What are the differences in production equipment between valve-sealed gluing bottom bags and sewn bottom bags?

In the industrial packaging sector, valve-sealed gluing bags and sewn-bottom bags are two common packaging forms, widely used in industries such as cement, fertilizer, grain, and chemical raw materials. While they may appear similar, their structural design and production methods differ significantly, especially the production equipment, which directly impacts the bag's performance, cost, and application scenarios. This article will delve into the differences in production equipment for valve-sealed gluing bags and sewn-bottom bags, providing a comprehensive analysis from equipment composition and process flow to key technical aspects.

I. Basic differences between valve-sealed gauze bottom bags and sewn-bottom bags

Before discussing production equipment, we first need to clarify the basic characteristics of valve-sealed gluing-bottom bags and sewn-bottom bags. Valve-sealed gluing-bottom bags (commonly known as gluing-bottom bags) are bags made by bonding multiple layers of composite material to the bottom with an adhesive. They are usually equipped with a valve for filling materials. These bags have good sealing performance and high strength, making them suitable for high-speed automated filling lines, and are commonly used for powders or granular materials. Sewn-bottom bags (commonly known as sewn-bottom open bags) have the bottom sewn shut with thread, leaving the opening open. They need to be sealed separately after filling. Their production cost is lower, but their sealing performance and automation compatibility are slightly inferior to gluing-bottom bags.

The essential difference between these two types of bags lies in the bottom treatment: glued-bottom bags rely on adhesive bonding, while sewn-bottom bags rely on sewing thread. This difference directly leads to the differentiation in the structure, function, and process of production equipment.

II. Detailed Explanation of Valve-Nose Paste Bag Production Equipment

The equipment for producing valve-sealed bottom-glued bags is usually called a bottom-glued bag making machine or a valve bag production line. Its core function lies in the precise application, folding, and pressing of multi-layer composite materials (such as kraft paper, plastic film, or aluminum foil), while also integrating valve seam fabrication. The entire set of equipment includes multiple modules, from unwinding and printing to forming and bonding, each requiring high-precision control.

1. Unwinding and tension control systems are essential
   components of gluing bag production equipment. These systems typically include multiple unwinding units to handle rolls of different materials, such as outer kraft paper, inner plastic, or composite film. The tension control system is a critical component, using magnetic powder brakes or servo motors to achieve constant tension control, ensuring the material does not shift or wrinkle during operation. Because gluing bags often employ a multi-layered structure, uneven tension can lead to weak adhesion or bag distortion.
2. Printed
   bottom-glued bags often require the printing of brand information, instructions for use, or barcodes. The equipment uses flexographic or gravure printing units and supports multi-color printing. The printing unit operates synchronously with subsequent processes to ensure accurate pattern positioning. Compared to sewn bottom-glued bag equipment, bottom-glued bag printing places greater emphasis on the drying system, as residual solvents can affect adhesive performance.
3. The gluing and bottom-sealing system
   is the core component of the bottom-sealing bag equipment. The gluing system applies hot melt or cold glue to a predetermined area on the bottom of the bag using a precise glue gun or roller applicator. The bottom-sealing system includes a folding mechanism and a pressing mechanism: first, the bag bottom is folded according to the design, and then bonded using a heating plate or pressure roller. Valve fabrication is completed simultaneously in this stage; the equipment must insert the valve material at a specific location on the bag body and ensure a firm bond. The precision of the gluing directly affects the bag quality. The equipment is typically equipped with photoelectric sensors or CCD cameras to monitor the glue distribution in real time. The bottom-sealing pressure and time need to be adjusted according to the material thickness: excessive pressure may cause glue overflow, while insufficient pressure will result in weak adhesion. Furthermore, the valve installation requires high positioning accuracy to avoid leakage during filling.
4. After production, glued-bottom bags require a drying
   tunnel to fully cure the adhesive. The equipment uses hot air circulation or infrared heating, with the temperature controlled between 50–80°C to prevent material deformation. Drying time depends on the type of adhesive and generally takes several seconds to tens of seconds. In contrast, sewn-bottom bags do not require this step because sewing does not rely on chemical bonding.
5. After being formed in the slitting and stacking unit
   , the bags are slitted into individual products by a rotary knife, and then automatically stacked and counted. The slitting knife of the bottom-sealing bag equipment needs to be specially designed to avoid damaging the valve. The stacking unit achieves high-speed sorting via a robot or conveyor belt, typically producing 60–120 bags per minute.

The production equipment for glued bottom bags is highly complex and requires significant investment, but it is also highly automated and suitable for mass production. The technical challenges lie in ensuring the stability of the adhesive strength and the sealing of the valve, necessitating regular maintenance of the gluing system and temperature control module.

III. Detailed Explanation of Bottom-Sealing Bag Production Equipment

Bottom-sewn bag production equipment is commonly referred to as a bottom-sewn bag making machine or an open-pocket sewing production line. Its core function is to sew the bottom of the bag together using a sewing machine. While the structure is relatively simple, it emphasizes sewing strength and efficiency. The equipment mainly includes modules for unwinding, printing, folding, sewing, and finishing.

1. The unwinding and feeding system
   for bottom-sewing bags is also equipped with multiple unwinding devices, but the tension control requirements are slightly lower than those for bottom-gluing bags because the sewing process requires less precision in material alignment. The feeding system continuously transports the material to the sewing station via rollers or belts, and the speed is adjustable to accommodate different bag types.
2. Similar to the
   bottom-gluing bag, the bottom-sewing bag equipment also integrates printing functions, but with a greater emphasis on economy. It often employs simple letterpress or monochrome printing, and the drying system is relatively simple because the sewing process does not have high requirements for ink drying.
3. Before sewing, the folding and pre-sealing system
   folds the roll material into a bag shape. The folding mechanism uses guide plates or templates to achieve U-shaped or cylindrical folds, and then temporarily fixes the bag edges (e.g., by applying adhesive or heat sealing) for subsequent sewing. This step does not require complex adhesive application, but it is essential to ensure neat folding to prevent misalignment during sewing.
4. The sewing system
   is the core component of the bottom-sewing bag equipment, employing an industrial sewing machine head (typically a single-thread chain stitch or double-thread lockstitch). The sewing machine head is equipped with automatic thread trimming, shuttle changing, and needle breakage detection functions to ensure continuous production. The stitch length, thread, and tension need to be adjusted according to the bag material: for example, heavy-duty bags require a smaller stitch length and high-strength thread, while ordinary bags can have more lenient requirements. The sewing system also includes a bobbin thread supply and a top thread control device. Modern equipment often uses servo motors to drive the sewing machine, achieving precise needle synchronization. Compared to bottom-sewing equipment, the sewing system is easier to maintain, but requires frequent needle and thread replacements, resulting in higher operating costs.
5. After being sewn together by the sorting and counting unit
   , the bags are automatically stacked following inspection. The equipment may integrate a checkweighing or vision inspection system to detect sewing defects (such as skipped stitches or broken threads). Stacking speed is generally fast, reaching 80–150 bags per minute, but attention should be paid to the issue of thread tangling.

The equipment for producing sewn bottom bags has a relatively simple structure and lower investment costs, but it relies on manual intervention (such as changing threads or adjusting stitch length). Its advantage lies in its strong adaptability, as it can handle thick materials or composite materials, but the seam may become a weak point in strength.

IV. Key Differences Analysis of Production Equipment

As can be seen from the above description, the production equipment for valve-sealed gluing bags and sewn-bottom bags differs fundamentally in several aspects, mainly in the following areas:

1. Core process module

• Sealing bag equipment : Centered on a glue application, folding, and pressing system, it emphasizes uniform adhesion and valve integration. The equipment requires precise control of glue volume, temperature, and pressure, making it technically demanding.
• Bottom bag sewing equipment : Centered on the sewing system, emphasizing sewing strength and stability. The equipment requires optimized needle-thread dynamics and necessitates frequent maintenance.

1. Automated
   bottom-gluing bag equipment typically achieves fully automated production, requiring no manual intervention from unwinding to stacking, making it particularly suitable for delicate operations such as valve positioning. While bottom-sewing bag equipment can also be automated, the sewing process is susceptible to factors such as thread tension and needle wear, often requiring manual monitoring.
2. Due to the time required for adhesive curing, the overall production
   speed of glued bottom bag equipment may be slightly lower than that of sewn bottom bag equipment. However, glued bottom bags have a higher one-time forming rate and a lower scrap rate. Sewn bottom bag equipment has a faster production speed, but sewing defects (such as skipped stitches) may lead to a higher defect rate.
3. Equipment Costs and Maintenance:
   The initial investment for gluing bag equipment is higher due to its multiple precision modules (such as the glue applicator and drying system). Maintenance focuses on cleaning the glue path and calibrating the sensors. Sewing bag equipment has lower initial costs, but requires continuous investment in consumables such as sewing needles and thread during operation, and maintenance focuses more on mechanical adjustments.
4. Flexible
   bottom-sewing bag equipment is more adaptable to materials of different textures and thicknesses because the sewing process is less sensitive to material changes. In contrast, glue-on bag equipment requires adjustments to the type and parameters of adhesive based on material characteristics, making changeover processes more complex.

V. Equipment Selection and Industry Applications

The choice between gluing-bottom bags and sewn-bottom bags production equipment depends on product requirements, cost budget, and industry standards. For example, in the cement or chemical industries, valve-sealed gluing-bottom bags are more suitable for automated filling lines due to their superior sealing properties, so equipment selection tends to favor high-precision gluing-bottom bag production lines. In the grain or feed industries, sewn-bottom bags, due to their lower cost and ease of recycling, may require more emphasis on sewing efficiency and durability in equipment selection.

Furthermore, environmental trends are also influencing equipment development. Gluing bag equipment is evolving towards the use of water-based adhesives and energy-efficient drying systems, while sewing bag equipment is innovating in areas such as exploring biodegradable sewing threads and reducing thread consumption.

The differences in production equipment for valve-sealed gluing bags and sewn-bottom bags ultimately stem from their design philosophies and performance requirements. Gluing bag equipment achieves sealing and strength through adhesive technology; the equipment is complex but produces consistent output. Sewn-bottom bag equipment balances cost and efficiency through sewing technology; its structure is simple but its application is flexible. Understanding these differences helps companies make more informed choices when investing in equipment, optimizing production processes and product quality.

With the advancement of Industry 4.0, these two types of equipment are gradually integrating intelligent control systems, such as IoT sensors and AI quality inspection. The differences may further narrow in the future, but the core process modules will retain their uniqueness. Regardless of which equipment is chosen, maintenance and process optimization are crucial to ensuring efficient production.