung erh6hen die Formteilqualit~it, 13 Kunststoffkolloquium, Aachen (1986). Doxie, P, F Lofffler, K Schulte and M-M Sulzbach. "Polyurethan-Sch~iumu. RIM-Anlagen", in: Auotmatisierung in der Kunststoff. Verarbeitung. MOnchen, Wien: Carl Hanser Verlag (1986).
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MATERIALS & DESIGN Vol. 9 No. 6 NOVEMBER/DECEMBER 1988
329
Abstract To produce high.quality polyurethane.reaction injection moulding (PUR.RIM) of the sort used in automotive exterior applications, the essential requirements are high.performance machinery and equipment plus a thorough understanding of aU the processing parameters. Successful production of blemish free articles at fast cycles, ready for painting and requiring no post. treatment is only possible if the interconnected chemical and technical processing sequences all function in perfect harmony. Working towards this goal, several teams of chemists, processing engineers and manufacturers have been co.operating on intensive programmes of research and developmen~ and today it can justifiably be claimed that the RIM process is remarkably mature for such a young technology. A determined effort is now required to incorporate the latest findings into the design of new machinery and to modify existing machinery accordingly. In this paper, a detailed discussion is presented of the two most important processing parameters (temperature and pressure) and the various factors which depend on them, and the need for accurate control of these parameters during the manufacturing process is stressed Details are also given of a production line complete with tooling designed specifically for the process. Together with an appropriate system of measuring, monitoring and recording the processing parameters, this is an essential prerequisite for cost- efficient production~
Introduction Three successful, key areas of development have made an essential contribution towards further rationalising the RIM process: • the chemical development of easy-release, IMR systems (In Mould Release) means that it is now possible to largely dispense with the external application of release agent to the mould prior to each injection cycle. • mastering the "on-the-spot" chemistry no longer presents any problems. The three states of aggregation that have to be processed - liquid (starting components), solid (eg, milled glass fibre) and gaseous (eg air or nitrogen) can be reliably controlled during the process. • significant knowledge has been acquired in the field of mould engineering in terms of a suitably-tailored mould lay-out and design for PUR. This paper looks into the basic improvements and findings.
Multiple-head Metering The metering system that is generally employed in the production of foamed parts has proved to be a weak point in the process engineering. The arrangement whereby several mixing heads and moulds are fed from a single metering unit via distributor stations does not always permit a suitably-configured pipeline system for the process or the constant temperature and pressure that this would ensure. A sensible compromise between the "one-to-one unit" in exclusive use in the USA (one
MATERIALS & DESIGN Vol. 9 No. 6 N O V E M B E R / D E C E M B E R 1988
metering unit to one mixing head) and the multiple-head metering system used in the past (where one metering unit feeds ten or more mixing heads) would be to have a symmetrical distribution system incorporating a maxim u m of two mixing heads. These are the only conditions that will allow an optimum pipeline configuration. Such a configuration requires: • the shortest possible link between the machine tank, the positive displacement piston metering unit and the mixing head • optimum pipeline cross-sections: Pipe dimensions should be kept as small as possible so that flow rates of approximately ~> 0.5 m / s can be achieved, thereby avoiding any settling out of the glass fibre-filled polyol. There should not, however, be an excessive loss of pressure in the pipeline system between the metering unit and the mixing head in order to ensure that most of the energy introduced, and the operating pressure of 150 to 250 bar, can be used for the impingement injection mixing process.
Temperature Control The temperature control of the starting materials is very important in reaction injection moulding. The two basic components are pre-heated to approximately 25°C in the tank farm. The polyol c o m p o n e n t is conveyed from the tank farm to the glass fibre mixing station. Whilst the glass fibre is being mixed in, the polyol is heated to the
325
i Z Fig i
Schematic diagram of a RIM unit with multiplehead metering (showing only the polyol section): (a) machine tank, (b) positive displacement piston metering unit, and (c) clamping unit with mould and mixing head
subsequent processing temperature of approximately 45°C. As the two chief c o m p o n e n t s are conveyed into the buffer and machine tanks (preferably in quantities of less than 10% of the effective tank capacity at a time) they are maintained at a constant temperature, and the heat of dissipation that has been introduced through highpressure circulation is removed by a closed-circuit cooling system. The physical correlation between temperature and viscosity m a k e s it essential to keep the temperature constant to < +1.5cC in order to achieve a constant pressure profile during the process. Pressure
Control
When one considers the pressure that the starting c o m p o n e n t s and, later, the reaction mix are subjected to, then the vital importance of this process parameter b e c o m e s evident. The starting pressure in the machine tank of 3-10 bar,
Fig2
Schematic diagram of a RIM plant with two positive displacement piston metering units, each supplying two mixing heads (showing only the polyol section): (a) machine tank, (b) positive displacement piston metering uniL and (c) clamping unit with mould and mixing head
which is also the pressure at which the polyol c o m p o n e n t receives its 20 to 70% gas loading, is increased to as high as 20 bar when the positive displacement pistons are filled, in order to make full use of the effective volume of the metering stroke. In the high-pressure circulation phase, which lasts s o m e 3-5 s, the c o m p o n e n t s are c o m p r e s s e d to between 150 and 250 bar. With highly reactive RIM systems, the injection process takes between 1 and 1.5 s. When the reaction mix flows into the mould it first of all relaxes to atmospheric pressure. This can then immediately rise to a level of 30 bar by the end of the injection phase, close to the gate, as a function of the flow resistance in the mould, the viscosity of the reaction mix and the output. Once injection is complete, high-pressure circulation of the c o m p o n e n t s is continued for a further 0.5 s or so, whilst the chemical reaction is taking place in the mould itself and a pressure profile develops up to the point of demoulding. The switchover from circulation to
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The constituent units of a RIM plant (showing only the polyol section): (a) storage tank, (b) glass fibre preparation station, (c) buffer tank, (d) machine tank with gas loading uni~ (e) positive displacement piston metering uniL (i) clamping unit with mould and mixing head
/ ~
~0 0 2
3
4
5
6 t
Fig 4
;
7
T] e ~ s o , ,
A typical operating pressure profile for polyol and polyisocyanate.
MATERIALS & DESIGN Vol. 9 No. 6 NOVEMBER/DECEMBER 1988
include a standardised gate design (such as a dam gate) and an optimally configured venting system in conjunction with a precision-machined parting surface, which can be achieved with a gap of < 40/z today for contoured parts. The design of the venting system at the end of the flow path is particularly important on account of the internal
30 28 26 24 22 28 18 ;6 near tile gate r
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injection should be completed in < 10 ms. The resultant pressure peaks should not exceed 20 to 30 bar. Maximum shot reproducibility can only be obtained if rapidswitching mixing head systems are used - a requirement that is particularly important for operation with internal holding pressure.
Internal Holding Pressure The mould cavity is filled to 95-97% capacity with liquid reaction mix. The gas-loaded reaction mix relaxes once injection is completed and exerts an internal holding pressure for the full duration of the reaction. The maximum reaction pressures are between 10 and 15 bar. This produces blemish-free surfaces without sink marks. The pressure profiles in the mould, recorded close to and away from the gate, display a virtually identical course, ensuring a uniform density gradient over the whole of the moulding.
F~g6 Dam gate with an upstream flow restricton (a) mixing head, (b) interchangeable gate insert, (c) restrictor bar gate with flow restrictor, and (d) moulding. ¢2
b
Clamping Unit The cavity pressure profiles established give an indication of the clamping forces that are required. The pressure peak when the reaction mix enters the mould can be as high as 30 bar, whilst the pressure prevailing during the reaction generally lies between 10 and 15 bar. This then gives locking forces of > 2000 kN for large-area mouldings with a projected area of 1 m 2. By using easyrelease IMR systems, which largely obviate the need for release agent to be sprayed in the mould prior to each shot, it will be possible in some cases in the future to dispense with the open-book technology with its high outlay on design (ie tilting clamping plates to allow easier reach inside the mould). In addition, the level of automation has been considerably increased through the installation of parts-removal robots.
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Mould Design Considerable importance must also be attached to a suitably-tailored mould design for PUR. All the mould engineering details must be discussed in depth right at the design stage, with customers, processors and process engineers working closely together, and these must be adapted to the requirements of PUR. These requirements
MATERIALS 8, DESIGN Vol. 9 No. 6 N O V E M B E R / D E C E M B E R 1988
Fig7
Design of the venting region with an overflow chamber: (a) parting plane, (b) recess, (c) flash chamber, (d) moulded part, (e) venting and overflow slot, and (f) load removal slot.
327
holding pressure required. Flash chambers must be carefully connected to the moulded part and provision made for load removal whilst the mould is being run in. /
Fig8
reached an advanced stage of development. The pressure sensors, in particular, are subject to extreme fluctuations in load. Sensors working on the strain gauge principle will satisfy the requirements. Apart from the continuous monitoring of the injection pressure, it is also possible for individual pressure curves to be presented on a monitor with the aid of diagnostic units. The operator then sees what is currently happening at the workstation in question. Diagnostic units of this type are also required for setting up, ie, when changing moulds, in order to ensure that the circulation and injection pressure can be rapidly and reliably adjusted to the new values, which are a function of
Filling pattern for a car bodyside moulding compiled with the CADMOULD-Mephisto program.
I],,,L,'I ..........: I 7,5
45
Comparative observations of partial shots and filling pattern calculations have shown that the advance calculation method for the flow front, which has long been used in the field of thermoplastics, is also suitable for application with RIM. It is also possible to determine the optimum position of the gate in advance. It is, however, r e c o m m e n d e d that the recesses for the gate units be made somewhat larger than necessary (eg, twice the length of the gate) so that corrections can still be made at the running-in stage. The amount of time-intensive and costly alterations required to the mould during the running-in stage can be reduced at all events by using the flow front calculations. Tests in which a dye is injected illustrate the striking effect of a design that is not correctly tailored to PUR. With this method, a dye is briefly injected into the polyol section (eg, for 0.1 s) prior to entry into the mixing head. This not only shows up how the reaction mix settles into layers with time but also reveals the flow engineering problems that are created by sudden, extreme changes in wall thickness. Further design details that require careful consideration include: • the layout of grille sections with vertical shear edges and mating cams • a favourable layout for openings in flow engineering terms in order to ensure that the flow fronts meet up preferentially in a V-shaped configuration • gradual transitions to different wall thicknesses • the layout of wall thickness at the end of the moulded part, plus many more
Monitoring of Process Parameters Modern positive displacement piston metering units, with a linear amplifier drive and servo valve or proportional valve controls, satisfy the stringent requirements for accurate metering and maintenance of the requisite stoichiometric ratio. In addition, rapid-switching mixing head systems ensure a high shot reproducibility of < + 1% of the particular moulding weight. As already mentioned, precise monitoring of the temperature and pressure during the process is very important. These two key process parameters should be recorded in the highpressure section just prior to entry into the mixing head. Any deviation from the set target values can be displaye~l directly, thereby providing the operator with information on the cause of the malfunction and the means of rectifying it. The pressure and temperature sensors have
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temperature, operating pressure and gas loading of the polyol as a function of production time. lain lq 0 Jilt , ,
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Fig I 0 Time breakdown for a 60 sec cycle. the output. Since the process parameters of pressure, temperature, shot weight and gas loading are monitored for each injection cycle on each mould, it is also possible to record the current values and draw up production analyses at the end of a shift, for instance. If the temperature, pressure and gas loading are plotted as a function of the number of articles produced, then this will provide information as to the accuracy of process control on one hand, and will also indicate malfunctions and other down-time on the other. This ensures a transparent and reliable production sequence and means that selective measures may then be taken to correct any irregularities in the process. Cycle times Since the introduction of easy-release IMR systems, the cycle time for RIM mouldings has been reduced considerably. The prerequisite for this has been rapid, precisely-
MATERIALS & DESIGN Vol. 9 No. 6 NOVEMBER/DECEMBER 1988
operating RIM machines and clamping units with a rapid opening and clamping movement, which make it possible to dispense with the time-consuming tilting clamping plates in some cases, as already mentioned above. If the movements required for the mould, such as on core pullers and mechanical ejectors, are performed in a coordinated sequence, then cycle times of 60 sec are no longer impossible in large-scale production. The improved process dynamics becomes clear when the cycle is broken down into individual steps. Conclusion Making due allowance for all the findings and advances described, and also employing the latest in technology, the investment required for RIM machinery and equipment will inevitably be higher than it was a number of years ago. There is, however, no doubt but that the intensive development work undertaken has brought the process to maturity and given it a high level of economic efficiency. Being able to produce mouldings that are ready for painting and require no finishing in a 60 sec cycle makes the RIM process capable of standing up to competition from rival processing methods on all counts.
Acknowledgement This article was presented at the Polyurethanes World
Congress 198 7 and is reproduced by kind permission of the author, the US Society of the Plastics Industry and Fachoerband Schaumkunststoffe e V Federal Republic of Germany. General References Knipp, U Herstellung yon Grossteilen aus Polyurethan.Schaumstoffen Speyer, Zechner u H(ithig Verlag (1974). Piechota, H and H Rhhr lntegralschaurnstoffe. MLinchen, Carl Hanser Verlag (1975). Becker, W Reaction Injection Moulding, New York: van Nostrand Comp (1979). Boden, H, K Schulte and H Wirtz. "Verfahrenstechnik der P(_IRHerstellung", in Polyurethane, KunststoffHanclbuch, Bd 7 Munchen, Wein: Carl Hanser Verlag (1983). Mfiller, H, B K6per, U/V~ier and L Pierkes. "Neues zur Formteilfertigung aus Polyurethanen", 12 Kunststofftechnisches Kolloquium Aachen (1984). M611er, H "RIM-Technologie Beitrag zur Verbesserung und Sicherung der Fertigung technisch hochwertiger Formteile", Dissertation an der RW-rH, Aachen (1985). Begemann, M, U Maier and L Plerkes. "RIM-verbesse~e Maschinentechnik und gezielte Werkzeugauslegung erh6hen die Formteilqualit~it, 13 Kunststoffkolloquium, Aachen (1986). Doxie, P, F Lofffler, K Schulte and M-M Sulzbach. "Polyurethan-Sch~iumu. RIM-Anlagen", in: Auotmatisierung in der Kunststoff. Verarbeitung. MOnchen, Wien: Carl Hanser Verlag (1986).
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