The invention relates to a method for treating an inner surface of a duct fouled with grease deposit.

Ducts, and particularly extraction ducts which are used to extract air from kitchens, soon become fouled with grease deposit during use. This on the one hand decreases the extracting action of the duct but, much more importantly, it greatly increases the risk of fire. If a flame reaches the extraction duct, which is not unthinkable in a kitchen, the grease deposit in the extraction duct can catch fire and the duct can be destroyed by fire. Such a fire in an extraction duct can spread and eventually burn down a whole building.

Insurance companies therefore lay down strict requirements for the maintenance of extraction ducts. Such ducts have to be cleaned regularly in order to prevent grease deposit and thereby reduce the risk of fire in the duct.

Cleaning extraction ducts is difficult and unpleasant work. Such ducts are first of all difficult to access. They are after all long and often narrow, and usually also have bends or sharp corners. In addition, extraction ducts are not usually suitable for the use of liquid cleaning agents because they are not liquid-tight. Extraction ducts are usually formed from sheet steel, usually rectangular or round, and the attachment between the various duct parts does not normally form a liquid-tight connection. Spirally wound ducts of thin sheet metal also exist, which are provided along the edges with folded seams which do not form a liquid-tight connection either. Liquid cleaning agents will thus leak out of the duct to be cleaned. Stains on ceilings or walls behind which the ducts run often occur here. Being unable to make use of cleaning liquids makes it almost impossible to properly clean extraction ducts and remove the grease deposit formed therein by hand. Such ducts are therefore cleaned less regularly and less thoroughly in practice than would be desirable with a view to fire prevention.

The invention now has for its object to provide a method for treating an inner surface of a duct fouled with grease deposit, whereby the fire hazard can be limited in simple and effective manner. This is achieved according to the invention by applying over the grease deposit a coating which adheres thereto. With such a coating the grease deposit is as it were "sealed in" between the coating and the wall of the duct so that it cannot come into contact with a flame possibly shooting into the duct. Because the coating adheres to the grease deposit, which is in turn adhered to the inner surface of the duct, the coating is held in place in the duct. "Sealing in" the grease deposit in this way thus provides a fundamentally different solution to the problem of fire hazard due to grease deposit than removal of the grease deposit, which has always been the objective heretofore. Although "sealing in" the grease deposit obviates the acute fire hazard, it is recommended that the coating comprise a fire-resistant material. Combustion in the duct is thus further prevented.

The coating is preferably applied over substantially the whole length of the duct. Although the risk of combustion is greatest close to the suction side of the duct where a flame can be drawn in, such flames can displace over great distances in a duct.

In order to enable quick and simple covering of the inner surface of the duct it is recommended that the coating be applied in liquid form and then cures. The coating can advantageously be sprayed here onto the grease deposit.

When the coating is sprayed onto the grease deposit by moving a spray head connected to a reservoir for liquid coating material through the duct, the duct can be treated in rapid and simple manner.

The invention otherwise envisages the coating being applied without pretreatment to the grease deposit so that the work can be carried out quickly.

The coating with the grease deposit adhered thereto is preferably removed from the duct. The fire hazard is thus further reduced since no flammable material remains in the duct.

It can be advantageous in this case that, after the removal of the coating and the grease deposit, a subsequent coating is applied to the inner surface of the duct. It thus becomes easier to subsequently keep the duct free of grease deposit.

The coating is preferably liquid-tight, and the duct is cleaned with liquid after the coating has been applied. Because of the liquid-tight coating liquid cleaning agents can be used in the duct for the purpose of removing future grease deposit, this in contrast to untreated ducts. This makes it easily possible to comply with the requirement of periodic inspection and cleaning of the duct.

It is also recommended in this respect that the coating is applied in a light colour.

Fouling of the duct by grease deposit can thus be detected in simple manner, and it will also be clearly visible whether the duct is completely clean after a cleaning operation.

Finally, the invention also relates to a duct with an inner surface and an adhering coating evidently formed by the treatment method as described above.

The invention will now be elucidated on the basis of an embodiment, wherein reference is made to the accompanying drawing, in which:

Fig. 1 is a schematic view of an extraction duct with a typical path from a kitchen to the outside of a building,

Fig. 2 is a schematic perspective view of a part of a duct as shown in Fig. 1 , in which grease deposit and a coating are shown,

Fig. 3 is a schematic perspective view of a spray head for applying the coating in the duct,

Fig. 4 shows a flow diagram with the steps of the treatment method according to the invention, and

Fig. 5 shows a flow diagram with the steps of an alternative embodiment of the treatment method according to the invention.

An extraction duct 1 (Fig. 1) runs from a kitchen 2 to an opening in an outside wall 3 of a building. A suction side of duct 1 connects to an extractor hood 4 which is suspended above a kitchen range 5 in kitchen 2. A blowing side of duct 1 is connected to a fan unit 6 mounted on outside wall 3. In the shown embodiment duct 1 is trained along a ceiling 7 of kitchen 2. It is equally possible to envisage fan unit 6 being located on a roof and extraction duct 1 being oriented vertically and running to a roof duct.

When fan unit 6 is operating, the air above kitchen range 5 is suctioned into extractor hood 4, and from there discharged to the outside through duct 1 and unit 6. Present in the extracted air are grease particles and other contaminants which deposit on inner wall 8 of duct 1 (Fig. 2). This grease deposit 9 forms a layer on inner wall 8 which can develop relatively quickly because grease particles and contaminants from the passing airflow are caught therein.

Grease deposit 9 is highly flammable and can thus easily combust when a flame from kitchen range 5 is suctioned into duct 1. Insurance companies therefore require that measures be taken in order to reduce this fire hazard. This usually entails users periodically having to remove the grease deposit 9 from duct 1. This is almost not feasible in practice, resulting in these regulations occasionally being disregarded.

In order to control the fire hazard in a wholly new way, and thereby comply with the regulations of the insurance companies, the invention envisages a coating 10 being applied over grease deposit 9. This coating 10 is applied directly to grease deposit 9 and adheres thereto. In the figure the grease deposit 9 and coating 10 are shown offset for the sake of clarity, although in practice the coating 10 extends over the whole surface area of grease deposit 9. Coating 10 thus completely seals in the grease deposit 9, whereby it can no longer combust in the event a flame is suctioned into duct 1. In the shown embodiment the coating 10 is itself fire-resistant, thereby further limiting the fire hazard.

Coating 10 can further be liquid-tight, whereby it becomes possible after the treatment to further clean duct 1 periodically with liquid cleaning agents. This would not be possible without treatment of duct 1, because duct 1 consists of a spirally rolled strip of sheet metal 11 which has folded seams 12 along its edges. These folded seams 12 are not liquid-tight, so that the use of cleaning liquids would result in leakage which in the shown embodiment would become manifest in the form of stains in ceiling 7. In order to enable the result of such cleaning operations to be determined in simple manner the coating 10 has a relatively light colour in the shown embodiment, so that grease deposit 9 will contrast clearly therewith.

In the shown embodiment coating 10 is applied in liquid form over grease deposit 9 (step A in Fig. 4) and then cures (step B). Once coating 10 has cured, duct 1 can if necessary be cleaned periodically with liquid cleaning agents (step C).

The liquid material of the coating can be applied by means of spraying. Use can for instance be made here of a spray head 13 which is arranged rotatably on the end of a somewhat flexible compressed air conduit 14 and connected to a likewise somewhat flexible feed conduit 15 for the coating material. Spray head 13 has a number of substantially radially extending, flexible spacers 16 which are mounted in pairs on spray head 13 and curved in opposite directions. A user can move spray head 13 through the whole duct 1 by manipulating flexible conduits 14, 15. Spray head 13 is held in the centre of the duct here by spacers 16 which engage on inner surface 8 of duct 1. The liquid coating material is dispensed in uniform distribution in all directions by rotating the spray head 13 so that a uniform layer thickness is created.

In an alternative embodiment of the treatment method (Fig. 5) a double coating 10 is applied. Once this has adhered to grease deposit 9 and has cured, coating 10 is pulled loose from inner wall 8 and removed from duct 1 (also referred to as peeling) (step D). Grease deposit 9 is thus removed, whereby the fire hazard is further reduced. A new coating 10 can then be applied (step E) directly to inner wall 8. Once this has cured (step F), duct 1 is once again suitable for periodic cleaning with liquid cleaning agents.

The invention thus makes it possible in simple and effective manner to protect a duct 1 with grease deposit 9 present therein against fire.

Although the invention is elucidated above on the basis of an embodiment, it will be apparent that this can be varied in many ways within the scope of the following claims.