GB1578086A - Electrostatic apparatus for spraying synthetic fibres - Google Patents

Description

(54) ELECTROSTATIC APPARATUS FOR SPRAYING SYNTHETIC FIBRES (71) We, HAJTÓMUVEK ES FES TOBERENDEZESEK GYARA, of Budapest XI, Fehervári ut 98, Hungary, a body corporate organised under the laws of Hungary, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to electrostatic apparatus for spraying synthetic fibres, comprising a housing in which an air transport device for the fibres fed into the apparatus and an electrical charging grid connected to a source of high voltage power supply are accommodated.

Spraying devices are customarily employed to apply synthetic fibres to a surface to be coated, which surface is coated with an adhesive before spraying. Known spraying devices operate on pneumatic or electrostatic principles, or a combination of the two.

In pneumatically operated spraying apparatus the synthetic fibres are conveyed by compressed air at a high speed to the surface coated with an adhesive material. A considerable drawback of this principle is that the fibres arrive to the tacky surface irregularly oriented and not perpendicularly to the surface.

Due to the disordered state of the fibres the coating obtained in this way cannot achieve the desired aesthetical effect. On the other hand, it is an advantage of pneumatic spraying that surfaces that are electrically screened may also be coated.

In electrostatic spraying apparatus the fibrous material is electrostatically charged and the fibres are applied to the surface coated with an adhesive with the aid of the attractive force existing between two poles of opposite polarity. Under electrostatic charging, however, the fibrous material cannot acquire a sufficiently high velocity to achieve the necessary depth of penetration of the fibres into the adhesive layer; consequently, the desired quality and durability of the coating are not achieved. A portion of the fibres may fall off the adhesive material. A further drawback of this method is that electrically screened surfaces cannot be coated in this manner.

Devices are already known in which electrostatic charging of the fibres is combined with pneumatically operated fibre transport.

Such combined apparatus is provided with a housing in which an air transport device for the fibres fed into the apparatus and an electrical charging grid connected to a high voltage power supply are accommodated. The compressed air agitates the material to be sprayed in the so-called feeding space located upstream of the charging grid, then the fibres passing through the charging grid are electrically charged and are considerably accelerated by the stream of compressed air to arrive at the surface of the object which has been coated with an adhesive material and which is either earthed or has a polarity opposite to that of the charging grid. This apparatus gives better results than the electrostatic or pneumatic spraying apparatus; however, it still has certain disadvantages. Thus the problem arises from the high velocity of the air flow which limits the magnitude of the electrostatic charge that can be transferred to the fibres and so the quality of the coating is still not fully satisfactory.

It is a common drawback of all known fibre spraying apparatus that the separation and the continuouss feeding of the fibres into the apparatus, the elimination of lumps and knots and efficient charging out of the fibres can only partially be achieved. The spraying output of known apparatus is low and therefore their application on an industrial scale is limited.

An aim of the present invention is to elim- inate, or at least to mitigate, the drawbacks described above and to provide an apparatus which ensures a high quality of coating of sprayed synthetic fibres independently of the shape and material of the object to be coated.

The invention is based on the discovery that this objective can be achieved in a combined electrostatic and pneumatic spraying apparatus for synthetic fibres by disposing upstream of the charging grid a classifying (sorting) device expediently a classifying grid, of a polarity opposite to the polarity of the charging grid.

According to the invention there is provided electrostatic spraying apparatus for spraying a workpiece with synthetic fibres, comprising a housing accommodating an air transporting device, an electrical charging grid connectable to a high voltage power supply; a classifying device disposed between the air transporting device and the charging grid and connected to a polarity opposite to that of the charging grid or earthed; and an electrode disposed in front of or behind the said workpiece and also connected to a polarity opposite to that of the charging grid or earthed.

To extend the applicability of the apparatus according to the invention to the coating of large surfaces of electrically insulating materials, e.g. walls and floors, the electrode is arranged in the region of the spraying outlet within the apparatus and is constructed in the form of a grid. The electrostatic spraying apparatus for synthetic fibres constructed in this way may readily be used virtually as a hand-tool,.

For the coating of other kinds of workpieces or objects, the electrode may expediently be arranged as a supporting plate to be placed behind the workpiece or object. To co ordinate the function of the charging grid and the classifying device it is preferable to dispose the charging grid in a positionally adjustable manner in the housing.

The charging and directing of the synthetic fibres may be improved by providing needle ioniser(s) on the charging grid.

According to preferred embodiments of the invention the air transport device may consist of a nozzle system or a blower (fan) disposed within or externally of the housing, or a com bination of a nozzle system and blower.

With the apparatus according to preferred embodiments of the invention, high quality coatings of synthetic fibres can be produced on objects of any shape and material.

The invention is described purely by way of example in the accompanying schematic drawings, wherein: Figure 1 is a cross-sectional view of an embodiment of electrostatic spraying apparatus for synthetic fibres according to the invention wherein a grid-shaped electrode is arranged within the housing of the apparatus, and Figure 2 is a view similar to Figure 1 but showing an embodiment wherein the earthing electrode, arranged outside of the housing of the apparatus, is in the form of a supporting plate placed behind the object to be coated.

Like or functionally equivalent parts of the apparatus shown in Figures 1 and 2 have been allotted like reference numbers, unless otherwise specified.

In the drawings, in-feeding and loosening of the fibrous material and separation of lumps is carried out in the loading space 1 of the housing of the apparatus. The loading space 1 is bounded at its bottom (as viewed) by a classifying device 2 which in these embodiments is a classifying device 2 which is made of an electrically conducting material. The classifying device 2 is earthed.

A nozzle system 3 is arranged to supply the fibre-transporting air stream and is arranged at the upper part of the loading space 1. It is connected via a pipe line 4 and a valve 5 to a source of compressed air.

The nozzles 6 of the nozzle system 3 are set to debouch tangentially into the interior 18 of the housing. Underneath the classifying device 2 an electrostatic charging grid 9 having a' frame 8 made of electrically insulating material is arranged within the housing and is connected to a high voltage power supply 15.

Between the charging grid 9 and the classifying device 2 a pre-charging space 7 is formed.

The charging grid 9 is provided with needle jonisers facing downstream, i.e. towards the direction of spraying.

In the embodiment according to Figure 1 the objects 17 to be coated are advanced by a conveyor 13 along a path extending beneath the spraying apparatus. An electrode 16, formed in this embodiment as a grid, is arranged in the region of the spray outlet but still inside the housing. The electrode 16 and the classifying device 2 are electrically identically connected, i.e. earthed. Between the grid-shaped electrode 16 and the charging grid a spraying space or outlet 12 is formed inside the housing of the apparatus. The grid 16 is carried on a longitudinally adjustable frame 19.

The appartus illustrated in Figure 2 differs from the embodiment according to Figure 1 essentially in that the electrode is disposed externally of the housing and takes the form of an earthed supporting plate 14 placed under the conveyor band 13 or, where the workpiece to be coated is a band, then under the band of the material to be coated.

The position of the charging grid 9 is longitudinally adjustable by means not shown and thus the dimensions of the pre-charging space 7 can be changed to suit different materials.

In operation of the apparatus according to the invention the fibrous material fed into the loading space 1 is agitated, loosened and conveyed continuously by the air discharged from the nozzles 6 through the classifying device 2 into the pre-charging space 7. Due to the effect of the charging grid 9 connected to the voltage source 15 and the oppositely connected grid 2 forming the classifying device, the fibres receive a low electrical charge and so they begin to line up (be aligned with each other) with their longitudinal axis pointing towards the general direction of spraying. The flow and alignment of the fibres is, of course, enhanced by the conveying air stream.

The air flow drives the already lined-up and slightly charged fibres through the charging grid 9 where, through contact with the grid 9, the fibres receive additional electric charges, accelerate to high velocities and flow through the spraying space 12. The needle ionisers 10 ionise the air molecules whereby charging of the fibres is maximised, the fibres are accelerated to very high velocities and line up in the direction of the spraying with a very high state of alignment. Due to the effect of the air stream as well as attractive forces generated by the charging grid 9 and the grid 16 in Figure 1 or the supporting plate 14 in Figure 2, the fibres impinge evenly on the adhesive-covered surface of the workpiece to be coated, with the required depth of penetration.

The apparatus according to Figure 1 may in practice also be generally applied for coating electrically non-conducting workpieces of large dimensions. It is eminently suitable for coating walls and floorings, because the grid operating as an earthing electrode is part of the apparatus and can be moved together with the apparatus over the surface to be coated If such objects are to be coated, the fibres are accelerated to high velocities between the charging grid 9 and the earthing electrode which is formed as a grid of larger dimensions than those of the charging grid 9, and then the fibres stream through the grid 16 to impinge without appreciable loss of velocity on the adhesive layer.

WHAT WE CLAIM IS:- 1. Electrostatic spraying apparatus for spraying a workpiece with synthetic fibres, comprising a housing accommodating an air transporting device, an electrical charging grid connectable to a high voltage power supply, a classifying device disposed between the air transporting device and the charging grid and connected to a polarity opposite to that of the charging grid or earthed; and an electrode disposed in front of or behind the said workpiece and also connected to a polarity opposite to that of the charging grid or earthed.

2. Apparatus according to claim 1, wherein the electrode is arranged inside the housing in the region of the spraying outlet is formed as a grid.

3. Apparatus according to claim 1, wherein the electrode is arranged externally of the housing behind the workpiece to be coated and is formed as a supporting plate.

4. Apparatus according to any preceding claim, wherein the position of the charging grid in the housing is adjustable in relation to the position of the classifying device.

5. Apparatus according to any preceding claim, wherein at least one ioniser is secured to the charging grid.

6. Apparatus according to claim 5, wherein the or each ioniser is a needle ioniser pointing in the direction of spraying, i.e. downstream.

7. Apparatus according to any preceding claim wherein the air transport device consists of a nozzle system arranged inside the housing of the apparatus.

8. A method of spray-coating a workpiece with fibrous material comprising directing the fibres at the workpiece after transporting them successively through a classifying device and an electrical charging device with the assistance of a pressurised fluid medium, disposing an earthing device adjacent the workpiece, and either earthing the classifying device or connecting it to a polarity opposite to that of the charging device.

9. Apparatus according to claim 1 or a method according to claim 8, substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. enhanced by the conveying air stream. The air flow drives the already lined-up and slightly charged fibres through the charging grid 9 where, through contact with the grid 9, the fibres receive additional electric charges, accelerate to high velocities and flow through the spraying space 12. The needle ionisers 10 ionise the air molecules whereby charging of the fibres is maximised, the fibres are accelerated to very high velocities and line up in the direction of the spraying with a very high state of alignment. Due to the effect of the air stream as well as attractive forces generated by the charging grid 9 and the grid 16 in Figure 1 or the supporting plate 14 in Figure 2, the fibres impinge evenly on the adhesive-covered surface of the workpiece to be coated, with the required depth of penetration. The apparatus according to Figure 1 may in practice also be generally applied for coating electrically non-conducting workpieces of large dimensions. It is eminently suitable for coating walls and floorings, because the grid operating as an earthing electrode is part of the apparatus and can be moved together with the apparatus over the surface to be coated If such objects are to be coated, the fibres are accelerated to high velocities between the charging grid 9 and the earthing electrode which is formed as a grid of larger dimensions than those of the charging grid 9, and then the fibres stream through the grid 16 to impinge without appreciable loss of velocity on the adhesive layer. WHAT WE CLAIM IS:-

1. Electrostatic spraying apparatus for spraying a workpiece with synthetic fibres, comprising a housing accommodating an air transporting device, an electrical charging grid connectable to a high voltage power supply, a classifying device disposed between the air transporting device and the charging grid and connected to a polarity opposite to that of the charging grid or earthed; and an electrode disposed in front of or behind the said workpiece and also connected to a polarity opposite to that of the charging grid or earthed.

2. Apparatus according to claim 1, wherein the electrode is arranged inside the housing in the region of the spraying outlet is formed as a grid.

3. Apparatus according to claim 1, wherein the electrode is arranged externally of the housing behind the workpiece to be coated and is formed as a supporting plate.

4. Apparatus according to any preceding claim, wherein the position of the charging grid in the housing is adjustable in relation to the position of the classifying device.

5. Apparatus according to any preceding claim, wherein at least one ioniser is secured to the charging grid.

6. Apparatus according to claim 5, wherein the or each ioniser is a needle ioniser pointing in the direction of spraying, i.e. downstream.

7. Apparatus according to any preceding claim wherein the air transport device consists of a nozzle system arranged inside the housing of the apparatus.

8. A method of spray-coating a workpiece with fibrous material comprising directing the fibres at the workpiece after transporting them successively through a classifying device and an electrical charging device with the assistance of a pressurised fluid medium, disposing an earthing device adjacent the workpiece, and either earthing the classifying device or connecting it to a polarity opposite to that of the charging device.

9. Apparatus according to claim 1 or a method according to claim 8, substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.