GB2095159A

GB2095159A - Foam block manufacture

Info

Publication number: GB2095159A
Application number: GB8137521A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-03-21
Filing date: 1981-12-11
Publication date: 1982-09-29

Abstract

A method of forming blocks of foam material in block form is proposed wherein a closed mixing chamber (6) is provided within or directly adjacent a mould (1) and foam-making ingredients are delivered to such mixing chamber (6), the ingredients being mixed in such chamber and then discharged to the mould. The mixing chamber (6) may be formed as an extension to the mould cavity and may include a piston (7) therein for discharge of mixed ingredients to the mould. The ingredients may be fed to the mixing chamber from dosing containers (10) which are movable to and from a position immediately adjacent the mixing chamber. When making polyurethane it is also possible to use a premixing container (111) in which tin catalyst is blended with polyol and water prior to introduction to the mixing chamber (6). <IMAGE>

Description

SPECIFICATION Foam block manufacture This invention relates to the manufacture of blocks of foam material, particularly although not exclusively blocks of polyurethane foam.

In a known continuous process for the production of polyurethane foam, foam-forming ingredients are continuously fed to a mixing head where they are mixed together and then discharged to a moving conveyor belt. The ingredients react together and expand on the belt and a continuous length of foam is produced having a width determined by the apparatus invoived and a height dependent, at least in part, on the rate of feed of foam-forming materials in relation to the rate of advance of the conveyor belt. The ingredients are fed simultaneously to the mixing head, and are mixed together and applied to the conveyor belt within a time scale determined by the time taken for the mix to gel or cream.The nature of this conventional process, and particularly the continuous feed character thereof, is such that the quantities of material which must necessarily be mixed and delivered per unit of time can be handled before onset of creaming, and accordingly uniformity of product along the length thereof can readily be attained.

It is also known to produce single blocks of polyurethane foam by introducing relatively large metered quantities of foam-forming ingredients into a mixing chamber, mixing the ingredients in the chamber, and then discharging the mixed ingredients through an opened bottom of the chamber into a box-shaped mould wherein the ingredients react with each other and expand to fill the mould. However, with this known method, faults tend to arise in the finished product due to trapping of air and non-uniform distribution of the ingredients within the mould having regard to the limited time available for effecting mixing of the ingredients and subsequent transfer thereof to the mould.In this respect, it is to be understood that, mould volumes of, say eighty litres may be involved, and on the one hand thorough and satisfactory mixing is required bearing in mind that various of the ingredients, although present in very small quantities, are critical to satisfactory cell formation and a truly homogeneous mix is essential if uniformity of product is to be achieved; and on the other hand the maximum rate of mixing is conditioned by the need to avoid air entrapment such as would result from vigorous agitation of the mix, since such entrapment tends to give rise to the occurrence of splits in the end product.

An object of the present invention is to provide a method of manufacturing foam blocks in which problems due to trapping of air and non-uniform distribution of foam-forming ingredients can be avoided or at least appreciably reduced.

According to the invention therefore there is provided a method of forming blocks of foam material in which mixed foam-forming ingredients are allowed to react and expand in a mould, characterised in that, said ingredients are discharged into a mixing chamber defined in the mould, the ingredients are mixed in the chamber, and the mixed contents of the mixing chamber are allowed to flow therefrom into the mould.

With this arrangement, due to the close proximity of the mixing chamber and the mould the entire charge of ingredients can be thoroughly mixed and smoothly transferred to the mould, thereby to achieve a substantially uniform mixture thereof in the mould without appreciable entrapment of air within the limited time available before reaction and foaming has occurred to any appreciable extent. Accordingly, with the method of the invention it is possible to produce a substantially fault-free finished product in a simple, convenient and efficient manner.

It is anticipated that the invention will find particular application in the context of manufacture of polyurethane foam blocks, in which case the said ingredients may comprise, for example, a polyol (such as polypropylene glycol), toluene di-isocyanate (TDI), water, silicone foam stabilizing agent, and activators (e.g. amine and tin catalysts) to control the rate of gas formation and gelling. It is, however, to be understood that the invention is not intended to be restricted to the use of such ingredients nor to polyurethane foams, and the above-described method may find application in the context of other foam materials formed from ingredients which when mixed react and expand.

With regard to the said mixing chamber, this is preferably formed in the mould in the sense that the mould cavity and the interior of the mixing chamber are separated, when the chamber is sealed relative to the mould, by a common openable wall whereby, on opening of said wall, mixed ingredients can flow directly into the mould cavity, and without need to negotiate any conduit therebetween. Preferably, the said common wall constitutes or is level with the bottom of the mould so that the mould can fill evenly from the bottom thereof. Preferably also the said mixing chamber has a boundary surface thereto which is also adapted to form a boundary surface of the mould.

In accordance with one embodiment of the invention, the mixing chamber is recessed into a surface, preferably the bottom surface of the mould, and a removable closure plate is provided to cover the chamber at said mould surface for sealing the chamber relative to the mould. One or more openings may be provided in the closure plate for admission of one or more of said ingredients. A piston may be provided to eject mixed ingredients from the charnber into the mould, such piston having a final ejection position in which it is flush with the said mould surface.

In an alternative embodiment of the invention the mixing chamber is defined by an open-ended housing which is positioned inside the mould with the open end thereof in sealing engagement with a mould surface, preferably the mould bottom surface, so as to seal the chamber relative to the mould. Sealing of the open end of the housing relative to the mould surface may be facilitated by provision of a resilient sealing structure around such open end and/or on the mould surface.

The ingredients may be discharged into the mixing chamber either separately or pre-mixed in any suitable manner.

In one embodiment the ingredients are discharged to the mixing chamber from one or more containers positioned immediately adjacent the chamber in which case the containers may be retracted away from the mould after mixing has occurred. Thus the or each said container may be mounted on the aforementioned said closure plate or housing.

Said containers may contain single charges of the ingredients, the entire contents of the containers being discharged to the mixing chamber. In the case where the method of the invention is performed repeatedly to manufacture successive foam blocks using the same or successive moulds, the said containers may be filled with metered charges of the ingredients from supplies thereof when in retracted positions thereof, the containers thereby acting as intermediaries to transfer the ingredients from the supplies to the mixing chamber Conveniently, the containers may be open-topped flasks which are reciprocated, preferably vertically, between retracted positions thereof, at which the open tops thereof are located beneath metering supply outlets to receive charges therefrom, and operational positions, at which lower gated outlets thereof can discharge into the mixing chamber.

Alternatively or additionally to the use of one or more said ingredient container located adjacent the mixing chamber it is possible simply to discharge one or more ingredient to the mixing chamber through a feed pipe passing through an opening in a wall of such chamber or through an open top of the chamber prior to closure thereof as desired and as appropriate.

In a particularly preferred embodiment of the invention, some of the ingredients are pre-mixed before admission to the mixing chamber. Thus one or more ingredients comprising catalysts or activators which represent a minor and relatively small proportion of the overall volume of ingredients may be pre-mixed with only one or some of the other ingredients representing a relatively large proportion of the overall volume of ingredients.In particular, the invention in one embodiment thereof is applied to the production of open-cell polyurethane foam in a single block form from a chemical formulation which includes a polyol, an isocyanate (such as toluene diisocyanate), water, catalyst/activator substances (such as a tin compound and an amine), a blowing agent and if desired one or more additives (such as a silicone); and a pre-blend of the polyol, water, catalyst/activator and if desired any additive (such as silicone and/or other additive) by mixing together requisite relative quantities thereof in a pre-mixing container having a capacity sufficient to contain a small part only of the total volume of pre-blend required and collecting at least a substantial proportion of the total volume of preblend in said mixing chamber which is of a capacity sufficient to receive all of the ingredients of the formulation before mixing of the pre-blend and toiuene di-isocyanate the blowing agent being included in the pre-blend or added with the isocyanate as preferred.

With this procedure, uniform mixing of the ingredients can be much facilitated without adverse affect on the activity thereof. In this respect it is observed that water and tin catalyst are not normally considered to coexist without loss of activity of the catalyst. However, quite contrary to expectation, these ingredients can coexist in the pre-blend within the available time, without undue deleterious affect on the control properties of the tin catalyst in the context of cell foam production possibly due to the stabilizing effect of the polyol.

According to a preferred feature, all of the preblend is formed in a common pre-mixing container, the ingredients of the pre-blend being passed continuously to the container and being intimately mixed during passage through such container.

According to a further preferred feature, at least 50% of the pre-blend is collected in the mixing chamber before the bringing together and intimate mixing of the pre-blend and isocyanate.

The invention will now be described further by way of example only and with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic representation of one form of apparatus used in performing the method of the invention; Fig. 2 is an enlarged view of part of the apparatus of Fig. 1 illustrating different operational positions thereof; Fig. 3 is a diagrammatic representation of an alternative form of apparatus; Figs. 4 and 5 are enlarged views of alternative forms of a detail of the apparatus of Fig. 3; and Figs. 6 and 7 are views similar to Fig. 1 of modified versions thereof.

With reference to Figs. 1 and 2, a mould for forming a large block of polyurethane foam comprises an open-topped box-shaped structure 1 having readily dismantlable side walls 2 and a base 3 with a central hole 4 of circular or other shape. The box structure 1 is mounted in elevated disposition on a wheeled trolley 5 and has an integral, vertically extending cylinder 6 beneath the said base 3, the top of the cylinder 6 being open and in communication with the hole 4 in the base 3. A piston 7 is mounted within the cylinder 6 and a supply 8 of polyol is connected to the cylinder 6 beneath the piston 7.

The box structure 1 is located beneath a container assembly 9 which can be moved vertically upwards and downwards by suitable mechanism (not shown), such assembly 9 comprising four open-topped flasks 10 mounted on top of a horizontal disc 11 and having respective gated outlets which extend downwardly from the bottom ends of the flasks 10 through the disc 11. Mixer vanes 12 are located beneath the disc 11 on a rotary shaft 1 3 which extends vertically through a bearing in the centre of the disc 11 and is drivably connected to a motor 14 mounted on top of the disc 11.

At a fixed position above the container assembly 9 there are four metering outlet devices 15 connected respectively to supplies of four different ingredients (not shown), namely polyol, TDI and two different activators. The outlet devices 1 5 are operable to deliver different respective predetermined quantities of the ingredients.

In use, the box structure 1 is located directly beneath the container assembly 9 (with the shaft 13 aligned with the axis of the cylinder 6) and such assembly 9 is moved to its uppermost position at which the open tops of the individual flasks 10 are directly beneath respective ones of the outlet devices 15, as shown in full lines in Fig.

1. Valves on said outlet devices 1 5 are then simultaneously opened and the predetermined quantities of the ingredients contained therein fall into the respective flasks 10.

With the piston 7 at the bottom of the cylinder 6, the container assembly 9, including the disc 11, the filled flasks 10, shaft 13, motor 14 and vanes 12, is lowered into the box structure 1 to the position shown in dotted lines in Fig. 1. In such position the disc 11 covers the hole 4 with the periphery thereof resting on the base 3 aound the hole 4 and the vanes 12 are located within the cylinder 6.

Valves at the bottom outlet ends of the flasks 10 are then simultaneously opened by a suitable mechanism (not shown), whereupon the entire contents of the flasks 10 fall rapidly into the closed cylinder 6. At the same time the shaft 13 is rotated by the motor 1 4 and the ingredients are thoroughly mixed in the cylinder 6.

After a short mixing period (say one to five seconds), the container assembly 9 is retracted back to the uppermost position. The homogeneously mixed ingredients in the cylinder 6 resting on top of the piston 7 now react and form a foam of increasing volume and viscosity. As this happens, the piston 7 is smoothly raised until its top surface is flush with the surface of the base 3 of the box structure 1. The expanding foam 16 is thereby distributed evenly and smoothly over the bottom of the mould, as indicated in Fig. 2, and the expansion continues until the box is filled and the requisite foam block 1 7 is formed.

The mould 1 is then removed on the trolley 5 from under the container assembly 9, the sides 2 are detached when the foam has stabilized (say after five to ten minutes), and the formed block of foam is removed. If the internal surfaces of the base 3 and the sides 2 of the box structure 1 are appropriately treated, for example by covering with polyethylene, or polytetrafluoroethylene, or by polishing, or by application of a mould release material thereto, the foam block will separate from such surface leaving them clean enough for re-use in a subsequent block-forming operation.

The box structure 1 is then re-assembled and moved back under the container assembly 9, and the above described procedure is repeated. In order to facilitate rapid, repeated block formation, the flasks 10 may be refilled with the ingredients as soon as they are retracted back to their uppermost positions and whilst the foam block is forming in the mould.

With the procedure described above, the various ingredients are delivered rapidly yet smoothly from the supplies thereof to the chamber in which they are mixed (i.e. the cylinder 6). In such mixing chamber, the ingredients are quickly and thoroughly mixed and the mixture is then smoothly distributed over the base of the mould.

Accordingly, there is little tendency for splashing of ingredients to occur, and homogeneous mixing of the ingredients and smooth, even introduction thereof into the mould can be achieved in a simple and convenient manner and without appreciable trapping or air in the mixed ingredients. A good, fault-free product can therefore be efficiently obtained. The use of polyol beneath the piston 7 can ensure that the cylinder 6 is always kept clean of reaction products.

With reference to Fig. 3, an arrangement is shown therein which is similar to the arrangement of Fig. 1 (and for which like reference numerals are used for like parts) except that the base of the box structure 1 has no hole 4 therein and the piston 7 and cylinder 6 are omitted, and, in place of the disc 11 there is a cylindrical (or other shaped) open-bottomed housing 20. The mixer vanes 1 2 are located within the housing 20 and the flasks 10 and motor 14 are located on top of a top end wall 21 of the housing 20. Only two flasks 10 (and correspondingly only two outlet devices 1 5) are shown and in the case of polyurethane foam block formation there would therefore be a mixture of ingredients delivered to one or both of the flasks 10. However, if desired, there may be four (or any other suitable number) of flasks 10.

The container assembly 9, including the housing 20, the mixer vanes 12 on the shaft 13, the motor 14, and the flasks 10, is shown in the uppermost position in full lines in Fig. 3 in which the flasks 10 can be filled with the ingredients.

After filling of the flasks 10, the container assembly 9 is moved vertically to a lowermost position (shown in dotted lines in Fig. 3) at which the periphery of the open bottom of the housing 20 is pressed firmly onto the surface of the base 3 of the mould 1 so that a sealed mixing chamber is defined within the housing 20. The ingredients are then discharged into and are mixed within this chamber. The container assembly 9 is raised slightly (say by about 1 cm) to allow the mixed ingredients to spill out evenly over the bottom surface of the mould, and the container assembly 9 is then retracted to its uppermost position as the foam block is formed.

As can be seen from Figs. 4 and 5, in order to ensure good sealing between the periphery of the housing 20 and the bottom 3 of the mould 1 during mixing, a sealing structure may be provided around such periphery, the structure comprising, as shown in Fig. 4, a flexible strip or skirt 22, or, as shown in Fig. 5, an inflated tube 23.

In a modification of the above embodiments, if desired, vacuum may be applied to the moulds during foaming to improve expansion and assist removal of trapped air.

Also, and particularly with reference to the embodiment of Fig. 1, the mixer blades 12 may, if desired, be flexible blades which scrape the sides of the cylinder 6.

With reference to Fig. 6, this shows a modification of the embodiment of Fig. 1 and like reference numerals are used to indicate like parts.

Contrary to the arrangement of Fig. 1, the individual ingredients of the polyurethane mix are applied to a pre-mixing chamber 111 in which the intimately-mixed pre-blend of such ingredients is delivered to the mixing cylinder 6, whilst the remaining ingredient (or ingredients) is (or are) fed directly to the mixing cylinder therein to be mixed with the pre-blend.

The mixing chamber 111 is of a volume which is significantly less than the volume of the mixing cylinder 6 (say 10% of such volume), and the ingredients to be mixed in the chamber are fed continuously to such chamber for corresponding delivery of a mixed pre-blend therefrom.

In practice, the individual ingredients fed to the mixing chamber 111 comprise all of the ingredients of the foam-forming formulation except for the isocyanate (e.g. toluene diisocyanate), which latter ingredient is delivered directly to the mixing cylinder at an appropriate time in the production cycle.

A stirrer 112 is provided within the mixing chamber 111, which chamber is so formed as to isolate the ingredients from ambient air to avoid introduction of such air into the mix on agitation thereof, and such stirrer is operated at, say, four throusand revolutions per minute, although other speeds may be preferred. In one arrangement the mixing chamber is surmounted by a bulk container 113 thereby effectively to close the upper end thereof although other configurations are possible.

As with the embodiment of Fig. 1 a further stirrer 12 is located within the mixing cylinder 6, such further stirrer, in order to avoid air entrapment, being intended to operate at, say, seven hundred cycles per minute.

In general, all of the polyol pre-blend, that is to say the polyol, tin catalyst (such as stannous octoate), water, amine catalyst, blowing agent (for example, freon), silicone and any other additive will be intimately mixed in the mixing chamber 111 and delivered to the mixing cylinder 6 before addition to such pre-blend of the toluene diisocyanate, but it may be found convenient, in some instances, to commence adding the toluene di-isocyanate when a substantial part only, said 50%, of the pre-blend has been delivered. It may also be convenient to omit the blowing agent from the ingredients of the pre-blend and to add such blowing agent to the pre-blend when adding the toiuene di-isocyanate.

On completion of the mixing of the pre-blend and toluene-di-isocyanate, the resultant mix is discharged from the mixing cylinder to the mould.

As shown, the pre-blend is fed to the cylinder via a pipe 114 connecting with a gated inlet 1 15 in the closure plate 11 and the isocyanate is fed through a gated inlet 1 16 from a dosing container 10 mounted on the plate 11 (although alternative arrangements may be employed).

In a modification of the embodiment of Fig. 6, not shown, the tin catalyst, silicone, amine and water (and blowing agent, if desired) are delivered directly into a polyol delivery pipe connected to the cylinder, the said pipe being utilised in place of the mixing chamber 111, and the high pressure delivery of the ingredients into such pipe ensuring intimate mixing, and thereby avoiding (or at least reducing) the need for any stirring or agitation device before the cylinder 6.

In a further modification, as shown in Fig. 7, the pre-blend formed as described with reference to Fig. 6, is fed to the cylinder 6 prior to application of the closure plate 11 thereto, via a chute 117, this acting to facilitate release of trapped air. After the requisite quantity of pre-blend has been fed to the cylinder 6 the chute 1 17 is retracted away from the mould, the closure plate 11 is fitted across the cylinder 6, the isocyanate is introduced with stirring and the resulting mixture is then expelled into the mould to foam therein as hereinbefore described. With this arrangement, a batch of pre-blend is delivered to the cylinder 6 but such batch is still pre-mixed on a continuous flow-through basis as described above.

If desired, the modification of Figs. 6 and 7 may be applied to the embodiment of Fig. 3 rather than the embodiment of Fig. 1.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only.

Claims

1. A method of forming blocks of foam material in which mixed foam-forming ingredients are allowed to react and expand in a mould, characterised in that, said ingredients are discharged into a mixing chamber defined in the mould, the ingredients are mixed in the chamber, and the mixed contents of the mixing chamber are allowed to flow therefrom into the mould.

2. The method as claimed in claim 1, wherein the mixing chamber is provided in the bottom of the mould and passage of mixed ingredients to the mould is piston assisted.

3. The method as claimed in claim 1, wherein the mixing chamber comprises an open-ended housing of which an open end thereof engages a mould surface in sealing relationship therewith, the method including the step of retracting the housing to allow flow of mixed ingredients into the mould.

4. The method as claimed in claim 3, wherein the housing engages the bottom of the mould and such housing is retracted vertically to allow mixed ingredients to flow across the bottom of the mould.

5. The method as claimed in any one of claims 1 to 4, wherein at least one said ingredient is discharged into the mixing chamber from a container or containers positioned immediately adjacent the chamber and such container or containers are retracted away from the mould after said mixing in the chamber.

6. The method as claimed in claim 5, wherein there is a plurality of said containers and these are charged with predetermined amounts of respective said ingredients when in the retracted positions thereof.

7. The method as claimed in claim 5 or 6, wherein there is a plurality of said containers and these are each charged with a predetermined requisite amount of a respective ingredient, or combination thereof, and the entire content of each container is discharged into the mixing chamber.

8. The method as claimed in claim 1 or 2, wherein one or more ingredients comprising catalysts or activators or more ingredients comprising catalysts or activators which represent a relatively small proportion of the overall volume of ingredients is pre-mixed with only one or some of the other ingredients representing a relatively large proportion of the overall volume of ingredients.

9. The method as claimed in claim 8, applied to the production of open cell polyurethane foam in single block form from a chemical formulation which includes a polyol, a isocyanate (such as toluene di-isocyanate), water, catalyst/activator substances (such as tin compound and an amine), a blowing agent and if desired one or more other additives (such as a silicone); and a pre-blend of the polyol, water, catalyst/activator and if desired any additive (such as silicone and/or other additive) by mixing together requisite relative quantities thereof in a pre-mixing container having a capacity sufficient to contain a small part only of the total volume of pre-blend required and collecting at least a substantial proportion of the total volume of pre-blend in said mixing chamber which is of a capacity sufficient to receive all of the ingredients of the formulation before mixing of the pre-blend and toluene di-isocyanate, the blowing agent being included in the pre-blend or added with the isocyanate as preferred.

10. The method as claimed in claim 9, wherein all of the pre-blend is formed in a common premixing container the ingredients of the pre-blend being passed continuously to the container and being intimately mixed during passage through such container.

1 The method as claimed in claim 9 or 10, wherein at least 50% of the pre-blend is collected in the mixing chamber before the bringing together and intimate mixing of the pre-blend and isocyanate.

1 2. The method according to any one of claims 8 to 11, wherein the pre-blend is fed to the mixing chamber via an open chute.

13. Apparatus for use in the manufacture of foam material in block form according to claim 1, comprising a mould, a mixing chamber directly adjacent the mould and in fluid flow relationship therewith, means for delivering foam-forming ingredients to the mixing chamber for mixing therein, and means for effecting discharge of the contents of the mixing chamber to the mould.

14. Apparatus as claimed in claim 13, wherein the mixing chamber is defined by a recess in an inner surface of the mould, and a removable closure plate is provided to cover the chamber at the said inner surface for sealing the chamber relative to the mould.

15. Apparatus as claimed in claim 14 further including a piston located in the recess and movable therein to discharge mixed ingredients therefrom into the mould.

1 6. Apparatus as claimed in claim 15, wherein the piston is movable between a retracted position remote from the surface of the mould and a forward position substantially flush with the said surface in discharging mixed ingredients from the mixing chamber.

1 7. Apparatus as claimed in claim 1 5 or 16, wherein the volume swept by the piston is equal to the capacity of the mixing chamber.

18. Apparatus as claimed in any one of claims 15 to 17, wherein the mixing chamber is cylindrical in form.

19. Apparatus as claimed in any one of claims 14 to 18, wherein containers for said ingredients are mounted on the closure plate for movement therewith and each has a respective gated outlet passing through the plate.

20. Apparatus as claimed in claim 19, further including supply outlets for respective foamforming ingredients and wherein the containers are movable between a position directly adjacent the mixing chamber whereat the respective contents thereof are discharged and a retracted position remote from the mixing chamber and adjacent the said supply outlets.

21. Apparatus as claimed in claim 20, wherein each supply outlet is adapted and arranged to supply a pre-determined measured quantity of foam-forming ingredient to the respective container.

22. Apparatus as claimed in any one of claims 14 to 21, wherein the closure plate supports a motor-driven shaft having mixing vanes thereon, the said vanes being located within the mixing chamber.

23. Apparatus according to any one of claims 13 to 18, further including a pre-mixing container adapted for connection to and of smaller capacity than said mixing chamber.

24. The method of forming blocks of foam material substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

25. Apparatus for use in the manufacture of foam material in block form substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.