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Safety factor should be taken into account in the design of tonnage bags and container bags

2013-09-04 11:16:33

The national standard GB10454-2000 "Container Bag" mentions "Safety Factor", but it is worth discussing. The standard stipulates in Clause 5.5.1: "Periodic lifting test" that "the contents should be evenly filled into the packed bags to the full load, and the loads equal to twice the maximum load should be hung up, the limited bags should be used 70 times, the one-time bags should be used 30 times, and the lifting should be repeated. Whether the container bags are qualified or not depends mainly on whether the contents and bags are abnormal, whether the connecting part is damaged or not, and if there is no damage, it means that the test is passed.

In clause 4.3, it is stipulated that the safety factor of the pulling force of the sling and the sling is 6. In this way, the product passes the final test in the overall test which takes 3 times rated load as standard. Then, in a relatively (shorter) product life, due to natural aging, when the strength of the product drops to 50%, its ability to ensure safe use is only 1.5 times, and the instantaneous stress generated in the hoisting process is close to this value. Plus the inherent performance differences between individual products, which means that the proportion of broken packages will probably increase, and the safety of products will be greatly discounted. Of course, this is only a theoretical speculation. In fact, due to the difference between the internal materials and the use environment, as well as the performance tolerance between products, it is difficult to know exactly when the performance of a batch of products in use has dropped below 50%. However, it is an indisputable fact that the 5-fold safety factor container bags can be safely used longer than the 3-fold safety guarantee products. The container bags filled with anti-UV ultraviolet additives have a wider range of applications. Therefore, they also have a broader international market.

The standard 10454-89 stipulates that the total pulling force of the sling (rope) should be greater than or equal to 6 times the rated load in accordance with the design form, and the pulling force on a single sling (rope) in different types of sling rings should be assigned. The safety factor is given as "6". In practice, this safety factor is different from the whole lifting test. The six-fold coefficient of the lifting ring can not prove that the whole bag has six-fold safety factor. It only represents the higher pulling force index that the lifting belt needs to achieve when it is tested separately. When the suspension belt is connected with the bag body, there are various types of suspension, such as top suspension, side suspension and bottom suspension, and they are connected by sutures. In side and top suspension, if the strength performance of base cloth and stitches can not reach a certain level, the high strength of suspension belt alone can not ensure the high performance of the overall test; furthermore, the strength loss of suspension belt and base cloth is between 10-30% according to different sewing patterns and sewing methods. Therefore, the whole bag lifting test requires three times the full load and repeated lifting, while the specific structure of the product is neglected in determining the performance of the lifting belt. In order to ensure the safe handling of bags, the lifting bags and side-lifting bags in the original standard were cancelled when the 2000 edition standard of Container Bags was revised. This method seems inappropriate. Quality assurance mainly depends on proven manufacturing technology and reliable material quality. The top-suspended and side-suspended bags still have their advantages in processing and cost, especially in light bag products. The principle of the standard should be to point out the direction, not to stipulate rules and regulations to limit the effective use of Designers'intelligence.

In addition, the "speed" of integral lifting test of container bags and the "filler" of drop test of container bags should be clearly stipulated. Experiments show that the bulk, granular or powdery fillers in the sample have an important influence on the test results, and the physical density and the degree of looseness of the contents have obvious differences on the overall test results. We believe that the test speed should imitate the actual lifting speed of the crane at the port, and the performance of the filling material should be as close as possible to the products loaded by the customers. In order to prevent disputes, the standard should describe a special "standard filling material" for testing, as a basis for judging the performance of container bags, so as to make the technical standards meet the challenges brought by market economy as well as possible.

Safety factor, as the guarantee of product safety performance, determines the mechanical properties of each component of the bag in different structural forms. It reflects the comprehensive performance of the product, simple and clear, so it is an important basis for product design, and the main force structure has an important relationship with it. In the design, first determine it, and then around its strength allocated to each component, determine the lowest unit weight that can be guaranteed according to the drawing ability of the company. Other concrete designs should be arranged around this index. At the same time, for finished products, if the "safety factor" test is qualified, it should cover other tests.

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