EP0160362B1

EP0160362B1 - Methods of cleaning articles

Info

Publication number: EP0160362B1
Application number: EP85301549A
Authority: EP
Inventors: Henry Michael Pattison
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-03-13
Filing date: 1985-03-06
Publication date: 1988-10-19
Also published as: EP0160362A1; DE3565637D1

Description

This invention relates to methods of cleaning articles, and is concerned particularly with cleaning plants which are adapted to clean articles in a volatile solvent.
Cleaning plants are known in which articles to be cleaned are immersed in successive baths of solvent. Usually, a transport means performs an automatic cycle, to transport such articles between the baths. Usually, the transport means is so arranged that, after each immersion, the respective article is suspended above the bath from which it has emerged, to enable any drips to return into the bath. Flap drip trays are provided between the baths, to catch any drips of excess solvent, which is then usually allowed to evaporate.
It will be appreciated that, in such an arrangement, the cycle time (and therefore the efficiency) of the plant is limited to some extent by the dwell time for which an article must be suspended over a bath, after immersion. Also, evaporation of solvent from the flat drip trays leads to further expense, either in loss of solvent altogether, or costs in running a reclamation plant for the solvent.
Patent Application GB-A-2 052 564 shows equipment which is adapted to perform a method of degreasing and/or cleaning articles in a plant which comprises a plurality of baths which contain a volatile organic solvent and are disposed in an enclosed housing adapted to contain air laden with evaporated solvent, the method comprising the steps of:

introducing the articles into the housing where they are received by a transport means;
transporting the articles to a first one of the baths;
immersing the articles in the solvent contained in the first bath;
lifting the articles out of the solvent in the first bath after immersion;
allowing solvent to drip from the articles lifted from the first bath;
transporting the articles that have been lifted from the first bath to a second one of the baths;
successively repeating the steps of immersing, lifting, dripping and transporting of the articles, with respect to the second and subsequent baths;
removing the articles from the housing after transport from a last one of the baths; and
operating the plant in a continuous manner, whereby articles are transported through the plant by the transport means and cleaned in the baths in a continuous succession.

GB-A-2 052 564 discloses flat trays between the various baths, which trays may be provided with drainage troughs leading to suitable drainage outlets. The document particularly points out the problem of loss of solvent due to evaporation inside the equipment, during the transfer of articles from one bath to the next. However, in order to deal with this problem, GB-A-2 052 564 provides refrigeration coils which are mounted above the treatment baths, in order to condense the evaporated solvent. It will be appreciated that such refrigeration coils are relatively expensive to provide, and the condensed solvent falls anyway upon the flat trays between the treatment baths.
The present invention aims to provide improved methods of cleaning articles.
According to one aspect of the present invention, there is provided a method of cleaning articles in a plant which comprises a plurality of baths which contain a volatile solvent and are disposed in an enclosed housing adapted to contain air laden with evaporated solvent, the method comprising the steps of:

introducing the articles into the housing where they are received by a transport means;
transporting the articles to a first one of the baths;
immersing the articles in the solvent contained in the first bath;
lifting the articles out of the solvent in the first bath after immersion;
allowing solvent to drip from the articles lifted from the first bath;
transporting the articles that have been lifted from the first bath to a second one of the baths;
successively repeating the steps of immersing, lifting, dripping and transporting of the articles, with respect to the second and subsequent baths;
removing the articles from the housing, after transport from a last one of the baths; and
operating the plant in a continuous manner, whereby articles are transported through the plant by the transport means and cleaned in the baths in a continuous succession;

the drips of solvent are caught on a drip tray which is disposed between said previous and subsequent baths and is inclined to the horizontal; and
the drips of solvent caught on the drip tray are directed by the incline into a receptacle for the solvent.

It may be appreciated that, in such a method, the dwell time of an article over a bath, after its immersion therein, may be reduced relative to present practice, as the inclined drip tray serves to catch and redirect into said receptacle any drips of solvent from the article.
Preferably, the receptacle used in the method comprises one of the two baths adjacent the drip tray. The drip tray used in the method may have two inclined portions, each inclined towards a respective one of the two adjacent baths. Alternatively, the drip tray may be inclined towards only one of the two adjacent baths. In this latter case, said one bath is preferably upstream of the drip tray, with respect to the direction of transport of the articles.
The drip tray used in the method is preferably formed with drainage channels. It may advantageously be made of stainless steel.
The drip tray used in the method may be formed along at least one lower edge with a plurality of recesses arranged to receive securing bolts or the like. Said recesses may open downwardly, such that the drip tray may be positioned simply over existing bolts.
The baths of the cleaning plant may be disposed on a curved path, along which the articles to be cleaned are transported. The curved path may be a circular path.
The articles may be introduced into and removed from the housing at an entry and exit station disposed on the said curved path.
The method may include the step of conveying articles towards and/or away from the housing on a conveyor means.
The method may include the steps of exhausting air laden with evaporated solvent from the housing and reclaiming the solvent in liquid form therefrom.
For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing, in which:

Figure 1 is a plan view of a cleaning plant;
Figure 2 is a plan view of a drip tray for use with the cleaning plant;
Figure 3 is a side view of the drip tray;
Figure 4 shows a cross-section of the drip tray on the line IV-IV of Figure 2; and
Figure 5 is a view similar to Figure 4, but showing the cross-section of an alternative drip tray.
Figure 1 is a diagrammatic representation of a cleaning plant which is made by Techno Chemie AG of Zurich, and is known as a "Carousel" cleaning plant.

The cleaning plant 1 comprises four baths B1 to B4 and an entry/exit station 2, which are spaced at regular angular intervals (72°) around a circular path, in the manner of a carousel.
A drip tray D1 is disposed between the two adjacent baths B1 and 82. In plan view, the drip tray D1 is triangular, and it may conveniently be secured to the baths B1 and B2 by means of bolts which pass through flanges in lower edges of the drip tray D1, and engage in tapped holes in the sides of the baths B1 and B2. Similarly, a drip tray D2 is positioned between the two baths B2 and B3, and a further drip tray D3 is positioned between the two baths B3 and B4. Infill panels 3 and 4 are disposed between the entry/exit station 2 and the first and fourth baths B1, B4 respectively. The infill panels 3 and 4 are, in plan, of similar shape to the drip trays but, as will become apparent from the following description, do not themselves have to serve as drip trays, in use. A conveyor belt 10 serves to convey articles to be cleaned, towards and away from the entry/exit station 2.
In the centre of the cleaning plant 1 there is defined a space 5 in which there is disposed a transporter 6. This comprises a central piston 7 from which there radiate five arms 8, at 72° intervals. A basket carrier 9 depends from the outer end of each arm 8.
Briefly, operation of the illustrated cleaning plant 1 is as follows.
Firstly, the baths B1 to B4 are filled with solvent. Typically, they may contain perchloroethylene (e.g. "PERKLONE" - Registered Trade Mark, as sold by I.C.I. Chemicals Limited). In the first bath B1, the perchloroethylene solvent may be heated to 15°C-32°C (60°F-90°F), for example. In the second and third baths B2 and B3, the solvent may be cold. In the fourth bath B4, the temperature of the solvent may be elevated e.g. at 49°C (120°F), and there may in fact be relatively little solvent in this bath.
A basket of machined parts ready to be cleaned is loaded onto the conveyor 10, upstream of the entry/exit station 2. The piston 7 is lowered, such that the respective basket carrier 9'is disposed at a predetermined height above the conveyor belt 10. The conveyor belt 10 is then operated, to bring the basket of machined parts into the entry/exit station, where it engages with the respective basket carrier 9. The conveyor 10 is then stopped.
The piston 7 is then raised, and the various basket carries 9 maintained at a semi-elevated position for a predetermined dwell time. After this, the piston 7 is raised to a maximum elevated position and then rotated clockwise (as illustrated in Figure 1 by the arrow), so that each arm 8 and its respective basket carrier 9 becomes positioned over the successive station. In the case of the basket carrier 9 that was initially in the entry/exit station 2, this is now moved to a position above the first bath B1.
The piston 7 is then lowered to its lowermost position, immersing the respective basket of machined parts into the first bath B1. It remains there for a predetermined time, during which the piston 7 may move up and down to agitate the basket of parts within the hot solvent. At the end of the predetermined time, the piston 7 then raises again to its semi-elevated position, and remains stationary for the aforementioned dwell time. During this time, any solvent may drip off the basket of parts which is suspended over the bath B1, and back into the bath.
The piston 7 is then raised to its maximum height and rotate through 72°, so that the basket of parts which was previously immersed in bath B1 is now positioned over bath B2. The sequence of movements of the piston 7 is then repeated, such that the basket of parts is immersed and agitated in the second bath B2, to effect a primary rinsing operation. It will readily be appreciated that, in a similar way, the basket of parts successively undergoes a second rinsing operation in the third bath B3, and a final drying operation in the fourth bath B4. After this, the basket of parts is returned to the entry/exit station. After the piston has been lowered to place the basket of parts onto the conveyor 10, the conveyor is then caused to move, to take the basket of cleaned parts away from the cleaning plant.
Thus, the cleaning plant 1 operates continuously such that, at any one time, there is a basket of parts immersed in each one ofthefour baths B1 to B4 (or just entering or leaving the respective bath), and a further basket of parts either entering or exiting from the station 2.
In a conventional apparatus, each of the drip trays D1 to D3 is flat. The predetermined dwell time, for which a respective basket is suspended over each of the baths B1 to B3 in particular, is so chosen that dripping of solvent from the basket is substantially finished, before the piston 7 is rotated. Any occasional drips of excess solvent which fall on the drip trays D1 to D3 evaporate. Thus, the rate at which the plant 1 may operate is limited to some degree by the fairly significant dwell time that is required, to ensure that dripping of solvent is substantially finished before rotation of the piston 7.
Itwill be appreciated that the solvent that is used in the cleaning plant 1 is hazardous to operators, and that the plant 1 is therefore necessarily enclosed within its own housing. A certain amount of the solvent will be continuously evaporating, and this is withdrawn from the main enclosure by means of an extraction fan, and reclaimed for subsequent use, through a reclamation plant, including stills, pumps, etc. Although such reclamation minimizes direct loss of the solvent, it will be appreciated that it involves a certain amount of running costs.
To improve upon the conventional arrangement of the cleaning plant 1, each of the drip trays D1 to _' D3 is of the form of the drip tray 20 which is shown in Figures 2 to 4. The drip tray 20 is of triangular form in plan view, as is illustrated in Figure 1. However, as will be seen with particular reference to Figures 3 and 4, the drip tray 20 comprises two oppositely inclined portions 21, which meet at an apex ridge 22. A plurality of drainage channels 23 are formed in each of the inclined portions 21. Along the lower edge 24 of each portion 21 there is formed a series of part circular recesses 25, each of which is open downwardly.
Thus, an existing conventional cleaning plant 1 which has a general form as illustrated in Figure 1 may be converted for use in accordance with the invention, simply by adopting a respective drip tray 20 for each of the drip trays D1 to D3. In a particularly convenient arrangement, existing securing bolts for conventional flat drip trays may be slackened, and the new drip trays 20 fitted directly over the conventional flat drip trays, such that each recess 25 fits over a respective one of the securing bolts. Upon retightening the securing bolts, each drip tray 20 is secured in place.
Thus, in use, each of the drip trays 20 is adapted to catch any drips of solvent which may fall from the basket of machined parts, as it is transported between two adjacent baths. Thus, the drip tray D1, when constructed as shown in Figures 2 to 4, is arranged to catch drips of solvent and direct them either into the first bath B1 or the second bath B2.
This arrangement means that the dwell time of the basket over the respective baths may be significantly reduced. If the solvent continues to drip from one of the baskets as it is transported from one of the baths to the next, then the solvent is simply caught by the drip tray beneath it, and directed back into an adjacent bath. In consequence, the cycle time of the cleaning plant 1 may be significantly reduced, leading to greater efficiency and therefore reduced operating costs. This is particularly important in view of the fact that the cleaning plant 1 is typically arranged to be run continuously. If it is ableto clean a significantly increased number of articles during the working day, then this may effectively reduce capital investment in such cleaning plants.
Another advantage is that, because the drip trays 20 are adapted to return solvent directly to adjacent baths, there is less likelihood of solvent evaporating. This means that the solvent returned from the drip trays may be used immediately, rather than having to be reclaimed in the reclamation plant, at some appreciable cost.
It will be appreciated that, when a basket is travelling from one bath to the next, it may be desired to minimize the amount of returned solvent being directed into the succeeding bath. This may particularly be the case in respect of the first bath B1, which is naturally the dirtiest bath. It may be undesirable to have a significant amount of relatively dirty solvent from the first bath B1 dripping into the succeeding rinsing bath B2.
Therefore, an alternative drip tray 30 may be used, as shown in Figure 5. This is generally similarto the drip tray 20 of Figures 2 to 4, but itwill be seen that it has only one inclined portion 31, and a vertical side wall 32. The lower edges 34 of the inclined portion 31 and the vertical wall 32 may be provided with recesses 25 as shown in Figures 2 to 4, and the inclined portion 31 may be provided with drainage channels such as 23, generally as illustrated in Figures 2 to 4. However, when the drip tray 30 is positioned between the first and second bath B1, B2, it will return any drips of solvent falling from a passing basket only into the first bath B1, rather than into the rinsing bath B2.
It will be appreciated that, the higher the apex ridge 22 of the drip trays 20 or 30, and the steeper the incline of the inclined portions 21,31, thefaster solvent will return to the adjacent baths. Thus, the piston 7 should raise to as great a height as possible, so that the drip trays 20, 30 may be as tall as possible. If necessary, this may be achieved by raising the roof of the enclosure within which the cleaning plant 1 is housed.
As an alternative to the illustrated arrangement, the drip trays 20, 30 may be arranged to direct collected solvent to an additional receptacle, rather than directly back into the respective baths.
As another alternative, the drip trays 20, 30 may be free standing on existing drip trays and/or the sides of the adjacent baths.
Although the apex ridge 22 is shown in Figure 3 as itself inclined, the inclined portions 21,31 of the driptrays 20, 30 may be so contoured that the apex ridge 22 is of substantially constant height - i.e. substantially horizontal.

Claims

1. A method of cleaning articles in a plant (1) which comprises a plurality of baths (B1 to B4) which contain a volatile solvent and are disposed in an enclosed housing adapted to contain air laden with evaporated solvent, the method comprising the steps of:

introducing the articles into the housing where they are received by a transport means (6);

transporting the articles to a first one (B1) of the baths;

immersing the articles in the solvent contained in the first bath (B1);

lifting the articles out of the solvent in the first bath (B1) after immersion;

allowing solvent to drip from the articles lifted from the first bath (B1);

transporting the articles that have been lifted from the first bath (B1) to a second one (B2) of the baths;

successively repeating the steps of immersing, lifting, dripping and transporting of the articles, with respect to the second and subsequent baths (B2 to B3);

removing the articles from the housing after transport from a last one (B4) of the baths; and

operating the plant (1) in a continuous manner, whereby articles are transported through the plant (1 )_'by the transport means (6) and cleaned in the baths (B1 to B4) in a continuous succession; characterised in that, following immersion of the articles in at least one of the baths (B1) and lifting of the articles out of that bath (B1), transport of the articles to the subsequent bath (B2) is commenced before dripping of the solvent from the articles into the previous bath has substantially finished;

the drips of solvent are caught on a drip tray (20, 30) which is disposed between said previous and subsequent baths (B1, B2) and is inclined to the horizontal; and

the drips of solvent caught on the drip tray (20, 30) are directed by the incline into a receptacle for the solvent.

2. A method according to Claim 1, wherein the drips of solvent caught on the drip tray (20, 30) are directed by the incline into one of the two baths (B1, B2) adjacent the drip tray (20, 30).

3. A method according to Claim 2, wherein the drips of solvent are caught on a drip tray (20) which has two inclined portions (21), each inclined towards a respective one of the two adjacent baths (B1, B2).

4. A method according to Claim 2, wherein the drips of solvent are caught on a drip tray (30) which is inclined towards one only of the two adjacent baths (B1, B2).

5. A method according to Claim 4, wherein said one bath (B1) is.upstream of the drip tray (30), with respect to the direction of transport of the articles.

6. A method according to any preceding claim, wherein the drips of solvent are caught on a drip tray (20, 30) which is formed with drainage channels (23) for the solvent.

7. A method according to any preceding claim, wherein the drips of solvent are caught on a drip tray (20, 30) which is formed along at least one lower edge (24) with a plurality of recesses (25) arranged to receive securing bolts.

8. A method according to Claim 7, wherein said recesses (25) are open downwardly.

9. A method according to any preceding claim, wherein said baths (B1 to B4) are disposed on a curved path, along which the articles to be cleaned are transported.

10. A method according to Claim 9, wherein said curved path is a circular path.

11. A method according to Claim 9 or 10, wherein the articles are introduced into and removed from the housing at an entry and exit station disposed on said curved path.

12. A method according to any preceding claim, including the step of conveying the articles towards and/or away from the housing on a conveyor means.

13. A method according to any preceding claim, including the steps of exhausting air laden with evaporated solvent from the housing and reclaiming the solvent in liquid form therefrom.