GB2147819A - Improvements to chemical mixing apparatus - Google Patents

Abstract

Chemical mixing apparatus comprises a reservoir 23 for mixing hot and cold water or other solvent, storage containers 22 containing chemical concentrates and a mixing chamber 1 for receiving the solvent and concentrates which is equipped with a motor driven agitator/circulator 5,3. A calibration means or measure 2 within the mixing chamber 1 has level sensing probes 13, 14 and a solenoid operated valve 15, 17 for emptying the calibration measure into the mixing chamber 1. Transfer devices, such as linear oscillating pumps 21, transfer the solvent and concentrates into the calibration measure at a constant flow rate. <IMAGE>

Description

SPECIFICATION improvements to chemical mixing apparatus The present invention relates to apparatus for mixing chemicals, usually in liquid form, in precise ratios and sequences. The invention has particular, but not sole application to photographic processing solutions.

Modern photographic and other chemicals frequently have a limited storage life when compounded and are therefore supplied as separate components to be mixed just prior to use. Furthermore some chemicals contain a large volume of a solvent or carrier, often water, and it is convenient to transport them as concentrates, adding the water when they are to be used.

The process of mixing consists of taking a quantity of the solvent or carrier and adding to it a precise quantity of one of the concentrates and mixing until it has dissolved or dispersed. The sequence is repeated in turn for the remaining concentrates.

There are a number of ways of carrying out this mixing operation but they usually involve a calibrated container, measuring vessels and some form of stirrer. Sometimes a circulating pump is used to turbulate the solution by drawing the liquid out of the bottom of the container and returning it at another point. It is frequently necessary to transfer the mixed chemicals to a storage tank and the circulating pump is sometimes also used for this purpose.

Many solutions oxidise easily and it is very important in certain applications to avoid aeration when mixing.

When mixing apparatus is used for several different substances precautions must be taken to avoid cross-contamination between different parts or concentrates.

Mixing of chemicals is critical to the correct operation of many processes, but is unpleasant and inconvenient. In recent years apparatus to carry this task out automatically has become available and this has the further advantage of economy through being able to use bulk packages of concentrates because of its ability to mix small batches as and when required.

Up to the present time automatic mixing apparatus has consisted of a series of metering pumps, controlled by sequence timers, for pumping small quantities of solvent or carrier and concentrates into a mixing chamber where they are mixed, sometimes with the assistance of a mechanical agitator. The mixed solutions then flow or are pumped into holding tanks or into the chemical processing device.

Mixers of this type suffer from a number of disadvantages which have discouraged their widespread use.

Metering pumps are fairly complicated, and hence costly.

Many metering pumps use non return valves, and if one of these should fail, the pump not only meters incorrectly, but is likely to cross-contaminate the concentrates.

Mixers, which are normally used unattended for long periods oftime, require some form of warning in case of a malfunction of any type. Automatic mixers, of the type in use at present, use detectors to monitor exhaustion of the solvent and concentrate containers, but it is not always practical to detect breakdowns of the equipement. It is difficult to make fairly complicated equipment, operating under hostile conditions, sufficiently reliable not to require process monitoring.

It is an object of this invention to provide improved mixing apparatus.

Apparatus according to the invention does not use conventional metering pumps for dispensing the liquid concentrates or solvent, but uses any device which can provide a constant flow over a short period of time and can be switched on and off quickly. Devices, among others, which meet these criteria include linear oscillating pumps and solenoid valves controlling flow from either a pressurised or constant head gravity reservoir or most types of pump. In this invention the constant flow devices are switched on and calibrated for flow rate, each time they are used and switched off when the required amount of fluid has passed. This eliminates the need for accurate metering pumps, but more importantly provides means for monitoring each stage of the mixing operation.

Apparatus constructed in accordance with the invention comprises means for storing chemical concentrates, in liquid or other form, means for supplying water or solvent at a predetermined temperature, atleast one mixing chamber for receiving measured quantities of said concentrates and said water or solvent for mixing and means for transferring said measured quantities to the mixing chamber under control of calibration means, wherein the transfer means transfers said quantities at a substantially constant rate over a short period of time determined dynamically by the calibration means.

The mixing of quantities is preferably accomplished by means of devices as described hereafter.

The transfer means can be linear oscillating pumps which operate for the transfer time determined by the calibration means. The calibration means can take the form of a funnel, or the like, several level sensing probes and closure means for closing and opening the funnel outlet.

In another aspect the invention provides a method of mixing chemical concentrates and a carrier or solvent, said method comprising storing said concentrates, supplying said carrier or solvent at a pre-determined temperature, transferring measured quantities of said concentrates and said carrier in sequence for mixing by selectively operating transfer means to transfer said quantities, at a substantially constant rate, over periods of time determined dynamically by calibration means operating during the transfer periods.

The invention may be understood more readily, and various other features of the invention may become apparent, from consideration of the following description.

An embodiment of the invention will now be described, by way of example only, with reference to the acompaning drawings which are schematic representations of mixing apparatus constructed in accordance with the invention.

Figure 7a is a side view of the main mixing chamber constructed in accordance with the invention.

Figure ib is a plan view of the main mixing chamber.

Figure 2 is a representation of a complete chemical mixing system.

Figure 3 is a side view of the holding tank of the apparatus.

Figure 4a is a side view of the water reservoir.

Figure 4b is a plan view of the water reservoir.

A chemical mixing apparatus according to the invention can consist of a number of units each arranged to mix a number of concentrates with a solvent or carrier, usually water. Figure 2 shows a mixing system for mixing 2 separate solutions, but systems could be built according to the invention for a different number of solutions.

The components of the system are mounted in a frame 35 and comprise main mixing units 33, a holding tank 34, a water reservoir 23, a control unit 36, a drain tray 37, solution concentrate containers 22 and linear oscillating pumps 21. The control unit 36 is fitted with an alphanumeric display 39 and control switches 40.

Figure 3 shows the holding tank 34 to which the solution is transferred after mixing. It consists of a container 41, level sensing conductivity probe 42, an inlet tube 43, an outlet 45 and a drain overflow 44.

The drain overflow 44 is arranged so that if solution is pumped into the holding tank at high velocity, through inlet 43, it will pass over the top of the drain overflow 44 and into the holding tank 34. If on the other hand solution is pumped in at low velocity, it will flow to waste via the drain overflow 44. This facility is used in order to flush out the main mixing unit 33.

Figure 1 shows the main mixing unit 33 consisting of a main mixing chamber 1 in which is fitted a measure 2, an anti vortex device 7, an outlet tube 8, a stator 4, and an impeller 3 driven by a motor 5 preferably through a coupling such as a magnetic coupling 6. The measure 2 is fitted with an overflow 47 and the mixing chamber 1 with a drain overflow 48.

On top of the measure 2 is a lid 10 which has a number of concave chambers 49 into which are fixed inlet tubes 11. At the centre of the lid 10 is fixed a probe mounting 12 containing level sensing probes 13 surrounded by a splash shield 14. In the bottom of the measure 2 is a valve seal 15 raised and lowered by an actuator rod 16 which in turn is raised and lowered by a solenoid 17 mounted on an sealing plate 18 and spacer blocks 19.

The purpose of the upward facing inlets 11 and the concave chambers 49 is to ensure that the flow stops instantly when the pumps 21 are switched off and to direct the liquid to enter the measure 2 without running down the sides which could cause measure ment errors.

The shape of the measure 2 is such that, taking into account the volume of liquid displaced by the probes 13, acutator rod 16 and splash shield 14, that a given unit change in level will alter the volume of liquid contained in the measure by the same percentage, irrespective of the level of the liquid.

When the solenoid 17 is activated the valve seal 15 is raised and closes off the bottom of the measure 2 so that it will hold any liquid which has been passed into it through the inlet tubes 11. As soon as the solenoid is de-energised the valve seal 15 is lowered a small amount and any liquid in the measure is allowed to flow out, but due to the narrow annular opening flows out in a near horizontal trajectory striking the walls of the mixing chamber 1 at a point 20 only a little below the bottom of the measure 2.

The purpose of this will become apparent in the flush mode described a little later on.

In the embodiment of the invention here described the controlled constant flow devices are linear oscillating pumps 21 which pump the concentrates from containers 22 or in the case of water from a water reservoir 23. The concentrate containers 22 are conventionally made of flexible plastic and, being sealed from the atmosphere collapse as the fluid is pumped out impeding the entry of air which could oxidise the concentrates.

The function of the water reservoir 23 is to provide a volume of water at the correct temperature for mixing. As shown in figure 4 the reservoir 23 consists of a vessel 24 with a small drain 25 which will allow the container to empty in about 30 minutes, a hot water solenoid valve 26, a cold water solenoid valve 27 a temperature sensing probe 28, level sensing conductivity probes 30, an overflow 31 and an outlet 32.

The solenoid valves 26 and 27 feed respectively hot and cold water to inlet injectors 29 arranged to inject the water horizontally near the temperature sensor 28. The shape of the vessel 24 and the position of the injectors is arranged to maximise swirl and avoid vertical layering of temperature within the vessel 24. Means, such as electronic control elements of a control system (not shown), are arranged to open the two solenoid valves 26 and 27 so as to mix the water to obtain a predetermined temperature. The solenoid valves 26 and 27 are shut off when the water has reached the level sensing conductivity probes 30. However, if the temperature is not within specified limits one of the solenoid valves 26 or 27 will be opened to force the temperature back within those limits. Any surplus water overflows to drain. The drain 25 ensures that the system empties when not in use, avoiding the possibility of microbiological growth in the water container 24.

The sequence of operation of the mixing apparatus is as follows: When the level of mixed chemicals in the holding tank 34 has fallen below the level sensing probe 42, the control unit 36 initiates a mixing cycle. This commences by activating the water reservoir 23 as described above so as to provide a volume of water at the correct temperature.

The valve 15 in the measure 2 is closed and one of the pumps 21 activated to pump water from the water reservoir. The control unit senses when the level in the measure 2 reaches the various level sensing probes 13. As soon as the water level has reached the top probe the solenoid 17 is released so that the valve 15 opens and the water runs from the measure 2 into the main mixing chamber 1.

By measuring the time for the level to change from the bottom probe to one ofthe other level sensing probes 13 the control unit 36 is able to calculate the flow rate ofthe pump 21 and allow the pump to run until the requisite amount of water has been pumped into the mixer.

At the completion of the waterfill a similar sequence takes place for the 1 st concentrate.

The motor 5 now starts and rotates the impeller 3 causing vigorous agitation between the impeller 3 and the stator 4. The stator 4 is shaped in the form of a number of petals and in addition to creating vigorous agitation will create a circulating motion of the liquid drawing it down in the centre and forcing it upward at the sides of the mixing vessel 1. In this way "oily" or other immiscible concentrates are dragged down and forced between the stator and impeller. The device 7, mounted above the impeller, prevents a vortex forming and thus avoids drawing air into the solution. It has been found that this arrangement provides very efficient mixing of chemicals without aeration.

After a suitable time, to allow the 1 sot concentrate to dissolve or disperse in the solvent or carrier, the dispensing and mixing procedure is repeated for the remaining concentrates.

During each pumping sequence the calibration time, ie. the time for the liquid level to rise between appropriate level probes 13, is compared with standard values stored in the control unit 36. Variatins from standard, beyond certain limits, indicate that the mixing process is not taking place correctly, or that one of the concentrate containers 22 is empty, and are used to give warning. Details of the fault are shown on the control unit display 39.

After the last concentrate has been added a further quantity of water is pumped into the mixing chamber 1. When the level of solution reaches the mixing chamber level sensing probe 46, the water pump 21 and the motor 5 are stopped and thus the wave created by the impeller 3 is allowed to subside. The level of liquid in the mixing chamber 1 will drop below the level sensing probe 46. The water pump 21 is now restarted and the time for the level to rise to the probe 46 is measured. This time is a measure of the height of the wave created by the impeller 3 and hence a check that the mixer is functioning correctly. The time is compared with a standard stored in the control and if not within limits warning is given.

The standard times referred to above and stored in control unit 36 may either be placed there during manufacture or acquired heuristically from the characteristics of the system when it is known to be operating correctly.

When the correct volume of solution is in the mixing chamber 1 a transfer pump 21 draws the solution out via the outlet 8 and pumps it at high veliocity into the holding tank 34.

When the mixing chamber 1 is empty a flush routine cleanses it. A small volume of water, or other solvent, is pumped into the measure 2 and, after the valve 15 opens, impinges on the walls of the chamber 1 flushing away chemicals. The motor 5 is now run for a few seconds and thereafter the water is pumped away slowly via the outlet 8 and runs to waste via the drain overflow 44.

In another embodiment of the invention no holding tank 34 is provided and the mixed chemicals are drawn off for use via the outlet 8. An additional level sensing probe is then provided in the mixing chamber 1 to start the process.

An important feature of apparatus constructed according to the invention is that the different concentrates are separated by an air break, ie. the measure 2, and thus, even under fault conditions, there is no possibility of contamination.

Claims (15)

1. Apparatus for mixing flowable chemicals comprising containers for storing chemical concentrates, means for supplying solvent, such as water, at a predetermined temperature, at least one mixing chamber for receiving and mixing measured quantities of said concentrates and solvent and means for transferring said measured quantities to the mixing chamber under control of calibration means, where in the transfer means transfers said quantities at a substantially constant rate over a short period of time determined dynamically by the calibration means.

2. Apparatus according to claim 1, where in the means for providing solvent at a predetermined temperature comprises a chamber in which solvent above and below the predetermined temperature can be mixed in the correct proportions to provide the solvent at the pre-determined temperature.

3. Apparatus according to claim 1 or 2, where in the transfer means comprises linear oscillating pumps.

4. Apparatus according to claims 1 or 2, where in the transfer means comprises pumps operated in conjunction with solenoid valves.

5. Apparatus according to claim 2, where in the solvent-containing chamber and the storage containers are pressurised and the transfer means at least includes solenoid valves to permit or inhibit the flow therefrom.

6. Apparatus according to any of the proceeding claims, where in at least the storage containers are disposed above the mixing chamber so that transfer occurs under gravity.

7. Apparatus according to any one of claims 1 to 6, where in the calibrating means is composed of a funnel shaped calibration measure, at least two level sensing probes within the measure and a solenoid operated valve to allow the measure to be emptied.

8. Apparatus according to claim 7, where in the inlets connect the calibration measure to the solvent supply and concentrate containers and the inlets are disposed to direct fluid upwards against individual concave reception chambers to avoid cross contamination.

9. Apparatus according to any of the claims 1 to 8 where in the mixing chamber is provided with a motor driven impellor surrounded by stator blades which co-operate to create vigorous agitation and circulation of fluids in the chamber during mixing.

10. Apparatus according to any one of the claims 1 to 9, where in the mixing chamber is provided with anti vortex baffles to avoid aeration of the solutions during mixing.

11. Apparatus according to any of the claims 1 to 10, where in the mixing chamber is provided with level sensing probes to detect when the chamber is nearly empty and to detect a wave created during mixing.

12. Apparatus according to any of the preceding claims and further comprising at least one holding tank for receiving solutions from the mixing chamber, said holding tank containing a level sensing probe and an inlet pipe and drain leading to the holding tank, the inlet pipe serving to direct its flow into the holding tank or directly to the drain depending on the inlet flow rate.

13. Apparatus according to any of the claims 1 to 12 and further comprising sensing means for sensing the variations from standards of the solvent or concentrate flow rates, as determined by the calibration means, to provide warning indicator of an empty concentrate container or faults.

14. Apparatus according to any one of the claims 1 to 13 where in the concentrate containers are flexible and collapse as evacuation occurs and a change in flow rate caused by the collapse of one of the flexible containers is used to provide an indication of an empty container.

15. Apparatus for chemical mixing substantially as described herein with reference to any one or more of the Figures of the accompanying drawings.