DE MULDER, Luc (Moerhofstraat 47, Moerbeke-Waas, B-9180, BE)
| Claims 1. Process for filling a container (1 ) with a powdery material, said container having a filling opening (2) at the end of a flexible sleeve (3), by using a filling spout (4) having an outer wall (7), said spout comprising a material supply pipe (5) and a dust extraction pipe (11 ), comprising the steps of: - fitting the filling opening (2) of said sleeve over said outer wall (7) of said spout (4), thereby defining an air gap (16) between said sleeve (3) and said outer wall (7), - filling the container (1 ) through the supply pipe (5) with said powdery material, whilst simultaneously removing air from the bag through said dust extraction pipe (11 ) so as to create a Bernoulli effect in said air gap (16) pushing a portion of said sleeve (3) towards said outer wall (7). 2. Process according to claim 1 , wherein by creating said Bemouilli effect a portion of said sleeve (3) is pushed against said outer wall (7). 3. Process according to claims 1 or 2, wherein said filling spout (4) further comprises an inflatable seal (8) fitted around said outer wall (7), and comprising the steps of: - fitting the filling opening (2) of said sleeve over said outer wall (7) of said spout (4), thereby defining an air gap (16) between said sleeve (3) and said outer wall comprising said inflatable seal (8), - inflating said seal (8) to eliminate said air gap (16), whereby said sleeve is held tightly by said seal, - filling the container (1 ) through the supply pipe (5) with a volume of powdery material, whilst simultaneously removing air (14) through said dust extraction pipe (11 ), - deflating said seal (8) whilst continuing to fill the container through the supply pipe (5) with powdery material, thereby releasing said sleeve (3), forming again said air gap (16), and creating a Bernoulli effect in said air gap (16), by continuing to remove a volume of air through said dust extraction pipe (11 ). 4. Process according to claim 3, wherein after the deflating of said seal and releasing of said sleeve, the flow rate of powdery material through said material supply pipe (5) is lower than before. 5. Process according to any one of claims 1 to 4, further comprising the subsequent step of terminating the filling of said container, inflating said seal (8), whereby said air gap (16) is eliminated and said sleeve is held tightly by said seal, whilst removing air (14) through said dust extraction pipe (11 ). 6. Process according to claim 5, wherein after said subsequent step of terminating the filling of said container and inflating of said seal, said flexible sleeve is closed tighly under said seal, said seal is deflated and said filling opening (2) of said sleeve is removed from said outer wall (7) of said spout (4), whilst continuing to remove air through said dust extraction pipe (11 ). 7. Process according to any one of claims 1 to 6, wherein said powdery material is a dustforming material. |
The invention relates to a dosing (or weighing) and packaging installation for bags or containers with a flexible filling sleeve, whereby the sleeve is fit over an inflatable seal (or bellows) being part of the material filling spout. More precisely, very accurate and dust free performances are guaranteed by an apparatus enabling to break the mechanical seal during filling by suction of a concentric air stream from the exterior.
Generally spoken, dosing, weighing and packaging installations are one of the most critical installations regarding dust emissions, and often lack weighing accuracy. For systems based on the known bottom weighing concept - through the use of load- cells-, the connection between the filling spout of the installation and the sleeve of the container - mostly by using an inflatable seal or bellows - originates errors on the dosing by influencing the stress on the load-cells. Several attempt have been made in the past to develop so-called "dust-free" filling and weighing systems. Most of these systems use a filling spout having an air and dust suction tube forming a dust extraction pipe around the material filling tube of the installation. This dust extraction pipe is connected to a vacuum pump by an air/dust suction pipe comprising also a dedusting filter. Such systems are described in e.g. JP08-011803, JP09-309501 , US4,703,782 and US4,182,386. They are mostly able to prevent dust formation during the filling operation, but fail to provide for a dust-free removal of bags that have been filled. At the same time, due to the very reduced "compensation" vacuum during the filling operation, material will settle very fast on the walls of the dust extraction pipe and will create lagging material fall in a later phase. Also, the use of the inflatable seal prevents an accurate weighing, forcing the operator to correct the weight by hand after having detached the flexible sleeve of the bag, with an increased risk of dust formation, and a lower filling rate of the overall installation.
It is an object of the present invention to increase the accuracy of the dosing or weighing installation and to provide for an overall performant dust control system, including the prevention of dust formation from the material settling on the walls of the dust extraction pipe. This aim is achieved by a process for filling a container (1 ) with a powdery material, said container having a filling opening (2) at the end of a flexible sleeve (3), by using a filling spout (4) having an outer wall (7), said spout comprising a material supply pipe (5) and a dust extraction pipe (11 ), comprising the steps of: - fitting the filling opening (2) of said sleeve over said outer wall (7) of said spout (4), thereby defining an air gap (16) between said sleeve (3) and said outer wall (7),
- filling the container (1 ) through the supply pipe (5) with said powdery material, whilst simultaneously removing air from the bag through said dust extraction pipe (11 ) so as to create a Bernoulli effect in said air gap (16) pushing a portion of said sleeve (3) towards said outer wall (7).
By creating said Bernouilli effect a portion of the sleeve (3) is pushed against the outer wall (7).
Preferably, when filling spout (4) further comprises an inflatable seal (8) fitted around said outer wall (7), the process further comprising the steps of:
- fitting the filling opening (2) of said sleeve over said outer wall (7) of said spout (4), thereby defining an air gap (16) between said sleeve (3) and said outer wall comprising said inflatable seal (8),
- inflating said seal (8) to eliminate said air gap (16), whereby said sleeve is held tightly by said seal,
- filling the container (1 ) through the supply pipe (5) with a volume of powdery material, whilst simultaneously removing air (14) through said dust extraction pipe
(11 ),
- deflating said seal (8) whilst continuing to fill the container through the supply pipe (5) with powdery material, thereby releasing said sleeve (3), forming again said air gap (16), and creating a Bernoulli effect in said air gap (16), by continuing to remove a volume of air through said dust extraction pipe (11 ). It is preferable that, after deflating the seal and releasing the sleeve, the flow rate of powdery material through the material supply pipe (5) is lower than before.
In a preferred embodiment, the process comprises the subsequent step of terminating the filling of the container, inflating the seal (8), whereby the air gap (16) is eliminated and the sleeve is held tightly by the seal, whilst air (14) is removed through the dust extraction pipe (11 ). Also, after said subsequent step of terminating the filling of the container and inflating of the seal, the flexible sleeve can be closed tighly under said seal, and then the seal is deflated and the filling opening (2) of the sleeve is removed from the outer wall (7) of the spout (4), whilst continuing to remove air through the dust extraction pipe (11 ). The process is especially adapted for filling powdery material that is dustforming.
It is believed that the main feature of the novel process consists of breaking the mechanical seal between the sleeve of the container - or the filling opening of the bag - allowing a calibrated downwards concentric air stream to flow between the sleeve and filling spout, and practically in most installations this air stream is realized between the sleeve and the deflated bellows or seal. This stream will keep the sleeve in place by taking advantage of the Bernoulli law. The air stream 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).
For efficiency reasons, the process of the invention is used during the last phase of the material dosing only, since before, the major amount of the material is filled whilst the sleeve is fixed to the filling spout by the inflated bellows (seal). During this last filling phase there is no more sleeve stress, and the final filling operation continues until the exact set weight is reached. Obviously, there is no need for adjusting the weight by hand afterwards.
The calibrated air stream hence allows to achieve three objectives: accurate dosing during filling and packaging, - dust free material handling, and elimination of "lagging" material falling from the walls of the suction pipe, acting as a dust extraction pipe.
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: Final filling step
Fig. 4: Closure and removal of bag
Fig. 5: Conical vacuum valve 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 tube (5), having a concentric cylindrical double wall, forming the dust extraction pipe (11 ) around the filling tube, - connected to a vacuum suction pipe (6) provided with a dust trap downstream, and connected to a vacuum suction device, 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 at least 3 positions located on the air/dust suction pipe (or any other known type of false air infeed valve - e. g. an adjustable element in the form of a hinged flap or a slide element positioned relative to an opening in a duct), and
- a conical product valve (9) located at the outer edge of the filling tube.
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. Indeed, the material entering the bag carries with it air and also displaces air previously 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).
3) Final filling step (see Fig. 3)
Once the weight reaches a preset value, near to the end value, the speed of the feeding screw is reduced. At the same moment, the inflatable seal is deflated and releases the stress on the bag. The conical vacuum valve is partially closed, just enough to allow an airflow (a draft) entering the container (or bag) between the inflatable seal and the top part of the container. Due to the Bernoulli law, the plastic sheet will not drop off - see also the practical example below. In this situation, the container is totally free and the weighing without any error due to upward stress.
4) Closure and removal of bag (see Fig. 4)
When reaching the exact weight, the feeding screw is stopped instantly and the conical product valve (10) is closed. The inflatable seal (8) is blown up again to seal the opening of the packaging. At that time, as the conical vacuum valve (10) is closed completely, the 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.
The movement of the conical vacuum valve during the filing sequence is shown in Fig. 5: top: steps 1 )-2), middle: step 3), bottom: step 4).
The process and apparatus can be used for filling from small plastic bags (e.g. of 20 kg) up to bulk big bags (e.g. of 500 kg). The filling accuracy achieved is equal to or better than 0.025% (e.g. <5 g for a 20 kg bag), whereby no manual weight adjustment is needed anymore. The process can be used to fill powdery materials with a d 50 of 1 -10 μm, which powders are known to be very dusty.
In a practical example, a bag of 20 kg is to be filled with a very dusty material having a d50 of 6-7 μm. The bags are provided with a filling sleeve having a diameter which is 40 mm larger than the diameter of the deflated bellows. Steps 1 and 2 of the process are applied, to reach an intermediate weight in the bag of 18.6 kg. Step 3 is used to proceed further to 20 kg, whereby the conical vacuum valve is set to create a 60 mbar vacuum. The filling rate of step 3 is slower than of steps 1 and 2: 2 kg vs. 10 kg/min, since it is adjusted to prevent air (carrying dust) being evacuated by the vacuum system from the shrinking volume on top of the product in the bag from perturbating the inward air flow between sleeve and bellows. The Bernouilli effect created between sleeve and bellows causes the plastic bag to being pushed (by the outside air pressure) against the bellows at part of the sleeve's circumference, which part can change over time, causing a flapping effect. This again "decreases" the diameter of the flexible sleeve, and consequently the (empty) upper part of the bag is prevented from falling under its own weight. At the same time there are no forces lifting the sleeve upwards. Hence, the Bernouilli effect is thought to be responsible for holding upward the sleeve in a contact-free mode, enabling the accurate weighing of the bag, whilst all dust is sucked off from the sleeve and bag's inside. The maximum dust deposit during a filling cycle is 2 mg/m 2 . The dust emission is kept well under 20 μg/m 3 . The example above illustrates the process of the invention. However, it should be understood that for each individual bag or container a different setting is necessary: the stiffness of the bag, its dimensions, especially the diameter of the sleeve versus the diameter of the filling spout, together with the filling speed, determine the pressure to be created by the vacuum valve for causing the Bernouilli effect. The tuning of the pressure should prevent the bag either from imploding (vacuum too high), or falling under its own weight and/or dust emission when the inward air flow is too low (vacuum too small).
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