Made to measure

The advantage of flexible bulk containers, as reusable packaging, is that they can be folded up and that they have a low tare weight equivalent to less than 1% of the filling weight. Handling big-bags is easy and safe, providing suitable equipment is available. Practically every branch of industry – from chemicals through foodstuffs and pharmaceuticals to building materials – either uses products supplied in big-bags or fills such bags with finished products. Big-bags are manufactured in many different shapes and sizes to suit specific requirements. The bulk materials that need to be transported place a variety of demands on the packaging. Dust-proofness, mechanical protection, air-tightness, elimination of electrostatic charge, protection against the weather, bacteria and light, stability in transit, resistance to corrosion, effective utilisation of the filling capacity and straightforward, complete emptying all influence the filling method. The technology of the filling machines has to ensure strict compliance with the filling parameters. As production processes become more and more flexible, it must be possible to change the big-bag filling machines over quickly to new product variants with a wide range of attributes as well as to different container shapes and sizes. Nowadays, the central control system is expected to carry out this change-over automatically, without any intervention by the operator.

The design of modern big-bag filling machines not only has to satisfy the above requirements, but must do so in the most economical way possible – something that is not always easy. On the one hand the extremely wide variety of dimensions and variants appears to make job order manufacturing essential, while on the other hand users generally tend to prefer tried-and-tested standard solutions, which they see as minimising their risk. The consistent use of proven partial solutions in the form of building blocks is the only viable remedy here.

Careful design of the filling stations not only embraces sizing and coordination of the ratings, but also hygienic aspects. This is particularly important if the stations are used in the food or pharmaceutical industries, as well as in any production area in which product mixing and recontamination (e.g. by the extraction system) are prohibited. Weighing compensators made of seamless, injection-moulded, liquid silicone are one good example of compliance with hygiene regulations. These compensators are made in the plant on special, automatic injection-moulding machines and set extremely high standards with regard to hygiene, temperature stability, vibration isolation and mechanical strength. As the parts are injection-moulded, the surface of the silicone material is smooth and non-porous. The FDA certification for this material means that the compensators can be used without any reservations. The operator is able to observe the continuous metering process and monitor the cleaning function through the transparent compensator.

The modular design of these machines means that different weighing systems can be used. Depending on the filling material and the logistics concept, the stations can be built for suspended, stationary or combined weighing. Suspended weighing is advisable for free-flowing bulk material if large a-mounts of dirt accumulate, while stationary weighing is more suitable for filling if the pallet or other container (e.g. a shuttle container, drum, Octabin, etc.) is positioned underneath the weigher. The filling material can be compacted as it is metered.

A special isolating device protects the scales against vibrations. Combined weighing in conjunction with a mechanised charging head facilitates ergonomic working, even if the big bags are extremely high. The bags are attached to the charging head in the „lowered“ position, then filled and sealed automatically after the head has been raised. The slings and the filling nozzle are also released automatically.

Customers‘ preferences for specific makes can be taken into account when choosing the weighing cells and the metering controls. The interface between the weighing terminals and the customer’s existing data processing equipment or master computer is designed individually and implemented rationally with the aid of software modules.

An example of a „made-to-measure“ big-bag filling station is a system, which was delivered to a chemical firm as an extremely compact, mobile, calibrated bag-filling scale. The ultimate system concept was elaborated jointly with the owner prior to the tendering phase and then taken as a basis for the actual tender. The scale is used to fill an intermediate pharmaceutical product underneath an existing dryer and granulator. The station can be transported using a standard fork-lift truck, which also operates it when pallets are gathered and removed. It manages without a lifting unit, as all the big-bags that are filled are of the same height. Once the slings have been attached to the holders and the filling nozzle fitted over the expanding terminal, the start button is pressed to set the automatic filling cycle in motion. The inliner of the big-bag is fitted onto the expanding terminal, so that it is crease-free and dust-tight. At the same time, it is inflated with air or nitrogen and pressed onto the outer bag true to shape in just a few seconds. The inflater is designed to match the filling capacity and characteristics of the big bag exactly, to ensure that no time is wasted. Coarse and fine streams are metered into the inflated big-bag. The filling times are often less than one minute and the filling accuracy is well within the tolerances permitted by calibra-tion legislation. Despite its compactness, the station is just as convenient to operate and just as accurate as the majority of far larger stations. All the parts are made of stainless, non-corroding steel, and the parts in contact with the product are designed in accordance with hygiene regulations. The frame consists of totally enclosed sections with smooth surfaces, to ensure that those parts that are not in contact with the product are also easy to clean.

The explosion-proof filling and metering controller is mounted on the equipment. After attaching an empty big-bag manually and starting the metering cycle in the terminal program menu, the operator is guided through the data and metering value input dialog. Consequently, no special programming experience is necessary to operate the station. The variable system parameters are saved together with the product names, so that each product is filled optimally without having to be reprogrammed by the operator every single time.

Erich Emde

Fax: ++49/2604/970340

Further information cpp-232