GB2049164A

GB2049164A - Suction box

Info

Publication number: GB2049164A
Application number: GB7940292A
Authority: GB
Original assignee: Svenska Flaktfabriken AB
Current assignee: Svenska Flaktfabriken AB
Priority date: 1978-11-24
Filing date: 1979-11-21
Publication date: 1980-12-17
Also published as: DE2947334A1; FI793693A; FR2442084A1; NO793782L; SE7812139L; GB2049164B; DK149711B; FR2442084B1; DK149711C; DK500479A

Abstract

A suction box is used for evacuating contaminated air, e.g., such as is caused by surface treatment of objects, whereby ventilating air is caused to flow from the outside and into the box through an opening in the front wall (1) of the box. The contaminated air is sucked through one or several evacuation channels from a processing zone (9) which is mainly defined by the side walls (5, 6) of the box. An air guide or scoop (12, 14) is arranged along at least part of the edges (13) of the opening in the front wall and extends inwards and outwards from the front wall. The portion (12) extending inwards from the front wall forms an inner guide surface which is arranged to change the direction of part of the contaminated air which is not sucked away immediately and strives to flow along the side walls towards the opening in the front wall. <IMAGE>

Description

SPECIFICATION Suction box The present invention relates to a suction box for evacuating contaminated air, caused by the processing of objects, e.g. surface treatment such as spray painting, grinding, washing and gluing with preparations containing dangerous solvents. In such boxes ventilating air is caused to flow from the outside and into the box through an opening in the front wall of the box. The contaminated air is exhausted through evacuation channels from a processing zone, which is mainly defined by the walls of the box.

Suction boxes of this kind are previously well known and used, inter alia, in connection with grinding or spray painting and surface treatment of small objects. These known suction boxes are big, however, and require great quantities of air if they are to attain acceptably limited concentrations of air pullutants and prevent contaminated air from spreading in the area outside the box. Since these known suction boxes are designed for great air quantities the energy consumption will be high and consequently the equipment will be rather costly in operation. Another drawback with equipment hitherto known is, for instance, that spray painting of small surfaces on vehicles has to be carried out in relatively big plants, where the whole vehicle is brought into a bay of chamber where air is supplied through ventilation openings in the ceiling and is evacuated through a grating in the floor.The operator must consequently remain in the chamber to carry out the work and if it were to be done without a protective mask the flow of air must be in the order of magnitude of 100,000 m3/hour. Such plant is of course extremely expensive to instal and the operating costs are also high, due to the large air flow during operation and the energy consumption related thereto.

One object of the suction box in accordance with the present invention is to provide a box, e.g., for spray painting with dimensions considerably less than those presently used.

According to one aspect of the present invention a suction box for evacuating contaminated air resulting from processing objects has peripheral walls which define a processing zone having a front opening through which ventilating air is caused to flow from outside the box, the contaminated air being sucked through at least one evacuation channel, at least part of the front opening being defined by an air guide which extends inwards from the front wall towards, but not up to, the back of the box, the air guide being spaced inwardly from said peripheral walls.

The air guide and the peripheral walls may together define an annular trap which is open at the rear.

According to another aspect of the present invention a suction box has peripheral walls which define a processing zone having a front opening through which ventilating air is caused to flow from outside, the contaminated air being sucked out through at least one evacuation channel, at least part of the front opening being defined by an air guide which extends inwards from the front wall towards, but not up to, the back of the box and which guide is arranged to alter the direction of and trap turbulent contaminated air which is not immediately sucked away and which strives to flow along said peripheral walls towards the front of the box.

The air guide may also extend outwards from the front of the box to form a funnelshaped air entrance which encourages air to flow from outside the box past the air scoop round the edges of the front opening and to the processing zone, this air being substantially free from turbulence.

The design of the suction box according to the invention provides substantial reduction of the box dimensions without causing any contamination of the ambient air. Moreover, surface treatment such as spray painting confined areas on large objects e.g., vehicles, can also be performed by means of the box according to the invention and can be carried out by a person who stays outside the box, which considerably reduces the risk of harmful effects from solvents.

This last-mentioned object is realized substantially in that the back wall is at least partially formed by two curtain plates which are pivotally connected to the side walls of the box and together with a surface of the object will form the back wall of the box.

One embodiment of the invention is now described in more detail with reference to the accompanying drawings where Figure 1 is a sectional side view of a suction box in accordance with the invention for spray painting the side of a bus Figure 2 is a front view of a suction box according to Fig. 1 and Figure 3 is a plan view of a suction box according to Fig. 1 adapted for spray painting the corner of a bus.

The suction box as shown in Fig. 1 comprises a front wall 1 and a back wall 2, side walls 3 and 4, an upper wall 5 and a lower wall 6. The box is placed against the side of a bus which then forms a portion of the back wall 2 of the box. The side walls 3 and 4 are formed as two evacuation ducts, connected upwardly to evacuation channels 7 and 8 for evacuating air from a processing zone 9, mainly defined by the walls of the box. The front wall 1 is provided with an opening, which permits access to the zone 9 and also permits air to flow from the outside of the box through filters 10 and 11 into the evacuation ducts 3 and 4 which lead the flow or air to the evacuation channels 7 and 8.An air scoop 12, 1 4 is arranged along the four edges 1 3 of the opening in the front wall 1, and the part 12 of the scoop extending from the front wall 1 towards the back wall 2 to form an inner guide member which is arranged to alter the direction of, and trap such that it is in turbulent motion, part of the contaminated air which is not immediately sucked off through the ducts 3, 4. Another part 14 of the air scoop extends outwards from the front wall 1 to form a funnel-shaped member which encourages air to flow past said scoop from outside the box round the edges of the opening to the zone 9 such that this air is substantially free from turbulence.

The air scoop 12, 14 thus has a double function, i.e. to provide a turbulence-free air entrance to the zone 9 and to form a turbulence zone 15, which is defined by the respective parts of the side and front walls and said part 1 2 in which the air, which would otherwise escape from the box, is trapped and ketp in turbulent motion until it is sucked away through the evacuation channels There are many reasons for the escape of contaminated air occurring in a suction box of conventional form. In spray painting of objects for instance, the paint particles are propelled at relatively great velocity into the box, where a portion of them is laterally deflected mainly due to the effect of the air stream.

Since the particles have great velocity, some of them will remain entrained in the air stream in the box, a portion of which will move along the inside of the walls towards the opening and back to the air outside the box. This dissipation of contaminated air from the box and out into the vicinity thereof is difficult to prevent in conventional spray painting boxes, and several measures have been taken to overcome this drawback, e.g. by increasing the air flow through the box. The back flow of contaminated air from the box and to the surrounding air also occurs, when the particles or contaminants have no initial velocity at all, e.g. when objects are treated with strong and dangerous solvents. A person standing in front of the suction box and working with objects inside the box will cause a turbulent zone in the vicinity of that part of the body which is turned towards the box.This is of course a result of the person forming an obstruction to the air which is streaming from the space around the box and into it. In the turbulent zones created by the body portions of the person the pressure is lower than in the ambient zones with unobstruted air flow and this causes the contaminated air which is not immediately sucked away through the side ducts to flow back towards the turbulent low pressure zones behind the person's body.

This back flow of contaminated air will cause a concentration of contaminants in these turbulent zones just behind the body of the person and consequently also just behind the face, which has been clearly shown in recently published research work. It has also been observed in the use of conventional suction boxes, which will generally provide a low concentration of air contaminations in the ambient space around the box, that the degree of contamination in the turbulent zones just behind the body of a person standing in front of the box will considerably exceed the limiting safety values for the contaminants in question. This is of course particularly serious in a turbulent area just around the face of such a person.Through the arrangement with the air scoop 12, 14, according to the invention the contaminated air which tends to flow back into the air space round the box will be given a new direction and trapped in turbulent motion in a vortex zone 1 5 restricted by the inner surface of the air scoop 1 2 and the inside of the front wall 1. Since air is continu ously sucked away from the box the contami nations in these air vortices will be disposed of at the circumferences thereof when they are moved towards the evacuation ducts by centrifugal force. The vortex zones 1 5 are not only created at the sides, but at the lower and upper walls of the suction box as well, and the air in these vortex zones will be sucked off towards the side ducts 3, 4, which are con nected to the evacuation channels 7, 8.

The suction box shown on Fig. 1 is sup ported in a frame 1 6 which is movable on wheels 1 7 and can easily be positioned close to an object, for instance the side of a bus, which is to be sprayed. The box can of course be stationary and provided with a rigid back wall when intended for use in conjunction with the treatment of smaller objects, as indi cated above.

The embodiment shown in Fig. 3 is pro vided with two curtain plates 18 and 1 9 which are pivotally connected to the side walls 3 and 4 of the box and can be manoevered such that, together with the object 20 to be treated, they will form the back wall of the suction box. When serving the purpose of the back wall, said plates are also provided with a "ceiling" and a "floor" in order to separate the processing zone from the surroundings. In the embodiment illustrated in this Figure, the object 20 is a corner of a bus which, in accordance with the inventive principle, can be spray painted without paint particles or solvent coming into the ambient air, which means that the work can be carried out by a person who does not need a protective mask.

The curtain plates 18 and 1 9 shown on the Figure can be hinged 21 to form a plurality of sections, so that they can be easily adapted to the distance to the object which is to be treated. They can also be opened out for completely closing the back of the suction box, so that it can be utilized in the treatment 1 of other objects which can then be placed within its processing zone.

According to a further embodiment of the invention the suction box can be stationarily arranged e.g. for surface treatment of goods which, by means of a conveyor are brought into the processing zone of the box, where they are spray painted for instance and then removed for drying and finishing.

The suction box according to the invention can optionally be provided with suction ducts along the upper and/or lower walls which in that case should be designed in the form of evacuation ducts.

Claims

1. A suction box for evacuating contaminated air resulting from processing objects, the box having peripheral walls which define a processing zone having a front opening through which ventilating air is caused to flow from outside the box, the contaminated air being sucked through at least one evacuation channel, at least part of the front opening being defined by an air guide which extends inwards from the front wall towards, but not up to, the back of the box, the air guide being spaced inwardly from said peripheral walls.

2. A suction box as claimed in Claim 1 in which the air guide and the peripheral walls together define an annular trap which is open at the rear.

3. A suction box for evacuating contaminated air resulting from processing objects, the box having peripheral walls which define a processing zone having a front opening through which ventilating air is caused to flow from outside, the contaminated air being sucked out through at least one evacuation channel, at least part of the front opening being defined by an air guide which extends inwards from the front wall towards, but not up to, the back of the box and which guide is arranged to alter the direction of and trap turbulent contaminated air which is not immediately sucked away and which strives to flow along said peripheral walls towards the front of the box.

4. A suction box as claimed in any one of the preceding claims in which the air guide also extends outwards from the front of the box to form a funnel shaped air entrance.

5. A suction box as claimed in any one of the preceding claims including curtain plates pivotally connected to the side wall of the box one on each side and which together with a surface of an object to be processed can form a back to the box.

6. A suction box substantially as specifically described herein with reference to the accompanying drawings.