US3700389A

US3700389A - Spraying booth

Info

Publication number: US3700389A
Application number: US40592A
Authority: US
Inventors: Maurice Paul Wanner; Neil Rudolph Wallis
Original assignee: Aerocoat SA
Current assignee: Aerocoat SA
Priority date: 1969-06-25
Filing date: 1970-05-26
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: CH511066A; JPS4829297B1; AU1534370A; GB1265949A

Abstract

A spraying booth for facilitating the recovery of the surplus of pulverulent material used to coat an object includes at the rear means for enabling it to communicate with an air extraction installation. The booth is open at the front to give access to the gun, and is provided with a plurality of rotatable blades which when rotated into a first transverse plane move air uniformly through the rear of the booth and when rotated into a second perpendicular position may be returned to the interior of the booth without disturbing the air in the booth.

Description

United States Patent Wanner et a].

SPRAYING BOOTH Inventors: Maurice Paul Wanner, Geneva, Switzerland; Neil Rudolph Wallis, Goring on Thames, England Ass'ignee: Aerocoat S .A., Geneva, Switzerland Filed: May 26, 1970 Appl. No.: 40,592

Foreign Application Priority Data June 25, 1969 Switzerland ..9700/69 us. Cl. ..ss/413,'9s/11'o, 98/115 SB,

ll8/3l2,4l6/lO9,416/ll5 Int. cl..- ..B01d 49/00, F23j 1 1/00 Field of Search.....98/l l5 SB, 110; 416/101, 93, 1

416/109,, H0, H2, 111,98, 115; 55/415, 385,413; ll8/309,312

45] Oct. 24, 1972 [56] References Cited UNITED STATES PATENTS 1,794,764 3/ 1931 Goethe] ..98/l l5 SB 2,293,065 8/1942 Kiczales.'. ..98/1 10 2,449,203 9/1948 Clark et al ..98/1 15 SB Primary Examiner--Robert L. Lindsay, Jr. Attorney-Molinare, Alegretti, Newitt & Witcoff [57] ABSTRACT A spraying booth for facilitating the recovery of the surplus of pulverulent material used to coat an object includes at the rear means for enabling it to communicate with an air extraction installation. The booth is open at the front to give access to the gun, and is provided with a plurality of rotatable blades which when rotated into a first transverse plane move air uniformly through the rear of the boothand when rotated into a second perpendicular position may be returned to the interior of the booth without disturbing the air in the booth.

8 Claims, 3 Drawing Figures 1 SPRAYING noorn BACKGROUNDOFTHE INVENTION the object to be coated is usually placed in a booth,

open at the front to give access to the gun.

However, the various air currents which manifest themselves'near the opening of the e.g., the air currents that are to be found in any workshop or those that are set up under the convection effect of the operators body, cause a rather substantial amount of pulverulent material to be drawn out of the booth and to be disserninatedin the atmosphere of the workshop, instead of depositing on the base of the booth. To remedy this drawback, the rear of the booth is usually connected to an air extraction installation the effect of v which is to establish a negative pressure in the booth thereby tending to prevent the particles of pulverulent material from leaving the booth through the opening at ingup on the base of the booth. In order to recover the material that is entrained with the air, the extraction installation must be fitted with rather complex filtering apparatus in view not only of the amount of excess material to be recovered but also because of the low grain size of the particles (of theorder of a few microns).

An object of the present invention is to produce a spraying booth which eliminates, at least to a large extent, of the above-mentioned drawbacks.

SUMMARY OF THE INVENTION The booth provided by the invention includes at the rear means for enabling it to communicate with an air extraction installation, is open at thefront to give access to the gun, and comprises means for moving the air in the booth rearwards substantially uniformly along a substantially planar, vertical front.

With these means, the counter currentsmentioned earlier no longer manifest themselves,or only slightly, along the side walls of the booth so that the velocity that is imparted to the air aspirated by the extraction installation may be substantially reduced, thus enabling the major proportion of the excess material particles to be deposited on the base of the booth and in particular enabling the amount of excess material to be reduced in relation to the amount of material efi'ectively used on the object to be coated.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying diagrammatic drawing:

FIG. 1 is a perspective view of a preferred form of embodiment of the spraying booth provided by the invention;

FIG. 2 is a plan view of the booth shown in FIG. 1; and

FIG. 3 is a partial view, in plan and to a larger scale, of a mechanism used in the booth of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the spraying booth illustrated in the drawings, the rear wall 10, the

side walls

12 and 14 and the ceiling 16 are of insulating material, e.g., glass fiber, whereas the base 18 is of conductive material, e.g., aluminum, that is grounded. The object to be coated, e.g., a metal chair 20, is suspended by a metal hook 21 to a transverse rodv 22, of conductive material, which is secured to the

side walls

12 and 14 and which is grounded.

To coat the chair 20 with a layer of pulverulent material by means of an electrostatic gun, the operator stands before the booth, which is open at the front, and aims the gun at the chair. Upon actuation of the gun, pulverulent material is fed under pressure to the head of the gun where the particles are charged by means of a high-voltage direct-current source to which the gun is connected in order to be moved towards the chair 20, the latter being the conductive object nearest thegun head.

To recover the excess pulverulent material that has not adhered to the chair and to prevent this excess material from being drawn out, as explained earlier, the

- booth is, on the one hand, connected to an air extraction installation and is, on the other hand, fitted with means promoting air displacement towards the extraction installation.

The connection between the booth and the air extraction installation (not shown) is established through holes 24 formed in the rear wall 10, which holes open out into a chamber'26 located behind the wall 10 and communicating through a horizontal series of holes that are not visible with a semi-cylindrical collector 28 connected to a discharge conduit 30.

As for the means promoting air displacement towards the extraction installation, or more exactly towards the holes 24, they comprise a series of vertical blades 32, e.g., eight, which are suspended by spindles 34, rigid therewith, to a horizontal cross-bar 36 lying parallel to the wall 10 and resting at its ends on supports consisting of horizontal rails 38 fixed to the

side walls

12 and 14 near the ceiling 16.

The cross-bar 36 is moreover suspended by a rod 40, extending through a slot 42 formed in the middle of the ceiling 16, to a trolley 44 mounted on rails 46 fixed to the-ceiling on opposite sides of the slot 42, parallel to the'rails 38.

Rails

38 and 46 extend over slightly less than the depth of the booth, between the wall 10 and the rod 22, the latter lying here about halfway between the opening of the booth and the wall. 10. These

rails

38 and 46 enable the cross-bar 36 and the trolley 44, and hence the blades 32, to be reciprocated by means of a jack 48 which is secured to the ceiling 16 in alignment with the slot 42 and whose rod 50 is secured to the trolley 44.

When the blades 32 are moving towards the wall 10, they occupy the positions shown in FIG. 1, i.e., parallel to the wall 10, so that they may entrain the air in the booth towards the holes 24, over the entire width and almost over the entire height of the booth.

In order that the blades should not subsequently cause air to flow in the opposite direction during the return stroke of the blades, means are provided to rotate them through 90 at the end of the inward stroke so as to bring them into the position shown by the dotted lines in FIG. 3. These means must of course also be able to rotate them once again through 90 to return them to their initial operative position at the end of the return stroke in readiness for the next inward stroke.

These means consist of a mechanism shown in FIG. 3 which cooperates with two pairs of

cams

52 and 54 fixed to the underside of the ceiling 16 near the opposite ends of the slot 42. As shown in FIG. 3, the blades 32 are attached to the cross-bar 36 (which is, as will be observed, hollow) by means of spindles or shafts 34 to which the blades 32 are rigidly attached. The stem or rod 40 comprises means by which the cross-bar 36 is suspended from the trolley 44. The mechanism is located inside the crossbar 36 and consists of a sliding rod 56 on which are secured, on the one hand, two pins 58 extending through two slots (not shown), formed in the top of the cross-bar 36 lengthwise thereof, so that they may come into engagement with the

cams

52 and 54, and, on the other hand, a series of pegs 60 which engage each in a slot 62 formed in an eccentric cam member 64 rigidly attached to each spindle 34.

Thus, when the cross-bar 36 reaches the end of an inward stroke, towards the wall 10, the two pins 58 come into engagement with the two earns 54 to cause the rod 56 to slide to the left over a distance such that the members 64 and the blades 32 may be moved to the positions illustrated by dotted lines through the intermediary of the pegs 60 and of the slots 62, and when the cross-bar 36 reaches the end of a return stroke, the two pins 58 come into engagement with the two cams 52 to return therod 54, together with the parts 64 and the blades 32, to their starting positions.

To facilitate the reciprocating motion of the crossbar 36 and of the trolley 44, the trolley is preferably fitted with rollers cooperating with the

rails

38 and 46. The rails are moreover preferably angled so as to have side faces against which the cross-bar and the trolley can abut, e.g., through the intermediary of horizontal rollers; in particular during the sliding displacements of the rod 56.

In order to reduce friction between the spindles 34 and the cross-bar 36, rolling element bearings are preferably provided where required, in particular beneath the members 64, subject to slight modification of the arrangement as shown in FIG. 3.

By so displacing the blades 32, the air is thus made to move towards the holes 24 substantially uniformly along a substantially planar, vertical, front. As a result the air can have a relatively low displacement velocity (of about, say, meters per minute) in the vicinity of the chair and still be able to achieve sufficient velocity near the opening of the booth, and more particularly near the edges of this opening, for there not to be any counter air currents liable to extract pulverulent material out at the front.

This relatively low displacement speed of the air in the vicinity of the chair 20 enables a larger proportion of the pulverulent material being sprayed in the course of a coating operation to be deposited on the chair 20 and further enables the excess material that has not adhered to the chair to deposit to a large extent on the base 18 rather than be entrained out of the booth via the holes 24. The fact that the base 18 is made of conductive material and is grounded helps this depositing action also. This latter action is moreover further helped by the fact that the diameter of the holes 24 decreases from the top downwards, as can be seen from FIG. 1.

It is preferred that the volume of air extracted from the booth through the holes 24 be equal to the volume of air displaced by the blades 32.

Because it may at times be desirable to modify the speed with which the air must be extracted from the booth to suit particles of different sizes, and hence also the speed at which the blades 32 move towards the wall 10, it is recommended to provide control means for simultaneously adjusting to the required extent the motor of the extraction installation and the piston of the jack 48.

In order that the speed at which the mass of air displaced by the blades 32 should not slow down at each return stroke thereof, the jack 48 is preferably so adapted that the return strokes of the blades 32 should be carried out much more quickly than the inward strokes, e.g., ten times more quickly.

The spraying booth illustrated in the drawing can be varied in various respects. For instance, in order that the process for coating objects to be sprayed may be automated to a certain extent, rod 22 could be dispensed with, a transverse slot could be formed in the ceiling 16 and an endless chain could be provided which passes above the booth over the transverse slot and which is fitted with a succession of hooks successively passing through the booth along the slot. In order that the objects which are to be sprayed and which are to be carried by the hooks may enter the booth and subsequently issue therefrom, openings of suitable size are made in the

side walls

12 and 14. In such a variant, the jack 48 is placed on the other side of the trolley 44.

What is claimed is:

1. In a spraying booth of the type which includes an open front end by which spray material from a spray gun may enter said booth and have access to the interior of the booth and a rear end having means for communication with booth air extraction means, the improvement of a plurality of parallel blade elements mounted within said booth transverse to the direction of air flow from said open front through said rear end, and means for alternately translating said elements uniformly in a plane from the interior of said booth in a direction toward said rear end and thence back to the interior to substantially uniformly transport air within said booth from said booth through the rear end.

2. The improvement of claim 1 including means for rotating said blades from a substantially transverse plane whenever said blades are moved toward said rear end, said blades then being operative to uniformly transport air from said booth, to a position of less air transport when said blades are being moved from said rear end to the interior.

3. The improvement of claim 2 wherein the blades are suspended by spindles attached to a cross bar, .said cross bar being connected to a rod which extends and is supported through a slot formed in the ceiling ofthe booth.

4. The improvement of claim 3 wherein the rod extending through theslot in the ceiling of the booth is connected to a trolley mounted on the ceiling and wherein the means for alternately translating the blades comprises a piston and cylinder device acting on the trolley.

5. The improvement of claim 3 wherein the means for rotating the blades includes a sliding rod mounted on the cross-bar and co-operating with each of the spindles to cause them to rotate through 90 with each sliding motion of the rod, said rod co-operating with two cams against which said rod abuts through the intermediary of an abutment, one of said cams being engaged at the end of each operative stroke of the blades, the other of said cams being engaged at the end of each return stroke thereof.

6. The improvement of claim 1 including a rear transverse wall for said booth, said wall including holes having a greater diameter towards the top of said rear 7 transverse wall than the diameter of holes towards the

Claims

3. The improvement of claim 2 wherein the blades are suspended by spindles attached to a cross bar, said cross bar being connected to a rod which extends and is supported through a slot formed in the ceiling of the booth.

4. The improvement of claim 3 wherein the rod extending through the slot in the ceiling of the booth is connected to a trolley mounted on the ceiling and wherein the means for alternately translating the blades comprises a piston and cylinder device acting on the trolley.

5. The improvement of claim 3 wherein the means for rotating the blades includes a sliding rod mounted on the cross-bar and co-operating with each of the spindles to cause them to rotate through 90* with each sliding motion of the rod, said rod co-operating with two cams against which said rod abuts through the intermediary of an abutment, one of said cams being engaged at the end of each operative stroke of the blades, the other of said cams being engaged at the end of each return stroke thereof.

6. The improvement of claim 1 including a rear transverse wall for said booth, said wall including holes having a greater diameter towards the top of said rear transverse wall than the diameter of holes towards the bottom of the rear transverse wall.

7. The improvement of claim 1 wherein said booth includes a base made at least partially of conductive material which may be grounded.

8. The improvement of claim 1 wherein said means for alternately translating said blade elements includes means for moving said blade elements from the rear end to the interior faster than from said interior to said rear end.