GB2081126A - Spraybooth - Google Patents

Abstract

A spraybooth, particularly but not exclusively, for use in a paint spraying installation wherein air, in use contaminated with overspray particles or droplets, is drawn from a spraying area into a washing chamber 13, at high speed over the exposed surface of a liquid cleansing agent contained by a tank 11, the air entraining liquid cleansing agent, and within the washing chamber the overspray particles or droplets being washed from the airflow by the entrained cleansing agent, the washed air passing out of the spraybooth, and the cleansing agent containing the contaminants being returned to the tank wherein the contaminants settle in the form of a sludge the distribution plate 36, 36a of the washing chamber 13, against which the cleansing agent stream entrained by the air entering the chamber in use first impinges, is defined by first and second planar surfaces being disposed generally at right-angles to one another and extending, with their line of intersection horizontal, widthwise of the spraybooth, the first, lowermost surface 36 extending from below the cleansing agent level of the tank 11 rearwardly and upwardly, and the second, uppermost surface 36a thus extending upwardly and forwardly. <IMAGE>

Description

SPECIFICATION Spraybooths A spraybooth is an apparatus normally used in conjunction with a spraying installation, frequently a paint spraying installation, the apparatus having an area in which the spraying operation occurs, and from which air is drawn into the apparatus so that air contaminated during the spraying operation is drawn into the apparatus and away from the operator, to be replaced by fresh ambient air.

This invention relates to spraybooths, particularly but not exclusively for use in paint spraying installations, the booths being of the kind wherein air, in use contaminated with overspray particles or droplets, is drawn from a spraying area into a washing chamber, at high speed over the exposed surface of a liquid cleansing agent contained by a tank, the air entraining liquid cleansing agent, and within the washing chamber the overspray particles or droplets being washed from the airflow by the entrained cleansing agent, the washed air passing out of the spraybooth, and the cleansing agent containing the contaminants being returned to the tank wherein the contaminants settle in the form of a sludge.

Generally the cleansing agent is an emulsion of alkaline water and oil together with a small quantity of free oil, the cleansing agent serving to inhibit any tendency of the overspray particles or droplets to coagulate orto stick to the surface of the spraybooth.

In a known form of spraybooth of the kind specified above the air enters the washing chamber by passing at high speed between the surface of the cleansing agent in the tank and the lower edge of a generally vertically extending plate which defines the front wall of the washing chamber. The air, in passing over the cleansing agent at speed, entrains the cleansing agent and thus carries a turbulent stream of cleansing agent into the washing chamber.A wall within the washing chamber, known as the distribution plate, is concave, being shaped in a continuous curve of approximately 120 degrees to guide the path of the cleansing agent and air from a generally horizontal rearward path, through a vertical path, to an upward and slightly forward path so that the cleansing agent stream is directed onto the front wall of the chamber and onto a rearwardly and slightly downwardly directed deflector plate positioned at the top of the washing chamber. The combined action of the front wall of the chamber and the deflector plate is to divert the flow to a rearward and generally horizontal path whereby the air and cleansing agent enter a cleansing agent collection zone rather than the cleansing agent falling back in any significant quantity towards the inlet of the washing chamber.The sharp changes in direction in the flowpath to the collection zone ensure that the air is thoroughly washed by the cleansing agent to remove overspray particles and droplets from the air. The distribution plate of the washing chamber is, owing to its continuous curve, and owing to the fact that it extends across the full width of the spraybooth, a relatively complex, and thus expensive component to manufacture, and it is an object of the present invention to provide a spraybooth in a more simple, convenient and thus financially economic form.

According to the present invention, in a spraybooth of the kind specified, the distribution plate of the washing chamber, against which the cleansing agent stream entrained by the air entering the chamber in use first impinges, is defined by first and second intersecting planar surfaces, said first and second planarsurfaces being disposed generally at right angles to one another and extending with their line of intersection horizontal, widthwise of the spraybooth, the first, lowermost surface extending from below the cleansing agent level of the tank rearwardly and upwardly, and the second, uppermost surface thus extending upwardly and forwardly.

Preferably said first surface is disposed at approximately 18 degrees to the horizontal.

Conveniently said first and second surfaces are surfaces of respective sheet metal components.

Desirably said sheet metal components have integral strengthening flanges turned down from said surfaces.

Preferably the two components are interconnected by securing the turned down flanges of one of the components to said surface of the other component.

In the aforementioned known form of spraybooth of the kind specified the air is drawn upwardly through the booth from the cleansing agent collection zone and is caused to flow around a series of downwardly inclined eliminator plates which trap any cleansing agent droplets being carried upwardly by the airflow. The cleansing agent droplets captured by the eliminator plates coalesce on the plate and drip from the plates back into the collection zone. The collection zone overlies the cleansing agent tank and comprises a collector plate occupying the full width of the booth and extending rearwardly from the upper edge of the washing chamber distribution plate in a downwardly inclined orientation to the vertical rear wall of the booth.At its lower edge, that is to say the edge remote from said distribution plate the collector plate has a number of apertures spaced along the width of the booth, through which the collected cleansing agent containing overspray particles and droplets drains. The apertures communicate with guide channel members in the tank which direct the flow of collected cleansing agent first downwardly from the collection zone, and then forwardly across the base of the tank towards the front of the tank. The overspray particles thus settle in the tank in the region of the channel members.

It will be recognised that the fabrication of the collector plate and guide channel members utilizes considerable quantities of metal sh3et, and is a complex exercise, thus generating a significant proportion of the materials cost and the manufacturing cost of the spraybooth. Moreover, the effect of the guide channel members in concentrating the settlement of overspray sludge in the region of the channel members is disadvantageous in that it is necessary periodically to spread the settled sludge more evenly overthe base of the tank so that the flow of cleansing agent in the tank is not impeded. It is a further object of the present invention to provide a spraybooth wherein these disadvantages are minimised.

Preferably in a spraybooth according to the present invention as defined above the top of the cleans ing agent tank is open across substantially the whole width, and substantially the whole depth of the spraybooth, whereby cleansing agent passing with the airflow through the washing chamber falls directly back into the open top of the cleansing agent tank.

In the accompanying drawings; Figures 1, 2 and 3 are illustrative of a known construction of spraybooth; Figure 1 being a diagrammatic perspective representation of part of a known form of spraybooth; Figure 2 being a transverse sectional view of the part of the booth shown in Figure 1; Figure 3 being a sectional view along the line 3-3 in Figures 1 and 2; Figures 4 and 5 illustrate a spraybooth in accordance with one example of the present invention; Figure 4 being a diagrammatic perspective view similar to Figure 1; Figure 5 being a transverse sectional view similar to Figure 2.

Referring first to Figures 1,2 and 3 of the drawings it can be seen thatthe known form of spraybooth is a relatively complex structure comprising a sheet metal tank 11 occupying the full width, and the full depth of the spraybooth. The tank 11 in use contains a cleansing agent in liquid form, conveniently an emulsion of oil and water together with a small quantity of free oil which floats on the surface of the emulsion in the tank. The oil can conveniently be ordinary lubricating oil, and the water is treated to render it alkaline. This particular cleansing agent is particularly suited to dealing with air contaminated with paint spray droplets.

The rearwall 12 of the tank is extended upwardly to define the rear wall of a washing chamber 13. The front wall 14 of the chamber 13 is parallel to the rear wall 12 and terminates, at its lower end, just short of the normal liquid level of the tank 11. Additionally the front wall 14 of the chamber 13 is displaced rearwardly from the front wall of the tank 11. Thus an area 15 of the liquid surface is exposed between the front edge of the tank and the front face of the wall 14. The area of the spraybooth to the front of the wall 14 is usually designated the spraying compartment or station, and it is adjacent, or over the surface region 15 that spraying is intended to take place.

It will be recognised that since the wall 14 terminates above the liquid level in the tank 11 then across the whole width of the spraybooth an orifice is defined between the liquid level and the wall 14.

An inclined plate 16 extending across the full width of the booth extends from beneath the liquid level at the front of the wall 14, rearwardly beneath the wall 14 to emerge above the liquid level to the rear of the wall 14. The plate 16 is then bent in a continuous curve about a generally horizontal axis to produce a curved distribution plate 16a positioned to the rear of the wall 14. Immediately beneath the lower edge of the wall 14 the plate 16 is immersed in the cleansing agent. The distribution plate 16a presents its concave surface to the rear surface of the plate 14.

Extending rearwardly from the plate 14 and inclined downwardly towards the rear wall 12 is a deflector plate 17. The deflector plate 17 is positioned above the uppermost edge of the distribution plate 16a.

When a spraying operation is in progress a fan is energised to draw air upwardly through the chamber 13. Since air can only enterthe chamber 13 beneath the wall 14 then itwill be recognised that air passes beneath the wall 14 at high speed. Thus the surface of the cleansing agent immediately beneath the wall 14 is subject to considerable drag, and since the air velocity is high a turbulent and broken stream of cleansing agent is drawn from the tank along the distribution plate 16a and is swirled by the distribution plate 16a upwardly onto the rear of the wall 14 adjacentthe deflector plate 17.This region of the spraybooth is known as the washing or scrubbing area, and in this region the turbulent and broken stream of cleansing agent effects a washing action on the air stream which is being drawn from the spraying station into the washing chamber 13. During the spraying operation most of the paint which is sprayed will contact and stick to the article to be painted. Inevitably however there will be a degree of overspray. It is of course extremely desirable both in the interests of cleanliness, and operator safety, for the overspray droplets and particles to be removed from the spraying station.This removal is effected bythe airflow from the spraying station into the chamber 13, and as the air, laden with overspray droplets passes into the washing or scrubbing area the overspray droplets are washed from the air by the turbulent and broken stream of cleansing agent.

The oil component of the emulsion constituting the cleansing agent coats each of the overspray droplets with an oil film thus minimising coagulation of the droplets and also minimising any tendency for the droplets to stick to the inner surfaces of the spraybooth. The alkaline nature of the water component of the emulsion effects a chemical action on the resins in the paint to remove the "stickiness" of the resins thus in effect converting the stick spray droplets into non-sticky particles. The flow of air through the washing area is such that the stream of cleansing agent, now containing the overspray particles, is swept up onto the rear surface of the wall 14 and onto the deflector plate 17 from whence it is deflected rearwardly into the base of the chamber 13. Thus substantially no liquid falls back through the washing area and a continuous supply of cleansing agent is drawn from the front region of the tank 11. By the time the air stream reaches the base of the chamber 13 its speed is of course reduced by comparison with its speed entering and passing through the washing area. Thus the cleansing agent is no longer supported by the slower airflow, and falls under gravity into the collection zone of the spraybooth. The collection zone 18 is at the bottom of the chamber 13 and includes a collection plate 19 which occupies the full width of the booth, and which extends rearwardly from the upper edge of the distribution plate 16a to the rearwall 12 ofthe booth.The collection plate 19 is inclined downwardly towards the rear of the booth, and thus all of the contaminated cleansing liquid falling into the collection zone 18 is guided by the collection plate 19 to a position adjacent the rear wall 12 of the booth.

At intervals along the width of the booth the rear edge of the plate 19 is formed with apertures 21 through which the cleansing liquid drains. Each aperture 21 communicates with a channel shaped member 22 which initially extends vertically downwardly from the aperture 21 and defines with the rearwall of the tank a rectangular pipe. The channel shaped members 22 then curve around the lower rear corner of the tank and extend forwardly towards the front edge of the tank. In fact the channel shaped members extend slightly upwardly so that their lowermost edges diverge from the base of the tank.

Thus cleansing agent falling into the collection zone is returned to the tank 11 by way of the channel members 22 which guide the flow of returned cleansing agent to the front region of the tank. As the cleansing agent passes along its respective channel member 22 the now treated overspray particles settle in the form of a sludge.

This form of spraybooth is known, and is described in more detail in our British Patent No.

941,054. Although not shown in Figures 1,2 and 3 it is usual to provide at intervals along the vertical height of the chamber 13, eliminator plates around which the air from the collection zone 18 must flow.

The eliminator plates trap any droplets of cleansing agent which are still entrained by the airflow, and such droplets as are captured by the eliminator plates coalesce on the eliminator plates and ultimately drip back into the collection zone. Thus the air leaving the upper end of the chamber 13 is free of overspray droplets or particles, and is substantially moisture free also.

Booths of the kind described above have been manufactured and utilized successfully for a number of years, and have been thought to be the optimum in terms of constructional and operational efficiency.

However, it is clearthatthe curved distribution plate 16, 16a is a relatively complex and expensive item to produce and the collection zone arrangement including the plate 19 and the channel members 22 are also expensive both in manufacturing costs, and in material cost. Nevertheless, it has been believed that these areas of the booth are not susceptible to modification without sacrificing the efficiency of the booth.

Surprisingly it has now been found that improve menus can be made in both of these areas of the conventional booth without sacrificing efficiency.

One example of the present invention is illustrated in Figures 4 and 5 where it can be seen that the construction of the tank 11 and front and rear walls 12, 14 of the chamber 13 are unaltered. The complex and expensive curved distribution plate 16, 16a is however replaced by a distribution plate assembly comprising first and second planar plates 36, 36a.

Both of the plates 36, 36a are extremely simple and cheap flat metal pressings, each of the plates having strengthening flanges turned down at right-angles from the plane of the plate at the longitudinal edges of the plates. The two plates 36, 36a are inter connected so as to lie substantially at right-angles to one another by fastening one of the strengthening flanges of the plate 36 to the face of the plate 36a. As with the plate 16, 1 6a the distribution plate assembly 36, 36a is secured to the booth by being fastened at its ends to the side walls of the booth. The plate 36 is disposed at a small angle, fcr example 18 degrees, to the horizontal and thus since the plate 36a lies substantially at right-angles to the plate 36 then the plate 36a will be inclined at about 18 degrees from the vertical, in a forward direction.It might be expected that in use the distribution plate assembly 36, 36a would not prove so efficient in guiding the turbulent and broken stream of cleansing agent as the smoothly curved plate 16, 16a of the known construction. Surprisingly howeverthis proves to be untrue, and not only is the washing action as efficient in a booth using the combined distribution plate 36, 36a but also it is found that the operational efficiency of the booth is increased in that a fan of significantly reduced power can be used to draw air through the booth. Thus not only does the replace ment ofthe plate 16, 16a by the planar plates 36, 36a effect a significant reduction in the cost of the booth, but it also entails an improvement in efficiency whereby the power of the air fan can be reduced.

Returning briefly to the known construction of spraybooth illustrated in Figures 1,2 and 3, it has for a number of years been thought that the cleansing agent collection arrangement is essential in that it ensures an adequate flow of cleansing agent back to the front of the tank in readiness to be drawn through the gap between the plate 14 and the plate 16 into the washing chamber. However, again surprisingly in accordance with the present invention it is found thatthe plate 19 and the channel members 22 can be omitted without reducing the efficiency of the booth.Thus in accordance with the example of the present invention illustrated in Figures 4 and 5 the tank 11 is completely open to the rear of the distribution plate assembly 36, 36a and the cleansing agent diverted by the deflector plate 17 falls back immediately into the tank at the rear of the plate assembly 36, 36a. It will be noted that by comparison with the construction shown in Figure 2 the deflector plate 17 of the construction shown in Figure 5 is increased in length. This deflector plate 17, which extends at 30 degrees to the horizontal, is arranged to be of sufficient length of extent rearwardly from the wall 14 to occupy half of the depth (front to rear) of the chamber 13. Thus while there is a slight additional material cost in the production of the larger deflector plate 17 this slight extra cost is more than offset by the saving arising from dispensing with the collection plate 19 and channels 22. Furthermore, where in the known arrangement there may be as many as three eliminator plates spaced along the height of the chamber 13, it is found that using the larger deflector plate 17 in the arrangement of Figures 4 and 5, only a single eliminator plate in the chamber, above the deflector plate 17 and inclined in the opposite direction, is required. Usually however a second eliminator plate will be provided as a safeguard against liquid droplets being carried with the airflow out of the apparatus.

A further significant advantage is found to be attendant upon the removal of the channels 22. In the known construction utilizing the channel members 22 the sludge of treated overspray particles tend to collect adjacent the channel members 22 and periodically it is necessary for an operative to spread the sludge more evenly over the base of the tank 11 to achieve a maximum operating time before it becomes necessary to shut down the booth in in orderto remove the collected sludge from the tank.

With the completely open return arrangement of Figures 4 and 5 the periodic levelling of the sludge is of course not required, since by the natural action of the booth the sludge becomes evenly distributed across the full width of the base of the tank as it collects in the tank. Thus although the operational period before it becomes necessary to clean the sludge from the tank is not extended by comparison with the previous arrangement, there is no need to interrupt the operation of the booth to perform a sludge levelling operation.

It will be recognised that while the maximum advantage over the known arrangement is achieved by employing both features described with reference to Figures 4 and 5, that is to say the replacement of the curved plate 16, 16a bythe plate assembly 36, 36a, and the dispensing with the collection plate 19 and channel members 22. Nevertheless, significant advantages can be achieved by the substitution of the plate assembly 36, 36a for the curved plate 16, 16a without dispensing with the collection plate 19 and the channel members 22. Such a construction would be a significant advance over the known construction of Figures 1,2 and 3.

Claims (10)

1. A spraybooth, particularly but not exclusively, for use in a paint spraying installation wherein air, in use contaminated with overspray particles or droplets, is drawn from a spraying area into a washing chamber, at high speed over the exposed surface of a liquid cleansing agent contained by a tank, the air entraining liquid cleansing agent, and within the washing chamber the overspray particles or droplets being washed from the airflow by the entrained cleansing agent, the washed air passing out of the spraybooth, and the cleansing agent containing the contaminants being returned to the tank wherein the contaminants settle in the form of a sludge and wherein the distribution plate of the washing chamber, against which the cleansing agent stream entrained by the air entering the chamber in use first impinges, is defined by first and second planar surfaces being disposed generally at right-angles to one another and extending, with their line of intersection horizontal, widthwise of the spraybooth, the first, lowermost surface extending from below the cleansing agent level of the tank rearwardly and upwardly, and the second, uppermost surface thus extending upwardly and forwardly.

2. A spraybooth as claimed in claim 1, wherein said first surface is disposed at approximately 18 degrees to the horizontal.

3. A spraybooth as claimed in claim 1 or claim 2, wherein said first and second surfaces are surfaces of respective sheet metal components.

4. A spraybooth as claimed in claim 3, wherein said sheet metal components have integral strengthening flanges turned down from said surfaces.

5. A spraybooth as claimed in claim 4, wherein the two components are interconnected by securing the turned down flange of one of the componetsto said surface of the other component.

6. A spraybooth as claimed in anyone of claims 1 to 5, wherein the top of the cleansing agent tank is open across substantially the whole width, and substantially the whole depth of the spraybooth, whereby cleansing agent passing with the airflow through the washing chamber falls directly back into the open top of the cleansing agent tank.

7. A spraybooth as claimed in claim 6, wherein a deflector plate extending rearwardly of the spraybooth from the front wall of the washing chamber is so dimensioned as to occupy at least half of the distance between the front and rear walls of the washing chamber.

8. A spraybooth as claimed in claim 6 or claim 7, wherein only a single eliminator plate is positioned above the tank in the airflow from the washing chamber.

9. A spraybooth as claimed in claim 6 or claim 7, wherein only two eliminator plates are positioned above the tank in the airflow from the washing chamber.

10. Aspraybooth substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.