WO1995024979A1

WO1995024979A1 - Ultrasonic cleaning apparatus

Info

Publication number: WO1995024979A1
Application number: PCT/GB1995/000545
Authority: WO
Inventors: Philip John Slapp; Timothy Douglas Quartly-Watson; Jeffrey Jones; Christopher Galer; Terrence Bowen
Original assignee: Production Line Cleaning Limited
Priority date: 1994-03-12
Filing date: 1995-03-13
Publication date: 1995-09-21
Also published as: AU1858995A

Abstract

Ultrasonic cleaning apparatus for cleaning soiled objects comprising: (i) a tank for holding cleaning liquid; (ii) means for emitting sound waves of ultrasonic frequency into the liquid in the tank; (iii) a conveyor system for transporting soiled objects through the cleaning liquid in the tank; (iv) a filtration system adapted such that a proportion of the cleaning liquid in the tank is extracted and filtered prior to recirculating it back into the tank, in order to prevent a build-up of suspended and surface solids in the tank itself; Characterised in that the recirculating liquid is returned to the tank by means of an injector bar positioned in use at the end of the tank at which the objects exit the tank and located just beneath the surface of the liquid in the tank such that the objects being cleaned emerge from the liquid in the tank through a region of filtered, substantially debris-free cleaning fluid, thus preventing the cleaned items from being re-contaminated.

Description

ULTRASONIC CLEANING APPARATUS

Field of the Invention

The present invention relates to ultrasonic cleaning apparatus for cleaning a wide variety of soiled objects. It is particularly applicable, but not limited to, cleaning utensils, crates, containers and conveyors used in the food industry.

Background to the Invention

Ultrasonic cleaning apparatus is commonly used on a production line and it is already known to clean utensils and containers of the type mentioned above in a tank of detergent solution which is subjected to ultrasonic vibration. Such systems have already been described in GB 1 588 312 B, EP

0 125 054 Bl and PCT/JP92/00515. GB 1 588 312 B describes an arrangement which is typically used on a production line in the food processing industry. It describes an apparatus in which containers or utensils are progressed successively into and through an ultrasonically-vibrated detergent bath, the emerging containers being sprayed with detergent solution, drawn from the detergent bath, to remove residual dirt, which has been loosened by the ultrasonic vibration. The liquid detergent which falls off the containers is returned to the detergent bath and the containers themselves move forward to a rinsing stage where they are sprayed with relatively clean rinse water from another source. This is then typically followed by immersion of the articles to be cleaned into a separate disinfectant bath if sterilization is required.

It will be appreciated that the cleaning operation just described is a multi- stage process requiring not only an ultrasonic cleamng tank but separate filtration, rinse and disinfection stages. This can present very real difficulties when such a system has to be installed into an existing production line where space is often at a premium.

It is known to draw off a stream of detergent liquid from the main cleaning tank to control the level of solid particles in the detergent bath. A variety of filtration systems have been used including screen filters, centrifugal or cyclone separators, and continuous moving belt filters. These systems have become more and more complex and space consuming in an attempt to achieve satisfactory cleaning results over a long period of continuous operation.

The object of the present invention is to provide ultrasonic cleaning apparatus that overcomes or ameliorates these disadvantages and provides in a single tank assembly all the features necessary to clean and sterilize soiled objects.

Summary of the Invention

According to the present invention, in its broadest sense, there is provided ultrasomc cleaning apparatus for cleamng soiled objects comprising:

(i) a tank for holding cleaning liquid;

(ii) means for emitting sound-waves of ultrasonic frequency into the liquid in the tank;

(iii) a conveyor system for transporting soiled objects through the cleaning liquid in the tank;

(iv) a filtration system adapted such that a proportion of the cleaning liquid in the tank is extracted and filtered prior to recirculating it back into the tank, in order to prevent a build up of suspended and surface solids in the tank itself; characterised in that the recirculating liquid is returned to the tank by means of an injector bar positioned in use at the end of the tank at which the objects exit the tank such that objects being cleaned emerge from the liquid in the tank through a region of filtered, substantially debris-free cleaning liquid, thus preventing the cleaned items from being recontaminated.

Preferably the filtration system is incorporated into a weir mechanism.

Preferably the level of cleaning liquid in the tank is controlled by the weir mechanism which is adjustable between two or more positions such that the depth to which the soiled objects and/or the conveyor system are immersed in the tank can be varied by an operation at will.

Preferably the injector bar and the weir mechanism are located at opposite ends of the tank.

Preferably the width of the weir mechanism is substantially less than the width of the tank causing the cleaning liquid and any suspended or surface solids therein or thereon to accelerate towards the weir mechanism and thus the filtration system, this phenomenon being reinforced by the re-injection of filtered cleaning liquid through the injector bar at the opposite end of the tank.

Preferably the position of the injector bar is adjustable such that whatever the level of the cleaning liquid in the tank the injector bar can be positioned just beneath the surface of the liquid.

Preferably the tank is adapted to be movably mounted adjacent a conveyor system such that the conveyor passes through the cleaning solution in the tank and being further adapted such that the position of the tank can be adjusted whilst the conveyor is in motion.

Brief Description of the Drawings

A preferred embodiment of the present invention will now be more particularly described by way of example, with reference to the accompanying drawings, wherein:

Figure 1 is a diagrammatic elevation of a cleaning tank showing baskets suspended from a conveyor system passing through the tank;

Figure 2 is a cross section of the tank shown in Figure 1;

Figure 3 is a plan view of the tank shown in Figure 1 showing the heater tube and ultrasonic panel configuration;

Figure 4 is a diagrammatic side elevation of a tank adapted to wash shackles;

Figure 5 is a plan view of the tank shown in Figure 4;

Figure 6 is a diagrammatic side elevation of a tank in which the cleaning liquid level is adjustable between two positions, a high level (HL) and a low level (LL);

Figure 7 is a plan view of the tank shown in Figure 6;

Figure 8 shows the arrangement of objects to be cleaned as they pass through the tank shown in Figure 6;

Figure 9 shows a cross-section through a conveyor belt passing through an oven with an ultrasonic cleaning tank according to the present invention mounted beneath the oven. For clarity, the injector bar, weir, filtration system and pumps have been omitted;

Figure 10 shows the same arrangement as shown in Figure 9 with the ultrasonic tank moved into an acceptable position for maintenance purposes.

Description of the Preferred Embodiment

Various cleaning tank configurations have been investigated in order to develop ultrasonic cleaning apparatus that will clean and sterilise objects in a single operation. We have found that the combination of features described below overcome the problems inherent in the prior art as previously described.

With reference to figures 1-3 these illustrate a tank 10 of a split-frame construction wherein the tank is separate from the support frame 11. The frame is mounted on adjustable feet such that any irregularities in the surface beneath the tank can be accommodated. Inside the tank 10 is a tube heater 12 or the like and mounted on the side of the tank are ultrasound generators 13. A conveyor system 14 carries objects to be cleaned 15, in this case baskets, wholly beneath the surface of the cleaning liquid 16 in the tank 10.

A weir filtration system 17 is located at one end of the tank and in this example the weir is located at the same end of the tank as the conveyor system 14 enters the cleaning liquid.

A variety of ultrasound generators and transducers are available commercially and the most appropriate choice is made depending on the size of the tank, the number of ultrasound generators required and the nature of the objects to be cleaned. The optimum properties and the number of the generators can be determined by the intended skilled addressee of this specification and need not be further described here.

The geometric arrangement of the ultrasound generators 13 is important. These are preferably located on the sides of the tank 10 rather than on the bottom. Furthermore, these generators should preferably be offset from one another as shown in figure 3 such that as the objects to be cleaned traverse the tank they are always in close proximity to a source of ultrasound and the ultrasound fields from adjacent generators do not interact to any great extent but merely overlap to produce a continuous effect as experienced by the moving objects 15.

The heater tube 12 arrangement, shown in more detail in figure 6, can be run on a wide variety of fuels. The arrangement for a gas heater is shown in figure 6 and in this case a flue 18 is required. A flue 18 will, in fact, be necessary whenever heat is generated by a combustion process. Heat can just as well be provided by electricity, steam or the like and again this does not need further description here.

The solution in the cleaning liquid tank is preferably heated and maintained at a temperature ranging from 40°-60°C. In certain circumstances it may be advantageous to operate outside this range.

The cleamng tank liquid preferably contains a non-foaming detergent and disinfectant of a type and at a concentration depending upon the nature of the dirt to be removed and upon the degree of cleaning and sterilization required. For health and safety at work reasons, liquid detergents are preferred but powder detergents may also be used. For plastic objects 15 e.g.. plastic crates, a blend of alkali containing non-ionic detergent is preferred to effect dirt removal e.g. grease, fat, blood and other proteinatious soiling, as it effects cleaning by improved soil suspension and emulsification and suppresses foam formation. Silicate may be blended with the alkalis to act as a corrosion inhibitor in known fashion, which enables the detergent to be used on reactive metals. The detergent should be unperfumed so as to leave no taint or smell. Such detergent and disinfectant products are known as such and commercially available.

Operating the apparatus of the present invention, dirt is removed from the objects to be cleaned and comes to be present, held in suspension, in the hot cleaning liquid solution. This is clearly undesirable, particularly as such dirt tends not to settle out on the bottom of the tank but tends, due to the ultrasonic energy, to be broken down into a fine paniculate size.

Accordingly, it is known to be highly preferred to withdraw soiled detergent solution continuously from the tank, subject it to filtration, and return the filtered detergent solution to the tank.

In addition to the fine dirt which is removed from the objects in the tank, certain objects are often contaminated with larger debris e.g.. pieces of paper, plastic, leaves and the like that tend to float to the surface of the detergent solution in the tank. In order to remove gross contamination it is preferred to have a weir at the exit end of the tank over which liquid in the tank flows into a chamber containing mesh filters.

Figures 1-5 serve to illustrate the general arrangement of heaters and ultrasound generators within the cleaning tank. However using ultrasomc cleaning equipment has, in the past, required separate rinse and disinfecting operations to achieve the required degree of cleanliness.The arrangement shown in figure 6 overcomes this requirement and results in the objects emerging from the tank in a clean and sterilized state.

Specifically, liquid from the tank is directed towards the weir filtration system

18 in a number of ways. Firstly, the width of the weir 20 is substantially less than the width of the tank and the sides of the tank narrow as they approach the weir 20 in a funnel arrangement. This causes the cleaning liquid and any suspended or surface solids therein or thereon to accelerate over the weir itself.

Secondly, filtered cleaning liquid is reintroduced into the tank through an injector bar 21 which extends substantially across the tank at the opposite end of the tank to the weir but specifically directed towards it. This arrangement in itself sets up a circulation system within the tank.

Thirdly, it is generally necessary, in any event, to positively circulate the cleaning liquid in the tank over the heater 12 to minimise temperature gradients. This can be done by a variety of conventional means such as pumps, tubulators or the like (not shown) and these are designed to reinforce the two previous phenomena described above. Thus, very positive steps are taken to direct debris-laden cleaning liquid over the weir 20 and into the filtration system 17.

In this context an injector bar is any device by which liquid can be introduced or reintroduced into the tank 10. It might, for example, take the form of a series of independent nozzles or other inlets that are not associated with a "bar" as such. The injector bar 21 is arranged such that filtered liquid is pumped back into the tank just beneath the surface of the cleaning liquid. This provides two important advantage. Firstly, the detergent solution normally used in these tanks has a tendency to foam. This is highly detrimental to cleaning performance because not only is ultrasound absorbed by gas bubbles, but in being so absorbed it creates a great deal of noise. By reintroducing the filtered liquid below the surface of the cleaning liquid in the tank, this tendency is very much reduced.

Secondly, by positioning the injector bar 21 in the region of the tank where objects exit the cleamng liquid, these objects effectively pass through a region of clean, filtered liquid i.e. get rinsed as they leave the tank.

The result of this arrangement is that in tests carried out in a poultry factory where chicken are processed on shackles 22 as shown in figure 4, swabs taken of the shackles after cleaning in this manner showed no bacterial contamination (i.e. the tests used registered zero bacterial count).

The weir filtration system 17 will now be described in more detail with reference to figures 6 and 7. Cleaning liquid passing over the weir 20 passes directly onto a filter bed 23. On passing through this filter bed the liquid is recirculated by pump No 1 25 around or through the tank to the injector bar 21. If this first filter bed 23 becomes blocked, then the liquid automatically cascades over the sides of the filter 23 onto second and lower filter beds 24. Obviously, secondary and successively finer filters can be introduced as necessary.

The inlet pipe to pump No 1 25 is generally beneath a plate (not shown) to prevent foam or air bubbles entering the main tank.

It will be appreciated that additional filtration and water treatment systems can be incorporated into this recirculation system as necessary.

In an important modification to this system a dual level tank will be described. It is quite often the case that only the objects to be cleaned 15 will require cleaning on each circuit of the conveyor 14 but periodically the conveyor itself will need to be cleaned. Thus, the tank is usually run at a low level (LL in figure 6) wherein only the objects 15 pass through the cleaning liquid. However, by adjusting the height of the weir in relation to the tank, it is possible to fill the tank to a high level (HL in figure 6). This level adjustment is preferably achieved by making the weir in the form of a gate which can be opened or closed. In this context, a gate can be any aperture or barrier to the flow of cleaning fluid. By closing the gate the liquid level builds up until it reaches a higher gate or the top of the weir mechanism which it then flows over.

Conveniently, the position of the gate or gates is controlled by a lever mechanism operating on an over-centre action principle (not shown), the lever(s) being positioned at the edge of the tank and in easy reach of the operator.

Changing the filters in this arrangement is particularly simple. The filters conveniently take the form of screens or trays which sit in frames. When it becomes necessary to change or clean a filter it is simply lifted out and a fresh filter dropped in its place.

Alternatively the weir gate can be closed temporarily to prevent the flow of cleaning liquid over the filters whilst the filters are swopped over or cleaned.

An ultrasonic cleaning apparatus of the type described above can also be used to clean and sterilise a conveyor belt system or similar continuous moving production line assembly. It is an objective in many industries these days to automate processes and to do in a continuous process what was once conventionally done batch-wise. Typical examples of this are the food industry, where baking of bread and biscuits is now done continuously, and the electronics industry where components are manufactured on a production line. These are just two examples of many such fields but they serve as good illustrations of the types of conveyor systems used and which are of necessity complex and made up of many interlinking parts, which parts have an intricate shape or shapes. Keeping such conveyor system scrupulously clean is difficult in itself but when they also have to be germ-free, as in the food industry, this typically requires a multi-stage cleamng process if conventional technologies are used. This can present real problems for manufacturers not only in terms of capital cost, but also in terms of space and day-to-day running costs.

The single stage cleaning and sterilisation process described in UK application number 94 04834.5 can be applied effectively to overcoming these problems and one method of achieving this is shown in Figures 9 and 10.

Referring to Figure 9, a conveyor belt 30 is shown travelling through an oven

31 in the direction of arrow 32. After leaving the oven and depositing whatever is on the belt (not shown) the belt itself passing through an ultrasonic tank 33 mounted under the oven. In this example ultrasound energy is provided by a tubular or submersible ultrasonic transducer 34. The optimum shape and arrangement of transducers can be determined by the skilled addressee of this specification.

The tank 33 is mounted on a frame 35 such that the tank itself can be rolled or otherwise manoeuvred into a configuration in which it is wholly or partially accessible for maintenance or servicing. This configuration is shown in Figure 10. However, the tank does not have to be able to be rolled in and out; it can be fixed in position.

It is a further inventive feature of this application is that the arrangement of pulleys and rollers over which the conveyor belt 30 passes is such that the belt 30 remains taut at all times and thus the whole production line can remain in continuous operation no matter what position the ultrasonic bath is in. This is achieved by careful positioning of the rollers or pulleys, especially pulley 36, such that the distanced travelled by the conveyor 30 is constant as it passes along a pre-determined route in or associated with the cleaning tank no matter what position the tank itself is in.

Although omitted from Figures 9 and 10 for clarity, the ultrasonic tank would preferably be fitted with a weir and injector bar as previously described. A sanitising rinse can be incorporated when, for example, a caustic chemical is used in the tank.

It will be appreciated that this invention is particularly appropriate to situations where the production process involved does not include a process which would otherwise kill bacteria and other germs (ie cooking).

The belt 30 can be made of a wide variety of materials such as metal, plastics or other composites.

The belt itself can be fabricated into the form of utensils eg cooking pots. If the process requires, additional operations such as rinsing or drying can be carried out.

This technology is particularly useful for cleaning the belts on freezing towers such as those commonly used in the frozen foods industry and which are notoriously difficult to clean. In this instance, an additional step of cooling the belt as it leaves the ultrasonic cleaning apparatus could advantageously be included.

The reader is directed to the disclosure of patent specifications GB 1 588 213, EP 0 125 054, EP 0 291 202 and PCT/ JP92/00515 for any further details he may need to put the invention into practice.

Claims

1. Ultrasomc cleaning apparatus for cleaning soiled objects comprising:

(i) a tank for holding cleaning liquid;

(ii) means for emitting sound waves of ultrasonic frequency into the liquid in the tank;

(ϋi) a conveyor system for transporting soiled objects through the cleaning liquid in the tank;

(iv) a filtration system adapted such that a propoπion of the cleaning liquid in the tank is extracted and filtered prior to recirculating it back into the tank, in order to prevent a build¬ up of suspended and surface solids in the tank itself;

characterised in that the recirculating liquid is returned to the tank by means of an injector bar positioned in use at the end of the tank at which the objects exit the tank and located just beneath the surface of the liquid in the tank such that the objects being cleaned emerge from the liquid in the tank through a region of filtered, substantially debris- free cleaning fluid, thus preventing the cleaned items from be re- contaminated.

2. Ultrasonic cleaning apparatus as claimed in claim 1 wherein the filtration system is incorporated into a weir mechanism.

3. Ultrasonic cleaning apparatus as claimed in claim 2 wherein the level of cleaning liquid in the tank is controlled by the weir mechanism which is adjustable between two or more positions such that the depth to which the soiled objects and/or the conveyor system are immersed in the cleaning liquid can be varied by an operator at will.

4. Ultrasonic cleaning apparatus as claimed in any of the preceding claims in which the injector bar and the weir mechanism are located at opposite ends of the tank.

5. Ultrasonic cleaning apparatus as claimed in any preceding claim wherein the width of the weir mechanism is substantially less than the width of the tank causing the cleaning liquid and any suspended or surface solids therein or thereon to accelerate towards the weir mechanism and thus the filtration system, this phenomenon being reinforced by the re-injection of filtered cleaning liquid through the injector bar at the opposite end of the tank.

6. Ultrasonic cleaning apparatus as claimed in any of claims 1-5 wherein the position of the injector bar is adjustable such that whatever the level of the cleaning liquid in the tank the injector bar can be positioned just beneath the surface of the liquid.

7. Ultrasonic cleaning apparatus as claimed in any preceding Claim wherein the tank is adapted to be movably mounted adjacent a conveyor system such that the conveyor passes through the cleaning solution in the tank and being further adapted such that the position of the tank can be adjusted whilst the conveyor is in motion.

8. Ultrasonic cleaning apparatus substantially as herein described with reference to and as illustrated by any combination of the accompanying drawings.