WO1996025999A1

WO1996025999A1 - Storage and mixing of fluids

Info

Publication number: WO1996025999A1
Application number: PCT/GB1996/000400
Authority: WO
Inventors: Peter Leonard Ashcroft
Original assignee: Courtaulds Coatings (Holdings) Limited
Priority date: 1995-02-23
Filing date: 1996-02-22
Publication date: 1996-08-29
Also published as: TW312628B; AU4727496A; GB9503568D0; GB2298146B; GB2298146A

Abstract

Apparatus for storing and mixing a fluid comprises a flexible bag (11) divided into two compartments (13, 14) by an apertured plate (10) and mounted inside a container (21). The apertures (18, 19) are of two types, presenting different resistances to fluid flow therethrough from either side. The part of the bag which forms one of the compartments serves as a diaphragm (25) which, when vibrated, causes the fluid to circulate through the plate (10), thereby mixing it.

Description

Storage and Mixing of Fluids

Field of the invention

This invention relates to apparatus for storing and mixing fluids (i.e. liquids, including slurries and dispersions) . The apparatus is particularly suitable for storing and mixing paint, but can also be used for other viscous fluids or any other fluids which soil containers and mixing apparatus and present a cleaning problem.

Background to the invention

WO 84/03845-A1 and WO 85/02352-A1 describe apparatus for the non-intrusive mixing of fluid such as paint. The apparatus of WO 84/03845 comprises two compartments interconnected by conduits and means to vary the pressure in one compartment; the conduits are of two types each presenting a lower resistance to flow in the opposite direction to the other, so that under applied pressure vibration flow of the fluid back and forth through the conduits is promoted. The apparatus of WO 85/02352 comprises an impeller connected to the wall of the container and movable relative to the wall.

The apparatus of WO 84/03845 and WO 85/02352 is an effective and rapid method of mixing paint. It is particularly useful for storage and mixing of successive batches of the same paint, for example automotive and industrial coatings. In many markets, • such as marine paint and protective coatings for structural steelwork and buildings, the paint is sold either in drums which are discarded as waste, or in intermediate bulk containers (IBCs) , for example of capacity 500 to 2000 litres, which are returned to the coatings manufacturer for cleaning with solvent and re- use. The apparatus of WO 84/03845 and WO 85/02352 is in general too expensive to be discarded with a paint drum and adds considerably to the cost and difficulty of cleaning an intermediate bulk container. Summary of the invention

An apparatus according to the present invention for storing and mixing a fluid, comprises an apertured plate for mounting within an outer container, said plate having apertures of two types, at least one aperture of the first type presenting a lower resistance to flow of fluid in one direction through the plate and at least one aperture of the second type presenting a lower resistance to flow of fluid in the opposite direction through the plate, and is characterised in that a flexible bag is attached to the apertured plate so that the bag is divided by the plate into a first compartment and a second compartment which is adjacent to one end of an outer container when the plate and bag are mounted within said outer container, the part of the bag forming the second compartment acting as a diaphragm to transmit vibration so that when the bag is vibrated within the outer container the fluid flows from the second compartment to the first compartment through at least one aperture of the first type and from the first compartment to the second compartment through at least one aperture of the second type, thereby mixing the fluid within the apparatus.

Detailed description of preferred embodiments

Two embodiments of apparatus in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, of which

Figure 1 is a diagrammatic cross-section through a first embodiment of apparatus according to the invention,-

Figure 2 is a plan view of the plate used in the apparatus of Figure l; ** Figure 3 is a diagrammatic cross-section of the apparatus of Figure 1 in use in an outer container,-

Figure 4 is a diagrammatic section through a second embodiment of apparatus according to the invention during filling; and Figure 5 is a diagrammatic section through the apparatus of Figure 4 during discharge. The apparatus (5) of Figure l comprises an apertured plate (10) fixedly located within a flexible bag (11) . The bag (11) and plate (10) are both made of thermoplastics resin and the bag (11) is welded to plate (10) around the periphery (12) of the plate, dividing the bag (11) into a larger first compartment (13) and smaller second compartment (14) . The welded region can extend from the periphery (12) a small distance inwards on the lower surface of plate (10), forming a rim (15) for support of the plate (10) in use. The first compartment (13) has an opening (16) which is adapted to receive hoses for filling and discharging the bag (11) . In Figure 1, the opening (16) is shown closed. The plate (10) has apertures of two types. A central aperture (18) has a cross-section which narrows in the direction from compartment (14) to compartment (13), thus presenting a lower resistance to flow of fluid from the second compartment (14) to the first compartment (13) than from the first compartment (13) to the second compartment (14) . The second type of aperture are outer apertures (19) which have a cross-section which narrows in the direction from compartment (13) to compartment (14), thus presenting a lower resistance to fluid flow from the first compartment (13) to the second compartment (14) than from compartment (14) to compartment (13) . There need not be just a single central aperture (18) of the first type as shown in Figure 2 since a group of two to four central apertures can be provided. Similarly there can be two or more outer apertures (19) (for example four as shown in Figure 2) or six outer apertures as shown in WO 84/03845, or up to twelve outer apertures. Where a single central aperture (18) is used as shown, its diameter may be greater than the diameter of each of the outer apertures (19) , although it is usually preferred that the cross-sectional area of the central aperture (18) at its narrowest point, or the sum of such apertures in the case of a plurality of apertures (18) , is less than the sum of the cross-sectional areas of the outer apertures (19) at their narrowest point. Alternatively, the positions of the types of apertures can be reversed, so that the outer apertures could narrow towards the first compartment (13) with the central aperture or apertures narrowing towards the second compartment (14) . The plate (10) can be planar as shown in Figure 1 or can be curved, like a dish, so that the central aperture (18) is lower than the outer apertures (19) . The plate (10) can for example be formed by injection moulding, pressing or reaction injection moulding and can contain reinforcing fibres or a reinforcing filler.

In use, the apparatus (5) is placed inside an outer container (21) such as an IBC or paint drum which is fitted with means (22) for generating an oscillating pressure under the smaller compartment (14) of the bag (11) . The outer container (21) is preferably designed as a rigid intermediate bulk container, particularly if it is required to be transported by sea. The container (21) is preferably cylindrical. The plate (10) is preferably supported at a fixed height within the container (21) . The base of the container is preferably shaped to include a recess (23) the entry to which acts as a shelf to support the plate (10) ,^• this arrangement gives a robust overall package for transport. The plate can alternatively be supported by means (e.g. a continuous shelf) protruding inwardly from the wall of the container (21) . The apparatus (5) preferably includes means for locking the plate (10) in position relative to the container (21) so that the plate is not dislodged during mixing. The apparatus (5) can for example have lugs welded to the bag (11) at the level of the top of plate (10) which are secured by cooperating members on the base of container (21) after the apparatus (5) has been placed inside the container (21) .

The means (22) for generating an oscillating pressure comprises a diaphragm (25) mounted on a shaft (26) connected to a drive means (27) (not sectioned) for imparting reciprocating motion to the shaft (26) . The lower compartment (14) of the bag (11) rests on the diaphragm (25) . The shaft (26) is located in a bearing (28) as it passes through the base of the container (21) . A resilient seal (29) in the form of an "0" ring is preferably mounted on the base of the container (21) . The diaphragm (25) preferably has a locking device to hold it in sealing engagement against the "0" ring

(29) during transport of the container. The drive means (27), which is mounted on the container (21), can for example be adapted to cooperate with an external hydraulic or compressed air drive system to generate reciprocating motion, or can be adapted to receive a drive shaft and to convert rotary motion into reciprocating motion. Alternatively, the drive means (27) can include its own prime mover (e.g. an electric motor) with appropriate drive transmission to generate reciprocating motion therefrom.

When the apparatus of Figure 1 has been placed in container (21) , the bag (11) is filled with fluid, for example paint or ingredients which are to be mixed to form paint. The opening (16) is then sealed. If the paint is already mixed, the container full of paint is transported to the painting site, for example a shipyard. When the paint is to be used, or if the paint ingredients need to be mixed after filling, or during storage if required, the paint is mixed by reciprocating the shaft (26) and diaphragm (25) to generate an oscillating pressure within the lower portion of bag (11) . During the upstroke of diaphragm (25) pressure is increased in the lower compartment (14) of the bag (11) and fluid surges through the central aperture (18) of plate (10) , into the upper compartment (13). During the downstroke of diaphragm

(25) pressure is decreased in the lower compartment (14) and fluid now surges through the outer apertures (19) from compartment (13) into compartment (14) . Vibration of the diaphragm (25) thus generates vigorous circulation of fluid both in the larger upper compartment (13) and in the smaller lower compartment (14) of the bag (11) , the direction of circulation being generally downwardly adjacent to the sides of bag (11) and upwardly in the middle. For example, when a plate (10) whose central aperture (18) has a diameter of 50-60 mm is used in a 1000 litres IBC, the rate of flow through central aperture ' _ z ^'' can be 1000 litres/mi:. cr more. When required, fluid is discharged through opening (16) via a hose (31) which in the case of paint, for example, can feed to a pump leading to apparatus for spray application of the paint. In most cases, mixing of the fluid is continued during discharge and this can be achieved by continued vibration of the diaphragm (25) . This continued vibration will also aid withdrawal of the fluid through the hose (31) by a pump. The opening (16) and associated discharge means are adapted to prevent substantial ingress of air into the bag (11) during discharge, so that as the fluid is discharged, the upper compartment (13) of the bag (11) gradually collapses; for example the dashed line (A) in Figure 3 shows the apparatus about half discharged. Collapse of the bag (11) does not impede mixing or discharge of the fluid.

When the fluid has all been discharged, the apparatus (5), comprising the empty bag (11) and plate (10), can be removed from the container (21) . The container (21) is then substantially clean and ready for re-use. The used apparatus (5) is generally not cleaned; it can be sealed and returned with the container (21) for re-use in storing and mixing the same fluid. Alternatively (and in any case eventually) the apparatus (5) can be discarded. It can for example be burnt as fuel to recover energy. The environmental impact of discarding bag (11) and plate (10) is generally substantially less than that of solvent cleaning a container which is soiled by paint. The apparatus (5) can operate as a sealed system. It has the considerable advantage that the fluid never contacts any part of the oscillating pressure means (22) so that cleaning of this is never generally required.

The bag (11) and plate (10) are preferably formed of a thermoplastics synthetic resin. The material of bag (11) should be resistant to the fluid to be contained and mixed, for example it should be resistant to the solvents present in any paints it is to contain. Examples of thermoplastics resins which are resistant to substantially all marine and other heavy duty paints are polyester, particularly aromatic polyester such as polyethylene terephthalate, partially hydrolysed polyvinyl acetate or ionomer resin. Polyolefinε such as high density polyethylene, polypropylene or linear low density polyethylene can be used for many paints but not for those based on aromatic hydrocarbon solvents. The bag (11) is generally constructed from thermoplastics film which can optionally be a laminate of two or more thermoplastics polymers . The bag can be formed from a single film or from multiple layers of film. The bag (11^* and plate (12) are preferably formed of the same synthetic resin to maximise compatibility in welding. The apparatus (5) can for example be formed by welding the plate (10) inside a single bag (11) , or the upper and lower parts of the bag (11) can be separately welded to the plate (10) . The lower compartment (14) preferably has a depth of 5 to 50 mm below the plate (10) when filled or inflated, most preferably 10 to 20 mm. The upper compartment (13) is generally designed to be of a size that at least fills the remaining volume of the outer container (21) so that the filled bag does not experience stress. The bag (11) is preferably substantially airtight for use with paints so that the container with included bag can be stored in a partly discharged condition for a while without deterioration of the paint by reaction with atmospheric oxygen or moisture, or by loss of solvent. Thermoplastics resin bags have been used as part of flexible composite IBCs and in general such a bag is sufficiently thick to be robust and sufficiently impermeable to air. The bag (11) can be metallised on its inner and/or outer surface to reduce permeability. Alternatively the inner surface of the bag (11) can be fluorinated to improve its resistance to damage by the fluid and solvents contained therein,- this can be achieved by inflating the bag with a gaseous fluorinating medium such as fluorine or hydrogen fluoride. Alternative procedures can be used to treat the bag (11) , or the film from which it is made, to reduce solvent solubility, for example by crosslinking with UV radiation.

The amplitude of vibration of the diaphragm (25^ and shaft (26) is generally at least 1 mm and preferably at least 2 mm and can be up to 10 or 20 mm, but is preferably in the range 7 to 15 mm. The size and shape of the lower compartment (14) of the bag (11) is preferably such that it remains supported by diaphragm (25) throughout the movements of the diaphragm (25) and shaft (26) . The frequency of vibration is preferably at least 1 Hz (1 cycle per second) and can be up to 50 Hz but is most preferably in the range^'s to 10 Hz.

As an alternative to welding of the bag (11) to the plate (10) , the bag may mechanically engage the plate, for example the bag may clip into a recess in the rim (12) of the plate using a separate clip or by other means. The bag (11) can, for example, carry a bead on its inner surface extending around its circumference, which on location in a peripheral groove in the plate (10) divides the bag (11) into the two compartments (13 and 14) . If the bag (11) and plate (10) are not to be welded, neither need be thermoplastic, although a thermoplastics resin will generally be used for bag (11) to give the required flexibility and ease of manufacture. The plate (10) can be formed of a thermoset resin or of metal. It can also be separated from bag (11) after use if desired, and may be cleaned separately and re-used.

As a further alternative, the bag (11) can be clamped between the plate (10) and the container (21) ; for example the plate (10) may engage a recess in the inner wall of the container (21) , sandwiching the bag wall between them to divide the bag (11) into the required upper (13) and lower

(14) compartments, or a protruding bead on the inner wall of the container (21) can engage a recess in the rim (12) of plate (10) , once again sandwiching the bag wall between the bead and recess.

In the embodiment of apparatus (45) shown in Figures 4 and 5, the apparatus (45) comprises a bag (51) and plate (50) similar to bag (11) and plate (10) . The apparatus (45) is designed for use in a container (61) which is an open topped drum. The bag (51) and plate (50) are welded at the rim (52) of the plate (50), forming a larger compartment (53) and smaller compartment (54) . The apparatus (45) differs from apparatus (5) in that the inlet (56) of apparatus (45) is located in the smaller compartment (54) . The apparatus (45) is inserted in drum (61) and is filled through inlet (56) , which is then sealed. The drum (61) is also sealed by lid (63), and can then be transported to the painting site.

When the paint is to be used, the lid (63) is removed and means (62) for generating oscillating pressure is fitted to the top of the drum (61) . The oscillating means (62) can be similar to means (22) of Figures 1 to 3 except that the diaphragm of the oscillating means (62) has a hole to accommodate a discharge hose (71) from inlet/outlet (56) , and the associated shaft and drive unit are also arranged so as not to interfere with this discharge hose (71) . While the inlet (56) is still sealed, the drum (61) is inverted as shown in Figure 5. The oscillating pressure means (62) is then actuated to mix the fluid in apparatus (45) . When the fluid is thoroughly mixed, the discharge hose (71) is fitted to inlet/outlet (56) and the fluid is discharged. Mixing can be continued during discharge if required.

The drive means (27) may be attached to the container (21) , but is preferably a free-standing unit upon which the apparatus according to the invention may be placed or secured. The container (21) is conveniently designed so that it may alternatively be used as the outer container in a conventional IBC lined with a bag of plastics material. The plastics bag may be equipped with a suitable seal or valve in its base. The complete container can then be mounted on a dispensing cradle and the seal punctured or valve opened to allow the contents of the bag to run out under gravity, be pumped out by suction, or be expressed by application of pressure to the bag, for example pneumatically or hydraulicall .

Claims

1. Apparatus for storing and mixing a fluid, comprising an apertured plate for mounting within an outer container, said plate having apertures of two types, at least one aperture of the first type presenting a lower resistance to flow of fluid in one direction through the plate and at least one aperture of the second type presenting a lower resistance to flow of fluid in the opposite direction through the plate, characterised in that a flexible bag is attached to the apertured plate so that the bag is divided by the plate into a first compartment and a second compartment which is adjacent to one end of an outer container when the plate and bag are mounted within said outer container, the part of the bag forming the second compartment acting as a diaphragm to transmit vibration so that when the bag is vibrated within the outer container the fluid flows from the second compartment to the first compartment through the at least one aperture of the first type and from the first compartment to the second compartment through the at least one aperture of the second type, thereby mixing the fluid within the apparatus.

2. Apparatus according to claim l, characterised in that the bag is welded to the apertured plate.

3. Apparatus according to claim 2, characterised in that the bag is formed of two portions each welded to the apertured plate.

4. Apparatus according to claim 2 or claim 3, characterised in that the bag and the plate are each made of a thermoplastics material .

5. Apparatus according to claim 4, characterised in that the bag is made from the same thermoplastics material as the plate.

6. Apparatus according to claim 1, characterised in that the bag mechanically engages the rim of the plate.

7. Apparatus according to claim 1, characterised in that the bag is adapted to be clamped between the plate and the outer container.

8. Apparatus according to any of claims 1 to 7, characterised in that the apertures are tapered, the aperture of the first type narrowing towards the first compartment and the aperture of the second type narrowing towards the second compartment .

9. Apparatus according to any of claims 1 to 8, characterised in that the plate has at least one aperture of the first type at or near the centre of the plate surrounded by at least two apertures of the second type in the outer part of the plate.

10. Apparatus according to any of claims 1 to 9, characterised in that the first compartment of the bag is fitted with means for discharging the fluid from the bag.

11. Apparatus according to claim 10, characterised in that the discharge means is adapted to prevent substantial ingress of air into the bag during discharge of fluid therefrom so that the first compartment of the bag gradually collapses during discharge.

12. Apparatus according to any of claims 1 to 9, characterised in that the second compartment of the bag is fitted with means for discharging the fluid.

13. A process for mixing paint, characterised in that an apparatus according to any of claims 1 to 12 is mounted within a rigid outer container and a varying pressure is applied to that part of the bag within the outer container forming the second compartment.