GB2126490A - Mixing head and actuator mechanism suitable therefor - Google Patents

Abstract

The head (Fig. 2) has a sleeve (11), defining a mixing chamber (22) rotatable between first and second positions in body (10). In its first position, inlets (19, 20) in the sleeve register with component inlets (13, 14) in body (10) to permit mixing and in the second position, conduits (17, 18) in the sleeve (11) connect inlets (13, 14) and outlets (15, 16) to permit recirculation of the components. The invention further provides (eg. Fig. 3) a mixing head having a mixing chamber, fed by component inlets, inside which is a slideable piston (12) to cover and uncover the inlets and wherein the piston (12) is selectively expansible to provide a seal between itself and the chamber walls to prevent ingress of the mixing components. Also provided is an actuating mechanism (Figs. 7a-7c), for example for actuating a piston, comprising a first spring (54) and a second spring (55) which are simultaneously loaded by members (48, 53) when the actuator (38) is held in a first position by a trigger (44), upon release of which trigger (44) the actuator (38) moves rapidly under the action of spring (54) to a second position where it is held by trigger (43). Spring (55) remains loaded so that on release of trigger (43) the actuator (38) is moved rapidly by the spring (55) back to the first position. <IMAGE>

Description

SPECIFICATION Apparatus for the production of a mixture of two or more components and actuator mechanism suitable therefor The present invention relates to apparatus for the production of a mixture of two or more components and an actuator mechanism useful therefor.

Moulding techniques are known in which liquid components which will react together to produce a polymer material are supplied at high velocity for a predetermined length of time to a mixing chamber in a mixing head. In the chamber the liquids impringe upon each other and polymerisation commences. The partially polymerised mixture then passes to a mould for final hardening to occur. Examples of such techniques are Reaction Injection Moulding (RIM) and Reinforced Reaction Injection Moulding (RRIM). These two techniques are basically identical save that in RRIM one or more of the liquid components includes fillers which are thus incorporated in the final moulded article. In both techniques the impingement mixing is carried out only for such time as is required to fill the mould.

During periods of non-mixing, the liquids continue to be supplied to the head but are recirculated to the tanks from which they were originally, drawn.

One example of a known mixing head includes a central chamber and a hydraulically or pneumatically actuated piston slidable within the chamber. A plurality of lower liquid inlet ports each communicating with a supply of liquid component to be fed to the mixing head are provided in the head as are also a plurality of upper outlets. The piston has channels in its outer surface so that communication may be established between inlet and outlet ports. During impingement mixing, the piston is in a raised position such that the inlets are uncovered and liquid can enter the chamber. After mixing the piston is lowered so that inlet and outlet ports are in communication allowing liquid reactant to be recirculated. The lowering of the piston also has the effect of cleaning out the mixing chamber.

There are however a number of disadvantages associated with this construction.

Firstly, the liquids must enter the chamber as jets during mixing and this requires that the inlets be sufficiently narrow and that the liquid be passed therethrough the narrow inlets during recirculation and this is particularly disadvantageous in RRIM processes where these conditions may cause attrition of the filler during recirculation.

Secondly, the pneumatic or hydraulic actuators for the piston are not capable of giving the sufficiently rapid movements of the piston as are desired for covering and uncovering the inlet ports.

Thirdly, the piston must be machined to close tolerances to ensure that, during mixing, the liquids do not pass between the piston and the chamber walls since this would affect operation of the piston.

According to a first aspect of the present invention there is provided a mixing head comprising a body with a plurality of first liquid inlet ports and a plurality of liquid outlet ports, a sleeve rotatable within the body, a reaction chamber defined within the sleeve, a plurality of second inlet ports within the sleeve and capable, in a first position of the sleeve, of corresponding in position to said first inlet ports, and a plurality of conduits in said sleeve each capable in a second position of the sleeve, of providing communication between a first inlet port and an outlet port.

The mixing head of the invention is therefore such that, in a first rotational position of the sleeve, the first liquid inlets in the body are in alignment with the second liquid inlets in the sleeve so that liquid components are supplied to the reaction chamber and mixing may take place and, in a second rotational position of the sleeve, the conduits provide communication between the first liquid inlet ports and the outlet ports of the body so that recirculation may occur.

Preferably the mixing head incorporates a piston (preferably actuated in accordance with the third aspect of the invention (see below)) slidable within the chamber for cleaning out the chamber after the mixing operation has taken place.

Preferably also the second liquid inlets, i.e.

those in the sleeve, include liner pieces defining nozzles with an inner cross-section less that that of the first liquid inlets to create flow at a suitable velocity. With this construction, it is only during mixing and not recirculation, that liquid is required to pass through narrow nozzles so that fillers in the liquids are not subject to repeated attrition during recirculation.

According to a second aspect of the invention there is provided a mixing head for mixing of liquid components the head having an inner chamber with liquid inlets, a piston slidable within the chamber to cover and uncover the inlets and said head being operable in a mixing mode, in which liquid components are supplied into the chamber, and a recirculation mode in which liquid components are diverted out of the head wherein the piston is expansible to provide for sealing contact between itself and the chamber.

The piston may be expanded when it is at a rest position; i.e. at the end of its stroke, so as to be in sealing contact with the walls of the chamber. For movement of the piston it may be released from its expanded condition so as to be slidable along the chamber.

The piston as defined for use in the second aspect of the invention is particularly suitable for use in the mixing head of the first aspect of the invention where it is desired that such head should incorporate a piston.

According to a third aspect of the invention there is provided an actuating mechanism comprising an actuator element, means for retaining the actuator element selectively at first and second positions, a reaction member first with respect to the actuator element, first spring means loadable against the reaction member to provide for movement of the actuator element from the first to second position, a first actuator element to load said first spring when the actuator element is in the first position, a second spring loading member movable with respect to the actuator element, said second loading member being engageable with the reaction member and being movable away therefrom by said first loading member during loading of the first spring means, and second spring means loadable upon movement of the second loading member by the first loading member and normally urging siad second loading member towards the reaction member.

The actuating mechanism is thus such that, with the actuator element in the first position, the first spring may be loaded against the reaction member by movement of the first loading member which in turn moves the second loading member, thus loading the second spring. Qnce the retaining means are released, the first spring means urges the reaction member towards the second loading member (which is held in position by the first loading member) so that the actuator element moves rapidly under the influence of the first spring means from the first to the second position. The actuator element is held at the second position by the retaining means. The second loading member is now held in position by the reaction member, so that the first loading member may be returned to its original position.Release of the retaining means now allows the second spring means to urge the second loading member against the reaction member and move the actuator element from the second to first position.

Preferably the first and second springs are each loaded by compression.

Preferably the first loading member is movable by means of fluid pressure to load the first spring means. Preferably also the first loading member is returned to its starting position, as the fluid pressure is released, by third spring means. The third spring means may be loaded during movement of the first loading member to load the first spring.

The actuator mechanism is particularly suitable for actuating a piston provided in a mixing head of the type described above the first and second aspects of the invention.

It is however also envisaged that the actuator mechanism will have use in any application where fast working strokes are required.

The invention will be described by way of example only with reference to the accompanying drawings, in which: Figure 1 diagrammatically illustrates a RIM process; Figure 2 is a diagrammatic sectional view of a mixing head in accordance with the invention and taken along the line A-A of Fig. 3; Figure 3 is a sectional view along the line B-B of the mixing head shown in Fig. 2; Figure 4 is a sectional perspective view of the embodiment of mixing head in accordance with the invention in injection mode; Figure 5 is similar to Fig. 4 but shows the head in recirculation mode; Figure 6 is an exploded perspective view of one embodiment of piston in accordance with the second aspect of the invention for use in cleaning the central bore of the mixing head; and Figures 7A-7Care sectional views showing one embodiment of linear actuator in accordance with the third aspect of the invention in various stages of operation.

Fig. 1 illustrates the basics of a RIM or RRIM process. The purpose of the process is to produce a moulded polymer article in a mould 1 from two different liquids 2 and 3 (optionally including fillers for RRIM) which will react together when mixed. For example, to produce a polyurethane article one of the liquids will be an isocyanate and the other a polyol.

The liquids 2 and 3 are stored in tanks 4 and 5 respectively from where they are fed by respective displacement pumps 6 and 7 to a mixing head 8. The mixing head 8 has inlet ports 8a and 8b communicating with pumps 6 and 7 respectively, and outlet ports 8c and 8d communicating with tanks 4 and 5 respectively.

An internal valving arrangement (not shown) is provided within head 8 so that it may operate in one of two modes, namely (1) a first mode in which ports 8a and 8c and ports 8b and 8d are in communication, so that liquids 2 and 3 merely enter the head 8 and return to their respective tanks (as illustrated by solid lines in Fig. 1); and (2) a second mode in which outlet ports 8c and 8d are closed so that liquids entering the head 8 through ports 8a and 8b are injected into a central chamber of the head so that they mix together before exiting to one or other of moulds 1 to produce the moulded article.

It is important that head 8 does not build up deposits of solidified reactant or product, otherwise its operation is hindered. Mixing head 8 is thus operated alternatively between its injection and recirculation modes, the latter mode preventing ports 8a and 8b from be coming blocked by solidified reactant. Ad ditionally whilst the head 8 is in recirculation mode, the inner chamber is cleaned by a close fitting piston which "pushes out" any unwanted solidified reactant or product in readiness for the next injection operation.

Fig. 2 and 3 diagrammatically illustrate a mixing head 9 in accordance with the invention for use as described above. The head 9 is shown in recirculation mode.

The head 9 is formed of an outer annular body 10 within which is a rotatable, close fitting annular sleeve 11 the interior of which defines a mixing chamber 1 lea. Slidable within chamber 1 Ia is a piston 12.

Body 10 includes liquid inlet ports 1 3 and 14 spaced by 180 , and liquid outlet ports 1 5 and 1 6 again spaced by 180 , all ports 1 3-1 6 being at the same level and being equivalent to ports 8a-d respectively.

Sleeve 11 has two circumferentially extending channels 1 7 and 1 8 on its outer surfaces such that when sleeve 11 is so orientated, channel 1 7 provides for communication between ports 1 3 and 1 5 and channel 1 8 provides communication between ports 14 and 16, thus allowing head 9 to be in recirculation mode (as illustrated). Additionally, sleeve 11 includes two radially extending apertures 1 9 and 20 spaced by 180 and each having a linear 21 defining injection nozzles 22. Head 9 is in injection mode when each of the injection nozzles aligns with one of ports 13 and 14.

A rotary actuator 23 provides for rotation of sleeve 11 to alternate the head 9 between injection and recirculation modes.

The operation of the mixing head 9 in injection and recirculation modes will be best understood by reference to the sectional views of Figs. 4 and 5 which illustrate a similar construction of head. In these figures parts similar to those shown in Figs. 2 and 3 are designated by like reference numeral suffixed by a prime ('). Fig. 4 shows the injection mode in which injection nozzles 22' are aligned with inlet ports 13' and 14' so that streams of liquid 2 and 3 impinge upon each other in the chamber 11 'a and mix together before exiting to a mould. Fig. 5 shows the recirculation-mode in which the ports 13' and 15' and the ports 14' and 16' are in com-.

munication by channels 17' and 18 respectively.

It should be appreciated that a number of modifications may be made to head 9 (andthe corresponding heads 9' of Figs. 4 and 5).

Thus, each of the outlets 1 5 and 16, instead of being at the same level as its corresponding inlet 1 3 and 14, may be axially spaced therefrom. In this case the channels 1 7 and 1 8 will also extend axially to provide communication between the corresponding axially spaced inlet and outlets. Alternatively or additionally, the angular spacing between the inlets 1 3 and 14 or between outlets 1 5 and 1 6 may be other than 180 . It is thus possible for the head to have 3 or more liquid inlets and a corresponding number of liquid outlets for use in a moulding process in which more than two components are required.

Returning now to Figs. 2 and 3, piston 1 2 is slidable within chamber 11 a between a first position in which the radially inner ends of nozzles 22 are covered by the piston 1 2 and a second position (illustrated as an upper position in Fig. 3) in which the ends of the nozzles 22 are uncovered. Movement of the piston is by a linear actuator mechanism 24 (one example described later) which must be capable of producing extremely rapid strokes of the piston 1 2 between its first and second positions.

The piston 1 2 is operated in the following cycle. During the recirculation mode of head 9, the piston 1 2 is in its first position covering nozzles 22. During this stage, liquids 2 and 3 are circulating at comparatively low pressure.

To bring head 9 into injection mode, sleeve 11, is rotated by actuator 23 to align nozzles 22 with ports 1 3 and 14. A high pressure is thus built up in the lines supplying liquids 2 and 3 to nozzles 22. To commence mixing of liquids in chamber 11 a, piston 1 2 is moved rapidly to its second position to open nozzles 22 and allow liquids 2 and 3 to impinge on each other. Mixing is continued for a predetermined time after which sleeve 11 is rotated by actuator 23 to convert head 9 back to recirculation mode. Then piston 1 2 is moved rapidly back to its first position. The movement of piston 1 2 from its second to first position cleans the chamber 11 a by removing any unwanted products left therein after mixing.

It will be appreciated that, when the piston 1 2 is in its first postion and the nozzles 22 align with ports 1 3 and 14, the liquids 2 and 3 are supplied at high pressure against the outer walls of piston 1 2. It is thus essential that piston 1 2 is capable of being a sealing fit within chamber 1 1a to prevent liquid from the nozzles 22 seeping between the chamber 11 a and piston 12.

Nevertheless piston 1 2 must be easily movable between its first and second positions.

These two requirements are achieved, in accordance with the invention by making the piston 1 2 expansible, as represented by the double headed arrows in Fig. 3. For this purpose piston 1 2 includes a central cavity 1 2a which is in communication with a supply of pressurised fluid (not shown) e.g. a plasticizer liquid which will effect an expansion of, say 5 x 10-4 inches of the piston diameter when supplied to cavity 1 2a so that the outer surface of piston 1 2 provides a seal against chamber 11 a. Piston 1 2 is thus formed slightly "under-size" for chamber 11 a and in fact there is no necessity to machine piston 1 2 to the extremely close tolerances required to make an exact fit within the chamber 1 1a.

The operation of piston 1 2 will now be described. As mentioned above, piston 1 2 is in its first position when sleeve 11 is rotated to align nozzles 22 with ports 1 3 and 14.

Simultaneously, with this rotation piston 1 2 is expanded (in the manner described above) to provide a sealing fit between itself and chamber 11 a so that there is no liquid seepage between piston 1 2 and chamber 11 a. Mixing is commenced by relieving the pressure within piston 1 2 (so that the piston 1 2 is no longer a sealing fit within chamber 11 a) and simultaneously rapidly moving piston 1 2 from its first to second position to uncover nozzles 22. At its second position the piston 1 2 may, if desired, be once again expanded although this is not essential.

The advantage of the expansible piston is two-fold, firstly, and as pointed out above, the piston 1 2 may selectively be a sealing fit within chamber 1 la or may be easily slidable therein. Secondly, replacement of the piston 1 2 (should this prove necessary) is facilitated because the replacement piston need not be machined to be a sealing fit within chamber 11 a but, rather, can simply be a stock size.

One specific construction of expansible piston 25 is shown in Fig. 6. This piston 25 is comprised of a shaft 26 with a terminal bore section 27 (forming an expansible cavity for the assembled piston) continued by a second, threaded bore section 28 of lesser diameter. A narrow diameter bore section 29 communicates with bore section 28 and is adapted for connection to a pressurised supply (not shown). The piston 25 includes an end piece 30 for closing the bore 27 and defining an expansion cavity within this bore. This end piece 30 has a head 31 of similar diameter to shaft 26, a shoulder 32 which is an interference fit within the end of bore 27, and a shank 33 of lesser diameter than bore 27 and having a threaded end portion 34 to be screwed into bore 28. A narrow axial groove 35 is provided along threaded portion 34 as shown.When end piece 30 is screwed in position an annular chamber is defined within bore 27 around shank 33. Axial groove 35 provides communication between this chamber and the source of pressurised fluid via bore 29. When pressurised fluid is supplied to the chamber, expansion occurs in the manner described above with reference to Fig. 3.

A linear actuator mechanism 36 for producing linear movement of the aforedescribed pistons 1 2 and 24 between their first and second positions is shown in various stages of operation in Figs. 7A-7C.

As illustrated in Fig. 7A, the actuator 36 comprises an outer casing 37 through which extends an actuator element in the form of a rod 38 attached to the piston (not shown).

The interior of the casing 37 is divided by a step 39 into a lower, wide diameter chamber 40 and an upper, smaller diameter chamber 41. A top casing 37 is a retaining mechanism, in this case a ball bearing trigger mechanism, 42 including upper and lower ball bearing triggers 43 and 44 respectively.

Upper end of rod 38 has a latching head 45 with which either of triggers 43 and 44 will engage so as to hold rod 38 in position until the trigger is released.

Rigidly mounted on rod 38, and locating within chamber 40, is an annular flange 46 (forming a reaction member) with a short length of collar 47 around its undersurface.

Within chamber 40 is an annular body 48 with an internal diameter equal to the diameter of flange 46. As will be appreciated, body 48 provides a first spring loading body.

The body 48 has lower and upper walls 48a and 48b respectively separated by a step 48c, the walls 48a being of the same diameter as chamber 40 and a base 48d.

Body 48 is thus slidable within chamber 40. With both body 48 and the piston in their lowermost positions (i.e. when latching head 45 is in trigger 44) the top of the body 48 is level with the top of flange 46.

Rod 38 is relatively slidably located through the base 48d which has an upstanding circular collar 49 of the same diameter as collar 47 and locating around rod 38.

The base 48d of body 48 is sloped as shown defining cavities 50 (Fig. 7A) in communication with ports 51 in casing 37 for supply and discharge of oil.

A circular boss 52 forming (as will be appreciated) a second spring loading body is provided around the rod 38 above the body 48 and has a lower annular flange 53. Boss 52 is of a diameter less that chamber 41 and flange 53 is of the same diameter as the walls 48b of body 48.

Three springs 54-56 are provided for operating the mechanism, namely (1) a first spring 54 (illustrated as Belville washers) within body 48 between the lower surface of flange 46 and the upper surface of base 48d, the spring 54 being located around collars 47 and 49; (2) a second spring 55 (illustrated as Belville washers) provided mainly within chamber 41 and between the undersurface of trigger mechanism 42 and the upper surface of flange 53; and (3) a third coil spring 56 provided around the walls 48b of body 48 and between the steps 39 and 48c.

The operation of the actuating mechanism 36 will now be explained.

With the actuating mechanism as illustrated in Fig. 7A, the piston (not shown) is in its first position covering the injection orifices 22, the body 48 is at its lowermost position and all springs 54-56 are relaxed with spring 55 urging flange 53 against top of body 48.

This condition of the actuating mechanism occurs during the recirculation mode of the mixing head. During this recirculation mode, oil 57 is supplied to cavities 50 through the ports 51 causing the body 48 to move upwardly compressing spring 56. During this upward movement rod 38 remains stationary (being held in position by the latching head 45 locating in trigger 44) and thus spring 54 is also compressed. Finally flange 53 is moved upwardly by body 48 causing spring 55 to be compressed.

At the end of this sequence body 48 and flange 53 are in the position illustrated in Fig.

76 and the rod 38 is in the position shown by the dotted lines in that Figure representing flange 46. All springs 54-56 are in a state of compression.

To move the piston rapidly from its first to second position (as required at the commencement of mixing) it is merely necessary to release trigger 44. Spring 54 urges against flange 46 to effect movement of the rod 38 up to the point at which latching head is engaged and held by trigger 43, i.e. to the position shown in solid lines in Fig. 7B.

Whilst mixing takes place, oil 57 is exhausted through ports 51 and body 48 returns to its lowermost position under the action of springs 56. The configuration illustrated in Fig. 7C is thus reached in which flange 53 is held in its upper position by flange 46 on rod 38.

When the fast downward stroke of the piston is required, trigger 43 is released and spring 55 urges flange 53 and thus flange 46 (and hence rod 38) downwards so that the actuating mechanism returns to the configuration shown in Fig. 7A.

It will be seen therefore that all movements of the piston are effected purely under spring force and this allows very fast strokes to be obtained. In fact, for piston strokes of the length normally required in RIM and RRIM techniques, the illustrated apparatus can produce actuating times of approximately 7 x 10-3 seconds as compared with 100 x 10 - 3 seconds for conventionally used hydraulic actuating means.

Claims (11)

1. A mixing head comprising a body with a plurality of first liquid ports and a plurality of liquid outlet ports, a sleeve rotatable within the body, a reaction chamber defined within the sleeve, a plurality of second inlet ports within the sleeve and capable, in a first position of the sleeve, of corresponding in position to said first inlet ports, and a plurality of conduits in said sleeve each capable in a second position of the sleeve, of providing communication between a first inlet port and an outlet port.

2. A head as claimed in claim 1 wherein the second liquid inlets have liner elements defining nozzles with an inner cross-sectional area less than that of the first liquid inlets.

3. A head as claimed in claim 1 or 2 wherein the centre liner of the first and second liquid and the liquid outlets line in a common plane transverse to the rotational axis of the sleeve and said conduits extend circumferentially around the sleeve.

4. A head as claimed in claim 1 or 2 wherein each first liquid inlet is spaced from its associated liquid outlet is a direction parallel to rotational axis of the sleeve and said conduits extend axially along the sleeve.

5. A head as claimed in any one of claims 1 to 4 wherein there are two first liquid inlets spaced 180 from each other around the head.

6. A head as claimed in any one of claims 1 to 5 incorporating a piston slidable within the chamber for cleaning out the chamber after the mixing operation has taken place.

7. A head as claimed in claim 6 wherein the piston is expansible.

8. A mixing head substantially as hereinbefore described with reference to Figs. 2 and 3 or Figs. 4 and 5 of the accompanying drawings.

9. A mixing head for mixing of liquid components the head having an inner chamber with liquid inlets, a piston slidable within the chamber to cover and uncover the inlets and said head being operable in a mixing mode, in which liquid components are supplied into the chamber, and a recirculation mode in which liquid components are diverted out of the head wherein the piston is expansible to provide for sealing contact between itself and the chamber.

10. A head as claimed in claim 9 wherein the head of the piston has an interior expansion space to which an expansion fluid may be supplied.

11. A head as claimed in claim 10 wherein the piston comprises a shaft with a stepped bore such that the end section at the head of the piston as of greater cross-sectional area than the section adjacent thereto, and a closure member with a head sealingly closing the end of said bore and having a shank engaging in said adjacent section of the bore so that the closure member is mounted in position and an expansion space is defined in said end section, said shank having conduit for providing communication between said expansion space and a supply line for expansion fluid for expanding said piston.

1 2. A mixing head substantially as hereinbefore described with reference to Figs. 3 or 6 of the accompanying drawings.

1 3. An actuating mechanism comprising an actuator element, means for retaining the actuator element selectively at first and second positions, a reaction member fast with respect to the actuator element, first spring means loadable against the reaction member to provide for movement of the actuator element from the first to second position, a first spring loading member movable with respect to the actuator element to load said first spring when the actuator element is in the first position, a second spring loading member movable with respect to the actuator element, said second loading member being engageable with the reaction member and being movable away therefrom by said first loading member during loading of the first spring means, and second spring means loadable upon movement of the second loading member by the first loading member and normally urging said second loading member towards the reaction member.

1 4. An actuating mechanism as claimed in claim 1 3 wherein the first and second springs are each loaded by compression.

1 5. An actuating mechanism as claimed in claim 1 3 or 14 wherein the first loading member is movable by means of fluid pressure to load the first spring.

1 6. An actuating mechanism as claimed in claim 1 5 wherein third spring means are provided for returning the first loading member to its starting position as the fluid pressure is released.

1 7. An actuating mechanism substantially is hereinbefore described with reference to Figs. 7A, 7B and 7C of the accompanying drawings.