IMPROVED MOULDING PROCESSES AND APPARATUS

Abstract: A moulding apparatus and process is provided in which a plurality of streams (67a, b) of different feedstocks each from separate feedstock supply vessels (61a, b), are combined to form a mixed feedstock in a delivery head (65) prior to delivering to a mould (77) in a pour zone (81) relative to the delivery head (65) wherein separate pump means (62a, b) are provided to deliver, at constant speed of operation, a predetermined volume of the feedstock (67) at a predetermined flow rate to the mould (77) during a moulding cycle which additionally includes: first feedback control means (75) to control the feedstock material flow rate responsive to detected variations in the flow rate to within a set tolerance of the predetermined flow rate. The apparatus and process also provides for second feedstock control means (80) to identify a particular mould of the series of moulds, means (82) to select the feedstock flow rates for the mould and means (83a, b) to set the feedstock pumps (62) to the predetermined flow rates.

Description: IMPROVED MOULDING PROCESSES AND APPARATUS This invention relates to improvements in synthetic plastic materials moulding processes and apparatus and relates particularly but not exclusively to improvements in processes and apparatus for moulding of foamable synthetic plastics materials such as polyurethane foam plastics materials or elastomeric materials. In presently known processes for manufacturing moulded plastics material articles, feedstock materials 1Q required to produce the synthetic plastics material product are stored in separate storage vessels and delivered at high pressure during pouring of a mould via separate supply lines to a mixing and delivery head. The feedstocks are intimately mixed due to the impingement of the feedstocks at ις high pressure in the mixing head immediately prior to delivery or pouring of the mixed feedstocks into a mould to the pouring of mixed feedstock to succession of moulds is intermittent, the mixing head provides for the recirculation of individual feedstocks to the respective storage vessels 20 whilst a subsequent mould to be poured is being positioned in relation to the mixing head prior to pouring of the mixed feedstock into the mould. The recirculation of the feedstocks is designed to maintain, as near as possible, a homogeneous mix of the individual feedstocks and to maintain 25 as near as possible a uniform temperature of the individual feedstocks at any point in time, in the feedstocks storage and delivery system. The feedstocks are delivered to the mixing head by means of variable displacement hydraulic pumps driven at 30 constant speed by constant speed (i.e. at constant speed under constant load) electric motors. The output of the pumps may be varied by adjusting the displacement of the pump by manual, mechanical, hydraulic or electrical means. Such adjustment may be required to compensate for inherent -,. variations in the volumetric output of the pumps caused by mechanical tolerances in the pumps or caused, in the long term, by wear of the pump or in the shorter term by variations in the speed of operation of the pump caused by variations in the speed of operation of the electric motor driving the pump. The variation in the speed of operation of the "constant speed" electric motors is caused by variations in the load placed on the motors due to variations in the physical properties (such as specific gravity, viscosity etc.) of the feedstocks being pumped. The physical property variations may be caused by variations in temperature or composition, for example, of one or more of the feedstocks. In the case of the production of foamed plastics material products, particularly foamed polyurethane materials, small variations in the output of the pumps can produce relatively large variations in the physical characteristics of the resultant foamed polyurethane product. In the moulding of foam polyurethane products from polyol and isocyanate feedstocks, for example, it is possible for the volumetric output of the pumps to vary by + 1.5 % for the polyol feedstock and by + 3.0 % for the isocyanate feedstock. In the absence of any corrective measures, constant predetermined volumes of feedstock are not delivered via the mixing head to the mould. This results in the production of moulded products, over a period of time, with a variation in characteristics or properties which may be outside defined product tolerances. A high incidence of reject products can therefore result. Such adjustment may also be required if different feedstock mixes are required in successive moulds of a series of different moulds or if different feedstock mixes are required in different sections of an individual mould to produce for example a foamed plastics material article having sections with different hardness or resiliency characteristics such as in a motor vehicle seat or back rest cushion. The adjustment of the output of the pump by adjusting the displacement of the pump cannot be readily accomplished to compensate for inherent variations in output of the pump as the mechanical adjustment of the pump does not provide for sufficiently accurate volumetric adjustment. The volumetric output of the pumps may be manually varied to compensate for such charge but such variation will still result in the production of unacceptable products as the variations are made only when noticeable changes in the physical characteristics of product occur. The testing of the physical characteristics of a product is time consuming. Furthermore, as the products, in the case of foamed products, continue to cure after removal from a mould until a full cure is achieved, any testing of the characteristics 0 must be made at a specified time after removal of a product from a mould for any meaningful comparison of products to be made and to determine whether any variation of pump output is required. A high incidence of reject or unsatisfactory _. _ products can therefore result when variations in the volume of feedstock materials delivered to the mould vary as a result of changes in process operating parameters which are not corrected or adjusted instantaneously. It is an object of the invention to provide a 20 process and apparatus for production of moulded foam or elastomeric products which overcomes disadvantages of known processes and apparatus. The process and apparatus of the present invention overcomes or substantially alleviates some or all of the 25 disadvantages of known like processes and apparatus by providing feedback control means to control the feedstock material flow rate by adjustment of the speed of operation of the feedstock pump means. The process and apparatus also provide second feedback control means to set a predetermined 30 volume of feedstock for a particular mould of a series of different moulds. The process and apparatus also provide via the second feedback control means for the delivery of the predetermined volume of different feedstock mixes in different sections of a multi-compartment mould. -,. The present invention in one form therefore provides a moulding apparatus in which a plurality of streams of different feedstocks each from separate feedstock supply vessels, are combined to form a mixed feedstock in a delivery head or heads prior to delivering to a mould in a pour zone relative to the delivery head wherein separate pump means are provided to deliver, at constant speed of operation, a predetermined volume of the feedstock at a predetermined flow rate to the mould during a moulding cycle which additionally includes : first feedback control means to control the feedstock material flow rate responsive to detected variations in the flow rate to within a set tolerance of the 10 predetermined flow rate. Preferably the first feedback control means includes means to monitor the feedstock flow rate, means to compare the flow rate with a predetermined flow rate and means to vary the flow rate in response to deviations from _. j . the predetermined flow rate. Preferably the feedstock flow rate is monitored by means of a frequency controller, connected to a motor driving the pump, which detects and corrects variations in the speed of operation of the pump, which is directly related to the volume of feedstock 2Q delivered by the pump, to deliver the predetermined volume of feedstock. Preferably the second feedstock control means includes means to identify a particular mould of the series of moulds, means to select the feedstock flow rates for the mould and means to set the feedstock pumps to the __ predetermined flow rates. Preferably the apparatus includes means to control the moulding cycle between a low pressure recirculation cycle, a high pressure recirculation cycle, and a pour cycle. Preferably driving the low pressure recirculation cycle, feedstocks are recycled to the g0 feedstock supply vessels to maintain uniform composition of each feedstock, and during the high pressure recirculation cycle the second feedback control means sets the predetermined volume of feedstock for a mould in the pour zone. - c Preferably the feedstocks comprise of one or two polyol feedstock compositions and one or two isocyanate feedstock compositions each having separate supply systems to the delivery head. The present invention in another form also provides a moulding apparatus in which a plural: / of streams of different feedstocks each from a separate feedstock supply are combined to form a mixed feedstock prior to delivery through a delivery head or heads to one of a series of moulds in a pour zone relative to the delivery head wherein separate pump means are provided to deliver, at constant speed of operation, a predetermined volume of the feedstock at a predetermined rate to the mould during a moulding cycle which additionally includes : first feedback control means to control the feedstock material flow rate responsive to variations in the flow rate to within a set tolerance of the predetermined flow rate; and second feedback control means to set the predetermined volume of feedstock responsive to the particular mixed feedstock requirement of any mould in the pour zone. The present invention further provides a moulding apparatus in which a plurality of streams of different feedstocks each from a separate feedstock supply, are combined to form a mixed feedstock prior to delivery through a delivery head or heads to a mould in a pour zone relative to the delivery head wherein separate pump means are provided to delivery, at a constant speed of operation, a predetermined volume of the feedstock at a predetermined rate to the mould during a moulding cycle which additionally includes : means to monitor the rate of delivery of a feedstock by the pump means during the delivery cycle; means to compare the rate of delivery of the feedstock with a predetermined rate of delivery for the moulding cycle; and means to vary the speed of operation of the pump means to deliver during the moulding cycle a volume of feedstock within a set tolerance of the predetermined volume of feedstock for the mould in the pour zone. The present invention in a further variation also provides a moulding apparatus in which a plurality of streams of different feedstocks, each from a separate feedstock supply, are combined to form a mixed feedstock prior to delivery through a delivery head or heads to one of a series of moulds in a pour zone relative to the delivery head wherein separate pump means are provided to delivery, at a constant speed of operation, a predetermined volume of the feedstock at .a predetermined rate to the mould during a moulding cycle which additionally includes : means to monitor the rate of delivery of a feedstock by the pump means during the delivery cycle; means to compare the rate of delivery of the feedstock with a predetermined rate of delivery for the moulding cycle; means to vary the speed of operation of the pump means to deliver during the moulding cycle a volume of feedstock within a set tolerance of the predetermined volume of feedstock for the mould in the pour zone; and means to identify the one of the series of moulds in the pour zone and to set the predetermined volume of feedstock for the mould. The present invention also provides a moulding process in which a plurality of streams of different feedstocks each from separate feedstock supply vessels are combined to form a mixed feedstock in a delivery head prior to delivery to a mould wherein separate pump means are provided to deliver, at constant speed of operation, a predetermined volume of the feedstock at a predetermined flow rate to the mould during a moulding cycle which process includes the improvement which comprises the steps of : providing first feedback control means to control the feedstock flow rate responsive to detected variations in the flow rate to within a set tolerance of the predetermined flow rate. Preferably the first feedback control means includes means to monitor the feedstock flow rate, means to compare the flow rate with a predetermined flow rate and means to vary the flow rate in response to deviations from the predetermined flow rate. Preferably the feedstock flow rate is monitored by means of a flow meter which produces a signal to a central processor which controls the frequency controller connected to a motor driving the pump, which detects and corrects variations in the speed of operation of the pump, which is directly related to the volume of feedstock delivered by the pump, to deliver the predetermined volume of feedstock. Preferably the second 10 feedstock control means includes means to identify a particular mould of the series of moulds, means to select the feedstock flow rates for the mould and means to set the feedstock pumps to the predetermined flow rates. Preferably the moulding cycle includes a low pressure recirculation 15 cycle, a high pressure recirculation cycle, and a pour cycle. Preferably during the low pressure recirculation cycle, feedstocks are recycled to the feedstock supply vessels to maintain uniform composition of each feedstock and during the high pressure recirculation cycle the second 20 feedback control means sets the predetermined volume of feedstock for a mould in the pour zone. Preferably the process is a thermosetting polyurethane foam moulding process in which there are one or two polyol feedstock compositions and one or two isocyanate 25 feedstock compositions each having separate supply systems to the delivery head. In a variation the present invention provides a moulding process in which a plurality of streams of different feedstocks, each from a separate feedstock supply, -,Λ are combined to form a mixed feedstock prior to delivery through a delivery head to one of a series of moulds in a pour zone relative to the delivery head wherein separate pump means are provided to deliver, at substantially constant speed of operation, a predetermined volume of 25 feedstock at a predetermined rate to a mould during a moulding cycle which process includes the improvement which comprises the step of: providing first feedback control means to control the feedstock flow rate, responsive to variations in the flow rate, to within a set tolerance of the predetermined flow rate; providing second feedback control means to set the predetermined volume of feedstock responsive to the particular mixed feedstock requirement of any mould in the pour zone. The present invention also provides a moulding f . process in which a plurality of streams of different feedstocks, each from a separate feedstock supply, are combined to form a mixed feedstock prior to delivery through a delivery head to a mould wherein separate pump means are provided to deliver, at constant speed of operation, a C predetermined volume of the feedstock, at a predetermined rate to the mould during a moulding cycle which process includes the improvement which comprises the steps of : monitoring the rate of delivery of a feedstock by the pump means during the delivery cycle; comparing the rate of delivery of the feedstock 0 with a predetermined rate of delivery for the moulding cycle; and varying the rate of delivery of the feedstock by variation of the speed of operation of the pump means, to 5 deliver during the moulding cycle, a volume of feedstock within a set tolerance of the predetermined volume of the feedstock. The present invention also further provides a moulding process in which a plurality of streams of 0 different feedstocks, each from a separate feedstock supply, are combined to form a mixed feedstock prior to delivery through a delivery head to one of a series of moulds in a pour zone relative to the delivery head wherein separate pump means are provided to deliver, at constant speed of 5 operation, a predetermined volume of feedstock at a predetermined rate to a mould during a moulding cycle which process includes the improvement which comprises the steps of: monitoring the rate of delivery of a feedstock by the pump means during the delivery cycle; comparing the rate of delivery of the feedstock with a predetermined rate of delivery for the moulding cycle; varying the rate of delivery of the feedstock by variation of the speed of operation of the pump means, to deliver, during the moulding cycle, a volume of feedstock within a set tolerance of the predetermined volume of the feedstock; and 10 monitoring the identity of the mould in the pour zone by means of a feedback process controller to set the predetermined volume of feedstock required for the mould in the pour zone. _. _ Preferably the pump means includes a variable displacement pump set to deliver a predetermined volume of feedstock at a predetermined speed driven by a constant speed (constant speed at constant load) electric motor. Preferably the first feedback control means comprises a 20 variable drive for the electric motor which senses variations in the load on the motor and increases or decreases the speed of the motor and thus the pumps to maintain the predetermined feedstock flow rate. The apparatus preferably includes a second feedback 25 control means to set the predetermined volume of feedstock material and the feedstock flow rate for the mould. Alternatively, the apparatus includes a flow meter to monitor the predetermined feedstock flow rate, the flow meter being in communication with the second control means which comprises signals generated by the flow meter, and 30 indicative of flow rate, with the predetermined flow rate. Other preferred features of the process and apparatus of the invention will be readily apparent from the following description. 35 Preferred features of the process and apparatus of the invention will now be described with reference to the accompanying drawings in which : Figure 1 is a schematic representation of known plastics material moulding apparatus; Figure 2 is a schematic representation of a plastics material moulding apparatus in accordance with one form of the present invention; and Figure 3 is a schematic representation of a plastics material moulding apparatus in accordance with an alternative form of the invention. Figure 4 is a schematic representation of a 0 plastics material moulding apparatus including a plurality of moulds. Referring to Figure 1, there is shown a moulding system 10 comprising a mixing head 11 including a dispenser or pour nozzle 12 connected to a first feedstock supply 5 vessel 13 by supply line 15 and feedstock return line 17. Similarly, the mixing head 11 is connected to a second feedstock supply vessel 14 by supply line 16 and feedstock return line 18. The system additionally includes feedstock recycle o lines 17a and 18a including suitable valve means (not shown) to enable recycling of the feedstocks other than through the mixing head. This permits the system to operate in three modes : a first or recycle mode when the feedstocks are 5 recycled via lines 15, 17a and 17 or 16,18a and 18; a second or stand-by mode when the feedstocks are recycled via lines 15 and 17 or 16 and 18 through the mixing head 11 immediately prior to pouring; and a third or pour mode when the mixed feedstocks are 0 dispensed via nozzle 12 to a mould (not shown). The mixing head includes a dispenser or pour nozzle 12 to enable mixed feedstocks to be delivered to the mould for subsequent processing to form the desired moulded product. Storage vessel 13 may contain for example a polyol 5 feedstock and storage vessel 14 and appropriate isocyanate feedstock when the system is used to manufacture injection moulded foam polyurethane products. Each supply line 15, 16 includes pump means 19 to pump the feedstock materials in - li ¬ the system. The pumps operate at low pressure during the recycle mode and at high pressure during the stand-by or pour modes. The pumps deliver the feedstocks at high pressure to the mixing head 11 where mixing occurs by c impingement of the feedstocks under the high pressure as the feedstocks are dispensed via nozzle 12 to the mould. The mixing head can be controlled to dispense mixed feedstocks into a mould or can be controlled to a stand-by mode to separately recirculate the respective feedstocks via line 17 - Q and 18 to storage vessels 13 and 14. The stand-by mode is intended to maintain uniform composition and temperature of the feedstocks at high pressure immediately prior to the operation of the dispenser or pour mode for that particular mould. The recycle mode is operated whilst successive 15 moulds are removed or positioned in relation to the mixing head. Each of the pump means 19 comprises a variable output hydraulic pump 20 set to a specific output for any particular predetermined volume of feedstock depending on 2Q the composition of the mixed feedstock required for a particular injection moulding process. The pump 20 is driven by a constant speed electric motor 21. The output of the pump 20 may vary due to variations in ambient temperature or other conditions such as feedstock _ 5 composition variations which affect the viscosity of the feedstock for example. Any such variation in the output of one pump not in accord with an equivalent variation in the operation of the other pump will result in a mixed feedstock of incorrect composition with regard to the relative volumes _ 0 of the two feedstocks. Such variations lead to variations in the chemical and physical properties of the final moulded product which are difficult to control and lead to an unacceptably high level of reject products. The output of the pump 20 may be varied by g5 operation of electric, hydraulic or pneumatic servo-mechanism 22. The adjustment may be in response to perceived variations in the operation of the pump means such as a variation in the driving motor speed. Any adjustments made do not prevent the possibility of an incorrect volume of feedstocks being delivered to the mixing head as any adjustments made do not immediately rectify the perceived variation such that the variation is corrected without resulting in an inferior product being moulded. Such a conventional system displays substantial feedstock material flow variation for the reasons specified above. For example, in a system for injection moulding of foam polyurethane products, the typical volume accuracy values for the high viscosity (2000-2500cp) polyol feedstock are + 1.5%. The volume accuracy value for the low viscosity (40-60 cp) is isocyanate feedstock is + 3.0%. Such variations either separately or combined, for example +1.5% with -3.0% lead to foam polyurethane products with an unacceptably high rate of product being outside designated chemical or physical tolerances. An unacceptably high rate of rejected products therefore follows as a consequence. Referring to Figure 2, there is shown an improved injection moulding system 30 in accordance with one preferred form of the invention comprising, as for Figure 1, a mixing head 11 connected to storage vessel 13 by supply line 15, return line 17 and recycle line 17a. Similarly, as in Figure 1, the mixing head is also connected to storage vessel 14 by supply line 16, return line 18 and recycle line 18a. Again the mixing head includes dispenser or pour nozzle 12 and the return recycle and pour operations proceed as previously described in relation to pour, stand-by and recycle modes for Figure 1. Each of the pump means 19 comprises a variable displacement pump 31 set to deliver a predetermined volume of feedstock material at a predetermined speed of operation. The pump is driven by constant speed at constant load motor 32, the speed of which is controlled by variable drive 33. The variable drive 33 senses via feedback line 32a the load on the pump 31 and motor 32 and automatically adjusts the speed of the motor (and thus the output of the pump 31) to compensate for any deviation from a predetermined value. The predetermined value for each pour mode will depend on the pour requirements for any particular mould (not shown) of a series of different moulds to be poured whilst a mould is in a pour zone with respect to the mixing head 11 and nozzle 12. The predetermined value for - any particular mould is communicated to the variable speed drive 33 by process controller 34 via communication lines 33a is programmed to identify any particular mould, programmed with the particular pour characteristics for that mould and programmed to communicate an appropriate command 0 signal to the variable speed drive 33. The process controller also provides appropriate communication to the system in relation to the recycle, stand-by and pour modes of the system. The variation in the volume of material being delivered by the pump may be due to various reasons 5 such as varying ambient temperatures or pressures or varying feedstock material compositions which affect the viscosity of the feedstock materials and thus affect the load on the pump causing variations in its speed of operation and the volume of delivery of the feedstock materials. This is 0 compensated for by motor load sensing loop 84 which will cause appropriate change of the drive output frequency which in turn will alter motors and pumps speed and in effect will maintain a substantially constant output of the feedstock. The output of the pump 31 is thus controlled with greater c accuracy as compared to currently known processes. Referring to Figure 3, there is shown a further alternative injection moulding system 40 in accordance with the invention. Mixing head 11 is again connected to supply vessels 13 and 14 as before by supply lines 15 and 16 and 0 recycle lines 17a and 18a and return lines 17 and 18 as described with reference to Figure 2. The pump means 19 is also as described with regard to Figure 2 and includes a constant volume output pump 31 being a variable displacement pump set to deliver a predetermined constant volume of 5 feedstock material at constant speed of operation. The pump 31 is driven as before by motor 32 controlled by variable drive 33 via feedback line 32a. The system additionally includes flow meters 41 in high pressure supply lines 15 and 16 between the pumps 31 and the mixing head 11. These flow meters measure the actual volumetric flow rate of feedstock materials in the supply lines during the pour mode of operation of the system. The flow meters 41 generate and transmit signals to the process controller 43 via lines 42 which compares each signal with reference signals corresponding to predetermined feedstock volumes and flow rates. Where deviations occur from the reference signals, the process controller sends a command signal to the variable drive 33 via lines 33a to increase or decrease the speed of the motor 32 and thus to vary the output of pump 31 as required. In a process for the moulding of a variety of different complex polyurethane moulded products from polyol and isocyanate feedstocks it is possible using the present invention to inject a plurality of different polyol-isocyanate feedstock mixtures into different portions of the mould by varying the volumes of polyol feedstock and isocyanate feedstock introduced into different sections of the mould. It is also possible where the moulding system includes a variety of moulds for different products, to utilise a system with a second polyol storage vessel and appropriate pump, supply and control means to enable selection between two differing polyol feedstock materials for pouring into different sections of a mould or for pouring into different moulds for differing product requirements. The series of moulds required for the various products may be arranged sequentially on a conveyor system such that the process controller can be readily programmed to identify each individual mould. Referring to Figure 4, there is shown a schematic representation of the moulding apparatus 40 of Figure 3 in association with a production line 56 including a plurality of moulds 50, 51, 52, 53. The moulding apparatus is as described in Figure 3 with like parts having like numbering. The moulds 50 to 53 are mounted, along with other moulds (not shown) to circulate on a continuous production line 54. As mould 50 approaches pour zone 55 the system is in recycle mode where the feedstock materials are recycled at low pressure via supply lines 15, 17a and 17 and 16, 18a and 18 respectively. As the mould 50 enters pour zone 55, the process controller identifies the mould and selects the appropriate predetermined feedstock material and flow rate volume for each feedstock and selects the stand-by mode wherein the reedstock materials are recycled at the normal operating pressure through the mixing head 11. The process controller monitors the process parameters including the flow rate via flow meters 41 and 42 and selects pour mode to permit the feedstock materials to be mixed under pressure in the mixing head 11 and to be poured via nozzle 12 to mould 50. As the pour continues the process controller 43 monitors the flow rate of feedstock materials and provides appropriate commands as necessary to variable drives 33 as required if the feedstock material flow rates vary from the predetermined flow rate for mould 50. When pouring of mould 50 has been completed the process controller 43 sets the system to recycle mode and mould 50 passes from the pour zone 55. The cycle is repeated when the next mould 51 enters the pour zone with the process controller 43 selecting the appropriate predetermined feedstock material volumes and flow rates (which may be the same as or different from those of mould 50) for mould 51. Should mould 51 be a multi-section mould the process controller 43 selects the predetermined feedstock material volume and flow rate for each section of the mould. Referring to Figure 5 there is shown a particularly preferred plastics material moulding apparatus constructed in accordance with the invention. The apparatus 60 includes a mould line 74 including a series of moulds 77, 78, 79 which successively pass moulding station or pour zone 81. The moulds are successively filled with mixed polyurethane/ isocyanate moulding composition from mixing head 65 supplied with individual components via component pipelines 67, 68 from feedstock supply vessels 61. The components are delivered to the mixing head 65 by means of pumps 62. The present illustration is described in relation to the manufacture of polyurethane foam products and feedstock 61a is for example a polyol feedstock mix and feedstock 61b is a isocyanate feedstock mix. The pumps 62, driven by pump motors 63, are c controlled by frequency controllers 83 connected to the pump motors 63 to deliver a predetermined volume of feedstock at constant speed. Due to variations in ambient conditions the load on the motor from the pump may tend to vary causing a variation in the speed of operation of the pump. This load 10 variation is detected by the frequency controller which corrects the frequency of the pump motor to maintain the motor at a predetermined speed of operation and this maintains a predetermined speed of operation and delivery volume for the pump. . j . As the requirements of successive moulds or different cavities in a mould may be different as regards volumes of feedstock materials or ratios of feedstock materials the processor 75 sets the predetermined speed for a particular mould. 20 The mould carrier conveyor system 74 consists of a suitable drive (not shown in detail), conveying chain or carousel arrangement with attachments to accommodate desired number of moulds. A suitable mould heating and temperature control system is provided to maintain required mould 25 temperature in order to support the chemical process. The mould conveyor consists also of suitable means to provide all moulds necessary actions such as closing, locking, tilting, opening etc. The entire moulding apparatus is controlled by a 30 suitable control system such as a computer, a P.L.C. or a dedicated processor. The P.L.C. 75 has been chosen to accommodate all the field devices' inputs and outputs both digital and analogue. The P.L.C. ("the processor") 75 is connected to all the field devices in order to be capable of making and 35 sending appropriate signals to hold the production process within specification. The controller also has the capacity of performing some mathematic calculations including integration. Figure 5 illustrates a basic two chemical component or feedstock system. The chemical components (or feedstock) are stored in storage vessels 61 under constant and predetermined temperature. The feedstocks are fed via supply lines 67 to metering pumps 62 driven by suitable A.C. electric motors 63. Depending on the position of the valve means 64 the chemicals can recirculate via lines 69 and 70 and heat exchangers 66 back to the storage vessels 61 (low pressure recirculation mode) or when the valve means 64 are directed by the controller 75 to assume an alternative position the chemicals will recirculate from pump means 62 via flowmeter means 76 and supply lines 68 to the mix head 65 and then via return lines 71 and the valve means 64, the heat exchangers 66 back to the feedstock supply 61 (high pressure circulation mode). In the present embodiment the pump means 62 used are high pressure rotating pumps. However, any constant output rotating pump including a suitable gear pump will be effective if capable of delivering required output at required pressure, such as A2VK12 and A2VK28 Hydromatic or Rexroth. The pump means 62 run continuously so that by recirculation, the chemicals will retain constant temperature and viscosity. The system however, can run successfully in ON - OFF mode as well, providing other adequate chemical temperature control means are maintained. During normal operation the operation of the mould line 74 causes successive moulds 77, 78, 79 to pass through the moulding station or pour zone 81. Each mould successively activates sensor 80 which signals to controller 75 that a particular mould is approaching the moulding station 81. The controller 75 activates the valves 64 so that the system is in high pressure circulation mode with the feedstocks circulating via pipelines 67, 68, 71, 70 through the mixing head 65. At the same time the pumps 62 are set to their predetermined speeds for each feedstock material in order to deliver the required volume of feedstock materials through the mixing head 65 to the particular mould or mould cavity within the moulding station or pour zone 81. The processor confirms that all operating parameters are correct and the activation of sensor 82 causes the mixing head to be operated by hydraulic controller 73 (provided by hydraulic source 72) to open the 5 mixing head and permit the predetermined volume of mixed feedstock materials to pass into the mould. Once the pour mode is complete the controller returns the system to the. low pressure recirculation mode by operation of valves 64 so that the feedstock materials recirculate via lines 67, 69, 10 70 to the feedstock supply 61 until the next mould trigger sensor 80 causing the cycle to be repeated. In a further modification after the pour mode is complete the controller 75 causes the mixing head 73 to be closed causing the system to remain in a high pressure ις recirculation mode for a few seconds over which time pulses generated by chemical stream flowmeters means 76 are computed and compared with predetermined flow values. At that stage the controller 75 causes the system to move to the low pressure recirculation mode awaiting for the next 2o mould to activate the sensor 80 and then repeat the pouring sequence predetermined for the next mould. During the intervening time the controller 75 performs further calculations. Having calculated the chemical flows it computes by how much if at all the flow rate has to be 5 altered to meet the predetermined output values. When the sensor 80 is energised, new reference signals are generated by the controller 75 and the calculated correction factors are applied to them to achieve the desired current frequencies in the frequency controller 83 to set the pump 0 motor 63 (and thus pump 62) to the predetermined speed of operation which in turn will generate the correct feedstock flows in the correct ratios. As previously indicated the speed of operation and thus the volume delivered by the pump 62a is determined by 5 the speed of operation of the pump motor 63a. The speed of operation of the pump motor is controlled by frequency controller 83a which detects any changes from the speed of operation (predetermined for a particular mould by processor 75) caused by temperature or viscosity variations of feedstock materials which in turn result in variations in the load on motor 62a and thus its speed of operation, and compensates for such changes in order to maintain the speed of operation at the predetermined speed (whatever that may be) for the particular mould about to be filled. It will be apparent that the delivery of each feedstock 61a or 61b is independently controlled by the processor 75 to ensure that the feedstock materials are circulated and delivered to the mixing head in the correct volume ratios to accurately control the composition of the final foamed product produced. It will be readily apparent that the described apparatus may include more than one polyol or isocyanate feedstock so that differing polyol/isocyanate compositions may be delivered to a particular mould or section of a single mould. The apparatus may therefore include a second polyol and a second isocyanate feedstock supply system appropriately controlled by processor 75 to deliver either polyol or mixed polyol for example to a particular mould via one or more delivery or mixing heads. A different combination of feedstock material volumes may be used for different sections of the mould to enable a product having controlled varying physical characteristics to be moulded. In the case of the production of moulded foam polyurethane products from a polyol feedstock material, the variation of the predetermined volume of the isocyanate feedstock material with respect to the polyol feedstock material in different sections of the mould will result in a foamed polyurethane product having varying hardness and/or resiliency characteristics in different sections of the final moulded product. It will be evident therefore that accurate control of the actual volume of feedstock materials is possible as compared to known processes. In the processes of the present invention as applied to manufacture of injection moulded foamed polyurethane products, the volume accuracy of the polyol feedstock material is thus able to be controlled to + 0.3 % and the volume accuracy of the isocyanate feedstock is able to be controlled to + 0.4 %. The more accurate control of the feedstock materials in accordance with the present invention results in the unexpected reduction of "out of specification" final products by a factor of from 50 to 100. It will be readily apparent that whilst the invention has been described with particular reference to the manufacture of foamed polyurethane moulded products, the process of the invention may be applied to any injection moulding process for producing either foam or elastomer products from two or more streams of feedstock materials. It will also be readily apparent that the process of the invention may be applied to a system in which a series of moulds require different feedstock combinations to produce a different desired product in a particular mould. The system of the invention may equally well be applied to the situation where a single mould may require different feedstock combinations in different areas of the mould to produce, in the case of a foam product, different resiliency or hardness in different areas or sections of the final foam moulded product. In such cases, it may be desirable to include two or more different polyol feedstock and isocyanate feedstock supply systems including supply and recirculation lines, supply tanks and pump and control systems for each product stream. In such cases, the process controller includes means to recognise each individual mould and to control the mixing head to release the appropriate feedstock streams. The control of the actual volumes being delivered by references preset operating parameters monitored and controlled to deliver accurate volumes of feedstock streams as described with reference to Figures 2 and 3. The process of the invention is equally applicable to injection of mixed feedstock streams into an open mould which is subsequently closed or into a closed mould through an injection port. The process and apparatus of the present invention is readily able to be adapted to accurately control delivery of mixed feedstocks from two or more feedstock supply vessels through one or more mixing or delivery heads.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A moulding process in which a plurality of streams of different feedstocks each from separate feedstock supply vessels are combined to form a mixed feedstock in a delivery head or heads prior to delivery to a mould wherein separate pump means are provided to deliver, at constant speed of operation, a predetermined volume of the feedstock at a predetermined flow rate to the mould during a moulding cycle which process includes the improvement which comprises the steps of: providing first feedback control means to control the feedstock flow rate responsive to detected variations in the flow rate to within a set tolerance of the predetermined flow rate. 2. A process as claimed in claim 1 in which the first feedback control means includes means to monitor the feedstock flow rate, means to compare the flow rate with a predetermined flow rate and means to vary the flow rate in response to deviations from the predetermined flow rate. 3. A process as claimed in claim 1 or 2 in which the feedstock flow rate is controlled by means of a frequency controller connected to a motor driving the pump, which controller detects and corrects variations in the speed of operation of the pump, which speed is directly related to the volume of feedstock delivered by the pump, to deliver the predetermined volume of feedstock. 4. A process as claimed in claim 1, 2 or 3 in which the second feedback control means includes means to identify a particular mould of the series of moulds, means to select the feedstock flow rates for the mould and means to set the feedstock pumps to the predetermined flow rates. 5. A process as claimed in claim 1 in which the moulding cycle includes a low pressure recirculation cycle, a high pressure recirculation cycle, and a pour cycle. 6. A process as claimed in claim 5 in which during the low pressure recirculation cycle, feedstocks are recycled to the feedstock supply vessels to maintain uniform composition of each feedstock. 7. A process as claimed in claim 5 in which during the high pressure recirculation cycle the second feedback control means sets the predetermined volume of feedstock for a mould in the pour zone. 8. A process as claimed in any one of claims 1 to 7 in which the process is a thermosetting polyurethane foam moulding process. 9. A process as claimed in claim 8 in which there are one or two polyol feedstock compositions and one or two isocyanate feedstock compositions each having separate supply systems to the delivery head. 10. A moulding apparatus in which a plurality of streams of different feedstocks each form separate feedstock supply vessels, are combined to form a mixed feedstock in a delivery head or heads prior to delivery to a mould in a pour zone relative to the delivery head wherein separate pump means are provided to deliver, at constant speed of operation, a predetermined volume of the feedstock at a predetermined flow rate to the mould during a moulding cycle which additionally includes: first feedback control means to control the feedstock material flow rate responsive to detected variations in the flow rate to within a set tolerance of the predetermined flow rate. 11. Apparatus as claimed in claim 10 in which the moulding cycle includes a low pressure recirculation cycle, a high pressure recirculation cycle, and a pour cycle. 12. Apparatus as claimed in claim 11 in which during the low pressure recirculation cycle, feedstocks are recycled to the feedstock supply vessels to maintain uniform composition of each feedstock. 13. Apparatus as claimed in claim 11 in which during the high pressure recirculation cycle the second feedback control means sets the predetermined volume of feedstock for a mould in the pour zone. 14. Apparatus as claimed in claim 10 in which the first feedback control means includes means to monitor the feedstock flow rate, means to compare the flow rate with a predetermined flow rate and means to vary the flow rate in response to deviations from the predetermined flow rate. 15. Apparatus as claimed in claim 13 or 14 in which the feedstock flow rate is controlled by means of a frequency controller connected to a motor driving the pump, which controller detects and corrects variations in the speed of operation of the pump, which speed is directly related to the volume of feedstock delivered by the pump to deliver the predetermined volume of feedstock. 16. Apparatus as claimed in claim 13, 14 or 15 in which the second feedback control means includes means to identify a particular mould of the series of moulds, means to select the feedstock flow rates for the mould and means to set the feedstock pumps to the predetermined flow rates. 17. Apparatus as claimed in claim 10 in which there are one or two polyol feedstock compositions and one or two isocyanate feedstock compositions each having separate supply systems to the delivery head. SUBSTITUTESHEET

Inventors: MALECZEK WOJCIECH, MALECZEK, WOJCIECH
Applicants: HENDERSONS IND PTY LTD, HENDERSON'S INDUSTRIES PTY. LTD.
Application year: 1991
Main classification: B29C45
IPC codes: B29B7, B29C39, B29C43, B29C45, B29K21