HIGH PRESSURE MIXING HEAD FOR REACTIVE COMPONENTS

Abstract: A high pressure mixing head (1000) for mixing at least two reactive components for reaction injection molding or reinforced reaction injection molding pro­ cesses, and a reactive component injection valve (2) for such high pressure mixing head. The mixing head comprises a mixing head body (999) having an elongated mixing chamber with a first metering plunger (2010) therein, said mixing chamber communicating with an elongated quieting chamber disposed substantially normal to said mixing chamber, said mixing chamber having at least one inlet port through which a reactive component is injected by a reactive component injection valve. The quieting chamber has a second clean-out plunger therein (3010). The first metering plunger has at least one axially extending by-pass channel (2080) which provides fluid communication between an inlet port (500) to said chamber and an outlet passage when said plunger is in its recir­ culation position, said channel thereby providing for recirculation of reactive component through said mixing head in a path external to said reactive component injection valve. The reactive component injection valve comprises a valve body (600); an injection nozzle (604,605) disposed in said body; a reactive component supply passage disposed in said body; a first reciprocating member (620) disposed within the supply passage and selec­ tably positionable to open, partially open or close said nozzle, varying the flow of reactive component through said nozzle whereby the pour pressure of said component may be set; a reactive component recircu­ lation passage disposed in said body; and a second reciprocating member (650) disposed within the recirculation passage selectably positionable to open, partially open or close said passage, thereby varying the flow of reactive component through said passage, whereby the recirculation pressure of said component may be set and recirculation is effected in a path internal to said reactive component injection valve.

Description: The invention relates to high pressure mixing heads for at least two reactive components for reaction injection molding or reinforced reaction injection molding processes, whereby such components are mixed and the resulting mixture fed to a mold cavity. More particularly, the invention relates to a high pressure mixing head, having at least one reactive component injection valve of the invention, that mixes a plurality of reactive polymeric components for subsequent injection into a mold. Reaction injection molding, also called liquid injection molding, is a technique for combining liquid reactive components and injecting them into a mold where they rigidify to form a finished polymeric product. The component combination may be achieved by directing streams of two or more liquid reactive components, each under high pressure, to cause their impingement at a common point in a mixing chamber of a mixing head. The resultant component impact creates a homogeneous mix of material in the mixing chamber, which is then either injected under pressure into a closed mold to which the mixing head is connected, or the mix may simply be dispensed into an open mold. Reinforced reaction injection molding is a variation of that process in which one of the liquid reactive components is mixed with a reinforcing material, such as glass fiber or the like, before being introduced into the mixing chamber. In the production of urethane products, for example, a diisocyanate or polyisocyanate component is reacted with a diol or a polyol component to produce the reaction mixture by separately feeding these components into a mixing chamber, effecting impingement mixing, and thereafter displacing the intimately-formed mix from the chamber into a mold in which the mix can set. It is also known to include in one or both of the components, or their mixture, an additional foaming or blowing agent capable of expanding the polymerizing resin to form cells or pores therein. Expanding agents suitable for this purpose include those which are normally liquid but volitize at the mold temperature, those which are gaseous and are held under pressure until the material is introduced into the mold, and those which are released by chemical action during the mixing stage and thereafter. In general, the conditions under which the two compoents are mixed require that the two components be held separate from one another until the instant at which they enter the mixing chamber, since any premature contact of the two components with one another will result in hardening of the materials. Such premature contact often results in the formation of a mass obstructing further outflow of one or both of the components or the mixture. In order to prevent such obstructions, both components are generally provided in a highly flowable form and are circulated by pumps or the like, being provided to the mixing chamber by various means only when reaction to produce the product mix for molding is desired. One form, illustrated in Keuerleber et al., U.S. Patent No. 3,706,515, includes a body that has an elongated bore which defines a mixing chamber. A plurality of nozzle orifices open into the mixing chamber for conducting reactive polymeric components thereto. The orifices are ordinarily directed at a common point in the mixing chamber to effect impingement of each component with all others to accordingly mix the components together into a homogeneous fluid mass. Flow of all components through all nozzle orifices is simultaneously controlled by a plunger mounted for axially reciprocal movement in the mixing chamber. When the plunger is retracted into its injection position, the orifices in the mixing chamber are opened, permitting reactive components to issue therefrom in the form of high velocity impinging streams. The mixing head also includes a plurality of return passage means, each of which opens into the mixing chamber at a location axially displaced from its respective component nozzle orifice. The plunger is formed with a plurality of axially extending by-pass channels which respectively communicate, when the plunger is in an extended, recirculation position, between the nozzle orifice and return passage means for each component, whereby a closed loop leading back to the component supply is established, providing recirculation for all components simultaneously. Recirculation occurs only via a path external to the nozzle orifices and related valve means. It is not possible to recirculate components individually in the Keuerleber et al. mixing head, nor is it possible to set the recirculation pressure of each recirculating component by means located at the head, individually or otherwise. Another form of mixing head involves the provision of a second chamber leading to the mold and at substantially right angles to the mixing chamber, this second chamber being provided in turn with a second piston, plunger or ram to drive the mixture out of the chamber. Fiorentini U.S. Patent No. 4,332,335 discloses a high pressure mixing head in which the additional chamber has the effect of quieting the highly turbulent mixture driven from the mixing chamber into that chamber. The second piston in the quieting chamber serves to clear the channel at the end of each mixing phase and thus prevent the channel from being plugged up by the reacting mixture. The structure of the first chamber and plunger, and the recirculation means of that plunger (axially extending by-pass channels), are substantially identical to that illustrated by Keuerleber et al. Again, recirculation occurs only via a path external to the reactive component injection valves and related apparatus. It is not possible to recirculate components individually, nor is it possible to set the recirculation pressure of each recirculating component by means located at the mixing head, individually or otherwise. Another form of mixing head involves the provision of means in the reactive component injection valves which allow for recirculation of reactive components internally through the valve when mixing of that component is not ongoing. Schneider U.S. Patent NO. 4,239,732 illustrates a complex reaction injection component valve mechanism utilizing the combination of a solid metering plunger and a reciprocating valve member having an internal passageway with a constricted outlet through which the reactive component must flow. The force of the fluid provided by the acceleration resulting from passage through the restriction impacts on the solid piston when it is in an extended, recirculation position, which stops supply of the component into the mixing chamber and initiates component recirculation. Schneider provides no mechanism in the injection valve for stopping and starting the flow of reactant into the mixing chamber -- the injection port is simply blocked by the solid piston (see Figures 3 and 4). No mechanism is provided for selecting the pour pressure or varying the flow into the mixing chamber from said valve. The Schneider valve will not function if the plunger is provided with any type of recirculation or by-pass channel, such as disclosed by Keuerleber et al. U.S. Patent No. 3,706,515, to provide a recirculation path external to the injection valve. Yet another form of mixing head illustrated in Boden et al. U.S. Patent No. 4,378,335 involves the provision of external recirculation through axially extending by-pass channels in a metering piston with an injection valve which, although incapable of internal recirculation, does provide means for selecting the pour pressure or varying the flow of reactive component into the reaction chamber (Figure 1). The valve comprises only one reciprocating member, which opens and closes the valve and controls entry of reactive component to the mixing chamber. Not only does Boden et al. fail to provide for internal recirculation in said valve, but it also fails to provide any mechanism in said valve for varying the flow and/or back pressure of the recirculating reactive component. Boden et al. also discloses a second form of mixing head (Figure 2), which does not provide for recirculation external to the injection valve through the metering piston, incorporating instead a solid piston. Means are provided for selecting at least two pour pressure/flow varying positions of the single reciprocating member, whereby the opening and closing of the valve and entry of reactive component to the mixing chamber is controlled. While allegedly providing for internal recirculation of reactive component through the valve, the actual structure of the valve in Figure 2 is plainly inoperative for that function. No provision in that valve is made for any mechanism to vary the flow and/or back pressure of the recirculating reactive component. In EP-A-45,555 an apparatus for producing a mixture of two or more synthetic components and for feeding it into a mould is disclosed, said apparatus comprising a mixing chamber with inlet apertures for the individual components and a common aperture in the direction of the mould; there being associated with the mixing chamber a control piston by means of which the mixing of the components can be started or interrupted by opening or closing said apertures respectively. The mixing chamber is confronted by injector support units which can be moved hydraulically in order to define two operating positions, namely a component injection position when the control piston allows mixing to start, and a component recycle position when the control piston interrupts mixing. With the control piston there is associated a second piston mobile between two positions, namely a retracted position in which the outlet of the mixing chamber is open to an extent which can be variably throttled, and an extended position in which the outlet of the mixing chamber is closed and the conduit which runs from this latter to the mould is obstructed. Each of the systems suffered from a variety of serious shortcomings and problems. Valves affording external recirculation only through axially-extending metering plunger by-pass channels require that all reactive components supplied to the mixing chamber recirculate simultaneously. With those designs, it is impossible to selectively recirculate some, but not all, of the reactive components provided to the mixing chamber. Valves affording only on/off flow of a reactive component to the mixing chamber require the time consuming and expensive replacement of nozzle means or nozzle orifices to effect a change in pour pressure or amount of material provided to the mixing chamber. Valves affording internal recirculation, but neither external recirculation through metering plunger by-pass channels nor adjustment of recirculation back pressure in said valve, make difficult the appropriate setting of recirculation back pressure, and maintenance of the recirculation pressure close to the pour pressure at a point close enough to the mixing chamber to enable virtually instantaneous changeover of reactive component from recirculation to injection modes, as well as losing the ability to provide rapid cycling through external, axially-extending metering plunger by-pass channel recirculation for all components simultaneously where the same reactive components are continuously being provided to said mixing chamber. With the advent of multiple, particularly dual density or dual firmness urethane products, the shortcomings of the available mixing heads became acute. The preparation of dual firmness articles requires high pressure mixing head apparatus having the capability to mix reactive components interchangeably, thereby forming two different polymeric densities in the molded product. One mechanism for production of dual density articles involved the use of two separate high pressure mixing heads, one capable of mixing reactive chemicals resulting in polymeric material of a first density, the other capable of mixing different reactive chemicals resulting in material of a second density. Each head had to discharge the formulation into the same mold for production of the final product. The use of two heads had many disadvantages, including substantial expense, the weight of two heads (which makes the use of robotic apparatus to provide formulation to the molds impossible in most instances, becuase of the limited weight-bearing capacities of available apparatus), the complexities of supply and recirculate hosing and attendant equipment which the use of two heads entailed, and the complexity and expense of system controls which were necessary to coordinate the operation of the two heads. The manufacture of dual density products requires the ability to change the chemical composition of the formulation almost instantaneously, particularly where robotic apparatus is used to transport the mixing equipment and manipulate that equipment to lay down different formulations in a pattern in the mold. The need to make the changeover in the formulation "on the fly" presented additional problems over those already present in available mixing head apparatus, particularly if a single high pressure mixing head was to supply dual density material. The rapid change in density of material which would have to be satisfied in one head would require the combination of one reactive species, A, with another, B, at a first time (for example, the impingement mixing of a polyol 1 with isocyanate), while a third reactive species, A*, was recirculating in the system in some manner. The recirculating material would have to be maintained at a recirculation pressure very close to the desired pour pressure for that material, because there would be no time to build up pressure when formulation change was demanded. When the second density formulation was called for, the flow of first reactive species, A, into a mixing area would have to stop instantaneously, that material recirculated in some manner, and the A* reactant switched from recirculation to introduction to that same mixing chamber for impingement mixing with reactant B. At the same time, the formulation would have to be delivered from the head to the mold, and the mixing chamber and any quieting chamber kept clear of formulation to prevent fouling. Because of the combination of rapid formulation composition change and the need to expel formulation from the head while preventing fouling, the demands upon the recirculation capabilities of such a system is beyond that previously provided for. There is thus a need for mixing head apparatus that would provide dual density reactive component formulation for introduction into molds, useful for reaction injection molding and/or reinforced reaction injection molding processes, that 1. Requires only one mixing head to provide dual density formulation for the production of molded polymeric products; 2. Provides a choice of internal and external (with respect to the reactive component injection means) recirculation paths through the mixing head for each reactive component, to allow rapid changeover between different density formulations, yet provide flexibility and appropriate transport and clearance of mixed reactants from the head, 3. Provides an internal recirculation path independent of an external path using axially extending by-pass channels in a metering plunger for each reactive component, thereby allowing independent injection and recirculation capabilities for each reactive component affected by density changeover, yet able to make virtually instantaneous changeover at the desired pour pressure; 4. Provides for "in the head", independent ad]ustment and setting of both pour and recirculating pressures for each reactive component, whereby the necessary pressure balances for rapid changeover could be established at a point as close as possible to the impingement mixing location in the mixing chamber, while providing for more rapid system set-up and independent alteration of previously set pressures with convenience and speed; and 5. Operates at high pressure, assuring excellent mixing through impingement techniques. No available mixing head has a combination of these features, particularly failing to provide the choice of recirculation paths, including an internal recirculation path independent of an external path via axially extending by-pass channels in a metering plunger, and "in the head" adjustment of both pour and recirculation pressure. The invention thus provides a high pressure mixing head for mixing reactive components comprising: a mixing chamber (2050) communicating with a quieting chamber (3050), a reaction component injection valve (600) communicating with said mixing chamber (2050), a first plunger (2010) in said mixing chamber (2050) movable between a retracted position in which reaction component is injectable into said mixing chamber (2050) through said injection valve (600) and an extended position in which material in said mixing chamber (2050) is discharged into said quieting chamber (3050), first recirculation passage means in said mixing chamber (2050) and first plunger (2010) for recirculating reactive component injected into said mixing chamber (2050) through said injection valve (600) when said first plunger (2010) is in said extended position, first reciprocating means selectively movable between open and closed positions for selectively starting and stopping discharge of reaction component from said injection valve (600), and second recirculation passage means within said injection valve (600) for recirculating reaction component when said first reciprocating means is in said closed position blocking discharge of reactive component from said injection valve (600) into said mixing chamber (2050), whereby selective operation of said first reciprocating means provides selective use of only one or the other of said first and second recirculation passage means. The novel high pressure mixing head and reaction component injection valve of the invention provide for the preparation of dual density polymeric products through a single, high pressure head heretofore unavailable. The invention solves one or more of the needs which available mixing head designs were unable to provide, including providing high pressure impingement mixing for forming dual density product formulations in a mixing head having means for two different, independent recirculation paths: those interal to the reactive component injection valve(s), and those external to said valves; enabling the independent injection and recirculation of each reactive component whose introduction must be varied to change the chemical makeup of the formulations and thereby the density of the molded product; and providing for "in the head", independent adjustment and setting of both pour and recirculation pressures for each reactive component, whereby the necessary pressure balances for rapid changeover could be established at a point as close as possible to the impingement mixing location in the mixing chamber, while providing for more rapid system set up and independent alteration of previously set pressures with convenience and speed. The novel reaction component injection valve of the invention itself provides capabilities heretofore unavailable, including a recirculation path internal to the valve; means selectably positionable to open, partially open or close nozzle means in said valve,whereby the flow of reactive component and its pour pressure through said nozzle may be set; and means selectably positionable to open, partially open or close said internal recirculation path, whereby the recirculation flow of reactive component and recirculation pressure through that path may be set. It is therefore an object of this invention to provide a high pressure mixing head for the impingement mixing of reactive components for reaction injection molding or reinforced reaction injection molding processes to provide multiple density formulations for the production of molded polymeric products. It is another object of this invention to provide a single high pressure mixing head having two recirculation paths for each reactive component which may be chosen as necessary, one of said paths, being independent of the use of axially extending by-pass channels in a metering plunger, being internal to the injection valve, thereby providing independent injection and recirculation capabilities for each reactive component affected by density changeover, while affording virtually instantaneous changeover at the desired pour pressure. It is a further object of this invention to provide a single high pressure mixing head having means for "in the head", independent adjustment and setting of both pour and recirculation pressure for each reactive component, whereby the necessary pressure balances for rapid changeover may be established at a point as close as possible to the impingement mixing location in the mixing chamber. It is yet another object of this invention to provide a novel reactive component injection valve having a recirculation path internal to itselt; means to open, partially open or close nozzle means therein, whereby the flow of reactive component and its pour pressure thrugh said nozzle may be set; and means selectably positionable to open, partially open or close said internal recirculation path, whereby the recirculation pressure through the path may be set. Further embodiments of the invention are defined in the features of the dependent claims. Other objects and advantages of this invention will become apparent upon reading the following detailed description. Figure 1 is a top view of an embodiment of the high pressure mixing head of the invention. Figure 2 is a side view of an embodiment of the high pressure mixing head of the invention. Figure 3 is a sectional view of the reactive component injection valve of the high pressure mixing head of the invention, taken along line 3-3 in Figure 2. Figure 4 is a detail view of the reactive component injection valve illustrated in Figure 3. Figure 5 is a sectional detail view of the reactive component injection valve, taken along line 5-5 in Figure 4. Figure 6 is a sectional detail view of the reactive component injection valve, taken along line 6-6 in Figure 4. Figure 7 is an exploded view of internal means of the reactive component injection valve illustrated in Figures 3 to 5. A preferred embodiment of the high pressure mixing head of the invention is more fully illustrated in Figures 1 to 7. A high pressure mixing head 1000 is shown generally in Figure 1. In its major components, the mixing head has a mixing head body 999 , and a metering plunger assembly 2000 affixed thereto, which comprises a first metering plunger, a mixing chamber defined in combination with said body and a hydraulic, dual acting cylinder for imparting retracting and extending reciprocal axial movement to said plunger with respect to the longitudinal axis of the mixing chamber. Hydraulic conduits 2001 , 2002 are supply and return conduits for a fluid material, which lines are further connected to supply, pressurizing and control means of the type well known in the art. A clean-out plunger assembly 3000 is also affixed to body 999 , which assembly comprises a second, clean-out plunger, a quieting chamber defined in combination with said body and a hydraulic, dual acting cylinder for imparting retracting and extending reciprocal axial movement to said plunger with respect to the longitudinal axis of the quieting chamber. Assembly 3000 is disposed so that its longitudinal axis is substantially at a right angle to that of the metering plunger assembly 2000 . The configuration of the metering plunger assembly 2000 and the clean-out plunger assembly 3000 forms an "L" structure, and the mixing head may be referred to as an "L" mixing head. Hydraulic conduits 3001 and 3002 are supply and return conduits for a fluid material, which conduits are further connected to supply, pressurizing, and control means of the type well known in the art. Each plunger assembly bears position sensing means at its distal end. Means 2003 on metering assembly 2000 senses when the metering plunger is in its maximum position of retraction. Means 3003 on clean-out plunger assembly 3000 senses when the clean-out plunger is in its maximum position of retraction. These positioning means act in cooperation with the supply, pressurizing and control means for each of said assemblies, to enable the sequential retraction and extension of each of the metering and clean-out plungers during the operation of the mixing head, as explained more fully hereafter. The preferred embodiment is configured to provide for the injection of three reactive chemicals to the mixing chamber in metering assembly 2000 . These chemicals may preferably comprise an isocyanate, a first polyol component and a second polyol component. (additional foaming or blowing agent, if required, may be introduced into the supply line for any of these components, preferably a polyol, upstream of the mixing head.) A reactive component mix formed from the impingement mixing of the isocyanate with the first polyol component provides a liquid froth which, when molding is complete, is converted to a urethane product having a first density X. A reactive component mix formed from the impingement mixing of the isocyanate with the second polyol component provides a liquid froth which, when molding is complete, is converted to a urethane product having a second density, Y, which may be greater or less than first product density X. While two reactive component injection valves of the invention, valves 1 and 2 , arrayed so as to extend in substantially the same plane, normal to the axis of the clean-out assembly 3000 and substantially parallel to the axis of the metering assembly 2000 , and an isocyanate injection valve 3 , arrayed at an acute angle to the axis of the clean-out plunger assembly 3000 , comprise the preferred embodiment, additional reactive component rejection valves of the invention may be disposed radially about the mixing chamber. The number of reactive component injection valves of the invention that may be used is limited only by the physical constraints of the diameter of the mixing chamber and the size of mixing head body 999 . Four polyol reactive component injection valves, for exmaple, may be radially arranged so as to extend in substantially the same plane normal to the longitudinal axis of the metering assembly 2000 (and in a plane substantially parallel to the longitudinal axis of the clean-out assembly 3000 ), with the isocyanate injection valve arranged above that plane, at an acute angle thereto. In that manner, the injected components streams from all five injectors may be aligned so as to impinge at substantially the same point in the mixing chamber. Isocyanate injection valve 3 (Figures 1 and 2), as illustrated, is an injector of the type known to the art. The novel reaction component injection valve of the invention, however, may be used to supply isocyanate to the mixing chamber. Isocyanate is supplied to injection valve 3 by isocyanate supply conduit 31 , and is returned to the isocyanate source through conduit 30 . Metering pumps, storage tanks, heating means and related apparatus (not shown) make up the remainder of such isocyanate supply system, all as is well known to those skilled in the art. Reaction injection valve 1 , which provides a first polyol reactive component to the mixing chamber disposed in body 999 and assembly 2000 , is provided with supply conduit 11 and two return conduits, 12 and 13 . Conduit 12 returns recirculating polyol to the polyol source, when that recirculation is effected through a path external to the valve. Conduit 13 returns recirculating polyol to the polyol source, when that recirculation is effected through a path internal to the valve. Metering pumps, storage tanks, heating means and related apparatus (not shown) make up the remainder of such first polyol supply system, all as is well known to those skilled in the art. Reaction injection component valve 2, which provides a second polyol reactive component to the mixing chamber disposed in body 999 and assembly 2000 , is provided with supply conduit 21 and two return con duits , 22 and 23 . Conduit 22 returns recirculating polyol to the polyol source, when that recirculation is effected through a path external to the valve. Conduit 23 returns recirculating polyol to the polyol source, when that recirculation is effected through a path internal to the valve. Metering pumps, storage tanks, heating means and related apparatus (not shown) make up the remainder of such second polyol supply system, all as is well known to those skilled in the art. Assembly of the mixing head is provided by the use of threaded bolts, which are received in tapped receiving bores in the body 999 , in the case of the metering assembly 2000 (bolts 100 ). Clean-out assembly 3000 is fastened to body 999 by the use of threaded bolts 200 (Figure 2), which are received in threaded bores in the assembly. Each of the reaction component injection valves for each polyol component are mounted to a body member 601 having a reactive component chamber 660 by threaded bolts 101 , which are received in threaded bores in the body member 601 . The body member 601 is, in turn, fastened to mixing head body 999 by bolts 102 , which are received in threaded bores in the said body. Hydraulic conduits 14 , 15 in valve 1 are supply and return conduits for a fluid material, which conduits are further connected to supply, pressurizing and control means (not shown) of the type well known in the art, whereby the first and second reciprocating means in the first polyol valve (hereafter described) are actuated. Hydraulic conduits 24 , 25 in valve 2 are supply and return conduits for a fluid material, which conduits are further connected to supply, pressurizing and control means (not shown) of the type well known inthe art, whereby the first and second reciprocating means in the second polyol valve (hereafter described) are actuated. Hydraulic conduit 32 is a supply conduit for a fluid material, which conduit is further connected, along with another return conduit not shown in Figures 1 or 2, to supply, pressurizing and control means (not shown) of the type well known in the art, whereby the isocyanate injection means is actuated. The positional relationship between the mixing head body 999 , the metering assembly 2000 and the clean-out assembly 3000 , and the components comprised by each, is illustrated in Figure 2. Metering assembly 2000 comprises a first, metering plunger 2010 , which is in turn made up of a double acting piston 2020 and an elongated, axially extended plunger body 2030 . Plunger body 2030 is closely and slidably received in first bore 2050 , which defines in part an elongated mixing chamber, closed at the end proximal to position sensor 2003 by the end of plunger body 2030 when fully retracted and open at an outlet opening 2060 . By regulation of the fluid supply to double acting piston 2020 , so that fluid pressure is applied to face 2021 of that piston (through conduit 2002 ), plunger body 2030 may be retraced in an upwardly direction with respect to outlet opening 2060 , so that its end distal from piston 2020 leaves the opening 2060 unobstructed, while similarly leaving unobstructed inlet ports 500 disposed in the peripheral wall of first bore 2050 . That portion of bore 2050 unoccupied by the plunger body 2030 when the position 2020 is in its uppermost, retracted injection piston, comprises the mixing chamber of the mixing head. By applying fluid pressure to face 2020 of the double acting piston 2020 (through conduit 2001 ), the plunger body 2030 is displaced from its retracted, injection position to its extended, recirculation position, as illustrated in Figures 2 and 3. In displacing the plunger body 2030 towards outlet opening 2060 , the end of the plunger body serves to drive out all reactive chemical formulation present in the mixing chamber, thereby cleaning out materials which would otherwise harden and block the injection ports and mixing chamber. The movement of plunger body 2030 brings each of axially extending by-pass channels 2080 into alignment with an injection port 500 and an outlet passage 501 from the bore 2050 (Figure 3). Port 500 and the entrance to passage 501 are coaxial, the entrance being spaced axially in the peripheral wall of the bore with respect to the bore centerline therefrom. Although illustrated in Figure 3 as being vertically above port 500 , the entrance to passage 501 is located at a position below the port 500 as well. The by-pass channels 2080 are provided to correspond to each aligned pair of an inlet port 500 and outlet passage 501, through which combination fluid communication is established between each inlet port 500 and outlet passage 501 entering and leaving the mixing chamber. There is one by-pass channel 2080 formed in plunger body 2030 for each port, all having the same axial extent and each separated from the other by elongated finger lands 2070 . Because of the spatial arrangement between the reactive component injection valves and the by-pass channels, all channels 2080 align with all ports 500 and outlet passages 501 simultaneously. Recirculation of reactive component from port 500 through by-pass channel 2080 into outlet passage 501 and out of the mixing head body 999 results, if reactive component continues to be injected through port 500 . The extended, recirculation position of the plunger body 2030 provides the port 500 to by-pass channel 2080 to outlet passage 501 pathway by means entirely external to the reactive component injection valves 1 and/or 2 . The plunger body 2030 to bore 2050 fit is, by necessity, as close as can be attained by ordinary machining techniques, to prevent leakage of the high pressure reactive component streams as they are injected into the mixing chamber, and as they recirculate through the external path provided by axially extending by-pass channels 2080 and outlet passages 501 . Binding and/or seizing of the plunger body 2030 in the bore 2050 is prevented by sheathing substantially all of the plunger surface in a sleeve (not shown) of a friction reducing material. The plunger is formed to prevent this sleeve from flowing or otherwise being squeezed into the by-pass channels 2080 by machining the plunger wall surrounding the by-pass channels 2080 to form depressed regions for receiving the antifriction sleeve, yet leaving peripherally continous metal lands 2071 surrounding the respective channels to provide the necessary structural restraint for the sleeve. The outer surface of the plunger body 2030 is formed with a recess that completely encompasses the plunger intermediate its length and extends axially downwardly to form the elongated finger lands 2070 that lie between and are axially coextensive with the by-pass channels 2080 . The recess is milled in the plunger body 2030 so as to leave the finger lands 2070 which peripherally enclose channels 2080 and meld into the land 2071 at the free end of the plunger. The sleeve is suitably secured in this recess, as by cementing, so as to provide a major portion of the plunger body 2030 bearing surface, yet be supported laterally of the recess by the lands 2070 , 2071 which prevent extrusion of flow under pressure into the by-pass channels 2080 or endwise of the free end of the plunger body. The sleeve is preferably made of a polymeric material and defines a plunger body diameter which is slightly larger than the diameter of said bore 2050 prior to insertion therein, but is compressed when inserted into the bore 2050 to form a close sliding seal therewith. The nature of the friction reducing material of the sleeve is of some criticality. It has been found that a material sold under the trademark "RULON" by Dixon Corporation, Bristol, Rhode Island, is well suited for this purpose. Such material is described in U.S. Patent Nos. Re. 26,088 and 3,652,409 assigned to that company. In general, it is a composite consisting of a homogeneous mixture of three components comprising (a) polytetrafluoroethylene (PTFE); (b) a silicate such as glass, talc, mica or aluminum silicate; and (c) a metallic particulate of a metal such as molybdenum, copper, lead or silver. Additional information on several forms of the product is given in a Dixon Corporation catalog entitled "Design Engineering Manual 101." Another material useful as a possible equivalent comprises a homopolymer of p-oxybenzoyl repeating units, sold under the trade name "Ekanol" by the Carborundum Company, Niagara Falls, N.Y., in combination with PTFE (polytetrafluoroethylene) polymer and glass fiber. Clean-out assembly 3000 is arrayed at substantially a right angle to metering assembly 2000 , as shown in Figure 2, and comprises a second, clean-out plunger 3010 , which is in turn made up of double acting piston 3020 and an elongated, axially extended plunger body 3030 . Plunger body 3030 is slidably received in a second bore 3050 , which defines in part an elongated quieting chamber, closed at the end proximal to position sensor 3003 by the end of plunger body 3030 when fully retracted, and open at an outlet opening 3060 , which constitutes a longitudinal bore in output nozzle 4000 . The nozzle 4000 comprises the exit means from the mixing head of the reactive chemical formulation, which is in liquid froth form at the point. Nozzle 4000 , in operation of the head to produce molded polymeric articles, is positioned over a mold and liquid froth is provided to the mold therefrom. The mold is then closed and heated, causing a chemical reaction to take place and producing the resulting polymeric product. By regulation of the fluid supply to double acting piston 3020 , so that fluid pressure is applied to face 3021 of that piston (through conduit 3001 ), the plunger body 3030 may be retracted in an inward direction with respect to nozzle 4000 , away from outlet opening 3060 , so that its end distal from piston 3020 leaves the opening 3060 unobstructed. That portion of bore 3050 which is unoccupied by plunger body 3030 when the piston 3020 is in its innermost, retracted position, comprises the quieting chamber of the mixing head. Liquid reactive components resulting from high pressure impingement mixing of the components in the mixing chamber defined by plunger body 2030 and bore 2050 flows through outlet opening 2060 and into the side wall of bore 3050 . The impact of that stream with the wall of the bore, and the right angle taken by the flow path from bore 2050 to bore 3050 into outlet 3060 acts to convert the turbulent flow into a substantially laminar flow. Liquid reaction formulation is, as a result, discharged through nozzle 4000 into a mold without splashing of the formulation. By applying fluid pressure to face 3022 of the double acting piston 3020 (through conduit 3002), plunger body 3030 is displaced from its retracted position to its extended, clean-out position, as illstrated in Figures 2 and 3. In displacing the plunger body 3030 outwardly towards opening 3060 , the end of the plunger serves to drive out all of the reactive component formulation present in the quieting chamber, thereby cleaning out formulation which would otherwise harden and block the quieting chamber and mixing head exit means. The sequence of movements of plungers 2010 and 3010 during a mixing cycle begins with both plungers in their fully retracted positions. Reactive components are injected into the mixing chamber in bore 2050 , where they mix by high pressure impingement mixing and form a liquid froth. Outlet opening 2060 , being unblocked by plunger body 3030 , allows that liquid froth to pass from the mixing chamber into the quieting chamber in bore 3050 . Movement of plunger body 2030 is initiated by applying fluid pressure to face 2022 of piston 2020 , which drives the plunger down the length of the mixing chamber towards outlet opening 2060 . The liquid formulation is all forced through outlet opening 2060 into the quieting chamber. Axially extending by-pass channels 2080 simultaneously align with all injection ports 500 , providing fluid communication to one each of aligned passages 501 for each injection port. Reactive components injected through the ports are thereby recirculated through paths external to their respective injection valves. As plunger body 2030 reaches the maximum degree of its extending travel, movement of plunger body 3030 is initiated by applying fluid pressure to face 3022 of piston 3020, which drives the plunger along the length of the quieting chamber towards outlet 3060 . The remaining liquid formulation is all forced through outlet 3060 and nozzle 4000 to the enviroment proximate to the nozzle. In a normal use environment, formulation would be supplied to a mold. Plunger body 3030 is then returned to its fully retracted position by the application of fluid pressure to face 3021 of piston 3020 . Plunger body 2030 is thereafter returned to its fully retracted position by the application of fluid pressure to face 2021 of piston 2020 . Position sensor 3003 senses when the piston 3020 reaches maximum retraction, while position sensor 2003 senses when the piston 2020 reaches maximum retraction, which information is used by the control means to perform the cycle described. The withdrawal of plunger body 2030 breaks the external recirculation path between ports 500 , by-pass channels 2080 and outlet passages 501 , leading to the reinstitution of injection into the mixing chamber. No variation of the recirculation pressure experienced by reactive component externally recirculating between ports 500 , by-pass channels 2080 and outlet passages 501 is possible in the mixing head of the invention. The geometry of the path will, however, provide a certain inherent back pressure when recirculating through this path. Recirculation pressure adjustment in those paths can be effected if appropriate valving or other restricting means, downstream of passages 501 , are installed in the return lines upstream of the necessary reactive component pumps and storage tanks. The preferred embodiment of the mixing head of the invention provides a liquid reservoir 5 for introduction of components into the mixing chamber. Di-octyl phthalate, for example, may be provided to the liquid mix from reservoir 5 . An additional location for introduction of another reactive or non-reactive component is provided at port 900 , located opposite outlet 2060 at the junction of bores 2050 and 3050, and covered by plug 901 . An injector of the type known in the art may be connected to port 900 , or an injection means of the invention may instead be connected to the port. Any components may be supplied at port 900 to the formulation including, for example a polyol, colorant material, colorant borne in a polyol, and/or any other additive material. The reaction component injection valves of the preferred embodiment of the invention are best illustrated in Figures 3 to 7. Valves 1 and 2 are identical in structure, though opposite in orientation in relation to bore 2050 . The description of the function of valve 1 is applicable to valve 2 as well. Reactive component injection valve body 600 comprises the body member 601 , and reciprocating body 602 . The bodies are disposed so as to abut one another and are secured by bolts 101 , 102 as previously described. While it is contemplated that a one piece valve body 600 may be utilized, the two component construction affords easier machining, greater precision and the ability to effect rapid removal and replacement of the injection valve in the mixing head. Injection nozzle means comprises an injection orifice member 604 and an injection head 605 which are nestingly disposed, one within the other, in the central axial bore 35 of valve body 600 . Orifice member 604 is secured in the body member 601 by bayonet pins 603 , disposed to project radially inwardly towards the bore 35. The pins fit in openings 606 provided in the orifice member 604 . When the valve body 600 is secured to the mixing head body 999 , the orifice 604 is in alignment with inlet port 500 and may not be removed. The removal of bolts 102 , however, releases the valve from the mixing head body 999 and may readily and quickly be withdrawn. The injection orifice member 604 , is removed by rotation about its longitudinal axis to release openings 606 from the bayonet pins 603 , and a new orifice member may be put in its place and secured by reversing the sequence. The injection head 605 is provided with an externally threaded portion 607 , which is in threaded engagement with an internally threaded, forward portion of a first reciprocating member 620 . Ports 608 extend radially inwardly from a necked-down portion 608a of injectin head 605 into internal bore 610 (Figures 4 and 5), which extends rearwardly and inwardly towards the reciprocating member 620 . A further necked-down section 609 of injection head 605 extends forwardly from portion 608a . A shoulder portion 611 having a diameter greater than necked-down portions 608a and 609 , and approximately equal to the body diameter of threaded portion 607, extends outwardly from portion 609 . The diameter of the shoulder portion 611 is set such that it exceeds the diameter of bore 614 extending through the interior of orifice member 604 , whereby that shoulder is adapted to contact the rearward face 612 of orifice member 604 to act as a secondary stop to arrest forward travel of the injection head 605 into the orifice member 604 . A plurality of radially projecting fins 613 extend from the shoulder 611 towards a tip 615 of injection head 605. The fins 613 are separated by slots 616 and the combination of fins and slots serve to break up and disperse the reactive component liquid flow as it passes over the injection head 605 . Such break up results in a spray of the component being injected thrugh orifice member 604 and port 500 into the mixing chamber. While the fins 613 are illustrated as axially extending in a parallel relationship with each other, a helical or other convolute pattern may also be used, whereby greater break-up of the high pressure liquid stream can be effected. The tip 615 of injection head 605 is substantially frustoconical in shape and is machined to be seated against a complementary forwardmost seating portion 619 in the bore 614 of orifice member 604 . The engagement of tip against seating portion 619 must be sufficiently tight to prevent any unwanted flow of reactive component through orifice member 604 and port 500 when the valve is in a closed position. An O-ring 41 is provided to seal a front face 618 of the orifice member 604 against the mixing head body 999 . A second O-ring 42 is provided for the same purpose where body member 601 also fittingly contacts mixing head body 999 . Injection head 605 , as noted, is threadingly engaged with a threaded, forward portion of bore 617, which bore extends through the axial or longitudinal extend of the first reciprocating member 620 . The diameter of the threaded, forward portion of bore 617 is larger than that of the outside diameter of recirculation sleeve 621 , which is placed into the bore before the injection head 605 is threadedly attached and secured by lock nut 622 to the first reciprocating member 620 . The interior of the bore 617 is machined to provide a seat for the recirculation sleeve 621 which has a bore 623 extending therethrough. The bore 623 in the sleeve provides a substantially frustoconically shaped entrance portion 624 and a substantially frustoconically shaped exit portion 625 . Exit portion 625 is machined to be complementary to a frustoconical portion of a second reciprocating member 650 , whereby a seal is formed by contact of the reciprocating member 650 with recirculation sleeve 621. The sleeve 621 has a shoulder portion 629 of greater diameter than a body portion 626 which shoulder portion is retained by a shoulder 630 extending into the bore 617 of the reciprocating member 620 . The body portion 626 fits coaxially into surface 631 of the shoulder. A continuous path for liquid is thereby provided from the port 608 to the bore 610 and the bore 623 of recirculation sleeve 621 . The first reciprocating member 620 is coaxially disposed within the central axial bore 35 in valve body 600 . A forward portion of the central axial bore 35 , located in body member 601 , has a diameter larger than that of a first exterior portion 632 of the first reciprocating member 620 . The forward portion of bore 35 contains a reactive component chamber 660 which communicates with the reactive component supply conduit 11 through subpassage 661 . Reactive component chamber 660 has no permanent fluid communicating with orifice member 604 , bore 614 or port 500 . It only communicates intermittently, through the forwardmost portion of central axial bore 35 , with bore 614 through orifice member 604 and, when tip 615 is not seatingly engaged with the surface 619 . Rearward communication of reactive component chamber 660 with any additional portion of the central axial bore 35 is prevented by the presence of a set of seals 43 , 44 , consisting of an outermost O-ring seal 43 and an innermost step seal 44 , both of which are seated in an annular groove in the body member 601 . Most preferably, that groove is machined into the face of body member 601 at its junction with body member 602 (Figure 3). The first reciprocating member 620 has a second exterior portion 633 having a diameter greater than first portion 632 , and forming a shoulder 632a therebetween. The second portion 633 has a diameter less than double acting piston portion 634 (Figure 7). Rearwardly with respect to injection orifice 604 , central axial bore 35 in body member 602 changes in diameter, opening out from a diameter providing sliding fit with the first exterior portion 632 of the first reciprocating member 620 to a diameter providing a sliding fit with said second exterior portion 633 thereof (Figures 4-5, 7). The length of the first portion 632 of the first reciprocating member 620 having the smaller diameter is such that it extends into the opened-out portion of the bore 35 to provide a reactive component recirculation chamber 670 therebetween, which is connected by passage 671 to return conduit 13 . Chamber 670 has no permanent fluid communication with either reactive component chamber 660 or supply conduit 11 ; it communicates only intermittently with said chamber 660 and supply conduit 11 . Recirculation ports 672 , radially disposed in the reciprocating member 620 , effect fluid communication from the exterior portion 632 to the internal bore 617 of member 620 . Recirculation ports 672 , when member 620 is assembled in central axial bore 35 , provides means for fluid communication between the bore 617 and the recirculation chamber 670 . A pair of seals 44 and 45 are provided on the outer surface of portion 633 of the first reciprocating means 620 , the seals consist of an inner O-ring 44a and an outer seal 45 . The second reciprocating member 650 is disposed in the interior bore 617 of the first reciprocating member 620 . In the preferred embodiment, the internal recirculation path of the valve comprises a portion of internal bore 617 of member 620 . In alternative embodiments, however, an internal recirculation path may be provided which does not comprise the internal bore 617 through the first reciprocating member 620 . Instead, a separate internal recirculation path may be provided within which the second reciprocating member 650 is placed downstream of the recirculation sleeve 621 , which member 650 effects a sealing seat with the frustoconical surface 625 in bore 623 , in the same manner as is illustrated in Figures 4 and 5. Two sets of peripheral seals 46 , 47 and 48 , 49 surround the body of the reciprocating member 650 , consisting of inner O-ring seals 46 and 48 , outer seals 47 and 49 , providing sliding sealing engagement with the complementary surface of bore 617 (Figures 3 and 7). The length of the body of second reciprocating member 650 is such that it does not exceed the distance between radially arrayed recirculation ports 672 and hydraulic ports 675 , which ports 657 communicate with bore 617 of member 620 rearwardly of member 650 , while ports 672 communicate with bore 617 forwardly of member 650 (with respect to orifice member 604 ). A bottle-nosed spacer extension member 680 is disposed in bore 617 rearwardly of the second reciprocating member 650 . The extension member 680 is provided with seals 50 , 51 and 52 , 53 , consisting of inner O-ring seals 50 , 52 and outer step seals 51 , 53 . The seals 50 , 51 and 52 , 53 provide sliding sealing engagement for member 680 with the complementary surface of bore 617 (Figures 3 and 7). The first reciprocating means 620 includes the double acting piston portion 634 , which comprises a flange of a diameter greater than that of second portion 633 . Seals consisting of an inner O-ring 54 and an outer seal 55 , provides sealing engagement with the complementary surface portion 700 of central axial bore 35 . Piston portion 634 has a face 635 , disposed forwardly towards orifice member 604, and a face 636 , disposed rearwardly away from said orifice member 604. Hydraulic conduit 14 communicates with the chamber formed by surface portion 700 of bore 35 , piston portion 634 of reciprocating member 620 and end cap 692 , which is secured to body member 602 by bolts 101 (Figure 3). Hydraulic conduit 15 communicates through passage 15a with the chamber formed by surface portion 700 of bore 35 , and piston portion 634 of member 620 . End cap 692 has a forwardly projecting annular portion 693 , the outer surface of which slidingly engages the complementary surface of portion 700 of bore 35 and the inner surface of which engages an outer surface 633a of the first reciprocating member 620 (Figures 3, 7). A sealing fit to surface portion 700 is provided by an O-ring 56 . Inner O-ring 57 and outer seal ring 58 , provides sliding sealing engagement with the outer surface 633a of member 620 . The end cap 692 further includes a rearwardly projecting annular portion 694 which is internally threaded to receive an adjustable externally threaded stop member 695 . Stop member 695 has an inner surface 695a , which contacts and end surface 637 of the member 620 , thereby limiting the rearwardmost travel of member 620 away from orifice member 604 . A second adjustable stop member 690 is externally threaded for engagement with a threaded bore 690a extending through the first stop member 695 . A lock nut 691 , when backed off, allows adjustment of the second stop member 690 independently of the adjustment of the first stop member 695 , which is maintained in position by means of a set screw 697 and a split thread 695b which is spreadable by the screw 697 . The end of the second stop member 690 distal from the lock nut 691 contacts the spacer extension member 680 which, in turn, contacts the second reciprocating member 650 , thereby limiting the rearwardmost travel of member 650 away from orifice member 621 , independently of the limitation of the rearwardmost travel of member 620 away from orifice member 604 . While threaded stop members 690 and 695 requiring manual adjustment are employed in the preferred embodiment of the invention, other adjustable stop means known to the art may also be utilized, including adjustable piston stop means of the type disclosed in Boden, U.S. Patent No. 4,378,3 35 ; Schmitz et al. U.S. Patent No. 4,464,056 and Schmitz et al U.S. Patent No. 4,497,579, as well as the use of stepper motor driven adjustable stop means, including the application of independent stepper motors to each of means 690 and 695 . Combinations of cylindrical threaded adjustable stop means, adjustable piston stop means and/or stepper motor adjustable stop means may be used, such combinations including adjustable piston stop means for the first reciprocating member 620 and cylindrical threaded adjustable stop means for the second means for both the first and second reciprocating members 620 , 650 , The overall assembly of the first and second reciprocating members 620 , 650 of the preferred embodiment of the invention is illustrated in Figure 7, which shows the various subcomponents in an exploded perspective view. To assemble, the second reciprocating member 650 is inserted into the rearward opening of bore 617 of first reciprocating member 620 , and then the spacer extension member 680 is inserted to follow member 650 , insertion again being from the rearward opening of bore 617 . Into the forward opening of bore 617 is placed the orifice member 621 , which is advanced into the bore until the shoulder 629 is seated against the receiving shoulder 630 in the bore 617 of member 620 . The injection head 605 is then screwed into the threaded portion of bore 617 and lock nut 622 threaded onto the threaded portion 607 , to secure the head in member 620 . The orifice member 604 is secured on bayonet pins 603 before body member 601 is bolted to mixing head body 999 . All necessary seals are premounted to their various components. Final assembly of the valve comprises the insertion of the assembled components into the bore 700 of valve body 600 after body member 602 is mounted to body member 601 . End cap 692 , into which adjustable stop members 690 and 695 have previously been inserted, is then mounted on body member 602 with annular portion 693 being in a surrounding and in sliding engagement with portion 633a of the first reciprocating member 620 . Bolts 101 secure the entire valve assembly to body member 601 and mixing head body 999 . The operation of the reaction component injection valve of the invention is illustrated with respect to a cycle involving injection of reactive component, cessation of injection, internal recirculation, and the cessation and resumption of injection of reactive component. Figure 3 illustrates the reaction component injection valve in the internal recirculation state. The tip 615 of injection head 605 is in sealing contact with interior surface 619 of orifice member 604 , thereby preventing any injection of a reactive component into the mixing chamber. Hydraulic pressure, supplied through conduit 14 , acts against the rearward face 636 of the double acting piston portion 634 of the first reciprocating member 620 forcing the member 620 towards the orifice member 604 and thereby maintaining the sealing contact between the tip 615 and surface 619 . A reactive component enters chamber 660 through conduit 11 and, being unable to exit through orifice member 604 and port 500 , instead flows through ports 608 in injection head 605 into internal bore 610 , and then into bore 623 in recirculation sleeve 621 . The pressure of the reactive component passing into bore 623 drives second reciprocating member 650 back in bore 617 until it contacts the spacer extension member 680 , which in turn contacts second adjustable stop member 690 , stopping the rearward travel of member 650 . That movement opens an annular passage between the forward frustoconical portion of member 650 , and the rearwardly-disposed frustoconical surface 625 on the recirculation sleeve 621. The annular passage constitutes a throttling passage, whose dimension and thus throttling effect on the recirculating reactive component is established by the position of the second stop member 690 . The stop member 690 is set to extend into the valve and the narrower the annular space between member 650 and recirculation sleeve 621 , the greater the throttling constriction and the higher the recirculation back pressure. The reactive component, after flowing through the sleeve 621 , exits from the bore 617 through recirculation ports and 672 passes into recirculation chamber 670 , passage 671 and internal recirculation return conduit 13 . The larger effective area of rearward face 636 of portion 634 of member 620 allows the use of hydraulic fluid under pressure only slightly greater than that which the reactive component is under, as the component acts only on the end face of bore 617 and lock nut 622 , which have a much smaller effective area than face 636 . To initiate pour, hydraulic pressure is removed from conduit 14 and applied to conduit 15 and passage 15a . Hydraulic fluid pressure is thereby applied to forward face 635 of piston portion 634 of member 620 at the same time that the fluid is passing through ports 675 into that portion of the bore 617 located behind the second reciprocating member 650 . Because of the bottle-nose of spacer extension member 680 , hydraulic pressure is brought to bear on the rearward face of member 650, forcing it towards the sleeve 621 . The force applied to the much larger surface area of facial portion 634 of member 620 simultaneously acts to retract member 620 rearwardly, withdrawing the tip 615 of injection head 605 from its seated position with the surface 619 of the orifice member 604 . That opening immediately constitutes the path of least resistance to inflowing reactive component, which begins to flow through orifice member 604 and port 500 into the mixing chamber. In turn, such flow rapidly decreases the remaining flow of recirculating reactive component through sleeve 621 , allowing the hydraulic pressure behind member 650 (from liquid flowing through ports 675 ) to force the frustoconical portion thereof against the complementary seat 625 of sleeve 621 , stopping recirculation flow. Rearward motion of 620 continues until the face end 637 contacts the face 695a of the first stop member 695 , which stops further rearward travel. The reactive component thereafter travels from conduit 11 , into chamber 660 , between the fins 613 , and in slots 616 , and bore 614 of orifice member 604 , into the generally frustoconical space between the tip 615 and surface 619 and out of orifice member 604 and port 500 into the mixing chamber. The distance between the tip 615 and suface 619 is established by the first stop member 695 . This again constitutes an annular, throttling passage. The stop member 695 is set forwardly into the valve body, the narrower the annular space, the higher the pour pressure. Variation of the stop member 695 varies the pour pressure. To complete the cycle, hydraulic pressure is removed from conduit 15 and re-applied to conduit 14 . Pressure will thus be applied against rearward face 636 of piston portion 634 of member 620 , driving the assembly forward, so as to bring tip 615 of the injection head 605 into sealing contact with surface 619 of the orifice member 604 . That in turn stops injection of reactive component into and through port 500 to the mixing chamber. The forward movement of first reciprocating member 620 drives hydraulic fluid before forward face 635 of piston portion 634 , pushing fluid out through passage 15a and conduit 15 , which starts fluid draining ports 675 . As the reactive component ceases flow through orifice member 604 , it again flows through ports 608 , into bore 610 , through bore 623 in recirculation sleeve 621 , and again forces the second reciprocating member 650 back to open access to ports 672 , passage 671 and conduit 13 . The two reciprocating members therefore constantly follow a sequence of repeated rearward to forward, then forward to rearward movement, each hence shuttling between each of two positions; while one member is forward, the other is rearward, then vice versa . The first reciprocating member 620 of the reactive component injection valve of the invention thus constitutes a pour shuttle, and the second reciprocating member 650 of said valve constitutes a recirculation shuttle. Both act with orifice member and sleeve ( 604 and 621 , respectively) to provide an annular throttling flow path for the reactive component when in the injection and internal recirculation modes. The proximity of these throttling points to each other makes close and maintainable pressure balance readily attainable between pour and recirculation modes. This in turn affords virtually instantaneous transition from internal recirculation to injection and vice versa , valve characteristics essential to providing dual density mix through high pressure impingement mixing. The reaction component valve of the invention is hydraulically actuated to commence injection, with simultaneous hydraulic actuation to close off the internal recirculation path. While the cessation of injection by closing off orifice member 604 is also hydraulically actuated, however, the opening of the internal recirculation path is actuated by the flow of reactive component alone, without any hydraulic intervention. Only when the internal recirculation path is selected does liquid reactive component flow into the bore 617 in the first reciprocating member 620 ; when the valve is in the injection mode, no reactive component is flowing through, the bore 617 , or any other portion of said first or second reciprocating members 620 , 650 .

Claims: A high pressure mixing head for mixing reactive components comprising: a mixing chamber (2050) communicating with a quieting chamber (3050), a reaction component injection valve (600) communicating with said mixing chamber (2050), a first plunger (2010) in said mixing chamber (2050) movable between a retracted position in which reaction component is injectable into said mixing chamber (2050) through said injection valve (600) and an extended position in which material in said mixing chamber (2050) is discharged into said quieting chamber (3050), first recirculation passage means in said mixing chamber (2050) and first plunger (2010) for recirculating reactive component injected into said mixing chamber (2050) through said injection valve (600) when said first plunger (2010) is in said extended position, first reciprocating means selectively movable between open and closed positions for selectively starting and stopping discharge of reaction component from said injection valve (600), and second recirculation passage means within said injection valve (600) for recirculating reaction component when said first reciprocating means is in said closed position blocking discharge of reactive component from said injection valve (600) into said mixing chamber (2050), whereby selective operation of said first reciprocating means provides selective use of only one or the other of said first and second recirculation passage means. The mixing head according to claim1, wherein said injection valve comprises: 1. a valve body (600); 2. an injection nozzle (500) disposed in said body; 3. a reactive component supply passage (11) disposed in said body, having intermittent fluid communication with said nozzle; 4. a first reciprocating member (620) disposed within said reactive component supply passage in said body, selectably positionable to open, partially open or close said nozzle; 5. a reactive component recirculation passage disposed in said body, having intermittent fluid communication with said supply passage; and 6. a second reciprocating member (650), disposed within said recirculation passage in said body, and selectably positionable to open, partially open or close said passage. The mixing head of claim 1 or 2, wherein said injection nozzle (500) and said first reciprocating member (620) are coaxially disposed, and wherein said first reciprocating member (620) is positioned hydraulically with respect to said injection nozzle. The mixing head of claim 1-3 wherein said injection nozzle, said first reciprocating member and said second reciprocating member are coaxially disposed, and wherein said second reciprocating member is positioned by the flow of recirculating reactive component when recirculation is effected subsequent to injection, and positioned hydraulically to cease recirculation and resume injection. The mixing head of claim 1-4 including a first adjustable stop member (695) disposed in the path of said first reciprocating member (620), whereby at least one open position of said first reciprocating member with respect to said nozzle is established by contact of said reciprocating member therewith. The mixing head of claim 1-5, wherein said injection valve (600) includes a second adjustable stop member (690) disposed in the path of said second reciprocating member (650), whereby at least one open position of said second reciprocating member with respect to said recirculation passage may be established by contact of said reciprocating member therewith. The mixing head of claim 1-6, wherein said injection valve (600) includes an orifice member (604) within said recirculation passage, disposed upstream of said second reciprocating member (650), said orifice member and said second reciprocating member in combination forming a throttling means for reactive component recirculating through said passage, the separation between said orifice member and said second reciprocating member setting the degree of throttling. The mixing head of claims 2-7, wherein said first and second reciprocating members (620, 650) of said injection valve (600) coaxially disposed are shuttle valves. The mixing head of any one of claims 2-8, wherein said first reciprocating member (620) has a longitudinal bore (617) extending therethrough, said second reciprocating member (650) being disposed in said bore. The mixing head of any one of claims 2-9, wherein said first and second reciprocating members have substantially frustoconical surfaces disposed towards said nozzle (500). The mixing head according to claim 6, wherein said first adjustable stop member (695) comprises a cylindrical member threadably engaged with receiving means in said valve body. The mixing head according to claim 4-11, wherein said first adjustable stop member (695) comprises a piston displaceable in said valve body first reciprocable member (620) and defining therewith a chamber adapted to receive a hydraulic medium, and wherein an end of said piston forms a stop for said first reciprocating member. The mixing head according to claim 6-12 wherein said second adjustable stop member (690) comprises a cylindrical member threadably engaged with receiving means in said first adjustable stop member for said first reciprocating member, and being independently adjustable from said first adjustable stop member for said first reciprocating member. The mixing head according to claim 6-13, wherein said second adjustable stop member (690) comprises a piston member displaceable in said valve body and defining therewith a chamber adapted to receive a hydraulic medium, and wherein an end of said piston forms said second adjustable stop member (690) for said second reciprocating member (650). The mixing head according to claim 1-14, wherein a by-pass channel (2080) includes an orifice axially spaced from and axially aligned with said inlet port, and flow of reactive component being in one axial direction through said inlet port and being in an opposite axial direction through said orifice. Use of the mixing head of any one of the claims 1-15 for mixing at least two reactive components and feeding the resulting mixture to a mold cavity in a process for reaction injection molding or reinforced reaction injection molding.

Inventors: LEIDAL, SHIRLEY, MAYR, HUBERT ADMIRAL MASCHINENFABRIK GMBH
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: B29B7
IPC codes: B29C39, B29C45, B29B7, B29K105, B01F5, B29K75