Why is product pitch normally greater than product length?
Product pitch normally exceeds product length because the machine needs clear film between products for the end-seal jaws, normal dimensional variation and safe timing margin. The required gap depends on the jaw arrangement, seal width, product behaviour, pack presentation and how accurately the infeed controls position.
Reducing pitch without proving jaw clearance can create product damage, contaminated seals or unstable cut position. Use the most difficult production sample, not only the nominal drawing.
How do end-seal clearance and pack appearance change the repeat?
The pack repeat must include the product envelope plus the clear film and end-seal areas needed before and after it. A compact presentation may use less free film, while a fragile, variable or grouped product may need more allowance to remain clear of the jaws.
The accepted pack may also require a particular amount of film beyond the seal or a defined print position. Approve those features on a pack sample or drawing before format parts and artwork are fixed.
What is the relationship between printed-film repeat and finished pack length?
The printed-film repeat is the distance from one repeated artwork position or registration mark to the next, and it must match the machine’s intended pack repeat. The sensor can correct print-to-cut position, but it cannot make incompatible artwork repeat and pack geometry equivalent.
Supply the print repeat, mark dimensions, mark contrast, unwind direction and approved cut location. The film guide covers the complete reel information needed for approval.
Why can the same product need a different pitch with a different film or seal arrangement?
A different film or seal arrangement can change sealing time, jaw clearance, seam position, stiffness, shrink response and the amount of free film needed for an acceptable pack. A change from unprinted to registered film can also tie the format to a fixed artwork repeat.
Do not transfer a pitch value solely because the product dimensions are unchanged. Recheck the full product-film-pack combination and retain the approved recipe and reference pack.
How should grouped or multipack products be measured?
Measure the group in the condition that enters the wrapper, including the maximum length, width, height and movement between items. Record whether the group is pre-collated, constrained by a tray or carrier, held by the infeed or free to spread during acceleration and transfer.
The group’s dynamic envelope can be larger than a static bench measurement. A trial should show that the group stays together, clears the jaws and produces a repeatable pack.
What evidence proves the product stays clear of the crimp jaws?
Proof should combine representative product trials, recorded pitch settings, observed jaw position and accepted packs produced through normal starts, stops and product variation. Include the longest or most unstable product and any group that can spread or move inside the film tube.
Check more than one perfect cycle. The trial should include realistic arrival variation and restart conditions, with evidence of no product contact in the seal area.