Abstract:
Apparatus for mixing liquid in a container, comprises a hollow sleeve member for location in the lower regions of the container, a plurality of circumferentially spaced outlets being provided in the upper regions of the sleeve member, pump means for creating a reciprocating flow of liquid applied to the lower regions of the sleeve member, and in the flow path of liquid from the pump means to the sleeve member, a transducer mechanism cooperating with the sleeve member and subjected to the reciprocating flow of liquid such as to rotate the sleeve member about its central longitudinal axis in dependence upon said reciprocating flow.

Description:
TECHNICAL FIELD 
     This invention relates to mixing apparatus, and has particular though not exclusive application to such apparatus for mixing liquids in relatively large containers, for example paints in intermediate bulk containers (IBC). 
     BACKGROUND 
     It is often necessary, prior to application or use, to mix the contents of large containers, in particular paint containers, to condition the paint for smooth and effective application. 
     Heretofore, such mixing has been achieved in a variety of ways all of which suffer from various disadvantages. 
     Impellers such as propellers comprising a plurality of spiral blades on a rotating shaft are commonly used. However, removal of the propeller after mixing invariably results in paint dripping from the propeller onto the outside of the container. Furthermore, the use of a propeller in anything other than a full container can result in considerable splashing of paint within and without the container, as well as undesirable entrainment of air into the paint by way of the central vortex created by the rotating propeller. 
     Impellers are conventionally inserted through the top of a container to effect mixing, and, as mentioned above, can create problems if the container is only partially full. 
     It has been proposed to achieve mixing by means of a unit attached to the bottom of a container and reacting with the contents of the lower regions of the container to create mass movement throughout the volume of the container which is effective even if the container is other than full. 
     More particularly the unit includes a disc extending transversely of the lower regions of the container and provided with a central aperture surrounded by a plurality a circumferentially spaced apertures adjacent the periphery of the disc. 
     A diaphragm below the disc is alternately moved upwards and downwards relative to the disc, the configuration of the apertures in the disc being such that, on upward movement of the diaphragm liquid is preferentially forced upwardly through the central aperture, and, on downward movement of the diaphragm, liquid is preferentially drawn downwardly through the peripheral apertures. Thus a swirling motion is created within the container which serves to mix the contents thereof. 
     Such equipment, although non-intrusive, is complex and expensive, the mixing effect being very dependent upon the frequency of movement of the diaphragm, and is only suited to cylindrical containers. 
     An alternative to the above equipment utilises a static funnel from which radiate a plurality of circumferentially spaced jet outlets, an air-operated double diaphragm pump creating mass movement of the liquid towards and away from the funnel. On movement of the liquid towards the funnel, the liquid is preferentially forced through the outlets to create jets of liquid within the lower regions of the container, and, on movement of the liquid away from the funnel, liquid is drawn down through the centre of the funnel, the overall system being such as to create a swirling motion within the body of liquid. 
     Such a static jet mixer has been found to create closed cells within the body of liquid which remain unmixed and in which there is considerable heat build-up. Overall, mixing is unsatisfactory. 
     SUMMARY OF THE INVENTION 
     It would be desirable to be able to provide mixing apparatus which overcame the problems of the prior art, and in particular which ensured effective mixing of the full volume of contained liquid in an economic and cost effective manner. 
     According to the present invention there is provided, for a liquid container, mixing apparatus comprising a hollow sleeve member for location in the lower regions of the container, a plurality of circumferentially spaced outlets being provided in the upper regions of the sleeve member, and pump means for creating a reciprocating flow of liquid applied to the lower regions of the sleeve member, characterised by, in the flow path of liquid from the pump means to the sleeve member, a transducer mechanism co-operating with the sleeve member and subjected to the reciprocating flow of liquid such as to rotate the sleeve member about its central longitudinal axis in dependence upon said reciprocating flow. 
     It will be appreciated that, with such an arrangement, and as a result of the rotation of the sleeve member, which is typically through 15° for each pulse of liquid, the jets of liquid emanating from the outlets are each directed in continuously changing directions within the container, thereby ensuring thorough mixing of the liquid and avoiding the establishment of any substantially static regions of non-agitation within the liquid. 
     In one embodiment of the invention, the pump means comprise a double acting diaphragm pump, the reciprocating movement of the diaphragm creating a mass movement of liquid into and out of the container. 
     Preferably the transducer mechanism comprises a ratchet wheel secured to, to be rotatable with, the sleeve member, and one or more pawls adapted to engage the ratchet wheel and linearly movable by, in the direction of movement of, the reciprocating liquid. 
     Conveniently there are two pawls mounted on a carrier and engaging diametrically opposite teeth of the ratchet wheel, the reciprocating movement of the liquid resulting in reciprocating movement of the carrier and attached pawls, each such movement of the carrier resulting in consequential stepped rotation of the sleeve member, each step being in the same direction of rotation. 
     Preferably there are two diametrically opposed outlets from the upper regions of the sleeve member, each outlet being directed substantially radially from the sleeve member. 
     The sleeve member and associated transducer mechanism may be located wholly within the lower regions of the associated container to provide a non-intrusive mixing system. 
     Alternatively, the sleeve member may extend through an aperture in the container to locate the outlets therefrom within the lower regions of the container, the lower regions of the sleeve member and the transducer mechanism being external of the container to provide an intrusive mixing system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic vertical section through mixing apparatus according to the invention in a container; 
     FIG. 2 a  shows the apparatus of FIG. 1 to a larger scale; 
     FIG. 2 b  is a plan view of the ratchet wheel, pawls and carrier of FIG. 2 a;    
     FIG. 2 c  is an end view of the carrier of FIGS. 2 a  and  2   b;    
     FIG. 3 is a diagrammatic vertical section through an alternative mixing apparatus according to the invention in a container; 
     FIG. 4 shows the apparatus of FIG. 3 to a larger scale; and 
     FIGS. 5 and 6 show, schematically and respectively, a non-intrusive and an intrusive mixing apparatus according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, there is shown a container  2 , typically an intermediate bulk container for holding paint, in the bottom wall  4  of which is mounted mixing apparatus according to the invention and generally referenced  6 . 
     The mixing apparatus  6  comprises an outer cylindrical housing  8  secured through the bottom wall  4  of the container in sealed relationship therewith, and a hollow sleeve  10  coaxially within the housing  8  and rotatable relative thereto about its central longitudinal axis on a bearing  12 . 
     An inlet  14  in the lower regions of the sleeve  10  feeds into the hollow interior thereof from the annular volume between the housing  8  and the sleeve  10 , while a pair of diametrically opposed outlets  16  are formed in the sidewalls of the sleeve  10  adjacent the upper regions thereof, the outlets  16  being defined by substantially radially extending nozzles  18 . 
     A circular one-way valve mechanism or flow restrictor  20  is mounted within the sleeve  10  above the inlet  14  such as to permit upward flow through the sleeve but to prevent downward flow therethrough. 
     An annular one-way valve or flow restrictor  22  is mounted in the annular volume between the housing  8  and the sleeve  10  adjacent the upper regions of the housing  8  to permit downward flow as indicated by arrows  22 ′ through this annular volume but to prevent upward flow therethrough. 
     An annular ratchet wheel  24  is secured around the lower regions of, to be rotatable with, the sleeve  10 , the ratchet wheel carrying a plurality of external teeth  26 . 
     A discharge pipe  28  feeds from the lower regions of the housing  8 , a pawl mechanism indicated generally at  30  being slidably mounted in the pipe  28 . 
     The mechanism  30  comprises an annular disc  32  extending transversely of the pipe  28  to be guided thereby, a yoke  34  extending from the disc  32  longitudinally of the pipe  28  the opposed arms of which each carry at the free ends thereof a pawl  36 . The pawls  36  co-operate with the teeth  26  of the ratchet wheel  24  as best seen in FIG. 2 b  and such that, on either forward or rearward movement of the mechanism  30  relative to the sleeve  10 , the ratchet wheel  24 , and therefore the sleeve  10 , is rotated in a clockwise direction as viewed in FIG. 2 b.    
     Connected to the end of the discharge pipe  28  is one chamber of a double acting diaphragm pump schematically illustrated at  38  the piston assembly  40  of which is reciprocal between the two extreme positions shown in full lines and dotted lines in FIG. 2 a , the overall displacement of the assembly being indicated by the arrow ‘D’. 
     An isolating valve  42  is provided in the discharge pipe  28  between the mechanism  30  and the pump  38  which is selectively operable to connect the pump  28  into the discharge pipe  28 . 
     The described apparatus operates as follows. With the container  2  holding liquid to be mixed, and with the isolating valve  42  open, the pump  38  is actuated to reciprocate the piston assembly  40 . This creates a reciprocating flow in the discharge pipe  28  as indicated by arrow ‘F’, the effects of which are applied to the mechanism  30  and to the lower regions of the container  2 . 
     More particularly, and as the pump  38  pulses liquid towards the container  2 , said liquid flows through the centre of the disc  32 , through the inlet  14  as indicated by arrow ‘I’, through the one-way valve  20  and out of the sleeve  10  through the outlets  16 /nozzles  18  as pressurised jets of liquid as indicated by arrows ‘J’. The one-way valve  22  prevents upward flow of liquid from the annular space between the housing  8  and the sleeve  10  into the container  2 . 
     At the same time, the flow created by the pump  38  impinges upon the disc  32  to move the mechanism  30  to the left as viewed in FIGS. 2 a  and  2   b , whereby one of the pawls  36  engages an associated tooth  26  on the wheel  24  to rotate the wheel and attached sleeve  10  in a clockwise direction as viewed in FIG. 2 b , while the other pawl  36  rides over an opposite associated tooth  26 . 
     On return movement of the piston  40 , a reverse flow is created in the discharge pipe  28  and is transmitted to the mechanism  30  and the liquid in the container  2 . 
     More particularly, liquid then flows from the container  2  into the annular space between the housing  8  and the sleeve  10  and through the one-way valve  22  as indicated by arrows  22 ′, and then into the discharge pipe  28  as indicated by arrow ‘P’. Flow from the hollow sleeve  10  into the discharge pipe  28  is prevented by the one-way valve  20 . 
     This reverse flow moves the disc  32 , and therefore the mechanism  30 , to the right as viewed in FIG. 2 a  whereby the other pawl  36  engages an associated tooth  26  of the wheel  24  to further rotate the wheel  24  and attached sleeve  10  in a clockwise direction as viewed in FIG. 2 b , the one pawl  36  riding over an opposite associated tooth  26 . 
     Thus it will be appreciated that the pump  38  creates a constantly pulsating flow of liquid in the discharge pipe  28 , the energy of this flow being used to rotate the sleeve  10  by way of the mechanism  30  and at the same time to create pulses or jets of liquid emanating from the nozzles  18 . 
     The jets are directed into the body of liquid as seen in FIG.  5  and serve to create a mixing flow as indicated by the arrows in that Figure. 
     The pump  38  is typically operated at a frequency of  60  pulses per minute, with the sleeve  10  being rotated through typically 15° for each pulse of the pump. 
     The constantly rotating sleeve  10 , and the consequential constantly changing positions of the nozzles  18  within the container  2  ensure extremely thorough mixing of the contents of the container  2  is achieved. Depending upon the application, the nozzles  18  may be directed upwardly and or downwardly of the horizontal. 
     Once mixing is completed, the isolating valve  42  is closed and the pump  38  is removed from the pipe  28  to permit discharge of the contents of the container  2 . 
     Alternatively, a T-junction may be provided in the pipe  28  to enable discharge without removal of the pump  38  as shown in FIG.  6 . 
     FIGS. 1 and 2 illustrate an intrusive mixing system in which the mixing head of the apparatus  6  extends through a wall of the container  2 . 
     FIGS. 3 and 4 illustrate what can be termed a non-intrusive system in which the mixing head of the apparatus  6  is totally housed within the container  2 . 
     Referring to FIGS. 3 and 4, there is shown an alternative mixing apparatus in which components equivalent to those of FIGS. 1 and 2 are similarly referenced. 
     The fundamental operation of the embodiment of FIGS. 3 and 4 is exactly the same as that of the embodiment of FIGS. 1 and 2, the only differences being in the position of the one way valve  22  and the flow path of liquid from the container into the discharge pipe  28 . 
     The valve  22  or flow restrictor is located at the lower end of the housing  8  such that, on return movement of the piston assembly  40  of the pump  38 —ie. to the right as viewed in FIG.  4 —liquid flows through the valve  22  into the annular space between the housing  8  and the sleeve  10  as indicated by the arrow ‘S’ and into the discharge pipe  28  to move the mechanism  30  to the right. 
     Thus there is provided mixing apparatus which is capable of thoroughly mixing large volumes of liquid in an efficient and effective manner. Although primarily developed for mixing coating materials such as paint, the apparatus can be used to mix a variety of substances such as pharmaceuticals, speciality chemicals, foodstuffs, mixtures requiring gaseous blankets and any substance that requires isolation from the surrounding environment. 
     The mixing apparatus can be readily mounted on standard IBC&#39;s using simple tools, the system being such as to enable users to mix without compromising product integrity or resorting to specialised containers. 
     Alternatively, and as illustrated in FIGS. 3 and 4, the mixing apparatus can be mounted within the lower regions of a container and retained in position by co-operation with the internal wall of the discharge pipe as it exits the container. 
     In all cases, the pneumatic drive to the pump provides a reciprocating backwards and forwards motion within the liquid in the discharge pipe the energy from which is used to rotate the outlet nozzles such as to create extensive agitation of the liquid within the container and throughout the volume of said liquid. 
     The frequency of the pump, and the degree of rotation of the sleeve per pulse of liquid can be chosen to suit particular requirements depending upon the product and the application. 
     Clearly the precise construction of the apparatus can vary from that described and illustrated without departing from the scope of the invention. In particular the transducer mechanism to convert the flow energy of the liquid into rotation of the jets may be other than the pawlratchet mechanism detailed above, the reciprocating flow within the discharge pipe may be created other than by a double diaphragm pump, and there may be more than two jets per sleeve. Other modifications and variations will be apparent to those skilled in the art.