Filling Bottles: Go with the Flowmeter
As bottle-filling machines look for greater speed and consistency, some users move from older weigh cell technology to flowmeter-based systems, but it’s a tough application.
U.S. Bottlers in Charlotte, N.C., is a manufacturer of high-speed liquid packaging equipment used by the food, pharmaceutical, chemical, and automotive industries. Our products include rotary cleaning, filling, and capping machines that operate at speeds from 20 to more than 1,000 bottles per minute. In 2012, U.S. Bottlers will celebrate its 100th anniversary.
Over the years, the liquid bottling industry has moved from mechanical fillers and weigh-scale fillers using load cell technology to flowmeter-based fillers. The flowmeter filler is now the preferred style over the weigh-scale filler. In fact, many mechanical and weigh-scale filler customers have been converting older machines to flowmeter-based fillers for more modern support and better bottle handling control.
To meet the demand for new and upgraded liquid filling machines, U.S. Bottlers uses magnetic and Coriolis flowmeters from Endress+Hauser on all its filling machines. These families of flowmeters were selected after significant research and rigorous comparison to competitive products on a variety of attributes.
Inside a liquid bottling machine
Liquid bottling machines are available in several styles including pressure gravity, vacuum, piston, electronic weigh scale, flow, and mass measurement. All have advantages and disadvantages in various applications but—in general—flowmeter-based filling machines have emerged as the first choice for most of our customers.
In a flowmeter-based system, an external tank system moves liquid product to the roof of the filler for disbursement through a distribution manifold. Empty containers are fed onto a rotary table, separated, and then positioned on individual filling stations under custom-designed filling valves. When a container is positioned under the valve, the filling process begins at a rate designed to suit the container's particular shape and dimensions, and the product’s flow characteristics. Once the target fill volume is achieved, the filling process stops.
Complicating the matter is the need to fill bottles and containers as fast as possible. Consequently, liquid bottling machines can have up to 120 filling heads—and can handle containers such as metal cans, PET bottles, and pails at speeds up to 1,000 bottles per minute. The entire machine design process is a matter of balancing speed, filling accuracy, and cleanliness, so accurate and repeatable flow measurements are critical.
The ability of the meter to measure the liquid flow properly is the most critical step in the filler cycle. The selection of the flowmeter is influenced significantly by the flow characteristics of the product, any pulp or particulates, foaming tendencies, as well as sensitivity of the liquid ingredients.
We have the ability to program the stages of filling in a fast or slow mode. In a two-stage fill, it can be programmed to start fast and slow down at the end; for example, with a small tapered neck container. Or it can start slow, gradually speeding up to avoid splashing and foaming, like pouring a foaming beer in a glass. Sometimes with a handled container we will slow down halfway to let air get out of the handle area. And, thanks to the flowmeter accuracy, we can dribble feed the last 10% for better filling accuracy.
Flowmeter selection requires a combination of expertise with sensor electronics and software—and also a strong background in valve design, manifold distribution systems, pressure control, and cleaning velocity requirements.
The best way to measure flow
To obtain the best accuracy, we use magnetic and Coriolis flowmeters in a variety of sizes with sanitary flanges. Our first choice is normally a magnetic design assuming the product is conductive, but we will switch to a Coriolis when necessary. Magnetic sensors are typically smaller and easier to fit into the tight spaces of a filling machine.
Typically, the meters are mounted at the manifold so the valves can move up and down, with an individual sensor for each filling head. We use 3/4- and 1-in. ID flanges, and the flow rates can range quite widely from 0.5 to 4 gpm. The flowmeters send pulse output signals to the PLC (programmable logic controller) on the filling station, which shuts the fill valve when a container is full.
The PLC uses our proprietary algorithm to determine volume from the flow signal. This algorithm is the main reason why our liquid fillers perform well when compared to competitive fillers that also use flowmeters. The algorithm we use originated with our weigh scale fillers and has been tweaked to work with signals from a flowmeter instead of with totalizing values from load cells. Since the flow starts and stops within seconds, there is no time to wait for the flowmeter to stabilize. The piping design must also ensure that there are no bubbles or slugs of air in the line and that the pipes and sensor are always completely filled with liquid.
There is no universal liquid filling machine design; instead, every application is unique and custom. The bottles-per-minute rating for a machine is almost always dictated by the number of flowmeters that we can fit into the physical size of the machine, so having small sensors is a major advantage.
Liquid filling machines are rarely “level fillers.” That is, we never can guarantee the precise level. We also can’t guarantee filling accuracy that’s equal to the accuracy the flowmeters can achieve because the total tolerance stack-up is affected by valves, solenoids, pneumatics, vibration, and pressure swings that don’t allow filling accuracies to be that tight. However, the accuracy of flowmeters currently in use is better than any previous sensor technology for liquid filling, making our machines among the most accurate on the market.
Flowmeters allow for a much simpler valve construction versus a traditional mechanical filling system. Mechanical filling systems use seals and bottle contact to establish shut-off—much like the mechanism that stops the flow when you’re filling your car with gasoline, but with an overflow return leg to establish level in the container. However, this means there are more surface areas to clean and more gallons of cleaning solutions to flush.
Because flowmeter-based filling machines are so accurate, they don’t need an overflow to establish a liquid fill level, as with mechanical fillers. Thus, a flowmeter system requires about half the total amount of piping, hoses, nipples, manifolds, etc. It also doesn't require as much pressure, cleaning solutions, and time to clean as a mechanical filling system. Flowmeter-based systems also promote a noncontact valve design, which means no contact with the bottle finish, allowing for aseptic options. Coriolis and magnetic flowmeters have no moving parts or obstructions, which makes them easy to clean and flush. The internal parameters of the sensors can be set using the manufacturer’s software, but in operation, the meter and all measurements are controlled by our system.
The addition of a flow sensor may seem like expensive complexity at first glance, but it leads to savings in overflow, return pumps, and extra control systems—not to mention a more sanitary and cleanable design throughout. With a flowmeter system, changing product doesn’t require calibration as we simply store recipes based on empirical data from previous runs to allow quicker switching between bottle sizes and ingredient change. A filling machine can only run certain types of related products; for example, we can easily switch from a fruit juice to a low-sodium version of the fruit juice, but not from fruit juice to motor oil.
Retrofitting older machines
Liquid filling machines can last for years, requiring only periodic updates and replacement of parts. U.S. Bottlers rebuilds its older machines as a service to its customers. Part of the process involves rebuilding and replacing valves, rotary unions, silicone hoses, fittings, slide rods, bushings, rollers, and roller blocks. We also repair the main drive motor, bearings, gearboxes, and belts as needed. In most cases, customers also ask us to convert weigh-type filling machines to flowmeters during the rebuilding process.
One of our unusual observations is that it appears that when rebuilding an older weigh-filler into a flowmeter machine, the new fillers appear to be more accurate over and above what would expected by the improvement in flow measurement. We don’t exactly understand why, but clients tell us the improvement is measurable. Part of the reason could be that during the conversion process, the entire machine is given an overhaul and brought into spec; or it could be that the flowmeter is less susceptible to vibration and electrical noise in a bottling plant. In the lab, we don’t really see an unexpected improvement in fill accuracy, but in the field flowmeters are solid state warriors.
Since we have been using the same supplier for flowmeters long enough, we typically handle all of the start-up issues ourselves, and we also train our clients how to support the meters in the field. Factory technical personnel assist us regularly on our front-end calibration needs and meter selection process.
The flowmeters’ success is measured in two ways from our perspective: First, every one of our fillers equipped with E+H flowmeters not only meets all of our quoted accuracy guarantees, but is as good as any filler we’ve produced in the history of our company. Second—and probably more important—many customers that purchased a flowmeter-based filler have come back for repeat orders since improved liquid measurement is a large part of overall customer satisfaction.
Tom Risser is president of U.S. Bottlers, Charlotte, N.C.
Advantages of a flowmeter vs. load cells in liquid filling applications
• Faster measurement with higher repeatability
• No container tare weight needed
• Fill duration shorter and machine throughput increased
• Long-term instrument stability, less machine drift
• No moving parts with virtually no maintenance costs related to the meter
• Sensors can generally be replaced by another off-the-shelf unit, not a special part
• Valve monitoring and automatic compensation possible via the controller
• Coriolis sensors offer direct mass measurement with flexibility to convert to volume if needed
• No volume limits (container size not restricted by range of load cell)
• Higher stability and less recalibration costs over a longer working life
• Environmental influences reduced from mechanical vibration, agitation, splashing, etc.
• Built-in temperature compensation for accuracy over a broad range
• Self-diagnostics with status output for immediate operator notification, and
• Fully drainable and easy to clean in place.