Automating Product Flow on Food Packaging Lines

Overall equipment effectiveness (OEE) improves when packers and processors understand the interactions between each component of the packaging line, as demonstrated by Iso-Flo shakers feeding potato strips to multihead weighers. Image courtesy of Key Technology.

How Processors and Packers Can Harmonize Machinery

By Rudy Sanchez, Food Handling Systems Product Manager at Key Technology

The performance of food packaging lines depends on how all the equipment works together. Packaging distribution systems that take solid food products from the processing line to form-fill-seal (FFS) packaging machines typically include conveyors with gates, scale feed shakers and multihead weighers that feed either the vertical- or horizontal-form-fill-seal machines. By understanding the interaction of these components and considering the system as a whole, processors and packers can maximize the output of the FFS machine while maintaining the highest product quality and easing operations.

In this article, we will consider the physical relationships between each of these machines and explore analog versus digital call signals, flood feeding versus steady state feeding, mass flow versus volumetric flow, proportional gates versus standard gates and more. The objective is to help food processors and packers optimize their operations by integrating control systems that enable their packaging machines to work together harmoniously.

A distribution shaker with side discharge chutes feeds green beans to snippers. Image courtesy of Key Technology.

Form-Fill-Seal Equipment

A vertical-form-fill-seal (VFFS) or horizontal-form-fill-seal (HFFS) machine is the anchor of many food packaging lines. Increasing its output is a primary goal because the quantity of saleable bags produced has a direct effect on the processor’s or packer’s bottom line.

The success of the operation is dependent, in part, on the ability of upstream equipment to deliver the ideal amount of product to the FFS machine at the perfect speed with the necessary separation between product charges that allows the jaws to seal properly without product interfering and compromising the quality of the seal. To achieve this, the FFS machine and the scale upstream are integrated – the FFS machine is the “initiating” system because its demand for product controls the “responding” upstream equipment.

Multihead Weighers

Regardless the number of buckets and the size of the buckets on the multihead weigher, the speed of the scale should be set slightly faster than the speed of the FFS machine so the FFS machine is never starved for product. The FFS machine will provide a signal to the multihead weigher when it is ready to accept the next product charge.

Overfeeding the multihead weigher by delivering too much product results in fewer available bucket combinations within the scale. This affects the weigher’s ability to hit the perfect total weight of the charge, which hurts weighing accuracy. Underfeeding the scale requires more buckets in a combination to achieve the total weight, which hurts the speed of the system since the buckets will need time to refill before being available again.

For these reasons, feeding the scale at the proper rate has a direct effect on the efficiency of the scale and thus the output of FFS machine. Infeed rings, infeed funnels and linear feed pan designs help present a constant waterfall of product to each bucket. Yet it’s the relationship between the weigher and the upstream scale feed shaker that ultimately controls the flow of product to the scale. The better the integration between the weigher and the scale feed shaker, the better the FFS machine’s output.

Scale Feed Shakers

A series of Impulse electromagnetic shakers feed a weighing hopper. Image courtesy of Key Technology.

Scale feed shakers are specialized vibratory conveyors that feature either mechanical drives or electromagnetic drives. The goal of these shakers is to spread product uniformly across the pan and evenly feed the scale so it is never overfed or underfed.

The most basic relationship between the scale and the scale feed shaker uses the scale’s infeed funnel as an accumulation device and a load cell or a level eye at the top cone of the scale that sends a digital on/off signal to the scale feed shaker to stop and start, as needed. This method of integration, referred to as “plop and drop” or “flood feeding,” is less than optimal because it has a tendency to overfeed the scale at the start and then starve the scale before turning back on, which hurts accuracy and speed. Unfortunately, this method of scale feeding is widely used.

Fortunately, there are several alternatives available to optimize scale feeding and scale operations, which increase FFS machine efficiency and ultimately profitability.

Utilizing a load cell or optical sensor at the top cone of the scale enables an analog signal to be sent to the scale feed shaker based on the weight or the height of product on the weigher’s top cone. The signal will speed up or slow down the flow rate of product from the scale feed shaker to maintain a constant weight or height of product on the scale to assure good product distribution to each bucket, which optimizes weights and speed.

A further improvement, called volumetric flow control, integrates the analog scale signal with a photo eye on the scale feed shaker, which monitors the volume of product and controls the distribution shaker upstream to feed a specific amount of product to the scale feed shaker. Since bags are filled by weight, not volume, volumetric flow can be improved upon, especially when the density of the product varies.

The most accurate way to achieve a steady stream is called mass flow control. It integrates the analog scale signal with a load cell on the scale feed shaker, which monitors the weight of product and regulates the distribution shaker upstream to feed the perfect amount of product to the scale feed shaker.

Distribution Shakers

Distribution shakers transport product from the processing line to the scale feed shakers. This system of conveyors, whether traditional vibratory shakers or a horizontal-motion shakers, can be fitted with standard slide gates, flip gates, pivot gates or proportional-control gates to discharge product to downstream equipment. While standard gates simply open and close, proportional gates allow the aperture to vary and thus better control the amount of product flowing to the next stage.

On the most basic lines with the fewest sensors and the least integration, if the FFS machine goes down, a signal causes a cascading effect on the “responding” systems, shutting down the upstream equipment. However, this basic line is incapable of making more minor adjustments to compensate for constant changes in line flow. Such lines often overfeed the first scales in the line, which reduces the accuracy of fills, followed by underfeeding subsequent scales, which starves the scales and reduces the output of these FFS machines.

On sophisticated lines with more integration, each FFS machine controls the line flow of its scale, which controls its scale feed shaker, which controls the gates on the distribution system so each machine is optimized individually as well as in combination. Each FFS machine can operate at different rates, producing different size bags, and the distribution shaker opens and closes each gate to discharge the exact amount of product to each scale feed shaker to optimize each scale and maximize the output of saleable bags being produced by every FFS machine.

Conclusion

Selecting the ideal equipment for the specific product and package is only the beginning of integrating a highly effective production line. To optimize the operation, processors and packers must understand the interaction of the components and consider the line holistically rather than as separate machines that are connected.

Fully integrating the controls costs more up front, but the added cost is quickly recovered thanks to improvements in overall equipment effectiveness (OEE) and the increased output of the FFS machine producing saleable bags.

About the Author

Rudy Sanchez is the Food Handling Systems Product Manager at Key Technology. Learn more at www.key.net.

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