How Should Curtain Strip Overlap Width Be Matched to the Tunnel Size of a Food Inspection Machine?

How Should Curtain Strip Overlap Width Be Matched to the Tunnel Size of a Food Inspection Machine?

Match overlap to the tunnel in three steps. First, use the tunnel opening width and the strip engagement at each side frame to find how many strips of a chosen width and overlap fit across. Second, use the separation at each seam and the steepest straight-ray angle from the machine builder to set a minimum overlap that closes a straight path through the seam. Third, check package weight, rigidity, and belt speed, because more overlap also adds contact resistance. No catalogue value fixes overlap in advance. Newlife - Radbar treats strip width, overlap, length, and return as one layout decision, confirmed by whole-machine shielding measurement while representative packages pass (Food inspection application).

Why overlap and tunnel size interact

The curtain is part of the machine shielding. Broken, missing, or non-returning strips reduce that integrity (FAQ). Overlap closes the seams between adjacent strips and sets how much material a package must push aside. A wide tunnel built from narrow strips has many seams. Each seam is a possible leakage path, and each extra strip adds contact force on light items.

Record the equipment tube voltage and the tunnel opening width and height. The food-scanner curtain grades are listed at 90 / 120 kV. Then record package size, weight, rigidity, belt speed, and scan mode (Food inspection application).

Strip count from tunnel width and overlap

For one row, strips of width $w$ with uniform overlap $o$ ($w>o$) and side-frame engagements $e_L$ and $e_R$ must cover the clear tunnel width $W_t$:

The smallest whole number of strips is:

Use one length unit throughout. Apply the relation to each row. As overlap grows, the pitch $w-o$ shrinks and the strip count rises quickly. Measure $e_L$ and $e_R$ on the frame.

Hanging mass of a row scales with strip count, strip area, and the grade areal density. Extra strips also add cut edges, holes, and spares.

Minimum overlap from seam geometry

Overlapping strips do not hang flat. On a multi-row curtain the seams may be staggered, so a straight ray can cross a seam at an angle. Let $s$ be the face separation at the seam, and let ${\theta }_{\mathrm{m}\mathrm{a}\mathrm{x}}$ be the largest lateral angle of a straight ray at that plane, as given by the machine builder. A straight path is closed when:

${\theta }_{\mathrm{m}\mathrm{a}\mathrm{x}}$ is an angle, so $\tan {\theta }_{\mathrm{m}\mathrm{a}\mathrm{x}}$ is dimensionless and $o$, $s$, and $\delta$ share one length unit. Evaluate the tangent in the angle unit the calculation uses. $\delta$ is the allowance for sway, cutting tolerance, and hole-position tolerance. The builder supplies ${\theta }_{\mathrm{m}\mathrm{a}\mathrm{x}}$ and $s$. Tunnel width sets strip count through the pitch relation; it changes this minimum overlap only through $s$ and ${\theta }_{\mathrm{m}\mathrm{a}\mathrm{x}}$. If the required overlap approaches strip width, one seam cannot close that ray: add a row with staggered seams, then measure on the machine. These relations are a geometric screen. Leakage acceptance is the assembled-machine measurement.

Catalogue lead equivalent applies at the stated tube voltage. Compare values only when filtration and measurement geometry match, including narrow-beam or broad-beam conditions (Lead-free X-ray shielding technology).

Strip length must cover the opening height and leave clearance above the belt that limits under-hem leakage without dragging.

Catalogue grades that set the starting point

Select the grade from the item-weight reference, then run the overlap estimate on that grade. The three lead-free food-scanner curtain grades below are from the product page (Food scanner curtains).

Item weight is a catalogue selection reference. Confirm passage with representative packs on the machine. The page states a supply width of 600 mm / max 1200 mm; confirm the width supplied. Choose cut strip width when laying out the row. A soft pouch and a rigid tray of the same mass do not load the strips the same way. Match the grade to the package reference for that line.

Layout trade-offs at the tunnel

Wet or oily strips can stick or separate unevenly, which changes $s$. The product page describes a lead-free shielding substrate and a light-blue polyurethane surface, plus a wear-resistant coating for cleaning with neutral or alkaline detergents (Food scanner curtains). Record the detergent, concentration, temperature, contact time, and fat or oil exposure, then check seam closure after representative washdown cycles.

Acceptance on the assembled machine

Treat the calculated layout as a candidate. Accept it by leakage measurement at the tunnel openings, with representative products moving at line speed and the curtain in its post-cleaning state. For cabinet x-ray systems, 21 CFR 1020.40 limits emission outside the external surface. The machine manufacturer carries that compliance. The curtain is part of the enclosure.

Replacement strips must match the original overlap, hole pitch, and strip count. Record those values in the maintenance documents. Replace torn, curled, or permanently deformed strips that no longer close the seam.

The product-page source notes FDA food-contact requirements, RoHS, and REACH Annex XVII. Request a declaration naming the supplied material and the intended contact conditions.

How Newlife - Radbar supports the overlap design

Newlife - Radbar supplies these curtains as rolls, OEM curtain sets, or single strips, so the strip width and hole pattern from the layout can be ordered as cut parts. Each grade lists lead equivalent together with tube voltage on the product page. Include the tunnel drawing, beam angles, package range, and cleaning conditions with the enquiry so the cut parts match the line.

FAQ

Does a wider tunnel always need more overlap? A wider tunnel needs more strips at the same pitch. Minimum overlap increases when seam separation or the largest straight-ray angle increases. Take both from the machine geometry.

Can the overlap of the old curtain be copied when the grade changes? Start from the existing overlap. A different areal density changes hang and return, so measure leakage and passage again after the change.

Which grade fits very light items? Start with 0125JBU, listed for items at or above 80 g. Confirm passage with the actual packages at line speed.

Next steps

1. Record equipment tube voltage, tunnel width and height, side-frame engagement on each side, and the straight-ray angles from the machine builder. 2. List package dimensions, weight range, rigidity, belt speed, and scan mode. 3. Estimate strip count and minimum overlap with the two relations above, then select a grade from the table. 4. Record cleaning chemistry, concentration, temperature, contact time, and oil exposure. 5. Run leakage and passage trials on the assembled machine with representative products, before and after washdown. 6. Send these records to Newlife - Radbar with the curtain enquiry. Product page: Food scanner curtains.

References

1. Newlife - Radbar. Food Scanner Curtains, product page, specification table. https://www.newlifexray.com/en/products/food-scanner-curtains 2. Newlife - Radbar. Food Inspection, application page. https://www.newlifexray.com/en/applications/food 3. Newlife - Radbar. Lead-Free X-ray Shielding, technology page. https://www.newlifexray.com/en/technology/lead-free-xray-shielding 4. Newlife - Radbar. Radiation Protection FAQ. https://www.newlifexray.com/en/faq 5. U.S. Code of Federal Regulations, Title 21, §1020.40, Cabinet x-ray systems. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-J/part-1020/section-1020.40