GB2124468A

GB2124468A - Process and apparatus for the continuous electrostatic deposition of a powdered substance, particularly dextrose, on a food substrate

Info

Publication number: GB2124468A
Application number: GB08319998A
Authority: GB
Inventors: Lorenzo Cillario
Original assignee: Ferrero SpA
Current assignee: Ferrero SpA
Priority date: 1982-08-03
Filing date: 1983-07-25
Publication date: 1984-02-22
Also published as: DE3328079C2; DE3328079A1; DK353283A; GB8319998D0; IT1212665B; DK353283D0; GB2124468B; IT8267977A0; DK169053B1

Abstract

In a process for the continuous electrostatic deposition of a powdered food substance, such as dextrose, on a food substrate (4), such as a layer of bread or cake, the steps of electrically charging the substrate by means of electrostatic charging means (13, 13%), charging the particles of powder to be deposited with an electric charge opposite that of the substrate by means of electrostatic spray guns (14), and dispersing the powder over the substrate by means of the guns are carried out in an environment (1) which is isolated from the exterior and into the substrate inlet and outlet zones (6, 8) of which are introduced through openings 12, 12% air flows with controlled humidity and temperature. An air flow of less than the sum of the flows introduced into the inlet and outlet zones is withdrawn through openings 15, 15% from an intermediate zone (7) of the environment, between the inlet and outlet zones, in which the powder is deposited. <IMAGE>

Description

SPECIFICATION Process and apparatus for the continuous electrostatic deposition of a powdered substance, particularly dextrose, on a bread substrate The present invention relates to apparatus used in the food industry for depositing a layer of powdered food substance on a food substrate, particularly the deposition of powdered dextrose on a bakery product, for example, a sponge cake.

Conventional apparatus generally uses roller spreaders and/or brush spreaders which deposit the powder on the substrate by direct contact. The layer obtained in this manner is not very uniform, however, and it is difficult to limit the thickness of the layer deposited to the minimum required for good quality in the finished product. Moreover, because of the poor adherence of the powder to the substrate, losses of the powdered substance occur during packing after the deposition.

Furthermore, lumps of powder often form on the conveyor belts, making it necessary to stop the apparatus frequently for cleaning.

In order to avoid the disadvantages mentioned above, it has been proposed, in the case of flavouring deposits, to deposit the powder on the substrate by means of an electrostatic process including the steps of charging the substrate with an electric charge by means of electrostatic charging means, charging the powder particles to be deposited with an electric charge opposite that of the substrate by means of electrostatic spray guns, and dispersing the powder over the substrate by means of the guns while the substrate is advanced continuously relative to the spray guns.

Electrostatic deposition processes have been shown to be unsuitable when the powder to be sprayed is hygroscopic and forms an explosive mixture with air within specific concentration limits. This is particularly the case with dextrose.

The object of the present invention is to solve these problems and provide a process in which the electrostatic deposition is carried out in an environment where there is a circulation of air with a temperature, humidity and powder concentration which are controlled to avoid risk of explosion and/or clogging of the spray guns.

According to the invention this object is achieved by means of a process for the continuous electrostatic deposition of a layer of powdered food substance on a food substrate, in which the steps of charging the substrate with an electric charge and dispersing the powder on the substrate are carried out in an environment which is isolated from the exterior and into the substrate inlet and outlet zones of which are introduced air flows with controlled humidity and temperature, an air flow of less than the sum of the flows introduced into the inlet and outlet zones being withdrawn from an intermediate zone of the environment between the inlet and outlet zones, in which the powder is deposited.

According to a further object, the present invention provides apparatus for performing the aforesaid process, including a casing which defines an environment isolated from the exterior and having an initial chamber with an inlet for the substrate in which the electrostatic charging means for the substrate are located, a final chamber with an outlet for the substrate, and an intermediate chamber communicating with the initial and final chambers in which the spray guns are located, and further including delivery means for directing predetermined air flows with controlled humidity and temperature into the initial and final chambers, and intake means for withdrawing from the intermediate chamber of the casing an air flow of less than the sum of the flows introduced into the initial and final chambers, so as to obtain two outward currents of air from the inlet and outlet of the casing.

The apparatus and process of the invention will now be described, by way of example, with reference to the appended drawings, in which: Figure 1 is a general schematic view of electrostatic deposition apparatus according to one embodiment of the present invention; Figure 2 is a perspective view of the casing of the apparatus of Figure 1, within which the electrostatic deposition is carried out; Figure 3 is a partially-sectioned side view of the casing of Figure 2; Figure 4 is a partially-sectioned view of the casing taken along the line IV--IV of Figure 3, and Figure 5 is a plan view of the casing of Figure 2.

In the drawings, a casing 1 of non-metallic material is constituted by a parallelepiped in which the base surface is missing. It is located astride a conveyor belt 10 on which a substrate 4 advances in the direction of the arrow F in the space between two adjustable guides 22 of selflubricating plastics material, for example "Teflon" (Registered Trade Mark). The surface of the conveyor belt 10 and the walls of the casing 1 define an environment which is substantially isolated from the exterior, in which the electrostatic deposition of the powder is carried out.

The casing 1 has respective apertures 3, 3' in its front wall 2 and its rear wall 2', the heights of opening of which are adjustable so as to allow them to be adapted to the thickness of the substrate 4, enabling its input and output but minimising the area open to the outer atmosphere.

Separating partitions 5, 5' divide the casing 1 into an initial chamber 6, an intermediate chamber 7 and a final chamber 8. The partitions 5, 5' are located in planes perpendicular to the path of advancement F of the substrate 4 and are fixed to the side walls 9, 9' and the upper wall 11 of the casing 1. The separating partitions 5, 5' extend from the upper wall 11 for a distance such as to allow advance of the substrate and the circulation of air within the casing 1.

The initial and final chambers 6, 8 each have two openings 12, 12' in the upper wall 11, through which dehumidified air is supplied to the respective chambers through ducting 1 2a, 1 2b, 1 2c by a delivery unit 30.

The supply of the air to the initial chamber 6 and the final chamber 8 and its inlet velocity may be regulated by means of butterfly valves 32, in order to achieve the desired air flow from the apertures 3, 3' and particularly to avoid turbulence which could harm the uniformity of the powder deposited on the substrate in the final chamber 8.

Two intake openings 15, 15' for withdrawing air from the intermediate chamber 7 are fixed to each of the side walls 9, 9' of the casing 1 and communicate with the intermediate chamber 7 through apertures 31 formed in the walls 9, 9'.

In the initial chamber 6 there is located a device 13 for charging the substrate electrostatically, which is preferably constituted in known manner by blades (not shown) located in the manner of a bridge above the substrate 4.

Electrostatic spray guns 14 of known type are located in the intermediate chamber and are fixed to the upper wall 11 of the casing 1.

The electrostatic device 13 for charging the substrate and the spray guns 14 are connected to respective high-voltage electrostatic generators of different potentials. Preferably, the electrostatic device 13 for charging the substrate is connected to the positive pole of an electrostatic generator 27 and the electrostatic guns 14 are connected to the negative pole of an electrostatic generator 28.

In the embodiment illustrated in the drawings, there are nine electrostatic guns 14 located in three groups 1 4a, 1 4b, 1 4c which are spaced apart and each of which includes one row of three electrostatic spray guns 14 arranged transverse the parth of advancement F of the substrate. The transverse row arrangement allows the powder to be dispersed uniformly across the entire width of the substrate.

In the illustrated embodiment, further electrostatic charging means 1 3' for the substrate are also provided, these being located in the intermediate chamber 7 in a zone between the second and third groups of electrostatic guns 1 4b, 1 4c and connected to the electrostatic generator 27.

In order to allow the powder to be sprayed and the substrate 4 to be electrostatically charged in separate sections of the intermediate chamber 7, the latter is divided, by means of separating partitions 16, 16' similar to the partitions 5, 5' and fixed to the side walls 9, 9' and the upper wall 11 of the casing, into three distinct sections: a first section 1 7 for the spraying of powder in which there are the first two groups of electrostatic guns 1 4a, 1 4b, an intermediate section 18 in which there are the electrostatic charging means 13' for the substrate, and a second section 1 9 for the spraying of the powder in which the third group of electrostatic guns 1 4c is located.

The first or second group 1 4a, 1 4b of electrostatic guns is an emergency group intended to operate only in the event of failure of the other of the first or second groups or of the third groups 14c.

The casing 1 has inspection and access panels 33 of transparent material in its side walls 9, 9', provided with automatic cut-outs which shut off the electrical supply to the electrostatic generators 27,28 if the panels are opened during operation of the apparatus. The intake opening 1 5, 1 5' extend from the side walls 9, 9' into the spaces between the partitions 5, 1 6 and the partitions 1 6', 5', in correspondence with the spray sections 17, 1 9. The flows taken in by each pair of intake openings 1 5, 1 5' converge in respective manifolds 20, 20' which join together into piping 21. The piping 21 supplies a powder filtration and extraction unit 23 preferably constituted by cartridge filters 34 located in a hopper 35.The filtration and extraction unit 23 is arranged to recover continuously powder carried by the air taken in by the manifolds 20, 20'.

The delivery unit 30 comprises an airconditioning section supplied by both an external air flow C and by the powder-free air from the filtration and extraction unit 23, which is supplied to it by piping 24a in which recirculation means, generally indicated 24, are located.

Afluidized-bed supply device 25 supplies powder to the electrostatic spray guns 14. The device 25 comprises a fluidization chamber 29 and known ejectors 36 (of Vibro-Venturi type) for pneumatically withdrawing the powder by suction.

A duct 26a supplies the chamber 29 with fresh powder from a loading hopper 26. A duct 23a supplies the chamber 29 with pwder recovered by the filtration and extraction unit 23. The powder is fluidized in the chamber 29 by a compressed air flow A of controlled temperature and humidity supplied through the bottom of the chamber 29.

The fluidized powder is withdrawn by means of the ejectors 36 which are supplied with a compressed air flow B of the same controlled temperature and humidity. The powder withdrawn is supplied to the spray guns 14 through piping 29a.

The loading hopper 28 containing the fresh powder to be deposited and the fluidization chamber 29 are located in a closed environment 37, with a controlled humidity and temperature, defined by broken lines in Figure 1.

The choice of the temperature and humidity of the air introduced into the casing 1 and the air in the flows A, B depends on the properties of the powder to be deposited.

All the parts of the apparatus which are in contact with the dextrose powder or with the food product substrate are constructed from materials which are permitted by the regulations governing the treatment of food substances.

One example of the application of the process of the present invention is the deposition of a layer of dextrose on a substrate 10 constituted by a filled cake in the form of a layer, which comes from a baking oven and has a layer of paste already deposited thereon by conventional spreading methods.

The dextrose used is preferably Meritose DS produced by "Amylum G.R." or a particularly pure commercial anhydrous dextrose. This dextrose is highly hygroscopic and has a very fine grain size, with 30% by weight of the particles being less than 200 microns, 55% by weight being between 100 and 200 microns, and 15% by weight being greater than 200 microns. When mixed with air, the particles of dextrose powder may form an explosive mixture in concentrations greater than 35 g/m3.

The layer of cake has a width of about 720 mm and it is desired to give the finished product a quantity of dextrose of about 3.5 g/dm2 uniformly distributed thereon. The layer of cake is advanced on the conveyor belt 1 at a constant speed of about 3.5 m per minute, and the powder deposition is carried out within the casing 1.

With reference to the drawings, in its advance within the casing 1, the layer of cake 10 encounters the electrostatic charging means 13 connected to the electrostatic generator 27 which has a positive potential of +90 kV, within the chamber 6 of the casing 1.

The positively-charged substrate then enters the first spraying section 17 of the intermediate chamber 7. During the normal operating cycle, the dextrose powder is sprayed onto the layer of cake only by the first or second of the two groups 1 4a, 1 4b of electrostatic guns 14.

Indeed, as described above, one of the groups 1 4a, 1 4b of electrostatic guns is an emergency group arranged to operate only in the event of failure of the other group or of the third group.

The electrostatic guns, which are connected to the electrostatic generator 28 having a negative potential of kV, charge the dextrose particles with a negative electric charge and then disperse them over the substrate.

The deposition of powder partially or completely annuls the positive charge of the substrate. The process then provides a second step of charging the substrate electrostatically by the means 13' in the'section 1 8 and a second deposition of the powder in the section 19. The subdivision of the spraying operation into two steps allows the formation of a dextrose layer with improved adhesion.

Substantially equal and constant dehumidified air flows of about 550 m3/h with a temperature of about 200C and a residual humidity of about 35% are introduced continuously into the initial chamber 6 and the final chamber 8 during the process. The overall air flow withdrawn by the manifolds 20, 20' is about 1,000 m3/h, thus achieving at the outlets of both the initial chamber 6 and the final chamber 8 air flows of about 50 m3/h directed outwardly through the apertures 3, 3'. Thus, a closed pneumatic system is achieved which prevents the ingress of external atmospheric air into the environment in which the powder spraying is carried out.

The continuous circulation of dehumidified air within the casing prevents the possibility of lumps forming and avoids the risk of explosion within the chamber.

The temperature and humidity of the respective air flows A, B used for the fluidization of the powder in the fluidization chamber 29 and for the withdrawal of the powder by the ejectors are substantially the same as for the air from the delivery unit 30.

The quantity of powder dispersed by each gun is about 280 g/min, giving a total for the six active guns of about 1700 g/min.

The powder deposition yield is 77%.

The dextrose-coated cake 4 from the casing 1 is then cut into portions having a width of 36 mm and a length of 120 mm and these are then packed in protective bags.

Even after the cutting and packing, the food product has a quantity of dextrose on its surface which is almost equal to that deposited during the electrostatic spraying operation, confirming the excellent adhesion of the layer deposited.

Claims

1. Process for the continuous electrostatic deposition of a layer of a powdered food substance on a food substrate, including the steps of charging the substrate with an electric charge by means of electrostatic charging means, charging the powder particles to be deposited with an electric charge opposite that of the substrate by means of electrostatic spray guns, and dispersing the powder above the substrate by means of the guns while the substrate is advanced continuously relative to the spray guns, in which the steps charging the substrate with an electric charge and dispersing the powder on the substrate are carried out in an environment which is isolated from the exterior and into the substrate inlet and outlet zones of which are introduced air flows with controlled humidity and temperature, an air flow of less than the sum of the flows introduced into the inlet and outlet zones being withdrawn from an intermediate zone of the environment between the input and outlet zones, in which the powder is deposited.

2. Process as claimed in Claim 1, in which the entire air flow withdrawn from the intermediate zone of the environment is filtered and purified of powder which has not been deposited on the substrate, this powder being recovered.

3. Process as claimed in Claim 2, in which the air flows introduced into the substrate inlet and outlet zones of the environment in which the electrostatic powder deposition occurs come from an air-conditioning section supplied in part by the powder-free air from the intermediate zone of the environment.

4. Process as claimed in Claim 1, in which the powder is supplied to the spray guns by fluidizing the powder in a fluidization chamber and withdrawing it from the fluidization chamber pneumatically by suction withdrawal means, air having a controlled humidity and temperature being used for the fluidization and withdrawal, and in which a loading hopper and said withdrawal means are also located in an environment having a controlled humidity and temperature.

5. Process as claimed in Claim 1, in which the steps of charging the substrate with an electric charge by means of electrostatic charging means and dispersing the particles of powder charged with an electric charge opposite that of the substrate over said substrate are repeated in the environment.

6. Process as claimed in Claim 5, in which each of the steps of charging the substrate with an electric charge and dispersing the particles of powder charged with the opposite electric charge from that of the substrate over the substrate is carried out in a respective distinct zone within the environment, and in which the withdrawal of air from the environment is carried out in correspondence with each zone in which the particles of powder are dispersed.

7. Process as claimed in Claim 1, in which the substrate is positively charged by means of the electrostatic charging means and the particles of powder are negatively charged by means of the electrostatic spray guns.

8. Process as claimed in any of the preceding claims, in which the substrate on which the powder is deposited is a bread in the form of a layer and the powder consists of anhydrous dextrose.

9. Process for the continuous electrostatic deposition of a layer of a powdered food substance on a food substrate, substantially as herein described with reference to, and as shown in, the appended drawings.

10. Apparatus for the electrostatic deposition of a layer of powdered food substance on a food substrate, including electrostatic charging means for charging the substrate with an electric charge, and electrostatic spray guns for charging the particles of powder with an electric charge opposite that of the substrate and dispersing them over the substrate while the latter is advanced continuously relative to the spray guns, in which it further includes a casing which defines an environment isolated from the exterior and having an initial chamber with an inlet for the substrate in which the substrate charging means are located, a final chamber with an outlet for the substrate, and an intermediate chamber communicating with the initial and final chambers in which the spray guns are located, and in which it includes delivery means for directing predetermined air flows with controlled humidity and temperature into the initial and final chambers, and intake means for withdrawing from the intermediate chamber of the casing an air flow of less than the sum of the flows introduced into the initial and final chambers, so as to obtain outward currents of air from the inlet and outlet of the casing.

11. Apparatus as claimed in Claim 10, in which the casing is subdivided into the initial, intermediate and final chambers by means of separating surfaces which allow the circulation of air and the advance of the substrate within the casing and which are located in planes perpendicular to the path of advancement of the substrate, and the means for withdrawing air from the intermediate chamber comprise manifolds having intake openings in the walls of the intermediate chamber.

12. Apparatus as claimed in Claim 10, in which the electrostatic spray guns are located in spacedapart groups each of which includes at least one row of electrostatic spray guns arranged transverse the path of advancement of the substrate within the intermediate chamber of the casing.

13. Apparatus as claimed in Claim 12, in which it includes further means for the electrostatic charging of the substrate located in the intermediate chamber between one group of spray guns and the next.

14. Apparatus as claimed in Claim 13, in which the intermediate chamber of the casing comprises, in series relative to the path of the substrate, a first section for the spraying of the powder, an intermediate section in which are located means for the electrostatic charging of the substrate, and a second section for the spraying of the powder, these sections being separated from each other by partitions fixed to the walls of the casing and the manifold intake openings being located in the walls of the two spraying sections.

15. Apparatus as claimed in Claim 14, in which there are three groups of electrostatic spray guns of which the first and second are located in the first spraying section and the third is located in the second spraying section, and in which one of the first and second groups constitutes an emergency group arranged to operate only in the event of failure of the other of the first and second groups or of the third group.

1 6. Apparatus as claimed in Claim 11, in which it further includes means for filtering and extracting the powder supplied by the manifolds, said means extracting and recovering that powder not deposited on the substrate and carried by the air taken in by the manifolds.

17. Apparatus as claimed in Claim 16, in which the delivery means include an air-conditioning section, and in which recirculation means are provided for directing powder-free air from the filtration and extraction means to the air-conditioning section.

1 8. Apparatus as claimed in any of Claims 10 to 17, in which it includes fluidized bed means for supplying the powdered substance to the electrostatic spray gun.

1 9. Apparatus for continuous electrostatic deposition of a layer of a powdered food substance or a food substrate, substantially as herein described with reference to, and as shown in, the appended drawings.