Box and bag filling systems are used in a wide spectrum of commercial enterprises throughout the world to rapidly fill bulk containers to a precise net weight. These containers, of course, rapidly find their way into the wider commercial marketplace serving end users and as well as manufacturers that produce the goods we all expect to find in our local market places.
At the very core of any well-designed B/B filling system lie several fundamental characteristics. First and perhaps foremost is recognition of the fact that all materials possess differing flow characteristics. When subjected to angular motion, sand, for example, moves differently than rocks and dry materials move differently than materials containing an appreciable amount of internal moisture. Why is this fact so important? Because systems that are designed to handle the movement of one type of material may be inefficient or even critically troublesome when attempting to move materials of radically differing physical characteristics. A system, for example, that employs a strategy to move rice into boxes or bulk bags will find it impossible to efficiently handle the movement of freshly processed shrimp or squid.
Anyone considering the purchase of a box or bulk bag filling system that is not guaranteed by the manufacturer to effectively handle a specific material is well advised to ask that the manufacturer test the proposed system using sample material provided by the customer.
Gravity vs. vibratory movement methods. When to employ which.
The standard methods of moving sizable quantities of dry, particluated materials from point A to point B generally come in one of two forms: 1) systems that are designed to exploit the natural force of gravity and 2) systems employing an electro/mechanical vibrating device to really get things moving along quickly and still achieve precise net weigh filling objectives.
Most B/B filling systems commercially available on the market today typically use only the second strategy as the primary transport method. Systems designed to exploit the force of gravity to move products are available and are best applied to materials that are not easily susceptible to damage or breakage.
Gravity-feed options, although perhaps efficient in moving sizable amounts of material in a very short timeframe, are often stressful to the material and frequently cause an unacceptable level of product breakage. Companies often reject incorporating gravity-feed options into their systems for this very reason. Producers of fresh walnut meats, for example, are very sensitive to this issue. Gravity-feed options, however, are welcome additions to systems designed to fill bulk bags of in-shell almonds and walnuts.
Regardless of whether or not one chooses to incorporate a gravity-feed option in their system, a vibrating device is always used to at least complete the dribble-feed (aka “top-off”) portion of the fill cycle. If a vibrating pan is used to fulfill both phases of the filling cycle (bulk and dribble-feed) the pans are typically configured with a bulk and dribble-feed division. More often than not, the bulk side of the pan is also equipped with a flow restricter gate designed to hold back bulk flow movement while the dribble-feed portion of the pan completes its mission. Dribble-feed sections are also specially configured with “deep valley” channels that aid in precision discharge of product during the last phase of the filling cycle.
Direct or indirect filling strategies
Box and bulk bag filling systems utilize one of two different strategies to fill containers: direct and indirect filling methods.
Direct bag and box filling systems are designed to directly deliver material to a container placed on a weighing platform. Basic units of this type have become ubiquitous in the agricultural, industrial and petro/chemical marketplace due to their low cost, their ability to be rapidly installed in almost any production environment and their ease of use; an operator simply places the container on a scale, presses the TARE button and then places material directly into the container until the targeted net weight is achieved. Systems of this variety are typically used to complete sample or short-run production orders.
Manually operated systems of this variety are also very easy to automate thanks to the numerous weighing instrument manufacturers offering high quality, weight-based controllers that are specifically designed for the purpose of retrofitting the many manual or semi-automated systems of this type that are operational in many industries today.
Indirect B/B filling systems, on the other hand, first deliver a precise amount (by weight) of product to a discrete hopper that’s equipped with a discharge “clamshell.” When the precise target weight of material in the hopper is achieved, the clamshell at the hopper’s terminus opens (automatically if the system is equipped with a proximity sensor to detect the presence of a waiting container and by delayed action if a foot press device is utilized to signal a discharge-ready condition) releases the measured product to the waiting container.
Software control is king
One of the most critical elements of any bag or box filling system is very frequently overlooked by potential buyers – the software controls used to manage every hardware component that’s incorporated into the system. The sophistication of the control instrumentation coupled with a robust software application could mean the difference in thousands of dollars to any project of this type. The ability to control vibrator speeds via application software, for example, will determine whether or not a company will have to use independent potentiometers on each vibrator for this purpose. Extra components create a larger system ”footprint” and add additional costs and maintenance protocols that could have been avoided entirely if the controller was capable of addressing issues of this type with user applied software.
Having participated in the development of a great many bag and box filling systems over the course of my career, I know of only one manufacturer of weighing and process control instrumentation that offers excellent solutions for vibrator speed control needs – The Avery Weigh-Tronix GSE 660 series Process Controller. Their 660 line of process controllers offer a programmable digital I/O section that easily interfaces to their specially designed Silicon Controlled Rectifier (SCR) option, enabling impressive control of an electrical current’s sine wave and thus vibrator pan “action.”
Identify and avoid systems with built-in obsolescence
System software should be able to not only efficiently monitor and control the system’s components (motors, solenoids, vibrators, proximity sensors, etc.) but it should also provide a pathway to integration with a company’s back-office management system(s). Data collection, data reporting and data exchange capabilities with a company’s increasingly networked systems are quickly becoming standard expectations of businesses concerned with production, inventory, auditing and traceability issues. The true test of a controller’s capabilities – beyond the expected ability to adequately control system hardware and rapidly fill containers to a precise net weight – is how well the system is software amenable to collecting information about the process in its charge, communicating that data to a wider network of production and business interests and enabling the system operators to set the system on a path of self-correcting operation, requiring minimal operator intervention once set in motion. Only a few controllers available on the international market today are manifestly capable of living up to performing these tasks with equal gusto.
Few inconveniences are more costly than discovering that the system that you’ve selected and have placed in service is unable to meet the progressively challenging demands that all users quite naturally place on them during the course of their lifespan. If your company is considering the purchase of a net weigh filling system, it’s critical that you give serious consideration to the system controller’s capabilities. Discovering, at the precise moment that you wish to attach a barcode reader and label printer to the system, that it only has a single communications port will make for a very bad (and expensive) day.
If you’re uncertain about the equipment that you’re considering, consult with others in your industry that may have had more experience with the type of equipment that you’re considering purchasing. You’ll quickly find that most industry professionals are happy to share their experiences with you. Moreover, they often provide a level of insight and advice unmatched by any other source that you’re likely to find.
Al Blazo is an independent consultant with twenty years of experience in the weighing, measurement and process control industry. Al specializes in applications development for the GSE® line of process control instrumentation. He can be reached at firstname.lastname@example.org.