All filling involves directing a liquid’s flow into a target. This becomes especially hard when the liquid doesn’t flow easily and the target is a moving one.
Viscous and semi-viscous liquids are challenging to handle in any circumstances, even when they’re dispensed into rigid containers. The challenge increases when they must be dropped into open spaces like tray cavities, or used in a processing step like being deposited onto, or into, a product, such as a filling or frosting for baked goods.
“Let’s say they’re flowable and runny but they’re still barely flowable and runny,” says Rod Gregg, executive vice president at Hinds-Bock. “That’s the challenging part for a company that makes filling and depositing equipment.”
The challenges start with getting the material through the filler in the first place: “If you can’t get it to flow into the machine consistently, you’re not going to fill or deposit consistently,” Gregg says.
Almost all such fillers are gravity-fed from a hopper above. If the product is too viscous to flow freely from the hopper, it needs to have some kind of action or agitation. This can be done with downward pressure, to start and maintain the flow, or a simple mixing action, to keep the contents stirred and in suspension. The latter is a good option for liquids made of immiscible components, like oil and water, or with particulates, especially large and/or delicate ones. Another option is jacketed hoppers, for material that has to be kept hot or cold. They can also be fitted with level sensors that trigger automatic replenishment, allowing for uninterrupted throughput.
Once the product leaves the filler’s hopper, there are three basic variables that determine how, and how much, it will flow: the propulsion mechanism, the shape of the nozzle, and how the nozzle moves during filling (if it does at all). The nozzle shape is the most customizable, and it has to be matched carefully to the product’s characteristics. Icing for sheet cakes, for instance, would be best dispensed from a wide, flat nozzle instead of a round one.
“A variety of nozzles and attachments can be used to tackle common depositing challenges such as dealing with mixtures that don’t have enough liquid to self-level or that contain mainly particulates with little liquid to make the product flowable,” says Steven Belyea, applications manager at Unifiller. The best way to find the right nozzle for a given application is to try it out, preferably at the supplier’s facility; Unifiller has a technology center that allows customers to try out a full range of nozzles, Belyea says.
The push for pistons
The means of propelling material that doesn’t flow freely has to be carefully chosen. It must apply sufficient force while allowing precise portioning. That usually means pistons.
“The core of Unifiller’s product portfolio is volumetric depositors using pistons to portion the product,” Belyea says. “Unifiller depositors are gentle on a wide range of products, from liquid to viscous with or without chunks, including salsas, deli salads, and sauces, where other propulsion methods tend to be damaging.”
Pistons combine force with precision, but for maximum precision, there should be one piston per portion. In other words, the amount deposited by an individual piston should be a single portion – no more, no less.
“The machines are sized by number of pistons needed, depending on how many containers you’re filling at one time,” Gregg says. Trying to fill several containers, or top several muffins, from a single large piston would be inaccurate.
Axis Automation uses several types of feeding mechanisms, depending on the application, says Chuck Sena, business development manager. One option is a combination of positive displacement pumps feeding either a single piston or a manifold.
“The combination of precise positioning with fine manual adjustment of individual pistons allows us to deliver repeatable performance with each deposit, regardless of the number of deposits across the production line,” Sena says. Axis also offers a lobed depositor, which uses interlocking rollers to draw fragile products through the system consistently and evenly.
Nozzles on the move
It’s often desirable for nozzles to move while they apply viscous product. This speeds up the line, because it doesn’t have to stop dead to let a piston push out a thick slurry. It also enables the filler to cover large targets, like a big cake or a sheet of doughnuts. Nozzles can move in a variety of ways, depending on the application, says Aaron Dodds, development director at FEMC.
“There are three types of traveling heads that we use,” Dodds says. “Linear travelling heads which follow the container, diving nozzles which go down into a container to fill from the bottom, and orbital heads which combine the linear travel with a diving nozzle to fill at higher speeds.” He explains that a linear traveling head is used when it needs to spend more time over a tray or other target, when it needs to hit a specific small spot, or if product needs to be splayed over a large target. Diving nozzles are used to reduce splashing, especially for less viscous liquids that are going into deep containers.
Another reason for a diving or vertical motion for a nozzle would be if an application required an extra amount of product delivered to small target.
“Some types of products may require vertical movement of the depositing head in order to provide the proper finish,” says Sena of Axis Automation. “For example, depositing jelly onto a thumbprint cookie can require using the depositing head to create a ‘dimple’ to define the depositing area before the product is dispensed. Another example is ensuring a ‘tip’ of frosting when decorating cupcakes or certain pastries.”
Other aspects of nozzle and pump operation are also customizable. “You can also customize when nozzles open, the velocity the pumps push, and other key parts about filler timing,” Dodds says. “These can be saved as a recipe and called up for different products, allowing you to have a customized filling profile that fits each unique product.”
Pneumatics or servos?
Fillers that handle viscous products are examples of applications in which servomotors can replace pneumatics. It depends on how much precision users require, and how much they’re willing to spend.
Unifiller uses depositors with pistons driven by servos. “Servo-based depositors are not affected by fluctuating air pressure from the compressed air system and are therefore more consistent and repeatable to give the most consistent and repeatable depositing solutions,” Belyea says.
FEMC offers both pneumatic- and servo-driven piston fillers. “The pneumatic devices have a lower up-front cost and are a familiar device with teams that have older equipment,” Dodds says. “The servo-driven devices offer enhanced speed and control settings, and allow for saving recipes.”
Axis also offers both kinds. “Servos allow us to precisely control the movement of components on the equipment. This helps us be very accurate when it comes to positioning products and controlling the volume of deposits,” Sena says. “Pneumatics are a cost-effective and reliable way to accomplish machine movements where precision is not as critical. Often we use pneumatics for handling slower cycle requirements such as raising or lowering a depositing head or controlling product flow along conveyors.”
Gregg of Hinds-Bock says the servo vs. pneumatics question is mainly one of expense. “It’s 80% pneumatics, but more and more customers would like to have servomotors to drive pistons and valves and things that are moving on these machines,” he says. “That’s typically the larger customer who can afford it, because it’s not cheap technology. If it were not expensive, everybody would do it and we would have it on every machine.”
Viscous and semi-viscous products are challenging to dispense, especially in applications that call for high accuracy. But a judicious choice of options will bring end users the combination of speed, reliability and versatility they need.