Nitrogen Dosing Before Capping: Headspace, Dose Timing and the Seal Check

Controlling internal bottle pressure begins with the physical phase change of liquid nitrogen and the fill-level accuracy of the upstream liquid filler.

According to Vacuum Barrier Corporation, liquid nitrogen has a boiling temperature of -320°F (-196°C) and will rapidly boil away when exposed to room temperatures, so insulated equipment must be used to ensure efficiency and safety.

According to Vacuum Barrier Corporation, when boiling from liquid to gas, nitrogen expands roughly 700 times; safety relief valves (SRVs) are installed on tanks, piping, and dosers to prevent over-pressurization and potential equipment ruptures, and a safety relief valve must be placed between any two shut-off valves where nitrogen could be trapped.

According to the Chart Inc. CryoDoser manual, the normal oxygen content of air is approximately 21%, and when humans are exposed to an atmosphere containing only 8 to 12% oxygen, unconsciousness can be immediate with virtually no warning.

According to Vacuum Barrier Corporation, too small of a dose can lead to unstable containers, the possibility of collapse, or food spoilage in inerting processes, whereas if containers are dosed with too much nitrogen, there is a risk of containers bulging or bursting, which could cause jamming and downtime.

According to Vacuum Barrier Corporation, to reliably and accurately control the liquid nitrogen dose for each container up to speeds of 2000 bottles per minute and meet the production goals of pressurization, a doser relies on consistent fill heights from the filler, because even a small change in fill height can lead to under or over-pressurization.

In our edible oil filling configurations, oil left on the nozzle after shut-off runs down the neck and onto the bottle where a clean neck matters for the cap and label, while air carried in with the oil can foam in the bottle and a fast fill can splash, so filling from the bottom up or slowing near the end are the usual ways to limit foam and splash, used alongside nozzle shut-off, drip trays, and bottle spacing.

Vacuum Barrier Corporation's 3-D Technology (Directional Dose Dispersion) addresses shallow headspace in lightweight and hot-fill beverages to eliminate splash while accurately providing pressure, delivering discrete dosing at all line speeds to a target pressure of ± 1% psi even during extreme acceleration or deceleration.

Packaging Europe reports that Sidel's rPET-compatible Nitro Square bottle for nitrogen-dosed still water with liquid nitrogen dosing apparently reaches an hourly output of 2,600 bottles per mould on Sidel machinery, where its rigid sections and flexible pressure-absorbing surfaces work together to maintain the bottle's shape.

Where the dosing head sits along the conveyor between the filler discharge and the capper infeed depends on whether the primary engineering goal is headspace oxygen removal or internal container pressurization.

According to the Chart Inc. CryoDoser 2K manual, inerting is the process of removing oxygen (O2) from a container by dosing a relatively large amount of LN2 in the container so the liquid dose quickly converts into gas displacing air and oxygen, and the ideal location for the CryoDoser unit must allow for enough time between dosing and capping so that the liquid dose is converted into a gas.

According to the Chart Inc. CryoDoser 2K manual, pressurization occurs by dosing a relatively small amount of LN2 into a container where the liquid dose quickly converts into gas and the container is then capped or sealed to capture the expanding gas, so the CryoDoser unit should be installed as close to the capper as possible.

According to Vacuum Barrier Corporation, travel time from the doser to the seamer or capper should be minimized to prevent excess boiling or loss of nitrogen.

According to Vacuum Barrier Corporation, shaking or bouncing containers on the conveyors can force nitrogen and product out of the package before closure.

When space near the capper is limited, Chart Inc.'s Hot Chute nozzle handles narrow to wide mouth openings with discrete dosing up to 400 cpm and is recommended for discrete dosing with limited space near the capper.

According to the Chart Inc. CryoDoser 2K manual, the dosing head should be directly over the container opening, is typically installed 1/2" - 3/4" above the container opening, and the CryoDoser unit must be manually adjusted to accommodate different sized containers running on the same production line.

According to the Chart Inc. CryoDoser 2K manual, three nozzles are supplied with the CryoDoser 2K system in 0.040 inch, 0.050 inch, and 0.060 inch sizes, and custom sizes may be ordered from Chart.

For support stand mounting, the Chart Inc. CryoDoser manual specifies measuring 32.5" (825mm) back from the dosing head location (the distance from the center of the support stand to the farthest point on the dosing head) and installing the four 5/8" bolts included with the support stand.

According to the Chart Inc. CryoDoser 2K manual, the CryoDoser unit has a self-regulating dosing head heater with a maximum temperature of 150°F (65°C) that prevents frost or ice formation at the dosing head area, and the dosing head heater has a built-in splash guard to minimize the dosing nozzle's exposure to splashed product or LN2.

Once the bottle enters the capper, the closure must trap the expanding nitrogen gas and hold internal pressure through storage and distribution.

In our automatic capping machine line integration guide, ASTM D2063/D2063M-24 describes manual measurement of removal torque over time for matching continuous-thread packages under specified environmental conditions, and a leaking pack also needs the agreed leak check because a torque reading alone does not identify a damaged liner, contaminated sealing face, or mismatched neck.

According to ASTM D2063/D2063M-24 Clause 1.1, this test method is a quantitative method that measures removal torque of continuous thread closures on containers, with matching finishes for predetermined environmental conditions over time.

According to ASTM D2063/D2063M-24 Clauses 5.2 and 5.3, this test method can be used for the evaluation of container/continuous thread closure systems under controlled conditions (where the application torque is known and the applied downward force to the closure is zero), with the use of a non-automated, spring torque-meter (with either a dial indicator or a digital readout) or a torque wrench.

According to Antares Vision Group, as nitrogen vaporises to pressurise the headspace and rigidify the bottle, the process introduces two distinct failure modes that affect product quality and production efficiency: bottle leaks (N2 escaping through a defective seal), and doser malfunctions (one or more dosing valves applying too little or too much nitrogen).

According to Antares Vision Group, because every container is individually measured, an in-line inspection system can build a statistical profile of the pressure distribution across the production batch and correlate each reading with the specific capping head or dosing valve that handled that container, so if one doser valve is under-performing by applying too little N2, the system identifies it by cycle number and valve position.

In Chart Inc.'s MicroDose application findings, utilizing sensors to detect filling line speed, pocket detection, bottle presence, inputs independent of the filler, and electronic adjustments for fine tuning, 3.0 +/-1 psig internal bottle pressure is achieved at the 99% level (.5 L size), with sample size 1,000 findings showing 99% at 2 to 4 psi and 56% at 3 psi.

In Chart Inc.'s larger MicroDose sample size of 27,000 (.5 L size), findings showed 96.5% at 2 to 5 psi and 67% at 3 to 4 psi alongside the 1,000-bottle sample where 3.0 +/-1 psig internal bottle pressure is achieved at the 99% level.