WO1992008554A1

WO1992008554A1 - An apparatus for cleaning workshop products

Info

Publication number: WO1992008554A1
Application number: PCT/SE1991/000759
Authority: WO
Inventors: Stig Larsson
Original assignee: Holmstrands Machinery Ab
Priority date: 1990-11-12
Filing date: 1991-11-11
Publication date: 1992-05-29
Also published as: SE467484B; SE9003585D0; SE9003585L

Abstract

An apparatus for cleaning printed circuit cards by means of alcohol is described. According to the invention the apparatus has a washing chamber (3) enclosed in a housing and a sluice disposed vertically above said washing chamber and being formed by a drying chamber (2) having an opening (7) closable by means of an outer hatch (8) to enable a basket (6) filled with printed circuit cards to be moved in and out of the drying chamber (2), and an opening (9) closable by means of an inner hatch (10) to enable a basket (6) to be moved down into and up out of the washing chamber containing a tank (14) with alcohol. Furthermore, the apparatus has a vertically displaceable support means (17) carrying a basket (6) in order to transport it between the drying chamber and the washing chamber for immersion of the basket into the alcohol, a pneumatic cylinder (24) being disposed externally on the housing and connected to the support means via a connection element (18) in order to effect the vertical displacement of the support means. An exhaust air channel system (33) is connected to the washing chamber and drying chamber to create a vacuum in the housing (1) for evacuation of the explosive alcohol from the chambers (2, 3). The hatches are controlled by a control means so that only one of the hatches can be opened at a time.

Description

An apparatus for cleaning workshop products

The present invention relates to an apparatus for cleaning workshop products such as printed circuit cards, using highly inflammable alcoholic cleaning liquid, said printed circuit cards being placed in a basket of predetermined size.

Many of the solvents hitherto used for cleaning printed circuit cards are damaging to the environment, among other things, and their use must therefore be limited or stopped in order to fulfil government regulations in this respect.

Considerable efforts are therefore being made in industry to find other cleaning agents which are not as damaging to the environment as those previously used, such as solvents of halogenated hydrocarbon, such as trichlorethylene and freons. Such alternative cleaning agents are alcohol-based and include, for instance, ethanol, methanol and isopropyl alcohol.

However, handling alcoholic solvents entails considerable problems due to the great risk of explosion and fire and special regulations therefore apply to such handling. An apparatus for washing printed circuit cards with alcoholic cleaning liquid must therefore be designed to fulfil these regulations with respect to the risk of fire and explosion as a result of the electrical equipment included and surfaces of solid material which come into contact with each other. Thus, no metal surfaces or other electrically conducting surfaces that are brought into contact with each other are permitted within the apparatus since metal surfaces or said other surfaces can produce sparks. The apparatus must be classified in accordance with a special classification plan stating which zone values shall apply for various sections of the apparatus. A zone value of 0 denotes that risk area of the apparatus which entails particular risks of fire or explosion. The requirements for electrical equipment are stricter in zone 0 than in zones 1 and 2, and special regulations must be followed.

The object of the invention is therefore to provide an apparatus for washing printed circuit cards with alcoholic cleaning liquid, the apparatus being designed and equipped in such a manner as to fulfil all safety requirements applicable during the handling of the highly inflammable alcoholic cleaning liquid.

The apparatus according to the invention is characterized by a housing which is closed during operation; at least one treatment chamber enclosed therein and comprising at least one washing chamber; a sluice disposed vertically above said washing chamber and comprising a chamber having an opening closable by means of a first, outer hatch to enable a basket filled with printed circuit cards to be moved in and out of the chamber, and an opening closable by means of a second, inner hatch to enable a basket to be moved down into and up out of the washing chamber, said chamber containing a tank of cleaning alcoholic liquid; a vertically displaceable support means arranged to carry a basket and transport it between the sluice chamber and the washing chamber for immersion of the basket into the alcoholic cleaning liquid, a pneumatic cylinder disposed externally on the housing and connected to said support means via a substantially horizontal connection element in order to effect said vertical displacement of the support means carrying the basket, said housing being provided with a vertical gap through which said connection element extends; an exhaust air channel system which is connected to the washing chamber and the sluice chamber, and arranged to create a vacuum in the housing for continuous evacuation of explosive alcoholic gas from the chambers; and control means arranged to control the hatches of said sluice so that only one of them can be opened at a time.

The invention will be described further in the following, with reference to the accompanying drawings.

Figure 1 is a side view of an apparatus according to the invention.

Figure 2 is an end view of an apparatus according to Figure 1.

Figure 3 shows a portion of a vertical side wall of the apparatus, having a gap closed by brush strips.

Figures 1 and 2 shows schematically an apparatus for cleaning printed circuit cards or other goods manufactured in the workshop industry, by means of cleaning liquid which contains alcohol. The apparatus comprises a housing or casing 1 which is closed during operation, and two treatment spaces consisting of a drying chamber 2 and a washing chamber 3. The apparatus is connected to earth. The drying chamber 2 is located vertically above the washing chamber 3. The apparatus also includes a machine room 4 which, in the embodiment shown, is also enclosed in the housing 1. A horizontal table 5 is disposed above the upper side of the machine room 4, on which open baskets 6 open on all sides and made of wire or the like are intended to be placed for feeding into the apparatus. The vertical wall of the drying chamber 2 which faces the table 5 is provided with an opening 7, which is larger than the opposite side surface of a basket 6, and closable by means of a first hatch 8. The horizontal partition 30 between the drying chamber 2 and the washing chamber 3 is provided with an opening 9 which is somewhat larger than the bottom surface of the basket 6, for instance, and is closable by means of a second, inner hatch 10. A plurality of nozzles 11 are disposed in the drying chamber 2 for the supply, via a conduit 13, of hot air from a hot-air equipment 12 located externally on the housing 1. The washing chamber 3 contains a tank 14 for alcoholic cleaning liquid, which is replenished from a storage tank 15 in the adjacent machine room 4. The tank 14 contains a heating device 31 which heats the cleaning liquid to the desired operating temperature, e.g. 50°C. At the top of the washing chamber 3 there are a plurality of nozzles 16 to rinse the washed printed circuit cards with clean alcoholic cleaning liquid from the tank 15.

The apparatus also includes a transport device to move a basket 6 between the drying chamber 2 and the washing chamber 3. In Figures 1 and 2 one and the same basket 6 is shown in various positions before (A), during (B, C, D) and after (E) a programmed work cycle. The transport device comprises a support means 17 to carry a basket 6 without engagement. The support means in turn comprises a horizontal connection arm 18 extending through a narrow, vertical gap 19 in one of the vertical walls 20, 21 which forms a right angle with the wall in which the hatch 8 is located, close to the table 5. The gap 19 is closed by two opposing brush strips 22, 23, which cooperate with each other and sealingly surrounding the connection arm 18. The connection arm 18 of the support means 17 is rigidly mounted to the piston of a double-operating, pneumatic cylinder 24 disposed vertically close to and outside the vertical wall 20 provided with the gap. The support means 17 also includes a horizontal part 25 of suitable design to carry a basket 6 down and up inside the housing 1. The carrying part 25 is shaped to pass unimpeded through the opening 9 in the wall 30. In the embodiment shown, a vertical stand 26, e.g. an arm, is provided extending between the connection arm 18 and the horizontal carrying part 25. The carrying part 25 preferably consists of an open or perforated table on

_* which the basket 6 is placed. The table 25 is arranged to be parallel-displaced by means of the pneumatic cylinder ζ 5 24 from the upper drying chamber 2 to the lower washing chamber 3 and back again in the same pre-programmed work cycle. In its uppermost position in the drying chamber 2 the movable table 25 is at the same level as the external table 5, so that a basket 6 can be moved between these 10 two tables without any difficulty. In its lowermost position the table 25 is located in the tank 14, immediately above its bottom, so that a basket 6, or at least the printed circuit cards placed in the basket 6, will be completely submerged in the alcoholic cleaning 15 liquid. The table 25 can also be retained in an intermediate position above the tank 14 to allow the printed circuit cards to be subjected to a rinsing operation if so desired, during which time the hatch 10 is still kept closed. The hatch 10 is arranged to be 20 displaced with the aid of a double-operating, pneumatic cylinder 27 suspended horizontally in the roof of the machine room 4. The partition 32 between the washing chamber 3 and the machine room 4 is provided with a horizontal gap 28 through which the hatch 10 can be 25 displaced for opening and shutting the hatch 10. The hatch 10 slides in two parallel tracks which are connected to the piston of the cylinder 27. In the embodiment shown, the hatch 8 is opened manually and the basket 6 is inserted into and removed from the drying 30 chamber 2 manually.

The washing chamber 3, drying chamber 2 and machine room 4 are provided with a common outlet channel 33 for exhaustion of air so that a vacuum is created in all these spaces 2, 3 and 4. All parts of the apparatus which are made of electrically conducting material are equipotentially connected and no insulating material is permitted between two metal parts which are joined together.

The outer hatch 8, the inner hatch 10 and the intermediate drying chamber 2 together form a sluice by means of which the baskets 6 are fed into and removed from the washing chamber 3. Except for the outer hatch 8, all operation of the apparatus is effected automatically by means of a PLC equipment, i.e. the apparatus is computer-controlled. After a basket 6 containing printed circuit cards placed side by side has been placed on the table 25 in the drying chamber 2, and the hatch 8 has been closed manually, the apparatus can be started in accordance with a predetermined washing program. The washing program commences with the inner, automatically operated hatch 10 being moved to the side by activating the cylinder 27. The vertical cylinder 24 is then activated to lower the table 25 with the basket 6 into the alcoholic cleaning liquid. The inner hatch 10 is closed again as soon as the basket 6 has passed through the opening 9. The basket 6 with the circuit cards remains in the cleaning liquid for a predetermined time, after which the cylinder 24 is again activated in order to lift the basket 6 out of the cleaning liquid, setting the basket 6 in the mentioned intermediate position below the closed hatch 10. The circuit cards are rinsed in this intermediate position with alcoholic cleaning liquid via the nozzles 16. After this rinsing process and when the cleaning liquid has had time to run off the circuit cards and the basket 6, the hatch 10 is opened again and the basket 6 is moved into the upper, drying chamber 2. As soon as the table 25 has passed through the opening 9 this is once again closed by the inner hatch 10. The inner hatch 10 is thus kept in closed position throughout the whole work operation except during the short periods of time it takes to transport the basket 6 and table 25 down and up through the exposed opening 9. When the drying process is finished after a pre-programmed time in the drying chamber 2, as the last stage of the program, the outer hatch 8 is permitted to be opened again and the basket 6 is pulled off the table 25 and out onto the table 5 through the exposed opening 7. The outer, manually operated hatch 8 is thus in closed position throughout the entire programmed cycle of the work operation.

Inside the washing chamber 3 the highly infammable alcoholic cleaning liquid is openly exposed in the tank 14, which may have an evaporation surface of e.g. 30-60 dm², and in the rinsing process during a part of the cycle. This implies protracted discharge from the tank 14 and from the nozzles 16 so that the washing chamber 3 is assessed as a zone 0 area. Zone 0 is equivalent to the condition that there is permanent or protracted risk of explosion. The exhaust air ventilation and the fact that the opening 9 is closed during normal operation ensure that the explosive alcohol gas is not spread in an uncontrolled manner outside the washing chamber 3.

Inside the drying chamber 2, the risk of explosion is considered to occur temporarily when the basket 6 comes up from the washing chamber 3 and until the printed circuit cards have dried. The exhaust air ventilation and the fact that the openings 7, 9 are closed during normal operation ensure that the explosive alcoholic gas is not spread in an uncontrolled manner outside the drying chamber 2.

Inside the machine room 4, with the storage tanks and pump, an explosion risk is considered to occur temporarily when pure alcoholic cleaning liquid is pumped to the washing chamber 3. The exhaust air ventilation and the fact that the machinery room 4 is well sealed also ensure that the explosive gas is not spread in an uncontrolled manner outside the machine room 4.

The explosive alcoholic gas is thus evacuated from all the spaces 2, 3 and 4 through the continuous exhaust air ventilation which produces a vacuum of about 0.1 bar in each chamber during normal operation, i.e. when the hatches 8 and 10 are in closed position.

The alcoholic cleaning liquid used is, for instance, ethanol, methanol, isopropyl alcohol, or mixtures thereof.

The programming device which controls the work cycle of the apparatus includes control means arranged via the program to control the hatches 8 and 10 so that only one of them may be opened at a time.

Besides a storage tank 15 for fresh alcoholic cleaning liquid, the machine room 4 also contains a storage tank (not shown) for used cleaning liquid which is emptied from the treatment tank 14. An ultra-sound device may be disposed in the washing chamber 3 in order to improve the washing effect when required. The table 25 may also be moved up and down several times by the cylinder 24, while the basket 6 is in the tank 14, thus giving rise to currents in the liquid around the circuit cards to improve the washing effect. A device with a cooling loop may be disposed in the rinsing zone between the hatch 10 and the washing zone to cool the alcoholic gas, thereby reducing the withdrawal of alcohol. When such a cooling device is used, the teperature of the cleaning agent can be increased to boiling point so that a vapour-phase zone is formed in the washing chamber below the hatch 10. The alcohol vapour will then condense on the circuit .cards, thereby effecting an additional washing treatment.

Claims

C A I M S

1. An apparatus for cleaning workshop products such as printed circuit cards, using highly inflammable alcoholic cleaning liquid, said printed circuit cards being placed in a basket of predetermined size, characterized by a housing (1) which is closed during operation; at least one treatment chamber enclosed therein and comprising at least one washing chamber (3); a sluice disposed vertically above said washing chamber and comprising a chamber (2) having an opening (7) closable by means of a first, outer hatch (8) to enable a basket (6) filled with printed circuit cards, etc. to be moved in and out of the chamber (2), and an opening (9) closable by means of a second, inner hatch (10) to enable a basket (6) to be moved down into and up out of the washing chamber (3), said chamber (3) containing a tank (14) of cleaning alcoholic liquid; a vertically displaceable support means (17) arranged to carry a basket (6) and transport it between the sluice chamber (2) and the washing chamber (3) for immersion of the basket (6) into the alcoholic cleaning liquid; a pneumatic cylinder (24) disposed externally on the housing and connected to said support means (17) via a substantially horizontal connection element (18) in order to effect said vertical displacement of the support means (17) carrying the basket (6), said housing being provided with a vertical gap (19) through which said connection element (18) extends; an exhaust air channel system (33) which is connected to the washing chamber (3) and the sluice chamber (2), and arranged to create a vacuum in the housing (1) for continuous evacuation of explosive alcoholic gas from the chambers (2, 3); and control means arranged to control the hatches (8, 10) of said sluice so that only one of them can be opened at a time.

2. An apparatus as claimed in claim 1, characterized in that said sluice chamber forms a drying chamber (2)

- with nozzles (11) disposed therein to blow dry air towards printed circuit cards, etc. placed in the drying 5 chamber.

3. An apparatus as claimed in claim 1, characterized in that the second, inner hatch (10) is arranged to be operated automatically by means of a pneumatic cylinder (27) .located outside the washing chamber (3) or the

10 sluice chamber (2).

4. An apparatus as claimed in any of claims 1-3, characterized in that it also includes a machine room (4), enclosed by the housing (1) and containing a tank (15) for fresh alcoholic cleaning liquid and a tank for

15 used alcoholic cleaning liquid, and that the machine room (4) is connected to said exhaust air channel system (33).

5. An apparatus as claimed in claims 3 and 4, characterized in that the cylinder (27) for operating the second, inner hatch (10) is disposed in the machine room

20 (4).

6. An apparatus as claimed in any of claims 1-5, characterized in that the first, outer hatch (8) is arranged to be operated manually only before and after a pre-programmed work operation.

25 7. An apparatus as claimed in any of claims 1-6, characterized in that the washing chamber (3) is provided with nozzles (16) for rinsing the printed circuit cards, etc. with fresh alcoholic cleaning liquid, said nozzles (16) being disposed above and at a distance from said

30 tank (14).

8. An apparatus as claimed in any of claims 1-7, characterized in that a cooling device is disposed in the washing chamber (3) in the space above said tank (14).

9. An apparatus as claimed in claim 8, characterized in that a vapour-phase zone is arranged to be maintained within the area of the cooling device.