GB2229106A

GB2229106A - Mixing apparatus

Info

Publication number: GB2229106A
Application number: GB9004334A
Authority: GB
Inventors: Malkit Singh Brom
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-03-02
Filing date: 1990-02-27
Publication date: 1990-09-19
Anticipated expiration: 2010-02-27
Also published as: GB8904756D0; GB2229106B; GB9004334D0

Abstract

Apparatus for mixing two or more liquid or pasty components delivered in discrete quantities from respective supplies (1, 2) by pumps (3, 4) has inlet passage means (5) through which the components are delivered to an inlet (6) of a mixer means (7), from an outlet (8) of which the mixture is delivered. In order to improve the uniformity of the mixture, the inlet passage means (5) has flow control means including a chamber (13) in which the components combine before entering the mixer means (7). The arrangement is such that in the chamber (13) one component enters the centre of a stream of the other components, and the flow control means also ensures that the velocities of the components are similar before they are combined. The flow control means also includes a valve (9) controlling flow to the inlet (6) in dependence on the delivery from the supplies (1, 2). The mixer means (7) may comprise one or more of motionless or rotary dynamic mixers. <IMAGE>

Description

MIXING APPARATUS This invention relates to apparatus for, and a method of, mixing two or more liquid or pasty components delivered discontinuously in discrete quantities from respective supplies.

Mixing apparatus is used for mixing many different types of such components, and the object of the apparatus is to produce a uniform and consistent mixture. However, it is often difficult to mix satisfactorily components whose viscosities and/or proportions in the mixture differ greatly, as tends to happen with chemical components of resins, such as epoxies, polyesters, polyurethanes and the like.

In known mixing apparatus, components are delivered discontinuously in discrete quantities from pumps, either directly or indirectly through a metering system, and progress through one or more mixers to an outlet. In each case, the discontinuous nature of the supply tends to result in surges in the streams of the individual components, so that the streams delivered to the mixers have small solid patches. These patches tend not to be mixed properly by the mixers, resulting in a zonal concentration effect in the final mixture, that is, zones where one component is in excess relative to a uniform mixture on either side of the zones. Various types of mixers are known, and these comprise either motionless mixers, or dynamic mixers.

Motionless mixers may be of a helical type, in which the components are passed through a helical element, or of an interfacial surface generator type, in which streams of the components passing through a tube are successively sub-divided and re-combined. The interfacial surface generator mixers are usually more efficient than the helical mixers, but they use small diameter passages, which create back pressures in the apparatus. This necessitates operating the apparatus at higher pressures, which is disadvantageous where the components have high viscosities. The dynamic mixers, in which a rotary member is used to perform the mixing, tend to be more efficient than the motionless mixers, but even these do not eliminate the zonal concentration effect. Known mixing apparatus therefore has the disadvantage that it can be unable to produce a suitably uniform and consistent mixture.

According to a first aspect of the present invention apparatus for mixing two or more liquid or pasty components delivered discontinuously in discrete quantities from respective supplies comprises mixer means having an inlet to which the components are delivered, and an outlet from which the mixture is delivered, means for delivering discrete quantities of each component to the inlet through inlet passage means, and flow control means provided in the inlet passage means to control the flow of the components to the inlet, the flow control means including a chamber in the inlet passage means where the components first combine.

Using flow control means, including the chamber, to control the flow of the components in the inlet passage means before they reach the mixer inlet reduces any solid patches in the components and prevents them from entering the mixer means, thus ensuring a more uniform mixture. The zonal concentration effect is therefore substantially reduced, or even eliminated.

The arrangement of the chamber in the inlet passage means is such that one component enters the centre of a stream of the other component or components. Restrictor means may also be provided as part of the flow control means. A first restrictor means controls the flow of the individual components before they come together, so that their velocities are similar. A second restrictor means may also be provided to control flow of the combined components out of the chamber.

The flow control means conveniently also includes valve means provided in the inlet passage means to control flow of the components to the inlet in dependence on their delivery from the supplies.

Preferably the valve means is closed to prevent flow into the mixer means, at the start of operation of the delivery means, and then opens after a predetermined time interval to allow flow into the mixer means. The valve means closes at completion of operation of the delivery means. The valve means may be provided between the chamber and the mixer inlet.

Conveniently, a second valve means is provided at the mixer outlet, and is operated to control flow from the mixer means in the same way as the first Valve means controls the flow into the mixer means. As a result, the flow of the components through the mixer means is controlled fully, which ensures continuity of the mixture at the outlet, as there can be no air gaps, and further improved uniformity.

The valve means preferably comprise pneumatic valves, and a pneumatic control unit is provided to operate them. The unit operates the valve means in response to operation of the delivery means. The predetermined time interval will need to be varied in accordance with the particular components being mixed, and the characteristics of the inlet passage means, and the control unit is preferably adjustable to accommodate this. The valve means could instead be solenoid-operated valves, operated by an electronic control unit.

The mixer means may comprise one or more mixers of any suitable motionless or dynamic type. Where a dynamic mixer is used, the zonal concentration effect is substantially eliminated. The dynamic mixer comprises a rotary member working in a mixing chamber, which is provided with a single inlet. Preferably the inlet is close to the axis of rotation of the rotary member. The delivery means preferably comprises a pump for each component. The pumps may be single or double-acting. The inlet passage means may also include diverter valves, enabling the proportions of the components to be sampled.

The use of mixing apparatus in accordance with the first aspect of the invention provides a substantially more uniform and consistent mixture. A second aspect of the invention relates to a method of mixing two or more liquid or pasty components.

According to a second aspect of the present invention, a method of mixing two or more liquid or pasty components comprises the steps of delivering discrete quantities of each component to inlet passage means, controlling the flow of the components in the inlet passage means to an inlet of a mixer means by flow control means, including combining the components in a chamber, mixing the components in the mixer means, and delivering the mixture to a mixer outlet.

This method increases the uniformity of the resulting mixture by virtue of the control of the flow of the components to the mixer inlet, as this prevents solid patches of individual components entering the mixer means. Again, this reduces or even eliminates the zonal concentration effect.

The combination of the components in the chamber has one component entering the centre of a stream of the other component or components. The step of controlling flow to the mixer means may also include controlling the flow of each component into the chamber by first restrictor means; controlling the flow of the components out of the chamber by second restrictor means; and operating a valve means in dependence on the delivery of the components.

Preferably the valve means is closed to prevent flow to the inlet at the start of the delivery step, and opens after a predetermined time interval to allow flow to the inlet.

Conveniently the method includes the further step of controlling the flow of the mixture at the mixer outlet by operation of a second valve means in the same way as the first valve means. This allows full control of the flow of the components through the mixer means, ensuring continuity and even better uniformity.

An embodiment illustrating both aspects of the invention is illustrated, by way of example, in the accompanying drawings, in which: Figure 1 is a schematic diagram of mixing apparatus for mixing two liquid or pasty components; Figures 2 and 3 show the final mixture using conventional mixing apparatus and the apparatus of Figure 1 respectively; and Figures 4 to 6 show modified flow control restrictors.

The mixing apparatus shown in Figure 1 has containers 1,2 for the two components, from which discrete amounts of the components are delivered discontinuously by pumps 3,4, via inlet passage means 5, to an inlet 6 of a mixer means 7, where the components are mixed, the mixture being delivered to an outlet 8. The inlet passage means 5 has flow control means, including inlet and outlet valve means 9,10 provided on the inlet 6 and outlet 8 respectively and operated by a control unit 11 to control flow through the mixer means 7.

Each pump 3,4 is of the single-acting reciprocating type, which on each delivery stroke delivers a discrete amount of the component, the amount being determined by the required proportions of the components in the mixture.

Each component is delivered through a diverter valve 12, which allows samples of the components to be taken so that the proportions of the components in the mixture can be checked. The containers 1,2 are arranged so that the first component (in container 1) is the more viscous. Because of the discrete nature of the delivery of the components from the pumps 3,4, they tend to have small solid patches, which are not completely mixed by the mixer means 7. The flow control means in the inlet passage means substantially eliminates the solid patches before the components are actually mixed. The first component is delivered to a chamber 13 in the inlet passage means 5 through a restrictor 14 in the form of a single aperture, which controls its velocity.The second component, which is arranged to have a similar velocity, enters the chamber 13 at an intermediate point, and the arrangement is such that it enters the centre of the stream of the first component, which envelopes the second component. Both components then pass through a further velocity-controlling single aperture restrictor 15 before reaching the valve means 9 and the inlet 6. The second restrictor 15 forces the components into intimate contact and then allows them to expand into a larger volume. As a result of this process, the solid patches are substantially eliminated, but a final flow control is exercised by the valve means 9.

The valve means 9,10 are pneumatic ball valves which open and close in order to control flow into and out of the mixer means 7. The valves 9,10 operate simultaneously, in order to ensure full control of the flow, with no discontinuity of the mixture at the outlet 8. The control unit 11 is a pneumatically-operated actuator, which operates the valves 9,10 in accordance with signals from the pumps 3,4. The unit 11 closes the valves 9,10 at the end of each delivery stroke of the pumps 3,4 to prevent flow in the mixer means 7. At the start of the delivery stroke of the pumps 3,4, the actuator 11 receives a signal from the pumps 3,4, but delays the opening of the valves 9,10 for a predetermined time interval of between 1 and 2 seconds.On opening of the valves flow is allowed through the mixer means 7 until the end of the delivery stroke, when the actuator 11 closes the valves 9,10 immediately. The closing and opening of the inlet valve 9 in particular helps prevent any remaining patches of the individual components from entering the mixer means 7. The control unit 11 is adjustable in order to vary the time interval in accordance with the components used.

The mixer means 7 comprises four separate motionless mixers of known types arranged in series.

Two helical mixers 16 are provided, together with two interfacial surface generator mixers 17.

In use, the control unit 11 is set for the appropriate predetermined time interval in accordance with the components and their proportions in the mixture. The pumps 3,4 are then operated to deliver the components to the inlet passage means 5, from where they pass to the inlet 6, under the control of the valve 9. The mixer means 7 then mix the components, and the mixture is discharged from the outlet 8 under the control of the valve 10. The valves 9,10 are initially closed, and are operated by the unit 11 as described above, remaining closed at the start of the delivery stroke of the pumps, opening after the delay of the predetermined time interval, and closing again at the end of the delivery stroke. This sequence is repeated until the required amount of mixture has been dispensed.

The apparatus, by controlling flow through the inlet passage means 5 into the mixer means 7, provides a much more uniform and consistent mixture than has been obtainable with conventional apparatus, as can be seen by comparing Figures 2 and 3. Figure 2 shows a section of mixture obtained using conventional apparatus with zones 18,19 of individual component between uniform zones 20. In Figure 3, the current apparatus reduces the zones 18,19 to faint traces 21, so that the zonal concentration effect is substantially eliminated.

It will be understood that the aperture and length of restrictors 14 and 15 are chosen in accordance with components used, and can be modified as required.

Figure 4 shows an alternative for the restrictor 14, in the form of an angled flow path 22. Figures 5 and 6 show alternative constructions for the restrictor 15; in Figure 5 the restrictor is a mesh 23, and in Figure 6 a plurality of apertures 24.

In a modification, not shown, the pumps 3,4 may be of the double-acting reciprocating type. In a further modification, not shown, the pumps 3,4 supply a metering system, operated by valves. In each case, modification of the operation of the unit 11 may be required.

In a further modification, not shown, the mixer means 7 has a dynamic mixer instead of the motionless mixers 16,17. The dynamic mixer comprises a rotary member working in a mixing chamber, which is provided with a single inlet, rather than separate inlets for each component, as is the case with conventional rotary mixers, and of course an outlet. The inlet passage means is connected to the inlet, which is located as close as possible to the axis of rotation of the rotary member. With this arrangement, it is possible to omit the valve 10, and the delay in the opening of the valve 9 following the start of the delivery stroke, and still obtain a mixture from which the zonal concentration effect is virtually or wholly eliminated. The mixer means 7 may have dynamic mixers as well as, rather than instead of, the motionless mixers.

In yet a further modification, not shown, the valves 9,10 may be solenoid-operated, and the control unit 11 is then electronic.

Claims

1. Apparatus for mixing two or more liquid or pasty components delivered discontinuously in discrete quantities from respective supplies, comprising mixer means having an inlet to which the components are delivered, and an outlet from which the mixture is delivered, means for delivering discrete quantities of each component to the inlet through inlet passage means, and flow control means provided in the inlet passage means to control the flow of the components to the inlet, the flow control means including a chamber in the inlet passage means where the components first combine.

2. Mixing apparatus as claimed in claim 1, in which one component enters the centre of a stream of the other component or components in the chamber.

3. Mixing apparatus as.claimed in Claim 1 or Claim 2, in which the flow control means includes restrictor means.

4. Mixing apparatus as claimed in claim 3, in which the restrictor means includes first restrictor means controlling the flow of individual components before they combine.

5. Mixing apparatus as claimed in claim 3 or claim 4, in which the restrictor means includes second restrictor means controlling flow of the combined components out of the chamber.

6. Mixing apparatus as claimed in any preceding claim, in which the flow control means includes valve components to the inlet in dependence on their delivery from the supplies.

7. Mixing apparatus as claimed in claim 6, in which the valve means is closed to prevent flow into the mixer means at the start of the operation of the delivery means, and then opens after a predetermined time interval to allow flow into the mixer means.

8. Mixing apparatus as claimed in claim 7, in which the valve means closes at the completion of operation of the delivery means.

9. Mixing apparatus as claimed in claim 7 or claim 8, in which the valve means is located between the chamber and the mixer inlet.

10. Mixing apparatus as claimed in any of claims 7 to 9, in which a second valve means is provided at the mixer outlet, and is operated to control flow from the mixer means in the same way as the first valve means controls the flow into the mixer means.

11. Mixing apparatus as claimed in any of claims 7 to 10, in which each valve means comprises a pneumatic valve, operated by a pneumatic control unit.

12. Mixing apparatus as claimed in any preceding claim, in which the mixer means comprises one or more mixers.

13. Mixing apparatus as claimed in any preceding claim, in which the mixing means includes a dynamic mixer comprising a rotary member working in a mixing chamber provided with a single inlet.

14. Mixing apparatus as claimed in any preceding claim, in which the delivery means comprises a pump for each component.

15. A method of mixing two or more liquid or pasty components, comprising the steps of delivering discrete quantities of each component to inlet passage means, controlling the flow of the components in the inlet passage means to an inlet of a mixer means by flow control means, including combining the components in a chamber, mixing the components in the mixer means, and delivering the mixture to a mixer outlet.

16. A mixing method as claimed in claim 15, in which the combination of the components in the chamber has one component entering the centre of a stream of the other component or components.

17. A mixing method as claimed in claim 16, in which the step of controlling the flow includes controlling the flow of each component into the chamber by first restrictor means.

18. A mixing method as claimed in claim 16 or claim 17, in which the step of controlling the flow includes controlling the flow of the combined components out of the chamber by second restrictor means.

19. A mixing method as claimed in any of claims 15 to 18, in which the step of controlling the flow includes operating a valve means in dependence on the delivery of the components.

20. A mixing method as claimed in claim 19, in which the valve means is closed to prevent flow to the inlet at the start of the delivery step, and opens after a predetermined time interval to allow flow te the inlet.

21. A mixing method as claimed in any of claims 15 to 20, which includes the further step of controlling the flow of the mixture at the mixer outlet by operation of a second valve means in the same way as the first valve means.

22. Apparatus for mixing two or more liquid or pasty components delivered discontinuously in discrete quantities from respective supplies substantially as described herein with reference to and as illustrated in the accompanying drawings.

23. A method of mixing two or more liquid or pasty components substantially as described herein with reference to the accompanying drawings.