In vertical form–fill–seal (VFFS) granule packaging machines, the horizontal and vertical sealing units are the two core stations that determine the final seal quality and overall package appearance. Through coordinated heating and pressure, they thermally bond the packaging film to create a complete, protective bag structure.
1. Definitions and coordinated roles of vertical and horizontal seals
The vertical seal unit forms the longitudinal seam along the back or side of the bag, serving as the foundational seal for bag styles such as centre-seal, three-side-seal, and four-side-seal. It uses heated elements to melt the overlapping longitudinal edges of the film, producing a continuous and strong side seal.
The horizontal seal unit forms the transverse seal at the top or bottom of the bag, likewise applicable to various bag formats. After the vertical seal establishes the bag profile, the horizontal seal applies heat and pressure to close the bag mouth, completing the final sealing action. This step directly dictates the flatness and reliability of the finished seal.
The two units work in a sequential "vertical‑first, horizontal‑later" cycle: the vertical seal first creates the basic bag contour, and the horizontal seal then cuts and seals the top, producing a continuous, fully sealed package. Any deviation in either unit can compromise overall seal integrity and operational stability.
2. Causes of horizontal seal wrinkling and systematic troubleshooting
Wrinkling at the horizontal seal is a common quality defect, characterised by uneven folds, stretching, or shrinkage in the sealing area. It not only degrades appearance but may also weaken seal strength and lead to leakage. Below are four typical causes and corresponding corrective actions:
(1) Excessive horizontal seal temperature
When the sealing temperature exceeds the recommended thermal sealing window for the film, the material may over‑melt or shrink unevenly, resulting in wave‑like wrinkles.
Remedies: Recalibrate the temperature controller to the appropriate range based on the actual film type (e.g., for PE films, typically 120–150 °C). Regularly clean the sealing cutter blade with a soft brush to remove carbon deposits and polymer residues, which can cause localised heat transfer irregularities.
(2) Mismatch between feeding rate and sealing cycle
If the auger or volumetric feeder delivers granules too quickly relative to the horizontal sealing cycle, product may accumulate in the seal area. This causes the film to stretch unevenly under pressure, producing "entrapped‑material" wrinkles.
Remedies: Adjust the cam or servo parameters to synchronise material feeding with the sealing action. Also verify that the discharge chute is clear, ensuring smooth, surge‑free material flow.
(3) Uneven horizontal seal pressure
Insufficient or unbalanced pressure across the sealing width can allow the film to slip or produce weak spots during sealing, which promotes wrinkling.
Quick check: With the sealing jaws at room temperature, place a sheet of A4 paper between the upper and lower sealing faces, manually index the machine to perform a single press, then remove the paper. If the imprint depth varies noticeably across the width, the pressure system is imbalanced.
Remedies: Adjust the pressure spring pre‑load or pneumatic cylinder supply pressure at both ends of the seal jaws to achieve uniform distribution. For machines equipped with pressure sensors, use real‑time feedback for fine calibration.
(4) Poor packaging film quality
Variations in film thickness, excessive heat‑shrinkage rate, or inconsistent slip‑agent blooming can directly lead to abnormal seals.
Remedies: Conduct comparative tests using film from different batches or suppliers. Prefer co‑extruded films with good thermal stability and high tensile resistance, and verify the roll's edge straightness and width consistency before loading.
3. Preventive maintenance and operational tips
- Pre‑start parameter verification: Before daily start‑up, confirm that the horizontal seal temperature, pressure, and pulling speed are within the specified process range as per the machine's setup card.
- Routine cleaning of sealing surfaces: At the end of each shift, use a dedicated brass brush or soft cloth to remove residual adhesive and dust from the sealing jaws, preventing foreign matter from causing local stress concentrations.
- Trial sealing when changing film lots: Whenever a new film type or batch is introduced, run a small‑batch trial to verify seal appearance and strength before commencing full‑scale production.
- Operator training: Ensure that line operators are proficient in PID temperature tuning, pneumatic pressure adjustments, and basic fault diagnosis, enabling rapid response to sealing abnormalities.
By systematically addressing temperature, speed, pressure, and film‑related factors, most horizontal seal wrinkling issues can be effectively resolved, thereby improving packaging quality and production efficiency.
For custom‑manufactured components and retrofit support
If your equipment requires non‑standard adaptation at the structural or part level-for example, to accommodate specific film characteristics or upgrade sealing assemblies-please feel free to contact our technical team with your detailed drawings. We specialise in precision manufacturing of customised spare parts for packaging machinery, supporting made‑to‑print fabrication for both single‑piece and small‑batch requirements. Our engineering capabilities are at your disposal to address bespoke component needs, ensuring your lines run smoothly with optimised, application‑specific solutions.
Disclaimer: This technical note is provided for informational purposes only. Actual equipment maintenance and parameter adjustments should always be carried out in accordance with the machine manufacturer's manual and under proper site‑specific conditions.
