Filling Machinery for Free Flowing Liquids
Viscosity is a well-known term in the packaging industry, especially when it comes to preparing liquids for the shelf. In general packaging terms, the viscosity of a product is referring to how freely a product flows. Low viscosity products, such as water, flow freely and easily. The higher the viscosity of a liquid climbs, the less freely it flows. Motor oil and honey would be slightly higher in viscosity, and products such as putty and sealant would be at the top of a viscosity chart. Common sense dictates that water flows more freely than honey, motor oil or putty, so that a general idea of a products viscosity can often be garnered just by seeing the product and whether it is thick or thin.
When using an automated machine for filling bottles or other containers, some are built more suited to handle free flowing liquids, in that product may be recirculated or may be delivered to bottles without assistance from a pump. Both overflow filling machines and gravity fillers are popular choices for packaging lines preparing low viscosity products, and each offers a unique fill principle which may serve a packager better depending on product, package and other factors.
Overflow filling machines fill each container to the same level, allowing any liquid that exceeds the desired level to flow back in to a holding tank. The fill to level principle is ideal for products packaged in clear containers, allowing for a clean shelf presence. However, the overflow filler really only works with low to medium viscosity products. While thicker products may be able to travel the pathway, the slower moving liquids can result in truly inefficient fill times to reach the level fills and allow excess product to overflow. In addition, while any product may change viscosity based on temperature, thin products typically require a more drastic change in temperature to effect viscosity while thicker products may change on more subtle temperature fluctuation. If product is delivered to a overflow machine at different temperatures, the fills can become inconsistent and a packager may spend excessive time adjusting the filler settings.
A gravity filling machine, on the other hand, fills by volume using - as the name suggests - gravity. Gravity fillers will include a tank above the fill heads that holds product. Using a time-based fill, nozzles will open and close for a set amount of time to allow the product to flow from the tank in to the waiting bottles. Thicker products in a gravity filler simply would not flow fast enough, or at all, without the assistance of a pump to make the machine efficient. (Note that a gravity filler may use a pump to supply the tank, but not to fill the bottles, though pump filling machines are available for thicker products.) Also, like the overflow filler, changes in viscosity of thicker products can lead to inconsistent fills over time.
So while the overflow and gravity filler offer ideal fills for lower viscosity products based on fill level and volume, efficiency and consistency will typically restrict these types of liquid fillers when thicker products are in use. For those packagers preparing high viscosity products, other options exist, including piston fillers, pump fillers and even hot fills to lower viscosity in some situations. For more information on all of the different filling machines offered by Liquid Packaging Solutions, browse the Filling Machinery section of the website.