The invention relates to a filling head or spout of a weighing and packaging installation for bags or containers, and the process of filling said bags or containers. More precisely, when a dustforming material is to be filled, dust free performance is guaranteed by the use of a filling spout provided with a double wall, accomodating both the material supply pipe and a concentric outer dust extraction pipe, that can be closed independently from the supply pipe.

Generally spoken, dosing, weighing and packaging installations are one of the most critical installations regarding dust emissions. Most known systems are built for filling bags or containers having a flexible filling sleeve, whereby the sleeve is fit over an inflatable seal (or bellows) being part of the material filling spout. The filling head carrying the inflatable seal is provided with a double wall, the interior being the material supply pipe, and the exterior a dust extraction pipe connected to a vacuum dedusting system, comprising a suction pipe and a downstream dust trap. Most of the time, when the filling operation stops and while removing the filled container (and after), the dust extraction pipe stays open and will emit a lot of dust, that has been settling on the walls of that chamber during the filling operation.

Sometimes the filling head is provided with a "pan", moving over the head before the container is removed. Even when this pan closes the head, experience learns that there is no hermetical seal and dust will still escape from the gap between the pan and the edges of the dust extraction pipe.

Such systems are described in e.g. US7,063,111 B2 and EP1319599 B1. In US7, 063,111 B2 there is provided a closing cone for covering both the material supply pipe and the dust extraction pipe.

A further improved system is shown in DE10247291 A1. Here the filling head is provided with a dust extraction pipe operating during the filling of the container. However, there is no valve to close the inlet of this extraction pipe, and the extraction is stopped before the container's filling opening is released from the inflatable seal. Dust trapped in the extraction pipe can be emitted to the exterior, and dust accumulated on top of the material in the container can escape also.

It is an object of the present invention to provide for an overall performant dust control system, including the prevention of dust formation from the material falling from the walls of the dust extraction pipe once the air extraction is turned off.

This aim is achieved by a process for filling a container (1 ), having a filling opening (2) at the end of a flexible sleeve (3), with a quantity of dustforming product, using a filling spout (4) provided with a product supply pipe (5) and a dust extraction pipe (11 ), comprising the steps of:

- fitting the filling opening (2) of said sleeve (3) over the extremity of said spout (4) in an airtight manner,

- filling the container (1 ) through the product supply pipe (5) whilst extracting dust by suction through the dust extraction pipe (11 ),

- closing the outlet of said supply pipe (5), whilst increasing the suction to remove dust from the filling opening (2), subsequently

- releasing the filling opening (2) from the extremity of the spout (4), and subsequently - closing the inlet of the dust extraction pipe (11 ).

The references signs are illustrated on the drawings below.

Preferably, the upper part of the sleeve (3) is fitted over the extremity of the spout (4), hereby longitudinally stretching said flexible sleeve. Also, during the suction step after closing the outlet of said supply pipe (5):

- the distance between the filling spout (4) and the container (1 ) is decreased, hereby unstretching the flexible sleeve (3),

- subsequently squeezing diametrically and tightly closing the sleeve,

- releasing the filling opening (2) of the container (1 ) from the filling spout (4), and - closing the inlet of the dust extraction pipe (11 ).

In another embodiment, between the steps of:

- subsequently squeezing diametrically and tightly closing said sleeve (3), and

- releasing the filling opening (2) of said container (1 ) from said filling spout (4); the suction through the dust extraction pipe (11 ) is further increased. The process is especially suitable when the container (1 ) is a big-bag having a circular sleeve (3) and a filling opening (2).

An apparatus for carrying out the process above comprises a filling spout having a cylindrical material supply pipe fitted within a dust extraction pipe, a product valve, adapted for closing the outlet of the supply pipe hermetically; and a ventilation valve, adapted for closing the inlet of said dust extraction pipe hermetically. The product valve can be a conically or frusto-conically formed member having a circular edge, adapted to fit with the annular face of the outlet of said supply pipe. The dust extraction pipe can be in the form of a frusto-conical hood fitted around the extremity of the material supply pipe, and is connected to at least one exhaust tube. The ventilation valve is preferably a frusto-conically formed member adapted to tightly fit into the hood and around the supply pipe, in order to close the inlet of said dust extraction pipe. As the dust extraction pipe closes after filling of the container and after the container has been removed from the filling head, this guarantees that no material can fall from the filling spout while and after removing the filled container. The removing action of the container is performed whilst maintaining the dedusting vacuum. Under the same conditions, the dust extraction pipe will be finally closed, i.e. before cutting the vacuum.

Hence, the invention further describes an apparatus for filling a container (1 ) with a dustforming product, said container having a filling opening (2), the apparatus comprising a filling spout (4) provided with a product supply pipe (5) and a dust extraction pipe (11 ), means to fit said filling opening (2) over said filling spout (4), a product valve (9), adapted for closing the outlet of said supply pipe (5) hermetically, and a ventilation valve (16), adapted for closing the inlet of said dust extraction pipe (11 ) hermetically characterized in that said ventilation valve (16) can be operated independently from said product valve (9). The product supply pipe (5) is preferably cylindrical, and centered inside the dust extraction pipe (11 ). ALso, both the product supply pipe (5) and the dust extraction pipe (11 ) can be provided with an outwardly formed frusto-conical extension so as to form an annular inlet (17) of the dust extraction pipe facing away from the outlet of the supply pipe (5). In that case, the product valve (9) is preferably a conically formed member, adapted to close the outlet of said supply pipe (5). Also, the ventilation valve (16) is then preferably a frusto-conically formed member adapted to tightly close the inlet of said dust extraction pipe (11 ).

In a particular embodiement, the apparatus further comprising a mechanism (18), preferably situated inside the supply pipe (5), adapted to move the product and ventilation valve (16) together, whilst also permitting to move the ventilation valve (16) independently when the product valve (9) closes the outlet of the supply pipe (5).

The above described apparatus can be connected to a container (1 ), wherein said container is a big-bag having a circular sleeve (3) and filling opening (2). The apparatus preferably also comprises a weighing system for carrying a container, that is capable of lifting or lowering said container during the filling process.

It is believed that the main feature of the novel process consists in using an independent closing mechanism for both the material supply pipe and the outer dust extraction pipe, together with the process of continuing and even increasing the suction of air carrying dust through the dust extraction pipe after having closed the material supply pipe.

The air stream through the dust extraction pipe evacuates: - all the dust that is present on the walls of the bag's sleeve,

- dust being formed above the material already present in the bag, and

- dust in the pipe providing the suction through the filling spout (the dust extraction pipe).

The sleeve of the bag or container is released from the filling spout before the closure of the dust extraction pipe. Once all of the dust has been removed the dust extraction pipe is closed whilst continuing the air suction.

The invention is illustrated with the following figures: Fig. 1 : Start-up position of filling station Fig. 2: High-speed filling bulk material Fig. 3: Closure and removal of bag Fig. 4: Sectional view of filling head during high-speed filling

Fig. 5 a-b-c: Position of different parts of the filling head during the filling operation

For using the process of the invention, a typical bag filling installation comprises the following well-known parts (see also the Figures):

- A screw feeder or rotary valve (12) with frequency controller,

- a filling sput (4), having a concentric double wall, forming the dust extraction pipe (11 ) around the filling tube (5), - connected to a vacuum suction pipe (6) provided with a dust trap downstream, and connected to a vacuum suction device,

- a conical product valve (9) located at the outer edge of the filling tube, and

- a lifting and weighing table (15) (with or without rollers) Preferably also, the installation comprises - an inflatable seal (8), the so-called "bellows" located around the filling tube,

- a conical vacuum valve (10) with 3 positions located on the air/dust suction pipe.

A typical filling sequence for this apparatus is now described.

1 ) Start-up position of filling station (see Fig. 1 )

The initial height of the lifting roller table (15) is adjusted (manually), depending upon the operator's choice and the kind of packaging. The vacuum suction device (not shown on the Figure, situated downstream of the vacuum valve (10)) is started, and the opening (2) of the plastic bag (1 ) or the sleeve (3) of the bulk bag (liner) is slided over the inflatable seal (8) by the operator.

2) High-speed filling bulk material (see Fig. 2)

Once the sleeve is in place, the operator starts the filling sequence: the weight processor puts to zero the net weight. The seal is inflated and holds the opening of the bag stretched. The conical vacuum valve (10) opens, together with the product valve (9). The feeding screw (12) starts conveying the product (13) to the filling spout (5) with a high flow rate. Note that the conical vacuum valve (10) is set to its full open position in order to allow only a small vacuum, just enough to compensate the product volume increase in the bag. The air (14) carrying dust from above the product level is removed via the dust extraction pipe (11 ) and the vacuum suction pipe (6). Fig. 4 shows the filling spout assembly during this phase

3) Closure and removal of bag (see Fig. 3) When reaching the exact weight, the feeding screw is stopped instantly and the conical product valve (10) is closed. At that time, the conical vacuum valve (10) is closed completely, and full vacuum is applied to the filled packaging. At the same moment, the roller table (15) is progressively lifted so that the plastic bag will shrink above the product level. The operator can now seal the bag just above the product level with a plastic strap. Next, he releases the inflatable seal (by manual command). Note that the conical vacuum valve remains in the full vacuum position. The operator finally removes the plastic bag or sleeve under vacuum by forcing the opening downwards. This action will mechanically clean the inner wall of the bag or sleeve and will avoid dust to diffuse in the surroundings. After a few seconds, the roller table is progressively returned to its original lower position. After another few seconds, when all the dust remaining on the walls of the dust extraction pipe has disappeared, the conical vacuum valve (10) is fully opened again. The apparatus is now ready for a new filling sequence.

Fig. 5 a-b-c shows the position of the different parts of the filling head during the filling operation and when the plastic bag is removed:

Fig. 5a: product valve and ventilation valve are open during phase 2: High-speed filling bulk material;

Fig. 5b: product valve is closed, ventilation valve remains open when: - reaching the exact weight,

- lifting the roller table and

- sealing and removing the bag;

Fig. 5c: ventilation valve is now closed also, but only after the bag has been removed.