GB2306681A

GB2306681A - Apparatus for the mixing of materials and a method therefor

Info

Publication number: GB2306681A
Application number: GB9522461A
Authority: GB
Inventors: Robert Dearing
Original assignee: Spiroflow Ltd
Current assignee: Spiroflow Ltd
Priority date: 1995-11-02
Filing date: 1995-11-02
Publication date: 1997-05-07
Also published as: GB9522461D0

Abstract

Materials to be mixed are located in containers 1 to 5. The weight of each container is monitored continuously in order that its rate of weight discharge can be determined. The materials mix sequentially by the use of screws 31-38 that add material from the container 1 to the material from the container 2 with that mix then falling before having the material from container 3 added. Should the weight discharge rate of a particular container vary from a desired norm then either the weight discharge rate of that particular container can be altered by varying the rate of rotation of the screw associated with delivering material from that container or by appropriately varying one or more of the rates of rotation of the screws delivering material from the other containers.

Description

APPARATUS FOR THE MIXING OF MATERIALS AND A METHOD THEREFOR This invention relates to apparatus for mixing materials and also to a method of mixing materials.

Previous material mixing apparatus has relied on volumetric metering to control the relative amounts of material being mixed together. When volumetric metering is used an assumption is rade that the density of the material is constant. A particularly dense region in the material being controlled volumetrically would be discharged as if it had been of the standard density. The result of the dense region being discharged would be that a greater proportion of the material than was intended would be introduced into the mix. Uncontrollable variation in the proportions of components of a mix is highly undesirable. In previous mixing apparatus unintended variations in the relative proportions of the components of the mix could only be detected at the output of the apparatus; where it is too late to effect adjustment of the relative proportions of the mix.

Previous material mixing apparatus has mixed the materials in a single portion of the apparatus. In the mixing portion of the apparatus large amounts of the mix components are mixed together concurrently. In a system such as this regions of unmixed material are likely to remain if the mixing is incomplete. Given the large volumes being mixed the likelihood of incomplete mixing is significant. Incomplete mixing is highly undesirable and can be costly to remedy.

It is an object of the present invention to attempt to alleviate at least one of the above described disadvantages.

According to one aspect of the present invention, material mixing apparatus comprises means for monitoring the weight discharge rate of at least one of a plurality of materials in a mix and means for controlling the relative weight discharge rate of the material being monitored.

The apparatus ray have means for altering the weight discharge rate of one material when the weight discharge rate of another material varies.

Preferably a plurality of materials to be mixed have weight discharge monitoring means and means for controlling the relative weight discharge rate.

Preferably the apparatus has means for altering a desired discharge rate for at least one of the materials.

The monitoring means ray comprise at least one load cell, which may monitor a weight change of a container of material, for instance over consecutive predetermined time periods.

Preferably, the monitoring means comprises three load cells for the, or each, container, hich load cells may be connected to form a Wheatstone bridge.

The signals from the, or each, load cell(s) may be aggregated.

The signals from the, or each, load cell(s) are preferably used to control the rate of discharge of material from the container to which the signals relate.

The aggregated signals may be used with a programmable logic control (PLC) circuit.

The apparatus may be arranged to provide for continuous mixing.

The material ray be arranged to be carried through the apparatus during mixing. The materials may be arranged to fall one or more times during their passage through the apparatus.

The mixing of the materials and the transport of the materials through the apparatus may be effected by a combined mixing and transport means. The combined mixing and transport means may comprise at least one screw. The screw may be powered, which power may be electrical. The, or each screw may provide transport of the material or materials mainly along rather than up or done.

material to be mixed ray be introduced into another material or mix of materials by discharge from an open end of a first screw inserted into a second screw of greater internal diameter.

The first and second screws are preferably arranged and operated to transport material in the same direction.

The or each screw may extend completely through a container of material to be mixed.

The mixing apparatus may have sets of screws on different levels. Different levels may be joined by chutes, down which material may fall.

The material may be arranged to be conveyed to and fro across the apparatus.

According to another aspect of the present invention, a method of mixing materials comprises monitoring the weight discharge rate of at least one material in a mix and altering the relative discharge rates of the materials if the monitored weight discharge rate alters.

The present invention includes any combination of the herein referred to features or limitations.

The present invention may be carried into practice in various ways but one embodiment will now be described by way of example and with reference to the accompanying drawings in which Figure 1 is a schematic cross-section of the mixing apparatus; and Figure 2 is a plan view of the mixing apparatus.

The mixing apparatus of this particular embodiment has containers 1 to 5 (see Figure 2), from which materials which it is desired to mix are dispensed. Each container 1 to 5 is supported on a stand 6. Each stand 6 has three supports 7 (only two shown). Within each support 7 there is a load cell 8, which comprises a piezoelectric portion, the resistance of which changes in response to changes in pressure on the load cell 8. The load cells 8 in each of the three supports 7 of the containers 1 to 5 are connected together and the signals are aggregated and used as the variable resistance in a Wheatstone bridge, the use of which is well known in the art. This embodiment uses currents of the order of 4 to 24 mA, although this should not be taken as a limitation of the apparatus.Signals from the Wheatstone bridges for each container are fed to a programmable logic control (PLC) circuit, in which circuit the rate of discharge of material from the containers 1 to 5 is evaluated and compared with preprogrammed desired values. The signal is then inverted.

Discrepancies between the desired and actual rate of discharge will result in a signal to either increase or decrease the rate of discharge, whichever is necessary, the mechanism for zilch will be described below.

Material held in one of the containers 1 to 5 falls down into a connected cylindrical tube 11 to 15, which is flexibly suspended from its container 1 to 5 (only containers 1 to 3 are shown in side view, containers 4 and 5 are arranged in the same way). Each tube 11 to 15 has a base 21 to 25 and the material fills the tubes 11 to 15.

Close to the base of the tube 11 an internally threaded Archimedean screw 31 extends horizontally through the tube 11. One end of the screw 31 is connected to a variable speed electric motor 41. The screw 31 extends through the lower end of tube 12 and into the internally threaded Archimedean screw 32, which is of greater internal diameter than the screw 31. Openings (not shown) in the outer walls of the screw 31 allow material to fall into the screw in the tube 11. Thereafter the material is retained within the screw 31, through the tube 12 until it is expelled from the free end of the screw 31 into a mid section of the screw 32.

One end of the screw 32 opens into the tube 12, close to its base. The tube 12 receives material from the container 2. The opposite end of the screw 32 extends through a subsidiary vertical tube 16 and to its driving variable speed electric motor 42. Openings (not shown) in the screw 32 allow naterial being transported from both of the tubes 11 and 12 to drop down the subsidiary tube 16.

A further Archimedean screw 33 is attached to a variable speed electric motor 43 at one end. The screw 33 as described before in relation to the screw 31 takes material from the tube 13 through the tube 16 before discharging into a further screw 34. The screw 34 which has a larger internal diameter than the screw 33 takes material in from the tube 16 and discharges it together with material from the screw 33, into a vertical subsidiary tube 17. A variable speed electric motor drives the screw 34.

In a similar manner a screw 35 driven by a motor 45 takes material from the tube 14 and discharges it into a screw 36. That screw 36, driven by a motor 46, takes material from the tube 17 and discharges it into a tube 18. The tube 18 thus has a mixture of material from each of the containers 1 to 4.

A screw 37 driven by a motor 47 then takes material from the final container 5 and discharges it into a screw 38. That screw 38 then takes material from the tube 18 and discharges the mixed material into an outlet tube 19.

The screw 38 is driven by a motor 48.

The Archimedean screws 32 to 38 not only draw the material through the apparatus but also mix the materials, assisted by the action of the mixed materials falling down the tubes 16 to 18.

Control of the correct proportions of the five materials is achieved by monitoring the rate of weight loss from the containers and comparing this with a desired rate of weight loss for each of the containers 1 to 5.

For example, a desired value for rate of weight loss for a particular container would be double that of the rest if that material was needed in a quantity twice as great as the other materials.

If the weight discharge from the container 1 is too great because a particularl dense section of material has dropped into the tube 11 from the container 1, then the signal to the PLC circuit ;sill be larger than expected.

The signal, after being inverted, will result in a smaller signal being passed to the variable speed motor 41. The motor 41 will then slow down to compensate for the excess of weight being discharged into the screw 31 by drawing less material from the tube 11. A similar increase in the speed of the screw may follow if the weight discharge rate becomes too small.

In this way the weight of material which is discharged into the system is continuously measured and errors are corrected. Unwanted variations in the relative weights of materials are thus reduced considerably. Also, continuous mixing of the materials is achieved from the point 50 where the first to of the materials are mixed.

Should one of the motors be at its maximum operating speed and yet it is still desired to increase its rate of weight discharge relative to the other containers then the speeds of some or all of the other motors could be reduced by an appropriate amount.

Claims

1. Material mixing apparatus comprising means for monitoring the weight discharge rate of at least one of a plurality of materials in a mix and means for controlling the relative weight discharge rate of the material being monitored.

2. Apparatus as claimed in Claim 1 including means for altering the weight discharge rate of one material when the weight discharge rate of another material varies.

3. Apparatus as claimed in any preceding claim including a plurality of materials to be mixed having weight discharge monitoring means and means for controlling the relative weight discharge rate.

4. Apparatus as claimed in any preceding claim including means for altering a desired discharge rate for at least one of the materials.

5. Apparatus as claimed in any preceding claim in which the monitoring means includes at least one load cell arranged to monitor a weight change of a container of material.

6. Apparatus as claimed in Claim 5 in which the load cell is arranged to monitor the weight change of a container over consecutive predetermined time periods.

7. Apparatus as claimed in Claim 5 or 6 in which the monitoring means comprises three load cells for the or each container with the load cells associated with each container being connected to form a Wheatstone bridge.

8. Apparatus as claimed in any of Claims 5 to 7 in which the signals from the load cells are aggregated.

9. Apparatus as claimed in any of Claims 5 to 8 in which the signals from the load cells are used to control the rate of discharge of material from the container to which the signals relate.

10. Apparatus as claimed in Claim 8 or Claim 9 when dependent upon Claim 8 in which the aggregated signals are used with a programmable logic control circuit.

11. Apparatus as claimed in any preceding claim in which the apparatus provides for continuous mixing.

12. Apparatus as claimed in any preceding claim in which material is arranged to be carried through the apparatus during mixing.

13. Apparatus as claimed in any preceding claim in which the materials are arranged to fall during their passage through the apparatus.

14. Apparatus as claimed in any preceding claim in which the mixing of the materials and the transport of the materials to the apparatus is effected by combined mixing and transport means.

15. Apparatus as claimed in Claim 14 in which the combined means comprise at least one screw.

16. Apparatus as claimed in Claim 15 in which the screw is powered.

17. Apparatus as claimed in Claim 15 or 16 in which the or each screw provides transported material or materials in a direction transverse to the vertical.

18. Apparatus as claimed in any preceding claim in which material to be mixed is introduced into another material or mixing materials by discharge from an open end of a first screw inserted into a second screw of greater internal diameter.

19. Apparatus as claimed in Claim 18 in which the first or second screws are arranged and operated to transport material in the same direction.

20. Apparatus as claimed in any of Claims 15 to 19 in which the or each screw extends completely through a container of material to be mixed.

21. Apparatus as claimed in any of Claims 15 to 20 in which the control for the relative discharge rate of the material being monitored is arranged to be achieved by varying the rate of rotation of a screw associated with transporting material from that particular container.

22. Apparatus as claimed in any of Claims 15 to 21 including sets of screws on different levels.

23. Apparatus as claimed in Claim 22 in which the different levels are joined by chutes down which material may fall.

24. Apparatus as claimed in any preceding claim in which the material is arranged to be conveyed to and fro across the apparatus.

24. Mixing apparatus substantially as herein described with reference to, and as shown in Figures 1 or 2 of the accompanying drawings.

25. A method of mixing material comprising monitoring the weight discharge rate of at least one material in a mix and altering the relative weight discharge rates of the material if the monitored weight discharge rate alters.

26. A method of mixing materials substantially as herein described with reference to, and as shown in either of the accompanying drawings.

27. A method of mixing materials as claimed in either of Claims 25 or 26 when using apparatus as claimed in any of Claims 1 to 24.