GB2459088A

GB2459088A - Coating dispersal apparatus

Info

Publication number: GB2459088A
Application number: GB0806276A
Authority: GB
Inventors: Peter King
Original assignee: Spice Application Systems Ltd
Current assignee: Spice Application Systems Ltd
Priority date: 2008-04-07
Filing date: 2008-04-07
Publication date: 2009-10-14
Anticipated expiration: 2028-04-07
Also published as: GB0806276D0; GB2459088B

Abstract

An apparatus for delivering a coating substance 2 towards a product to be coated, comprises an inclined chute 1 for conveying the coating substance, the chute comprising a base 11 and a pair of sidewalls 10, and a tongue projection 12 from an exit end 3 of the chute beyond the side walls; and a gas jet nozzle, which may be in the form of an air knife 7 for location substantially immediately beneath said tongue, and arranged in use to provide a gas flow for dispersing the coating substance falling from the tongue. The tongue may be semi-elliptical or semi-circular in shape. An electrode 6 used to impart a charge to the coating substance falling from the tongue may be located proximate to the tongue. The application is particularly applicable to the coating of snack food products with a dry powdered flavouring but can be used to coat other products including pharmaceuticals. Coating substances other than dry powdered substances such as liquids and suspensions may also be used.

Description

COATING DELIVERY METHOD AND APPARATUS

Field of the Invention

The present invention relates to an improved apparatus for delivering a coating substance and more particularly, though not necessarily, to an improved apparatus for delivering a powder coating.

Background

There exists a wide variety of products that require to be coated with a substance (e.g. powder, liquid, suspension, etc) during their preparation. For example, snack foods such as potato crisps and corn chips are usually coated with a flavouring. It is generally desirable to be able to achieve a uniform and controllable coating over the entire surface of a product.

A traditional method used for coating snack foods involves the use of a rotating drum which has its axis generally aligned with the horizontal, but with a slight tilt. Products introduced into one end of the drum tend to travel to the other end as the drum rotates. Flavouring in the form of a powder is delivered via an inclined chute to a location within the drum so that the flavouring is sprinkled onto the products to be coated. This technique tends to result in a non-uniform coating of products, with flavour concentration varying between product pieces and across the surfaces of individual pieces.

It has been recognised that coating uniformity may be improved by placing a charge on the powder, using for example a needle electrode located in the transit path of the product. If the product delivery mechanism, e.g. a rotating drum, is grounded, the products to be coated will also tend to be grounded as they pass under the powder delivery mechanism. The charged powder will be attracted to the products in a generally uniform manner, in turn resulting in a generally uniform coating.

An alternative electrostatic coating apparatus comprises a venturi tube through which the coating substance is forced by a pressurised gas. Upon emerging from an exit nozzle, the substance passes a charging electrode. A blockage problem can arise due to the coating substance building up within the venturi tube. Such blockage results in production downtime, increasing operating costs and decreasing productivity.

Figure 1 illustrates an apparatus for coating a product as described in GB 2,385,810. The apparatus comprises an inclined chute 1 for conveying a coating substance 2, with an exit end 3 and an entry end 4. A gas jet nozzle 5 and a needle electrode 6 are located beneath the exit end 3 of the chute 1.

The pressurised gas stream becomes charged as it passes through the electric field created by the charged needle electrode. The charged gas then impacts on the falling coating, dispersing it and imparting a charge to it.

As described in GB 2,385,810, the chute used to convey the coating substance is narrow, with a width of 75mm or less, and the coating tends to continue moving in the (longitudinal) direction of the chute (as shown by the arrows in Figure 1) after exiting from the chute, such that the coating is only applied within a narrow region beneath it. Multiple chutes, each with their own gas nozzle and needle electrode, are then required in order to coat a wider region. The use of multiple chutes leads to additional expense on equipment and maintenance.

Summary

The present invention is applicable in particular to the coating of snack food products with a dry, powdered flavouring. However, the invention may also be used to coat other products including, but not limited to, pharmaceuticals. The invention may also be used to coat products with substances other than dry powdered substances including, for example, liquids and suspensions.

According to a first aspect of the present invention there is provided an apparatus for delivering a coating substance towards a product to be coated, the apparatus comprising an inclined chute for conveying the coating substance to a location above a surface carrying said product, the chute comprising a base, a pair of sidewalls and a tongue projection from an exit end of the chute beyond said side walls; and a gas jet nozzle for location substantially immediately beneath said tongue, and arranged in use to provide a gas flow for dispersing the coating substance falling from said tongue.

Embodiments of the present invention provide a wider distribution or spread of the coating substance away from the central axis of the base of the chute, as compared to the prior art. In processes that require the application of a coating across a wide area, the apparatus described here can reduce or eliminate the need for multiple coating delivery mechanisms, reducing the cost of equipment and the associated maintenance.

In a preferred embodiment, the apparatus further comprises an electrode located proximate to said exit end of said chute; and means for charging the electrode; wherein in the charged electrode acts so as to impart a charge onto the coating substance falling from the tongue.

Preferably, the tongue is substantially semi-elliptical or semi-circular in shape.

According to a second aspect of the present invention there is provided a method of delivering a coating substance towards a product to be coated, the method comprising conveying the coating substance along an inclined chute to a location above a surface carrying the product, the chute comprising a base, a pair of sidewalls and a tongue projection from an exit end of the chute beyond said side walls; allowing said coating substance to fall from the tongue in the direction of said surface; and during its fall, and substantially immediately beneath the exit end of said inclined chute, subjecting the coating substance to at least one pressurised gas stream, whereby the falling coating substance is dispersed.

In a preferred embodiment, the method further comprises during its fall under gravity, and proximate to the exit end of said inclined chute, subjecting the coating substance to an electric field, whereby the coating substance is charged.

Brief Description of the Drawings

Figure 1 illustrates a known coating delivery apparatus; Figure 2 is a perspective view of a coating delivery apparatus according to an embodiment of the present invention; Figure 3a is a side elevation of the chute of the coating delivery apparatus of Figure 2; and Figure 3b is a plan view of the chute of the coating delivery apparatus of Figure 2.

Detailed Description

Figure 2 shows a coating delivery apparatus comprising an inclined chute 1 for conveying a powder coating 2, with an exit end 3 and an entry end 4. A gas jet nozzle in the form of an air knife 7 is located beneath the exit end 3 of the chute I and is coupled via a hose 8 to a source of pressurised air. A needle electrode 6 is located in front of the exit end 3 of chute 1 and is coupled via a conductor 9 to a high voltage charging circuit.

As shown in Figures 3a and 3b, the chute 1 comprises two planar sides lOand a planar base 11. The base 11 extends out beyond the exit end 3 of the chute by an extended base portion or "tongue" 12 that lies in the plane of the base or that may be inclined downward relative to the base. The tongue 12 is substantially semi-circular (or semi-elliptical) in shape. Of course, the tongue can take any other suitable shape, e.g. triangle, semi-hexagonal.

Having explained the structure of the apparatus with reference to Figures 2, 3a and 3b, the operation of the apparatus will now be described.

As described in GB 2,385,810, a powder coating 2 is delivered from a hopper to the entry end 4 of chute 1 and, due to its inclined angle, is conveyed along the chute 1 towards the exit end 3 and tongue 12 of chute 1. A motor may be provided in order to vibrate or shake the chute to aid the transfer of the coating substance along it.

As the powder coating 2 reaches the exit end 3 of the chute 1, it will spill over the edge of the tongue 12 and begin falling under gravity. Directly beneath the exit end of the chute 1, air is forced through the nozzle of an air knife 7 and the airflow from the nozzle disperses the falling powder. The powder also becomes charged either as a result of direct exposure to the electric field created by the charged electrode 6 or by a charge transfers mechanism from the pressurised gas.

The product to be coated travels beneath the coating delivery apparatus on a conveyor (i.e. a rotating inclined drum, inclined chute or conveyor belt) that is grounded, as described in GB 2,385,810. As the conveyor is grounded, the product travelling on the conveyor is also grounded and the charged and dispersed powder is attracted to the product coating its exposed surfaces.

The addition of a tongue extending beyond the sides of the chute provides a wider distribution or spread of the coating substance away from the central axis of the base of the chute, as compared to the apparatus of GB 2,385,810.

In processes that require the application of a coating across a wide area, the apparatus described here can reduce or eliminate the need for multiple coating delivery mechanisms, reducing the cost of equipment and the associated maintenance.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention. For example, alternative nozzles may be used instead of an air knife.

Claims

Claims: 1. Apparatus for delivering a coating substance towards a product to be coated, the apparatus comprising: an inclined chute for conveying the coating substance to a location above a surface carrying said product, and comprising a base and a pair of sidewalls, and a tongue projection from an exit end of the chute beyond said side walls; and a gas jet nozzle for location substantially immediately beneath said tongue, and arranged in use to provide a gas flow for dispersing the coating substance falling from said tongue.
2. Apparatus according to claim 1 and further comprising: an electrode located proximate to said exit end of said chute; and means for charging said electrode; wherein in said charged electrode acts so as to impart a charge onto the coating substance falling from said tongue.
3. Apparatus according to any preceding claim wherein the tongue is substantially semi-elliptical or semi-circular in shape.
4. A method of delivering a coating substance towards a product to be coated, the method comprising: conveying said coating substance along an inclined chute to a location above a surface carrying said product, said chute comprising a base and a pair of sidewalls, and a tongue projection from an exit end of the chute beyond said side walls; allowing said coating substance to fall from the tongue in the direction of said surface; during its fall, and substantially immediately beneath the exit end of said inclined chute, subjecting the coating substance to at least one pressurised gas stream, whereby the falling coating substance is dispersed.
5. A method according to claim 4 further comprising during its fall under gravity, and proximate to the exit end of said inclined chute, subjecting the coating substance to an electric field, whereby the coating substance is charged.
6. A method according to any of claims 4 or 5 wherein the tongue is substantially semi-elliptical or semi-circular in shape.