GB2066701A

GB2066701A - Electrostatic paint spraying pistol having a rotary atomiser

Info

Publication number: GB2066701A
Application number: GB8041622A
Authority: GB
Original assignee: Mueller Ernst & Co
Current assignee: Mueller Ernst & Co
Priority date: 1980-01-02
Filing date: 1980-12-31
Publication date: 1981-07-15
Also published as: SE441650B; JPH0147230B2; JPS56161856A; DK554880A; DE3000002A1; FI68983C; FR2472954B1; BR8008618A; DK149975B; FI804045L; SE8009152L; GB2066701B; FR2472954A1; DK149975C; FI68983B; DE3000002C2

Abstract

An electrostatic paint spraying pistol having a rotary atomiser, the atomiser including a boss (14) substantially in the shape of a mushroom, the boss being seated on the free end of a rotatable shaft (12) and the pistol having an atomiser bell (15) which is mounted on and coaxially surrounds the boss. Paint is supplied through a first pipe (16) and a second pipe (20, 21) is provided to supply washing liquid. The second pipe has two outlet openings (22, 23) of which one is arranged to discharge on the back (14a) of the boss and of which the other is arranged to discharge substantially centrally on the front (14b) of the boss, so as to achieve a swift and thorough washing of the atomiser without dismantling so that another coloured paint, for example, can be used directly after. <IMAGE>

Description

SPECIFICATION Electrostatic paint-spraying pistol having a rotary atomiser This invention relates to an electrostatic paintspraying pistol having a rotary atomiser.

Such an atomiser is known which has a boss substantially in the shape of a mushroom, the boss being seated on a free end of a rotatable shaft of the pistol, the pistol also having an atomiser bell which is mounted on and coaxially surrounds the boss. Paint is applied through a paint supply pipe to the back of the boss, distributed from the outside edge thereof by centrifugal force on to the internal surface of the bell and sprayed from the edge of the bell.

Paint-spraying pistols having such rotary atomisers have long been known and are used in many fields. In operation, it is not possible to avoid the atomiser head having to be freed from time to time from paint residues, i.e. having to be cleaned.

The general procedure in such a case is for washing liquid containing a solvent to be supplied through the paint pipe, and in fact with the atomiser head rotating. This washing of the atomiser head is of particular importance when it is necessary to change over from one paint to another. However, it has been found in practice that paint residues, after switching off the pistol, are not only formed along the actual path of the paint, i.e. on the back of the boss and the internal surface of the bell, but also on the front side of the boss, it then not being possible for these residues to be affected by the washing liquid following the paint path or route.The origin of the paint deposit on the front side of the boss is that reduced pressures are set up in the interior of the paintspraying cone, more especially with atomiser heads running at a speed higher than about 4000 r.p.m., with the consequence that some of the atomised droplets of paint are drawn inwardly and are transported opposite to the spraying direction on to the front surface of the boss. In order that these paint residues may also be removed, the front side of the boss either has to be cleaned manually or the residues have to be "washed off" from the front with a jet of washing liquid, both operations precluding an automatic operation of the pistol having automatic colour change.

According to the present invention, there is provided an electrostatic paint-spraying pistol having a rotary atomiser, the atomiser including a boss substantially in the shape of a mushroom, the boss being seated on the free end of a rotatable shaft of the pistol and the pistol having an atomiser bell which is mounted on and coaxially surrounds the boss, there being a first pipe to supply paint to the back of the boss, from whence paint is distributed, in use, from the outer edge of the boss and by centrifugal force on to an internal surface of the bell and sprayed from the edge of the bell, and there being a second pipe to supply washing liquid, which latter pipe has two outlet openings, of which one is arranged to discharge on the back of the boss and of which the other is arranged to discharge substantially centrally on the front of the boss.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which the single figure shows a section through a front portion of a paint spray pistol having a rotary atomiser and being able to spray different coloured paints in succession.

The figure shows the front end of a tube or barrel 10 of a paint-spraying pistol. The barrel 10 is closed by a plate 11 , through the centre of which extends a rotatable shaft 12. The shaft 12 is driven by a compressed air motor 13, which is only indicated diagrammatically, and is seated in the pistol barrel 10 and carries at its free end a boss 14 which is substantially in the shape of a mushroom. An atomiser bell 1 5 is fixed on the boss 14 and coaxially surrounds it. A paint-supply pipe 1 6 extends through the wall of the pistol barrel 10, and a valve 17 is provided to regulate paint supply through the pipe 16. A nozzle 1 6a of the paint-supply pipe is directed towards the rear side 1 4a of the boss 14.Supply of high-voltage electrical energy to the atomiser bell 1 5 to facilitate atomisation of the paint is, for example, achieved through the rotatable shaft 12 or through some other electric supply line which is not shown.

In use, the shaft 12, together with the boss 14 and bell 15, are set in rotation by the motor 13, the high voltage is switched on and the valve 17 is opened. Paint then flows, under low pressure, through the pipe 16 and is sprayed through the nozzle 1 6a on to the rear side 1 4a of the boss 14.

The paint is distributed thereon because of the centrifugal force provided by the rotating boss and is projected outwardly on to the inside surface 15a of the bell 1 5. From the latter, the paint travels as a film to the edge of the bell and is sprayed oFF the latter under the action of the centrifugal force and of the electrostatic field and transported to a workpiece (not shown). The speed of rotation of the atomiser head may, for example, be from 20,000 to 40,000 r.p.m.

The wall of the pistol barrel 10 is also provided therein with a supply pipe 1 8 with an associated valve 19. The pipe 18 is continued by way of a bore 20 in the plate 11 and opens into an annular passage 21 between the shaft 12 and boss 14.

From the annular passage 21, an annular gap 22 leads to the rear side 1 4a of the boss 14 and bores 23 extend along the periphery of the shaft 12 as far as an indentation 24 on the front side 14b of the boss 14.

The pipe 18 serves for the supply of washing liquid. If the valve 1 9 is opened, then washing liquid passes through the pipe 1 8 and the bore 20 into the annular passage 21. From the annular passage 21, some of the washing liquid flows through the gap 22 on to the rear side 1 4a of the boss and is distributed thereon by a stepped edge 1 4c uniformly over the rear side 14a, from whence the liquid then reaches the inside 15a of the bell 1 5 and is sprayed off the rim thereof.The remainder of the washing liquid flows from the annular passage 21 through the bores 23 into the indentation 24 and is distributed from thence over the front surface 1 4b of the boss 14, whereupon also the washing liquid which has taken this route then reaches the internal surface 15a and is sprayed off the rim of the bell 1 5. Thus, the washing liquid which flows through the gap 22 is to serve for cleaning the back 1 4a of the boss 14, and the washing liquid which flows through the bores 23 is to serve for cleaning the front of the boss 14; all of the washing liquid flows over and cleans the internal surface 1 5a of the bell 15.

The annular passage 21 distributing the washing liquid towards the two outlet paths is in addition connected to the compressed air motor 13 through an annular gap 25 extending longitudinally of the shaft 12, the result thereby being obtained that compressed air passes into the passage 21 and assists the discharge of the washing liquid. However, an additional, important advantage is also achieved by the compressed air being guided in this way.During the spraying of the paint, i.e. with the valve 17 open and the valve 1 9 closed, a small amount of compressed air flows through the annular gap 25, the annular passage 21 and the bores 23 into the indentation 24, with the result that the reduced pressure or vacuum forming in front of the boss 14 is decreased and thus the tendency for paint to be deposited on the front side 1 4b of the boss is reduced; it is additionally thereby assured that substantially no deposit of paint can be formed in the indentation 24 itself.

Practical tests have shown that, when the valve 19 is opened to supply washing liquid, the rotary atomiser is very quickly and very thorouqhly cleaned, so that it is possible after a short time once again to close the valve 19 and to re-open the valve 1 7 for continuance of the paint-spraying operation, and in fact also if a different paint is being used. Even in the formerly very critical cases of spraying metal-pigmented lacquers, very good results are produced, more especially when solvent is supplied at certain time intervals, so that any drying of metal pigments on the spraying head is avoided. It is obvious that the washing operations can be made automatic, because it is only necessary for the two valves 1 7 and 1 9 to be suitably controlled.

The construction of the supply means for the washing medium along the motor shaft may be modified in that channels or grooves can be provided. Also, the washing operation can be carried out in conjunction with known washing sleeves which enable the washing medium to be recovered.

When spraying dispersion lacquers and watersoluble lacquers, the problem exists that the lacquer particles already dry out before reaching the workpiece, and this substantially impairs the adhesion of the particles on the workpiece. On the other hand, it is impossible, however, to dilute such lacquers so strongiy with water that a premature evaporation of the water is completely avoided. Accordingly, assistance has hitherto been obtained in this connection by the spraying being undertaken in a very humid atmosphere, i.e. a relative air humidity of at least 60% is maintained at comparatively great expense in a spraying cabin. By means of the present pistol, this problem can now be solved simply, achieved in fact by the additional supply pipe 1 8 being connected to a water supply pipe during the spraying operation, with the consequence that a fine water mist is sprayed from the boss 14 and this mist prevents the drying out of the lacquer particles leaving the edge edge 15a. In similar manner, it is possible to use so-called APS systems (Aqua-Powder Suspension) during the spraying; in this case, the powder is sprayed from the spraying edge 15a and the water from the boss 14. For washing the spraying head after the spraying operation, the pipe 18 is then once again connected to a supply of washing medium.

Claims

1. An electrostatic paint spraying pistol having F arotary atomiser, the atomiser including a boss substantially in the shape of a mushroom, the boss being seated on the free end of a rotatable shaft of the pistol and the pistol having an atomiser bell which is mounted on and coaxially surrounds the boss, there being a first pipe to supply paint to the back of the boss, from whence paint is distributed, in use, from the outer edge of the boss and by centrifugal force on to an internal surface of the bell and sprayed from the edge of the bell, and there being a second pipe to supply washing liquid, which latter pipe has two outlet openings, of which one is arranged to discharge on the back of the boss and of which the other is arranged to discharge substantially centrally on the front of the boss.

2. A paint spraying pistol as claimed in claim 1, wherein said second pipe includes an annular passage surrounding said rotatable shaft, said annular passage extending between said rotatable shaft and said boss and leading to one of said outlet openings, which is formed by an indentation in the front of the boss.

3. A paint spraying pistol as claimed in claim 2, wherein an annular gap leads from said annular passage to the other of said outlet openings, which faces the back of said boss.

4. A paint spraying pistol as claimed in claim 2 or 3, wherein said annular passage is constituted by bores extending along the rotatable shaft where the shaft passes inside said boss, and there being a further bore leading away from said annular passage, through which latter bore washing liquid is intended to be supplied.

5. A paint spraying pistol as claimed in claim 2, 3 3 or 4, wherein a compressed air motor is provided to drive said shaft and an air path is provided to supply some of the compressed air to said annular passage.

6. A paint spraying pistol as claimed in claim 5, wherein said compressed air motor is situated in a barrel of the pistol, said barrel being closed by a plate through which said shaft extends, a gap being provided between said shaft and said plate so as to provide said air path.

7. A paint spraying pistol as claimed in any one of the preceding claims, wherein the back of said boss is provided with a stepped edge to facilitate distribution of washing liquid over the back of the boss.

8. A paint spraying pistol as claimed in any one of the preceding claims and having means to connect said second pipe to two separate supply sources, one of the sources being intended to supply washing liquid and the other of the sources being intended to supply water or another solvent through said second pipe so that this water or other solvent can be sprayed concurrently with the paint being supplied through said first pipe.

9. An electrostatic paint spraying pistol having a rotary atomiser, substantially as hereinbefore described with reference to the accompanying drawing.