The Bag Former, also known as the forming tube or collar, is the heart of a Vertical Form Fill and Seal (VFFS) machine. It is the critical component that transforms flat roll film into a specific bag shape, directly determining the package’s dimensions, appearance, and quality. This guide provides a complete overview of its function, types, selection, and maintenance.
Function and Working Principle
Core Function: The Bag Former’s primary role is to guide and shape the flat polyethylene or laminated film from the roll into a consistent, seamless tube. This formed tube is the prerequisite for creating the final sealed pouch.
- Film Forming: Transforms flat film into a tube with a specific cross-section.
- Dimension Setting: The width of the former determines the final bag width (film width must be matched accordingly).
- Guidance and Stabilization: Ensures the film remains flat and wrinkle-free during the pulling process, laying the foundation for precise subsequent sealing.
How it Works:
- Film Guidance: The film web is drawn over the former’s precision-machined surfaces.
- Tube Formation: The film is folded and wrapped around the former’s specific geometry—typically a curved “shoulder”—to create a continuous tube.
- Sealing Preparation: The overlapping edges of the film are brought together under the former, ready for the longitudinal (vertical) sealer to create the back seal.
- Product Channel: The hollow center of the former acts as a chute, allowing the measured product to fall directly into the newly formed bag below.
Main Types of Bag Formers
The design of the Bag Former is dictated by the desired final bag style. Our VFFS machines can produce various bag types, each requiring a specific former.
| Bag Style | Description | Former Characteristics |
|---|---|---|
| Pillow Bag | The most common bag style, with a back seal and two end transverse seals, cross-section is round or oval. | Uses a “Collar Type” or similar former; film curls around the former to form a tube. |
| 3 Side Seal Bag | The bag has three sealed edges (usually the back and two sides), with one side open. | The former guides the film to form a fold, with longitudinal sealing on both sides. |
| 4 Side Seal Bag | All four edges of the bag are sealed, common for small-sized packaging. | The former structure causes the film to fold, and both sides and both ends are sealed. |
| Gusset Bag/Flat Bottom Bag | The bag bottom has gussets or a flat bottom structure, allowing the bag to stand upright. | The former includes a special gusset-forming device, making the structure more complex. |
| Box Bag | The formed bag is box-shaped, usually with a back seal, offering a strong three-dimensional feel. | The former design is complex, capable of guiding the film to form predetermined crease lines. |
Selection and Customization
A Bag Former is not a universal part. It must be custom-made based on two key parameters:
- Film Width: The actual width of the roll film you will use. This is the primary dimension for former sizing.
- Bag Width: The desired finished width of your package. A general rule is: Bag Width ≈ Film Width – (Back Seal Width x 2). The back seal typically uses about 10mm of overlap on each side.
- Product Characteristics: The shape of the material (granules, powder, liquid), flowability, and whether it is corrosive can affect the internal finish, material, and special design of the former (e.g., anti-clogging).
Important Notes on Customization:
- Standard Inclusion: The price of a packaging machine includes one Bag Former for a default film/bag width.
- Replacement Required: If you need to change your bag width (by changing the film roll width), you must purchase a new, corresponding Bag Former.
- Multiple Sizes: For production lines that frequently switch between different bag sizes, it is necessary to have a separate Bag Former for each primary width.
Material and Structural Details of Formers
- Materials:
- Contact Parts: Parts in contact with the product are usually made of SS 304 stainless steel or food-grade plastic to meet hygiene and safety requirements.
- Non-contact Parts: May use aluminum alloy or other lightweight, high-strength materials to reduce weight and ensure rigidity.
- Key Structural Components:
- Former Body: The core curved surface that determines the film path.
– The forming surfaces are smoothly polished to prevent film drag, scratching, or inconsistent forming which can cause wrinkles. - Film Guide Roller/Plate: Guides the film to enter smoothly.
- Forming Tube: The tubular part where the film finally forms; its interior may integrate special functions.
- Gas Charging Device Interface: Holes can be made above the former tube to connect a gas source (nitrogen or air) to inflate the bag for preservation or anti-crushing.
- Longitudinal Seal Mold Mounting Position: Located near the outlet of the forming tube, used to install the longitudinal seal heating block.
- Former Body: The core curved surface that determines the film path.
Operation, Adjustment, and Maintenance
- Bag Length Adjustment: The bag length is easily adjusted via the machine’s touchscreen and is controlled by the film feed motor. This is independent of the Bag Former, which controls the width.
- Installation & Alignment: Proper mounting and alignment of the former are crucial. It must be centered perfectly to ensure the film feeds evenly and the back seal is straight.
- Cleaning: The former must be cleaned regularly to remove any product dust or residue that could contaminate the film or impede the film path.
- Inspection: Periodically check for any damage, dents, or burrs on the forming surfaces that could tear the film.
Common Issues and Troubleshooting
| Problem | Potential Cause | Solution |
|---|---|---|
| Film runs crooked, bag misformed. | 1. Former misaligned. 2. Film guide rollers unbalanced. 3. Poor quality film. | 1. Re-center and secure the former. 2. Adjust guide rollers. 3. Check film roll. |
| Wrinkles on the finished bag. | 1. Wrong former for the film width. 2. Incorrect film tension. 3. Dirty or damaged former surface. | 1. Verify former specification. 2. Adjust tension system. 3. Clean or replace the former. |
| Product jams in the tube. | 1. Former tube inner diameter is too small for the product. 2. Sticky products adhering to the tube. | 1. Use a former with a larger tube or screen product. 2. Request a former with a special non-stick coating or larger funnel. |
| Uneven or crooked back seal. | Former is guiding the film edges inconsistently. | Adjust the former’s horizontal/vertical position to ensure even film overlap. |
Summary and Best Practices
Selecting and using the right Bag Former is fundamental to successful VFFS operation.
- Define Needs: Determine your product, target bag style, and size range (width and length).
- Choose Machine Series: Select VFJ or VFH series based on the required bag style and features.
- Order Formers: Custom-order your first Bag Former based on your primary film width. If you have multiple standard sizes, order additional formers upfront.
- Train Operators: Ensure staff knows how to correctly install, align, and clean the former.
- Plan for Spares: Consider keeping a spare former for your most critical bag size to minimize production downtime.
Final Recommendation: During project planning, communicate all intended bag specifications in detail with your machine supplier. This allows them to provide the most cost-effective former configuration and an accurate quotation.
Contact HonorPack today. Customizing VFFS machines to your needs, helping you seal your success.
