How Should the Curtain Opening Be Adjusted When Lightweight Snack Packages Get Blocked by X-Ray Curtains?

How Should the Curtain Opening Be Adjusted When Lightweight Snack Packages Get Blocked by X-Ray Curtains?

Short answer: a lightweight snack package stalls when the strips it must deflect ask for more horizontal force than the belt can transfer by friction. Use the food-curtain series whose stated shielding meets the requirement at the actual tube voltage, filtration, measurement geometry and named standard, and, among those series, the lowest stated areal density. Match strip length to the real opening and package height. Keep overlapping rows from being held open together. Space packages so strips can return. Narrower strips help when a pack would otherwise lift strip width it only partly touches; they do not, by themselves, cut the total mass a pack lifts if it already spans the full engaged width, and they add seams. Every opening change then has to pass on the complete machine for both product flow and radiation leakage.

This note is for equipment OEMs, line engineers and buyers who need to clear jams without weakening the shielding design.

Lighter Packaging and Faster Lines Are Making Curtain Jams a Design Issue

Curtain jamming on snack lines is a system problem, not only a maintenance nuisance. The pressures act in the same direction:

- Packs are lighter and softer. Thin film and single-serve formats have little stiffness with which to push a strip aside. - Higher belt speeds and tighter pitch leave less time for a strip to fall back before the next pack arrives. - A change of curtain construction changes surface friction. Cleanability, oil and washdown belong in the specification, not in a later workaround. - A curtain that lets snacks through but opens a leakage path is not an acceptable fix.

The Newlife - Radbar radiation protection application engineering team treats the choice in that order: package mass and conveying conditions first, then grease, temperature and cleaning, then the contact-use documents required in the destination market, then measured performance after installation.

Compare 125A-UB, 175A-UB and 250A-UB Only at the Stated Beam Condition

Grade choice sets strip mass, so it is the first lever. The food-inspection series are 125A-UB, 175A-UB and 250A-UB. They are not interchangeable. Stated lead equivalent, tube voltage, areal density and thickness are: 125A-UB, 0.125 mmPb at 90 kV, 1.9 kg/m², 0.65±0.05 mm; 175A-UB, 0.175 mmPb at 90 kV, 2.5 kg/m², 0.84±0.05 mm; 250A-UB, 0.25 mmPb at 120 kV, 3.9 kg/m², 1.18±0.05 mm. Tensile strength is stated as greater than 3.5 MPa and hardness as 76±2 Shore A. Operating temperature is -10°C to 70°C. Lead equivalent is usable only with the tube voltage, filtration, measurement geometry and standard stated for that value. Areal density and thickness are separate quantities and use different units. A figure stated at one tube voltage does not apply at a higher tube voltage, and a diagnostic X-ray result does not describe high-energy gamma or neutron shielding.

Among grades that meet the stated shielding condition, the lowest areal density gives the lowest strip mass for the same strip area. That is a selection rule, not a claim that one series is universally light enough for snacks. The catalog initial selection maps the three grades to item references of ≥80 g, ≥150 g and ≥200 g, and also takes package stiffness and belt speed into account. Pass-through and durability depend on the equipment and the test conditions. No series is a general approval for every food package.

Security X-ray curtains are a separate product. Food-inspection selection and security-scanning selection both list food-inspection curtains and security X-ray curtains, but surface and strip overlap have to be validated on the complete machine. Do not copy one product's data onto the other.

A First-Order Force Balance Explains Why Light Snack Packages Stall

Strip mass follows from areal density and strip geometry. With areal density ${\sigma }_A$ in kg/m² and strip length $L$ and width $w$ in metres:

The result is in kilograms. Mixing millimetres into this expression without converting will overstate mass by orders of magnitude. Thickness does not appear: a thicker strip is heavier only so far as that thickness is already reflected in ${\sigma }_A$.

For a uniform rigid strip, hinged at the top and held at an angle $\theta$ from the vertical by a horizontal force at the free end, moment balance gives:

Here $g$ is gravitational acceleration. The package keeps moving only while the belt can supply that force, approximately $n{F}_s<\mu m_{p}g$, where $n$ is the number of strips that must be deflected together, $\mu$ is the belt-to-package friction coefficient and $m_p$ is the package mass. Equality is the stall point. This is a flat-belt, quasi-static limit. It does not include the extra force needed to accelerate strips up to belt speed, so a layout that only just satisfies it can still jam in production.

What the balance does and does not say:

- Resistance of one strip scales with areal density, length and width. Available belt force scales with package weight, and it disappears once the pack slips. - If a pack fully spans every strip it touches, and the strips do not overlap, total lifted mass is ${\sigma }_{A}L{W}_c$, where $W_c$ is the engaged width. Dividing that width into more slits does not reduce the total. - Narrower strips do reduce lifted mass when contact is partial. A small or soft pack that only clips the edge of a wide strip still has to move the whole strip. That is the case in which more slits help a light snack pack. - Overlap can make engaged width larger than package width, so total mass is higher than the no-overlap estimate. Overlap is both a coverage feature and a resistance term. - A short pack on the belt pushes the strip near the free end. Extra length lying on the belt adds drag that this pendulum model misses. Strips cut so short that they clear the belt open a gap instead. - Flexibility, strip-to-pack friction, impact and package stiffness are omitted. Use the balance to rank options, then measure on the line.

Each Opening Change Trades Pass-Through Against Continuous Coverage

Record the tube voltage (the catalog lists 90 kV and 120 kV) and the tunnel opening before drawing the strip layout. Select the initial series at that beam condition, using the catalog item references of ≥80 g, ≥150 g and ≥200 g together with package stiffness and belt speed. Set width, overlap, length and return together. Write down the cleaning conditions. Validate on the line with the packs that actually jam.

Write Down the Machine, Package and Cleaning Window Before Changing the Curtain

A curtain change is predictable only if these inputs are fixed first:

- Tube voltage, filtration and tunnel width and height. Do not treat a lead-equivalent value as valid at a voltage the stated grade data do not give. Catalog tube voltages are 90 kV and 120 kV. - Lightest and heaviest package mass, package height, stiffness and film type. Catalog item references for the three grades are ≥80 g, ≥150 g and ≥200 g. - Belt speed, product pitch and belt surface. - Operating temperature, checked against the stated range of -10°C to 70°C. - Cleaning-agent composition, concentration, temperature, contact time, and any oil or grease. The curtains are specified as waterproof, oil-resistant and alkaline-resistant; the actual agents and contact conditions are still recorded and checked on the line. - The food-contact and substance declarations required in the destination market, for the exact series.

Compliance and Acceptance Rest on Whole-Machine Testing

Acceptance is a property of the complete machine, not a number read off a curtain roll. A narrow-beam lead-equivalent measurement is not the same result as a broad-beam or cabinet leakage survey, and the two must not be substituted for each other.

Where the machine is a cabinet X-ray system subject to 21 CFR 1020.40, radiation emitted from the system shall not exceed an exposure of 0.5 milliroentgen in one hour at any point five centimetres outside the external surface. That is a system limit. It does not certify a curtain grade. In the European Union, Council Directive 2013/59/Euratom sets basic safety standards that national rules implement; it is not itself a curtain lead-equivalent specification. Food-contact materials in the EU are governed by Regulation (EC) No 1935/2004 and the measures that apply to the specific material. A declaration has to match the series and the market.

These food-inspection curtains are lead-free and non-toxic, for direct food contact. The materials comply with food-grade contact-material requirements and are safe and harmless. The product meets RoHS requirements and FDA food-contact material requirements, and no harmful substance leaches in aqueous or dairy solutions. Do not infer that statement from another series, or from a registration. Registration is not approval. Those material statements do not waive end-of-life controls.

Modified Openings Fail in Repeatable Ways, and Food-Curtain Data Stop at the Tested Beam

The usual failure after an opening change is a new leakage path, or a jam that returns at production speed. Modes that follow from the layout itself:

- Seam leakage where slits are many or overlap is too small once strips deflect. - A gap at belt level where strips were shortened below the real clearance, including clearance with the belt loaded. - Strips held open by a queue of closely spaced packs, including two rows engaged by one long pack. - Oil, product debris or cleaning agents that change surface friction over time, so a layout that passed when clean later stalls or hangs open. - Extra belt drag where strips are longer than the opening and lie on the belt.

Pass-through and durability from one machine and one test setup do not transfer to every snack film or every scanner. Food-curtain results at the tube voltage stated for that test do not extend to a different beam quality, and they do not extend to other radiation types.

Newlife - Radbar Supplies the Food-Curtain Series for This Opening Problem

The Newlife - Radbar radiation protection application engineering team supplies lead-free food-inspection curtains in the 125A-UB, 175A-UB and 250A-UB series, with a light blue polyurethane surface, and flexible shielding sheet by model with the parameters and test conditions stated for that model. The food curtains are prepared by special mixing and calendering of radiation-absorbing metal powder and resin. The product is light, soft and has excellent radiation shielding, and is specified as not blocking food. The materials used comply with food-grade contact-material requirements and are safe and harmless. Standard size is stated as 600 mm x 10 m or 20 m, with customization supported. Supply uses the Newlife group's functional-materials platform. Group scale is not a specification of these curtain grades, and a formulation described for another shielding product is not the formulation of a curtain series unless that series datasheet says so.

Strip width, length, overlap and row spacing are set with the equipment builder and confirmed on the complete machine for the stated tube voltage, opening, package range and cleaning method. Security X-ray curtains remain a separate product: surface and strip overlap are validated on the complete scanner, and those results are not food-curtain data.

How to read lead equivalent, areal density, layer orientation and test geometry is set out on the lead-free X-ray shielding technology page. That page is manufacturer material and applies to the constructions it covers. Distinctions between lead equivalent and thickness, and between narrow-beam and broad-beam measurements, are summarized in the FAQ.

Buyers Ask Four Practical Questions Before Changing a Snack-Line Curtain

Can the curtain simply be cut shorter? Only if the shorter strips still close the opening at belt level, loaded and unloaded, and the complete machine still passes its leakage survey. Less length means less mass, which is why a shorter strip can help a light pack. Cut to the empty-tunnel impression rather than the real clearance, and the bottom gap is a leakage path.

Should the line drop to a lower series for light packs? Only if that series meets the shielding requirement at the actual tube voltage, filtration, geometry and standard. Among series that meet that condition, the lowest stated areal density is the mass-saving choice. That lowest stated value is 1.9 kg/m² for 125A-UB at 90 kV; 175A-UB is 2.5 kg/m² at 90 kV and 250A-UB is 3.9 kg/m² at 120 kV. Do not step down solely because the pack is light, and do not reuse a rating stated at a lower tube voltage. Then confirm pass-through on the machine.

Do narrower strips reduce shielding or jamming? Slit count does not change the lead equivalent of the strip material, but every slit is a seam. Overlap has to keep coverage while the strips are deflected, which a machine survey has to show. Narrower strips reduce the mass lifted by a partial contact. They do not reduce total lifted mass when the pack already spans the engaged width.

Will one layout cover every snack SKU? No. Pass-through and durability depend on the machine, the belt, pack mass and stiffness, and the test conditions. Validate with the lightest and softest pack, and with the pack that holds the strips open longest.

Resolve the Jam by Recording the Line, Ranking the Opening Changes, and Validating Both Flow and Leakage

1. Record tube voltage, filtration if known, tunnel opening, and the current series and strip layout. 2. Measure the package mass, height and belt speed at which jamming occurs, including the lightest soft pack. 3. Rank changes with the force balance: lowest compliant areal density, strip length against the real opening, rows engaged at once, then strip width for partial contact. Do not start from slit count alone. 4. Write down cleaning agents, temperatures and oil exposure, and the declarations the destination market requires for that series. 5. Trial the revised layout with representative packs at production pitch, and run a whole-machine leakage survey. A narrow-beam datasheet figure does not replace that survey. 6. Use the English site at https://www.newlifexray.com/en/ to reach the Newlife - Radbar radiation protection application engineering team. Send the machine model, tube voltage, opening size, package mass and height range, belt speed and pitch, target shielding basis, and cleaning and maintenance limits. The team can then propose a series and a strip layout for on-line validation. The proposal is not a leakage clearance until the complete machine has been tested.

References

1. U.S. Code of Federal Regulations, 21 CFR 1020.40, Cabinet x-ray systems. Exposure limit in paragraph (c)(1): 0.5 milliroentgen in one hour at any point five centimetres outside the external surface. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-J/part-1020/section-1020.40 2. Council Directive 2013/59/Euratom of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation. https://eur-lex.europa.eu/eli/dir/2013/59/oj 3. Regulation (EC) No 1935/2004 of 27 October 2004 on materials and articles intended to come into contact with food. https://eur-lex.europa.eu/eli/reg/2004/1935/oj 4. Newlife - Radbar, lead-free X-ray shielding technology page, manufacturer material on absorption, areal density, layer orientation and test geometry. Applies to the constructions covered there; not a food-curtain pass-through certificate. https://www.newlifexray.com/en/technology/lead-free-xray-shielding 5. Newlife - Radbar, FAQ, including lead equivalent versus thickness and beam-measurement distinctions. https://www.newlifexray.com/en/faq