National standard GB10454-2000, "Bulk Bags," mentions the issue of "safety factors," but the degree of emphasis placed on them is questionable. Section 5.5.1, "Periodic Lifting Test," stipulates that "the contents should be evenly filled into the bulk bag to full capacity. A load equivalent to twice the load should be attached. This should be repeated 70 times for limited-use bags and 30 times for single-use bags. The acceptance of the bulk bag is primarily determined by whether there are any abnormalities in the contents and the bag body, and whether the joints are damaged. A bag that has no damage passes this test."
Section 4.3 stipulates that "the safety factor for the tensile strength of slings and ropes is 6." Thus, even if a product passes the overall test based on 3 times the rated load, due to natural aging, its ability to guarantee safe use will only be 1.5 times its rated load over a relatively short product lifespan. Furthermore, the transient stresses generated duringthe lifting approach this value. Combined with the inherent performance differences between individual products, this means the rate of bag breakage is likely to increase, significantly compromising product safety. Of course, this is only theoretical speculation. In reality, due to variations in packaging materials, operating environments, and performance tolerances between products, it's difficult to accurately determine when the performance of a batch of products in use drops below 50%. However, it's an indisputable fact that FIBCs with a 5x safety factor can be used safely longer than those with a 3x safety factor, and that FIBCs with UV-resistant additives have a wider range of applications, thus enjoying a broader international market.
"FIBC Standard" 10454-89 stipulates that the combined tensile strength of the slings (rope) (based on the design) must be greater than or equal to 6 times the rated load, distributed across the tensile strength of the individual slings (rope) for different types and types of lifting loops, and a safety factor of "6" is assigned. In practice, this safety factor is inconsistent with the overall lifting test. The 6x factor for the lifting loop does not guarantee a 6x safety factor for the entire bag; it simply represents the higher tensile strength that the slings must meet when individually tested. The sling is connected to the bag body in various styles, including top-hang, side-hang, and bottom-hang, and is connected by stitching. In side-hang and top-hang styles, if the base fabric and stitching do not meet a certain level of strength, high sling strength alone cannot guarantee high overall performance in testing. Furthermore, depending on the sewing pattern and method, the strength loss of the sling and base fabric can range from 10-30%. Therefore, the whole-bag lifting test requires repeated lifting at three times the full load, ignoring the specific structural type of the product when determining the sling's performance. When the 2000 edition of the "Container Bag" standard was revised, top-hang and side-hang styles were removed from the original standard to ensure safe loading and unloading of bags. This approach seems inappropriate. Quality assurance should primarily rely on proven manufacturing techniques and reliable material quality. Top-hang and side-hang styles do have their advantages in terms of processing and cost, especially in lightweight bags. The principle of standards should be to provide direction, not to impose rigid rules that restrict the effective use of designers' ingenuity.
Furthermore, the "speed" for the bulk bag lifting test and the "filling material" for the bulk bag drop test should be clearly defined. Experiments have shown that the filler's bulk, granular, or powdered form significantly influences the test results. The physical density and bulkiness of the contents also significantly affect the overall test results. We believe the test speed should mimic the actual lifting speed of cranes at ports and terminals, and the filler's performance should be as close as possible to the product intended for loading. To prevent disputes, the standard should describe a dedicated "standard filler" for testing as the basis for evaluating bulk bag performance, ensuring that the technical standard is well-suited to the challenges of a market economy.
The "safety factor" ensures the product's safe performance and determines the mechanical properties required of each bag component under different structural configurations. It reflects the product's overall performance and is simple and clear, making it a crucial factor in product design. The main load-bearing structures are significantly impacted by it. This factor should be determined first during design, and then the strength allocated to each component should be determined based on it, determining the unit weight that can be guaranteed based on the company's wire drawing capabilities. Other specific design decisions should be made around this indicator. At the same time, for finished products, if the "safety factor" test is qualified, it should have a covering effect on other tests.