The present invention relates to a process for filling a bag with a measured quantity of powdered or granular material, for example powdered cement.

It has long been known to fill a bag with powdered material such as cement by dispensing measured quantities of the material into the bag from a hopper.

However, using a conventional filling process, the packing density of the powdered material within a filled bag is typically very low, which has a number of disadvantages. Firstly, the loosely packed material within the bag will make the bag difficult to manipulate. Secondly, when the bag is opened, for example by hitting the bag with the blade of a shovel, a large amount of the powdered material may be dispersed into the surrounding atmosphere, thereby giving rise to a potential health hazard. Thirdly, a loosely packed bag, if sealed, will be more likely to burst when subjected to external pressure, for example when the bag is stored in a stack.

We have now devised a process for filling a bag with powdered material which overcomes the limitations of existing processes.

According to a first aspect of the present invention, there is provided a process for filling a bag with a powdered or granular material wherein a measured quantity of said material is subjected to a vacuum to compact the material prior to its being dispensed into the bag and once the bag has been filled with said material, said process further comprises fully sealing the mouth of the bag, and is characterised by compressing and/or vibrating the sealed bag to cause air within the bag to collect adjacent a point, forming a puncture hole in the bag at the point and then subjecting the bag to a vacuum and/or compressing the bag to remove air from the interior of the bag through the puncture hole.

It will be appreciated that by increasing the density of the powdered or granular material, the volume of air within the filled bag will be minimised.

Preferably the material is compacted within a chamber and is dispensed by positioning the chamber within the bag, such that the base of the chamber extends substantially to the base of the bag, and then releasing the compacted material from the base of the chamber whilst simultaneously separating the base of the chamber from the base of the bag.

The compacted material will thus remain relatively undisturbed as it is dispensed and therefore will maintain its high packing density.

Preferably, having been evacuated to compact the powdered or granular material, the top of the chamber is pressurised to encourage the release of the compacted material into the bag.

The chamber may be positioned within the bag by lowering the chamber into bag and/or by raising bag to envelop the chamber.

The base of the chamber may be separated from the base of the bag by raising the chamber and/or by lowering bag.

Once filled, the volume of air within the bag may be further reduced by inserting a suction device into the material contained in the bag, via the mouth of the bag, and applying suction via the suction device.

The volume of air within the bag may be further reduced by fully sealing the mouth of the bag, forming a small puncture hole in the side of the bag and then compressing the bag and/or subjecting the bag to a vaccuum, to expel air from the interior of the bag through the puncture hole.

Once the bag has been compressed and/or subjected to a vaccuum, the puncture hole is preferably closed, for example by a weld or by applying an adhesive patch to the bag to cover the hole.

Prior to forming the small puncture hole, the fully sealed bag may be vibrated and/or compressed to cause air within the bag to collect adjacent the point at which the puncture hole is to be formed.

In accordance with this invention as seen from a second aspect there is provided apparatus for filling a bag with powdered or granular material in accordance with the process of the first aspect.

DE-A-4107495 discloses a method and apparatus for filling a bag with powdered material, wherein a quantity of the material is subject to a vacuum in a form chamber to compact the material prior to being dispensed into a bag.

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawing which is a schematic illustration of an in-line bag packing process in accordance with the present invention.

Referring to the drawing, a hopper 2 is shown, from which powdered material is fed by an screw 4 to a weighing chamber 6. Once the desired weight of material has accumulated in the weighing chamber, the material is discharged into a conditioning chamber 8, within which the material is compacted by evacuating air from the chamber.

The compacted material is then released from the base of the conditioning chamber 8 into a plastics bag 10 which is positioned such that it envelops the conditioning chamber, with the base of the chamber extending substantially to the base of the bag. As the compacted material is being released, the plastics bag 10 is gradually lowered away from the conditioning chamber 8, thereby minimising any disturbance which might loosen the compacted material. To assist in the release of material from the conditioning chamber, a pressure differential is preferably established by re-introducing air into the top of the chamber.

The filled bag is then transported to a possing station where the mouth of the bag is held open as its contents are subjected to a low frequency jog, for example by repeatedly raising and dropping the bag or by subjecting the bag to a series of blows.

The filled bag may pass through a series of possing stations according to the rate at which filled bags are delivered from the conditioning chamber and the level of deaeration required.

A suction device (not shown) is then inserted into the material contained in the bag, via the mouth of the bag, and suction applied via the suction device to further compact the material. The apparatus is preferably arranged such that, between successive suction operations, air is blown through the suction device to dislodge any residual material therefrom, which might otherwise reduce the suction capability of the device.

In a process not covered by the claims the bag is then partially sealed by forming a series of welds 12 across its mouth and then compressed between a pair of opposed plates 14 to expel excess air from its interior through the partially sealed mouth. A pair of opposed rollers 16 run across the top of the bag 10 as it is compressed to expel any remaining air from the ullage region of the bag.

Excess air may also or otherwise be expelled from the interior of the partially sealed bag by subjecting the bag to a vaccuum, for example by placing the partially sealed bag in a vaccuum chamber which is then evacuated.

A second series of welds 18 is finally formed across the top of the bag 10, in parallel with the first series of welds 12, with the two series of welds being staggered to provide a series of convoluted channels which allow further air to escape from the bag, for example if the bag is compressed within a stack, but which also inhibit the release of the powdered or granular material from, or the ingress of moisture into, the bag.

In an alternative process which is covered by the claims, the mouth of the bag is fully sealed and the bag transported on its side along a vibrating conveyor belt, causing any remaining air to accumulate against the upper surface of the bag.

The fully sealed bag may also or otherwise be compressed, before the uppermost side of the bag is punctured and the bag compressed and/or subjected to a vaccuum, e.g. within a vaccuum chamber, to expel the accumulated air.

Finally, the puncture hole is scaled by a weld or by applying an adhesive patch over the hole.

The processes thus described result in a tightly packed bag of powdered material which contains a minimal volume of air.