Several problems existing in the design of the hot

Several problems in the design of containerized bags (middle)

in addition, the speed of the overall lifting test of containerized bags and the filler during the drop test of containerized bags should be clearly specified. Experiments show that the filling of the sample is massive and granular, which has an important impact on the test results, and the physical density and looseness of the content are also significantly different from the overall test results. Therefore, the test speed should imitate the actual hoisting speed of the crane at the port, and the performance of the filling material should be as close as possible to the product to be loaded by the customer. In order to prevent disputes, the standard should describe a special "standard filler" for testing, so that the technical standard can better meet the challenges brought by the market economy as far as possible

"safety factor" is the guarantee of the safe use performance of the product, which determines the mechanical properties of each part of the bag under different structural forms. It reflects the comprehensive performance of the product and is simple and clear. Therefore, it is an important basis in product design, mainly because the stress structure has an important relationship with it. It is determined first in the design, and then according to the minimum unit weight that can be guaranteed by the wire drawing ability of our company. Other table 12 test items, cycles and requirements of seat belts. The specific design should be based on this index. For finished products, if the "safety factor" test can pass, it should cover other tests

overall test method

article 5.5 "overall test method" in the national standard gb10454-2000 stipulates that in addition to periodic lifting, there are five tests, namely, drop test, pressure test, positive test and tear propagation test. From the product experiments conducted by the author for many years, it is recognized that the overall lifting test that meets the five times safety factor can also meet other tests

in the lifting test, because the load of 5 times is the force of all parts of the bag at the same time, and the force on the unit area is 5 times that of the rated load. If this test can be passed, when the height is 0.8m and 3M respectively in the drop test and the dump test, the sum of the self gravity acceleration in its free fall with the rated load is much smaller than that of 5 times the load. The force distributed to all parts of the whole bag is much smaller than that when the load is 5 times and from inside to outside, which is not a threat to the product

the significance of the test is to imitate the actual working state of the product. The chord of the international ocean going cargo ship is more than 0.8m or 0.3m higher than the wharf, which is of little significance. If the bag really falls down when lifting at the port, there are only two possibilities: first, the port operation is wrong, and second, the product fails to pass the lifting test

if the safety factor can reach 5 times, two of the four rings or one of the two rings must also have a tensile performance of more than 2.5 times the rated load. During the positive position test, the bag body lies horizontally on the ground, and the hook is used to hang two or one lifting ring on the side close to the ground and lift it up until the bag body is righted and lifted off the ground, and there will be no problem with the bag body. When the bag body is off the ground, due to the external size and inclination of the single ear hook host, a non vertical component will be generated, which will damage the relative position of the sewing position at the root of the ring. Generally, this tearing force is equivalent to 20-25% of gravity, and will not pose a threat to the sling that withstands the test of five times the safety factor

during tear propagation, if more than 5 times of the load is distributed on 10cm of a certain part of the bag, the force distributed there when the rated load is just lifted for tear propagation is 1/5f. The gravity direction of the contents of the bag is mainly downward, and there is a certain pressure on the fabric on the side wall, but it is relatively small. The magnitude of this pressure is related to the height of the material surface of the contents and the size of the bag body. At the same time, this pressure is affected by the longitudinal and transverse direction of the warp and weft yarn, and the end of the knife edge at 45 ° to the vertical central axis of the bag body will generate two components to transmit to the flat yarn in the warp and weft direction of the bag body respectively. Through more complex calculation, the magnitude of these two components can be obtained. As a part of the overall force analysis of the container bag, the discussion is always "complex", but practice has proved that the knife edge will not be extended at the rated load

to sum up, there are many items of the overall test method in international, which are mutually restrained in function, and the inspection is complex. They are also important veto items in the standard inspection. There are many bag tests, long test cycles and high test costs, which are not suitable for the characteristics of today's fast-paced and low-cost society. In the contract environment, it has the function of simple, clear and rapid quality judgment of products. It is the function of quality judgment of products, and it is the development direction of current standards

the strength of the base cloth, the performance of flat wires, and the aging law of woven cloth

first, in order to meet the safety factor, the base cloth should have a higher strength, but it is not that the higher the strength of the base cloth, the better. In a specific "The implementation of green building is based on the weight of the base fabric. Under the general law that the tensile force is inversely proportional to the elongation, the flat yarn for weaving should maintain a good elongation while pursuing the absolute tensile force. Without a good elongation, excessive pursuit of tensile force will be counterproductive, and the aging performance of the product will be greatly reduced. When no additives are added, the elongation is one of the main indicators to judge the performance of the fabric. Once the strength of the base fabric is determined by the design, it is necessary to For a given width, the tensile force and actual strength of each monofilament cannot be equal to the measured strength of the base cloth, and there will be 5% - 15% weaving loss. This is related to the difference of equipment structure and the degree of new and old, as well as the melt index of raw materials (material softness and hardness), ratio and process method of flat silk. In addition, the loss of weft strength is relatively larger than that of warp strength to make it right

secondly, the addition of recycled materials should be resolutely avoided in the production of container bags, because this involves safety issues. Although polypropylene has good mechanical properties, its ability to resist natural aging is very poor. If you want to maintain relatively long-term performance, it is an inevitable choice to add additives scientifically and reasonably. If recycled materials are used, first, the composition is difficult to control, and the performance of the finished product is not easy to grasp. Second, the molecular chain is plasticized twice or even many times, and the effect of adding "anti-aging agent" is not reliable

third, anti natural aging is an unpopular subject involving many theories and complex mechanisms. However, with regard to the anti-aging of plastic woven products, in the 7th issue of China Plastics in 1998, there was an article titled "anti natural aging of polypropylene fabrics", which discussed the theory and effect of shutdown. (to be continued)