GB2149691A - Coating and spraying solids - Google Patents

Abstract

A spray head which will deliver a spray of solids and liquid utilises an air mover into which compressed air is fed creating a low pressure zone A at one end, and nozzle outlet B at the other. In use solids from pipe 19 and a spray of liquid from jet 16 are directed into the low pressure zone whence they are mixed and flung out of the nozzle outlet. The air mover comprises a Coanda nozzle 12-15. <IMAGE>

Description

SPECIFICATION Improvements in or relating to spray equipment This invention relates to spray equipment, and in particular to a spray head which will deliver a spray of solids and liquid.

In the spraying of solids particularly fibres, and liquid, such as for example in the spraying of a fibrous insulation where the fibres are to be coated with a liquid binder it is a problem to ensure intimate blending of the fibres and liquid without danger of clogging. In the past such spraying has utilized, for example, a spray head in which two or more spray jets to deliver the liquid spray are mounted on the exterior of a larger nozzle through which a mixture of air and fibres is blown, the jets being arranged so that the liquid spray impinges on fibres emerging from the nozzle. This arrangement is free from clogging but does not give a complete mixing of the liquid and fibres under all conditions, so that some of the fibres are not properly coated with liquid. In spraying of insulation coatings this can lead to insufficient adhesion.

Similar mixing problems arise in the spraying of other systems, such as in the manufacture of fibre reinforced cement.

The present invention provides a spray head with a construction which is aimed at alleviating this problem.

According to the present invention a spray head comprises an air mover, with a compressed air feed adapted to create a low pressure zone at one end and a nozzle outlet at the other end, an inlet for a current of air and air-borne solids leading to the low pressure zone, and a spray jet located in the inlet and arranged to spray liquid into the low pressure zone, whereby in use air and solids are drawn through the inlet, into the low pressure zone where they are sprayed with liquid from the jet, the air, solids and liquid being ejected from the spray head through the nozzle at the other end of the air mover.

Preferably the spray jet for the liquid is arranged in the inlet so that it is aligned along the axis of the air mover, its spray then being symmetricaily disposed about that axis.

In order to provide an air-bleed in the event of the supply of air and solids to the inlet being cut off there is preferably provided an air gap, or series of holes or slots, between the inlet and the end of the air mover itself, the gap thus providing a means for a secondary air bleed into the low pressure zone created by the air mover in operation.

If desired the liquid may be foamed, for example by injection of air into the liquid at, or before it reaches the spray jet, in order that a spray of foam is produced.

In one mode of use of the spray head a current of air and fibres is provided by means of a centrifugal fan which blows air into the inlet and is fed with fibre eg by such means as an auger bringing fibre from a hopper.

The fibre may, for example, be a fibre used for insulation purposes, such as cellulose, and the liquid is preferably a binder such as a polymer solution or dispersion. Urea-formaldehyde resin solution and/or polyvinyl acetate dispersion are aqueous based binders which may be used.

Where the liquid is a resinous binder, catalyst may be mixed with the liquid before it is sprayed from the spray jet, or in an alternative arrangement means may be provided for injecting a liquid catalyst into the compressed air feed of the air mover to produce mixing of resin and catalyst within the air mover.

In an alternative use of the spray head, the liquid may be water and a binder may be carried on or with the fibres in the current of air and fibres as, for example, when the binder is a water-setting material such as hydraulic cement or gypsum. In such a case the binder would normally be mixed with the fibres before they are blown into the inlet of the spray head.

In a further use of the spray head, for the manufacture of fibre reinforced cement or gypsum, e.g.

in panel form, a mixture of solids is metered directly into the inlet of the spray head, whence it is carried into the low pressure zone in the air stream generated solely by suction effect of the air mover and sprayed with water as mentioned above where the liquid is water for use with hydraulic binders, additives such as dispersants, superplasticizers and catalysts may be added to the water.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing which is a cross-sectional view of a spray head.

The spray head consists principally of an air mover 1 and an inlet pipe 2 for a current of air and fibres.

The air mover is a known device which utilizes the Coanda effect to generate a low pressure zone at A and force a current of air out through zone B.

The device briefly consists of a metal tube 3, whose outer surface is threaded at 4 and contains a groove 5, and a metal sleeve 6, which is internally threaded at 7. The sleeve 6 also contains a compressed air inlet 8 and an internal groove 9 and ends in a flange portion 10.

The sleeve 6 is screwed onto the tube 3 and positioned so that the two grooves 9 and 5 together form an annular chamber to which compressed air can be fed through the inlet 8. The tube portion 15 and inner surface of the sleeve and flange are so dimensioned and positioned that a narrow annular gap 11 for passage of air from the annular chamber remains between the two turning through a right angle and forming an annular slit 12 on the interior of one end of the air mover device 1.

The surfaces 13 and 14 of the flange portion 10 and tube portion 15 are accurately shaped in curved cross section, and the slit 12 is so dimensioned that in operation when compressed air is applied to the inlet 8 the air is forced through the slit 12 and exits from the interior of the air mover through zone B creating a low pressure zone at A.

The operation of the air mover utilizes the Coanda effect, which is the tendency of a fluid coming out of a jet to travel close to a wall contour, even if the wall's direction of curvature is away from the jet's axis.

Creation of a low pressure zone at A applies suction to the inlet pipe 2.

The inlet pipe 2 is separated from the air mover 1 by a small annular air gap 18, to act as an air bleed in the event of the inlet pipe being closed off. The inlet pipe has a bend, thus enabling a spray jet 16 to be mounted in the wall of the pipe at 17, the jet 16 being positioned on the axis of the air mover 1, without interferring with the fibre flow through the pipe.

A flexible pipe 19 connects the inlet pipe 2 with a supply of fibres and air (not shown) eg a centrifugal fan with a feed means for fibres, arranged to blow air and fibres along the flexible pipe 19.

In operation compressed air is applied to the inlet 8 of the air mover, and fibres, such as celllose fibres, are blown along the pipe 19 and into inlet pipe 2. The suction generated by the air mover pulls the fibres into zone A and accelerates them out of the air mover through the nozzle zone B.

The spray jet 16 sprays a liquid, such as UF resin binder solution, onto the fibres in zone A, the effect of the air mover being to intimately mix the liquid spray droplets and the fibres and fling them out through the nozzle zone B.

The spray head thus described is particulary suitable for spraying a fibrous insulation material onto a substrate such as a wall, ceiling or roof interior.

Claims (5)

1. A spray head comprising an air mover with a compressed air feed adapted to create a low pressure zone at one end of the air mover and a nozzle outlet at the other end, an inlet for a current of air and air-borne solids leading to the low pressure zone, and a spray jet located in the inlet and arranged to spray liquid into the low pressure zone, whereby in use air and solids are drawn through the inlet into the low pressure zone where they are sprayed with liquid from the jet, the air, solids and liquid being ejected from the spray head through the nozzle at the other end of the air mover.

2. A spray head according to claim 1 in which the spray jet is positioned along the axis of the air mover.

3. A spray head according to claim 1 or 2 in which an air bleed is provided between the air mover and the inlet.

4. A spray head according to any preceding claim in said compressed air feed is provided with an inlet for liquid to facilitate injection of liquid into the compressed air stream when the spray head is in use.

5. A spray head substantially as described herein with reference to the accompanying drawing.