PROCESS AND DEVICE FOR CONTROLLING THE FEEDING AND DOSING OF A GRANULAR PRODUCT IN A PACKAGING PLANT

Technical Field

The present invention relates to the technical field concerning the packaging of granular or powder products in sacks containing predetermined amounts of the same products.

In particular, the invention relates to a process and a corresponding device for controlling the feeding and dosing of granular products coming from more feeding lines, and usually being products of different kinds, to a sacking machine of this packaging plant.

Background Art

It is known that different types of industrial products supplied in granular form, beginning from bulk product stocked in silos or otherwise available, are packed in sacks having substantially standardized form and dimensions, usually included between 10 and 50 kg.

The packaging is carried out in suitable automatic sacking machines, provided with hoppers for continuous receiving the product coming from the silos through various types of conveyors, for example pipes, and for supplying an already closed sack at the outlet. The product can be conveyed from the silos to the sacking machine by gravity, if the silos are situated at the higher level with respect to the sacking machine, or by known pneumatic or mechanical conveying means.

The sacking machines are provided with a section, from which sacks are withdrawn or in which they are made from a preformed sack or a band of tubular material having suitable characteristics wound on a bobbin. Depending on the kind of machine, the preformed sack is withdrawn from a storage container or formed from a tubular band in a suitable section of the machine.

In the latter case, inside the aforesaid section the band is unwound, cut to measure and welded crosswise with a welding bar so as to define the sack bottom. The sack mouth is hooked with pliers and delivered to the outlet of the loading hopper, from which the product to be packaged goes out. The flow of the product at the outlet is controlled by means of a suitable valve situated in the region of the bag-mouth, that is, the lower portion of the hopper. This valve is operated by the machine control computer, as a result of information received from a device weighing the product introduced in the sack, situated in the lower part of the hopper.

Once the filling operation is completed, that is when the sack reaches the prefixed weight, its mouth is closed by means of a transversal welding carried out by another welding bar. The reaching of the prefixed weight is checked by a weighing device integrated with the hopper.

Then the sack is brought to the outlet of the sacking machine, squared and withdrawn by a palletizing machine which places it on a pallet, in a stack of predetermined dimensions.

The above described operative sequence of sacking and palletizing does not create serious problems until the packaging line works always and only with a single product. However, in the manufacturing world, the plants are designed to package different products in succession. In general, a plant includes a certain number of silos, each of which contains a different granular product.

Each silo has a duct at its bottom, said duct being provided with a valve for closing the outlet mouth, through which the product is conveyed to the loading hopper of the sacking machine.

According to the normal manufacturing procedure, as a result of an order for a batch of product composed of a certain number of sacks (usually one or more pallets containing a predetermined number of sacks), the silo valve related to this product is opened for a period of time sufficient to fill the loading hopper. The capacity of this hopper is usually equal to the product of some sacks.

During the sacking operations, the valve can be kept always open or be opened and closed intermittently, with the help of level sensors provided in the hopper, so as to keep the quantity of product in the hopper sufficient to make the sacking machine work continuously.

When the number of sacks prefixed for the batch have been filled and palletized, another batch is packaged, often of a product different from the previous one. In this case, there is inevitably a certain amount of the first product left in the loading hopper. The quantity of the remaining product depends on the degree of approximation with which the moment of the last closure of the silo outlet valve can be determined, and it can be equivalent even to a significant portion of the hopper capacity.

Disclosure Of Invention

Technical Problem

The residue of the first product constitutes a serious drawback fot the production line operation. Actually, it is necessary to avoid the contamination of the subsequent production batch with the product of the previous batch.

Since the definition of the amount of the first product remained in the loading hopper is uncertain, it is necessary to interrupt the production to empty the hopper manually, or to continue the packaging until the hopper is completely empty and to obtain a quantity of sacks sufficient to complete a pallet, as well as an incomplete sack. Otherwise, the second batch can be packaged and the first sacks of the new production can be set aside.

In any case, there is a considerable waste of time and a substantial discard of product and material used for making the sacks.

Technical Solution

It is an object of the present invention to propose a process for controlling the feeding and dosing of different granular products in a sacking machine which allows to minimize, or even eliminate, the residue of the product in the loading hopper when the packaging operations of a prefixed number of sacks are completed.

Another object of the invention is to propose a device for controlling the feeding and dosing which carries out the above described process.

The above mentioned objects are wholly obtained in conformity with the present invention, according to the contents of claims 1 and 5.

Advantageous Effects

Description of Drawings

The characteristics of the invention, as they will result from the claims, are pointed out in the following detailed description, with reference to the enclosed drawings, in which:

figure 1 is a schematic lateral view of a plant for packaging granular products into respective sacks, which incorporates a device for controlling the feeding and dosing obtained according to the invention;

figures from 2 to 5 show schematically a significant portion of the plant of figure 1, in as many subsequent steps of the operative feeding sequence, according to the process of the present invention;

figure 6 is a view of the whole packaging plant comprising a second embodiment of the control device in accordance with the invention.

Best Mode

A preferred, but not exclusive embodiment of the present invention will be described in the following with reference to figure 1, which is a lateral schematic view of a plant 50 for packaging granular products into corresponding sacks.

The plant 50 includes, in particular, a sacking machine 30, aimed at receiving bulk products coming from storage containers 2, 3 to form, and fill in sequence the sacks 1 with the above mentioned products, until production batches are completed, each being composed of a prefixed number of sacks. The sacks 1 are then stacked in one or more pallets 6 by means of a special palletizing machine 60. In general, each batch is constituted by one or more complete pallets.

As a pure and not exhaustive example, the figures and the followig description refer to a plant 50 consisting of two storage containers 2, 3, each of which contains a different product to be packaged. However, it is understood that, for the purposes of the present invention, the number of storage containers in the plant can be arbitrary.

In any case, it is extremely important to avoid contamination among various products inside the sacks or to maintain such contamination marginal.

The operations for forming and filling the sacks, for their closing and stacking on pallets are entirely known and not relevant to the invention, or some structural innovative characteristics of the apparatuses that carry them out, are in any case subjects of different patent applications. Therefore, these operations and structural characteristics will not be further described in detail in the continuation of the present description.

The sacking machine 30 receives the product to be packaged through a loading hopper 31, whose upper part protrudes from the top of the machine 30. Known first weighing means for the sacks 35, associated to the hopper 31, are substantially formed by a load cell type weighing machine, schematized in figures from 2 to 5. The first weighing machine 35 is aimed at weighing the sack 1 being filled so as to supply in real time information about the actual quantity of product already inserted into the sack, and at defining in this way when the mouth of the hopper 31 should be closed.

Such information is transmitted to a control computer 40, provided with a suitable software for managing the packaging operations. The computer 40, in turn, is intended for controlling the opening and closing of the hopper loading mouth 36, so as to pour the product into the sack 1.

In the same figures, the sacking machine 30 is further schematized for the sake of simplicity and clearness of the description. They show only the loading hopper 31 and the forming means 37, transport means 38 and closing means 39 for the sack 1, in various operative positions.

The product is fed from the storage containers 2, 3 to the loading hopper 31 by means of ducts 10, 20 which join in the region of the upper part of the same hopper 31.

In accordance with a first and preferred embodiment of the invention, illustrated in figures from 1 to 5, in which the product is fed to the hopper 31 by gravity, the packaging plant 50 includes a device 100 for controlling the feeding and dosing of the product to be packaged. The device 100 includes, for each storage container 2, 3, a corresponding outlet valve Vul, Vu2, controlled by the control computer 40 in order to cut off the flow of product coming from the relative storage container 2, 3. For this purpose, they preferably consist of electromagnetic valves of suitable dimensions and mechanical characteristics, and are electrically connected to the aforesaid computer 40.

The outlet valves Vul,Vu2 are mounted between the outlet mouth of the relative storage containers 2, 3 and the proximal end 10a, 20a of the corresponding ducts 10, 20.

Supply cut off means Va, also provided in the region of the distal end 10b, 20b of the ducts 10, 20, are likewise controlled by the control computer 40 and aimed at interrupting the flow of product to the hopper 31 in cooperation with the outlet valves Vul, Vu2. In particular, in the present first embodiment, the supply cut off means Va are formed by a pair of separate and independent feed valves Val, Va2, mounted at the head of the respective ducts 10, 20.

The device 50 of the invention includes also second weighing means 32, associated to the loading hopper 31, connected electrically to the control computer 40 and aimed at supplying the latter with periodic or continuative information data regarding the weight of the product contained in the hopper 31. Also the above mentioned second weighing means 32 are formed by a load cell type weighing machine, mounted on supports 34 of the hopper 31.

The process for controlling feeding and dosing of granular products supplied to the sacking machine 30 in accordance with the invention includes, for each batch of sacks 1, a sequence of working steps related to the release of the product to be packaged from a respective storage container 2 to the loading hopper 31. The above mentioned management software, run on the computer 40, manages carrying out and timing of the aforesaid working steps on the basis of the number of sacks of each batch and of the amount of the product to be introduced into each sack. For better clearness and by way of example, in the following, reference will be made to a batch of 80 sacks of a granular product contained in the storage container 2.

The computer 40 manages, in a completely known way, also the operations of forming, filling and closing the sack 1. One of the advantages of the invention actually derives from the fact that carrying out of the process does not involve the use of additional control means besides those already provided for the conventional sack filling operation.

The packaging operation of the preferred, but not exclusive embodiment, will be described in the following, beginning from an initial situation schematized in figure 2, in which the outlet valves Vul, Vu2 as well as the feed valves Val, Va2 are closed and there is no product inside the hopper 31.

In the first step of the process, the computer 40 operates the first outlet valve Vul and the first feed valve Val to open (see figure 3), so as to make the product contained in the first storage container 2 reach the hopper 31. The amount of product present in the hopper 31 is constantly monitored by the same computer 40 by means of the second weighing machine 32. Consequently, the computer 40 starts the normal operations of filling the sacks 1, acting on the outlet mouth of the hopper 31 and on the first outlet valve Vul of the first storage container 2, so as to keep a certain amount of product in the hopper 31, typically, equivalent to the contents of 3 or 4 sacks.

When the number of the sacks 1 of the batch already filled gets near the total number of the sacks in the batch and, for example, reaches 75 sacks, the computer 40 modulates the aperture of the outlet Vul and feed Val valves, so as to adjust the flow of product towards the hopper 31. In particular, the feed valve Val is initially closed, while the outlet valve Vul is partially closed, so as to reduce considerably the flow of product at the outlet of the storage container 2 (see figure 4). Afterwards, the feed valve Val is partially opened (figure 5) and, at the same time, the contents of the product present inside the hopper 31 is monitored until the amount of the product is almost equal to the amount necessary to complete the batch, or to a slightly bigger amount, defined as a minimum value sufficient to compensate the tolerances present in the operation times of the valves and in the measuring of the weights by the device 100. At this point, the feed valve Val and outlet valve Vul are operated to close completely. In the hopper 31 there remains only the exact amount of product sufficient to fill the sacks necessary to complete the batch, or, at the most, a small residue that can be quantified empirically in few tens or few hundreds of gram of product.

At this point, the packaging plant 50 is ready to package another batch of sacks 1, for example with the product contained in the second storage container 3. Therefore, the process is repeated exactly as the one described above, operating the second outlet valve Vu2 and the second feed valve Va2.

A second embodiment of the invention is illustrated in figure 6 and relates to a type of plant 50, in which the products are supplied by force to the hopper 31 by means of pneumatic conveying means 70. The latter include substantially a blowing or sucking pump, which can be controlled by the control computer according to prefixed timing, when it is necessary to convey the product from inside the terminal portion 25 to the hopper 31. Such a configuration of the plant is usually adopted when the outlet mouths of the storage containers 10, 20 are positioned at a lower level with respect to the hopper 31, and thus the product cannot be supplied by gravity.

In this case, the ducts 10, 20 have a common terminal portion 25, connected to the pump 70 and having, at the opposite end, supply cut off means Va, composed of a single feed valve.

According to the process for controlling the feeding and dosing in accordance with the invention in said second embodiment, during the opening modulation step of the outlet valve Vul and feed valve Va, the outlet valve Vul is partially closed in the beginning, so as to reduce the flow of product inside the duct 10, and the feed valve Va is completely closed.

Afterwards, the control computer 40 operates the feed valve Va to open, partially or completely, for prefixed periods of time, depending on the information data received from the second weighing machine 32 regarding the content of residual product in the loading hopper 30, and on the number of remaining sacks 1 to be filled, so as to complete the batch. Consequently, the outlet valve Vul is closed when the exact amount of product is delivered sufficient to complete the filling of the last sack of the batch.

It is understood that what has been described above by way of mere examples and is not limiting. Therefore, possible modifications and variations of the invention are considered within the protective scope granted to the present technical solution, as described above and claimed below.