WO1991014509A1

WO1991014509A1 - A device for spray painting and similar treatment of objects

Info

Publication number: WO1991014509A1
Application number: PCT/SE1991/000207
Authority: WO
Inventors: Eric Von Gertten
Original assignee: Eric Von Gertten Ab
Priority date: 1990-03-19
Filing date: 1991-03-19
Publication date: 1991-10-03
Also published as: SE464222B; EP0592405A1; SE9000998D0; JPH05505972A; CA2078449A1; AU7576691A

Abstract

A device for spray painting, spray gluing and similar treatment of objects (2) comprises a spray gun (5) and a housing (6) containing the objects (2) to be sprayed. The spray gun (5) is positioned outside the housing (6), just in front of an opening (9) therein. The cross-sectional area of the opening (9) is considerably smaller than the internal cross-sectional area of the housing (6) that is perpendicular to the direction of spraying and located in a plane (13) through the object (2). Only a restricted air flow need be used in the spray device (1), since excess paint is effectively wet-separated and collected in a trap (16) in the housing (6), whence it is conveyed to a recovery vessel (17). This reduces the amount of paint particles that stick to the filter (11) of the spray device (1), for which reason the filter (11) need not be exchanged as often as in prior art spray booths.

Description

A DEVICE FOR SPRAY PAINTING AND SIMILAR TREATMENT OF

OBJECTS

The present invention relates to a device for spray painting, spray gluing and similar treatment of objects- Prior art spray chambers or booths (see, for instanc US-A-3,048,146, EP-A-0,369, 78 and EP-A-0,291,423) usuall contain a comparatively large space in which the objects be sprayed are conveyed past a number of spray guns which are activated and inactivated by photocells and/or time- controlled devices. In the nozzle of the spray gun, the paint is disintegrated into droplets suspended in the air in the form of a mist which is directed as a jet towards the objects to be sprayed. Some of the mist sticks to the object, while some rebounds under the -action of the air pressure forming at the surface of the object, and the remaining mist passes by the object. Owing to the high velocity of the spray jet, a negative pressure arises, an the jet entrains surrounding air. The technical term for this phenomenon is coejection. In the spray chamber, ther is a negative pressure around the spray nozzle, and a positive pressure at the surface of the object. The mean ^"pressure in the chamber is below the pressure outside the chamber, and the rebounding spray mist therefore is drawn to the adjacent spray gun whose nozzle is clogged and, sooner or later, is liable to cause stoppage.

To avoid this, a large air flow must be drawn throug the chamber to remove the spray mist, which at least temp rarily obviates the inconvenience of clogging. However, i cannot be avoided that useful spray-mist, which should ha been applied to the object, is also expelled from the chamber.

The air flow thus drawn out of the chamber must be cleaned by a filter to -protect ducts and adjacencies in general. The filter is rapidly clogged with paint which, when dried, allows free passage of solvents. Owing to the rapid clogging, the filter has to be exchanged frequently an operation which not only is difficult, but also exposes the personnel to dangerous paints and solvents. In addi¬ tion, production is interrupted.

When the filter is clogged, the air flow through the chamber is reduced, and the spray nozzles are choked, whic leads to the inconveniences discussed above. Generally, th entire spray chamber has to be cleaned, which is both ex¬ pensive and dangerous. When the filters are clogged, the spray mist cannot be removed from the chamber but whirls around therein, which aggravates the inconveniences of rebound and too large a coejection. As mentioned earlier, this leads to clogging of the spray guns and. further requires frequent cleaning of the inner walls of the spray booth to which the spray mist adheres. Thus, the use of large air flows does not obviate the inconveniences mentioned, and is furthermore very expen¬ sive, since a great amount of energy is required to heat the .air taken in and press it through the spray chamber. Moreover, this prior art arrangement involves considerable waste of paint, since large volumes of paint stick to the filter, and the inner walls of the spray chamber.

One object of the invention is, therefore, to provide a spray device which obviates the above-mentioned incon¬ veniences while using considerably smaller air flows. Another object of the invention is to provide a spray device in which the spray mist is used more effectively than in prior art spray booths, thereby drastically re¬ ducing rebound, coejection and the above inconveniences. Yet another object of the invention is to provide a spray device in which the filter need not be exchanged as often as in prior art spray booths and in which the spray mist that does not stick to the object is effectively collected.

'A further object of the invention is to reduce the amount of solvents which, despite the filter equipment, is emitted from the spray device to the surroundings. According to the invention, these objects, as well a other aims apparent from the following description, are attained in a simple and ingenious fashion by a spray device of the type stated in appended claim 1. Other features of the invention are recited in the appended subclaims.

The invention and its many advantages will be de¬ scribed in more detail below, reference being had to the accompanying drawings of embodiments. In the drawings, Fig. 1 is a schematic vertical section of a spray device according to the invention,

Fig. 2 is an enlarged section taken along line II-II in Fig. 1,

Fig. 3 is an enlarged, partly sectional view of part of the upper portion of the spray device in Fig. 1, Fig. 4 illustrates a lower portion of a housing forming part of the spray device in Fig. 1,

Fig. 5 illustrates a slightly modified embodiment of the spray device in Figs 1-4, Figs 6 and 7 show two variants of the placement of a spray gun near to an elongate opening in the housing, and

Fig. 8 illustrates an example of a driving device fo moving the spray gun reciprocatingly along the elongate opening of the housing. Fig. 1 shows a spray device 1 according to the inven tion, which is intended for spray painting objects 2 whic in this embodiment, are elongate door frames of wood. It should be observed that the spray device 1 may also be us with varnishes, glues and like coating substances. The spray device 1' comprises a lower part 3 in the form av a closed space in which air flows in the direction of the arrows, as well as an upper part 4 where spray guns 5 are positioned (only one gun is shown in the Figure).

The spray gun 5 is placed outside a housing 6 which will be described in more detail below and through which the object 2 to be sprayed passes and preferably is con¬ veyed in a direction perpendicular to the plane of the drawing, by means of a conveyor 7, only schematically shown. Thus, the object 2 is conveyed through the housing and past the spray gun 5 in a direction which is substan¬ tially perpendicular to the direction of spraying. At th ends, the housing 1 has openings (not shown) through whi the object 2 is introduced into and removed from the housing 6. A diverging paint jet 8 is directed from the. spray gun 5 towards the object 2 via an opening 9 in the housing 6. This opening 9 is formed of a bore in a nozzl 10 which is mounted on the housing 6 (see Figs 2 and 3).

Thus, the paint jet 8 impinges upon the object 2, and sp mist, i.e. paint that does not stick to the object, is e trained by the air flow past the object 2. .

At its lower part 3, the spray device 1 has a filte 11 for intercepting particles of paint entrained by the spray mist in the air flow. The air is then conducted ou of the lower part 3 of the spray device 1 via an exhaust air outlet 12, where there is in known manner a negative pressure for producing an outward suction action. Since the spray gun 5 is positioned just outside th special housing 6 where the actual spray painting takes place, the amount of coejected air, i.e. air entrained b the jet 8 from the immediate surroundings of the spray g 5 into the housing 6, is reduced. Quite simply, only an extremely limited amount of air is entrained by the jet 8 from the space above the housing 6, through the opening 9 and towards the object 2. Thus, the air coejected into t housing 6 is completely clean. The decrease in coejeted flow also reduces the rebound of spray mist from the obj 2. On the whole, spraying takes place in a restricted volume inside the essentially closed housing 6, and the spray mist is better controlled than has been possible u to now in prior art spray booths.

The housing 6, which preferably is elongate perpendi cular to the plane of the drawing, has a much smaller volume than the_. lower part 3 of the spray device 1. The spray mist which nevertheless forms is either conducted of the housing 6 and sticks to the filter 11, or sticks t the lower inner walls of the housing 6 which are easy to clean. The paint particles not adhering to the object 2 o the housing 6 are thus conducted further downwards, and discharged through an outlet 14 in a lower funnel-shaped portion 15 of the housing 6 to be described below. The special design of the housing 6, with its vaulted central portion, gives a favourable spraying result and effective contributes to the removal of spray mist from the housing and the collection of spray mist adhering therein. Thus, takes an extremely small air flow to remove the spray mis To keep the coejection of air into the housing 6 on reasonably low level,^' the cross-sectional area of the opening 9 is considerably smaller than the internal, cross sectional area of the housing 6 that is perpendicular to the direction of spraying and located in a plane through the object 2 in the housing 6. This plane is schematicall indicated by a dashed line 13 in Fig. 1. Thus, the jet 8 diverges through the opening 9 and impinges upon the obje 2, which suitably is placed in the centre of the housing In this embodiment, it is unavoidable that a certain amount of air is coejected through the opening 9, and thi is, in some cases, even desirable considering that 'there has to be an air flow through the spray device 1. There- fore, the cross-sectional area of the opening 9 is pre¬ ferably adjustable by means of a special device, which wi be described below. The air coejected through the opening affects the paint jet 8 whose appearance and behaviour ca be controlled from the outside by the operator who, when need be, adjusts the cross-sectional area of the opening in such a manner as to produce a neat paint jet 8 without "fluttering".

As mentioned before, a certain amount of excess pain adheres to the lower inner walls of the housing 6, and these walls thereby come to serve as wet separators. Sinc the lower portion 15 of the housing 6 is essentially funnel-shaped, excess paint runs down the lower inner wal of the housing 6 and is collected in a lower wet-separati trap or collecting pocket 16. Then, the excess paint is conducted to a recovery vessel 17 via the outlet 14. Natu rally, it is a great advantage that the excess paint is intercepted in the spraying direction. Preferably, the collecting trap 16 of the housing 6 is slightly inclined the longitudinal direction, such that the excess paint ma accumulate at one end of the housing 6 and be conducted down into the vessel 17 in a simple manner. It is advan- tageous that the recovery vessel 17 is placed inside the lower, closed part 3 of the spray device 1, so that it is automatically ventilated by the air flow passing by or through it. In prior art spray chambers, special ventilat ing devices were usually required for such recovery vessels.

Tests have shown that the collection and recovery of excess paint described above is extremely effective. Sinc much of the spray mist is intercepted already in the housing 6, only minor amounts of paint particles are conducted any further. Thus, the air passing through the filter 11 contains a low proportion of paint particles, "a the filter 11 thus need not be exchanged as frequently as in prior art spray booths. Quite simply, the filter 11 is not clogged as rapidly as before. Neither are the spray guns 5 clogged as rapidly as before, since they are placed outside the special housing 6. The amount of spray mist rebounding towards the nozzle of the spray gun 5 is appreciably reduced compared with prior art spray booths. Further, tests have shown that the air flow required can be greatly reduced. Prior art spray booths normally u

3 air flows of 5000-6000 m /h, which involves extreme power requirements for heating the air taken in and for the fan equipment. In the spray device according to the invention

3 air flows as insignificant as 500-600 m /h have been used with excellent results. The outflow generated by the nega tive pressure in the suction chamber only need be slightl larger than the total of the coejected air flow and the a flow generated by the compressed-air operation of the spr guns.

Anyone skilled in the art will immediately appreciat that a great deal of money can thus be saved as to invest ments in equipment, as well as running operational and maintenance costs. Since it is not necessary to exchange clean the filters as often as before, the number of stop¬ pages is reduced, as is the personnel requirement. Fig. 2 shows a frame 18 which is arranged above the housing 6 at a distance therefrom and on which the spray gun 5 is mounted by means of a fastening device 19, schematically shown, which may be a clamping-screw. The spray gun 5 is positioned just above the nozzle 10 whose diverging bore, which has the form of a. truncated cone, forms the opening 9. In a variant not described in detail the position of the spray gun 5 can be adjusted in the longitudinal direction, which makes it possible to alter the distance between the nozzle of the spray gun 5 and th nozzle 10.

Further, the nozzle 10 is provided with a device 20, only schematically shown, for adjusting the cross-section area of the opening 9. The device 20 may be of a type kno per se,. e.g. a throttle. The nozzle 10 is preferably ex- changeable for- other nozzles which may be provided with other types of openings and/or adjusting devices. In a variant, the nozzle 10 is also axially adjustable in rela tion to the direction of the jet 8. Further, the nozzle 1 can be movable between the openings 9 in the housing 6. It is further apparent from Fig. 2 how the elongate housing 6 is advantageously divided into several sections or modules. However, Fig. 2 only shows one section, whic is defined by two partitions 21 and 22 in the housing 6. Preferably, the housing 6 contains several sections of t type, each equipped with a spray gun 5 and a nozzle 10. Since there is only one spray gun 5 in each section, the jets 8 will not interfere with one another, which makes more reliable the control of the spray mist. Under certa conditions, two spray guns 5 may be arranged in each sec tion, in which case they are positioned close to one another. Fig. 3 illustrates in more detail another placement the spray gun 5. Preferably, the housing 6 is formed wit several openings or nozzles 10 for spray painting in different directions. To this end, the spray guns 5 can moved between different positions on the frame 18. It is preferred that spray painting can take place in any dire tion whatsoever in relation to the dome-shaped semicircl formed by the upper part of the housing 6 and in relatio to the dome-shaped frame 18 (cf. Fig. 1). Of course, it also conceivable that several spray guns 5 simultaneousl spray the object 2 from different directions. In Fig. 3, is also indicated that the conveyor 7 might comprise a number of rollers 7' which optionally are driven.

In a variant not shown in detail, the spray gun 5 i mounted directly in the opening 9 of the housing 6, in which case the spray nozzle proper is essentially on a level, with the inner wall of the housing 6. The coejecti from the space above the housing 6 is then restricted, a the jet 8 from the spray gun 5, which usually is driven compressed air, generates the main part of the air flow down through the housing 6. If one wishes to increase th coejection of clean air, small ducts may be arranged in housing 6 where the spray gun 5 is mounted. Further, a device for adjusting the cross-sectional area of the opening may be arranged at the nozzle of the spray gun 5. Also, the spray gun 5 can be mounted in the nozzle 10.

Fig. 4 illustrates in more detail the design of the lower funnel-shaped portion 15 of the housing 6, in par¬ ticular the collecting trap 16 where excess paint accumu lates to be drawn off through the outlet 14. The funnel- shaped portion 15 is supported or carried by holders 23, which in addition may serve to impart light vibrations t the lower part of the housing 6 to make the excess paint run faster down along the inner walls.

A variant of the inventive spray device 1 is shown i Fig. 5, where like numerals refer to like components in Figs 1-4. In this embodiment, the spray device 1 comprise a lower and an upper chamber 3 and 4 through which air flows. For this purpose, the upper chamber 4 has an intak 25 where air is blown in to pass through a prefilter 26 a subsequently reach the upper side of the housing 6. As before, the spray gun 5 is arranged outside the housing 6 The opening in the housing 6 through which the spray gun is to spray has, in this case, the shape of an elongate g or slit 9' whose longitudinal extension is apparent from Fig. 5. The slit 9' is comparatively narrow, and preferab has a width slightly exceeding the outer diameter of the nozzle 10.

As illustrated by arrows in Fig. 5, the spray gun 5 reciprocatingly movable along the slit 9' by means of a driving device not shown. This enables the spray gun 5 to sweep to-and-fro over a certain width in keeping with the object 2 to be sprayed. In the example shown, the object is a tabletop which is to be spray painted from above. Owing to the sweeping movements of the spray gun 5 transversely of the direction of motion of the tabletop 2 which is perpendicular to the plane of the drawing, a ver favourable spraying result is obtained. To prevent not on that spray mist rebounds out of the elongate slit 9' , but also that the coejected air flow becomes too large, the slit is equipped with a movable cover device 27 which follows the movements of the spray gun 5. Preferably, the cover is such that only the nozzle opening communicates with the slit 9' when the spray gun 5 is moving. The housing 6 may preferably be equipped with various means f controlling the air flow therein. Fig. 5 shows an example in the form of a guide baffle 28. Between the air intake 25 and the prefilter 26, ther is a certain positive pressure which slightly exceeds the outside pressure. After the prefilter 26, the pressure drops somewhat, but should still slightly exceed the out¬ side pressure. This prevents dust particles in the outsid air from entering the housing 6 where the pressure is bel the outside pressure. Through the remainder of the spray device 1, the pressure drops successively to be at its lowest at the outlet 12, where the air is sucked off.

Fig. 6 is a sectional view taken in the longitudinal direction of the slit 9'. For covering and sealing, the slit 9' has two elongate, elastic lips 29, preferably of rubber, which yield to the nozzle 10 when the spray gun 5 is moved to-and-fro along the slit 9'. Thus, the slit 9'. covered everywhere except where the nozzle 10 is at the moment.

In another variant, shown in the corresponding sec- tional view of Fig. 7, the upper portion of the housing 6 diverges, thus reducing the risk of spray-mist rebound. T mist sticks to the inner walls of the housing 6. In this case, the slit 9' may be completely open or partly covere No nozzle is required here, since the slit 9' is narrow a the spray gun 5 is positioned just above the slit 9'. The spray jet has no time to spread on the upper side of the housing 6.

Fig. 8 illustrates yet another embodiment, in which the spray gun 5 is, by means of a holder 30, fixed to a belt 31 which i.s driven to-and-fro along the elongate sli 9' in the housing 6 by means of wheels 32. Also the nozzl 10 is attached to the belt 31. Thus, the slit 9' is cover by the belt 31 everywhere except at the very place of the nozzle 10. This makes it possible to spray broad objects the manner shown in Fig. 5.

In an embodiment not shown, the slit has the form of an endless track with two semicircle-shaped curves and tw straight stretches therebetween. The spray gun is driven along this track and may be controlled in such a manner that it only sprays at some parts of the track, e.g. the straight stretches. The spray device of the invention is based on the principle that spray painting is to take place inside a special, closed housing. The spray guns may be fixed or movable, depending on the type of objects to be sprayed. However, the spray guns should, according to the invention be placed outside the housing at an opening therein.

Finally, it should be observed that the preceding^' . description only deals with such components as are require to elucidate the inventive idea. For reasons of clarity, many components have not been included, e.g. feeders for paint and compressed air to the spray guns. Further, there may be photocells and other transducers, such as time- controlled devices for controlling the spray paint in response to the conveyance of the objects, through the housing.

It goes without saying that the invention is by no means restricted to the embodiments described above, and that a great deal of modifications are conceivable within the scope of the appended claims.

Claims

1. A device for spray painting, spray gluing and similar treatment of objects, comprising at least one, preferably more than one, spray gun (5) directed at the object (2), c h a r a c t e r i s e d in that it comprises a housing (6) adapted to accommodate the object (2) to be spray painted, and that each spray gun (5) is positioned outside the housing (6), just in front of or i an opening (9) in said housing.

2. The spray device of claim 1, c h a r a c t e r ¬ i s e d in that the cross-sectional area of the opening (9) is considerably smaller than the internal cross-sec- tional area of the housing (6) that is perpendicular to t direction of spraying and located in a plane (13) through the object (2) in said housing (6).

3. The spray device of claim 1 or 2, c h a r a c ¬ t e r i s e d in that a device (20) for adjusting the cross-sectional area of the opening (9) is arranged at ea opening (9).

4. The spray device of claim 1, 2 or 3, c h a r a c t e r i s e d in that the opening (9) is delimited by a nozzle (10) whose bore has the form of a truncated cone a diverges in the spraying direction.

5. The spray device of any one of the preceding claims, c h a r a c t e r i s e d by a frame (18) which is positioned outside the housing (6) at a distance therefrom and on which the spray guns (5) are mounted in such a manner as to be movable between different openings (9) in the housing (6) to spray in different directions towards the object (2).

6. The spray device of any one of the preceding claims, c h a r a c t e r i s e d in that the housing ( is elongate and divided into several sections defined by partitions (21, 22) and each containing a spray gun (5).

7. The spray device of any one of the preceding claims, c h a r a c t e r i s e d in that the housing ( comprises a substantially funnel-shaped portion (15) whic forms a trap (16) for wet separation and collection of excess paint.

8. The spray device of claim 7, c h a r a c ¬ t e r i s e d in that the collecting trap (16) of the housing (6) leads to a recovery vessel (17) arranged insi the spray device (1) and ventilated by an air flow.

9. The spray device of claim 8, comprising- an air ou let (12) and a filter (11) which, as seen in the directio of the air flow, is placed in front of said outlet, there being a negative pressure between said outlet and said filter, c h a r a c t e r i s e d in that the collectin trap (16) is placed before the filter (11), as seen in th direction of the air flow.

10. The spray device of any one of the preceding claims,- c h a r a c t e r i s e d in that the opening ( is an elongate slit (9' ), and that the spray gun (5) is reciprocatingly movable, preferably driven, along the sli (9')..