The task:
Emptying bulk solids, precise dosing and gentle conveying
The requirements for bulk material handling systems are sometimes difficult to fulfil due to special product properties. However, if special structural features are added to this, the planning of such a system becomes a real challenge.
Precise dosing and gentle conveying of raw materials to the mixer are decisive for the quality of the end product. This is all the more important if high-quality films are to be produced later. If just one of the many parameters is not correct, it can lead to problems not only in film production, but also in the subsequent application. Until now, a film specialist has therefore monitored the dosing and feeding of the starting products into the mixing process with Argus eyes and virtually by hand. Now, however, a new system was to be integrated into the production process to automatically feed the raw materials into the mixer.
The new filling and dosing system consists of six stations, comprising three big bag emptying stations and three bag emptying devices.
Only one operator is required to control the system. The entire dosing and conveying process is automated. Special focus was placed on the product transfer from the sacks and big bags, where attention was paid to dust-tightness everywhere. Filters and an automatic extraction system were also installed. In addition, some Atex zones had to be taken into account.
However, these were by no means the only challenges: For example, the floor slab on which the system was installed is only twelve centimetres thick. The load of the system therefore had to be distributed as widely as possible. The entire filling and dosing system was therefore placed in a specially constructed base frame.
Self-willed bulk solids
Unusual paths in the system.
Normally, a product would first be conveyed to the mixer and then dosed directly in front of the mixer. In this case, however, the spatial conditions did not allow for this, as the space for the system was extremely limited. It was therefore decided that the products would be dosed directly after emptying and then fed to the mixer via a very long conveyor line.
Three bag emptying systems and three big bag emptying systems were integrated for filling. Each of these stations was designed for the specific properties of the six raw materials: Two raw materials with different bulk densities come as bagged goods and are easy to pour. Two other product types are delivered in big bags and are more similar in consistency to flour, i.e. they form bridges. Two other raw materials also have their pitfalls. One colourant virtually sticks to metallic surfaces, while the other tends to form lumps.
Thanks to the integrated walking device, even bridge-forming products can be emptied easily.
Essential: High dosing accuracy
Dosing at its finest
Depending on where the film will be used later, for example indoors or outdoors, or the colour or desired film thickness, the mixture consists of different compositions. Around 140 mixtures are possible. The requirements for precision in the filling of each individual raw material are therefore very high. Any deviation has a direct effect on the quality of the film. This is why, for example, a high dosing accuracy (plus minus 50 grams) must be maintained for the colourant.
The JEL AV discharge device is used to empty the big bag containing the colourant. This discharge device with agitator and side scrapers was specially developed for the continuous discharge of poorly flowing products. The discharge arms are wedge-shaped and run along the edge of the container wall. This ensures forced discharge – without bridging and core flow. A negative-conical container favours the sliding of the material from above. When the discharge device is started, the scraper at the bottom of the container begins to rotate. The discharge rate can be controlled by changing the speed. The container and scraper are easy to clean. In addition, the low speeds enable very gentle product discharge.
The JEL AV discharge device reliably discharges even products that are difficult to flow.
Properly shaken up
The raw material from the bagged goods is first emptied into the collection container. A dust-tight discharge hopper, which is made entirely of stainless steel and has a double seal, ensures a clean process. The bag dumping cabin is also equipped with dust extraction filters. The advantage is the space-saving design and the ease of operation and cleaning. The product is then conveyed via a pusher and a dosing screw, which is equipped with lateral flexing pads and pressurised with compressed air.
To improve the discharge of this product, it first passes through a strainer with a dosing screw. The compact JEL PS straining sieve is used for free-flowing bulk materials for passing through oversize-free product and for deagglomerating cohesive bulk materials. The straining sieve is driven by a shaft-mounted geared motor. The product falls out from below the sieve in the desired degree of comminution and can be precisely dosed.
Two other raw materials, on the other hand, are less complicated to handle; they require neither a straining sieve nor an additional push from the fulling pads.
To ensure a clean process, the bag chute cabin is equipped with dust extraction filters.
Bulk materials that stick together are deagglomerated after emptying the bag using the JEL PS passing sieve.
Keeping the process running
Trials provide process reliability
The downstream dosing screws make dosing even more precise. The coarse dosing starts first and then the fine dosing. To prevent trickling, the closing lid on the auger is automatically activated and the outlet is closed. As a result, the dosing screw is emptied very cleanly and product discharge is avoided.
All dosing screws are mounted on load cells. Once dosing is complete, the products are conveyed to the mixer via a vacuum conveyor. An unusual feature of the system is its long conveyor line of 25 metres. The vacuum conveyor was therefore also redesigned to cope with the distance. Despite the length, the components had to be transported to the storage container in less than twelve seconds. This also had to be adapted due to its size of 95 litres. A heavy-duty flap was specially developed here to hold the weight of the products before they are fed into the mixer.
All products are conveyed one after the other. The pipework is shut off after each product via pinch valves and the pipework is drained. Ball valves have been integrated into the system for this purpose. Any residues in the pipework, such as the strongly adhesive dye, are shaken free by ultrasonic converters.
Outlook: To ensure that all processes in the system are perfectly harmonised, three months of tests were carried out in the Engelsmann technical centre in advance. This meant that the system could be installed in December 2023 despite the highly diverse properties of the products to be dosed and the complex structural requirements due to the limited space available. After the first preliminary tests were also successful, the system has been in operation since the beginning of 2024.
All products are dosed with high precision and conveyed cleanly and, above all, dust-free into the connected mixer, meaning that high-quality films can now be produced.